FIBER OPTIC SMART SWITCH

Abstract: A regulating add/drop optical switch controls the switching and output power levels by manipulating signals to polarization modulators. At each input port, the beam is separated into horizontal and vertically polarized components of the light wave. One beam is shifted and the resulting like polarized beams pass through a polarization modulator that controllably rotates polarization to a selected extend to determine whether horizontal or vertical polarization will predominate. If horizontal, the beams pass through a polarization beam separator without deflection. If vertical the beams are reflected. The beams pass through an additional polarization controller to determine if they are to be directed to one of the output ports or dissipated. If selected for output, the beams are collimated before they are launched. A wavelength-selective interference filter allows the present invention to function as a fully configurable n-channel add/drop multiplexer.

Description: FIBER OPTIC SMART SWITCH RELATED APPLICATIONS The present application is a continuation-in-part of the Applicants' co-pending U.S. Patent Application Ser. No. 08/897,353 entitled "BROADBAND OPTICAL POWER REGULATOR" filed on July 20, 1998, which is incorporated by reference, and is related to co- pending application Attorney Docket Number 55872-P048US-992837, entitled "HIGH EXTINCTION RATIO POLARIZATION BEAMSPLITTER," which is hereby incorporated herein by reference; and Attorney Docket Number 55872-P042CP3CP1-993121, entitled "OPTICAL SLICING NETWORK UTILIZING A HIGH EXTINCTION RATIO POLARIZATION BEAMSPLITTER," which is hereby incorporated herein by reference. TECHNICAL FIELD The present invention relates generally to the field of optical switches for fiber optic networks. More specifically, the present invention relates to a system and method for constructing and using an optical switch having multiple switching modes and for incorporating regulation of the optical output power. BACKGROUND Optical amplifiers and the associated wavelength-division multiplexing (WDM) technology have become the industry standard for backbone fiber optic transmission networks. In WDM systems, multiple wavelength optical carriers are launched into optical fibers, each carrier with the potential to carry gigabits of information per second. Forty or more of these individual optical carriers, each of a slightly different wavelength, can travel on a single-mode fiber. In a typical group of 16 carriers, 4 carriers might need to be dropped for distribution to a local metropolitan area, while the other 12 earners are passed on to remote destinations. This is typically accomplished by demodulating all 16 optical carriers to obtain 16 electronic signals, then remodulating the carriers that are to go to the remote destination. Optical-to- electrical (O-E) converters are used at switching centers to demodulate all the optical signals, including those not intended for local distribution. The long-haul signals are processed to modulate a laser (E-O) converter for launch into optical fiber to their ultimate destinations. The channels vacated by taking off signals for local distribution can then be filled by new carriers to move signals from local switches to the remote destination. In the current art, there is no effective non-OEO method of simultaneously dropping a DWDM carrier with mixed traffic for local distribution while simultaneously passing the carrier through to a remote location. A related problem is the distorted gain vs. wavelength response characteristic of erbium-doped-fiber optical power amplifiers (EDFA) used in the current art to boost the power level of weak DWDM signals before they are demodulated. Such amplifiers are also used to restore transmission levels on long sections of fiber. The ideal amplifier would provide a flat response characteristic to amplify all wavelengths equally, so that the power levels of all carriers of a DWDM signal are identical. However, all state of the art EDFA amplifiers share the common limitation of a characteristic 2-humped response curve. When the power of the least-amplified wavelength is set to the correct level the signal levels for wavelengths near the response humps are excessive. These differences are multiplied by successive EDFAs in the signal path, and if uncorrected would greatly increase data error rates. Current practice uses optical attenuators to correct for the uneven signal levels by reducing the excess power in specific channels. This is effective in static networks requiring only rare configuration changes. Dynamic networks use real-time optical switching to route, drop, and add traffic in real time. This results in continual level shifts of individual carriers, exacerbating the difficult problem of keeping each of the different wavelengths (40 or more) at the same optimum level. In addition, sudden changes in network power levels can result in lost data and damage to the photodetector diodes used to demodulate the optical signals. Very good optical power regulators, such as that taught by Wu, et al, are available as external system adjuncts to control these power variations. By incorporating such power regulators, system performance can be improved, unfortunately at the expense of many additional optical connections and greater system complexity. SUMMARY OF THE INVENTION These and other objects, features and technical advantages are achieved by a system and method which combines the functions of a solid-state polarization-based optical switch and a solid-state optical power regulator in the same device. This type of switch provides very low attenuation in the selected signal path, a great degree of isolation in the signal path not selected, automatic regulation of optical power levels, and fast switching times. The automatic power control feature of the smart switch allows fiber optic networks to dynamically reconfigure themselves to adjust for circuit loading or to restore service throughout the network in the event of failure or damage. The present invention provides an optical switch with a main input port and a secondary input port, a main output port