J. Nagle

Phase matching using an isotropic nonlinear optical material

Frequency conversion in nonlinear optical crystals, is an effective means of generating coherent light at frequencies where lasers perform poorly or are unavailable. For efficient conversion, it is necessary to compensate for optical dispersion, which results in different phase velocities for light of different frequencies. In anisotropic birefringent crystals such as LiNbO3 or KH2PO4 (‘KDP’), phase matching can be achieved between electromagnetic waves having different polarizations. But this is not possible for optically isotropic materials, and as a result, cubic materials such as GaAs (which otherwise have attractive nonlinear optical properties) have been little exploited for frequency conversion applications. Quasi-phase-matching schemes,, which have achieved considerable success in LiNbO3 (ref. 4), provide a route to circumventing this problem,, but the difficulty of producing the required pattern of nonlinear properties in isotropic materials, particularly semiconductors, has limited the practical utility of such approaches. Here we demonstrate a different route to phase matching — based on a concept proposed by Van der Ziel 22 years ago — which exploits the artificial birefringence of multilayer composites of GaAs and oxidised AlAs. As GaAs is the material of choice for semiconductor lasers, such optical sources could be integrated in the core of frequency converters based on these composite structures.

Second-harmonic generation at λ=1.6 μm in AlGaAs/Al2O3 waveguides using birefringence phase matching

We demonstrate phase-matched second-harmonic generation from a λ=1.6 μm pump in a GaAs-based waveguide. Phase matching is obtained by using the form birefringence in an AlGaAs/Al2O3 multilayer obtained by selective wet oxidation.

Achievement of ultrahigh quality factors in GaAs photonic crystal membrane nanocavity

The authors realized an ultrahigh quality factor nanocavity in a GaAs membrane with the highest loaded Q reported to date of 250u2009000 in a side-coupled cavity-waveguide system. This result could be obtained using an original aluminum-free material system combined with a carefully adjusted fabrication technology, yielding a device with small roughness and very good verticality of holes as well as small disorder. The authors show that the intrinsic Q factor is around 3.0×105 using a coupled-mode model.

Optimization of an inductively coupled plasma etching process of GaInP∕GaAs based material for photonic band gap applications

In this article, we investigate the dry etching of GaInP∕GaAs based material system using an inductively coupled plasma (ICP) etching system. In a view to develop a suitable ICP process for the etching of aluminum-free material, ridge waveguides have been fabricated and the effects of the ICP parameters have been assessed. The coil power and the platen power have been varied at constant pressure and temperature for a chlorine-based process. The surface quality, sidewall profile, and selectivity have been reported. We also demonstrate the optimization of the chlorine-based process for deep etching and its subsequent implementation in photonic band gap device fabrication for 1.55μm optical applications. The optimized process has been shown to provide a high aspect ratio and a good selectivity for 250nm diam holes with a depth of 3μm in the GaInP∕GaAs material system. The influence of the ICP parameters on this material system have been analyzed mainly by scanning electron microscopy with particular attentio...

5.2-5.6-µm source tunable by frequency conversion in a GaAs-based waveguide

A tunable mid-IR source obtained by difference-frequency generation is demonstrated in a selectively oxidized GaAs–AlAs multilayer waveguide. We designed the waveguide to present the required form birefringence for phase matching of the nonlinear interaction. We took special care to lower losses for the mid-IR radiation. IR tunability from 5.2 to 5.6??µm was achieved by variation of the waveguide temperature and one pump wavelength. IR output power as great as 0.12xa0µW was obtained with the product of two pump powers of 7xa0mW2.?Losses of ?50xa0cm-1 were measured for the mid-IR radiation. These losses are attributed to surface scattering.

Room‐temperature excitons in Ga0.47In0.53As‐InP superlattices grown by low‐pressure metalorganic chemical vapor deposition

Very high quality Ga0.47In0.53As‐InP heterojunctions, quantum wells, and superlattices have been grown by low‐pressure metalorganic chemical vapor deposition. Excitation spectroscopy shows evidence of strong and well‐resolved exciton peaks in the luminescence and excitation spectra of GaInAs‐InP quantum wells. Optical absorption spectra show room‐temperature excitons in GaInAs‐InP superlattices.

High-purity GaAs layers grown by low-pressure metalorganic chemical vapor deposition

We report electrical and optical properties of very high purity GaAs epilayers grown by low‐pressure metalorganic chemical vapor deposition using AsH3 and triethylgallium as As and Ga sources. An electron mobility of 335u2009000 cm2/Vu2009s at 38 K has been measured for a 12‐μ‐thick layer.

Monolayer epitaxy of III-V compounds by low-pressure metalorganic chemical vapor deposition

We report, in this letter, the successful growth of Ga0.5In0.5As/InP heterostructures by alternating the growth of n(GaAs) and n(InAs) atomic layers. Such structures are designed as (GaAs)n(InAs)n. The influence of parameters such as n or the introduction of a purging time between the InAs‐GaAs monolayers has been investigated. Low‐temperature photoluminescence experiments showed that (GaAs)n(InAs)n/InP multiquantum wells had a better uniformity in composition and thickness than the conventional Ga0.5In0.5As/InP system.

Surface emitted second-harmonic generation from a quasi-phase matched waveguide in an Al x Ga 1-x As/Al 2 O 3 microcavity

A nonlinear Al(x)Ga(1-x)As waveguide consisting of a quasi-phase matched heterostructure embedded in a microcavity has been designed and fabricated. The microcavity resonator is formed by Al(2)O(3)/Al(0.32)Ga(0.68)As multilayer mirrors located above and below the waveguide core. The cavity resonantly enhances the surface emitting second-harmonic generation. The SH conversion efficiency has been measured for wavelengths between l = 1525 and 1575 nm. A simple waveguide loss measurement technique based on the SH autocorrelation of short optical pulses in a III-V waveguide is also demonstrated.

A third-order-mode laser diode for quantum communication

A third-order-mode emitting laser diode, which is also intended for use with a phase-matched waveguide, is demonstrated and analysed. The AlGaAs/GaAs heterostructure is engineered to down-convert the laser photons into photon pairs through a parametric process. Device design is hampered by competing requirements arising from the laser diode and nonlinear waveguide parts. The optimization strategy is discussed.