MXPA99003970A - Programmable wavelength router - Google Patents

Abstract

A programmable wavelength router (1300) having a plurality of cascaded stages (100) where each stage (100) receives one or more optical signals (101) comprising a plurality of wavelength division multiplexed (WDM) channels. Each stage (100) divides the received optical signals (101) into divided optical signals (116, 117) comprising a subset of the channels and spatially positions the divided optical signals (116, 117) in response to a control signal applied to each stage (100). Preferably each stage (100) divides a received WDM signal (101) into two subsets (116, 117) that are either single channel or WDM signals (101). A final stage (300) outputs optical signals at desired locations. In this manner, 2N optical signals in a WDM signal (101) can be spatially separated and permuted using N control signals.

Description

WIRING LENGTH OF PROGRAMMABLE WAVE BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates / in general, to communication systems, and, more particularly, to a programmable wavelength encaeter for optical communication multiplexed by wavelength division (WDM). 2. Establishing the Problem Although optical fiber has a very wide transmission bandwidth of the order of 10-20 THz, the system data rates transmitted on the fiber are currently limited to the modulation speed of the electro-optical modulators for communications of a fiber. only channel using typical optical sources such as distributed feedback lasers tuned by wavelength. The information communication efficiency of a fiber optic transmission system can be increased by optical wavelength division multiplexing (WDM). WDM systems employ signals consisting of a number of optical signals of different lengths of REF .: 29983 wave, known as signals or carrier channels, to transmit the information on an optical fiber. Each carrier signal is modulated by one or more information signals. As a result, a significant number of information signals can be transmitted on a single optical fiber using WDM technology. Despite the use of the substantially larger fiber bandwidth provided by WDM technology, numerous serious problems must be overcome in order for those systems to become commercially available. For example, the multiplexing, demultiplexing and routing of optical signals. The addition of the wavelength domain increases the complexity for handling the interconnection because the processing now involves both filtering and routing. Multiplexing involves the process of combining multiple channels, each defined with its own frequency spectrum in a single WDM signal. Demultiplexing is an opposite process in which a single WDM signal is decomposed in the individual channels. The individual channels are spatially separated and coupled to specific output gates. The routing differs from the demultiplexing in that the router spatially separates the optical input channels in output gates and swapped those outgoing channels. according to the control signals to a desired coupling between the input channel and an output gate. A method prior to routing by wavelength has been to de-multiplex the WDM signal into a number of component signals using a prism or diffraction grating. The component signals are each coupled to a plurality of 2x2 optical switches which are usually implemented as optomechanical switches. Optionally a signal to be added to the WDM signal is also coupled to one of the 2x2 switches. An output of each of the 2x2 optical switches coupled to a retained output multiplexer which combines the signals retained, and which includes the aggregate signal, and couples them into an output gate of the retained signal. A second signal is coupled by each of the 2x2 optical switches to a multiplexer of the lowered signal. By appropriate configuration of the optical switches, a signal can be coupled to the output gate of the lowered signal, all remaining signals pass through the output gate of the retained signal. This structure is also known as optical down filter. The structure is complicated, depends on optomechanical switches, and tends to make interconnections difficult. A wavelength space switch of the "passive star" type has been used in some WDM networks, for example the LAMBDANET network and the RAINBOW network. This passive star network has the broadest capacity and control structure and this implementation is remarkably simple. Nevertheless, the loss of division of the transmission star can be very high when the number of users is large. Also, the wavelength space switches used are based on tunable filters of either the Fabry-Perot type or filters based on the acousto-optic devices, which typically have a narrow resonant peak or a small lateral lobe compression ratio. A third type of space switch selected per wavelength is shown in U.S. Patent No. 5,488,500 issued to Glance. The Glance filter provides the advantage of an arbitrary channel array but suffers from significant optical coupling losses due to the two arrays of leveling demultiplexers of the waveguide and the two couplers used in the structure. Another problem with the prior art method and with optical signal processing in general is the high crosstalk between channels. Crosstalk occurs when the optical energy of one channel causes a signal or noise to appear in another channel. Crosstalk must be reduced to a minimum to provide reliable communication. Also they Filters used in optical routing often depend on polarization. Polarization dependence usually produces greater crosstalk since the particular polarization orientation optical energy may leak between the channels or be difficult to orient especially so that it can be properly launched to a selected output gate. Similarly, the optical filters provide an imperfect pass band operation since they provide too much attenuation or compression of the signal in the side lobes of the pass band is not high enough. All these characteristics lead to imperfect or inefficient data communication using optical signals. What is needed is a routing structure that provides low crosstalk to eliminate unnecessary interference from other channels in a large network, a flat-bandband response in the optical spectrum of interest, so that the wavelength router can tolerate small variations in wavelength due to laser wavelength shifting, polarization insensitivity, and moderation of fast switching speed for network routing. Also, a router with low insertion loss is desirable so that the router has a minimal impact on the network and limits the need for optical amplifiers. 3. Solution of the Problem These and other problems of the prior art are solved by the digitally programmable wavelength router that can demultiplex any number of channels of a WDM signal and simultaneously spatially separate the channels and perform the wavelength routing. Using optical switching elements for conventional logic level signals provides faster switching and minimal power consumption during operation. By employing filters with distortion of the flat band, broad band, and signal attenuation limits, a desirable channel selectivity is provided at the same time. Routing with low crosstalk is achieved, reliable, with high immunity to the polarization of the incoming WDM signal or any of the channels in the incoming WDM signal. Using a scalable design, any number of channels can be placed in the WDM signal depending on the transmitter / detector technology and the available optical fiber.

