159 research outputs found
Temporal cloak based on tunable optical delay and advance
No full textA temporal cloak scheme based on tunable optical delay and advance is theoretically proposed. An input optical signal is divided into two parts, and the front part is advanced while the rear part is delayed. A temporal gap which contains negligible optical energy is opened to hide events from observers, which can be closed by doing the inverse process. Different from the previous schemes that use continuous wave light, we use an optical data stream as the probe beam. Simulations have been done to investigate performance of the temporal cloak. The developed scheme can be applied in fiber-optical signal processing and secure communications. (C) 2015 Optical Society of Americ
Pulse noise-hidden image reconstruction and visualization via stochastic resonance
No full textWe investigate the nanosecond pulse noise-hidden image reconstruction and visualization using stochastic resonance implemented by modulation instability. In particular, this dynamical stochastic resonance holds with coupling between the pulse incoherent noise and pulse coherent signal, and provides a substantial enhancement of the signal-to-noise ratio and cross-correlation. This means that the pulse noise-hidden image can be effectively reconstructed with high visibility and fidelity via stochastic resonance at appropriate system parameters. Such a simple and convenient method has potential applications in image processing under noisy environment
Noise-hidden signal recovery via stochastic resonance in the SOI waveguide resonator
No full textWe propose a method to recover weak pulse signals buried in noise via stochastic resonance (SR) based on optical bistability induced by the free-carrier dispersion effect in the siliconon- insulator (SOI) waveguide resonator. The bistable system threshold is determined by the resonator parameters including the waveguide length, mirror reflectivity, and the free-carrier lifetime. A signal with different power levels can be detected by changing the free-carrier lifetime using a reverse-biased p-i-n junction embedded in the SOI waveguide. The influence of the system parameters on the SR is quantitatively analyzed by calculating the cross-correlation coefficient between the input and output signals. A cross-correlation gain of 5.6 is obtained by optimizing the system parameters of the SOI waveguide resonator. The results show the potential of using this structure to reconstruct and extract weak signals in all-optical integrated systems
Numerical analysis of pulse signal restoration by stochastic resonance in a buckled microcavity
No full textA novel scheme is proposed to restore weak pulse signals immersed in noise by stochastic resonance based on photothermal-effect-induced optical bistability in a buckled dome microcavity. The bistable properties of the dome microcavity are analyzed with different initial detuning wavelengths and effective cavity lengths, and bistable transmission can be obtained for input powers in submilliwatt range. A theoretical model is derived to interpret the nonlinear process of pulse signal recovery through double-well potential theory. The cross-correlation coefficient between output signals and pure input pulses is calculated to quantitatively analyze the influence of noise intensity on stochastic resonance. A cross-correlation gain of 7 is obtained, and the noise-hidden signal can be recovered effectively though the buckled dome microcavity with negligible distortion. The simulation results show the potential of using this structure to restore low-level or noise-hidden pulse signals in all-optical integrated systems. (C) 2016 Optical Society of Americ
Influence of absorption on stability of terahertz difference frequency generation
No full textThis work presents numerical studies of the stability feature of terahertz difference frequency generation (THz-DFG) with a ZnGeP2 crystal using two pump wavelengths. We found that the maximum output of a THz wave is located in the unstable output region because of the competitive equilibrium between the absorption and the gain. Furthermore, the output stability is dependent on the pump stability. Different from the results at the pump wavelength of 9.588 mu m, there is neither an appropriate stable output region nor gain saturation region at the pump wavelength of 1.064 mu m for a larger absorption coefficient. This work demonstrates that the stable output region of the THz wave is difficult to obtain when the pump absorption is excessively large in DFG. (C) 2016 Optical Society of Americ
Reduction of phase noise to amplitude noise conversion in silicon waveguide-based phase-sensitive amplification
No full textWe use a vector phase sensitive amplification (PSA) scheme, which can eliminate the inherent phase noise (PN) to amplitude noise (AN) conversion in a conventional PSA process. A dispersion-engineered silicon strip waveguide is used to investigate the vector PSA scheme at the telecom wavelengths. The phase-dependent gain and phase-to-phase transfer functions as well as constellation diagram at different signal polarization states (SPSs) are numerically analyzed. It is found that the PN to AN conversion is completely suppressed when the SPS is identical to one of the pump polarization states. Moreover, the binary phase shift keying signal is regenerated by the proposed vector PSA scheme, and the error vector magnitude is calculated to assess the regeneration capacity. Our results have potential application in all-optical signal processing. (C) 2016 Optical Society of Americ
Extracting signal via stochastic resonance in the semiconductor optical amplifier
No full textThe stochastic resonance based on optical bistability in the semiconductor optical amplifier is numerically investigated to extract a weak pulse signal buried in noise. The output property of optical bistability under different system parameters is analyzed, which determines the performance of the stochastic resonance. Through optimizing these parameters, the noise-hidden signal is extracted via stochastic resonance, in which the maximum cross-correlation gain higher than nine is obtained. This provides a novel technology for detecting a weak optical signal in various signal processing fields. © 2016 Chinese Optics Letters
Nonlinear restoration of pulse and high noisy images via stochastic resonance
No full textWe propose a novel scheme for restoring pulse and high noisy images using stochastic resonance, which is based on the modulation instability and provides a cross-correlation gain higher than 8. As opposed to previously reported designs, this unique approach employs a continuous noise and pulse signal for the generation of modulation instability. The visibility and quality of output images can be improved by appropriately adjusting the system parameters. This provides a simple and feasible method for detecting low-level or hidden pulse images in various imaging applications
Multi-channel terahertz wavelength division demultiplexer with defects-coupled photonic crystal waveguide
No full textTerahertz (THz) wavelength division demultiplexer based on a compact defects-coupled photonic crystal waveguide is proposed and demonstrated numerically. This device consists of an input waveguide that perpendicularly coupled with a series of defects cavities, each of which captures the resonance frequency from the input waveguide. Coupled-mode theory and finite element method are used to analyze the transmission properties of the structure. It is found that the transmission wavelength centered around 1THz can be adjusted by changing the geometrical parameters of defects cavities, which equals to THz waves generated by optical methods such as difference frequency generation and optical rectification. Applications in this frequency range are urgently needed. Furthermore, the highest transmission efficiency of 0.94 can be achieved when a perfect wavelength-selective mirror is set in the output waveguide
Broadband and efficient wavelength conversion in a slot-width switching silicon-organic hybrid waveguide
No full textWe propose a slot-width switching (SWS) silicon-organic hybrid waveguide for broadband and efficient wavelength conversion. By switching the slot width of different lengths, the quasi-phase-matching can be obtained. Compared with width-modulated silicon-on-insulator (SOI) waveguide, the non-linear absorption can be ignored in slot waveguide which is filled with p-toluene sulphonate. Consequently, the conversion efficiency at a particular signal wavelength is improved, and the 3-dB conversion bandwidth is also extended. The numerical simulation results indicate that, for a continuous-wave pump at 1550 nm, a conversion bandwidth of 570 nm and a peak conversion efficiency of 11.32 dB can be realized in a 7.5-mm-long SWS waveguide, which is better than that of width-modulated SOI waveguide
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