Abstract:
An optical device for combining optical signals of different wavelengths is described wherein an array of laser output beams are collimated, directed to propagate along a similar path, and coupled into an optical fiber through a single molded part. The single-part optical coupling module can be constructed in various ways to achieve the desired configuration. One example is a single plastic-injection molded part, containing mechanical alignment features, an array of collimating lenses, and a focusing lens housed within a fiber optic connector ferrule. The laser output beams are separately passed through separate radial sectors of the focusing lens.

Description:
CROSS-REFERENCE TO RELATED APPLICATION  
       [0001]     This application claims the benefit of and priority from United States Provisional Application Ser. No. 60/541,573 filed Feb. 4, 2004. 
     
    
     BACKGROUND AND BRIEF SUMMARY OF THE INVENTION  
       [0002]     The present invention pertains to optical communications. More particularly, this invention relates to an optical multiplexing device which spatially combines multi-wavelength light from a plurality of lasers into an optical fiber. In certain preferred embodiments, the improved multiplexing device of the present invention is particularly suited for wavelength division multiplexing systems for the fiber-optic data-communications and telecommunications systems.  
         [0003]     In prior art wavelength division multiplexed optical communication systems, many different optical wavelength carriers provide independent communication channels in a single optical fiber. Future computation and communication systems place ever-increasing demands upon communication link bandwidth. It is generally known that optical fibers offer much higher bandwidth than conventional coaxial communications; furthermore a single optical channel in a fiber waveguide uses a small fraction of the available bandwidth of the fiber (typically a few GHz out of several tens of THz). By transmitting several channels at different optical wavelengths into a fiber (i.e., wavelength division multiplexing, or WDM), this bandwidth may be more efficiently utilized.  
         [0004]     Prior art optical multiplexing devices combine or separate multiple light signals with varying optical wavelengths. Such optical multiplexing devices have applications for both dense and course wavelength division multiplexing (DWDM &amp; CWDM) for both multi-mode and signal-mode fiber optic data communications and telecommunications. Multiple wave-length light sources are combined into a single optical path for transmission.  
         [0005]     The prior art includes inherent problems overcome by the present invention. Prior art wavelength division multiplexed (WDM) devices are typically designed using dielectric filters requiring alignment or expensive waveguides. The combiner/WDM device described herein utilizes plastic-mold injection to create a compact device capable of combining multiple optical signals into a single optical fiber, and which avoids the use of dielectric filters and the use of expensive waveguides. While a single molded device can be constructed to create one embodiment of the present invention, two or more parts can be combined to accomplish the same function, and may be necessary to achieve certain environmental conditions.  
         [0006]     The prior art also includes an optical power combiner which utilizes collimators and a focusing lens to concentrate multiple output beams to increase power density; see Lee et al U.S. Pat. No. 5,377,287. The Lee et al device combines the outputs of, for example,  19  passive optical fibers arranged concentrically together with 19 collimating lenses and a Fresnel focusing lens. The Lee et al design does not achieve isolation from unwanted reflections or a uniform coupling efficiency between each fiber optic input and the single output. The present invention, in contrast, uses a separate radial sector of the focusing lens to focus each separate laser output. Each laser output beam of the present invention therefore has the same degree of refraction as it passes through the focusing lens; this feature simultaneously creates a uniform coupling efficiency (as shown below) and prevents unwanted reflections back through the optical pathway to the input lasers. Furthermore, the Lee et al combiner does not multiplex n different wavelength channels, as does the present invention. Therefore, for the above reasons, the Lee et al combiner simply is not effective for communication purposes, which is the primary purpose of the present invention.  
         [0007]     The present invention provides, for the first time, an inexpensive, injection molded, one piece optical combiner capable of combining, separately collimating and focusing the output of multiple lasers into a single optical fiber with a uniform, high coupling efficiency. The invention includes optional passive alignment pins molded into the combiner. An optional two piece combiner is also provided for use in certain environments. For example, the invention in one embodiment combines the output of four lasers arranged in a two dimensional, two by two array into a single fiber.  
         [0008]     One of the key objects of the present invention is to provide a compact and cost effective optical combiner for both single-mode or multimode fiber optic communication systems, all without requiring the use of dielectric filters and the alignment necessitated by those filters or expensive waveguides.  
