Megahertz OCT for ultrawide-field retinal imaging with a 1050nm Fourier domain mode-locked laser

Abstract

We describe a novel buffering technique for increasing the A-scan rate of swept source optical coherence tomography (SSOCT) systems employing low duty cycle swept source lasers. This technique differs from previously reported buffering techniques in that it employs a fast optical switch, capable of switching in 60 ns, instead of a fused fiber coupler at the end of the buffering stage, and is therefore appreciably more power efficient. The use of the switch also eliminates patient exposure to light that is not used for imaging that occurs at the end of the laser sweep, thereby increasing the system sensitivity. We also describe how careful management of polarization can remove undesirable artifacts due to polarization mode dispersion. In addition, we demonstrate how numerical compensation techniques can be used to modify the signal from a Mach-Zehnder interferometer (MZI) clock obtained from the original sweep to recalibrate the buffered sweep, thereby reducing the complexity of systems employing lasers with integrated MZI clocks. Combining these methods, we constructed an SSOCT system employing an Axsun technologies laser with a sweep rate of 100kHz and 6dB imaging range of 5.5mm. The sweep rate was doubled with sweep buffering to 200 kHz, and the imaging depth was extended to 9 mm using coherence revival. We demonstrated the feasibility of this system by acquiring images of the anterior segments and retinas of healthy human volunteers.

Optical coherence tomography today: speed, contrast, and multimodality

“…Axial resolution improvement (prerequisite 1) has been the key technological milestone in the history of OCT in its first decade, [10][11][12][13][14] which has been achieved by using ultra-broadband sources. OCT imaging speed improvements (prerequisite 2) evolved in its second decade, which were accomplished by Fourier domain (FD)/spectral domain (SD) [15][16][17][18] and swept source (SS) OCT. [19][20][21][22][23] While in FD/SD OCT speed is mainly determined by the readout time of the camera in a spectrometer, the wavelength-tuning speed of swept sources is the decisive factor in SS OCT. In the past 5 to 10 years, different swept source technologies have emerged to significantly improve imaging speed in (commercial) OCT systemsespecially the ones using wavelengths >1 μm.…”

Optical Coherence Tomography: its role in the non-invasive structural examination and conservation of cultural heritage objects—a review

“…This may be accomplished in two ways: in Spectral-domain OCT (SdOCT), a broadband light source is used together with a detector comprising a spectrograph equipped with a single-line CCD or CMOS camera; in Swept-Source OCT (SSOCT), a laser with rapidly scanned wavelength is used as the source, with a single photodiode as the detector. Both FdOCT modalities are available commercially or laboratory-made, and are able to scan with frequency range from 100 kHz to 1.4 MHz [4] over a broad range of wavelengths. The state-of-the-art of and prospects for very high speed OCT have been reviewed recently by Wojtkowski [5].…”

Fourier Domain Optical Coherence Tomography for Retinal Imaging with 800-nm Swept Source: Real-time Resampling in k-domain

“…In addition, FD/SS-OCT can be used to remove the DC autocorrelation noise by employing a dual-balanced detector. Finally, a faster acquisition speed is possible since the rise time of a photodiode is faster than that of cameras based on charge-coupled device (CCD) and complementary metal-oxide semiconductor (CMOS) chips [13][14][15].…”