T. Melton, J. F. McMillan, J. Yang, W. Wang, Y. Lai, M. Gerber, M. Rodriguez, J. P. Hubschman, K. Nouri-Mahdavi, C. W. Wong
Spectral-domain optical coherence tomography is a pervasive, non-invasive, in vivo biomedical imaging platform that currently utilizes incoherent broadband superluminescent diodes to generate interferograms from which depth and structural information are extracted. Advancements in laser frequency microcombs have enabled the chip-scale broadband generation of discrete frequency sources, with prior soliton and chaotic comb states examined in discrete spectral-domain optical coherence tomography at 1.3 μm. In this work, we demonstrate coherence tomography through Si3N4 microresonator laser frequency microcombs at 1 μm, achieving imaging qualities on-par with or exceeding the equivalent commercial optical coherence tomography system. We characterize the noise performance of our frequency comb states and additionally show that inherent comb line amplitude fluctuations in a chaotic state and the resultant tomograms can be compensated via multi-scan averaging.
{"title":"Optical coherence tomography imaging and noise characterization based on 1-μm microresonator frequency combs","authors":"T. Melton, J. F. McMillan, J. Yang, W. Wang, Y. Lai, M. Gerber, M. Rodriguez, J. P. Hubschman, K. Nouri-Mahdavi, C. W. Wong","doi":"10.1063/5.0215574","DOIUrl":"https://doi.org/10.1063/5.0215574","url":null,"abstract":"Spectral-domain optical coherence tomography is a pervasive, non-invasive, in vivo biomedical imaging platform that currently utilizes incoherent broadband superluminescent diodes to generate interferograms from which depth and structural information are extracted. Advancements in laser frequency microcombs have enabled the chip-scale broadband generation of discrete frequency sources, with prior soliton and chaotic comb states examined in discrete spectral-domain optical coherence tomography at 1.3 μm. In this work, we demonstrate coherence tomography through Si3N4 microresonator laser frequency microcombs at 1 μm, achieving imaging qualities on-par with or exceeding the equivalent commercial optical coherence tomography system. We characterize the noise performance of our frequency comb states and additionally show that inherent comb line amplitude fluctuations in a chaotic state and the resultant tomograms can be compensated via multi-scan averaging.","PeriodicalId":8198,"journal":{"name":"APL Photonics","volume":"165 1","pages":""},"PeriodicalIF":5.6,"publicationDate":"2024-08-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142199482","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Peijun Gong, Imogen Boman, Renate Zilkens, Chris Yeomans, Mireille Hardie, Anmol Rijhumal, Christobel M. Saunders, Brendan F. Kennedy
Mechanical load imparted to tissue, for example via handheld imaging probes, leads to tissue deformation, altering the distribution of tissue microstructure and, consequently, attenuation of light and image formation in optical imaging. In mechanically heterogeneous tissue, the load can result in spatially varying deformation and, therefore, spatially varying changes in the attenuation of light, which may provide additional image contrast. To investigate this potential, an assessment of the spatially resolved impact of mechanical deformation of the tissue on optical imaging is critical; however, it is challenging to incorporate stress mapping into optical imaging without obscuring the detection of photons. To address this, we present the novel integration of stress imaging using optical palpation with attenuation imaging based on optical coherence tomography (OCT). The method was implemented using a compliant silicone sensor incorporated into a custom handheld OCT probe, providing two-dimensional stress imaging with concurrent attenuation imaging. Attenuation imaging with varying mechanical loads was demonstrated on 19 tissue regions acquired from eight freshly excised human breast specimens. The results demonstrated distinct characteristics for different breast tissue types: benign stroma showed relatively large increases in attenuation (e.g., ∼0.3 to 0.4 mm−1/kPa) over a low stress range (∼2 to 10 kPa), while cancerous tissue showed markedly small increases in attenuation (e.g., ∼0.005 to 0.02 mm−1/kPa) mainly over a medium to high stress range (∼10 to 90 kPa). The integration of stress imaging with attenuation imaging provided a pilot assessment of the spatially resolved impact of tissue mechanical heterogeneity on optical attenuation, providing novel image contrast by encoding variations in mechanical properties on optical attenuation in tissue.
