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2021
Volume: 19 Issue 10
17 Article(s)
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Reviews
Optical Design and Fabrication
Overview of refractive index sensors comprising photonic crystal fibers based on the surface plasmon resonance effect [Invited] | On the Cover
Chao Liu, Jingwei Lü, Wei Liu, Famei Wang, and Paul K. Chu
Optical fibers have been widely applied to telecommunication, imaging, lasers, and sensing. Among the different types of fibers, photonic crystal fibers (PCFs), also called microstructured optical fibers, characterized by air holes arranged along the length of fibers have experienced tremendous advance due to their unique advantages. They are regarded as a desirable platform to excite surface plasmon resonance (SPR) because of easy realization of phase matching conditions between the fundamental core mode and the plasmonic mode, which plays a critical role in miniaturization and integration of SPR sensors. In this mini-review, the current status of PCF sensors based on SPR is summarized. The theory of SPR is discussed, and simulation methods for PCF-SPR sensors are described. The important parameters including the refractive index detection range, resonance wavelength, and spectral sensitivity responsible for the sensing properties of PCF-SPR sensors are reviewed. The fabrication and the comparison of performances are also illustrated, and, finally, the challenges and future perspectives are outlined.Optical fibers have been widely applied to telecommunication, imaging, lasers, and sensing. Among the different types of fibers, photonic crystal fibers (PCFs), also called microstructured optical fibers, characterized by air holes arranged along the length of fibers have experienced tremendous advance due to their unique advantages. They are regarded as a desirable platform to excite surface plasmon resonance (SPR) because of easy realization of phase matching conditions between the fundamental core mode and the plasmonic mode, which plays a critical role in miniaturization and integration of SPR sensors. In this mini-review, the current status of PCF sensors based on SPR is summarized. The theory of SPR is discussed, and simulation methods for PCF-SPR sensors are described. The important parameters including the refractive index detection range, resonance wavelength, and spectral sensitivity responsible for the sensing properties of PCF-SPR sensors are reviewed. The fabrication and the comparison of performances are also illustrated, and, finally, the challenges and future perspectives are outlined..
Chinese Optics Letters
- Publication Date: Oct. 10, 2021
- Vol. 19, Issue 10, 102202 (2021)
Research Articles
Atmospheric, Oceanic, Space, and Environmental Optics
Reconstitution of optical orbital angular momentum through strongly scattering media via feedback-based wavefront shaping method
Lanting Li, Yuanlin Zheng, Haigang Liu, and Xianfeng Chen
Orbital angular momentum (OAM) is a fundamental physical characteristic to describe laser fields with a spiral phase structure. Vortex beams carrying OAMs have attracted more and more attention in recent years. However, the wavefront of OAM light would be destroyed when it passes through scattering media. Here, based on the feedback-based wavefront shaping method, we reconstitute OAM wavefronts behind strongly scattering media. The intensity of light with desired OAM states is enhanced to 150 times. This study provides a method to manipulate OAMs of scattered light and is of great significance for OAM optical communication and imaging to overcome complex environment interference.Orbital angular momentum (OAM) is a fundamental physical characteristic to describe laser fields with a spiral phase structure. Vortex beams carrying OAMs have attracted more and more attention in recent years. However, the wavefront of OAM light would be destroyed when it passes through scattering media. Here, based on the feedback-based wavefront shaping method, we reconstitute OAM wavefronts behind strongly scattering media. The intensity of light with desired OAM states is enhanced to 150 times. This study provides a method to manipulate OAMs of scattered light and is of great significance for OAM optical communication and imaging to overcome complex environment interference..
