Volume: 7 Issue 8
18 Article(s)

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Special Issue on Quantum Photonics
Transmission of photonic polarization states through 55-m water: towards air-to-sea quantum communication
Cheng-Qiu Hu, Zeng-Quan Yan, Jun Gao, Zhi-Qiang Jiao, Zhan-Ming Li, Wei-Guan Shen, Yuan Chen, Ruo-Jing Ren, Lu-Feng Qiao, Ai-Lin Yang, Hao Tang, and Xian-Min Jin
Quantum communication has been rapidly developed due to its unconditional security and successfully implemented through optical fibers and free-space air in experiments. To build a complete quantum communication network involving satellites in space and submersibles in ocean, the underwater quantum channel has been investigated in both theory and experiment. However, the question of whether the polarization encoded qubit can survive through a long-distance and high-loss underwater channel, which is considered as the restricted area for satellite-borne radio waves, still remains. Here, we experimentally demonstrate the transmission of blue-green photonic polarization states through 55-m-long water. We prepare six universal quantum states at the single photon level and observe their faithful transmission in a large marine test platform. We obtain complete information of the channel by quantum process tomography. The distance demonstrated in this work reaches a region allowing potential real applications, representing a step further towards air-to-sea quantum communication.
Photonics Research
  • Publication Date: Jul. 25, 2019
  • Vol.7 Issue, 8 08000A40 (2019)
Special Issue on Semiconductor UV Photonics
Magnesium ion-implantation-based gallium nitride p-i-n photodiode for visible-blind ultraviolet detection
Weizong Xu, Yating Shi, Fangfang Ren, Dong Zhou, Linlin Su, Qing Liu, Liang Cheng, Jiandong Ye, Dunjun Chen, Rong Zhang, Youdou Zheng, and Hai Lu
In this work, a GaN p-i-n diode based on Mg ion implantation for visible-blind UV detection is demonstrated. With an optimized implantation and annealing process, a p-GaN layer and corresponding GaN p-i-n photodiode are achieved via Mg implantation. As revealed in the UV detection characterizations, these diodes exhibit a sharp wavelength cutoff at 365 nm, high UV/visible rejection ratio of 1.2×104, and high photoresponsivity of 0.35 A/W, and are proved to be comparable with commercially available GaN p-n photodiodes. Additionally, a localized states-related gain mechanism is systematically investigated, and a relevant physics model of electric-field-assisted photocarrier hopping is proposed. The demonstrated Mg ion-implantation-based approach is believed to be an applicable and CMOS-process-compatible technology for GaN-based p-i-n photodiodes.
Photonics Research
  • Publication Date: Jul. 12, 2019
  • Vol.7 Issue, 8 08000B48 (2019)
Review of encapsulation materials for AlGaN-based deep-ultraviolet light-emitting diodes
Yosuke Nagasawa, and Akira Hirano
This paper reviews and introduces the techniques for boosting the light-extraction efficiency (LEE) of AlGaN-based deep-ultraviolet (DUV: λ<300 nm) light-emitting diodes (LEDs) on the basis of the discussion of their molecular structures and optical characteristics, focusing on organoencapsulation materials. Comparisons of various fluororesins, silicone resin, and nonorgano materials are described. The only usable organomaterial for encapsulating DUV-LEDs is currently considered to be polymerized perfluoro(4-vinyloxy-1-butene) (p-BVE) terminated with a ─CF3 end group. By forming hemispherical lenses on DUV-LED dies using p-BVE having a ─CF3 end group with a refractive index of about 1.35, the LEE was improved by 1.5-fold, demonstrating a cost-feasible packaging technique.
