Abstract:
In embodiments, the present invention is directed to systems and methods for operating an incoherently beam combined (IBC) laser. The IBC laser may comprise an integrated set of emitters or a set of discrete emitters. Each emitter is associated with a high-pass, low-pass, or bandpass optical filter. The emitters and filters are disposed in an ordered arrangement thereby defining a common optical path. Near the end of the common optical path, a focusing lens may be utilized to focus the output beams from each of the emitters into a fiber. A partially reflective component may be embedded in the fiber to provide feedback to each of the emitters. By selecting the optical characteristics of the filters, light originating from a specific emitter is fed back to the same emitter and to no other emitter. Accordingly, multiple external laser cavities are created on the same optical path.

Description:
RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Application Ser. No. 60/316,812, filed Aug. 31, 2001 entitled “INDIVIDUAL EMITTERS IN IBC LASERS,” and U.S. Provisional Application Ser. No. 60/313,774, filed Aug. 20, 2001 entitled “SYSTEMS AND METHOD FOR MULTIPLEXING OUTPUT BEAMS OF LASER DIODE CELLS.” 
    
    
     FIELD OF THE INVENTION 
     The present invention is directed in general to systems and methods for incoherently combining a plurality of output beams. 
     BACKGROUND OF THE INVENTION 
     At the present time, telecommunication systems are largely based on fiber optic cables. For example, optical networks based on fiber optic cables are currently utilized to transport Internet traffic and traditional telephony information. In such applications, it is frequently necessary to provide an optical signal over significant distances (e.g., hundreds of kilometers). As optical signals travel through the optical fibers, a portion of their power is transferred to the fiber, scattered, or otherwise lost. Over appreciable distances, the optical signals become significantly attenuated. To address the attenuation, optical signals are amplified. Typical optical amplifiers include rare earth doped amplifiers (e.g., Erbium-doped fiber amplifiers). 
     Raman amplifiers may be utilized. A Raman amplifier relies upon the Raman scattering effect. The Raman scattering effect is a process in which light is frequency downshifted in a material. The frequency downshift results from a nonlinear interaction between light and the material. The difference in frequency between the input light and the frequency downshifted light is referred to as the Stokes shift which in silica fibers is of the order 13 THz. 
     When photons of two different wavelengths are present in an optical fiber, Raman scattering effect can be stimulated. This process is referred to as stimulated Raman scattering (SRS). In the SRS process, longer wavelength photons stimulate shorter wavelength photons to experience a Raman scattering event. The shorter wavelength photons are destroyed and longer wavelength photons, identical to the longer wavelength photons present initially, are created. The excess energy is conserved as an optical phonon (a lattice vibration). This process results in an increase in the number of longer wavelength photons and is referred to as Raman gain. 
     The probability that a Raman scattering event will occur is dependent on the intensity of the light as well as the wavelength separation between the two photons. The interaction between two optical waves due to SRS is governed by the following set of coupled equations: 
           ⅆ     I   P         ⅆ   z       =           λ   S       λ   P       ⁢     g   R     ⁢     I   S     ⁢     I   P       -       α   P     ⁢     I   P             
           ⅆ     I   S         ⅆ   z       =         g   R     ⁢     I   S     ⁢     I   P       -       α   S     ⁢     I   S             
 
where I s  is the intensity of the signal light (longer wavelength), I p  is the intensity of the pump light (shorter wavelength), g R  is the Raman gain coefficient, λ s  is the signal wavelength, λ p  is the pump wavelength, and α s  and α p  are the fiber attenuation coefficients at the signal and pump wavelengths respectively. The Raman gain coefficient, g R , is dependent on the wavelength difference (λ s −λ p ) as is well known in the art.
 
     As is well understood in the art, SRS is useful for generating optical gain. Optical amplifiers based on Raman gain are viewed as promising technology for amplification of WDM and DWDM telecommunication signals transmitted on optical fibers. Until recently, Raman amplifiers have not attracted much commercial interest because significant optical gain requires approximately one watt of optical pump power. Lasers capable of producing these powers at the wavelengths appropriate for Raman amplifiers have come into existence only over the past few years. These advances have renewed interest in Raman amplifiers. 
