In order achieve beyond 400 Gb/s serial optical transmission using commercially available equipment, in this work, we
propose the use of channel capacity achieving modulation formats. We present a method to determine the optimum
signal constellation for an arbitrary dispersion map. This method can be described by the following steps. (i) Determine
the probability density functions (pdfs) of the fiber-optics channel, which can be approximated by complex Gaussian
function or estimated by evaluating histograms. (ii) Use the resulting pdfs to determine the optimum input distribution to
achieve the channel capacity. A split-step method is presented to perform the optimization over the probabilities and
mass points of input distributions. (iii) After quantizing the optimum input distribution the optimum signal constellation
can be determined. We study two types of dispersion maps currently in use, which are suitable for metro and mediumhaul
applications. For each of them we determine the optimum signal constellation. The numerical results demonstrate
the efficiency of this method and show that the optimized signal constellation can increase the transmission distance at
most by three spans against its counterpart.
The bias drift effect in the packaged LiNbO<sub>3</sub> modulator is investigated. The Bessel expansion of the dithered clock
shows that the harmonic component equal to the dither frequency can be synchronously demodulated to get the bias drift
and avoid the random phase difference between the clock or data and the dither signal. By using the time division control
method one control system can track two modulator bias drift in 40Gb/s RZ optical transmission system because the
optimum bias point changes very slowly.
Using broadband dispersion compensation CFBGs, over 500km-40Gbps NRZ transmission
system on G.652 fiber will be demonstrated without electric regenerator, FEC and Raman amplifier.
The power penalty is about 2dB @ BER =10<sup>-10</sup>.The CFBGs have better performance: 3dB band is
about 1.2nm, group delay ripple is less than 25ps near center wavelength, power ripple is less than 2dB,
and DGD is less than 1ps. In order to stabilize the DC bias of the LiNbO<sub>3</sub> MZ modulator, a
semiconductor cooler is applied to control the temperature. The effect is perfect.
This paper proposes a single source SBS slow light scheme. This approach splits the incoming pulse train into two beams. One of the beam is used as the "probe"; the other beam is modulated at a frequency which is close to or identical to the half Brillouin shift, and can be used as multiple "pump". The quantitative model shown that the delay and slow light bandwidth can be controlled by the modulation amplitude and the maximum bandwidth is approximately two times of Brillouin shift by choosing an optimum value of the modulation amplitude.
Free-space optical (FSO) communication has attracted considerable attention in recent years due to its widely
applications as an alternative to fiber transmission and radio frequency communication system. In this paper an
experiment on 10Gbit/s free-space optical communication channel transmission over 37m was demonstrated and the
system performance was evaluated according to the bit error rate (BER) curve. Using the phase-screen method and
Kolmogorov spectrum, in addition the impact on signal in free-space communication due to atmospheric turbulence was
studied in detail.
It is well known that the optical pick-up (OPU) plays a very important role in optical storage system. And the quality of OPU can be measured by the characteristics of OPU read-out spot for high density optical storage. Therefore this paper mainly designs an OPU model for high density optical storage to study the characteristics of OPU read-out spot. Firstly it analyses the optical read-out principle in OPU and contrives an optical read-out system based on the hereinbefore theory. In this step it chiefly designs the grating, splitter, collimator lens and objective lens. Secondly based on the aberrations analysis and theory involved by the splitter, the collimator lens and the optical lens, the paper uses the software CODE V to calculate the aberrations and to optimize the optical read-out system. Then the author can receive an ideal OPU read-out spot for high density optical storage and obtain the characteristics of the ideal OPU read-out spot. At the same time this paper analyses some influence factors which can directly affect the characteristics of the OPU read-out spot. Thirdly according to the up data the author practically manufactures a real optical pick-up to validate the hereinbefore designed optical read-out system. And it uses the Optical Spot Analyzer to get the image of the read-out spot. Comparing the ideal image to the actual image of the designed optical read-out system, the author finds out that the upwards analyses and design is suitable for high density storage and can be used in the actual production. And the author also receives the conclusion that the mostly influences on characteristics of OPU read-out spot for high density optical storage factors is not only the process of designing the grating, splitter, collimator lens and objective lens, but also the assembling work precision
Based on the focus pre-search a method is presented to measure the characters of the traverse focus error detection system. In the pre-search of traverse focus servo system, the traverse focus offset is measured by the focus error occurring time, and the traverse focus error sensitivity and linear range are measured by the focus error slope and peak-to-peak value. A traverse focus error detection system is measured. The results show that the traverse focus offset is too high to stable the focus servo.
Phase locked loop (PLL) is a closed loop automatic control system, which can track the phase of input signal. It widely applies in each area of electronic technology. This paper research the phase locked loop in optical memory servo area. This paper introduces the configuration of digital phase locked loop (PLL) and phase locked servo system, the control theory, and analyses system's stability. It constructs the phase locked loop experiment system of optical disk spindle servo, which based on special chip. DC motor is main object, this system adopted phase locked servo technique and digital signal processor (DSP) to achieve constant linear velocity (CLV) in controlling optical spindle motor. This paper analyses the factors that affect the stability of phase locked loop in spindle servo system, and discusses the affection to the optical disk readout signal and jitter due to the stability of phase locked loop.
