Optical Coherence Tomography (OCT) is a relatively new interferometric technology that allows for high-resolution and non-destructive tomographic imaging. One of its primary current uses is for in vivo and ex vivo examination of medical samples. It is used for non-destructive examination of ocular disease, dermatological examination, blood vessel imaging, and many other applications. Some primary advantages of OCT imaging include rapid imaging of biological tissue with minimal sample preparation, 3D high-resolution imaging with depth penetrations of several millimeters, and the capability to obtain results in real time, allowing for fast and minimally invasive identification of many diseases. Current commercial OCT systems rely heavily on optical fiber-based designs. They depend on the robustness of the fiber to maintain system performance in variable environmental conditions but sacrifice the performance and flexibility of free-space optical designs. We discuss the design and implementation of a free-space OCT interferometer that can automatically maintain its alignment, allowing for the use of a free-space optical design outside of tightly controlled laboratory environments. In addition, we describe how similar enhancements can be made to other optical interferometric systems. By extending these techniques, we can provide similar improvements to many related fields, such as interferometric metrology and Fourier Transform Spectroscopy. Improvements in these technologies can help bring powerful interferometric tools to a wider audience.

Because of the need to move large amounts of data effienciently, optical based communications are a critical component of modern telecommunications. And as a key enabler of optical communications, electrical components play a critical role in optical data links. Optoelectronic integrated circuits provide the bridge between the optical and electrical realms. Electronic integrated circuits are also integral parts of the optical link, interfacing with post processing circuitry and compensating for any limitations along the link. In this investigation, three circuits for optical data link applications are studied. Two optoelectronic integrated circuit front-ends for freespace and long haul applications, respectively and an active filter for near end cross talk cancellation associated with high data rate transmission. The first circuit is an 8x8 monolithic receiver array for a Spatial Division Multiplexing optical link. A compact and low power 8x8 array was designed and demonstrated a channel that received data at rates of 1Gb/s. It is the first completely monolithic demonstration of a 2D receiver array within a conventional ion implanted GaAs MESFET process. The second circuit demonstrated a long wavelength (1.55 m) optoelectronic receiver for long haul applications. The circuit utilized a TWA topology, which maximizes the available bandwidth from the GaAs MESFET process. It incorporated a thin-film inverted MSM photodetector to achieve nearly monolithic integration. The final circuit is a tunable high pass active filter in 0.18 m CMOS technology. As part of a NEXT noise canceller architecture, it will provide the means to extend data transmission in FR-4 legacy backplanes into the tens of Gb/s datarate.

<p>Free Space Optics (FSO) has received a great deal of attention lately both in the military and civilian information society due to its potentially high capacity, rapid deployment, portability and high security from deception and jamming. The main issue is that severe weather can have a detrimental impact on the performance, which may result in an inadequate availability. </p><p>This report contains a feasibility study for an all-optical free-space link intended for short-range communication (200-500 m). Laboratory tests have been performed to evaluate the link design. Field tests were made to investigate availability and error performance under the influence of different weather conditions. Atmospheric impact due to turbulence related effects have been studied in detail. The most crucial part of the link design turned out to be the receiver optics and several design solutions were investigated. The main advantage of an all-optical design, compared to commercially available electrooptical FSO-systems, is the potentially lower cost.</p>

Thesis (M.S.)--Naval Postgraduate School, 2004. / Title from title screen (viewed Aug. 13, 2004). "March 2004." Includes bibliographical references (p. 71-73). Also issued in paper format.

ITC/USA 2013 Conference Proceedings / The Forty-Ninth Annual International Telemetering Conference and Technical Exhibition / October 21-24, 2013 / Bally's Hotel & Convention Center, Las Vegas, NV / We address the problem of detection in orbital angular momentum (OAM). The focus of our analysis will be on the power efficient Q-ary Pulse Position Modulation (Q - PPM). Free space optical signals sent through wireless channels are degraded by atmospheric turbulence. In this paper a novel detection approach based on a factor graph representation of OAM Q-PPM signalling is presented to equalize for the crosstalk among orbital angular momentum vortices. It will be shown that our proposed detection algorithm significantly outperforms the separate detection scenario in terms of error rate performance.

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Multipulse pulse position modulation (MPPM) has been widely proposed to improve data rate over the traditional pulse position modulation (PPM) in free-space optical communication systems. However, there is no known efficient method of encoding MPPM codewords. Furthermore, MPPM is not the optimal coding scheme (in terms of data rate) given the two main constraints of optical systems (duty cycle and zero runlength). In this work, an improved encoding technique for MPPM is provided as well as an analysis of regions where significant rate gain over MPPM is achievable. A new coding technique based on constrained coding is introduced that allows construction of codes which achieves considerable rate gain over comparable MPPM systems. In addition, our new codes allow for convenient concatenation with an outer-code and are suitable for iterative decoding. Simulation results show that these codes can achieve a $6$ dB coding gain over comparable MPPM systems.

