MXPA00002816A - Wavelength-selective optical switching apparatus, optical communications apparatus using the same, and method for use in the optical communications apparatus - Google Patents

Abstract

An optical switching apparatus is designed to implement a serial switching architecture for wavelength division multiplexed (WDM) optical communication systems. The design allows for add/drop switching of a selected wavelength channel without switching a non-selected wavelength channel, thereby avoiding potential data loss on the non-selected channel during the add/drop switching interval. Exemplary implementations utilize fiber-optics and free-optics based approaches. The serial architecture readily accommodates new wavelength plans and/or the addition of new wavelength channels.

Description

OPTICAL SWITCHING APPARATUS OF LENGTH OF LENGTH WAVE, APPARATUS OF OPTICAL COMMUNICATIONS USED THEREOF AND METHOD FOR USE ON THE DEVICE OF OPTICAL COMMUNICATIONS REFERENCE CROSSED TO RELATED REQUEST This application claims the benefit of the application of E.U.A. No. 60 / 059,214, filed September 18, 1997 and incorporated herein by reference.

BACKGROUND OF THE INVENTION This invention relates to optical communication systems multiplexed by wavelength division (WDM). The invention relates more particularly to a novel wavelength selective switching scheme for such systems which is based on a simple serial structure, and with an optical switching apparatus designed to increase the structure. In a preferred embodiment, the apparatus is constituted as a selective wavelength addition / extraction switch. The invention is also related to an optical communications apparatus and methodology that takes advantage of the structure.

In an optical communication system WDM, the optical transmission spectrum is divided into a plurality of bands or channels of wavelength for communication. Multiple optical signals can be transmitted simultaneously over a common path (usually an optical fiber), each signal being in a different wavelength channel. This allows different groups of users or end devices to communicate at the same time in different channels. A typical WDM optical communication system is constructed as a network of nodes interconnected by fiber optic links. Users and end devices connect to the network in corresponding nodes. To optimize network utilization, node designs commonly incorporate signal addition / extraction functionality, whereby signals in one or any combination of wavelength channels can be extracted and / or added to the node. For this purpose, a node can be constructed as, or may include, a wavelength addition / extraction multiplexer (WADM). The components that make up the node should add as little loss as possible to the system, should be highly reliable and should provide active switching capacity of the WADM so that signals on individual channels can be passed, extracted and added to the node as dictated the communication requirements. Most WADM-capable node designs have relied on parallel structures to provide signal addition / extraction functionality. For example, a proposed design uses an arrangement of switches connected in parallel between a multiplexer and a demultiplexer to enable the switching of individual channels. Another proposed design uses a pair of star couplers interconnected by a wavelength selective parallel switching arrangement. Figure 1 shows a WADM 10 of the first mentioned design. The WADM 10 includes a demultiplexer (DEMUX) 12 connected to an input line 14 (e.g., a fiber optic or flat optical path) to receive optical signals multiplexed at wavelengths? -? N. The DEMUX 12 demultiplexes the optical signals, and outputs them individually to corresponding 2x2 optical switches S? -Sn connected to its output side. As shown in Figure 1 a, the switches S -? - Sn are connected to the input side of a multiplexer (MUX) 16, which combines the signals that come from the switches for transmission on an output line 20. The S? -Sn switches, under electronic control, can assume either a "lock" state or a "crossover" state. In the blocking state, a signal that enters a switch from the DEMUX 12 goes to the MUX 16, so it is retained for transmission on the output line 20. It is said that the channel carrying said signal is in a state on the way". Switches for wavelength channels? I and? N are shown in the blocking state. In the crossing state, shown by the switch for the channel?, the signal entering the switch is directed to a corresponding extraction line 18, such as for transmission to an end user, and does not pass to the output line 20. optionally, another signal at the same wavelength? can be entered into the system, by means of a corresponding addition line 19, for transmission on the output line 20. It is then said that the channel for the wavelength? It is in a state of "addition / extraction". The WADM 10 shown in Figure 1 a is complex, expensive and is based on an inflexible design. The design, more specifically, is not easily expandable to receive the addition of new wavelength channels to the communications network. This means that the initial node design must include excess capacity to allow future possible wavelength channels, or that special components and an additional WADM structure can be added to receive new channels in the future. The first option is not affordable, since capital must be allocated for equipment with which to manage more channels than initially required. The latter option may require a substantial future cost and can be problematic due to additional system losses. Parallel structures based on star couplers are also problematic. For example, the star coupler approach is inherently lost, and the loss increases with the number of channels (the loss increases as n2 where n is the number of additions / extractions required in a node). In addition, like the design of Figure 1 a, designs based on star couplers are complex, expensive and are not easily expandable to receive additional wavelength channels beyond the initial design capacity. Figure 1 b illustrates a signal addition / extraction component 30 based on a series structure. This component can be manufactured by arranging a Bragg grating device 33 tuned to a desired wave length between two optical circulators 32, 36 as shown. Bragg grid devices can be implemented in several ways, including fiber and flat devices. Each of the circulators 32, 36 includes respective ports 1, 2 and 3. The component 30 receives a mixed group of signals at different wavelengths? -? N on an input line 14 (e.g., a fiber optic or flat optical path) in port 1 of the optical circulator 32. The signals are propagate via port 2 of the circulator 32 to the Bragg grid 33. The Bragg grid passes all the signals except the signal at the wavelength? to an output line 20 via ports 2 and 3 of the circulator 36 The signal at the wavelength λ, which is the signal that will be extracted, is reflected by the Bragg grid and propagated to an extraction line 38 by means of ports 2 and 3 of the circulator 32. A signal which will be added in the wavelength? can be entered in port 1 of the circulator 36, by means of an addition line 39, and is combined with the remaining signals for its transmission in the output line 20. The component 30 has the advantage of a relatively simple design, p But it is not switchable. In this way, the signal in the channel reflected by the Bragg grid 33 must be extracted. The component can be designed to extract / add signals at multiple wavelengths by including additional grids between the circulators. However, the signals at all wavelengths that are reflected by the grids have yet to be extracted. Therefore, component 30 can not provide the optional addition / extraction functionality required for efficient utilization of a WDM network. Figure 1 c shows a proposed WADM design 30 'based on a switchable serial structure. This design includes a plurality of 2x2 optical switches connected in series S? -Sn + (n is the number of channels) arranged between a pair of optical circulators 32, 36, each having three ports as described above in relation to Figure 1 b. The optical circulators 32,36 are connected, respectively, to an input line 14 and to an output line 20. Adjacent switches in the series are coupled to each other by selective Bragg gratings of wavelength 33¡ (I = 1 an) tuned to corresponding wavelengths of the system and by complementary branch lines 35. An extraction line 38 and an addition line 39 are connected, respectively, to the optical circulators 32, 36. During the operation of the WADM 30 ', the switches Si- Sn +? they are configured (using the blocking and crossover states) to route the input WDM signal to the grid (s) that corresponds (n) to the signal (s) that will be extracted (s). The grids reflect the corresponding signals back to the optical circulator 32 so that they are extracted by means of the extraction line 38. The remaining signals (passage channels) pass through the grids to the circulator 36 and to the outlet line 20. extracted signals can be replaced by new signals input to the circulator 36 by means of the addition line 39. When it is necessary to receive additional wavelengths, the WADM 30 'can be expanded. This is achieved by adding new switches and Bragg gratings suitably tuned into the existing series arrangement. WADM 30 'can then be designed to satisfy the initial channel capacity of a network, without providing excess capacity, and subsequently expanding as necessary. Although its switchable serial structure offers adequate flexibility for expansion, the WADM 30 'has a significant risk of data loss. This is because the signals in all the wavelength channels, including the pass-through channels, are switched. For example, when the signal at the wavelength? ^ Is to be extracted, the corresponding switch S is switched to the crossover state so that all the channels are routed to the grid 33 ?. As a result, the signal data in the through channels may be lost during the switching interval.

