Abstract
Considering the compensation of thermo-optic coefficients (TOC) between GaN-based cavity and TiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> photonic crystal (PhC) layer, we have theoretically designed a photonic crystal surface emitting laser (PCSEL) with temperature-insensitive wavelength. The structure includes a freestanding GaN membrane with embedded multiple InGaN/GaN quantum well (QW) layer and the top TiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> PhC layer. The high refractive index (RI) of PhC and the freestanding membrane cavity structure cooperate to enable a stronger field-coupling in PhC, thus fulfill the athermal coupling condition. Interestingly, the wavelength temperature dependence is only 0.0015 nm/°C for such PCSEL with a 82% PhC confinement factor, and its athermal property is proportional to the field confinement factor in TiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> PhC layer. To illustrate, a general formula has been developed after the investigations of thermo-optic effect and thermal expansion effect.
Highlights
Semiconductor lasers with either bulk or quantum well (QW) active regions suffer from poor temperature stability due to self-heating and variation of the ambient temperature
We have only considered the TiO2 thermal expansion effect on lattice constant regardless of the small effect on the wavelength from the photonic crystal (PhC) layer thickness and hole radius
The confinement factor, gain threshold, field distribution, resonant wavelength temperature-dependent properties were investigated by RCWA, finite difference time domain (FDTD) simulation and theoretical analysis
Summary
Semiconductor lasers with either bulk or quantum well (QW) active regions suffer from poor temperature stability due to self-heating and variation of the ambient temperature. Shchukin et al [11] Different from those passive components, achieving wavelength stability in lasers is more challenging and rarely reported, because of the strict lasing conditions, including the requirements of refractive index (RI), high mode quality factor and coupling strength in gain media. Another method is using temperature-insensitive bandgap material [12]–[14]. The negative TOC compensation effect of TiO2 to positive TOC GaN based cavity could be promoted Based on this configuration, the stable effective refractive index (ERI) condition and low loss mode resonance in PhC and active media are satisfied simultaneously, to realize GaN-based laser exhibiting a temperature-insensitive resonant wavelength
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