Optical fiber cable for transmission of high power laser energy over great distances

This application is a divisional of U.S. application Ser. No. 12/706,576, filed on Feb. 16, 2010, which:

is a continuation-in-part of U.S. patent application Ser. No. 12/544,136, now issued as U.S. Pat. No. 8,511,401, filed Aug. 19, 2009 title Method and Apparatus for Delivering High Power Laser Energy over Long Distances, which claims the benefit of the filing date of Oct. 17, 2008 under 35 § 119(e)(1) of U.S. Provisional Application Ser. No. 61/106,472, titled Transmission of High Optical Power Levels via Optical Fibers for Applications such as Rock Drilling and Power Transmission;

and this application claims the benefit of priority under 35 U.S.C. § 119(e)(1) of the following listed applications: U.S. Provisional Application Ser. No. 61/295,562, filed Jan. 15, 2010, title Optical Fiber Cable for Transmission of High Power Laser Energy Over Great Distances

and U.S. Provisional Application Ser. No. 61/153,271, filed Feb. 17, 2009, title Method and Apparatus for an Armored High Power Optical Fiber for Providing Boreholes in the Earth; the entire disclosure of each of the above mentioned regular and provisional patent application are incorporated herein by reference.

This invention was made with Government support under Award DE AR0000044 awarded by the Office of ARPA-E U.S. Department of Energy. The Government has certain rights in this invention.

The present invention relates to the construction and composition of optical fiber cables and laser systems utilizing such cables that provide for the ability to transmit high power laser energy over great distances, which distances and power transmission levels were heretofore believed to be unobtainable. The present invention further relates to the construction of such cables to withstand harsh environments, in particular, the present invention relates to a unique and novel combination of an optical fiber and a multi-layered structure for such cables.

As used herein, unless specified otherwise “high power laser energy” means a laser beam having at least about 5 kW (kilowatt) of power. As used herein, unless specified otherwise “great distances” means at least about 500 m (meter). As used herein the term “substantial loss of power” and “substantial power loss” means more than about 2.0 dB/km (decibel/kilometer) for a selected wavelength. As used herein the term “substantial power transmission” means at least about 50% transmittance.

Discussion of Related Art

Until the present invention, it was believed that a paradigm existed in that the transmission of high power laser energy over great distances without substantial loss of power was unobtainable. As a consequence, it was further believed that there was no reason to construct, or investigate the composition of, an optical fiber or an optical fiber cable for the transmission of high power laser energy over great distances.

Power loss over long distances occurs in an optical fiber from many sources including: absorption loss, and in particular absorption loss from hydroxyl ions (OH − ); Rayleigh scattering; Brillouin scattering; Raman scattering; defects; inclusions; and bending loss. These problems have been documented in the literature.

For example, in the 2006, Crystal Fiber White Paper, titled “Towards 100 kW fiber laser system Scaling up power in fiber lasers for beam combining” it is provided, at page 4, that for stimulated Brillouin scattering (SBS) “the threshold scales as the square of signal mode field diameter (MFD) and inversely with the effective fiber length. Hence, larger core size and short fiber length are desired for power scaling.” (emphasis original) In Corning paper, NIST-SOFM 2004, titled “Stimulated Brillouin Scattering: An Overview of Measurements, System Impairments, and Applications” it is provided, at page 1, that “[o]f the three types of scattering events [Rayleigh, Raman and Brillouin] stimulated Brillouin scattering (SBS) is recognized as the dominant optical fiber nonlinearity.” (bracketed matter added) The Corning paper, at page 3, goes on to provide that “[t]he output power curve . . . also shows that the signal power becomes depleted beyond a certain input power. This deleterious result will effectively clamp the signal output power, but continue to transfer power to the Stokes (reflected) signal via the electrostrictive process which underlies the stimulated Brillouin phenomenon.” Thus, the Corning paper, at page 4, provides that “[s]timuated Brillouin scattering is known to grossly limit the design of several optical transmission systems, amplifiers, and lasers.”

