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2021
Volume: 9 Issue 7
32 Article(s)
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DEEP LEARNING IN PHOTONICS
Toward simple, generalizable neural networks with universal training for low-SWaP hybrid vision
Baurzhan Muminov, Altai Perry, Rakib Hyder, M. Salman Asif, and Luat T. Vuong
Speed, generalizability, and robustness are fundamental issues for building lightweight computational cameras. Here we demonstrate generalizable image reconstruction with the simplest of hybrid machine vision systems: linear optical preprocessors combined with no-hidden-layer, “small-brain” neural networks. Surprisingly, such simple neural networks are capable of learning the image reconstruction from a range of coded diffraction patterns using two masks. We investigate the possibility of generalized or “universal training” with these small brains. Neural networks trained with sinusoidal or random patterns uniformly distribute errors around a reconstructed image, whereas models trained with a combination of sharp and curved shapes (the phase pattern of optical vortices) reconstruct edges more boldly. We illustrate variable convergence of these simple neural networks and relate learnability of an image to its singular value decomposition entropy of the image. We also provide heuristic experimental results. With thresholding, we achieve robust reconstruction of various disjoint datasets. Our work is favorable for future real-time low size, weight, and power hybrid vision: we reconstruct images on a 15 W laptop CPU with 15,000 frames per second: faster by a factor of 3 than previously reported results and 3 orders of magnitude faster than convolutional neural networks.
Speed, generalizability, and robustness are fundamental issues for building lightweight computational cameras. Here we demonstrate generalizable image reconstruction with the simplest of hybrid machine vision systems: linear optical preprocessors combined with no-hidden-layer, “small-brain” neural networks. Surprisingly, such simple neural networks are capable of learning the image reconstruction from a range of coded diffraction patterns using two masks. We investigate the possibility of generalized or “universal training” with these small brains. Neural networks trained with sinusoidal or random patterns uniformly distribute errors around a reconstructed image, whereas models trained with a combination of sharp and curved shapes (the phase pattern of optical vortices) reconstruct edges more boldly. We illustrate variable convergence of these simple neural networks and relate learnability of an image to its singular value decomposition entropy of the image. We also provide heuristic experimental results. With thresholding, we achieve robust reconstruction of various disjoint datasets. Our work is favorable for future real-time low size, weight, and power hybrid vision: we reconstruct images on a 15 W laptop CPU with 15,000 frames per second: faster by a factor of 3 than previously reported results and 3 orders of magnitude faster than convolutional neural networks.
.Photonics Research
- Publication Date: Jun. 14, 2021
- Vol. 9, Issue 7, B253 (2021)
Research Articles
Holography, Gratings, and Diffraction
Super-resolution imaging by optical incoherent synthetic aperture with one channel at a time
Angika Bulbul, and Joseph Rosen
Imaging with an optical incoherent synthetic aperture (SA) means that the incoherent light from observed objects is processed over time from various points of view to obtain a resolution equivalent to single-shot imaging by the SA larger than the actual physical aperture. The operation of such systems has always been based on two-wave interference where the beams propagate through two separate channels. This limitation of two channels at a time is removed in the present study with the proposed SA where the two beams pass through the same single channel at any given time. The system is based on a newly developed self-interference technique named coded aperture correlation holography. At any given time, the recorded intensity is obtained from interference between two waves co-propagating through the same physical channel. One wave oriented in a particular polarization is modulated by a pseudorandom coded phase mask and the other one oriented orthogonally passes through an open subaperture. Both subapertures are multiplexed at the same physical window. The system is calibrated by a point spread hologram synthesized from the responses of a guide star. All the measurements are digitally processed to achieve a final image with a resolution higher than that obtained by the limited physical aperture. This unique configuration can offer alternatives for the current cumbersome systems composed of far apart optical channels in the large optical astronomical interferometers. Furthermore, the proposed concept paves the way to an SA system with a single less-expensive compact light collector in an incoherent optical regime that may be utilized for future ground-based or space telescopes.Imaging with an optical incoherent synthetic aperture (SA) means that the incoherent light from observed objects is processed over time from various points of view to obtain a resolution equivalent to single-shot imaging by the SA larger than the actual physical aperture. The operation of such systems has always been based on two-wave interference where the beams propagate through two separate channels. This limitation of two channels at a time is removed in the present study with the proposed SA where the two beams pass through the same single channel at any given time. The system is based on a newly developed self-interference technique named coded aperture correlation holography. At any given time, the recorded intensity is obtained from interference between two waves co-propagating through the same physical channel. One wave oriented in a particular polarization is modulated by a pseudorandom coded phase mask and the other one oriented orthogonally passes through an open subaperture. Both subapertures are multiplexed at the same physical window. The system is calibrated by a point spread hologram synthesized from the responses of a guide star. All the measurements are digitally processed to achieve a final image with a resolution higher than that obtained by the limited physical aperture. This unique configuration can offer alternatives for the current cumbersome systems composed of far apart optical channels in the large optical astronomical interferometers. Furthermore, the proposed concept paves the way to an SA system with a single less-expensive compact light collector in an incoherent optical regime that may be utilized for future ground-based or space telescopes..
Photonics Research
- Publication Date: Jun. 07, 2021
- Vol. 9, Issue 7, 1172 (2021)
Free-space realization of tunable pin-like optical vortex beams
Domenico Bongiovanni, Denghui Li, Mihalis Goutsoulas, Hao Wu, Yi Hu, Daohong Song, Roberto Morandotti, Nikolaos K. Efremidis, and Zhigang Chen
We demonstrate, both analytically and experimentally, free-space pin-like optical vortex beams (POVBs). Such angular-momentum-carrying beams feature tunable peak intensity and undergo robust antidiffracting propagation, realized by judiciously modulating both the amplitude and the phase profile of a standard laser beam. Specifically, they are generated by superimposing a radially symmetric power-law phase on a helical phase structure, which allows the inclusion of an orbital angular momentum term to the POVBs. During propagation in free space, these POVBs initially exhibit autofocusing dynamics, and subsequently their amplitude patterns morph into a high-order Bessel-like profile characterized by a hollow core and an annular main lobe with a constant or tunable width during propagation. In contrast with numerous previous endeavors on Bessel beams, our work represents the first demonstration of long-distance free-space generation of optical vortex “pins” with their peak intensity evolution controlled by the impressed amplitude structure. Both the Poynting vectors and the optical radiation forces associated with these beams are also numerically analyzed, revealing novel properties that may be useful for a wide range of applications.We demonstrate, both analytically and experimentally, free-space pin-like optical vortex beams (POVBs). Such angular-momentum-carrying beams feature tunable peak intensity and undergo robust antidiffracting propagation, realized by judiciously modulating both the amplitude and the phase profile of a standard laser beam. Specifically, they are generated by superimposing a radially symmetric power-law phase on a helical phase structure, which allows the inclusion of an orbital angular momentum term to the POVBs. During propagation in free space, these POVBs initially exhibit autofocusing dynamics, and subsequently their amplitude patterns morph into a high-order Bessel-like profile characterized by a hollow core and an annular main lobe with a constant or tunable width during propagation. In contrast with numerous previous endeavors on Bessel beams, our work represents the first demonstration of long-distance free-space generation of optical vortex “pins” with their peak intensity evolution controlled by the impressed amplitude structure. Both the Poynting vectors and the optical radiation forces associated with these beams are also numerically analyzed, revealing novel properties that may be useful for a wide range of applications..
