USA As Represented by Secretary of the Navy

Irl N Duling, Iii

Michael L Dennis

Ronald D Esman

Thomas F Carruthers

William K Burns

Alan D Kersey

Martin A Putnam

Jin Ung Kang

Keith J Williams

Carl A Villarruel

David G Cooper

James L Dexter

E Joseph Friebele

The ultrashort fiber laser with a dispersion-managed cavity. The laser is an actively mode-locked sigma laser, typically locked at a repetition rate of 10 GHz, driven by an external frequency source and actively length stabilized, and nearly 10,000 pulses circulate within the laser cavity. A Mach-Zehnder modulator is placed in a loop of polarization-maintaining (PM) fiber. The polarization state of light injected into the non-PM branch evolves in a random manner but is transformed into an orthogonal state by a Faraday mirror; linearly polarized light injected into the branch by a polarizing beamsplitter returns to the beamsplitter also linearly polarized but rotated by 90&#xb0;. The cavity of the laser is composed of several fibers. The average dispersion Dis anomalous and is approximately equal to 0.1 ps/(nm&#xb7;km).

Ultrashort-pulse fiber laser with a dispersion-managed cavity

A method and apparatus for increasing the upper frequency range of an optical communication system, particularly one designed to communicate over, repeaterless, distances. A series of temporally interleaved optical solitons of different frequencies are generated, and transmitted and detected by wavelength division multiplexing. An adiabatic transmission line forms part of the transmission link, and serves to narrow the bandwidth of the pulses during propagation. As a result, one can generate the solitons with substantially overlapping spectra, thus increasing the rate at which they are produced, but, because of the narrowed spectra, still resolve them in frequency at the system's receiver.

Apparatus and method for high repetition rate optical communication over long unrepeated spans

An optical receiver for receiving a signal from an optical fiber in a fiber-optic digital transmission system that includes a first low noise optical amplifier to amplify an input optical signal. The first low noise optical amplifier has an input 3 dB compression point lower than the desired system input sensitivity at a desired bit rate. A high power optical amplifier further amplifies the amplified optical signal, and has an automatic gain control for output signal leveling at a desired operation point of the transmission system. A high current photodetector converts the further amplified optical signal from the high power optical amplifier to an electrical signal that drives a retiming circuit without requiring further amplification of the electric signal.

High-sensitivity, high-speed digital optical photoreceiver

An optical fiber laser source comprising a polarization-maintaining loop and a birefringence-compensating branch preferably operatively connected to a length-stabilizing element is disclosed. The optical fiber laser source provides soliton pulse compression to reduce the duration of the pulses of the output pulse train to 1.3 ps or less.

Actively mode-locked, single-polarization, picosecond optical fiber laser

In accordance with one aspect of the invention, a ring laser configuration having a polarizer, and whose cavity loop has substantially no net dispersion, permitting mode locked pulsing of high intensity and large bandwidth. In accordance with another aspect of the invention, a system using this laser to interrogate a plurality of arrays of Bragg gratings by use of both time and wavelength division multiplexing, increasing the total number of interrogatable gratings. In accordance with a third aspect of the invention, a system for interrogating one or more fiber Bragg gratings separated from the optical source by a dispersive optical fiber. As such a grating distends responsive to some measurand, its reflection frequency changes, and the traversal time of the reflection over the dispersive fiber changes, permitting inference of the measurand.

Broadband mode-locked fiber laser, particularly for fiber Bragg grating

This invention is a demultuplexer consisting on a sequential division of the data stream in a series of Sagnac interferometer amplitude modulators (SIAMs), wherein each modulator in the series is driven by a single microwave frequency derived directly from a radio frequency (RF) data rate clock, with the RF phase properly adjusted to extract a channel of interest.

Sagnac interferometer amplitude modulator based demultiplexer

A system that uses all optical elements for transmission, regeneration and reception of solitons in point-to-point, broadcast, ring and multi-user trunk type communication systems. Soliton pulses from an optical clock source are modulated by optical data pulses in an optical modulator producing a modulated channel of data pulses. Several channels are combined by an optical multiplexer into a network optical bit stream. This stream is carried by an optical fiber and one or more of optical regenerators which recover the system clock and regenerate the signal with the recovered system clock rather than just amplifying the signal. Each of the regenerators can, in addition to regenerating the data, act as part of a data drop or insert node in a ring network where the node can synchronously remove data from or insert data into the stream. Intermediate nodes can include packet drop/replace nodes if the network is a packet type network. The destination can include an optical demultiplexer which demultiplexes the network stream into the individual channels, an optical clock recovery system that recovers the clock of the system and a receiver that receives the pulses of one of the demultiplexed channels. The system can also include optical logic for decoding and routing optical packets.

Ultra high bit rate all optical communication system

An optical intensity modulator which uses a Sagnac interferometer having an electro-optic phase modulator therein. An electric modulation signal is delivered to the modulator, and the latter is selected so that the phase velocity of optical and electrical signals are comparable in it. This causes the optical signal from one interferometer arm to copropagate through the modulator with the electrical signal, increasing interaction time with it, and causes the optical signal from the other arm to counterpropagate with the electric signal, reducing interaction time. In addition to phase modulating the optical signals by the electrical signal, the electro-optic effect in the modulator phase shifts the optical signals with respect to one another, permitting them to form a non-zero interference pattern, whose intensity corresponds to the electrical signal. In one embodiment, the interferometer has a non-reciprocal device to impose a constant phase difference between the counterpropagating optical signals, which permits one to place the system's setpoint to any arbitrary point on the system's transmissivity versus phase response, e.g. large signal and/or linear response.