BRIEF DESCRIPTION OF THE INVENTION Briefly stated, the present invention involves a programmable wavelength router that it has a plurality of cascade stages wherein each stage receives one or more optical signals comprising a plurality of channels multiplexed by wavelength division (WDM). Each stage divides the optical signals received into divided optical signals comprising a subset of the channels and spatial positions in the optical signals divided in response to a control signal applied to each stage. Preferably each stage divides a received WDM signal into two subsets that are either single-channel or WDM signals. A final stage sends multiplexed optical signals to the desired places. In this way, they can be spatially separated 2N optical signals in a WDM signal and be routed to 2N output lines using N control signals.

BRIEF DESCRIPTION OF THE DRAWINGS FIGURE 1 illustrates a block diagram of the functionality of the optical router in accordance with the present invention; FIGURE 2 and FIGURE 3 illustrate in simplified schematic form a portion of a router according to the present invention; FIGURE 4 illustrates a spectral wavelength versus energy diagram of a WDM signal; FIGURE 5 illustrates a spectral diagram of an intermediate signal resulting from the horizontally polarized input energy; FIGURE 6 illustrates a spectral diagram of an intermediate optical signal resulting from the vertically polarized input; Figures 7 to 10 illustrate diagrams -s. spectral of several intermediate signals polarized horizontally and vertically after filtration according to the present invention; FIGURE 11 and FIGURE 12 illustrate spectral diagrams of spatially separated output signals routed in accordance with the present invention; FIGURE 13 illustrates in block diagram form a multi-stage programmable host according to an embodiment of the present invention; FIGURE 14 illustrates spectral diagrams of the passband of each stage of the multi-stage filter shown in FIGURE 13; FIGURE 15 illustrates in detail a portion of the wavelength filter of FIGURE 2 and FIGURE 3 according to the present invention; and FIGURE 16A and FIGURE 16B illustrate a computer simulated pass band of a filter implementation of flat top according to the present invention.

DETAILED DESCRIPTION OF THE DRAWINGS 1. General View The preferred implementation of the present invention demultiplexes (i.e., spectrally separates) and routes (i.e., spatially swapped) an optical signal multiplexed by wavelength division (WDM). FIGURE 1 illustrates a block diagram of the functionality of the present invention. A WDM signal 101 comprises multiple channels, each channel having its own wavelength range or frequency. 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 placed uniformly separated from the adjacent channels, although this is not necessary. The non-uniform separation may result in some inefficiency or complexity in the design, but, as will be seen, the present invention can be adapted for such a channel system. This flexibility is important since channel placement is largely driven by the technical capabilities of the transmitters (ie, laser diodes) and detectors and in this way flexibility is of significant importance. It should be understood that a complete permutation routing of N channels would require no possible output permutations, which is not practical. As used herein, the term permutation includes the partial or incomplete permutation that is commonly used in the routing of signals. Desirably, each of the multiplexed input channels can be selectively routed to any of the available output lines and all of the input channels can be placed on some line. This requires that the router includes at least the same number of outputs as the number of channels in the input signal, unless some of the output signals remain multiplexed when they leave the router. The present invention is scalable, and thus supports a greater number of output lines than the number of input channels in the multiplexed input signal. In such cases, some of the output lines will not carry any signal that increases the flexibility of the routing, although it is a less efficient use of the physical components. Those and other equivalent variations of the specific examples described herein are considered equivalent to the wavelength router according to the present invention.

