Polymer substrates, in particular polyimide substrates, and polymer laminates for optical applications are described. Polyimide substrates are polished on one or both sides depending on their thickness, and single-layer or multi-layer waveguide structures are deposited on the polished polyimide substrates. Optical waveguide devices are machined by laser ablation using a combination of IR and UV lasers. A waveguide-fiber coupler with a laser-machined groove for retaining the fiber is also disclosed.

Polished polymide substrate

Phase generated carrier (PGC) demodulation schemes are widely used in fiber-optic interferometric sensors Basic PGC schemes required the certain value of the phase modulation depth to work properly In this paper, a novel phase modulation depth evaluation and correction technique for PGC demodulation schemes based on the integral control feedback is presented The proposed scheme provides the phase modulation depth stabilization to the certain predefined optimal value Detailed theoretical analysis and mathematical modeling of the proposed scheme and the PGC-Atan demodulation scheme were performed to estimate their required parameters The suggested technique with the PGC-Atan demodulation scheme was implemented in the field-programmable gate array-based electronic processing circuit of the single interferometric fiber Bragg grating sensor Experimental results are consistent with theoretical analysis and the proposed scheme provides real-time stabilization of the phase modulation depth to its optimal value 263 rad with the standard deviation less than $5\ast 10^{-4}$ rad

Phase Modulation Depth Evaluation and Correction Technique for the PGC Demodulation Scheme in Fiber-Optic Interferometric Sensors

The deformation of single-mode fibers resulting from a longitudinally applied static force has been measured experimentally by means of high resolution heterodyne interferometry and analyzed theoretically using the second-order theory of elasticity and the photoelastic effect. Both the elongation of the fiber and the phase change of light propagating through the fiber have been measured as a function of tensile force. The values of the elastic constants measured for fibers with pure silica core and B 2 O 3 doped cladding are E = 6.41 \times 10^{10} N/m2for the Young's modulus, \delta = -4.0 for the nonlinearity constant of the longitudinal strain, and \beta = -2.3 for the nonlinearity constant of the transverse strain. For unit elongations up to 0.3 percent, no creep, hysterisis, or relaxation effects have been observed within a resolution of one part in 104.

Deformation of single-mode optical fibers under static longitudinal stress

Fiber-optic interferometers have been studied extensively for sensing applications. Recently a technique described as the J1 … J4 technique was reported for the linear measurement of dynamic phase changes in a fiber interferometer that requires no phase bias and for which the measurement is independent of random phase fluctuations. However, the implementation of the J1 … J4 technique is limited because only the magnitude of the J1 … J4 Bessel components can be measured on a spectrum analyzer without information available on the sign of the Bessel function. Here a modified signal-processing technique that overcomes the limitations mentioned above is described.

Modified J(1) ... J(4) method for linear readout of dynamic phase changes in a fiber-optic homodyne interferometer.

Measurement of nonlinear refraction index and two-photon absorption in a novel organometallic compound

A new technique that provides linear measurement of dynamic phase change in a no-feedback, no-phase-bias fiberoptic interferometer is described. The phase measurement is unaffected by random changes in phase, source intensity, and fringe visibility. A minimum detectable phase shift of 0.1 rad has been measured for the configuration reported.

Linear readout of dynamic phase change in a fiber-optic homodyne interferometer.

A new technique for dynamic phase calibration that utilizes only visual observation of the fringe pattern is demonstrated for use in fiber-optic interferometric sensors and phase modulators. The need for a photodetector and its associated electronic circuitry is completely eliminated. Observations show that random changes in phase, source intensity, and fringe visibility do not affect the phase calibration. Since no phase bias or feedback is necessary, the new method is simple and fast. This technique is of universal applicability to any two-beam interferometer incorporating dynamic sinusoidal displacements.

Universal dynamic phase-calibration technique for fiber-optic interferometric sensors and phase modulators.

A simple and reliable fringe-counting method is used to determine the fiber static elastic response in fiber-optic sensors and modulators. Large strain hysteresis and nonlinearity have been observed in the commonly employed configuration of bonding a bare fiber onto a strain element. Jacketed fibers show reduced hysteresis and nonlinearity in their elastic response. Reductions in hysteresis from 23% to 1% of the maximum strain and in the nonlinearity by a factor of 3 have been measured.

K. Srinivasan

Papers

Linear readout of dynamic phase change in a fiber-optic homodyne interferometer.

Universal dynamic phase-calibration technique for fiber-optic interferometric sensors and phase modulators.

Interferometric measurement of fiber strain hysteresis and nonlinearity for sensitivity optimization.