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2021
Volume: 19 Issue 4
16 Article(s)
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Reviews
Integrated Optics
Electro-optic polymer ring resonator modulators [Invited] | Editors' Pick
Feng Qiu, and Yu Han
Electro-optic (EO) ring resonator modulators have a number of communications and scientific applications, including analog optical links, optical signal processing, and frequency comb generation. Among the EO materials used to fabricate ring modulators, the EO polymer has many promising characteristics, including a high EO coefficient of 100–200 pm/V (3–7 times larger than that of LiNbO3), an ultrafast EO response time (10 fs), a low dielectric constant (3 to 4) with very little dispersion up to at least 250 GHz, and a straightforward spin-coating fabrication process. These inherent characteristics will be able to combine excellent EO properties with simple processing in achieving exceptional performance in a variety of high-speed optical modulation and sensing devices. This review focuses on the research and recent development of ring resonator modulators based on EO polymers. The first part describes the operation principle of EO ring resonator modulators, such as modulation mechanism, EO tunability, and 3 dB bandwidth. Subsequently, the emphasis is placed on the discussion of the ring modulators with EO polymers as the waveguide core and the improvement of EO modulation by using an EO polymer/titanium dioxide hybrid core. At the end, a series of EO polymers on silicon platforms including slot modulators, etching-free modulators, and athermal modulators are reviewed.Electro-optic (EO) ring resonator modulators have a number of communications and scientific applications, including analog optical links, optical signal processing, and frequency comb generation. Among the EO materials used to fabricate ring modulators, the EO polymer has many promising characteristics, including a high EO coefficient of 100–200 pm/V (3–7 times larger than that of
Chinese Optics Letters
- Publication Date: Apr. 10, 2021
- Vol. 19, Issue 4, 041301 (2021)
Research Articles
Fiber Optics and Optical Communications
Influence of the sparsity of random speckle illumination on ghost imaging in a noise environment
Long Pan, Chenjin Deng, Cuiping Yu, Shuai Yue... and Shensheng Han|Show fewer author(s)
The influence of the sparsity of random speckle illumination on traditional ghost imaging (GI) and GI via sparsity constraint (GISC) in a noise environment is investigated. The experiments demonstrate that both GI and GISC obtain their best imaging quality when the sparsity of random speckle illumination is 0.5, which is also explained by some parameters such as detection of the signal to noise ratio and mutual coherence of the measurement matrix.The influence of the sparsity of random speckle illumination on traditional ghost imaging (GI) and GI via sparsity constraint (GISC) in a noise environment is investigated. The experiments demonstrate that both GI and GISC obtain their best imaging quality when the sparsity of random speckle illumination is 0.5, which is also explained by some parameters such as detection of the signal to noise ratio and mutual coherence of the measurement matrix..
Chinese Optics Letters
- Publication Date: Apr. 10, 2021
- Vol. 19, Issue 4, 041103 (2021)
Imaging Systems and Image Processing
Enhancement of rapid lifetime determination for time-resolved fluorescence imaging in forensic examination
Xin Zhong, Xinwei Wang, Liang Sun, and Yan Zhou
An enhancement method of rapid lifetime determination is proposed for time-resolved fluorescence imaging to discriminate substances with approximate fluorescence lifetime in forensic examination. In the method, an image-exclusive-OR treatment with filter threshold adaptively chosen is presented to extract the region of interest from dual-gated fluorescence intensity images, and then the fluorescence lifetime image is reconstructed based on the rapid lifetime determination algorithm. Furthermore, a maximum and minimum threshold filtering is developed to automatically realize visualization enhancement of the lifetime image. In proof experiments, compared with traditional fluorescence intensity imaging and rapid lifetime determination method, the proposed method automatically distinguishes altered and obliterated documents written by two brands of highlighters with the same color and close fluorescence lifetime.An enhancement method of rapid lifetime determination is proposed for time-resolved fluorescence imaging to discriminate substances with approximate fluorescence lifetime in forensic examination. In the method, an image-exclusive-OR treatment with filter threshold adaptively chosen is presented to extract the region of interest from dual-gated fluorescence intensity images, and then the fluorescence lifetime image is reconstructed based on the rapid lifetime determination algorithm. Furthermore, a maximum and minimum threshold filtering is developed to automatically realize visualization enhancement of the lifetime image. In proof experiments, compared with traditional fluorescence intensity imaging and rapid lifetime determination method, the proposed method automatically distinguishes altered and obliterated documents written by two brands of highlighters with the same color and close fluorescence lifetime..