This perceived paradigm, expressed in the art to be believed to exist between length of fiber and power transmittance is further illustrated in the May 31, 2007, Vol. 5, Supplement, pages S39-S41, CHINESE OPTICS LETTERS, Muto et al., titled “Laser cutting for thick concrete by multi-pass technique”, although Muto states that 4 kW of power were delivered down a 1 km fiber, when 5 kW of laser power was put into the fiber, Muto, however, fails to eliminate the stimulated Raman scattering SRS phenomena. As shown by Muto's paper this deleterious phenomenon will effectively clamp the output power as length or power is increased. The SRS phenomenon is seen by the spectrum that is shown in FIG. 3 of Muto, which figure is provided herein as FIG. 2 in this specification. In FIG. 2 the laser beam is shown as band 200 and the SRS is shown as band 201 . Thus, prior to the present invention, it was believed that as input laser power, or the length of the fiber increased, the power output of a fiber would not increase because of the SBS, SRS and other nonlinear phenomenon. In particular, SBS would transfer the output power to back up the fiber toward the input. Further, SBS, SRS, as well as the other deleterious nonlinear effects, in addition to limiting the amount of power that can be transmitted out of the fiber, can result in fiber heating and ultimate failure. Thus, as recognized by Muto, at page S41 “[i]t is found that 10-kW power delivery is feasible through a 250-m-long fiber with the core diameter of 150 μm. The physical phenomenon which restricts the transmitted power is SRS.” Thus, Muto, as did others before him, failed to deliver high power laser energy over great distances.

The present invention breaks this length-power-paradigm, and advances the art of high power laser delivery beyond this paradigm, by providing an optical fiber cable laser system that overcomes these and other losses, brought about by nonlinear effects, and provides for the transmission of high power laser energy over great distances without substantial power loss.

It is desirable to have an optical fiber cable that provides for the delivery of high power laser energy over great distances and without substantial power loss. The present invention, among other things, solves this need by providing the articles taught herein.

Thus there is provided herein an optical fiber cable for transmitting high power laser energy over great distances, the cable can have a length that is greater than about 0.5 km, greater than 2 km greater than about 3 km or greater than about 5 km; the cable is a layered structure comprising: a core; a cladding; a coating; a first protective layer; and, a second protective layer, the cable is capable of transmitting laser energy having a power greater than or equal to about 1 kW, about 5 kW or about 10 kW, over the length of the cable with a power loss of less than about 2 dB/km and preferably less than about 1 dB/km and more preferably less than about 0.3 dB/km for a selected wavelength. There is further provided such an optical fiber cable that delivers the laser energy to a tool or surface having a spectrum that is substantially free from SRS phenomena.

A system for delivering high power laser energy to a tool, the system having a high power laser having a power of at least about 1 kW, at least about 5 kW or at least about 10 kW. The system having an optical fiber cable having a core; cladding; coating; and, a first protective layer. The system having a tool. The cable in the system having first and second ends and a length between the first and second end; the length of the cable being greater than 0.5 km, greater than about 1 km, greater than about 2 km, or greater than about 3 km. The first end of the cable being optically associated or connected to the laser and the second end of the cable being associated with and preferably optically associated with or connected to the tool. The laser beam, from at least in part the laser, transmitted in the cable and having a power of at least about 1 kW at the first end of the cable, and, the power loss of the laser beam in the cable from the first end to the second end being less than about 2 dB/km and preferably being less than about 1 db/km and more preferably less than about 0.5 dB/km for a selected wave length. There is further provided such an optical fiber cable that delivers the laser energy to a tool or surface having a spectrum in which the SRS phenomena is substantially absent.

A spool of optical fiber cable for transmitting laser energy over great distances. The spool having a cable wound around the spool, the cable being capable of being unwound from and wound onto the spool, and thus being rewindable. The cable having a length greater than about 0.5 km, about 1 km, about 2 km or about 3 km and comprising: a core; a cladding; a coating; a first protective layer; and, a second protective layer. The cable is capable of transmitting high power laser energy for its length with a power loss of less than about 2 dB/km and more preferably less than about 1 dB/km and still more preferably less than about 0.5 dB/km and yet more preferably about 0.3 dB/km. The outer diameter of the spool when wound is less than about 6 m to facilitate transporting of the cable by truck.

FIG. 1A is a transverse cross sectional view, not necessarily to scale, showing the structure of an optical fiber cable of the present invention.

FIG. 1B is a longitudinal cross sectional view of the optical fiber cable of FIG. 1A .

FIG. 2 is a prior art spectrum showing the presence of SRS phenomena.

FIG. 3 is a schematic of a testing system.

FIGS. 4-6 are spectrums of laser energy transmitted by the present invention showing the absence of SRS phenomena.

In general, the present inventions relate to optical fiber structures for transmitting high power laser energy over great distances without substantial loss of power. This invention further relates to the structure of optical fiber cables and, without limitation, the structure of such cables for use in harsh environments.

Thus, in general there is provided in FIGS. 1A and 1B an optical fiber cable having a core 1 , a cladding 2 , a coating 3 , a first protective layer 4 , and a second protective layer 5 . Although shown in the figures as being concentric, it is understood that the components may be located off-center, off-center and on-center at different locations, and that the core, the core and cladding and the core, cladding and coating maybe longer or shorter than the one or more of the protective layers.

