WO2000076252A1

WO2000076252A1 - Optical add/drop wavelength switch using a high extinction ratio polarization beamsplitter

Info

Publication number: WO2000076252A1
Application number: PCT/US2000/015432
Authority: WO
Inventors: Jian-Yu Liu; Shifu Yuan
Original assignee: Chorum Technologies Lp
Priority date: 1999-06-04
Filing date: 2000-06-02
Publication date: 2000-12-14

Abstract

An optical add/drop wavelength switch is controllably changed from a bridge state, in which output is identical to input, e.g. a Wavelength Division Multiplexed (WDM) input, and an add/drop state, in which a signal input to an add port is substituted for a particular wavelength subrange of the WDM input, other wavelengths of the WDM input being unchanged. In one embodiment, the wavelength subrange of the WDM signal is given a polarization different from other wavelengths of the WDM, such as by using a stacked waveplate or other optical filter or polarization discriminator. The differently-polarized wavelengths can be spatially separated, e.g. by a birefringent element or a polarization beamsplitter, preferably in a bit-controlled fashion, such as by using a liquid crystal or other polarization controller. Polarization controllers and discriminators can be used similarly to selectably align or combine the add signal with the portion of the WDM signal outside the subrange. The add/drop wavelength switch can be used, e.g. in an optical token ring network and/or to make-up an optical crossbar for exchanging arbitrarily designatable channels, e.g. among a plurality of multi-channel optical fibers.

Description

OPTICAL ADD/DROP WAVELENGTH SWITCH USING A HIGH EXTINCTION RATIO POLARIZATION BEAMSPLITTER

RELATED APPLICATIONS

The present application is a continuation-in-part of the Applicants' co-pending U.S. Patent Application Ser. No. 09/273,920, entitled "OPTICAL WAVELENGTH ADD/DROP MULTIPLEXER," filed on March 22, 1999, which is hereby incorporated herein by reference, and is related to co-pending applications Attorney Docket Number 55872-P048US-992837, entitled "HIGH EXTINCTION RATIO POLARIZATION BEAMSPLITTER," which is hereby incorporated herein by reference; 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; and Attorney Docket Number 55872-P043CP1-993120, entitled "FIBER OPTIC SMART SWITCH," 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

This application relates in general to optical communication systems, and in specific to an add/drop wavelength switch for wavelength division multiplex (WDM) optical communications.

BACKGROUND

Optical wavelength division multiplexing (WDM) has gradually become the standard backbone network for fiber optic communication systems. WDM systems employ signals consisting of a number of different optical wavelengths, known as carrier signals or channels, to transmit information on optical fibers. Each carrier signal is modulated by one or more information signals. As a result, a significant number of information signals may be transmitted over a single optical fiber using WDM technology.

Despite the substantially higher fiber bandwidth utilization provided by WDM technology, a number of serious problems must be overcome, for example, multiplexing, demultiplexing, and routing optical signals, if these systems are to become commercially viable. The addition of the wavelength domain increases the complexity for network management because processing now involves both filtering and routing. Multiplexing involves the process of combining multiple channels (each defined by its own frequency spectrum) into a single WDM signal. Demultiplexing is the opposite process in which a single WDM signal is decomposed into individual channels. The individual channels are spatially separated and coupled to specific output ports. Routing differs from demultiplexing in that a router spatially separates the input optical channels into output ports and permutes these channels according to control signals to a desired coupling between an input channel and an output port. Currently, filters based on fiber Bragg gratings (FBG) are the most popular add/drop wavelength filters used in WDM networks for the add/drop operation. Another approach in the add/drop operation is the use of an array-waveguide-grating filter. In both cases, the add/drop operation is always on, which is not a very effective way to utilize the optical channel. Although another 2x2 optical switch can be integrated with the FBG such that add/drop operation can be controlled by a switching gate, this is fundamentally cumbersome and ineffective. Furthermore, optical switches available in the market are mostly mechanical optical switches that are not suitable in network wavelength routing because of their short lifetime (i.e., a moving motor wears out in time) and high power consumption. Although other types of optical switches are available, such as thermal optical switches, crosstalk is generally too high to permit large scale systems. SUMMARY OF THE INVENTION

