GaAs Photonic Crystal Waveguide Research Articles

Numerical investigation of highly efficient and tunable terahertz-wave generation using a low-group-velocity and low-dispersion two-dimensional GaAs photonic crystal waveguide

Efficient terahertz (THz)-wave generation via difference frequency generation (DFG) in a GaAs-based two-dimensional photonic crystal waveguide (PhC-WG) was proposed and investigated through numerical simulations. A PhC-WG with a low-group-velocity and low-dispersion mode (LVLD PhC-WG) was designed, and THz–DFG spanning sub- to several THz in frequency was obtained. Electric field enhancement and phase-matching between two fundamental light pulses in the LVLD PhC-WG generated THz–DFG approximately 280 times that in a GaAs strip waveguide. This method is applicable to highly efficient and tunable small-footprint THz-emitting devices based on semiconductor materials.

Operation of an InAs quantum-dot embedded GaAs photonic crystal slab waveguide laser by using two-photon pumping for photonics integrated circuits

The development of small sized laser operating above room temperature is important in the realization of optical integrated circuits. Recently, micro-lasers consisting of photonic crystals (PhCs) and whispering gallery mode cavities have been demonstrated. Optically pumped laser devices could be easily designed using photonic crystal-slab waveguides (PhC-WGs) with an air-bridge type structure. In this study, we observe lasing at 1.3μm from two-photon pumped InAs-quantum-dots embedded GaAs PhC-WGs above room temperature. This type of compact laser shows promise as a new light source in ultra-compact photonics integrated circuits.

Theory and experiments of disorder-induced resonance shifts and mode-edge broadening in deliberately disordered photonic crystal waveguides

We study both theoretically and experimentally the effects of introducing deliberate disorder in a slow-light photonic crystal waveguide on the photon density of states. We first introduce a theoretical model that includes both deliberate disorder through statistically moving the hole centres in the photonic crystal lattice and intrinsic disorder caused by manufacturing imperfections. We demonstrate a disorder-induced mean blueshift and an overall broadening of the photonic density of states for various amounts of deliberate disorder. By comparing with measurements from a GaAs photonic crystal waveguide, we find good qualitative agreement between theory and experiment which highlights the importance of carefully including local field effects for modelling high-index contrast perturbations. Our work also demonstrates the importance of using asymmetric dielectric polarizabilities for modelling positive and negative dielectric perturbations when modelling a perturbed dielectric interface in photonic crystal platforms.

Broadband Purcell enhanced emission dynamics of quantum dots in linear photonic crystal waveguides

The authors investigate the spontaneous emission dynamics of self-assembled InGaAs quantum dots embedded in GaAs photonic crystal waveguides. For an ensemble of dots coupled to guided modes in the waveguide, we report spatially, spectrally, and time-resolved photoluminescence measurements, detecting normal to the plane of the photonic crystal. For quantum dots emitting in resonance with the waveguide mode, an ∼21× enhancement of photoluminescence intensity is observed as compared to dots in the unprocessed region of the wafer. This enhancement can be traced back to the Purcell enhanced emission of quantum dots into leaky and guided modes of the waveguide with moderate Purcell factors up to ∼4×. Emission into guided modes is shown to be efficiently scattered out of the waveguide within a few microns, contributing to the out-of-plane emission and allowing the use of photonic crystal waveguides as broadband, efficiency-enhancing structures for surface-emitting diodes or single photon sources.

A Waveguide-Coupled On-Chip Single-Photon Source

We investigate single photon generation from individual self-assembled InGaAs quantum dots coupled to the guided optical mode of a GaAs photonic crystal waveguide. By performing confocal microscopy measurements on single dots positioned within the waveguide, we locate their positions with a precision better than 0.5 \mum. Time-resolved photoluminescence and photon autocorrelation measurements are used to prove the single photon character of the emission into the propagating waveguide mode. The results obtained demonstrate that such nanostructures can be used to realize an on-chip, highly directed single photon source with single mode spontaneous emision coupling efficiencies in excess of beta~85 % and the potential to reach maximum emission rates >1 GHz.