Chinese Optics Letters
- Publication Date: Apr. 10, 2021
- Vol. 19, Issue 4, 041101 (2021)
Feedback ghost imaging by gradually distinguishing and concentrating onto the edge area
Junhao Gu, Shuai Sun, Yaokun Xu, Huizu Lin, and Weitao Liu
Applications of ghost imaging are limited by the requirement on a large number of samplings. Based on the observation that the edge area contains more information thus requiring a larger number of samplings, we propose a feedback ghost imaging strategy to reduce the number of required samplings. The field of view is gradually concentrated onto the edge area, with the size of illumination speckles getting smaller. Experimentally, images of high quality and resolution are successfully reconstructed with much fewer samplings and linear algorithm.Applications of ghost imaging are limited by the requirement on a large number of samplings. Based on the observation that the edge area contains more information thus requiring a larger number of samplings, we propose a feedback ghost imaging strategy to reduce the number of required samplings. The field of view is gradually concentrated onto the edge area, with the size of illumination speckles getting smaller. Experimentally, images of high quality and resolution are successfully reconstructed with much fewer samplings and linear algorithm..
Chinese Optics Letters
- Publication Date: Apr. 10, 2021
- Vol. 19, Issue 4, 041102 (2021)
Anisotropy of the thermal and laser output properties in Yb,Nd:Sc2SiO5 crystal
Yuqing Zhao, Qiangguo Wang, Lihua Meng, Yongping Yao... and Yuping Zhang|Show fewer author(s)
The anisotropy of thermal property in an Yb,Nd:Sc2SiO5 crystal is investigated from the temperature of 293 to 573 K. Based on the systematical study of thermal expansion, thermal diffusivity, and specific heat, the thermal conductivity in Yb,Nd:Sc2SiO5 crystals orientated at (100), (010), (001), and (406) is calculated to be 3.46, 2.60, 3.35, and 3.68 W/(m·K), respectively. The laser output anisotropy of a continuous-wave (CW) and tunable laser is characterized, accordingly. A maximum output power of 6.09 W is achieved in the Yb,Nd:Sc2SiO5 crystal with (010) direction, corresponding to a slope efficiency of 48.56%. The tuning wavelength range in the Yb,Nd:Sc2SiO5 crystal orientated at (100), (010), and (001) is 68, 67, and 65 nm, separately. The effects of thermal properties on CW laser performance are discussed.The anisotropy of thermal property in an
Chinese Optics Letters
- Publication Date: Feb. 05, 2021
- Vol. 19, Issue 4, 041405 (2021)
Instrumentation, Measurement, and Optical Sensing
Simultaneous measurement of strain and temperature using Fabry–Pérot interferometry and antiresonant mechanism in a hollow-core fiber
Chong He, Cheng Zhou, Qian Zhou, Shiyi Xie... and Yong Yao|Show fewer author(s)
A fiber-optic sensor for the simultaneous measurement of strain and temperature is proposed and experimentally demonstrated based on Fabry–Pérot (FP) interference and the antiresonance (AR) mechanism. The sensor was implemented using a single-mode fiber (SMF)–hollow-core fiber–SMF structure. A temperature sensitivity of 21.11 pm/°C was achieved by tracing the troughs of the envelope caused by the AR mechanism, and a strain sensitivity of 2 pm/με was achieved by detecting the fine fringes caused by the FP cavity. The results indicate that the dual-parameter sensor is stable and reliable.A fiber-optic sensor for the simultaneous measurement of strain and temperature is proposed and experimentally demonstrated based on Fabry–Pérot (FP) interference and the antiresonance (AR) mechanism. The sensor was implemented using a single-mode fiber (SMF)–hollow-core fiber–SMF structure. A temperature sensitivity of 21.11 pm/°C was achieved by tracing the troughs of the envelope caused by the AR mechanism, and a strain sensitivity of 2 pm/με was achieved by detecting the fine fringes caused by the FP cavity. The results indicate that the dual-parameter sensor is stable and reliable..