The present invention combines the characteristics of add/drop operation of a filter and the switching capability of an optical switch. The add/drop wavelength switch has two input ports for the incoming WDM signal and the add signal, and two output ports for the WDM pass-through signal and the drop signal. The wavelength switch is operated in two modes, referred to as the bridge state and add/drop state, respectively. In the bridge state, the incoming WDM signal continuously flows through the optical node without being disturbed. When controlled to do so by either the local optical node or the WDM network, the wavelength switch changes to the add/drop state in which a pre-defined optical channel is dropped from the WDM signal and the add signal is substituted into the WDM signal. The add signal can be a single channel or multiple channels. A unique feature of this add/drop wavelength switch is that the pass-through channels are not disturbed by the transition during switching between states. This assures the uninterrupted flow of WDM signals through the network. Based on this feature, an optical token ring can be realized in which multiple add/drop wavelength switches are cascaded. An array of these add/drop switches can be used to implement a wavelength crossbar that enables optical channels to be arbitrarily exchanged between multiple WDM networks.

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 DRAWING

The present invention can be more readily understood in conjunction with the accompanying drawings, in which:

FIGURES 1 A to IC depict a high extinction ratio polarization beamsplitter for use as an add/drop switch;

FIGURES 2 A to 2C depict the operations of the switch of FIGURES 1 A to IC;

FIGURE 3 depicts a system using the switch of FIGURES 1A to IC;

FIGURES 4 A to 4 B depicts a 4 x4 arrangement of the switch of FIGURES 1A to IC;

FIGURE 5A and 5B depict an arbitrary add/drop switch using the switch modules of FIGURES 4A to 4B; and

FIGURE 6 depicts a wavelength management system using switch module of FIGURES 4A to 4B.

DETAILED DESCRIPTION

As used herein, the term "channel" refers to a particular range of frequencies or wavelengths that define a unique information signal. Each channel is ideally evenly spaced from adjacent channels, although this is not necessary. Uneven spacing may result in some complexity in design, but, as will be seen, the present invention can be adapted to such a channel system. This flexibility is important in that the channel placement is driven largely by the technical capabilities of transmitters (i.e., laser diodes) and detectors, so flexibility is of significant importance.

FIGURES 1A to IC depicts a polarization beamsplitter (PBS) for use WDM optical systems, and in particular to replace the birefringent based add/drop switch, shown in

FIGURES 1(A) and 1(B) of "OPTICAL WAVELENGTH ADD/DROP MULTIPLEXER" application referenced above, and used in the systems described therein. This PBS is further described in Attorney Docket Number 55872-P048US-992837, entitled "HIGH EXTINCTION RATIO POLARIZATION BEAMSPLITTER," which is hereby incorporated by reference. The PBS operates by splitting an incoming beam into its polarization components, specifically the horizontal component (which is also referred to as the p component and sometimes represented as "|") and vertical component (which is also referred to as the s component and sometimes represented as "•").

As shown in FIGURE 1 A, this PBS includes two beamsplitting (BS) surfaces 701 and 706. These BS surfaces are coated with multi-layer dielectric films, to form the polarization

BS surface. The surface quality of these surfaces should exceed 40:20. These surfaces would have extinction ratios of Tp/Ts > 40 dB and Rs/Rp > 20 dB. The PBS 700 further includes four input/output surfaces 702, 703, 704, 705. These surfaces should have an anti-reflective (AR) coating to minimize light loss from reflection during input into and output from the PBS 700. The surface quality of these surfaces should exceed 40:20. This PBS 700 is constructed from three sub-elements. The BS surface 701 could be located on either of its adjacent sub- elements. The BS surface 706 could be located on either of its adjacent sub-elements. The three sub-elements would be attached together with a high quality optical adhesive.