BRIEF DESCRIPTION OF THE INVENTION The present invention provides a switchable and improved serial structure for WDM network applications. As will be seen hereinafter, the invention offers the simplicity and easy expandability associated with the serial structure, while avoiding the potential for data loss associated with designs requiring the switching of pass-through channels (see the previous description of Figure 1 c). According to one of its main aspects, the invention provides a switching apparatus for WDM optical communications, comprising a wavelength selective optical switching assembly that includes an input port built to receive multiple optical wavelength channels, a output port, a selective optical wavelength filter and an optical switching device. The selective wavelength filter is constructed and arranged to direct signals in a plurality of the received wavelength channels for propagation to the output port and to direct a signal in another of the wavelength channels received to the device. Optical switching. The optical switching device is arranged and operates to switch the other wavelength channel between a step state and an extraction or addition / extraction state without switching the plurality of wavelength channels.

In a preferred embodiment, the optical switching assembly comprises first and second optical circulators, each having at least first, second and third ports. The first port of the first circulator constitutes the port of entry, while the third port of the second circulator constitutes the port of exit. The selective wavelength filter includes a reflecting grid connected between the second ports of the first and second circulators. The optical switching device is connected between the third port of the first circulator and the first port of the second circulator. In another preferred embodiment, the optical switching assembly comprises first and second optical couplers, each having at least first, second and third ports. The first port of the first coupler constitutes the input port, while the second port of the second coupler constitutes the output port. The selective wavelength filter includes a reflecting grid connected between the second port of the first coupler and the first port of the second coupler. The optical switching device is connected between the third ports of the first and second couplers. In another preferred embodiment, the wavelength selective filter comprises a four-port filter device having a thin film notch filter coupled to the first through four ports. The first port and the fourth port constitute the port of entry and the port of departure, respectively. The signals in the plurality of channels received in the first port are reflected from the thin film filter to the fourth port, and the signal in the other received channel passes through the filter to the second port. The optical switching device is connected between the second and third ports. Another additional preferred embodiment employs a selective wavelength Mach-Zehnder filter device. The Mach-Zehnder device can include first and second 2x2 optical couplers, each having first, second, third and fourth ports. The first port of the first coupler constitutes the input port. The third and fourth ports of the first coupler are connected by first and second phase shift optical paths to the first and second ports, respectively, of the second coupler. A portion of the reflecting grid is arranged in the first and second phase shift optical paths. The optical switching device is connected between the second port of the first coupler and the third port of the second coupler, and the fourth port of the second coupler constitutes the output port. Another preferred embodiment employs a wavelength selective thin film filter which is reflective to the plurality of wavelength channels received and transmissive to the other wavelength channel received, and arranged in a signal path propagating from the wavelength. input port. The switching device has a switchable element between a first position and a second position. In the first position, the switchable element intercepts the signal transmitted through the thin film filter to cause that signal to propagate to the output port. In the second position, the switchable element allows the signal transmitted through the filter to be extracted. In another preferred embodiment, all the optical components of the wavelength selective filter and the optical switching device are free optics components (non-waveguide components). The structures based on free optics can be advantageous from the point of view of reducing the number of components as much as possible, and in this way reducing the overall cost of the apparatus. According to another main aspect of the invention, a switching device for optical communications WDM may comprise an input port constructed to receive a plurality of optical signals multiplexed each in a different wavelength channel, an output port, a first optical path from the port of entry to the port of departure, and a second optical path from the port of entry to the port of exit. The second optical path includes an optical switching device, and the first optical path includes a selective wavelength filter that is constructed to cause at least one of the selected signals to propagate to the switching device and to cause the rest The signals are propagated to the output port by means of a path that includes the first optical path. The switching device has a first state to cause the at least one selected signal propagated from the selective wavelength filter to propagate to the output port by means of the second optical path, and a second state in which the at least one selected signal propagated from the optical wavelength selective filter is extracted so that it does not propagate to the output port. Again, preferred embodiments include incorporations that are based on the use of optical circulators, optical couplers, a notch filter device or free optics components. In accordance with yet another principal aspect, the present invention provides an apparatus for adding / removing a signals for an optical communication system WDM, the apparatus comprises a plurality of selective wavelength addition / extraction switches coupled in series, each switch being constructed to switch a corresponding wavelength channel between a step state and a state of addition / extraction without switching another wavelength channel present in that switch. As will be noted hereinafter, other main aspects of the invention relate to the design of a selective wavelength addition / extraction switching device having redundant addition / extraction switching capability, and to devices and methods for taking out Advantage of the design. The foregoing and other aspects of the invention, as well as its features and advantages, will be more fully appreciated from the following detailed description taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 a is a schematic illustration of a WADM design based on a parallel structure. Figure 1 b is a schematic illustration of a signal addition / extraction component based on a series structure. Figure 1 c is a schematic illustration of a design of WADM based on a switchable serial structure. Figure 2 schematically illustrates the serial connection of a plurality of switch modules according to the invention. Figure 3 is a schematic illustration of a selective wavelength addition / extraction switch according to the invention. Figures 4a and 4b illustrate the "step" state and the "add / remove" state, respectively, of a 4-port optical switch. Figure 5 schematically illustrates the serial connection of two fiber Bragg reijllas. Figures 6 and 7 illustrate 4-port fiber optic switches that can be used in selective wavelength addition / extraction switches of the invention.

