Miniaturization and cost reduction of OCT systems are important for enabling many new clinical applications as well as accelerating the development of existing applications. Silicon photonics is an important low-cost, high-volume, multi-functional platform for integrated optics because it can benefit from existing semiconductor fabrication techniques to integrate many advanced optical functions onto a single microchip. We present a miniaturized silicon photonic integrated swept source OCT receiver, measuring 3×4mm2, with advanced functionalities including dual polarization, dual balanced, in-phase and quadrature detection, essentially enabling the detection of the full vector field (amplitude, phase, and polarization) of the optical signal. With this integrated receiver, we demonstrate full-range OCT for complex conjugate artifact suppression, polarization diversity detection for removing polarization fading artifact, and polarization sensitive OCT for tissue birefringence imaging. The silicon photonic integrated receiver is a key advance towards developing a miniaturized, multi-functional swept source OCT system.
Eric Swanson discusses the migration of optical coherence tomography (OCT) into clinical practice in, "Clinical Translation in OCT: Role of Research, Funding, and Entrepreneurism."
The translation from research to successful clinical impact is challenging and often the process passes through several stages including product development, initial sales and product iteration, market growth, and, finally, the next generation products. Each step can take several years, requiring persistence and perseverance on the parts of technologists and investors alike. The first release of a reliable, manufacturable, and supportable commercial product into the hands of clinicians is a critical milestone. It allows for fine tuning of the product attributes on the road to proving clinical utility and sometimes results in discovery of unforeseen applications.
Clinical translation of OCT has been impactful, scientifically, clinically, and economically. Over 20M patients per year undergo OCT diagnostic imaging and the cumulative OCT system sales over the past decade are well in excess of $1B. Many applications remain to be commercialized could potentially further benefit healthcare and improve quality of life. Startups have played, and continue to play, an important role in the translation of new applications of OCT.
Optical coherence tomography (OCT) is a recently developed optical imaging technique that uses low coherence interferometry to perform high resolution, cross-sectional imaging in biological systems. While in vitro studies have been performed to demonstrate the feasibility of performing optical biopsy in human tissues, key technologies must be developed to extend this technique to in vivo internal organ systems. These advances include improvements in image acquisition speed, and the development of an OCT compatible catheter-endoscope. A fast scanning OCT system has recently been constructed. This system employs a high power (200 mW) chromium doped forsterite laser as the low coherence source and a piezoelectric fiber stretcher to induce reference arm optical path length delay. The fast scanning system acquires OCT images with an acquisition rate of four images per second, an axial resolution of 15 micrometers, and a signal to noise ratio of 112 dB. When incorporated with the recently constructed OCT compatible catheter-endoscope, this system is capable of obtaining high resolution endoscopic diagnostic images of tissue microstructure in vivo.
We describe an all-optical network testbed deployed in the Boston area, and research surrounding the allocation of optical resources -- frequencies and time slots -- within the network. The network was developed by a consortium of AT&T Bell Laboratories, Digital Equipment Corporation, and Massachusetts Institute of Technology under a grant from ARPA. The network is organized as a hierarchy consisting of local, metropolitan, and wide area nodes tea support optical broadcast and routing modes. Frequencies are shared and reused to enhance network scalability. Electronic access is provided through optical terminals that support multiple services having data rates between 10 Mbps/user and 10 Gbps/user. Of particular interest for this work is the 'B-service,' which simultaneously hops frequency and time slots on each optical terminal to allow frequency sharing within the AON. B-service provides 1.244 Gbps per optical terminal, with bandwidth for individual connections divided in increments as small as 10 Mbps. We have created interfaces between the AON and commercially available electronic circuit-switched and packet-switched networks. The packet switches provide FDDI (datacomm), T3 (telecomm), and ATM/SONET switching at backplane rates of over 3 Gbps. We show results on network applications that dynamically allocate optical bandwidth between electronic packet-switches based on the offered load presented by users. Bandwidth allocation granularity is proportional to B-Service slots (10-1244 Mbps), and switching times are on the order of one second. We have also studied the effects of wavelength changers upon the network capacity and blocking probabilities in wide area all-optical networks. Wavelength changers allow a change in the carrier frequency (within the network) without disturbing the data modulation. The study includes both a theoretical model of blocking probabilities based on network design parameters, and a computer simulation of blocking in networks with and without wavelength changers. Theory and simulation are in good agreement, and the results allow classification of those optical networks where wavelength changers provide benefit.