FIGURE IB depicts the passage of p light through the PBS 700 from two p input signals p 707 and p₂ 708. Input p, 707 enters the PBS 700 through input surface 702 and is incident onto BS surface 701. Note that the point of incidence is off of the center of the BS surface 701. Most of the p light passes through the BS surface, but a noise portion 709 is deflected by the BS surface 701. This noise portion 709 is incident onto output surface 703, however it is off-axis with respect to the collection point for the p₂ signal, and thus will not be collected and is removed from the PBS 700. This portion of the surface 703 could also be ground and/or coated with an absorption material to block the noise portion 709. Thus, no noise should leak through to form crosstalk noise with respect to the second input signal p₂. After passing through BS 701, most of the p, input light is incident onto the output surface704 and exits the PBS 700 as p, signal 710. The second p input signal 708 enters the PBS 700 through input surface 705 and is incident onto BS surface 701. Note that the point of incidence is off of the center of the BS surface 701. Most of the p light passes through the BS surface and exits the PBS 700 through output surface 703 as p₂ signal 713, but a noise portion 711 is deflected by the BS surface 701. This noise portion 711 is incident onto BS surface 706, where most of the light passes through the surface and falls onto surface 704, but is off axis with the collection point of the p_! signal

710. A portion of this light 711 is deflected by BS surface 706 and is again incident onto BS surface 701. Most of the noise portion passes through the BS surface 701 and exits the beamsplitter similar to noise 709. Some of noise portion is deflected by BS surface 701 and exits the PBS 700 as leakage noise p_2L 712 along with the p, signal 710 through output surface 704. This noise portion p_2L 712 is crosstalk noise with respect to the first input signal p₂, as this noise is a portion of the second input signal p₂. Note that the noise portion p₂ 712 has resulted from the passage of light through three BS surfaces (as depicted here, through the surface 701 twice and surface 706 once). Since the Rs/Rp extinction ratio is 20 dB per BS surface, p_2L 712 has 60 dB. Thus, the PBS 700 results in a high extinction ratio PBS as the element extinction ratio for Rs/Rp > 60 dB.

FIGURE IC depicts the passage of s light through the PBS 700 from a single s input signals s, 714. Since only one signal is passing through the PBS 700, then no crosstalk can occur.

The use of a beamsplitter allows for a different arrangement of the unitary add/drop switch. This arrangement 800 is shown in FIGURE 2A. Thus, for add/drop switching to occur, p light is incident onto the beamsplitter, as shown in FIGURE 2B. This causes the input signal to be routed to the drop path 802, as the p light passes through the PBS 700. Similarly, the new signal to be added to the system, i.e. add signal 803 is routed to the output path 804, as the p light passes through the PBS 700. Note that while the light from the two input paths is passing through the PBS 700, the input signal 801 is switched to the drop path 802. This mode is referred to as the add/drop mode or state.

The other mode of the add/drop switch is the bypass or bridge mode, wherein the input signal 801 is routed to the output path 804. This is accomplished by causing s light to be incident onto the beamsplitter. As shown in FIGURE 2C, the s light is deflected by the PBS 700 to be routed to the output path 804. Since no signal is to be added, then no add signal 803 is shown. However, if such a signal was sent to the PBS, it will not be received by the drop port 802 because it is off the light path between 801 and 802.

Note that by using a polarization rotator, e.g. liquid crystal rotator, to control the input signal the add/drop switch can have a drop and continue operation. For example, if the rotator changes the input signal to half p and half s, then half of the input signal will be routed to the drop port, and half of the input signal will be routed to the output port. This operation allows for the input signal to be split, and thus shared between two network components. The operation also allows for the regulation of the output signal by shunting a portion of the input signal to the drop port. This prevents the output signal from this switch to be greater than output signals from other switches. The add signal can be similarly controlled. Note that the output signal can also be controlled in such a manner.