{"title":"Load-dependent optical coherence tomography attenuation imaging: How tissue mechanics can influence optical scattering","authors":"Peijun Gong, Imogen Boman, Renate Zilkens, Chris Yeomans, Mireille Hardie, Anmol Rijhumal, Christobel M. Saunders, Brendan F. Kennedy","doi":"10.1063/5.0208026","DOIUrl":"https://doi.org/10.1063/5.0208026","url":null,"abstract":"Mechanical load imparted to tissue, for example via handheld imaging probes, leads to tissue deformation, altering the distribution of tissue microstructure and, consequently, attenuation of light and image formation in optical imaging. In mechanically heterogeneous tissue, the load can result in spatially varying deformation and, therefore, spatially varying changes in the attenuation of light, which may provide additional image contrast. To investigate this potential, an assessment of the spatially resolved impact of mechanical deformation of the tissue on optical imaging is critical; however, it is challenging to incorporate stress mapping into optical imaging without obscuring the detection of photons. To address this, we present the novel integration of stress imaging using optical palpation with attenuation imaging based on optical coherence tomography (OCT). The method was implemented using a compliant silicone sensor incorporated into a custom handheld OCT probe, providing two-dimensional stress imaging with concurrent attenuation imaging. Attenuation imaging with varying mechanical loads was demonstrated on 19 tissue regions acquired from eight freshly excised human breast specimens. The results demonstrated distinct characteristics for different breast tissue types: benign stroma showed relatively large increases in attenuation (e.g., ∼0.3 to 0.4 mm−1/kPa) over a low stress range (∼2 to 10 kPa), while cancerous tissue showed markedly small increases in attenuation (e.g., ∼0.005 to 0.02 mm−1/kPa) mainly over a medium to high stress range (∼10 to 90 kPa). The integration of stress imaging with attenuation imaging provided a pilot assessment of the spatially resolved impact of tissue mechanical heterogeneity on optical attenuation, providing novel image contrast by encoding variations in mechanical properties on optical attenuation in tissue.","PeriodicalId":8198,"journal":{"name":"APL Photonics","volume":"29 1","pages":""},"PeriodicalIF":5.6,"publicationDate":"2024-08-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142199488","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Fanqi Meng, Zhenling Tang, Petr Ourednik, Jahnabi Hazarika, Michael Feiginov, Safumi Suzuki, Hartmut G. Roskos
Oscillators based on resonant tunneling diodes (RTDs) are able to reach the highest oscillation frequency among all electronic THz emitters. However, the emitted power from RTDs remains limited. Here, we propose linear RTD oscillator arrays capable of supporting coherent emission from both in-phase and anti-phase coupled modes. The oscillation modes can be selected by adjusting the mesa areas of the RTDs. Both the modes exhibit constructive interference at different angles in the far field, enabling high-power emission. Experimental demonstrations of coherent emission from linear arrays containing 11 RTDs are presented. The anti-phase mode oscillates at ∼450 GHz, emitting about 0.7 mW, while the in-phase mode oscillates at around 750 GHz, emitting about 1 mW. Moreover, certain RTD oscillator arrays exhibit dual-band operation: changing the bias voltage allows for controllable switching between the anti-phase and in-phase modes. Upon bias sweeping in both directions, a notable hysteresis feature is observed. Our linear RTD oscillator array represents a significant step forward in the realization of large arrays for applications requiring continuous-wave THz radiation with substantial power.
