An amplified 16 channel dense wavelength division multiplexing (DWDM) array architecture is presented for
interferometric fibre optic sensor array systems. This architecture employs a distributed Erbium doped fibre amplifier
(EDFA) scheme to decrease the array insertion loss, and employs time division multiplexing (TDM) at each wavelength
to increase the number of sensors that can be supported. The first experimental demonstration of this system is reported
including results which show the potential for multiplexing and interrogating up to 4096 sensors using a single telemetry
fibre pair with good system performance.
Photonic methods for electric field sensing have been demonstrated across the electromagnetic spectrum from near-DC to millimeter waves, and at field strengths from microvolts-per-meter to megavolts-per-meter. The advantages of the photonic approach include a high degree of electrical isolation, wide bandwidth, minimum perturbation of the incident field, and the ability to operate in harsh environments. <p> </p>Aerospace applications of this technology span a wide range of frequencies and field strengths. They include, at the high-frequency/high-field end, measurement of high-power electromagnetic pulses, and at the low-frequency/low-field end, in-flight monitoring of electrophysiological signals. The demands of these applications continue to spur the development of novel materials and device structures to achieve increased sensitivity, wider bandwidth, and greater high-field measurement capability. <p> </p>This paper will discuss several new directions in photonic electric field sensing technology for defense applications. The first is the use of crystal ion slicing to prepare high-quality, single-crystal electro-optic thin films on low-dielectricconstant, RF-friendly substrates. The second is the use of two-dimensional photonic crystal structures to enhance the electro-optic response through slow-light propagation effects. The third is the use of ferroelectric relaxor materials with extremely high electro-optic coefficients.
Remote sensing systems, such as LIDAR, have benefited greatly from nonlinear sources capable of generating tunable mid-infrared wavelengths (3-5 microns). Much work has focused on improving the energy output of these sources so as to improve the system's range. We present a different approach to improving the range by focusing on improving the receiver of a LADAR system employing nonlinear optical techniques. In this paper, we will present results of a receiver system based on frequency converting mid-infrared wavelengths to the 1.5 μm region using Periodically-Poled Lithium Niobate (PPLN). By doing so, optical amplifiers and avalanche photodetectors (APDs) developed for the fiber optics communications industry can be used, thus providing very high detection sensitivity and high speed without the need for cryogenically cooled optical detectors. We will present results of laboratory experiments with 3 μm, 2.5 ns FWHM LADAR pulses that have been converted to 1.5 μm. Detection sensitivities as low as 1.5 x 10^-13 Joules have been demonstrated. The performance of the Peltier-cooled 1.5 μm InGaAs APD quasi photon-counting receiver will be described.
SRICO has developed a revolutionary approach to physiological status monitoring using state-of-the-art optical chip technology. The company’s patent pending Photrode is a photonic electrode that uses unique optical voltage sensing technology to measure and monitor electrophysiological parameters. The optical-based monitoring system enables dry-contact measurements of EEG and ECG signals that require no surface preparation or conductive gel and non-contact measurements of ECG signals through the clothing. The Photrode applies high performance optical integrated circuit technology, that has been successfully implemented in military & commercial aerospace, missile, and communications applications for sensing and signal transmission. SRICO’s award winning Photrode represents a new paradigm for the measurement of biopotentials in a reliable, convenient, and non-intrusive manner. Photrode technology has significant applications on the battlefield for rapid triage to determine the brain dead from those with viable brain function. An ECG may be obtained over the clothing without any direct skin contact. Such applications would enable the combat medic to receive timely medical information and to make important decisions regarding identification, location, triage priority and treatment of casualties. Other applications for the Photrode include anesthesia awareness monitoring, sleep medicine, mobile medical monitoring for space flight, emergency patient care, functional magnetic resonance imaging, various biopotential signal acquisition (EMG, EOG), and routine neuro and cardio diagnostics.
This paper describes a paradigm shift in the technology for sensing electro-physiological signals. In recent years, SRICO has been developing small lithium niobate photonic electrodes, otherwise called "Photrodes” for measuring EEG and ECG signals. These extrinsic fiber-optic sensing devices exploit the extremely high electrical input impedance of Mach-Zehnder Intensity (MZI) electro-optic modulators to detect microvolt and millivolt physiological signals. Voltage levels associated with electrocardiograms are typically on the order of several millivolts, and such signals can be detected by capacitive pickup through clothing, i.e., the Photrode may be used in a non-contact mode. Electroencephalogram signals, which typically have an amplitude of several microvolts, require direct contact with the skin. However, this contact may be dry, eliminating the need for conductive gels. The electrical bandwidth of this photonic electrode system stretches from below 0.1 Hz to many tens of kHz and is constrained mainly by the signal processing electronics, not by the Photrode itself. The paper will describe the design and performance of Photrode systems and the challenging aspects of this new technology.
The PhotonStar SETI project is an enterprise to detect extraterrestrial laser signals that involves many individual small telescopes acting together as a geographically diverse large array which together comprise a large collection area, thereby, offering a better chance of detection if signals exist. Widely separated small telescopes, each with a sensitive photon detection capability, can be aimed simultaneously at the same star system with precise timing that enables looking at the same time for short pulse detection. Each individual telescope can be located via GPS so that the differential distance from the star compared to every other telescope can be determined beforehand. Coordination via the Internet would enable each telescope to operate as one element of the array. This project allows direct public participation by amateur astronomers into the search for extraterrestrial intelligence as there are thousands of telescopes of eight inches or greater in use, so that the total collection area can be very substantial with public participation. In this way, each telescope is part of a larger array with data being sent via the Internet to a central station. This approach is only feasible now with the advent of GPS, the Internet, and relatively low- cost single photon detector technology.
