Patent Description:
High power laser systems typically use a signal combiner to combine multiple high power beams to produce a beam of additively higher power. The construction of the combiner typically provides a number of input ports based on a particular packing geometry. Each of the ports is typically used to propagate a high power beam in order to fill the available ports and to avoid possible deleterious effects associated with allowing ports to remain unused. <CIT> discloses an optical connector having a plurality of directional taps and connecting between a plurality of optical waveguides. <CIT> discloses a modular and scalable high-power fiber laser system. <CIT> discloses a beam dump which is configured for not increasing a temperature of a laser.

According to one aspect of the disclosed technology, an apparatus is provided as claimed in claim <NUM>.

In further examples, the apparatus includes a beam dump half including an interior situated to diffuse, absorb, or otherwise dump light, and including an inlet extending from an exterior surface of the beam dump half to the interior so as to either receive light or so as to direct the received light to a photodetector, wherein the beam dump half is situated to receive a substantially identical other beam dump half so that the other inlet of the other beam dump half is situated so as to oppositely either direct the received light to a photodetector or to receive the light.

According to another aspect of the disclosed technology, a method as claimed in claim <NUM>.

The foregoing and other features and advantages of the disclosed technology will become more apparent from the following detailed description, which proceeds with reference to the accompanying figures.

As used in this application and in the claims, the singular forms "a," "an," and "the" include the plural forms unless the context clearly dictates otherwise. Additionally, the term "includes" means "comprises. " Further, the term "coupled" does not exclude the presence of intermediate elements between the coupled items.

Although the operations of some of the disclosed methods are described in a particular, sequential order for convenient presentation, it should be understood that this manner of description encompasses rearrangement, unless a particular ordering is required by specific language set forth below. Moreover, for the sake of simplicity, the attached figures may not show the various ways in which the disclosed systems, methods, and apparatus can be used in conjunction with other systems, methods, and apparatus. Additionally, the description sometimes uses terms like "produce" and "provide" to describe the disclosed methods. The actual operations that correspond to these terms will vary depending on the particular implementation and are readily discernible by one of ordinary skill in the art.

In some examples, values, procedures, or apparatus' are referred to as "lowest", "best", "minimum," or the like. It will be appreciated that such descriptions are intended to indicate that a selection among many used functional alternatives can be made, and such selections need not be better, smaller, or otherwise preferable to other selections.

As used herein, optical radiation refers to electromagnetic radiation at wavelengths of between about <NUM> and <NUM>, and typically between about <NUM> and <NUM>. Examples based on available laser diode sources and optical fibers generally are associated with wavelengths of between about <NUM> and <NUM>. In some examples, propagating optical radiation is referred to as one or more beams having diameters, asymmetric fast and slow axes, beam cross-sectional areas, and beam divergences that can depend on beam wavelength and the optical systems used for beam shaping. For convenience, optical radiation is referred to as light in some examples, and need not be at visible wavelengths.

Representative embodiments are described with reference to optical fibers, but other types of optical waveguides can be used having square, rectangular, polygonal, oval, elliptical or other cross-sections. Optical fibers are typically formed of silica (glass) that is doped (or undoped) so as to provide predetermined refractive indices or refractive index differences. In some, examples, fibers or other waveguides are made of other materials such as fluorozirconates, fluoroaluminates, fluoride or phosphate glasses, chalcogenide glasses, or crystalline materials such as sapphire, depending on wavelengths of interest. Refractive indices of silica and fluoride glasses are typically about <NUM>, but refractive indices of other materials such as chalcogenides can be <NUM> or more. In still other examples, optical fibers can be formed in part of plastics. In typical examples, a doped waveguide core such as a fiber core provides optical gain in response to pumping, and core and claddings are approximately concentric. In other examples, one or more of the core and claddings are decentered, and in some examples, core and cladding orientation and/or displacement vary along a waveguide length.

In the examples disclosed herein, a waveguide core such as an optical fiber core is doped with a rare earth element such as Nd, Yb, Ho, Er, or other active dopants or combinations thereof. Such actively doped cores can provide optical gain in response to optical or other pumping. As disclosed below, waveguides having such active dopants can be used to form optical amplifiers, or, if provided with suitable optical feedback such as reflective layers, mirrors, Bragg gratings, or other feedback mechanisms, such waveguides can generate laser emissions. Optical pump radiation can be arranged to co-propagate and/or counter-propagate in the waveguide with respect to a propagation direction of an emitted laser beam or an amplified beam.