The WDM signal is fed to an input using conventional optical signal coupling techniques at lx2N routers 1300. Router 1300 receives N control signals C? -CN. In the particular example, N is 3, however, any number of control signals may be received by the router 1300 due to the highly scalable nature of the present invention. The router 1300 generates 2N unique output signals on the Pi-P2N output gates such as optical fibers or other suitable optical transmission means. The router 1300 serves to spatially separate each channel in the WDM signal 101. Each channel is programmably positioned on one of the output gates according to that selected by the configuration bits C? -CN. In a preferred embodiment, the configuration bits C? -CN are conventional TTL compatible logic level signals that allow easy integration with conventional electronic systems. The three output diagrams shown in FIGURE 1 are examples of channel location outputs on each of the eight output gates of the 1300 router. To facilitate discussion, the eight channels in the WDM 101 signal, as shown separately in FIGURE 1, they will be referred to as channels 1-8 with channel 1 being the lowest wavelength and channel 8 being the largest pool wavelength. With an input (0.0,0) on the configuration bits C? -CN, the lowest wavelength channel (i.e., channel 1) is coupled to the output gate Pi. In the first configuration, channel 1 is presented to output gate Pi, channel 2 to output gate P2, and channel 8 to output gate P2N. In contrast, when the configuration bits are set to (0,0,1) the channel 2 is coupled to the output gate Pi, the channel 1 is coupled to the output gate P2, and the remaining channels are coupled as shown in FIG. shows in FIGURE 1. Similarly, when the configuration bits are set to (1,0,0) in channel 1 it is coupled to gate P5, channel 2 to gate P6, channel 3 to gate P7 , and channel 4 to gate P2, and the remaining channels are coupled as shown in FIGURE 1. Table 1 illustrates all possible couplings with router 1300. It can be seen that control bits C -.- CN offer the routing functionality, so that 2 combinations (ie, eight combinations with N = 3) of channel routing can be achieved.

TABLE 1 Although the channels 1-8 are illustrated uniformly apart, the channels may be non-uniformly separated or one or more channels may be absent if transmitters / detectors are not available or not needed in the channel. The channels may also be more closely spaced. More or less channels can be provided. Current systems are implemented with up to eight WDM channels in signal 101 and sixteen and forty four channel optical transceivers are available. 2. Basic channel routing element. FIGURE 2 and FIGURE 3 illustrate a basic channel routing element 100 in schematic form in two control positions. According to the preferred embodiment, each basic element is under the binary control of one of the control bits C? -CN, and hence has two states. Each basic element 100 serves to separate several portions of the frequency spectrum applied to an input gate to select which of the two input gates of each of the separate signals must be coupled.