     Existing high power lasers dispose individual discrete lasers in, for example, 14 pin butterfly packages. The output beams from the individual devices are either polarization division multiplexed or wavelength division multiplexed into a single beam. To the extent that these systems multiplex more beams, the systems are able to generate a higher power output beam. In addition, WDM and DWDM telecommunications systems operate over large bandwidth ranges and require broad wavelength pump lasers to effectively use Raman amplification. These multiplexing schemes address this by operating at multiple wavelengths. However, these lasers become quite cumbersome and costly when the number of butterfly packages exceeds a relatively small number. Accordingly, the power that that can be achieved cost-effectively is limited. 
     Another type of high power laser is referred to as an incoherently beam combined (IBC) laser. An example of a known IBC laser is described in U.S. Pat. No. 6,208,679. Known IBC lasers utilize a dispersive external cavity and various optics to selectively provide feedback to emitters of a unitary emitter array. The selective feedback causes emitters of the unitary emitter to laser across a relatively broad, although limited, spectrum. Additionally, the dispersive external cavity and optics multiplex output beams from emitters of the unitary emitter array. 
     BRIEF SUMMARY OF THE INVENTION 
     In embodiments, the present invention is directed to systems and methods for multiplexing the output beams from a plurality of laser cells. Each cell advantageously comprises a laser diode, a detector for measuring back facet power, a collimator lens, and a high-pass, low-pass, or bandpass optical filter. Each cell is advantageously disposed in an ordered arrangement in association with a common optical path. Within the arrangement, the filters of the cells selectively transmit a predefined wavelength range. The frequencies that are not passed by the filters are reflected by the filters. 
     Moreover, the cells are oriented on a platform such that light from a given cell is reflected by its own filter. The filter then transmits the light from each cell before it onto the next cell. At the end of the daisy-chained group of cells, a focusing lens is utilized to focus the output beams from each of the cells into a fiber. A partially reflective component (e.g., a fiber Bragg grating) may be embedded in the fiber to provide feedback to each of the laser cells. In this manner, light originating from a specific cell is advantageously fed back to the same cell and to no other cell. Accordingly, multiple external laser cavities are created on the same optical path. It shall be appreciated that the operating wavelength or wavelengths of each cell are determined, in part, by the wavelengths that its filter allows to pass. 
     In other embodiments, a similar daisy-chain configuration is utilized. However, the filter of each cell transmits the output beam generated by its laser diode. Also, the filter reflects the output beams generated by the laser diodes of each previous cell. 
     Embodiments of the present invention may provide several advantages. Specifically, embodiments of the present invention generate a high power, multi-wavelength output beam. Moreover, each cell may be manufactured separately using the same tooling and assembly process. The components of the cells may advantageously be interchangeable. Moreover, the cell size is advantageously selected in a manner to place the cells in an individual butterfly package to be fiber coupled using a focusing lens. Accordingly, embodiments of the present invention enable a high power multiple wavelength beam to be generated from a relatively small device at a low cost. Embodiments of the present invention may be utilized for any number of applications such as providing a pump for Erbium-Doped Fiber Amplifiers (EDFAs) or Raman gain amplifiers. 