Mark Stevens, B. Hemenway, Daniel Castagnozzi, Salil Parikh, Douglas Marquis, Eric Swanson, Ivan Kaminow, Uziel Koren, C. Dragone, Thomas Koch, Robert Thomas, C. Ozveren, E. Grella
An experimental all-optical, wavelength-routed network testbed has been constructed in the Boston metropolitan area. The network has 20 optical channels, space by 50 GHz and provides dedicated circuit-switched wide-band service at user defined modulation formats and rates up to 10 Gbps, and time-slotted WDM services for medium and low-rate users. We are now characterizing the deployed network which spans over 87 km interconnecting four all-optical local-area networks in Littleton, Lexington, and Cambridge Massachusetts. We discuss wavelength sharing and reuse, local broadcast, routing, multi-cast and multi-hop connections at 1.244, 2.488, and 10 Gbps. We present the system design and the performance (e.g. BER and cross-talk) of local-broadcast, metropolitan-area-routed and broadcast transmission modes.
We describe an all-optical network testbed deployed in the Boston metropolitan area, and some of the experimental applications running over the network. The network was developed by a consortium of AT&T Bell Laboratories, Digital Equipment Corporation, and Massachusetts Institute of Technology under a grant from ARPA. The network is an optical WDM system organized as a hierarchy consisting of local, metropolitan, and wide area nodes that support optical broadcast and routing modes. Frequencies are shared and reused to enhance network scalability. Electronic access is provided through optical terminals that support multiple services having data rates between 10 Mbps/user and 10 Gbps/user. Novel components used to implement the network include fast-tuning 1.5 micrometers distributed Bragg reflector lasers, passive wavelength routers, and broadband optical frequency converters. An overlay control network implemented at 1.3 micrometers allows reliable out-of-band control and standardized network management of all network nodes. We have created interfaces between the AON and commercially available electronic circuit-switched and packet-switched networks. We will report on network applications that can dynamically allocate optical bandwidth between electronic packet-switches based on the offered load presented by users, without requiring interfaces between users and the AON control system. We will also describe video and telemedicine applications running over the network. We have demonstrated an audio/video codec that is directly interfaced to the optical network, and is capable of transmitting high-rate digitized video signals for broadcast or videoconferencing applications. We have also demonstrated a state-of-the-art radiological workstation that uses the AON to transport 2000 X 2000 X 16 bit images from a remote image server.
Optical Coherence Tomography (OCT) is a new technique that is used to obtain cross- sectional images of highly scattering tissue. OCT has been applied to image both architectural and cellular morphologic structures in clinically relevant in vitro human tissues, including the human epiglottis and full-thickness skin. The performance of OCT at 850 nm and 1300 nm is compared. In addition, high numerical aperture OCT enhanced confocal microscopy have potential for non-invasive in vivo diagnosis.
Optical Coherence Tomography (OCT) is a new, non-invasive diagnostic technique for high resolution optical 3D imaging, which was developed and applied to several different biological materials during the lasi; five years [1, 2, 3]. A unique application ofthis technique is the microscopical cross-sectional imaging ofpostenor structures ofthe eye which are not accessable with other high resolution techniques in-vivo neither with x-ray-imaging nor with high frequency ultrasound scanning. The superior spatial resolution on the order ofabout lOtm laterally and axially, the high signal-to-noise ratio ofmore than 100 db and the fast acquisition-time of one second for a two dimensional scan provides a technique for cross-sectional in-vivo-momtoring ofintraocular structures and therefore the possibility to study the time course of anatomical and pathological developments in the eye. The acute morphological changes of ocular structures and their biological healing response after shortterm impacts such as high-intensity laser exposures are ofparticular interest for the understanding of the mechanisms responsible for therapeutic laser-application in ophthal-mology as well as for laser injury to the eye. A correlation between cross-sectional OCT-images and structural findings using classical histopathological techniques facilitates a better interpretation ofthe characteristic patterns seen in OCTimages and defines the sensitivity ofthe OCT-technique to image morphological details. On the other hand preparational artefacts not avoidable in all histological procedures can be identified and analyzed by comparing histological micrographs with OCT-images of exactly the same structure. First results of an experimental study where retinal effects were produced in monkey eyes using laser pulses from 200 ms to 130 fs in duration are presented in this article. The applied energies from 5tJ to 50 mJ were able to induce the whole spectrum of biological effects possible in the eye, ranging from intraretinal microruptures to extensive thermal denaturation and massive preretinal hemorrhages [4, 5, 6].