Photonics Research
- Publication Date: Jun. 11, 2021
- Vol. 9, Issue 7, 1204 (2021)
Imaging Systems, Microscopy, and Displays
Focus-tunable microscope for imaging small neuronal processes in freely moving animals
Arutyun Bagramyan, Loïc Tabourin, Ali Rastqar, Narges Karimi, Frédéric Bretzner, and Tigran Galstian
Miniature single-photon microscopes have been widely used to image neuronal assemblies in the brain of freely moving animals over the last decade. However, these systems have important limitations for imaging in-depth fine neuronal structures. We present a subcellular imaging single-photon device that uses an electrically tunable liquid crystal lens to enable a motion-free depth scan in the search of such structures. Our miniaturized microscope is compact (10 mm×17 mm×12 mm) and lightweight (≈1.4 g), with a fast acquisition rate (30–50 frames per second), high magnification (8.7×), and high resolution (1.4 μm) that allow imaging of calcium activity of fine neuronal processes in deep brain regions during a wide range of behavioral tasks of freely moving mice.Miniature single-photon microscopes have been widely used to image neuronal assemblies in the brain of freely moving animals over the last decade. However, these systems have important limitations for imaging in-depth fine neuronal structures. We present a subcellular imaging single-photon device that uses an electrically tunable liquid crystal lens to enable a motion-free depth scan in the search of such structures. Our miniaturized microscope is compact (
Photonics Research
- Publication Date: Jun. 28, 2021
- Vol. 9, Issue 7, 1300 (2021)
Integrated Optics
Efficient and wideband acousto-optic modulation on thin-film lithium niobate for microwave-to-photonic conversion | Editors' Pick
Ahmed E. Hassanien, Steffen Link, Yansong Yang, Edmond Chow, Lynford L. Goddard, and Songbin Gong
Microwave photonics, a field that crosscuts microwave/millimeter-wave engineering with optoelectronics, has sparked great interest from research and commercial sectors. This multidisciplinary fusion can achieve ultrawide bandwidth and ultrafast speed that were considered impossible in conventional chip-scale microwave/millimeter-wave systems. Conventional microwave-to-photonic converters, based on resonant acousto-optic modulation, produce highly efficient modulation but sacrifice bandwidth and limit their applicability for most real-world microwave signal-processing applications. In this paper, we build highly efficient and wideband microwave-to-photonic modulators using the acousto-optic effect on suspended lithium niobate thin films. A wideband microwave signal is first piezoelectrically transduced using interdigitated electrodes into Lamb acoustic waves, which directly propagates across an optical waveguide and causes refractive index perturbation through the photoelastic effect. This approach is power-efficient, with phase shifts up to 0.0166 rad/√mW over a 45 μm modulation length and with a bandwidth up to 140 MHz at a center frequency of 1.9 GHz. Compared to the state-of-the-art, a 9× more efficient modulation has been achieved by optimizing the acoustic and optical modes and their interactions.Microwave photonics, a field that crosscuts microwave/millimeter-wave engineering with optoelectronics, has sparked great interest from research and commercial sectors. This multidisciplinary fusion can achieve ultrawide bandwidth and ultrafast speed that were considered impossible in conventional chip-scale microwave/millimeter-wave systems. Conventional microwave-to-photonic converters, based on resonant acousto-optic modulation, produce highly efficient modulation but sacrifice bandwidth and limit their applicability for most real-world microwave signal-processing applications. In this paper, we build highly efficient and wideband microwave-to-photonic modulators using the acousto-optic effect on suspended lithium niobate thin films. A wideband microwave signal is first piezoelectrically transduced using interdigitated electrodes into Lamb acoustic waves, which directly propagates across an optical waveguide and causes refractive index perturbation through the photoelastic effect. This approach is power-efficient, with phase shifts up to
Photonics Research
- Publication Date: Jun. 07, 2021
- Vol. 9, Issue 7, 1182 (2021)
Monolithic and single-functional-unit level integration of electronic and photonic elements: FET-LET hybrid 6T SRAM
Antardipan Pal, Yong Zhang, and Dennis D. Yau
A broad range of technologies have been developed for the chip and wafer scale connections and integrations of photonic and electronic circuits, although major challenges remain for achieving the single-functional-unit-level integration of electronic and photonic devices. Here we use field-effect transistor/light-effect transistor (FET–LET) hybrid 6T static random-access memory (SRAM) as an example to illustrate a novel approach that can alleviate three major challenges to the higher-level integration of the photonic and electronic elements: size mismatch, energy data rate, and cascadability. A hybrid 6T SRAM with two access FETs being replaced by LETs and the electrical word lines replaced by optical waveguides is proposed. This hybrid 6T SRAM is analyzed to reveal its potential in improvement of the switching speed and thus total energy consumption over the conventional 6T SRAM. Numerical analyses, for instance, for a prototype 64 kB hybrid SRAM array, show a factor of 4 and 22 reduction in read delay and read energy consumption, and 3 and 4 in write delay and write energy consumption, respectively, when the access FETs are replaced by LETs. The potential impacts on the peripheral and assist circuits due to this hybrid structure and application of the LETs there are also briefly discussed.A broad range of technologies have been developed for the chip and wafer scale connections and integrations of photonic and electronic circuits, although major challenges remain for achieving the single-functional-unit-level integration of electronic and photonic devices. Here we use field-effect transistor/light-effect transistor (FET–LET) hybrid 6T static random-access memory (SRAM) as an example to illustrate a novel approach that can alleviate three major challenges to the higher-level integration of the photonic and electronic elements: size mismatch, energy data rate, and cascadability. A hybrid 6T SRAM with two access FETs being replaced by LETs and the electrical word lines replaced by optical waveguides is proposed. This hybrid 6T SRAM is analyzed to reveal its potential in improvement of the switching speed and thus total energy consumption over the conventional 6T SRAM. Numerical analyses, for instance, for a prototype 64 kB hybrid SRAM array, show a factor of 4 and 22 reduction in read delay and read energy consumption, and 3 and 4 in write delay and write energy consumption, respectively, when the access FETs are replaced by LETs. The potential impacts on the peripheral and assist circuits due to this hybrid structure and application of the LETs there are also briefly discussed..
