High-speed optical frequency-domain imaging

Abstract

We demonstrate high-speed, high-sensitivity, high-resolution optical imaging based on optical frequency-domain interferometry using a rapidly-tuned wavelength-swept laser. We derive and show experimentally that frequency-domain ranging provides a superior signal-to-noise ratio compared with conventional time-domain ranging as used in optical coherence tomography. A high sensitivity of -110 dB was obtained with a 6 mW source at an axial resolution of 13.5 microm and an A-line rate of 15.7 kHz, representing more than an order-of-magnitude improvement compared with previous OCT and interferometric imaging methods.

Fig. 1

Basic configuration of OFDR.

Fig. 2

Experimental configuration of the optical frequency domain imaging system.

Fig. 3

(a) Integrated output spectrum (solid, black) of the wavelength-swept laser operating at a sweep rate of 15.7 kHz, Gaussian fit of the integrated spectrum (dashed, black), and instantaneous spectrum (solid, red). (b) Laser intensity output as a function of time (three cycles).

Fig. 4

(a) Interference signal for a weak reflector sample measured with dual balanced receiver, (b) background component measured by blocking the sample arm. The upper trace is the gating pulse train used for the data acquisition.

Fig. 5

Sensitivity measured as a function of the reference-arm optical power (black dots) and the theoretical curve (green dashed line).

Fig. 6

Sensitivity measured (a, black solid line) with a −55 dB partial reflector, (b, green solid line) with the sample arm blocked. (c, blue dashed line) and (d, red dash-dot line) are theoretical maximum sensitivity of hypothetical shot-noise limited frequency-domain and time-domain OCT with a detection bandwidth of 5 MHz.

Fig. 7

(a) Image of a human finger (300 axial × 520 transverse pixels) acquired in vivo with the OFDI system at 30 fps. The vertical axis of this image contains 300 pixels and extends over a depth of 3.8 mm, where the horizontal axis of this image contains 520 pixels and extends over a transverse distance of 5.0 mm. (b) OCT image of the same human finger (250 axial × 500 transverse pixels, 2.5 × 5.0 mm) acquired at 4 fps using a state-of-the-art time-domain OCT system with a sensitivity of −110 dB. Despite of the 8 times faster imaging speed and lower source power, the OFDI image exhibits as large a penetration depth as the time-domain image. The scale bar represents 0.5 mm. Arrows in (a) mark axial locations of residual fixed pattern noise.