Jeonghyun Huh

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.

All-Optical Reconfigurable Signal Processing Based on Cross Phase Modulation Time Lensing

A system is proposed for all-optical reconfigurable time-to-frequency (T-to-F) conversion and temporal magnification of optical waveforms using a design based on a cross phase modulation-induced time lens combined with group-velocity dispersion. In this design, the T-to-F conversion ratio and magnification factor can be easily tuned by exploiting the direct dependence of the time-lens chirp with the peak power of a parabolic pump pulse. In a proof-of-concept experiment, T-to-F conversion and temporal magnification of picosecond optical waveforms are demonstrated using a fiber-optics scheme, where the T-to-F conversion and magnification factors are effectively tuned over a twofold range by controlling the gain of an optical amplifier. The same system can be additionally adjusted to provide a time-mapped Fourier transform of the input waveform.

Generation of parabolic pulses with optimized duration & energy by use of dispersive frequency-to-time mapping

Parabolic pulses with durations ranging from the picosecond to the sub-nanosecond range (100-ps reported here) were generated through frequency-to-time mapping. A virtual time-lens was applied in the spectral shaping stage in order to relax the constraints imposed by the far-field condition.