Photonics Research
- Publication Date: Jul. 01, 2021
- Vol. 9, Issue 7, 1369 (2021)
Ultra-compact titanium dioxide micro-ring resonators with sub-10-μm radius for on-chip photonics
Meicheng Fu, Yi Zheng, Gaoyuan Li, Wenjun Yi, Junli Qi, Shaojie Yin, Xiujian Li, and Xiaowei Guan
Microring resonators (MRRs) with ultracompact footprints are preferred for enhancing the light-matter interactions to benefit various applications. Here, ultracompact titanium dioxide (TiO2) MRRs with sub-10-μm radii are experimentally demonstrated. Thanks to the large refractive index of TiO2, the quality factors up to ∼7.9×104 and ∼4.4×104 are achieved for TiO2 MRRs with radii of 10 μm and 6 μm, respectively, which result in large nonlinear power enhancement factors (>113) and large Purcell factors (>56). The four-wave mixing (FWM) measurements indicate that, compared to the large MRR, the FWM conversion efficiency of the ultracompact TiO2 MRRs can be greatly improved (e.g., -25 dB versus -31 dB), a harbinger of significant superiorities. Demonstrations in this work provide more arguments for the TiO2 waveguides as a promising platform for various on-chip photonic devices.Microring resonators (MRRs) with ultracompact footprints are preferred for enhancing the light-matter interactions to benefit various applications. Here, ultracompact titanium dioxide (
Photonics Research
- Publication Date: Jul. 01, 2021
- Vol. 9, Issue 7, 1416 (2021)
Lasers and Laser Optics
Superior performance of a 2 kHz pulse Nd:YAG laser based on a gradient-doped crystal
Meng’en Wei, Tingqing Cheng, Renqin Dou, Qingli Zhang, and Haihe Jiang
Herein, we report a homemade new Nd:YAG crystal rod that contains a gradient dopant of 0.39–0.80 at.% Nd3+ from end to end, achieving superior performance of a 2 kHz Nd:YAG pulse laser at 1064 nm. The optical-to-optical conversion efficiency reached 53.8%, and the maximum output power of the laser was 24.2 W, enhanced by 35.9% compared with a uniform crystal rod with the same total concentration of Nd3+. Significantly, our experiments revealed that the gradient concentration crystal produced a relatively even pumping distribution along the rod axis, greatly reducing the temperature gradient as well as having a smaller thermal effect. The pump and thermal distribution smoothing obviously improved the features of laser oscillation and output.Herein, we report a homemade new Nd:YAG crystal rod that contains a gradient dopant of 0.39–0.80 at.%
Photonics Research
- Publication Date: Jun. 08, 2021
- Vol. 9, Issue 7, 1191 (2021)
Modeling of a SiGeSn quantum well laser
Bahareh Marzban, Daniela Stange, Denis Rainko, Zoran Ikonic, Dan Buca, and Jeremy Witzens
We present comprehensive modeling of a SiGeSn multi-quantum well laser that has been previously experimentally shown to feature an order of magnitude reduction in the optical pump threshold compared to bulk lasers. We combine experimental material data obtained over the last few years with k·p theory to adapt transport, optical gain, and optical loss models to this material system (drift-diffusion, thermionic emission, gain calculations, free carrier absorption, and intervalence band absorption). Good consistency is obtained with experimental data, and the main mechanisms limiting the laser performance are discussed. In particular, modeling results indicate a low non-radiative lifetime, in the 100 ps range for the investigated material stack, and lower than expected Γ-L energy separation and/or carrier confinement to play a dominant role in the device properties. Moreover, they further indicate that this laser emits in transverse magnetic polarization at higher temperatures due to lower intervalence band absorption losses. To the best of our knowledge, this is the first comprehensive modeling of experimentally realized SiGeSn lasers, taking the wealth of experimental material data accumulated over the past years into account. The methods described in this paper pave the way to predictive modeling of new (Si)GeSn laser device concepts.We present comprehensive modeling of a SiGeSn multi-quantum well laser that has been previously experimentally shown to feature an order of magnitude reduction in the optical pump threshold compared to bulk lasers. We combine experimental material data obtained over the last few years with
Photonics Research
- Publication Date: Jun. 15, 2021
- Vol. 9, Issue 7, 1234 (2021)
Intermittent dynamical state switching in discrete-mode semiconductor lasers subject to optical feedback
Zhuqiang Zhong, Da Chang, Wei Jin, Min Won Lee, Anbang Wang, Shan Jiang, Jiaxiang He, Jianming Tang, and Yanhua Hong
Intermittent dynamics switching on the route to chaos in a discrete-mode laser with long time-delayed feedback is experimentally and numerically studied by analyzing the time series, power spectra, and phase portraits. The results show two types of dynamics switching: one or multiple times regular intermittent dynamics switching between stable state and square-wave envelope period-one oscillation within one feedback round time, and the irregular intermittent dynamics switching between stable state and quasi-periodic or multi-states or chaos with higher feedback ratio and bias currents. The relationship between the duty cycle of period-one oscillation and the feedback ratio has been analyzed. The map of the dynamics distribution in the parameter space of feedback ratio and bias current is plotted for a better understanding of dynamics evolution in long external cavity discrete-mode lasers.Intermittent dynamics switching on the route to chaos in a discrete-mode laser with long time-delayed feedback is experimentally and numerically studied by analyzing the time series, power spectra, and phase portraits. The results show two types of dynamics switching: one or multiple times regular intermittent dynamics switching between stable state and square-wave envelope period-one oscillation within one feedback round time, and the irregular intermittent dynamics switching between stable state and quasi-periodic or multi-states or chaos with higher feedback ratio and bias currents. The relationship between the duty cycle of period-one oscillation and the feedback ratio has been analyzed. The map of the dynamics distribution in the parameter space of feedback ratio and bias current is plotted for a better understanding of dynamics evolution in long external cavity discrete-mode lasers..
Photonics Research
- Publication Date: Jun. 28, 2021
- Vol. 9, Issue 7, 1336 (2021)
Nanophotonics and Photonic Crystals
Inflection point: a perspective on photonic nanojets
Guoqiang Gu, Pengcheng Zhang, Sihui Chen, Yi Zhang, and Hui Yang
When light propagates through the edge or middle part of a microparticle’s incoming interface, there is a basic rule that light converges and diverges rapidly or slowly at the output port. These two parts are referred to as the region of rapid change (RRC) and region of slow change (RSC), respectively. Finding the boundary point between RRC and RSC is the key to reveal and expound upon this rule scientifically. Based on the correlation between light convergence–divergence and the slope of emergent light, combined with the relationship between a natural logarithm and growth in physical reality and the second derivative of a function in practical significance, we determine the boundary point between RRC and RSC, namely, the inflection point. From such a perspective, a photonic nanojet (PNJ) and near-field focusing by light irradiation on RSC and RRC, as well as the position of the inflection point under different refractive index contrasts and the field distribution of light focusing, are studied with finite-element-method-based numerical simulation and ray-optics-based theoretical analysis. By illuminating light of different field intensity ratios to the regions divided by the inflection point, we demonstrate the generation of a photonic hook (PH) and the modulation of PNJ/PH in a new manner.When light propagates through the edge or middle part of a microparticle’s incoming interface, there is a basic rule that light converges and diverges rapidly or slowly at the output port. These two parts are referred to as the region of rapid change (RRC) and region of slow change (RSC), respectively. Finding the boundary point between RRC and RSC is the key to reveal and expound upon this rule scientifically. Based on the correlation between light convergence–divergence and the slope of emergent light, combined with the relationship between a natural logarithm and growth in physical reality and the second derivative of a function in practical significance, we determine the boundary point between RRC and RSC, namely, the inflection point. From such a perspective, a photonic nanojet (PNJ) and near-field focusing by light irradiation on RSC and RRC, as well as the position of the inflection point under different refractive index contrasts and the field distribution of light focusing, are studied with finite-element-method-based numerical simulation and ray-optics-based theoretical analysis. By illuminating light of different field intensity ratios to the regions divided by the inflection point, we demonstrate the generation of a photonic hook (PH) and the modulation of PNJ/PH in a new manner..
Photonics Research
- Publication Date: Jun. 07, 2021
- Vol. 9, Issue 7, 1157 (2021)
Nonlinear Optics
Broad-intensity-range optical nonreciprocity based on feedback-induced Kerr nonlinearity
Lei Tang, Jiangshan Tang, Haodong Wu, Jing Zhang, Min Xiao, and Keyu Xia
Nonreciprocal light propagation plays an important role in modern optical systems, from photonic networks to integrated photonics. We propose a nonreciprocal system based on a resonance-frequency-tunable cavity and intensity-adaptive feedback control. Because the feedback-induced Kerr nonlinearity in the cavity is dependent on the incident direction of light, the system exhibits nonreciprocal transmission with a transmission contrast of 0.99 and an insertion loss of 1.5 dB. By utilizing intensity-adaptive feedback control, the operating intensity range of the nonreciprocal system is broadened to 20 dB, which relaxes the limitation of the operating intensity range for nonlinear nonreciprocal systems. Our protocol paves the way to realize high-performance nonreciprocal propagation in optical systems and can also be extended to microwave systems.Nonreciprocal light propagation plays an important role in modern optical systems, from photonic networks to integrated photonics. We propose a nonreciprocal system based on a resonance-frequency-tunable cavity and intensity-adaptive feedback control. Because the feedback-induced Kerr nonlinearity in the cavity is dependent on the incident direction of light, the system exhibits nonreciprocal transmission with a transmission contrast of 0.99 and an insertion loss of 1.5 dB. By utilizing intensity-adaptive feedback control, the operating intensity range of the nonreciprocal system is broadened to 20 dB, which relaxes the limitation of the operating intensity range for nonlinear nonreciprocal systems. Our protocol paves the way to realize high-performance nonreciprocal propagation in optical systems and can also be extended to microwave systems..
