Gordon S. Kino

In the above titled paper (ibid., vol. 27, no. 24, pp. 5648-5656, Dec. 09), there was an error with some embedded fonts.

Using a new full-vectorial finite-difference mode solver utilizing a hexagonal Yee's cell, we calculated the dispersion diagram of a slightly multimode (16 modes) air-core photonic-bandgap fiber (PBF) and the electric-field profiles of all of its core modes. Careful comparison shows striking similarities between these properties and those of the hybrid modes of a conventional step-index fiber, in terms of the modes' field profiles, the modes' degeneracy, the order in which the modes mode cut off in the wavelength space, and the maximum number of modes. Based on these similarities, we propose for the first time a systematic nomenclature for the modes of a PBF, namely hybrid HE and EH modes and of quasi-TE and quasi-TM modes. Other small but relevant similarities and differences between the modes of these two types of fibers are also discussed.

We propose using a frequency-modulated laser in a fiber-optic gyroscope (FOG) in a minimum configuration. Compared to the traditional broadband source, a narrow-band laser offers two significant advantages, namely the elimination of excess noise and thus improved sensitivity to rotation, and a more stable mean wavelength, hence a greater scale-factor stability. We show that the strong back-reflection and coherent backscattering noise introduced by the use of a laser is greatly reduced by modulating the laser frequency. In both a conventional FOG and in a FOG using an air-core fiber, we demonstrate experimentally that this technique reduces these two sources of noise by at least a factor of 4 compared to the same gyros operated with an unmodulated laser.

We demonstrate analytically that long-period fiber gratings operating near the maximum of a cladding mode's phase-matching curve can be designed to exhibit far broader bandwidths (around 800 nm ) than reported to date, at any center wavelength and with any peak attenuation. In a given fiber, the center wavelength and attenuation are controlled independently by properly selecting the grating period and length, respectively, Extremely large bandwidths are obtained by increasing the grating index perturbation, by increasing the fiber core radius, and∕or optimizing the numerical aperture. Implemented with a mechanically induced grating, this concept produced a 1465 nm filter with a record 10 dB bandwidth of 360 nm .

A cylinder-assisted Maker-fringe technique to probe second-order optical nonlinearity profiles is introduced. This technique presents several significant advantages over existing methods, including the measurement of fringes up to a record incidence angle of 89.6°, which is particularly useful for the accurate determination of the nonlinearity profiles of thin layers.

The basic Sagnac acoustic sensor array consists of a set of fiber hydrophones placed asymmetrically in a long Sagnac loop. It uses time division multiplexing (TDM) to address individual sensors. A new Sagnac-based array is described that uses a folded loop to reduce acoustic pick-up along the loop. This configuration also enables the use of polarization biasing to provide every sensor in the array with a stable phase bias of arbitrary value (including +/- (pi) /2, for maximum sensitivity), thus eliminating signal fading. A further benefit is the use of balanced detection to eliminate the excess noise from the broadband Er-doped fiber source. These improvements are demonstrated experimentally, as well as a minimum detectable signal close to the shot-noise limit (~0.06 (mu) rad/(root)Hz).