We present the first in vivo study using Optical Coherence Tomography (OCT) as the imaging device for lenticular cataracts in the geriatric rhesus monkey. OCT is a non-invasive imaging technique that produces a 2D cross sectional image of intraocular tissue similar to ultrasound B scan. In OCT the images are formed by measuring optical reflections from the tissue. Eighteen geriatric subjects with documented lenticular opacities and one control subject were imaged. The OCT images produced are compared to current and previous clinical cataract grading exams and slit-lamp photography. Histopathology was collected on one subject and is compared to the OCT image. OCT provides information on nuclear, cortical and subcapsular opacities. The image formation is presented based on a color coded computer generated log reflective scale. The log reflective scale is converted to a qualitative grading system. Although movement and shadow artifact can occur, these are readily identifiable and can be differentiated from underlying lenticular abnormalities. OCT has great potential to assist in further characterization of cataracts.
High data rate communications systems will soon be needed for space applications. Technology and applications which support high data rates are already in place for ground- based telecommunications, or will be in the future. The advantages of an optical system over a traditional RF link for free space communications are particularly compelling for high data rates. We have been developing the necessary technology to demonstrate the feasibility of high rate free-space optical communications technology at 1.5 micrometers . The existence of a large, mature technology base at 1.5 micrometers developed for the telecommunications industry has allowed us to focus our development effort on two key technologies needed for space applications that have not been developed for the ground: a 1 Watt class optical power amplifier and a near quantum limited receiver. This paper will describe the overall system design for a high data rate optical communications system and present experimental results demonstrating < 50 photons/bit sensitivity at 10 Gbps with 1 Watt of optical power. The existence of a feasibility demonstration at this data rate enables downward scalability to data rates of 1 Gbps or less with small, inexpensive terminals.
Wavelength Division Multiplexing (WDM) is currently being investigated for ground-based fiber optic networks as a means to achieve high aggregate data rates and/or to allow the use of lower power lasers at a given rate by adding additional channels. A drawback to using WDM techniques for space applications has been that most of the WDM devices used to combine wavelengths are lossy, particularly when implemented with integrated optics or fiber gratings. The additional loss is not important for ground-based applications because it can be overcome by adding gain (with an erbium-doped fiber amplifier, for example). For space applications, where size, weight, and power consumption are critical, the excess loss is a serious drawback. We describe here a very low-loss technique for wavelength combining using standard fiber components. The technique is scalable to moderate numbers of wavelengths while maintaining low loss. Low loss means that these multiplexers can be used for applications such as power combining that are not feasible with traditional techniques. Experimental results confirming low loss power combining will be presented.
In order to simplify system architectures and make efficient use of laser power, space lasercom system designers often try to consolidate the receiver subsystems. In this paper, we present a receiver which uses a single subsystem for both spatial tracking error sensing and communication signal reception. It makes use of an electro-optic crystal as a conical scanner for tracking error measurement, couples the scanned light into a single mode fiber, and uses standard fiber-based heterodyne techniques to derive an intermediate frequency signal. This signal is processed to retrieve both the binary FSK signal and the tracking error signal, as well as an estimate of signal power for use in normalizing the tracking error. The fiber-coupled receiver makes possible a modular architecture, whereby the transmitter, receiver, and telescope subsystems can reside in different parts of the spacecraft. Such an architecture is known to have a number of desirable properties. We present a discussion of the frequency plan, data demodulation, frequency tracking, spatial tracking, and gain control subsystems. Design considerations and experimental results are presented.