Electro-optic modulator and method

An optical device includes a polarization section having a port, the polarization section being for receiving light at the port and for outputting light at the port with a state of polarization orthoconjugate to the light received at the port. The polarization section includes a reflector, a bidirectional nonreciprocal rotator and a bidirectional polarizer. The bidirectional nonreciprocal rotator has first and second ends, the first end being operatively coupled to the port. The bidirectional polarizer has first and second ends, the first polarizer end being operatively coupled to the reflector and the second polarizer end being operatively coupled to the second rotator end. The optical device further includes an amplifying section having a port and a rotator-reflector, the amplifying section being for receiving light at the amplifying section port and for outputting light at the amplifying section port with a state of polarization orthoconjugate to the light received at the amplifying section port and being amplified with respect thereto. The optical device includes means for transmitting light in both directions between the polarization section port and the amplifying section port, and means responsive to light internal to the polarization section for outputting coherent light having a stable and known state of polarization.

Polarization-stable laser

A pulsed laser includes a polarization section having a port, the polarization section being for receiving light at the port in a selected state of polarization and for outputting light at the port having a state of polarization orthogonal to the selected state of polarization. The laser also includes an amplifying section having a port, a bidirectional amplifier, and a rotator-reflector, the amplifying section being for receiving light at the amplifying section port and for outputting light at the amplifying section port amplified with respect thereto, the bidirectional amplifier being operatively coupled to the amplifying section port at a first end and operatively coupled to the rotator-reflector at a second end. The pulsed laser further includes means for transmitting light in both directions between the polarization section port and the amplifying section port, an amplitude modulator responsive to a modulation signal for actively mode-locking light internal to the pulsed laser, and means responsive to light internal to the polarization section for outputting coherent light.

Polarization-stable pulsed laser

An apparatus and method for converting a signal of arbitrary polarization one of preselected polarization, e.g. for use by a sensor, transducer, etc. A signal splitter divides the input signal into its orthogonal linearly polarized components, and launches the components from a pair of output ports. The signals counterpropagate to the opposite port, and, while counterpropagating, are rotated into the same linear polarization state. In one embodiment, the rotation is done by a pair of complementary 45.degree. Faraday rotators; in another, by one 90.degree. rotator. In the former, the signal is recombined at the splitter in the initial state of polarization that in which the signal initially entered the splitter; in the latter, the recombined signal is of orthoconjugate polarization to the input signal.

Apparatus and method for eliminating polarization sensitivity in

An optical pulse generator for producing mode-locked optical pulses comprises: a beam splitter; first and second optical loops coupled together by the beam splitter so as to define a figure eight optical path in which a light beam propagating toward the beam splitter in one of the first and second optical loops is split by the beam splitter to form two light beams propagating in opposite directions around the other one of the first and second optical loops; a direction dependent loss element disposed in the first optical loop for reducing the intensity of light propagating in a predetermined direction around the first optical loop; a nonlinear element disposed in the second optical loop and having an intensity dependent nonlinear optical transmission characteristic; an optical gain medium disposed in a selected one of the first and second optical loops; coupling apparatus for coupling pump light into the selected one of said first and second optical loops having the gain medium, and for coupling mode-locked optical pulses out of the optical pulse generator; and a feedback structure, coupled to the coupling apparatus, being responsive to light propagating therethrough for controlling the repetition rate of the mode-locked optical pulses.

High repetition rate, mode locked, figure eight laser with extracavity

A single-polarization fiber optical amplifier and corresponding method is provided capable of amplifying an optical input signal by a fiber optic amplifier constructed of fiber which may be non-polarization-maintaining. The single-polarization fiber optical amplifier provides a direction-selective coupler which receives an optical input at a first port and outputs an optical output at a second port. A fiber optic amplifier is operatively connected to the direction-selective coupler at a bidirectional port for amplifying the optical input. A retro-reflecting orthogonal polarization converter is operatively connected to the fiber optic amplifier, reflecting the amplified optical input from the fiber optic amplifier in a return direction through the fiber optic amplifier and in an orthogonal polarization to the amplified optical input. The direction-selective coupler outputs the reflected amplified orthogonal optical input at the second port as the optical output of the direction-selective coupler. Further configurations adapting the input and output ports to transmit the optical signal through cavity or other structures may be provided to produce, for example, an ultrashort pulse optical source; a single-wavelength, single-polarization, widely-tunable laser source; or an amplified spontaneous emission source.

Method and apparatus for polarization-maintaining fiber optical

An antiresonant nonlinear mirror to replace one mirror of a laser for passive modelocking of the laser, the antiresonant nonlinear mirror comprising: a beam splitter for coupling the mirror to a laser cavity; a mirror arrangement for defining an optical ring with the beam splitter in which two light beams produced by the beam splitter in response to a light beam from the laser cavity can counterpropagate around the ring; an intensity dependent anisotropic nonlinear element disposed within the ring; and a polarization sensitive element disposed within the ring for adjusting the birefringence thereof to produce spontaneous modelocking in the coupled laser cavity.

Antiresonant nonlinear mirror for passive laser modelocking

An optical pulse source for producing short optical pulses comprises first and second optical loops coupled together by a beam splitter so as to define a figure eight optical path in which a light beam propagating toward the beam splitter in one of the first and second loops is split by the beam splitter to form two light beams propagating in opposite directions around the other of the first and second loops. The first loop includes a direction dependent loss element for reducing the intensity of light propagating in a predetermined direction around the first loop, and the second loop includes an element having an intensity dependent nonlinear optical transmission characteristic. One of the first and second loops includes an optical gain medium. Coupling apparatus is also provided for coupling pump light into the loop including the gain medium and for coupling optical pulses out of the source.

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Round Hill, VA, United States of America

Irl N Duling, Iii