Jds Uniphase Corporation

Sdl Inc.

Hughes Electronics Corporation

Other

University of Southern California

Stuart MacCormack

Robert G Waarts

Steven Sanders

Jack L Feinberg

David F Welch

Stephen G Grubb

Vincent G Dominic

Mehrdad Ziari

Edward C Vail

Paul Nathan Freeman

Marvin B Klein

Erji Mao

David M Giltner

Greg Roth

Donald R Scifres

David M Pepper

Robert J Lang

Thomas R O'Meara

Bernard G Fidric

David G Mehuys

Bardia Pezeshki

Ronald Regis Stephens

Barry A Wechsler

Vincent E Dominic

Ramon E Alvarez

Jianping Zhang

A laser apparatus for generating optical pulses is disclosed, said laser apparatus has a reflecting gain element preferably including a fiber gain medium. The reflecting gain element is coupled to a controllable reflecting/transmitting module having a reflecting state and a transmitting state, wherein the controllable reflecting/transmitting means are operable to switch from the transmitting state to the reflecting state to initiate a build-up of an optical pulse, and to switch back to the transmitting state for outputting the optical pulse before it reaches the reflecting/transmitting means after a cavity roundtrip. In a preferred embodiment, the controllable reflecting/transmitting module includes an acousto-optic switch at an output end of a laser operable to output the optical pulse in zeroth diffraction order.

Pulsed laser apparatus and method

The present application relates to a Raman amplifier having an increased dynamic range, and particularly for laser pump sources and a method of pumping Raman fiber amplifiers over a greater dynamic range. In a multi-channel optical system, optical amplifiers must be able to provide gains over a large dynamic range, which is determined by the distribution of node-to-node distances in the network, as well as the number of channels. The present invention has found that the dynamic range of a Raman amplifier can be significantly increased by using pulse width modulation to pulse pump current at or near the minimum current stability threshold, in order to produce lower power output. The duty cycle of the pulsed current is selected to achieve a time-averaged operating condition, thus the time averaged pump power can be reduced in a linear fashion well below the capability of a continuous wave system.

Wider dynamic range to a FBG stabilized pump

The invention relates to a method for automatic dynamic gain control in optical Raman amplifiers and an optical Raman amplifier adapted for the same. The present invention has found that in multiple pump Raman amplifiers a substantially linear relationship exists between total amplified signal power and pump power for each of different wavelength pumps, in order to maintain an original gain profile and gain levels for an optical link with a fully loaded channel configuration, in response to dropped channels. In accordance with the method, and an amplifier programmed to practice the method, a set of pump power values and signal level values required to maintain the characterized gain profile and gain levels for a plurality of channel loading configurations are pre-established for the each pump wavelength. A linear function from each set of pre-established values is derived for each pump wavelength. Advantageously, a single photodiode can replace a costly and complex channel monitor for providing signal responsive pump control.

Automatic raman gain control

A semiconductor pump laser uses a depolarzer to depolarize the pump light entering the fiber amplifier. The depolarized light source is useful for reducing polarization dependent gain of fiber amplifiers. The pump laser includes one or more semiconductor, coherence-collapsed laser sources emitting polarized pump outputs, and one or more depolarizers disposed to depolarize the polarized pump output from the lasers. One or more fiber outputs are coupled to the one or more depolarizers to receive depolarized pump light. The depolarizer may include an N&times;M polarization preserving coupler having N inputs and M outputs, N and M being at least 2, an input to the depolarizer at a first coupler input, an output port from the depolarizer at a first coupler output. A polarization-controlling optical path is coupled between a second coupler output and a second coupler input. A polarization of light exiting the N&times;M coupler through the second coupler output is substantially orthogonal to a polarization of light entering the N&times;M coupler through the second coupler input.

Depolarized semiconductor laser sources

The gain of a fiber amplifier is typically not uniform across the bandwidth used for amplifying optical communications signals. In a power fiber amplifier unit, having a fiber pre-amplifier and a fiber power amplifier, the gain tilt of the fiber power amplifier is generally set by the level of gain saturation. The gain tilt of the fiber pre-amplifier is adjustable by controlling the population inversion density in the amplifying medium. The gain tilt of the fiber pre-amplifier may be adjusted so as to at least partially compensate for the gain tilt of the power amplifier.

Power fiber amplifier with flat gain

All-fiber coupling architectures include at least one fiber gain media, e.g. a fiber amplifier or a fiber laser, providing for the coupling light from one or more multi-wavelength pump sources propagating in a multimode core fiber at multiple points along a double clad fiber or at least at one point along multiple double clad fibers having their inner claddings fused to the multimode core fiber. The latter arrangement provides for a low cost utility multi-signal fiber amplifier for telecommunication applications.

Side coupled pumping of double clad fiber gain media

Optical pumping arrangements are provided for the broadband or multiple wavelength pumping of optical sources. Sources may be based on Raman gain media and may use multiple output couplers to couple out different wavelength ranges. Cascaded Raman resonator (CRR) configurations may also be used. Overlapping resonators at different wavelengths may be configured to share gain media, and may have separate portions in separate optical paths. Attenuation filters may also be used that are matched to the gain profile of a gain medium, to flatten the gain spectrum and allow equalization of gain to different output wavelengths. In one embodiment, polarization maintaining fiber is used to develop resonant conditions at different wavelengths in different polarization states. Wideband output gratings may be substituted for narrowband gratings to provide CRR configurations with a broader output band. Broadband amplification may also be provided by using a laser source operating in coherence collapse. The multiple wavelength pumping lends itself to a pumping arrangement in which sources at different wavelengths are combined into separate transmission/gain media such as the different fibers of an optical fiber cable.

