Study of Resolution and SNR on Cr4+:YAG Based Optical Coherence Tomography

For optical coherence tomography (OCT), axial resolution is determined by center wavelength and bandwidth of the light source, whereas signal-to-noise ratio (SNR) is affected by instability of the light source. Our proprietary Cr4+:YAG double-clad fiber is not only broad in bandwidth but also highly stable; therefore, it is eminently suitable for the development of high axial resolution and high SNR near infrared OCT systems. By means of laser heated pedestal growth (LHPG) method, we have successfully developed a Cr4+:YAG double-clad fiber, generating broadband amplified spontaneous emission (ASE) centered at 1.38 um with a bandwidth of 265 nm and 0.03% instability by an 1064-nm Yb fiber pump laser. Using the ASE as light source of the OCT system, we have demonstrated an interference signal of 6-um-thick single-layer human pulmonary adenocarcinoma cells. With dispersion compensation, we have promoted the axial resolution from 5.1 um to 3.75 um with 68.3-dB SNR simultaneously. We have constructed a modified SNR simulation model, which can be applied to any kinds of OCT light sources. Based on experiment and simulation results, we conclude that it is not likely that shot-noise limited system can be reached through adjusting the reflectivity of the reference light. Besides, since our light source is quite stable, we also conclude that our SNR performance is close to theoretical limit in a single-detector system.