To solve the problem on coarse tracking and fine tracking of single detector multiple-axis in space laser communication, a necessary condition was obtained by analyzing the two-dimensional matrix associated control. Based on this condition, a single detector composite shaft structure was proposed that worked in a new way. In the process of tracking, the camera directly worked with a sub axis actuator to complete the fine tracking, while the spindle tracking information was provided by the shaft axis angle deflector of the sub axis actuator. And then the image processing algorithm, position detecting algorithm, and the coarse and fine servo control algorithm were implemented in field programmable gata array that effectively realized the light and compact design of the system. An experimental system was built in the laboratory, and the field programmable gata array hardware and the system tracking performance were tested. The results show that the accuracy of tracking by the single detector compound control system is better than 3 μrad, which lays a certain foundation for the engineering.

Based on phase noise and phased array antenna theory, using original linear array antenna pattern function and optical fiber link noise figure function, the theoretical formulas that describe relationship between the figure in optical fiber delay line links noise, the number of antenna elements and beam pointing error were derived by reasonable approximation according to actually beam pointing error. The normal optical fiber link parameters were applied to the simulation. The results demonstrated that mean square deviation of phased array antenna beam pointing error increases with the increasing of optical fiber link noise figure and decreases with the increasing of elements number of the array, the phased array antenna beam pointing error is in proportion to 1/2 power of optical fiber delay line links noise figure, in inverse proportion to 3/2 power of number of array elements. In phased array antenna operating frequency bands, it is more obvious impact of optical fiber delay line links noise in low frequency band.

With the development of broadband access network, Ethernet Passive Optical Network (EPON) becomes a candidate for fiber to the home. As the huge amount of Optical Network Units(ONUs), the deployment of EPON is affected by the cost of ONU. A low cost EPON (ONU using Bi-directional Optical Sub-Assembly (BOSA) with Flexible Printed Circuit (FPC) was proposed. The FPC-BOSA is mounted directly to the ONU board. Small signal response of FPC was simulated by Finite Element Method (FEM), the results prove that the high speed performance do not degrade. However, there is no individual transceiver module in this proposal, so bit error tester can not be used to test the optical performance. Measurement system using network tester was set up. For the transmitter, the extinction ratio over 10 dB and the average optical power over 1 dBm were obtained from 0℃ to 70℃. For the receiver, the estimated sensitivity achieves -27 dBm.

Aiming at the issue that image-resolution of the electro-optical imaging system can be depressed by the image jitter, a ration analysis method of the requirement of jitter was proposed. The jitter was classified into high frequency jitter and low frequency jitter, the high frequency jitter divides into Gauss, sine and linear, the low frequency jitter was defined as linear jitter, the modulation transfer function of them was given, and the modulation transfer function of the whole system was built. Based on the resolution equal notion and the modulation transfer function model, the ration analysis method of the jitter was given, the analysis flow and arithmetic was also presented. At last, the method was simulated through computer based on specially appointed system parameter and the analysis flow. The simulation results indicate that the low frequency linear jitter tolerance is max, the high linear jitter tolerance is next, the high frequency Gauss jitter tolerance and the high frequency sine jitter tolerance is min.

Traditional climbing search algorithm cannot usually focusing accurately due to the interference of evaluation function local extremum effected by measure environment. A searching algorithm of auto-focusing based on MTF auxiliary focal judgment was introduced to improve the climbing method. Definition evaluation function and MTF values of images were considered at the same time. And based on those results, search direction was judged. Slanted-edge method was improved to calculate the image MTF values accurately based on the auto-selection of slanted-edge area. At last, the principle and implementation of the improved algorithm was given. In the theodolite auto-fousing system, the system imaging effect was validated, and different initial position and circumstance were considered using the proposed searching algorithm. The experiment results of theodolite auto-focus system show that the improved climbing search algorithm can effectively eliminate the local extremum disturbance, and make the system searching focusing accurately and reliably.

According to polarization imaging theory, at least three linear polarized images of the same scene were required. A polarization imaging system based on division of aperture technique was designed in this paper so that the moving objects or a rapid changing scene was able to be imaged simultenously. The system MTF in all the view fields at 56 lp/mm was no less than 35% after optimization. Finally, polarization imaging experiments were conducted in a low light level condition and experimental results were analyzed qualitatively. Moreover, polarization imaging precision versus illumination was intestigated. By changing the incident illumination level and computing the acquired polarization images, the degree of polarization and angle of polarization were compared with the corresponding true values. The results show that polarization imaging can improve the quality of low light level images.

