Control of dual-wavelength laser emission via optical feedback phase tuning

Abstract

We propose and demonstrate a technique to control the balance between the two amplitudes of a dual-wavelength laser based on a phase-controlled optical feedback. The feedback cavity length is adjusted to achieve a relative phase shift between the desired emission wavelengths, introducing a boost in gain for one wavelength while the other wavelength experiences additional losses. Tuning the optical feedback phase proves to be an effective way to control the gain & losses, and, thus, to select one or balance the amplitude of the two emission wavelengths. This concept can be easily adapted to any platform, wavelength range and wavelength separations providing that a sufficient carrier coupling and gain can be obtained for each mode. To demonstrate the feasibility and to evaluate the performance of this approach, we have implemented two dual-wavelength lasers with different spectral separations together with individual optical feedback loops onto a InP generic foundry platform emitting around 1550 nm. An electro-optical-phase-modulator is used to tune the feedback phase. With this single control parameter, we successfully achieved extinction ratios of up to 38.6 dB for a 10 nm wavelength separation and up to 49 dB for a 1 nm wavelength separation.

Integrated multi-wavelength lasers for all-optical processing of ultra-high frequency signals

“…To further test this assumption in-depth, we have designed dual-wavelength lasers on a generic foundry platform 16 coupled to a monolithically integrated optical feedback loop including an electro-optic phase modulator (EOPM). With this system, we have demonstrated complete switching with up to 50 dB selective suppression of each mode via the EOPM control 55 . The principle is relatively straightforward: the external cavity forms a weak Fabry-Perot resonator, resonating modes will experience a gain boost while anti-resonant modes will have slightly higher losses.…”

“…the two modes come back to the laser in anti-phase after a roundtrip in the external cavity, we can maximize the effect of the resonator. The EOPM makes the resonator tunable and allows us to select the desired mode at will 55 . Besides the compactness and that it only requires a single control parameter, this technique benefits from the fast response time of the EOPM which leads to fast switching at the nanosecond timescale.…”

“…Using the same devices as in Ref. 16,55 and by detuning the two DBRs, we were able to trigger additional longitudinal modes. Since the external cavity length cannot be modified as it is monolithically integrated with the laser, the feedback parameter including the feedback phases are likely sub-optimal.…”