Zhe Li

The irradiation damage effects of erbium-doped fibers for space laser communications have been extensively studied, however, there are few reports on how the performance of erbium-doped fibers changes under the conditions of temperature changing and irradiation in the space environment. In this work, the temperature dependence of loss and gain performance in erbium-doped fibers before and after irradiation was investigated. Temperature induced loss variation after irradiation is -19.7 and 21.08 dB/km at 1200 nm in -25 ℃ and 70 ℃, respectively. Notably, the loss in the non-irradiated fiber is almost unchanged in this temperature range. In the gain performance test, the 1550 nm laser output power of the irradiated fiber decreased 43% when temperature rose from -25 ℃ to 70 ℃. In contrast, the variation of pristine fiber is only 10%. This work helps to understand the properties of erbium-doped optical fiber change under irradiation and temperature-varying environments. It is also proposed that the absorption intensity of Al-OHC defects varies with temperature leading to the fiber’s temperature dependence.

Dual-wavelength fiber lasers operating with a wide spectral separation are of considerable importance for many applications. In this study, we propose and experimentally explore an all-fiberized dual-wavelength random fiber laser with bi-directional laser output operating at 1064 and 1550 nm, respectively. A specially designed Er/Yb co-doped fiber, by optimizing the concentrations of the co-doped Er, Yb, Al and P, was developed for simultaneously providing Er ions gain and Yb ions gain for RFL. Two spans of single mode passive fibers are employed to providing random feedback for 1064 and 1550 nm random lasing, respectively. The RFL generates 5.35 W at 1064 nm and 6.61 W at 1550 nm random lasers. Two power amplifiers (PA) enhance the seed laser to 50 W at 1064 nm with a 3 dB bandwidth of 0.31 nm and 20 W at 1550 nm with a 3 dB bandwidth of 1.18 nm. Both the short- and long-term time domain stabilities are crucial for practical applications. The output lasers of 1064 and 1550 nm PAs are in the single transverse mode operating with a nearly Gaussian profile. To the best of our knowledge, this is the first demonstration of a dual-wavelength RFL, with a spectral separation as far as about 500 nm in an all-fiber configuration.

In this work, we demonstrate a three-stage all-fiber master oscillator power amplifier (MOPA) system emitting over 1 W of the linearly polarized narrow-linewidth pulse output power with 10 kHz pulse repetition frequency and 400 ns pulse width without the amplified spontaneous emission (ASE) at ~1.5 µm. Initially, we analyze the effect of the ASE on the first derivative of backscatter intensity via a contrast experiment. The experiment results show that the noise intensity with angle of inclination is affected by the ASE of the amplifier, thereby decreasing the signal-to-noise ratio of the output power. The laser is characterized by a very low or no ASE level of the output signal when acquiring the first derivative of backscatter intensity with low noise. This condition provides a reference for improving the properties of the laser used for cloud detection.

Based on Dammann vortex grating and adaptive gain stochastic parallel gradient descent algorithm, we theoretically proposed a phase control technology scheme of the coherent beam combining system for generating perfect vectorial vortex beams (VVBs). The simulated results demonstrate that the discrete phase locking for different types of VVBs (including vortex beams, vector beams, and generalized VVBs) can be successfully realized. The intensity distributions, polarization orientation, Pancharatnam phases, and beam widths of different |H_m,n〉 states with the obtained discrete phase distribution further prove that the generated beams are perfect VVBs. Subsequently, the phase aberration residual for different VVBs is evaluated using the normalized phase cosine distance function, and their values range from 0.01 to 0.08, which indicates the obtained discrete phase distribution is close to the ideal phase distribution. In addition, benefitting from the high bandwidth of involved devices in the proposed scheme, the influence of dynamic phase noise can be negligible. The proposed method could be beneficial to realize and switch flexible perfect VVBs in further applications.

