In this paper, three types of scanner which their width are varied with parabolic, hyperbolic and exponential
functions are studied. The equations of deflection angle and ray trajectory of three types of electro-optic scanner are
given and their deflection properties are investigated by numerical analysis. The deflection characteristics and
sensitivities are compared to each other. It is helpful for the design of electro-optic scanners with fine performance.
Using a coherent detection technique, the measurement of the phase-relation between transmitted and reflected paths for beam splitters is presented. A change in the phase of p and s polarization components of the reflected and transmitted light for a beam splitter can be determined. Two measurement schemes are presented: one for polarizing beam splitters and one for nonpolarizing beam splitters. Experimental results for the case of a polarizing beam splitter are discussed.
An optical 90-deg hybrid of birefringent crystals for freely propagating laser beams is presented. It consists principally of a quarter-wave plate, two pairs of birefringent crystal plates, and a polarization analyzer. The splitting and recombination of the signal and local-oscillator beams are achieved through the birefringence of the crystals, and a 90-deg phase shift is introduced between orthogonally polarized beam components by use of a quarter-wave plate. The optical hybrid has a self-compensating light path, and its correct function is demonstrated in a self-heterodyne measurement setup.
This paper researches the phenomenon of bi-grating imaging by the computer simulation. The process that white lights
are diffracted by two gratings with different space frequencies is simulated and the imaging characteristics are studied. A
bi-grating imaging relationship is given based on the simulation results. It agrees basically with the experiments.
Characteristic of electro-optic modulation of light propagating near the optic axis in a uniaxial crystal is well
known but not for the cases of propagating bias the optic axis. In this paper, two pairs of LiNbO3 crystal plates with the
same sizes consist of an optical system in where the sum of geometrically optical length of o-ray and e-ray is equal. And
then the characteristics of electro-optic modulation of light propagating bias the optic axis in LiNbO3 are studied
experimentally through a coherent received system. The additional phase shift caused by electro-optic effect is
measured. The relation of phase shift varying with applied
electric-field is reported when the angle between incident
beam and the optic axis is 45°. Based on above experiments, a new 90º optical hybrid will be developed.
of grating. First, we studied the reversibility of optical path of grating illuminated by monochromatic light, and then
illuminated by polychromatic light. We found that the optical path of diffraction of grating has partial reversibility.
Using the partial reversibility of optical path of diffraction of grating, we analyzed the spectral combination
characteristic of grating and the bi-grating diffraction imaging effect.
Two gratings consist of an imaging system in which a clear virtual image of an object is formed. The diffraction
properties of gratings have important influence on the information of images. In this paper, the imaging characteristics
of bi-reflection, bi-transmission gratings system and the transmission-reflection grating system are studied. The imaging
process and the quality of images of three systems are compared and some characters are summarized. It is useful for
the deep understanding of bi-grating imaging effect and its new applications.
Using the birefringence properties and the electro-optic effect of LiNbO3 crystal, an optical 90°-hybrid
with 2 input ports and 4 output ports is designed in this paper. The new optical hybrid consists mainly of two
pairs of LiNbO3 crystal plates with the same sizes, the modulating electrodes and a polarization analyzer. One
pair of LiNbO3 crystal plates split incoming signal beam ES and local oscillator beam ELO into four light
beams and the other mix them into two synthetic beams. By adjusting applied voltage on the LiNbO3 crystal
plates, 4 output ports from the polarization analyzer give the narrow mixed beams with a relative phase shift
90°. The optical hybrid has the advantage of low losses and good stability of the phase shift. It has the great
potential for wide applications in free-space coherent laser communications and laser radar.
