Seung-June Choi

Microdisk tunable resonant filters and switches

Tunable, vertically coupled InP microdisk resonant filters having a p-i-n active region and utilizing free carrier injection (FCI) to alter the index of refraction are presented for the first time. The fabricated devices allow single-mode operation and exhibit a large free spectral range (FSR=10 nm) with high Q values of 7000. Tuning of the resonant characteristics by free carrier injection is demonstrated. The resonant wavelengths of the disk cavity blue-shifts at a rate of 1 nm/mA.

Vertically coupled InP microdisk switching devices with electroabsorptive active regions

InP vertically coupled microdisk resonator/waveguide switching devices with an electroabsorptive (EA) active region are demonstrated for the first time. The devices exhibit single-mode operation, large free spectral range of 10.5 nm and a high quality factor of 5700. The EA effect provides a way of loss-trimming the resonant characteristics. Active switches, routers, and fast modulators based on these devices are envisioned as part of a WDM system.

Two-dimensional photonic crystal Mach–Zehnder interferometers

Mach-Zehnder interferometers were fabricated from suspended membrane photonic crystal waveguides. Transmission spectra were measured and device operation was shown to be in agreement with theoretical predictions.

Active semiconductor microdisk devices

The design of active semiconductor microdisk switches, modulators, or wavelength routers enabled by modulating the transfer characteristics of a resonant cavity is investigated. A simple theoretical model based on coupled-mode theory is used to elucidate design trends and constraints in the cases where electroabsorption, gain, and free carrier injection are employed to modulate the resonator characteristic.

High-Q vertically coupled InP microdisk resonators

High-quality factor vertically coupled InP microdisk resonators have been fabricated. Wafer bonding techniques have been used as a main approach to enable this three-dimensional structure. The devices exhibit smooth sidewalls, single mode operation, and high-quality factors in excess of 7000.

Nanofabrication of photonic crystal membrane lasers

We present techniques for fabricating photonic crystal (PC) membrane defect lasers. These nanostructures operate as optically pumped lasers under pulsed conditions at room temperature. The thin membrane PC defect structures are formed by transferring an electron-beam lithographically defined lattice pattern into an epitaxial layer structure by a sequential process of ion beam etching, reactive ion etching, and electron cyclotron resonance etching steps. A V-shape undercut channel is formed by a wet chemical etching using a 4:1 mixture of HCl and H2O to create the suspended membrane. We include a detailed description of a dependable and repeatable HCl undercut process for the PC structure.

Gain trimming of the resonant characteristics in vertically coupled InP microdisk switches

InP, vertically coupled microdisk resonator/waveguide switches with a gain active region are demonstrated. The devices exhibit single-mode operation, large free-spectral range of 10 nm, and a high-quality factor of 5700. The introduction of a quantum-well region inside the cavity provides a way of gain trimming the resonant characteristics. Active switches, routers, and filters with tunable bandwidth based on these devices are envisioned as part of a wavelength division multiplexing system.

Optical Modulators based on depletion width translation in semiconductor microdisk resonators

Optical modulation using a depletion width translation mechanism in microdisk devices is investigated. The devices are designed to operate at low drive voltages and have high bandwidths. Analog modulators that operate at drive voltages below 1 V with a 3-dB bandwidth of over 8 GHz were achieved. Eye diagrams showed that the device is capable of operating as a digital switch with speeds up to 10 Gb/s. Since the speed in the case of depletion width modulation is essentially determined by the junction area of the device, it can be improved by further reduction in the active area.

Linewidth and modulation response of two-dimensional microcavity photonic crystal lattice defect lasers

Linewidth and small-signal modulation response measurements are reported for room-temperature-operating microcavity two-dimensional photonic crystal lasers. The measured optical linewidth versus the output power was found to saturate at values on the order of 1 GHz. The modulation bandwidth for these low-power lasers was demonstrated to be on the order of 10 GHz

Optical phase characterization of active semiconductor microdisk resonators in transmission

The optical phase characteristics of an indium phosphide (InP) vertically coupled microdisk were experimentally demonstrated. Overcoming the material losses by injecting current into the active quantum well microdisk layer has allowed us to observe the phase behavior in all three coupling regimes. The ability to tune the resonant wavelength of this device makes it suitable for use as a phase modulator or tunable optical delay element.