A remote energy control system for shengguang-II high power laser is designed, including a half-wave plate-polarizer combination attenuation device and a closed-loop negatinve feedback control method. For the optical adjustment programs, a half-wave plate-polarizer combination attenuation device is designed to control the laser energy. For the control algorithm, a closed-loop proportion integral derivative control adjustment of energy is realized. For the adjustment precision, it achieves a regulation accuracy of 1% and the ralative error is lower to 0.1%. The remote energy control system of high power pulsed laser in this article uses the communication of eneryg meter, stepper motor and computer software to achieve the closed-loop proportion intergral derivative control of the laser energy. It has the feature of widdly range of applications, easy adjustment, high control accuracy and good expansibility.

A high average power passively Q-switched LD side-pumped laser system at 1 064 nm was set up by using Nd∶YAG/Cr∶YAG/YAG composite crystal. With 85% initial transmission of Cr∶YAG, the average output power of 1 064 nm was measured. Under the maximum pump power of 187.5 W, the maximum average output power of 83.68 W at 1 064 nm was obtained. By frequency doubling the 1 064 nm laser output in a KTP nonlinear crystal, 27.2 W green laser pulses at 532 nm with the corresponding pulse width of 210 ns and the repetition rate of 21.2 kHz were produced under the maximum pump power. The green laser single-pulse energy was 1.28 mJ and the peak power was 6.1 kW. And the optical-to-optical conversion efficiency of pump light to frequency-doubling light was 14.5%.

Femtosecond laser processing has litle-thermal effects, high precision, and is not particular about materials. Aiming at the machining requirement for nozzle′s spray holes, as a key part of the high pressure common rail injection system for diesel engine, a femtosecond laser processing apparatus with three-wedge scanning system was designed for technical research of taper holes′ machining. Then tests of the taper holes′ physical dimensions and the flow rate of the fuel jet nozzles were carried out with three coordinates measuring machine (measurement accuracy 1.2 μm) and high-pressure liquid flow test bench for the injector(measurement accuracy ±0.1%). The experimental results show that the designed apparatus can machine nozzles, and the performance is able to meet the application requirement of Euro V emission regulations. The technique has important significance for improving the level of automobile industry and domestic emission standard of diesel engined car.

The light path stability of ring laser gyro determines its performance, while the internal and external pressure difference of resonator is one of the important factors influencing the light path stability of gyro. To study the low air pressure assembly causing light path variations and the loss changes of ring laser gyro, the micro-deformation of mirrors was simulated and calculated by ANSYS software. The results indicate that under the condition of the low air pressure, there is maximum-deformation in the center of the mirror, therein to, the maximum-deformation of spherical mirror is 545 nm, and the maximum-deformation of plane mirror is 31 nm, thus this deformation leads to the light path′s deviation of 390 nm from the center of diaphragm and brings out a curvature variation of 174 mm for the spherical mirror. Furthermore, the deformation influence on the light path variation and the loss changes of ring laser gyro is calculated in theory,the results show that this deformation synthetically cause about 2%~3% loss variation of resonator, among them the variation of curvature is the main cause of loss variation. To increase the groove depth or decrease the air difference between outer and inner of the resonator will effectively reduce the light path variation. A test system is built and verifies that the results of calculation are correct.

To overcome the disadvantage of the system uniformity reduction when a freeform surface constructed on the point source assumption is applied to the extended sources systems, a new feedback optimization algorithm based on the partial differential equation was proposed. Based on the point approximation, the initial surface structure were obtained through the numerical solution of the partial differential equation under the establishment of the radiation model of the extended light source. Then the shortcoming of the initial surface structure was analyzed when used for uniform illumination with extended sources under the circumstance that the rays transmission direction and the optical axis intersect. Therefore the proposed algorithm re-optimized the reflector to improve the uniformity by renewing the distribution of the target region, with the illuminance distribution in last simulation experiment as feedback. To illustrate the effectiveness of the proposed method, simulation experiments were carried out with TracePro. An extended light source with the size of 3 cm in diameter was used in experiments, in which total five million rays were computed. The light tracing experiments show that the uniformity of the object region increases from 60% to more than 90%, which demonstrates that the feedback design method can improve the illumination uniformity of the target surface effectively and provide some theoretical guidance for the improvement of the realistic lighting systems.