The performance of direct viewing low light level (LLL) imaging system is mainly determined by three factors: photons noise, MTF of optical system(OS) and human eyes characteristic. And the image detecting theory which denotes the optimal performance of imaging system has been a positive impetus for the development of the LLL imaging and night vision technique. The system minimum resolvable angle was traditionally used to estimate the image detecting performance which is mainly determined by photons noise at low target illuminance and by MTF at high target illuminance. This criterion can represent the system performance on the whole; however, assuming the signal to noise ratio (SNR)of the image and MTF of OS uncorrelative, is theoretically not complete, since the two factors interrelate actually. From the viewpoint of signal response, the MRC (minimum resolvable contrast) model of the ideal direct viewing LLL imaging system was deduced on the basis of human eyes characteristic. It is a more comprehensive evaluation method for imaging system performance, and can combine with the forecasting model of operating distance to analyze the general performance of night vision system. In conclusion, the relationship and the difference between the MRC model and the traditional detecting equation were investigated.
Proc. SPIE. 5633, Advanced Materials and Devices for Sensing and Imaging II
KEYWORDS: Signal to noise ratio, Image fusion, Eye, Visual process modeling, Imaging systems, Spatial frequencies, Spectral resolution, Modulation transfer functions, Night vision systems, Night vision goggles
Aimed at improving the detection ability of the night vision system, a new method to design the optimum spectral band is presented. The new method uses MRC (Minimum Resolvable Contrast) as the criteria of the system performance and brings the spectrum characteristic of the scene and the night vision system into the MRC evaluation. According to the MRC variety of the night vision system under the different working spectral bands, the optimum spectral band is the one which can maximize the scent contrast and doesn't obviously decrease the cut-off spatial frequency of the MRC curve. Finally by the design method and the MRC model, the optimum spectral band of a night vision system example under the special scene is given.
Proc. SPIE. 5640, Infrared Components and Their Applications
KEYWORDS: Signal to noise ratio, Eye, Visual process modeling, Imaging systems, Interference (communication), Bismuth, Modulation transfer functions, Quantum optics, Signal detection, Electro optical modeling
The MRC (Minimum resolvable contrast) is used to evaluate the performance of watched directly imaging system. The MRC mode is deduced on the basis of human visual system and signal detection. The model which involves the influence of spatial and temporal factors reflects the limited sensitivity in different object illuminance and contrast. The simulation result shows: The calculated limited sensitivity by MRC model is consistent with the reality of system. It is a more perfect model for evaluating the performance of low- light level imaging system.
A three band infrared integrated radiometer was developed for field measurement. The composition and work theory of the radiometer are described in this paper. The detailed calibration methods are analyzed for extended source and point source, and corresponding measurement results are given. With test data, the experimental results and instrument performance are analyzed in detail, in respect of the equivalent temperature of inter reference blackbody, linearity with target temperature, measurement error of point source and extended source. To lessen the influents of calibration for measurement, the attentive problems in actual calibration of extended source and point source are summarized, and satisfied results are acquired.
Proc. SPIE. 4922, Color Science and Imaging Technologies
KEYWORDS: Image fusion, Visual process modeling, Spatial frequencies, Composites, Colorimetry, Visual system, Human vision and color perception, Modulation transfer functions, Contrast sensitivity, Color vision
There are lots of experimental results concerned with chromatic contrast detection (based on changes in chromatic distribution over space or time), but compared with luminance contrast detection, there has been no theory to describe chromatic contrast detection and thus no mathematic model for isoluminant contrast sensitivity function. After reviewing of many papers, two reasons may contribute to this: I . Isoluminant contrast sensitivity function has the same description method as the isochromatic contrast sensitivity function which is unfit to express the chromatic changes. 2. The color vision is so complicated that further study is needed. Based on detailed analysis of previous works, this paper utilizes colorimetry fundamental principle to present a new theory for color contrast detection, and indicates that isoluminant contrast sensitivity function can be described by two aspects of chromatic changes——dominant wavelength and colorimetric purity. This theory can well explain that red-green and yellow-blue contrast sensitivity functions have similar characteristics.
The performance evaluation model (MRCeye model) of CCD low light level imaging system is deduced on the basis of human eye models and experimental data. It is involved signal to noise in time frequency and modulation transfer function in spatial frequency. It is showed by calculation that the minimum value of MRC is obtained when spatial frequency equals to f0 C/ mrad , MRC increase with the decrease of spatial frequency when spatial frequency f is less than f0 C/ mrad , MRC increase with the increase of spatial frequency when spatial frequency f is larger than f0 C/ mrad , namely, The MRC has band-pass characteristic that is according to the characteristic ofhuman eye.