Light synthesis with linearly chirped fibre Bragg gratings (FBGs) for optical coherence tomography (OCT) applications

A simple technique of using a combination of linearly chirped fibre Bragg gratings (FBGs) to generate light to enhance depth resolution in optical coherence tomography (OCT) is introduced. A [3 × 3] fused fibre coupler was used to couple and redistribute super luminescent diode (SLD) light to linearly chirped FBGs connected to the fibre output arms of the coupler. Reflected and/or transmitted light from each linearly chirped FBG was collected and combined by the same fibre coupler before being applied to an OCT system. By applying a strain gradient on two of the FBGs the spectrum of the synthesised light was altered resulting in OCT depth resolution enhancement by factor ∼1.5 when compared to a measured depth resolution of around 21 μm obtained by directly applying the SLD output light.