Narrow Linewidth Tuneable Laser with Cascaded MZI Filter

This example shows a 60 nm tuning range laser with an ultra narrow line width created by a cavity of three cascaded tuneable MZIs simulated using PICWave.

PICWave simulates the spectral response of the laser and how it evolves over time as multiple voltages are tuned. A standard desktop computer performs this 3D, time evolving simulation, spanning over 17 mm in physical length in just few minutes. 

Instead of re-inventing the wheel, instructions on how to calibrate this PICWave example with your epitaxy are available by getting in contact with the Photon Design team (bottom of page).

Creating Narrow Linewidth
Three MZIs are connected in series, where each MZI contributes a unique spectral response as each are designed with different path imbalances. Combining these together results in picking out finer and finer wavelengths which produce the laser’s narrow linewidth.

Using PICWave’s linewidth calculator we can quickly see results with one click in the UI. Even modelling very narrow linewidths in an arbitrary laser design, results can be found without the need for long simulation times.

Tuning
Each MZI includes a modulator section where PICWave simulates the effect of the applied voltage on the waveguide mode’s effective index. This allows designers to tune the MZI imbalances ultimately tuning the lasing wavelength created by the cavity.

Prevent Mode Hopping
A fourth phase modulator is included in the circuit to tune the effective optical path length of the entire cavity. Tuning this at the same rate that any MZIs are tuned prevents mode hopping over the entire tuning range. Avoiding discontinuities in tuning ensures no chirp in the laser’s output power.

• Passive components such as directional couplers or y-splitters can be rigorously modelled in software FIMMPROP (including GDS-II export) and results exported to PICWave for use in circuit level simulations. This includes facet reflectivity.
• Gain spectra for the SOA section can be found with software Harold with results and epitaxy imported to PICWave simply.
• PICWave includes a bend mode solvers so the maximum curvature before loss.