     The foregoing has outlined rather broadly the features and technical advantages of the present invention in order that the detailed description of the invention that follows may be better understood. Additional features and advantages of the invention will be described hereinafter which form the subject of the claims of the invention. It should be appreciated by those skilled in the art that the conception and specific embodiment disclosed may be readily utilized as a basis for modifying or designing other structures for carrying out the same purposes of the present invention. It should also be realized by those skilled in the art that such equivalent constructions do not depart from the spirit and scope of the invention as set forth in the appended claims. The novel features which are believed to be characteristics of the invention, both as to its organization and method of operation, together with further objects and advantages will be better understood from the following description when considered in connection with the accompanying figures. It is to be expressly understood, however, that each of the figures is provided for the purpose of illustration and description only and is not intended as a definition of the limits of the present invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       For a more complete understanding of the present invention, reference is now made to the following descriptions taken in conjunction with the accompanying drawing, in which: 
         FIG. 1  depicts a laser diode cell according to embodiments of the present invention; 
         FIG. 2  depicts an incoherently beam combined laser according to embodiments of the present invention; 
         FIG. 3  depicts another incoherently beam combined laser according to embodiments of the present invention; 
         FIGS. 4A-4C  depict wavelength responses that may utilized in an incoherently beam combined laser according to embodiments of the present invention; 
         FIGS. 5A-5C  depict other wavelength responses that may utilized in an incoherently beam combined laser according to embodiments of the present invention; 
         FIG. 6A  depicts another incoherently beam combined laser according to embodiments of the present invention; 
         FIG. 6B  depicts an optical wedge that may be utilized in an incoherently beam combined laser according to embodiments of the present invention; 
         FIG. 7  depicts a multi-cavity incoherently beam combined laser according to embodiments of the present invention; 
         FIG. 8  depicts an optical communication system that comprises an amplifier according to embodiments of the present invention; 
         FIG. 9A  depicts a plurality of plates that may be utilized for fabrication of an optical component to be used in an incoherently beam combined laser incoherently according to embodiments of the present invention; 
         FIG. 9B  depicts wavelength responses that may utilized in an incoherently beam combined laser according to embodiments of the present invention; 
         FIG. 10  depicts processing of an optical component for use in an incoherently beam combined laser according to embodiments of the present invention; 
         FIG. 11  depicts further processing of an optical component for use in an incoherently beam combined laser according to embodiments of the present invention; and 
         FIG. 12  depicts an incoherently beam combined laser that comprises the optical component processed according to  FIGS. 10 and 11  according to embodiments of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The present invention is directed to systems and methods for multiplexing the output beams of a plurality of laser diode cells. As depicted in  FIG. 1 , each cell  101  comprises a number of components mounted on substrate  106  including laser diode  102 . Laser diode  102  may comprise any suitable semiconductor or other lasing material including but not limited to GaAlAs, GaAs, InP, InGaAs, InGaAsP, AlGalnAs, and/or the like. Additionally, laser diode  102  may be implemented utilizing any number of designs such as edge emitters, vertical cavity surface emitting lasers (VCSELs), and grating surface emitting lasers. 
     Furthermore, cell  101  may comprise detector  105  for determining the back facet optical power. The back facet optical power may be utilized to determine the amount of power launched into an optical fiber by the multiplexing systems and methods for the wavelength or wavelengths of light generated by the particular cell  101 . The back facet may be utilized to vary the power to laser diode  102  to spectrally tailor the multiplexed output beams launched into an optical fiber (not shown). 
     Each cell  101  may comprise collimator  103  to collimate the light emitted by laser diode  102 . Any suitable optical collimating component may be utilized for collimator  103  such as a collimating lens. 
     Each cell  101  advantageously comprises filter  104 . Filter  104  may be implemented utilizing a dielectric film or films, although any suitable wavelength-dependent coating or filter may be utilized. Filter  104  possesses a selected wavelength response as will be discussed in greater detail with respect  FIGS. 4A through 4C  and  FIGS. 5A through 5C . For example, filter  104  may be a high-pass filter, a low-pass filter, or a notch filter. 
       FIG. 2  depicts an exemplary block diagram according to embodiments of the present invention. System  200  depicts a linear arrangement of cells  101 - 1  through  101 -N. The output beam from each cell  101  may be incident on its filter  104  at a forty-five degree angle. Also, the wavelength of each output beam is depicted by λ 1 . For case of discussion, it is assumed that the wavelengths of cells  101 - 1  through  101 -N are arranged in a monotonic order, λ 1 &lt;λ 2 &lt;λ 3 &lt; . . . λ N  or λ 1 &gt;λ 2 &gt;λ 3 &gt; . . . λ N . However, it shall be appreciated that the present invention does not require a monotonic arrangement as filters  104  may be implemented as notch filters. Specifically, as will be discussed in greater detail below, the wavelengths (λ I ) are largely controlled by the selection of filters  104 - 1  through  104 -N. 
     The optical properties of filters  104 - 1  through  104 -N are selected to permit each filter to reflect the wavelength λ 1 ) associated with its cell  101 . Additionally, the optical properties of filters  104 - 1  through  104 -N are selected to permit each filter to transmit the wavelengths (λ I+1  through λ N ) associated with each previous cell  101 -I+1 through  101 -N. 