In <FIG>, a laser system <NUM> is shown that produces a laser output beam <NUM> that is continuous-wave or quasi continuous-wave and that typically provides an average power of greater than <NUM> kW. The laser output beam <NUM> is directed to a target <NUM>, such as a metallic surface, for precision laser cutting, welding, or other high power applications. The laser system <NUM> includes a laser signal sources <NUM>, <NUM> situated to produce and couple signal beams into respective signal fibers <NUM>, <NUM>. For example, in the generation of a laser output beam <NUM> of <NUM> kW, <NUM> kW signal beams propagate through each of the signal fibers <NUM>, <NUM>. The signal fibers <NUM>, <NUM> are spliced at repetitive fiber splices <NUM>, <NUM> to signal combiner inputs fibers <NUM>, <NUM> of a signal combiner <NUM>. The signal combiner <NUM> receives and combines the signal beams to form a combined signal beam <NUM> that is coupled into a combiner output fiber <NUM>. The combiner output fiber <NUM> emits the combined signal beam <NUM> as the laser output beam <NUM>. In some embodiments, one or more additional output fibers, such as a delivery fiber, are coupled to the combiner output fiber <NUM> to deliver the laser output beam <NUM> to a laser head situated to direct the laser output beam <NUM> in relation to the target <NUM>.

The signal combiner input fibers <NUM>, <NUM> are coupled to an input end <NUM> of the signal combiner <NUM> along with a separate input fiber <NUM> that is not coupled to a laser signal source <NUM>. In representative examples, the separate input fiber <NUM> corresponds to a fiber that could otherwise be used as a signal combiner input fiber and be coupled to an additional or replacement laser signal source. An input end <NUM> of the separate input fiber <NUM> is coupled to an interior region of a beam dump <NUM>. During operation of the laser system <NUM>, a separate beam <NUM> can be formed that is associated with the laser output beam <NUM> and that propagates in a reverse direction from the laser output beam <NUM>. The beam dump <NUM> is situated to receive the separate beam <NUM> and to diffuse the separate beam <NUM> in an interior integrating volume <NUM> having one or more curved surfaces <NUM> so that the optical energy of the separate beam <NUM> is removed through a thermally conductive housing <NUM>. In some examples, the separate beam <NUM> is diffused through multiple specular reflections or through diffusive reflections. In some examples, the beam dump <NUM> forms an enclosure that defines a cavity in which the separate beam <NUM> is absorbed. Thermal energy is directed away through an attached conductive housing <NUM>, such as a water-cooled cooling block. In representative examples, <NUM> W or greater of continuous power is received as the separate beam <NUM>.

In representative examples of the laser system <NUM>, during active operation the laser output beam <NUM> can reflect at a surface of the target <NUM> and cause a portion of the laser output beam <NUM> to be coupled back into the combiner output fiber <NUM> so as to form a backward propagating beam <NUM> that propagates in a direction opposite to that of the combined signal beam <NUM>. The backward propagating beam <NUM> can propagate back through the signal combiner <NUM> to reach and potentially damage the signal sources <NUM>, <NUM> or other components, such as the signal combiner <NUM>. The combiner output fiber <NUM> or an associated delivery fiber can break or fail causing additional resonant cavities to form within the laser system <NUM>, such as between the fiber break and one or more Bragg gratings associated with the signal sources <NUM>, so as to produce the backward propagating beam <NUM>. In some examples, the backward propagating beam <NUM> includes light at the wavelength at or near that of the signal sources <NUM>, <NUM> and light at one or more Raman wavelengths that are associated with stimulated Raman scattering (SRS). The separate beam <NUM> includes at least a portion of the backward propagating beam <NUM> and the beam dump <NUM> is situated to remove at least some of the optical energy associated with the backward propagating beam <NUM>. By directing the separate beam <NUM> to the beam dump, technicians repairing or performing maintenance on the laser system <NUM> can avoid injury from high power laser light reflecting within the interior of the housing of the laser system <NUM>.