The core 1 is preferably composed of fused silica having a water content of at most about 0.25 ppm. The core may be composed of other materials, such as those disclosed in patent application Ser. No. 12/544,136, the entire disclosure of which is incorporated herein by reference. Higher purity materials, and the highest purity material available, for use in the core are preferred. Thus this higher purity material minimizes the scattering losses caused by defects and inclusions. The core is about 200 to about 700 microns in diameter, preferably from about 500 to about 600 microns in diameter and more preferably about 600 microns in diameter. As used herein the term “about” would include ranges of plus or minus 10%.

The cladding 2 is preferably composed of fluorine doped fused silica. The cladding may be composed of other materials such as fused silica doped with index-altering ions (germanium), as well as those disclosed in patent application Ser. No. 12/544,136, the disclosure of which is incorporated herein by reference. The cladding thickness, depending upon the wavelength being used and the core diameter, is from about 50 microns to about 250 microns, preferably about 40 microns to about 70 microns and more preferably about 60 microns. As used herein with respect to a multi-layer structure, the term “thickness” means the distance between the layer's inner diameter and its outer diameter. The thickness of the cladding is dependent upon and relative to the core size and the intended wavelength. In general for 1.1 micron wavelength the outer diameter of the cladding should be 1.1× the outer diameter of core or greater; and, for a 1.5 micron wavelength the outer diameter of the cladding should be 1.5× the outer diameter of the core or greater. Although a single cladding is illustrated, it is understood that multiple cladding may be utilized.

The coating 3 is preferably composed of a high temperature acrylate polymer, for higher temperatures a polyimide coating is desirable. The coating may be composed of other materials, such a metal, as well as those disclosed in patent application Ser. No. 12/544,136, the disclosures of which are incorporated herein by reference. The coating thickness is preferably from about 50 microns to about 250 microns, preferably about 40 microns to about 150 microns and more preferably about 90 microns. The coating thickness may even be thicker for extreme environments, conditions and special uses or it may be thinner for environments and uses that are less demanding. It can be tailored to protect against specific environmental and/or physical risks to the core and cladding that may be encountered and/or anticipated in a specific use for the cable.

The first protective layer 4 and the second protective layer 5 may be the same or they may be different, or they may be a single composite layer comprising different materials. Preferably the first and second protective layers are different materials.

The first protective layer is preferably thixotropic gel. In this preferred embodiment, this layer primarily protects the fiber from absorption loss from hydroxyl ions and vibration. The thixotropic gel protects the fiber from mechanical damage due to vibrations, as well as, provides support for the fiber when hanging vertically because its viscosity increases when it is static. A palladium additive is be added to the thixotropic gel to provide hydrogen scavenging. The hydrogen which diffuses into the fiber may be problematic for Germanium or similar ion doped cores. When using a pure slica doped core, it is less of an effect. The first protective layer may be composed of other materials, such as those disclosed in patent application Ser. No. 12/544,136, the entire disclosure of which is incorporated herein by reference. The thickness of the first protective layer should be selected based upon the environment and conditions of use as well as the desired flexibility and/or stiffness of the cable. Thus, the composition and thickness of the first protective layer can be tailored to protect against specific environmental and/or physical risks to the core, cladding and coating that may be encountered and/or anticipated in a specific use for the cable. Thus, the use of the preferred thixotropic gel provides the dual benefit of adding in the manufacture of the cable as well as providing mechanical protection to the core once the cable manufacturing is completed.

The second protective layer is preferably a stainless steel tube composed of 316 stainless. The second protective layer preferably provides physical strength to the fiber over great distances, as well as, protection from physical damage and the environment in which the cable may be used. The second protective layer may be composed of other materials, such as those disclosed in patent application Ser. No. 12/544,136, the entire disclosure of which is incorporated herein by reference. The second protective layer thickness should be selected based upon the requirements for use and the environment in which the cable will be used. The thickness my further be dependent upon the weight and strength of the material from which it is made. Thus, the thickness and composition of the second protective layer can be tailored to protect against specific environmental and/or physical risks to the core, cladding and coating that may be encountered and/or anticipated in a specific use for the cable.

