Abstract:
A multiplexer and demultiplexer may be formed so that two input wavelengths from an optically multiplexed signal may be demultiplexed. A demultiplexer may be in the form of an integrated filter and photodetector. The filter may reflect one wavelength and may pass another wavelength. The reflected wavelength is detected by a first detector and the passed wavelength is detected by a second detector. For example, the second detector may be combined with the filter by forming the filter directly on the second detector. In one embodiment, the second detector may be L-shaped.

Description:
BACKGROUND  
       [0001]     This invention relates generally to optoelectrical systems.  
         [0002]     Optoelectrical systems transmit signals both by optical and electrical means. Transducers are utilized to convert optical to electrical signals and vice versa.  
         [0003]     Commonly, light information must be converted into electrical information. In many cases, the light information may be multiplexed so that a number of different wavelengths are transmitted over the same optical fiber. For example, in wavelength division multiplexing, a large number of signals may be transmitted over the same fiber.  
         [0004]     Thus, there is a need for ways to demultiplex the signals and/or add additional signals to the optical stream. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0005]      FIG. 1  is a top plan view of one embodiment of the present invention;  
         [0006]      FIG. 2  is a partial, cross-sectional view of a portion of the embodiment shown in  FIG. 1  in accordance with one embodiment of the present invention; and  
         [0007]      FIG. 3  is an enlarged, cross-sectional view of a portion of the embodiment shown in  FIG. 1  in accordance with one embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION  
       [0008]     Referring to  FIG. 1 , an optical connector  12  may connect to an optical cable or fiber. A fiber  14  conveys a signal from the connector  12  to a silicon electrooptical bench  16 . The fiber  14  may be coupled to the bench  16  through a fiber mount  18  mounted on the bench  16  so that the fiber  14  is fixed between the mount  18  and a V-shaped groove  19  formed in the upper surface of the bench  16 . A fiber-waveguide interface  20  converts the signal from the fiber  14  to an appropriate form to be transmitted over a waveguide  22  formed within the bench  16 .  
         [0009]     Thus, in one embodiment, at least two wavelengths, indicated as wavelengths A and B, may be transmitted from the cable through the fiber  14  to the waveguide  22 . A signal from the cable may be wavelength division multiplexed in one embodiment of the present invention. That signal passes through a coupler  34  to a filter  24 . The filter  24  may pass one wavelength, such as the wavelength B. The wavelength B may then be detected by the detector  26  and connected to an electrical signal.  
         [0010]     Another wavelength, such as the wavelength A, is not passed by the filter  24  but, instead, is reflected by it, over the path  38 , to be detected by a wavelength A detector  30 . The detected optical signal may be converted into an electrical signal by the detector  30 .  
         [0011]     At the same time, a laser  32  generates a signal of wavelength C which is partially transmitted over the curved waveguide  40  through the coupler  34  to a power monitor  36  for monitoring the power of the signal of wavelength C. The remainder of the wavelength C signal may be impressed onto the waveguide  22  across the coupler  34 . The signal of wavelength C may be provided by the bench  16  back through the fiber  14  and the coupler  12  to the cable. As a result, two wavelengths may be removed and detected and a third wavelength may be added back to the multiplexed communication system. Of course, any number of signals may be added or removed in other embodiments. In one embodiment, the wavelengths A and B are wavelength division multiplexed wavelengths such as 1490 and 1550 nm, and the wavelength C is in a separate wavelength band such as 1310 nm.  
         [0012]     Referring to  FIG. 2 , the laser  32  may be arranged to be fit within a trench defined within the surface of the bench  16 . The laser  32  is connected to the lead  54  by thermocompression or other bonding techniques. The laser  32  is aligned with the laser waveguide  34  adjusted to the waveguide  40  embedded in the silicon electro-optical bench  16 .  
         [0013]     The filter  24  and detector element  44  may be implemented as an integrated unit to form the detector  26  as indicated in  FIG. 3 . The filter  24  may be formed by a film that is secured to the photodetector element  44 . The detector  26  may include an L-shaped package, including a relatively vertical portion  46  and a relatively horizontal portion  48  that may be secured to the bench  16  by an adhesive  50  in one embodiment. The detector element  44  may be secured and electrically interconnected to the L-shaped package portions  46  and  48  by thermocompression bonding in one embodiment, or by solder in another embodiment. Alternatively, wire bonding may also be utilized for the electrical connection, with adhesive for the mechanical connection. In one embodiment, the portions  46  and  48  may be multilayer packages electrically connected at 90 degrees to form an L-shaped mount. The L-shaped package may be made of two multilayer packages connected at ninety degrees by brazing or soldering. The second multilayer package provides easy access for the electrical connections to the silicon electrooptical bench  16 . As another embodiment, the L-shaped mount may be formed of a lead frame instead of a second multilayer package that may be soldered down onto the silicon optical bench at ninety degrees.  
         [0014]     Electrical signals may be coupled to and from the detector  26  as indicated by the wire bond  52 .  
         [0015]     In one embodiment, the filter  24  may be formed of a conventional, commercially available, thin film filter component. Such thin film filters may have alternate layers of appropriate thin films like Al 2 O 3 , TiO 2 , SiO 2 , etc., which may be deposited on an appropriate substrate, such as a glass substrate. The filter  24  may be adhesively secured on the photodetector element  44  by way of an optical adhesive in one embodiment.  
         [0016]     In some embodiments, the integrated structure may be advantageous since a separate pick and place operation for placing the thin film filter and for placing the detector  26  may be avoided.  
         [0017]     A second approach may be to directly deposit alternate layers of appropriate thin films on the photodetector element  44 . Of course, this deposition may be done while the photodetector element  44  is still in the wafer format. This approach may be advantageous, in some embodiments, as it may decrease optical losses by eliminating the thickness of the glass substrate that is found in commercial thin film filters.  
         [0018]     The detector  26  detects the wavelength that is transmitted through the thin film filter  24 . The reflected wavelength is coupled to the path  38  in the silicon electrooptical bench  16 . As the optical angle of incidence at the detector  26  may be important to make sure the losses are reduced, a precision trench sidewall  58  may be used for reference during assembly in some embodiments. After the filter detector hybrid is picked and placed, it is slid to the sidewall of the trench  58  to couple to the waveguide  72 . The base of the trench  58  serves as the bottom reference plane for alignment and provides stability during the pick and place operations. To provide mechanical robustness, the gap between the filter detector hybrid may be filled using optical epoxy on the waveguide side, and on the non-active side as well, as needed.  
         [0019]     The L-mount arrangement may facilitate electrical connections from the detector  26  that are in the vertical plane and may transfer them to the horizontal plane on top of the silicon optical bench  16 , essentially providing a ninety degree bend for electrical connections. On the horizontal plane, electrical connections to the silicon optical bench may be made using wire bonding or solder bonding.  
         [0020]     While the present invention has been described with respect to a limited number of embodiments, those skilled in the art will appreciate numerous modifications and variations therefrom. It is intended that the appended claims cover all such modifications and variations as fall within the true spirit and scope of this present invention.