Abstract:
The present invention discloses an optic based wavelength division multiplexer device made by a micro lithography and etching process, utilizing the special crystal lattice structure of a silicon wafer. The device comprises a silicon substrate with grooves, an input fiber optic of incoming port with its front lens, a fiber optic of pass port with its front lens, a fiber optic of reflect port with its front lens, and a thin-film filter. The fiber optics, lenses, and the thin-film filter are inserted into grooves to complete the fiber-to-fiber alignment and coupling. The present invention provides both functions of wavelength multiplexing and wavelength demultiplexing. The present invention also has the characteristics of automatic alignment and passive alignment.

Description:
FIELD OF THE INVENTION  
       [0001]     The present invention relates to the optic communication field and, more particularly, to a method using micro lithography, etching and the special crystal lattice structure of the silicon wafer to manufacture an optic wavelength division multiplexing device.  
       BACKGROUND OF THE INVENTION  
       [0002]     A wavelength division multiplexer (WDM) is used to merge lights with different wavelengths for transmission on the same fiber optic, or split lights with different wavelengths for transmission on separate fiber optics. The device is widely used in fiber optic communication networks, bi-directional transmission and CATV systems.  
         [0003]      FIG. 1  of the attached drawings shows a thin-film filter WDM, comprising fiber optics  111 ,  112 ,  113 , a dual-core collimator  121 , a single-core collimator  122 , and a thin-film filter  130 . The thin-film filter WDM has the advantages of good optical characteristics, and high stability. However, it also has the disadvantages of requiring active alignment for assembly, and using expensive components, such as collimators.  
         [0004]      FIG. 2  shows a fused-type WDM manufactured with the fused biconic taper technology to fuse the fiber optics  211 ,  212 ,  213  to form a WDM  220 . The fused-type WDM has a low production cost. However, it also has the disadvantages of having poor optical characteristics, such as narrow pass bandwidth, and low wavelength isolation. It is important to find a method to manufacture a WDM with good optical characteristics at a low production cost.  
       SUMMARY OF THE INVENTION  
       [0005]     The objective of the present invention is to provide a WDM that is good in automatic alignment, feasible in passive alignment, small in size, and low in production cost. To achieve the foregoing objective, the present invention utilizes the special crystal lattice structure of the silicon wafer, uses a micro lithography and etching process to manufacture specific grooves, and moves the fiber optics, lenses, and thin-films into the grooves under the passive alignment conditions to manufacture a WDM for both multiplexing and demultiplexing lights.  
         [0006]     The main feature of the present invention is that it does not require an adjustment base with a multi-degree of freedom for active alignment. Instead, the present invention is a high-precision alignment optic device with a high-precision passive alignment.  
         [0007]     The silicon optic based WDM of the present invention comprises a silicon substrate with grooves, an input fiber optic of incoming port with its front lens, a fiber optic of pass port with its front lens, a fiber optic of reflect port with its front lens, and a thin-film filter. The fiber optics, lenses, and the thin-film filter are inserted into grooves to complete the fiber-to-fiber alignment.  
         [0008]     The WDM of the present invention can act as a wavelength demultiplexer, which is to input two lights with different wavelengths through the same fiber optic, and use the lenses and the filter to split the two lights for outputting through different fiber optics. By reversing the foregoing process, the present invention can also act as a wavelength multiplexer to input two lights through different fiber optics, and use the lenses and filter to deflect and reflect so that both lights can be outputted through the same fiber optic.  
         [0009]     These and other objects, features and advantages of the invention will be apparent to those skilled in the art, from a reading of the following brief description of the drawings, the detailed description of the preferred embodiment, and the appended claims. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]      FIG. 1  shows a schematic diagram of a thin-film WDM.  
         [0011]      FIG. 2  shows a schematic diagram of a fused biconic tapered WDM.  
         [0012]      FIG. 3  shows a first embodiment of a silicon optic based WDM of the present invention.  
         [0013]      FIG. 4  shows a second embodiment of a silicon optic based WDM of the present invention.  
         [0014]      FIG. 5  shows a third embodiment of a silicon optic based WDM of the present invention.  
         [0015]      FIG. 6  shows a fourth embodiment of a silicon optic based WDM of the present invention.  
         [0016]      FIG. 7  shows a schematic diagram of the silicon substrate of the present invention.  
         [0017]      FIG. 8  shows a perspective view of the grooves of the present invention.  