Photonics Research
- Publication Date: Jun. 14, 2021
- Vol. 9, Issue 7, 1218 (2021)
Tunable photon blockade with a single atom in a cavity under electromagnetically induced transparency
Jing Tang, Yuangang Deng, and Chaohong Lee
We present an experimental proposal to achieve a strong photon blockade by employing electromagnetically induced transparency (EIT) with a single alkaline-earth-metal atom trapped in an optical cavity. In the presence of optical Stark shift, both the second-order correlation function and cavity transmission exhibit asymmetric structures between the red and blue sidebands of the cavity. For a weak control field, the photon quantum statistics for the coherent transparency window (i.e., atomic quasi-dark-state resonance) are insensitive to the Stark shift, which should also be immune to the spontaneous emission of the excited state by taking advantage of the intrinsic dark-state polariton of EIT. Interestingly, by exploiting the interplay between the Stark shift and control field, the strong photon blockade at atomic quasi-dark-state resonance has an optimal second-order correlation function g(2)(0)～10-4 and a high cavity transmission simultaneously. The underlying physical mechanism is ascribed to the Stark shift enhanced spectrum anharmonicity and the EIT hosted strong nonlinearity with loss-insensitive atomic quasi-dark-state resonance, which is essentially different from the conventional proposal with emerging Kerr nonlinearity in cavity-EIT. Our results reveal a new strategy to realize high-quality single photon sources, which could open up a new avenue for engineering nonclassical quantum states in cavity quantum electrodynamics.We present an experimental proposal to achieve a strong photon blockade by employing electromagnetically induced transparency (EIT) with a single alkaline-earth-metal atom trapped in an optical cavity. In the presence of optical Stark shift, both the second-order correlation function and cavity transmission exhibit asymmetric structures between the red and blue sidebands of the cavity. For a weak control field, the photon quantum statistics for the coherent transparency window (i.e., atomic quasi-dark-state resonance) are insensitive to the Stark shift, which should also be immune to the spontaneous emission of the excited state by taking advantage of the intrinsic dark-state polariton of EIT. Interestingly, by exploiting the interplay between the Stark shift and control field, the strong photon blockade at atomic quasi-dark-state resonance has an optimal second-order correlation function
Photonics Research
- Publication Date: Jun. 14, 2021
- Vol. 9, Issue 7, 1226 (2021)
Directly accessing octave-spanning dissipative Kerr soliton frequency combs in an AlN microresonator
Haizhong Weng, Jia Liu, Adnan Ali Afridi, Jing Li, Jiangnan Dai, Xiang Ma, Yi Zhang, Qiaoyin Lu, John F. Donegan, and Weihua Guo
Self-referenced dissipative Kerr solitons (DKSs) based on optical microresonators offer prominent characteristics allowing for various applications from precision measurement to astronomical spectrometer calibration. To date, direct octave-spanning DKS generation has been achieved only in ultrahigh-Q silicon nitride microresonators under optimized laser tuning speed or bi-directional tuning. Here we propose a simple method to easily access the octave-spanning DKS in an aluminum nitride (AlN) microresonator. In the design, two modes that belong to different families but with the same polarization are nearly degenerate and act as a pump and an auxiliary resonance, respectively. The presence of the auxiliary resonance can balance the thermal dragging effect, crucially simplifying the DKS generation with a single pump and leading to an enhanced soliton access window. We experimentally demonstrate the long-lived DKS operation with a record single-soliton step (10.4 GHz or 83 pm) and an octave-spanning bandwidth (1100–2300 nm) through adiabatic pump tuning. Our scheme also allows for direct creation of the DKS state with high probability and without elaborate wavelength or power schemes being required to stabilize the soliton behavior.Self-referenced dissipative Kerr solitons (DKSs) based on optical microresonators offer prominent characteristics allowing for various applications from precision measurement to astronomical spectrometer calibration. To date, direct octave-spanning DKS generation has been achieved only in ultrahigh-Q silicon nitride microresonators under optimized laser tuning speed or bi-directional tuning. Here we propose a simple method to easily access the octave-spanning DKS in an aluminum nitride (AlN) microresonator. In the design, two modes that belong to different families but with the same polarization are nearly degenerate and act as a pump and an auxiliary resonance, respectively. The presence of the auxiliary resonance can balance the thermal dragging effect, crucially simplifying the DKS generation with a single pump and leading to an enhanced soliton access window. We experimentally demonstrate the long-lived DKS operation with a record single-soliton step (10.4 GHz or 83 pm) and an octave-spanning bandwidth (1100–2300 nm) through adiabatic pump tuning. Our scheme also allows for direct creation of the DKS state with high probability and without elaborate wavelength or power schemes being required to stabilize the soliton behavior..
Photonics Research
- Publication Date: Jul. 01, 2021
- Vol. 9, Issue 7, 1351 (2021)
Optical and Photonic Materials
Mimicking the gravitational effect with gradient index lenses in geometrical optics
Wen Xiao, Sicen Tao, and Huanyang Chen
General relativity establishes the equality between matter-energy density and the Riemann curvature of spacetime. Therefore, light or matter will be bent or trapped when passing near the massive celestial objects, and Newton’s second law fails to explain it. The gravitational effect is not only extensively studied in astronomy but also attracts a great deal of interest in the field of optics. People have mimicked black holes, Einstein’s ring, and other fascinating effects in diverse optical systems. Here, with a gradient index lens, in the geometrical optics regime, we mimic the Schwarzschild precession in the orbit of the star S2 near the Galactic Center massive black hole, which was recently first detected by European Southern Observatory. We also find other series of gradient index lenses that can be used to mimic the possible Reissner–Nordstr?m metric of Einstein’s field equation and dark matter particle motion. Light rays in such gradient lenses will be closed in some cases, while in other cases it would be trapped by the center or keep dancing around the center. Our work presents an efficient toy model to help investigate some complex celestial behaviors, which may require long period detection by using high-precision astronomical tools. The induced gradient lenses enlightened by the gravitational effect also enrich the family of absolute optical instruments for their selective closed trajectories.General relativity establishes the equality between matter-energy density and the Riemann curvature of spacetime. Therefore, light or matter will be bent or trapped when passing near the massive celestial objects, and Newton’s second law fails to explain it. The gravitational effect is not only extensively studied in astronomy but also attracts a great deal of interest in the field of optics. People have mimicked black holes, Einstein’s ring, and other fascinating effects in diverse optical systems. Here, with a gradient index lens, in the geometrical optics regime, we mimic the Schwarzschild precession in the orbit of the star S2 near the Galactic Center massive black hole, which was recently first detected by European Southern Observatory. We also find other series of gradient index lenses that can be used to mimic the possible Reissner–Nordstr?m metric of Einstein’s field equation and dark matter particle motion. Light rays in such gradient lenses will be closed in some cases, while in other cases it would be trapped by the center or keep dancing around the center. Our work presents an efficient toy model to help investigate some complex celestial behaviors, which may require long period detection by using high-precision astronomical tools. The induced gradient lenses enlightened by the gravitational effect also enrich the family of absolute optical instruments for their selective closed trajectories..