As discussed below, those basic elements are cascaded to form the lx2N 1300 router in accordance with the present invention. In FIGURE 2 and FIGURE 3, the black solid lines indicate the optical paths comprising the full spectrum of the channels in the WLM 101 input signal. The thin solid lines indicate optical paths of the signals comprising a first subset of channels. . The thin dotted lines indicate optical channels comprising a second subset of channels. It is important to understand that each of the subsets can comprise more than one channel, and can itself be a WDM signal even though it has a smaller bandwidth than the original WDM 101. Each line is marked as H, indicating horizontal polarization, V indicating vertical polarization, or HV indicating horizontal and vertical polarization mixed in the optical signal at that point.WDM 101 signal enters a birefringent element 102 that spatially separates the horizontally and vertically polarized components of the signal 101. The birefringent element 102 comprises a material that allows the vertically polarized portion of the optical signal to pass through without change of course due to "being ordinary waves in the element 102. In contrast, horizontally polarized waves are redirected at an angle due to the effect of birefringent deviation. The redirection angle is a well-known function of the materials chosen in particular. Examples of materials suitable for the construction of the birefringent elements used in the preferred embodiments include calcite, rutile, lithium niobate, crystals based on YV04, and similar. The horizontal component travels along the path 103 as an extraordinary signal in the birefringent element 102, while the vertical component 104 moves as an ordinary signal, and passes through without spatial orientation. The signals 103 and 104, both comprise the full spectrum of the WDM signal 101. The horizontally and vertically polarized components 103 and 104 are coupled to a programmable polarization rotator 106 under the control of a control bit, such as d-CN shown in FIGURE 1. The polarization rotator 106 serves to selectively rotate the polarization state of each signal 103 and 104 in the predefined amount. In the preferred embodiment, the rotator 106 rotates the signals, either 0 ° (ie, without rotation) or 90 °. Polarization converter or rotator 106, comprises one or more types of known elements, including twisted nematic liquid crystal rotators, ferroelectric liquid crystal rotators, liquid crystal rotators based on the pi cell, Faraday rotators based on devices magneto-optics, 'polarization rotators based on acousto-optic and electro-optical devices. Commercially available rotators that have a liquid crystal-based technology are preferred, although other rotator technologies may be applied to meet the needs of a particular application. The switching speed of these elements fluctuates from a few milliseconds to nanoseconds, therefore, it can be applied to a wide variety of systems to meet the needs of a particular application. These and similar basic elements are considered equivalent and can be replaced and exchanged without departing from the spirit of the present invention. FIGURE 2 illustrates the condition where the signals are rotated 0o, so that the signals coming out of the rotator 106 do not change polarization. FIGURE 3 illustrates the second case, wherein the polarization is rotated 90 ° and the horizontally polarized component entering the rotator 106 comes out with a vertical polarization and the vertically polarized component comes out with horizontal polarization. Again, in this step, both horizontal and vertical components comprise the entire spectrum of the channels in the WDM signal 101. The element 107 comprises a plurality of birefringent wave plates (107a-107n in FIGURE 15) a selected orientations. By placing the element 107 between the two polarizers, namely 102 and 108, the combination becomes a polarization interference center serving to pass selected frequencies with horizontal polarization and a complementary set of frequencies with vertical polarization. Ideally, the polarization interference filter has a response curve of the comb filter with a substantially flat part or a square wave spectral response. The polarization interference filter is sensitive to the polarization of the incoming optical signal. The spectral response to the horizontally polarized input signal, when viewed at some exit point of the birefringent element 108, is complementary to the spectral response of a vertically polarized input signal. The details of the construction of the element 107 are described more fully with reference to FIGURE 15. The optical signals 105 and 115 are coupled to the birefringent element 108. The birefringent element 108 has a construction similar to the birefringent element 102, and serves to spatially separate the horizontally and vertically polarized components of the input optical signals 105 and 115. As shown in FIGURE 2, the optical signal 115 is separated into a vertical component 111, comprising the first set of channels and a component horizontal 112, which comprises the second set of frequencies. Similarly, the optical signal 105 is divided into a vertical component 113 comprising the second set of frequencies and a horizontal component 114, comprising the first set of frequencies. The geometry of the birefringent element 108 is selected such that the horizontal component 112 joins the vertical component 113 and its output as the optical signal 116 comprises the second set of frequencies. The optical signal 116 includes both horizontal and vertical components. The optical combining means 109 and 110 serve to combine the vertical component 111 with the horizontal component 114 to produce an output signal 117, which comprises the first set of frequencies. The combination elements 109 and 110 may take a variety of known forms, including a retroreflector, mirror, prism or other signal combining means. The output signals 116 and 117 can be physically aligned with an output gate, such as an optical fiber or a subsequent optical processing element. In contrast, in FIGURE 3 the vertical component 111 comprises a second set of channels while the horizontal channel 112 comprises the first set of channels. Likewise, the vertical component 113 