and a secondary output port. In the event of complete electrical power failure, the optical signal at the primary input port is routed to the primary output port to accomplish fail-safe operation. Under normal conditions, the present invention provides continuous regulation of optical power at both output ports regardless of switching condition or variations in optical power at either or both input ports. An electro-optic feedback controller provides adjustable regulation levels and includes status output signals to warn of network power faults. Optical signals entering at the primary input port pass through a collimator then a beamdisplacer of birefringent materials. This separates the light into its horizontal and vertical polarization components. A half-wave plate of birefringent material shifts the polarization of the horizontally polarized beam by 90°. The resulting pair of vertically polarized beams pass through a solid-state polarization modulator that rotates the vertical polarization of the beams to an extent determined by electronic signals from a control circuit. The effect of these signals is to determine whether horizontal, vertical, or neither polarization will predominate at the output of the polarization modulator. The resultant beams enter a polarization beamseparator containing a polarization-selective interface transparent to horizontally polarized light, reflective to vertically polarized light. The horizontally polarized component passes directly to a second polarization modulator also under control of the said electronic circuit. If the beams are toward the primary output port, horizontally polarized beams toward an absorptive material that dissipates their energy. The beams from the primary input port enter a polarization beamseparator that directs vertically polarized beams toward the secondary output port, horizontally polarized beams toward the primary output port. By proper excitation of the polarization modulators by the control circuit the optical signal from the primary input port can be divided between both output ports. At each output, the intensity of the optical signal present is sampled by an optical coupler feeding the control electronics circuit, which in turn adjusts the amount of driving voltage applied to the two applicable liquid crystal polarization modulators to maintain the power level at the set point established by the external power command which governs that particular output port. Comparator circuitry determines if the power at either or both ports is out of regulation limits and causes alarm signal(s) to be sent to an external device such as a network controller. Additionally, incorporation of wavelength-selective interference filters allows the present invention to function as a fully configurable -channel add/drop multiplexer. Accordingly, it is a technical advantage of this invention that signals can be routed as follows: primary input to primary output, primary input to secondary output, primary input to both outputs, or primary input to secondary output and secondary input to primary output. This flexibility makes the present invention the ideal building block for the construction of optical add/drop multiplexers of any required degree of complexity. Another technical advantage of this invention is that the switch does not block the primary signal path in the event of power failure. When all power is removed, it instead completes the primary optical circuit with very low attenuation. Thus a local power outage does not disable the long-haul circuit. Another technical advantage of this invention is that the output optic power level is monitored at all output ports and the monitored signals are used to selectively adjust the optic power level. These and other advantages, features, and objects of the present invention will be more readily understood in view of the following detailed description and the drawings. 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. BRIEF DESCRIPTION OF THE DRAWINGS For a more complete understanding of the present invention, and the advantages thereof, reference is now made to the following descriptions taken in conjunction with the accompanying drawing, in which: FIGURE 1 is a simplified block diagram showing the smart switch input and output signals; FIGURE 2 is a block diagram showing signal flow through the smart switch in the through and default (power failure) mode; FIGURE 3 is a block diagram of the regulator/ switch control circuit card assembly as used in conjunction with the present invention; FIGURE 4 is a block diagram showing signal flow through the smart switch in the drop mode; FIGURE 5 is a block diagram showing signal flow through the smart switch in the drop-and-continue mode; FIGURE 6 is a block diagram showing signal flow through the smart switch in the add/drop mode; FIGURE 7A AND FIGURE 7B are block diagrams showing various methods of connecting a passive optical wavelength router to the smart switch for applications requiring manipulation of individual carriers of a WDM system, such as needed for add/drop multiplexing and similar automatic switching; FIGURE 8 is a conceptual diagram showing how the passive optical wavelength routers of FIGURE 7 can be interconnected to achieve a completely reconfigurable n-channel add/drop multiplexer; FIGURES 9 and 10 show alternate embodiments; and FIGURES 11 A to 1 IC depict an alternative arrangement for the smart switch. DETAILED DESCRIPTION NORMAL MODE OPERATION IN UNENERGIZED (FAIL-SAFE) MODE The following discussion of operation in the through mode assumes that power has been interrupted. Normal through-mode operation, as well as drop mode, drop and continue and add/drop mode are described below. As shown in FIGURE 1, a first incoming optical signal arrives at IN port 12 and a second incoming optical signal arrives at ADD port 11 of switch 10. The out level 101 and the drop level 102 signals are power levels provided by the network to the switch for the respective signals from the out port 13 and the drop port 14. The smart switch will then maintain the power levels of the out and drop signals from the out and drop ports based on these signals. The out alarm 103 and the drop alarm 104 are signals sent from the switch 10 to the network if the power levels of the out or drop signals exceeds the levels set by signals 101 and 102. Switch mode signal 105 configures the switch for add/drop operations, bypass or through operations, or regulation operations (including drop and continue operations). As will be seen with respect to FIGURES 7A, 7B or 8, smart switch 10 can be selectively set to accept only one carrier (λ,...