Photonics Research
- Publication Date: Jun. 08, 2021
- Vol. 9, Issue 7, 1197 (2021)
On-chip chalcogenide microresonators with low-threshold parametric oscillation
Bin Zhang, Pingyang Zeng, Zelin Yang, Di Xia, Jiaxin Zhao, Yaodong Sun, Yufei Huang, Jingcui Song, Jingshun Pan, Huanjie Cheng, Dukyong Choi, and Zhaohui Li
Chalcogenide glass (ChG) is an attractive material for highly efficient nonlinear photonics, which can cover an ultrabroadband wavelength window from the near-visible to the footprint infrared region. However, it remains a challenge to implement highly-efficient and low-threshold optical parametric processes in chip-scale ChG devices due to thermal and light-induced instabilities as well as a high-loss factor in ChG films. Here, we develop a systematic fabrication process for high-performance photonic-chip-integrated ChG devices, by which planar-integrated ChG microresonators with an intrinsic quality (Q) factor above 1 million are demonstrated. In particular, an in situ light-induced annealing method is introduced to overcome the longstanding instability underlying ChG film. In high-Q ChG microresonators, optical parametric oscillations with threshold power as low as 5.4 mW are demonstrated for the first time, to our best knowledge. Our results would contribute to efforts of making efficient and low-threshold optical microcombs not only in the near-infrared as presented but more promisingly in the midinfrared range.Chalcogenide glass (ChG) is an attractive material for highly efficient nonlinear photonics, which can cover an ultrabroadband wavelength window from the near-visible to the footprint infrared region. However, it remains a challenge to implement highly-efficient and low-threshold optical parametric processes in chip-scale ChG devices due to thermal and light-induced instabilities as well as a high-loss factor in ChG films. Here, we develop a systematic fabrication process for high-performance photonic-chip-integrated ChG devices, by which planar-integrated ChG microresonators with an intrinsic quality (in situ light-induced annealing method is introduced to overcome the longstanding instability underlying ChG film. In high-
Photonics Research
- Publication Date: Jun. 24, 2021
- Vol. 9, Issue 7, 1272 (2021)
Optical Devices
Bandpass-filter-integrated multiwavelength achromatic metalens | Spotlight on Optics
Hanmeng Li, Xingjian Xiao, Bin Fang, Shenglun Gao, Zhizhang Wang, Chen Chen, Yunwei Zhao, Shining Zhu, and Tao Li
The design of large-scale, high-numerical-aperture, and broadband achromatism is a big challenge in metalens research. In fact, many colorful imaging systems have RGB color filters, which means the achromatism only for RGB lights would be sufficient. Avoiding broadband achromatism is expected to greatly improve the working efficiency of metalenses. Nevertheless, a proper bandpass filter is necessary under a white light illumination in the metalens integrated imaging system. Here we propose a bandpass-filter-integrated multiwavelength achromatic metalens (NA=0.2), which is designed using a searching optimization algorithm to achieve the achromatism of RGB lights with high efficiencies. The bandpass filter is implemented by composite DBRs and defect layers, by which three desired wavelengths are selected out. The simulations and experiments on the filter-integrated metalens definitely show a good RGB achromatism. Further imaging experiments demonstrate a higher signal-to-noise ratio and resolution compared with the one without the filter. Our approach provides not only an RGB achromatic meta-imaging device but also a new route to access a highly efficient spectrum tailoring metasystem by incorporating bandpass filter designs.The design of large-scale, high-numerical-aperture, and broadband achromatism is a big challenge in metalens research. In fact, many colorful imaging systems have RGB color filters, which means the achromatism only for RGB lights would be sufficient. Avoiding broadband achromatism is expected to greatly improve the working efficiency of metalenses. Nevertheless, a proper bandpass filter is necessary under a white light illumination in the metalens integrated imaging system. Here we propose a bandpass-filter-integrated multiwavelength achromatic metalens (
Photonics Research
- Publication Date: Jul. 01, 2021
- Vol. 9, Issue 7, 1384 (2021)
Optoelectronics
Nanohole array structured GaN-based white LEDs with improved modulation bandwidth via plasmon resonance and non-radiative energy transfer
Rongqiao Wan, Guoqiang Li, Xiang Gao, Zhiqiang Liu, Junhui Li, Xiaoyan Yi, Nan Chi, and Liancheng Wang
Commercial white LEDs (WLEDs) are generally limited in modulation bandwidth due to a slow Stokes process, long lifetime of phosphors, and the quantum-confined Stark effect. Here we report what we believe is a novel plasmonic WLED by infiltrating a nanohole LED (H-LED) with quantum dots (QDs) and Ag nanoparticles (NPs) together (M-LED). This decreased distance between quantum wells and QDs would open an extra non-radiative energy transfer channel and thus enhance Stokes transfer efficiency. The presence of Ag NPs enhances the spontaneous emission rate significantly. Compared to an H-LED filled with QDs (QD-LED), the optimized M-LED demonstrates a maximum color rendering index of 91.2, a 43% increase in optical power at 60 mA, and a lowered correlated color temperature. Simultaneously, the M-LED exhibits a data rate of 2.21 Gb/s at low current density of 96 A/cm2 (60 mA), which is 77% higher than that of a QD-LED. This is mainly due to the higher optical power and modulation bandwidth of the M-LED under the influence of plasmon, resulting in a higher data rate and higher signal-to-noise ratio under the forward error correction. We believe the approach reported in this work should contribute to a WLED light source with increased modulation bandwidth for a higher speed visible light communication application.Commercial white LEDs (WLEDs) are generally limited in modulation bandwidth due to a slow Stokes process, long lifetime of phosphors, and the quantum-confined Stark effect. Here we report what we believe is a novel plasmonic WLED by infiltrating a nanohole LED (H-LED) with quantum dots (QDs) and Ag nanoparticles (NPs) together (M-LED). This decreased distance between quantum wells and QDs would open an extra non-radiative energy transfer channel and thus enhance Stokes transfer efficiency. The presence of Ag NPs enhances the spontaneous emission rate significantly. Compared to an H-LED filled with QDs (QD-LED), the optimized M-LED demonstrates a maximum color rendering index of 91.2, a 43% increase in optical power at 60 mA, and a lowered correlated color temperature. Simultaneously, the M-LED exhibits a data rate of 2.21 Gb/s at low current density of
Photonics Research
- Publication Date: Jun. 14, 2021
- Vol. 9, Issue 7, 1213 (2021)
Achieving high-responsivity near-infrared detection at room temperature by nano-Schottky junction arrays via a black silicon/platinum contact approach
Fei Hu, Li Wu, Xiyuan Dai, Shuai Li, Ming Lu, and Jian Sun
A room temperature sub-bandgap near-infrared (λ>1100 nm) Si photodetector with high responsivity is achieved. The Si photodetector features black Si made by wet etching Si (100), Si/PtSi nano-Schottky junction arrays made from black Si/Pt contacts, and chemical and field-effect passivation of black Si. Responsivities are 147.6, 292.8, and 478.2 mA/W at reverse voltages of -1.0,-1.5, and -2.0 V for 1550 nm light, respectively, with corresponding specific detectivities being 9.79×108, 1.88×109, and 2.97×109 cm·Hz1/2/W. This work demonstrates a practical room temperature sub-bandgap near-infrared Si photodetector that can be made in a facile and large-scale manner.A room temperature sub-bandgap near-infrared (
Photonics Research
- Publication Date: Jun. 28, 2021
- Vol. 9, Issue 7, 1324 (2021)
Physical Optics
Single-cavity bi-color laser enabled by optical anti-parity-time symmetry
Yao Duan, Xingwang Zhang, Yimin Ding, and Xingjie Ni
The exploration of quantum inspired symmetries in optical systems has spawned promising physics and provided fertile ground for developing devices exhibiting exotic functionalities. Founded on the anti-parity–time (APT) symmetry that is enabled by both spatial and temporal interplay between gain and loss, we demonstrate theoretically and numerically bi-color lasing in a single micro-ring resonator with spatiotemporal modulation along its azimuthal direction. In contrast to conventional multi-mode lasers that have mixed-frequency output, our laser exhibits stable, demultiplexed, tunable bi-color emission at different output ports. Our APT-symmetry-based laser may point out a new route for realizing compact on-chip coherent multi-color light sources.The exploration of quantum inspired symmetries in optical systems has spawned promising physics and provided fertile ground for developing devices exhibiting exotic functionalities. Founded on the anti-parity–time (APT) symmetry that is enabled by both spatial and temporal interplay between gain and loss, we demonstrate theoretically and numerically bi-color lasing in a single micro-ring resonator with spatiotemporal modulation along its azimuthal direction. In contrast to conventional multi-mode lasers that have mixed-frequency output, our laser exhibits stable, demultiplexed, tunable bi-color emission at different output ports. Our APT-symmetry-based laser may point out a new route for realizing compact on-chip coherent multi-color light sources..