Chinese Optics Letters
- Publication Date: Oct. 10, 2021
- Vol. 19, Issue 10, 100101 (2021)
Diffraction, Gratings, and Holography
Dual-band independent phase control based on high efficiency metasurface [Invited]
Jinxing Li, Yueyi Yuan, Qun Wu, Shah Nawaz Burokur, and Kuang Zhang
A general method to realize arbitrary dual-band independent phase control is proposed and demonstrated in this paper. A double-layered C-shape reflective meta-atom is designed to realize independent phase control with high efficiency. As a proof of concept, we propose two functional metasurfaces in the microwave region; the first metasurface performs beam steering in different directions, and the second metasurface generates achromatic beam steering at two distinct frequencies. Both simulation and measurement results agree well with the theoretical pre-setting. The maximum measured efficiency is 88.7% and 92.3% at 6.8 GHz and 8.0 GHz, respectively, for one metasurface, and 91.0% and 89.8% at 6.9 GHz and 8.6 GHz, respectively, for the other.A general method to realize arbitrary dual-band independent phase control is proposed and demonstrated in this paper. A double-layered C-shape reflective meta-atom is designed to realize independent phase control with high efficiency. As a proof of concept, we propose two functional metasurfaces in the microwave region; the first metasurface performs beam steering in different directions, and the second metasurface generates achromatic beam steering at two distinct frequencies. Both simulation and measurement results agree well with the theoretical pre-setting. The maximum measured efficiency is 88.7% and 92.3% at 6.8 GHz and 8.0 GHz, respectively, for one metasurface, and 91.0% and 89.8% at 6.9 GHz and 8.6 GHz, respectively, for the other..
Chinese Optics Letters
- Publication Date: Oct. 10, 2021
- Vol. 19, Issue 10, 100501 (2021)
Imaging Systems and Image Processing
Computational ghost imaging with compressed sensing based on a convolutional neural network
Hao Zhang, and Deyang Duan
Computational ghost imaging (CGI) has recently been intensively studied as an indirect imaging technique. However, the image quality of CGI cannot meet the requirements of practical applications. Here, we propose a novel CGI scheme to significantly improve the imaging quality. In our scenario, the conventional CGI data processing algorithm is optimized to a new compressed sensing (CS) algorithm based on a convolutional neural network (CNN). CS is used to process the data collected by a conventional CGI device. Then, the processed data are trained by a CNN to reconstruct the image. The experimental results show that our scheme can produce higher quality images with the same sampling than conventional CGI. Moreover, detailed comparisons between the images reconstructed using the deep learning approach and with conventional CS show that our method outperforms the conventional approach and achieves a ghost image with higher image quality.Computational ghost imaging (CGI) has recently been intensively studied as an indirect imaging technique. However, the image quality of CGI cannot meet the requirements of practical applications. Here, we propose a novel CGI scheme to significantly improve the imaging quality. In our scenario, the conventional CGI data processing algorithm is optimized to a new compressed sensing (CS) algorithm based on a convolutional neural network (CNN). CS is used to process the data collected by a conventional CGI device. Then, the processed data are trained by a CNN to reconstruct the image. The experimental results show that our scheme can produce higher quality images with the same sampling than conventional CGI. Moreover, detailed comparisons between the images reconstructed using the deep learning approach and with conventional CS show that our method outperforms the conventional approach and achieves a ghost image with higher image quality..
Chinese Optics Letters
- Publication Date: Oct. 10, 2021
- Vol. 19, Issue 10, 101101 (2021)
Instrumentation, Measurement, and Optical Sensing
Generic nonlinear error compensation algorithm for phase measuring profilometry
Xin Yu, Shanshan Lai, Yuankun Liu, Wenjing Chen... and Qican Zhang|Show fewer author(s)
In this Letter, the periodical errors, which are caused by the nonlinear effect of the commercial projector and camera, are analyzed as a more generic single-coefficient model. The probability density function of the wrapped phase distributions is used as a tool to find the compensation coefficient. When the compensation coefficient is detected, on the premise of ensuring accuracy, a correlation algorithm process is used to replace the traditional iterative process. Therefore, the proposed algorithm improves the efficiency of coefficient detection dramatically. Both computer simulation and experiment show the effectiveness of this method.In this Letter, the periodical errors, which are caused by the nonlinear effect of the commercial projector and camera, are analyzed as a more generic single-coefficient model. The probability density function of the wrapped phase distributions is used as a tool to find the compensation coefficient. When the compensation coefficient is detected, on the premise of ensuring accuracy, a correlation algorithm process is used to replace the traditional iterative process. Therefore, the proposed algorithm improves the efficiency of coefficient detection dramatically. Both computer simulation and experiment show the effectiveness of this method..