{"title":"High-power in-phase and anti-phase mode emission from linear arrays of resonant-tunneling-diode oscillators in the 0.4-to-0.8-THz frequency range","authors":"Fanqi Meng, Zhenling Tang, Petr Ourednik, Jahnabi Hazarika, Michael Feiginov, Safumi Suzuki, Hartmut G. Roskos","doi":"10.1063/5.0213695","DOIUrl":"https://doi.org/10.1063/5.0213695","url":null,"abstract":"Oscillators based on resonant tunneling diodes (RTDs) are able to reach the highest oscillation frequency among all electronic THz emitters. However, the emitted power from RTDs remains limited. Here, we propose linear RTD oscillator arrays capable of supporting coherent emission from both in-phase and anti-phase coupled modes. The oscillation modes can be selected by adjusting the mesa areas of the RTDs. Both the modes exhibit constructive interference at different angles in the far field, enabling high-power emission. Experimental demonstrations of coherent emission from linear arrays containing 11 RTDs are presented. The anti-phase mode oscillates at ∼450 GHz, emitting about 0.7 mW, while the in-phase mode oscillates at around 750 GHz, emitting about 1 mW. Moreover, certain RTD oscillator arrays exhibit dual-band operation: changing the bias voltage allows for controllable switching between the anti-phase and in-phase modes. Upon bias sweeping in both directions, a notable hysteresis feature is observed. Our linear RTD oscillator array represents a significant step forward in the realization of large arrays for applications requiring continuous-wave THz radiation with substantial power.","PeriodicalId":8198,"journal":{"name":"APL Photonics","volume":"74 1","pages":""},"PeriodicalIF":5.6,"publicationDate":"2024-08-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141968834","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Christian Hensel, Lenard Vamos, Igor Tyulnev, Ugaitz Elu, Jens Biegert
We study and describe the reshaping of ultrashort and broadband mid-IR optical pulses in an ambient atmosphere. While all pulse propagation undergoes dispersion and absorption, which causes pulse reshaping, the effects are strongly pronounced for broadband radiation in the mid-IR due to the orders of magnitude greater oscillator strengths of molecular constituents of our atmosphere. A noticeable macroscopic impact is a transition of the measured autocorrelation function from squared hyperbolic secant to Lorentzian, which we fully explain based on pulse propagation, including molecular free induction decay. Electro-optical sampling directly reveals the light wave response to atmospheric molecular free induction decay, and a Kramers–Kronig-based propagation model thoroughly explains the observation. The findings are essential for applications in sensing, standoff detection, high-energy pulse propagation, and energy delivery.
{"title":"Propagation of broadband mid-infrared optical pulses in atmosphere","authors":"Christian Hensel, Lenard Vamos, Igor Tyulnev, Ugaitz Elu, Jens Biegert","doi":"10.1063/5.0218225","DOIUrl":"https://doi.org/10.1063/5.0218225","url":null,"abstract":"We study and describe the reshaping of ultrashort and broadband mid-IR optical pulses in an ambient atmosphere. While all pulse propagation undergoes dispersion and absorption, which causes pulse reshaping, the effects are strongly pronounced for broadband radiation in the mid-IR due to the orders of magnitude greater oscillator strengths of molecular constituents of our atmosphere. A noticeable macroscopic impact is a transition of the measured autocorrelation function from squared hyperbolic secant to Lorentzian, which we fully explain based on pulse propagation, including molecular free induction decay. Electro-optical sampling directly reveals the light wave response to atmospheric molecular free induction decay, and a Kramers–Kronig-based propagation model thoroughly explains the observation. The findings are essential for applications in sensing, standoff detection, high-energy pulse propagation, and energy delivery.","PeriodicalId":8198,"journal":{"name":"APL Photonics","volume":"141 1","pages":""},"PeriodicalIF":5.6,"publicationDate":"2024-08-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141968854","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Shuo Sun, Jin Li, Xiaoxun Li, Xiangyu Huang, Yi Zhang, Liang Chen
Holographic display is considered the holy grail of photorealistic three-dimensional (3D) visualization technology because it can provide arbitrary wavefronts related to the essential visual cues of 3D images. Metasurfaces with exceptional high-pixel light modulation capability are increasingly favored for implementing high-quality 3D holography. However, current 3D metasurface holography always has some trade-offs among lots of algorithmic data, acceptable time, image quality, and structure complexity. Therefore, the development of a high-efficiency 3D metasurface holography device is still necessary to meet the increasing high space bandwidth product (SBP) of 3D technology. Here, based on the holographic-lens (HL) computer-generated hologram (CGH) algorithm, we experimentally demonstrate a new 3D metasurface holography device that integrates the 3D image phase cues and multiple layers of virtual lenses with different focal lengths, which exhibits significant capabilities in terms of ultra-high spatial pixel modulation and the generation of high-quality 3D holography characterized by high-efficiency, broadband response, low-crosstalk, and reduced acceptable time. The HL-CGH algorithm was efficiently integrated into parameter-optimized α-Si nanopillar meta-atoms, enabling enhanced visualization of 3D clues in a lens-free system. The prepared 3D HL-metasurface holography presented the presence of multiple depths of a 3D holographic image across a broad spectral range (400–900 nm), providing enhanced 3D visual cues. Our work provides a new perspective on designing metasurface-driven high-SBP 3D holography.
