United States of America As Represented by the Secretary of the Air Force

The United States of America As Represented by the United States

Gerald T Moore

Thomas M Shay

Jacob R Grosek

Leanne J Henry

Karl W Koch, Iii

Mark T Gruneisen

Craig A Denman

Paul D Hillman

John M Telle

Brent W Grime

Joshua C Bienfang

John R Marciante

Stephen H Chakmakjian

Eric C Cheung

A desired N-order Stokes output and zeroth-order Stokes pump input are seeded into a rare-earth doped amplifier where the power of the zeroth-order Stokes signal is amplified prior to both signals entering a Raman amplifier comprised of N&#x2212;1 Raman resonators, each uniquely tuned to one of the N&#x2212;1 Stokes orders, in various configurations to include one or more nested and/or in-series Raman resonators. The zeroth-order Stokes signal is converted to the N&#x2212;1-order Stokes wavelength in steps and the power level of the N-order Stokes wavelength is amplified as the two signals propagate through the Raman resonators. Each Raman resonator includes a photosensitive Raman fiber located between a pair of Bragg gratings. The linewidths of the Stokes orders can be controlled by offsetting the reflectivity bandwidths of each pair of Bragg gratings respectively located in the Raman resonators.

Laser generation using dual seeded nested and/or in-series Raman resonators, for telecommunications applications

A third-order Stokes wavelength seed signal at the desired output wavelength of 1240 nm and a zeroth-order Stokes wavelength signal at 1066 nm are input into a Raman amplifier comprised of two Raman resonators in a linear configuration. The first resonator converts the zeroth-order Stokes wavelength signal at 1066 nm into a first-order Stokes wavelength signal at 1118 nm, and also outputs the third-order Stokes wavelength seed signal at 1240 nm. The second resonator then converts the 1118 nm output from the first resonator into a second-order Stokes wavelength signal at 1176 nm, which amplifies the 1240 nm seed signal power level. Each Raman resonator includes a photosensitive Raman fiber communicating with a plurality of high-reflector Bragg gratings. The linewidths of the second and third Stokes orders are controlled by adjusting the resonant bandwidth of the second Raman resonator by offsetting the respective center wavelengths of the high-reflector Bragg gratings.

Seeded Raman amplifier in a linear configuration for generating a 1240 nm laser

A third-order Stokes signal at the desired output wavelength of 1240 nm and a zeroth-order Stokes pump wavelength at 1066 nm are seeded into a Raman amplifier comprised of two nested resonators tuned to the first-order Stokes line at 1118 nm and second-order Stokes line at 1176 nm, respectively. The pump wavelength is first amplified and then sequentially converted into the first and second-order Stokes wavelengths as the light traverses the nested resonators. The desired third-order Stokes output wavelength is then amplified by the second-order Stokes wavelength as it propagates through the outermost resonator. Each Raman resonator includes a photosensitive Raman fiber located between a pair of Bragg gratings. The linewidths of the various Stokes orders can be controlled through adjusting the resonant bandwidths of the Raman resonators by offsetting, through heating, the reflectivity bandwidths of each pair of Bragg gratings respectively located in the Raman resonators.

Seeded Raman amplifier in a nested configuration for generating a 1240 nm laser

A desired N-order Stokes output and corresponding zeroth-order Stokes pump wavelengths are seeded into a Raman amplifier comprised of one or more Raman resonators in series sequentially tuned to the 1, 2, . . . N&#x2212;1Stokes orders. The pump wavelength is amplified and sequentially converted to the 1, 2, . . . N&#x2212;1order Stokes wavelengths as it propagates through the apparatus. The desired N-order Stokes output wavelength is then amplified by the N&#x2212;1Stokes order as it propagates through the final resonator tuned to the N&#x2212;1Stokes order. Each Raman resonator includes a Raman photosensitive Raman fiber located between a pair of Bragg gratings. The linewidths of the various Stokes orders can be controlled through adjusting the resonant bandwidths of the Raman resonators by offsetting, through heating, the reflectivity bandwidths of each pair of Bragg gratings respectively located in the Raman resonators.

