We have demonstrated a single frequency mid-infrared optical parametric oscillator pumped by a high power continuous wave single frequency fiber amplifier. The pump power was 15W and the corresponding extraction efficiency was 56%, which is close to the theoretical calculated maximum efficiency of 70% under Gaussian beam assumption. In the experiments the volume Bragg grating was 14.9 mm long with the diffractive efficiency of 99.5% at 1550.5 nm. The diffractive spectral linewidth was 0.27 nm. When the working temperature of the PPLN crystal was 51.5°C and the poling period was 30.5μm a stable idler radiation at 3400 nm was generated. To obtain single frequency operation, an uncoated YAG inter-cavity etalon with 5 mm thickness was inserted into the folded cavity. Stable single frequency operation was obtained with the spectral linewidth of 37.5 MHz and the output power of 2.2 W. The central wavelength stability was better than 520 MHz over 1 hour, which was limited by the resolution of the spectrometer. By changing the angle of the YAG etalon the central wavelength of the idler was varied in the range of 0.24 nm.
Laser echo signal simulator is one of the most significant components of hardware-in-the-loop (HWIL) simulation systems for LADAR. System model and time series model of laser echo signal simulator are established. Some influential factors which could induce fixed error and random error on the simulated return signals are analyzed, and then these system insertion errors are analyzed quantitatively. Using this theoretical model, the simulation system is investigated experimentally. The results corrected by subtracting fixed error indicate that the range error of the simulated laser return signal is less than 0.25m, and the distance range that the system can simulate is from 50m to 20km.
LADAR echo signal simulator is one of the most significant components of hardware-in-the-loop (HWIL) simulation systems for LADAR, which is designed to simulate the LADAR return signal in laboratory conditions. The device can provide the laser echo signal of target and background for imaging LADAR systems to test whether it is of good performance. Some key technologies are investigated in this paper. Firstly, the 3D model of typical target is built, and transformed to the data of the target echo signal based on ranging equation and targets reflection characteristics. Then, system model and time series model of LADAR echo signal simulator are established. Some influential factors which could induce fixed delay error and random delay error on the simulated return signals are analyzed. In the simulation system, the signal propagating delay of circuits and the response time of pulsed lasers are belong to fixed delay error. The counting error of digital delay generator, the jitter of system clock and the desynchronized between trigger signal and clock signal are a part of random delay error. Furthermore, these system insertion delays are analyzed quantitatively, and the noisy data are obtained. The target echo signals are got by superimposing of the noisy data and the pure target echo signal. In order to overcome these disadvantageous factors, a method of adjusting the timing diagram of the simulation system is proposed. Finally, the simulated echo signals are processed by using a detection algorithm to complete the 3D model reconstruction of object. The simulation results reveal that the range resolution can be better than 8 cm.
With the development of optical fiber communication, dense wavelength division multiplexing (DWDM) system is important for the rapid management of multi-wavelength in the core node of the optical transmission network. In this paper, a reconfigurable optical add-drop multiplexer (ROADM) based on the tunable Fabry-Perot (F-P) array is proposed. An optical switch with high isolation and low crosstalk is designed by using the characteristics of filtering and tuning for the F-P array. The principle, structure, and function of the tunable F-P array are introduced. The characteristics of filtering and tuning for the F-P filter are also calculated, and the factor for the isolation, crosstalk, response time and insertion loss are analyzed. A single physical channel ROADM with 16 signal channels, which operates in C-band, is designed and optimized by simulation.
An infrared scene projector with high spatial resolution using the visible to infrared transducer is described in this paper. The film transducer is fabricated by MEMS technology. The single pixel with 25×25μm in sizes and 35um at intervals in a transducer which is 76.2mm (3 inch) diameter is realized. So, the array size of the film transducer is more than 1024×1024. Illuminated by a visible light projector with different intensities, the equivalent black body temperature of the transducer could be varied in the range of 293K to 573K. The emission spectrum is similar with the blackbody and the gray scale is more than 200.
Infrared target simulator is an important unit in guidance hardware-in-the-loop simulation systems. It is used to simulate
the radiation and motion characteristics of target, decoy and background. This paper proposed a multi-channel IR target
simulator. It could generate one IR point target, two pairs of IR decoys and background respectively in the same field of
view of the seeker’s optical system simultaneously. An IR imaging fiber bundle as the focal plane of the projection optical
system was used to compound the target, decoys and background. The compound scene was projected to the seeker by the
projection optical system. In IR imaging channel, IR scene was generated by an optical film chip as a visible to thermal
transducer which was placed in a vacuum cell. The simulated temperature range of IR scene could be from room
temperature to 430K.The thin film transducer had 512×512 pixels. Its frame rate could reach to 100Hz. Light sources with
high equivalent black body temperature were adopted in IR target and decoy channels. The size and the radiation intensity
of the IR point target and decoys could be controlled by pin holes and attenuators. The point target and decoys driven by
high precise motors could travel through the whole instantaneous field of view of the seeker’s optical system. Two pairs of
decoys could move away from the center to the edge of the instantaneous field of view. The highest simulated black body
temperature of the point source was 1200K.
