The Spectral Separation Assembly is a key component of the Flexible Combined Imager, an instrument that will be on-board Meteosat Third Generation. It splits the input beam coming from the telescope into five spectral groups, for a total of 16 channels, from 0.4 to 13.3 μm. It comprises a set of four dichroics separators followed by four collimating optics for the infrared spectral groups, which feed the cold imaging optics. The visible spectral group is directly imaged on a detector. This paper presents the optical design of the assembly, the mechanical mounting of the optical components, and the coatings developed for the dichroics, mirrors and lenses.
Glaucoma is a disease of the optic nerve that is usually associated with an increased internal pressure of the eye and can
lead to a decreased vision and eventually blindness. It is the second leading cause of blindness worldwide with more than
80 million people affected and approximately 6 million blind. The standard clinical treatment for glaucoma, after
unsuccessful administration of eyedrops and other treatments, is performing incisional surgery. However, due to post-surgical
complications like scarring and wound healing, this conventional method has a global success rate of only about
60%. In comparison, as femtosecond laser surgery may be performed in volume and is a priori less invasive and less
susceptible of causing scarring, glaucoma laser surgery could be a novel technique to supplement the conventional
glaucoma surgery. We have been working on the development of a new tool for glaucoma treatment that uses an
optimized femtosecond laser source centered at 1.65 μm wavelength for making the surgery and an imaging system
based on optical coherence tomography (OCT) for guiding the laser surgery. In this proceeding, we present the results
obtained so far on the development and utilization of Fourier-domain OCT imaging system working at 1.3 μm center
wavelength for guiding the laser incision. Cross-sectional OCT image of pathological human cornea showing the
Schlemm's canal, where the surgery is intended to be done, is presented. By coupling OCT imaging system with the
laser incision system, we also demonstrate real-time imaging of femtosecond laser incision of cornea.
Optical biopsies are aimed at providing fast and thorough screening of biological tissues in vivo. Disease diagnosis is
based on the morphological structures and biochemical features of tissues that can be sampled in situ with high
resolution. Some optical screening techniques, such as fluorescence confocal microendoscopy, provide a limited imaging
depth due to the shallow penetration of visible light. Despite confocal microendoscopy's high resolution and image
quality, morphological changes that occur deeper in the tissue cannot be detected. Other imaging techniques, such as
optical coherence tomography (OCT), are able to obtain information at greater depth into tissue. A combination of
fluorescence confocal and OCT into a single instrument capable of rapidly switching between these modalities, has the
potential of providing complementary en face confocal images showing the morphologic features of cells within a
surface layer, and cross-sectional OCT images showing tissue microarchitecture below the surface. The concept for this
dual system is to utilize the optical train of an existing multi-spectral confocal microendoscope as a spectral-domain
OCT system. Progress made on the implementation of this combined dual integrated imaging system is presented. A
performance analysis, discussion of the limitations inherent to the use of an imaging fiber bundle, and recent imaging
results are presented.
Slit-scanning geometries for confocal microendoscopy represent a compromise between acquisition rate and optical
performance. Such systems provide high frame rates that freeze motion but recent Monte Carlo simulations show that
scattered light severely limits the practical imaging depth for in vivo applications. A new multi-point scanning
architecture for confocal microendoscopy has been developed. The new scanner is based on a relatively simple
modification to the slit-scanning geometry that results in a parallelized point-scanning confocal microendoscope that
maintains the high frame rate of a slit-scanning system while providing optical performance close to that of a single point
scanning system. The multi-point scanner has been incorporated into an existing multi-spectral slit-scanning confocal
microendoscope. The new confocal aperture consists of a slit and a rotating low duty cycle binary transmission grating,
which effectively produces a set of continuously moving widely spaced illumination points along the slit. The design
maintains the ability to rapidly switch between grayscale and multi-spectral imaging modes. The improved axial
resolution of the multi-point scanning confocal microendoscope leads to significantly better confocal sectioning and
deeper imaging, which greatly improves the diagnostic potential of the instrument.
We demonstrate the implementation of a Fourier domain optical coherence tomography (OCT) imaging system
incorporated into the optical train of a fluorescence confocal microendoscope. The slit-scanning confocal system has
been presented previously and achieves 3μm lateral resolution and 25μm axial resolution over a field of view of 430μm.
Its multi-spectral mode of operation captures images with 6nm average spectral resolution. To incorporate OCT imaging,
a common-path interferometer is made with a super luminescent diode and a reference coverslip located at the distal end
of the fiber bundle catheter. The infrared diode spectral width allows a theoretical OCT axial resolution of 12.9μm. Light
from the reference and sample combine, and a diffraction grating produces a spectral interferogram on the same 2D CCD
camera used for confocal microendoscopic imaging. OCT depth information is recovered by a Fourier transform along
the spectral dispersion direction. Proper operation of the system scan mirrors allows rapid switching between confocal
and OCT imaging modes. The OCT extension takes advantage of the slit geometry, so that a 2D image is acquired
without scanning. Combining confocal and OCT imaging modalities provides a more comprehensive view of tissue and
the potential to improve disease diagnosis. A preliminary bench-top system design and imaging results are presented.
We describe the design and operation of a multispectral confocal microendoscope. This fiber-based fluorescence imaging system consists of a slit-scan confocal microscope coupled to an imaging catheter that is designed to be minimally invasive and allow for cellular level imaging in vivo. The system can operate in two imaging modes. The grayscale mode of operation provides high resolution real-time in vivo images showing the intensity of fluorescent signal from the specimen. The multispectral mode of operation uses a prism as a dispersive element to collect a full multispectral image of the fluorescence emission. The instrument can switch back and forth nearly instantaneously between the two imaging modes (less than half a second). In the current configuration, the multispectral confocal microendoscope achieves 3-µm lateral resolution and 30-µm axial resolution. The system records light from 500 to 750 nm, and the minimum resolvable wavelength difference varies from 2.9 to 8.3 nm over this spectral range. Grayscale and multispectral imaging results from ex-vivo human tissues and small animal tissues are presented.
We present a modified multi-spectral configuration of a slit-scanning confocal microendoscope that provides higher
spectral resolution in a fully automated interface. Tissue fluorescence signal is directed through a dispersive element that
spreads the spectral information across the CCD camera mapping spectral information perpendicular to the confocal slit.
The dispersive element may be chosen to meet the specific requirements defined by the user. Our current system uses a
BK7 prism with a 45o wedge angle and a 20mm diameter clear aperture. The prism is shifted from the optical axis
allowing automated switching from grayscale (beam on-axis) to multi-spectral (beam off-axis) imaging by tilting a
computer controlled mirror. The system records over a spectral range of 450nm to 750nm. The minimum resolvable
wavelength difference varies from 2.1nm to 8.3nm over the spectral range. The lateral and axial resolution of the system
is approximately 3&mgr;m by 30&mgr;m, respectively, and is the same for both grayscale and multi-spectral imaging modes.
Multi-spectral imaging results from ex-vivo tissues are presented.