Polarization data of a SM gyroscope coil may correlate to drift that provides a method to statically predict a
performance range of a coil during manufacturing or at a minimum before integration into a FOG assembly. The
Crossover Free (CF) coils described here are thermally symmetric and lack fiber crossovers. This design allows
possible expansion of depolarized FOGs beyond the research environment. To that end a series of double sided
CF gyroscope coils were manufactured and analyzed using a 4 channel fiber coupled polarimeter. In addition the
coils were tested on a single axis rate table in a FOG testbed. A polarimeter was used to measure the output
polarization state of the stand-alone coils and when integrated into an experimental FOG testbed. In addition
Shupe data of the CF coils was taken to determine the thermal sensitivity of the coils. Coil geometry and
construction, polarimetric and traditional drift data, and Shupe performance will be presented.
We describe experiments of fiber coils using different lengths, coil diameters, and configurations wound on a innovative
winder. Geometric and polarimetric analyses of coils and effects on Sagnac area and bending induced birefringence are
examined.
The DoD goals for inertial sensors have included achieving high accuracy performance and small size at a low cost. This goal has always been a challenging endeavor, since small size and high accuracy have often been costly and technically difficult to achieve. In 1998, the Army patented a fiber sensor coil winding concept that would facilitate the opportunity to make the Fiber Optic Gyroscope (FOG) more competitive in cost with relation to the commonly-used Ring Laser Gyro (RLG). Recent advances in FOG sensor coil winding techniques appear to show great promise in the improved performance. The novel Crossover-Free (CF) winding technique eliminates fiber crossovers and allows the use of inexpensive single-mode fiber (SMF). Experiments were conducted with the use of an analog, open-loop testbed, which was characterized with a 1 km quadrupolar SM sensor coil. Various sensor coil configurations were spliced into the FOG testbed and bias drift tests were conducted. Different fiber lengths, coil diameters, and fiber wind configurations were evaluated. The Crossover-Free sensor coils were precision wound by a semi-automated Fiber Placement Machine (FPM) developed by Stanley Associates. The Crossover-Free sensor coils test results are compared to standard precision wound coils. The bias errors caused by the fiber crossovers in standard SM sensor coils are also discussed and compared to the near elimination of the crossovers in the CF design.
High accuracy polarized fiber optic gyroscopes require sensor coils comprised of relatively expensive polarization maintaining fiber. While this fiber insures minimal polarization cross coupling and thus increased sensitivity, the long required fiber lengths result in sensor coils that are quite expensive. Reduced cost single mode fiber based coils are attractive, but exhibit poor polarization selectivity due to cross coupling that manifests as signal fading and reduced detected signal amplitude. Moreover, random birefringences induced at fiber crossover points impart a nonreciprocity that tends to exacerbate this problem. A crossover-free winding scheme employing a single mode fiber wound in an Archimedean spiral can potentially improve the performance of single mode fiber coils by eliminating these random birefringences, thereby improving coil sensitivity. As well, the bending induced birefringence of these coils can serve to improve polarization maintenance. Geometric and polarimetric analyses of spirally wound coils describing the effects on overall Sagnac area, bending induced birefringence, and polarization mode coupling are examined here. The spatially varying induced birefringence, beat length, and associated mode coupling are modeled and it is found that elimination of the cross coupling due to random crossovers renders the spiral geometry potentially useful for high accuracy inertial guidance systems.
A fiber optic system intended to perform Structural Health Monitoring (SHM) of composite motor cases has been investigated. The method described here allows for commercial-of-the-shelf (COTS) optical fiber to be integrated into a cylindrical composite motor case prior to cure. The fiber requires no pre-processing before it can be placed inside the composite material. This allows the fiber to act as a distributed sensor not a point sensor as is the case with Bragg gratings and etalons. The distributed nature of the sensor also allows the output data to be naturally multiplexed without the need for complex software or hardware interfaces. After cure the optical fiber can be interrogated to determine a base-line scan of the motor. Subsequent scans can be taken of the motor to determine if damage of a sufficient nature has occurred that would require further investigation or retiring of the motor. In this study optimum wind patterns and proper placement of the optical fiber was investigated. In addition cost reductions of the instrumentation and the practicality of optical fiber egress options were undertaken.
Interrogation and analysis of hazardous agents in a hostile environment is difficult using currently available visible spectroscopic instrumentation due to both the size and cost of existing devices. One proposed method to decrease the size and cost of current visible spectrometers uses Micro-Opto-Electro Mechanical Systems (MOEMS) and die-level photo-diodes instead of static bulk gratings and linear detector arrays. We propose a grating based electrostatic comb driven visible micro-spectrometer that allows spectroscopy to be performed in the harshest of environments for a cost that, up until now, has been restricted. Our proposed device is approximately 50 mm2 in size, which makes it portable enough to gather spectroscopic data discreetly and remotely. The use of MOEMS and precision micro-machined optics allows this device a level of accuracy and mechanical ruggedness that conventional bulk grating spectrometers lack. Commercial-off-the-shelf (COTS) optical components are combined with state-of-the-art (SOA) photolithography techniques that reduce production costs while increasing manufacturability. The novel design of this spectroscopic device allows it to be utilized in a wide range of applications, from collecting data on an unmanned ground vehicle or acting as a passive sensor that remotely evaluates the introduction or reduction of certain reagents. Principles of assembly, operation and testing will be presented in this paper.
Several techniques for measuring the oxygen saturation of blood in retinal vessels have been reported. One interesting application of retinal vessel oximetry is the identification of occult blood loss in trauma victims. However, all the devices described to date are too bulky and cumbersome to be used in a trauma bay or in the field. We present a design for a handheld instrument that performs four-wavelength retinal vessel oximetry. This device is comparable in size and weight to a commercially available camcorder, and is suitable for use in the trauma bay. The compact size of this device could also extend its applications beyond traditional clinical settings, as it could be used by primary care physicians and home health care workers for the screening and monitoring of ophthalmic diseases. Principles of operation and preliminary data from the device will be described.
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