Patent Application
20110091155
The invention relates generally to optical waveguides and more particularly to an optical connector having a plurality of directional taps and connecting between a plurality of optical waveguides (e.g., such as a connector between a waveguide that is part of, or leads from, a seed laser and/or an initial optical-gain-fiber power amplifier, and a waveguide that is part of, or leads to, an output optical-gain-fiber power amplifier and/or a delivery fiber), wherein one of the directional taps extracts a small amount of the forward-traveling optical output signal from the seed laser or initial power amplifier (wherein this forward-tapped signal is optionally monitored using a sensor for the forward-tapped signal), and wherein another of the directional taps extracts at least some of any backward-traveling optical signal that may have been reflected, formed from amplified spontaneous emission at a signal wavelength in a downstream amplifier, or generated by some non-linear process such as may occur in a delivery fiber (wherein this backward-tapped signal is optionally monitored using a sensor for the backward-tapped signal).
Optical systems that produce high-power optical output signals such as optical-fiber based lasers and power amplifiers can suffer damage if a backward-traveling optical signal (e.g., from a reflection of a forward-traveling high-power optical output signal after it has left the power-amplification stage of the laser system) re-enters the power-amplification stage where it can get amplified and then damage components in the laser system. Thus, there is a need in the art for technology and methods that can detect, prevent, and/or mitigate problematic backward-traveling beams, especially in fiber-based optical amplification systems.
Further, spectral beam combining (SBC) of beams from fiber lasers is a promising technology enabling a very-high-power laser system with excellent beam quality. An efficient fiber laser type for such systems can be the ytterbium-doped (Yb) fiber laser, which lases around 1,060 nm. If the output beams from a plurality of such fiber lasers are spectral-beam combined, the resulting optical beam can have extraordinarily high power. There can be a need to detect, prevent, and/or mitigate problematic backward-traveling beams (e.g., from reflections or stimulated Brillouin scattering (SBS)) in SBC systems.
Even when a fiber amplifier or fiber laser is designed to compensate for the above effects, there will be a limit on the maximum power that can be obtained from a single fiber when scaling to larger fiber sizes and/or lengths, pump powers, and the like.
U.S. Pat. No. 6,192,062 to Sanchez-Rubio et al. titled “Beam combining of diode laser array elements for high brightness and power” and U.S. Pat. No. 6,208,679 to Sanchez-Rubio et al. titled “High-power multi-wavelength external cavity laser” describe the fundamental techniques of spectral beam combining, and both are incorporated herein by reference.
In some embodiments of the present invention, the gratings used for spectral-beam combining are “blazed,” i.e., formed with V-grooves having sidewall angles that are asymmetrical with respect to a vector normal to the overall surface of the grating. U.S. Pat. No. 3,728,117 to Heidenhain et al. titled “Optical Diffraction Grid” (incorporated herein by reference) describes a method for making blazed gratings having asymmetric grooves. U.S. Pat. No. 4,895,790 to Swanson et al. titled “High-efficiency, multilevel, diffractive optical elements” (incorporated herein by reference) describes a method for making blazed gratings having asymmetric grooves using binary photolithography to create stepped profiles. U.S. Pat. No. 6,097,863, titled “Diffraction Grating with Reduced Polarization Sensitivity” issued Aug. 1, 2000, to Chowdhury (incorporated herein by reference) describes a reflective diffraction grating with reduced polarization sensitivity for dispersing the signals. The Chowdhury grating includes facets that are oriented for reducing efficiency variations within a transmission bandwidth and that are shaped for reducing differences between the diffraction efficiencies in two orthogonal directions of differentiation. U.S. Pat. No. 4,313,648 titled “Patterned Multi-Layer Structure and Manufacturing Method” issued Feb. 2, 1982, to Yano et al. (incorporated herein by reference) describes a manufacturing method for a patterned (striped) multi-layer article.
U.S. Pat. No. 6,822,796 to Takada et al. titled “Diffractive optical element” (incorporated herein by reference) describes a method for making blazed gratings having asymmetric grooves with dielectric coatings. U.S. Pat. No. 6,958,859 to Hoose et al. titled “Grating device with high diffraction efficiency” (incorporated herein by reference) describes a method for making blazed gratings having dielectric coatings.
U.S. Pat. No. 5,907,436 titled “Multilayer dielectric diffraction gratings” issued May 25, 1999, to Perry et al., and is incorporated herein by reference. This patent describes the design and fabrication of dielectric grating structures with high diffraction efficiency. The gratings have a multilayer structure of alternating index dielectric materials, with a grating structure on top of the multilayer, and obtain a diffraction grating of adjustable efficiency, and variable optical bandwidth.
U.S. Pat. No. 6,212,310 titled “High power fiber gain media system achieved through power scaling via multiplexing” issued Apr. 3, 2001, to Waarts et al., and is incorporated herein by reference. This patent describes certain methods of power scaling by multiplexing multiple fiber gain sources with different wavelengths; pulsing or polarization modes of operation is achieved through multiplex combining of the multiple fiber gain sources to provide high power outputs, such as ranging from tens of watts to hundreds of watts, provided on a single mode or multimode fiber.
U.S. Pat. No. 7,586,671 to Eiselt issued Sep. 8, 2009, titled “Apparatus and method for Raman gain control” and is incorporated herein by reference. The Eiselt patent pertains to optical fiber transmission systems, and optical transport systems employing Raman optical amplifiers, and describes an apparatus and method to control the Raman gain based upon power measurements at one end of the transmission fiber.
There is a need for a method and for an optical device that “taps” (obtains at least a portion of) both a forward-propagating optical output beam from a laser system as well as a backward-propagating optical beam (such as from a reflection), and, based on automatic analyses of the forward and backward portion(s), controls at least one aspect of the operation of the laser system.
