Fiber optic delay line based on optical switch

Principle of Fiber optic delay line

In all-optical signal processing, optical fiber can realize the functions of signal delay, broadening, interference, etc. The reasonable application of these functions can realize the information processing in the all-optical field. Among them, the Delay function of the optical Fiber can be made into a Fiber optic delay line, taking the ordinary single-mode optical fiber as an example, when the transmission of the optical signal working wavelength of 1550nm, the transmission of 200 meters can achieve a delay of 1μs, and the accompanying insertion loss is only 0.04dB. In comparison, the insertion loss caused by the traditional microwave delay line is dozens of dB, and the optical fiber delay line reduces the insertion loss by nearly 2 orders of magnitude, which significantly improves the competitiveness of the Fiber optic delay line. In addition, Fiber optic delay line also have the characteristics of small size, light weight, large delay bandwidth product, strong anti-electromagnetic interference ability, and become a strong competitor of microwave delay lines, and can completely replace microwave delay lines in many fields. Compared with the traditional microwave delay line, the optical fiber delay line has a high time bandwidth product, which indicates that the system has a good resolution of frequency measurement, high sensitivity and high signal interception ability, and can meet the requirements of high resolution radar systems such as delay lines. And FDL operating frequency is very high, can be much higher than 100GHz, compared with the surface acoustic wave delay line of hundreds of megahertz operating frequency and CCD delay line of tens of megahertz operating frequency compared with several orders of magnitude, and based on the future communication radar and other systems will shift to the trend of high frequency band, FDL is a significant advantage; In addition, the fiber delay line also has the characteristic that the unit delay loss is independent of frequency. The unique advantages of these fiber optic delay lines undoubtedly prove its potential in signal processing.

Application of Fiber optic delay line

The basic function of Fiber optic delay line is to delay the signal, which can realize the function of all-optical storage and shift equality by using the delay, and has a wide range of applications in phased array radar, optical fiber communication system, optical computer system and electronic countermeasures. In phased array radar, phased array antenna is the core component, the main function of the phased array antenna is to change the pattern function of the synthesized beam, so as to achieve the change of the antenna beam shape and the rapid scanning of the beam, and this function is achieved by controlling the amplitude and phase information of the signal in the antenna unit, so the delay line is an indispensable part. Compared with microwave delay line, FDL has a larger bandwidth, and there is no problem of beam tilt. In optically controlled phased array antenna, FDL can realize accurate phase allocation and control of microwave signal and remove the associated noise of echo signal, so FDL can be the best choice in phased array antenna. In radar target simulator, FDL is used to simulate signals of different distances. With the requirements of modern radar system for radar target simulator, such as high frequency band, fast target switching speed and long target simulation distance, traditional delay lines have been far from meeting the requirements of radar system, so fiber optic delay line has become the only applicable delay line. In addition to the above, in the optical fiber communication system, FDL can also realize the function of signal coding and caching. In summary, it can be seen that fiber optic delay line have important applications and irreplaceable status in many fields, so the study of high-performance fiber optic delay line has great scientific significance for the application of microwave photon technology.

Design of Fiber optic delay line

The fiber optic delay line based on the optical switch selects different optical paths to achieve different time delays through the optical switch. The basic principle of this kind of scheme is to achieve different delays by changing the optical path. It is a typical discrete Fiber optic delay line, and its typical structure is shown in the figure.

 

After the modulated optical signal is transmitted through the optical fiber, the optical path that generates the corresponding delay is selected by the optical switch array, and the required delay can be achieved by turning on the optical switch and ensuring that the other optical switches are turned off. The advantage of this kind of optical fiber delay line is that it can achieve a large delay, the realization method is simple, and the corresponding characteristics are different according to the selection of different optical switches.