全息显示被认为是逼真三维（3D）可视化技术的圣杯，因为它可以提供与 3D 图像基本视觉线索相关的任意波面。具有卓越的高像素光调制能力的元表面在实现高质量三维全息技术方面越来越受到青睐。然而，目前的三维超表面全息技术总是需要在大量算法数据、可接受时间、图像质量和结构复杂性之间进行权衡。因此，为了满足三维技术日益增长的高空间带宽积（SBP）的要求，开发一种高效的三维元面全息设备仍然是必要的。在此，我们基于全息透镜（HL）计算机生成全息图（CGH）算法，实验演示了一种新型三维元面全息设备，该设备集成了三维图像相位线索和多层不同焦距的虚拟透镜，在超高空间像素调制和生成高质量三维全息图方面表现出显著的能力，具有高效率、宽带响应、低串扰和缩短可接受时间等特点。HL-CGH 算法被有效集成到参数优化的 α-Si 纳米柱元原子中，从而在无透镜系统中增强了三维线索的可视化。制备的三维 HL-元原子表面全息图在宽光谱范围（400-900 nm）内呈现出多深度的三维全息图像，提供了增强的三维视觉线索。我们的工作为设计元表面驱动的高 SBP 三维全息技术提供了一个新的视角。
{"title":"High-efficiency, broadband, and low-crosstalk 3D holography by multi-layer holographic-lens integrated metasurface","authors":"Shuo Sun, Jin Li, Xiaoxun Li, Xiangyu Huang, Yi Zhang, Liang Chen","doi":"10.1063/5.0218862","DOIUrl":"https://doi.org/10.1063/5.0218862","url":null,"abstract":"Holographic display is considered the holy grail of photorealistic three-dimensional (3D) visualization technology because it can provide arbitrary wavefronts related to the essential visual cues of 3D images. Metasurfaces with exceptional high-pixel light modulation capability are increasingly favored for implementing high-quality 3D holography. However, current 3D metasurface holography always has some trade-offs among lots of algorithmic data, acceptable time, image quality, and structure complexity. Therefore, the development of a high-efficiency 3D metasurface holography device is still necessary to meet the increasing high space bandwidth product (SBP) of 3D technology. Here, based on the holographic-lens (HL) computer-generated hologram (CGH) algorithm, we experimentally demonstrate a new 3D metasurface holography device that integrates the 3D image phase cues and multiple layers of virtual lenses with different focal lengths, which exhibits significant capabilities in terms of ultra-high spatial pixel modulation and the generation of high-quality 3D holography characterized by high-efficiency, broadband response, low-crosstalk, and reduced acceptable time. The HL-CGH algorithm was efficiently integrated into parameter-optimized α-Si nanopillar meta-atoms, enabling enhanced visualization of 3D clues in a lens-free system. The prepared 3D HL-metasurface holography presented the presence of multiple depths of a 3D holographic image across a broad spectral range (400–900 nm), providing enhanced 3D visual cues. Our work provides a new perspective on designing metasurface-driven high-SBP 3D holography.","PeriodicalId":8198,"journal":{"name":"APL Photonics","volume":"33 1","pages":""},"PeriodicalIF":5.6,"publicationDate":"2024-08-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141881822","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Jasper Riebesehl, Holger R. Heebøll, Aleksandr Razumov, Michael Galili, Darko Zibar
Performing noise characterizations of lasers and optical frequency combs on sampled data offers numerous advantages compared to analog measurement techniques. One of the main advantages is that the measurement setup is greatly simplified. Only a balanced detector followed by an analog-to-digital converter is needed, allowing all the complexity to be moved to the digital domain. Secondly, near-optimal phase estimators are efficiently implementable, providing accurate phase noise estimation in the presence of measurement noise. Finally, joint processing of multiple comb lines is feasible, enabling the computation of the phase noise correlation matrix, which includes all information about the phase noise of the optical frequency comb. This tutorial introduces a framework based on digital signal processing for phase noise characterization of lasers and optical frequency combs. The framework is based on the extended Kalman filter (EKF) and automatic differentiation. The EKF is a near-optimal estimator of the optical phase in the presence of measurement noise, making it very suitable for phase noise measurements. Automatic differentiation is key to efficiently optimizing many parameters entering the EKF framework. More specifically, the combination of EKF and automatic differentiation enables the efficient optimization of phase noise measurement for optical frequency combs with arbitrarily complex noise dynamics that may include many free parameters. We show the framework’s efficacy through simulations and experimental data, showcasing its application across various comb types and in dual-comb measurements, highlighting its accuracy and versatility. Finally, we discuss its capability for digital phase noise compensation, which is highly relevant to free-running dual-comb spectroscopy applications.
