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25 years is a relatively short period of time for a medical technology to become a standard of care impacting the treatment of millions of people every year. Yet 25 years ago there were no OCT companies, no OCT products, no OCT markets, and only one journal article published using the term OCT (optical coherence tomography). OCT has had a tremendous scientific, clinical, and economic impact on society. Today, it is estimated that there are ~30 Million OCT imaging procedures performed worldwide every year and the OCT system market is approaching $1B per year. OCT has helped diagnose patients with retinal disease at early treatable stages, preventing or greatly reducing irreversible vision loss. The technology has facilitated pharmaceutical development and contributed to fundamental understanding of disease mechanisms in multiple fields. The invention and translation of OCT from fundamental research to daily clinical practice would not have been possible without a complex ecosystem involving interaction among physics, engineering, and clinical medicine; government funding of fundamental and clinical research; collaborative and competitive research in the academic sector; entrepreneurship and industry; addressing real clinical needs; harnessing the innovation that occurs at the boundaries of disciplines; and economic and societal impact. This invited review paper discusses the translation of OCT from fundamental research to clinical practice and commercial impact, as well as describes the ecosystem that helped power OCT to where it is today and will continue to drive future advances. While OCT is an example of a technology that has had a powerful impact, there are many biomedical technologies which are poised for translation to clinical practice, and it is our hope that highlighting this ecosystem will help accelerate their translation and clinical impact.

We present a numerical approach to extract the dispersion mismatch in ultrahigh-resolution Fourier domain optical coherence tomography (OCT) imaging of the retina. The method draws upon an analogy with a Shack-Hartmann wavefront sensor. By exploiting mathematical similarities between the expressions for aberration in optical imaging and dispersion mismatch in spectral / Fourier domain OCT, Shack-Hartmann principles can be extended from the two-dimensional paraxial wavevector space (or the x-y plane in the spatial domain) to the one-dimensional wavenumber space (or the z-axis in the spatial domain). For OCT imaging of the retina, different retinal layers, such as the retinal nerve fiber layer (RNFL), the photoreceptor inner and outer segment junction (IS/OS), or all the retinal layers near the retinal pigment epithelium (RPE) can be used as point source beacons in the axial direction, analogous to point source beacons used in conventional two-dimensional Shack-Hartman wavefront sensors for aberration characterization. Subtleties regarding speckle phenomena in optical imaging, which affect the Shack-Hartmann wavefront sensor used in adaptive optics, also occur analogously in this application. Using this approach and carefully suppressing speckle, the dispersion mismatch in spectral / Fourier domain OCT retinal imaging can be successfully extracted numerically and used for numerical dispersion compensation to generate sharper, ultrahigh-resolution OCT images.

We have developed a simple, wide-optical-bandwidth, high-resolution system for performing rapid optical frequency domain reflectometry measurements and applied it to multidimensional tomographic imaging. The source is a grating-tuned external cavity semiconductor laser with a tuning capability of 25 nm in 100 ms. We discuss system performance and show a two-dimensional optical coherence tomography image of a thin glass sandwich structure as a preliminary demonstration of the systems depth and resolution capabilities.

The development of techniques for high-speed image acquisition in optical coherence tomography (OCT) systems is essential for suppressing motion artifacts when one is imaging living systems. We describe a new OCT system for performing micrometer-scale, cross-sectional optical imaging at four images/s. To achieve OCT image-acquisition times of less than 1 s, we use a piezoelectric fiber stretcher to vary the reference arm delay. A Kerr-lens mode-locked chromium-doped forsterite laser is employed as the low-coherence source for the highspeed OCT system. Dynamic, motion-artifact-free in vivo imaging of a beating Xenopus laevis (African frog) heart is demonstrated.

We propose and analyze the use of optical coherence domain ref lectometry (OCDR) in multilayer optical storage, permitting higher data density and detection sensitivity with lower interlayer cross talk and scattering. An experimental OCDR image of data on a CD-ROM is compared with an image obtained with direct detection.

We describe a novel technique, based on optical coherence tomography, for enhanced optical sectioning in confocal microscopy. Confocal imaging deep into highly scattering media is demonstrated and compared with the predictions of a single-backscatter theory.

We describe what are to our knowledge the first in vivo measurements of human retinal structure with optical coherence tomography. These images represent the highest depth resolution in vivo retinal images to date. The tomographic system, image-processing techniques, and examples of high-resolution tomographs and their clinical relevance are discussed.

Experimental results of linewidth reduction in AlGaAs diode lasers with frequency-selective Rayleigh scattering from a fiber-optic ring resonator are presented. The intermediate-frequency signal produced by two such lasers is shown to have less than a 100-Hz intermediate-frequency linewidth. Self-homodyning measurements indicate an estimated laser linewidth of 0.6 Hz. Observing the intermediate-frequency beat signal and a Fabry-Perot interferometer, we demonstrate frequency mode stability and tuning. This tuning allowed us to lock a heterodyne optical phase-locked loop successfully. The narrow-linewidth ring laser also produced a stimulated Brillouin scattering wave.

We describe a new technique, femtosecond transillumination optical coherence tomography, for time-gated imaging of objects embedded in scattering media. Time gating is performed with a fiber-optic interferometer with femtosecond pulses and coherent heterodyne detection to achieve a 130-dB dynamic range. A confocal imaging arrangement provides additional spatial discrimination against multiply scattered light. By time gating ballistic photons, we achieve 125-microm-resolution images of absorbing objects in media 27 scattering mean free paths thick. We derive a fundamental limit on ballistic imaging thickness based on quantum noise considerations.

Design considerations for a heterodyne spatial tracking system utilizing pupil plane processing techniques and its advantages over traditional focal plane processing are described. Noise performance bounds, optimal and suboptimal local oscillator distributions, pull-in performance, and applications other than spatial tracking are discussed. Experimental verification of a one-axis closed-loop tracking system is presented.

High-speed electronic steering of the output beam of a 10-stripe laser-diode array is reported. The array was injection locked to a single-frequency laser diode. High-speed steering of the locked 0.5 degrees -wide far-field lobe is demonstrated either by modulating the injection current of the array or by modulating the frequency of the master laser. Closed-loop tracking bandwidths of 70 kHz and 3 MHz, respectively, were obtained. The beam-steering bandwidths are limited by the FM responses of the modulated devices for both techniques.