5 Bit Based On Fiber Bragg Grating Optical Fiber Delay Line

Recently, optical fiber delay line is been extensively studied, which is used as a delay device for phased array radar. With optical fiber delay line, optical control phased array radar, compared to the traditional phased array radar, has higher instantaneous operating frequency and its beams do not appear frequency offset. In addition, optical fiber delay line has many advantages, like small size, light weight, low loss, electromagnetic interference and etc.Optical fiber delay line can be made by using optical switch, prism or mirror that they can select the path for light wave. This structure of optical fiber delay line has more higher precision, but its size is a litter larger. Dispersion fiber and fiber grating can choose wavelength of the light source, so they can make optical fiber delay line too. This structure of optical fiber delay line has lower delay time. But it is all-fiber optical delay line, so it has smaller size and lower loss.This paper studies the fiber grating optical delay line. In the article, the principle of fiber grating, composition of the delay time and research status at home and abroad are introduced firstly. Then possible types of the grating fiber delay line structure are introduced, and theory of the fiber grating is analyzed. We use the classic coupled mode theory to analyze and simulate the reflectance spectra, delay curve and transmission characteristic. The analysis points out that the fiber grating spectral characteristic and the delay time through the fiber grating is depend on grating length, refractive index modulation depth, apodization and chirp. At last, a structure of5bit fiber grating delay line using fast tunable laser is designed by paralleling four chirped grating.At last of this paper, the structure of5bit fiber delay line based on chirped fiber grating is simulated using Optisystem, and every delay time is calculated in Matlab with a time domain waveform method.A chirped grating, whose grating linear period factor is0.005μm, is selected, with middle reflection frequency193.4THz and length18.75mm, which is apodizated by a Gaussian function with a factor of0.3. When the middle frequency of the light pulse source is193.1THz,193.2THz...193.8THz, with pulse width50ps, those pulse can reflect effectively and the reflected optical power is just good. The delay step of the structure of5bit fiber delay line based on chirped fiber grating is10ps, and its delay precision is1.56ps.