Linewidth narrowing via low-loss dielectric waveguide feedback circuits in hybrid integrated frequency comb lasers.

Jesse Mak,Peter J M Van Der Slot,Dimitri Geskus,Klaus.-J Boller,Edwin J Klein,Albert Van Rees,Youwen Fan

doi:10.1364/oe.27.013307

Abstract

We present an integrated hybrid semiconductor-dielectric (InP-Si3N4) waveguide laser that generates frequency combs at a wavelength around 1.5 μm with a record-low intrinsic optical linewidth of 34 kHz. This is achieved by extending the cavity photon lifetime using a low-loss dielectric waveguide circuit. In our experimental demonstration, the on-chip, effective optical path length of the laser cavity is extended to 6 cm. The resulting linewidth narrowing shows the high potential of on-chip, highly coherent frequency combs with direct electrical pumping, based on hybrid and heterogeneous integrated circuits making use of low-loss dielectric waveguides.

Highlights

Providing optical frequency comb sources in a chip-sized format is of high interest for a wide range of fields, for instance for dual-comb sensing [1], metrology [2], coherent optical communications [3], and microwave photonics [4]
We have presented a hybrid integrated indium phosphide (InP)-Si3N4 laser that generates frequency combs with a record-low intrinsic linewidth of the comb lines of 34 kHz
Our measured linewidth is more than a factor of 7 narrower than in previous work [6], and already approaches similar values as Kerr combs pumped by narrow-linewidth diode lasers [5]

Summary

Introduction

Providing optical frequency comb sources in a chip-sized format is of high interest for a wide range of fields, for instance for dual-comb sensing [1], metrology [2], coherent optical communications [3], and microwave photonics [4]. The second requirement is that the spectral linewidth of the individual comb lines has to be extremely narrow, preferably in the kHz range or below This corresponds to having a low frequency jitter of the optical output. Chip-based diode laser frequency combs, which are most attractive due to direct pumping with an electric current, usually fail to meet this requirement. This failure is due to a combination of intrinsic properties of semiconductor lasers, namely a short cavity length, high optical losses, and strong gain-index coupling [7]. The resulting linewidths are typically tens of MHz in monolithically integrated diode lasers, e.g., indium phosphide (InP) lasers [8]

Methods

Results

Conclusion