Volume: 6 Issue 5
36 Article(s)

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Parity-time-symmetric whispering-gallery mode nanoparticle sensor [Invited]
Weijian Chen, Jing Zhang, Bo Peng, Şahin Kaya Özdemir, Xudong Fan, and Lan Yang
We present a study of single nanoparticle detection using parity-time (PT) symmetric whispering-gallery mode (WGM) resonators. Our theoretical model and numerical simulations show that, with balanced gain and loss, the PT-symmetric WGM nanoparticle sensor, tailored to operate at PT phase transition points (also called exceptional points), exhibits significant enhancement in frequency splitting when compared with a single WGM nanoparticle sensor subject to the same perturbation. The presence of gain in the PT-symmetric system leads to narrower linewidth, which helps to resolve smaller changes in frequency splitting and improve the detection limit of nanoparticle sensing. Furthermore, we also provide a general method for detecting multiple nanoparticles entering the mode volume of a PT-symmetric WGM sensor one by one. Our study shows the feasibility of PT-symmetric WGM resonators for ultrasensitive single nanoparticle and biomolecule sensing.
Photonics Research
  • Publication Date: Apr. 04, 2018
  • Vol. 6, Issue 5, A23 (2018)
Circular Bragg lasers with radial PT symmetry: Design and analysis with a coupled-mode approach
Ziyao Feng, Jingwen Ma, Zejie Yu, and Xiankai Sun
Parity–time (PT) symmetry has been demonstrated in the frame of classic optics. Its applications in laser science have resulted in unconventional control and manipulation of resonant modes. PT-symmetric periodic circular Bragg lasers were previously proposed. Analyses with a transfer-matrix method have shown their superior properties of reduced threshold and enhanced modal discrimination between the radial modes. However, the properties of the azimuthal modes were not analyzed, which restricts further development of circular Bragg lasers. Here, we adopt the coupled-mode theory to design and analyze chirped circular Bragg lasers with radial PT symmetry. The new structures possess more versatile modal control with further enhanced modal discrimination between the azimuthal modes. We also analyze azimuthally modulated circular Bragg lasers with radial PT symmetry, which are shown to achieve even higher modal discrimination.
Photonics Research
  • Publication Date: Apr. 11, 2018
  • Vol. 6, Issue 5, A38 (2018)
Dual-polarization wavelength conversion of 16-QAM signals in a single silicon waveguide with lateral p-i-n diode [Invited]
Francesco Da Ros, Andrzej Gajda, Erik Liebig, Edson P. da Silva, Anna Pęczek, Peter D. Girouard, Andreas Mai, Klaus Petermann, Lars Zimmermann, Michael Galili, and Leif K. Oxenløwe
Photonics Research
  • Publication Date: Apr. 11, 2018
  • Vol. 6, Issue 5, B23 (2018)
Photonic microwave true time delays for phased array antennas using a 49  GHz FSR integrated optical micro-comb source [Invited]
Xingyuan Xu, Jiayang Wu, Thach G. Nguyen, Tania Moein, Sai T. Chu, Brent E. Little, Roberto Morandotti, Arnan Mitchell, and David J. Moss
We demonstrate significantly improved performance of a microwave true time delay line based on an integrated optical frequency comb source. The broadband micro-comb (over 100 nm wide) features a record low free spectral range (FSR) of 49 GHz, resulting in an unprecedented record high channel number (81 over the C band)—the highest number of channels for an integrated comb source used for microwave signal processing. We theoretically analyze the performance of a phased array antenna and show that this large channel count results in a high angular resolution and wide beam-steering tunable range. This demonstrates the feasibility of our approach as a competitive solution toward implementing integrated photonic true time delays in radar and communications systems.
