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. The TWLM models are parameterized in the Root Element Editor. The parameters are defined in the “Property Editor” tab and include the “left facet phase” and “right facet phase” that are both swept from 0 to 2π rad in the next stage.
The parameters listed above are mapped to the corresponding TWLM properties through a script located in the Scripts → Setup tab of the Root Element Editor. In the setup script, multisection parameters are assigned using the multisection definition property, which accepts a structure (struct) as input. The structure is created as shown below:
The property names defined within the structure must exactly match the corresponding property names in the UI. For each property, the number of values provided must be equal to the number of sections and consistent across all multisection properties. To disable the multisection feature, assign an empty structure to the multisection definition property. The “run setup script” parameter in the UI must be set to “always” to ensure that the script is executed for each simulation run.
Post-processing of the simulation results is integrated into the Root Element Scripts section. Two result variables, “smsr (partially corrugated grating)” and “smsr (uniform grating)” are defined in the “Results” tab. A script in Scripts→Analysis tab extracts the analyzer results, calculates the SMSR, and assigns the values to the Root Element results.
A nested sweep is created using the built-in parameter sweep utility. The “left facet phase” and the “right facet phase” variables defined in the Root Element are swept from 0 to 2π rad. The SMSRs of both the DFB lasers, returned by the Root Element are chosen as the sweep results, along with the laser spectra from the OSAs. When simulations are run from sweeps, the script in the Analysis tab of the Root Element is automatically run after each simulation run. The user also has the ability to resave the simulation files after the analysis by checking the “resave files after analysis” checkbox in the inner sweep. While running a standalone simulation, the user must use runanalysis; to perform the post-processing after the simulation run.
- Open and run [[facetPhaseSweep.lsf]].
The script loads the simulation file, sets the input parameters, runs the nested sweep, and plots the results. It generates two image plots to illustrate the SMSR variation in the partially corrugated DFB laser and the uniform grating DFB laser. In addition, it calculates single-mode yield (SMY) for SMSR > 35 dB.
The results show that the uniform grating DFB laser exhibits a lower SMSR compared to the partially corrugated grating DFB laser across most facet phase combinations. This indicates that the partially corrugated design is less sensitive to facet-phase variations and maintains stronger single-mode operation across the parameter space. The calculated SMY defined using an SMSR threshold of 35 dB, stands at 84% for the partially corrugated and 54% for the uniform grating. This is consistent with the findings in the literature [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