Hoshin Yee

A stable multiwavelength SOA-based fiber ring laser with ultra-narrow wavelength spacing

This investigation demonstrates a stable multiwavelength fiber ring laser with ultra-narrow wavelength spacing using a semiconductor optical amplifier (SOA). A delay interferometer and a mirror are used as a double-pass interferometer to improve the signal-to-noise ratio in this experiment. Up to 181 stable lasing wavelengths with a wavelength spacing of 10.7 GHz and a signal-to-noise ratio of over 24 dB are produced at room temperature.

Double Sideband With Optical Carrier Suppression Scheme for Broadcasting Transmission

This letter presents a novel broadcast scheme using a double sideband with optical carrier suppression (DSBCS) modulation. Broadcast data and unicast data are delivered simultaneously by a DSBCS and an optical carrier from a single wavelength, whose states of polarization are orthogonal, respectively. The broadcast data and the unicast data modulate DSBCSs and an optical carrier using a reflective semiconductor optical amplifier, respectively, at the optical line terminal, and are detected at the optical network unit without resorting to any polarization tracking. The broadcasted data can be applied for both wireless and wireline services. The transmitting broadcast data and unicast data over a 25-km single-mode fiber are experimentally demonstrated with a power penalty at the bit error rate (BER) = 10-9 of below 1 dB and is sufficiently independent in a single wavelength channel.

Employing Fabry-Perot Etalon and Split-Band Technique to Improve Directly Modulated Fiber Optical CATV System Performances

A directly modulated AM-VSB CATV EDFA-repeated system that uses Fabry-Perot (FP) etalon and split-band technique is proposed and demonstrated. Good performances of CNR, CSO and CTB were achieved for the full channel band over a-100 km single-mode fiber (SMF) transport.

Implication of rapid thermal annealing-induced cracks on the performance of multiple-quantum-well laser diodes

We investigated the effects of rapid thermal annealing (RTA)-induced cracks on the diode performance fabricated with GaAs-AlGaAs microstructures. These effects were examined and characterized after quantum-well intermixing within an epitaxial structure capped by either SiO2 or SrF2 layers. The results show clearly that the density of surface crackes strongly depends on the atomic interdiffusion between the well and the barrier layers and on the quality of the dielectric caps as well. Moreover, surface-crack correlation with the RTA process an dielectric deposition parameters, and the cracking effects on diode performance were observed and analyzed in detail. The results demonstrate that diode characteristics can be greatly improved by good surface morphology. Most importantly, we explored an effective way of reducing the density of RTA-induced cracks for the dielectrics grown by plasma-enhanced chemical vapor deposition, which was beneficial for dielectric-cap quantum-well disordering.

FTTH and Two-Band RoF Transport Systems Based on an Optical Carrier and Colorless Wavelength Separators

A hybrid fiber-to-the-home (FTTH) and radio-over-fiber (RoF) transport system is proposed to transmit one wired signal and two wireless signals simultaneously through an optical lightwave. By properly utilizing the polarization characteristic of a phase-remodulated and polarization-remodulated optical lightwave, the first- and second-order sidebands of the lightwave can be colorlessly separated for optical double- and quadruple-frequency RoF transmissions. Experimental results prove that the independent FTTH and two-band RoF signals can be simultaneously generated and separated by relatively low-frequency radio-frequency devices, optical modulators, and polarization beam splitters. The transmission performances are proven by proper bit error rate (BER) performance and clear eye and constellation diagrams. The interference among the transmitted wired signal and double- and quadruple-frequency RoF signals is acceptable. In this case, the wavelength of the optical carrier can be flexibly assigned, and the frequency of the transmitted wireless signals can be easily adjusted without affecting the functionality of the developed optical fiber transport system. The presented architecture can be flexibly employed to support various types of FTTH and microwave and millimeter-wave over fiber transmissions.

Radio-on-DWDM Transport Systems Based on Injection-Locked Fabry-Perot Laser Diodes

A radio-on-dense-wavelength-division-multiplexing (DWDM) transport system based on injection-locked Fabry-Perot laser diodes (FP LDs) with four microwave carriers and large effective area fiber (LEAF) transmission was proposed and demonstrated. Good performance of bit error rate (BER) and intermodulation distortion to carrier ratio (IMD/C) over a-50km of LEAF was obtained. Signal quality meets the demands of personal handy system (PHS)/vehicle information and communication system (VICS)/electronic toll collection (ETC)/satellite broadcasting (SB).

Directly modulated fiber optical CATV transport systems without optical amplification

We propose and demonstrate a repeaterless directly modulated fiber optical CATV transport system based on half-split-band and remote light injection techniques. Good performances of carrierto-noise ratio (CNR), composite second order (CSO) and composite triple beat (CTB) were obtained over a 50-km single mode fiber (SMF) transmission without optical amplification. Our proposed repeaterless directly modulated fiber optical CATV transport systems are simpler and cost lower than conventional externally modulated ones.

Improved surface characteristics of n-GaN epitaxial structures after reactive ion etching

Reactively ion etched (RIE) n-GaN epitaxial films with differ- ent degrees of surface damage are investigated. To realize prominent effects resulting from RIE damage on electrical and optical properties, the samples are processed at various rf power levels and particularly under relatively high dc self-bias. We find that the restoration of crystal damage in optical properties evaluated by photoluminescence (PL) peak enhancements for samples thermally annealed at 750 °C for 3 min could achieve up to 60 to 65% of those before RIE processing. Under high dc self-bias, it is evident that higher rf power produces rougher etched sur- faces with more severe damage and higher surface resistance, so the damaged crystal is more difficult to recover. A transmission-line model is used to estimate the variation of ohmic contact resistance. Note that KOH surface treatment prior to contact deposition is more effective in lowering contact resistance than that of a damaged surface restored only by rapid thermal annealing (RTA) processing.

The 1/f noise associated with electromigration in AlSiCu thin films

Noise measurements were performed on electromigration-damaged single-layer AlSiCu films, that show no resistance change and on multilayer AlSiCu/TiW films that show obvious resistance increase before the samples open. The experimental results showed that single-layer AlSiCu films have 1/f noise only, and no 1/f2 noise is observed during the entire stress period. Moreover, the 1/f noise increases drastically shortly before the samples open. For multilayer samples, 1/f2 noise was observed during the stress period, and increased with the stress current density. This result implies that the theory of resistance-drift-induced 1/f2 noise is valid in electromigration-damaged metal thin films.

Surface-grating distributed bragg reflector quantum-well lasers fabricated in AlGaAs-GaAs asymmetric epitaxial waveguides.

Ridge waveguide lasers, integrated with single deep-surface distributed Bragg reflectors (DBRs) in the passive section, were fabricated with a GaAs-AlGaAs double-quantum-well structure in an asymmetric waveguide. Third-order gratings, with a period of 389 nm and defined by holographic lithography, were formed by low-damage reactive ion etching processes. The grating losses and optical coupling coefficients were estimated, in particular, by use of the relationship between the real and the effective grating lengths that were computed and reexamined by measurements of grating periodicity and mode spacing. By use of two different geometries, we produced guide lines for obtaining high-performance lasing properties for these surface-grating DBR lasers. Additionally, a detailed analysis of lasing wavelength shifts was carried out for this study. It was found that injected-carrier-induced effects shift the lasing wavelength much more than gain-loss competition within an extended DBR laser cavity.