Chinese Optics Letters
- Publication Date: Oct. 10, 2021
- Vol. 19, Issue 10, 101201 (2021)
Broadband instantaneous multi-frequency measurement based on chirped pulse compression
Beibei Zhu, Min Xue, Changyuan Yu, and Shilong Pan
A broadband instantaneous multi-frequency measurement system based on chirped pulse compression, which potentially has a sub-megahertz (MHz) accuracy and a hundred-gigahertz (GHz) measurement range, is demonstrated. A signal-under-test (SUT) is converted into a carrier-suppressed double-sideband (CS-DSB) signal, which is then combined with an optical linearly frequency-modulated signal having the sweeping range covering the +1st-order sideband of the CS-DSB signal. With photodetection, low-pass filtering, and pulse compression, accurate frequencies of the SUT are obtained via locating the correlation peaks. In the experiment, single- and multi-frequency measurements with a measurement range from 3 to 18 GHz and a measurement accuracy of <±100 MHz are achieved.A broadband instantaneous multi-frequency measurement system based on chirped pulse compression, which potentially has a sub-megahertz (MHz) accuracy and a hundred-gigahertz (GHz) measurement range, is demonstrated. A signal-under-test (SUT) is converted into a carrier-suppressed double-sideband (CS-DSB) signal, which is then combined with an optical linearly frequency-modulated signal having the sweeping range covering the +1st-order sideband of the CS-DSB signal. With photodetection, low-pass filtering, and pulse compression, accurate frequencies of the SUT are obtained via locating the correlation peaks. In the experiment, single- and multi-frequency measurements with a measurement range from 3 to 18 GHz and a measurement accuracy of <±100 MHz are achieved..
Chinese Optics Letters
- Publication Date: Oct. 10, 2021
- Vol. 19, Issue 10, 101202 (2021)
Integrated Optics
Human-like stereo sensors using plasmonic antenna embedded MZI with space–time modulation control [Invited] | Editors' Pick
A. Garhwal, A. E. Arumona, P. Youplao, K. Ray... and P. Yupapin|Show fewer author(s)
A micro stereo sensor system is proposed for human sensors, where eyes, ears, tongue, nose, body, and brain are applied by six panda rings embedded in a Mach–Zehnder interferometer (MZI). The input power is applied to the upper branch of MZI and propagates within the system. The six antennas (sensors) are formed by the whispering gallery modes of the panda rings. The space–time modulation signal is applied to the MZI lower branch. The modulated stereo signals can be configured as the plasmon (electron) spin orientations, which can be identified and applied for quantum codes and quantum consciousness.A micro stereo sensor system is proposed for human sensors, where eyes, ears, tongue, nose, body, and brain are applied by six panda rings embedded in a Mach–Zehnder interferometer (MZI). The input power is applied to the upper branch of MZI and propagates within the system. The six antennas (sensors) are formed by the whispering gallery modes of the panda rings. The space–time modulation signal is applied to the MZI lower branch. The modulated stereo signals can be configured as the plasmon (electron) spin orientations, which can be identified and applied for quantum codes and quantum consciousness..
Chinese Optics Letters
- Publication Date: Oct. 10, 2021
- Vol. 19, Issue 10, 101301 (2021)
Silicon non-blocking 4 × 4 optical switch with automated polarization adjustment
Xiaorui Li, Liangjun Lu, Wei Gao, Xin Li... and Linjie Zhou|Show fewer author(s)
We demonstrate a polarization-insensitive silicon 4×4 optical switch based on Mach–Zehnder interferometer (MZI) switch elements. On-chip polarization controllers are integrated before the switch fabric to automatically adjust an arbitrary input polarization to the transverse electric mode. The 4×4 switch fabric is based on a dilated double-layer network architecture to completely cancel the first-order crosstalk. Thermo-optic phase shifters are integrated in the MZI switch elements and the polarization controllers for adjustment of the switching state and polarization, respectively. We develop a polarization control algorithm based on a gradient descent method for automated polarization control. The polarization recovery time is less than 4 ms, and the measured polarization-dependent loss is ∼2 dB. The scheme provides a new solution for realizing polarization-insensitive silicon optical switches.We demonstrate a polarization-insensitive silicon
Chinese Optics Letters
- Publication Date: Oct. 10, 2021
- Vol. 19, Issue 10, 101302 (2021)
Lasers, Optical Amplifiers, and Laser Optics
Narrow vertical beam divergence angle for display applications of 645 nm lasers
Yufei Jia, Yufei Wang, Xuyan Zhou, Linhai Xu... and Wanhua Zheng|Show fewer author(s)
