- Special Issue
- Optical Microresonators
- 13 Article (s)
Optical Microresonators feature issue introduction
Yun-Feng Xiao, Kartik Srinivasan, Pascal Del’Haye, and Mengjie Yu
We give an introduction to the feature issue composed of twelve articles on Optical Microresonators. We give an introduction to the feature issue composed of twelve articles on Optical Microresonators.
Photonics Research
- Publication Date: Nov. 24, 2023
- Vol. 11, Issue 12, OM1 (2023)
Noise canceled graphene-microcavity fiber laser sensor for ultrasensitive gas detection
Yuchen Wang, Yiwei Li, Yicheng Li, Hao Zhang, Zihan Liu, Yanhong Guo, Zeping Wang, Jun He, Xuhan Guo, Yiping Wang, and Baicheng Yao
Optical microcavities offer a promising platform for highly efficient light–matter interactions. Recently, the combination of microresonators and 2D materials in the nanoscale has further enriched the optoelectronics of microcavity geometries, spurring broad advances including lasers, nonlinear converters, modulators, and sensors. Here, we report the concept of compact dual-laser cogeneration in a graphene-microcavity fiber, which offers a way to cancel the optical common mode noises. Driven by a single 980 nm pump, orthogonally polarized laser lines are generated in a pair of degeneracy breaking modes. The two laser lines produce a heterodyne beat note at 118.96 MHz, with frequency noise down to 200 Hz2/Hz at 1 MHz offset, demonstrating a linewidth of 930 Hz in vacuum. This compact device enables on-line and label-free NH3 gas detection with high resolution, realizing a detection limit on a single pmol/L level, and a capability to quantitatively trace gas–graphene interactions. Such a combination of graphene optoelectronics and microcavity photonics demonstrates a novel physical paradigm for microlaser control and offers a new scheme for in situ chemical sensing. Optical microcavities offer a promising platform for highly efficient light–matter interactions. Recently, the combination of microresonators and 2D materials in the nanoscale has further enriched the optoelectronics of microcavity geometries, spurring broad advances including lasers, nonlinear converters, modulators, and sensors. Here, we report the concept of compact dual-laser cogeneration in a graphene-microcavity fiber, which offers a way to cancel the optical common mode noises. Driven by a single 980 nm pump, orthogonally polarized laser lines are generated in a pair of degeneracy breaking modes. The two laser lines produce a heterodyne beat note at 118.96 MHz, with frequency noise down to 200 Hz2/Hz at 1 MHz offset, demonstrating a linewidth of 930 Hz in vacuum. This compact device enables on-line and label-free NH3 gas detection with high resolution, realizing a detection limit on a single pmol/L level, and a capability to quantitatively trace gas–graphene interactions. Such a combination of graphene optoelectronics and microcavity photonics demonstrates a novel physical paradigm for microlaser control and offers a new scheme for in situ chemical sensing.
Photonics Research
- Publication Date: Jul. 20, 2023
- Vol. 11, Issue 8, A1 (2023)
Mitigating fast thermal instability by engineered laser sweep in AlN soliton microcomb generation
Kewei Liu, Zihao Wang, Shunyu Yao, Yanan Guo, Jianchang Yan, Junxi Wang, Changxi Yang, and Chengying Bao
Transient thermal instability represents a significant challenge in generating soliton microcombs. Fast laser sweep can be an efficient method to mitigate thermal instability, but it requires an ultrahigh laser sweep rate for crystalline microresonators with fast thermal relaxation. Here, we engineer a laser sweep waveform to generate AlN-on-sapphire soliton microcombs with an intermediate sweep speed (<30 GHz/μs). Two laser sweep methods with backward plus forward tuning or two-step backward tuning added after the fast forward laser sweep were demonstrated to stabilize solitons. Reducing the soliton number is found to be useful to stabilize solitons in fast laser sweep. The effectiveness of the methods was numerically verified. Our measurements and simulations also reveal the impacts of different thermal relaxation processes occurring at quite different time scales on thermal instability. The requirement of the laser sweep protocols is discussed. Transient thermal instability represents a significant challenge in generating soliton microcombs. Fast laser sweep can be an efficient method to mitigate thermal instability, but it requires an ultrahigh laser sweep rate for crystalline microresonators with fast thermal relaxation. Here, we engineer a laser sweep waveform to generate AlN-on-sapphire soliton microcombs with an intermediate sweep speed (<30 GHz/μs). Two laser sweep methods with backward plus forward tuning or two-step backward tuning added after the fast forward laser sweep were demonstrated to stabilize solitons. Reducing the soliton number is found to be useful to stabilize solitons in fast laser sweep. The effectiveness of the methods was numerically verified. Our measurements and simulations also reveal the impacts of different thermal relaxation processes occurring at quite different time scales on thermal instability. The requirement of the laser sweep protocols is discussed.
