Abstract:
An optical energy eraser is implemented by the controlled movement of an optical fiber and an optical absorber into close proximity to permit coupling of energy between them. The eraser is used in conjunction with two optical switches to implement a node switch useful for optical fiber networks. An integrated optic implementation permits analogous results by a controlled change in the properties of the region separating a waveguide from an optical absorber so that significant coupling occurs between them.

Description:
FIELD OF THE INVENTION 
     This invention relates to optical networks and to functional waveguide elements useful for node switching in such a network. 
     BACKGROUND OF THE INVENTION 
     An optical fiber is a typical example of a waveguide and the invention is described herein illustratively in terms of such a fiber. Fiber optic networks are knwon to be highly desirable. Because of the expected cost effectiveness of such systems and the high information handling capabilities, fiber optic networks are the subject of considerable interest and effort in the industry. Unfortunately, various components necessary for implementing such a system have proven to be illusive. One such component is a node switch. A typical fiber optic system requires a relatively large number of node switches in a series or ring type organization. But commercially available node switches adapted to connect and disconnect nodes, at present, are lossy. Consequently, the number of nodes which can be connected into a ring is limited. 
     BRIEF DESCRIPTION OF THE INVENTION 
     The present invention employs the controlled coupling between an optical fiber and an optical absorber to absorb light energy and information being carried by the fiber. An information carrying optical fiber and an eraser are installed in closely spaced opposing positions on facing portions of the internal surface of a hollow quartz sleeve. The facing portion of the fiber has its cladding reduced in thickness or removed to foster energy coupling. The eraser is a block of quartz having characteristics to absorb light energy. The sleeve is filled with a fluid (liquid or gas) having an index of refraction equal to or less than the cladding of the fiber. An actuator such as a piezoelectric element is disposed on the external surface of the sleeve to apply a force to the sleeve when activated. The force reduces the separation between the fiber and the eraser from a first position at which only negligible coupling occurs to a closer spacing at which essentially all optical energy is absorbed. An optical eraser is thus implemented. 
     The fiber included within the sleeve is the fiber which connects one node to another. Second and third fibers, connected to a receiver node and from a transmitter node respectively, are coupled to the first fiber on first and second sides of the eraser by means of first and second switches. A switch operative in this manner is fully disclosed in my copending application Ser. No. 750,805, entitled &#34;Optical Switch Arrangement&#34; and filed on even date herewith. Such a switch employs two fibers instead of a fiber and an absorber. The separation between the two fibers is controlled by a pressure transducer. Only when the fibers are forced into close proximity does information switch from one fiber to another. The arrangement of two switches separated by an optical eraser connected as described provides a functional node switch for an optical fiber network. Particularly, when such elements share a common support, a convenient functional network component is provided. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     FIG. 1 is a cross-sectional view of an eraser in accordance with one aspect of this invention; 
     FIG. 2 is a projection view of a node switch in accordance with another aspect of the invention employing the eraser of FIG. 1; 
     FIG. 3 is a schematic representation of the node switch of FIG. 2, and 
     FIG. 4 is a schematic representation of a portion of a fiber optic network including node switches of the type shown in FIGS. 2 and 3. 
    
    
     DETAILED DESCRIPTION 
     FIG. 1 is a cross sectional view of an optical energy eraser 10 suitable for use in an optical network in accordance with one aspect of this invention. The eraser comprises a sleeve 11 having an internal surface 12. The vertical dimension of sleeve 11 as viewed in the figure, is relatively small to bring top and bottom portions of surface 12 into closely spaced apart positions. The top portion includes longitudinal slot 14 in which optical fiber 15 is secured. A relatively large volume quartz block 16 is fixed in position opposite fiber 15 as shown in the figure. 
     Fiber 15 is shown as having a relatively large core 17 (diameter=100 microns) and a cladding 18 (diameter=140 microns) shown absent in the area opposite block 16. The sleeve includes an open area 19 which, in the illustrative embodiment includes a liquid with an index of refraction equal or less than that of cladding 18. The sleeve is sealed at both ends in a manner to contain the liquid yet permit fiber 15 to extend beyond the sleeve. 
