We report high-throughput optical coherence tomography (OCT) that offers 1,000 times higher axial scan rate than conventional OCT in the 800 nm spectral range. This is made possible by employing photonic time-stretch for chirping a pulse train and transforming it into a passive swept source. We demonstrate a record high axial scan rate of 90.9 MHz. To show the utility of our method, we also demonstrate real-time observation of laser ablation dynamics. Our high-throughput OCT is expected to be useful for industrial applications where the speed of conventional OCT falls short.
[Show abstract][Hide abstract] ABSTRACT: We analyze the benefits and problems of in vivo optical coherence tomography (OCT) imaging of the human retina at A-scan rates in excess of 1 MHz, using a 1050 nm Fourier-domain mode-locked (FDML) laser. Different scanning strategies enabled by MHz OCT line rates are investigated, and a simple multi-volume data processing approach is presented. In-vivo OCT of the human ocular fundus is performed at different axial scan rates of up to 6.7 MHz. High quality non-mydriatic retinal imaging over an ultra-wide field is achieved by a combination of several key improvements compared to previous setups. For the FDML laser, long coherence lengths and 72 nm wavelength tuning range are achieved using a chirped fiber Bragg grating in a laser cavity at 419.1 kHz fundamental tuning rate. Very large data sets can be acquired with sustained data transfer from the data acquisition card to host computer memory, enabling high-quality averaging of many frames and of multiple aligned data sets. Three imaging modes are investigated: Alignment and averaging of 24 data sets at 1.68 MHz axial line rate, ultra-dense transverse sampling at 3.35 MHz line rate, and dual-beam imaging with two laser spots on the retina at an effective line rate of 6.7 MHz.
[Show abstract][Hide abstract] ABSTRACT: Dispersive Fourier transformation is an emerging measurement technique
that overcomes the speed limitations of traditional optical instruments
and enables fast continuous single-shot measurements in optical sensing,
spectroscopy and imaging. Using chromatic dispersion, dispersive Fourier
transformation maps the spectrum of an optical pulse to a temporal
waveform whose intensity mimics the spectrum, thus allowing a
single-pixel photodetector to capture the spectrum at a scan rate
significantly beyond what is possible with conventional space-domain
spectrometers. Over the past decade, this method has brought us a new
class of real-time instruments that permit the capture of rare events
such as optical rogue waves and rare cancer cells in blood, which would
otherwise be missed using conventional instruments. In this Review, we
discuss the principle of dispersive Fourier transformation and its
implementation across a wide range of diverse applications.
[Show abstract][Hide abstract] ABSTRACT: Real-time wideband digitizers are the key building block in many systems including oscilloscopes, signal intelligence, electronic warfare, and medical diagnostics systems. Continually extending the bandwidth of digitizers has hence become a central challenge in electronics. Fortunately, it has been shown that photonic pre-processing of wideband signals can boost the performance of electronic digitizers. In this article, the underlying principle of the time-stretch analog-to-digital converter (TSADC) that addresses the demands on resolution, bandwidth, and spectral efficiency is reviewed. In the TSADC, amplified dispersive Fourier transform is used to slow down the analog signal in time and hence to compress its bandwidth. Simultaneous signal amplification during the time-stretch process compensates for parasitic losses leading to high signal-to-noise ratio. This powerful concept transforms the analog signal's time scale such that it matches the slower time scale of the digitizer. A summary of time-stretch technology's extension to high-throughput single-shot spectroscopy, a technique that led to the discovery of optical rouge waves, is also presented. Moreover, its application in high-throughput imaging, which has recently led to identification of rogue cancer cells in blood with record sensitivity, is discussed.
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