Photonics Research
  • Publication Date: Apr. 12, 2018
  • Vol. 6, Issue 5, B30 (2018)
Nonlinear optical properties of integrated GeSbS chalcogenide waveguides
Samuel Serna, Hongtao Lin, Carlos Alonso-Ramos, Anupama Yadav, Xavier Le Roux, Kathleen Richardson, Eric Cassan, Nicolas Dubreuil, Juejun Hu, and Laurent Vivien
In this paper, we report the experimental characterization of highly nonlinear GeSbS chalcogenide glass waveguides. We used a single-beam characterization protocol that accounts for the magnitude and sign of the real and imaginary parts of the third-order nonlinear susceptibility of integrated Ge23Sb7S70 (GeSbS) chalcogenide glass waveguides in the near-infrared wavelength range at λ=1580 nm. We measured a waveguide nonlinear parameter of 7.0±0.7 W 1·m 1, which corresponds to a nonlinear refractive index of n2=(0.93±0.08)×10 18 m2/W, comparable to that of silicon, but with an 80 times lower two-photon absorption coefficient βTPA=(0.010±0.003) cm/GW, accompanied with linear propagation losses as low as 0.5 dB/cm. The outstanding linear and nonlinear properties of GeSbS, with a measured nonlinear figure of merit FOMTPA=6.0±1.4 at λ=1580 nm, ultimately make it one of the most promising integrated platforms for the realization of nonlinear functionalities.
Photonics Research
  • Publication Date: Apr. 13, 2018
  • Vol. 6, Issue 5, B37 (2018)
Nonlinear optics on silicon-rich nitride—a high nonlinear figure of merit CMOS platform [Invited]
D. T. H. Tan, K. J. A. Ooi, and D. K. T. Ng
CMOS platforms with a high nonlinear figure of merit are highly sought after for high photonic quantum efficiencies, enabling functionalities not possible from purely linear effects and ease of integration with CMOS electronics. Silicon-based platforms have been prolific amongst the suite of advanced nonlinear optical signal processes demonstrated to date. These include crystalline silicon, amorphous silicon, Hydex glass, and stoichiometric silicon nitride. Residing between stoichiometric silicon nitride and amorphous silicon in composition, silicon-rich nitride films of various formulations have emerged recently as promising nonlinear platforms for high nonlinear figure of merit nonlinear optics. Silicon-rich nitride films are compositionally engineered to create bandgaps that are sufficiently large to eliminate two-photon absorption at telecommunications wavelengths while enabling much larger nonlinear waveguide parameters (5x–500x) than those in stoichiometric silicon nitride. This paper reviews recent developments in the field of nonlinear optics using silicon-rich nitride platforms, as well as the outlook and future opportunities in this burgeoning field.
Photonics Research
  • Publication Date: Apr. 16, 2018
  • Vol. 6, Issue 5, B50 (2018)
Tuning the second-harmonic generation in AlGaAs nanodimers via non-radiative state optimization [Invited]
Davide Rocco, Valerio F. Gili, Lavinia Ghirardini, Luca Carletti, Ivan Favero, Andrea Locatelli, Giuseppe Marino, Dragomir N. Neshev, Michele Celebrano, Marco Finazzi, Giuseppe Leo, and Costantino De Angelis
Photonics Research
  • Publication Date: Apr. 11, 2018
  • Vol. 6, Issue 5, B6 (2018)
Type-II micro-comb generation in a filter-driven four wave mixing laser [Invited]
Hualong Bao, Andrew Cooper, Sai T. Chu, Dave J. Moss, Roberto Morandotti, Brent E. Little, Marco Peccianti, and Alessia Pasquazi
We experimentally demonstrate the generation of highly coherent Type-II micro-combs based on a micro-resonator nested in a fiber cavity loop, known as the filter-driven four wave mixing (FD-FWM) laser scheme. In this system, the frequency spacing of the comb can be adjusted to integer multiples of the free-spectral range (FSR) of the nested micro-resonator by properly tuning the fiber cavity length. Sub-comb lines with single FSR spacing around the primary comb lines can be generated. Such a spectral emission is known as a “Type-II comb”. Our system achieves a fully coherent output. This behavior is verified by numerical simulations. This study represents an important step forward in controlling and manipulating the dynamics of an FD-FWM laser.
