Multisection lasers consist of multiple connected sections with different cavity and gain properties in each section. TWLM allows directly defining the properties per section for an arbitrary number of sections and simulating and visualizing the results of the whole structure.
Defining a Multisection TWLM Element
Multiple sections can be defined with a structure in Lumerical script and assigned to the “multisection definition” property of the TWLM INTERCONNECT element. This struct encapsulates properties specific to each individual section.
This structure consists of attributes with the names of TWLM properties as an array. Each array must be the same length as the number of sections. The figure below illustrates how this structure defines the multisection laser. The spatial coupling within each section is the exact same as that between sections.
Assigning Structure to a Multisection Element
To assign the struct defining the multisection element, the setnamed script command should be used to set the structure to the property “multisection definition”.
Example
setnamed(“TWLM_1”, “multisection definition”, LaserParam); #Assign a structure called LaserParam to the multisection element.
?get(“TWLM1”, “length”); #This command will return a previously set value that is NOT used in the simulation. This command will NOT return the length array in LaserParam
Multisection vs. Cascaded Elements
While multisection TWLM seem very similar to separately cascaded TWLM elements, cascaded TWLM elements could cause inaccuracies in results. Therefore, it is recommended to always use multisection options when heterogeneous sections need to be modeled.
When multiple elements are cascaded together, the connection in between elements introduce a delay in the traveling optical wave equal to one time step of the simulation. Therefore, if multiple TWLM elements are chained together, the delay in the cavity will be larger than the real structure, leading to inaccurate results in important figures of merit such as free spectral range.
Other elements, such as waveguides, can compensate for this delay through settings in the element. However, this option is not available in the TWLM, and as such, the multisection options is needed to model these devices accurately.
Application Example
For a specific example that uses a multisection TWLM element, see Multisection DFB laser with partially corrugated gratings.
See Also
INTERCONNECT as a Laser Design Platform, Laser TW – INTERCONNECT Element, Multisection DFB laser with partially corrugated gratings.