Figure 8 is a schematic illustration of another embodiment of a selective wavelength addition / extraction switch employing fiber couplers. Figure 9 schematically illustrates another embodiment of a wavelength selective addition / extraction switch employing a Mach-Zehnder filter. Figure 10 schematically illustrates another embodiment of a selective wavelength addition / extraction switch employing a 4-port thin film notch filter. Figure 11 shows the output spectra in both the add / remove and step states for a wavelength selective addition / extraction switch. Figure 12 shows the extraction port transmission spectra in both the add / remove and step states for a selective wavelength addition / extraction switch. Figure 13 schematically illustrates another embodiment of the invention based on a free optics design. Figure 14 shows a modification of the embodiment of Figure 13. Figure 15 schematically illustrates a further embodiment based on a free optics design. Figure 16 shows a modification of the mode of Figure 15.

Figure 17 schematically illustrates an application of the invention for bidirectional communication. Figure 18 schematically illustrates a selective wavelength addition / extraction device used in the embodiment of Figure 17. Figures 19 and 20 show variations of the device of Figure 18.

DESCRIPTION OF THE PREFERRED MODALITIES Figure 2 illustrates a WADM system based on a switchable serial structure according to the present invention. The basic building block of the system is a selective wavelength addition / extraction switch (WSA / D switch). In the embodiment shown, the system includes a serial connection of WSA / D switch modules, a switch module being provided for each wavelength channel ?? -? N present in the system. Depending on the system requirements, switch modules constructed to switch more than one wavelength channel can be used. The modular nature of the system allows easy reconfiguration and expansion to receive plans for new channels and the addition of new channels. Reconfiguration can be achieved by simply re-arranging individual modules within the system. The expansion simply includes adding new switch modules built to switch the new channels that are added to the system. A WSA / D switch design that is preferred for the system shown in Figure 2 will be substantially transparent for all wavelength channels, except the channel or channels of interest. It will also allow the active switching of the channel or channels of interest between a step state and an addition / extraction state (or extracting state if no signal will be added) without switching the other channels. The switching of the channel of interest does not therefore interrupt the transmission of the other channels. Figure 3 is a schematic diagram of a WSA / D switch design. The WSA / D switch 40 shown in Figure 3 is composed of an optical switching device - here, a 4-port 2 x 2 switch S¡- connected to a wavelength selective filter assembly 45 including two optical circulators 42 and 46 and a single fiber Bragg grid 43 tuned to a wavelength? selected The port 1 of the circulator 42 and the port 3 of the circulator 46 respectively constitute the input port and the output port of the WSA / D switch. The switch S i, which is preferably wave-insensitive (non-selective wavelengths) is connected to the assembly 45 in port 3 of the circulator 42 and port 1 of the circulator 46 via lines 44. The WSA switch / D can have any of two states - a state of passage or an addition / extraction state - with respect to the channel at the wavelength? ¡, Depending on the state of the 4-port switch S¡. The corresponding states of the commutator S i are shown diagrammatically in Figures 4a and 4b. The input signals at the channel wavelengths? R? N are supplied to the input port of the switch WSA D via an input line 14. All the input signals are propagated through the circulator 42 to the grid 43 , which is tuned to the selected wavelength. The pass-channel signals (those at all wavelengths except?) Propagate through the grid 43 and the circulator 46 to the output line 20. The signal on the channel? Which is selected by the grid 43 is reflected back through the circulator 42 and propagates from port 3 thereof to switch S1. When the switch S i is in the step state (FIGS. 3 and 4 a), the selected signal is propagated via port 4 of the switch to port 1 of the circulator 46, and from port 3 of the circulator to the output line 20. When the switch S i is in the addition / extraction state (FIG. 4 b), the selected signal is propagated via port 3 of the switch to an extraction line 48. In this state, a signal at the wavelength? it can be added to port 2 of switch S, by means of an addition line 49. Ports 2 and 3 of switch S, thus constitute the addition and extraction ports, respectively, of switch WSA / D 40.

As will be appreciated from the above description, the structure of Figure 3 provides two paths from the input port to the output port of the switch WSA / D 40. More particularly, the signals in the through channels are propagated to the output port by means of a first path including the circulator 42, the grid 43 and the circulator 46. The signal in the selected channel at wavelength? ¡propagates to the output port by means of a second path that it includes the circulator 42, the line assembly 44 and the switch S i, and the circulator 46. Since the passage channel signals propagate only through the circulators 42, 46 and the grid 43, there is no interruption of its propagation during the commutation interval of the switch S¡. The arrangement of the switch S i in the second path then makes it possible to switch the selected channel between a passing state and an addition / extraction state without subjecting the switching channels. This avoids the risk of data loss that could accompany the switching of pass-through channels. Other attributes of the WSA / D 40 switch include its low loss, and its modularity and reduced complexity - the switch can be constructed with only two individual components, the filter assembly 45 and the 4-port switch S i. The switch WSA / D 40 can be modified to add or extract a plurality of signals providing a grid for each signal wavelength. For example, the signals at the wavelengths? I and? 2 can be extracted and added from the WSA / D switch by replacing the grid 43 with the series connection of grids 66 and 67 shown in Fig. 5. Various types of optical switches they can be used as the 4-port switch S¡. Figure 6 shows an overcoated fiber optic switch 50, whose operating principles are described in the U.S.A. 4,763,977 and 5,353,363 (both incorporated herein by way of reference). The switch 50 includes a fiber optic coupler WDM 51 having two optical fibers. The ends 52a and 52b of a fiber exit from opposite ends of the coupler 51, and the ends 53a and 53b of the other fiber exit from the opposite ends of the coupler. The coupler 51 is fixed at one end by suitable fixing means 54, and the other end of the coupler is folded switchably by a bending device 56. Electromagnetic, piezoelectric, bimetallic and other types of devices can provide small and controlled movement which is required to bend the coupler. The switch 50 operates in such a way that one optical signal applied to the fiber end 52a is coupled to the other fiber and appears at the fiber end 53b when the coupler is unfolded. Similarly, a signal applied to the fiber end 53a is coupled to the other fiber and appears at the fiber end 52b when the coupler is unfolded. When the coupler is bent, an optical signal applied to the fiber end 52a remains uncoupled and appears at the fiber end 52b. The coupler 51 can be biased to the bent condition by means such as those described in US Patents. 31, 579; 4,204,744; 4,303,302; 4,318,587 and 4,337,995 (all incorporated herein by reference). The rotary action of the switch described in the US patent. 5,146,519 (incorporated herein by reference) is also well suited for commutating switch 50; the linear movement of the switch activation device would simply be converted into a torsion movement. The 4-port switch Sj can also be constructed according to FIG. 7. In the structure of FIG. 7, a switchable optical fiber 59, which is connected to an input port 1, can be switched between an extraction port. 3 and an exit port 4 as indicated by the double-headed arrow a. In a similar way, a switchable optical fiber 58, which is connected to an add port 2, can be switched to, and away from, the output port 4 as indicated by the double-headed arrow b. In the non-switched state, the switchable fibers 58 and 59 are in the position represented by solid lines, and the signal channel is connected from port 1 to port 4. In the switched state, the switchable fibers 58 and 59 are in the positions represented by dotted lines 58 'and 59'. Therefore, the signal channel is connected from port 1 to port 3, and port 2 is connected to port 4. Switchable fibers 58 and 59 can be switched between the two illustrated states by means such as those described in the patents from the USA 31, 579; 4,204,744; 4,303,302; 4,318,587 and 4,337,995.

