Circuit for external Cavity Laser

External cavity laser system scheme. All the blocks require heaters for WL and feedback strength tuning. All the WG outputs in the Vernier filter block present grating couplers (not shown here) to monitor the performance and to avoid back-reflections

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

On going

  • Improving tuning and insertion loss performance