comprises the first set of channels and the horizontal component 114 comprises a second set of channels. The combining means 109 and 110 operate in a manner similar to that described in FIGURE 2 to provide a first output signal 117 comprising a first set of frequencies and a second output signal 117 comprising a second set of frequencies. In this way, a single control signal is applied to the rotator 106 which optically routes the subdivided WDM input signal. The wavelength selection functionality of the apparatus shown in FIGURE 2 and FIGURE 3 is better understood with reference to the spectral diagrams shown in FIGURE 4 - FIGURE 6. FIGURE 4 illustrates eight channels constituting signal WDM 101. In FIGURE 4 -FIGURE 6, the wavelength is illustrated on the horizontal axis while the amplitude of the signal is illustrated on the vertical axis. Although each channel is illustrated as a well-defined separate square, it should be understood that in practice the channels may comprise a range of frequencies having various amplitudes over the entire frequency range. The particular range of frequencies may be larger or smaller than that shown in FIGURE 4. In FIGURE 5, a horizontally polarized input functionality of the stacked birefringent wave plates 107 (shown in FIGURE 2) is illustrated. The dotted line box indicates the portion of the entry horizontally polarized that happened with vertical polarization. The portion of the signal outside the dotted line box passed horizontally (ie, without rotation). Hence, as shown in FIGURE 5, channels 1-4 come out with vertical polarization if birefringent wave plates 107 with horizontal polarization enter. In contrast, channels 5-8 exit as stacked birefringent wave plates 107 with horizontal polarization and enter with horizontal polarization. FIGURE 6 illustrates a spectral diagram when the input to the stacked birefringent wave plates 107 has vertical polarization. This is shown in FIGURE 2 by the lower signal and in FIGURE 3 by the upper signal coming out of the rotator 106. The dotted line indicates rotated wavelengths (ie, wavelengths that will come out as plates). of birefringent wave stacked 107 with horizontal polarization). As shown in FIGURE 6, channels 1-6 are rotated and come out as stacked birefringent wave plates 107 with horizontal polarization while channels 5-8 are not rotated and come out with their original vertical polarization. In this way, the different frequency sets can be distinguished although they will still be displaced in the same optical paths 105 and 115 shown in FIGURE 2 and FIGURE 3. The construction of a filter to complete the function shown by the line dotted in FIGURE 5 and in FIGURE 6 will be described in more detail here later. Figures 7 to 10 illustrate the different components separated in the birefringent element 108. FIGURE 7 shows the vertically polarized component 111 comprising channels 1-4. If the control signal applied to the rotator 106 were inverted, the signal 111 will comprise the vertically polarized components of the channels 5-8. In FIGURE 8, the component 112 comprises horizontally polarized portions of the channels 5-8 while if the control bit is inverted, the signal 112 will comprise the horizontally polarized components of the channels 1-4. FIGURE "9 illustrates the signal 114, which comprises the horizontally polarized component of channels 1-4 while the opposite would be true if the control bit were inverted, likewise, in FIGURE 10, the component of the signal 113 comprises the vertically polarized portions of the channels 5-8 while if the configuration bit was inverted the component 113 comprises the vertically polarized components of the channels 1-4 The signals 111 and 114 are combined optically as illustrated in FIGURE 2 to form the output signal 11 / comprising the horizontally and vertically polarized components of channels 1-4 if the control bit was inverted, the output signal 117 would comprise the horizontally and vertically polarized components of channels 5-8. In contrast, the components 112 and 113 are combined optically when the output birefringent element 108 forms the output signal 116 comprising the horizontally and vertically polarized components of the channels 5-8. If the control bit was inverted, the output signal 116 will comprise the horizontally and vertically polarized components of channels 1-4. A feature according to the present invention is that the routing is carried out while retaining substantially only the optical energy available in the WDM signal 101. That is to say, that regardless of the polarization of the signals in the signal WDM 101 both components horizontally and vertically polarized are used and recombined in the output signal 116 and the output signal 117 resulting in a very low loss pass router 1300 according to the present invention. It should be noted from FIGURE 11 and FIGURE 12 that the output signals 116 and 117 comprise more than one channel and thus are themselves WDM signals. The routing of channel groups may be useful in some circumstances, however, the preferred embodiment of the present invention uses the multiple stage design to further decompose the WDM signals 116 and 117 as shown in FIGURE "11 and in FIGURE 12 in individual channel components that are spatially separated. 3. Multistage Router FIGURE 13 illustrates in block diagram form the router 1300 according to the present invention. The 1300 router is a three-stage router, each stage accepts a Ca-CN control bit. The first stage 100 comprises a single 1x2 router by rotating the router 100 shown in FIGURE 2 and FIGURE 3. The first stage 100 responsive to the division of the WDM signal 101 into two groups. The second stage 200 comprises two substantially identical routers "which are similar to a router 100 in stage 1. The routers 200 also divide the WDM signals received on the lines 116 and 117 into two output signals. The routers 200 differ from the router 100 in that the passband of its polarization interference filter has narrower "teeth" and more frequent teeth. In a particular example, the step band of steps 200 is half the width of the step band of step 100 and has twice its frequency. This is achieved by adding additional wave plates or by increasing the delay of the wave plates in the element 107 shown in FIGURE 2 and FIGURE 3.