Photonics Research
- Publication Date: Jun. 28, 2021
- Vol. 9, Issue 7, 1280 (2021)
Topological scattering singularities and embedded eigenstates for polarization control and sensing applications
Zarko Sakotic, Alex Krasnok, Andrea Alú, and Nikolina Jankovic
Epsilon-near-zero and epsilon near-pole materials enable reflective systems supporting a class of symmetry-protected and accidental embedded eigenstates (EEs) characterized by a diverging phase resonance. Here we show that pairs of topologically protected scattering singularities necessarily emerge from EEs when a non-Hermitian parameter is introduced, lifting the degeneracy between oppositely charged singularities. The underlying topological charges are characterized by an integer winding number and appear as phase vortices of the complex reflection coefficient. By creating and annihilating them, we show that these singularities obey charge conservation, and provide versatile control of amplitude, phase, and polarization in reflection, with potential applications for polarization control and sensing.Epsilon-near-zero and epsilon near-pole materials enable reflective systems supporting a class of symmetry-protected and accidental embedded eigenstates (EEs) characterized by a diverging phase resonance. Here we show that pairs of topologically protected scattering singularities necessarily emerge from EEs when a non-Hermitian parameter is introduced, lifting the degeneracy between oppositely charged singularities. The underlying topological charges are characterized by an integer winding number and appear as phase vortices of the complex reflection coefficient. By creating and annihilating them, we show that these singularities obey charge conservation, and provide versatile control of amplitude, phase, and polarization in reflection, with potential applications for polarization control and sensing..
Photonics Research
- Publication Date: Jun. 28, 2021
- Vol. 9, Issue 7, 1310 (2021)
6 GHz hyperfast rotation of an optically levitated nanoparticle in vacuum
Yuanbin Jin, Jiangwei Yan, Shah Jee Rahman, Jie Li, Xudong Yu, and Jing Zhang
We report an experimental observation of a record-breaking ultrahigh rotation frequency about 6 GHz in an optically levitated nanoparticle system. We optically trap a nanoparticle in the gravity direction with a high numerical aperture (NA) objective lens, which shows significant advantages in compensating the influences of the scattering force and the photophoretic force on the trap, especially at intermediate pressure (about 100 Pa). This allows us to trap a nanoparticle from atmospheric to low pressure (10-3 Pa) without using feedback cooling. We measure a highest rotation frequency about 4.3 GHz of the trapped nanoparticle without feedback cooling and a 6 GHz rotation with feedback cooling, which is the fastest mechanical rotation ever reported to date. Our work provides useful guides for efficiently observing hyperfast rotation in the optical levitation system and may find various applications such as in ultra-sensitive torque detection, probing vacuum friction, and testing unconventional decoherence theories.We report an experimental observation of a record-breaking ultrahigh rotation frequency about 6 GHz in an optically levitated nanoparticle system. We optically trap a nanoparticle in the gravity direction with a high numerical aperture (NA) objective lens, which shows significant advantages in compensating the influences of the scattering force and the photophoretic force on the trap, especially at intermediate pressure (about 100 Pa). This allows us to trap a nanoparticle from atmospheric to low pressure (
Photonics Research
- Publication Date: Jul. 01, 2021
- Vol. 9, Issue 7, 1344 (2021)
Ultrabroadband microwave absorber based on 3D water microchannels
Yan Chen, Kejian Chen, Dajun Zhang, Shihao Li, Yeli Xu, Xiong Wang, and Songlin Zhuang
In this paper, an ultrathin and ultrabroadband metamaterial absorber based on 3D water microchannels is proposed. The experimental results show an absorption rate over 90% and a relative bandwidth up to 165% in the frequency band between 9.6 and 98.9 GHz. This polarization-independent absorber can work at a wide angle of incidence and exhibits good thermal stability. Benefiting from ultrabroadband absorption, thin thickness, low cost, and environmentally friendly materials, the proposed metamaterial absorber can be used in the fields of electromagnetic wave stealth and electromagnetic radiation protection. Related device design and research methods can be extended to the applied research in the terahertz and optical bands.In this paper, an ultrathin and ultrabroadband metamaterial absorber based on 3D water microchannels is proposed. The experimental results show an absorption rate over 90% and a relative bandwidth up to 165% in the frequency band between 9.6 and 98.9 GHz. This polarization-independent absorber can work at a wide angle of incidence and exhibits good thermal stability. Benefiting from ultrabroadband absorption, thin thickness, low cost, and environmentally friendly materials, the proposed metamaterial absorber can be used in the fields of electromagnetic wave stealth and electromagnetic radiation protection. Related device design and research methods can be extended to the applied research in the terahertz and optical bands..
Photonics Research
- Publication Date: Jul. 01, 2021
- Vol. 9, Issue 7, 1391 (2021)
Quantum Optics
Hybrid level anharmonicity and interference-induced photon blockade in a two-qubit cavity QED system with dipole–dipole interaction
C. J. Zhu, K. Hou, Y. P. Yang, and L. Deng
We theoretically study a quantum destructive interference (QDI)-induced photon blockade in a two-qubit driven cavity quantum electrodynamics system with dipole–dipole interaction (DDI). In the absence of dipole–dipole interaction, we show that a QDI-induced photon blockade can be achieved only when the qubit resonance frequency is different from the cavity mode frequency. When DDI is introduced the condition for this photon blockade is strongly dependent upon the pump field frequency, and yet is insensitive to the qubit–cavity coupling strength. Using this tunability feature we show that the conventional energy-level-anharmonicity-induced photon blockade and this DDI-based QDI-induced photon blockade can be combined together, resulting in a hybrid system with substantially improved mean photon number and second-order correlation function. Our proposal provides a nonconventional and experimentally feasible platform for generating single photons.We theoretically study a quantum destructive interference (QDI)-induced photon blockade in a two-qubit driven cavity quantum electrodynamics system with dipole–dipole interaction (DDI). In the absence of dipole–dipole interaction, we show that a QDI-induced photon blockade can be achieved only when the qubit resonance frequency is different from the cavity mode frequency. When DDI is introduced the condition for this photon blockade is strongly dependent upon the pump field frequency, and yet is insensitive to the qubit–cavity coupling strength. Using this tunability feature we show that the conventional energy-level-anharmonicity-induced photon blockade and this DDI-based QDI-induced photon blockade can be combined together, resulting in a hybrid system with substantially improved mean photon number and second-order correlation function. Our proposal provides a nonconventional and experimentally feasible platform for generating single photons..