λ n ) and reject the others. The rejected carriers remain on the line. The signal connection would typically be to an optical fiber transmission line. As shown in FIGURE 2, the signal passes through collimator 208 and is directed into beamdisplacer 209, which separates the H- and V-components (horizontal, vertical) into two discrete beams. The V-beam travels directly to polarization modulator 211. The H-beam is applied to half-wave plate 210 causing its polarization to change from H to V. The V-beam exits half- wave plate 210 and enters polarization modulator 211 along with the original V-beam from beamdisplacer 209. Because polarization modulator 211 is unenergized the vertical polarization of the two beams is rotated 90° to become horizontally polarized. The two H- beams now enter polarization beamseparator 212. Because both beams are H-beams, they pass with negligible deflection through the polarization-selective interface 22 within polarization beamseparator 212. Had either or both beams been V-beams, they would have been deflected downward toward polarization beamseparator 229. The two undeflected H-beams now pass through polarization modulator 213 which, being unenergized, rotates their polarization 90° so that two V-beams exit toward beamdisplacer 215. The lower V-beam must first pass through half-wave plate 214 which converts it to an H-beam. Beamdisplacer 215 combines this H-beam with the V-beam from polarization modulator 213. The VH leaving beamdisplacer 215 contains roughly equal amounts of V- and H - components. This VH-signal passes through collimator 216 and 5/95 coupler 217 to emerge as the data signal at the OUT port 13) NORMAL THROUGH-MODE OPERATION During normal operation in the through mode, signal flow is the same as during failsafe operation except that the smart switch now provides tight control of power levels at the OUT and DROP ports. Regulation is implemented by an optical-electronic-optical feedback loop between 5/95 coupler 217, regulator/switch control circuit card assembly (cca) 30 as contained in the above-identified application entitled BROADBAND OPTICAL POWER REGULATOR. In this feedback arrangement 5% of the total optical signal output from collimator 216 is picked off by 5/95 coupler 217 and routed by fiber to regulator/switch control (cca) 30. Although not the subject of this application, the functions of the regulator/switch control cca 30 must be summarized in order to fully appreciate the operation of the present invention. The block diagram of FIGURE 3 shows the following six inputs to regulator/switch control (cca) 30: OUT SAMPLE, OUT LEVEL SET, SWITCHING MODE, DC POWER, DROP SAMPLE, and DROP LEVEL SET. Outputs are OUT ALARM, LC DRIVE 1, LC DRIVE 2, LC DRIVE 3, LC DRIVE 4 and DROP ALARM. Cca 30 uses SWITCHING MODE commands to control the degree of optical rotation imposed by polarization modulators. In the regulator circuit, a sample of the outgoing optical signal from coupler 213 (FIGURE 2) is applied to a photo diode detector. The detector provides a dc signal proportional to the power of the optical output signal 13 at the OUT port (FIGURE 2). The dc signal at input 3 lis amplified by a photo diode amplifier. The resulting signal is applied to a comparator circuit that also receives the external OUT LEVEL SET signal 32. The comparator constantly monitors these two signals. An error signal output of the comparator changes state whenever the level of the optical signal 13 at the OUT port exceeds the level set by OUT LEVEL SET. The error signal is processed by analog and switching circuits themselves under control of logic circuits that respond to the SWITCHING MODE signal. The resulting signals are LC DRIVE 1, LC DRIVE 2, LC DRIVE 3, and LC DRIVE 4. These signals control the amount of polarization rotation to be imposed by each of the four polarization modulators 204, 211, 213 and 228, thereby controlling switching path and signal amplitude. If the level of the optical signal 13 at the OUT port (FIGURE 2) is below the set level, logic circuits in regulator/switch control CCA cause the OUT ALARM signal to change state, signaling a network failure to external devices. The foregoing paragraphs describe operation of the regulator/switch control cca in the through mode; only the OUT port carries a signal in this mode. In modes where the DROP port is active (drop, drop-and-continue, add/drop) an additional regulator circuit detects the sampled signal from 5/95 optical coupler 222 and adjusts LC DRIVE 1, LC DRIVE 2, LC DRIVE 3, and LC DRIVE 4 accordingly. DROP MODE OPERATION An incoming optical signal arrives at IN port 11 (FIGURE 4) of smart switch 10. For further information see Attorney Docket Number 55872-P046CP1CP1-993118 entitled " N X M DIGITALLY PROGRAMMABLE OPTICAL ROUTING SWITCH USING HIGH EXTINCTION RATIO POLARIZATION BEAMSPLITTER" which is hereby incorporated herein by reference. The signal passes through collimator 208 and beamdisplacer 209, which separates the H- and V-components into two discrete beams. The H-beam is applied to half- wave plate 210 causing its polarization to change from H to V. These beams arrive at polarization modulator 211 as described above. As both are V-beams and because polarization modulator 211 is energized, their vertical polarization is not changed. The two V-beams now enter polarization beamseparator 212. Because both beams are V-beams, they cannot pass through the polarization-selective interface 22 within polarization beamseparator 212. Instead, they are deflected downward toward polarization beamseparator 229. The two deflected V- beams cannot pass through the polarization-selective interface (23) within polarization beamseparator 