High-index-contrast Subwavelength Grating Research Articles

Polarization-dependent coupling between a polarization-independent high-index-contrast subwavelength grating and waveguides

We investigated the optical coupling between a polarization-independent high-index-contrast subwavelength grating (HCG) and two orthogonal in-plane waveguides. We fabricated the HCG with waveguides on a silicon-on-insulator substrate and demonstrated that a waveguide with a strong output is switched by changing the polarization of light injected into the HCG. The light coupled more strongly to the waveguide in the direction perpendicular to the polarization of the incident light than to that in the parallel direction. If this waveguide-coupled HCG is incorporated into a polarization bistable vertical-cavity surface-emitting laser (VCSEL), the output waveguide can be switched by changing the lasing polarization of the VCSEL.

155-μm VCSEL with polarization-independent HCG mirror on SOI

We designed and fabricated a vertical-cavity surface-emitting laser (VCSEL) incorporating a polarization-independent high-index-contrast subwavelength grating (HCG) mirror on silicon-on-insulator (SOI) for a novel polarization-bistable device on a silicon substrate. The VCSEL consists of the HCG mirror, an active layer with InGaAsP quantum wells having optical gain around 1.55 μm, and an Al0.9Ga0.1As/Al0.16Ga0.84As DBR. We used direct wafer bonding for the bonding between the active layer and the AlGaAs DBR, and benzocyclobutene (BCB) bonding for the bonding between the active layer and the polarization-independent HCG mirror. The reflectivity of the HCG embedded with BCB was measured, resulting in a 200-nm-high reflectivity band with reflectivity higher than 99% and a small polarization dependence of ± 1%. We achieved lasing of the fabricated HCG-VCSEL at 1527 nm under an optical short pulse excitation with an average power of 50 mW (~0.2 mJ/cm2) at 240 K.

Optical phased array using high contrast gratings for two dimensional beamforming and beamsteering

We have developed a microelectromechanical system (MEMS) optical phased array incorporating a high-index-contrast subwavelength grating (HCG) for beamforming and beamsteering in a range of ± 1.26° × 1.26°. Our approach needs only a thin single-layer HCG made of silicon, considerably improving its speed thanks to the low mass, and is suitable for high optical power applications. The measured resonant frequency of HCG is 0.32 MHz.

1060-nm Tunable Monolithic High Index Contrast Subwavelength Grating VCSEL

We present the first tunable vertical-cavity surface-emitting laser (VCSEL) where the top distributed Bragg reflector has been completely substituted by an air-cladded high-index-contrast subwavelength grating (HCG) mirror. In this way, an extended cavity design can be realized by reducing the reflection at the semiconductor-air interface using an anti-reflective coating (ARC). We demonstrate how the ARC can be integrated in a monolithic structure by oxidizing AlGaAs with high Al-content. The HCG VCSEL has the potential to achieve polarization stable single-mode output with high tuning efficiency. The HCG VCSEL shows a total tuning range of 16 nm around an emission wavelength of 1060 nm with 1-mW output power.

Broadband MEMS-Tunable High-Index-Contrast Subwavelength Grating Long-Wavelength VCSEL

A widely-tunable single-mode 1.3 μm vertical-cavity surface-emitting laser structure incorporating a microelectromechanical system-tunable high-index-contrast subwavelength grating (HCG) mirror is suggested and numerically investigated. A linear tuning range of 100 nm and a wavelength tuning efficiency of 0.203 are predicted. The large tuning range and efficiency are attributed to the incorporation of the tuning air gap as part of the optical cavity and to the use of a short cavity structure. The short cavity length can be achieved by employing a HCG design of which the reflection mechanism does not rely on resonant coupling. The absence of resonance coupling leads to a 0.59 λ-thick penetration depth of the HCG and enables to use a 0.25 λ-thick tuning air gap underneath the HCG. This considerably reduces the effective cavity length, leading to larger tuning range and efficiency. The basic properties of this new structure are analyzed, and shown to be explained by analytical expressions that are derived in the paper. In this context, the penetration depth of the HCG is introduced and shown to be an important characteristic length scale. Throughout the tuning wavelength range, strong single mode operation was maintained and uniform output power is expected.

Tunable VCSEL with ultra-thin high contrast grating for high-speed tuning

We report a nano-electromechanical optoelectronic (NEMO) tunable vertical-cavity surface-emitting laser (VCSEL) with an ultra-thin (145 nm) electrostatically actuated high-index-contrast subwavelength grating (HCG) designed to strongly reflect TE-polarized light. Single mode emission (SMSR >45 dB) and continuous wavelength tuning (approximately 4 nm) were obtained at room temperature with output power up to 2 mW under continuous wave (CW) operation. A record short wavelength tuning time (approximately 90 ns) is experimentally demonstrated, which is >100 times faster than previously reported DBR-based tunable VCSELs and a 1.7 times improvement over the previously reported TM polarized NEMO tunable VCSELs.

Large Fabrication Tolerance for VCSELs Using High-Contrast Grating

We report the experimental demonstration of a large fabrication tolerance for a single-layer, highly reflective high-index-contrast subwavelength grating (HCG) mirror. HCG vertical-cavity surface-emitting lasers (VCSELs) are demonstrated with plusmn20% variation in the HCG critical dimension. Emission wavelength of the HCG-VCSEL shifts only 2 nm with 40% change in grating spacing and 8% change in grating period.

Nano electro-mechanical optoelectronic tunable VCSEL

We report a novel electrostatic actuated nano-electromechanical optoelectronic (NEMO) tunable vertical-cavity surface-emitting laser (VCSEL) centered at 850 nm. By integrating a movable, single-layer (230 nm), high-index-contrast subwavelength grating (HCG) as the VCSEL top mirror, single mode emission (SMSR >40 dB) and continuous wavelength tuning (~2.5 nm) was obtained at room temperature under CW operation. The small footprint of HCG enables the scaling down of each of the cantilever dimensions by a factor of 10, leading to 1000 times reduction in mass, which potentially increases the mechanical resonant frequency and tuning speed.