A novel log-polar image sensor based on non-uniform lens array was proposed in this paper. Non-uniform sampling and log-polar mapping were testified by building mathematic model. The validity of the model was verified by some design examples. Meanwhile, some key parameters were analyzed and simulated, including blank spot radius (r0), growth coefficient (q) and fill factor (ηf). Several conclusions can be obtained from the simulation. r0 decreases with M on the condition that N is unchanged and increases with N on the condition that M is unchanged. Meanwhile, ηf increases with N and tends to π/4 if N≥40. So, appropriate growth coefficient (q=1.106) was obtained on the condition that N=40. The results from the simulation support theoretical foundation for realizing log-polar transformation of based on non-uniform lens array and useful to design a novel log-polar image sensor.

Motion parallax stereoscopic display exists the problems of multi-viewing field, sudden jumps between subzones, narrow main watching field, blurring etc, because of its low NA and aberration. In this paper, the idea of discrete sampling was applied to analysis the motion parallax stereoscopic display system. Based on the analysis and considering the manufacture procedure, a double micro-lens array screen combined with curve reflection surface was proposed. The simulation results show that this design makes improvement on the 3D display performance and viewing angle achieves almost 60 degrees. This proposal is of great significance to promote the practical application of the three-dimensional system.

A optical system of lander optical payload was designed for the requirement of focusing on objects. A noval focusing type was made that the optical system could keep fixed focal length during focusing. An approaching telecentric optical structure is designed, the optical system was made up of front fixing lens unit and rear focusing lens unit. The front fixing lens is a kind of afocal optical system. The rear focusing lens is at the back of fixing lens unit. The optical can image objects from 0.8 m to infinity in focus by moving rear focusing lens unit. The optical system with spectral range from 400 to 1 000 nm, fixed focal length of 50 mm and F number of 8 can focus on objects located within the range of 0.8 meter to infinity. At last, The modulation transfer function of the optical system can reach to diffraction limit, and distortion is less 1%. The image quality can meet the requirement to the optical system. By the analysis of optical system tolerance, the optical system can keep good imaging quality after fabrication. The optical system can be used to explore moon, mars and asteroids.

The combination of flexure and PZT actuator is a significant method to achieve precision adjustment. A precision adjusting mechanism with flexure hinges was introduced and theoretical calculations were carried out to get the working principle of it. The optimization design and finite element analysis were also taken to acquire the axial stiffness of a typical opto-mechanic structure. The results show that the maximum axial displacement of the optics can be bigger than 200 μm under the yield limit of the material. Secondly, a modal analysis is taken to obtain the natural frequency of the mechanism. The results indicated that the first resonant frequency of the structure is 185.1 Hz. It can be seen that the natural frequency can satisfy the work specification of the lithographic lens. At last, the influence of the applied force of the PZT to the surface figure of an optical element was obtained. The result shows that the influence of the force F=14N to the RMS of the optic element is 4.41 nm. All these results provide useful evidences for the applyment of this mechanism for optic adjusting.

In order to evaluate the temperature effect of telescopes, a precise thermal finite element model consists of telescope optical assembly systems, mount structure and electrical equipment was established. Temporal and spatial temperature distributions of the optical assembly and telescope structure were calculated under various thermal conditions including conductions, air convections，radiation and heat flux loading. Moreover, the thermo-elastic analysis was made to obtain thermal deformations of the telescope structure based on the resulting temperature distributions. The obtained results show that temperature variation has large effect on telescope mount and main optical system, and induced displacement between primary and second mirror has a magnitude of millimeter, so it must be controlled strictly. At last some thermal control ways were given in terms of protection dome, mount, primary mirror and so on.

The design of an infrared zoom optical system based on 480×6 focal plane array detector was introduced. The zoom theory, diffractive theory and aspheric design method were used in the aberration balance. The operating wavelength region was 7.7 to 10.3 μm, F-number was 2.62, and zoom ratio was 15 to 1. The result indicates that the zoom optical system could obtain better optical performance in all zoom range, by the general analysis and evaluation of modulation transfer function, distortion curve, diffractive optical element, and zoom curve analysis. The overall length of optical system is 480 millimeter, back focal length is 28 millimeter, modulation transfer function is more than 0.3 and distortion is less than 5 percent.