229, but are instead deflected toward polarization modulator 228 which, being energized does not change their vertical polarization. The upper V-beam travels directly to beamdisplacer 225. The lower V-beam must first pass through half- wave plate 227 which converts it to an H-beam. Beamdisplacer 225 combines this H-beam with the V-beam from polarization modulator 228. The VH signal passes through collimator 224 and 5/95 coupler 212 to emerge at the drop port 14. The drop port is a connection to a local network. DROP-AND-CONTINUE MODE OPERATION In the drop-and-continue mode an optical signal at IN port 11 (FIGURE 5) is divided equally between the OUT and the DROP ports. An incoming optical signal arrives at IN port 11, FIGURE 5, of smart switch 10. The signal passes through collimator 208 that directs it into beamdisplacer 209, which separates the H- and V-components into two discrete beams. The V-beam travels directly to polarization modulator 211. The H-beam is applied to half- wave plate 209 causing its polarization to change from H to V. The V-beam exits half-wave plate 210 and enters polarization modulator 211 along with the original V-beam from beamdisplacer 209. Because polarization modulator 211 is partially energized the vertical polarization of the two beams is changed to two components, one vertical and one horizontal. The ratio of the two components depends on voltage applied to modulator 211. The horizontal component will be routed to output 13, and the vertical components will be routed to drop 14. ADD/DROP MODE This operation effectively splits the signal at beamseparator 212 with a portion of the signal going towards output 13 and a portion of the signal going towards output 14. The proportion can be equal or it can be adjusted under control of polarization modulator 11 which in turn is driven by circuit 30 in a manner previously described. FIGURE 6 shows a circuit where the add/drop mode is activated. In this configuration the signal from input 11 is directed via beamsplitter 212 to beamsplitter 229 as previously described with respect to the drop mode shown in FIGURE 4 as the signal then passes through the circuit to drop output 14. The signal to be added is applied via input 12 collimator 201 and beamdisplacer 202. Modulator 204 is on, such that no rotation occurs; the vertical light is then deflected by beamsplitter 205 and is again deflected by beamsplitter 212 and will route to outport 13. Thus, a signal coming on input 11 is directed to a local network via drop 14 while a signal is added to the cable via add input 12 and output 13. Note that when the circuit was in the modes other than the add/drop mode, any signal on the add 12 input would be directed to a sync 206 and have no effect on the circuit. As shown in FIGURE 7 A, a multicarrier signal 71 enters collimator 208 and passes to interference filter 73 which passes a single wavelength (in this case λ 2 ) on to beamdisplacer 209 for switching and regulation as previously described. All other wavelengths (λ, and λ,...λ n „) are reflected back into collimator 208 and enter outgoing fiber 72 with low attenuation. FIGURE 7B shows a similar arrangement with interference filter 73A installed separately from collimator 208. The wavelengths rejected by interference filter 73 A enter outgoing fiber 72 through a separate collimator 208A. These interference filters could also be mounted elsewhere in the optical path, such as at the collimators immediately before the OUT and DROP ports. FIGURE 8 shows one way of arranging these building blocks 800-814 to allow any number of WDM carriers to be individually manipulated - dropped, added, or split - all the while maintaining prescribed network power levels under all switching conditions. For further information see Attorney Docket Number 55872-P042CP2CP1-993119 entitled "OPTICAL ADD/DROP WAVELENGTH SWITCH USING A HIGH EXTINCTION RATIO POLARIZATION BEAMSPLITTER" which is hereby incorporated herein by reference. Turning now to FIGURE 9, there is shown an alternative embodiment for smart switch 10 shown as switch 90. In this switch there is a beamseparator 91 which is shown in more detail in above-identified copending and concurrently filed application entitled "HIGH EXTINCTION RATIO POLARIZATION BEAMSPLITTER". Beamseparator 91 has a dual plate 901, 902 in operation. Signals on input 11 pass through collimator 208 and beamdisplacer 209 separates the horizontal and vertical polarizations. The vertical polarization is passed through halfwave plate 210 to change its polarization to horizontal. Then both horizontal beams enter polarization modulator 211, which depending upon the voltage applied from vector 94, serves to allow the beams to pass through unrotated or rotated. In a situation where the beams are rotated, they leave modulator 211 as vertical leads which impact on plate 901 of separator 91, then impact on surface 902 again impacting on surface 901 at point A causing the beam to impact on surface 902 and then again impact on surface 901 at point B becoming deflected into polarization modulator 213 which allows input beam 11 to pass to output 13. This beam passes through partially reflecting surface 92 which causes approximately 5 five percent of the light to be reflected and measured by detector 93, which provides a signal level for detector 94 to control the rotators 211 and 213. This serves to modify the power levels to maintain a proper output level by controlling the amount of light that reflects off of surfaces 901 and 902 based upon the rotation of the signal. Note that in the through mode of FIGURE 9 there is no signal on the add input 12. Turning now to FIGURE 10 the add/drop mode will be described. In this situation the polarization modulator 211 is operated to put the beams in the horizontal mode which allow the beams then to pass through plates 901 and then to drop output 14 as previously discussed. At this time a signal is on the add/input 12 which is polarized in a horizontal direction as it impacts plate 901 and moves through plate 901 to polarization modulator 213 and then to output 13 as previously discussed. By controlling the amount of voltage between 0 and 15 