Photonics Research
  • Publication Date: Apr. 16, 2018
  • Vol. 6, Issue 5, B67 (2018)
Toward mid-infrared nonlinear optics applications of silicon carbide microdisks engineered by lateral under-etching [Invited]
David Allioux, Ali Belarouci, Darren Hudson, Eric Magi, Milan Sinobad, Guillaume Beaudin, Adrien Michon, Neetesh Singh, Regis Orobtchouk, and Christian Grillet
Photonics Research
  • Publication Date: Apr. 19, 2018
  • Vol. 6, Issue 5, B74 (2018)
Inverse-designed photonic fibers and metasurfaces for nonlinear frequency conversion [Invited]
Chawin Sitawarin, Weiliang Jin, Zin Lin, and Alejandro W. Rodriguez
Typically, photonic waveguides designed for nonlinear frequency conversion rely on intuitive and established principles, including index guiding and bandgap engineering, and are based on simple shapes with high degrees of symmetry. We show that recently developed inverse-design techniques can be applied to discover new kinds of microstructured fibers and metasurfaces designed to achieve large nonlinear frequency-conversion efficiencies. As a proof of principle, we demonstrate complex, wavelength-scale chalcogenide glass fibers and gallium phosphide three-dimensional metasurfaces exhibiting some of the largest nonlinear conversion efficiencies predicted thus far, e.g., lowering the power requirement for third-harmonic generation by 104 and enhancing second-harmonic generation conversion efficiency by 107. Such enhancements arise because, in addition to enabling a great degree of tunability in the choice of design wavelengths, these optimization tools ensure both frequency- and phase-matching in addition to large nonlinear overlap factors.
Photonics Research
  • Publication Date: Apr. 20, 2018
  • Vol. 6, Issue 5, B82 (2018)
Fiber Optics and Optical Communications
20.231  Gbit/s tricolor red/green/blue laser diode based bidirectional signal remodulation visible-light communication system
Liang-Yu Wei, Chin-Wei Hsu, Chi-Wai Chow, and Chien-Hung Yeh
Photonics Research
  • Publication Date: Apr. 19, 2018
  • Vol. 6, Issue 5, 422 (2018)
Optical Devices
Tapering-induced enhancement of light extraction efficiency of nanowire deep ultraviolet LED by theoretical simulations
Ronghui Lin, Sergio Valdes Galan, Haiding Sun, Yangrui Hu, Mohd Sharizal Alias, Bilal Janjua, Tien Khee Ng, Boon S. Ooi, and Xiaohang Li
A nanowire (NW) structure provides an alternative scheme for deep ultraviolet light emitting diodes (DUV-LEDs) that promises high material quality and better light extraction efficiency (LEE). In this report, we investigate the influence of the tapering angle of closely packed AlGaN NWs, which is found to exist naturally in molecular beam epitaxy (MBE) grown NW structures, on the LEE of NW DUV-LEDs. It is observed that, by having a small tapering angle, the vertical extraction is greatly enhanced for both transverse magnetic (TM) and transverse electric (TE) polarizations. Most notably, the vertical extraction of TM emission increased from 4.8% to 24.3%, which makes the LEE reasonably large to achieve high-performance DUV-LEDs. This is because the breaking of symmetry in the vertical direction changes the propagation of the light significantly to allow more coupling into radiation modes. Finally, we introduce errors to the NW positions to show the advantages of the tapered NW structures can be projected to random closely packed NW arrays. The results obtained in this paper can provide guidelines for designing efficient NW DUV-LEDs.
Photonics Research
  • Publication Date: Apr. 23, 2018
  • Vol. 6, Issue 5, 457 (2018)
Research Articles
Integrated Optics
InP-based directly modulated monolithic integrated few-mode transmitter
Zhaosong Li, Dan Lu, Yiming He, Fangyuan Meng, Xuliang Zhou, and Jiaoqing Pan
A monolithic integrated few-mode transmitter comprising of two directly modulated distributed feedback lasers and a multimode-interference-coupler-based mode converter-multiplexer with 66% mode conversion efficiency was designed and demonstrated. A fundamental TE0 mode and a first-order TE1 mode were successfully generated from the transmitter, with the output power of 4 and 5.5 mW at a pump current of around 150 mA, respectively, at the common output port. The small signal modulation bandwidth of the TE0 and TE1 channels reached 17.4 and 14.7 GHz, respectively. Error-free 2×10-Gbit/s direct modulation of the two-mode transmitter was demonstrated, with a power penalty of 4.3 dB between the TE0 mode and the TE1 mode at the bit error rate of 1×10 9.