Figure 8 illustrates a WSA / D switch 70 in which the circulators of Figure 3 have been replaced by optical couplers 72, 76. As shown in Figure 8, a filter assembly 75 includes two couplers 72 and 76 of 32 dB, each with respective ports 1-3, and a fiber Bragg 43 grid. Channel signals at wavelengths? ? n are received on the input line 14 of the switch 70 and coupled by ports 1 and 2 of the coupler 72 to the grid 43. Except for the signal at the wavelength? ¡, the received signals are propagated to port 1 of the coupler 76 and of port 2 thereof to the output line 20. The signal at wavelength? is reflected back to port 2 of coupler 72 and port 3 thereof to the 4-port switch S, in where it may or may not be extracted depending on the state of the switch S¡. When the switch S i is in the pass state, the signal at the wavelength λ propagates to the port 3 of the coupler 76, where it is coupled to port 2 and placed on the output line 20. When the switch S Is in the state of addition / extraction, the signal propagates to the extraction line 48. Depending on the system in which the WSA / D 70 switch is used, it may be desirable to place an isolator on the line 14. It is clear that the WSA / D switch 70 provides two optical paths from its input port to its output port similarly to the arrangement of Figure 3, with inherent advantages as previously described.

Figure 9 shows an additional WSA / D switch 80 according to the invention, in which the two optical circulators and the fiber Bragg grid of Figure 3 have been replaced by a selective wavelength filter assembly of Mach -Zehnder (MZ) 85, whose operation is described in the US patent 4,900.1 19 (incorporated herein by reference). Briefly, the MZ 85 filter assembly operates as follows. The multi-wavelength input channel signals are supplied by the input line 14 and enter the filter assembly 85 through the port 1 of a first coupler 82. After passing through the coupler 82, the lengths of wave are divided, and the signals in each limb are displaced in phase by p / 2. The wavelengths that are not resonant with the Bragg gratings 83 in the phase shift paths are transmitted to a coupler 86 where again, due to an additional p / 2 phase shift, all the light is intermittently coupled to port 4 of coupler 86 and leaves the switch MZ-WSA / D to the output line 20. The wavelength? ¡is reflected by the Bragg gratings and undergoes a second phase shift p / 2 after its propagation. return to coupler 82 and thus exit the filter assembly in port 2 of the coupler and propagate to the 4-port switch S1. Any signal on? Propagated from the 4-port switch S¡ to the coupler 86 will be reflected by the Bragg grids and routed from port 3 to port 4 of the coupler 86 in the same way as the input signal at? ¡Is routed from port 1 to port 2 of coupler 82. The 4-port switch S i functions in the manner described in relation to figure 3. In this way, when the 4-port switch is in the pass state, the selected signal for the filter assembly MZ 85 is reflected around the path containing the switch Si and routed out of the switch MZ-WSA / D 80 by means of ports 3 and 4 of the coupler 86. When the switch S i is in the state of addition / extraction, the signal selected by the filter assembly MZ 85 is extracted in port 3 of the switch Yes, and a new signal in the same wavelength can be added to the port 4 of the switch (see figure 4b) . Figure 10 shows another WSA / D switch 90 according to the invention. This switch employs a 4-port thin film notch filter assembly 95 and does not use a Bragg grid. The notch filter assembly 95 can be constructed in accordance with the teachings found in, for example, Macleod, H.A., Thin-film Optical Filters, American Elsevier, 1969 (incorporated herein by reference). The switch 90 operates as follows. The input channel signals at different wavelengths? R? N are supplied via the input line 14 and enter the WSA / D switch 90 through the input port 1 of the filter assembly 95. All signals of the input channel except the channel signal? are reflected from the surface 92a of a thin-film notch filter 92 and exit at the output port 4 of the filter assembly to the output line 20. The channel signal? it propagates through the notch filter 92 and from the surface 92b thereof to the port 2 of the filter assembly, where it is coupled by means of one of two lines 44 to the 4 port switch S i. When the 4-port switch is in the pass state, the channel signal? ¡Propagates around the path containing lines 44 and switch S¡ and is routed to port 3 of the filter assembly, from where it propagates back through the notch filter 92 to be emitted from port 4. Incidentally, ports 1-4 are optically coupled to the thin film filter 92, such as by respective GRIN lenses (gradient refractive index lenses -not shown ) connected to those ports. When the switch S i is in the add / extract state, the channel signal ¡from port 2 is routed to the extraction line 48, and a new signal can be added in the same channel by means of the line addition 49. The added signal is propagated from the switch S1 to port 3, from which it propagates through the notch filter 92 to port 4 and the output line 20. The operation of an addition / extraction switch has been demonstrated selective wavelength of two channels of the type described in connection with FIGS. 3 and 5. The switch was constructed from two commercially available optical circulators and a multi-facing bending coupler switch of the type shown in FIG. 6. Two Bragg gratings of fiber connected in series were manufactured to operate at wavelengths of 1554.8 nm and 1555.8 nm. In addition, an individual channel switch operating at a wavelength of 1557 nm has been demonstrated. The performance of the individual channel switch is similar to that of the two channel switch. Figure 11 shows the output spectrum transmission spectrum of the two-channel device when the 4-port switch is in both the add / pull and bypass state. In the step state, the insertion loss was 3.7 dB and 1.9 dB for the selected and adjacent channels, respectively (curves 98 and 99). The directivity was 36 dB (curves 100 and 101) and was limited by the bending coupler switch. The transmission spectrum in the extraction port is shown in figure 12. The insertion loss with the switch in the state of addition / extraction was 1.8 dB (curves 102 and 103) and the directivity was 34 dB ( curves 104 and 105). Rejection of the adjacent channel was limited by the sidebands of the fiber Bragg grid used. The insertion loss of the commutator was limited by the loss of the circulators and the fusion divisions between the high-delta fiber used for the Bragg gratings and the standard single-mode fiber optic used for the circulators (the insertion loss of the commutator bending is only 0.15 dB). By reducing division losses to negligible levels, the insertion loss could be reduced to 1.75 and 0.8 dB for selected and adjacent channels, respectively. Assuming these low losses, it is estimated that 32 individual channel switches could be concatenated before accumulating 30 dB of total insertion loss. In fact, using a Mach-Zehnder filter-type switch like that described in relation to FIG. 9, the total insertion loss for 32 switches would be as low as 18 dB. The experimental results indicate that the switches WSA / D according to the invention can be manufactured with low insertion loss and high directivity. Figures 13-16 illustrate additional WAS / D switch designs according to the invention. The designs in Figures 13-16 use selective wavelength thin-film filters, but unlike the modality of Figure 10, they are based on the use of free optics components (non-waveguide components). to achieve both the wavelength selection and the channel switching functions. This allows the thin film filter and the channel switching portion to be integrated into a single device. The counting of parts and the number of fiber divisions in the general switch design, and consequently the production costs, can thus be reduced. Figure 13 shows a WSA / D switch 100. The switch has four optical ports, including an input port 1 connected to the input line 14, an output port 4 connected to the output line 20, an add port 2. connected to the addition line 109, and an extraction port 3 connected to the extraction line 108. The input port is coupled to the other ports by means of GRIN 102 lenses. - 1024 respective and a selective wavelength switching assembly 105, including a thin film filter 103 and a switchable element formed here by a movable mirror element Mj. Of course, if the signal addition capability is not desired, the addition port and the associated GRIN lens can be omitted. The thin film filter 103 is transmissive to the light of a selected channel wavelength? And is reflective to the light of the rest of the channel wavelengths. The filter is suitably arranged to reflect the light of the remaining channel wavelengths for propagation to the output port by means of the GRIN 1024 lens. The light of the selected wavelength is transmitted by the filter to the GRIN lens of extraction port 1023, which is aligned substantially optically with the GRIN lens of input port 102? through the thin film filter. The switchable element M i has first and second mirror surfaces 104, 106 mounted on a common support element 107 and is movable between a position corresponding to the passage state of the channel at the wavelength λ (position shown in solid lines in Figure 13) and a position corresponding to the state of addition / extraction of the channel (position shown in faded lines). In the passage position, the first mirror surface 104 is arranged to intercept the light of wavelength? Transmitted by the thin filter 103. This light is then reflected to the second mirror surface 106 which, in turn, reflects the light back through the thin film filter to the output port GRIN lens 102 for placement on the output line 20. In the addition / removal position of the switchable element M, the first and second mirror surfaces 104, 106 are removed from the respective optical paths between the input and extraction GRIN lenses 102 ?, 1023 and the output and addition GRIN lenses 1024, 1022. In this way, the wavelength light? ¡Transmitted by the filter The thin film is propagated to the extraction port 3 and to the line 108 by means of the GRIN 1023 lens. Optionally, the extracted signal can be replaced by a signal of the same wavelength introduced in the port. addition 2 by means of line 109. The new signal is propagated from the addition port, through the GRIN 1022 lens, the thin film