In this paper, a simple approach to generate the time-wavelength interleaved sampling clock for photonic A/D converters is proposed using commercially available mode-locked femtosecond fiber laser and optical wavelength/time division multiplexing (WDM/OTDM) techniques with low cost passive optical components. A time and wavelength mapping module is configured using specially designed wavelength division multiplexer and mechanical tunable fiber stretchers. OTDM modules with low optical insertion loss and flexibly configurable multiple factor are implemented with the fused-biconical optical fiber couplers. Experiment is carried out using 18 WDM channels and 128 times OTDM to demonstrate the generation of 83.9Gs/s time-wavelength interleaved sampling clock.

In this paper, we experimentally demonstrate an ultra-long haul and multi-access fiber-optic time synchronization system over the equivalent 13 134 km fiber link based on the bidirectional time division multiplexing transmission over a single fiber with the same wavelength (BTDM-SFSW) scheme. The 13 134 km fiber link is simulated by re-circulating the time signals 33 laps in the 398 km fiber loop. Intermediate stations containing bidirectional optical-electrical-optical repeaters are simultaneously used to implement a high-symmetry low-noise bidirectional signal regeneration for extending transmission distance, and provide the time signals for multi-access time synchronization applications. The results illustrate that time signals aligned with the master station can be available at the slave station and arbitrary intermediate stations without requiring link calibrations. Time synchronization stability in terms of time deviation (TDEV) of less than 32 ps/10 s and the combined uncertainty of less than 89.6 ps can be obtained for the 13 134 km fiber recirculating link. The intermediate stations also have the similar performance with the main fiber link. The simple, robust and accurate ultra-long haul fiber-optic time synchronization technique demonstrated here represents a new class of high-accuracy time synchronization that could be used for national/intercontinental atomic clock comparison campaigns and opens up a possibility for providing synchronized time signals to multiple users over the large-scale fiber-optic networks.

We investigate the effects of the photonic sampling pulse’s temporal width and the photodetection bandwidth on the channel response of time-interleaved photonic analog-to-digital converters (TIPADCs). Each sampling channel is modeled as a linear analog channel with a sampler, where the channel response is derived and analyzed theoretically. The results show that the finite temporal width of photonic sampling pulse will limit the channel analog bandwidth and the minimum feasible bandwidth of photodetection is the half of single channel sampling rate. The inter-symbol interference (ISI) induced by the finite bandwidth of photodetection will cause periodic ripples on the channel frequency response. Neither the photonic sampling with finite temporal width nor the ISI induced by the finite bandwidth of photodetection will result in excess noise. Experimental measurements on the channel responses of a TIPADC under different temporal widths and photodetection bandwidths verify the theoretical results.

We present a photonic compressive receiver, where the frequency information of the captured signal is directly mapped to the time intervals between compressed pulses for multiple microwave frequency measurement. The theoretical measurement error, multiple-frequency resolution and effective measurement range are derived. The effects of dispersion deviation and the electrical bandwidth are also discussed. The theoretical results are verified by the measured pulse waveforms and frequency-time mapping relationship. A photonic compressive receiver with an effective measurement range of 42 GHz, a multiple-frequency resolution of 1.2 GHz, a measurement accuracy of 88 MHz and a signal interception period of 27 ns is experimentally obtained.

We propose a photonic scheme to digitize RF signals with a programmable equivalent analog prefilter, where the filter impulse response is directly proportional to the time-reversed temporal shape of the sampling pulse and hence can be adjusted by shaping sampling pulses. The model of the proposed scheme is presented to prove its principle and derive its operation conditions. A four-channel scheme with program-controlled pre-filters is demonstrated experimentally, where bandpass filters with the phase shifts of 0°, 90°, 180°, and 270° are synthesized, respectively, by changing temporal shape of the sampling pulses. The experimental results agree well with the theoretical analysis, indicating the validity of the proposed scheme.

We report on the realization of an optical phase noise cancellation technique by passively embedding the optical phase noise information into a radio frequency signal and creating a copy of the optical frequency signal, which is pre-corrected by the amount of phase noise introduced by optical phase perturbations. Neither phase discrimination nor an active servo controller is required due to the open-loop design, mitigating some technical problems, such as the limited compensation speed and finite phase/timing jitter, in conventional phase noise cancellation. We experimentally demonstrate that this technique maintains the same delay-limited bandwidth and phase noise suppression capability as in conventional techniques, but significantly shortens the response speed and phase recovery time. Passive decoupling optical phase perturbation represents a powerful technique in the domains of optical frequency standard comparisons and tools for future optical atomic clocks, which are now under investigation for a potential redefinition of the International Time Scale.