As shown in FIGURE 4B, the input signal is split into two components during processing, and recombined by a birefringent element 1007 prior to outputting. A rotator placed prior to the birefringent element can introduce both p and s polarizations into each branch of the signal. Normally, the vertical branch passes through the element, and thus the output collection point is located along this path. The horizontal branch is deflected into the path of the vertical branch for collection. However, if the vertical branch has been changed to include a horizontal component, then this component is deflected out of the element and away from the collection point. Similarly, if the horizontal branch has been changed to include a vertical component, then this component will pass through the element and away from the collection point. Thus, this rotator will provide for regulation of the output signal. The drop signal can be similarly controlled. These aspects of the add/drop switch are explained in more detail in "FIBER OPTIC SMART SWITCH," Attorney Docket Number 55872-P043CP1- 993120, which is incorporated herein by reference.

FIGURE 3 depicts a WDM system 900 using the PBS 700. The different signals on the input fiber 901 are encoded by wavelength, e.g. λl, λ2, λ3, λ4... λn. These signals are demultiplexed by DEMUX 902. Each wavelength signal is then feed into a respective PBS 700, e.g. 700-1..J00-n via a respective input path 801, e.g. PBS 700-1 is connected to INPUT 801-1. Each PBS also coupled to respective add and drop paths, e.g. PBS 700-1 is coupled to

ADDl and DROPl. The output path of each respective PBS is coupled to a multiplexer MUX 903 which encodes the signals by wavelength onto output fiber 904. Thus, each particular input signal, e.g. λl, can either be passed through to the output path, or be dropped and replaced with a new ADD signal, which is then delivered to the output path. Note that a number of the PBSs 700 can be arranged together to form a module. By virtue of their operation, the module would provide interconnection capability or cross connect in addition to add/drop operations.

FIGURE 4A depicts a 4 x 4 array 1000 of PBSs 700. In front of each input path to each respective PBS is a polarization controller (not shown) which controls the polarization of the light entering the respective PBS, i.e. the controller could change the light such that the light incident onto the PBS is p light or s light. In the add/drop mode, where the input goes to drop, and the add goes to output, each of the add signals, ABCD, would go to a respective output paths, 5678, similarly each input signals, EFGH, would go to a respective drop path 1234. The add/drop mode is accomplished by setting the various rotators to emit only p light. In the bypass mode, each input signal, EFGH, could be directed to any one of the outputs paths 5678.

Thus, inputs EFGH could be outputted to 5768, 5867, etc. The bypass mode is accomplished by setting particular ones of the rotators to s light.

For example, to have the E input switched to output 6, the input rotator for unit 1001 would be set to provide s light to the unit. The other units in the E input column would be set to provide p light such that the light would pass through the PBSs, until encountering unit 1001. The output rotator from 1001 would be set to provide p light such that the light passes through the units of the output 6 row, and consequently be delivered to output 6. Thus, the various rotators are used to control the polarization of the light that is incident onto the various PBSs of the switch module, and thus control their connection. Note that various combinations of the switch and pass through states can be achieved.

For example, input E could be routed to drop, inputs FGH could be routed to outputs 567, respectively, and add D could be routed to output 8. As general rules, input E can be routed to any of 15678, input F can be routed to any of 25678, input G can be routed to any of 35678, input H can be routed to any of 45678, while input A can be routed to 5, input B can be routed to 6, input C can be routed to 7, and input D can be routed to 8. Note that the 4 x 4 arrangement is by way of example only, as the PBS can be arranged in a N x M array, see "N x M DIGITALLY PROGRAMMABLE OPTICAL ROUTING SWITCH USING HIGH EXTINCTION RATIO POLARIZATION BEAMSPLITTER," Attorney Docket Number 55872-P046CP1CP1-993118, which is incorporated herein by reference. The switch described above is actually more than 4 x 4, as defined by the conventional definition. It has a total of 16 ports, 4 input and 4 output ports are cross connected. The other set of 4/4 input/output ports are used for add/drop operation. This feature is not available in the prior art.