filter 103 and the GRIN 1024 output port lens, to the output port 4. The motor energy for the movable element M i can be easily provided by a variety of mechanisms. For example, a permanent magnet can be attached to the mirror holder and two electromagnets can be arranged in respective movement detents corresponding to the positions of the passage state and the addition / extraction state of the movable element. It will be appreciated that, like the modalities described above, the light of the passage channels (channels that will not be switched by the optical switching device) and the light of the selected channel wavelength? follow different paths from the input port to the output port of switch WSA / D 100, only the light path of the selected channel wavelength being switched. More particularly, the passage channels follow a path that includes the input port GRIN lens 102 ?, the incident surface of the thin film filter 103 and the output port GRIN lens 102. The light of the selected wave length 102 ?, a first pass through the thin film filter 103, the first and second reflecting surfaces 104 and 106 of the movable element M i, a second passage through the thin film filter 103 and the GRIN lens of output port 1024. In this way, as in the previous modes, the channel selected in the wavelength? ¡can be switched between the step and addition / extraction states without switching the pass channels. Although not necessary in practice, the illustrative arrangement of the first and second mirror surfaces 104 and 106 in a common movable support member is advantageous, because it facilitates a precise and stable alignment of the mirror surfaces. As an alternative, the switchable element may be constituted by a prism, the mirror surfaces being constituted by end reflecting surfaces on the prism. The alignment of the GRIN 102? -1024 lenses during construction can be achieved simply by "following the light path" starting with the entry port and following the exit port, the addition port and the extraction port (with the mirrors) moved out of the way in the last two cases). The outlet port and addition port GRIN lenses 102, 1022 are aligned substantially optically with each other through the thin film filter 103, as are the inlet port and extraction port GRIN lenses 102? , 1023. Another advantage of the free optics design is that it allows permanent fixation of all the optical fibers associated with the WSA / D 100 switch so that they remain stationary. In contrast, opto-mechanical switches such as those described in connection with prior embodiments allow movement of the fibers within the switch. The optical performance of the WSA / D switch is optimized for pitch channels, for which the insertion loss is expected to be only about 0.5 dB. The switchable channel will experience the greatest loss in the pass state, but even in this case, the insertion loss is expected to be less than 1.5 dB. Since the switching occurs on the back side of the filter 103, the passage channels are not affected during the switching interval. Crosstalk is also limited only to cross-band crosstalk that can be obtained by the filter element. Furthermore, since the thin film filter will only allow light of the selected wavelength to pass through it, the optical signal beam is protected against unauthorized wavelengths. Any wavelength outside the band of the device passed into the add port will be reflected by the thin film filter into the extraction port and out of the output port. This is advantageous for security purposes. Furthermore, since the second reflecting surface 106 is placed in the path from the addition port to the output port in the switching position of the switchable element, even the light at the selected wavelength can not be introduced by means of the port of addition, except in the state of addition / extraction of the switch. Figure 14 illustrates a modality that provides additional capacity for adding / removing channels in a modification of the design of Figure 13. In Figure 14, switch WSA / D 100 'includes two selective wavelength switching assemblies 105, 105' coupled in series, each having a thin film filter tuned to a different wavelength, arranged (optically) between the port input 1 and output port 4. Additional addition and extraction ports 2 ', 3' and associated GRIN lenses 1022 'and 1023' are provided to receive the addition / extraction functionality for the additional wavelength. In the embodiment of Figure 14, the signals of the through channel follow a first optical path including the input port GRIN lens 102, the first thin film filter 103, the second thin film filter 103 'and the lens Output port GRIN 1024. The channel signal switchable by the first selective wavelength switching assembly 105 follows (in a step state) a path from the input port to the output port including the channel path step just described, plus a portion that includes the switchable element Mj '. Most particularly, this light follows a trajectory that includes the input port GRIN lens 102 ?, a first pass through the thin film filter 103, the first and second mirror surfaces of the element Mj, a second pass through the thin film filter 103, and the incident surface of the second thin film filter 103 ', from which it is reflected to the output port GRIN lens 102. The channel signal switched by the second optical switching assembly 105 'follows (in a passing state) an analogous path, except that the light thereof is reflected by the first thin film filter 103 and transmitted by the second filter. thin film 103 'and redirected by the second switchable element M' 'to the output port GRIN lens 1024. As will be appreciated in Fig. 14, the basic free optics design of Fig. 13 can be advantageously expanded by simply inserting devices of additional selective wavelength switching and corresponding addition and extraction GRIN lenses, without having to go back to the fiber. By the way, the arrangements shown in figures 13 and 14 might not provide adequate optical performance for some applications, due to the polarization-dependent losses caused by the large angles of incidence on the filter. However, the free optics approach can be easily implemented using smaller reflection angles. Figure 15 illustrates said modality. In the embodiment of Figure 15, a switch WSA / D 300 includes a plurality of selective wavelength filters 303a-303c tuned to a selected wavelength? And mounted on a set of parallel mounting rails 350 to define a zig-zag portion of an optical path that couples the input port 1 and the output port 4. The channel signals received at port 1 through the input line 14 are propagated from the lens GRIN 302? to the first filter 303a. The filter 303a, which is a reflector at the pass-channel wavelengths, reflects the signals to the filter 303b, from which the signals are reflected to the filter 303c and then to the GRIN 302 lens, for its propagation in the output line 20. A switchable element M i 'includes a pair of mirrors 304, 306 mounted to a common movable support platform 307. Platform 307 is movable, as indicated by a double-headed arrow, between a first position (solid line) which corresponds to the step state for the wavelength? and a second (faded) position corresponding to the state of addition / extraction. The alternate positions of the mirrors 304, 306 are not shown in Figure 15 to simplify the drawing. In the first position of the platform 307, the mirror 304 is disposed between the extraction port GRIN lens 3023 and the first thin film filter 303a, and the mirror 306 is disposed between the add port lens GRIN 3022 and the third thin film filter 303c. The light entering the switch at the selected channel wavelength? Is initially transmitted by the first filter 303a to propagate to the extraction port GRIN lens 3023. However, the transmitted light is intercepted by the mirror 304, which reflects the light to the mirror 306. The mirror 306 reflects the light back to the path of the passage channel, by means of the filter 303c. The light thus propagates to the GRIN 302 lens and to the output port 4. Also in this state, the positioning of the mirror 306 will prevent a foreign signal from being introduced by means of the addition port 2. The addition / extraction position, the movable support element 307 is arranged such that the mirrors 304, 306 do not obstruct the respective optical paths between the extraction GRIN lens 3023 and the first thin film filter 303a, and between the addition port lens GRIN 3022 and the third thin film filter 303c. Accordingly, the light entering the switch at the selected channel wavelength? ¡Is transmitted through the first thin film filter 303a and then propagated to the extraction port 3 by means of the GRIN 3023 lens. An additional signal in the channel wavelength? can be added by means of the addition port 2, from which the added signal will propagate through the GRIN 3022 lens, the third thin film filter 303c and the GRIN 3024 lens towards the port 4. In a variation of the structure shown in Figure 15, the second thin film filter 303b may be replaced by a mirror. However, the use of a filter as shown may be preferred. In particular, the filter will transmit, and therefore remove, the residual light at the wavelength? Not removed in the filter 303a, thus allowing the use of filters with a reduced transmission capacity for the length cool ?. The WSA / D switch shown in Figure 15, like the previous modes, provides two optical paths from the input port to the output port. For the pass-through channels, the path includes the input port GRIN lens 302 ?, the first to third filter elements 303a-303c and the output port GRIN lens 302. On the other hand, the switchable channel follows a second path including the input port GRIN lens 302 ?, a pass filter 303a, the mirror 304, the mirror 306 and a pass filter 303c to the output port GRIN lens 302 Also in this design, the switching of the addition / extraction channel occurs beyond a thin film filter that transmits to that channel, and not to the passage channels, whereby the propagation of the passage channels is not affected by the switching operation. The arrangement of Figure 15 is easily expandable by providing additional thin film filters suitably tuned to the mounting rails 350 to extend the zig-zag path, and providing additional addition and extraction ports, moving mirrors and GRIN lenses arranged in an analogous manner. to the corresponding structures of Figure 15. Of course, the exit port would be relocated in correspondence with the end of the extended zig-zag path.

