2012 Vol. 5, No. 2
This paper reviews the development of a new configuration of interferometry, Self-mixing Interferometry(SMI). SMI is attractive because it doesn't require any optical part external to the laser and can be employed in a variety of measurements, ranging from the traditional measurements related to optical path length like displacements, small-amplitude vibrations, velocity; to sensing of weak optical echoes, like return loss and isolation factor measurements; and also to a special feature for the interaction with the medium, measurements of physical parameters, like laser line width, coherence length, and the alfa factor. Because it is also a coherent detection scheme, the SMI operation is close to the quantum limit of received field and the minimum detectable amplitudes of 20 pmHz or better are currently achieved upon operation on diffusive targets, whereas a corner cube allows half-wavelength counting mode or 0.5 m resolution on a dynamic range up to 2 m. SMI has a compact setup, and is easy to deploy in the field and can interface a variety of experiments from MEMS testing to rotating machine vibration testing to pickup of biological motility as described in the paper.
This paper reviews the outstanding advantages of space laser communication and gives the operating plans of main foreign communication links and their technological parameters. It describes the present situation of space laser communication in the United States, Europe and Japan in detail, and explains the key technologies of space laser communication. It points out that the transmission speed of the laser communication will be faster and faster in future and the communicating model also can be changed from the points to points to the relaying repeater and constructing space communication networks. Finally, this paper introduces the development of space laser communication briefly in China.
This paper reviews the functions of telescope enclosures in brief and summarizes the universal principle of observatory site selection. Then, it introduces the structure types, working characteristics and environmental conditions of typical telescope enclosures at abroad. By taking an enclosure with an aperture of 3.67 m in the advanced electro-optical system as an example, the thermal control scheme for the enclosure is analyzed, and the golden rule and methods of thermal design of modern telescope enclosures are proposed in detail. Furthermore, several kinds of key factors to be taken into account in design are pointed out. Finally, the design and analysis method for telescope piers are also discussed.
According to the basic properties of the plasma channel induced by femtosecond lasers, some issues about plasma channel guiding the electric energy and the Radio Frequency(RF) electromagnetic energy are analyzed, and several new concepts and technologies about this field are overviewed. The latest achievements of the theory and applications in this field are described emphatically. Finally, the development trends of femtosecond laser induced plasma channel to transmit energies are given.
In order to improve the performance of optical information processing components and to achieve high efficiency optical signals for static storage, a four-level double-Lambda cold 87Rb atomic system driven by two counter-propagating travelling wave fields is established, and the necessary Stationary Pulse Light(SLP) conditions of controlling coupling fields and phase modulation ways to control probe intensity are studied. First, the four-level double-Lambda cold 87Rb atomic energy level driven by two counter-propagating travelling wave fields is selected, and the forward resonance coupling field is switched on to guide only one forward incident signal into samples for detection. Then, the optical signals are stored and efficient SLPs are generated through switching on and turning off two coupling fields. The necessary conditions to generate efficient SLPs are obtained according to selecting different fine structures of energy level. Finally, the phase modulation method of control stationary light intensity is attained. The results indicate that the system can generate efficient SLPs with continue time nearly 80 s and the phase modulation can adjust the stationary light intensity periodically. Obtained SLPs satisfy the optical signal processing requirements for higher efficiency, higher fidelity, all-optical control and long timeliness.
In order to obtain accurate, reliable thermal boundary conditions for the thermal design, thermal analysis and thermal tests of space cameras, the transient space heat fluxes of space cameras working in sun-synchronous circle orbits are calculated. The relations of six orbit elements in space orientation of satellites are summarized, and the necessary parameters for the sun-synchronous circle orbit are given. The relative positions between sun vector and orbit, angles are calculated with STK program for the given sun-synchronous circle orbit, thus the upper temperature orbit and lower temperature orbit are oriented. Based on the theory calculation of space heat fluxes and taking some space cameras working in the given orbit as examples, a Finite Element(FE) calculation model for the space fluxes is constructed. Using IDEAS/TMG module, the transient space heat fluxes of upper temperature orbit and lower temperature orbit are calculated particularly. The transient change curves of solar radiation heat fluxes, earth and solar reflection heat fluxes and the earth and infrared radiation heat fluxes in an orbit period are obtained. The calculation results could be taken as input data of space cameras for thermal analysis and the simulation of space heat fluxes in space environment thermal tests.
The primary tube of a visible zoom lens and its mounting are designed by UG advanced simulation according to the characteristcs of a wide temperature range(-40-+55 ℃) and little optical axis variation(0.2 mrad), and the deformation patterns in different conditions are gotten by using finite element analysis. An estimation way to get the optical axis variation is proposed, by which the more reasonable structure type is obtained. The results from the lens transfer function test and vibration test show that the Modulation Transfer Function(MTF) is above 0.2 and the fundamental frequency is 117 Hz. The practical image is stable and clear, which indicates that the optimized design of zoom lens is reasonable.
