Role of beat noise in limiting the sensitivity of optical coherence tomography

Abstract

The sensitivity and dynamic range of optical coherence tomography (OCT) are calculated for instruments utilizing two common interferometer configurations and detection schemes. Previous researchers recognized that the performance of dual-balanced OCT instruments is severely limited by beat noise, which is generated by incoherent light backscattered from the sample. However, beat noise has been ignored in previous calculations of Michelson OCT performance. Our measurements of instrument noise confirm the presence of beat noise even in a simple Michelson interferometer configuration with a single photodetector. Including this noise, we calculate the dynamic range as a function of OCT light source power, and find that instruments employing balanced interferometers and balanced detectors can achieve a sensitivity up to six times greater than those based on a simple Michelson interferometer, thereby boosting image acquisition speed by the same factor for equal image quality. However, this advantage of balanced systems is degraded for source powers greater than a few milliwatts. We trace the concept of beat noise back to an earlier paper [J. Opt. Soc. Am. 52, 1335 (1962)].

Feasibility study on bonding quality inspection of microfluidic devices by optical coherence tomography

“…19 In our experiment, the maximum signal is the saturation voltage 8.8 V. Considering the system noise is 10 mV, the system SNR is 20 lg(8.8 V/10 mV) = 59 dB. In these experiments, the SNR is mainly limited by the low reflected light from the interface.…”

Methods to assess sensitivity of optical coherence tomography systems

“…Since the early days of OCT, SNR has been calculated as [3][4][5][6][7] I samp is the background-subtracted image intensity from a reflecting object placed in the interferometer's sample arm, and σ bg is the standard deviation of the image background intensity (i.e., with no sample present). Squaring the signal and noise terms is needed to convert OCT image intensity values, proportional to the amplitude of the interference fringes resulting from cross-correlation of sample and reference fields, to power values.…”

Optical Coherence Tomography in a Needle Format

“…Firstly, they can appear as unwanted structure in the OCT image or generate parasitic "ghost images" of the sample if they are within the imaging depth range (as they are typically situated at negative distances from the zero delay, they also often appear as broadened bands in the image after numerical dispersion compensation). Secondly, even if they are outside the imaging depth range, they will add shot noise and beat noise which reduce the system sensitivity [77][78][79]. Fortunately, such backreflections can be kept very low in fusion-spliced all-fiber probes so that needle OCT systems can operate close to the shot-noise limit if the round-trip loss g P of the probe is minimized.…”