Abstract
We characterize the frequency response of channel-interleaved photonic analog-to-digital converters (CI-PADCs) theoretically and experimentally. The CI-PADC is composed of a photonic frontend for photonic sampling and an electronic backend for quantization. The photonic frontend includes a photonic sampling pulse generator for directly high-speed sampling and an optical time-division demultiplexer (OTDM) for channel demultiplexing. It is found that the frequency response of the CI-PADC is influenced by both the photonic sampling pulses and the OTDM, of which the combined impact can be characterized through demultiplexed pulse trains. First, the frequency response can be divided into multiple frequency intervals and the range of the frequency interval equals the repetition rate of demultiplexed pulse trains. Second, the analog bandwidth of the CI-PADC is determined by the optical spectral bandwidth of demultiplexed pulse trains which is broadened in the OTDM. Further, the effect of the OTDM is essential for enlarging the analog bandwidth of the CI-PADC employing the photonic sampling pulses with limited optical spectral bandwidth.
Highlights
P HOTONIC analog-to-digital converters (PADC) are applied to receive and digitize high-speed microwave signal in next-generation radar and communication systems thanks to the superiorities of ultra-broad input bandwidth and ultra-high sampling rate [1]–[5]
The results indicate that the analog bandwidth of channel-interleaved PADC (CI-PADC) is expanded through the optical time-division demultiplexer (OTDM) when the optical spectral bandwidth of photonic sampling pulses is limited
The OTDM in the two-channel CI-PADC is composed of a dual-output Mach-Zehnder modulators (DO-MZMs) (EOSpace AX-1x2-0MSS-20, bandwidth = 20 GHz) and the microwave driver is at 10 GHz
Summary
P HOTONIC analog-to-digital converters (PADC) are applied to receive and digitize high-speed microwave signal in next-generation radar and communication systems thanks to the superiorities of ultra-broad input bandwidth and ultra-high sampling rate [1]–[5]. In order to meet the need of working at different frequency bands with different bandwidths in next-generation radar systems, the PADC with flat frequency response and large analog bandwidth is necessary. The analog bandwidth is the frequency range over which the signal power is attenuated by less than 3 dB of the maximum signal transmission [16] It can be measured with the frequency response of PADCs. Ref. [16] has verified the frequency response of single- channel PADCs only depends on the bandwidth of the electronic-optical modulator (EOM) and the temporal width of photonic sampling pulses. High-speed photonic sampling pulses in CI-PADCs directly generated by cascaded modulators has a limited optical spectral bandwidth compared with mode-locked lasers [4], [10], [18].
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