<FIG> shows another example of a laser system <NUM> that forms and delivers a laser output beam <NUM> to a target <NUM>. The laser output beam <NUM> can be a high power beam, and in typical examples, has an average power of <NUM> to <NUM> kW. The laser beam <NUM> is produced by combining a plurality of signal beams 204A, 204B with a signal combiner <NUM>. The signal beam 204B is produced with a fiber laser system <NUM> that includes an oscillator <NUM> coupled to and pumped by diode pump sources <NUM> combined with a pump or pump signal combiner <NUM>. The signal beam 204A is produced with a fiber laser system <NUM> that includes a master oscillator <NUM> coupled to one or more fiber power amplifiers <NUM>. The signal beams 204A, 204B are coupled to corresponding signal combiner inputs 216A, 216B of the signal combiner <NUM> through respective input fibers 217A, 217B spliced to the respective fiber laser systems <NUM>, <NUM>. A separate input 216C of the signal combiner <NUM> is coupled to a length of fiber <NUM> having an end <NUM> that is coupled to an interior volume <NUM> of a beam dump <NUM>. The interior volume <NUM> is typically defined by one or more curved surfaces <NUM> that are suited for diffusing a reverse-propagating beam <NUM> associated with the laser output beam <NUM> that is directed into the interior volume <NUM> through the end <NUM> of the fiber <NUM>. The beam dump <NUM> is situated to remove the reverse-propagating beam <NUM> from the laser system <NUM> by reflecting the reverse-propagating beam <NUM> multiple times in the interior volume <NUM> and absorbing the diffused beam with a conductive housing <NUM>.

A photodetector <NUM>, such as a photodiode, is coupled to the beam dump <NUM> and is in optical communication with the interior volume <NUM>. The photodetector <NUM> is situated to detect one or more optical characteristics of the reverse-propagating beam <NUM>, such as wavelength or power. A thermal sensor <NUM>, such as a thermistor, is coupled to the conductive housing <NUM> of the beam dump <NUM> and is situated to detect a temperature variation of the conductive housing <NUM> that is associated with the power level and duration of the reverse-propagating beam <NUM>. A controller <NUM> is situated to receive a signal from the photodetector <NUM> corresponding to the optical characteristics of the reverse-propagating beam <NUM> and a signal from the thermal sensor <NUM> corresponding to a temperature of the conductive housing <NUM>. The controller <NUM> is further coupled to the diode pump sources <NUM> and is situated to change or disconnect power delivered to the diode pump sources <NUM> based on the detected characteristics of the reverse-propagating beam <NUM> and/or the conductive housing <NUM> so that the signal beams 204A, 204B can be deenergized. Thus, the beam dump <NUM> becomes a useful diagnostic tool to monitor and potentially disable one or more components of the laser system <NUM> based on the detection of selected characteristics of the reverse-propagating beam <NUM>.

<FIG> show an example of a signal combiner <NUM> having three input fibers <NUM>, <NUM>, <NUM> coupled to a combiner input face <NUM>. An output fiber <NUM> is coupled to a combiner output face <NUM>. A central portion <NUM> extends and adiabatically tapers between the input and output faces <NUM>, <NUM>. In some examples, the three input fibers <NUM>, <NUM>, <NUM> are fused to the combiner input face <NUM>. In further examples, the three input fibers <NUM>, <NUM>, <NUM> are fused and tapered together so as to form the central portion <NUM>. In typical examples, a signal cross-section <NUM> of the output fiber <NUM> is the same or smaller than signal cross-sections 318A, 318B, 318C of the input fibers <NUM>, <NUM>, <NUM>. In some examples, the input fibers <NUM>, <NUM> are situated to propagate high power input beams 317A, 317B in the signal cross-sections 318A, 318B and to deliver the input beams 317A, 317B to the central portion <NUM> of the signal combiner <NUM> to become combined and coupled into the signal cross-section <NUM> of the output fiber <NUM> as an output beam <NUM> having an output power approximately equal to the sum of the input beams 317A, 317B. A separate beam <NUM> can form that propagates in the opposite direction as the output beam <NUM> and that can damage optical components, including the signal combiner <NUM> and optical components associated with the generation of the input beams 317A, 317B. The third fiber <NUM> can be situated so as to receive at least a portion <NUM> of the separate beam <NUM>. Based on the optical characteristics of the received portion <NUM>, the power levels of the input beams 317A, 317B can be reduced to reduce a probability of failure of the signal combiner <NUM> or other optical components. In various examples, combiner input fibers, such as the input fibers <NUM>, <NUM>, <NUM>, and combiner output fibers, such as output fiber <NUM>, can be single-mode, few-mode, or multi-mode.