We design a 645 nm laser diode (LD) with a narrow vertical beam divergence angle based on the mode expansion layer. The vertical beam divergence of 10.94° at full width at half-maximum is realized under 1.5 A continuous-wave operation, which is the smallest vertical beam divergence for such an LD based on the mode expansion layer, to the best of our knowledge. The threshold current and output power are 1.07 A and 0.94 W, limited by the thermal rollover for the 100 µm wide and 1500 µm long broad area laser, and the slope efficiency is 0.71 W/A. The low coherence device is fabricated with the speckle contrast of 3.6% and good directional emission. Such 645 nm LDs have promising applications in laser display.We design a 645 nm laser diode (LD) with a narrow vertical beam divergence angle based on the mode expansion layer. The vertical beam divergence of 10.94° at full width at half-maximum is realized under 1.5 A continuous-wave operation, which is the smallest vertical beam divergence for such an LD based on the mode expansion layer, to the best of our knowledge. The threshold current and output power are 1.07 A and 0.94 W, limited by the thermal rollover for the 100 µm wide and 1500 µm long broad area laser, and the slope efficiency is 0.71 W/A. The low coherence device is fabricated with the speckle contrast of 3.6% and good directional emission. Such 645 nm LDs have promising applications in laser display..
Chinese Optics Letters
- Publication Date: Oct. 10, 2021
- Vol. 19, Issue 10, 101401 (2021)
Micro displacement reconstruction of self-mixing grating interferometer based on Littrow structure
Xiufang Wang, Lina Feng, Peng Chen, Zhen Huang, and Ye Yuan
An improved self-mixing grating interferometer based on the Littrow structure has been proposed in this Letter to measure displacement. The grating is integrated inside the interferometer to reduce the impact on the vibration parameters of the object caused by the grating attached to the vibrating object. The +1st diffracted light returns to the laser cavity after being reflected by the target object, and self-mixing interference occurs. The displacement can be reconstructed by processing the self-mixing signals. The feasibility of the proposed interferometer is demonstrated by experimental measurements, and results show that it can achieve micro displacement measurement with the maximum absolute errors of less than 50 nm.An improved self-mixing grating interferometer based on the Littrow structure has been proposed in this Letter to measure displacement. The grating is integrated inside the interferometer to reduce the impact on the vibration parameters of the object caused by the grating attached to the vibrating object. The
Chinese Optics Letters
- Publication Date: Oct. 10, 2021
- Vol. 19, Issue 10, 101402 (2021)
Light-matter Interaction
Perfect light absorption in monolayer MoS2 empowered by optical Tamm states
Yangwu Li, Hua Lu, Jiadeng Zheng, Shichang Li... and Jianlin Zhao|Show fewer author(s)
We present the perfect light absorption of monolayer molybdenum disulfide (MoS2) in a dielectric multilayer system with two different Bragg mirrors. The results show that the strong absorption of visible light in monolayer MoS2 is attributed to the formation of optical Tamm states (OTSs) between two Bragg mirrors. The MoS2 absorption spectrum is dependent on the layer thickness of Bragg mirrors, incident angle of light, and the period numbers of Bragg mirrors. Especially, the nearly perfect light absorption (99.4%) of monolayer MoS2 can be achieved by choosing proper period numbers, which is well analyzed by the temporal coupled-mode theory.We present the perfect light absorption of monolayer molybdenum disulfide (
Chinese Optics Letters
- Publication Date: Oct. 10, 2021
- Vol. 19, Issue 10, 103801 (2021)
Microwave Photonics
Photonic-assisted FSK signal generation based on carrier phase-shifted double sideband modulation
Muguang Wang, Yu Tang, Jian Sun, Jing Zhang... and Fengping Yan|Show fewer author(s)
An approach to generate high-speed and wideband frequency shift keying (FSK) signals based on carrier phase-shifted double sideband (CPS-DSB) modulation is proposed and experimentally validated. The core part of the scheme is a pair of cascaded polarization-sensitive LiNbO3 Mach–Zehnder modulators and phase modulators, whose polarization directions of the principal axes are mutually orthogonal to each other. A proof-of-concept experiment is carried out, where a 0.5 Gb/s FSK signal with the carrier frequencies of 4 and 8 GHz and a 1 Gb/s FSK signal with the carrier frequencies of 8 and 16 GHz are generated successfully.An approach to generate high-speed and wideband frequency shift keying (FSK) signals based on carrier phase-shifted double sideband (CPS-DSB) modulation is proposed and experimentally validated. The core part of the scheme is a pair of cascaded polarization-sensitive LiNbO3 Mach–Zehnder modulators and phase modulators, whose polarization directions of the principal axes are mutually orthogonal to each other. A proof-of-concept experiment is carried out, where a 0.5 Gb/s FSK signal with the carrier frequencies of 4 and 8 GHz and a 1 Gb/s FSK signal with the carrier frequencies of 8 and 16 GHz are generated successfully..