Figure 16 illustrates an embodiment in which the arrangement of Figure 15 has been expanded to provide selective addition / extraction functionality for a second channel at the wavelength j j. The added components corresponding to the components controlling the first channel at the wavelength? Are indicated by corresponding prime reference numbers in FIG. 16. In this embodiment, the signal light at the wavelength? through the filter 303c from the mirror 306 (passing state) or from the GRIN 3022 lens (addition / extraction state) propagates in the zig-zag optical path portion from the 303c filter to the port GRIN lens output 3024, because the thin film filters 303a'-303c 'are tuned to? j. The channel at wavelength? Is switchable between a step state and an add / extract state as described in connection with FIG. 15. The channel at the wavelength? J is switchable in the same manner by means of of corresponding additional components. Figure 17 illustrates how the basic serial structure of the invention can be used to provide a node structure that supports redundant communication, as in a bidirectional ring network, for example. Simply speaking, a bidirectional ring network uses a plurality of nodes interconnected by one or more pairs of fiber optic transmission lines to form a ring. The two fiber lines can be installed along different routes and carry information in opposite directions from one another around the ring. This improves the survivability of the network in the event of multiple failures such as fiber outages and / or failures in the node components. See for a more comprehensive description of bi-directional networks, including ring networks and protection against network failures, see Ramaswami, R. et al., Optical Networks. A Practical Perspective. Morgan Kaufmann Publishers, Inc., 1998 (incorporated herein by reference). In the arrangement of Figure 17, a network node N includes a plurality of bi-directional selective wavelength addition / extraction devices AD? -ADn. These devices include respective signal processing devices SPD? -SPDn, each constructed to receive and transmit signals at one of the corresponding wavelengths? -? N. The signal processing devices may, for example, be synchronous optical network addition / extraction multiplexing terminals (SONET), SONET line terminal equipment, or Internet protocol (IP) routers. Of course, different types of signal processing devices can be used for the different wavelength channels depending on the design requirements of the node. The signal processing devices electronically process the received data and the data to be sent as optical signals over the optical WDM communication network. Each signal processing device is connected to the respective addition and extraction ports of a pair of selective wavelength addition / extraction switches (WSA / D) for the corresponding optical wavelength channel. Each WSA / D switch belongs to one of two series of provisions provided to switch the east and west limit signals, respectively. Each of the WSA / D switches is constructed in accordance with the principles of the invention as previously described. For example, the construction of any of Figures 3, 8-10 and 13 may be used, or a plurality thereof may be used in combination. The arrangements such as those shown in Figs. 14 and 16 can, of course, be used to provide addition / extraction switching for multiple signal processing devices unless discrete switching modules are preferred for the individual wavelengths. It will be appreciated that the arrangement shown in Figure 17 can be easily modified and / or expanded to meet the changing requirements of the system. To modify the provision, the addition / extraction devices AD? -ADn can be ordered in a different serial order. Alternatively one (or more) of the devices can be changed by a similar device operating on a new wavelength (or new respective wavelengths). Even another modification could involve replacing or exchanging the pair of WSA / D switches of one or more devices and adjusting the associated signal processing devices to operate at the respective wavelengths at which their new switch pairs WSA D are tuned. The expansion is achieved by adding one or more addition / extraction devices, each operating at a new respective wavelength, either at the end or at an intermediate point of the series arrangement. Fig. 18 is a more detailed diagram showing a construction example for a bi-directional wavelength addition / extraction device ADi of Fig. 17. The device includes a signal processing device SPDi, a WSA switch / D for the east boundary (upper as shown), and a switch for the western boundary (lower as shown) WSA / D. In the illustrative construction, each of the WSA / D switches includes a selective wavelength filter assembly tuned to the wavelength λ and an optical switching device S i constituted by an optical switch of 2 × 2 fibers. Thus, for example, the specific construction can be as explained in connection with any of Figures 3 and 8-10. The signal processing device SPD i is connected by the addition lines 49 and the extraction lines 48 to the switches S i 2 x 2 of the switches of the east and west boundary WSA / D. In the step state of the 2x2 switch on the east boundary, the signal received on the supply fiber of the east boundary 14 at the channel wavelength λ will propagate to the east boundary output fiber 20 for transmission with the east boundary. by channel signals. In the add / remove state of the 2x2 switch on the east boundary, the signal received at the channel wavelength? ¡Is extracted by the west extraction line to the signal processing device SPD¡. The signal processing device can also introduce a new signal on the same channel through the east addition line to propagate with the pass channels on the output fiber of the east boundary 20. The switch of the west limit switch 2x2 provides the same functionality of addition / extraction for the transmissions of the western limit in the wavelength? ¡of the channel. The SPD signal processor device and the optical switches are controlled by a common network management and control system (not shown). The control operations specific to the network control and management system will depend on the type of network involved and its failure protection procedures. For example, in a unidirectional switched ring (UPSR) network, signal traffic is transmitted concurrently in both directions towards the east boundary and west boundary. In this case, the signal processing device will process the received signal from one of the extraction lines 48 and will emit any new signal on the selected wavelength channel in both directions by the addition lines 49. In the case of a failure , such as a fiber cut or a 2x2 commutator failure on the side of the selected extraction line, the signal processing device will switch to a "protective" mode to receive the data through the other extraction line and continue transmitting new signals using one or both lines of addition depending on the failure mode. For a more comprehensive discussion of UPSR and other ring networks, see the text mentioned above by Ramaswami et al.

