The circuit for an external cavity laser allows extending the tuning range of an edge-emitting laser. The coupling of the gain-chip to the photonic integrated circuit (PIC) is done using a spot-size converter. The working principle is based on the presence of a filter with a large tuning range on the PIC which selects the lasing wavelength (WL). A reflectivity-tunable mirror is used to provide the feedback to the gain-chip.
In the proposed configuration, the filter is composed of two ring resonators in a Vernier configuration. Only when both the passbands of the two rings are aligned the feedback is effective. The mirror is based on a Mach-Zehnder interferometer. Heaters are present on the fine-tuning, filter and mirror blocks for tuning the emission WL and the feedback strength.
For deployment in applications requiring wide tuning.
- Broadband tuning: > 50 nm
- Compatible with free-space coupled light sources with modal area ~ 8 µm2 (4.7 x 1.7 µm2) near 3.4 µm
- Improving tuning and insertion loss performance