Michael C. Y. Huang

Ultrabroadband mirror using low-index cladded subwavelength grating

We report a novel subwavelength grating that has a very broad reflection spectrum and very high reflectivity. The design is scalable for different wavelengths. It facilitates monolithic integration of optoelectronic devices at a wide range of wavelengths from visible to far infrared.

Broad-band mirror (1.12-1.62 /spl mu/m) using a subwavelength grating

We report the first experimental demonstration of a novel single-layer subwavelength grating (SWG) that has >500-nm-wide reflection spectrum from 1.12-1.62 /spl mu/m and very high reflectivity (>98.5%). This SWG is scalable for different wavelengths by simply changing the grating dimensions, which, thus, facilitates monolithic integration of devices over a wide range of wavelengths.

High-Index-Contrast Grating (HCG) and Its Applications in Optoelectronic Devices

We review recent advances in subwavelength high-index-contrast gratings (HCGs) and a variety of applications in optoelectronic devices, including vertical-cavity surface-emitting lasers (VCSELs), tunable VCSELs, high-Q optical resonators, and low-loss hollow-core waveguides (HWs). HCGs can serve as broadband (Delta lambda/lambda ~ 35%), high-reflectivity (>99%) mirrors for surface-normal incident light, which is useful to replace conventional distributed Bragg reflectors in optical devices. HCGs can also be designed as high-Q resonators with output coupling in the surface-normal direction. Finally, we discuss a novel design of HCG as shallow angle reflectors and HWs.

Surface-normal emission of a high-Q resonator using a subwavelength high-contrast grating

We report a novel high-quality (Q) factor optical resonator using a subwavelength high-contrast grating (HCG) with in-plane resonance and surface-normal emission. We show that the in-plane resonance is manifested is by a sharp, asymmetric lineshape in the surface-normal reflectivity spectrum. The simulated Q factor of the resonator is shown to be as high as 500,000. A HCG-resonator was fabricated with an InGaAs quantum well active region sandwiched in-between AlGaAs layers and a Q factor of >14,000 was inferred from the photoluminescence linewidth of 0.07 nm, which is currently limited by instrumentation. The novel HCG resonator design will serve as a potential platform for many devices including surface emitting lasers, optical filters, and biological or chemical sensors.

High-Contrast Grating VCSELs

Recent advances in a single-layer 1-D high-index-contrast subwavelength grating structure are reviewed. Its incorporation into a vertical-cavity surface-emitting laser (VCSEL) structure enabled simple fabrication, lithographically defined polarization control and large aperture, single-transverse-mode control. Extraordinarily large fabrication tolerance is demonstrated with plusmn20% variation of the high-contrast grating (HCG) critical dimension. Emission wavelength of HCG-VCSEL varied 0.2% with a 40% change in lithography linewidth. Tunable VCSELs are fabricated using HCG, which led to a 8000 times reduction in the tunable mirror size and 160 times improved tuning speed of 63 ns. This configuration will open the door for a wide spectrum of optoelectronic devices in large wavelength regimes.

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.

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.

Fabrication and design of an integrable subwavelength ultrabroadband dielectric mirror

We have designed and fabricated a subwavelength grating (SWG) broadband mirror whose performance depends on key factors, including SWG period, duty cycle, and angle of incident light. The fabricated SWGs exhibit high reflectivity (⩾96%), when the grating periods are varied from 650to750nm and duty cycles are varied from 55% to 65%. The bandwidth and reflectivity of these mirrors are remarkably robust to variations in design and fabrication. The SWGs can be designed as broadband mirrors from microwave to visible wavelengths.

Compact label-free biosensor using VCSEL-based measurement system

We report an ultracompact label-free biosensor that uses a vertical-cavity surface-emitting laser (VCSEL)-based measurement system for the characterization of biomolecular interactions. It consists of a VCSEL, a plastic guided-mode resonant filter, and two p-i-n detectors. The system has demonstrated very high sensitivity to molecules on top of the sensor.