The third stage comprises four routing elements 300 which are similar in construction to the routing elements 200 and 100 discussed above. Each output of step 200 comprises two WDM channels. Each stage 300 further divides the two WDM channels that are received in two outputs of a single channel on the outputs P? ~ P2N. Each router element 300 is coupled to a single configuration bit Ci which selects the binary state. The cascaded design of the binary routing elements 100, 200, and 300 shown in FIGURE 13 allows three control bits to implement any of 2N routing arrangements of the WDM signal 101 over the P? -P2N outputs. However, each router element 100, 200 and 300 could be controlled or programmed individually or in some way to not receive configuration bit and have a fixed demultiplexing function to meet the needs of a particular application. These or other equivalent embodiments are contemplated and are within the scope and spirit of the present invention. FIGURE 14 illustrates how the pass bands of the router stages 100, 200 and 300 differ from the signal WDM 101 illustrated in the upper part of FIGURE 14. As shown, a pass band of the indicated stage 100 the shaded portions in FIGURE 14 pass channels 1-4 if they enter with horizontal orientation without change the orientation. The optical energy that enters with the vertical polarization in step 100 will pass without rotation if it was within channels 5-8. It is advantageous to have a substantially flat pass band operation of each stage 100, 200 and 300 as shown in FIGURE 14. Turning now to step 200 shown in FIGURE 14 it can be seen that channels 1-2 and 5-6 pass if they enter with horizontal polarization while channels 3-4 and 7-8 pass if they enter with vertical polarization. The channels that did not pass or did not rotate with an opposite polarization according to that described here above. Similarly, step 300 defines a passband in which the channels 1, 3, 5, and 7 pass with horizontal polarization and the channels 2, 4, 6, and 8 pass with vertical polarization. By controlling the orientation of each signal after entering the polarization interference filter in each stage, the special location of each set of channels can be determined. 4_. Flat top optical filter design. FIGURE 15 illustrates in more detail the construction of a planar upper polarization interference center controlled by the polarization converter 106. The filter 205 comprises N cascaded birefringent elements 107 sandwiched by the rotator of FIG. polarization 106 and birefringent elements 104 and 108. The conventional filter design creates a spectral response shaped by sandwiching birefringent elements such as 107A-107N between two polarizers. The conventional design offers the control provided by the polarization converter. The conventional design also discards the optical energy by filtering all the energy of a particular polarization in an output polarizer. The present invention conserves this energy using the birefringent elements 104 and 108 in place of a conventional polarizer. Each of the birefringent elements 107A-107N is oriented at an angle of the single optical axis with respect to the optical axis of polarization converter 106. Any optical transmission function can be approximated by N terms of a Fourier series. From the coefficients of the approximate Fourier series, the response of the filter pulse can be estimated. A filter of N elements allows the approximation of the desired function in N + l terms of an exponential Fourier series. An example of the use of five wave plates to synthesize the flat top spectrum is shown in FIGURE 16. Appropriately orienting the optical axis of the wave plates a relatively flat upper part is reached with a compression ratio of the lateral lobe of 30 dB.

