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OPTICAL MICROCAVITIES
Contents
OPTICAL MICROCAVITIES
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10 Article(s)
Unidirectional lasing in semiconductor microring lasers at an exceptional point [Invited]
Stefano Longhi, and Liang Feng
Recent experiments demonstrated that chiral symmetry breaking at an exceptional point (EP) is a viable route to achieve unidirectional laser emission in microring lasers. By a detailed semiconductor laser rate equation model, we show here that unidirectional laser emission at an EP is a robust regime. Slight deviations from the EP condition can break preferential unidirectional lasing near threshold via a Hopf instability. However, above a “second” laser threshold, unidirectional emission is restored.
Recent experiments demonstrated that chiral symmetry breaking at an exceptional point (EP) is a viable route to achieve unidirectional laser emission in microring lasers. By a detailed semiconductor laser rate equation model, we show here that unidirectional laser emission at an EP is a robust regime. Slight deviations from the EP condition can break preferential unidirectional lasing near threshold via a Hopf instability. However, above a “second” laser threshold, unidirectional emission is restored.
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Photonics Research
Publication Date: Jun. 23, 2017
Vol. 5, Issue 6, 060000B1 (2017)
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Tensile-strained Ge/SiGe multiple quantum well microdisks
Xiaochi Chen, Colleen S. Fenrich, Muyu Xue, Ming-Yen Kao, Kai Zang, Ching-Ying Lu, Edward T. Fei, Yusi Chen, Yijie Huo, Theodore I. Kamins, and James S. Harris
An efficient monolithically integrated laser on Si remains the missing component to enable Si photonics. We discuss the design and fabrication of suspended and tensile-strained Ge/SiGe multiple quantum well microdisk resonators on Si for laser applications in Si photonics using an all-around SiNx stressor. An etch-stop technique in the Ge/SiGe system is demonstrated and allows the capability of removing the defective buffer layer as well as providing precise thickness control of the resonators. Photoluminescence and Raman spectroscopy indicate that we have achieved a biaxial tensile strain shift as high as 0.88% in the microdisk resonators by adding a high-stress SiNx layer. Optical gain calculations show that high positive net gain can be achieved in Ge quantum wells with 1% external biaxial tensile strain.
An efficient monolithically integrated laser on Si remains the missing component to enable Si photonics. We discuss the design and fabrication of suspended and tensile-strained Ge/SiGe multiple quantum well microdisk resonators on Si for laser applications in Si photonics using an all-around SiNx stressor. An etch-stop technique in the Ge/SiGe system is demonstrated and allows the capability of removing the defective buffer layer as well as providing precise thickness control of the resonators. Photoluminescence and Raman spectroscopy indicate that we have achieved a biaxial tensile strain shift as high as 0.88% in the microdisk resonators by adding a high-stress SiNx layer. Optical gain calculations show that high positive net gain can be achieved in Ge quantum wells with 1% external biaxial tensile strain.
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Photonics Research
Publication Date: Aug. 05, 2017
Vol. 5, Issue 6, 060000B7 (2017)
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LED-pumped whispering-gallery laser
Simon J. Herr, Karsten Buse, and Ingo Breunig
A low-cost light-emitting diode (LED) is sufficient to pump a quasi-continuous-wave bidirectional high-Q whispering-gallery resonator laser made of Nd:YVO4. This is remarkable because of the very limited spatial and spectral coherence of an LED. The LED, delivering up to 3.5 W, centered around 810 nm, is turned on in intervals of 100 μs duration, and for these periods a laser output exceeding 0.8 mW has been verified. Furthermore, 0.1-s-long laser pulses are demonstrated. To the best of our knowledge, this is the first demonstration of an LED-pumped high-Q whispering-gallery laser. The concept can be extended easily to other laser active materials. A prospect is also to pump several of such lasers with a single LED.
A low-cost light-emitting diode (LED) is sufficient to pump a quasi-continuous-wave bidirectional high-Q whispering-gallery resonator laser made of Nd:YVO4. This is remarkable because of the very limited spatial and spectral coherence of an LED. The LED, delivering up to 3.5 W, centered around 810 nm, is turned on in intervals of 100 μs duration, and for these periods a laser output exceeding 0.8 mW has been verified. Furthermore, 0.1-s-long laser pulses are demonstrated. To the best of our knowledge, this is the first demonstration of an LED-pumped high-Q whispering-gallery laser. The concept can be extended easily to other laser active materials. A prospect is also to pump several of such lasers with a single LED.
