This paper presents a high-speed, high-sensitivity, and high-resolution optical imaging technique based on optical frequency-domain interferometry using a rapidly-tuned wavelength-swept laser. The authors demonstrate that frequency-domain ranging provides a superior signal-to-noise ratio compared to conventional time-domain ranging used in optical coherence tomography (OCT). A high sensitivity of -110 dB was achieved with a 6 mW source at an axial resolution of 13.5 μm 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. The paper describes the principle of optical frequency-domain reflectometry (OFDR), which uses a tunable light source and a fiber-optic interferometer to measure the axial reflectivity profile. The detector current is related to the reflection profile via the Fourier transform relation. The axial resolution is determined by the spectral envelope of the source and the group refractive index of the sample. The signal-to-noise ratio (SNR) is derived and shown experimentally to be significantly higher in frequency-domain imaging compared to time-domain imaging. The experimental configuration of the OFDI system is described, including the use of a wavelength-swept laser, a dual balanced detection system, and a 50/50 coupler. The system achieves a ranging depth of 3.8 mm, an A-line acquisition rate of 15.7 kHz, a free-space axial resolution of 13.5 μm, and a high sensitivity of -110 dB. The sensitivity is defined as the reflectivity that produces signal power equal to the noise power. The results show that the OFDI system achieves a high sensitivity of -110 dB, which is comparable to the best time-domain OCT systems. The OFDI system also demonstrates a higher imaging speed and better penetration depth compared to time-domain OCT. The system is capable of detecting signals with a high dynamic range of >55 dB. The axial resolution was determined from Gaussian fits of the measured point spread functions and was 13.5 ± 1 μm throughout the entire depth range. The paper concludes that OFDI has significant potential in biomedical imaging applications where high speed and high sensitivity are critical. The system offers a simple way of implementing polarization diversity and does not suffer from phase washout due to sample arm motion during pixel integration time.This paper presents a high-speed, high-sensitivity, and high-resolution optical imaging technique based on optical frequency-domain interferometry using a rapidly-tuned wavelength-swept laser. The authors demonstrate that frequency-domain ranging provides a superior signal-to-noise ratio compared to conventional time-domain ranging used in optical coherence tomography (OCT). A high sensitivity of -110 dB was achieved with a 6 mW source at an axial resolution of 13.5 μm 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. The paper describes the principle of optical frequency-domain reflectometry (OFDR), which uses a tunable light source and a fiber-optic interferometer to measure the axial reflectivity profile. The detector current is related to the reflection profile via the Fourier transform relation. The axial resolution is determined by the spectral envelope of the source and the group refractive index of the sample. The signal-to-noise ratio (SNR) is derived and shown experimentally to be significantly higher in frequency-domain imaging compared to time-domain imaging. The experimental configuration of the OFDI system is described, including the use of a wavelength-swept laser, a dual balanced detection system, and a 50/50 coupler. The system achieves a ranging depth of 3.8 mm, an A-line acquisition rate of 15.7 kHz, a free-space axial resolution of 13.5 μm, and a high sensitivity of -110 dB. The sensitivity is defined as the reflectivity that produces signal power equal to the noise power. The results show that the OFDI system achieves a high sensitivity of -110 dB, which is comparable to the best time-domain OCT systems. The OFDI system also demonstrates a higher imaging speed and better penetration depth compared to time-domain OCT. The system is capable of detecting signals with a high dynamic range of >55 dB. The axial resolution was determined from Gaussian fits of the measured point spread functions and was 13.5 ± 1 μm throughout the entire depth range. The paper concludes that OFDI has significant potential in biomedical imaging applications where high speed and high sensitivity are critical. The system offers a simple way of implementing polarization diversity and does not suffer from phase washout due to sample arm motion during pixel integration time.