Paul O. Leisher

Single mode photonic crystal vertical cavity lasers

We report the accuracy of the photonic crystal model in describing the characteristics of vertical cavity surface-emitting lasers with lateral optical confinement consisting of a periodic array of etched circular holes. Experiments were carried out to compare predictions of the photonic crystal model to observed modal device characteristics, and the oxide aperture size was optimized to give maximum output power and lower threshold. The role of loss in improving modal properties was also investigated. Optimized lasers exhibit submilliamp threshold current and operate in the fundamental lateral mode for all currents.

In-phase evanescent coupling of two-dimensional arrays of defect cavities in photonic crystal vertical cavity surface emitting lasers

In-phase evanescent coupling in 2×1 and 2×2 arrays of defect cavities in photonic crystal (PhC) vertical cavity surface emitting lasers (VCSELs) is reported. Two-dimensional PhC patterns of air holes containing multiple defects are etched into the top distributed Bragg reflector of VCSELs. The resulting modification of the effective index and optical loss results in evanescent coupling between the multiple defect cavities of the PhC VCSEL. Far field measurements and simulations show good agreement and demonstrate the in-phase results.

Mode Control in Photonic Crystal Vertical-Cavity Surface-Emitting Lasers and Coherent Arrays

We demonstrate transverse mode control in vertical-cavity surface-emitting lasers (VCSELs) and 2-D VCSEL arrays. By etching a periodic arrangement of circular holes into the top distributed Bragg reflector mirror, we are able to control the lasing modes through index and loss confinement. Theoretical modeling of these confinement effects are shown to be consistent with experimental measurements. Photonic crystal etched patterns and ion-implanted photonic lattices have been employed to fabricate coherently-coupled 2-D arrays. Control of the array supermodes from the out-of-phase and in-phase conditions is discussed. Designs of photonic crystal coherent VCSEL arrays for high-power emission and beam steering applications are described.

Photonic crystal structure effect on the enhancement in the external quantum efficiency of a red LED

The enhancement in external quantum efficiency of a red light-emitting diode (LED) from photonic crystal (PhC) hole patterns was investigated. A red LED was chosen because its epitaxial layers are relatively free from defects as compared to GaN-based LEDs. The peak emission wavelength was 642 nm, and a triangular-lattice PhC was designed with a hole diameter to lattice distance ratio of 0.5. The lattice distance to wavelength ratio (a/lambda) was varied from 0.2 to 4.6 in order to evaluate the enhancement in the external quantum efficiency. An improvement in efficiency greater than 75% was obtained for a/lambda between 0.6 and 2.0. This improvement of the optical characteristics occurred with unchanged electrical properties

Loss-Induced Confinement in Photonic Crystal Vertical-Cavity Surface-Emitting Lasers

Through calculations and comparison with experimental results, we verify that loss introduced by an etched photonic crystal in a vertical-cavity surface-emitting laser (VCSEL) contributes significantly to the transverse optical confinement and supported modes. The optical loss is examined theoretically using a simple waveguide model from the scalar Helmholtz equation. The modal loss of fabricated lasers is extracted from the observed spectral-mode splitting. The effect of modal loss on the slope efficiency and modal behavior is examined. The model is found to be consistent with experimental measurements, and provides a means of accurate design of single-mode photonic crystal VCSELs.

Temperature Analysis of Threshold Current in Infrared Vertical-Cavity Surface-Emitting Lasers

The temperature dependence of threshold current Ith in vertical-cavity surface-emitting lasers (VCSELs) can be approximated by the equation Ith(T)=alpha+beta(T-Tmin)2 , where Tmin is the temperature of lowest Ith,alpha and beta are parameters, and temperature is T. We compare the temperature dependence of threshold current in VCSELs with GaAs, InGaAs, and strain compensated InGaAs-GaAsP quantum wells. From our analysis we find the coefficient beta is related to the gain properties of the quantum well, and is shown to serve as a benchmark for the VCSEL temperature sensitivity. The incorporation of strain-compensated high-barrier GaAsP layers in the active region of 980-nm VCSELs is demonstrated to reduce the threshold dependence on temperature

Photonic Crystal Vertical Cavity Lasers With Wavelength-Independent Single-Mode Behavior

We report on two-dimensional photonic crystal designs in vertical-cavity surface-emitting lasers that yield single-transverse mode operation over a wide range of wavelengths (780, 850, and 980 nm). These single-mode photonic crystal designs are consistent with predictions of a theoretical model that considers design parameters such as hole diameter, lattice constant, and etching depth. The single-mode lasers demonstrate side mode suppression of > 35 dB and > 1 mW output power using the same photonic crystal pattern.

Single-mode 1.3-/spl mu/m photonic crystal vertical-cavity surface-emitting laser

We report the use of a photonic crystal in a 1.3-mum vertical-cavity surface-emitting laser to achieve single fundamental-mode operation. A focused ion beam was used to mill the photonic crystal into a top dielectric distributed Bragg reflector. The laser operated continuous-wave at room temperature with greater than 1 mW of single-mode output power observed with a sidemode suppression ratio of more than 37 dB and little change to the electrical properties of the device

Loss and Index Guiding in Single-Mode Proton-Implanted Holey Vertical-Cavity Surface-Emitting Lasers

Wedge-shaped holes are fabricated in the top mirror of proton-implanted vertical-cavity surface-emitting lasers (VCSELs). A radially symmetric fill factor approach is used to calculate the resulting transverse index profile. To investigate both the index confinement provided by the etched pattern and its effect on optical loss, continuous-wave (CW) and pulsed experiments are performed. Under CW operation, we show proper wedge design leads to improved fundamental-mode output power, decreased threshold, and increased efficiency. We report a significant decrease in threshold under pulsed operation for the etched device compared to an unetched device, indicating a significant reduction in diffraction loss to the fundamental mode due to strong index guiding. Single-mode output is maintained over the entire operating range of the VCSEL due to increased loss for the higher order modes

Relative phase tuning of coupled defects in photonic crystal vertical-cavity surface-emitting lasers

Evanescent coupling can be achieved by patterning the top facet of a vertical-cavity surface-emitting laser (VCSEL) with a multiple defect photonic crystal pattern. We show that for 2×1 coupled defect arrays, the phase between these emission sites changes as the current is varied. The phase variation is manifest in the far field pattern and may be determined using antenna array theory. It is found that the phase varies 81 deg between transversely coupled cavities as the current to the VCSEL is varied by 24 mA. This corresponds to a far field angular change of approximately 1.5 deg.