An algorithm based on phase spectrum analysis is proposed that can be used to correct the timing distortion between the multiple parallel demultiplexed post-sampling pulse trains in wavelength demultiplexing analog-to-digital converters. The algorithm is theoretically presented and its operational principle is explained. The algorithm is then applied to two parallel demultiplexed post-sampling signals from a proof-of-principle system and fairly good results are obtained. This algorithm is potentially applicable in other opto-electronic hybrid systems where an interleaving and/or multiplexing mechanism is utilized, such as optical time-division multiplexing and optical clock division systems, photonic arbitrary waveform generators, and so on.
A method for generation of a time- and wavelength-interleaved pulse train is demonstrated, that can be used to attain a multiwavelength pulse train with a 40-Gbps or a potentially even higher repetition rate. This method is highly flexible because the repetition rate, the intensity, and pulse width of each wavelength and the time interval between adjacent wavelengths can be readily and independently adjusted. A time- and wavelength-interleaved pulse train with a repetition rate of 40-Gbps is experimentally demonstrated. Potential of generating a multiwavelength pulse train with a 100-Gbps repetition rate is also discussed.
A noninterferometric configuration for an optical phase-shifter module (OPSM) is presented and demonstrated, which is a key component in phase-shifted optical quantization (PSOQ) systems. In a PSOQ system employing such an OPSM, the input electrical analog signal is applied on two LiNbO3 intensity modulators in parallel, and the OPSM takes the outputs of the intensity modulators as its input and yields N-channel optical outputs, which are thresholded to generate digitized values of the input analog signal. The feasibility of this OPSM configuration is demonstrated by a proof-of-principle PSOQ experiment, in which a 2.5-GHz single tone is applied to the modulators and 16 transmission curves are recorded. Based on these transmission curves, software sampling indicates that an effective number of bits equal to 4.17 is attainable for a frequency as high as 2.5 GHz. Benefits of such an OPSM are easier control and high precision of desired phase shifts.
High-speed Photonic Analog-to-Digital Convertor (ADC) has attracted intense interest of researchers for the past three
decades, for it has the potential applications in areas that have extreme bandwidth requirements, such as radio astronomy,
real-time measurements and so on. Photonic ADCs can be categorized into two major classes: optical assisted ADC and
all-optical ADC. In optical assisted ADC, the sampling is performed in optical domain and the quantization is done in
electrical domain. In all-optical ADC, the sampling, quantization and coding are done in optical domain. Optical assisted
ADC combines the ultra-stable, ultra-low time jitter characterizations of mode-locked lasers and mature high-speed
electronic circuits, therefore it is much easier to implement in practical systems. However, the ultra-short (less than tens
of pico-seconds) post-sampling pulse sequence required by high resolution ADC places a challenge for the following
electrical processing, because ultra-high-speed (>2GHz) "integrate-hold" circuits are hard to design and manufacture. In
this paper, an optical hold module (OHM) is proposed, theoretically analyzed, numerically simulated and experimentally
demonstrated, which can be used to replace ultra-high-speed "integrate-hold" circuits and has more merits than the latter.
This optical hold module has potential applications in several other areas, such as fiber sensors, and so on.
An approach to generate ultrawideband (UWB) monocycle pulses is proposed and experimentally demonstrated, based on a dual-output intensity modulator and tunable optical time delay. Positive and negative pulses are obtained from two output ports of the modulator, respectively, and are coupled together through different time delays. The generated monocycle pulse has a 10-dB bandwidth of 6.5 GHz and a central frequency of 3.7 GHz.