Photonics Research
  • Publication Date: Jul. 29, 2019
  • Vol.7 Issue, 8 08000B55 (2019)
Research Articles
Holography, Gratings, and Diffraction
Design and experimental verification of a monolithic complete-light modulator based on birefringent materials
Yingfei Pang, Axiu Cao, Jiazhou Wang, Hui Pang, Wei Yan, Xiangdong Wu, Lifang Shi, and Qiling Deng
This paper presents a method to design a monolithic complete-light modulator (MCLM) that fully controls the amplitude, phase, and polarization of incident light. The MCLM is made of birefringent materials that provide different refractive indices to orthogonal eigen-polarizations, the ordinary o and extraordinary e states. We propose an optimization method to calculate the two relief depth distributions for the two eigen-polarizations. Also, a merging algorithm is proposed to combine the two relief depth distributions into one. The corresponding simulations were carried out in this work and the desired light distribution, including information on amplitude, phase, and four polarization states, was obtained when a laser beam passed through a 16-depth-level micro-structure whose feature size is 8 μm. The structure was fabricated by common photolithography. An experimental optical system was also set up to test the optical effects and performances of the MCLM. The experimental performance of the MCLM agrees with the simulation results, which verifies the validity of the algorithms we propose in this paper.
Photonics Research
  • Publication Date: Jul. 17, 2019
  • Vol.7 Issue, 8 08000875 (2019)
Imaging Systems, Microscopy, and Displays
Optimal illumination scheme for isotropic quantitative differential phase contrast microscopy
Yao Fan, Jiasong Sun, Qian Chen, Xiangpeng Pan, Lei Tian, and Chao Zuo
Differential phase contrast microscopy (DPC) provides high-resolution quantitative phase distribution of thin transparent samples under multi-axis asymmetric illuminations. Typically, illumination in DPC microscopic systems is designed with two-axis half-circle amplitude patterns, which, however, result in a non-isotropic phase contrast transfer function (PTF). Efforts have been made to achieve isotropic DPC by replacing the conventional half-circle illumination aperture with radially asymmetric patterns with three-axis illumination or gradient amplitude patterns with two-axis illumination. Nevertheless, the underlying theoretical mechanism of isotropic PTF has not been explored, and thus, the optimal illumination scheme cannot be determined. Furthermore, the frequency responses of the PTFs under these engineered illuminations have not been fully optimized, leading to suboptimal phase contrast and signal-to-noise ratio for phase reconstruction. In this paper, we provide a rigorous theoretical analysis about the necessary and sufficient conditions for DPC to achieve isotropic PTF. In addition, we derive the optimal illumination scheme to maximize the frequency response for both low and high frequencies (from 0 to 2NAobj) and meanwhile achieve perfectly isotropic PTF with only two-axis intensity measurements. We present the derivation, implementation, simulation, and experimental results demonstrating the superiority of our method over existing illumination schemes in both the phase reconstruction accuracy and noise-robustness.
Photonics Research
  • Publication Date: Jul. 25, 2019
  • Vol.7 Issue, 8 08000890 (2019)
Integrated Photonics
Ge-on-Si modulators operating at mid-infrared wavelengths up to 8  μm
Tiantian Li, Milos Nedeljkovic, Nannicha Hattasan, Wei Cao, Zhibo Qu, Callum G. Littlejohns, Jordi Soler Penades, Lorenzo Mastronardi, Vinita Mittal, Daniel Benedikovic, David J. Thomson, Frederic Y. Gardes, Hequan Wu, Zhiping Zhou, and Goran Z. Mashanovich
Photonics Research
  • Publication Date: Jul. 11, 2019
  • Vol.7 Issue, 8 08000828 (2019)
Lasers and Laser Optics
Generation of wavelength-tunable and coherent dual-wavelength solitons in the C + L band by controlling the intracavity loss
Tianyu Zhu, Zhaokun Wang, D. N. Wang, Fan Yang, and Liujiang Li
A wavelength-tunable and dual-wavelength mode-locking operation is achieved in an Er-doped fiber laser using a hybrid no-core fiber graded index multimode fiber as the saturable absorber. In the tuning operation, continuously wavelength-tunable pulses with a tuning range of 46.7 nm, stable 3-dB bandwidth of around 5 nm, and pulse duration of ~850 fs are obtained by increasing the intracavity loss of a variable optical attenuator. In the dual-wavelength operation, the two solitons at different wavelengths demonstrate the characteristics of mutual coherence. By increasing the intracavity loss, the spectral spacing can be tuned from 11 to 33.01 nm while maintaining the coherence of the solitons. Such coherent solitons have high potential for applications in dual-comb frequency and multicolor pulses in nonlinear microscopy.