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Photonics Research
Publication Date: Oct. 11, 2017
Vol. 5, Issue 6, 06000B34 (2017)
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Constructing the scattering matrix for optical microcavities as a nonlocal boundary value problem
Li Ge
We develop a numerical scheme to construct the scattering (S) matrix for optical microcavities, including the special cases with parity-time and other non-Hermitian symmetries. This scheme incorporates the explicit form of a nonlocal boundary condition, with the incident light represented by an inhomogeneous term. This approach resolves the artifact of a discontinuous normal derivative typically found in the R-matrix method. In addition, we show that, by excluding the aforementioned inhomogeneous term, the non-Hermitian Hamiltonian in our approach also determines the Periels–Kapur states, and it constitutes an alternative approach to derive the standard R-matrix result in this basis. Therefore, our scheme provides a convenient framework to explore the benefits of both approaches. We illustrate this boundary value problem using 1D and 2D scalar Helmholtz equations. The eigenvalues and poles of the S matrix calculated using our approach show good agreement with results obtained by other means.
We develop a numerical scheme to construct the scattering (S) matrix for optical microcavities, including the special cases with parity-time and other non-Hermitian symmetries. This scheme incorporates the explicit form of a nonlocal boundary condition, with the incident light represented by an inhomogeneous term. This approach resolves the artifact of a discontinuous normal derivative typically found in the R-matrix method. In addition, we show that, by excluding the aforementioned inhomogeneous term, the non-Hermitian Hamiltonian in our approach also determines the Periels–Kapur states, and it constitutes an alternative approach to derive the standard R-matrix result in this basis. Therefore, our scheme provides a convenient framework to explore the benefits of both approaches. We illustrate this boundary value problem using 1D and 2D scalar Helmholtz equations. The eigenvalues and poles of the S matrix calculated using our approach show good agreement with results obtained by other means.
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Photonics Research
Publication Date: Sep. 17, 2017
Vol. 5, Issue 6, 06000B20 (2017)
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Genetically optimized on-chip wideband ultracompact reflectors and Fabry–Perot cavities
Zejie Yu, Haoran Cui, and Xiankai Sun
Reflectors are an essential component for on-chip integrated photonics. Here, we propose a new method for designing reflectors on the prevalent thin-film-on-insulator platform by using genetic-algorithm optimization. In simulation, the designed reflector with a footprint of only 2.16 μm×2.16 μm can achieve ~97% reflectivity and 1 dB bandwidth as wide as 220 nm. The structure is composed of randomly distributed pixels and is highly robust against the inevitable corner rounding effect in device fabrication. In experiment, we fabricated on-chip Fabry–Perot (FP) cavities constructed from optimized reflectors. Those FP cavities have intrinsic quality factors of >2000 with the highest value beyond 4000 in a spectral width of 200 nm. The reflectivity fitted from the FP cavity resonances is >85% in the entire wavelength range of 1440–1640 nm and is beyond 95% at some wavelengths. The fabrication processes are CMOS compatible and require only one step of lithography and etch. The devices can be used as a standard module in integrated photonic circuitry for wide applications in on-chip semiconductor laser structures and optical signal processing.
Reflectors are an essential component for on-chip integrated photonics. Here, we propose a new method for designing reflectors on the prevalent thin-film-on-insulator platform by using genetic-algorithm optimization. In simulation, the designed reflector with a footprint of only 2.16 μm×2.16 μm can achieve ~97% reflectivity and 1 dB bandwidth as wide as 220 nm. The structure is composed of randomly distributed pixels and is highly robust against the inevitable corner rounding effect in device fabrication. In experiment, we fabricated on-chip Fabry–Perot (FP) cavities constructed from optimized reflectors. Those FP cavities have intrinsic quality factors of >2000 with the highest value beyond 4000 in a spectral width of 200 nm. The reflectivity fitted from the FP cavity resonances is >85% in the entire wavelength range of 1440–1640 nm and is beyond 95% at some wavelengths. The fabrication processes are CMOS compatible and require only one step of lithography and etch. The devices can be used as a standard module in integrated photonic circuitry for wide applications in on-chip semiconductor laser structures and optical signal processing.
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Photonics Research
Publication Date: Sep. 07, 2017
Vol. 5, Issue 6, 06000B15 (2017)
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Single-mode lasing via loss engineering in fiber-taper-coupled polymer bottle microresonators
Fuming Xie, Ni Yao, Wei Fang, Haifeng Wang, Fuxing Gu, and Songlin Zhuang
Due to the lack of mode selection capability, single whispering-gallery-mode (WGM) lasing is a challenge to achieve. In bottle microresonators, the highly nondegenerated WGMs are spatially well-separated along the long-axis direction and provide mode selection according to their axial mode numbers. In this work, we use a loss-engineering approach to suppress the higher-order WGMs and demonstrate single-mode lasing emission in small polymer bottle microresonators. The fiber tapers are not only used to couple pump light into the bottle microresonators to excite the WGMs but also to bring optical losses that are induced from the diameter mismatch between fiber tapers and microresonators. By adjusting the coupling positions, the diameters of fiber tapers, and the coupling angles, single fundamental-mode lasing is efficiently generated with side-mode suppression factors over 15 dB. Our loss-engineering approach is convenient just by moving the fiber taper and may find promising applications in miniature tunable single-mode lasers and sensors.
