Growth of engineered QPM structures in orientation-patterned gallium arsenide and gallium phosphide (Conference Presentation)

Abstract

Orientation-patterned gallium arsenide (OP-GaAs) and gallium phosphide (OP-GaP) have enabled exciting advances in frequency-combs for spectroscopy in the molecular fingerprint region beyond the transparency limits of quasi-phase matched (QPM) oxides like PPLN and PPKTP. These QPM semiconductors also offer much higher nonlinearities for pumping at 1-m (OP-GaP, d14 ~ 70 pm/V), 1.5m (OP-GaP, d14 ~ 35 pm/V), or 2m (OP-GaAs, d14 = 94 pm/V). In ferroelectric oxides like PPLN, the periodic QPM structure is created by the use of electric-field poling through a photo-lithographically defined insulator to reverse the polarity (and hence the sign of the nonlinear coefficient) of alternating domains. Nonlinear optical semiconductors like GaAs and GaP are not ferroelectric, however, so the QPM grating structure must is created instead by polar-on-nonpolar MBE whereby an inverted GaAs (GaP) epi-layer (grown on a on a thin, lattice-matched non-polar Ge (Si) layer) photolithographically patterned, etched, and regrown to produce thick QPM layers (t ~ 1mm) for in-plane laser pumping. A primary advantage of QPM is that the frequency conversion process can be engineered in various ways through the design and layout of the grating structure to achieve discrete and continuous wavelength tuning by translation across multiple adjacent gratings or fan gratings respectively. Tandem grating periods enable sequential processes such as photon recycling for enhanced efficiency, and chirped grating structures allow spectral tailoring of the frequency conversion process. While previously achieved in ferroelectric oxides, here we demonstrate the same novel structures in QPM semiconductors and discuss the implications for device design.