A widely-wavelength-tunable Brillouin fiber laser(BFL)with improved optical signal-to-noise ratio(OSNR)based on parity-time(PT)symmetric and saturable absorption(SA)effect is present.This novel BFL realizes PT symmetr...A widely-wavelength-tunable Brillouin fiber laser(BFL)with improved optical signal-to-noise ratio(OSNR)based on parity-time(PT)symmetric and saturable absorption(SA)effect is present.This novel BFL realizes PT symmetry and SA effect through polarization-maintaining erbium-doped fiber(PM-EDF)Sagnac loop,which is composed of a PM-EDF,a coupler and two polarization controllers(PCs).By using the inherent birefringence characteristic of PM-EDF,two feedback loops in orthogonal polarization state are formed when the Strokes signal in injected.One of these loops provides gain in the clockwise direction with in the Sagnac loop,while the other loop generates loss in the counterclockwise direction.By adjusting the PCs to control the polarization state of the PM-EDF,a single-longitudinal-mode(SLM)BFL can be achieved,as the PT symmetry is broken when the SA participating stimulated Brillouin scattering(SBS)gain and loss are well-matched and the gain surpasses the coupling coefficient.Compared to previous BFLs,the proposed BFL has a more streamlined structure and a wider wavelength tunable range,at the same time,it is not being limited by the bandwidth of the erbium-doped fiber amplifier while still maintaining narrow linewidth SLM output.Additionally,thanks to SA effect of the PM-EDF,the PT symmetric SBS gain contract is enhanced,resulting in a higher optical signal-to-noise(OSNR).The experimental results show that the laser has a wide tunable range of 1526.088 nm to 1565.498 nm,an improved OSNR of 77 dB,and a fine linewidth as small as 140.5 Hz.展开更多
In this paper, we study the phenomenon of stochastic resonance （SR） in a periodically driven bistable system with correlations between multiplicative and additive white noise terms when there, are two different kind...In this paper, we study the phenomenon of stochastic resonance （SR） in a periodically driven bistable system with correlations between multiplicative and additive white noise terms when there, are two different kinds of time delays existed in the deterministic and fluctuating forces, respectively. Using the small time delay approximation and the theory of signal-to-noise ratio （SNR） in the adiabatic limit, the expression of SNR is obtained. The effects of the delay time T in the deterministic force, and the delay time 8 in the fluctuating force on SNR are discussed. Based on the numerical computation, it is found that： （i） There appears a reentrant transition between one peak and two peaks and then to one peak again in the curve of SNR when the value of the time delay θ is increased. （ii） SR can be realized by tuning the time delay T or 8 with fixed noise, i.e., delay-induced stochastic resonance （DSR） exists.展开更多
As a sampling technique for CCD output video signal, the correlated double sampling(CDS) technique is described as well as the filtering effects of the CDS technique on the output noise of CCD including the reset nois...As a sampling technique for CCD output video signal, the correlated double sampling(CDS) technique is described as well as the filtering effects of the CDS technique on the output noise of CCD including the reset noise of CCD, the white noise of output amplifier and 1/f noise. From real application of CDS device——TH7982A, it is concluded that the output signal-to-noise ratio of 50dB for CCD signal can be obtained.展开更多
In this paper, the authors propose a new approach to image compression based on the principle of Set Partitioning in Hierarchical Tree algorithm （SPIHT）. Our approach, the modified SPIHT （MSPIHT）, distributes entr...In this paper, the authors propose a new approach to image compression based on the principle of Set Partitioning in Hierarchical Tree algorithm （SPIHT）. Our approach, the modified SPIHT （MSPIHT）, distributes entropy differently than SPIHT and also optimizes the coding. This approach can produce results that are a significant improvement on the Peak Signal-to-Noise Ratio （PSNR） and compression ratio obtained by SPIHT algorithm, without affecting the computing time. These results are also comparable with those obtained using the Embedded Zerotree Wavelet （EZW） and Joint Photographic Experts Group 2000 （JPG2） algorithms.展开更多
文摘A widely-wavelength-tunable Brillouin fiber laser(BFL)with improved optical signal-to-noise ratio(OSNR)based on parity-time(PT)symmetric and saturable absorption(SA)effect is present.This novel BFL realizes PT symmetry and SA effect through polarization-maintaining erbium-doped fiber(PM-EDF)Sagnac loop,which is composed of a PM-EDF,a coupler and two polarization controllers(PCs).By using the inherent birefringence characteristic of PM-EDF,two feedback loops in orthogonal polarization state are formed when the Strokes signal in injected.One of these loops provides gain in the clockwise direction with in the Sagnac loop,while the other loop generates loss in the counterclockwise direction.By adjusting the PCs to control the polarization state of the PM-EDF,a single-longitudinal-mode(SLM)BFL can be achieved,as the PT symmetry is broken when the SA participating stimulated Brillouin scattering(SBS)gain and loss are well-matched and the gain surpasses the coupling coefficient.Compared to previous BFLs,the proposed BFL has a more streamlined structure and a wider wavelength tunable range,at the same time,it is not being limited by the bandwidth of the erbium-doped fiber amplifier while still maintaining narrow linewidth SLM output.Additionally,thanks to SA effect of the PM-EDF,the PT symmetric SBS gain contract is enhanced,resulting in a higher optical signal-to-noise(OSNR).The experimental results show that the laser has a wide tunable range of 1526.088 nm to 1565.498 nm,an improved OSNR of 77 dB,and a fine linewidth as small as 140.5 Hz.
基金Supported by the Natural Science Foundation of Yunnan Province under Grant No.08C0235
文摘In this paper, we study the phenomenon of stochastic resonance （SR） in a periodically driven bistable system with correlations between multiplicative and additive white noise terms when there, are two different kinds of time delays existed in the deterministic and fluctuating forces, respectively. Using the small time delay approximation and the theory of signal-to-noise ratio （SNR） in the adiabatic limit, the expression of SNR is obtained. The effects of the delay time T in the deterministic force, and the delay time 8 in the fluctuating force on SNR are discussed. Based on the numerical computation, it is found that： （i） There appears a reentrant transition between one peak and two peaks and then to one peak again in the curve of SNR when the value of the time delay θ is increased. （ii） SR can be realized by tuning the time delay T or 8 with fixed noise, i.e., delay-induced stochastic resonance （DSR） exists.
文摘As a sampling technique for CCD output video signal, the correlated double sampling(CDS) technique is described as well as the filtering effects of the CDS technique on the output noise of CCD including the reset noise of CCD, the white noise of output amplifier and 1/f noise. From real application of CDS device——TH7982A, it is concluded that the output signal-to-noise ratio of 50dB for CCD signal can be obtained.
文摘In this paper, the authors propose a new approach to image compression based on the principle of Set Partitioning in Hierarchical Tree algorithm （SPIHT）. Our approach, the modified SPIHT （MSPIHT）, distributes entropy differently than SPIHT and also optimizes the coding. This approach can produce results that are a significant improvement on the Peak Signal-to-Noise Ratio （PSNR） and compression ratio obtained by SPIHT algorithm, without affecting the computing time. These results are also comparable with those obtained using the Embedded Zerotree Wavelet （EZW） and Joint Photographic Experts Group 2000 （JPG2） algorithms.