Due to the lack of mode selection capability, single whispering-gallery-mode (WGM) lasing is a challenge to achieve. In bottle microresonators, the highly nondegenerated WGMs are spatially well-separated along the long-axis direction and provide mode selection according to their axial mode numbers. In this work, we use a loss-engineering approach to suppress the higher-order WGMs and demonstrate single-mode lasing emission in small polymer bottle microresonators. The fiber tapers are not only used to couple pump light into the bottle microresonators to excite the WGMs but also to bring optical losses that are induced from the diameter mismatch between fiber tapers and microresonators. By adjusting the coupling positions, the diameters of fiber tapers, and the coupling angles, single fundamental-mode lasing is efficiently generated with side-mode suppression factors over 15 dB. Our loss-engineering approach is convenient just by moving the fiber taper and may find promising applications in miniature tunable single-mode lasers and sensors.
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Photonics Research
Publication Date: Sep. 13, 2017
Vol. 5, Issue 6, 06000B29 (2017)
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Kerr frequency combs in large-size, ultra-high-Q toroid microcavities with low repetition rates [Invited]
Jiyang Ma, Xiaoshun Jiang, and Min Xiao
By overcoming fabrication limitations, we have successfully fabricated silica toroid microcavities with both large diameter (of 1.88 mm) and ultra-high-Q factor (of 3.3×108) for the first time, to the best of our knowledge. By employing these resonators, we have further demonstrated low-threshold Kerr frequency combs on a silicon chip, which allow us to obtain a repetition rate as low as 36 GHz. Such a low repetition rate frequency comb can now be directly measured through a commercialized optical-electronic detector.
By overcoming fabrication limitations, we have successfully fabricated silica toroid microcavities with both large diameter (of 1.88 mm) and ultra-high-Q factor (of 3.3×108) for the first time, to the best of our knowledge. By employing these resonators, we have further demonstrated low-threshold Kerr frequency combs on a silicon chip, which allow us to obtain a repetition rate as low as 36 GHz. Such a low repetition rate frequency comb can now be directly measured through a commercialized optical-electronic detector.
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Photonics Research
Publication Date: Oct. 31, 2017
Vol. 5, Issue 6, 06000B54 (2017)
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Universal single-mode lasing in fully chaotic two-dimensional microcavity lasers under continuous-wave operation with large pumping power [Invited]
Takahisa Harayama, Satoshi Sunada, and Susumu Shinohara
For a fully chaotic two-dimensional (2D) microcavity laser, we present a theory that guarantees both the existence of a stable single-mode lasing state and the nonexistence of a stable multimode lasing state, under the assumptions that the cavity size is much larger than the wavelength and the external pumping power is sufficiently large. It is theoretically shown that these universal spectral characteristics arise from the synergistic effect of two different kinds of nonlinearities: deformation of the cavity shape and mode interaction due to a lasing medium. Our theory is based on the linear stability analysis of stationary states for the Maxwell–Bloch equations and accounts for single-mode lasing phenomena observed in real and numerical experiments of fully chaotic 2D microcavity lasers.
For a fully chaotic two-dimensional (2D) microcavity laser, we present a theory that guarantees both the existence of a stable single-mode lasing state and the nonexistence of a stable multimode lasing state, under the assumptions that the cavity size is much larger than the wavelength and the external pumping power is sufficiently large. It is theoretically shown that these universal spectral characteristics arise from the synergistic effect of two different kinds of nonlinearities: deformation of the cavity shape and mode interaction due to a lasing medium. Our theory is based on the linear stability analysis of stationary states for the Maxwell–Bloch equations and accounts for single-mode lasing phenomena observed in real and numerical experiments of fully chaotic 2D microcavity lasers.
