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.

Recently, there has been great interest in the application of photonic sampling to help achieve analog-to-digital conversion (A/D) with high resolution at multi-GHz sampling rates (f/sub s/). Conceptually, the low-jitter picosecond pulses generated by a mode-locked laser are ideal vehicles that would enable one to accomplish impulse sampling of an analog signal. To this end we have developed a 4-bit 20 Gsample/s flash analog-to digital converter in InP HBT technology with monolithically integrated optical signal and optical clock receivers.

A chip-level integrated optoelectronic modulation circuit is described for high-speed digital interconnects. This circuit is composed of an electroabsorption modulator with surface-normal operation at 1550-nm wavelengths and a high-speed electronic driver. A growth/etch/regrowth procedure is used to fabricate the multiple-quantum well modulators and the heterojunction bipolar transistors (HBTs) of the circuit on a common InP substrate. The measured bandwidth is approximately 30 GHz.

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.

RF-photonic approaches have been evaluated for distributing electrically generated local oscillator (LO) signals as well as for performing frequency conversion with optically generated LO signals. For high-fidelity distribution of electrically generated signals, a switched RF photonic link was measured to have a residual phase noise of -145 dBc/Hz at an offset of 10 kHz from the X-band carrier. The switch isolation was better than 80 dB. For efficient frequency conversion with the RF-photonic approach, a relative conversion loss of 6.2 dB was measured for an LO modulation index of 0.97.

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

A scalable switched photonic link has been used to select RF local-oscillator (LO) signals. The LO signals transmitted by these externally modulated photonic links have phase noise as low as - 145 dBc/Hz at an offset of 10 kHz from an X-band signal, The optoelectronic switch selects among different LO inputs with an isolation of better than 80 dB. This performance is suitable for many radar and communications applications.