Seeded Raman amplifier in linear configuration for laser applications in the 1100-1500 nm spectral range

A broad linewidth, zeroth Stokes order 1069 nm pump and a narrow linewidth second Stokes order 1178 nm seed propagate through a wavelength division multiplexer and then through a rare-earth-doped amplifier. After passing through a 1121 nm long period or tilted Bragg grating, the amplified 1069 nm Stokes signal and the 1178 Stokes signal are injected into a 1121 nm resonator Raman cavity, which includes a pair of highly reflective Bragg gratings having a center wavelength of 1121 nm. The amplified 1069 nm Stokes signal is Raman converted to high power levels of 1121 nm which then, in turn, amplifies the 1178 nm Stokes seed as it traverses the cavity. The linewidth of the amplified 1178 nm Stokes signal can be controlled by offsetting, through heating, the reflectivity bandwidth of the Bragg grating located near the output end of the Raman cavity.

Generating narrow linewidth 1178 NM laser output using a seeded raman amplifier

A method of generating high-power laser output in the 1100 to 1500 um spectral region having a controllable linewidth. A Raman amplifier comprised of one or more nested pairs of fiber Bragg grating cavities tuned to the 1, 2, . . . N&#x2212;1order Stokes wavelengths is seeded with both the desired Nth order Stokes output wavelength and the corresponding zeroth-order Stokes pump wavelength. As the pump wavelength propagates through the apparatus, it is sequentially converted to the 1, 2, . . . N&#x2212;1order Stokes wavelengths in the nested fiber Bragg grating cavities. The desired Nth order Stokes output wavelength is then amplified by the N&#x2212;1Stokes order as it propagates through the nested fiber Bragg grating cavities. The linewidths of various Stokes orders can be controlled through adjusting resonant bandwidths of the fiber Bragg grating cavities by offsetting, through heating, the reflectivity bandwidths of each pair of cavity gratings.

Seeded raman amplifier for applications in the 1100-1500 nm spectral region

A single-mode optical fiber segment incorporating liquid-filled holes parallel to the core that are sealed at each end. Heating the liquid produces stress in the fiber and thereby increases the birefringence level. Alternatively the holes may be filled and sealed at a temperature lower than the temperature at which the fiber will be operated, the temperature difference determining the stress level for given hole characteristics.

Optical fiber with tunable birefringence using pressurized liquid capillaries

An in-fiber optical isolator for high-power operation using two kinds of fiber, not including the active fiber where laser gain occurs. A hi-birefringence passive fiber with a tilted Bragg grating is connected to the active fiber at one end with the connection region stripped and potted to remove pump and s-polarized signals. The other end of the hi-bi fiber is fusion spliced to a low-birefringence fiber and oriented so that the birefringent axes are parallel. The low-bi fiber then passes straight through a gap in a linear magnetic array calculated to cause a 45 degree Faraday rotation. The far end of the low-bi fiber is connected to another hi-birefringence passive fiber with a tilted Bragg grating but with the birefringent axes of the hi-bi rotated by 45 degrees with respect to those of the low-bi fiber. Backward light transmitted by the second Bragg grating will then be removed by the first Bragg grating.

In-fiber optical isolator for high-power operation

1064-nm and 1319-nm light respectively generated by two lasers is combined and injected into a doubly resonant sum-frequency generator. The optical path length of the sum-frequency generator is adjusted responsive to feedback of the 1319-nm light to maintain 1319-nm resonance. Feedback of 1064-nm light is concurrently used to adjust the 1064-nm laser responsive to the optical path length to maintain 1064-nm resonance. Light output from the sum-frequency generator is compared to the sodium Dwavelength i.e., approximately 589 nm, and the 1319-nm laser is responsively adjusted to eliminate any differential. This abstract is provided to comply with the rules requiring an abstract, and is intended to allow a searcher or other reader to quickly ascertain the subject matter of the technical disclosure. It is submitted with the understanding that it will not be used to interpret or limit the scope or meaning of the claims.

