Single-mode Optical Fiber Waveguides Research Articles

Implementation of a Reference Interferometer for Nanodetection

A thermally and mechanically stabilized fiber interferometer suited for examining ultra-high quality factor microcavities is fashioned. After assessing its free spectral range (FSR), the module is put in parallel with a fiber taper-microcavity system and then calibrated through isolating and eliminating random shifts in the laser frequency (i.e. laser jitter noise). To realize the taper-microcavity junction and to maximize the optical power that is transferred to the resonator, a single-mode optical fiber waveguide is pulled. Solutions containing polystyrene nanobeads are then prepared and flown to the microcavity in order to demonstrate the system’s ability to sense binding to the surface of the microcavity. Data is post-processed via adaptive curve fitting, which allows for high-resolution measurements of the quality factor as well as the plotting of time-dependent parameters, such as resonant wavelength and split frequency shifts. By carefully inspecting steps in the time-domain response and shifting in the frequency-domain response, this instrument can quantify discrete binding events.

Implementation of a reference interferometer for nanodetection.

A thermally and mechanically stabilized fiber interferometer suited for examining ultra-high quality factor microcavities is fashioned. After assessing its free spectral range (FSR), the module is put in parallel with a fiber taper-microcavity system and then calibrated through isolating and eliminating random shifts in the laser frequency (i.e. laser jitter noise). To realize the taper-microcavity junction and to maximize the optical power that is transferred to the resonator, a single-mode optical fiber waveguide is pulled. Solutions containing polystyrene nanobeads are then prepared and flown to the microcavity in order to demonstrate the system's ability to sense binding to the surface of the microcavity. Data is post-processed via adaptive curve fitting, which allows for high-resolution measurements of the quality factor as well as the plotting of time-dependent parameters, such as resonant wavelength and split frequency shifts. By carefully inspecting steps in the time-domain response and shifting in the frequency-domain response, this instrument can quantify discrete binding events.

Influence of the spectrum width of a nonmonochromatic radiation source on blurring of ultrashort optical pulses in telecommunication single-mode optical fiber waveguides

We consider the influence of the spectrum width of a nonmonochromatic radiation source on blurring of ultrashort optical pulses when they propagate through single-mode optical telecommunication waveguides with very weak linear birefringence. This pulse widening is due to the presence of random irregularities of the dielectric permittivity tensor in such waveguides. The latter effect, in turn, influences the polarization mode dispersion of the radiation. The numerical simulation method was used to find the dependences of the envelope evolution of ultrashort optical pulses and their frequency spectra on the length of the single-mode optical fiber waveguide with random irregularities. It is shown that the pulse duration increases obeying the diffusion law, i.e., in proportion to the square root of the fiber length, and the proportionality coefficient depends significantly on the width of the frequency spectrum of the radiation source. The pulse duration is shown to increase with increasing length of the single-mode optical fiber waveguide significantly faster for the radiation source with a wider frequency spectrum, and the influence of the width of the spectral line of the source becomes noticeable when it is equal to the inverse pulse duration.

Correlation of single-mode fiber radiation response and fabrication parameters

Statistically significant correlations have been established between certain fabrication parameters of matched clad, single-mode optical fiber waveguides and their response to an ionizing radiation dose of 2000 rad. The reCOVE:ry data measured at -35 degrees C following exposure have been fit to nth-order kinetic behavior where the adjustable parameters are the initial and permanent incremental losses (A(o) and A(f), respectively), the half-life of attenuation tau, and the order of kinetics n. The set of fibers chosen for analysis had Ge-doped silica cores. In fibers with Ge-F-doped silica clads, A(o) correlates with the concentration of Ge-doped into the fiber core; A(f) correlates with the ratio of oxygen to reagents used during core deposition; and tau and n correlate with a two-way interaction of core oxygen and fiber draw speed. In P-F-doped clad fibers, the P concentration has been found to correlate with the order of the kinetics of recovery.

Distributed strain measurement in a rectangular plate using an array of optical fiber sensors

Single mode optical fiber waveguide has been used to determine the two-dimensional strain distribution on a simply supported rectangular plate. Each of the fifty individual fibers in the rectangular grid array attached to one surface of the plate yields a measurement of the strain integrated along the length of that fiber on the specimen. By using similar sensor information from all of the fibers, both the functional form and the amplitude of the distribution may be determined. Limits on the dynamic range and spatial resolution are indicated. Applications in the measurement of internal strain and the monitoring of physically small critical-structural components are suggested.

Optical Fiber Gyroscope

With the development of low loss single mode optical fiber waveguides, it is possible to construct a gyroscope using optical fibers. The configuration is a multi-turn Sagnac interferometer. Light from an external source is split and injected into the fiber ends, travels in clockwise and counterclockwise directions and is recombined to form interference fringes. When the coil is rotated, a phase shift is produced between the two beams causing a fringe shift ΔZ. This fringe shift is proportional to the rotation rate Ω and is given by the equation ΔZ=4Ω→⋅A→/λc, where A is the total effective area enclosed, i.e., N times the area enclosed by a single turn of the fiber where N is the number of turns. Several models using discrete components have been constructed in our laboratory using up to 1.5 kilometers of single mode optical fiber. In measurements made to date, sufficient accuracy to detect earth rotation has not been made available. The difficulty is with the phase shift measurement which requires accurate measurement of a fringe shift of 10−4 fringes. We are investigating different forms of Sagnac interferometers to improve the accuracy. Integrated optics and modulation techniques might allow us to reach the range needed for navigation. Problems of noise peculiar to optical fibers are described.