<FIG> shows another example of a signal combiner <NUM> that includes a hexagonal arrangement of seven input fibers 402A-<NUM> coupled to an input face <NUM>. The input fibers 402A-<NUM> are fused and tapered to form a combiner output <NUM> having a smaller diameter than the input face <NUM>. In some examples, input fibers 402B, 402C, 402E, 402F are situated to receive and couple corresponding high power input signals into signal combiner <NUM> through the input face <NUM>. For example, each high power input signal can have powers of <NUM> W, <NUM> kW, <NUM> kW, <NUM> kW, or greater. The input fibers 402A, 402D can be coupled together (e.g., with a splice) to form a fiber loop, providing the input fibers 402A, 402D as potential expansion or backup inputs to the signal combiner <NUM>. The centrally situated input fiber <NUM> does not propagate an input signal and instead is used to detect reverse-propagating light received from the combiner output <NUM> so as protect laser sources coupled to the input fibers 402B, 402C, 402E, 402F during normal operation or during a failure event. The central position of the input fiber <NUM> can allow reverse propagating light propagating along a central path to become better coupled into the input fiber <NUM> so as to improve removal of the reverse propagating light. In further examples, one or more of the input fibers 402A-402F situated on the periphery can be used to detect or remove reverse propagating light. In further examples, <NUM>:<NUM>, <NUM>:<NUM>, <NUM>:<NUM>, <NUM>:<NUM>, and other ratios of combiner inputs to combiner outputs can be used.

<FIG> show an example of a beam dump <NUM> that includes a first half portion <NUM> having an interior face <NUM> and a second half portion <NUM> that can have the same or substantially the same or identical shape as the first half portion <NUM>. As seen in <FIG>, the second half portion <NUM> is flipped and rotated by <NUM>° with respect to the first half portion <NUM> so that the interior face <NUM> of the first half portion <NUM> comes in contact with a corresponding an interior face (not shown) of the second half portion <NUM>. The first and second half portions <NUM>, <NUM> are made of a thermally conductive material, such as aluminum or copper, so as to form a thermally conductive block <NUM>. Each half portion <NUM>, <NUM> includes an interior volume <NUM> that is defined by one or more curved surfaces <NUM>. In representative examples, surfaces of the interior volume <NUM> are nickel-coated to enhance optical absorption. In some examples, the interior volume <NUM> has a hemispherical shape, and in some examples, the interior volume <NUM> can be defined by one or more planar surfaces <NUM>. One or more holes <NUM> can be bored through the interior face <NUM> and fasteners <NUM> inserted through the holes <NUM> to provide an mechanism for aligning and securing the first and second half portions <NUM>, <NUM>.

The first half portion <NUM> includes a notch <NUM> forming an inlet in which an optical fiber <NUM> is secured. The optical fiber <NUM> includes an end portion <NUM> with a polymer buffer removed so as to expose a cladding surface <NUM>. A cleaved end <NUM> of the optical fiber <NUM> is positioned in the interior volume <NUM> and a portion of the end portion <NUM> of the optical fiber <NUM> is secured in the notch <NUM> with a low index polymer suitably lower than the cladding surface <NUM> so as to guide light that propagates through the optical fiber <NUM> and end portion <NUM> to emit from the cleaved end <NUM>. The low index polymer can also cause buffer-guided light to become directed into the interior volume <NUM>. In some examples, the cleaved end <NUM> is cleaved at a non-perpendicular angle with respect to a longitudinal axis of the optical fiber <NUM>. In further examples, the cleaved end <NUM> includes a coated fiber endcap. In representative examples, the cleaved end <NUM> is coated with an anti-reflection coating. The second half portion <NUM> includes a notch <NUM> that is situated at a different position from the notch <NUM> with the first and second half portions <NUM>, <NUM> secured to each other. The notch <NUM> provides an optical path for diffuse light in the interior volume <NUM> to propagate to a photodetector (not shown) situated in or coupled to the notch <NUM>.