     By arranging cells  101  in the configuration shown in FIG.  2  and by selecting the optical properties of filters  104 , the output from the laser diodes may be multiplexed. Specifically, filter  104  of each cell  101  transmits the output of each previous cell  101 . This process is repeated until cell  101 - 1 . After cell  101 - 1 , the various output beams encounter fiber coupling lens  202 . Fiber coupling lens  202  focuses the output beams from each of cells  101 - 1  through  101 -N into optical fiber  203  to multiplex the beams. 
     Within optical fiber  203 , fiber Bragg grating  204  is embedded to provide a partially reflective component. Fiber Bragg grating  204  is a broadband partially reflective grating to thereby reflect each of the wavelengths (λ 1  through λ N ) associated with cells  101 - 1  through  101 -N. Fiber Bragg grating  204  transmits a portion of the optical power associated with wavelengths (λ 1  through λ N ). The transmitted power may be utilized for any desired application. For example, the transmitted power may be utilized to pump either an EDFA or a Raman amplifier. Additionally, fiber Bragg grating  204  reflects a portion of the optical power associated with wavelengths (λ I  through λ N ) as feedback for laser diodes  102 - 1  through  102 -N. Accordingly, this configuration is referred to as an external cavity laser. Although fiber Bragg grating  204  is shown, any suitable partially reflective component may be utilized. 
     The feedback provided by fiber Bragg grating  204  is returned to the cells  101 -I through  101 -N. Specifically, the feedback is controlled by filters  104 - 1  through  104 -N such that the wavelength, λ I , is returned to the same cell  104 -I that emitted that wavelength, λ I . For example, the wavelength λ I  of the feedback is only returned to cell  101 - 1 . When wavelength λ I  of the feedback encounters filter  104 - 1 , it is reflected by filter  104 - 1 . However, all other wavelengths (λ 2  through λ N ) are transmitted by filter  104 - 1 . Likewise, this process is repeated. Each filter  104 -I reflects its own wavelength λ I  and transmits all subsequent wavelengths (λ I+1  through λ N ) on the feedback path. 
     It shall be appreciated that the wavelength(s) of the feedback provided to each laser diode  104 - 1  through  104 -N controls the operating wavelength(s) of the laser diode. Since the wavelengths of the feedback to the respective laser diodes  104 - 1  through  104 -N are determined by filters  104 - 1  through  104 -N, the resonant wavelengths are determined by selecting the characteristics of the filters. 
       FIG. 3  depicts another embodiment of the present invention. As depicted in exemplary system  300  of  FIG. 3 , cells  101 - 1  through  101 - 8  are shown in an arrangement where the cells are disposed in an alternating or crisscross manner. Each filter  104  transmits the wavelength generated by its respective cell  101 . Moreover, the filters  104 - 2  through  104 - 8  reflect the wavelengths associated with each preceding cell, i.e, filter  104 -I reflects wavelengths λ 1  through λ I−1 . For example, filter  104 - 2  reflects wavelength λ 1 , filter  104 - 3  reflects wavelengths λ 1  and λ 2 , filter  104 - 4  reflects wavelengths λ 1 , λ 2 , and λ 3 , etc. 
     By arranging cells  101 - 1  through  101 - 8  as shown in FIG.  3  and by appropriately selecting the optical characteristics of filters  104 - 1  through  104 - 8 , the output beams of laser diodes  102 - 1  through  102 - 8  are directed towards fiber coupling lens  202 . The output beams from cells  101 - 1  through  101 - 8  are multiplexed when the output beams are focused into fiber  203  by fiber coupling lens  202 . 
     A partially reflective component (not shown) returns feedback to the laser diodes  102  of cells  101 - 1  through  101 - 8 . Moreover, system  300  controls the feedback with filters  104 - 1  through  104 -N such that the wavelength, λ I , is returned to the same cell  104 -I that emitted that wavelength, λ I . For example, the wavelength λ 8  of the feedback is only returned to cell  101 - 8 . When the wavelength λ 8  of the feedback encounters filter  104 - 8 , it is transmitted by filter  104 - 8 . However, all other wavelengths (λ 1  through λ 7 ) are reflected by filter  104 - 8 . Likewise, this process is successively repeated. Each filter  104 -I transmits its own wavelengths λ I  and reflects all subsequent wavelengths (λ 1  through λ I−1 ) on the feedback path. 