The SiC scanning reflective mirror with a dimension of 460 mm290 mm used in a spaceborne optical remote sensor is studied. The composite form of triangle and quadrangle and the combination of open and closed back are explored for the design of lightweight scanning mirror. A new kinematic mount and a flexible structure in axis is taken to hold the mirror around the lateral surface. The flexible structure in axis is used as an interface to the kinematic mount to support the mirror, which can eliminate the impact of thermal stress induced by the mismatch of thermal expansion coefficient among the materials on the mirror surfaces. Optical performance of the mirror is analyzed by using Finite Element Method(FEM). Results indicate that the surface figure errors are 4.5 nm and 20.3 nm under a gravity load of 1 g and the temperature load change of 8 ℃ in different directions. The results show that the lightweight designing and supporting structure of this scanning reflective mirror meet the requirements of optical imaging, and can improve the stability of structure effectively. It can be an important reference for the design of big size scanning reflective mirror components.
Calculation of the effective emissivity of blackbody cavities by the Monte-Carlo method is reviewed. Firstly, the theoretical basis of Monte-Carlo method is expounded, and then the forward and backward ray tracing methods are illustrated. Compared with the forward ray tracing method, the backward ray tracing method can easily calculate the directional effective emissivity, and can get average normal effective emissivity and the hemispherical effective emissivity. Finally, the Monte-Carlo and theoretical calculation methods are compared, and it is confirmed that Monte-Carlo method is accurate in calculating the effective emissivity of blackbody cavities, whereas the disadvantage is slow computing speed.
To estimate displacement parameters for uniform linear motion-blurred images, a method of image registration based on phase-only correlation is introduced. The method is based on the translation characteristics of Fourier transform to search the translation between the images. The inverse Fourier transform of the normalized cross power spectrum for a pairs of images is a two dimension impulse function, and the translation displacement between the images can be finely retrieved from the location of the correlation peak. Combined with the image registration principle of phase-only correlation and the degradation model of spatially variant blur, the mathematical expressions of Point Spread Function(PSF) and Optical Transfer Function(OTF) for the uniform linear motion blur are described, and the effect of motion blur on the correlation registration is discussed. The relation between the variance of normalized cross power spectrum and the degradation of blurred images is demonstrated, which is only dependent on the displacement between the images and not on the blur in images. The experimental result shows that this method can detect sub-pixel-level shift parameters accurately and efficiently and the maximum registration error is only 0.489 pixel, the root of mean square error of image registration is 0.16 pixel.
In order to reduce or eliminate the image blur caused by the degradation in imaging process of a space remote sensing camera, the acquired images were restored to enhance the characteristic objects of images. First, a frequency-domain notch filter was adopted to remove noises in the remote sensing images. Then, the degradation function, namely, Point Spread Function(PSF) of the imaging system was estimated by ground characters with the knife-edge shape, and the estimated PSF was corrected with Gaussian fitting. Finally, the images were restored by using adaptive Wiener filtering with the fitted PSF. Experimental results show that almost all strip noises in the image are eliminated. After the denoised image is restored, its variance and gray mean gradient increase by 4.395 and 1.799, respectively, and also Laplacian gradient increases by 10.014. Experiments demonstrate that the restoration with Gaussian fitted PSF is beneficial to interpreting and analyzing the remote sensing images. After restoration, the blur phenomenon of the images is reduced, the characters are highlighted, and the visual effects of the images are clearer.
In order to solve the problem of low accuracy( 10 arcsec) in traditional real-time horizontal measurement methods, this paper introduces a new real time measurement method for the dynamic attitudes of a survey ship based on optical measurement. The model of precise optical angle encoder measurement+inertia synchronous duplex platform+horizontal attitude error detection tool is designed to ensure the tracking stability and to improve the measurement accuracy. Experimental results show that this method can provide more stable attitude data of the survey ship with greater precision(pitch:5.37 arcsec, rolling:3.60 arcsec) than those of the traditional Inertial Navigation System(INS). As a universal standard of precise measurement for moving carriers, this design can provide accurate real-time level of baseline information, or the accuracy level for INS accreditation of moving carriers.
Norland Optical Adhesive(NOA), a new type of polymer material, is used to fabricate the Mach-Zehnder thermo-optic switch in this paper. The optical properties of NOA film materials are characterized. The waveguides with good profiles are fabricated by the Inductively Coupled Plasma(ICP) method. The insertion loss of a 2.2 cm-length straight waveguide is 8.3 dB at 1 550 nm. The extinction ratio of the thermo-optic switch is 11 dB and the driving power is 83 mW when the DC bias is loaded on the electrodes. The switching property of the device is tested with DC bias, and the rise time and the fall time of the switch are 1.085 ms and 489.5 s, respectively. Experimental results show that the NOA material has great potentials in fabricating thermo-optic switches and other polymer waveguide integrated devices.