Self-mode-locking in a high-power hybrid silicon nitride integrated laser

Abstract

Integrated mode-locked lasers are useful tools in microwave photonic applications as a local oscillator. In particular, hybrid integrated lasers could easily be integrated with passive processing circuits. In this Letter, we report on the self-mode-locking of a hybrid integrated laser comprising two indium phosphide gain sections and a silicon nitride feedback circuit that filters light using two ring resonators. The hybrid laser is shown to mode-lock and to have a mostly frequency-modulated field in the cavity using a stepped-heterodyne optical complex spectrum analysis. A mostly frequency modulated field output is good for high powers per line due to a more continuous emission, compared with mode-locked lasers using a saturable absorber; additionally, the filter limits the bandwidth of the comb, condensing the power to the fewer comb lines.

Using hybrid integrated InP-Si3N4 diode lasers for the generation of sub-GHz repetition rate frequency combs

“…However, the authors also noted signs of dynamic instability seen as independent locking of subgroups of modes, which we would address to an insufficiently narrow Bragg filtering. In contrast, stable FDML has been observed in hybrid integrated lasers using sharp spectral filtering with two microring resonators [9,10]. However, the repetition rates of these lasers were significantly higher than the 1-GHz limit imposed by the inverse of the upper-state lifetime.…”

Extending hybrid integrated diode lasers to multi-frequency oscillation

“…In contrast, in all cases the output was observed to comprise multiple light frequencies in a comb-shape if the laser parameters were properly set. Specifically, in [58] it was shown via measurements of the modal phases and a reconstructed output time trace that the output was mostly frequency modulated, confirming that the mode-locking dynamics in such narrowband feedback lasers are based on FM mode-locking.…”

“…This includes own work, which formed the first experimental report of this type of modelocking based on narrowband feedback [57], presented in Chapter 4. Our study was followed by a detailed experimental analysis at lower repetition rates around 2.2 GHz [58] while a full physical explanation of the working principle based on numerical modeling was given in [61]. Recently, with another type of integrated, narrow-feedback laser indeed much lower repetition rates have been observed, down to 360 MHz [59].…”

“…In that case, the output is not based on ultrashort pulses but ideally features minimum intensity variations, i.e., quasi-continuous light exhibiting a comb spectrum. There have recently been reports of a new mode-locking concept in hybrid lasers based on narrowband feedback without saturable absorber, which seem to fall into this category [57][58][59][60][61]. This includes own work, which formed the first experimental report of this type of modelocking based on narrowband feedback [57], presented in Chapter 4.…”

“…We note that with bulk feedback based on a fiber Bragg grating, an even lower repetition rate of 255 MHz [60] was realized. Among the mentioned publications is also the first hybrid laser with mode-locking based on Vernier feedback [57] as presented in Chapter 4 of this thesis, which was later followed by a more detailed experimental analysis [58].…”