A hybrid refractive/harmonic diffractive infrared lens beyond normal temperature was designed. The infrared lens was consisted of three lenses, including one aspheric surfaces and a harmonic diffraction surface which made the lens have compact structure and light weight. The experimental results show that the modulation transfer function is above 0.42 and 0.35 in the temperature range of -120～100 ℃ when the working wavelength in 3.8～4.2 μm and 8.8～11.2 μm, and the efficient focal length is 54.68 mm. It is compatible with infrared dual-color detector which had a format of 320×240 and the pixel pitch of 30 μm.

Based on sintering process and screen printing technique, a novel groove shape cold cathode was developed. The black insulation slurry was sintered to fabricate the bottom insulation layer, in which a gradient surface existed. The silver slurry was screen-printed on the bar electrode. With the baking and sintering process in proper sequence, the silver electrode was formed. Using fine sandpaper, a proper polishing process for silver electrode was conducted, so a smooth electrode surface was obtained. Due to the special silver electrode shape, a larger field enhancement factor was achieved easily. Carbon nanotubes were prepared on the silver electrode to form the field emitters. The dense carbon nanotube layer would cover the silver electrode surface completely. Owing to the special edge field enhancing effect, lots of electrons would be emitted from the carbon nanotube. The top insulation layer was used to restrain the side electron emission of carbon nanotube. With the groove shape cold cathode, a triode field emission display was fabricated, which exhibited good field emission properties and better luminescence image uniformity. Comparing with the common cold cathode field emission display, the turn-on electric field could be reduced from 1.86 V/μm to 1.78 V/μm, the maximum field emission current had been increased from 1 537 μA to 2 863 μA, and the maximum luminescence image brightness would be enhanced from 1 386 cd/m2 to 1 865 cd/m2. The developed fabrication technology had a potential practical application in field emission display.

An integrated device was designed which was composed of thermo-optic switch and delay line array. Rsoft software was used to optimize the parameters of digital multi-mode interference thermo-optic switch, and the varied output signal intensity can be achieved with changing the temperature of an electrode. Then a delay line with a helical structure was designed. Spiral waveguide structure was simulated by BPM software. Considering the size of the device and the loss parameter, a reasonable bend radius of the spiral structure was designed. The integrated delay line array structure with the thermo-optic switch has a maximum delay time of 399.4 ps and the corresponding delay interval is 9.2 ps. The device has three layers, which are fabricated by using SiO2 as lower cladding layer, SU-8 photoresist as core layer and polymethylmethacrylate as upper cladding layer. By spin coating, lithography and wet etching, an integrated device with 1×4 MMI thermo-optic switch and delay line array was fabricated, and near-infrared field patterns of the delay line array was tested with insertion loss of 15~19 dB.

In order to improve the retroreflctance of the retroreflect sheeting, the properties of invalid light in micro corner cube prism were studied theoretically. By using the theory of geometrical optics, the outgoing way of invalid light in single cube was analyzed, and the properties of invalid light in single cube corner were given. Based on the single cube, the characteristics of invalid light of cube array were studied, the result that a part of invalid light could turns to effective light was found. The reflection principle, and variation law with the bottom thickness of invalid light which in corner cube array were analyzed. Testing and verifying by the optical software Tracepro, the retroreflection curve of single invalid area and small array were obtained. The analysis and the importance of corner array thickness on invalid light were proved by the simulation results. With practice, suggestions of design corner array were given. The obtained results provide theoretical foundations for improving retroreflection ratio of the micro prisms and reasonable design of micro prisms bottom thickness.

In order to obtain high-precision displacement measurement, a mathematical model for measurement deviation was constructed according to the ideal position model and signal processing methods of position sensitive detector. It indicated that the measurement deviation of system decreased with the increase of the light spot intensity, while increased with the increase of the electrical noise. A displacement measurement experiment was designed to verify the model. The experimental system included an infrared light-emitting diode and a pillow type position sensitive detector and its test circuit board. Displacement measurement experiments of 21 position points were carried out in nine different groups of spot intensities separately. The distance between every two position points each was 0.3 mm. Each group of displacement measurement data was fitted by using MATLAB CFTOOL tool, with root mean square error as a parameter evaluating the precision of position sensitive detector displacement measurement. The result shown that the precision value and its variation trends in the displacement experiment are consistent with that of model calculation.