Chinese Optics Letters
- Publication Date: Oct. 10, 2021
- Vol. 19, Issue 10, 103901 (2021)
Optical Design and Fabrication
Multi-focused droplet lens array inspired by movable-type printing technology
Bo Dai, Zhengmeng Zhou, Yan Long, Mingliang Pan... and Dawei Zhang|Show fewer author(s)
A straightforward, cost-effective scheme for fabricating multi-focus droplet lens arrays is proposed. Mini lenses can be rapidly produced by dripping liquid-state polydimethylsiloxane droplets on the square glass substrate. The focal length of the lenses can be precisely controlled by adjusting the mass of the droplet. A group of prepared mini lenses can be flexibly assembled in a three-dimensional printed mount. The lenses are tightly packed together, ensuring a high filling factor of the lens array. The lens array consisting of the mini lenses with a proper combination of focal length can capture images of interests at different depth.A straightforward, cost-effective scheme for fabricating multi-focus droplet lens arrays is proposed. Mini lenses can be rapidly produced by dripping liquid-state polydimethylsiloxane droplets on the square glass substrate. The focal length of the lenses can be precisely controlled by adjusting the mass of the droplet. A group of prepared mini lenses can be flexibly assembled in a three-dimensional printed mount. The lenses are tightly packed together, ensuring a high filling factor of the lens array. The lens array consisting of the mini lenses with a proper combination of focal length can capture images of interests at different depth..
Chinese Optics Letters
- Publication Date: Oct. 10, 2021
- Vol. 19, Issue 10, 102201 (2021)
Physical Optics
Dual-frequency fringe for improving measurement accuracy of three-dimensional shape measurement
Zixiao Miao, and Qican Zhang
A new phase unwrapping method based on dual-frequency fringe is proposed to improve both high accuracy and large measurement range of three-dimensional shape measurement by synthesizing the projected dual-frequency fringes obtaining higher and lower frequencies. The lower-frequency one is their phase difference, which can help unwrap the wrapped phase of the higher-frequency one from their phase sum. In addition, the relationship between the measuring accuracy and the frequencies of the projected fringes is studied to guide the frequency selection in actual measurement. It is found that the closer the two frequencies are, the higher the measurement accuracy will be. The computer simulation and experiment results show the viability of this method.A new phase unwrapping method based on dual-frequency fringe is proposed to improve both high accuracy and large measurement range of three-dimensional shape measurement by synthesizing the projected dual-frequency fringes obtaining higher and lower frequencies. The lower-frequency one is their phase difference, which can help unwrap the wrapped phase of the higher-frequency one from their phase sum. In addition, the relationship between the measuring accuracy and the frequencies of the projected fringes is studied to guide the frequency selection in actual measurement. It is found that the closer the two frequencies are, the higher the measurement accuracy will be. The computer simulation and experiment results show the viability of this method..