volts, the output signal can be controlled to maintain the signal level at the proper level. Of course, the same type of control can be used on polarization modulator 228 to maintain the drop output at a desired level if the user desires to so modify and control the output. Under the condition signals on the drop output can be monitored as described herein before affecting this control. FIGURES 11 A to 1 IC depict an alternative arrangement for the inventive smart switch 1100. The switch in FIGURES 11 A to 1 IC includes an in port 1101 for providing a input signal, an add port 1102 for providing an add signal, first and second birefringent elements 1103, 1104 for separting, respectively, the input signal and the add signal into s (vertical or "•") and p (horizontal or "|") polarization components and laterally (spatially) separating the componenets. The switch 1100 also includes first and second halfwave plates 1105, 1106 which convert one of the components into the other component (as shown here the p component is converted in an s polarization by plate 1105 and the s component is converted into a p polarization by plate 1114, however the plates could be reversed). The switch 1100 also includes first and second polarization rotators, 1107, 1108 which are used to change the polarizations of the light being passed to the beamsplitters 1109, 1110. The switch further includes first and second polarization beamsplitters 1109, 1110, which will deflect s polarized light, and allow p polarized light to pass through. The switch also includes third and fourth polarization rotators 1111, 1112 to control the polarizations of the light being outputted from the beamsplitters 1109, 1110. The switch also includes third and fourth halfwave plates 1113, 1114, and third and fourth birefringent elements 1115, 1116, which process the light similar to the input side elements for outputting to drop port 1117 and out port 1118. FIGURE 11 A depicts the switch 1100 being used in an add drop operation, wherein the rotators 1107, 1108 are in the off state (0 volts) and thus convert the s polarized light into p polarized light, which is sent to the beamsplitters 1109, 1110. Since the light is p polarized, the beamsplitters 1109, 1110 do not deflect the light, but rather pass the light through to rotators 1111, 1112. These rotators 1111, 1112 are also in the off state, and thus convert the p polarized light to s polarized light. This light is recombined by the halfwave plates 1113, 1114, and the birefringent elements 1115, 1116 into signals for the drop port 1117 and the add port 1118. Note that the In signal is sent to the drop port, and the add signal is sent to the out port. FIGURE 1 IB depicts the switch 1100 being used in a through or bypass operation, wherein the rotators 1107, 1108 are in the on state (15 volts) and thus do not rotate the s polarized and passes the light to the beamsplitters 1109, 1110. Note that only the In port 1101 has a signal. Since the light is s polarized, the beamsplitters 1109, 1110 deflect the light. These rotators 1111, 1112 are also in the on state, and thus pass the s polarized light. This light is recombined by the halfwave plate 1114 and the birefringent element 1116 into the signal for the add port 1118. Note that the In signal is sent to the out port. FIGURE 11C depicts the switch 1100 being used in a drop and continue operation, wherein the rotator 1107 is in a variable state (0-15 volts), and thus partially rotates the light. This causes the two branches to each have both s and p polarized light. Note that only the In port 1101 has a signal. The beamsplitter 1109 will pass the p polarized light onto rotator 1111, which is in the off state, and thus rotates the light into s light, which is then recombined and sent to the drop port 1117. The beamsplitter 1109 will deflect the s light to beamsplitter 1110, which deflects the s light to rotator 1112. This rotator is in the on state, and thus does not rotate the light. The s light is then recombined and sent to the out port 1118. Thus, a portion of the In signal is sent to both the out port and the drop port. The portions of the signals being sent to the port is determined by the voltage being applied to the rotator 1107. To control the voltage, this switch 1100 would include the partially reflective mirror, the detector, and the control electronics of FIGURE 9. Note that the add signal could be similarly controlled, such that the add signal is dropped and continued. Note that the arrangement of FIGURE 1 IC also allows for power regulation of the signal being sent to the output port, as a portion of the signal can be shunted to the drop port. The signal being sent to the drop port can also be regulated, as a portion of the signal can be shunted to the out port. Further note that varying the voltage to the rotators 1111, 1112 would allow the signals being sent to the drop port and the out port to be regulated. The rotator 1111, 1112 can introduce both p and s polarizations into each branch of their respective signals that are being sent to birefringent elements 1115, 1116. Normally, the vertical branch 1119 passes through the elementl 115, and thus the output collection point 1121 is located along this path. The horizontal branch 1120 is deflected into the path of the vertical branch 1119 for collection. However, if the vertical branch 1119 has been changed to include a horizontal component, then this component is deflected out of the element and away from the collection point 1121. Similarly, if the horizontal branch 1120 has been changed to include a vertical component, then this component will pass through the element and away from the collection point 1121. This description also applies to element 1116. Thus, the rotators 1111,1112 can be used to individually control the amount of the light reaching the drop port and the out port. The above disclosure sets forth a number of embodiments of the present invention. Other arrangements or embodiments, not precisely set forth, could be practiced under the teachings of the present invention and as set forth in the following claims. 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.