An electrically controlled continuously focusing lens was introduced based on Polymer Dispersed Liquid Crystal (PDLC). Etching a hole on the upper surface of the electrode attaching to the PDLC cell to form an asymmetric electrode, a non-uniform electric field was induced. Then the non-uniform distribution of the refractive index in the PDLC cell was generated and a controlled zoom lens was formed. The basic principle of the focusing lens was also introduced, the effects of the lens aperture on the focal length of the PDLC lens were analyzed, and the relation between the focal length and voltage was measured with the diameter of 3 mm and 6 mm respectively. The results show that, with voltage ranging from 50 V to 170 V, the focal length of the PDLC lens was reduced from 1.361 63 m to 0.429 21 m in the diameter 3 mm or from 1.769 92 m to 0.548 43 m in the diameter 6 mm of the hole.

In order to meet the requirements of nano or even hypo-nano measurement accuracy in phase-shifting interferometry, multi-step phase-shifting algorithms with lower sensitivity to errors are needed. Based on traditional 4 and 3 steps algorithms, class A and class B of 5 to 13 steps phase-shifting algorithms were deduced based on extended averaging technique.Take 5, 6, 7 and 13 steps algorithms as example, suppression characteristics of algorithms to PZT phase shift error and CCD non-linearity error were compared through simulation and numerical calculation.The results show that the error suppression effect to above two error sources becomes better with the increasing of its steps, but when the steps reach a certain number, the values of errors are insignificant for the measurement.Class B algorithms have enhanced phase shift error suppression effect, and as for large phase shift error,class B algorithms are preferred.Class A algorithms are almost completely immune to 2nd order CCD non-linearity error, class B algorithms have some sensitivity to this error,but the influence are very small for most high accuracy CCD in common measurement.Also, the phase noise should not be neglected in measurement, and maximum value of PV wavefront measurement error caused by phase shift noise is larger than the noise itself in many times calculation. Wavefront errors of different algorithms caused by different errors were acquired, and the research can provide favorable reference for the using or choosing of suitable phase-shifting algorithm in actual interferometry.

Liquid crystals with dielectric and optical anisotropy have the ability of optical phase efficient modulation. When the liquid crystal system is placed in external electric field, the director of liquid crystal system will be redistributed. In this paper, the optical modulated effect of electronically controlled liquid crystal light valve was studied experimentally and theoretically. The result shows that threshold voltage of light valve is about 4 volts. And when external voltage is higher than the threshold voltage, the transmitted intensity of liquid crystal light valve will present the aperiodic properties. According to the continuum elasticity theory model, the liquid crystal director distributions in the electric field were studied by numerical methods, and found that the aperiodic modulation of transmitted intensity is depending on the distribution of the liquid crystal directors critically. It is the theoretical and experimental basis for the study of polarization-modulation characteristics.

According to the second-order moment of nonparaxial scalar beam based on the accurate definition of light intensity, the beam waists, far-field divergence angles and quality factors of truncated nonparaxial scalar Gaussian beams under different waists and diaphragm apertures were calculated, and the parameters were compared with the counterpart ones of free Gaussian beams and planar waves diffracted by small circular aperture. Numerical calculation results show that truncation parameter, which is defined by the ratio of aperture radius to beam waist, plays an important role in the propagation characteristics of truncated Gaussian beams. Truncated nonparaxial scalar Gaussian beams follow the same propagation laws of free Gaussian beams when R/ω0>2 which implies that the influence of diaphragm aperture can be ignored when diaphragm aperture is twice of waist for nonparaxial scalar Gaussian beams defined by accurate definition of light intensity. Meanwhile, truncated nonparaxial scalar Gaussian beams tend to truncated planar waves when R/ω0<0.3. This means that Gaussian beams can be treated as planar waves when aperture radius is 0.3 times of beam waist. When truncation parameter is between 0.3 and 2, both the effects of waists and diaphragm apertures should be taken into account.

