Method and apparatus for performing optical frequency domain

Abstract

Method of performing OFDR on a sample comprising steps of: providing an external-cavity frequency-tuned laser having an optical cavity of effective length; tuning the laser to generate a change in wavelength; changing the effective length of the optical cavity proportionally to the change in wavelength so as to tune the longitudinal cavity mode frequency at the same rate as the wavelength is changed; directing light from the laser onto the sample; receiving light reflected from the sample; combining light reflected from the sample with light from the external-cavity frequency-tuned laser; detecting the combined light and generating a beat signal in response thereto; and performing digital signal processing to extract spatial information about the sample in response to the detected beat signal. An OFDR system is also disclosed comprising: a laser comprising an output port; an optical ring having a round trip time, a center frequency and a broad-bandwidth gain medium; a wavelength selecting device in optical communication with the gain medium; a frequency shifter in optical communication with the gain medium and the wavelength selecting device; and an optical coupler in optical communication with the optical gain medium, the wavelength selecting device, and the frequency shifter. The optical coupler couples light from the optical ring to the output port, wherein the wavelength selecting device tunes the center wavelength at a rate equal to the incremental change in frequency caused by the frequency shifter divided by the round trip time of the optical ring thereby providing nearly continuous frequency sweep.