Broadband laser ranging uses spectral interferometry and a dispersive Fourier transform to perform high repetition rate position measurements of explosively-driven surfaces typically moving at several km/s. A broadband fiber laser and fiber interferometer record distance as a relative delay between short pulses, and the beat spectrum of the pulses is mapped into the time domain via long propagation in dispersive fiber. Optical amplification and a fast oscilloscope allow the dispersed spectrum to be recorded in real-time, often at measurement rates of 20-40 MHz. The third-order phase of the dispersive fiber causes distortions in mapping the spectrum into time that must be compensated for when analyzing the measured data.
We characterize the accuracy and precision of BLR systems by performing a scan of static positions and comparing our single-shot measurements against position measurements from a commercial Michelson interferometer. We demonstrate a combination of hardware and data analysis that measures position to within 30 microns over a 27 cm range with very high precision.
This paper presents an overview of non-intrusive electric field sensing. The non-intrusive nature is attained by creating a
sensor that is entirely dielectric, has a small cross-sectional area, and has the interrogation electronics a long distance
away from the system under test. One non-intrusive electric field sensing technology is the slab coupled optical fiber
sensor (SCOS). The SCOS consists of an electro-optic crystal attached to the surface of a D-shaped optical fiber. It is
entirely dielectric and has a cross-sectional area down to 0.3mm by 0.3mm. The SCOS device functions as an electric
field sensor through use of resonant mode coupling between the crystal waveguide and the core of a D-shaped optical
fiber. The resonant mode coupling of a SCOS device occurs at specific wavelengths whose spectral locations are
determined in part by the effective refractive index of the modes in the slab. An electric field changes the refractive
index of the slab causing a shift in the spectral position of the resonant modes. This paper describes an overview of the
SCOS technology including the theory, fabrication, and operation. The effect of crystal orientation and crystal type are
explained with respect to directional sensitivity and frequency response.
When fiber Bragg gratings (FBG) are tightly packed in a mesh and their peaks get close at a distance on the order of individual FBG spectrum widths, they start overlapping and there is a distance below which both peaks won’t be detectable anymore using standard peak detection method. Ability to determine locations of individual peaks even after they overlap allows more gratings in a mesh and an increase in shape sensing resolution. We use a linear interpolation method to estimate peak locations when peaks overlap and become undetectable with standard peak finding technique. We test this algorithm on experimentally obtained data and compare peak locations obtained by the algorithm to exact peak locations. We analyze the error to show that algorithm performs well when velocity of peaks stays uniform during peak crossing. However, the error rapidly increases if the velocity changes during crossing and the maximum error can occur in a situation when peaks change direction during peak crossing.
This paper presents improvements to slab-coupled optical fiber sensors (SCOS) for electric-field sensing. The improvements are based on changing the crystal cut and orientation of the slab waveguide in combination with altering the input light polarization. Traditional SCOS are fabricated using z-cut potassium titanyl phosphate crystals and are operated with TM polarized light. They have been shown to detect fields as low as 100 V/m. By using an x-cut crystal and TE polarized light, the sensitivity to electric fields is increased 8x due to, primarily, an increase in electric field penetration into the slab by exploiting a tangential boundary condition, and secondly, an increase to the effective electro-optic coefficient of the slab.
This paper presents innovations that reduce the dimensions and interrogation complexity of a previously developed
multi-axis electric field sensor. These devices are based on slab coupled optical sensor (SCOS) technology. SCOS
are sensitive to electric fields that are parallel to the optic axis of the electro-optic slab. Electric fields are measured
in two axes by mounting SCOS devices, which have slabs with optic-axes perpendicular to the fiber (z-cut),
orthogonal to each other. In order to reduce dimensions of the sensor, the third-axis is measured by having a slab
with the optic-axis parallel to the fiber (x-cut). Since the resonant mode coupling of a SCOS device occurs at
specific wavelengths whose spectral locations are determined in part by the effective refractive index of the modes
in the slab, rotating a z-cut slab waveguide relative to the optical fiber will cause the spectral position of the
resonance modes to shift. This method allows the resonance modes to be tuned to specific wavelengths, enabling a
multi-axis SCOS to be interrogated with a single laser source.
Modern electronics are often shielded with metallic packaging to protect them from harmful electromagnetic
radiation. In order to determine the effectiveness of the electronic shielding, there is a need to perform non-intrusive
measurements of the electric field within the shielding. The requirement to be non-intrusive requires
the sensor to be all dielectric and the sensing area needs to be very small. The non-intrusive sensor is attained
by coupling a slab of non-linear optical material to the surface of a D shaped optical fiber and is called a slab
coupled optical fiber sensor (SCOS). The sensitivity of the SCOS is increased by using an organic electro-optic
(EO) polymer.
High powered microwave weapons use electric fields to overload electronics. We developed a non-intrusive sensor
using a technology based on slab coupled optical sensing (SCOS). Each sensor detects the electric field component
normal to the surface of the slab. By mounting two of these sensors orthogonally to each other, a more complete
image of the electrical field can be obtained. One of the major hurdles of creating a multi-axial SCOS is keeping the
size of the sensor small. The size is limited by (1) the size of the sensing material and (2) the ability to package the
sensor to maintain its structural integrity and orientation. Good sensitivity is attained with SCOS with a length less
than 3 mm and the D-fiber platform has a small core which allows for much less bending loss than standard single
mode fiber. We have developed a mounting system that is heat resistant and structurally robust to protect the sensor
that is extremely small when compared to traditional electric field sensors.
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