Photonics Research
- Publication Date: Jun. 21, 2021
- Vol. 9, Issue 7, 1264 (2021)
Motional n-phonon bundle states of a trapped atom with clock transitions
Yuangang Deng, Tao Shi, and Su Yi
Quantum manipulation of individual phonons could offer new resources for studying fundamental physics and creating an innovative platform in quantum information science. Here, we propose to generate quantum states of strongly correlated phonon bundles associated with the motion of a trapped atom. Our scheme operates in the atom–phonon resonance regime where the energy spectrum exhibits strong anharmonicity such that energy eigenstates with different phonon numbers can be well-resolved in the parameter space. Compared to earlier schemes operating in the far dispersive regime, the bundle states generated here contain a large steady-state phonon number. Therefore, the proposed system can be used as a high-quality multiphonon source. Our results open up the possibility of using long-lived motional phonons as quantum resources, which could provide a broad physics community for applications in quantum metrology.Quantum manipulation of individual phonons could offer new resources for studying fundamental physics and creating an innovative platform in quantum information science. Here, we propose to generate quantum states of strongly correlated phonon bundles associated with the motion of a trapped atom. Our scheme operates in the atom–phonon resonance regime where the energy spectrum exhibits strong anharmonicity such that energy eigenstates with different phonon numbers can be well-resolved in the parameter space. Compared to earlier schemes operating in the far dispersive regime, the bundle states generated here contain a large steady-state phonon number. Therefore, the proposed system can be used as a high-quality multiphonon source. Our results open up the possibility of using long-lived motional phonons as quantum resources, which could provide a broad physics community for applications in quantum metrology..
Photonics Research
- Publication Date: Jun. 28, 2021
- Vol. 9, Issue 7, 1289 (2021)
Experimental demonstration of robustness of Gaussian quantum coherence
Haijun Kang, Dongmei Han, Na Wang, Yang Liu, Shuhong Hao, and Xiaolong Su
Besides quantum entanglement and steering, quantum coherence has also been identified as a useful quantum resource in quantum information. It is important to investigate the evolution of quantum coherence in practical quantum channels. In this paper, we experimentally quantify the quantum coherence of a squeezed state and a Gaussian Einstein–Podolsky–Rosen (EPR) entangled state transmitted in Gaussian thermal noise channel. By reconstructing the covariance matrix of the transmitted states, quantum coherence of these Gaussian states is quantified by calculating the relative entropy. We show that quantum coherence of the squeezed state and the Gaussian EPR entangled state is robust against loss and noise in a quantum channel, which is different from the properties of squeezing and Gaussian entanglement. Our experimental results pave the way for application of Gaussian quantum coherence in lossy and noisy environments.Besides quantum entanglement and steering, quantum coherence has also been identified as a useful quantum resource in quantum information. It is important to investigate the evolution of quantum coherence in practical quantum channels. In this paper, we experimentally quantify the quantum coherence of a squeezed state and a Gaussian Einstein–Podolsky–Rosen (EPR) entangled state transmitted in Gaussian thermal noise channel. By reconstructing the covariance matrix of the transmitted states, quantum coherence of these Gaussian states is quantified by calculating the relative entropy. We show that quantum coherence of the squeezed state and the Gaussian EPR entangled state is robust against loss and noise in a quantum channel, which is different from the properties of squeezing and Gaussian entanglement. Our experimental results pave the way for application of Gaussian quantum coherence in lossy and noisy environments..
Photonics Research
- Publication Date: Jun. 28, 2021
- Vol. 9, Issue 7, 1330 (2021)
Wave and particle properties can be spatially separated in a quantum entity | On the Cover
Pratyusha Chowdhury, Arun Kumar Pati, and Jing-Ling Chen
Wave and particle are two fundamental properties of nature. The wave–particle duality has indicated that a quantum object may exhibit the behaviors of both wave and particle, depending upon the circumstances of the experiment. The major significance of wave–particle duality has led to a fundamental equation in quantum mechanics: the Schrödinger equation. At present, the principle of wave–particle duality has been deeply rooted in people’s hearts. This leads to a common-sense perception that wave property and particle property coexist simultaneously in a quantum entity, and these two physical attributes cannot be completely separated from each other. In classical physics, a similar common-sense thought is that a physical system is inseparable from its physical properties. However, this has been recently challenged and beaten by a quantum phenomenon called the “quantum Cheshire cat,” in which a cat and its grin can be spatially separated. In this work, we propose a thought experiment based on the technology similar to the quantum Cheshire cat. We find that wave and particle attributes of a quantum entity can be completely separated, thus successfully dismantling the wave–particle duality for a quantum entity. Our result is still consistent with the complementarity principle and deepens the understanding of quantum foundations.Wave and particle are two fundamental properties of nature. The wave–particle duality has indicated that a quantum object may exhibit the behaviors of both wave and particle, depending upon the circumstances of the experiment. The major significance of wave–particle duality has led to a fundamental equation in quantum mechanics: the Schrödinger equation. At present, the principle of wave–particle duality has been deeply rooted in people’s hearts. This leads to a common-sense perception that wave property and particle property coexist simultaneously in a quantum entity, and these two physical attributes cannot be completely separated from each other. In classical physics, a similar common-sense thought is that a physical system is inseparable from its physical properties. However, this has been recently challenged and beaten by a quantum phenomenon called the “quantum Cheshire cat,” in which a cat and its grin can be spatially separated. In this work, we propose a thought experiment based on the technology similar to the quantum Cheshire cat. We find that wave and particle attributes of a quantum entity can be completely separated, thus successfully dismantling the wave–particle duality for a quantum entity. Our result is still consistent with the complementarity principle and deepens the understanding of quantum foundations..