Photonics Research
  • Publication Date: Apr. 20, 2018
  • Vol. 6, Issue 5, 463 (2018)
Lasers and Laser Optics
Integrated heterogeneous silicon/III–V mode-locked lasers
Michael L. Davenport, Songtao Liu, and John E. Bowers
Photonics Research
  • Publication Date: Apr. 20, 2018
  • Vol. 6, Issue 5, 468 (2018)
Multifunctional metasurface: from extraordinary optical transmission to extraordinary optical diffraction in a single structure
Zi-Lan Deng, Yaoyu Cao, Xiangping Li, and Guo Ping Wang
We show that a metasurface composed of a subwavelength metallic slit array embedded in an asymmetric dielectric environment can exhibit either extraordinary optical transmission (EOT) or extraordinary optical diffraction (EOD). The cascaded refractive indices of the dielectrics can leverage multiple decaying passages into variant subsections with different diffraction order combinations according to the diffraction order chart in the k-vector space, providing a flexible mean to tailor resonance decaying pathways of the metallic slit cavity mode by changing the wavevector of the incident light. As a result, either the zeroth transmission or 1st reflection efficiencies can be enhanced to near unity by the excitation of the localized slit cavity mode, leading to either EOT or EOD in a single structure, depending on the illumination angle. Based on this appealing feature, a multifunctional metasurface that can switch its functionality between transmission filter, mirror, and off-axis lens is demonstrated. Our findings provide a convenient way to construct multifunctional miniaturized optical components on a single planar device.
Photonics Research
  • Publication Date: Apr. 23, 2018
  • Vol. 6, Issue 5, 443 (2018)
Nonlinear Optics
Self-locked orthogonal polarized dual comb in a microresonator
Weiqiang Wang, Wenfu Zhang, Zhizhou Lu, Sai T. Chu, Brent E. Little, Qinghua Yang, Lei Wang, and Wei Zhao
Dual combs are an emerging tool to obtain unprecedented resolution, high sensitivity, ultrahigh accuracy, broad bandwidth, and ultrafast data updating rate in the fields of molecular spectroscopy, optical metrology, as well as optical frequency synthesis. The recent progress in chip-based microcombs has promoted the on-chip dual-comb measuring systems to a new phase attributed to the large frequency spacing and broad spectrum. In this paper, we demonstrate proof-of-concept dual-comb generation with orthogonal polarization in a single microresonator through pumping both the transverse-electric (TE) and transverse-magnetic (TM) modes simultaneously. The two orthogonal polarized pumps are self-oscillating in a fiber ring cavity. The generated dual comb exhibits excellent stability due to the intrinsic feedback mechanism of the self-locked scheme. The repetition rate of the two orthogonal combs is slightly different because of the mode spacing difference between the TE and TM modes. Such orthogonal polarized dual-combs could be a new comb source for out-of-lab applications in the fields of integrated spectroscopy, ranging measurement, optical frequency synthesis, and microwave comb generation.
Photonics Research
  • Publication Date: Apr. 13, 2018
  • Vol. 6, Issue 5, 363 (2018)
Spectrally flat supercontinuum generation in a holmium-doped ZBLAN fiber with record power ratio beyond 3  μm
Linyong Yang, Bin Zhang, Ke Yin, Tianyi Wu, Yijun Zhao, and Jing Hou
A spectrally flat mid-infrared supercontinuum (MIR-SC) spanning 2.8–3.9 μm with a maximum output power of 411 mW was generated in a holmium-doped ZBLAN fiber amplifier (HDZFA). A broadband fiber-based SC covering the 2.4–3.2 μm region was designed to seed the amplifier. Benefiting from the broadband seed laser, the obtained SC had a high spectral flatness of 3 dB over the range of 2.93–3.70 μm (770 nm). A spectral integral showed that the SC power beyond 3 μm was 372 mW, i.e., a power ratio of 90.6% of the total power. This paper, to the best of our knowledge, not only demonstrates the first spectrally flat MIR-SC directly generated in fluoride fiber amplifiers, but also reports the highest power ratio beyond 3 μm obtained in rare-earth-doped fluoride fiber until now.