Chinese Optics Letters
- Publication Date: Oct. 10, 2021
- Vol. 19, Issue 10, 102601 (2021)
Donut-like photonic nanojet with reverse energy flow
Hao Wang, Jingjing Hao, Baifu Zhang, Cheng Han... and Jianping Ding|Show fewer author(s)
Photonic nanojets (PNJs) are subwavelength jet-like propagating waves generated by illuminating a dielectric microstructure with an electromagnetic wave, conventionally a linearly polarized plane wave. Here, we study the donut-like PNJ produced when a circularly polarized vortex beam is used instead. This novel PNJ also has a reverse energy flow at the donut-like focal plane depending on both the optical vortex topological charge and microsphere size. Our tunable PNJ, which we investigate numerically and analytically, can find applications in optical micromanipulation and trapping.Photonic nanojets (PNJs) are subwavelength jet-like propagating waves generated by illuminating a dielectric microstructure with an electromagnetic wave, conventionally a linearly polarized plane wave. Here, we study the donut-like PNJ produced when a circularly polarized vortex beam is used instead. This novel PNJ also has a reverse energy flow at the donut-like focal plane depending on both the optical vortex topological charge and microsphere size. Our tunable PNJ, which we investigate numerically and analytically, can find applications in optical micromanipulation and trapping..
Chinese Optics Letters
- Publication Date: Oct. 10, 2021
- Vol. 19, Issue 10, 102602 (2021)
Spectroscopy
Identifying self-trapped excitons in 2D perovskites by Raman spectroscopy [Invited] | Editors' Pick
Junze Li, Junchao Hu, Jiaqi Ma, Xinglin Wen, and Dehui Li
Two-dimensional (2D) perovskites exhibit broadband emission due to strong exciton–phonon coupling-induced self-trapped excitons and thus would find important applications in the field of white-light emitting devices. However, the available identifying methods for self-trapped excitons are currently rather limited and complex. Here, we identify the existence of self-trapped excitons by Raman spectroscopy in both excited and non-excited states. Under excited states, the shifting of the Raman peak indicates the presence of the lattice distortion, which together with the extra Raman scattering peak reveals the presence of self-trapped excitons. Our work provides an alternative simple method to study self-trapped excitons in 2D perovskites.Two-dimensional (2D) perovskites exhibit broadband emission due to strong exciton–phonon coupling-induced self-trapped excitons and thus would find important applications in the field of white-light emitting devices. However, the available identifying methods for self-trapped excitons are currently rather limited and complex. Here, we identify the existence of self-trapped excitons by Raman spectroscopy in both excited and non-excited states. Under excited states, the shifting of the Raman peak indicates the presence of the lattice distortion, which together with the extra Raman scattering peak reveals the presence of self-trapped excitons. Our work provides an alternative simple method to study self-trapped excitons in 2D perovskites..
Chinese Optics Letters
- Publication Date: Oct. 10, 2021
- Vol. 19, Issue 10, 103001 (2021)
Ultrafast Optics and Attosecond/High-field Physics
Polarization dependent clamping intensity inside a femtosecond filament in air
Hao Guo, Xiang Dong, Tie-Jun Wang, Xuan Zhang... and Ruxin Li|Show fewer author(s)
Laser polarization and its intensity inside a filament core play an important role in filament-based applications. However, polarization dependent clamping intensity inside filaments has been overlooked to interpret the polarization-related filamentation phenomena. Here, we report on experimental and numerical investigations of polarization dependent clamping intensity inside a femtosecond filament in air. By adjusting the initial polarization from linear to circular, the clamping intensity is increased by 1.36 times when using a 30 cm focal length lens for filamentation. The results indicate that clamping intensity inside the filament is sensitive to laser polarization, which has to be considered to fully understand polarization-related phenomena.Laser polarization and its intensity inside a filament core play an important role in filament-based applications. However, polarization dependent clamping intensity inside filaments has been overlooked to interpret the polarization-related filamentation phenomena. Here, we report on experimental and numerical investigations of polarization dependent clamping intensity inside a femtosecond filament in air. By adjusting the initial polarization from linear to circular, the clamping intensity is increased by 1.36 times when using a 30 cm focal length lens for filamentation. The results indicate that clamping intensity inside the filament is sensitive to laser polarization, which has to be considered to fully understand polarization-related phenomena..
Chinese Optics Letters
- Publication Date: Oct. 10, 2021
- Vol. 19, Issue 10, 103201 (2021)
About the Cover
Here is the caption of the cover image: Surface plasmon resonance (SPR) sensor that consists of a D-shaped photonic crystal fiber with plasmonic coatings. The structure is a desirable platform to excite SPR because of easy realization of phase matching.
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