Chinese Optics Letters
- Publication Date: Apr. 10, 2021
- Vol. 19, Issue 4, 041201 (2021)
Highly sensitive torsion sensor based on triangular-prism-shaped long-period fiber gratings
Senyu Wang, Yiwei Ma, Xiaoyang Li, Yang Yi... and Libo Yuan|Show fewer author(s)
We propose and investigate a compact optical fiber sensor that aims to measure the torsion in both amount and direction with high sensitivity. This sensor is configured by a triangular-prism-shaped long-period fiber grating, which is fabricated by the high frequency CO2 laser polished method. The unique design of the triangular-shaped structure breaks the rotational symmetry of the optical fiber and provides high sensitivity for torsion measurement. In preliminary experiments, the torsion response of the sensor achieves a good stability and linearity. The torsion sensitivity is 0.54 nm/(rad/m), which renders the proposed structure a highly sensitive torsion sensor.We propose and investigate a compact optical fiber sensor that aims to measure the torsion in both amount and direction with high sensitivity. This sensor is configured by a triangular-prism-shaped long-period fiber grating, which is fabricated by the high frequency
Chinese Optics Letters
- Publication Date: Apr. 10, 2021
- Vol. 19, Issue 4, 041202 (2021)
Lasers, Optical Amplifiers, and Laser Optics
Dimming control scheme based on hybrid LACO-SCFDM for visible light communications
Siqiao Li, Tiantian Zhang, Yaojun Qiao, and Ji Zhou
This paper proposes a hybrid layered asymmetrically clipped optical (HLACO) single-carrier frequency-division multiplexing (SCFDM) scheme for dimmable visible light communication. It designs a signal structure that combines layered asymmetrically clipped optical (LACO)-SCFDM and negative LACO-SCFDM in proportion for improving the inherent weaknesses of orthogonal frequency-division multiplexing (OFDM)-based dimmable schemes and further enhancing the system performance. Compared to the HLACO-OFDM-based dimming scheme, it obtains a lower bit error ratio and enables efficient communication over broader dimming range. Its spectral efficiency realizes 2.875 bit·s-1·Hz-1 within the dimming range of 30%–70%, and the attainable average spectral efficiency gains exceed at least 19.21% compared to other traditional dimmable schemes.This paper proposes a hybrid layered asymmetrically clipped optical (HLACO) single-carrier frequency-division multiplexing (SCFDM) scheme for dimmable visible light communication. It designs a signal structure that combines layered asymmetrically clipped optical (LACO)-SCFDM and negative LACO-SCFDM in proportion for improving the inherent weaknesses of orthogonal frequency-division multiplexing (OFDM)-based dimmable schemes and further enhancing the system performance. Compared to the HLACO-OFDM-based dimming scheme, it obtains a lower bit error ratio and enables efficient communication over broader dimming range. Its spectral efficiency realizes 2.875 bit·s-1·Hz-1 within the dimming range of 30%–70%, and the attainable average spectral efficiency gains exceed at least 19.21% compared to other traditional dimmable schemes..
Chinese Optics Letters
- Publication Date: Apr. 10, 2021
- Vol. 19, Issue 4, 040601 (2021)
Wavelength-flexible all-polarization-maintaining self-sweeping fiber laser based on intracavity loss tuning
Kaile Wang, Zengrun Wen, Haowei Chen, Baole Lu, and Jintao Bai
We reported a wavelength-flexible all-polarization-maintaining self-sweeping fiber laser based on the intracavity loss tuning brought by the bent optical fiber. The bidirectional cavity structure achieved the self-sweeping effect due to the appearance of the dynamic grating in the active fiber with the spatial hole burning effect. Under this, a section of fiber was bent into a circle for adjusting the loss of the cavity. With a descending diameter of bent fiber circle, the sweeping range moves to the shorter wavelength and covers a wide range from 1055.6 to 1034.6 nm eventually. Both the initial wavelength of self-sweeping regime and the threshold of the fiber laser show exponential correlation with the diameter of the circular fiber. Our work provides a compact and low-cost way to achieve the broad wavelength-flexible self-sweeping operation.We reported a wavelength-flexible all-polarization-maintaining self-sweeping fiber laser based on the intracavity loss tuning brought by the bent optical fiber. The bidirectional cavity structure achieved the self-sweeping effect due to the appearance of the dynamic grating in the active fiber with the spatial hole burning effect. Under this, a section of fiber was bent into a circle for adjusting the loss of the cavity. With a descending diameter of bent fiber circle, the sweeping range moves to the shorter wavelength and covers a wide range from 1055.6 to 1034.6 nm eventually. Both the initial wavelength of self-sweeping regime and the threshold of the fiber laser show exponential correlation with the diameter of the circular fiber. Our work provides a compact and low-cost way to achieve the broad wavelength-flexible self-sweeping operation..