The phase-sensitive optical time-domain reflectometer systemissensitive to ambient environmentsuch as sound waves, air flow and transient high-frequency noise. Thus the practical signal-to-noise-ratio is always low, the real intrusion signals are always severely obscured and difficult to be detected, as a consequence, false alarm occurs frequently. To solve the problem, a signal processing schemeusing feed-forward neural network together with singular spectrum feature extraction algorithm was presented for disturbance detection. The main points of the method were mapping the slidinglongitudinal time series to a sequence of multi-dimensional lagged vectors which form trajectory matrix and computing the singular value decompositionof the trajectorymatrix. This method can effectively eliminate sound waves and transient high-frequency acoustic noise, etc. Performance results showthat with breeze interference, the correct detection rate is 90% and false alarm rate is less than 2% at a range of 14 km.

Optical fiber methane gas sensing system based on differential absorption was investigated. Two distributed feedback laser diodes were used in the system. The wavelength of the reference light source was 1551nm and the wavelength of the measurement light source was 1653nm, which was located around the absorption peak wavelength of methane. The methane absorption peak was detected by scanning the wavelength of the measurement light source, and then the concentration of methane was measured by comparing the output power at the absorption peak with that not at the absorption band. The system possesses the properties of high resolution, good stability and a measurement resolution of 0.038% is achieved for methane detection.

The Offner imaging spectrometer was built on the basis of the double mirror system, and its initial structure was obtained through solving optical path function. Through simulating and optimizing the initial structure using professional optical design software (Code V), the high image quality of spectrometer was obtained. Its root mean square spot diameter decreased obviously, and modulation transfer function curves in meridianal and sagittial had good imaging results. The study can eliminate overly complex aberration derivation process, and obtain high image quality Offner spectrometer structure in a wide spectrum (400~1 300 nm). It can provide a theoretical basis for the construction of the spectrometer.

To address the limitations of conventional techniques, a method of principal component analysis and BP neural network was discussed to diagnose and classify citrus HuangLongBing. Data was obtained by a hyperspectral imaging system with the wavelength range of 370~988 nm, its high dimension data was reduced by principal component analysis, and then BP neural network was used to model for classification. The results showed that the first four principal components cumulative variance contribution rate achieved 97.42%. On one hand, BP neural network classification accuracy rate achieved 85% or more; on the other hand, after the principal component analysis, classification of BP neural network accuracy substantially was more than 90%. This method for nondestructive testing of citrus HuangLongBing is feasible.

Based on the Off-axis Cavity Enhanced Absorption Spectroscopy (OA-CEAS) technique, a high sensitivity pollution gas detection system was made by using a tunable near infrared diode laser as light source and a high finesse optical cavity with two plan-concave mirrors of reflectivity of 97.97% as absorption cell. The absorption spectra of N2O gas mixtures centered at 6 561.39 cm-1 were obtained. The relationship between the absorption intensity and gaseous concentration was obtained by recording the absorption spectra of N2O gas mixtures at different concentration. The line-width of absorption spectroscopy vs the gas pressure and the detection limit was discussed as well. The minimum detection concentration was found to be 86 ppm using this cavity enhanced absorption spectroscopy system. Indicating the cavity enhanced absorption spectroscopy is a sensitive, easy manipulated, robust and simplified technique, which can be used for rapid gas analysis.

Surface plasmon polaritons propagting along the silver nanowire was studied by near field scanning optical microscopy with twoprobes. In the experiment, one of the probe connected tolaser is positioned on one end of the silver nanowire to exicte surface plasmon polariton in near field, and the other probe scans along the silver nanowire to collect surface plasmon polariton in near field. The experimental result shows that surface plasmon polaritons are excited by the probe efficiently, and someof them reach the distalend facet of silver nanowire by propagating along the gap of silver nanowire and silica substrate. Finite element method is used to calculate the field distribution of surface plasmon polaritons modes on silver nanowire, which shows there are two surface plasmon polaritons modes with one as fundamental mode and the one as high mode. The fundamental mode of surface plasmon polariton, with its energy bounded to the gap of silver nanowire and silica substrate, suffers less scattering loss and can reach the other end of the silver nanowire. And the high modeof surface plasmon polariton attenuates quickly due to the scattering on the surface deffects. With the fundamental mode of surface plasmon polariton as information carrier, the efficiency of integrated optical device can be increased for its low propagation loss. What is more, the security of information transmission is improved since theenergy of the fundamental mode is bounded to the gap without scattering during propagtion, which is important in optical conmunication.