Claims: WHAT IS CLAIMED IS: 1. An optic switch comprising: a first input for accepting at least one optic carrier; a first output for selectively delivering at least one optic carrier; means for sensing certain characteristics of optic carriers prior to said optic carriers being communicated to said first output; and means for selectively adjusting certain characteristics of said carriers delivered to said output in accordance with sensed ones of said certain characteristics. 2. The switch in claim 1 wherein said optic carrier is selectively delivered to said first output from said first input. 3. The switch in claim 2 wherein said selectively adjusting means includes means for controlling the polarization of selected ones of said optic carriers. 4. The switch in claim 1 wherein said optic switch further includes: a second output for selectively delivering at least one optic carrier; and means for selectively communicating to said second output at least one optic carrier accepted from said input. 5. The switch in claim 4 wherein said last-mentioned selectively communicating means further includes means for at least partially directing at least one optic carrier from said first output to said second output. 6. The switch in claim 5 wherein said partially directing means includes means for delivering said optic carrier exclusively to said first output in the event of a switch power failure. 7. The switch in claim 4 further including: means for sensing certain characteristics of optic carriers prior to said optic carriers being communicated to said second output; and means for selectively adjusting certain characteristics of said carriers delivered to said second output in accordance with sensed ones of said certain characteristics. 8. The switch in claim 4 further including: a second input for accepting at least one optic carrier; and means for selectively communicating accepted ones of said optic carriers from said second input. 9. The switch in claim 8 wherein said last-mentioned selectively communicating means is operative only when said accepted ones of said optic carriers from said first input are communicated exclusively to said second output. 10. The switch in claim 8 wherein said last-mentioned selectively communicating means includes means for controlling the polarization of selected ones of said optic carriers. 11. The switch in claim 8 wherein said optic switch includes: means for selectively delivering an optic carrier to said first output from said first input, and wherein said last-mentioned selectively communicating means and said selectively delivering means are a unified device. 12. The switch in claim 11 further including a polarized beamsplitter that receives at least one input light beam and outputs at least one output light beam, said polarized beamsplitter comprising: a first polarized beamsplitting surface; a second polarized beamsplitting surface that is aligned parallel to said first polarized beamsplitting surface; and a first input surface oblique to said first polarized beamsplitting surface that receives at least one input light beam; said first input light beam incident on said first polarized beamsplitting surface at a point that is adjacent to the center point of said first polarized beamsplitting surface. 13. The switch in claim 1 wherein said sensing means includes a control circuit whose operation is based on sensing a percentage of the optic material. 14. The switch in claim 13 wherein said control circuit provides signals to said selecting adjusting means to control the optic magnitude at least one selected point within said switch. 15. The switch in claim 13 wherein said optic magnitude control includes controlling the phase rotation of the optic carrier. 16. The switch in claim 1 wherein said optic switch includes: means for accepting a selected one of a plurality of optic carriers. 17. A method of switching signals through an optic switch, said method comprising the steps of: accepting at least one optic carrier; selectively delivering to a first output at least one optic carrier; sensing certain characteristics of said at least one optic carrier prior to said optic carrier being delivered to said first output; and selectively adjusting certain characteristics of said one optic carrier being delivered to said output in accordance with sensed ones of said certain characteristics. 18. The method of claim 16 wherein said selectively adjusting step includes the step of: controlling the polarization of said selected optic carrier. 19. The method of claim 16 further includes the step of: selectively delivering at least one optic carrier to a second output. 20. The method of claim 18 wherein said last-mentioned step includes the step of: partially directing at least one optic carrier from said first output to said second output. 21. The method of claim 18 further including the steps of: sensing certain characteristics of said optic carrier prior to said optic carrier being delivered to said second output; and selectively adjusting certain characteristics of said carrier delivered to said second output in accordance with sensed ones of said certain characteristics. 22. The method of claim 18 further including the step of: accepting an optic carrier from a second input; and delivering said accepted optic carrier from said second input to said first output. 23. The method of claim 21 wherein said last-mentioned step is further operative only when said accepted optic carrier from said first input is delivered exclusively to said second output. 24. The method of claim 22 wherein said last-mentioned step is further operative for controlling the polarization of selected ones of said optic carriers. 