Application areas of fibre optic delay lines

At present, fibre optic delay lines have been widely used in many occasions, especially in the application of military devices with high requirements for the external electromagnetic environment. A phased array radar antenna system. High-performance phased array radar requires a large scanning range, beam without skew, transmission band, fibre optic real-time delay is the key technology to meet these requirements. B Pseudo-random programme generator. Pseudo-random program generators can be implemented using integrated optical parity generators with fibre optic delay line elements or programmable delay lines. c Electronic Countermeasures. Representative applications are spoofed jammers and radiated rate signal direction finding, where the performance required for broadband jammers can be met using the wide bandwidth and very short delay resolution of optical delay lines. D Radar system performance testing. In this field, fibre optic delay lines have been used in Doppler radar system noise testing and radar transponder test targets. The sensitivity of the test system is proportional to the delay size, and high system sensitivity can be obtained by using fibre-optic delay lines with large delays. E Optical computer systems. Fibre optic delay lines have been developed as buffer registers or recording memories for optical computers.

Phased Array Antenna (PAA, Phased Array Antenna) has been in use since the early 1970s, and has an increasingly important role in the fields of radar and communications, etc. , and has received more and more research attention. The PAA has many advantages, such as steering without physical motion, high two-dimensional scanning flexibility, extremely accurate beam pointing, and the achievement of precise phase and amplitude control. However, their RF electronic beam forming network is large and bulky, which affects their wider application. The use of optical technology can significantly reduce the size and weight of this network, making optical systems very suitable for use in mobile radar systems. Through the theoretical analysis of the microwave beam pointing angle of the phased array radar antenna and the time delay difference between adjacent array elements, he satisfies the following equation:

Where d is the distance between neighbouring array elements, the significance is that the microwave beam pointing angle of the fixed structure phased array antenna is only related to the neighbouring time delay difference, and has nothing to do with the transmitted frequency. In other words, control the neighbouring array element time delay difference, you control the beam pointing angle, so as to achieve the delay control. To achieve the same beam pointing angle, if the delay accuracy is small, the neighbouring array element distance can be made notes oh ah small, can be effectively smaller phased array antenna volume. Optical real-time delay control process is the microwave signal as, the subcarrier loaded on the laser, were sent to a number of optical paths, for different time delay processing. The processed optical signal is then demodulated out of the microwave signal. These microwaves with corresponding time delay difference are used as the input control signal of each transmitting array element. By controlling the optical time-delay difference, the time-delay difference of the microwaves emitted by the neighbouring array elements is controlled, thus achieving the purpose of controlling the beam pointing angle. Since optical fibres can highly isolate electromagnetic interference, optical fibre delay lines have excellent application prospects in phased arrays that require long time delays. In addition, for large monitoring arrays or for the weight and volume requirements of the relatively high recorded phased array, the microwave phased array antenna phase control by means of fibre optic delay line is a very attractive prospect. Delay = control of phase The delay difference formed between two transmitting units can control the direction of the antenna transmitting beam to achieve the purpose of scanning in a certain area. Optical phased array system structure based on optical fibre delay technology has the following characteristics: 1, delay precision is small, the delay range is large. the minimum delay amount of FDL can reach 1 fs, and the range of the delay amount across 9 orders of magnitude, to adapt to a variety of use occasions. 2, the operating frequency is high. 2, high operating frequency, FDL can work in more than 100GHz operating frequency, can adapt to the transmission of high-frequency signals, but by the modulator performance limitations. 3, small signal loss, FDL per kilometre transmission loss of only 0.3db, and it has a unique advantage that the signal loss is independent of the signal frequency. Other delay technologies such as surface acoustic wave delay line, metal waveguide, coaxial cable, etc. , the transmission loss are with the increase in transmission signal frequency and increase, ASW for example, when the signal frequency reaches 10GHz, the loss increases to about 100 db per kilometre, losing the value of the application. Of course, fibre optic delay line in the application of some disadvantages, such as the demand for light sources, and the performance requirements of optoelectronic modulation / demodulation equipment, etc. , but with the rapid development of optical communication technology, in the field of nano-light sources and other areas have significant breakthroughs, for the development of fibre optic delay line technology to provide conditions.