In FIGURE 16A and FIGURE 16B, the flat top spectra displayed before and after the bias converter 106 were switched. In FIGURE 16A and FIGURE 16B the vertical axis represents the normalized transmission and the horizontal axis represents the wavelength. As can be seen by comparing FIGURE 16A and FIGURE 16B, the two spectra are complementary to each other, which is one of the key factors in the design of the wavelength router. This is because this orthogonal feature of that polarization rotator 106 can select any of the spectra and separate them later using birefringent crystals. Increasing the sampling points or the number of wave plates results in a better transmission function that more closely approximates a flat top transmission with gradual transitions. Theoretically this transmission function can be a perfect square waveform in the desired spectral bandwidth. Minimal side slopes, 100% transmission, and flat top responses are possible. Practically, however, the physical size does not indicate the number of stages so that a practical device will sacrifice some of the characteristics such as ripple on the top, a less steep slope, and lateral lobe fluctuation.

It should be evident that the programmable wavelength router offers faster switching, provides a reliable and simple design, and a scalable architecture. It should be expressly understood that the claimed invention should not be limited to the description of the preferred embodiment but covers other modifications and alterations within the scope and spirit of the inventive concept.

It is noted that in relation to this date, the best method known to the applicant to carry out the aforementioned invention, is that which is clear from the present description of the invention.

Claims (23)

