Abstract
In optical frequency domain imaging (OFDI) or swept-source optical coherence tomography, balanced detection is required to suppress relative intensity noise (RIN). A regular implementation of balanced detection by combining reference and sample arm signal in a 50/50 coupler and detecting the differential output with a balanced receiver is however, not perfect. Since the splitting ratio of the 50/50 coupler is wavelength dependent, RIN is not optimally canceled at the edges of the wavelength sweep. The splitting ratio has a nearly linear shift of 0.4% per nanometer. This brings as much as +/-12% deviation at the margins of wavelength-swept range centered at 1060nm. We demonstrate a RIN suppression of 33dB by spectrally corrected balanced detection, 11dB more that regular balanced detection.
Highlights
Optical coherence tomography (OCT) is mostly used for biomedical subsurface imaging
Optical frequency domain imaging (OFDI) measures the spectrally resolved interference by rapidly tuning the source wavelength before it enters the interferometer such that the temporally encoded wavelength resolved signal can be detected with one single detector [10, 12, 15, 29, 30]
With conventional hardware balanced detection, we have scanned a range of reference arm powers by a neutral density filter to find the optimal power level
Summary
Optical coherence tomography (OCT) is mostly used for biomedical subsurface imaging It can be implemented by either time-domain or Fourier-domain architectures [1,2,3]. Optical frequency domain imaging (OFDI) measures the spectrally resolved interference by rapidly tuning the source wavelength before it enters the interferometer such that the temporally encoded wavelength resolved signal can be detected with one single detector [10, 12, 15, 29, 30]. Unlike SDOCT[31], the theoretically predicted shot-noise-limited sensitivity is still not reached in OFDI This can be attributed to a number of factors, such as incomplete RIN suppression and significant thermal noise (detector noise) for high bandwidth balanced detectors. Instead of using the differential amplifier in the detector to balance the two output fiber leads, we digitize the two output channels separately and process the balanced detection in digital domain after correction of the spectrally dependent splitting ratio
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