         [0009]     Another object of the present invention is to minimize optical loss due to divergence of light between the source coupling optics and the fiber optic connector coupling optics.  
         [0010]     Another object of the present invention is to minimize reflections directly back to the same focal position from which they were emitted.  
         [0011]     A further object is to provide an optical combiner wherein a single focusing lens is utilized to uniformly and efficiently combine n separate wavelength channels by passing each channel through a separate radial sector of the focusing lens.  
         [0012]     Another object of the present invention is to integrate a fiber optic connector within the optical module, to passively align an optical fiber to the coupling optic.  
         [0013]     Further objects and advantages will become apparent from the following description and drawings. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0014]      FIG. 1  is a side elevational, sectional view of a combiner of the present invention;  
         [0015]      FIG. 2  is an isometric top view of the combiner of  FIG. 1 ;  
         [0016]      FIG. 3  is an isometric bottom view of the combiner of  FIGS. 1 and 2 ;  
         [0017]      FIG. 4  is a cross-sectional isometric side view of the combiner of  FIGS. 1-3 ;  
         [0018]      FIG. 5  is an isometric view of a second embodiment of the invention;  
         [0019]      FIG. 6  is an isometric cross-sectional view of the second embodiment of  FIG. 5 ;  
         [0020]      FIG. 7  is a perspective view of a third embodiment of the invention;  
         [0021]      FIG. 8  is a sectional view of a portion of the third embodiment shown in  FIG. 7 ;  
         [0022]      FIG. 9  is a perspective view of the third embodiment shown in  FIGS. 7 and 8 , wherein a slice of the molded coupling optic is shown to illustrate the invention;  
         [0023]      FIG. 10  is a side elevational view of a fourth embodiment of the invention; and  
         [0024]      FIG. 11  is a top isometric view of the fourth embodiment shown in  FIG. 10 . 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0025]      FIGS. 1-4  show an optical combiner  10  that illustrates a first embodiment of the present invention. The combiner  10  in this embodiment includes four spaced apart input collimating lenses  21 , 22 ,  23 , 24  and output focusing lens  30 . Lasers  11 , 12  are located at the focal points of the input lenses and the light is collimated, reflected off a prism  40  and focused by the focusing lens  30  onto a spot at which a single optical fiber (not shown) is stopped by fiber stop or seat  60  formed in ferrule  80 . Pins  71 , 72 , 73 , 74  are located to aid in affixing the combiner device  10  to the support (not shown) for the lasers. The integrated ferrule  80  enables one to place an output fiber optic cable into the pre-aligned connector.  
         [0026]     This combiner device has the ability to combine individual light signals into an optical path  90  that can be directed towards an optical fiber (not shown for clarity). Matching the NA of the larger focusing lens  30  and the NA of the fiber (not shown) inserted into ferrule  80 , seated at the fiber stop  60 , as well as the spot size  50  of the focused beam being made smaller then the fiber core couples a maximum amount of the collimated light into the fiber. Similarly, by arranging four (in this embodiment) collimating lenses  21 , 22 , 23 , 24  of a size small enough to fit inside the diameter of the focusing lens  30 , and matching their NA to the light sources, the maximum amount of light will couple into the collimated output beam  95 .  
         [0027]     The first embodiment of the invention is a combiner  10  comprised of a single piece plastic molded coupling module  16  consisting of four collimating lenses  21 - 24  and one lens  30  for focusing several geometrically placed collimated beams onto the output fiber (not shown) and a prism  40  for reflecting the plurality of collimated beams for maximum coupling efficiency into the output fiber.  
         [0028]     The plastic molded coupling module  16  is formed by integrating an aspherical on-axis, offset collimating lens array  21 - 24 , a redirectional prism  40 , a focusing lens  30 , a fiber optic ferrule  80 , and mechanical pins  71 - 74  for alignment of the optical part  16  to an array of four lasers, all within a single part  16 .  
         [0029]     The invention is usable with n lasers and n collimating lenses. The embodiment shown in  FIGS. 1-4  illustrates the case of n=4. Furthermore,  FIGS. 1-4  utilize a two-dimensional, two by two array of input lasers as well as collimating lenses.  
         [0030]      FIGS. 5 and 6  show a second embodiment of the invention  110  which does not include a prism for translating the optical beams from one axis to another. This particular embodiment is beneficial for mating to a standard “TO” style laser chip package. Similar to the embodiment described in  FIGS. 1-4 , the embodiment shown here utilizes a two-dimensional array of four lenses  121 , 122 , 123 , 124  for collimating the input light signals from a two-dimensional, two by two, array of lasers (not shown), a single focusing lens  130 , and a fiber connector  180  that allows one to place a fiber optic cable into the pre-aligned connector.  
