High-contrast Grating Reflector Research Articles

Numerical investigation of vertical-cavity surface-emitting lasers incorporating a high-contrast grating using 3-D FDTD method

This paper presents the design and numerical simulation of vertical-cavity surface-emitting laser (VCSEL) incorporating a high-contrast grating (HCG) by using a three-dimensional (3-D) finite difference time domain (FDTD) method. The polarization dependence of HCG parameters as well as HCG reflector properties are numerically studied. We investigate the resonant spectra behavior and modal properties with respect to different aperture size. Furthermore, the quality factor (Q factor) related to modal loss is calculated, and is used to explain the mode selection of the HCG-VCSELs. Based on the simulation and analysis, it is found that the designed HCG-VCSELs exhibit larger mode discrimination compared to the conventional VCSELs. Our work could provide guidelines for designing and optimizing polarization-stable, single-mode VCSELs for use in chip-scale Cs atomic clocks.

Demonstration of polarization control GaN-based micro-cavity lasers using a rigid high-contrast grating reflector

We reported on GaN microcavity (MC) lasers combined with one rigid TiO2 high-contrast grating (HCG) structure as the output mirror. The HCG structure was directly fabricated on the GaN structure without an airgap. The entire MC structure comprised a bottom dielectric distributed Bragg reflector; a GaN cavity; and a top HCG reflector, which was designed to yield high reflectance for transverse magnetic (TM)- or transverse electric (TE)-polarized light. The MC device revealed an operation threshold of approximately 0.79 MW/cm2 when pulsed optical pumping was conducted using the HCG structure at room temperature. The laser emission was TM polarized with a degree of polarization of 99.2% and had a small divergence angle of 14° (full width at half maximum). This laser operation demonstration for the GaN-based MC structure employing an HCG exhibited the advantages of HCGs in semiconductor lasers at wavelengths from green to ultraviolet.

High contrast circular grating reflector on silicon-on-insulator platform.

A compact circular high contrast grating (HCG) reflector with a footprint of only 4.03 μm×4.32 μm on 220 nm silicon-on-insulator (SOI) platform is proposed and experimentally demonstrated. The proposed device breaks the high wavelength selectivity limitation for the conventional grating reflectors on a thin SOI platform by using the circular structure in a compact region. In addition, the device provides a high polarization selectivity over a wide wavelength range which is useful for applications such as tunable laser cavities and resonators to provide wide tuning range and high polarization stability. The circular structure based HCG reflector has an ultra-wide operational bandwidth (Δλ) of over 385 nm with the center wavelength (λ) set at 1550 nm, providing a Δλ/λ=24.83%. An average reflectance high of 94.15% is observed from 1525 to 1610 nm in the experimental measurement. The polarization extinction ratio is greater than 13 dB over the entire measured wavelength range.

Polarization-independent beam focusing by high-contrast grating reflectors

A kind of high-contrast grating (HCG) reflector for beam focusing has been proposed. We design a planar grating structure with a parabolic surface and numerical simulations using a finite different time domain (FDTD) method to verify that the structure has the capability of focusing both transverse-magnetic (TM) and transverse-electric (TE) polarized lights. Finally, we expand the design structure into a three-dimensional (3D) case. Numerical results demonstrate that the power intensities at the focal point are all greater than 8.5dB compared with incident intensity, which means the structure has a better focusing effect. Further analysis of incident wavelength sensitivity (1.55, 1.79 and 2μm) reveals that the proposed structure has a wide range of working wavelength.

Sub-wavelength GaN-based membrane high contrast grating reflectors

The GaN-based membrane high contrast grating (HCG) reflectors have been fabricated and investigated. The structural parameters including grating periods, grating height, filling factors and air-gap height were calculated to realize high reflectivity spectra with broad bandwidth by the rigorous coupled-wave analysis and finite-difference time-domain method. Based on the optimized simulation results, the GaN-based membrane HCGs were fabricated by e-beam lithography and focused-ion beam process. The fabricated GaN-based membrane HCG reflectors revealed high reflectivity at 460 nm band with large stopband width of 60 nm in the TE polarization measured by using the micro-reflectivity spectrometer. The experimental results also showed a good agreement with simulated ones. We believe this study will be helpful for development of the GaN-based novel light emitting devices in the blue or UV region.

Long-Wavelength High-Contrast Grating Vertical-Cavity Surface-Emitting Laser

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> A novel long-wavelength vertical-cavity surface-emitting laser (VCSEL) structure based on a subwavelength high-contrast grating (HCG) as the output mirror has been realized. By design, these devices are highly polarization stable, are single mode at large apertures, and solve the VCSEL-mirror problem at long wavelengths in an elegant way. With cost-effective mass fabrication in mind, the top HCG reflector consists of amorphous silicon on isolator (amorphous silica). The single-mode laser emission is tailored to be around 1320-nm wavelength, targeting applications in high-speed optical data transmission, particularly those for passive optical networks. We report single-mode emission for devices with apertures as large as 11 <formula formulatype="inline"><tex Notation="TeX">$\mu\hbox{m}$</tex> </formula> operating in continuous wave with output powers in excess of 0.4 mW. Pulsed operation with output powers up to 4 mW at room temperature is demonstrated as well. This is the first electrically pumped VCSEL structure realized in this wavelength regime utilizing an HCG mirror. </para>