Kostadin Djordjev

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.

Microdisk lasers vertically coupled to output waveguides

Semiconductor microdisk resonator lasers vertically coupled to bus waveguides are demonstrated for the first time. These structures have many of the characteristics required for a light source in photonic integrated circuits because they can be coupled to other optical elements (switches, routers, filters, etc.) through common bus lines. A continuous-wave single-mode laser at 1579 nm with a side-mode suppression ratio greater than 30 dB has been achieved for an 8-/spl mu/m-radius microdisk. For larger disks, mode competition between modes near the maximum gain wavelength is observed from the light output-current (L-I) characteristics. Improved heat sink design is required for future devices.

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.

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.

CH4-based dry etching of high Q InP microdisks

CH4-based InP dry etching techniques have been investigated by using electron cyclotron resonance etching and reactive ion etching (RIE) methods to obtain microdisk and ring structures having smooth, vertical sidewalls, and specular etched surfaces. The RIE method is chosen for the device etch process owing to the higher perfection of the surfaces generated by this process. Excess CH4 introduced in the InP RIE process was found to generate excessive polymers and resulted in sloped, rough sidewalls. A multistep RIE process involving a high-pressure (75 mTorr) condition, followed by a lower pressure (15 mTorr) etching to the completion of the structure was developed that leads to very smooth sidewalls. This process was successfully utilized in the fabrication of vertically coupled microdisk resonators.

Microring resonators vertically coupled to buried heterostructure bus waveguides

The authors demonstrate all epitaxial semiconductor microring resonators vertically coupled to buried heterostructure (BH) bus waveguides for the first time. Planar vertically stacked waveguides are successfully grown on BH mesas by conducting a two-step regrowth process. This approach is potentially important for any buried waveguide technology where subsequent surface planarity is required. The measured transmission spectra show resonance dips (1.55/spl sim/1.60) /spl mu/m with quality factors, extinction ratios, and free spectral ranges of 2500-3.5 dB, and /spl sim/11 nm, respectively, for 10-/spl mu/m-radii microrings.

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.

Laterally coupled buried heterostructure high-Q ring resonators

All-buried InP-InGaAsP ring resonators laterally coupled to bus waveguides are demonstrated. The buried configurations offer a lower built-in refractive index step along the resonator periphery, which affords enhanced optical coupling coefficients between the waveguides and reduced scattering losses caused by the resonator sidewall imperfections. Very low optical intensity attenuations of 0.4 cm/sup -1/ and coupling-limited quality factors of greater than 10/sup 5/ are observed from 200-/spl mu/m-radii ring resonators. The measured spectral linewidth is as narrow as 0.0145 nm.

Carrier-induced refractive index changes in InP-based circular microresonators for low-voltage high-speed modulation

Optical InP-based microresonator modulators which achieve low-voltage high-bandwidth modulation are presented, where resonant wavelength tuning of a circular resonator by free carrier injection is used as the modulation mechanism. Since thermal effects in small resonant cavities and switching speed limitations posed by minority carrier lifetime are the primary concerns in such types of devices, ion bombardment in microtoroidal structures is used to increase the speed of response. The modulation speed is enhanced by an order of magnitude.

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.