All-optical Differentiation Research Articles

All-optical ultrafast differentiation and integration for femtosecond pulse shaping based on programmable differential group delay

We propose and demonstrate a novel scheme of multi-functional all-optical ultrafast signal processor for femtosecond pulse shaping based on programmable differential group delay (DGD), which is capable of performing both all-optical differentiation and integration simultaneously, and can easily switch two functionalities by simply tuning the orientation of a polarizer. The differentiation waveforms and integration windows length can be adjusted by programming the DGD time. Utilizing numerical simulation we obtain the differential pulses and their autocorrelation of ~400-fs Gaussian signal for DGD of 0.5 ps and 4 ps, while achieve its integral pulses and their autocorrelation for DGD of 0.5 ps, 1.5 ps, and 3.5 ps. We further experimentally demonstrate the all-optical differentiation and all-optical integration of ~400-fs Gaussian signals whose results agree well with the theoretical prediction and simulation result. Using autocorrelation method, we observe in detail the differential and integral processing of femtosecond pulses at various DGD for the first time according to our knowledge. Our scheme can work over the whole communication band with variable operation wavelength, and is competitive in ultrafast pulse shaping for quantum control due to highly reconfigurable and flexible features.

All-optical temporal differentiation in hot standing-wave-dressed atoms

We propose a scheme to realize all-optical temporal differentiation calculation to input pulse in an inverse Y-type four-level atomic system driven by a strong standing-wave. Two optical blockades are created at individual wavelengths of two probe fields in presence of one single strong standing-wave field. On one hand, ultra-narrow transmission windows are produced for probe pulse field 1 when probe field 2 is so strong as a controlling field in EIT configuration. The system can be designed as a phase-reverter of weak probe field 1 and can perform temporal differentiation calculation to it because aπ phase shift is created. On the other hand, the blockade at probe field 2 can be burst in two-photon resonance configuration when probe field 1 becomes strong and saturated absorption takes effect. So a two-photon switching is also expected in this standing-wave-dressed atomic system. The scheme has a potential for an all-optical transistor in quantum logical circuits.

Tunable 360° Photonic Radio-Frequency Phase Shifter Based on Polarization Modulation and All-Optical Differentiation

A continuously tunable photonic radio-frequency (RF) phase shifter based on polarization modulation and all-optical differentiation using a polarization modulator (PolM) and an optical frequency discriminator is proposed, theoretically analyzed and experimentally demonstrated. In the proposed phase shifter, two light waves at different wavelengths are injected into a PolM which is driven by an RF signal to be phase shifted. For one wavelength, the state of polarization (SOP) of the light wave is aligned with one principal axis of the PolM, thus the PolM operates jointly with an optical frequency discriminator as an optical differentiator to produce a quadrature (Q) signal. For the other wavelength, the SOP of the light wave is oriented with 45° or 135° with the principal axis of the PolM, thus the PolM operates jointly with a polarizer as an intensity modulator to produce an in-phase (I) signal. By detecting the I-Q optical signals at a photodetector (PD), a phase-shifted RF signal is generated. The value of the phase shift is determined by the amplitudes of the I-Q signals, which can be continuously tuned by controlling the powers of the light waves. An experiment is performed. A phase shifter with a full tunable range of 360° at an RF frequency tunable from 3 to 10 GHz is demonstrated.

An ultra-high-speed photonic temporal differentiator using cascaded SOI microring resonators

A high-speed photonic temporal differentiator based on cascaded SOI microring resonators is proposed and experimentally demonstrated in this study. The first-order all-optical differentiation functionality is realized through approaching the critical coupling condition of the cascaded microring resonators. A three-stage double channel side-coupled cascaded microring structure is used to provide wider bandwidth and larger notch depth in its transmission spectrum. The fabricated cascaded SOI microring device is experimentally verified by Gaussian-like pulse trains with a data rate of up to 80 Gbit s−1. Due to the use of cascaded microring resonators, the notch depth in the transmission spectrum is increased from less than 30 dB to larger than 30 dB, thus the quality of the differentiated signal is improved.

Reconfigurable optical differential phase-shift-keying pattern recognition based on incoherent photonic processing

We propose and experimentally demonstrate asynchronous optical differential phase-shift-keying (DPSK) pattern recognition using a fully reconfigurable technique. The proposed method uses optical phase-to-bipolar intensity conversion through all-optical differentiation in conjunction with an incoherent time-spectrum convolution system where the pattern to be recognized is implemented directly in the spectral domain through optical amplitude-only linear filtering. Full reconfigurability in terms of bit rate, pattern sequence, and pattern length is achieved using electronically programmable optical filters. We demonstrate dynamically switching recognition of different 64 bit patterns in a continuous 12 Gb/s DPSK pseudorandom optical bit stream with contrast ratio up to 3.8 dB.

Single-shot real-time frequency chirp characterization of telecommunication optical signals based on balanced temporal optical differentiation

A simple single-shot frequency chirp characterization technique for telecommunication optical waveforms is introduced. The proposed technique is based on what we believe to be a novel balanced all-optical ultrafast differentiation scheme, and it enables a real-time conversion of the instantaneous frequency variation of an arbitrary complex (amplitude and phase) optical signal into a temporal intensity profile while simultaneously providing an efficient cancellation of the intensity noise. Single-shot real-time frequency chirp measurements of gigahertz-bandwidth phase-only and amplitude and phase temporal modulation waveforms are performed.

Picosecond and sub-picosecond flat-top pulse generation using uniform long-period fiber gratings

We propose a novel linear filtering scheme based on ultrafast all-optical differentiation for re-shaping of ultrashort pulses generated from a mode-locked laser into flat-top pulses. The technique is demonstrated using simple all-fiber optical filters, more specifically uniform long period fiber gratings (LPGs) operated in transmission. The large bandwidth typical for these fiber filters allows scaling the technique to the sub-picosecond regime. In the experiments reported here, 600-fs and 1.8-ps Gaussian-like optical pulses (@ 1535 nm) have been re-shaped into 1-ps and 3.2-ps flat-top pulses, respectively, using a single 9-cm long uniform LPG.