Compared with direct detection, homodyne binary phase shift keying receivers can achieve the best sensitivity
theoretically, and became the trend of the research and application in inter-satellite coherent laser communications. In
coherent optical communication systems an optical hybrid is an essential component of the receiver. It demodulates the
incoming signal by mixing it with the local oscillator. We present a design of a 2*6 optical hybrid. 4 output ports of the
hybrid give the narrow mixed beams of the incoming signal and the local oscillator shifted by 90°for communication,
and the others give the wide mixed beams with a shifted degree of 180°for position errors detection. CCD captures the
interference pattern from the wide beams, and then the pattern is processed and analyzed by the computer. Target
position information is obtained from characteristic parameter of the interference pattern. The position errors as the
control signals of PAT (pointing, acquisition and tracking) subsystem drive the receiver telescope to keep tracking to the
target. The application extends to coherent laser rang finder.
The comparison of bi-grating diffraction imaging and the displaying of ordinary transmission hologram with white light
source, shows two different imaging methods have same essence, but different characteristic. In these two processes of
imaging, the light-wave of the object has been diffracted twice, both methods have to combine the dispersed image of
different wave length, so both of them have to employ the spectral combination characteristic of grating. The bi-grating
imaging equation not only is fit for the bi-grating imaging process, but also has guidance meaning in ordinary
transmission hologram displaying with white light source and the aid of grating.
Grating is well known for its dispersion characteristic. A new characteristic that we call spectral combination has
been studied in this paper. It is a reverse phenomenon of grating dispersion. Light incident on a grating is dispersed into
a spectrum. The same order diffracted lights of different wavelengths come from different places of the first grating
converged on the second grating and outgoing beam at the same diffraction angle is spectral combination. Both using
dispersion and spectral combination characteristic of grating, two gratings consist of an imaging system and a novel
grating imaging phenomenon will occur. In this case, a virtual objective image can be formed after the object waves are
diffracted by two gratings. This new grating imaging effect has close relation to spectral combination characteristic of
grating. The characteristic is studied by theoretical analysis and numerical simulation. A relationship between the two
gratings' spatial frequencies and diffraction orders that reflecting the spectral combination quality on certain condition is
given. The spectral combination property of Grating on general condition is discussed by numerical calculation. To
recognize the new property of grating deeply is very helpful for its application.
A novel experimental instrument of diffraction imaging and its applications are introduced in this paper. This apparatus is composed of movable mechanical parts, optical elements and computer image acquisition system. It can be readily used in the confirmation of bi-grating imaging phenomena and observation of the ordinary transmission hologram displaying with white light source.
For the test of communication-performances of intersatellite laser communication terminals (LCT's) in lab, we had designed an optical simulator for long-distance propagation of laser beams based on optical Fourier transformer and the cascaded imaging systems. Its maximum equivalent propagation distance reaches several hundred thousands kilometers and it can be used to evaluate the communication performances of LCT's under exact transmission distance. In this paper, effects of wavefront aberrations of lens on the simulator are studied in detail. Firstly, we estimate the influence of wavefront aberrations of Fourier transform lens and the cascaded imaging lens according to the 'Strehl intensity'. We found that the wavefront aberrations of Fourier transform lens caused important measurement error. Secondly, using the aberration theory, the influence of typical aberrations such as spherical aberrations, Coma aberrations, Tip/tilt aberrations of Fourier transform lens is analyzed. Finely, the measurement error caused by these aberrations is provided.
The gain of a transmitter for intersatellite communications is closely related to the performance of all the links. We calculate the transmitter telescope's gain with the help of the rigorous scalar diffraction theory and equivalent optical layout method. Furthermore, a comparison is performed with the conventional imaging method. The results show that the stop inside the telescope can affect the gain of the telescope. Finally, the gain is calculated under the condition of the aberrations. We find that different aberrations cause different effects.
We describe the rigorous results of a wide-angle laser beam scanner, obtained with the help of the vector refraction theory. Using the rigorous results, the distortion of the beam shape is discussed. The distortion to the beam varies with the different relative angles of double prisms. The scanner expands the beam in some directions while it contracts the beam in other directions. According to the conservation of energy, the distribution of the laser intensity is changed as well.