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Photonics Research
Publication Date: Oct. 24, 2017
Vol. 5, Issue 6, 06000B39 (2017)
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Self-adjustment of a nonlinear lasing mode to a pumped area in a two-dimensional microcavity [Invited]
Yuta Kawashima, Susumu Shinohara, Satoshi Sunada, and Takahisa Harayama
We numerically performed wave dynamical simulations based on the Maxwell–Bloch (MB) model for a quadrupole-deformed microcavity laser with spatially selective pumping. We demonstrate the appearance of an asymmetric lasing mode whose spatial pattern violates both the x- and y-axes mirror symmetries of the cavity. Dynamical simulations revealed that a lasing mode consisting of a clockwise or counterclockwise rotating-wave component is a stable stationary solution of the MB model. From the results of a passive-cavity mode analysis, we interpret these asymmetric rotating-wave lasing modes by the locking of four nearly degenerate passive-cavity modes. For comparison, we carried out simulations for a uniform pumping case and found a different locking rule for the nearly degenerate modes. Our results demonstrate a nonlinear dynamical mechanism for the formation of a lasing mode that adjusts its pattern to a pumped area.
We numerically performed wave dynamical simulations based on the Maxwell–Bloch (MB) model for a quadrupole-deformed microcavity laser with spatially selective pumping. We demonstrate the appearance of an asymmetric lasing mode whose spatial pattern violates both the x- and y-axes mirror symmetries of the cavity. Dynamical simulations revealed that a lasing mode consisting of a clockwise or counterclockwise rotating-wave component is a stable stationary solution of the MB model. From the results of a passive-cavity mode analysis, we interpret these asymmetric rotating-wave lasing modes by the locking of four nearly degenerate passive-cavity modes. For comparison, we carried out simulations for a uniform pumping case and found a different locking rule for the nearly degenerate modes. Our results demonstrate a nonlinear dynamical mechanism for the formation of a lasing mode that adjusts its pattern to a pumped area.
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Photonics Research
Publication Date: Oct. 31, 2017
Vol. 5, Issue 6, 06000B47 (2017)
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Optical microcavities: new understandings and developments
Li Ge, Liang Feng, and Harald G. L. Schwefel
Optical microcavities have attracted tremendous interest in both fundamental and applied research in the past few decades, thanks to their small footprint, easy integrability, and high quality factors. Using total internal reflection from a dielectric interface or a photonic band gap in a periodic system, these photonic structures do not rely on conventional metal-coated mirrors to confine light in small volumes, which have brought forth new developments in both classical and quantum optics. This focus issue showcases several such developments and related findings, which may pave the way for the next generation of on-chip photonic devices based on microcavities.
Optical microcavities have attracted tremendous interest in both fundamental and applied research in the past few decades, thanks to their small footprint, easy integrability, and high quality factors. Using total internal reflection from a dielectric interface or a photonic band gap in a periodic system, these photonic structures do not rely on conventional metal-coated mirrors to confine light in small volumes, which have brought forth new developments in both classical and quantum optics. This focus issue showcases several such developments and related findings, which may pave the way for the next generation of on-chip photonic devices based on microcavities.
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Photonics Research
Publication Date: Nov. 15, 2017
Vol. 5, Issue 6, 06000OM1 (2017)
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Topics
Adaptive Optics
Array Waveguide Devices
Atmospheric and Oceanic Optics
Coherence and Statistical Optics
Comments
Correction
Diffraction and Gratings
Digital Holography
Dispersion
Editorial
Fiber Devices
Fiber Optic Sensors
Fiber Optics
Fiber Optics and Optical Communications
Group Iv Photonics
Holography
Holography, Gratings, and Diffraction
Image Processing
Image Processing and Image Analysis
Imaging
Imaging Systems
Imaging Systems, Microscopy, and Displays
Instrumentation and Measurements
Integrated Optics
Integrated Optics Devices
Integrated Photonics
INTEGRATED PHOTONICS: CHALLENGES AND PERSPECTIVES
Interferometry
Interview
Laser Materials
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Lasers and Laser Optics
Light-emitting Diodes
Liquid-Crystal Devices
Materials
Medical Optics and Biotechnology
Metamaterials
Microlasers
Microscopy
Microwave Photonics
Mode-locked Lasers
Nanomaterials
Nanophotonics
Nanophotonics and Photonic Crystals
Nanostructures
Nonlinear Optic
Nonlinear Optics
Optical and Photonic Materials
Optical Communications
Optical Communications and Interconnects
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OPTICAL MICROCAVITIES
Optical Resonators
Optical Trapping and Manipulation
Optical Vortices
Optics at Surfaces
Optoelectronics
Photodetectors
Photon Statistics
Photonic Crystals
Photonic Crystals and Devices
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Photonic Manipulation
Physical Optics
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Polarization Rotators
Pulse Propagation and Temporal Solitons
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Resonators
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Semiconductor UV Photonics
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Terahertz Photonics: Applications and Techniques
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Thin Films
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