T. J. Pinguet

All-epitaxial fabrication of thick, orientation-patterned GaAs films for nonlinear optical frequency conversion

Orientation-patterned GaAs (OPGaAs) films of 200 μm thickness have been grown by hydride vapor phase epitaxy (HVPE) on an orientation-patterned template fabricated by molecular beam epitaxy (MBE). Fabrication of the templates utilized only MBE and chemical etching, taking advantage of GaAs/Ge/GaAs heteroepitaxy to control the crystal orientation of the top GaAs film relative to the substrate. Antiphase domain boundaries were observed to propagate vertically under HVPE growth conditions so that the domain duty cycle was preserved through the thick GaAs for all domain periods attempted. Quasiphase-matched frequency doubling of a CO2 laser was demonstrated with the beam confocally focused through a 4.6 mm long OPGaAs film.

Optical parametric oscillation in quasi-phase-matched GaAs

We demonstrate a GaAs based OPO. The singly resonant, pulsed OPO utilized an all-epitaxially-grown orientation-patterned GaAs (OP-GaAs) crystal. By tuning either near-IR pump wavelength or OP-GaAs temperature, we achieved broad tunability between 2 and 10 microns.

Improved dispersion relations for GaAs and applications to nonlinear optics

The refractive index of GaAs has been measured in the wavelength range from 0.97 to 17 μm, which covers nearly the entire transmission range of the material. Linear and quadratic temperature coefficients of the refractive index have been fitted to data measured between room temperature and 95 °C. In the midinfrared, the refractive index and temperature dependence are obtained from analysis of etalon fringes measured by Fourier-transform spectroscopy in undoped GaAs wafers. In the near infrared, the refractive index is deduced from the quasiphasematching (QPM) wavelengths of second-harmonic generation in orientation-patterned GaAs crystals. Two alternative empirical expressions are fitted to the data to give the refractive index as a function of wavelength and temperature. These dispersion relations agree with observed QPM conditions for midinfrared difference-frequency generation and second-harmonic generation. Predictions for various nonlinear optical interactions are presented, including tuning curves f...

Measurement of the nonlinear coefficient of orientation-patterned GaAs and demonstration of highly efficient second-harmonic generation

Quasi-phase-matched (QPM) GaAs structures, 0.5 mm thick, 10 mm long, and with 61-mum grating periods, were grown by a combination of molecular-beam epitaxy and hydride vapor phase epitaxy. These were characterized by use of mid-IR second-harmonic generation (SHG) with a ZnGeP(2) (ZGP) optical parametric oscillator as a pump source. The SHG efficiencies of QPM GaAs and QPM LiNbO(3) were directly compared, and a ratio of nonlinear coefficients d(14)(GaAs)/d(33) (LiNbO(3))=5.01+/-0.3 was found at 4.1-mum fundamental wavelength. For input pulse energies as low as 50muJ and approximately 60-ns pulse duration, an internal SHG conversion efficiency of 33% was measured in QPM GaAs.

Difference frequency generation of 8-µm radiation in orientation-patterned GaAs

First-order quasi-phase-matched difference frequency generation of narrowband tunable mid-infrared light is demonstrated in orientation-patterned GaAs. The all-epitaxial orientation-patterned crystal is fabricated by a combination of molecular beam epitaxy and hydride vapor phase epitaxy. Lasers at 1.3 and 1.55 microm were mixed to give an idler output at 8 microm, with power and wavelength tuning consistent with theoretical estimates, indicating excellent material uniformity over the 19-mm-long and 500-microm-thick device.

Template design and fabrication for low-loss orientation-patterned nonlinear AlGaAs waveguides pumped at 1.55 μm

All-optical networks with dynamic wavelength channel switching and routing are alternatives to existing networks that may help meet the need for ever-increasing bandwidth. In this context, nonlinear optical (NLO) waveguide devices are promising candidates for all-optical wavelength conversion, for example in WDM systems. Channel shifting was recently demonstrated in periodically-poled LiNbO/sub 3/ waveguides. AlGaAs is also an attractive platform for NLO devices, due to its large second-order nonlinearity, polarization independence, and potential for monolithic integration with other optical devices. However, because of its optical isotropy, phasematching can only be achieved through artificial schemes. We have developed an all-epitaxial orientation-patterning technique allowing us to grow QPM AlGaAs waveguides. However, the performance of these devices was limited mainly by the intrinsic corrugation between core and cladding, due to template itself We are investigating a new template structure that will minimize this corrugation, and will drastically reduce losses, thus significantly increasing the conversion efficiency.

Optical parametric oscillator based on microstructured GaAs

We demonstrate an optical parametric oscillator (OPO) based on GaAs. The OPO utilized an all-epitaxially-grown orientation-patterned GaAs (OP-GaAs) crystal, 0.5-mm-thick, 5-mm-wide, and 11-mm-long, with a domain reversal period of 61.2 μm. By tuning either the near-IR pump wavelength between 1.75 and 2 μm, or the temperature of the GaAs crystal, the mid-IR output tuned between 2 and 11 μm, limited only by the spectral range of the OPO mirrors. The pump threshold of the singly-resonant OPO was 16 μJ for the 6-ns pump pulses, and the photon conversion slope efficiency reached 54%. Also, we show experimentally the possibility of pump-polarization-independent frequency conversion in GaAs.

Long-wave IR chemical sensing based on difference frequency generation in orientation patterned GaAs

Lightsources employing quasiphasematched (QPM) nonlinear materials have demonstrated unique attributes for chemical sensing in the near- to mid-infrare spectral range (1 - 5 micrometers ). The advent of patterned-growth GaAs allows the first practical extension of QPM materials to operation in the long-wave IR (5 - 12 micrometers ). That wavelength range is particularly attractive for chemical sensing because it contains an atmospheric window, many molecular groups absorb there at distinct frequencies, and their absorptions tend to be strong relative to those in the near- and mid-IR. Here, the application of orientation-patterned GaAs (OPGaAs) for use in a continuous wave (cw) difference frequency spectrometer is described. The outputs of two external- cavity diode lasers operating in the 1.3 and 1.5 micrometers telecom bands are mixed in a OPGaAs crystal, producing tunable radiation at wavelengths near 8 micrometers . The application of the source to the measurement of a water vapor rovibrational absorption line is presented.

Optical parametric oscillator based on orientation-patterned GaAs

We demonstrate an optical parametric oscillator (OPO) based on GaAs. The OPO utilized an all-epitaxially-grown orientation-patterned GaAs (OP-GaAs) crystal, 0.5-mm-thick, 5-mm-wide, and 11-mm-long, with a domain reversal period of 61.2 microns. By tuning either the near-IR pump wavelength between 1.75 and 2 microns, or the temperature of the GaAs crystal, the mid-IR output tuned between 2 and 11 microns, limited only by the spectral range of the OPO mirrors. The pump threshold of the singly-resonant OPO was 16 micro-J for the 6-ns pump pulses, and the photon conversion slope efficiency reached 54%. Also, we show experimentally the possibility of pump-polarization-independent frequency conversion in GaAs.

Continuously tunable long-wave IR frequency generation in orientation patterned GaAs

Summary from only given. Quasi-phase-matched wavelength conversion in orientation patterned GaAs (OP-GaAs) is a useful method to create coherent long-wave IR radiation. GaAs offers wide transparency range between 0.9 and 17 /spl mu/m, low absorption, high thermal conductivity and large nonlinear susceptibility.