Research On The Tuning Characteristics Of DFB Lasers Based On Local Mean Decomposition

The tuning characteristics of Distributed-Feedback (DFB) diode laser in thetuning process is dynamic time-varying, so learning the dynamic and instantaneousproperty of DFB diode laser in the tuning processs is very important to the heterodynemeasurement applications. In this paper, we measured the linewidth and tuningcharacteristics of DFB diode laser by the tunable heterodyne measurement system,and after processed the beat signals with the time-frequency analysis method based onhilbert-huang transform and local mean decomposition, we have not only obtained theinstantaneous linewidth of DFB diode laser tuned by the pulse and the step current,but also the instantaneous characteristics of DFB diode laser tuned by sawtoothcurrent.The main content of the work and innovation include the following three aspects:1. A local mean decomposition method based on the trendency of the signal（TLMD） is proposed. According to the trend feature of the beat signal, we definedthe trend function, the slow trend function, and the main trend function of the trendsignal, gave the process of the local mean decomposition method based on the maintrend function, confirmed the instantaneous frequency by turning signal via halfperiod, determined phase time-frequency spectrum, and have proved theeffectiveness of this time-frequency analysis method. The local mean decompositionmethod based on the main trend function avoided the mode mixing of the main trendfunction, enhanced the decomposed efficiency, offered the novel thinking andmethods to time-frequency analysis method based on hilbert-huang transform.2. The research on the application of TLMD, and the instantaneous linewidth ofDFB diode laser in tuning process is obtained for the first time. First, we set theheterodyne measurement system with10cm optical path difference, made local meandecomposition based on the main trend function to the beat signals, extracted thetime-frequency spectrum of the beat signal’s phase noise power, and obtained theinstantaneous linewidth of DFB diode laser under the pulse current and ultrashortdelay; Secondly, by means of making time-frequency analysis to the beat signal underlong time delay incoherent light field and the power time-frequency spectrum of thebeat signals we gained the instantaneous linewidth of DFB laser tuned by step current, and verified the best tuning current range of DFB diode laser was0.5~0.8times tothe maximum current.3. Obtained the dynamic and instantaneous characteristics of DFB diode laser inthe tuning process and proposed a mathematical model for compensating to the tuningnonlinearity of the diode laser. Defined the frequency modulation coefficient whichcould be calculated by the ratio between the beat frequency and the current variationwhen the current variation when was very small to describe the tuning characteristicsof DFB diode laser, we gained the dynamic and instantaneous characteristicsseparately after making the dispose in time domain and TLMD analysis to the beatsignals, and made the mathematical models for compensating to the tuningnonlinearity of the diode laser, the veracity of the dynamic and instantaneouscharacteristics have been proved by the forecast to beat frequency and inversingthe optical path difference.The work in this paper provided a novel thinking to hilbert-huang transform, andbringed a new method to heterodyning signal processing, and it’s expected to initiatea new situation in the research on the laser tuning characteristics.