A Novel Chirped Bragg Grating Based Spectral Domain Delay Generator

Abstract

Abstract Light dispersion and chirping of spectral lines of a broadband light source is major issue with spectral domain optical coherence tomography. We designed a novel spectral delay line using multimode interference coupler and chirp Bragg grating. We considered the waveguide material as S-1813 polymer. Light from the broad-band light source is first dispersed then delayed in time. The bunches of delayed spectra produce chirping. The design ensures that the bandwidth of each bunch is about 30nm linewidth at a central wavelength of 1.55µm, corresponding to a coherence length of 15µm. The design is optimized for maximum dispersion with (i) minimum possible number of Bragg gratings and (ii) low attenuation and radiative losses. Tolerance measurements for differential refractive index also reported.