     The sleeve is supported by a rigid support member 25 to which rigid bridge 26 also is secured. Pressure element 27 is suspended from bridge 26 and is adapted to apply pressure to the sleeve in a manner to move fiber 15 and block 16 towards one another. Initially, fiber 15 is on the order of forty microns from block 16. When pressure element 27 applies pressure to the sleeve, fiber 15 is moved into contact with block 16. 
     Element 27 conveniently comprises a piezoelectric element operative to apply eight to sixteen oounces of force against sleeve 11 in response to a command signal. Control circuit 30 is operative to apply such a (steady state) voltage to element 27 to produce the force when required. 
     Eraser 10 is utilized conveniently with switches disclosed in copending application Serial No. 750,805. FIG. 2 shows such an arrangement in which the positions of an eraser 30 and first and second sleeve switches 31 and 32 share a common support member 34. Separate pressure elements (not shown in FIG. 2) are used as shown in FIG. 1. A common circuit operates the two switches and the eraser to form a node switch. 
     FIG. 3 shows a schematic representation of the node switch of FIG. 2 showing the various components of the node switch with a common control circuit 38. The node switch as shown in FIG. 4 comprises eraser 30 and switches 31 and 32 of FIG. 2 with pressure transducers 40, 41 and 42 of eraser 30 and switches 31 and 32 respectively. The three components share a common optical fiber 50 also connected between adjacent node switches as indicated. Three adjacent node switches are designated NS1, NS2, and NS3 for convenience. Switch 31 of node switch NS2 includes an additional fiber 52. Fiber 52 is sealed within the sleeve of switch 31 at one end 53 as shown, but extends beyond the sleeve at the other end terminatng at a receiving node. Similarly, switch 32 includes an additional fiber 55. Fiber 55 also terminates within the sleeve of switch 32 at end 56, originating from a transmitting node at the other end. 
     FIG. 4 shows the overall organization of three node switches NS1, NS2 and NS3 with respective receiving and transmitting nodes and a control circuit 58. The receiving and transmitting nodes are deisgnated RN1, RN2 and RN3, and TN1, TN2 and TN3 for node switches NS1, NS2 and NS3 respectively. The operation of a node switch of FIG. 2 and 3 is now described in the context of the portion of a network described in connection with FIG. 4. 
     The network operates to route information carried by a light beam much as railroad cars are switched from track to track. Accordingly, if fiber 50 of FIG. 3 is visualized as a railroad track and if information in the fiber is visualized as a train, node switch NS2 of FIG. 3 operates to route a train on track 50 to track 52 and to switch a train on track 55 to track 50. If tracks 52 and 55 are visualized as leading to a railhead and originating at a railhead respectively, the operation is operative to take a train out of service and to substitute a new train. 
     The control signals to control such an operation would be operative to close switch 41 and switch 42 and to deactivate the train on track 52 and activate the train on track 55. Of course this is just an analogy and information carried by an energy beam is not divided into a physical package such as a train. Thus, each node switch requries an optical energy absorber to extinguish any optical energy (viz: any train) not switches. Accordingly, a node switch utilizes steady state voltages applied to piezoelectric transducers to physically move adjacent fibers into close proximity in switches 31 and 32, and to move a fiber and absorber closer together in eraser 30. The voltage signals operate to isolate nodes NS1 and NS3 from one another and to connect RN2 and TN2 of FIG. 4 to nodes NS1 and NS3, respectively. 
     The invention has been described in terms of an optical fiber embodiment. But the invention can be implemented with an integrated optic circuit as well. In an integrated optic implementation, no physical components actually move. Instead, a waveguide and an absorber are separated by a region of the circuit which is capable of having its optical properties changed controllably. Copending application Ser. No. 750,805 entitled &#34;Optical Switch Arrangement&#34; describes details of an analogous integrated optic switch which are applicable to integrated optical eraser design in accordance with this invention.