Modification of optical response in quantum dots embedded in a photonic crystal waveguide via photonic band engineering

ABSTRACTWe propose to use Purcell effect emerged at slow light regions in photonic crystal waveguide (PC-WG) modes for controlling the relaxation time of excited carriers in QDs. Straight GaAs PC-WGs including InAs-QDs with various lattice constants of PC were prepared in order to control the wavelength of the slow light in the PC-WG modes. PL measurements of the PC-WGs indicated enhancements of emission from QDs at the localized wavelength of slow light regions due to the Purcell effect. The enhanced emission peak wavelength was continuously shifted with the PC lattice constant. These results suggest that the PC-WG can be utilized to modify the spontaneous emission rate and carrier relaxation time of the embedded QD. This modification can be applied and useful for various QD-based optical devices as well as our proposed all-optical switching device based on PC-WG/QD.

Lasing in localized modes of a slow light photonic crystal waveguide

We demonstrate lasing in GaAs photonic crystal waveguides with InAs quantum dots as gain medium. Structural disorder is present due to fabrication imperfection and causes multiple scattering of light and localization of light. Lasing modes with varying spatial extend are observed at random locations along the guide. Lasing frequencies are determined by the local structure and occur within a narrow frequency band which coincides with the slow light regime of the waveguide mode. The three-dimensional numerical simulation reveals that the main loss channel for lasing modes located away from the waveguide end is out-of-plane scattering by structural disorder.

Efficient Second Harmonic Generation Through Selective Photonic Crystal-Microcavity Coupling

In this paper, a new 2-D frequency converter based on second harmonic generation (SHG) in GaAs photonic crystal waveguides is proposed. The input waveguide, where the second order nonlinear process takes place, is coupled to a secondary waveguide that is designed to allow only SH propagation. A row of photonic crystal microcavity resonators is then placed parallel to the waveguides in order to assist the field coupling. By tuning the resonance of the microcavities at second harmonic wave, the waveguides-microcavities arrangement showed good enhancement of conversion efficiency and selectivity. The performance of the proposed frequency converter has been analyzed by using multiresolution time domain (MRTD) scheme developed for nonlinear problems in conjunction with uniaxial perfectly matched layer (UPML) boundary conditions that rigorously truncate the computational window.

Near Field Imaging of a GaAs Photonic Crystal Cavity and Waveguide Using a Metal Coated Fiber Tip

We report optical near field characterization of a GaAs photonic crystal waveguide which is side coupled to a nano cavity. We observe the effect of the metal coated probe on the resonance wavelength and the intensity distribution. The measurements fit well to finite difference time domain simulations.

Light localization induced enhancement of third order nonlinearities in a GaAs photonic crystal waveguide

Nonlinear propagation experiments in GaAs photonic crystal waveguides (PCW) were performed, which exhibit a large enhancement of third order nonlinearities, due to light propagation in a slow mode regime, such as two-photon absorption (TPA), optical Kerr effect and refractive index changes due to free-carriers generated by TPA. A theoretical model has been established that shows a very good quantitative agreement with experimental data and demonstrates the important role that the group velocity plays. These observations give a strong insight into the use of PCWs for optical switching devices.

Sum and difference frequency generation as diagnostics for leaky eigenmodes in two-dimensional photonic crystal waveguides

We experimentally demonstrate how sum frequency generation (SFG) and difference frequency generation (DFG) of 150fs pulses can be enhanced and serve as diagnostics for leaky eigenmodes in a two-dimensional GaAs photonic crystal waveguide. SFG at 795nm is obtained in reflection from s-polarized 1900nm and p-polarized 1360nm pulses, with both input beams coupled to leaky eigenmodes; the SFG is enhanced by >350× compared to that from an untextured GaAs surface. We are able to detect Drude induced subnanometer blueshifts of the SFG, corresponding to refractive index changes of ⩽10−3. DFG of 1360nm light obtained in reflection from s-polarized 1900nm and p-polarized 793nm pulses displays an enhancement of >500× via three different leaky eigenmodes. As the 793nm beam polarization is varied from p polarized to right and left circularly polarized, the DFG remains essentially linearly polarized but with a reduced, albeit different, intensity for right and left circularly polarized 795nm pulses. Futhermore, the plane of polarization also rotates by different amounts for the left and right circularly polarized light, demonstrating interference of the components generated by s- and p-polarized 793nm pulses. Overall, our results demonstrate how enhanced DFG and SFG from leaky eigenmodes can be used to characterize their properties more precisely than linear optical techniques.