{"title":"Digital signal processing techniques for noise characterization of lasers and optical frequency combs: A tutorial","authors":"Jasper Riebesehl, Holger R. Heebøll, Aleksandr Razumov, Michael Galili, Darko Zibar","doi":"10.1063/5.0212592","DOIUrl":"https://doi.org/10.1063/5.0212592","url":null,"abstract":"Performing noise characterizations of lasers and optical frequency combs on sampled data offers numerous advantages compared to analog measurement techniques. One of the main advantages is that the measurement setup is greatly simplified. Only a balanced detector followed by an analog-to-digital converter is needed, allowing all the complexity to be moved to the digital domain. Secondly, near-optimal phase estimators are efficiently implementable, providing accurate phase noise estimation in the presence of measurement noise. Finally, joint processing of multiple comb lines is feasible, enabling the computation of the phase noise correlation matrix, which includes all information about the phase noise of the optical frequency comb. This tutorial introduces a framework based on digital signal processing for phase noise characterization of lasers and optical frequency combs. The framework is based on the extended Kalman filter (EKF) and automatic differentiation. The EKF is a near-optimal estimator of the optical phase in the presence of measurement noise, making it very suitable for phase noise measurements. Automatic differentiation is key to efficiently optimizing many parameters entering the EKF framework. More specifically, the combination of EKF and automatic differentiation enables the efficient optimization of phase noise measurement for optical frequency combs with arbitrarily complex noise dynamics that may include many free parameters. We show the framework’s efficacy through simulations and experimental data, showcasing its application across various comb types and in dual-comb measurements, highlighting its accuracy and versatility. Finally, we discuss its capability for digital phase noise compensation, which is highly relevant to free-running dual-comb spectroscopy applications.","PeriodicalId":8198,"journal":{"name":"APL Photonics","volume":"79 1","pages":""},"PeriodicalIF":5.6,"publicationDate":"2024-08-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141881906","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
We introduce a broadband tunable femtosecond laser source in the long-wave infrared (LWIR) band, covering the range of 5–13.5 μm, based on the integration of optical parametric amplification and difference frequency generation techniques. We utilize a dual-stage tuning method, combined with the high nonlinear coefficient and broadband phase matching range of the BaGa4Se7 crystal, to facilitate significant improvements in spectral coverage and energy efficiency. The laser yields a peak output energy of 43 μJ and maintains energies above 10 μJ across the entire tuning range, with an average power output exceeding 10 mW. The pulse duration at the central wavelength of 8.3 μm is measured at 72 fs full width at half-maximum using the electro-optic sampling method. This LWIR femtosecond laser can be used in many applications, such as molecular fingerprint spectral analysis, ultrafast chemical reaction spectral analysis, materials science, and ultrafast physics research, providing an important research basis for the generation and application of mid-infrared ultrafast laser sources.
{"title":"5–13.5 μm broadband tunable long-wave infrared femtosecond laser","authors":"Yunpeng Liu, Junyu Qian, Renyu Feng, Wenkai Li, Yanyan Li, Yujie Peng, Yuxin Leng","doi":"10.1063/5.0221273","DOIUrl":"https://doi.org/10.1063/5.0221273","url":null,"abstract":"We introduce a broadband tunable femtosecond laser source in the long-wave infrared (LWIR) band, covering the range of 5–13.5 μm, based on the integration of optical parametric amplification and difference frequency generation techniques. We utilize a dual-stage tuning method, combined with the high nonlinear coefficient and broadband phase matching range of the BaGa4Se7 crystal, to facilitate significant improvements in spectral coverage and energy efficiency. The laser yields a peak output energy of 43 μJ and maintains energies above 10 μJ across the entire tuning range, with an average power output exceeding 10 mW. The pulse duration at the central wavelength of 8.3 μm is measured at 72 fs full width at half-maximum using the electro-optic sampling method. This LWIR femtosecond laser can be used in many applications, such as molecular fingerprint spectral analysis, ultrafast chemical reaction spectral analysis, materials science, and ultrafast physics research, providing an important research basis for the generation and application of mid-infrared ultrafast laser sources.","PeriodicalId":8198,"journal":{"name":"APL Photonics","volume":"34 1","pages":""},"PeriodicalIF":5.6,"publicationDate":"2024-08-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141881905","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Photonic crystal (PhC) structures with subwavelength periods are widely used for diffractive optics, including high reflectivity membranes with nanoscale thickness. Here, we report on a design procedure for 2D PhC silicon nitride membrane mirrors providing optimal crystal geometry using simulation results obtained with rigorous coupled-wave analysis. The Downhill Simplex algorithm, a robust numerical approach to finding local extrema of a function of multiple variables, is used to optimize the period and hole radius of PhCs with both hexagonal and square lattices, as the membrane thickness is varied. Following these design principles, nanofabricated PhC membranes made from silicon nitride have been used as input couplers for an optical cavity, resulting in a maximum cavity finesse of 33 000, corresponding to a reflectivity of 0.999 82. The role played by the spot size of the cavity mode on the PhC was investigated, demonstrating the existence of an optimal spot size that agrees well with predictions. We find that, compared to the square lattice, the hexagonal lattice exhibits a spectrally wider reflective range, less sensitivity to fabrication tolerances, and higher reflectivity for membranes thinner than 200 nm, which may be advantageous in cavity optomechanical experiments. Finally, we find that all of the cavities that we have constructed exhibit well-resolved polarization mode splitting, which we expect is due primarily to a small amount of anisotropic stress in the silicon nitride and PhC asymmetry arising during fabrication.