     It shall be appreciated that the number of cells  101  in a particular system are not limited according to the present invention. However, it shall be appreciated that each filter  104  provides a small degree of attenuation to the optical beams. Accordingly, it may be appropriate for a particular application, to limit the number of filters  104  that an optical beam may encounter. Furthermore, the practicalities of optical coatings will impose limitations on the proximity of wavelengths. In such applications, it may be appropriate to utilize a polarization multiplexer to combine outputs from a plurality of systems  200 , systems  300 , or other multiple cell  100  systems. 
       FIGS. 4A through 4C  depict exemplary wavelength responses that may be utilized by filters  104  of system  200 . Response  401  corresponds to a notch filter. Response  401  is substantially fully reflective at and adjacent to wavelength λ I . However, response  401  is not appreciably reflective at other wavelengths (accordingly these other wavelengths are substantially transmitted). Responses  402  and  403  are step or edge responses. Response  402  may be substantially fully reflective at wavelength λ I  and wavelengths less than λ I  (other wavelengths are substantially transmitted). Similarly, response  403  is substantially fully reflective at wavelength λ I  and wavelengths greater than λ I  (other wavelengths are substantially transmitted). Responses  402  and  403  impose a monotonic arrangement of wavelengths when utilized for filters  104  according to system  200 . 
       FIGS. 5A through 5C  also depict exemplary wavelength responses that may be utilized by filters  104  of system  300 . Response  501  corresponds to a notch filter. Response  501  is substantially fully transmissive at and adjacent to wavelength λ I . However, response  501  is not appreciably transmissive at other wavelengths (accordingly these other wavelengths are substantially reflected). Responses  502  and  503  are step or edge responses. Response  502  is substantially transmissive at wavelength λ I  and at wavelengths less than λ I  (other wavelengths are substantially reflected). Similarly, response  503  is substantially transmissive at wavelength λ I  and at wavelengths greater than λ I  (other wavelengths are substantially reflected). Responses  502  and  503  impose a monotonic arrangement of wavelengths when utilized for filters  104  according to system  300 . 
     It shall be appreciated that responses  401 - 403  and  501 - 503  are idealized responses as the first derivatives of responses are not continuous. Nonetheless, these responses may be approximated with suitable precision by utilizing multiple-film, thin-film filters. Accordingly, suitable filters  104  according to the embodiments of the present invention may be implemented by approximating one of responses  401 - 403  or  501 - 503 . 
       FIG. 6A  depicts an alternative embodiment of the present invention. System  600  comprises a plurality of laser diodes  102 - 1  through  102 - 5  with collimators  103 - 1  through  103 - 5 . System  600  further comprises optical wedge  601  and fully reflective component  602 . Optical wedge  601  and fully reflective component are operable to multiplex the output beams from laser diodes  102 - 1  through  102 - 5 . As shown in greater detail in  FIG. 6B , optical wedge  601  may be coated with a gradient dielectric films. The dielectric films may implement filters  104 - 1  through  104 - 5  so that each wavelength, λ I  generated by laser diode  102 -I, is substantially transmitted by filter  104 -I. Also, filter  104 -I advantageously substantially reflects the wavelengths (λ I −λ I−1 ) generated by each previous laser diode ( 102 - 1  through  102 -(I−1)). Accordingly, after each output beam exits optical wedge, it continues propagating along the common optical path between optical wedge  601  and fully reflective component  602 . Eventually, the output beams may be coupled into fiber  204  by fiber coupling lens  202 . 
     It shall be appreciated that the geometry of systems  200 ,  300 , and  600  are merely exemplary as different configurations may be utilized. For example, it may be advantageous to disposes cells  101  in a three-dimensional arrangement such as helix type structure to obtain a more compact device. 
     It shall be appreciated that the multiplexing of the output beams from cells  101  in system  200 , system  300 , and system  600  occurs by precisely positioning the optical components to cause the respective beams to overlap. The positioning of the various optical components may occur manually. However, it shall be appreciated that pick-and-place mechanics and machine vision techniques may be utilized to precisely position the optical components according to embodiments of the present invention. By utilizing pick-and-place mechanics and machine vision techniques, suitable high power lasers may be built in a rapid and cost efficient manner. 