Ultrafast tuning of two-dimensional planar photonic-crystal waveguides via free-carrier injection and the optical Kerr effect

Femtosecond pump–probe reflectivity and second-harmonic spectroscopy experiments are used to investigate the optical tuning of leaky modes in a two-dimensional GaAs photonic-crystal waveguide. For above bandgap excitation with 270 fs, 800 nm pulses with a pump fluence of 100 μJ cm−2, a blueshift of 16±2 nm is measured for a 1900 nm leaky mode, as observed from the shift of the resonantly enhanced second-harmonic pulse. Theoretical calculations of carrier-induced changes in the refractive index from band filling, bandgap shrinkage, and Drude contributions are in good agreement with the results. Recovery occurs within 2 ps and is attributed to recombination via deep-centered defects. For below bandgap excitation with 166 fs, 1900 nm pulses with a fluence of 800 μJ cm−2, redshifts ≥1.5 nm of the 1360 nm leaky mode are induced via the optical Kerr effect during the early part of the pump pulse, but thereafter the mode is blueshifted, owing likely to free carriers injected into or from deep-centered defects.

Resonant second-harmonic generation in a GaAs photonic crystal waveguide

Second-harmonic generation (SHG) measurements in reflection on a ${\mathrm{G}\mathrm{a}\mathrm{A}\mathrm{s}/\mathrm{A}\mathrm{l}}_{0.25}{\mathrm{Ga}}_{0.75}\mathrm{As}$ photonic crystal waveguide show a resonant enhancement when the pump beam is frequency and momentum matched with the photonic modes in the slab. The enhanced SH signal is observed in the form of resonant peaks, unlike in linear reflectance spectra. The observations are in very good agreement with a full 3D calculation of the anisotropic mode dispersion in the photonic crystal slab. The present results open the way towards realizing the extraordinary enhancement of SHG which was recently predicted [A. R. Cowan and J. F. Young, Phys. Rev. B $65,$ 085106 (2002)], and also demonstrate the potential of SHG as a nonlinear spectroscopic tool for optical studies of photonic crystals.

Second-harmonic generation measured on a GaAs photonic crystal planar waveguide

Second-harmonic (SH) reflection and diffraction measurements are performed, at the wavelengths of a Ti:sapphire laser on a GaAs/AlGaAs photonic crystal waveguide patterned with a square lattice, the basis consisting of rings of air in the dielectric matrix. The measured angles of diffracted SH beams agree with those predicted from nonlinear diffraction conditions. Results for reflected and diffracted SH intensities as a function of incidence angle, polarization, and pump wavelength show that, due to the low air fraction of the photonic crystal, the reflected one is dominated by the crystalline symmetry of GaAs, while the diffracted one is related to the photonic crystal structure. The large diffraction-to-reflection ratio points to the importance of nonlinear diffraction in photonic crystals. Preliminary measurements in the 1500 nm range reveal explicit features related to photonic modes.

Second-harmonic generation in reflection and diffraction by a GaAs photonic-crystal waveguide

Nonlinear reflection and diffraction measurements have been performed on a GaAs/AlGaAs photonic-crystal waveguide patterned with a square lattice: The basis in the two-dimensional unit cell consists of rings of air in the dielectric matrix. The measured angles of diffracted second-harmonic beams agree with those predicted for nonlinear diffraction conditions. Results for second-harmonic intensities as a function of incidence angle, polarization, and pump wavelength show that the reflected second-harmonic signal is dominated by the crystalline symmetry of GaAs, whereas nonlinear diffraction is determined by the photonic-crystal structure.

Optical properties and photonic bands of GaAs photonic crystal waveguides with tilted square lattice

Reflectance measurements at variable angle of incidence are performed on GaAs photonic crystal waveguides with unconventional square lattices. The technique yields the dispersion of photonic bands for the investigated lattices, as first shown by Astratov et al. [Phys. Rev. B 60, R16225 (1999)]. A sample with a square lattice of air rings and small air fraction yields narrow resonant structures and a dispersion of photonic modes close to that of free photons. Another sample with a square lattice of dielectric squares and large air fraction leads to broader structures and to a dispersion of photonic modes which differs strongly for the two polarizations of light: this sample has a pseudo-gap around 1 micron wavelength. The experimental results are in good agreement with theoretical calculations of the reflectance and of the photonic mode dispersion in the photonic crystal slabs.