25. An optic switch comprising: a first input for accepting an optic carrier for selective delivery to a first or second output; means for sensing certain characteristics of said accepted optic carrier prior to said optic carriers being delivered to either said first or second output; and means for selectively adjusting certain characteristics of said carrier delivered to either of said outputs in accordance with sensed ones of said certain characteristics. 26. The method of claim 24 wherein said selective delivery means includes: means for directing at least a portion of said accepted optic carrier to each of said first and second outputs. 27. The method of claim 24 further including: a second input for accepting an optic carrier for selective delivery to said first output when said optic carrier from said first input is exclusively directed to said second output. 28. The method of claim 26 wherein said last-mentioned selective delivery means includes means for controlling the polarization of said optic carriers from said first and second inputs. 29. The method of claim 27 wherein said last-mentioned means is a unified device for handling said optic carriers from said first and second inputs. 30. The method of claim 27 wherein said last-mentioned means includes a device having dual beam rotations thereat. 31. A regulating optical add/drop switch comprising: (a) a primary input port receiving an optical signal beam; (b) a secondary input port receiving an optical signal beam; (c) a primary output port; (d) a secondary output port; (e) an electronic circuit containing switching logic circuits and a closed-loop electronic regulator that individually controls the optical power levels at the two output ports, each at a different predetermined level; (f) at the primary input port, a collimator illuminating a beam deflector element of birefringent material that spatially separates said input beam into two orthogonally polarized beams; (g) a half-wave plate of birefringent material rotating the polarization of one of the beams by 90° to produce two like-polarized beams; (h) a polarization modulator controlling the polarization of both of said like- polarized beams to an extent determined by a control voltage from; (i) an electro-optical control circuit operating as a closed-loop regulator wherein; (i) a proportional optical coupler at one or both of the output ports delivers a sample of the optical output power to a photo diode detector; (ii) the light signal is converted to an electrical signal, processed, and compared to the appropriate set point signal(s); (iii) the results of this comparison are used to determine the amount of excitation voltage applied to the polarization modulator; (j) a polarization beamseparator containing a polarization-selective interface which; (i) is essentially transparent to light of one polarization, in this case horizontal, passing it undeflected toward the primary output port; (ii) does not pass light of the opposite polarization, but instead reflects at a specific angle, in this case 90°, toward a second polarization beam deflector that again reflects said beam toward the secondary output port; (k) in the optical path to the primary output port a polarization modulator operating under the control of the closed-loop regulator and switching logic circuits previously summarized such that; (i) the polarization of the incoming beams may be rotated by 90° to result in two beams of vertical polarization (ii) the polarization of the incoming beams may be rotated by zero degrees (unchanged); (iii) the polarization of the incoming beams may be rotated by an amount either somewhat greater than 0° or somewhat less than 90° but not an intermediate value such as 45°; (I) a half-wave plate that rotates the polarity of one of the beams by 90°; (m) a beamdisplacer of birefringent material that; (i) combines any horizontally polarized light from said half-wave plate with any vertically polarized light from said polarization modulator; (ii) directs any vertically polarized light from said half-wave plate, and any horizontally polarized light from said polarization modulator toward dissipative surfaces away from the optical path; (n) a collimator that launches the combined beam into an optical coupler providing a feedback sample to the control circuit previously summarized and hence to the primary output port, (i.e., "through-mode" operation). 32. The regulating optical add/drop switch of claim 30 wherein said beam directed toward the secondary output port passes along an optical path comprising; (a) a polarization modulator operating under the control of the closed-loop regulator and switching logic circuits previously summarized such that; (i) the polarization of the incoming beams may be rotated by 90° to result in two beams of horizontal polarization (ii) the polarization of the incoming beams may be rotated by zero degrees (unchanged); (iii) the polarization of the incoming beams may be rotated by any amount between 0° and 90°. (b) a half-wave plate that rotates the polarity of one of the beams by 90°; (c) a beamdisplacer of birefringent material that; (i) combines any horizontally polarized light from said half-wave plate with any vertically polarized light from said polarization modulator; (ii) directs any vertically polarized light from said half-wave plate, and any horizontally polarized light from said polarization modulator toward dissipative surfaces away from said optical path; (d) a collimator that launches the combined beam from said beam deflector into an optical coupler that; (i) provides a small sample of the optical signal to said control circuit; (ii) passes the remaining optical signal to the secondary output port (i.e., "drop- mode" operation). 