Various embodiments of the present invention provide a device and method that provide simultaneous taps of forward-propagating and backward-propagating optical signals in fiber-optic systems for sensing, analysis and/or control. The figures depict a number of various illustrative embodiments of the present invention. Some embodiments include circuits and/or microprocessors that analyze the signals from the forward tap(s) and backward tap(s) (e.g., to determine power levels, spectral content, or the like), and that provide control signals to operate laser seed source(s), pump lasers, light gates, or the like.
In some embodiments, the tapping and sensing provide a measurement of the forward-propagating signal that indicates the health of the optical-signal source (e.g., the seed laser and/or optical-amplification stages in some embodiments) that precedes the measurement point (i.e., the upstream parts of the system that generate the forward-propagating signal). In some embodiments, one or more power-level measurements of the forward-propagating signal are used in a feedback loop to maintain the forward signal's power level at a desired (e.g., constant) value. In the case of significant reduction (or increase) of the forward signal, the feedback system can turn off the laser system to mitigate any catastrophic damage that might otherwise occur to the amplifier stage(s).
The backward-propagating signal may contain amplified spontaneous emission (ASE) signals, stimulated Brillouin scattered (SBS) signals generated in a downstream amplifier stage, and/or reflections of the forward-propagating signal. In some embodiments, the SBS power level measured in the backward-propagating signal (using signals obtained from the backward tap(s)) is used in a feedback loop to turn off the laser system if the SBS signal power exceeds a preset level, in order to mitigate any catastrophic damage to the amplifier. ASE measurement is useful for characterizing amplifier saturation. Forward ASE-level measurement may be difficult or not feasible in some laser systems due to lack of access to the high-power laser output (at the output of a downstream optical amplifier). In such cases, the backward power measurements (measurements of the backward-propagating signal from the input end of the downstream optical amplifier) can be used for determining the ASE level and amplifier saturation of the downstream optical amplifier.
In some embodiments, the present invention accomplishes the following: the various discussed embodiments enable the measurement of the generated SBS and ASE, as well as forward-propagating-signal level in high-power fiber lasers (which may include power oscillator configurations in which the high-power amplification is within the lasing cavity, as well as master-oscillator-power-amplifier (MOPA) configurations in which the high-power amplification is outside and downstream of the lasing cavity). The measured power of the forward-propagating signal can then be used in feedback loops to maintain the laser-system stability and safe operation of the system in the long term. Various specific benefits of each of the embodiments are discussed in their respective sections below.
In some embodiments, the present invention provides an integrated isolator with tap ports, in order to provide a signal monitor, power monitor, and/or SBS monitor for a fiber laser and/or fiber amplifier that may generate ASE, SBS, or incur reflections of the output optical signal back into the system.
Although the following detailed description contains many specifics for the purpose of illustration, a person of ordinary skill in the art will appreciate that many variations and alterations to the following details are within the scope of the invention. Accordingly, the following preferred embodiments of the invention are set forth without any loss of generality to, and without imposing limitations upon the claimed invention. Further, in the following detailed description of the preferred embodiments, reference is made to the accompanying drawings that form a part hereof, and in which are shown by way of illustration specific embodiments in which the invention may be practiced. It is understood that other embodiments may be utilized and structural changes may be made without departing from the scope of the present invention.
The leading digit(s) of reference numbers appearing in the Figures generally corresponds to the Figure number in which that component is first introduced, such that the same reference number is used throughout to refer to an identical component that appears in multiple figures. Signals and connections may be referred to by the same reference number or label, and the actual meaning will be clear from its use in the context of the description.
In some embodiments, the present invention provides an apparatus and process wherein both the forward-propagating signal and the backward-propagating signal are tapped and analyzed (e.g., the power levels at one or more spectral wavelengths of both the forward-propagating signal and the backward-propagating signal are sensed and one or more electrical signals based on the sensed optical signals are generated) and the resulting sense signals are used (e.g., in a feedback circuit) to control operation of the optical system.
In some embodiments, power amplifier 140 includes a plurality of pump lasers 142 that are connected by optical fibers to a pump combiner 144 that inserts the seed signal from power-amplifier input fiber 138 into a core of a multi-clad combiner output LMA fiber 145 and inserts the pump light from pump lasers 142 into an inner cladding (also called a pump cladding) and/or the core of combiner output LMA fiber 145. In some embodiments, combiner output LMA fiber is fusion spliced to gain fiber 147 at splice 146. In some embodiments, gain fiber 147 has a fiber output end 148 (or is spliced to an output fiber 148), wherein fiber 148 is fusion spliced to pump dump 149, which eliminates the residual pump light from the pump lasers 142 and outputs the amplified seed signal from the gain fiber 147 into the core of delivery fiber 150. Backward-propagating light (e.g., from reflected light (going right-to-left from delivery fiber 150) or from amplified spontaneous emission (ASE), stimulated Brillouin scattering (SBS) or other non-linear effects in gain fiber 147 can cause problems if mitigation measures are not taken. In some embodiments, a selected fiber 141 of the plurality of input fibers 143 into pump combiner 144 is not connected to a pump laser, but instead is used as a “backward tap” to obtain a portion of any backward-propagating light from gain fiber 147 and/or delivery fiber 150, and this backward-propagating light is coupled to one or more sensors 124 (e.g., in some embodiments, sensors that detect particular wavelengths that indicate the amount of ASE, or the amount of SBS light, or other wavelengths or other properties of the backward-propagating light that are of interest). The selected fiber 141 is called the “backward tap fiber” and carries an optical signal called the “backward-tap light signal.” In some embodiments, the sensors 124 generate one or more electrical signals 125 (called the “backward-tap electrical signal(s)”) that are each indicative of the different respective optical properties of the backward-tap signal that were measured by sensors 124.