Photonics Research
  • Publication Date: Apr. 18, 2018
  • Vol. 6, Issue 5, 417 (2018)
Active macroscale visible plasmonic nanorod self-assembled monolayer
Yue Li, Jian Li, Taixing Huang, Fei Huang, Jun Qin, Lei Bi, Jianliang Xie, Longjiang Deng, and Bo Peng
Although plasmonic nanostructure has attracted widespread research interest in recent years, it is still a major challenge to realize large-scale active plasmonic nanostructure operation in the visible optical frequency. Herein, we demonstrate a heterostructure geometry comprising a centimeter-scale Au nanoparticle monolayer and VO2 films, in which the plasmonic peak is inversely tuned between 685 nm and 618 nm by a heating process since the refractive index will change when VO2 films undergo the transition between the insulating phase and the metallic phase. Simultaneously, the phase transition of VO2 films can be improved by plasmonic arrays due to plasmonic enhanced light absorption and the photothermal effect. The phase transition temperature for Au/VO2 films is lower than that for bare VO2 films and can decrease to room temperature under the laser irradiation. For light-induced phase transition of VO2 films, the laser power of Au/VO2 film phase transition is ~28.6% lower than that of bare VO2 films. Our work raises the feasibility to use active plasmonic arrays in the visible region.
Photonics Research
  • Publication Date: Apr. 18, 2018
  • Vol. 6, Issue 5, 409 (2018)
Experimental realization to efficiently sort vector beams by polarization topological charge via Pancharatnam–Berry phase modulation
Shuiqin Zheng, Ying Li, Qinggang Lin, Xuanke Zeng, Guoliang Zheng, Yi Cai, Zhenkuan Chen, Shixiang Xu, and Dianyuan Fan
This paper reports the experimental realization of efficiently sorting vector beams by polarization topological charge (PTC). The PTC of a vector beam can be defined as the repetition number of polarization state change along the azimuthal axis, while its sign stands for the rotating direction of the polarization. Here, a couple of liquid crystal Pancharatnam–Berry optical elements (PBOEs) have been used to introduce conjugated spatial phase modulations for two orthogonal circular polarization states. Applying these PBOEs in a 4-f optical system, our experiments show the setup can work for PTC sorting with a separation efficiency of more than 58%. This work provides an effective way to decode information from different PTCs, which may be interesting in many fields, especially in optical communication.
Photonics Research
  • Publication Date: Apr. 18, 2018
  • Vol. 6, Issue 5, 385 (2018)
Wavelength-switchable vortex beams based on a polarization-dependent microknot resonator
Jinqiu Zheng, Ao Yang, Teng Wang, Xianglong Zeng, Ning Cao, Mei Liu, Fufei Pang, and Tingyun Wang
We experimentally demonstrated a method of generating continuously wavelength-switchable optical vortex beams (OVBs) in an all-fiber laser. A polarization-dependent microknot resonator (MKR) functions as comb filter and accounts for the narrow linewidth (0.018 nm) of multiwavelength channels. The wavelength interval corresponds to the free spectral range of the MKR. We exploit a fused SMF–FMF (single mode fiber–few mode fiber) mode coupler to obtain broadband mode conversion and successfully achieve multiwavelength switchable OVBs. As far as we know, this is the first report about identical multiwavelength vortex beams with topological charges of ±1. It has been verified that each channel of the vortex beams preserves the same orbital angular momentum (OAM) properties through their clear spiral interferograms. Multiwavelength vortex beams with identical OAM properties are desirable for multiplexing, exchanging, and routing to further improve the capacity of optical fiber transmission.