         [0031]      FIGS. 7, 8  and  9  illustrate a third embodiment of the invention. The combiner is shown generally as  210  and includes a circular array of four lasers  211 , 212 , 213  and  214 . Each laser  211 - 214  has a different output wavelength. Each laser is mounted to a support  215 . The lasers  211 - 214  are co-planar and the output beam of each of the lasers  211 - 214  is directed towards the center of the array. At the center of the array is a coupling optic  216  formed of a single monolithic optical block. Four collimating lenses (only two of which  221  and  222  are visible) are formed in the four side walls  231 , 232 , 233  and  234 , respectively, of the module or coupling block  216 . The focusing lens  250  is formed on the top surface of the module  216 . The surface of focusing lens  250  is smooth and includes four pie-shaped radial quadrants  251 - 254 . Each of the quadrants  251 - 254  transmits a separate output beam of the lasers  211 - 214 , respectively.  
         [0032]     As shown best in  FIG. 8 , the bottom surface  240  of module  216  is recessed with four separate inclined surfaces that form four separate prisms to reflect collimated light to the output lens  250 . In the view shown in  FIG. 8 , collimating lenses  222  and  224  receive the output beams from lasers  212  and  214 , respectively. Prisms  242  and  244  reflect the output beams from collimating lenses  222  and  224  and direct those beams through separate pie-shaped quadrants  252  and  254  of focusing lens  250 .  
         [0033]     It is significant to note that, as shown in  FIG. 8 , the output beams of lasers  212  and  214  are refracted through output lens  250  through equal angles. This is significant because the beam passing through quadrant  252  will not be reflected by the stopped single fiber optic back into laser  212 . Rather, the laser output  212  passing through quadrant  252  will tend to be reflected from the stopped fiber optic back towards quadrant  254 . Since the output of laser  212  is of a different wavelength than the output of laser  214 , that reflection that passes back through quadrant  254  from laser  212  will not adversely affect the performance of laser  214 , since it operates at a different wavelength.  
         [0034]      FIG. 9  shows a single slice of optic  216  to more clearly illustrate the interaction with the module  216  with the circular array of lasers  211 - 214 .  
         [0035]      FIGS. 10 and 11  illustrate a fourth embodiment of the invention. In this embodiment, the combiner shown generally as  310  includes a two-piece molded module including a separately molded output lens  350  and separately molded collimating lenses  321 - 324 . The collimating lenses  321 - 324  are preferably molded into a single but separate monolithic block of molded material so that the combiner  310  includes two separate molded optics. The focusing lens  350  is supported in its position shown in  FIG. 10  by means known to those skilled in the art which are deleted in the interest of brevity. As shown in  FIG. 10 , an array of four lasers are supported in housing  319 . In the view shown in  FIG. 10 , only two lasers  311  and  312  are visible. Their output beams are directed through collimating lenses  321  and  322  and in the embodiment shown in  FIGS. 10 and 11  travel directly to and through focusing lens  350  without being reflected by a prism. Collimating lenses  321 - 324  are supported by the top of housing  319 .  
         [0000]     Key Features:  
         [0036]     Manufacturing throughput Replication procedures are extremely fast, thus reducing the overall cost of the manufactured device.  
         [0037]     Passive Alignment All of the optical components within the multiplexer could utilize passive alignment mechanisms.  
         [0038]     Monolithic Coupling Optics Each optical coupling and redirectional component is integrated within a single monolithic plastic-molded device in most embodiments.  
         [0039]     Cost Reduction Fewer parts are required such as filters and reflector blocks.  
         [0040]     Offset Launch Spots may be focused on a section of the fiber which is offset from the center of the fiber, thus creating an offset launch condition, which is known by those skilled in the art to produce a better condition for resisting modal partition noise.  
         [0000]     Potential Applications:  
         [0000]    
       
         
           
              1) Wavelength division multiplexing/demultiplexing (WDM)  
              2) Optical signal routing  
              3) Spectroscopy  
              4) Biological and chemical integrated optical sensors  
              5) Optical computing  
           
         
       
     
         [0046]     The foregoing description of the invention has been presented for purposes of illustration and description and is not intended to be exhaustive or to limit the invention to the precise form disclosed. Modifications and variations are possible in light of the above teaching. The embodiments were chosen and described to best explain the principles of the invention and its practical application to thereby enable others skilled in the art to best use the invention in various embodiments and with various modifications suited to the particular use contemplated. The scope of the invention is to be defined by the following claims.