The Optical Search for Extraterrestrial Intelligence is now 40 years old. However, it was only during the closing years of the 20th Century, after a 25-year hiatus, that the optical search has regained respectability in the SETI community at large. The quarter-of-a-century delay in American Optical SETI research was due to a historical accident and not for the lack of any enabling technology. This review paper describes aspects of past, present and future Optical SETI programs. Emphasis is placed on detecting fast, pulsed attention-getting laser beacon signals rather than monochromatic, continuous wave beacons. Some examples of commercial detection equipment that may be employed for either type of OSETI are given.
A Mach-Zehnder interferometer designed as an electric field transducer operates without metal electrodes by incorporating a novel substrate configuration. The lithium niobate device uses reverse poling of one of the interferometer arms, which provides opposing optical phase changes in the two interferometer arms when placed in an electric field. The fabricated devices exhibit a measured minimum detectable field of 0.22 V/m(root)Hz and frequency response greater than 6 GHz. Theoretical calculations show that fields in excess of 330 kV/m can be detected before appreciable distortion occurs.
The Optical Search for Extraterrestrial Intelligence (OSETI) is based on the premise that there are ETIs within our galaxy which are targeting star systems like our own with free-space beams. Upon these beams will ride attention- getting beacon signals and wideband data channels. Perhaps the wideband channels form part of a Galactic Information Superhighway, a Galactic Internet to which we are presently oblivious. The Columbus Optical SETI Observatory described in this paper is intended to be a prototype observatory which might lead to a new renaissance in both optical SETI and optical astronomy. It is hoped that the observatory design will be emulated by both the professional and amateur communities. The modern-day OSETI observatory is one that is more affordable than ever. With the aid of reasonably priced automatic telescopes, low-cost PCs, software and signal processing boards, Optical SETI can become accessible to all nations, professional scientific groups, amateur astronomy societies and even individuals.
This paper strongly suggests that the microwave rationale behind modern-day SETI lore is suspect, and that our search for electromagnetic signals from extraterrestrial technical civilizations may be doomed to failure because we are 'tuned to the wrong frequencies'. The old idea that lasers would be better for interstellar communications is revisited. That optical transmissions might be superior for CETI/SETI has generally been discounted by the community. Indeed, there is very little in the literature about the optical approach, as its efficacy was more or less dismissed by SETI researchers some twenty years ago. The main reason that the laser approach to SETI has been given a bad 'press' is the assumption that ETIs lack the skills to target narrow optical beams into selected stars. This assumption of ineptitude is shown to be erroneous, and calls into question some aspects of the rationale for Microwave SETI. The detectability of both continuous wave and pulsed visible/infrared laser signals is described in some detail.
In the companion review paper on so-called Professional Optical SETI, it was suggested that ETIs are more likely to use lasers to contact emerging technical civilizations, and that such optical ETI signals will have very high EIRPs. This paper further proposes, that it is a sensible activity for amateur optical astronomers to construct their own Optical SETI observatories. Details are given of the equipment required and the approximate costs. The author describes the Optical SETI Observatory which is presently under construction in Columbus, Ohio. A coordinated Amateur Optical SETI (AMOSETI) activity could make a useful contribution to SETI research by conducting a low-sensitivity Targeted Search in the visible and near-infrared spectrum. This could be done in parallel with the present NASA Targeted Search that is part of the High Resolution Microwave Survey (HRMS). Signal processing techniques and data-handling procedures developed for this AMOSETI research activity, would set the stage for NASA's eventual extension of HRMS into the optical regime.
We present a distributed fiber optic acoustic sensor technology that could be used to measure and locate leaks within either fluid- or gas-filled distribution lines. For these applications, the optical fiber sensor would be placed inside the pipe and could potentially locate leaks to within several meters by listening to the acoustic emission produced by the fluid or gas as it escapes from the pipe.
Leaks in dielectric fluid-filled, high-voltage distribution lines can cause significant problems for the electric power industry. Often, these lines run over long distance and are difficult to access. Operators may know that a leak exists because additional fluid is required to maintain pipe pressure; however, locating the leak is often a significant challenge. A system that could monitor and locate leaks within the electrical distribution pipe lines would be highly desirable. We present a distributed fiber optic acoustic sensor technology that could be used to measure and locate leaks within fluid-filled, high-voltage distribution lines. In this application, the optical fiber sensor is placed inside the fluid-filled pipe and can potentially locate leaks to within several meters. The fiber optic acoustic sensor is designed such that it can listen to the sound produced by the fluid as it escapes from the pipe into the surrounding soil. The fluid inside the pipe is typically maintained at a pressure of 200 psi and escapes at high velocity when a leak occurs. The distributed fiber optic sensing system being developed is based upon the Sagnac interferometer and is unusual in that range information is not obtained by the more common method of optical time domain reflectometry or optical frequency domain reflectometry, but by essentially a CW technique which works in the frequency domain. It is also unusual in that the signal processing technique actually looks for the absence of a signal.