In some embodiments, the forward-tap electrical signal(s) 127 (from forward tap 120 and representing one or more certain properties of the forward-propagating light) and the backward-tap electrical signal(s) 125 (from backward-tap sensors 124 and representing one or more certain properties of the backward-propagating light) are coupled to controller 130 that is used to control one or more operations of system 101 (e.g., in some embodiments, controller 130 can turn off the electrical power to the pump lasers 142 via electrical control or power line(s) 132, and/or can alter the operation of the seed source 110 via electrical control or power line(s) 131 (e.g., in some embodiments, if the backward tap 141 and sensors 124 indicate a buildup of excess ASE power from gain fiber 147 (e.g., perhaps caused by a lack of seed-signal pulses that would normally use up the optical pump power), controller 130 can force the seed source 110 to emit a continuous-wave (CW) signal that would bleed the excess stored energy from the gain fiber).
In some embodiments, four-port beam-splitter assembly 201 has a partially reflective front surface 231 and a partially reflective back surface 232. In some embodiments of four-port beam-splitter assembly 201, partially reflective front surface 231 reflects about 0.5% of the input forward-propagating beam 281 from input fiber 221, which is reflected as forward-tap light 282 toward the lens (or other focusing element) of forward-tap ferrule 228, which in turn focusses the forward-tap light 282 into forward-tap fiber 227. In some embodiments, front surface 231 of beam splitter 236 transmits about 99.5% of the forward-propagating beam 281 toward the lens (or other focusing element) of ferrule 224, which focusses forward-propagating light 283 into output fiber 223. Ferrule 224 also collimates the backward-propagating beam 291 from fiber 223 into a collimated beam that propagates in free space to beam splitter 236. In some embodiments of four-port beam-splitter assembly 201, partially reflective back surface 232 of beam splitter 236 reflects about 0.5% of the backward-propagating beam 291 from output fiber 223 as reflected backward-tap light 292 toward the lens (or other focusing element) of backward-tap ferrule 226, which in turn focusses the backward-tap light 292 into backward-tap fiber 225.
In some embodiments, forward-tap fiber 227 is connected to an optical-fiber connector 237 that is then coupled to one or more sensors used to measure one or more characteristics of the forward-propagating beam (e.g., its power at a signal wavelength), and backward-tap fiber 225 is connected to an optical connector 235 that is then coupled to one or more sensors used to measure one or more characteristics of the backward-propagating beam (e.g., its power at a wavelength that is associated with SBS in a downstream gain fiber, its power at a wavelength that is associated with ASE in a downstream gain fiber, and/or its power at a signal wavelength that is associated with a back reflection of the output signal from a far end of a downstream delivery fiber). In some embodiments, due to multiple reflections, a beam dump (e.g., a black light-absorbing surface 261, shown in
In some embodiments of each system described herein, at least some of the internal optical parts are laser-welded to a glass substrate within enclosure 220 or the other respective enclosures.
In other embodiments, each system described herein uses or is modified to use other percentages of transmitted and reflected light rather than the about 99.5% and about 0.5%, respectively described for the various beam splitters herein. For example, in some embodiments, the beam splitter transmits about 99.9% and reflects about 0.1% of the light. In some embodiments, the beam splitter transmits about 99.8% and reflects about 0.2% of the light. In some embodiments, the beam splitter transmits about 99.5% and reflects about 0.5% of the light. In some embodiments, the beam splitter transmits about 99% and reflects about 1% of the light. In some embodiments, the beam splitter transmits about 98% and reflects about 2% of the light. In some embodiments, the beam splitter transmits about 95% and reflects about 5% of the light. In some embodiments, the beam splitter transmits about 90% and reflects about 10% of the light. In some embodiments, the beam splitter transmits at least 99.9% and reflects less than 0.1% of the light. In some embodiments, the beam splitter transmits at least 99.8% and reflects less than 0.2% of the light. In some embodiments, the beam splitter transmits at least 99.5% and reflects less than 0.5% of the light. In some embodiments, the beam splitter transmits at least 99% and reflects less than 1% of the light. In some embodiments, the beam transmits at least 98% and reflects less than 2% of the light. In some embodiments, the beam splitter transmits about 95% and reflects about 5% of the light. In some embodiments, the beam splitter transmits at least 90% and reflects less than 10% of the light.
In some embodiments, beam splitter 233 has a highly-transmissive/partially-reflective front surface 234 and an anti-reflective back surface 235, which has the benefit of a reduced need for a beam dump. In some embodiments, the beam splitter 233 partially reflective front surface 234 reflects about 0.5% of the forward-propagating beam 281 from input fiber 221, reflecting forward-tap light 282 toward the lens (or other focusing element) of forward-tap ferrule 228, which focusses the forward-tap light 282 into forward-tap fiber 227, and front surface 234 transmits about 99.5% of the forward-propagating beam 281 to forward-propagating light 283 toward the lens (or other focusing element) of ferrule 224, which focusses the forward-propagating light 283 into fiber 223. In some embodiments, the beam splitter 233 partially reflective front surface 234 reflects about 0.5% of the backward-propagating beam 291 from output fiber 223 reflecting backward-tap light 292 toward the lens (or other focusing element) of backward-tap ferrule 226, which focusses the backward-tap light 292 into backward-tap fiber 225.