The first half portion <NUM> also includes a first receiving portion <NUM> adjacent to the notch <NUM> and a second receiving portion <NUM> spaced apart from the first receiving portion <NUM> and in alignment with the notch <NUM> of the second half portion <NUM> that is in contact with the first half portion <NUM>. The second half portion <NUM> includes similar first and second receiving portions <NUM>, <NUM> that align with the respective second and first receiving portions <NUM>, <NUM> of the first half portion <NUM>. The receiving portions <NUM>, <NUM>, <NUM>, <NUM> can have various configurations, including being recessed into or extending outwardly from the conductive block <NUM>. In some examples, the receiving portions <NUM>, <NUM>, <NUM>, <NUM> can be shaped to receive attaching hardware associated with the notches <NUM>, <NUM>, such as optical fiber connectors or photodetector mating points or conforming shapes. With identical first and second half portions <NUM>, <NUM>, the part count of the beam dump <NUM> is reduced, and the frequency of operator error during manufacture and assembly is decreased. In some examples, substantially identical half portions can have minor variations from each other, for example, with respect to machining tolerances. In other examples, substantially identical half portions can include designed differences but the substantially identical characteristics provide simplicity of assembly or interchangeability between inlets and outlets. As shown, the notches <NUM>, <NUM> are centrally positioned relative to an exterior of the respective first and second half portions <NUM>, <NUM>, but non-central positions can be formed as well, so that the notches <NUM>, <NUM> are spaced apart from other including without relative rotation of the first and second half portions <NUM>, <NUM> as secured to each other.

<FIG> shows an example of a beam dump <NUM> coupled to a cooling block <NUM>. The beam dump <NUM> is situated to receive an end of an optical fiber (not shown) in a notch <NUM> and to multiply reflect and diffuse light emitted from the optical fiber in an interior volume of the beam dump <NUM>. The beam dump <NUM> includes a thermally conductive housing <NUM> situated to absorb thermal energy associated with the diffused light. A photodetector <NUM> is coupled to the interior volume of the beam dump <NUM> so as to detect the power level or wavelength of the diffused light. A thermistor <NUM> is coupled to a surface of the thermally conductive housing <NUM> and is situated to detect a temperature of the thermally conductive housing <NUM>. As the power level of the light emitted from the optical fiber increases, the thermistor <NUM> can detect a corresponding temperature change. Cooling block input and output ports 612A, 612B are situated between opposite ends of a cooling block channel <NUM>. Coolant (such as water) flowing through the cooling block channel <NUM> of the cooling block <NUM> can reduce the temperature of the conductive housing based on the detected temperature or power levels. In some examples, peltier coolers may be used.

<FIG> shows an example of an integrating beam dump <NUM> that includes two substantially identical halves 702a, 702b having a hexagonal shape on an exterior surface 704a, 704b. With the halves <NUM> facing each other and rotated about an axis <NUM>, corresponding notches 706a, 708b and notches 706b, 708a align to form a pair of inlets forming a communication path into a spherical interior volume <NUM> defined by the facing halves <NUM>. In some examples, holes can be used instead of notches including a single hole from one of the exterior surfaces <NUM> so that two holes are formed with the halves <NUM> facing each other. Communication paths into the interior volume <NUM> can be situated at angles other than perpendicular to the axis <NUM> and can be directed into the interior volume <NUM> along axes other than intersecting the axis <NUM>. The spherical shape of the interior volume <NUM> can produce an integrating effect that multiply reflects light coupled into the interior volume <NUM> to scatter and diffuse the light for improved detection and absorption. A surface of the interior volume <NUM> can be specularly or diffusely reflective (e.g., Lambertian, semi-Lambertian, etc.).

Claim 1:
An apparatus, comprising:
a plurality of input fibers (<NUM>, <NUM>, 217A, 217B, <NUM>, <NUM>, <NUM>, 402A, 402B, 402C, 402D, 402E, 402F, <NUM>) including a plurality of signal fibers (<NUM>, <NUM>) and one or more beam dump fibers (<NUM>, <NUM>);
a fiber combiner (<NUM>, <NUM>, <NUM>, <NUM>) having an input end (<NUM>, <NUM>) coupled to the plurality of input fibers so as to couple portions of a plurality of signal beams respectively propagating in a plurality of the signal fibers to form a combiner beam (<NUM>);
an output fiber (<NUM>, <NUM>) coupled to an output end of the fiber combiner so as to receive the combiner beam (<NUM>);
a beam dump (<NUM>, <NUM>, <NUM>, <NUM>, <NUM>) coupled to at least one of the one or more beam dump fibers so as to receive a light beam propagating from the output fiber that is associated with the combiner beam (<NUM>); characterized in that:
the beam dump includes a pair of substantially identical thermally conductive halves (<NUM>, <NUM>) having respective interior faces angularly rotated relative to each other and joined so as to define an interior volume (<NUM>), each half including a curved interior surface (<NUM>) situated to diffuse light propagating in the interior volume (<NUM>) and a notch input (<NUM>) situated to receive one of an output end of the at least one of the one or more beam dump fibers and a photodetector.