Study of the Effects of Cavity Mode Spacing on Mode-Hopping in III–V/Si Hybrid Photonic Crystal Lasers

We present a design methodology for hybrid lasers to realise mode-hop free operation by controlling the cavity mode spacing. In this study, a compact hybrid photonic crystal laser (H-PhCL) was employed which allowed a reduction of the Fabry–Perot length of the laser cavity and eliminated the need for an active mode stabilisation mechanism in order to realise mode-hop free operation. The H-PhCL was formed by butt-coupling a reflective semiconductor optical amplifier (RSOA) with a two-dimensional silicon (Si) photonic crystal (PhC) cavity. Continuous stable single frequency operation with >40 dB side-mode suppression ratio (SMSR) of the laser was achieved for gain currents of up to 100 mA, i.e., up to four times the threshold current. The shorter length of the laser cavity enabled single frequency operation due to the selection of a single longitudinal mode by the PhC narrowband reflector. Various longitudinal mode spacing regimes were studied to explain the mode-hop free characteristics of the H-PhCL. The proposed hybrid laser design methodologies can be adapted to eliminate mode-hopping in laser wavelength.

Поверхностно-излучающий квантово-каскадный лазер с кольцевым резонатором

The results of studies of quantum-cascade laser with a surface emission through a grating formed in the layers of the top cladding of the waveguide by ion beam milling are presented. The active region of the QCL heterostructure was formed based on a heteropair of In0.53Ga0.47As / Al0.48In0.52As solid alloys with two-phonon resonance design. It is shown that lasing at room temperature close to 7.9 µm is demonstrated for a laser with a ring diameter of 191 µm. The mode spacing corresponds to whispering gallery modes.

Efficient carrier-envelope phase tunable mid-infrared frequency combs based on CW-seeded optical parametric generation

We present an efficient method for generating frequency combs in the mid-infrared (MIR) spectral range in bulk lithium niobate crystals as well as in waveguides. Our approach is simple and robust, since it is based on single-pass configuration of femtosecond Optical Parametric Generation (OPG) seeded by a telecom continuous-wave laser. Precise and fast tuning of the seed laser allows to rapidly change the offset frequency of the generated MIR comb independent of its repetition rate. The MIR comb offset frequency is inherently known, so its direct detection is not required. An additional degree of freedom that further complements the versatility of our light source is a unique way of repetition rate or mode spacing adjustments. This is achieved by our new concept of coherent multi-seeding that depending on the configuration allows for pulse train modulation and mode spacing, or repetition rate division by an integer number.