In some embodiments, beam splitter 240 has a highly-reflective low-transmissive front surface 241 and an anti-reflective back surface 242, which has the benefit of a reduced need for a beam dump. In some embodiments, beam splitter 240 highly-reflective front surface 241 transmits about 0.5% of the forward-propagating beam 281 from input fiber 221 to forward-tap light 282 toward the lens (or other focusing element) of forward-tap ferrule 228, which focusses the forward-tap light 282 into forward-tap fiber 227, and front surface 241 reflects about 99.5% of the forward-propagating beam 281 to forward-propagating light 283 toward the lens (or other focusing element) of ferrule 224, which focusses the forward-propagating light 283 into fiber 223. Note that reflecting the high-power forward-propagating light has the advantage of minimizing the power of the light that goes through the beam splitter, which increases the power handling capability of the system. In some embodiments, the beam splitter 240 the partially reflective front surface 234 transmits about 0.5% of the backward-propagating beam 291 from output fiber 223 transmitting backward-tap light 292 toward the lens (or other focusing element) of backward-tap ferrule 226, which focusses the backward-tap light 292 into backward-tap fiber 225.
In some embodiments, four-port beam-splitter assembly 204 has a fused middle portion 251 of a first source fiber 221-223 that is fused to a fused middle portion 252 of a second fiber 225-227 to form an evanescent coupling. In some embodiments, the fusing of middle portion fiber 251 to middle portion 252 includes fusing the fiber cladding without fusing the fiber cores for a predetermined length, for example, by coupling a test signal into fiber end 221, and monitoring the forward-tap signal 282 while heating the central portion only until the cross-coupled output signal 282 reaches the desired proportion (e.g., until about (to a desired accuracy)0.5% coupling is achieved). In some embodiments, the desired proportion cross-coupling output is about 10% coupling. In some embodiments, the desired proportion cross-coupling output is about 5% coupling. In some embodiments, the desired proportion cross-coupling output is about 2% coupling. In some embodiments, the desired proportion cross-coupling output is about 1% coupling. In some embodiments, the desired proportion cross-coupling output is about 0.5% coupling. In some embodiments, the desired proportion cross-coupling output is about 0.1% coupling. In some embodiments, the desired proportion cross-coupling output is about 0.05% coupling. In some embodiments, the desired proportion cross-coupling output is about 0.01% coupling. In some embodiments, the desired proportion cross-coupling output is less than about 10% coupling. In some embodiments, the desired proportion cross-coupling output is less than about 5% coupling. In some embodiments, the desired proportion cross-coupling output is less than about 2% coupling. In some embodiments, the desired proportion cross-coupling output is less than about 1% coupling. In some embodiments, the desired proportion cross-coupling output is less than about 0.5% coupling. In some embodiments, the desired proportion cross-coupling output is less than about 0.1% coupling. In some embodiments, the desired proportion cross-coupling output is less than about 0.05% coupling. In some embodiments, the desired proportion cross-coupling output is less than about 0.01% coupling.
In some embodiments, the four-port beam-splitter assembly 204 partially couples the forward-propagating beam 281 from input fiber 221 to forward-tap light 282. In some embodiments, the four-port beam-splitter assembly 204 couples substantially all of the remainder of the forward-propagating beam 281 from input fiber 221 to output fiber 223 as forward-propagating light 283. In some embodiments, four-port beam-splitter assembly 204 partially couples backward-propagating beam 291 from output fiber 223 to backward-tap light 292. In some embodiments, (such as shown) no couplers are needed, but rather the fibers form an all-glass optical path. In some other embodiments, forward-tap fiber 227 is connected to an optical-fiber connector (such as connector 237 shown in
In some embodiments, the forward-tap electrical signal(s) 127 (from forward tap sensor(s) 126 and representing one or more certain properties of the forward-propagating light) and the backward-tap electrical signal(s) 125 (from backward-tap sensor(s) 124 and representing one or more certain properties of the backward-propagating light) are coupled to controller 130 that is used to control one or more operations of system 205 (e.g., in some embodiments, controller 130 can turn off the electrical power to the pump lasers 142 via electrical control or power line(s) 132, and/or can alter the operation of the seed source 110 via electrical control or power line(s) 131 (e.g., in some embodiments, if the backward tap 225 and sensors 124 indicate a buildup of excess ASE power from gain fiber 147 (e.g., perhaps caused by a lack of seed-signal pulses that would normally use up the optical pump power), controller 130 can force the seed source 110 to emit a continuous-wave (CW) signal that would bleed the excess stored energy from the gain fiber).
In some embodiments, four-port beam-splitter assembly 301 has a partially reflective front surface 231 and a partially reflective back surface 232. In some embodiments of four-port beam-splitter assembly 301, partially reflective front surface 231 reflects about 0.5% of the input forward-propagating beam 281 from input fiber 221, which is reflected as forward-tap light 282 toward the lens (or other focusing element) of forward-tap ferrule 228, which in turn focusses the forward-tap light 282 into forward-tap fiber 227. In some embodiments, front surface 231 of beam splitter 236 transmits about 99.5% of the forward-propagating beam 281 toward the lens (or other focusing element) of ferrule 224, which focusses forward-propagating light 283 into output fiber 223. Ferrule 224 also collimates the backward-propagating beam 291 from fiber 223 into a collimated beam that propagates in free space to beam splitter 236. In some embodiments of four-port beam-splitter assembly 301, partially reflective back surface 232 of beam splitter 236 reflects about 0.5% of the backward-propagating beam 291 from output fiber 223 as reflected backward-tap light 292 toward the lens (or other focusing element) of backward-tap ferrule 226, which in turn focusses the backward-tap light 292 into backward-tap fiber 225.
