| With the vigorous development of aerospace technology,space communications,especially microwave optical transmission systems,require high-power,high-efficiency lasers and amplifiers to meet the requirements of high speed,and long transmission distance in space communications.The inter-satellite microwave photonics subsystem transmits the microwave signal to another satellite by modulating the microwave signal to the laser.The signal loss is very large after long-distance transmission.It is necessary to use a fiber amplifier as a preamplifier to improve the signal power.The conversion efficiency of the fiber amplifier is a key performance index,which is related to the power efficiency,heat dissipation and weight of the entire laser amplifier.Aiming at the space application of optical fiber amplifiers,the design and experimental research of optical fiber amplifiers with compact structure,high output power and low power consumption have been carried out.In the electrical design,a semiconductor laser drive system with a digital signal processing chip as the core processor is designed,and a closed-loop control logic of output-detection-re-output is formed.Through the system power control,the security of the output power of the pump laser is guaranteed,the power consumption of the pump source during idle time is reduced,and the electro-optical efficiency is improved.The drive system is equipped with a temperature sensor and a semiconductor cooler to monitor temperature data in real time,and the semiconductor cooler will maintain the temperature stability of the pump laser.The power of the input signal light and the output signal light can be obtained by two photodetectors,and the real-time sampling and comparison algorithm realizes the automatic standby system when there is no input,and maintains the minimum power consumption operation.The mechanical design adopts photoelectric separation and modular design.Taking into account the temperature-sensitive characteristics of semiconductor lasers and the particularity of heat dissipation in the space,the optical part and the electronic part are respectively integrated in different spaces.The copper tube in the heat dissipation layer will transfer the high temperature to the external heat treatment equipment,so that all devices do not need to consider too much heat dissipation space or add the heat sink,keep the overall structure compact and small,and maintain good heat distribution.The integrated design reduces fixed parts and keeps the overall weight below 1 kg.The optical structure adopts a two-stage amplification structure design,and the signal light is amplified through the erbium-doped fiber and erbium-ytterbium co-doped fiber,so that high power output can be maintained while maintaining a high signal-to-noise ratio.This theses studies the output performance of the entire system under different pump powers,and compares the conversion efficiency,power consumption and spectral characteristics of the amplifier under different fiber lengths.In order to obtain a good gain and SNR,an 18 m long erbium-doped fiber and a 7.5 m erbium-ytterbium co-doped fiber were selected,the output spectrum of the signal light after the two stages were analyzed.Finally,the 1551nm milliwatt seed light is amplified to a 7.39W signal output,the signal-to-noise ratio is maintained at 40 d B,the output beam quality M~2is 1.05,and the overall power consumption does not exceed 80 W,proving the effective feasibility of the design.All optical designs use polarization-maintaining devices,and the polarization extinction ratio of the fiber amplifier is 17.5d B.The computer can be used to change the injection current of the pump source,thereby changing the final output power.All modules can be specially adjusted according to the environment,and can be flexibly used in various occasions.This compact fiber amplifier is 20 cm long,14 cm wide and 4 cm high,which is very suitable for space laser communication. |
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