Qiongqiong Zhang, Chengkai Pang, Yurong Wang, Guangyue Shen, Lei Yang, Zhaohui Li, Haiyan Huang, and Guang Wu

We demonstrate a portable system integrated with time comparison, absolute distance ranging, and optical communication (TRC) to meet the requirements of space gravitational wave detection. A 1 km free-space asynchronous two-way optical link is performed. The TRC realizes optical communication with 7.7×10-5 bit error rate with a Si avalanche photodiode single-photon detector, while the signal intensity is 1.4 photons per pulse with the background noise of 3×104 counts per second. The distance measurement uncertainty is 48.3 mm, and time comparison precision is 162.4 ps. In this TRC system, a vertical-cavity surface-emitting laser diode with a power of 9.1 µW is used, and the equivalent receiving aperture is 0.5 mm. The TRC provides a miniaturization solution for ultra-long distance inter-satellite communication, time comparison, and ranging for space gravitational wave detectors.

Oct. 10, 2022
Chinese Optics Letters
Vol. 20 Issue 10 100601 (2022)
DOI:10.3788/COL202220.100601
Bowen Zhu, Yanyi Wang, Weiping Li, Feng Wang, Jiaxuan Liu, Miao Kong, and Jianjun Yu

We experimentally built a photonics-aided long-distance large-capacity millimeter-wave wireless transmission system and demonstrated a delivery of 40 Gbit/s W-band 16-ary quadrature amplitude modulation (QAM) signal over 4600 m wireless distance at 88.5 GHz. Advanced offline digital signal processing algorithms are proposed and employed for signal recovery, which makes the bit-error ratio under 2.4×10-2. To the best of our knowledge, this is the first field-trial demonstration of >4 km W-band 16QAM signal transmission, and the result achieves a record-breaking product of wireless transmission capacity and distance, i.e., 184 (Gbit/s)·km, for high-speed and long-distance W-band wireless communication.

Oct. 10, 2022
Chinese Optics Letters
Vol. 20 Issue 10 103901 (2022)
DOI:10.3788/COL202220.103901
Jinmin Tian, Mengting Guo, Fan Wang, Chunlei Yu, Lei Zhang, Meng Wang, and Lili Hu

A home-made low loss Bi/P co-doped silica fiber was fabricated using the modified chemical vapor deposition (MCVD) technique combined with the solution doping method, where the background loss at 1550 nm was as low as 17 dB/km. We demonstrated for the first time, to the best of our knowledge, an all-fiber amplifier using the home-made Bi/P co-doped fiber achieving broadband amplification in the E-band. The amplifying performance was evaluated and optimized with different pumping patterns and fiber length. A maximum net gain at 1355 nm close to 20 dB and a minimum noise figure of 4.6 dB were obtained for the first time, to the best of our knowledge, using two 1240 nm laser diodes under bidirectional pumping with the input pump and signal powers of 870 mW and -30 dBm, respectively.

Oct. 10, 2022
Chinese Optics Letters
Vol. 20 Issue 10 100602 (2022)
DOI:10.3788/COL202220.100602
Xuerui Sun, Yinan Wu, Chuanyi Lu, Yuting Zhang, Hao Li, Shijie Liu, Yuanlin Zheng, and Xianfeng Chen

We design and fabricate an unbalanced Mach–Zehnder interferometer (MZI) via electron beam lithography and inductively coupled plasma etching on lithium niobate thin film. The single unbalanced MZI exhibits a maximum extinction ratio of 32.4 dB and a low extra loss of 1.14 dB at the telecommunication band. Furthermore, tunability of the unbalanced MZI by harnessing the thermo-optic and electro-optic effect is investigated, achieving a linear tuning efficiency of 42.8 pm/°C and 55.2 pm/V, respectively. The demonstrated structure has applications for sensing and filtering in photonic integrated circuits.

Oct. 10, 2022
Chinese Optics Letters
Vol. 20 Issue 10 101301 (2022)
DOI:10.3788/COL202220.101301
Jun Meng, Chen Li, Zhenhua Cong, Zhigang Zhao, Shang Wang, Gaoyou Liu, and Zhaojun Liu

Beam quality improvements by a large margin for signal and idler beams of a high energy 100 Hz KTiOAsO4 (KTA) non-critical phase matching (NCPM) optical parametric oscillator (OPO) were demonstrated using an unstable resonator configuration instead of a plane-parallel one. Theoretically, influences of cavity lengths and transmission of an output coupler on the OPO conversion efficiency for both were numerically simulated. For OPO based on an unstable resonator with a Gaussian reflectivity mirror, the maximum pulse energies at the signal (1.53 µm) and idler (3.47 µm) were about 75 mJ and 26 mJ, respectively. The corresponding beam quality factors of the signal were Mx2 = 9.8 and My2 = 9.9, and Mx2 = 11.2 and My2 = 11.5 for the idler. As a comparison, 128 mJ of signal and 48 mJ of idler were obtained with the plane-parallel resonator, and the M2 factors of the signal were Mx2 = 39.8 and My2 = 38.4, and Mx2 = 32.1 and My2 = 31.4 for the idler. Compared with a plane-parallel cavity, over eight times and three times brightness improvements were realized for the signal and idler light, respectively.