In some embodiments, forward-tap fiber 227 is connected to an optical-fiber connector 237 that is then coupled to one or more sensors used to measure one or more characteristics of the forward-propagating beam (e.g., its power at a signal wavelength), and backward-tap fiber 225 is connected to an optical connector 235 that is then coupled to one or more sensors used to measure one or more characteristics of the backward-propagating beam (e.g., its power at a wavelength that is associated with SBS in a downstream gain fiber, its power at a wavelength that is associated with ASE in a downstream gain fiber, and/or its power at a signal wavelength that is associated with a back reflection of the output signal from a far end of a downstream delivery fiber). In some embodiments, due to multiple reflections, a beam dump (e.g., a black light-absorbing surface, not shown in
In some embodiments of each system described herein, at least some of the internal optical parts are laser-welded to a glass substrate within enclosure 320 or the other respective enclosures.
In other embodiments, each system described herein uses other percentages of transmitted and reflected light rather than the about 99.5% and about 0.5%, respectively described for the systems herein. For example, in some embodiments, the beam splitter transmits about 99.9% and reflects about 0.1% of the light. In some embodiments, beam splitter transmits about 99% and reflects about 1% of the light. In some embodiments, beam splitter transmits about 90% and reflects about 10% of the light. In some embodiments, beam splitter transmits at least 99.5% and reflects less than 0.5% of the light. In some embodiments, beam splitter transmits at least 99.9% and reflects less than 0.1% of the light. In some embodiments, beam transmits at least 99% and reflects less than 1% of the light. In some embodiments, beam splitter transmits at least 90% and reflects less than 10% of the light.
In some embodiments, beam splitter 233 has a highly-transmissive/partially-reflective front surface 234 and an anti-reflective back surface 235, which has the benefit of a reduced need for a beam dump. In some embodiments, the beam splitter 233 partially reflective front surface 234 reflects about 0.5% of the forward-propagating beam 281 from input fiber 221, reflecting forward-tap light 282 toward the lens (or other focusing element) of forward-tap ferrule 228, which focusses the forward-tap light 282 into forward-tap fiber 227, and front surface 234 transmits about 99.5% of the forward-propagating beam 281 to forward-propagating light 283 toward the lens (or other focusing element) of ferrule 224, which focusses the forward-propagating light 283 into fiber 223. In some embodiments, the beam splitter 233 partially reflective front surface 234 reflects about 0.5% of the backward-propagating beam 291 from output fiber 223 reflecting backward-tap light 292 toward the lens (or other focusing element) of backward-tap ferrule 226, which focusses the backward-tap light 292 into backward-tap fiber 225.
In some embodiments, beam splitter 240 has a highly-reflective low-transmissive front surface 241 and an anti-reflective back surface 242, which has the benefit of a reduced need for a beam dump. In some embodiments, beam splitter 240 highly-reflective front surface 241 transmits about 0.5% of the forward-propagating beam 281 from input fiber 221 to forward-tap light 282 toward the lens (or other focusing element) of forward-tap ferrule 228, which focusses the forward-tap light 282 into forward-tap fiber 227, and front surface 241 reflects about 99.5% of the forward-propagating beam 281 to forward-propagating light 283 toward the lens (or other focusing element) of ferrule 224, which focusses the forward-propagating light 283 into fiber 223. Note that reflecting the high-power forward-propagating light has the advantage of minimizing the power of the light that goes through the beam splitter, which increases the power handling capability of the system. In some embodiments, the beam splitter 240 the partially reflective front surface 234 transmits about 0.5% of the backward-propagating beam 291 from output fiber 223 transmitting backward-tap light 292 toward the lens (or other focusing element) of backward-tap ferrule 226, which focusses the backward-tap light 292 into backward-tap fiber 225.
In other embodiments, each system described herein uses other percentages of reflected and transmitted light rather than the about 99.5% and about 0.5%, respectively described for the systems herein. For example, in some embodiments, the beam splitter reflects about 99.9% and transmits about 0.1% of the light. In some embodiments, the beam splitter reflects about 99% and transmits about 1% of the light. In some embodiments, the beam splitter reflects about 90% and transmits about 10% of the light. In some embodiments, the beam splitter reflects at least about 99.5% and transmits less than about 0.5% of the light. In some embodiments, the beam splitter reflects at least about 99.9% and transmits less than about 0.1% of the light. In some embodiments, the beam splitter reflects at least about 99% and transmits less than about 1% of the light. In some embodiments, the beam splitter reflects at least about 90% and transmits less than about 10% of the light.
In some embodiments, four-port beam-splitter assembly 304 has a fused middle portion 251 of a first source fiber 221-223 that is fused to a fused middle portion 252 of a second fiber 225-227 to form an evanescent coupling. In some embodiments, the fusing of middle portion fiber 251 to middle portion 252 includes fusing the fiber cladding without fusing the fiber cores for a predetermined length, for example, by coupling a test signal into fiber end 221, and monitoring the forward-tap signal 282 while heating the central portion only until the cross-coupled output signal 282 reaches the desired proportion (e.g., until about 0.5% coupling (to a desired accuracy) is achieved). In some embodiments, the four-port beam-splitter assembly 304 partially couples the forward-propagating beam 281 from input fiber 221 to forward-tap light 282. In some embodiments, the four-port beam-splitter assembly 304 couples substantially the remainder of the forward-propagating beam 281 from input fiber 221 to output fiber 223 as forward-propagating light 283. In some embodiments, four-port beam-splitter assembly 304 partially couples backward-propagating beam 291 from output fiber 223 to backward-tap light 292. In some embodiments (such as shown), no couplers are needed, but rather the fibers form an all-glass optical path. In some other embodiments, forward-tap fiber 227 is connected to an optical-fiber connector (such as connector 237 shown in
In some embodiments, the forward-tap electrical signal(s) 127 (from forward tap sensor(s) 126 and representing one or more certain properties of the forward-propagating light) and the backward-tap electrical signal(s) 125 (from backward-tap sensor(s) 124 and representing one or more certain properties of the backward-propagating light) are coupled to controller 130 that is used to control one or more operations of system 305 (e.g., in some embodiments, controller 130 can turn off the electrical power to the pump lasers 142 via electrical control or power line(s) 132, and/or can alter the operation of the seed source 110 via electrical control or power line(s) 131 (e.g., in some embodiments, if the backward tap 225 and sensors 124 indicate a buildup of excess ASE power from gain fiber 147 (e.g., perhaps caused by a lack of seed-signal pulses that would normally use up the optical pump power), controller 130 can force the seed source 110 to emit a continuous-wave (CW) signal that would bleed the excess stored energy from the gain fiber).
