A system for sensing subterranean acoustic waves emitted from an acoustic source includes a plurality of laser sources, each emitting light at different frequencies; a plurality of subterranean optical sensors, receiving and altering the light in response to acoustic waves; at least one optical detector, receiving the altered light and outputting an electrical signal; and electronics, receiving the electrical signal and converting it into seismic data format. Light from the optical sources is modulated at a plurality of modulation frequencies. The electronics can demodulate the signal by mixing the signal with periodic waveforms having frequencies corresponding to one and two times the modulation frequencies. The modulation frequencies are selected such that at least one of the second harmonic frequencies associated with the modulation frequencies is interleaved in a non-interfering manner within the corresponding set of first harmonic frequencies, and preferably such that at least one of the first harmonic frequencies is interleaved in a non-interfering manner within the corresponding set of modulation frequencies. The hydrophone for sensing the acoustic signals is able to operate at pressures and temperatures of at least 5,000 psi and 130° C., respectively. The hydrophone may be housed in a cable having a diameter less than about 1.5 inches. The hydrophone's sensor preferably includes a reference mandrel, two sensing mandrels, and a telemetry cam, which are aligned in a coaxial, end-to-end configuration to reduce the profile of the hydrophone. The mandrels have hemispherically-shaped endcaps and are joined by flexible interlinks having grooves for receiving optical fiber.

Acoustic sensing system for downhole seismic applications utilizing an array of fiber optic sensors

The disclosure is directed to the self-aligned coupling of the core of an optical fiber to the narrow stripe emitting spot in the active layer of a narrow stripe semiconductor laser. In this invention a V-groove is etched into the same substrate onto which the epitaxial layers for the narrow stripe laser have been grown.

Self-aligned coupling of optical fiber to semiconductor laser or LED

An optical fiber-to-waveguide coupler is disclosed which automatically aligns five of the six possible degrees of freedom associated with the alignment process. Silicon v-grooves (22) are used to hold the fibers (24) in place in the silicon substrate (20), but in contrast to prior art arrangements, the silicon substrate overlaps the top surface (12) of the waveguide substrate (14). A cover plate (26) disposed over the silicon substrate is cut and polished so that the endface of the cover plate (28) lies in the same plane as the ends of the fibers (30). When the endface of the cover plate is butted against the endface (16) of the waveguide substrate, and the silicon v-grooves have been etched to the proper predetermined depth, five of the six degrees of freedom are automatically aligned.

Fiber-waveguide self alignment coupler

A folded Sagnac fiber optic acoustic sensor array (1200) operates in a manner similar to a Sagnac Interferometer but uses a common delay path to reduce distributed pickup in downlead fibers. The fiber optic acoustic sensor (716) is used to detect acoustic waves in water. By basing the folded Sagnac sensor array on the operating principles similar to the Sagnac interferometer rather than basing the array on a Mach-Zehnder interferometer, the sensor array has a stable bias point, has reduced phase noise, and allows a broadband signal source to be used rather than requiring a more expensive narrowline laser. A large number of acoustic sensors (718(N)) can be multiplexed into the architecture of the folded Sagnac fiber optic acoustic array.

Folded sagnac sensor array

An arrangement for providing optical coupling between a pair of substrates is disclosed. The arrangement is capable of providing automatic alignment in the lateral direction, that is, the direction perpendicular to the direction of optical signal flow along the surface of the optical substrate. In accordance with the teachings of the present invention, an interlocking system of alignment grooves and alignment ridges are utilized to prevent this unwanted motion and aid in alignment between the two pieces. In particular, an alignment ridge, or ridges, are formed on the top surface of a first substrate and are disposed to be parallel with a plurality of optical waveguides formed in the first substrate. The corresponding alignment grooves are formed in the second substrate, where this substrate may contain a plurality of fibers held in associated v-grooves. Waveguide-to-waveguide communication is achieved by forming alignment ridges on a pair of waveguide containing substrates. The substrates may then be placed end-to-end, where the alignment grooves in the second substrate will interlock with both sets of alignment ridges. As long as the dimensions of the alignment ridges and grooves are formed to complement each other in size - and are spaced similarly in their respective substrates - the alignment ridges and grooves will interlock when the two substrates are joined, thus preventing motion between the two substrates in the lateral direction.

Optical waveguide lateral alignment arrangement

A Sagnac rotation sensing interferometer disposed on a rotating platform for use as a gyrsocope comprising a closed optical light path and a beam splitter for splitting an input light beam into two beams directed to transverse the closed optical path in opposite directions wherein the beam splitter is composed of a directional coupler with three input ports and three output ports. The first of the three input ports receives optical input and the second and third of the input ports are disposed symmetrically with respect to the first input port. Optical output from two output ports corresponding to the second and third input ports are directed to both ends of the closed optical fiber light path. A gyroscope according to this arrangement provides light output from the beam splitter which operates automatically near quadrature without a nonreciprocal π/2 phase bias applied in the fiber loop as required in conventional optical fiber gyroscopes.

Optical fiber gyroscope with (3×3) directional coupler

A multiwavelength multiplexer-demultiplexer constructed from units each cble of multiplexing or demultiplexing two wavelengths. As many such units as required can be interconnected to form multiplexer-demultiplexers of any number of wavelengths. Each two-wavelength multiplexer-demultiplexer unit includes a four-port power divider, a four-port phase shifter having two ports connected to two ports of the power divider, and another four-port power divider having two ports connected to two ports of the phase shifter. The power divider may be a single-mode optical fiber directional coupler, or a half-silvered mirror beam splitter. The phase shifter may include a pair of single mode optical fibers or a pair of oppositely disposed mirrors.

Wavelength multiplexer-demultiplexer

An electrooptical waveguide switching device comprising three sections of abutting crystalline substrates, the easy axis of each substrate being orthogonal to that of its neighbors. Each substrate is formed with a pair of waveguide sections which couple with those of the other sections, when the substrates are abutted, to form a pair of waveguide channels across the substrate sections. Sets of electrodes for directing horizontal and vertical electric fields through one waveguide channel are also formed on the substrate sections symmetrically about an axis of symmetry.

Electrooptically balanced alternating Δβ switch

An optical waveguide coupler having intersecting deep and shallow grooves in a planar solid substrate, in which the deep groove accommodates an alignment fiber for fine vertical alignment of an optical fiber with another optical fiber or with an optical component such as a switch, modulator, multiplexer or source of light. The shallow groove accommodates the optical fiber. The alignment fiber may be tapered or have any configuration such that its manipulation causes the alignment fiber to contact the underside of the optical fiber for raising or lowering the optical fiber. There may be a plurality of shallow and deep grooves for coupling more than one optical fiber.

End-butt optical fiber coupler

A Sagnac rotation sensing interferometer disposed on a rotating platform use as a gyroscope comprising a wound optical fiber light path, a beam splitter for splitting a light beam into two beams directed to traverse the optical path in opposite directions, a light source circuit for generating a light beam which is switched between two wavelengths at a switching or modulation frequency substantially higher than the speed of change of the phase due to rotation, and a detector for extracting a signal from the recombined beam interference pattern at the wavelength modulation frequency, this signal being proportional to the phase shift caused by rotation.

Sang K. Sheem

Papers

Optical fiber gyroscope with (3×3) directional coupler

Wavelength multiplexer-demultiplexer

Electrooptically balanced alternating Δβ switch

End-butt optical fiber coupler

Optical gyroscope with time dependent wavelength