We describe a new technique called femtosecond transillumination optical coherence tomography which combines femtosecond pulses, coherent heterodyne detection, and fiber- optic confocal imaging to achieve time-gated and spatially resolved imaging through diffusive biological tissue. Images of absorbing objects embedded in scattering biological media are demonstrated by selecting either the earliest arriving unscattered ballistic component or the least scattered portion of the diffuse transmitted light. Time and spatially resolved analysis of photon migration through model scattering systems is used to establish fundamental limits for this class of time-gated and spatially resolved optical imaging techniques, and to evaluate their potential biomedical applications in early tumor diagnosis.
For very high data rates, optical communications holds a potential performance edge over other technologies, especially for space applications where size, weight, and power are of prime importance. We report demonstrations of several Gigabit-per-second (Gbps) class all- semiconductor optical communications systems which have been developed for free-space satellite crosslink applications. These systems are based on the master-oscillator-power- amplifier (MOPA) transmitter architecture which resolves the conflicting requirements of high speed and high power on a single-laser coherent transmitter. A 1 Gbps, 1 Watt system operating at 973 nm with a frequency-shift-keyed (FSK) modulation format is the highest power coherent optical communications system using all semiconductor lasers reported to date. A 3 Gbps differential-phase-shift-keyed (DPSK) system uses a 2-stage injection-locked diode array as a power amplifier at 830 nm. At a wavelength of 1.5 micrometers , an optically- preamplified direct-detection on-off-keyed (OOK) receiver was demonstrated at both 3 and 10 Gbps. A 3 Gbps optically-preamplified direct-detection DPSK receiver was also demonstrated and represents, to our knowledge, the highest sensitivity DPSK receiver reported to date for data rates above 2 Gbps.
We present a new technique for coherent optical imaging of ocular structure based on optical coherence tomography (OCT). OCT is a noncontact, noninvasive, tomographic imaging technique with superior spatial resolution to ultrasound (< 20 micrometers ) and high sensitivity (100 dB dynamic range). We have used OCT to perform direct imaging of ocular structure in the anterior and posterior segments of human eyes in vitro and in vivo. In the anterior segment, we have measured corneal thickness and profile, anterior chamber depth and angle, and iris thickness and profile. These and other possible measurements have potential applications in diagnosis of pathologies of the cornea, angle, and iris, as well as in noncontact biometry for applications in cataract and corneal refractive surgeries. In the posterior segment, we have obtained high-resolution images of retinal structure in human subjects in vivo. These images demonstrate higher resolution than available with any other existing technique, and include characterization of optic disk morphology and topology. These measurements have potential applications in early diagnosis and assessment of glaucoma and other retinal diseases.
KEYWORDS: Optical tracking, Receivers, Single mode fibers, Interference (communication), Electro optics, Signal attenuation, Free space optical communications, Heterodyning, Signal detection, Free space optics
Recently, the potential advantages of using single-mode optical fibers within free-space laser communication systems has been recognized. Of particular importance within an optical receiver is the spatial tracking system, which must couple the received signal into a single-mode optical fiber in the presence of environmental disturbances. Because optical beamwidths are small (microrad) and typical disturbances can be large (mrad), this requirement makes the design of the spatial tracking subsystem an important and difficult part of an optical receiver. Previous systems have utilized mechanical techniques for nutating the tip of the receiving fiber to derive tracking information. A new technique, based on using a fixed fiber and an electro-optic beam deflector, is proposed. Design considerations and experimental results are presented.
The use of single mode fiber optics to simplify the design of space-based optical communication systems is explored. Design considerations concerning the issues of acquisition, pointing, tracking, communication performance, efficient source-to-fiber coupling, isolation, and transmitter power limitations are presented. Preliminary experimental results of a breadboard fiber-based coherent optical communication system are also presented.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.