Reza Maram

Noiseless intensity amplification of repetitive signals by coherent addition using the temporal Talbot effect

Amplification of signal intensity is essential for initiating physical processes, diagnostics, sensing, communications and measurement. During traditional amplification, the signal is amplified by multiplying the signal carriers through an active gain process, requiring the use of an external power source. In addition, the signal is degraded by noise and distortions that typically accompany active gain processes. We show noiseless intensity amplification of repetitive optical pulse waveforms with gain from 2 to ~20 without using active gain. The proposed method uses a dispersion-induced temporal self-imaging (Talbot) effect to redistribute and coherently accumulate energy of the original repetitive waveforms into fewer replica waveforms. In addition, we show how our passive amplifier performs a real-time average of the wave-train to reduce its original noise fluctuation, as well as enhances the extinction ratio of pulses to stand above the noise floor. Our technique is applicable to repetitive waveforms in any spectral region or wave system.

Spectral self-imaging of time-periodic coherent frequency combs by parabolic cross-phase modulation

Integer and fractional spectral self-imaging effects are induced on infinite-duration periodic frequency combs (probe signal) using cross-phase modulation (XPM) with a parabolic pulse train as pump signal. Free-spectral-range tuning (fractional effects) or wavelength-shifting (integer effects) of the frequency comb can be achieved by changing the parabolic pulse peak power or/and repetition rate without affecting the spectral envelope shape and bandwidth of the original comb. For design purposes, we derive the complete family of different pump signals that allow implementing a desired spectral self-imaging process. Numerical simulation results validate our theoretical analysis. We also investigate the detrimental influence of group-delay walk-off and deviations in the nominal temporal shape or power of the pump pulses on the generated output frequency combs.

Programmable Fiber-Optics Pulse Repetition-Rate Multiplier

We develop a strikingly simple fiber-optics pulse repetition-rate multiplication approach, based on dispersion-induced temporal self-imaging (TSI) effect, in which the rate multiplication factor can be electrically programmed to be any desired integer value. The multiplier setup is composed of an electrooptic phase modulator followed by a dispersive medium. In contrast to the conventional TSI-based rate-multiplication techniques, the required dispersion is fixed in this method and does not depend on the multiplication factor. Programming the output repetition rate will be then assigned to a preprocessing step where the overall phase of the input pulses is modulated by a phase modulator. Herein, we derive in detail a condition for the required dispersion and introduce an analytical equation for the temporal phase modulation. To validate the derived expressions, proof-of-concept experiments have been carried out and we have achieved high-quality tunable rate multiplication, by factors ranging from 1 to 4, of mode-locked fiber lasers with input repetition rates of 10 and 4.85 GHz, respectively.

Ultrafast all-optical clock recovery based on phase-only linear optical filtering

We report on a novel technique for all-optical clock recovery from RZ OOK data based on phase-only filtering, significantly enhancing the recovered clock quality and energy-efficiency compared to the use of a Fabry-Perot filter.

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.

Sub-harmonic periodic pulse train recovery from aperiodic optical pulse sequences through dispersion-induced temporal self-imaging

Temporal self-imaging effects (TSIs) are observed when a periodic pulse train propagates through a first-order dispersive medium. Under specific dispersion conditions, either an exact, rate multiplied or rate divided image of the input signal is reproduced at the output. TSI possesses an interesting self-restoration capability even when acting over an aperiodic train of pulses. In this work, we investigate and demonstrate, for the first time to our knowledge, the capability of TSI to produce periodic sub-harmonic (rate-divided) pulse trains from aperiodic sequences. We use this inherent property of the TSI to implement a novel, simple and reconfigurable sub-harmonic optical clock recovery technique from RZ-OOK data signals. The proposed technique features a very simple realization, involving only temporal phase modulation and first-order dispersion and it allows one to set the repetition rate of the reconstructed clock signal in integer fractions (sub-harmonics) of the input bit rate. Proof-of-concept experiments are reported to validate the proposed technique and guidelines for optimization of the clock-recovery process are also outlined.

High-speed all-optical NOT gate based on spectral phase-only linear optical filtering

We propose and analyze a novel concept for all-optical NOT gate (AONG) for high-speed telecommunication on-off-keying data signals based on spectral phase-only linear optical filtering, with applicability for speeds above 160Gb/s. Proof-of-concept experiments are reported to validate the proposed AONG working principle.

Electrically-tunable fiber-optics pulse repetition-rate multiplier

We propose and experimentally demonstrate a novel, simple and all-fiber method for repetition-rate multiplication of picosecond optical pulse trains based on temporal self-imaging, involving temporal phase modulation and dispersion, with an electrically reconfigurable repetition-rate multiplication factor.

Ultrafast All-Optical Clock Recovery Based on Phase-Only Linear Optical Filtering

We report on a novel technique for all-optical clock recovery from RZ OOK data based on phase-only filtering, significantly enhancing the recovered clock quality and energy-efficiency compared to the use of a Fabry-Perot filter.

Passive Waveform Amplification by Self-Imaging

We show experimentally undistorted, intensity amplification of optical pulse waveforms with gain from 2 to ~20 without using active gain by recycling energy already stored in the input repetitive signal.