     Referring now to  FIG. 7 , system  700  depicts an exemplary arrangement to combine the output from a plurality of systems  200  (shown as systems  200 - a  and  200 - b ). Although systems  200  are shown, it shall be appreciated that systems  300 , systems  600 , or other suitable systems according to the present invention may be utilized in lieu of systems  200 . System  200 - a  generates a multiplexed output consisting of wavelengthsλ 1  through λ N  and system  200 - b  generates a multiplexed output consisting of wavelengths λ N+1  through λ N+M . The multiplexed outputs of systems  200 - a  and  200 - b  are provided to polarization beam combiner  201 . The multiplexed outputs are coupled into fiber  204  by fiber coupling lens  202 . Fiber Bragg grating  203  provides feedback to laser diodes  102  of systems  200 - a  and  200 - b . In some situations, it may be more advantageous to utilize system  700  to achieve increased output power as compared to implementing additional cells  101  in a single system  200 . Specifically, a certain amount of attenuation may occur at each filter  104 . Accordingly, system  700  may operate more efficiently for greater numbers of cells  101  than a single system  200 . 
       FIG. 8  depicts exemplary optical system  800  which includes a Raman amplifier according to embodiments of the present invention. Optical system  800  includes optical signal source  801  which generates an optical signal to be detected by detector  802 . Detector  802  is disposed at some appreciable distance from optical signal source  801 . The optical signal generated by optical signal source  801  experiences attenuation in optical fibers  804  and  805 . Accordingly, it is desirable to amplify the optical signal generated by optical signal source  801 . To perform such amplification, system  800  utilizes system  200  to provide a Raman pump to multiplexer  803 . Specifically, the output wavelengths of system  200  are controlled by selecting the characteristics of filters  104  of system  200 . Additionally, the output power of system  200  at the respective wavelengths may be controlled to spectrally tailor the Raman pump. Multiplexer  803  causes the Raman pump to enter optical fiber  805  which also carries the optical signal generated by optical signal source  801 . Due to SRS, the optical signal experiences Raman gain at the desired wavelength(s) in fiber  805 . Additionally, by spectrally tailoring the Raman pump (system  200 ), the amplification of the optical signal is substantially flat, which is desirable if the signal is a WDM or DWDM signal. 
     Embodiments of the present invention provide several advantages. First, embodiments of the present invention do not require excessive amounts of semiconductor material as a unitary emitter array may require. Specifically, if a large number of emitters are implemented on a single array, a minimum amount of space is required between adjacent emitters to dissipate sufficient thermal energy to avoid degradation of emitter performance. To provide sufficient space on an emitter array, additional semiconductor material is required between adjacent emitters. Accordingly, embodiments of the present invention may utilize less expensive laser diode semiconductor devices to reduce the cost of high power laser devices. 
     Moreover, embodiments of the present invention may utilize laser diodes of differing capabilities for different wavelengths. For example, laser diodes, that possess quantum wells associated with different center wavelengths, may be utilized. By matching the center wavelengths associated with laser diodes  102  with the wavelength responses of filters  104 , the operating efficiency of laser diodes  102  may be improved. Additionally, Raman pump applications require high power at wavelengths at both ends of the pump spectrum. However, lower power is required at wavelengths in the middle of the pump spectrum. Accordingly, laser diodes, that possess lower power capabilities and that are, hence, less expensive, may be utilized for wavelengths corresponding to lower power requirements. 
     Additionally, it shall be appreciated that embodiments of the present invention provide greater manufacturing yields than unitary emitter arrays. For example, if a unitary emitter array includes ten emitters and the probability of a single emitter satisfying specification requirements is 0.9, the probability that all ten of the emitters on the unitary emitter array will satisfy the specification requirements is (0.9) 10 , which is clearly quite small. However, according to embodiments of the present invention, the laser diodes are not physically integrated on a single chip. If a single laser diode is inoperable, it may be replaced with another laser diode. Accordingly, manufacturing yields are greatly improved. 