In some versions of the first embodiment (see
In some embodiments, for each pump combiner, a leg having a proportion that is closest to the average value is selected, and optionally a calibration factor is applied (the signal is multiplied by a factor that provides a specified constant value regardless of the actual proportion going to the selected leg). For example, in the above table: for the first pump combiner, leg 4 is selected with a calibration factor of 100%, for the second pump combiner, leg 10 is selected with a calibration factor of 100%, for the third pump combiner, leg 5 is selected with a calibration factor of 100%, and for the fourth pump combiner, leg 3 is selected with a calibration factor of 111%. In each case, a pump-combiner leg having about 0.1 of the backward-propagating light is selected, and if the leg has less than 0.1, its sensed signal is increased by an amount that results in a desired constant proportion value (e.g., 0.1) while if the leg has more than 0.1, its sensed signal is decreased by an amount that results in the same desired constant proportion value (e.g., 0.1). In other embodiments, the leg having a proportion value closest to the desired proportion is selected and no calibration factor is applied. In yet other embodiments, only one leg is measured and its output is calibrated such that for a given backward-propagating signal, the measured signal is adjusted to match the desired calibrated value. For example, in some embodiments, for the pump combiners in the above table, the first leg of each pump combiner is selected and then measured and calibrated such that the calibration yields a constant (e.g., 0.1). Thus, pump combiner 1 leg 1 has a calibration factor of 125% (0.8*125%=0.1), pump combiner 2 leg 1 has a calibration factor of 167% (0.6*166.67%=0.1), pump combiner 3 leg 1 has a calibration factor of 142.86% (0.7*142.86%=0.1), and pump combiner 4 leg 1 has a calibration factor of 142.86% (0.7*142.86%=0.1). With a calibration factor applied, only one leg of each pump combiner need be measured and calibrated, saving time and cost in the manufacturing process.
In some of the second and third embodiments of the invention, a partially reflective, partially transmissive mirror is inserted inside a discrete fiber pigtailed package or inside an isolator package, respectively, immediately before the output-fiber collimator, as shown in
In some embodiments, for a polarized signal in the forward direction, the forward signal will be linearly polarized. However, the backward-propagating signal from the amplifier can be randomly polarized. As a result, in some embodiments, the coatings of the partial reflector should have the same reflectivity for both s- and p-polarization light at the angle of operation (e.g., 45 degrees).
In some embodiments of the systems shown in
In some embodiments, the Yb-doped pump lasers (e.g., gain fibers of fiber-laser module(s) 100 of
In some embodiments, the present invention provides a method that includes generating a laser beam; propagating the laser beam in a forward-traveling direction in an input optical fiber; splitting the forward-traveling laser beam from the input optical fiber into a plurality of portions including a first portion having majority of the forward-traveling laser beam and a second portion having a minority of the forward-traveling laser beam; directing the first portion of the forward-traveling laser beam into a first output optical fiber and directing the second portion of the forward-traveling laser beam into a second output optical fiber; and directing at least a first portion of a backward-traveling laser beam from the first output optical fiber into a third output optical fiber.
Some embodiments of the method further include opto-isolating the forward-traveling laser beam before the splitting of the forward-traveling laser beam from the input optical fiber into the plurality of portions.
Some embodiments of the method further include providing a sealed enclosure having a plurality of fittings including a first fitting for accepting the first output optical fiber, a second fitting for accepting the second output optical fiber, a third fitting for accepting the third output optical fiber, and a fourth fitting for accepting the input optical fiber, and performing, inside the sealed enclosure, the opto-isolating of the forward-traveling laser beam from the input optical fiber, and the splitting of the forward-traveling laser beam from the input optical fiber into a plurality of portions.
Some embodiments of the method further include providing a sealed enclosure having a plurality of fittings including a first fitting for accepting the first output optical fiber, a second fitting for accepting the second output optical fiber, a third fitting for accepting the third output optical fiber, and a fourth fitting for accepting the first input optical fiber, and performing, inside the sealed enclosure, wherein the splitting of the forward-traveling laser beam from the input optical fiber into the plurality of portions.
In some embodiments, the splitting of the forward-traveling laser beam from the input optical fiber into the plurality of portions includes reflecting the first portion of the forward-traveling laser beam and transmitting the second portion of the forward-traveling laser beam.
In some embodiments, the splitting of the forward-traveling laser beam from the input optical fiber into a plurality of portions includes evanescently coupling the second portion of the forward-traveling laser beam from the input optical fiber into the second output optical fiber, and wherein the directing of at least the first portion of the backward-traveling laser beam from the first output optical fiber into the third output optical fiber includes evanescently coupling at least the first portion of the backward-traveling laser beam from the first output optical fiber into the third output optical fiber.
Some embodiments of the method further include fusing a middle portion of a first source fiber to a middle portion of a second fiber to form an evanescent coupler, wherein the input optical fiber and the first output optical fiber are two end portions of the first source fiber at opposite sides of the middle portion of the first source fiber, and the second output fiber and the third output fiber are two end portions of the second fiber at opposite sides of the middle portion of the second fiber, wherein the splitting of the forward-traveling laser beam from the input optical fiber into a plurality of portions includes evanescently coupling the second portion of the forward-traveling laser beam from the input optical fiber into the second output optical fiber using the evanescent coupler, and wherein the directing of at least the first portion of the backward-traveling laser beam from the first output optical fiber into the third output optical fiber includes evanescently coupling at least the first portion of the backward-traveling laser beam from the first output optical fiber into the third output optical fiber using the evanescent coupler.