{"title":"Ultrahigh reflectivity photonic crystal membranes with optimal geometry","authors":"F. Zhou, Y. Bao, J. J. Gorman, J. R. Lawall","doi":"10.1063/5.0204067","DOIUrl":"https://doi.org/10.1063/5.0204067","url":null,"abstract":"Photonic crystal (PhC) structures with subwavelength periods are widely used for diffractive optics, including high reflectivity membranes with nanoscale thickness. Here, we report on a design procedure for 2D PhC silicon nitride membrane mirrors providing optimal crystal geometry using simulation results obtained with rigorous coupled-wave analysis. The Downhill Simplex algorithm, a robust numerical approach to finding local extrema of a function of multiple variables, is used to optimize the period and hole radius of PhCs with both hexagonal and square lattices, as the membrane thickness is varied. Following these design principles, nanofabricated PhC membranes made from silicon nitride have been used as input couplers for an optical cavity, resulting in a maximum cavity finesse of 33 000, corresponding to a reflectivity of 0.999 82. The role played by the spot size of the cavity mode on the PhC was investigated, demonstrating the existence of an optimal spot size that agrees well with predictions. We find that, compared to the square lattice, the hexagonal lattice exhibits a spectrally wider reflective range, less sensitivity to fabrication tolerances, and higher reflectivity for membranes thinner than 200 nm, which may be advantageous in cavity optomechanical experiments. Finally, we find that all of the cavities that we have constructed exhibit well-resolved polarization mode splitting, which we expect is due primarily to a small amount of anisotropic stress in the silicon nitride and PhC asymmetry arising during fabrication.","PeriodicalId":8198,"journal":{"name":"APL Photonics","volume":"213 1","pages":""},"PeriodicalIF":5.6,"publicationDate":"2024-07-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141870143","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Carlo Silvestri, Massimo Brambilla, Paolo Bardella, Lorenzo Luigi Columbo
We present a unified model to describe the dynamics of optical frequency combs in quantum cascade lasers (QCLs), incorporating both ring and Fabry–Pérot (FP) cavity configurations. The model derives a modified complex Ginzburg–Landau equation (CGLE), leveraging an order parameter approach, and is capable of capturing the dynamics of both configurations, thus enabling a comparative analysis. This result demonstrates that FP QCLs, in addition to ring QCLs, belong to the same universality class of physical systems described by the CGLE, which includes, among others, systems in the fields of superconductivity and hydrodynamics. In the modified CGLE, a nonlinear integral term appears that is associated with the coupling between counterpropagating fields in the FP cavity and whose suppression yields the ring model, which is known to be properly described by a conventional CGLE. We show that this crucial term holds a key role in inhibiting the formation of harmonic frequency combs (HFCs), associated with multi-peaked localized structures, due to its anti-patterning effect. We provide support for a comprehensive campaign of numerical simulations in which we observe a higher occurrence of HFCs in the ring configuration compared to the FP case. Furthermore, the simulations demonstrate the model’s capability to reproduce experimental observations, including the coexistence of amplitude and frequency modulation, linear chirp, and typical dynamic scenarios observed in QCLs. Finally, we perform a linear stability analysis of the single-mode solution for the ring case, confirming its consistency with numerical simulations and highlighting its predictive power regarding the formation of harmonic combs.