Atmospheric effects including absorption and scattering, and turbulence could introduce signal power loss and severe mode crosstalk for the orbital angular momentum (OAM)-based free-space optical communication (FSOC). Therefore, it is of great significance to simultaneously increase signal power and mitigate mode crosstalk. In this paper, for the OAM beam from a coherent laser array with a discrete vortex (CLA-DV) based on coherent beam combining, we investigate its propagation characteristics by employing theoretical derivation and the random phase screens simulation in atmospheric propagation, respectively. The probability density and OAM spectrum are given and compared for CLA-DV and Gaussian vortex beam. The results demonstrate that the Gaussian vortex beam exhibits smaller mode crosstalk under weak atmospheric turbulence conditions, while CLA-DV shows a good performance on crosstalk mitigation for strong atmospheric turbulence conditions in long-distance links. Furthermore, with a specially designed radial phase-locked Gaussian laser array composed of two orthogonal polarized coherent laser arrays carrying different OAM states, a scheme of optical communication system possessing simultaneously polarization-division multiplexing and OAM multiplexing is proposed. The normalized energy weight matrices of all 16 non-zeroth-order OAM modes are numerically calculated. To verify the feasibility of the proposed scheme, the performance of an eight-bit grayscale Lena image facing various atmosphere turbulences is evaluated. The quality of transmitted images becomes worse with the turbulence strength and transmission distance increase, which is confirmed by the trend of average optical signal error rates. This work will provide theoretical insight for improving the performance of OAM-based FSOC under scattering conditions.

Based on coherent beam combining, we propose a method for generating the perfect vectorial vortex beams (VVBs) with a specially designed radial phase-locked Gaussian laser array, which is composed of two discrete vortex arrays with right-handed (RH) and left-handed (LH) circularly polarized states and in turn adjacent to each other. The simulation results demonstrate that the VVBs with correct polarization order and topological Pancharatnam charge are successfully generated. The diameter and thickness of generated VVBs independent of the polarization orders and topological Pancharatnam charges further prove that the generated VVBs are perfect. Propagating in free space, the generated perfect VVBs can be stable for a certain distance, even with half-integer orbital angular momentum. In addition, constant phases φ₀ between the RH and LH circularly polarized laser arrays has no effect on polarization order and topological Pancharatnam charge but makes polarization orientation to rotate φ₀/2. Moreover, perfect VVBs with elliptically polarized states can be flexibly generated only by adjusting the intensity ratio between the RH and LH circularly polarized laser array, and such perfect VVBs are also stable on beam propagation. The proposed method could provide a valuable guidance for high power perfect VVBs in future applications.

In this study, we presented a 1550 nm, high-power, high-efficiency random fiber laser. A method, utilizing the single-mode erbium-ytterbium co-doped fiber with proper length and the highly reflective fiber Bragg grating with wide reflection bandwidth, is used to surmount the generation of Yb-ASE and low slope efficiency. More than 10 W output power is achieved, with a slope effi-ciency of 36.7% and single transverse mode output. The random fiber laser stably operates without significant amplitude fluctuation under maximum power, and which can provide a high-performance light source for a variety of applications.

The predecessor of China Optics was China Optics and Applied Optics Digest, which was founded in 1985. At that time, it was the only retrieval journal in the field of optics in China. At the end of 2008, China Optics and Applied Optics Digest was renamed 《中国光学》的前身是1985年创办的《中国光学与应用光学文摘》，当时是国内光学领域唯一的检索刊物。2008年底《中国光学与应用光学文摘》转型更名为《中国光学与应用光学》期刊，刊载内容突破了文摘的限制，正式成为学术刊物。

In this study, we presented a high-power widely tunable all-fiber narrowband superfluorescent fiber source (SFS) by employing two tunable bandpass filters and three amplifier stages. More than 935 W output power is achieved, with a slope efficiency of >75% and a beam quality factor of M²=1.40. The tuning of the narrowband SFS ranges from ∼1045 nm to ∼1085 nm with a full width at half maximum linewidth of less than 0.71 nm. The tunable narrowband SFS stably operates without the influence of parasitic oscillation and self-pulsing effects under maximum power. To the best of our knowledge, this study is the first to demonstrate a widely tunable all-fiber narrowband SFS around 1 µm wavelength region with output power reaching kilowatt-level.