Some embodiments of the method further include applying pump light to a gain fiber; amplifying the laser beam in the gain fiber; analyzing the second portion of the forward-traveling laser beam and at least the first portion of a backward-traveling laser beam; and controlling, based on results of the analyzing, at least one of the generating of the laser beam and the amplifying of the laser beam.
In some embodiments, the present invention provides an apparatus that includes a source of a laser beam; a signal-input fiber optically coupled to the source to propagate the laser beam in a forward-traveling direction in the input optical fiber; a signal-output fiber; a forward-tap output fiber; a backward-tap output fiber; a beam splitter optically coupled to the input fiber, the signal-output fiber, the forward-tap fiber, and the backward tap fiber, and configured to split the forward-traveling laser beam from the input optical fiber into a plurality of portions including a first portion having majority of the forward-traveling laser beam directed into the signal-output fiber and a second portion having a minority of the forward-traveling laser beam directed into the forward-tap output fiber and to direct at least a portion of any backward-propagating light from the signal-output fiber into the backward-tap output fiber.
Some embodiments of the apparatus further include an opto-isolator to optically isolate the forward-traveling laser beam before the beam splitter.
Some embodiments of the apparatus further include a sealed enclosure having a plurality of fittings including a first fitting for the signal-input fiber, a second fitting for the signal-output fiber, a third fitting for the forward-tap output fiber, and a fourth fitting for the backward-tap output fiber, and wherein the beam splitter and opto-isolator are enclosed within the sealed enclosure.
Some embodiments of the apparatus further include a sealed enclosure having a plurality of fittings including a first fitting for the signal-input fiber, a second fitting for the signal-output fiber, a third fitting for the forward-tap output fiber, and a fourth fitting for the backward-tap output fiber, and wherein the beam splitter is enclosed inside the sealed enclosure.
In some embodiments, the beam splitter reflects the first portion of the forward-traveling laser beam and transmits the second portion of the forward-traveling laser beam, in order to split the forward-traveling laser beam from the input optical fiber into the plurality of portions.
In some embodiments, the beam splitter includes an evanescent coupler that evanescently couples the second portion of the forward-traveling laser beam from the input optical fiber to direct the minority of the forward-traveling laser beam into the forward-tap output fiber, and wherein the beam splitter evanescently couples the portion of any backward-propagating light from the signal-output fiber into the backward-tap output fiber.
In some embodiments, the beam splitter further includes a middle portion of a first source fiber that is fused to a middle portion of a second fiber to form an evanescent-coupler beam splitter such that the input optical fiber and the first output optical fiber are two end portions of the first source fiber at opposite sides of the middle portion of the first source fiber, and the second output fiber and the third output fiber are two end portions of the second fiber at opposite sides of the middle portion of the second fiber.
Some embodiments further include a gain fiber; a source of pump light operative coupled to the gain fiber; an analyzer functionally coupled to the second portion of the forward-traveling laser beam and at least the portion of a backward-traveling laser beam and that generates an analysis signal; and a controller that is operatively coupled to receive the analysis signal from the analyzer and that, based on the analysis signal by the analyzer, controls at least one of the source of the laser beam and the source of the pump light.
In some embodiments, the present invention provides an apparatus that includes (structures as described herein and equivalents thereof) means for generating a laser beam; input optical-fiber means for propagating the laser beam in a forward-traveling direction; means for splitting the forward-traveling laser beam from the input optical-fiber means into a plurality of portions including a first portion having majority of the forward-traveling laser beam and a second portion having a minority of the forward-traveling laser beam; first output optical-fiber means for propagating a first forward laser signal output beam, second output optical fiber means for propagating a first forward laser beam tap signal, and third output optical fiber means for propagating a first backward-traveling laser beam tap signal; means for directing the first portion of the forward-traveling laser beam into the first output optical-fiber means; means for directing the second portion of the forward-traveling laser beam into the second output optical-fiber means; and means for directing at least a first portion of a backward-traveling laser beam from the first output optical fiber means into the third output optical-fiber means.
Some embodiments further include means for opto-isolating the forward-traveling laser beam before the means for splitting the forward-traveling laser beam from the input optical-fiber means into the plurality of portions.
In some embodiments, the means for splitting the forward-traveling laser beam from the input optical-fiber means into the plurality of portions includes means for evanescently coupling the second portion of the forward-traveling laser beam from the input optical fiber into the second output optical fiber means, and wherein the means for directing of at least the first portion of the backward-traveling laser beam from the first output optical fiber means into the third output optical fiber means includes means for evanescently coupling at least the first portion of the backward-traveling laser beam from the first output optical fiber means into the third output optical fiber means.
Some embodiments further include fiber means for amplifying the laser beam; means for applying pump light to the fiber means for amplifying; means for analyzing the first forward laser beam tap signal and at least the first portion of a backward-traveling laser beam; and means for controlling, based on results of the analyzing, at least one of the means for generating of the laser beam and the means for amplifying of the laser beam.
It is to be understood that the above description is intended to be illustrative, and not restrictive. Although numerous characteristics and advantages of various embodiments as described herein have been set forth in the foregoing description, together with details of the structure and function of various embodiments, many other embodiments and changes to details will be apparent to those of skill in the art upon reviewing the above description. The scope of the invention should, therefore, be determined with reference to the appended claims, along with the full scope of equivalents to which such claims are entitled. In the appended claims, the terms “including” and “in which” are used as the plain-English equivalents of the respective terms “comprising” and “wherein,” respectively. Moreover, the terms “first,” “second,” and “third,” etc., are used merely as labels, and are not intended to impose numerical requirements on their objects.