Photonics Research
- Publication Date: Aug. 01, 2023
- Vol. 11, Issue 8, A10 (2023)
Structural characterization of thin-walled microbubble cavities
Mohammed Zia Jalaludeen, Shilong Li, Ke Tian, Toshio Sasaki, and Síle Nic Chormaic
Whispering gallery mode (WGM) microbubble cavities are a versatile optofluidic sensing platform owing to their hollow core geometry. To increase the light–matter interaction and, thereby, achieve higher sensitivity, thin-walled microbubbles are desirable. However, a lack of knowledge about the precise geometry of hollow microbubbles prevents us from having an accurate theoretical model to describe the WGMs and their response to external stimuli. In this work, we provide a complete characterization of the wall structure of a microbubble and propose a theoretical model for the WGMs in this thin-walled microcavity based on the optical waveguide approach. Structural characterization of the wavelength-scale wall is enabled by focused ion beam milling and scanning electron microscopy imaging. The proposed theoretical model is verified by finite element method simulations. Our approach can readily be extended to other low-dimensional micro-/nanophotonic structures. Whispering gallery mode (WGM) microbubble cavities are a versatile optofluidic sensing platform owing to their hollow core geometry. To increase the light–matter interaction and, thereby, achieve higher sensitivity, thin-walled microbubbles are desirable. However, a lack of knowledge about the precise geometry of hollow microbubbles prevents us from having an accurate theoretical model to describe the WGMs and their response to external stimuli. In this work, we provide a complete characterization of the wall structure of a microbubble and propose a theoretical model for the WGMs in this thin-walled microcavity based on the optical waveguide approach. Structural characterization of the wavelength-scale wall is enabled by focused ion beam milling and scanning electron microscopy imaging. The proposed theoretical model is verified by finite element method simulations. Our approach can readily be extended to other low-dimensional micro-/nanophotonic structures.
Photonics Research
- Publication Date: Aug. 01, 2023
- Vol. 11, Issue 8, A19 (2023)
Optomechanical preparation of photon number-squeezed states with a pair of thermal reservoirs of opposite temperatures
Baiqiang Zhu, Keye Zhang, and Weiping Zhang
Photon number-squeezed states are of significant value in fundamental quantum research and have a wide range of applications in quantum metrology. Most of their preparation mechanisms require precise control of quantum dynamics and are less tolerant to dissipation. We propose a mechanism that is not subject to these restraints. In contrast to common approaches, we exploit the self-balancing between two types of dissipation induced by positive- and negative-temperature reservoirs to generate steady states with sub-Poissonian statistical distributions of photon numbers. We also show how to implement this mechanism with cavity optomechanical systems. The quality of the prepared photon number-squeezed state is estimated by our theoretical model combined with realistic parameters for various typical optomechanical systems. Photon number-squeezed states are of significant value in fundamental quantum research and have a wide range of applications in quantum metrology. Most of their preparation mechanisms require precise control of quantum dynamics and are less tolerant to dissipation. We propose a mechanism that is not subject to these restraints. In contrast to common approaches, we exploit the self-balancing between two types of dissipation induced by positive- and negative-temperature reservoirs to generate steady states with sub-Poissonian statistical distributions of photon numbers. We also show how to implement this mechanism with cavity optomechanical systems. The quality of the prepared photon number-squeezed state is estimated by our theoretical model combined with realistic parameters for various typical optomechanical systems.