Photonics Research
  • Publication Date: Apr. 18, 2018
  • Vol. 6, Issue 5, 396 (2018)
Optically spatial information selection with hybridly polarized beam in atomic vapor
Jinwen Wang, Xin Yang, Yunke Li, Yun Chen, Mingtao Cao, Dong Wei, Hong Gao, and Fuli Li
Vector beams with spatially variant polarization have attracted much attention in recent years, with potential applications in both classical optics and quantum optics. In this work, we study a polarization selection of spatial intensity distribution by utilizing a hybridly polarized beam as a coupling beam and a circularly polarized beam as a probe beam in Rb87 atom vapor. We experimentally observe that the spatial intensity distribution of the probe beam after passing through atoms can be modulated by the hybridly polarized beam due to the optical pumping effect. Then, the information loaded in the probe beam can be designedly filtrated by an atomic system with a high extinction ratio. A detailed process of the optical pumping effect in our configurations and the corresponding absorption spectra are presented to interpret our experimental results, which can be used for the spatial optical information locally extracted based on an atomic system, which has potential applications in quantum communication and computation.
Photonics Research
  • Publication Date: Apr. 23, 2018
  • Vol. 6, Issue 5, 451 (2018)
Quantum Optics
Generation of a continuous-variable quadripartite cluster state multiplexed in the spatial domain
Chunxiao Cai, Long Ma, Juan Li, Hui Guo, Kui Liu, Hengxin Sun, Rongguo Yang, and Jiangrui Gao
As a highly entangled quantum network, the cluster state has the potential for greater information capacity and use in measurement-based quantum computation. Here, we report generating a continuous-variable quadripartite “square” cluster state of multiplexing orthogonal spatial modes in a single optical parametric amplifier (OPA), and further improve the quality of entanglement by optimizing the pump profile. We produce multimode entanglement of two first-order Hermite–Gauss modes within one beam in a single multimode OPA and transform it into a cluster state by phase correction. Furthermore, the pump-profile dependence of the entanglement of this state is explored. Compared with fundamental mode pumping, an enhancement of approximately 33% is achieved using the suitable pump-profile mode. Our approach is potentially scalable to multimode entanglement in the spatial domain. Such spatial cluster states may contribute to future schemes in spatial quantum information processing.
Photonics Research
  • Publication Date: Apr. 26, 2018
  • Vol. 6, Issue 5, 479 (2018)
Surface-enhanced Raman scattering on dielectric microspheres with whispering gallery mode resonance
Steven H. Huang, Xuefeng Jiang, Bo Peng, Corey Janisch, Alexander Cocking, Şahin Kaya Özdemir, Zhiwen Liu, and Lan Yang
Conventionally, metallic nanostructures are used for surface-enhanced Raman spectroscopy (SERS), but recently there has been increasing interest in the enhancement of Raman scattering from dielectric substrates due to their improved stability and biocompatibility compared with metallic substrates. Here, we report the observation of enhanced Raman scattering from rhodamine 6G molecules coated on silica microspheres. We excite the whispering gallery modes (WGMs) supported in the microspheres with a tapered fiber coupler for efficient WGM excitation, and the Raman enhancement can be attributed to the WGM mechanism. Strong resonance enhancement in pump laser intensity and modified Raman emission from the Purcell effect in the microsphere resonator are observed from the experiment and compared with theoretical results. A total Raman enhancement factor of 1.4×104 is observed, with contribution mostly from the enhancement in pump laser intensity. Our results show that, with an efficient pumping scheme, dielectric microspheres are a viable alternative to metallic SERS substrates.
Photonics Research
  • Publication Date: Apr. 04, 2018
  • Vol. 6, Issue 5, 346 (2018)
Chimera states in plasmonic nanoresonators
Eesa Rahimi, and Kürşat Şendur
The chimera state is the concurrent combination of synchronous and incoherent oscillations in a set of identical oscillators. In this study, we demonstrate the states for optical nanoresonators where the oscillators are designed based on a plasmonic dimer cavity. This resonator interchanges radiative energy with an active medium located at its hotspot, and therefore forms an amplitude-mediated oscillating system. Finite-difference time-domain (FDTD)-based numerical analysis of a circular array of the coupled oscillators reveals that regardless of identical nature, oscillator phase is not concordant over time for all members. The effect of coupling strength on the phase escape/synchronization of the oscillators is investigated for the plasmonic nanoresonator system. It is shown that for identical oscillators, which are placed symmetrically over the perimeter of a disc, the array can be divided to several subgroups of concurrent coherent and incoherent members. While the oscillator of each subgroup seems to be locked together, one member can escape from synchronization for a while and return to coherency, or it can sync with the other groups. The effect of coupling strength and number of oscillators on the phase-escape pace is studied for this system, and strong coupling is shown to force the array members to fully synchronize while weaker coupling causes chimera states in the array.
