In this application example, we simulate a distributed feedback (DFB) laser with a passive feedback section and a partially corrugated grating, then compare the results with existing literature. To assess the single-mode operation sensitivity of the laser, we sweep the phases of the left and right facets and compute the side-mode suppression ratio (SMSR). The outcomes are contrasted with those from a uniform grating DFB laser to highlight the impact of the partially corrugated grating. Additionally, we showcase the newly released multisection feature in the 2024 R2 version.
Overview
Understand the simulation workflow and key results
This application example simulates a DFB laser with a passive feedback section, using parameters from reference [1]. DFB lasers with passive feedback sections are recognized for their high-speed operation but are also sensitive to cleavage yield and single-mode stability. DFB lasers with partially corrugated gratings and passive feedback (PCG-PFL) are designed to address these issues. The PCG structure enables DFB lasers to maintain a high single-mode yield (SMY), even with a high-reflection coating on the rear facet and strong reflection from the integrated passive section. The steps for characterization and comparison studies will be outlined. The SMSR will be calculated and plotted as a function of the facet phase of the DFB laser with a partially corrugated grating and compared to that of a DFB laser with a uniform grating. Lastly, the SMY will be computed for SMSR > 35 dB and contrasted with the results from reference [1].
Run and Results
Instructions for running the model and discussion of key results
Step 1: Set up the Interconnect model file
- Open [[MultisectionDFBLaser.icp]], project file
The project file contains two TWLMs: TWLM_1, which models a DFB laser with a partially corrugated grating, and TWLM_2, which models a DFB laser with a uniform grating.
- Open [[applyMultisectionParameters.lsf]] file and run the script.
The multisection parameters are set from property 'multisection definition' as a struct. The struct is constructed as shown above where the property name must match the property name in the UI. The number of fields for each property must be the same and is equation to the number of sections. To deactivate the multisection feature assign an empty struct to the property 'multisection definition'.
The calculation of SMSR as a function of facet phase can be automatized by using two for-loops and sweep over the Left and Right facet phase and save the spectrum results.
- Open and run [[runFacetPhaseSweep.lsf]]
This script runs two for loops to sweep the Left and Right facet phase from 0 to 360 degrees. It then calculates SMSR in dB by subtracting magnitudes of the two most dominant peaks.
Finally, plot the 2D SMSR image
- Open and run the script file named [[plotSMSR.lsf]]
The scripts generates a 2D SMSR image for both Partially corrugated DFB and uniform grating DFB lasers. In addition it calculates single-mode yield (SMY) for SMSR > 35dB.
The facet phase sweep results are depicted in the figure below for both partially corrugated and uniform grating DFB lasers. It is evident that the SMSR is lower for the uniform grating DFB compared to the partially corrugated one across most facet phase changes. The calculated SMY stands at 84% for the partially corrugated and 50% for the uniform grating, when the SMSR is greater than 35 dB. This is consistent with the findings in [1].
Important Model Settings
Description of important objects and settings used in this model
Sample rate
In transient sample mode simulations, it's crucial to have a high sample rate to ensure accurate results. The sample rate, which is equivalent to the bandwidth, needs to be substantial enough to encompass the significant parts of the gain and cavity spectral shapes. Additionally, the time step, which is the inverse of the sample rate, should correlate with the cavity section length through the group velocity, ensuring the sample rate provides adequate spatial resolution for the necessary number of sections.
OSA resolution
Enabling OSA resolution can reduce the noise in the measured signal. To facilitate smoother signal measurement and simplify SMSR calculation, the OSA resolution is configured to a Gaussian function with a selected bandwidth of 1GHz.
Grating period
The grating period was not specified in reference [1], leading to several fitting simulations being conducted to estimate this period. It is important to note that calculations of SMSR and SMY are sensitive to the parameter of the grating period.
Additional Resources
Additional documentation, examples and training material
Related publications
[1] S. Sulikhah, H. -W. Tsao and S. -L. Lee, "Enhancement of Modulation Responses of Directly Modulated Lasers with Passive Feedback and Partially Corrugated Grating," 2019 24th Microoptics Conference (MOC) , Toyama, Japan, 2019
See also
Related Ansys Innovation Courses