Sep. 10, 2022
Chinese Optics Letters
Vol. 20 Issue 9 091401 (2022)
DOI:10.3788/COL202220.091401
Xin Huang, Jin He, Yiguang Jiang, Zhuocheng Chen, Xing Duan, and Long Zhang

Zeolitic imidazolate framework-8 (ZIF-8), a metal-organic framework (MOF) with a non-centrosymmetric crystal structure, exhibits nonlinear optics (NLO) properties and can act as the nanoporous matrix of guest molecules. Amorphization of ZIF-8 can be achieved by pressure or high temperature. Both crystalline and amorphous states have their inherent features for optical applications. The effects of the crystalline-amorphous transition on the structural and optical properties under pressure were investigated in detail. Amorphization leads to the destruction of the ZIF-8 lattice structure, collapse of pores, and the change of spatial symmetry, which in turn alters the NLO properties of ZIF-8 and the luminescence properties of the guest Eu cations. Our results establish the structure–optical properties relationship in the amorphization process and provide new clues in designing novel MOFs optical materials.

Sep. 10, 2022
Chinese Optics Letters
Vol. 20 Issue 9 091603 (2022)
DOI:10.3788/COL202220.091603
Jipeng Wang, Zhenhua Li, Zhongqi Sun, Tianqi Dou, Wenxiu Qu, Fen Zhou, Yanxin Han, Yuqing Huang, and Haiqiang Ma

Reference frame independent and measurement device independent quantum key distribution (RFI-MDI-QKD) has the advantages of being immune to detector side loopholes and misalignment of the reference frame. However, several former related research works are based on the unrealistic assumption of perfect source preparation. In this paper, we merge a loss-tolerant method into RFI-MDI-QKD to consider source flaws into key rate estimation and compare it with quantum coin method. Based on a reliable experimental scheme, the joint influence of both source flaws and reference frame misalignment is discussed with consideration of the finite-key effect. The results show that the loss-tolerant RFI-MDI-QKD protocol can reach longer key rate performance while considering the existence of source flaws in a real-world implementation.

Sep. 10, 2022
Chinese Optics Letters
Vol. 20 Issue 9 092701 (2022)
DOI:10.3788/COL202220.092701
Qi Wu, Yixiao Zhu, Ziyu Cheng, Longjie Yin, and Weisheng Hu

A spectrally sliced heterodyne coherent receiver (SHCR) employing four balanced photodetectors and analog-to-digital converters with half of the signal bandwidth is proposed to complete the signal reception and field recovery. We first numerically characterize the performance of SHCR compared with an intradyne coherent receiver and then validate the principle of the SHCR in a proof-of-concept single-polarization experiment. A 60 GBaud 16-quadrature amplitude modulation transmission is experimentally demonstrated over 80 km standard single-mode fiber with a bit-error-rate of 8.5×10-4 below the 7% hard-decision forward error correction threshold of 3.8×10-3. The SHCR offers a low-cost, hybrid-free, and channel-skew-tolerant candidate for data center interconnects.

Sep. 10, 2022
Chinese Optics Letters
Vol. 20 Issue 9 090601 (2022)
DOI:10.3788/COL202220.090601
Pengwei Wang, Zhentao Liu, Jianrong Wu, Xia Shen, and Shensheng Han

Snapshot spectral ghost imaging, which can acquire dynamic spectral imaging information in the field of view, has attracted increasing attention in recent years. Studies have shown that optimizing the fluctuation of light fields is essential for improving the sampling efficiency and reconstruction quality of ghost imaging. However, the optimization of broadband light fields in snapshot spectral ghost imaging is challenging because of the dispersion of the modulation device. In this study, by judiciously introducing a hybrid refraction/diffraction structure into the light-field modulation, snapshot spectral ghost imaging with broadband super-Rayleigh speckles was demonstrated. The simulation and experiment results verified that the contrast of speckles in a broad range of wavelengths was significantly improved, and the imaging system had superior noise immunity.

Sep. 10, 2022
Chinese Optics Letters
Vol. 20 Issue 9 091102 (2022)
DOI:10.3788/COL202220.091102
Guoqing Ma, Changhe Zhou, Yongfang Xie, Ge Jin, Rongwei Zhu, Jin Zhang, Junjie Yu, and Guohai Situ

A planar-integrated optical system (PIOS) represents powerful optical imaging and information processing techniques and is a potential candidate for the realization of a three-dimensional (3D) integrated optoelectronic intelligent system. Coupling the optical wave carrying information into a planar transparent substrate (typically fused silica) is an essential prerequisite for the realization of such a PIOS. Unlike conventional grating couplers for nano-waveguides on the silicon-on-insulator platform, the grating couplers for PIOS enable to obtain a higher design freedom and to achieve much higher coupling efficiency. By combining the rigorous coupled wave algorithm and simulated annealing optimization algorithm, a high-efficiency asymmetric double-groove grating coupler is designed for PIOS. It is indicated that, under the condition of the normal incidence of TE polarization, the diffraction efficiency of the -1st order is over 95%, and its average value is 97.3% and 92.8% in the C and C+L bands. The simulation results indicate that this type of grating coupler has good tolerance and is expected to be applied in optical interconnections, waveguide-based augmented reality glasses, and planar-integrated 3D interconnection optical computing systems.

Sep. 10, 2022
Chinese Optics Letters
Vol. 20 Issue 9 090501 (2022)
DOI:10.3788/COL202220.090501
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