Photonics Research
- Publication Date: Aug. 22, 2023
- Vol. 11, Issue 9, A26 (2023)
Shape-tailored whispering gallery microcavity lasers designed by transformation optics|On the Cover
Yong-Hoon Lee, Honghwi Park, Inbo Kim, Sang-Jun Park, Sunghwan Rim, Byoung Jun Park, Moohyuk Kim, Yushin Kim, Myung-Ki Kim, Won Seok Han, Hosung Kim, Hongsik Park, and Muhan Choi
Semiconductor microdisk lasers have great potential as low-threshold, high-speed, and small-form-factor light sources required for photonic integrated circuits because of their high-Q factors associated with long-lived whispering gallery modes (WGMs). Despite these advantages, the rotational symmetry of the disk shape restricts practical applications of the photonic devices because of their isotropic emission, which lacks directionality in far-field emission and difficulty in free-space out coupling. To overcome this problem, deformation of the disk cavity has been mainly attempted. However, the approach cannot avoid significant Q degradation owing to the broken rotational symmetry. Here, we first report a deformed shape microcavity laser based on transformation optics, which exploits WGMs free from Q degradation. The deformed cavity laser was realized by a spatially varying distribution of deep-sub-wavelength-scale (60 nm diameter) nanoholes in an InGaAsP-based multi-quantum-well heterostructure. The lasing threshold of our laser is one-third of that of the same shaped homogeneous laser and quite similar to that of a homogeneous microdisk laser. The results mean that Q spoiling caused by the boundary shape deformation is recovered by spatially varying nanohole density distribution designed by transformation optics and effective medium approximation. Semiconductor microdisk lasers have great potential as low-threshold, high-speed, and small-form-factor light sources required for photonic integrated circuits because of their high-Q factors associated with long-lived whispering gallery modes (WGMs). Despite these advantages, the rotational symmetry of the disk shape restricts practical applications of the photonic devices because of their isotropic emission, which lacks directionality in far-field emission and difficulty in free-space out coupling. To overcome this problem, deformation of the disk cavity has been mainly attempted. However, the approach cannot avoid significant Q degradation owing to the broken rotational symmetry. Here, we first report a deformed shape microcavity laser based on transformation optics, which exploits WGMs free from Q degradation. The deformed cavity laser was realized by a spatially varying distribution of deep-sub-wavelength-scale (60 nm diameter) nanoholes in an InGaAsP-based multi-quantum-well heterostructure. The lasing threshold of our laser is one-third of that of the same shaped homogeneous laser and quite similar to that of a homogeneous microdisk laser. The results mean that Q spoiling caused by the boundary shape deformation is recovered by spatially varying nanohole density distribution designed by transformation optics and effective medium approximation.
Photonics Research
- Publication Date: Aug. 28, 2023
- Vol. 11, Issue 9, A35 (2023)
Soliton microcomb-assisted microring photonic thermometer with ultra-high resolution and broad range
Cheng Zhang, Jin Wang, Guoguo Kang, Jianxin Gao, Zhier Qu, Shuai Wan, Chunhua Dong, Yijie Pan, and Jifeng Qu
Whispering gallery mode resonators (WGMRs) have proven their advantages in terms of sensitivity and precision in various sensing applications. However, when high precision is pursued, the WGMR demands a high-quality factor usually at the cost of its free spectral range (FSR) and corresponding measurement range. In this article, we propose a high-resolution and wide-range temperature sensor based on chip-scale WGMRs, which utilizes a Si3N4 ring resonator as the sensing element and a MgF2-based microcomb as a broadband frequency reference. By measuring the beatnote signal of the WGM and microcomb, the ultra-high resolution of 58 micro-Kelvin (μK) was obtained. To ensure high resolution and broad range simultaneously, we propose an ambiguity-resolving method based on the gradient of feedback voltage and combine it with a frequency-locking technique. In a proof-of-concept experiment, a wide measurement range of 45 K was demonstrated. Our soliton comb-assisted temperature measurement method offers high-resolution and wide-range capabilities, with promising advancements in various sensing applications. Whispering gallery mode resonators (WGMRs) have proven their advantages in terms of sensitivity and precision in various sensing applications. However, when high precision is pursued, the WGMR demands a high-quality factor usually at the cost of its free spectral range (FSR) and corresponding measurement range. In this article, we propose a high-resolution and wide-range temperature sensor based on chip-scale WGMRs, which utilizes a Si3N4 ring resonator as the sensing element and a MgF2-based microcomb as a broadband frequency reference. By measuring the beatnote signal of the WGM and microcomb, the ultra-high resolution of 58 micro-Kelvin (μK) was obtained. To ensure high resolution and broad range simultaneously, we propose an ambiguity-resolving method based on the gradient of feedback voltage and combine it with a frequency-locking technique. In a proof-of-concept experiment, a wide measurement range of 45 K was demonstrated. Our soliton comb-assisted temperature measurement method offers high-resolution and wide-range capabilities, with promising advancements in various sensing applications.
