Mid-Infrared Photonic Integration in III-V Semiconductor Systems

Beschreibung

This thesis reports the development of InP and In0.53Ga 0.47As into a robust platform for mid-infrared (mid-IR) photonic integrated circuits (PICs). New fabrication processes for InGaAs/InP materials were developed, including a tri-layer hardmask method for high-resolution electron-beam pattern transfer into thick semiconductor structures and a cyclical etch technique that yields smooth, vertical sidewalls with high mask selectivity. Together, these processes establish a reliable basis for fabricating complex mid-IR photonic integrated circuits. Using the new processing techniques, waveguides were fabricated and subjected to post-processing based on wet chemical surface treatments, also developed within this thesis. The post-processing treatments resulted in the lowest reported propagation losses in the 5-6 µm wavelength range across all dielectric waveguiding platforms reported to date. Furthermore, the first broadband characterization of optical losses in InGaAs/InP waveguides across the mid-IR spectrum (λ=5-11 μm) was performed, establishing InGaAs and InP as a viable platform for mid-IR photonic integration over a broad range of frequencies and highlighting the fabrication dependent nature of mid-IR waveguide loss. Building on these advances, the third-order nonlinear optical properties of the InGaAs/InP materials platform within the mid-IR spectral range were investigated for the first time. Efficient four-wave mixing was demonstrated, confirming that InGaAs and InP possess intrinsic nonlinearities above that of other mid-IR photonic platforms reported to date, strong enough to support advanced mid-IR frequency conversion processes, including frequency comb and supercontinuum generation. Broadband wavelength-division multiplexers and micro-ring resonators were also experimentally realized and characterized. The micro-rings achieved the highest intrinsic quality factors reported to date at 5.2 and 5.7 µm, establishing them as promising candidates for Kerr frequency comb generation in this wavelength range. Based on their measured performance, the threshold power for frequency comb generation was estimated at ~20 mW, well within the capabilities of previously demonstrated integrated QCL devices. To pursue this goal, experimental attempts at Kerr frequency comb generation were carried out, supported by custom-designed mid-IR optical isolators and a frequency-locking scheme for stable resonator operation. While no combs were observed within this work, the experimental results, together with recent in-house progress integrating continuous-wave distributed feedback QCLs with passive InP/InGaAs waveguides, indicate that their realization is imminent.

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Kevin James Zhang

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