L. A. Eyres

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.

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...

Nanoscale backswitched domain patterning in lithium niobate

We demonstrate a promising method of nanoscale domain engineering, which allows us to fabricate regular nanoscale domain patterns consisting of strictly oriented arrays of nanodomains (diameter down to 30 nm and density up to 100 μm−2) in lithium niobate. We produce submicron domain patterns through multiplication of the domain spatial frequency as compared with the electrode one. The fabrication techniques are based on controlled backswitched poling.

MBE growth of antiphase GaAs films using GaAs/Ge/GaAs heteroepitaxy

Semiconductor films with periodic crystal orientation modulation have nonlinear properties useful for optical wave-mixing devices. We have developed an all-epitaxial technique for preparing orientation-patterned GaAs templates by GaAs/Ge/GaAs epitaxy and have used these to grow laterally orientation-patterned films. We have investigated the effects of substrate misorientation, substrate temperature, and prelayer to find conditions which will allow controlled MBE growth of antiphase GaAs using thin Ge interlayers. After fabricating templates from these films using lithography and etching techniques, we have regrown GaAs films with antiphase crystal orientation modulation in the plane of the film. The template-induced antiphase boundaries were observed to propagate vertically under all conditions examined.

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.

Depth profiling of the d33 nonlinear coefficient in annealed proton exchanged LiNbO3 waveguides

We report depth profiling of the d33 nonlinear coefficient in annealed proton exchanged LiNbO3 waveguides using reflected second‐harmonic generation from angle‐lapped samples. At depths greater than the initial proton exchange depth the d33 coefficient retains nearly its bulk LiNbO3 value, but within the initial proton exchange region the value of d33 varies with annealing time. These results reconcile previous conflicting measurements of the d33 coefficient and explain the variation in the efficiency of guided wave frequency conversion devices with annealing.

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.

Growth of alternating 〈100〉/〈111〉‐oriented II‐VI regions for quasi‐phase‐matched nonlinear optical devices on GaAs substrates

We present a technique for fabricating laterally patterned 〈111〉 and 〈100〉‐oriented regions of CdTe on GaAs by metalorganic chemical vapor deposition. Patterning of the crystal orientation is important for quasi‐phase‐matched nonlinear optical frequency conversion in semiconductor waveguides. Scanning electron micrographs and x‐ray diffraction analysis are used to confirm the presence of 〈111〉/〈100〉 grating structures. The CdTe layer is shown to be a suitable template to pattern the orientation of subsequently grown wide‐band‐gap films of ZnSe and ZnTe.

Formation of self-organized nanodomain patterns during spontaneous backswitching in lithium niobate

Abstract We show experimentally that spontaneous decay of highly non-equilibrium domain state in ferroelectric is achieved through the formation of self-organized nanoscale domain structures. The nanodomain structures have been observed by SEM and SFM in uniaxial ferroelectric lithium niobate during spontaneous backswitching after fast removing of switching field. The regular nanoscale domain patterns consist of strictly oriented arrays of nanodomains (diameter down to 30 nm, density up to 100 μm−2). The mechanisms of self-maintaining correlated nucleation effects are discussed.

Broadly-tunable narrow-linewidth micromachined laser/photodetector and phototransistor

The key limitation to dense wavelength division multiplexing (WDM) systems is the receiving end since laser linewidths are typically less than 1 /spl Aring/. By reverse biasing the p-i-n diode region, we demonstrated dual functionality of wavelength-tunable vertical-cavity surface-emitting lasers (VCSELs) as wavelength-tunable resonant cavity photodetectors (RCPs) with linewidths less than 2.5 nm. Additionally, we have fabricated wavelength-tunable resonant cavity phototransistors (RCPTs) with linewidths as narrow as 1.7 nm. Wavelength-tunable RCPTs are capable of high quantum efficiency, narrow linewidth, and high-speed operation, making them ideal devices for WDM receivers.