Photonics Research
- Publication Date: Sep. 21, 2023
- Vol. 11, Issue 10, A44 (2023)
Higher-order exceptional points in waveguide-coupled microcavities: perturbation induced frequency splitting and mode patterns
Julius Kullig, Daniel Grom, Sebastian Klembt, and Jan Wiersig
Exceptional points are degeneracies in the spectrum of non-Hermitian open systems where at least two eigenfrequencies and simultaneously the corresponding eigenstates of the Hamiltonian coalesce. Especially, the robust construction of higher-order exceptional points with more than two degenerate eigenfrequencies and eigenstates is challenging but yet worthwhile for applications. In this paper, we reconsider the formation of higher-order exceptional points through waveguide-coupled microring cavities and asymmetric backscattering. In this context, we demonstrate the influence of perturbations on the frequency splitting of the system. To generate higher-order exceptional points in a simple and robust way, a mirror-induced asymmetric backscattering approach is used. In addition to the exceptional-point enhanced sensing capabilities of such systems, also a cavity-selective sensitivity is achieved for particle sensing. The results are motivated by an effective Hamiltonian description and verified by full numerical simulations of the dielectric structure. Exceptional points are degeneracies in the spectrum of non-Hermitian open systems where at least two eigenfrequencies and simultaneously the corresponding eigenstates of the Hamiltonian coalesce. Especially, the robust construction of higher-order exceptional points with more than two degenerate eigenfrequencies and eigenstates is challenging but yet worthwhile for applications. In this paper, we reconsider the formation of higher-order exceptional points through waveguide-coupled microring cavities and asymmetric backscattering. In this context, we demonstrate the influence of perturbations on the frequency splitting of the system. To generate higher-order exceptional points in a simple and robust way, a mirror-induced asymmetric backscattering approach is used. In addition to the exceptional-point enhanced sensing capabilities of such systems, also a cavity-selective sensitivity is achieved for particle sensing. The results are motivated by an effective Hamiltonian description and verified by full numerical simulations of the dielectric structure.
Photonics Research
- Publication Date: Oct. 01, 2023
- Vol. 11, Issue 10, A54 (2023)
Whispering-gallery optical microprobe for photoacoustic imaging
Jialve Sun, Shui-Jing Tang, Jia-Wei Meng, and Changhui Li
Optical ultrasonic probes, exemplified by Fabry–Perot cavities on optical fibers, have small sizes, high sensitivity, and pure optical characteristics, making them highly attractive in high-resolution ultrasonic/photoacoustic imaging, especially in near-field or endoscopic scenarios. Taking a different approach, we demonstrate an ultrasensitive and broadband ultrasound microprobe formed by an optical whispering-gallery-mode polymer microcavity coupled to a U-shaped microfiber. With the high-quality (Q) factors (>106), the noise equivalent pressure of the ultrasound microprobe reaches 1.07 mPa/√Hz with a record broadband response of 150 MHz and a large detection angle of 180°. Our results show that this optical microprobe can overcome the strong decay resulting from ultrasound diverging and medium absorption through short working distances. We further demonstrate high-quality in vivo whole-body photoacoustic imaging of a zebrafish larva. Our implementation provides a new strategy for developing miniature ultrasound detectors and holds great potential for broad applications. Optical ultrasonic probes, exemplified by Fabry–Perot cavities on optical fibers, have small sizes, high sensitivity, and pure optical characteristics, making them highly attractive in high-resolution ultrasonic/photoacoustic imaging, especially in near-field or endoscopic scenarios. Taking a different approach, we demonstrate an ultrasensitive and broadband ultrasound microprobe formed by an optical whispering-gallery-mode polymer microcavity coupled to a U-shaped microfiber. With the high-quality (Q) factors (>106), the noise equivalent pressure of the ultrasound microprobe reaches 1.07 mPa/√Hz with a record broadband response of 150 MHz and a large detection angle of 180°. Our results show that this optical microprobe can overcome the strong decay resulting from ultrasound diverging and medium absorption through short working distances. We further demonstrate high-quality in vivo whole-body photoacoustic imaging of a zebrafish larva. Our implementation provides a new strategy for developing miniature ultrasound detectors and holds great potential for broad applications.