Photonics Research
  • Publication Date: Apr. 23, 2018
  • Vol. 6, Issue 5, 427 (2018)
Silicon Photonics
All-silicon carrier accumulation modulator based on a lateral metal-oxide-semiconductor capacitor
Kapil Debnath, David J. Thomson, Weiwei Zhang, Ali Z. Khokhar, Callum Littlejohns, James Byers, Lorenzo Mastronardi, Muhammad K. Husain, Kouta Ibukuro, Frederic Y. Gardes, Graham T. Reed, and Shinichi Saito
In silicon photonics, the carrier depletion scheme has been the most commonly used mechanism for demonstrating high-speed electro-optic modulation. However, in terms of phase modulation efficiency, carrier-accumulation-based devices potentially offer almost an order of magnitude improvement over those based on carrier depletion. Previously reported accumulation modulator designs only considered vertical metal-oxide-semiconductor (MOS) capacitors, which imposes serious restrictions on the design flexibility and integratability with other photonic components. In this work, for the first time to our knowledge, we report experimental demonstration of an all-silicon accumulation phase modulator based on a lateral MOS capacitor. Using a Mach–Zehnder interferometer modulator with a 500-μm-long phase shifter, we demonstrate high-speed modulation up to 25 Gbit/s with a modulation efficiency (VπLπ) of 1.53 V·cm.
Photonics Research
  • Publication Date: Apr. 18, 2018
  • Vol. 6, Issue 5, 373 (2018)
On-chip cyclic-AWG-based 12  ×  12 silicon wavelength routing switches with minimized port-to-port insertion loss fluctuation
Zepeng Pan, Songnian Fu, Luluzi Lu, Dongyu Li, Weijie Chang, Deming Liu, and Minming Zhang
With the rapidly increasing bandwidth requirements of optical communication networks, compact and low-cost large-scale optical switches become necessary. Silicon photonics is a promising technology due to its small footprint, cost competitiveness, and high bandwidth density. In this paper, we demonstrate a 12×12 silicon wavelength routing switch employing cascaded arrayed waveguide gratings (AWGs) connected by a silicon waveguide interconnection network on a single chip. We optimize the connecting strategy of the crossing structure to reduce the switch’s footprint. We develop an algorithm based on minimum standard deviation to minimize the port-to-port insertion loss (IL) fluctuation of the switch globally. The simulated port-to-port IL fluctuation decreases by about 3 dB compared with that of the conventional one. The average measured port-to-port IL is 13.03 dB, with a standard deviation of 0.78 dB and a fluctuation of 2.39 dB. The device can be used for wide applications in core networks and data centers.
Photonics Research
  • Publication Date: Apr. 18, 2018
  • Vol. 6, Issue 5, 380 (2018)
Ultrafast Optics
Control of soft X-ray high harmonic spectrum by using two-color laser pulses
Cheng Jin, and C. D. Lin
We demonstrate the suppression of soft X-ray high harmonics generated by two-color laser pulses interacting with Ne gas in a gas cell. We show that harmonic suppression can occur at the proper combination of the propagation distance and gas pressure. The physical mechanism behind is the phase mismatch between “short”-trajectory harmonics generated at the early and later times through the interplay of geometric phase, dispersion, and plasma effects. In addition, we demonstrate that the position and depth of harmonic suppression can be tuned by increasing the gas pressure. Furthermore, the suppression can be extended to other laser focusing configurations by properly scaling macroscopic parameters. Our investigation reveals a simple and novel experimental scheme purely relying on the phase mismatch for selectively controlling soft X-ray tabletop light sources without adopting the filters for applications.
Photonics Research
  • Publication Date: Apr. 23, 2018
  • Vol. 6, Issue 5, 434 (2018)