33. The regulating optical add/drop switch of claim 30 wherein said input beam from the primary input port passes through said collimator, beamdisplacer, and half-wave plate, whereupon; (a) said polarization modulator controls the polarization of said like-polarized beams to an extent determined by a said control voltage from said electro-optical control circuit such that; (b) the amount of polarization rotation is nominally 45°, resulting in roughly equal amounts of vertical and of horizontal components in the light moving from the polarization modulator to the polarization beamseparator such that; (c) the horizontally polarized component passes undeflected through polarization beamseparator and through said polarization modulator, half-wave plate, beamdisplacer, collimator, optical coupler and hence to the primary output port as stated in claim 1 ; (d) the vertically polarized component is reflected by said polarization-sensitive interface onto a second polarization beamseparator whereupon; (e) said vertical component passes through said polarization modulator, half-wave plate, beamdisplacer, collimator, optical coupler and hence to the secondary output port as stated in claim 2 (i.e., "drop-and-continue" operation). 34. The regulating optical add/drop switch of claim 31 , wherein said optical signal from the primary input port is routed with low loss to the secondary output port, and; (a) an optical signal enters the secondary input port through a collimator illuminating a beam deflector element of birefringent material that spatially separates said input beam into two orthogonally polarized beams; (b) a half-wave plate of birefringent material rotating the polarization of one of the beams by 90° to produce two like-polarized beams; (c) a polarization modulator controlling the polarization of both of said like- polarized beams to an extent determined by a control voltage from said electro-optical control circuit such that (i) the vertical polarization of the two beams from said half-wave plate and said beamseparator is not changed, or is changed by only a small amount; (d) a polarization beamseparator containing a polarization-selective interface which; (i) is essentially transparent to light of one polarization, in this case horizontal, passing it undeflected toward a dissipative surface; (ii) reflects light of the opposite polarization, in this case vertical, toward a second polarization beamdeflector that again reflects said beam toward the primary output port; (e) in the optical path to the primary output port a polarization modulator operating under the control of the closed-loop regulator and switching logic circuits previously summarized such that; (i) the polarization of the incoming beams may be rotated by 90° to result in two beams of vertical polarization (ii) the polarization of the incoming beams may be rotated by zero degrees (unchanged); (iii) the polarization of the incoming beams may be rotated by an amount either somewhat greater than 0° or somewhat less than 90° but not an intermediate value such as 45°; (f) a half-wave plate that rotates the polarity of one of the beams by 90°; (g) a beamdisplacer of birefringent material that; (i) combines any horizontally polarized light from said 10 half- wave plate with any vertically polarized light from said polarization modulator; (ii) directs any vertically polarized light from said half-wave plate, and any horizontally polarized light from said polarization modulator toward dissipative surfaces away from the optical path; (h) a collimator that launches the combined beam into an optical coupler providing a feedback sample to the control circuit previously summarized and hence to the primary output port, (i.e., "add/drop" operation). 35. The regulating optical add/drop switch of claim 30 wherein during loss of electrical power an optical signal entering the primary input port is passed with low attenuation to the primary output port. 36. The regulating optical add/drop switch of claim 30 wherein said polarization modulators use liquid-crystal material. 37. The regulating optical add/drop switch of claim 30 wherein said polarization modulators use PTTP liquid-crystal material. 38. The regulating optical add/drop switch of claim 30 wherein said controller prevents the optical power output at the primary output port from exceeding a predetermined level even when input power is excessive. 39. The regulating optical add/drop switch of claim 30 wherein said controller maintains the optical power output at the primary output port at a predetermined level regardless of input variations above a minimum threshold. 40. The regulating optical add/drop switch of claim 30 wherein said controller prevents the optical power output at the secondary output port from exceeding a predetermined level even when input power is excessive. 41. The regulating optical add/drop switch of claim 30 wherein said controller prevents the optical power output at the secondary output port from exceeding a predetermined level regardless of input variations above a minimum threshold. 42. The regulating optical add/drop switch of claim 30 wherein said collimators are fitted with said interference filters to allow selective processing of individual carriers of a WDM or DWDM signal. 43. The wavelength-selective regulating optical add/drop switch of claim 41 wherein said switches are interconnected to achieve any desired complexity of optical add/drop multiplexing.

Inventors: DERKS MICHAEL, LIU JIAN-YU, WU KUANG-YI, YUAN SHIFU, DERKS, MICHAEL, LIU, JIAN-YU, WU, KUANG-YI, YUAN, SHIFU
Applicants: CHORUM TECHNOLOGIES INC, CHORUM TECHNOLOGIES, INC.
Application year: 2000
Main classification: G02B26
IPC codes: G02B6, H04J14, H04Q11