Photonics Research
  • Publication Date: Jul. 17, 2019
  • Vol.7 Issue, 8 08000853 (2019)
Medical Optics and Biotechnology
Dark mode plasmonic optical microcavity biochemical sensor
Cheng Li, Lei Chen, Euan McLeod, and Judith Su
Whispering gallery mode (WGM) microtoroid optical resonators have been effectively used to sense low concentrations of biomolecules down to the single molecule limit. Optical WGM biochemical sensors such as the microtoroid operate by tracking changes in resonant frequency as particles enter the evanescent near field of the resonator. Previously, gold nanoparticles have been coupled to WGM resonators to increase the magnitude of resonance shifts via plasmonic enhancement of the electric field. However, this approach results in increased scattering from the WGM, which degrades its quality (Q) factor, making it less sensitive to extremely small frequency shifts caused by small molecules or protein conformational changes. Here, we show using simulation that precisely positioned trimer gold nanostructures generate dark modes that suppress radiation loss and can achieve high (>106) Q with an electric-field intensity enhancement of 4300, which far exceeds that of a single rod (~2500 times). Through an overall evaluation of a combined enhancement factor, which includes the Q factor of the system, the sensitivity of the trimer system was improved 105× versus 84× for a single rod. Further simulations demonstrate that unlike a single rod system, the trimer is robust to orientation changes and has increased capture area. We also conduct stability tests to show that small positioning errors do not greatly impact the result.
Photonics Research
  • Publication Date: Aug. 01, 2019
  • Vol.7 Issue, 8 08000939 (2019)
Nanophotonics and Photonic Crystals
Nanophotonic media for artificial neural inference | On the Cover
Erfan Khoram, Ang Chen, Dianjing Liu, Lei Ying, Qiqi Wang, Ming Yuan, and Zongfu Yu
Photonics Research
  • Publication Date: Jul. 03, 2019
  • Vol.7 Issue, 8 08000823 (2019)
Nonlinear Optics
Low threshold anti-Stokes Raman laser on-chip
Hyungwoo Choi, Dongyu Chen, Fan Du, Rene Zeto, and Andrea Armani
Raman lasers based on integrated silica whispering gallery mode resonant cavities have enabled numerous applications from telecommunications to biodetection. To overcome the intrinsically low Raman gain value of silica, these devices leverage their ultrahigh quality factors (Q), allowing submilliwatt stimulated Raman scattering (SRS) lasing thresholds to be achieved. A closely related nonlinear behavior to SRS is stimulated anti-Stokes Raman scattering (SARS). This nonlinear optical process combines the pump photon with the SRS photon to generate an upconverted photon. Therefore, in order to achieve SARS, the efficiency of the SRS process must be high. As a result, achieving SARS in on-chip resonant cavities has been challenging due to the low lasing efficiencies of these devices. In the present work, metal-doped ultrahigh Q (Q>107) silica microcavity arrays are fabricated on-chip. The metal-dopant plays multiple roles in improving the device performance. It increases the Raman gain of the cavity material, and it decreases the optical mode area, thus increasing the circulating intensity. As a result, these devices have SRS lasing efficiencies that are over 10× larger than conventional silica microcavities while maintaining low lasing thresholds. This combination enables SARS to be generated with submilliwatt input powers and significantly improved anti-Stokes Raman lasing efficiency.