Continuous wave sodium beacon excitation source

A multiplexing device using N-stages of double-coated planar glass mirrors or coated mirror pairs to coherently combine the output of 2 narrow-bandwidth, diffraction-limited, polarized, and phase-locked optical beams to produce a single diffraction-limited beam with a power close to 2 times that of a single beam. A multiplexer system is also disclosed to control the relative phases of the 2 beams used in conjunction with the multiplexing device.

Coherent optical beam combination using double-coated glass mirrors/mirror pairs

A high power fiber laser/amplifier is comprised of a multi-mode rare-earth-doped helical core disposed within a cylindrical inner cladding. The inner cladding is enclosed within an outer cladding whereby the core effectively produces single-mode operation with a circularly polarized near-diffraction-limited beam quality output when pump radiation is injected into the inner cladding.

Cladding-pumped fiber with helical rare-earth-doped core for fiber lasers and amplifiers

A specially cut uncoated birefringent crystal having three Brewster-cut faces with adjacent coated Brewster-cut coupling prisms are used for optical frequency conversion. Two input frequencies are used to obtain a third frequency by sum-frequency generation. The uncoated birefringent crystal permits high power input beams.

Brewster-cut crystal for nonlinear frequency conversion

A specially cut uncoated birefringent crystal having three Brewster-cut faces with adjacent coated Brewster-cut coupling prisms for optical frequency conversion. Two IR input frequencies are used to obtain a third visible light frequency by sum-frequency generation. The uncoated birefringent crystal permits high power input beams. The two Z-polarized IR beams enter the lower portion of the Brewster cut IR input end of the crystal and pass out the Brewster cut lower portion of the output end, generating a Y-polarized visible light beam. The visible wavelength beam is reflected at the Brewster cut Z-polarized surface at the output end and again reflected at the upper output end surface cut perpendicular to the Brewster cut. The visible beam travels back toward the IR input end near the top surface of the crystal and exits through an upper Brewster cut surface cut for Y-polarized light. Input and output prisms with appropriate optical coatings are used to facilitate the process.

Convex brewster-cut crystal for nonlinear frequency conversion

A stack of optically contacted birefringent crystals is configured to carry out coherent beam combination (multiplexing) of narrow-bandwidth phase-locked beams from multiple lasers or laser amplifiers (e.g., multimode Yb-doped fiber amplifiers). A stack of N crystals can multiplex the output of 2,laser amplifiers into a single diffraction-limited beam. Phase control of the beams is maintained by an electronic servo which monitors the optical power emitted into certain undesired beams and minimizes this power by means of phase adjusters (e.g., piezoelectric fiber stretchers) on each amplifier. A configuration is described where a front-end laser master oscillator (FMO) (e.g., a Nd:YAG laser) is demultiplexed by the crystal stack, passes through multiple laser amplifiers, is reflected back through the amplifiers by phase-conjugating mirrors (e.g., passive multimode fibers generating stimulated Brillouin scattering), and is multiplexed on the return trip through the crystal stack. Phase conjugation removes beam distortion and depolarization produced on a single pass through the amplifiers, and the reflected beams are generated with the spatial profiles and alignment needed for beam recombination. An additional back-end laser master oscillator (BMO) (e.g., a second Nd:YAG laser) seeds the phase-conjugate field to phase-lock the different amplifiers.

Crystal stack for coherent optical beam combination

The present invention is a beam scanner for use about a nonlinear optical crystal for frequency conversion. The scanner oscillates the high power laser beam passing through the crystal to reduce heat damage and does not change the direction or the position of the beam upon exiting the scanner. A pair of thick optical plates are affixed to a driven axle being parallel to the laser beam direction. The first plate is mounted at a given angle to the axle and the second plate is mounted at the same but negative angle to the axle so that they are mirror images about the crystal. As the axle rotates, the laser beam moves through the crystal in a cylindrical pattern and due to the manner of mounting the plates, the exiting laser beam is not displaced from the original beam direction or position. The beam scanner may be inserted into an existing optical resonator, for example, without modifications thereto.

Growing community of inventors

Albuquerque, NM, United States of America

Gerald T Moore