Tuning of a widely tunable monolithically integrated InP laser for optical coherence tomography

Step-wise tuning of a monolithically integrated widely tunable continuous wave semiconductor ring laser is investigated, for application in Fourier domain optical coherence tomography (OCT). The device operates around 1530 nm and was realized on an InP generic photonic integration technology platform. The laser is tuned using voltage-controlled electrooptic phase modulators with <100 μW thermal dissipation, which reduces time dependent thermal effects in the filter. Here we present a calibration method with progressively finer wavelength control steps and discuss the limits of wavelength accuracy and repeatability with respect to OCT requirements. It is shown that thermal effects due to light absorption in the phase modulators have a negligible effect on the tuning of the laser for six out of seven phase modulators. To bring the thermal dissipation of the seventh phase modulator in line with the others a design change is proposed. Wavelength switching dynamics are investigated with a numerical model of the laser. A simulation based on this model shows that it takes around 50 ns from the wavelength switching instant to establish a single mode operation with side mode suppression ratio of 30 dB.