{"title":"Unified theory for frequency combs in ring and Fabry–Perot quantum cascade lasers: An order-parameter equation approach","authors":"Carlo Silvestri, Massimo Brambilla, Paolo Bardella, Lorenzo Luigi Columbo","doi":"10.1063/5.0213323","DOIUrl":"https://doi.org/10.1063/5.0213323","url":null,"abstract":"We present a unified model to describe the dynamics of optical frequency combs in quantum cascade lasers (QCLs), incorporating both ring and Fabry–Pérot (FP) cavity configurations. The model derives a modified complex Ginzburg–Landau equation (CGLE), leveraging an order parameter approach, and is capable of capturing the dynamics of both configurations, thus enabling a comparative analysis. This result demonstrates that FP QCLs, in addition to ring QCLs, belong to the same universality class of physical systems described by the CGLE, which includes, among others, systems in the fields of superconductivity and hydrodynamics. In the modified CGLE, a nonlinear integral term appears that is associated with the coupling between counterpropagating fields in the FP cavity and whose suppression yields the ring model, which is known to be properly described by a conventional CGLE. We show that this crucial term holds a key role in inhibiting the formation of harmonic frequency combs (HFCs), associated with multi-peaked localized structures, due to its anti-patterning effect. We provide support for a comprehensive campaign of numerical simulations in which we observe a higher occurrence of HFCs in the ring configuration compared to the FP case. Furthermore, the simulations demonstrate the model’s capability to reproduce experimental observations, including the coexistence of amplitude and frequency modulation, linear chirp, and typical dynamic scenarios observed in QCLs. Finally, we perform a linear stability analysis of the single-mode solution for the ring case, confirming its consistency with numerical simulations and highlighting its predictive power regarding the formation of harmonic combs.","PeriodicalId":8198,"journal":{"name":"APL Photonics","volume":"45 1","pages":""},"PeriodicalIF":5.6,"publicationDate":"2024-07-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141778381","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Topological boundary modes, which are localized at the edge of topological materials, have received significant attention for their various applications in robust waveguides, optical cavities, and topological lasers. To envision their further applications in tunable devices, we propose and demonstrate a scheme to dynamically manipulate topological boundary modes by exploiting the two translation parameters of photonic crystals. We find that the translation not only transports the Wannier state similar to conventional Thouless pumping but also induces a nonzero Chern number in the two-dimensional synthetic space while preserving the time-reversal symmetry in the real space. Through changing the translation, gapless and tunable topological boundary modes are demonstrated. As a specific application, we show a dynamic bandpass filter with real-time tuning over 100% bandgap, a capability that cannot be achieved with only one translation parameter. Our design opens a venue for the development of tunable topological devices based on synthetic parameter dimension and can be generalized to other bosonic systems.
{"title":"Tunable topological boundary modes enabled by synthetic translation dimension","authors":"Zheng Guan, Xiao-Dong Chen, Hao-Chang Mo, Jian-Wei Liu, Qian-Yu Shu, Yuan Cao, Wen-Jie Chen, Jian-Wen Dong","doi":"10.1063/5.0211778","DOIUrl":"https://doi.org/10.1063/5.0211778","url":null,"abstract":"Topological boundary modes, which are localized at the edge of topological materials, have received significant attention for their various applications in robust waveguides, optical cavities, and topological lasers. To envision their further applications in tunable devices, we propose and demonstrate a scheme to dynamically manipulate topological boundary modes by exploiting the two translation parameters of photonic crystals. We find that the translation not only transports the Wannier state similar to conventional Thouless pumping but also induces a nonzero Chern number in the two-dimensional synthetic space while preserving the time-reversal symmetry in the real space. Through changing the translation, gapless and tunable topological boundary modes are demonstrated. As a specific application, we show a dynamic bandpass filter with real-time tuning over 100% bandgap, a capability that cannot be achieved with only one translation parameter. Our design opens a venue for the development of tunable topological devices based on synthetic parameter dimension and can be generalized to other bosonic systems.","PeriodicalId":8198,"journal":{"name":"APL Photonics","volume":"412 1","pages":""},"PeriodicalIF":5.6,"publicationDate":"2024-07-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141778384","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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