Abstract
We proposed a sensitivity enhancement method of the interference-based signal detection approach and applied it on a swept-source optical coherence tomography (SS-OCT) system through all-fiber optical parametric amplifier (FOPA) and parametric balanced detector (BD). The parametric BD was realized by combining the signal and phase conjugated idler band that was newly-generated through FOPA, and specifically by superimposing these two bands at a photodetector. The sensitivity enhancement by FOPA and parametric BD in SS-OCT were demonstrated experimentally. The results show that SS-OCT with FOPA and SS-OCT with parametric BD can provide more than 9 dB and 12 dB sensitivity improvement, respectively, when compared with the conventional SS-OCT in a spectral bandwidth spanning over 76 nm. To further verify and elaborate their sensitivity enhancement, a bio-sample imaging experiment was conducted on loach eyes by conventional SS-OCT setup, SS-OCT with FOPA and parametric BD at different illumination power levels. All these results proved that using FOPA and parametric BD could improve the sensitivity significantly in SS-OCT systems.
Highlights
Optical coherence tomography (OCT) is one of powerful imaging modalities for biological applications [1]
The 90% power was divided by another 90/10 coupler again, and the 10% branch went through the reference arm which consisted of a collimator, iris, dispersion compensator (LSM03DC, Thorlabs) and mirror, while the 90% one incident to the sample arm that was consisted of a collimator, galvo mirror and scanning lens (LSM03, Thorlabs)
The 76 nm bandwidth starting at 1575 nm was selected for the following reasons: First, the passband of the C/L band wavelength-division multiplexing (WDM) coupler in optical parametric amplifier for life-science (OPALS) starting at 1575 nm limits the shorter wavelength
Summary
Optical coherence tomography (OCT) is one of powerful imaging modalities for biological applications [1]. In conventional swept-source OCT (SS-OCT) systems, the illumination optical power is usually boosted by optical amplifiers, e.g. booster optical amplifier (BOA) [2,3] and Raman amplifier [4], right before the bio-samples for a good imaging sensitivity Those optical amplifiers are commonly required to operate in a broadband and low-noise regime since OCT offers an axial resolution inversely proportional to the spectral width of the laser source [5]. A lower optical power illumination is required for the in-vivo imaging when the photodamage, phototoxicity and photobleaching issues are concerned, in ophthalmology [8,9]. In these cases, one more amplification stage can be used to amplify the OCT’s interference signal to improve detection sensitivity. A broadband optical amplifier with superior noise performance for weak signal has a great demand in enhancing the sensitivity of those OCT systems
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