LADAR guidance technology is one of the most promising precision guidance technologies. In the aim of simulating the
return waveform of the target, a 3D geometrical model of a target is built and mathematical model of target echo signal
for imaging LADAR target simulator is established by using the coordinate transformation, radar equation and ranging
equation. First, the 3D geometrical data of the object model is obtained by 3D geometrical modeling. Then, target
coordinate system and viewpoint coordinate system are created respectively. 3D geometrical model is built in the target
coordinate system. The 3D geometrical model is transformed to the viewpoint coordinate system based on the derived
relationship between the two coordinate systems. Furthermore, the range information of the target could be obtained
under viewpoint coordinate system. Thus, the data of the target echo signal can be obtained by using radar equation and
ranging equation. Finally, the echo signal can be exported through corresponding data interface. In order to validate the
method proposed in this paper, the echo signal generated by a typical target is computed and compared with the theory
solutions. The signals can be applied to drive target simulator to generate a physical target LADAR image.
An infrared (IR, 3–5 and 8–12 μm)/microwave (MW, 2.7 GHz) micromirror array type of beam combiner was fabricated for test and analysis. A model based on transmission line theory, Snell’s law, and phase monopulse radar theory was built to analyze the boresight angle errors. Three types of boresight angle errors—inherent error, refraction-induced error and combiner inserting error—were calculated. The results indicated that combiner inserting error was the most important error. Using this theoretical model, a beam combiner was optimized, fabricated, and investigated experimentally. Measured by a phase monopulse radar, the boresight angle error introduced by the beam combiner was <0.1 deg , which coincided with the theoretical calculations. Infrared images were reflected by the beam combiner, the angular resolution of the reflected images in azimuth, and elevation directions were 40 and 80 in., respectively.
The performances of a display chip based on Fabry-Perot interferometer (FPI) array was stimulated theoretically.
Lighting by a single frequency laser, the grayscale of image pixels can be manipulated by transmission intensity
modulation of the FPIs which act as chip pixels. The F-P cavities were constructed by Lithium Niobate thin layer. The
cavity mirrors were deposited directly on the crystal surfaces. Using the converse piezoelectric effect of Lithium Niobate,
the cavity length was scanned by changing the applied voltage. Therefore, the single frequency laser transmission was
controlled. The electrodes were coated locally for corresponding chip pixel. A theoretical model for a display chip with
an array of 64×64 FPIs was built. The main parameters of the chip were optimized and the performances were stimulated.
The influences of mirror flatness, parallel of the cavity mirrors, linewidth and frequency stability of the lighting laser
were discussed. The simulation results indicated that this technique is promising for laser display.
Long range water vapor DIAL-systems require efficient and rugged laser sources. The quasi-three-level transition
from R<sub>1</sub> to Z<sub>5</sub> in Nd:GSAG with 943nm wavelength is a promising candidate. An actively Q-switched Nd:GSAG
laser was established. Up to 31mJ output pulse energy and up to 26Hz repetition rate was achieved. Injection
seeding was used to obtain single frequency operation. The seed laser is a distributed feedback laser diode. Laser
frequency was stabilized by ramp-hold-fire method. By tuning the wavelength of the seed laser a 0.83nm tuning
range of the pulsed Nd:GSAG laser was obtained. Measured by Fabry-Perot interferometer the spectral line width
was approximately 50MHz.
A Nd:GSAG laser operated at the <sup>4</sup>F<sub>3/2</sub>
→<sup>4</sup>I<sub>9/2</sub> transition was tuned by a FPI-etalon achieving a tuning range of
1.5 nm with a center wavelength at 942.7 nm. Three water vapor absorption wavelengths with different absorption
strength as suitable for a water vapor LIDAR are within this tuning range and lasing could be achieved at all
three wavelength. Q-switched pulse energies up to 26mJ were obtained as required for long range detection.
Wavelength around 940 nm lasing can be obtained by quasi-three-level operation of Nd doped laser crystal.
Diode end pumping provides the necessary high pump intensity in the laser crystal. In order to get high efficiency of the
end pumped laser system, the overlap coefficient between pump beam and laser beam should be optimized. Thermal lens
coefficient is one of the most important parameters to design the laser cavity structure. The time dependent heat
conduction equation is solved numerically in order to study the thermal lens effect in pulsed pumping laser crystal.
Calculated results showed that the thermal lens coefficients change with different pump frequencies. Experiments are
done with Nd:YAG and Nd:GSAG laser rod. The thermal lens coefficient of Nd:YAG at pump frequency 50 Hz with
pump beam diameter 1.5 mm is 10.2 Wm, while the thermal lens coefficient of Nd:GSAG at pump frequency 50 Hz with
pump beam diameter 1.75 mm is 5.9 Wm.
An actively Q-switched Nd:GSAG laser with 942nm wavelength was frequency doubled in a critically type-I
phase-matched LBO. Maximum pulse energy of 8mJ with 300ns pulse duration at 471 nm was obtained with 19mJ
incident radiation at 10Hz. The corresponding conversion efficiency was 42%. The frequency doubling of a focused
Gaussian beam involves spatially dependent phase mismatching due to beam divergence. It decreases the conversion
efficiency and deteriorates the beam quality. According to the theoretical calculation, elliptical focusing was used to
improve the second harmonic beam quality and slightly increase the conversion efficiency.