Multipulse pulse position modulation (MPPM) has been widely proposed to improve data rate over the traditional pulse position modulation (PPM) in free-space optical communication systems. However, there is no known efficient method of encoding MPPM codewords. Furthermore, MPPM is not the optimal coding scheme (in terms of data rate) given the two main constraints of optical systems (duty cycle and zero runlength). In this work, an improved encoding technique for MPPM is provided as well as an analysis of regions where significant rate gain over MPPM is achievable. A new coding technique based on constrained coding is introduced that allows construction of codes which achieves considerable rate gain over comparable MPPM systems. In addition, our new codes allow for convenient concatenation with an outer-code and are suitable for iterative decoding. Simulation results show that these codes can achieve a $6$ dB coding gain over comparable MPPM systems.

Optical Coherence Tomography (OCT) is a relatively new interferometric technology that allows for high-resolution and non-destructive tomographic imaging. One of its primary current uses is for in vivo and ex vivo examination of medical samples. It is used for non-destructive examination of ocular disease, dermatological examination, blood vessel imaging, and many other applications. Some primary advantages of OCT imaging include rapid imaging of biological tissue with minimal sample preparation, 3D high-resolution imaging with depth penetrations of several millimeters, and the capability to obtain results in real time, allowing for fast and minimally invasive identification of many diseases. Current commercial OCT systems rely heavily on optical fiber-based designs. They depend on the robustness of the fiber to maintain system performance in variable environmental conditions but sacrifice the performance and flexibility of free-space optical designs. We discuss the design and implementation of a free-space OCT interferometer that can automatically maintain its alignment, allowing for the use of a free-space optical design outside of tightly controlled laboratory environments. In addition, we describe how similar enhancements can be made to other optical interferometric systems. By extending these techniques, we can provide similar improvements to many related fields, such as interferometric metrology and Fourier Transform Spectroscopy. Improvements in these technologies can help bring powerful interferometric tools to a wider audience.

Performance requirements of short-distance digital communication links have increased considerably with the escalating demand for high speed and high density data links. The high aggregate bandwidth and channel density achievable by free-space optical interconnects (FSOIs) make them ideal replacement for electrical interconnection schemes. Optical interconnects potentially have low power consumption, and can facilitate the development of radically novel designs for VLSI architectures including heterogeneous multiprocessor systems, and highly parallel computing systems. Recent developments in the integration of Vertical-Cavity Surface-Emitting Laser (VCSEL) arrays and photodetector arrays with CMOS electronic circuitry have increased the practical potential of optical interconnects. However, VCSELs tend to operate in several transverse modes simultaneously, which will degrade the performance of FSOIs. Experimental investigation was performed to evaluate the operation characteristics and the intensity noise in VCSELs. The measurement results were later combined with optical simulations to analyse the effect of optical crosstalk in free-space optical interconnects. The VCSEL characterization included light-current-voltage relationships, relative intensity noise, modal spectral composition and modal beam profiles. The optical system simulation software (Code V) was used to simulate optical crosstalks in the FSOI system. Experimentally measured spectrally-resolved near-field images of VCSEL higher order modes were used as extended sources in the proposed simulation model. The simulation was performed using a combination of exact ray-tracing and the beam propagation method. A new type of crosstalk referred to as the stray-light crosstalk (SLC) was introduced. This type of crosstalk is caused by the overfill of the transmitter microlens by the VCSEL beam. It was discovered that part of the signal was imaged by the adjacent microlens to another channel, possibly far from the intended one. The simulation showed that the SLC is strongly dependent on the fill factor of the microlens, array pitch, and the channel density of the system. When comparing the diffraction-caused crosstalk (DCC) to SLC, an increase in the interconnection distance has little influence on the SLC. A simple behavioural model was developed which accurately approximates the crosstalk noise for a range of optical sources and interconnect configurations. The effect of transmitter and receiver array configurations on the performance of FSOIs was investigated. Our results demonstrate the importance of SLC in both square and hexagonal configuration. By changing the array lattice geometry from square to a hexagonal, we obtained an overall optical signal-to-noise ratio (SNR) improvement of 3 dB. The optical SNR is optimal for the hexagonal channel arrangement regardless of the transverse mode structure of the VCSEL beam was shown. Furthermore, the VCSEL drive current required for the best performance of the FSOI system was determined. The optimal focal length of the transmitter microlens array which maximises the SNR by minimising the combined effects of DCC and SLC was determined. Our results show that shorter focal length needs to be used for higher order modes to obtain optimal SNR in an FSOI system.