光谱学与光谱分析, 2019, 39 (4): 1025, 网络出版: 2019-04-11  

可调谐半导体激光器的瞬时光谱测量方法研究

The Research of the Instantaneous Spectral Performance Measurement for a Tunable Semiconductor Laser
作者单位
1 河北科技师范学院机电工程学院, 河北 秦皇岛 066004
2 国土资源部咨询研究中心, 北京 100035
摘要
可调谐半导体激光器在调谐过程中的瞬时光谱特性, 如瞬时的波长、 调谐率、 功率、 线型和线宽等参数影响着以激光器为光源的光学测量和光相干通信系统的精度。 然而, 能够同时测量这些瞬变参数的技术至今未见报道。 提出了一个基于时频分析的测量半导体激光器在调谐过程中瞬时光谱参数的方法, 利用一个短时延外差测量系统, 利用激光器瞬时光谱参数与差拍信号瞬时参数的关系, 最终获得了半导体激光器在连续电流调谐过程中的瞬时光谱。 测量系统采用了10 cm光程差的Mach-Zehnder干涉仪, 调谐电流是幅度为20~120 mA、 频率是1 kHz的锯齿波, 差拍信号可视为直流信号、 载波信号与噪声的叠加, 按照短时延相干光测量原理, 差拍信号中的直流分量幅度的大小反映了激光器输出光信号的功率; 载波信号是一种多项式相位信号, 由其频率可以推算激光器输出光谱的中心频率或波长; 噪声信号则与激光器输出光谱的线型和线宽相关, 通过对噪声信号进行时频分析, 可以获知激光器在连续电流调谐过程中每一时刻或每个电流下的瞬时线型、 线宽。 采用了趋势局部均值分解方法对差拍信号进行了准确分离, 并对分离信号分别进行处理, 同时获知了半导体激光器在调谐过程中的瞬时输出光功率、 光波长、 调谐率及线型、 线宽。 在去掉弛豫部分后截取的整周期差拍信号对应的调谐电流60~115 mA变化范围内, 半导体激光器(FRL15DDR0A31-18950, Furukawa)瞬时输出光功率变化范围是5.16~10.6 mW, 瞬时光波长变化范围为1 579.2~1 579.6 nm; 激光器的瞬时调谐率在0.004 8~0.011 5 nm·mA-1范围内单调变化; 线宽是852.55~954.95 kHz, 呈非线性随机分布。 基于短时延、 局部均值分解和时频分析方法的瞬时光谱参数测量系统可以准确得到各瞬时光谱参数, 测量结果与激光器的静特性相符, 且测量系统结构简单, 使我们更深入地理解激光器的工作原理, 具有广阔的应用前景。
Abstract
The instantaneous spectral characteristics of semiconductor lasers during the tuning process, such as the instantaneous wavelength, tuning rate, power, line shape, and linewidth, affect the accuracy of optical precision measurements and coherent optical communication systems that use tunable lasers as their light sources. Nevertheless, a method that can measure their performance simultaneously has not yet been reported. The purpose of this paper is to provide a novel method for the measurement of the instantaneous spectral performance of a semiconductor laser using time-frequency analysis. We designed a short-delayed self-heterodyne measuring system, described the time-frequency distributions of a laser’s optical field and the beat signal, determined the relationship between a laser’s instantaneous spectral performance during tuning and the parameters of the beat signal, and obtained the time-varying optical power spectrum of a semiconductor laser under continuous injection current tuning. The proposed short-delayed self-heterodyne measuring system used a Mach-Zehnder interferometer (MZI) with an optical path difference (OPD) of 10 cm. The tunable semiconductor laser (FRL15DDR0A31-18950, Furukawa) was tuned using a sawtooth injection current with an amplitude of 20 to 120 mA and a frequency of 1 kHz. According to the principle of coherent measurement, we considered a beat voltage as a superposed oscillation signal consisting of three components: the DC voltage signal, the noise, and the pure beat signal. The DC signal is directly proportional to the power of the laser. The noise generated from the laser’s phase variation can be used to calculate the linewidth and the line shape of the semiconductor laser. The pure beat signal is a mono-component amplitude and frequency modulation (AM-FM) signal, which can be named the carrier; its frequency is closely related to the wavelength of the laser. Using the trend local mean decomposition method, the instantaneous power, wavelength, tuning rate, and linewidth of a semiconductor laser were confirmed simultaneously during the continuous tuning process. The beat signal cut off the relaxation section is an oscillation with an increasing trend in the voltage as the injection current increases from 60 to 115 mA, in this range of changes, the power grows linearly from 5.16 to 10.6 mW, the wavelength changed linearly from 1 579.2 to 1 579.6 nm during the tuning process, the tuning rate increased from 0.004 8 to 0.011 5 nm·mA-1 and the instantaneous linewidth of the semiconductor laser ranges from 852.55 to 954.95 kHz during the entire duration. The results indicated that the time-varying spectral performance of a semiconductor laser can be obtained more accurately and conveniently. This instantaneous spectral performance measurement method based on the short-delayed self-heterodyne measuring system and time-frequency analysis can help in precisely obtaining the instantaneous characteristics of a semiconductor laser during the tuning process and requires only a simple optical system. This method makes possible a deeper and more fundamental understanding of the dynamic workings of a tunable laser, and we believe it should be widely applied.

安颖, 王春磊. 可调谐半导体激光器的瞬时光谱测量方法研究[J]. 光谱学与光谱分析, 2019, 39(4): 1025. AN Ying, WANG Chun-lei. The Research of the Instantaneous Spectral Performance Measurement for a Tunable Semiconductor Laser[J]. Spectroscopy and Spectral Analysis, 2019, 39(4): 1025.

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