Abstract
We propose a new type of photonic analog-to-digital converter (ADC), designed for high-resolution (>7 bit) and high sampling rates (scalable to tens of GS/s). It is based on encoding the input analog voltage signal onto the phase of an optical pulse stream originating from a mode-locked laser, and uses spatial oversampling as a means to improve the conversion resolution. This paper describes the concept of spatial oversampling and draws its similarities to the commonly used temporal oversampling. The design and fabrication of a LiNbO(3)/silica hybrid photonic integrated circuit for implementing the spatial oversampling is shown, and its abilities are demonstrated experimentally by digitizing gigahertz signals (frequencies up to 18GHz) at an undersampled rate of 2.56GS/s with a conversion resolution of up to 7.6 effective bits. Oversampling factors of 1-4 are demonstrated.
Highlights
Photonic analog-to-digital converters (ADC) have been the focus of great research interest in past years
Mode-locked lasers (MLL) have been shown to provide ultra-low jitter optical pulse streams, as low as a few femtoseconds [2], and are very attractive for photonic ADCs, allowing the resolution-bandwidth product to be increased by orders of magnitude [3]
Slower electronics are used to digitize and combine the channels, creating a time-interleaved ADC. This reduces the bandwidth requirements from the front end sample and hold of electronic ADCs, as the required electrical sampling rate is the overall optical sampling rate divided by the wavelength division multiplexing (WDM) parallelism factor
Summary
Photonic analog-to-digital converters (ADC) have been the focus of great research interest in past years. This makes the design of high resolution ADCs based on direct photonic quantization challenging An alternative to this is detecting the analog optical signal after modulation and using standard electrical ADCs for quantization [11]. This retains the low jitter characteristics of optical pulses, while taking advantage of the improvements in electrical ADC technology. Slower electronics are used to digitize and combine the channels, creating a time-interleaved ADC This reduces the bandwidth requirements from the front end sample and hold of electronic ADCs, as the required electrical sampling rate is the overall optical sampling rate divided by the WDM parallelism factor. This work presents a photonic ADC architecture, based on optical pulse sampling from an MLL source, employing phase modulation, coherent detection and our spatial oversampling concept
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