At least one parameter of at least one fluid in a pipe (12) is measured using a spatial array of acoustic pressure sensors (14, 16, 18) placed at predetermined axial locations x1,x2,x3 along the pipe (12). The pressure sensors (14, 16, 18) provide acoustic pressure signals P1(t), P2(t), P3(t) on lines (20, 22, 24) which are provided to signal processing logic (60) which determines the speed of sound amix of the fluid (or mixture) in the pipe (12) using acoustic spatial array signal processing techniques with the direction of propagation of the acoustic signals along the longitudinal axis of the pipe (12). Numerous spatial array processing techniques may be employed to determined the speed of sound amix. The speed of sound amix is provided to logic (48) which calculates the percent composition of the mixture, e.g., water fraction, or any other parameter of the mixture or fluid which is related to the sound speed amix. The logic (60) may also determine the mach number (MX) of the fluid. The acoustic pressure signals P1(t), P2(t), P3(t) measured are lower frequency (and longer wavelength) signals than those used for ultrasonic flow meters, and thus is more tolerant to inhomogeneities in the flow. No external source is required and thus may operate using passive listening. The invention will work with arbitrary sensor spacing and with as few as two sensors if certain information is known about the acoustic properties of the system.

Fluid parameter measurement in pipes using acoustic pressures

Modelocked fiber laser resonators may be coupled with optical amplifiers. An isolator optionally may separate the resonator from the amplifier. A reflective optical element on one end of the resonator having a relatively low reflectivity may be employed to couple light from the resonator to the amplifier. Enhanced pulse-width control may be provided with concatenated sections of both polarization-maintaining and non-polarization-maintaining fibers. Apodized fiber Bragg gratings and integrated fiber polarizers may also be included in the laser cavity to assist in linearly polarizing the output of the cavity. Very short pulses with a large optical bandwidth may be obtained by matching the dispersion value of the grating to the inverse of the dispersion of the intra-cavity fiber. Frequency comb sources may be constructed from such modelocked fiber oscillators. Low dispersion and an in-line interferometer that provides feedback may assist in controlling the frequency components output from the comb source.

Pulsed laser sources

A waveguide DBR laser or waveguide DBR laser array may be comprised of a semiconductor gain element, or a series of semiconductor gain elements, in combination with a waveguide grating functioning as a resonant cavity end reflector for lasing operation comprising either an optical fiber having a fiber grating (fiber DBR laser) or a planar waveguide (planar waveguide DBR laser). The gain element may be comprised of a laser diode which has high efficient AR coating on its front facet so that it functions as a modulated gain element in a resonant cavity established between its rear HR facet and the grating formed in the external waveguide. Disclosed are ways to form this resonant cavity so that gain element modulation rates can be carried out in excess of 2 Gb/sec with suppression of longitudinal mode hops and/or with trimming to compensate for wavelength changes, rendering the waveguide DBR laser or waveguide DBR laser array highly suitable for WDM transmitter, dense WDM transmission systems and other communications applications.

Thermal compensators for waveguide DBR laser sources

The present invention provides a wavelength division multiplexed optical communication system with dynamically stabilized wavelength selectors. To accurately correlate the wavelength of a wavelength selector to the wavelength emitted by an optical transmission source, the present invention uses an optical detector and feedback loop to optimize the wavelength of an optical selection element in accordance with a wavelength of an incident optical channel. In one embodiment, the optical selection element is a Bragg grating associated with a grating wavelength controller, such as a temperature regulator or strain tuning system, to adjust the wavelength band of maximum reflectivity of the grating. The feedback loop communicates with the optical detector and the wavelength controller to modify the grating's reflection wavelength band in accordance with the wavelength of an incident optical channel.

WDM optical communication systems with wavelength stabilized optical selectors

The different embodiments of the invention include tunable add-drop and cross connect devices. The add-drop and cross connect devices include materials with negative dependence of refractive index on temperature and temperature independent coincidence between resonator modes and a set of specified frequencies, e.g. for DWDM telecommunications channels. The free spectral range may be adjusted to equal a rational fraction of the specified frequency interval. The operating frequency may be selected without substantially tuning the cavity modes. This can be accomplished by means of a waveguide pair with differential thermal response.

Channel-switched cross-connect

A tunable optical waveguide laser arrangement includes a solid optical waveguide capable of guiding light along an axis between axially spaced ends thereof and being at least in part of an excitable material that emits light in response to stimulation by light. Stimulating light is launched into the waveguide for axial propagation therein and attendant emission of light by the excitable material. Two end reflectors are situated in the waveguide, each at one of the axially spaced ends thereof and extending normal to the axis to delimit a laser cavity. Each of the reflectors is constituted by a Bragg grating consisting of a multitude of axially consecutive grating elements constituted by periodic refractive index perturbations with a given periodicity. The length of the cavity, the peak reflectivity of the Bragg gratings and the gain of the excitable material are so coordinated with one another as to enable lasing in only a single longitudinal mode. The length of that portion of the optical waveguide that incorporates the two Bragg gratings and an intervening region of the optical waveguide is uniformly controlledly varied with attendant continuous tuning of the laser output wavelength without longitudinal mode hopping.

Continously tunable single-mode rare-earth doped pumped laser arrangement

An optical waveguide laser arrangement includes a solid optical waveguide having a waveguiding portion that extends along an axis between two spaced regions of the optical waveguide and is of a material capable of emitting stimulated light upon excitation by pumping light that is launched into the optical waveguide for axial propagation through the axially spaced regions of the optical waveguide Two reflectors are provided, each being disposed at one of the axially spaced regions of the optical waveguide to delimit a laser resonator At least one of the reflectors is constituted by a Bragg grating consisting of a multitude of axially consecutive periodic perturbations in the refractive index of the respective one of the axially spaced regions that cumulatively reflect the stimulated light at a reflectivity that decreases for adjacent longitudinal modes of the stimulated light with increasing deviation from a central wavelength The axial length of the laser resonator, the reflectivity of the Bragg grating and the gain of the excitable material are so coordinated with one another as to sustain lasing in only a single longitudinal mode

Single longitudinal mode pumped optical waveguide laser arrangement

An emedded Bragg grating laser Master-Oscillator and Power-Amplifier (MOPA), includes an optical waveguide which receives and propagates pump light of a predetermined wavelength launched into the optical waveguide; a first master oscillator laser, disposed in the waveguide in the path of the pump light, the laser having a laser cavity disposed between a first pair of reflectors and having a first laser gain medium within the first laser cavity which emits first lasing light in response to the pump light, the first reflectors reflecting a predetermined amount of the first lasing light within the first laser cavity and passing a predetermined amount of the first fusing light as first output laser light from the first laser, the first reflectors passing the pump light through the first laser; at least one of the first reflectors comprises a Bragg grating; and an optical waveguide power amplifier, disposed in the path of the first output laser light and the pump light, and having a first amplifier gain medium therein which emits first amplified laser light in response to the pump light and the first output laser light.

Gary A. Ball

Papers

Continously tunable single-mode rare-earth doped pumped laser arrangement

Single longitudinal mode pumped optical waveguide laser arrangement

Embedded Bragg grating laser master-oscillator and power-amplifier