Photonics Research
- Publication Date: Jul. 01, 2021
- Vol. 9, Issue 7, 1379 (2021)
Silicon Photonics
PIC-integrable, uniformly tensile-strained Ge-on-insulator photodiodes enabled by recessed SiNx stressor
Yiding Lin, Danhao Ma, Kwang Hong Lee, Rui-Tao Wen, Govindo Syaranamual, Lionel C. Kimerling, Chuan Seng Tan, and Jurgen Michel
Mechanical strain engineering has been promising for many integrated photonic applications. However, for the engineering of a material electronic bandgap, a trade-off exists between the strain uniformity and the integration compatibility with photonic-integrated circuits (PICs). Herein, we adopted a straightforward recess-type design of a silicon nitride (SiNx) stressor to achieve a uniform strain with enhanced magnitude in the material of interest on PICs. Normal-incidence, uniformly 0.56% tensile strained germanium (Ge)-on-insulator (GOI) metal-semiconductor-metal photodiodes were demonstrated, using the recessed stressor with 750 MPa tensile stress. The device exhibits a responsivity of 1.84±0.15 A/W at 1550 nm. The extracted Ge absorption coefficient is enhanced by ～3.2× to 8340 cm-1 at 1612 nm and is superior to that of In0.53Ga0.47As up to 1630 nm limited by the measurement spectrum. Compared with the nonrecess strained device, additional absorption coefficient improvement of 10%–20% in the C-band and 40%–60% in the L-band was observed. This work facilitates the recess-strained GOI photodiodes for free-space PIC applications and paves the way for various (e.g., Ge, GeSn or III-V based) uniformly strained photonic devices on PICs.Mechanical strain engineering has been promising for many integrated photonic applications. However, for the engineering of a material electronic bandgap, a trade-off exists between the strain uniformity and the integration compatibility with photonic-integrated circuits (PICs). Herein, we adopted a straightforward recess-type design of a silicon nitride (
Photonics Research
- Publication Date: Jun. 21, 2021
- Vol. 9, Issue 7, 1255 (2021)
Spectroscopy
Broadband mid-infrared molecular spectroscopy based on passive coherent optical–optical modulated frequency combs | Editors' Pick
Zhong Zuo, Chenglin Gu, Daowang Peng, Xing Zou, Yuanfeng Di, Lian Zhou, Daping Luo, Yang Liu, and Wenxue Li
Mid-infrared dual-comb spectroscopy is of great interest owing to the strong spectroscopic features of trace gases, biological molecules, and solid matter with higher resolution, accuracy, and acquisition speed. However, the prerequisite of achieving high coherence of optical sources with the use of bulk sophisticated control systems prevents their widespread use in field applications. Here we generate a highly mutually coherent dual mid-infrared comb spectrometer based on the optical–optical modulation of a continuous-wave (CW) interband or quantum cascade laser. Mutual coherence was passively achieved without post-data processes or active carrier envelope phase-locking processes. The center wavelength of the generated mid-infrared frequency combs can be flexibly tuned by adjusting the wavelength of the CW seeds. The parallel detection of multiple molecular species, including C2H2,CH4,H2CO,H2S, COS, and H2O, was achieved. This technique provides a stable and robust dual-comb spectrometer that will find nonlaboratory applications including open-path atmospheric gas sensing, industrial process monitoring, and combustion.Mid-infrared dual-comb spectroscopy is of great interest owing to the strong spectroscopic features of trace gases, biological molecules, and solid matter with higher resolution, accuracy, and acquisition speed. However, the prerequisite of achieving high coherence of optical sources with the use of bulk sophisticated control systems prevents their widespread use in field applications. Here we generate a highly mutually coherent dual mid-infrared comb spectrometer based on the optical–optical modulation of a continuous-wave (CW) interband or quantum cascade laser. Mutual coherence was passively achieved without post-data processes or active carrier envelope phase-locking processes. The center wavelength of the generated mid-infrared frequency combs can be flexibly tuned by adjusting the wavelength of the CW seeds. The parallel detection of multiple molecular species, including
Photonics Research
- Publication Date: Jul. 01, 2021
- Vol. 9, Issue 7, 1358 (2021)
Surface Optics and Plasmonics
Biochemical sensing exploiting plasmonic sensors based on gold nanogratings and polymer optical fibers
Francesco Arcadio, Luigi Zeni, Domenico Montemurro, Caterina Eramo, Stefania Di Ronza, Chiara Perri, Girolamo D’Agostino, Guido Chiaretti, Giovanni Porto, and Nunzio Cennamo
In this work, we present a novel biochemical sensing approach based on a plasmonic sensor chip, combined with a specific receptor, excited and interrogated via a custom 3D-printed holder through a transmission-based experimental setup, exploiting polymer optical fibers. The setup is designed to measure a disposable plasmonic chip based on a gold nanograting fabricated on a polymethylmethacrylate substrate. The examined sensor configurations here presented are simulated, realized, and experimentally tested. More specifically, first, a numerical analysis is carried out by changing several sensor parameters, then an experimental optical characterization of different sensor configurations is reported. Finally, to test the biosensing capabilities of the proposed method, as a proof of concept, we deposit on the best sensor configuration a biomimetic receptor specific for bovine serum albumin detection. The experimental results demonstrate that the proposed sensor shows an ultra-low limit of detection, equal to about 37 pmol/L.In this work, we present a novel biochemical sensing approach based on a plasmonic sensor chip, combined with a specific receptor, excited and interrogated via a custom 3D-printed holder through a transmission-based experimental setup, exploiting polymer optical fibers. The setup is designed to measure a disposable plasmonic chip based on a gold nanograting fabricated on a polymethylmethacrylate substrate. The examined sensor configurations here presented are simulated, realized, and experimentally tested. More specifically, first, a numerical analysis is carried out by changing several sensor parameters, then an experimental optical characterization of different sensor configurations is reported. Finally, to test the biosensing capabilities of the proposed method, as a proof of concept, we deposit on the best sensor configuration a biomimetic receptor specific for bovine serum albumin detection. The experimental results demonstrate that the proposed sensor shows an ultra-low limit of detection, equal to about 37 pmol/L..
Photonics Research
- Publication Date: Jul. 01, 2021
- Vol. 9, Issue 7, 1397 (2021)
Actively logical modulation of MEMS-based terahertz metamaterial | EIC Choice Award
Ruijia Xu, Xiaocan Xu, Bo-Ru Yang, Xuchun Gui, Zong Qin, and Yu-Sheng Lin
The integration of micro-electro-mechanical system (MEMS) with metamaterial has provided a novel route to achieve programmability via its reconfigurable capabilities. Here, we propose and demonstrate a MEMS-based metadevice by using switchable winding-shaped cantilever metamaterial (WCM) for active logical modulation. WCM can be actuated by external driving voltage, and the logical modulation bit is performed by releasing MEMS cantilevers to represent “on” and “off” states. While the underneath substrate surface of a MEMS-based metadevice is rough after releasing the cantilevers, the metadevice is allowed to operate on the reconfigurable switching state and avoid the snapping down of the device when the system is overloaded. Such a reconfigurable and programmable MEMS-based metadevice exhibits multifunctional characteristics to simultaneously perform the logic operations of “OR” and “AND” gates. By exploiting the tuning mechanism of the MEMS-based metadevice, the arbitrary metamaterial configuration can be implanted into WCM. This opens a wide avenue to further enlarge the operating frequency range and applications in optoelectronic fields. These unique results provide various possibilities in multifunctional switching, active logical modulating, and optical computing applications.The integration of micro-electro-mechanical system (MEMS) with metamaterial has provided a novel route to achieve programmability via its reconfigurable capabilities. Here, we propose and demonstrate a MEMS-based metadevice by using switchable winding-shaped cantilever metamaterial (WCM) for active logical modulation. WCM can be actuated by external driving voltage, and the logical modulation bit is performed by releasing MEMS cantilevers to represent “on” and “off” states. While the underneath substrate surface of a MEMS-based metadevice is rough after releasing the cantilevers, the metadevice is allowed to operate on the reconfigurable switching state and avoid the snapping down of the device when the system is overloaded. Such a reconfigurable and programmable MEMS-based metadevice exhibits multifunctional characteristics to simultaneously perform the logic operations of “OR” and “AND” gates. By exploiting the tuning mechanism of the MEMS-based metadevice, the arbitrary metamaterial configuration can be implanted into WCM. This opens a wide avenue to further enlarge the operating frequency range and applications in optoelectronic fields. These unique results provide various possibilities in multifunctional switching, active logical modulating, and optical computing applications..
Photonics Research
- Publication Date: Jul. 01, 2021
- Vol. 9, Issue 7, 1409 (2021)
Errata
Structured laser beams: toward 2-μm femtosecond laser vortices: publisher’s note
Yongguang Zhao, Li Wang, Weidong Chen, Pavel Loiko, Xavier Mateos, Xiaodong Xu, Ying Liu, Deyuan Shen, Zhengping Wang, Xinguang Xu, Uwe Griebner, and Valentin Petrov
This publisher’s note corrects the authors’ affiliations in Photon. Res.9, 357 (2021)PRHEIZ2327-912510.1364/PRJ.413276.This publisher’s note corrects the authors’ affiliations in Photon. Res. 9 , 357 (2021 )PRHEIZ 2327-9125 10.1364/PRJ.413276
Photonics Research
- Publication Date: Jun. 28, 2021
- Vol. 9, Issue 7, 1343 (2021)
About the Cover
A laser beam (pink, glow line) is reflected by a beam splitter (cyan cube) and enters a Mach–Zehnder interferometer. Due to the quantum Cheshire effect, its wave property (blue curves in the lower arm of the interferometer) and particle property (golden points in the upper arm of the interferometer) are spatially separated and propagates individually.
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