         [0018]      FIG. 9  shows a cross-sectional view of fiber-to-fiber coupling of various types of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0019]      FIG. 3  shows a first embodiment of a silicon optic based WDM of the present invention. The first embodiment uses a single thin-film filter. The embodiment comprises an input fiber optic  311  at an incoming port with its front lens  321 , an output fiber optic  313  at a pass port with its front lens  322 , an output fiber optic  312  at a reflect port with its front lens  321 , a thin-film filter  330  and a silicon substrate  340 . The operational mechanism is to input a first light with wavelength λ 1  and a second light with wavelength λ 2  from the same input fiber optic  311 , then to focus the lights with the lens  321  to form a parallel ray for transmission through air. When the parallel ray reach thin-film  330 , the first light with wavelength λ 1  penetrates the thin-film filter  330 , reaches lens  322 , and focuses into the fiber optic  313  for transmission. On the other hand, the second light with wavelength λ 2  is reflected back to lens  321 , and transmitted through fiber optic  312 . Therefore, the first light and the second light that are originally transmitted in the same fiber optic  311 , are split and transmitted in separate fiber optics  312 and  313 , respectively. This operation accomplishes wavelength demultiplexing.  
         [0020]     The wavelength multiplexing function is achieved by reversing the foregoing operation of the present invention. A first light λ 1  and a second light λ 2  are input from fiber optic  313  and  312 , respectively. By the combination of the lens  322 , lens  321 , and the thin-film filter  330 , the first light is deflected and the second light is reflected into a same fiber optic  311  for transmission.  
         [0021]      FIG. 4  shows a second embodiment of a silicon optic based WDM of the present invention. The second embodiment uses two thin-film filters. The embodiment comprises an input fiber optic  411  at an incoming port with its front lens  421 , an output fiber optic  412  at a pass port with its front lens  422 , an output fiber optic  413  at a reflect port with its front lens  423 , a first thin-film filter  431 , a second thin-film filter  432 , and a silicon substrate  440 . The operational mechanism is to input a first light with wavelength λ 1  and a second light with wavelength λ 2  from the same input fiber optic  411 , then to focus the lights with the lens  421  to form a parallel ray for transmission to reach the first thin-film  431 , the first light with wavelength λ 1  penetrates the first thin-film filter  431 , reaches lens  422 , and focuses into the fiber optic  412  for transmission. On the other hand, the second light with wavelength λ 2  is reflected back to the second thin-film filter  432 , then reflected by the second thin-film filter  432  to the lens  423  and transmitted through fiber optic  413 . Therefore, the first light and the second light that are originally transmitted in the same fiber optic  411 , are split and transmitted in separate fiber optics  412  and  413 , respectively. This operation accomplishes wavelength demultiplexing.  
         [0022]     The wavelength multiplexing function is achieved by reversing the foregoing operation of the embodiment. A first light λ 1  and a second light λ 2  are input from fiber optics  412  and  413 , respectively. By the combination of the first thin-film filter  431 , and the second thin-film filter  432 , the first light is deflected and the second light is reflected into a same fiber optic  411  for transmission.  
         [0023]      FIG. 5  shows a third embodiment of a silicon optic based WDM of the present-invention. The third embodiment uses two thin-film filters. The embodiment comprises An input fiber optic  511  at an incoming port with its front lens  521 , an output fiber optic  512  at a pass port with its front lens  522 , an output fiber optic  513  at a reflect port with its front lens  523 , a first thin-film filter  531 , a second thin-film filter  532 , and a silicon substrate  540 . The operational mechanism is to input a first light with wavelength λ 1  and a second light with wavelength λ 2  from the same input fiber optic  511 , then to focus the lights with the lens  521  to form a parallel ray for transmission through the air to reach the first thin-film  531 , the first light with wavelength λ 1  penetrates the first thin-film filter  531 , reaches lens  522 , and focuses into the fiber optic  512  for transmission. On the other hand, the second light with wavelength λ 2  is reflected back to the second thin-film filter  532 , then reflected by the second thin-film filter  532  to the lens  523  and transmitted through fiber optic  513 . Therefore, the first light and the second light that are originally transmitted in the same fiber optic  511 , are split and transmitted in separate fiber optics  512  and  513 , respectively. This operation accomplishes wavelength demultiplexing.  
         [0024]     The wavelength multiplexing function is achieved by reversing the foregoing operation of the embodiment. A first light λ 1  and a second light λ 2  are input from fiber optics  512  and  513 , respectively. By the combination of the first thin-film filter  531 , and the second thin-film filter  532 , the first light is deflected and the second light is reflected into a same fiber optic  511  for transmission.  