Chinese Optics Letters
- Publication Date: Apr. 10, 2021
- Vol. 19, Issue 4, 041401 (2021)
Combined studies of surface evolution and crack healing for the suppression of negative factors during CO2 laser repairing of fused silica
Chao Tan, Linjie Zhao, Mingjun Chen, Jian Cheng... and Wei Liao|Show fewer author(s)
In order to reveal the evolution mechanism of repaired morphology and the material’s migration mechanism on the crack surface in the process of CO2 laser repairing surface damage of fused silica optics, two multi-physics coupling mathematical models with different scales are developed, respectively. The physical problems, such as heat and mass transfer, material phase transition, melt flow, evaporation removal, and crack healing, are analyzed. Studies show that material ablation and the gasification recoil pressure accompanying the material splash are the leading factors in forming the Gaussian crater with a raised rim feature. The use of low-power lasers for a long time can fully melt the material around the crack before healing, which can greatly reduce the size of the residual air layer. Combined with the experimental research, the methods to suppress the negative factors (e.g., raised rim, deposited debris, air bubbles) in the CO2 laser repairing process are proposed.In order to reveal the evolution mechanism of repaired morphology and the material’s migration mechanism on the crack surface in the process of
Chinese Optics Letters
- Publication Date: Apr. 10, 2021
- Vol. 19, Issue 4, 041402 (2021)
High-power, ultra-broadband supercontinuum source based upon 1/1.5 µm dual-band pumping
Yihuai Zhu, Zhijian Zheng, Xiaogang Ge, Geguo Du... and Qitao Lü|Show fewer author(s)
We experimentally demonstrate an all-fiber supercontinuum source that covers the spectral region ranging from visible to mid-infrared. The ultra-broadband supercontinuum is realized by pumping a cascaded photonic crystal fiber and a highly nonlinear fiber with a 1/1.5 μm dual-band pump source. A maximum output power of 9.01 W is achieved using the system, which is the highest power ever achieved from a supercontinuum source spanning from the visible to mid-infrared.We experimentally demonstrate an all-fiber supercontinuum source that covers the spectral region ranging from visible to mid-infrared. The ultra-broadband supercontinuum is realized by pumping a cascaded photonic crystal fiber and a highly nonlinear fiber with a 1/1.5 μm dual-band pump source. A maximum output power of 9.01 W is achieved using the system, which is the highest power ever achieved from a supercontinuum source spanning from the visible to mid-infrared..
Chinese Optics Letters
- Publication Date: Apr. 10, 2021
- Vol. 19, Issue 4, 041403 (2021)
Speckle characteristics of simulated deep Fresnel region under shadowing effect
Zengshun Jiang, Xingqi An, Yuqin Zhang, Xuan Liu... and Hongsheng Song|Show fewer author(s)
After the three-dimensional self-affine fractal random surface simulation, we use the optical scattering theory to calculate the deep Fresnel region speckle (DFRS) under consideration of the more strict shadowing effect. The evolution of DFRS with the scattering distance and the intensity probability distribution are studied. It is found that the morphology of the scatterer has an antisymmetric relationship with the intensity distribution of DFRS, and the effect of micro-lenses on the scattering surface causes the intensity probability distribution of DFRS to deviate from the Gaussian speckle in the high light intensity area.After the three-dimensional self-affine fractal random surface simulation, we use the optical scattering theory to calculate the deep Fresnel region speckle (DFRS) under consideration of the more strict shadowing effect. The evolution of DFRS with the scattering distance and the intensity probability distribution are studied. It is found that the morphology of the scatterer has an antisymmetric relationship with the intensity distribution of DFRS, and the effect of micro-lenses on the scattering surface causes the intensity probability distribution of DFRS to deviate from the Gaussian speckle in the high light intensity area..
Chinese Optics Letters
- Publication Date: Apr. 10, 2021
- Vol. 19, Issue 4, 041404 (2021)
Quantum wells micro-ring resonator laser emitting at 1746 nm for gas sensing
Fangyuan Meng, Hongyan Yu, Xuliang Zhou, Yajie Li... and Jiaoqing Pan|Show fewer author(s)
Gas sensing for measurement of gas components, concentrations, and other parameters plays an important role in many fields. In this Letter, a micro-ring resonator laser used for gas sensing is experimentally demonstrated. The multi-quantum-wells micro-ring laser based on whispering-gallery modes with an annular resonator and an output waveguide was fabricated. A single-mode laser with a wavelength of 1746.4 nm was fabricated for the first time, to the best of our knowledge, experimentally. The output power of 1.65 mW under 40 mA injection current was obtained with a side-mode suppression ratio over 33 dB.Gas sensing for measurement of gas components, concentrations, and other parameters plays an important role in many fields. In this Letter, a micro-ring resonator laser used for gas sensing is experimentally demonstrated. The multi-quantum-wells micro-ring laser based on whispering-gallery modes with an annular resonator and an output waveguide was fabricated. A single-mode laser with a wavelength of 1746.4 nm was fabricated for the first time, to the best of our knowledge, experimentally. The output power of 1.65 mW under 40 mA injection current was obtained with a side-mode suppression ratio over 33 dB..
