Superdiffraction emitting, i.e. far-field spot compression without energy loss in main lob, in space laser communication can increase the main lob energy density. A smaller far-field spot in conjunction with a higher main lob energy density can improve the detection accuracy greatly, and enhance the communication capability of space laser communication system as a result. So superdiffraction emitting is of great significance to space laser communication. In most of the spot compression approaches, the main lob will suffer considerable loss of energy caused by the compression. Aiming at the superdiffraction emitting in space laser communication, we propose two schemes to obtain far-field spot compression without energy loss in main lob. One scheme is based on SA algorithm. We first design the intensity distribution in the far-field receiving plane to meet the particular requirement of space laser communication. According to the desired intensity distribution, we obtain the phase profile of the diffractive phase element (DPE) using the SA algorithm. Placing the designed DPE on the emitting plane, the superdiffraction emitting is achieved. The other scheme is based on YG algorithm. By using the algorithm, we convert the Gaussian beam into an appropriately designed high quality uniform beam in emitting plane. Using the high quality uniform beam as the emitting beam, we then gain far-field spot compression without energy loss in main lob. By means of the two schemes we proposed, the superdiffracion emitting in space laser communication is obtained.
A simple channel model of wireless optical links based spatial coding is described and two basic channel constraints are
outlined. For representing the spatial patterns as signal points, a signal space based 2-D orthonormal basis functions is
defined. After that, critical measures of performance are also defined as metrics for comparing candidate modulation
schemes. Then three candidate modulation schemes exploiting spatial dimensions are proposed, which are spatial on-off
keying, spatial pulse position modulation and spatial quadrature amplitude modulation schemes. At last, the three
modulation schemes are compared by power efficiency and bandwidth efficiency. The appropriateness of each scheme is
Based on electro-optic effect in crystal, a novel laser ranging method is proposed. A special designed mono-block LiNbO<sub>3</sub> crystal is laid after the laser transmitter. The <i>CW-</i>laser emitted from the transmitter propagates through the crystal and travels forward to the measured target. After being reflected by the target, the laser goes back and crosses the same crystal. Electric pulses with the steep enough edges are loaded on the crystal. Based on electro-optic effect, double refraction and internal double reflection effect in crystal, the crystal cuts off the round-trip light beams, and reflects a light pulse cut out by the crystal to a detector aside from the original beam path. The pulse width <i>T</i> is the period that laser goes forward and back between the crystal and the target. From the <i>T</i> one can get the measured range <i>R</i>. The feasibility of this method is proved by our experiments and a brand-new way for the laser ranging is provided.
An electrically controllable radial birefringent pupil filter is proposed in this paper. It consists of two polarizers and an improved electrically controllable optical azimuth rotator which has two λ/4 retarders, one electro-optical element and one radial birefringent crystal. Evolution and distribution of polarization states of this pupil filter is discussed. The most interesting and useful advantage of such a structure is that characteristic of intensity distribution near focus can be obtained merely controlling the applied-voltage for optimal electrical inductive phase difference Γ of the electro-optical element and azimuth angle of radial birefringent crystal. And the Γ zones are given where transverse superresolution and extended focal depth or focal shift can simultaneously be obtained.