This application claims benefit under 35 U.S.C. §119(e) of U.S. Provisional Patent Application No. 61/253,041 filed Oct. 19, 2009, by Tolga Yilmaz et al., titled “Fiber-Pigtailed Isolator with Tap Ports for Forward and Backward Optical Signal Monitoring”; U.S. Provisional Patent Application No. 61/263,736 filed Nov. 23, 2009, by Matthias P. Savage-Leuchs et al., titled “Q-Switched Oscillator Seed-Source for MOPA Laser Illuminator Method and Apparatus” (Attorney Docket 5032.051PV1); U.S. Provisional Patent Application No. 61/343,947 filed Apr. 12, 2010, by Matthias P. Savage-Leuchs, titled “High-Power Laser System having Delivery Fiber with Non-Circular Cross Section for Isolation Against Back Reflections” (Attorney Docket 5032.052PV1); U.S. Provisional Patent Application No. 61/343,948 filed Apr. 12, 2010, by Matthias P. Savage-Leuchs, titled “High Beam Quality and High Average Power from Large-Core-Size Optical-Fiber Amplifiers; Signal and Pump Mode-Field Adaptor for Double-Clad Fibers and Associated Method” (Attorney Docket 5032.053.055PV1); U.S. Provisional Patent Application No. 61/343,945 filed Apr. 12, 2010, by Yongdan Hu et al., titled “Apparatus for Optical Fiber Management and Cooling” (Attorney Docket 5032.058PV1); U.S. Provisional Patent Application No. 61/343,949 filed Apr. 12, 2010, by Yongdan Hu, titled “Method and Apparatus for In-Line Fiber-Cladding-Light Dissipation” (Attorney Docket 5032.061PV1); and U.S. Provisional Patent Application No. 61/343,946 filed Apr. 12, 2010, by Tolga Yilmaz et al., titled “Beam Diagnostics and Feedback System and Method for Spectrally Beam-Combined Lasers” (Attorney Docket 5032.062PV1); each of which is incorporated herein by reference in its entirety. This invention is related to U.S. Pat. No. 7,526,167 issued Apr. 28, 2009, to John D. Minelly, titled “Apparatus and method for a high-gain double-clad amplifier” (Attorney Docket 5032.001US1); U.S. patent application Ser. No. 11/165,676 titled “Apparatus and Method for Driving Laser Diodes” filed Jun. 24, 2005, by Lawrence A. Borschowa (Attorney Docket 5032.002US1), U.S. Pat. No. 7,620,077 issued Nov. 17, 2009, to Angus J. Henderson, titled “Apparatus and method for pumping and operating optical parametric oscillators using DFB fiber lasers” (Attorney Docket 5032.003US1); U.S. Pat. No. 7,539,231 issued May 26, 2009, to Eric C. Honea et al. titled “Apparatus and method for generating controlled-linewidth laser-seed-signals for high-powered fiber-laser amplifier systems” (Attorney Docket 5032.004US1); U.S. Pat. No. 7,471,705 issued Dec. 30, 2008, to David C. Gerstenberger et al., titled “Ultraviolet laser system and method having wavelength in the 200-nm range” (Attorney Docket 5032.005US1); U.S. Pat. No. 7,391,561 issued Jun. 24, 2008, to Fabio Di Teodoro et al., titled “Fiber- or rod-based optical source featuring a large-core, rare-earth-doped photonic-crystal device for generation of high-power pulsed radiation and method” (Attorney Docket 5032.008US1), U.S. Pat. No. 7,671,337 titled “System and Method for Pointing a Laser Beam” that issued Mar. 2, 2010 (Attorney Docket 5032.012US1); U.S. Pat. No. 7,199,924 issued Apr. 3, 2007, to Andrew J. W. Brown et al., titled “Apparatus and method for spectral-beam combining of high-power fiber lasers” (Attorney Docket 5032.013US1); U.S. Pat. No. 7,768,700 issued Aug. 3, 2010 to Matthias P. Savage-Leuchs, titled “Method and Apparatus for Optical Gain Fiber having Segments of Differing Core Sizes” (Attorney Docket 5032.014US1); U.S. patent application Ser. No. 11/536,642, titled “Apparatus and Method for Stimulation of Nerves and Automated Control of Surgical Instruments,” filed Sep. 28, 2006 by Mark P. Bendett et al. (Attorney Docket 5032.023US1); U.S. patent application Ser. No. 12/018,193 filed Jan. 22, 2008, by John D. Minelly et al., titled “High-energy eye-safe pulsed fiber amplifiers and sources operating in erbium's L-band” (Attorney Docket 5032.025US1); U.S. patent application Ser. No. 12/624,327 titled “Spectrally Beam Combined Laser System and Method at Eye-Safer Wavelengths,” filed Nov. 23, 2009 by Roy D. Mead (Attorney Docket 5032.050US1); and U.S. patent application Ser. No. 12/793,508 titled “Method and Apparatus for In-Line Fiber-Cladding-Light Dissipation” filed Jun. 3, 2010, by Yongdan Hu (Attorney Docket 5032.061US1); each of which is incorporated herein by reference in its entirety.
| Number | Date | Country | |
|---|---|---|---|
| 61253041 | Oct 2009 | US | |
| 61263736 | Nov 2009 | US | |
| 61343947 | Apr 2010 | US | |
| 61343948 | Apr 2010 | US | |
| 61343945 | Apr 2010 | US | |
| 61343949 | Apr 2010 | US | |
| 61343946 | Apr 2010 | US |