Figures 19 and 20 illustrate modified embodiments using optical switching devices S i, which incorporate multiple switches connected together (preferably non-wavelength responsive) to collectively provide the addition / removal functionality of the switches 2x2 previously described. Referring to Figure 19, each switching device includes two interconnected 1x2 optical switches S1¡ S2¡. The four 1x2 switches are preferably energized independently so that a failure in the power to one of the switches will not make the other switch inoperable. Each switch S1 has an output connected to the fiber 44 that runs from the corresponding wavelength selective optical filter assembly to receive the selected signal on the wavelength channel?, A first output port connected to the line corresponding extraction 48, and a second output port connected to an input port of the corresponding switch S2¡. The input port of each switch S1 can be switched between the two output ports thereof so that the signal at the input port can propagate either to the corresponding switch S2¡ or to the signal processing device SPD¡. Each switch S2i has a second input port connected to the corresponding extraction line 49 and an output port connected to the fiber 44 going back to the corresponding filter assembly. The output port of each of the switches S2i can be switched between the two input ports so that the signal on any of the input ports can be propagated to the corresponding filter assembly to be transmitted on the fiber of corresponding output. In Figure 19 the state of addition / extraction of each of the optical switching devices S i 'is represented as the continuous line state of the respective switching pair S1 ¡, S2¡. The state of passage is represented as the state in dotted lines. The construction shown in Fig. 19 increases the ability of the node to tolerate second faults compared to the construction in Fig. 18. For example, if the switch 2x2 of the east boundary in Fig. 18 fails (mechanically or due to power loss for the commutator), the addition / extraction device ADi can still transmit and receive via the 2x2 commutator of the west boundary. But, in the case of a second fault occurring on the side of the west boundary, such as a cut in the fiber of the west boundary or a fault in the switch 2x2 of the west boundary, the addition / extraction device ADi is isolated of the network (can not transmit and / or receive). In the AD / 'addition / removal device of Figure 19, a single fault in the switch on the east (or western boundary) side will only prevent reception or transmission on the east (or western boundary), but will not both The commutator remaining on that side can still be used. For example, if the west extraction switch fails, the addition switch can still be used for transmission on the east boundary. Then, the only additional faults on the west boundary side that could isolate the network addition / extraction device could be those that prevent reception at the western boundary, such as a cut in the feed fiber 14 'or a failure of the extraction switch this. An additional failure to interrupt the transmission at the west boundary, such as a cutoff at the output fiber 20 'or a failure at the west addition switch, would not isolate the addition / extraction device because the device can still transmit at the east limit on the output fiber 20 through the addition switch this. Figure 20 shows an addition / extraction device ADi "having the same switching arrangement as in figure 19. This device differs from that of figure 19 in that the west addition and extraction switches share a power source and the addition and extraction switches share another power source The fault tolerance of the device of Figure 20 for mechanical faults of the commutator is similar to the device of Figure 19. However, the tolerance for power failures of the switch is reduced relative to the device of Figure 19 due to the shared power source arrangement. Even, the total reliability is greater than that of the device in Figure 18. It will be appreciated by those skilled in the art that the preferred embodiments shown and described herein are illustrative only and that various changes and modifications are possible while maintaining the basic principles and the field of the present invention.