The optical fiber cables can be greater than about 0.5 km (kilometer), greater than about 1 km, greater than about 2 km, greater than about 3 km, greater than about 4 km and greater than about 5 km. The preferred fibers using the preferred first and second protective layers can withstand temperatures of up to about 300 degrees C., pressures of up to about 3000 psi and as great as 36,000 psi, and corrosive environments over the length of the fiber without substantial loss of power and for extended periods of time. The optical fiber cables can have a power loss, for a given wavelength, of less then about 2.0 dB/km, less than about 1.5 dB/km, less than about 1.0 dB/km, less than about 0.5 dB/km and less than about 0.3 dB/km. The optical fiber cables can have power transmissions of at least about 50%, at least about 60%, at least about 80%, and at least about 90%.

The flexibility and/or stiffness of the cable can be varied based upon the size and types of materials that are used in the various layers of the cable. Thus, depending upon the application a stiffer or more flexible cable may be desirable. It is preferred that the cables have sufficient flexibility and strength to be capable of being repeatedly wound and unwound from a spool or reel having an outside diameter of no more than about 6 meters. This outside diameter spool size can be transported by truck on public highways. Thus, the present invention encompasses a spool or reel having an outside diameter of less than about 6 meters and comprising between 0.5 meters and 5 km of the optical fiber cable of the present invention; a spool or reel having an outside diameter of less than about 6 meters and comprising greater than about 0.5 km (kilometer), greater than about 1 km, greater than about 2 km, greater than about 3 km, greater than about 4 km and greater than about 5 km in length of the optical fiber cable of the present invention.

Any type of high power laser may be used as a source of laser energy for use with the optical fiber cables of the present invention. Examples of such lasers are disclosed in patent application Ser. No. 12/544,136, the disclosures of which are incorporated herein by reference. The composition and construction of the optical fiber cable, and in particular the composition of the core and cladding, should be selected to optimize the reduction in power loss for the particular beam that the laser generates. It is believed that lasers that generate a beam having a wavelength of about 800 nm to about 2000 nm, may see acceptable power loss, i.e., have a benefit, when used with the cables of the present invention. However, wavelengths from about 1060 nm to about 1100 nm and about 1470 nm to about 1600 nm have a greater potential benefit. High power infrared lasers are preferable. At present wavelengths of about 1490 nm, about 1550 nm, and about 1080 nm have even greater potential benefits and are preferred. Further, broad band beams within these wavelength ranges may have greater benefits. Preferably, the laser should generate a laser beam in the infrared wavelength having a power of at least about 1 kW, at least about 3 kW, at least about 5 kW, at least about 10 kW, and at least about 20 kW or greater.

An example of such a preferred laser for use with the optical fiber cables of the present invention is the IPG 20000 YB. The detailed properties of this laser are disclosed in patent application Ser. No. 12/544,136, the disclosures of which are incorporated herein by reference. The preferred laser consists of 20 modules. The gain bandwidth of a fiber laser is on the order of 20 nm, the linewidth of the free oscillator is 3 nm, Full Width Half Maximum (FWHM) and may range from 3 nm to 5 nm (although higher linewidths including 10 nm are envisioned and contemplated). Each module's wavelength is slightly different. The modules further each create a multi-mode beam. Thus, the cumulative effect of combining the beams from the modules is to maintain the Raman gain and the Brillouin gain at a lower value corresponding to the wavelengths and linewidths of the individual modules, and thus, consequently reducing the SBS and SRS phenomenon in the fiber when the combined beams are transmitted through the fiber.

The testing system of FIG. 3 can be used to evaluate various fibers of the present invention. Thus, there is provided a laser 301 , a short, less than about 25 m, 300 μm fiber 302 connecting the laser to a QBH connector 303 , which connects the fiber 302 to a collimator 304 . The collimator 304 collimates the laser beam and passes the beam through a ¼% beam sampler 305 . The beam may be directed at this point in the system to ¼% beam sampler 306 , a beam dump 307 , or collimator 308 . Collimator 308 focuses the beam to input the beam into QBH connector 309 . Collimator 308 comprises a focusing lens, a heat sink, and a fiber receptacle. Connector 309 is connected to collimator 308 . Connector 309 is affixed to the long test fiber 310 . The long test fiber 310 has a QBH connector 311 , which connects long test the fiber 310 to a collimator 312 . The laser beam travels from collimator 312 to ¼% beam sampler 313 . From sampler 313 the beam can travel to a power meter 314 or an optical spectrum analyzer (OSA) 315 . Optical time domain reflectometer (OTDR) 316 , transmits and receives a timed laser beam through sampler 316 , to sampler 305 and then along fiber 310 . The OTDR 315 may also be used to test the fiber 310 separate from the laser 301 . The laser beam from laser 301 travels from sampler 306 to %% beam sampler 317 and then to either OSA 315 or to power meter 318 .