Multiple wavelength optical sources

A number of variations are provided of a device that provides an amplified single polarization optical signal. Each of these relies on the use of a non-polarization maintaining gain medium through which the signal is directed, and a polarization shifter and reflector that direct the signal back through the same gain medium with a shifted polarization state. An input polarization beamsplitter directs the returning optical signal away to an output, based on its shifted polarization state. The embodiments of the invention include the use of double-clad fiber. Multiple stages may be used to provide specific amplification parameters. In particular, a fiber with a relatively large mode field diameter may be used to enable high pulse power applications. Wavelength selective components are used in certain embodiments of the invention, to allow for wavelength selectivity, as well as a single polarization state, in amplifiers, lasers and amplified spontaneous emission (ASE).

Polarization maintaining fiber lasers and amplifiers

Double clad fiber gain medium systems particularly adapted for marking indicia on surfaces of articles are disclosed. These systems provide a modulated output from a pump or seed semiconductor laser source to a double clad fiber gain medium which provides an amplified marking output scanned over the article surface with an optical scanner forming a plurality of strokes, the completion of which results in the indicia.

Fiber gain medium marking system pumped or seeded by a modulated laser diode source and method of energy control

A number of variations are provided of a device that provides an amplified single polarization optical signal. Each of these relies on the use of a non-polarization maintaining gain medium through which the signal is directed, and a polarization shifter and reflector that direct the signal back through the same gain medium with a shifted polarization state. An input polarization beamsplitter directs the returning optical signal away to an output, based on its shifted polarization state. The embodiments of the invention include the use of double-clad fiber. Multiple stages may be used to provide specific amplification parameters. In one embodiment, both amplification stages reside in the same polarization shifting optical path. A polarization maintaining amplifier of this type may be used as part of a master oscillator-power amplifier, in which polarization maintaining fiber is used as part of the source laser. Wavelength selective components are also used in certain embodiments of the invention, to allow for wavelength selectivity, as well as a single polarization state, in amplifiers, lasers and amplified spontaneous emission (ASE). In one embodiment, an optical circulator is used to allow the amplified, shifted polarization state signals to be directed away from the input to a desired output port. A feedback loop may also be used to control the polarization state at the amplifier output. A polarization beamsplitter at the output directs light not having the desired polarization state to a photodetector, the output of which is used by a polarization controller at the input, such that the input polarization state is adjusted until the control signal from the photodetector is minimized.

An optical amplification system directs a diffraction-limited signal beam through a series of crossings, at substantially less than 90.degree. crossing angles, with a number of non-diffraction-limited pump beams in a photorefractive medium. The pump beams are e-polarized while the signal beam travels down the crystal medium's c-axis and is polarized in the same plane as the pump beam polarization, resulting in an energy transfer from the pumps to the signal beam while leaving the signal beam diffraction-limited. The photorefractive medium is preferably a series of BaTiO.sub.3 :Rh crystals that are aligned parallel to the angled edge of a wedged-shape prism through which the pump beams are transmitted, with the crystals cut so that their C-axes are parallel to the signal beam.

Optical amplification system with non-orthogonal signal and distributed

An optical amplification system directs a diffraction-limited signal beam through a series of approximately 90.degree. crossings with a number of non-diffraction-limited pump beams in a photorefractive medium. All of the beams are s-polarized, resulting in an energy transfer from the pumps to the signal beam while leaving the signal beam diffraction-limited. The photorefractive medium is preferably a series of BaTiO.sub.3 :Rh crystals that receive the pump and signal beams through orthogonal faces, with their C-axes at approximately 45.degree. to both beams. A binary tree optical distribution network is used to minimize waveguide splits in forming a large number of pump beams. The outputs of several amplification modules are combined into a single output beam using adaptive optics, with the outputs from the different modules phase matched to each other by diverting two minor portions of the combined beam, partially overlapping the diverted beams and adjusting the amplification module phases to cancel phase differentials between the overlapped portions. Similarly, sets of combined and phase-matched beams can be combined with each other (again using adaptive optics) to generate still higher powers using a super module approach.

Hybrid laser power combining and beam cleanup system using nonlinear and

A laser system includes a linear array of broad area lasers. Such a laser source produces a beam that has a polarization axis in the direction in which the array extends and a coherency axis orthogonal to that. The laser is injection locked by phase conjugating a portion of the array's light output. The phase conjugator has a conjugation axis. The coherency axis is aligned with this conjugation axis. External cavity optics include a polarization rotator to align the polarization axis with the coherency axis before the beam reaches the phase conjugator. Thus, the polarization, coherency, and conjugation axes are all aligned, optimizing the action of the phase conjugator. The approach works in both a single-beam and a dual-beam phase conjugation mode. The result is a laser system output of higher intensity, greater coherence, and a narrower frequency range.

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Mountain View, CA, United States of America

Stuart MacCormack