研究目的
Investigating the theoretical possibility of precisely controlling the time-resolved chirp in a directly modulated semiconductor laser using a single drive digital-to-analog converter (DAC) controlled via a novel digital signal processing (DSP) algorithm.
研究成果
The time-resolved frequency chirp control of a semiconductor laser was demonstrated using DSP and a single DAC operating at 2 samples per symbol for the drive current. The simulation results indicate the possibility of generating a 25-GHz peak-to-peak FM at an extinction ratio of 6 dB, while completely suppressing the transient chirp contribution. Furthermore, a bipolar frequency chirp signal resulting in a 2-level phase modulation for DPSK was achieved with an EVM below 1% at 28-Gb/s. A 5-bit look-up table (LUT) was found to adequately capture the requisite DSP generated drive current for completely suppressing the transient chirp.
研究不足
The primary drawback of this implementation is the need for a high resolution analog signal to allow for an accurate first order approximation, which is unattainable with current application specific integrated circuit (ASIC) technology. A look-up table (LUT) for the drive current is proposed as a nonlinear processing unit to overcome this limitation.
1：Experimental Design and Method Selection:
The study involves algebraic back-calculation of the large signal laser rate equations and a first-order numerical approximation of the optical power and chirp functional relationship to obtain a semi-analytical expression for the requisite drive current.
2：Sample Selection and Data Sources:
A multi-quantum-well DFB laser is simulated at a wavelength of 1531.5 nm, with parameters identical to those found in previous research.
3：5 nm, with parameters identical to those found in previous research.
List of Experimental Equipment and Materials:
3. List of Experimental Equipment and Materials: The study utilizes a digital-to-analog converter (DAC) and digital signal processing (DSP) algorithm for controlling the laser's drive current.
4：Experimental Procedures and Operational Workflow:
The target time-resolved frequency chirp profile is set to a binary pulse train with a raised cosine pulse shape. The numerical approximation procedure is calculated at an analog sampling rate of 64 samples per symbol to obtain the required target optical power profile, which is then used to obtain the back-calculation drive current.
5：Data Analysis Methods:
The effectiveness of the approach is demonstrated through simulation results showing a 25-GHz peak-to-peak frequency modulation at a bit-rate of 28-Gb/s and a bipolar frequency chirp signal resulting in a DPSK modulation format at a bit-rate of 28-Gb/s with an EVM below 1%.
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