Massachusetts Institute of Technology

Textron Systems Corporation

The Charles Stark Draper Laboratory, Inc.

Jason Edward Langseth

Christopher Hwang

Alexander E Mandl

Andrew Benedick

Kelsey Yee

H Charles Tapalian, Jr

Daniel Miller

David Fouche

Joshua Olitzky

John Kim

Yin Wan Tam

Seth Trotz

Darren A Rand

William Nowak

In coherent beam combining, the beams can be phase-modulated with a pseudo-random bit sequence (PRBS) to prevent stimulated Brillouin scattering (SBS) downstream. To coherently combine the phase-modulated beams, however, the PRBS waveforms should be true-time-delayed to within a small fraction of the bit duration. Traditionally, this true time delay is achieved by cutting optical fibers to length or with optical trombones. But trimming fibers is hard to do precisely, and optical trombones have large insertion loss. In addition, the path length mismatch varies as the fibers heat up and/or vibrate. Here, the beams are generated from a kilohertz linewidth seed split among N&#x3e;1 (e.g., N=100) arms. Each arm is phase-modulated with a separate copy of the unique PRBS pattern. The relative phase of the PRBS patterns is stabilized by phase-locking the master oscillators used to read out the PRBS patterns. The PRBS patterns can be phase shifted with respect to one another to compensate for physical path length mismatches of the optical fibers. Scanning the relative phase of the PRBS pattern used to modulate different arms yields a cross-correlation peak in combined power when the phases are matched at the combination plane.

SBS suppression and electronic path length matching in coherent beam combining

Incoherently combining light from different lasers while maintaining high brightness is challenging using conventional fiber bundling techniques, where fibers from different lasers are bundled adjacently in a tight-packed arrangement. The brightness can be increased by tapering the tips of the bundled fibers to match a single, multi-mode output fiber, e.g., one whose core that is just wide enough to fit the input cores. This increases the brightness of the beam combining. In addition, reducing the outer diameters of the signal fiber claddings allows the signal fibers to be bundled closer together, making it possible to couple more signal fiber cores to the core of a multi-mode output fiber. Similarly, reducing the outer diameter of the pump fiber cladding and/or etching away corresponding portions of the signal fiber cladding in a pump/signal combiner makes it possible to couple more pump light into the signal fiber cladding, again increasing brightness.

Incoherently combining lasers

Arrays of fiber pigtails can be used to project and receive light. Unfortunately, most fiber pigtail arrays are not aligned well enough for coherently combining different optical beams. This imprecision stems in part from misalignment between the optical fiber and the endcap spliced to the end of the optical fiber. The endcap is often polished, curved, or patterned, causing the light emitted by the endcapped fiber to refract or diffract as it exits the endcap. This refraction or diffraction shifts the apparent position of the beam waist from its actual position. Measuring this virtual beam waist position before and after splicing the endcap to the fiber increases the absolute precision with which the fiber is aligned to the endcap. This increase in absolute precision reduces the deviation in virtual beam waist position among endcapped fibers, making it easier to produce arrays of endcapped fibers aligned precisely enough for coherent beam combining.

Fabrication method for endcapped fiber laser pigtails with sub-micron virtual waist positional accuracy

When a soliton and a dispersive pulse propagate in an optical fiber, they can interact via cross-phase modulation, which occurs when one pulse modulates the refractive index experienced by the other pulse. Cross-phase modulation causes each pulse to shift in wavelength by an amount proportional to the time delay between the pulses. Changing the time delay between the pulses changes the wavelength shift of each pulse. This make it possible to produce pulses whose output wavelengths can be tuned over large ranges, e.g. hundreds of nm, in a time as short as the pulse repetition period of the laser (e.g., at rates of megahertz or gigahertz). Such a laser requires no moving parts, providing high reliability. The laser's optical path can be made entirely of optical fiber, providing high efficiency with low size, weight, and power consumption.

Short pulse wavelength tuning via timed soliton-dispersive wave interaction

A system configured to generate an optical beam from a fiber laser is presented. The system includes a fiber gain medium having a core and a cladding, the core being configured to convert radiation from a pump beam into an output beam, the cladding having a mode propagating section and a mode stripping section bounded on a near end and a distal end by the mode propagating section, the mode stripping section of the cladding being configured to scatter excess pump radiation received from the mode propagating section in a substantially outwardly radial direction. The system also includes a rigid support member into which the fiber gain medium is placed, the rigid support member completely encompassing the mode stripping section of the cladding and joined to the fiber at the mode propagating section of the cladding.

All glass fiber laser cladding mode stripper

A tapered fiber bundle device couples optical power from an optical power source into an output fiber. The tapered fiber bundle device includes a tapered fiber bundle including a set of bundled fibers having a near end and a distal end. The near end of the tapered fiber bundle is configured to collect the optical power from the optical power source. Each fiber k in the set of bundled fibers has a first cross-sectional area Aat the near end and a second cross-sectional area Aat the distal end such that Ais substantially smaller than A. Each fiber also has a substantially uniform core and a substantially uniform numerical aperture value NA. A cross-sectional area of the set of bundled fibers at the distal end has a cross-sectional area value Asubstantially equal to A.

High power fiber laser system

Systems, methods and devices relating to actuatably movable machines and with methods of using and manufacturing the same.

Growing community of inventors

Malden, MA, United States of America

Jason Edward Langseth