The characteristics of the terminals for the inter-satellite laser communication must be tested and verified on ground
before flight test. A pair of terminals for inter-satellite laser communications was developed for principle demonstration.
A terminal has two main subsystems. The first is one for the laser communications and the second one for acquisition,
pointing and tracking (APT). The optical methods and related system test-beds to measure and verify the performance of
the terminals in the lab room. In these programs, several novel ideas are proposed. With these ideas, whole programs can
be tested on ground in near-contacted field. The dynamic APT performances of an inter-satellite laser communication
terminal can be tested and verified by the combination of satellite trajectory simulator and a collimator-like laser
communication.
For on-ground performances testing and verification for intersatellite laser communication systems, a compact and multi-function optical testbed and a 2-D sub-micro-radian beamsteerer were designed. The testbed consists mainly of an optical simulator for long-distance propagation of laser beams, two CCD detectors, an autocollimation system, an interferometer, and a noise light source, for the uses is to measure far-field beam characteristics, transmitting powers, the wavefront errors and to evaluate the communication performances of any lasercom terminals with a aperture less than 280 mm in link level. The range of beam propagation distance of the optical simulator is from 2.8km to 3,5000km. An angular deviation yielded by the beamsteerer is to simulate the pointing error caused by all error sources. And a light source is to provide the noise-like illumination of changeable levels. Combined the testbed with the beamsteerer, it can measure the pointing errors and the tracking errors of the lasercom terminals, and estimates dynamic communication performances in the presence of random angular jitter. So the testbed has the potential to become all-purpose and tests the optical, communication and track performances for intersatellite lasercom terminals (ISLTs).
In this paper, an oscillatory characteristic of diffraction is observed in a weakly oxidized LiNbO3:Ce:Cu crystal during the holographic recording. Experiment indicates that, after the first diffraction maximum, there exists an optimal switching time from the recording step to the fixing step which can produce a high diffraction of fixed hologram. High diffraction efficiency of 70% is observed in LiNbO3:Ce:Cu crystal. For theoretical simulation, the time-space dynamic evolution of the nonvolatile holographic recording in doubly doped LiNbO3 crystals by jointly solving the two-center material equations and the coupled-wave equations is performed. The results show that the optimal switching will lead theoretically the fixed diffraction up to 100 % with a suitable switching time. This method provides us a new idea to obtain high persistent diffraction efficiency. The relationship between the optimal switching and the crystal thickness is studied.
It is required for the laser communication that laser beam transmitted from the optical terminal must be highly parallel. Optical diffraction limit angle is the minimum divergence the beam can obtain while limited by the definite aperture under ideal conditions, here wavefront still has an error of 0.3 wave. This paper introduces a new method for wavefront analysis. In this method a circular aperture diaphragm used to sample the tested wavefront, a focusing lens, a microscope objective and a fiber optic probe are arranged coaxial. Axial intensity profile behind the focusing lens is plotted by registering the positions of the microscope objective on the axis and the readings of the radiometer. The sampled wavefront height is estimated from the distance between two symmetrical positions along the axis where the intensity is zero. The tested wavefront height is calculated from the sampled wavefront height. The theory and the simulation results are given. It can be applied in coarse measurement of any wavelength laser wavefront. Due to simplicity of the method and its low cost, it is a promising method for checking the collimation of a laser beam.
As a step towards the development of a full scale intersatellite laser communication system, the on-ground simulation experiments and performances validation are necessary in the beginning. In this paper, we designed an optical simulator for on-ground communication performances validation of the free-space laser communication system. The simulator basically consists of a Four-transform lens of big aperture and long focal length and following three optical imaging amplifiers. It becomes possible to evaluate communication-performances of optical terminals by distance transform and background noise simulated. System analysis and simulated experiments show that the simulator is feasible and has the great potential for wide applications.
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