     Additionally, it shall be appreciated that embodiments of the present invention may possess greater bandwidth than known incoherently beam combined (IBC) laser devices. Specifically, the geometric constraints of IBC lasers (imposed by the dispersive element and the collimating optic) limit the bandwidth of the IBC lasers. However, this is problematic if a known IBC laser is utilized as a Raman pump. Specifically, amplification may be required over one or more telecommunication bands (e.g., S Band (1480 to 1525 nm), C Band (1530 to 1565 nm), L Band (1570 to 1610 nm), XL Band (1615 to 1660 nm)). A bandlimited IBC laser would not be capable of generating sufficient bandwidth to create reasonably flat gain over one or more of these bands. However, the bandwidth of embodiments of the present invention is not limited by their geometry. Instead, the bandwidth is only limited by the intrinsic bandwidth of the laser diodes and the characteristics of the selected filters. Accordingly, the bandwidth may be adjusted as desired to achieve reasonably flat Raman gain across one or more telecommunication bands. 
     Another issue with known IBC lasers is that the feedback provided to a particular emitter of an emitter array is highly peaked due to the dispersive element and the various optical components. Accordingly, the particular emitters tend to lase at either one particular longitudinal mode or wavelength. By causing the filter response of filter  104  to be substantially flat near selected wavelengths, laser diodes according to embodiments of the present invention may operate at several longitudinal modes or closely spaced wavelengths improving laser performance. 
       FIG. 9A  depicts a plurality of plates  901 - 904  that may be utilized to fabricate component for use in an IBC laser according to embodiments of the present invention. Each of plates  901 - 904  are coated with a thin dielectric film or films (shown as films  911 - 914 ). The reflectivity of each of films  911 - 914  as a function of wavelength is shown in  FIG. 9B  (as reflectivity responses  921 - 924 ). As shown by the reflectivity responses in  FIG. 9B , each of films  911 - 914  are highly reflective for wavelengths longer than a respective predetermined wavelength. The plurality of plates  901 - 904  may be diced or suitable cut along axes  951 - 955 . Axes  951 - 955  may be advantageously oriented at a forty-five degree angle with respect to plates  901 - 904 . By cutting plates  901 - 904  in this manner, a plurality of optical components ( 960 - 1  through  9604  as shown in  FIG. 9A ) may be fabricated. 
     An additional cut may be applied to each of optical components  960 - 1  through  960 - 4 . As shown in  FIG. 10 , optical component  960  may be cut along axis  1051 . After the additional cuts are made, additional coatings may be applied. As shown in  FIG. 11 , optical component  960  may be coated to provide broadband partial reflector  1151 . Also, optical component  960  may be coated to provide broadband reflector  1152 . 
     At this point, optical component  960  is suitable for implementation of an IBC laser according to embodiments of the present invention.  FIG. 12  depicts IBC laser  1200  that includes optical component  960  according to embodiments of the present invention. IBC laser  1200  comprises integrated emitter array  1205  which provides its output beams to micro-lens array  1201  to collimate the output beams. Each respective emitter beam is reflected by one of films  911  through  914  thereby multiplexing the beams. Additionally, the external cavity of IBC laser  1200  is completed by partial reflector  1151  which provides feedback to each of emitters  901 - 1  through  901 - 4 . Also, it shall be appreciated that the respective wavelength of the feedback provided to each of emitters  901 - 1  through  901 - 4  is determined by the reflectivity of surfaces  911  through  914 . The portion of the optical power that is not reflected by partial reflector  1151  may be coupled into fiber  1204  by fiber coupling lens  1203 . 
     Although the present invention and its advantages have been described in detail, it should be understood that various changes, substitutions and alterations can be made herein without departing from the spirit and scope of the invention as defined by the appended claims. Moreover, the scope of the present application is not intended to be limited to the particular embodiments of the process, machine, manufacture, composition of matter, means, methods and steps described in the specification. As one of ordinary skill in the art will readily appreciate from the disclosure of the present invention, processes, machines, manufacture, compositions of matter, means, methods, or steps, presently existing or later to be developed that perform substantially the same function or achieve substantially the same result as the corresponding embodiments described herein may be utilized according to the present invention. Accordingly, the appended claims are intended to include within their scope such processes, machines, manufacture, compositions of matter, means, methods, or steps.