Off-axis reference beam for full-field swept-source OCT and holoscopy

Abstract

In numerous applications, Fourier-domain optical coherence tomography (FD-OCT) suffers from a limited imaging depth due to signal roll-off, a limited focal range, and autocorrelation noise. Here, we propose a parallel full-field FD-OCT imaging method that uses a swept laser source and an area camera in combination with an off-axis reference, which is incident on the camera at a small angle. As in digital off-axis holography, this angle separates autocorrelation signals and the complex conjugated mirror image from the actual signal in Fourier space. We demonstrate that by reconstructing the signal term only, this approach enables fullrange imaging, i.e., it increases the imaging depth by a factor of two, and removes autocorrelation artifacts. The previously demonstrated techniques of inverse scattering and holoscopy can then numerically extend the focal range without loss of lateral resolution or imaging sensitivity. The resulting, significantly enhanced measurement depth is demonstrated by imaging a porcine eye over its entire depth, including cornea, lens, and retina. Finally, the feasibility of in vivo measurements is demonstrated by imaging the living human retina.

Imaging pulse wave propagation in human retinal vessels using full-field swept-source optical coherence tomography

“…The light backscattered by the retina is again collimated by the eye lens. After being limited by an adjustable aperture in the outside focal plane of the eye lens, the sample light is imaged onto the sensor of a high-speed camera (FASTCAM SA-Z, Photron), where it is superimposed with a reference wave incident at an angle of about 1.2°(off-axis geometry, see [9]). The central 896 × 368 pixels of the camera are read out at a frame rate of 60 kHz, acquiring 30 images during one wavelength sweep.…”

Reduction of frame rate in full-field swept-source optical coherence tomography by numerical motion correction [Invited]

“…2. The setup, which is described in detail elsewhere [4,30], is based on a Mach-Zehnder interferometer. The illumination of the tunable light source (Superlum Broadsweeper BS 840, 50 nm sweep range, 841 nm central wavelength) is split into reference and sample wave, where the sample illumination contains 5 mW radiant power.…”

“…For a collimated illumination of the retina a focus was generated in the outer focal plane of the eye using an achromatic lens. The light backscattered from the retina is imaged onto the camera and recombined with the reference wave, which is incident at an angle of 1.2 • with respect to the optical axis (off-axis geometry [30]). …”

In vivo imaging of the human cornea with high-speed and high-resolution Fourier-domain full-field optical coherence tomography

“…Despite the fast en face (2D) image acquisition and camera development efforts, TD-FF-OCT remains relatively slow volumetric (3D) imaging technique, which limits its use in high-resolution eye imaging. The concept of Fourier-domain FF-OCT (FD-FF-OCT) has been introduced in the past that can acquire volumetric images faster [27], but only recently it reached its potential when high-speed cameras with frame rates of tens of kilohertz were employed [28][29][30]. FD-FF-OCT, otherwise known as Full-Field Swept-Source OCT (FF-SS-OCT), also utilizes a tunable laser source, usually referred to as a swept laser source.…”

“…Another important full-field imaging benefit is that considerably higher power exposure is allowed on eye in both time-and Fourier-domain systems compared to the scanning OCT due to the power distributed across larger area [35]. FD-FF-OCT so far has been exclusively used for the retinal imaging [28][29][30][36][37][38], except one skin imaging demonstration [39]. Cornea arguably can be a good target for FD-FF-OCT because of low scattering that does not necessitate confocal detection.…”