1. RErVINDICATIONS Having described the invention as above, the content of the following claims is claimed as property. A wavelength host, characterized in that it comprises: a first birefringent element positioned to receive an optical signal multiplexed by wavelength division (WDM), the output of the first birefringent element defines the first path or optical path and a second one optical path or path, wherein the first and second pathways or optical paths have opposite polarization and are spatially separated; a polarization converter coupled to receive the first and second paths or optical paths of the first birefringent element, wherein the polarization converter rotates the polarization state of at least one of the first and second optical paths; a wavelength filter coupled to receive the first and second optical paths of the polarization converter, the wavelength filter has an optical transmission function that depends on the polarization, so that the first filtered optical path comprises a first set of frequencies with vertical polarization and a second set of frequencies with horizontal polarization, the second filtered optical path comprises the first set of frequencies with horizontal polarization and the second set of frequencies with vertical polarization, wherein the first and second set of frequencies are substantially complementary; a second birefringent element coupled to receive the first and second pathways or optical paths of the wavelength filter and spatially separate each of the first and second optical pathways into horizontally polarized and vertically polarized components; means for combining the horizontal component of the first path with the vertical component of the second path in A first output signal; and means for combining the vertical component of the first path with the horizontal component of the second path in a second output signal. The wavelength router according to claim 1, characterized in that the first and second birefringent elements are selected from the group of materials comprising calcite, rutile, and LiNb03. 3. The wavelength router according to claim 1, characterized in that the polarization converter comprises a polarization converter based on ferroelectric liquid crystal (FLC). . The wavelength router according to claim 1, characterized in that the polarization converter comprises a pneumatic liquid crystal polarization converter. The wavelength router according to claim 1, characterized in that the wavelength filter comprises a multistage polarization interference filter. The wavelength router according to claim 5, characterized in that at least one stage comprises multiple birefringent wave plate elements, wherein each of the multiple elements are coupled in series and each has a unique optical axis oriented with respect to the polarization converter. 7. The wavelength mask according to claim 6, characterized in that at least one stage comprises at least five birefringent elements. 8. The wavelength mask according to claim 5, characterized in that the wavelength filter is a comb filter with an optical transmission function, it is a square-wave shape attenuation function as a function of the wavelength. 9. The wavelength router according to claim 1, characterized in that the polarization converter is programmable. 10. A wavelength router for routing a wavelength division (WDM) multiplexed signal having a plurality of channels, the router is characterized in that it comprises: a plurality of stages in cascade, wherein each stage receives one or more optical signals comprising a plurality of WDM channels, each of the stages filters and divides the received optical signals into a plurality of signals divided optics, each of the divided optical signals comprises a subset of at least one and less of all the channels received for the stage, so that they can be separated and spatially switched up to 2N optical signals in the input WDM signal using N control signals, where N is the number of stages. The wavelength router according to claim 10, characterized in that the plurality of stages in cascade comprises: a first step for dividing the WDM signal into a plurality of spatially separated first phase optical signals, wherein each optical signal of the first stage comprises at least one and all of the plurality of channels in the WDM signal; Y a second step for dividing each of the plurality of optical signals of the first stage into a plurality of spatially separated second phase optical signals, wherein each optical signal of the second stage comprises a subset of channels received from one of the signals optics of the first stage. The wavelength router according to claim 11, characterized in that the plurality of cascaded steps comprises: a third step for dividing each of the plurality of optical signals of the second stage into a plurality of optical signals of the third stage spatially separated, wherein each optical signal of the third stage comprises a subset of channels received from one of the optical signals of the second stage. The wavelength router according to claim 10, characterized in that each stage includes an optical comb center that depends on the polarization having a flat upper-end wavelength response that passes a first subset of channels with polarization horizontal and a second subset of channels with vertical polarization, wherein the first and second sets of channels are mutually exclusive. 14. The wavelength router according to claim 13, characterized in that each stage further comprises: means for separating the received optical signal into a horizontal component and a vertical component; and means for rotating the polarization of at least one component of the separated optical signal and passing the rotated components to the comb filter. 15. A method for routing a wavelength division multiplexed optical signal (WDM), characterized in that it comprises the steps of: separating the WDM optical signal into horizontally and vertically spatially separated polarized components; selecting a polarization rotation for each of the components, so that the components continue to have complementary polarization after the selection step; dividing each of the components into a pair of complementary wavelength spectrum signals, wherein each of the two signals divided in each pair have opposite polarization; spatially separate the divided signals of each pair; spatially combining a divided signal of one of the pairs with a signal divided from the other of the pairs to form a first output signal comprising horizontally and vertically polarized components within a first wavelength spectrum and a second output signal that It comprises horizontally and vertically polarized components within a second wavelength spectrum. The method according to claim 15, characterized in that it further comprises: repeating the steps of separating, selecting, dividing, spatially separating and spatially combining each of the first and second output signals to produce four output signals having spectra of unique wavelengths in the selected positions. 17. A method for routing a wavelength division multiplexed optical signal (WDM), characterized in that it comprises the steps of: dividing the WDM signal into first and second subspecies having complementary wavelength spectra; selectively coupling each of the first and second subspecies to one of the first and second optical channels; divide the first subspectrum into third and fourth subspecies; selectively coupling each of the third and fourth sub-specs to one of the third and fourth optical channels; divide the second subspectrum into fifth and sixth subspecies; and selectively coupling each of the fifth and sixth sub-specs to one of the fifth and sixth optical channels. The method according to claim 17, characterized in that it further comprises: dividing the third and fourth subspecies into four unique sub-spectros; divide the fifth and sixth sub-specs into four unique sub-spectros; and selectively coupling each of the unique subspectroses to an especially unique optical channel. 19. A wavelength router, characterized by comprising: a plurality of stages in cascade, wherein each stage receives one or more optical signals comprising a plurality of channels multiplexed by wavelength division (WDM), divides the signals optics received in divided optical signals comprising a subset of channels, and spatially placed the divided optical signals in response to a control signal applied to each stage and, wherein, at least one of the steps includes: (a) means for spatially separating each optical signal in a horizontally polarized component along a first path or optical path and a component vertically polarized along a second path or optical path; (b) means for rotating the polarization of at least one component of the separated optical signal; (c) a wavelength filter coupled to receive the rotated components, the wavelength filter has an optical transmission function dependent on polarization, so that the first filtered path or optical path comprises a first set of channels with vertical polarization and a second set of channels with horizontal polarization, and the second path or optical path comprises the first set of channels with horizontal polarization and the second set of channels with vertical polarization, wherein the first and second sets of channels are substantially complementary; (d) means for spatially separating each of the first and second optical paths in horizontally polarized and vertically polarized components; (e) means for combining the horizontally polarized component of the first optical path with the component vertically polarized from the second optical path to produce the second set of channels; and (f) means for combining the vertically polarized component of the first optical path with the horizontally polarized component of the second path or optical path to produce the first set of channels. 20. The wavelength router according to claim 19, characterized in that the plurality of stages in cascade comprises: a first step for dividing the WDM signal into a plurality of spatially separated first phase optical signals, wherein each optical signal of the first stage comprises at least one and all of the plurality of channels in the WDM signal; and a second step for dividing each of the plurality of optical signals of the first stage into a plurality of spatially separated second phase optical signals, wherein each optical signal of the second stage comprises a subset of channels received from one of the optical signals of the first stage. The wavelength router according to claim 20, characterized in that the plurality of cascaded steps comprises: a third step for dividing each of the plurality of optical signals of the second stage into a plurality of spatially separated third stage optical signals, wherein each of the optical signals of the third stage comprises a subset of the channels received from one of the optical signals of the second stage. 22. The wavelength router according to claim 19, characterized in that the wavelength filter comprises an optical comb filter that depends on the polarization, having a flat upper wavelength response that passes a first subset of channels with horizontal polarization and a second subset of channels with vertical polarization, wherein the first and second sets of channels are mutually exclusive. 23. The wavelength router according to claim 19, characterized in that the means for rotating the polarization of at least one component of the separated optical signal are programmable.