In-fiber high-speed recognition of incoherent-light broadband energy spectrum patterns.

A fiber-optic system is proposed and experimentally demonstrated for real-time, on-the-fly identification of an incoherent-light energy spectrum pattern based on dispersion-induced time-spectrum convolution. In the proposed system, the incoming frequency-spectrum patterns to be identified are modulated by a time-mapped version of the target intensity profile. Following propagation through a suitable fiber-optic dispersive medium, the measured output temporal waveform provides a correlation of the incoming spectra with the programmed target pattern. This enables direct, real-time detection of the matching energy spectra, without any further numerical post-processing. We experimentally demonstrate successful recognition of a target infrared spectral pattern, extending over a bandwidth of 1.5 THz with a resolution of ∼12 GHz, with sub-megahertz update rates. A path for further performance improvements is also suggested.

Time-domain Vander-Lugt filters for in-fiber complex (amplitude and phase) optical pulse shaping.

The time-domain counterpart of spatial Vander-Lugt filters is proposed for the first time, to the best of our knowledge. The concept enables reshaping an ultrashort optical pulse into a desired complex (amplitude and phase) arbitrary temporal pulse waveform using a setup configuration similar to that of previously demonstrated fiber-optic time-domain pulse-intensity shapers, i.e., using a single temporal amplitude modulator between two opposite-dispersive all-fiber media. The proposal is experimentally validated through reconfigurable generation of two complex-valued pulse shapes, namely, a 60 ps asymmetrical triangular pulse with controlled parabolic phase and a 4-symbol 16-QAM picosecond pulse code sequence.

In-fiber reconfigurable generation of arbitrary (asymmetric) picosecond temporal intensity waveforms by time-domain optical pulse shaping.

A fiber-optic programmable optical pulse shaper is experimentally demonstrated using multi-level phase-only linear filtering, capable of synthesizing arbitrary (including asymmetric) temporal intensity waveforms. The reconfigurable filtering operation is implemented in the time domain with a single electro-optic phase modulator (EO-PM) driven by a high-speed electronic arbitrary waveform generator (AWG). The required multi-level modulation signal is calculated from a combination of optimization algorithms, namely the Gerchberg-Saxton algorithm (GSA) and a genetic algorithm (GA). We report the synthesis of high-quality, arbitrary temporal intensity profiles, including asymmetric triangular waveforms and ∼150 Gbaud random on-off keying (OOK) pulse and pulse amplitude-modulation (PAM) code sequences, with a temporal resolution of ∼2 ps over a maximum time window of ∼60 ps.

Observation of spectral self-imaging by nonlinear parabolic cross-phase modulation.

We report an experimental demonstration of spectral self-imaging on a periodic frequency comb induced by a nonlinear all-optical process, i.e., parabolic cross-phase modulation in a highly nonlinear fiber. The comb free spectral range is reconfigured by simply tuning the temporal period of the pump parabolic pulse train. In particular, undistorted FSR divisions by factors of 2 and 3 are successfully performed on a 10 GHz frequency comb, realizing new frequency combs with an FSR of 5 and 3.3 GHz, respectively. The pump power requirement associated to the SSI phenomena is also shown to be significantly relaxed by the use of dark parabolic pulses.

Generation of high-quality parabolic pulses with optimized duration and energy by use of dispersive frequency-to-time mapping.

We propose and demonstrate a novel linear-optics method for high-fidelity parabolic pulse generation with durations ranging from the picosecond to the sub-nanosecond range. This method is based on dispersion-induced frequency-to-time mapping combined with spectral shaping in order to overcome constraints of previous linear shaping approaches. Temporal waveform distortions associated with the need to satisfy a far-field condition are eliminated by use of a virtual time-lens process, which is directly implemented in the linear spectral shaping stage. Using this approach, the generated parabolic pulses are able to maintain most energy spectrum available from the input pulse frequency bandwidth, regardless of the target pulse duration, which is not anymore limited by the finest spectral resolution of the optical pulse spectrum shaper. High-quality parabolic pulses, with durations from 25ps to 400ps and output powers exceeding 4dBm before amplification, have been experimentally synthesized from a picosecond mode-locked optical source using a commercial optical pulse shaper with a frequency resolution >10GHz. In particular, we report the synthesis of full-duty cycle parabolic pulses that match up almost exactly with an ideal fitting over the entire pulse period.