Reinhard Ulrich

Measurement of index modulation along an optical fiber Bragg grating

We analyze a fiber Bragg grating by focusing the beam of a probe laser (λ = 633 nm) through the side of the fiber onto its core. Designed for Bragg retroreflection at some longer wavelength (λB = 1290 nm), the grating causes Bragg reflection of the probe beam if the input angle is chosen suitably. The reflected power is proportional to the square of the amplitude of the refractive-index modulation at the probed position. By scanning the probe beam along the fiber we measure the axial profile of the modulation amplitude with a spatial resolution of 10 μm. The measured profile is consistent with a single-photon UV writing process.

Side-hole fiber for fiber-optic pressure sensing

An optical fiber whose structure is similar to that of the PANDA fiber, but with two open channels in the place of the stress members, is investigated. Variations of the internal or external gas pressure permit tuning of the fiber birefringence (10−4 rad m−1 Pa−1) over a wide range, including sign reversal, and application as a pressure sensor.

Polarization holding in birefringent single-mode fibers

Perturbations in highly birefringent single-mode fibers couple the two polarization modes and degrade the polarization-holding ability. With a broadband source we demonstrate wavelength averaging of the power in either mode, permitting a simple measurement of the power transfer to the cross-polarized mode as a function of fiber length. Using this technique, we confirm experimentally the theory of random mode coupling between the polarization modes.

Low-noise fiber-optic rotation sensing

A major source of noise in fiber-optic Sagnac interferometers was identified to be the fluctuation of the phase of Rayleigh backscattering resulting from minute temperature variations and vibration. This noise can be reduced either by introducing a phase modulation into the fiber ring or by the use of a low-coherence source. A noise-equivalent rotation rate of 8 x 10(-4) deg/sec was achieved.

Quadrature outputs from fiber interferometer with 4 × 4 coupler

A broad stripe waveguide of width W and length L acts as a self-imaging 4 x 4 directional coupler if L = NW(2)/lambda, where N is the effective index. When the arms of a fiber-optic Mach-Zehnder interferometer are connected to two input ports of this coupler, the powers at the four output ports vary in phase quadrature.

Fiber-optic displacement sensor with 0.02 μm resolution by white-light interferometry

Abstract A system of fiber-optic displacement sensors is described. Interferometric transducers and receivers are linked in various combinations by multimode fibers. Michelson and Fabry-Perot interferometers serve as the transducers. Receivers are of the Michelson type, scanned either mechanically to provide a wide range (20 mm) at low repetition (1/s), or electronically with a CCD photodiode array, offering fast read-out (

Birefringent optical filters in single-mode fiber

In-line fiber-optic spectral-bandpass filters with one, two, three, and four elements are designed in analogy to the Sole filters of bulk optics by bending the fiber into the form of small coils, which are rotated to suitable angles and arranged between polarizers. One four-element filter has a bandwidth of 3.5% at a center wavelength of 704 nm and a free spectral range of 17%.

Susceptibility corrections in solid state NMR experiments with oriented membrane samples. Part II: theory.

In solid state NMR analysis of oriented biomembranes the samples typically have the shape of a rectangular block, formed by stacking a number of glass slides coated with the membranes under investigation. Reference material may be provided internally in the volume of the block or as an external layer on its surface, as described in the accompanying paper [J. Magn. Reson. 164 (2003) 104-114]. The demagnetizing field resulting in such non-spheroidal samples is inhomogeneous. It shifts and broadens the NMR lines of both the sample and of the reference, as compared to the ideal of a spherical sample. The magnitude of these effects is typically of the order of a few ppm. To determine the necessary corrections, a general analysis is presented here for the demagnetizing field of a layered sample of rectangular block geometry, with the normal of the layers parallel to the main field or tilted about an axis of the block. The correction to the line position of the block sample is found to be approximately equal to that of the spheroid which can be inscribed into the block, and for which the correction is well known. For an external reference layer, placed on top of the block, the correction can be found by the same approximation, invoking a simple mirror concept. The layered structure of the block can be accounted for by using an average magnetic susceptibility. Sample and support materials contribute to that average according to their volume filling factors. If the sample material is anisotropic at the molecular level, as e.g. lipid bilayers are, the resulting anisotropy of the block is reduced by the filling factor of the sample material.

Drawing glass fibers with complex cross section

Techniques are presented for fabrication of glass fibers with complex cross-sectional shapes by drawing from a composite preform. To prevent distortion of the fiber shape by surface tension during drawing, a soluble glass cladding is added to the preform complete its cross section to a circular shape. After the drawing process, the cladding is dissolved chemically. Fibers with zigzag and meander-like cross sections and minimum dimensions of 2 mu m are demonstrated. >

Grating–fiber coupler as a high-resolution spectrometer

An in-line, single-mode fiber-optic spectrometer is described and analyzed. Its key element is a photoresist grating placed in the evanescent field near the core on a side-polished fiber. Fabrication and nearly diffraction-limited performance (resolution Deltalambda asymptotically equal to 1 nm) are reported, and means are proposed to increase the resolution by several orders of magnitude.