Photonics Research
  • Publication Date: Jul. 26, 2019
  • Vol.7 Issue, 8 08000926 (2019)
Optical and Photonic Materials
Radiation-pressure-induced photoluminescence enhancement of all-inorganic perovskite CsPbBr3 quantum dots
Ying Zhang, Haiou Zhu, Taiwu Huang, Zongpeng Song, and Shuangchen Ruan
Perovskite quantum dots (QDs) are of great interest due to their outstanding optoelectronic properties and tremendous application potential. Improving photoluminescence (PL) spectra in all-inorganic perovskite QDs is of great importance for performance enhancement. In this work, the PL quantum yield of the CsPbBr3 perovskite QDs is enhanced from 70% to 95% with increasing radiation pressure. Such enhancement is attributed to the increased binding energy of self-trapped excitons (STEs) upon radiation pressure, which is consistent with its blue-shifted PL and other characterization results. Furthermore, we study ultrafast absorption spectroscopy and find that the dynamics of relaxation from free excitons to STEs in radiation pressure CsPbBr3 QDs is ascribed to stronger electron–phonon coupling in the contracted octahedral structure. It is further demonstrated that radiation pressure can boost the PL efficiency and explore effectively the relationship between the structure and optical properties.
Photonics Research
  • Publication Date: Jul. 11, 2019
  • Vol.7 Issue, 8 08000837 (2019)
2D-material-integrated whispering-gallery-mode microcavity
Lu Wang, Xuefei Zhou, Shuo Yang, Gaoshan Huang, and Yongfeng Mei
Optical microcavities, which support whispering gallery modes, have attracted tremendous attention in both fundamental research and potential applications. The emerging of two-dimensional materials offers a feasible solution to improve the performance of traditional microcavity-based optical devices. Besides, the integration of two-dimensional materials with microcavities will benefit the research of heterogeneous materials on novel devices in photonics and optoelectronics, which is dominated by the strongly enhanced light–matter interaction. This review focuses on the research of heterogeneous two-dimensional-material whispering-gallery-mode microcavities, opening a myriad of lab-on-chip applications, such as optomechanics, quantum photonics, comb generation, and low-threshold microlasing.
Photonics Research
  • Publication Date: Jul. 25, 2019
  • Vol.7 Issue, 8 08000905 (2019)
One-order-higher Cr4+ conversion efficiency in Cr4+:YAG transparent ceramics for a high-frequency passively Q-switched laser
Yingshuang Shan, Le Zhang, Tianyuan Zhou, Cen Shao, Lei Zhang, Yuelong Ma, Qing Yao, Zhigang Jiang, Farida A. Selim, and Hao Chen
The Cr4+-doped yttrium aluminum garnet (Cr4+:YAG) saturable absorber, a new generation of passively Q-switched solid-state laser material, faces a significant obstacle of low conversion rate of chromium from trivalent to tetravalent, degrading efficiency in a passively Q-switched laser. In this paper, highly transparent Cr4+:YAG ceramics were fabricated and committed to compare the laser performance with Cr4+:YAG crystals on a 1 μm passively Q-switched laser. Thanks to the grain boundary effect, the Cr4+ conversion efficiency of 0.05 at.% Cr4+:YAG transparent ceramics coated with high transparency (HT) films (T=86.46% at 1064 nm) was nine times higher than that of 0.1 at.% Cr4+:YAG single crystals coated with HT films (T=84.00% at 1064 nm). Differing from the counterpart Cr4+:YAG crystals, no absorption saturation tendency was observed for the 0.05 at.% Cr:YAG ceramics when the pump power exceeded ~1900 mW. Furthermore, the repetition frequency reached 217 kHz for 0.05 at.% Cr:YAG ceramics, which was a three-fold factor increase from that of the corresponding single crystal. The advantages of transparent ceramics over single crystals were proved through laser performance for the first time, to the best of our knowledge. This study also provided compelling evidence for replacing single crystals with ceramics for u
Photonics Research
  • Publication Date: Jul. 29, 2019
  • Vol.7 Issue, 8 08000933 (2019)
Experimental demonstration of an electrically tunable broadband coherent perfect absorber based on a graphene–electrolyte–graphene sandwich structure
Jin Zhang, Xingzhan Wei, Malin Premaratne, and Weiren Zhu
We propose and experimentally demonstrate the operation of an electrically tunable, broadband coherent perfect absorption (CPA) at microwave frequencies by harnessing the CPA features of a graphene–electrolyte–graphene sandwich structure (GSS). Using both a simplified lumped circuit model and full-wave numerical simulation, it is found that the microwave coherent absorptivity of the GSS can be tuned dynamically from nearly 50% to 100% by changing the Fermi level of the graphene. Strikingly, our simplified lumped circuit model agrees very well with the full-wave numerical model, offering valuable insight into the CPA operation of the device. The angle dependency of coherent absorption in the GSS is further investigated, making suggestions for achieving CPA at wide angles up to 80°. To show the validity and accuracy of our theory and numerical simulations, a GSS prototype is fabricated and measured in a C-band waveguide system. The reasonably good agreement between the experimental and the simulated results confirms that the tunable coherent absorption in GSS can be electrically controlled by changing the Fermi level of the graphene.
