We present a novel, high-speed, polarization-sensitive, optical coherence tomography set-up for retinal imaging operating at a central wavelength of 1060 nm which was tested for in vivo imaging in healthy human volunteers. We use the system in combination with a Fourier domain mode locked laser with active spectral shaping which enables the use of forward and backward sweep in order to double the imaging speed without a buffering stage. With this approach and with a custom designed data acquisition system, we show polarization-sensitive imaging with an A-scan rate of 350 kHz. The acquired three-dimensional data sets of healthy human volunteers show different polarization characteristics in the eye, such as depolarization in the retinal pigment epithelium and birefringence in retinal nerve fiber layer and sclera. The increased speed allows imaging of large volumes with reduced motion artifacts. Moreover, averaging several two-dimensional frames allows the generation of high-definition B-scans without the use of an eye-tracking system. The increased penetration depth of the system, which is caused by the longer probing beam wavelength, is beneficial for imaging choroidal and scleral structures and allows automated segmentation of these layers based on their polarization characteristics.
Optical coherence tomography (OCT) in the 1060nm range is interesting for in vivo imaging of the human
posterior eye segment (retina, choroid, sclera), as it permits a long penetration depth. Complementary to
structural images, polarization-sensitive OCT (PS-OCT) images visualize birefringent, polarization-maintaining
or depolarizing areas within the sample. This information can be used to distinguish retinal layers and structures
with different polarization properties. High imaging speed is crucial for imaging ocular structures in vivo in order
to minimize motion artifacts while acquiring sufficiently large datasets. Here, we demonstrate PS-OCT imaging
at 350 kHz A-scan rate using a two-channel PS-OCT system in conjunction with a Fourier domain mode-locked
laser. The light source spectrum spans up to 100nm around the water absorption minimum at 1060 nm. By
modulating the laser pump current, we can optimize the spectrum and achieve a depth resolution of 9 μm in air
(6.5 μm in tissue). We acquired retinal images in vivo with high resolution and deep penetration into choroid and
sclera, and features like the depolarizing RPE or an increasing phase retardation at the chorio-scleral interface
are clearly visualized.
Optical coherence tomography (OCT) in the 1060nm range is interesting for in vivo imaging of the human
posterior eye segment (retina, choroid, sclera) due to low absorption in water and deep penetration into the
tissue. Rapidly tunable light sources, such as Fourier domain mode-locked (FDML) lasers, enable acquisition
of densely sampled three-dimensional datasets covering a wide field of view. However, semiconductor optical
amplifiers (SOAs)-the typical laser gain media for swept sources-for the 1060nm band could until recently
only provide relatively low output power and bandwidth. We have implemented an FDML laser using a new SOA
featuring broad gain bandwidth and high output power. The output spectrum coincides with the wavelength
range of minimal water absorption, making the light source ideal for OCT imaging of the posterior eye segment.
With a moderate SOA current (270 mA) we achieve up to 100nm total sweep range and 12 μm depth resolution
in air. By modulating the current, we can optimize the output spectrum and thereby improve the resolution to
9 μm in air (~6.5 μm in tissue). The average output power is higher than 20mW. Both sweep directions show
similar performance; hence, both can be used for OCT imaging. This enables an A-scan rate of 350 kHz without
buffering the light source output.
We present a Bessel beam illumination FDOCT setup with FDML buffered swept source at 1300nm. An extended focus
is achieved due to the Bessel beam that preserves its lateral extend over a large depth range. Decoupling the illumination
from the Gaussian detection improves the sensitivity as compared to double passing the ring filter and enables dark field
imaging. Dark field imaging is useful to avoid strong reflexes from the sample's surface that adversely affect the
sensitivity due to the limited dynamic range of high-speed 8bit acquisition cards. Furthermore, Bessel beams exhibit a
self-reconstruction property that allows imaging even behind obstacles such as hairs on skin.
Densely sampled volumes of skin in-vivo with high lateral resolution are acquired at up to 440kHz A-Scan rate. In
addition the possibility of contrasting capillaries with high sensitivity is shown, using inter-B-scan speckle variance
analysis. High-speed imaging is of crucial importance for imaging small details since sample motion artifacts are
reduced and high sampling can be maintained while increasing the B-Scan rate.
We present a novel frequency-swept light source working at 1060nm that utilizes a tapered amplifier as gain
medium. These devices feature significantly higher saturation power than conventional semiconductor optical
amplifiers and can thus improve the limited output power of swept sources in this wavelength range. We
demonstrate that a tapered amplifier can be integrated into a
fiber-based swept source and allows for high-speed
FDML operation. The developed light source operates at a sweep rate of 116kHz with an effective average
output power in excess of 30mW. With a total sweep range of 70 nm an axial resolution of 15 μm in air (~11μm
in tissue) for OCT applications can be achieved.
We present a novel frequency-swept light source working at 1060nm that utilizes a tapered amplifier as gain
medium. These devices feature significantly higher saturation power than conventional semiconductor optical
amplifiers and can thus improve the limited output power of swept sources in this wavelength range. We
demonstrate that a tapered amplifier can be integrated into a fiber-based swept source and allows for high-speed
FDML operation. The developed light source operates at a sweep rate of 116kHz with an effective average
output power in excess of 30mW. With a total sweep range of 70 nm an axial resolution of 15 μm in air (~11μm in tissue) for OCT applications can be achieved.
We present a novel wavelength swept light source for Optical Coherence Tomography (OCT). Arbitrary sweep rates up
to 2x170kHz are achieved by phase-shifted control of two optical bandpass-filters to compensate light propagation
effects.
A Fourier Domain mode-locked (FDML) laser for polarization sensitive optical coherence tomography (OCT) is
presented. The laser generates an alternating sequence of wavelength sweeps with their polarization states 90° separated
on the Poincare sphere.
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