Chinese Optics Letters
- Publication Date: Apr. 10, 2021
- Vol. 19, Issue 4, 041406 (2021)
Physical Optics
Floquet spectrum and optical behaviors in dynamic Su–Schrieffer–Heeger modeled waveguide array | Editors' Pick
Ye Yu, Yiwen Song, Tao Chen, Huaiqiang Wang... and Qingqing Cheng|Show fewer author(s)
Floquet topological insulators (FTIs) have been used to study the topological features of a dynamic quantum system within the band structure. However, it is difficult to directly observe the dynamic modulation of band structures in FTIs. Here, we implement the dynamic Su–Schrieffer–Heeger model in periodically curved waveguides to explore new behaviors in FTIs using light field evolutions. Changing the driving frequency produces near-field evolutions of light in the high-frequency curved waveguide array that are equivalent to the behaviors in straight arrays. Furthermore, at modest driving frequencies, the field evolutions in the system show boundary propagation, which are related to topological edge modes. Finally, we believe curved waveguides enable profound possibilities for the further development of Floquet engineering in periodically driven systems, which ranges from condensed matter physics to photonics.Floquet topological insulators (FTIs) have been used to study the topological features of a dynamic quantum system within the band structure. However, it is difficult to directly observe the dynamic modulation of band structures in FTIs. Here, we implement the dynamic Su–Schrieffer–Heeger model in periodically curved waveguides to explore new behaviors in FTIs using light field evolutions. Changing the driving frequency produces near-field evolutions of light in the high-frequency curved waveguide array that are equivalent to the behaviors in straight arrays. Furthermore, at modest driving frequencies, the field evolutions in the system show boundary propagation, which are related to topological edge modes. Finally, we believe curved waveguides enable profound possibilities for the further development of Floquet engineering in periodically driven systems, which ranges from condensed matter physics to photonics..
Chinese Optics Letters
- Publication Date: Apr. 10, 2021
- Vol. 19, Issue 4, 042601 (2021)
Optical beam splitting and asymmetric transmission in bi-layer metagratings | On the Cover
Qiangshi Shi, Xia Jin, Yangyang Fu, Qiannan Wu... and Yadong Xu|Show fewer author(s)
In this work, inspired by advances in twisted two-dimensional materials, we design and study a new type of optical bi-layer metasurface system, which is based on subwavelength metal slit arrays with phase-gradient modulation, referred to as metagratings (MGs). It is shown that due to the found reversed diffraction law, the interlayer interaction that can be simply adjusted by the gap size can produce a transition from optical beam splitting to high-efficiency asymmetric transmission of incident light from two opposite directions. Our results provide new physics and some advantages for designing subwavelength optical devices to realize efficient wavefront manipulation and one-way propagation.In this work, inspired by advances in twisted two-dimensional materials, we design and study a new type of optical bi-layer metasurface system, which is based on subwavelength metal slit arrays with phase-gradient modulation, referred to as metagratings (MGs). It is shown that due to the found reversed diffraction law, the interlayer interaction that can be simply adjusted by the gap size can produce a transition from optical beam splitting to high-efficiency asymmetric transmission of incident light from two opposite directions. Our results provide new physics and some advantages for designing subwavelength optical devices to realize efficient wavefront manipulation and one-way propagation..
Chinese Optics Letters
- Publication Date: Apr. 10, 2021
- Vol. 19, Issue 4, 042602 (2021)
Ultrafast Optics and Attosecond/High-field Physics
Even-order high-harmonic generation from solids in velocity gauge | Editors' Pick
Jiayuan Cao, Na Li, Ya Bai, Peng Liu, and Ruxin Li
We present a velocity-gauge model for the generation of even-order high harmonics, and reveal that the even-order harmonics originate from the multiple-step transitions among the energy bands in momentum space, while the odd-order harmonics are mainly from direct transitions. The lower valence band is found vital for the generation of even harmonics. Relative intensity of even-order harmonics versus the odd orders is calculated and shows a growing trend as the laser field amplitude increases.We present a velocity-gauge model for the generation of even-order high harmonics, and reveal that the even-order harmonics originate from the multiple-step transitions among the energy bands in momentum space, while the odd-order harmonics are mainly from direct transitions. The lower valence band is found vital for the generation of even harmonics. Relative intensity of even-order harmonics versus the odd orders is calculated and shows a growing trend as the laser field amplitude increases..
Chinese Optics Letters
- Publication Date: Apr. 10, 2021
- Vol. 19, Issue 4, 043201 (2021)
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