Photonics Research
  • Publication Date: Jul. 17, 2019
  • Vol.7 Issue, 8 08000868 (2019)
Quantum Optics
Exceptional points of any order in a single, lossy waveguide beam splitter by photon-number-resolved detection | Editors' Pick
Mario A. Quiroz-Juárez, Armando Perez-Leija, Konrad Tschernig, Blas M. Rodríguez-Lara, Omar S. Magaña-Loaiza, Kurt Busch, Yogesh N. Joglekar, and Roberto de J. León-Montiel
Exceptional points (EPs) are degeneracies of non-Hermitian operators where, in addition to the eigenvalues, the corresponding eigenmodes become degenerate. Classical and quantum photonic systems with EPs have attracted tremendous attention due to their unusual properties, topological features, and an enhanced sensitivity that depends on the order of the EP, i.e., the number of degenerate eigenmodes. Yet, experimentally engineering higher-order EPs in classical or quantum domains remain an open challenge due to the stringent symmetry constraints that are required for the coalescence of multiple eigenmodes. Here, we analytically show that the number-resolved dynamics of a single, lossy waveguide beam splitter, excited by N indistinguishable photons and post-selected to the N-photon subspace, will exhibit an EP of order N+1. By using the well-established mapping between a beam splitter Hamiltonian and the perfect state transfer model in the photon-number space, we analytically obtain the time evolution of a general N-photon state and numerically simulate the system’s evolution in the post-selected manifold. Our results pave the way toward realizing robust, arbitrary-order EPs on demand in a single device.
Photonics Research
  • Publication Date: Jul. 17, 2019
  • Vol.7 Issue, 8 08000862 (2019)
Adaptive cavity-enhanced dual-comb spectroscopy
Weipeng Zhang, Xinyi Chen, Xuejian Wu, Yan Li, and Haoyun Wei
Resolution and bandwidth are critical for cavity-enhanced dual-comb spectroscopy (CE-DCS). Here, we pioneer an adaptive approach in CE-DCS to improve the broadband as well as the resolution. Postcorrections to dual-comb interferograms adaptively compensate the relative phase jitters of the optical frequency combs and result in both a mode-resolved spectral resolution and a signal-to-noise ratio of 440:1 in 1 s. Meanwhile, an adaptive comb-cavity locking scheme exploits more than 90% of the comb modes, covering 340 cm 1 (10 THz) at 6450 cm 1. For a single dual-comb interferogram, more than 40,000 comb teeth spaced by 250 MHz are measured in less than 7.5 ms, contributing to a noise equivalent absorption per spectral element of 2×10 10 cm 1 ·Hz 1/2. This adaptive cavity-enhanced dual-comb spectroscopy technique provides an attractive spectroscopic tool that may be utilized in trace-gas sensing, breath and cancer analysis, and engine combustion diagnosis.
Photonics Research
  • Publication Date: Jul. 23, 2019
  • Vol.7 Issue, 8 08000883 (2019)
Fiber Optics and Optical Communications
Optical Devices
Design of a low-filling-factor and polarization-sensitive superconducting nanowire single photon detector with high detection efficiency
Dezhi Li, and Rongzhen Jiao
Photonics Research
  • Publication Date: Jul. 12, 2019
  • Vol.7 Issue, 8 08000847 (2019)