Photonics Research
- Publication Date: Oct. 16, 2023
- Vol. 11, Issue 11, A65 (2023)
Multi-mode microcavity frequency engineering through a shifted grating in a photonic crystal ring|Spotlight on Optics
Xiyuan Lu, Yi Sun, Ashish Chanana, Usman A. Javid, Marcelo Davanco, and Kartik Srinivasan
Frequency engineering of whispering-gallery resonances is essential in microcavity nonlinear optics. The key is to control the frequencies of the cavity modes involved in the underlying nonlinear optical process to satisfy its energy conservation criterion. Compared to the conventional method that tailors dispersion by cross-sectional geometry, thereby impacting all cavity mode frequencies, grating-assisted microring cavities, often termed as photonic crystal microrings, provide more enabling capabilities through mode-selective frequency control. For example, a simple single period grating added to a microring has been used for single frequency engineering in Kerr optical parametric oscillation (OPO) and frequency combs. Recently, this approach has been extended to multi-frequency engineering by using multi-period grating functions, but at the cost of increasingly complex grating profiles that require challenging fabrication. Here, we demonstrate a simple approach, which we term as shifted grating multiple mode splitting (SGMMS), where spatial displacement of a single period grating imprinted on the inner boundary of the microring creates a rotational asymmetry that frequency splits multiple adjacent cavity modes. This approach is easy to implement and presents no additional fabrication challenges compared to an un-shifted grating, and yet is very powerful in providing multi-frequency engineering functionality for nonlinear optics. We showcase an example where SGMMS enables OPO across a wide range of pump wavelengths in a normal-dispersion device that otherwise would not support OPO. Frequency engineering of whispering-gallery resonances is essential in microcavity nonlinear optics. The key is to control the frequencies of the cavity modes involved in the underlying nonlinear optical process to satisfy its energy conservation criterion. Compared to the conventional method that tailors dispersion by cross-sectional geometry, thereby impacting all cavity mode frequencies, grating-assisted microring cavities, often termed as photonic crystal microrings, provide more enabling capabilities through mode-selective frequency control. For example, a simple single period grating added to a microring has been used for single frequency engineering in Kerr optical parametric oscillation (OPO) and frequency combs. Recently, this approach has been extended to multi-frequency engineering by using multi-period grating functions, but at the cost of increasingly complex grating profiles that require challenging fabrication. Here, we demonstrate a simple approach, which we term as shifted grating multiple mode splitting (SGMMS), where spatial displacement of a single period grating imprinted on the inner boundary of the microring creates a rotational asymmetry that frequency splits multiple adjacent cavity modes. This approach is easy to implement and presents no additional fabrication challenges compared to an un-shifted grating, and yet is very powerful in providing multi-frequency engineering functionality for nonlinear optics. We showcase an example where SGMMS enables OPO across a wide range of pump wavelengths in a normal-dispersion device that otherwise would not support OPO.
Photonics Research
- Publication Date: Oct. 26, 2023
- Vol. 11, Issue 11, A72 (2023)
Guest Editors
Yun-Feng Xiao
Peking University, China (Lead Editor)
Kartik Srinivasan
National Institute of Standards and Technology (NIST), USA
Pascal Del’Haye
Max Planck Institute for the Science of Light, Germany
Mengjie Yu
University of Southern California, USA
On the Cover of the virtual issue
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