Spectral linewidth analysis of semiconductor hybrid lasers with feedback from an external waveguide resonator circuit

Abstract

Abstract:We present a detailed analysis of a semiconductor hybrid laser exploiting spectral control from an external photonic waveguide circuit that provides frequency-selective feedback. Based on a spatially resolved transmission line model (TLM), we have investigated the output power, emission frequency, and the laser spectral linewidth. We find that, if the feedback becomes weaker, the spectral linewidth is larger than predicted by previous models that are based on a modified mean-field approximation, even if these take a strong spatial variation of the gain into account. The observed excess linewidth is caused by additional index fluctuations that are associated with strong spatial gain variations.

Hybrid integrated InP-Si3N4 diode laser with a 40-Hz intrinsic linewidth

“…and τ g is the roundtrip time of the solitary gain section. At resonance, i.e., when the center of the filter's reflection peak coincides with the oscillation frequency, B = 0 and A is maximum and equal to the ratio of the optical length of the feedback arm to the optical length of the gain section [21,38]. We find that ∆ν ST reduces with the inverse of L 2 f when keeping the end mirror reflectances constant, in agreement with our discussion on the photon lifetime above.…”

“…To illustrate the effect on the instrinsic linewidth, we consider the whole feedback arm as a lumped reflectance R f (ν) (see Fig. 2) and recall the expression for the intrinsic or Schawlow-Townes linewidth ∆ν ST [38] ∆ν ST = hν 4π…”

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

“…Locking of modes to equidistant frequencies that can be relatively far off the cavity mode center frequencies is enabled by relatively high roundtrip loss (see Table 1). We have confirmed the described behavior via our numerical model [42] based on [44], which predicts exactly equidistant output frequencies as well.…”

“…The parameters that were used here are listed in Table 1. These are the specified fabrication parameters, combined with parameters from our numerical [42]. For α, we use a value from literature that is typical for semiconductor lasers (α = 5) [43].…”

Integrated frequency comb laser with narrow intrinsic optical linewidth based on a dielectric waveguide feedback circuit

“…Locking of modes to equidistant frequencies that can be relatively far off the cavity mode center frequencies is enabled by relatively high roundtrip loss (see Table 1). We have confirmed the described behavior via our numerical model [38] based on [39], which predicts exactly equidistant output frequencies as well. F r e q u e n c y ( G H z )…”