FIGURE 4B depicts a block diagram for the 4 x 4 switch of FIGURE 4A. The module 1000 has two sets of inputs, namely the input signals 1002 (EFGH) and the add signal 1003 (ABCD), and two sets of outputs, namely the drop signal 1004 (1234) and output signal 1005

(5678). Each input includes a collimator 1006 to collimate the input light, a birefringent separator 1007 to separate the light into its p and s components and to laterally displace the p and s components. The first birefringent element 1007 is made of a material that allows the vertically polarized portion of the optical signal to pass through without changing course because they are ordinary waves in the birefringent element 1007. In contrast, horizontally polarized waves are redirected at an angle because of the birefringent walk-off effect. The angle of redirection is a well-known function of the particular materials chosen. Examples of materials suitable for construction of the birefringent elements used in the preferred embodiments include calcite, rutile, lithium niobate, YVO4 based crystals, and the like. Each input also includes a halfwave plate 1008 which changes one of the polarization components into the other component (as shown, the plate changes the p component into s light, however it could be placed in front of the s component), and thus all of the light incident onto the rotator is of the same polarization type.

Each output includes a reverse of the input elements. Each PBS 700 is surrounded by four polarization controllers or rotators 1009. The rotators 1009 are used to control the polarization of the light received by the PBSs. For example, if the light incident onto the PBS is made to be p light, the light will pass through the PBS, and if the light is made to be s light, the light will be deflected by the PBS. The switchable polarization rotators 1009 can be made of one or more types of known elements including parallel aligned liquid crystal rotators, twisted nematic liquid crystal rotators, ferro electric liquid crystal rotators, pi-cell liquid crystal rotators, magneto-optic based Faraday rotators, acousto-optic and electro-optic polarization rotators. Commercially available rotators using liquid crystal based technology are preferred.

FIGURE 5 A depicts an arbitrary drop/add switch 1100. This switch is comprised of two 4 x 4 modules of FIGURE 4B, note that only one set of input/output elements 1006, 1007, 1008 are needed. This arrangement permits any input signal ABCD to be dropped to any drop path 1234. Similarly any add signal EFGH can be delivered to any output path 5678. Also the input signals ABCD can be passed through to their respective output paths 5678.

FIGURE 5B depicts the arbitrary drop/add switch of FIGURE 5 A with wavelength conversion. In addition to operations described in FIGURE 5 A, each input signal λl, λ2, λ3, λ4, can be routed to any of the detectors 1101, where each signal is converted into an electrical signal and processed by electronics 1102. The output electrical signal are then sent to respective lasers 1103 for retransmission as light. Each light output from the lasers can be routed to any of the output paths.

FIGURE 6 depicts a drop/add switch for wavelength management and restoration. Note that FIGURE 6 includes four fibers 1201, and four 4 x 4 modules 1203. Note that the number of fibers is by way of example only, as more fibers would merely require a scaled drop/add switch. Also note that the modules are shown as being only partially connected to DEMUXes and MUXes to simplify the figure. Each fiber carries different signals which are encoded by wavelength, e.g. λl, λ2, λ3, λ4. These signals are demultiplexed by DEMUX 1202. Each wavelength from each fiber is provided to a particular 4 x 4 module, e.g. λl from each of the four fibers is provided to module 1203. Within each module 1203, the operations are as described with respect to FIGURE 4A. Thus, particular signals can be dropped or added or re-routed to the output. Note that the diagonal slash through each module indicates the orientation of the PBSs within the module. For a further discussion on multiple wavelength management, see related application "MULTI-WAVELENGTH CROSS CONNECT OPTICAL NETWORK," Application Serial Number 08/907,551 , which is incorporated herein by reference.

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. Apparatus for an optical add/drop switch comprising: a first input port which receives at least a first optical input signal; a second input port which receives at least a first optical add signal; a first output port which receives at least a first optical output signal; a first birefringent member which receives one of said at least a first optical input signal and said at least a first optical add signal and separates such received signal into first and second polarization components, and wherein said first birefringent member spatially displaces said first and second polarization components with respect to each other; a first polarization rotator that changes polarization of one of said first and second polarization components to the polarization of the other one of said first and second polarization components; and a routing member which directs said at least a first optical add signal to said first output port if said first and second polarization components have one polarization and directs said at least a first optical input signal to said first output port if said first and second polarization components have another polarization.

