|
Photonics Analog-to-Digital Converters (ADCs) utilize a train of optical pulses to sample an electrical input
waveform applied to an electrooptic modulator or a reverse biased photodiode. In the former, the resulting train of
amplitude-modulated optical pulses is detected (converter to electrical) and quantized using a conversional electronics
ADC- as at present there are no practical, cost-effective optical quantizers available with performance that rival
electronic quantizers. In the latter, the electrical samples are directly quantized by the electronics ADC. In both cases
however, the sampling rate is limited by the speed with which the electronics ADC can quantize the electrical samples.
One way to increase the sampling rate by a factor N is by using the time-interleaved technique which consists of a
parallel array of N electrical ADC converters, which have the same sampling rate but different sampling phase. Each
operating at a quantization rate of fs/N where fs is the aggregated sampling rate. In a system with no real-time operation,
the N channels digital outputs are stored in memory, and then aggregated (multiplexed) to obtain the digital
representation of the analog input waveform. Alternatively, for real-time operation systems the reduction of storing time
in the multiplexing process is desired to improve the time response of the ADC. The complete elimination of memories
come expenses of concurrent timing and synchronization in the aggregation of the digital signal that became critical for a
good digital representation of the analog signal waveform.
In this paper we propose and demonstrate a novel optically synchronized encoder and multiplexer scheme for
interleaved photonics ADCs that utilize the N optical signals used to sample different phases of an analog input signal to
synchronize the multiplexing of the resulting N digital output channels in a single digital output port. As a proof of
concept, four 320 Megasamples/sec 12-bit of resolution digital signals were multiplexed to form an aggregated 1.28
Gigasamples/sec single digital output signal.
|
