David L. Persechini

Nonlinearity of p-i-n photodetectors

At higher operating frequencies, the field dependence of the carrier velocity in p-i-n photodetectors generates harmonics and intermodulation products that can degrade the dynamic range of RF fiber-optic links. The authors present both a perturbational theory and measured harmonic data for a p-i-n photodiode operated at very high power densities which show that this and other detector nonlinear effects need not seriously compromise link performance. In particular, neither transit-time nor static nonlinearities in p-i-n photodiodes need limit the dynamic range of fiber-optic links operating below 5 GHz. The fact that the theoretical bandwidth of the photodiode, with all parasitic capacitance and inductance ideally removed, is 17 GHz, suggests that comparable spur-free performance should be achievable at X and Ku-band frequencies, once packaging parasitics are reduced.<<ETX>>

High-efficiency waveguide-coupled lambda =1.3 mu m In/sub x/Ga/sub 1-x/As/GaAs MSM detector exhibiting large extinction ratios at L and X band

The design and fabrication of a 1.3- mu m waveguide-coupled strained-layer In/sub x/Ga/sub 1-x/As/GaAs MSM detector with an optimized active layer thickness is reported. For 100- mu m-long devices, a responsivity of 0.58 mA/mW is observed. Using the detector as an optoelectronic switch, on/off ratios better than 40 dB were achieved at L and X band.<<ETX>>

Integrated optoelectronic circuits with InP-based HBTs

Integrated optoelectronic circuits that are capable of very high speeds or high functionality have been demonstrated using InP-based heterojunction bipolar transistors (HBTs). Optoelectronic receivers contain photodetectors fabricated from the same epitaxial material structure as the HBTs. High-functionality digital receivers, analog receiver arrays as well as analog-to-digital converters have been realized. Optoelectronic modulation circuits for signal transmission also contain separately grown, surface-coupled multiple- quantum-well (MQW) modulators.

Conformal pixellated MQW modulator structure for modulating retroreflector applications

We have developed a conformal optical modulator structure comprising pixellated InGaAs-InAlAs multiple-quantum-well (MQW) electroabsorption modulators embedded in a polymer membrane for operation in the 1550-nm optical region. The MQW modulators retain their electrical and optical characteristics after the polymer embedding process, with leakage currents of less than 50 nA and modulation contrast ratios of 2 : 1. The radio frequency response of these modulators was shown to be dependent on the pixel size, with a 3-dB modulation frequency of over 200 MHz for a 225/spl times/125 /spl mu/m/sup 2/ pixel. The conformal MQW modulator structure developed here can be used in applications requiring placement on a curved surface, such as in cats eye modulating retroreflectors.

Ultrahigh-speed photonic analog-to-digital conversion technologies

This paper summarizes our recent work on high-speed photonic analog-to-digital conversion (A/D) technologies, where picosecond pulses generated by a 10 GHz mode-locked laser source were used to accomplish low-jitter photonic sampling. In addition, we describe our progress in the generation of 40 GHz wavelength-coded pulses for time-interleaved A/D, and the demonstration of photonic bandpass (at 1.6 GHz) Δ-∑ quantizers clocked at 10 GHz.

High speed single- and multi-element fiber-grating coupled diode laser transmitters for WDM networks

We report single- and multi-element fibre grating coupled diode laser transmitter modules that emit at ITU-designated wavelengths. In addition, we demonstrate that they can attain a direct modulation bandwidth that is as high as 4.62 GHz. Previously, the highest speed reported for these devices was 3.5 GHz.

A 10.24GSPS photonic sampled bandpass /spl Delta//spl Sigma/ modulator direct-sampling at 12GHz

A 10.24GSPS photonic sampled DeltaSigma modulator was implemented with HRL laboratories InP HBT process. The 12GHz analog input is sampled by a LiNbO3 optical modulator with a 10.24GHz ultra-low jitter mode-locked laser. The intensity-modulated differential laser pulses are converted into electronic charges by on-chip GaInAs photo diodes and directly integrated into the first stage integrator of a 4th-order continuous-time bandpass DeltaSigma modulator with a passband centered at 1.8GHz. The high notch frequencies of the DeltaSigma ADC are achieved by using a special type of integrator. This ADC achieves 59.9dB SNDR in 1MH bandwidth with 1263 InP HBT transistors

Technique for fabricating integrated optical devices in glasses by electric field enhanced ion diffusion

An apparatus is described for electric field enhanced ion exchange, with excellent electrode isolation. This apparatus has been successfully used to fabricate channel waveguides for fiber optics applications.

Photonics technologies for analog-to-digital conversion at GHz sampling rates

Conceptually, picosecond pulses generated by a mode-locked (ML) laser are ideal vehicles that can help achieve accurate impulse sampling of an analog signal. As illustrated an electro-optic modulator can be used to impress the analog input onto the optical pulse train. After photodetection, the received signal due to the modulated pulse train is sent, in turn, to an electronic quantizer for digitization.

Array transmitters and their application in rf photonics systems

We describe the design of single frequency array transmitters and their application in RF-photonic systems. In addition, we present an array-based packaging technology that is based on passive-alignment with Si-waferboards.