2. The apparatus of claim 1, further comprising: a second output port which receives at least a first optical drop signal.

3. The apparatus of claim 2, wherein said routing member directs said at least a first optical input signal to said second output port if said first and second polarization components have said one polarization.

4. The apparatus of claim 1, further comprising: a polarization controller that controls the polarization of said at least a first optical input signal received by said first input port.

5. The apparatus of claim 4, wherein said polarization controller is selected from the group consisting of: parallel aligned liquid crystal rotator, twisted pneumatic liquid crystal rotator, ferro electric liquid crystal rotator, pi-cell liquid crystal rotator, magneto-optic based Faraday rotator, acousto-optic polarization rotator, and electro-optic polarization rotator.

6. The apparatus of claim 1, wherein said first output port comprises:

(a) a second polarization rotator that changes the polarization of said first and second polarization components so that said components are orthogonally polarized; and

(b) a second birefringent member that combines said first and second polarization components at said output port.

7. The apparatus of claim 1, wherein said first birefringent member is a material selected from the group consisting of: calcite, rutile, lithium niobate, YVO4 based crystals, and combinations thereof.

8. The apparatus of claim 1, wherein said first polarization component is vertical polarization and said second polarization component is horizontal polarization.

9. The apparatus of claim 8, wherein said first birefringent member allows a vertically polarized component to pass though without redirecting such component, and said first birefringent member redirects a horizontally polarized component.

10. The apparatus of claim 1, wherein said first polarization rotator is a halfwave plate.

11. The apparatus of claim 1 , wherein said routing member is a polarized beamsplitter.

12. The apparatus of claim 11 , wherein said polarized beamsplitter comprises: a first polarized beamsplitting surface; a second polarized beamsplitting surface that is aligned parallel to said first polarized beamsplitting surface; a first input surface oblique to said first polarized beamsplitting surface that receives a first input light beam; and said first input light beam incident on said first polarized beamsplitting surface at a point that is not the center point of said first polarized beamsplitting surface.

13. The apparatus of claim 12, wherein said polarized beamsplitter comprises: a second input surface oblique to said first polarized beamsplitting surface that receives a second input light beam; and said second input light beam incident on said first polarized beamsplitting surface at a point that is not the center of said first polarized beamsplitting surface.

14. The apparatus of claim 13, wherein said first input light beam and said second input light beam have a cross point that is not incident to said first polarized beamsplitting surface and that is not incident to said second beamsplitting surface.

15. An optical switch having an add/drop state and a bypass state, comprising: a first input port that receives at least a first optical input signal; a second input port that receives at least a first optical add signal; a first output port that receives at least a first optical output signal; a second output port that receives at least a first drop signal; a first birefringent member which receives one of said at least a first optical input signal and said at least a first optical add signal and separates such received signal into first and second polarization components, and wherein said first birefringent member spatially displaces said first and second polarization components with respect to each other; a first halfwave plate that changes polarization of one of said first and second polarization components to the polarization of the other one of said first and second polarization components; and a polarized beamsplitter which directs said one of said at least a first optical input signal and said at least a first optical add signal to said first output port if said first and second polarization components have one polarization, and directs said one of said at least a first optical input signal and said at least a first optical add signal to said second output port if said first and second polarization components have another polarization.

16. The optical switch of claim 15, further comprising: a polarization controller that controls the polarization of said at least a first optical input signal received by said first input port.

17. The optical switch of claim 15, wherein said polarization controller is selected from the group consisting of: parallel aligned liquid crystal rotator, twisted pneumatic liquid crystal rotator, ferro electric liquid crystal rotator, pi-cell liquid crystal rotator, magneto-optic based Faraday rotator, acousto-optic polarization rotator, and electro-optic polarization rotator.