         [0025]     The present invention is able to multiplex or demultiplex more than two different wavelengths based on the same structure.  FIG. 6  shows a fourth embodiment of a silicon optic based WDM of the present invention. The fourth embodiment uses a plurality of thin-film filters. The embodiment comprises an input fiber optic  611  at an incoming port with its front lens  621 , output fiber optics  612 ,  613 ,  614 ,  615  at a pass port with their front lenses  622 ,  623 ,  624 ,  625 , a first thin-film filter  631 , a second thin-film filter  632 , a third thin-film filter  633 , a fourth thin-film filter  634 , and a silicon substrate  640 .  
         [0026]     The operational mechanism is to input a first light with wavelength λ 1 , a second light with wavelength λ 2 , a third light with wavelength λ 3 , and a fourth light with wavelength λ 4  from the same input fiber optic  611 , then to focus the lights with the lens  621  to form a parallel ray for transmission through the air to reach the first thin-film  631 , the first light with wavelength λ 1  penetrates the first thin-film filter  631 , reaches lens  622 , and focuses into the fiber optic  612  for transmission. On the other hand, the other lights with wavelength λ 2 , λ 3 , λ 4  are reflected back to the second thin-film filter  632 . The second light λ 2  is reflected to the lens  623 , and focuses for transmission in fiber optic  613 . The third light λ 3  and the fourth light λ 4  penetrate the second thin-film filter  632  to reach the third thin-film  633 . The third light λ 3  is reflected by the third thin-film  633  to enter lens  624 , and focus into fiber optic  614  for transmission. Then, the fourth light λ 4  penetrates the third thin-film filter  633  and reaches the fourth thin-film filter  634 . The fourth light λ 4  is reflected by the fourth thin-film filter  634  to the lens  625  and transmitted through fiber optic  615 . Therefore, the four lights that are originally transmitted in the same fiber optic  611 , are split and transmitted in separate fiber optics  612 ,  613 ,  614 , and  615 , respectively. This operation accomplishes wavelength demultiplexing.  
         [0027]     The wavelength multiplexing function is achieved by reversing the foregoing operation of the embodiment. A first light λ 1 , a second light λ 2 , a third light λ 3 , and a fourth light λ 4  are input from fiber optics  612 ,  613 ,  614 ,  165 , respectively. By the combination of the first thin-film filter  631 , the second thin-film filter  632 , the third thin-film filter  633 , and the fourth thin-film filter  634 , the lights are deflected and reflected into a same fiber optic  611  for transmission.  
         [0028]     Furthermore, the silicon substrate of the foregoing embodiments is a silicon substrate comprising grooves, made by a micro lithography and etching process utilizing the special crystal lattice structure of a silicon wafer.  FIG. 7  shows a diagram of the silicon substrate. The grooves  711 ,  712 ,  713  on the silicon substrate  730  are for inserting fiber optics and lenses. The size of the grooves and the distance between grooves are controlled within the precision of ±0.5 μm. On the other hand, the grooves  721 ,  722 , made by etching or a precise dicing to form specific angles, are for inserting thin-film filters.  
         [0029]      FIG. 8  shows a perspective view of the grooves of the present invention. The grooves are V grooves  801 , V grooves with flat bottom  802 , U grooves  803 , U grooves with flat bottom  804 , necktie shape grooves  805 , and rhombus shape groves  806 .  
         [0030]     The fiber-to-fiber coupling of the embodiments of the present invention is done in various ways to reduce the fiber-to-fiber coupling loss.  FIG. 9  shows cross-sectional views of various couplings.  FIG. 9A  shows that the fiber-to-fiber coupling is done by using ball lenses, cylindrical lenses, or aspheric lenses. The cross-sections are shown as  911  and  912 .  FIG. 9B  shows that a fiber-to-fiber coupling is done by lenses with gradient refraction, with cross sections  921 ,  922 .  FIG. 9C  shows that a fiber-to-fiber coupling is done by plano-convex lenses, with cross-sections  931 ,  932 .  FIG. 9D  shows that a fiber-to-fiber coupling is done by a lens fiber, formed with a gradient refraction index micro lens and a fiber optic with cross-sections  941 ,  942 .  
         [0031]     The lens fiber is formed by fusing a micro lens with a fiber optic. Alternatively, a lens fiber is also formed by treating the tip of a fiber optic so that it can act as a lens. A lens fiber can be classified as conic lens, ball lens, aspheric lens, plano-convex, or thermal expanded core fiber. The cross sections  951 ,  952  of a thermal expanded core fiber are shown in  FIG. 9E .  
         [0032]     While the invention has been described in connection with what is presently considered to the most practical and preferred embodiment, it is to be understood that the invention is not to be limited to the disclosed embodiment, but, on the contrary, it should be clear to those skilled in the art that the description of the embodiment is intended to cover various modifications and equivalent arrangement included within the spirit and scope of the appended claims.