Seldon David Benjamin

Performance of a Multi-Gb/s 60 GHz Radio Over Fiber System Employing a Directly Modulated Optically Injection-Locked VCSEL

A multi-Gb/s 60 GHz radio over fiber (RoF) system employing direct modulation of an optically injection locked vertical-cavity surface-emitting laser is successfully demonstrated. Experimental results show that the RoF system is tolerant to fiber chromatic dispersion due to inherent single-sideband modulation produced by injection locking. A simple carrier-to-sideband equalization method is used to substantially improve the sensitivity of the RoF system by 18 dB, enabling both successful wireless signal transmission and multilevel signal modulation formats such as quadrature phase shift keying (QPSK). At least 3 Gb/s ASK-modulated data and 2 Gb/s QPSK-modulated data is transported over up to 20 km standard single-mode fiber and 3 m wireless distance with no penalty.

High-Speed, High-Efficiency, Large-Area p-i-n Photodiode for Application to Optical Interconnects from 0.85 to 1.55 μm Wavelengths

We demonstrate a novel InP-based photodiode structure with large active diameter (55 μm) for > 25 Gbit/s operation at optical wavelengths which range from 0.85 to 1.55 μm. By utilizing the large absorption constant (>3 μm -1) of In 0.53Ga 0.47As-based p-type absorption layer at 0.85 μm wavelength excitation, the slow hole transport can be eliminated in our structure and the tradeoff between RC-limited bandwidth and carrier transient time can be greatly released due to the excellent characteristics of electron transport in the intrinsic and thick In 0.53Ga 0.47As layer (~4 μm). Furthermore, in order to minimize the serious surface (absorption) recombination in the top p-type In 0.53Ga 0.47 As absorption layer, an additional p-type In 0.52Al x Ga 0.48-xAs-graded bandgap layer (GBL) is grown above it. Such a GBL cannot only provide uniform photoabsorption profile, but also accelerates the electron diffusion process. Under -1 V bias, these devices can achieve high-speed (14 and 22 GHz), and high responsivity (0.25 and 0.9 A/W), at 0.85 and 1.55 μm wavelength operation, respectively. Clear eye-opening (error-free) with data rate up to around 30 Gbit/s have also been demonstrated at both wavelengths.

Gain-flattened, extended L-band (1570-1620 nm), high power, low noise erbium-doped fiber amplifiers

In conclusion, we have presented the first demonstration of high-power, low-noise, gain-flattened, 60-channel, extended L-band EDFAs with full functionality over a large dynamic range, and showed that they can be strong candidates for future high-bit-rate, wide-band, ultra-long-haul systems.

Large-Area p-i-n Photodiode With High-Speed and High-Efficiency Across a Wide Optical Operation Window (0.85 to 1.55 μm)

We demonstrate novel InP based photodiodes, which eliminate the degradation in speed and efficiency under short wavelength (0.85 μm) operation and have a enlarged device diameter as compared to that of GaAs based PDs for the same desired speed performance. By inserting a p-type In0.52Al0.32Ga0.16As layer with an intermediary bandgap value (1.2 eV) between In0.52Al0.48As (1.47 eV) window and In0.53Ga0.47As (0.75 eV) absorption layers, the huge surface absorption (recombination), which would lead to efficiency degradation, under short wavelength excitation can be diluted. The slow hole transport in our structure can also be diminished due to the p-type doping in these absorption layers. Furthermore, the trade-offs between RC-limited bandwidth (device size) and carrier transient time in GaAs based PDs can be further released due to the excellent electron transport characteristic in the In0.53Ga0.47As (collector) layer. These devices with a large diameter as 62 μm, which is the usual size of 10 Gbit/s InP based PDs, can achieve wide 3-dB bandwidths; varying from 25 to 17 GHz when the operating wavelengths changes from 0.85 to 1.55 μm. A constant and high external efficiency (~74%) with a clear eye-opening at around 40 Gbit/s has also been achieved over this wide optical window.