18. The optical switch of claim 15, wherein said first output port comprises:

(a) a second halfwave plate that changes the polarization of said first and second polarization components so that said components are orthogonally polarized; and

19. The optical switch of claim 15, wherein said first birefringent member is a material selected from the group consisting of: calcite, rutile, lithium niobate, YVO4 based crystals, and combinations thereof.

20. The optical switch of claim 15, wherein said first polarization component is vertical polarization and said second polarization component is horizontal polarization.

21. The optical switch of claim 20, wherein said first birefringent member allows a vertically polarized component to pass though without redirecting such component, and said first birefringent member redirects a horizontally polarized component.

22. The optical switch of claim 15, wherein said polarized beamsplitter comprises: a first polarized beamsplitting surface; a second polarized beamsplitting surface that is aligned parallel to said first polarized beamsplitting surface; a first input surface oblique to said first polarized beamsplitting surface that receives a first input light beam; and said first input light beam incident on said first polarized beamsplitting surface at a point that is not the center point of said first polarized beamsplitting surface.

23. The optical switch of claim 22, wherein said polarized beamsplitter comprises: a second input surface oblique to said first polarized beamsplitting surface that receives a second input light beam; and said second input light beam incident on said first polarized beamsplitting surface at a point that is not the center of said first polarized beamsplitting surface.

24. The optical switch of claim 23, wherein said first input light beam and said second input light beam have a cross point that is not incident to said first polarized beamsplitting surface and that is not incident to said second beamsplitting surface.

25. An optical add/drop switch that is controllably changeable from a bypass state, wherein output is identical to input, to an add/drop state, wherein a signal input to an add port is substituted for a particular input, said optical add/drop wavelength switch comprising: a first input port that receives at least a first optical input signal; a second input port that receives at least a first optical add signal; a first output port that receives at least a first optical output signal; a second output port that receives at least a first drop signal; a first birefringent member which receives one of said at least a first optical input signal and said at least a first optical add signal and separates such received signal into first and second polarization components, and wherein said first birefringent member spatially displaces said first and second polarization components with respect to each other; a first halfwave plate that changes polarization of one of said first and second polarization components to the polarization of the other one of said first and second polarization components; a polarized beamsplitter that directs said one of said at least a first optical input signal and said at least a first optical add signal to said first output port if said first and second polarization components have one polarization, and directs said one of said at least a first optical input signal and said at least a first optical add signal to said second output port if said first and second polarization components have another polarization; and said first output port comprises

26. The optical add/drop switch of claim 25, further comprising: a polarization controller that controls the polarization of said at least a first optical input signal received by said first input port.

27. The optical add/drop switch of claim 26, wherein said polarization controller is selected from the group consisting of: parallel aligned liquid crystal rotator, twisted pneumatic liquid crystal rotator, ferro electric liquid crystal rotator, pi-cell liquid crystal rotator, magneto-optic based Faraday rotator, acousto-optic polarization rotator, and electro-optic polarization rotator.

28. The optical add/drop switch of claim 25, wherein said first birefringent member is a material selected from the group consisting of: calcite, rutile, lithium niobate, YVO4 based crystals, and combinations thereof.

29. The optical add/drop switch of claim 25, wherein said polarized beamsplitter comprises: a first polarized beamsplitting surface; a second polarized beamsplitting surface that is aligned parallel to said first polarized beamsplitting surface; a first input surface oblique to said first polarized beamsplitting surface that receives a first input light beam; and said first input light beam incident on said first polarized beamsplitting surface at a point that is not the center point of said first polarized beamsplitting surface.

30. The optical add/drop switch of claim 29, wherein said polarized beamsplitter comprises: a second input surface oblique to said first polarized beamsplitting surface that receives a second input light beam; and said second input light beam incident on said first polarized beamsplitting surface at a point that is not the center of said first polarized beamsplitting surface.

31. The optical add/drop switch of claim 30, wherein said first input light beam and said second input light beam have a cross point that is not incident to said first polarized beamsplitting surface and that is not incident to said second beamsplitting surface.