Claims (64)

1. NOVELTY OF THE INVENTION CLAIMS 1. - A switching device for optical communications WDM comprising: a wavelength selective optical switching assembly that includes an input port built to receive multiple optical wavelength channels, an output port, a selective optical filter of length of wave and an optical switching device; said selective wavelength filter being constructed and placed to direct signals over a plurality of received wavelength channels to propagate them to said output port and to direct a signal over another of the received length channels to said output device. Optical switching; said optical switching device being arranged and being operable to switch said other wavelength channel between a step state and an extraction or addition / extraction state without switching said plurality of wavelength channels.
2. 2. The apparatus according to claim 1, further characterized in that said optical switching device includes a non-selective optical wavelength 4-port switch.
3. 3. The apparatus according to claim 2, further characterized in that said selective wavelength filter includes at least one selective wavelength grid. 4. - The apparatus according to claim 1, further characterized in that all the optical components of said selective wavelength filter and said optical switching device are free optical components. 5. The apparatus according to claim 1, further characterized in that said selective wavelength filter includes a thin film filter transmissive to said other wavelength channel and reflector towards said plurality of wavelength channels, and disposed in a signal path that propagates from said input port and wherein said switching portion has an element that can be switched between a first position to intercept said signal on said other channel transmitted by said thin film filter and to cause that the signal propagates back through said thin film filter to said output port, and a second position to allow the signal to be extracted. 6. The WDM optical communications switching apparatus comprising: a wavelength selective optical switching assembly that includes an input port constructed to receive multiple optical wavelength channels, an output port, a first optical circulator, a second optical circulator, a selective optical wavelength filter and an optical switching device; each of said first and second circulators having first, second and third ports, the first port of said first circulator constituting said entrance port, the third port of said second circulator constituting said exit port; said selective wavelength filter including a reflecting grid connected between the second ports of said first and second circulators and constructed to direct signals on a plurality of wavelength channels received to propagate them to said output port by said second circulator and for directing a signal on another of the received wavelength channels towards said optical switching device; said optical switching device being connected between the third port of said first circulator and the first port of said second circulator and being operative to switch said other wavelength channel between a state of passage and an extraction state or state of addition / extraction without switching said plurality of wavelength channels. 7 '.- The apparatus according to claim 6, further characterized by said optical switching device includes a non-selective optical wavelength 4-port switch. 8. The WDM optical communication switching apparatus comprising: a wavelength selective optical switching assembly that includes an input port constructed to receive multiple optical wavelength channels, an output port, a first optical coupler, a second optical coupler, a selective wave optical filter and an optical switching device; each of said first and second couplers having a first, second and third ports, the first port of said first coupler constituting said input port, the second port of said second coupler constituting said output port; said selective wavelength filter including a reflecting grid connected between the second port of said first coupler and the first port of said second coupler and constructed to direct signals on a plurality of the wavelength channels received to propagate them to said port. output by said second coupler and to direct a signal on another one of the received wavelength channels towards said optical switching device; said optical switching device being connected between the third ports of said first and second couplers and being functional to switch said other wavelength channel between a step state and an extraction state or addition / extraction state without switching said plurality of wavelength channels. 9. The apparatus according to claim 8, further characterized in that said first and second couplers are fiber optic couplers. 10. The apparatus according to claim 8, further characterized in that said switching device includes a non-selective wavelength optical switch of 4 ports. 11. The WDM optical communication switching apparatus comprising: a wavelength selective optical switching assembly that includes an input port constructed to receive multiple optical wavelength channels, an output port, a selective optical filter of wavelength and an optical switching device; said selective wavelength optical filter comprising a 4-port notch filter device having a thin film notch filter coupled to a first port, a second port, a third port and a fourth port, constituting said first port and fourth said port of entry and said exit port, respectively; said notch filter being constructed to reflect signals on a plurality of the wavelength channels received to propagate them to said fourth output port and to transmit a signal on another of the received wavelength channels to propagate it to said switching device optics by said second port; said optical switching device being connected between said second port and said third port and being functional to switch said other wavelength channel between a step state and an extraction state or addition / extraction state without switching said plurality of channels wavelength. 12. The apparatus according to claim 1, further characterized in that said optical switching device includes a non-selective wavelength optical switch of 4 ports. 13. The WDM optical communication switching apparatus comprising: a wavelength selective optical switching assembly that includes an input port constructed to receive multiple optical wavelength channels, an output port, an optical filter device Mach-Zehnder selective wavelength, and an optical switching device; the filter of the Mach-Zehnder device being constructed and arranged to direct signals on a plurality of received wavelength channels to propagate them to said output port and to direct a signal on another of the received wavelength channels towards said device Optical switching; said optical switching device being arranged and being operable to switch said other wavelength channel between a step state and an extraction state or addition / extraction state without switching said plurality of wavelength channels. 14. The apparatus according to claim 13, further characterized in that said optical switching device includes a non-selective wavelength 4-port optical switch. 15. The apparatus according to claim 13, further characterized in that said Mach-Zehnder filter device comprises first and second optical couplers 2x2, each having a first port, a second port, a third port and a fourth port, constituting the first port of said first coupler said inlet port, the third and fourth port of said first coupler are connected by the first and second optical path of phase shift to the ports, respectively, of said second coupler, a portion of reflecting grid is disposed in said first and second optical phase shift paths, and said optical switching device is connected between the second port of said first coupler and the third port of said second coupler, and the fourth port of said second coupler constitutes said port of exit. 16. The apparatus according to claim 15, further characterized in that said reflecting grid portion comprises the first and second reflecting grids placed in said first and second optical phase shift paths, respectively, said first and second reflecting grids being tuned. with said other channel. 17. The switching device for optical communications WDM, comprising: an input port constructed to receive a plurality of optical signals multiplexed each on a different wavelength channel; an exit port; a first optical path from said port of entry to said exit door; and a second optical path from said port of entry to said exit port; said second optical path including an optical switching device and said first optical path including a selective wavelength filter which is constructed to cause at least one of said selected signals to propagate to said switching device and to cause the rest of said signals propagate to said exit port by means of a track including said first optical path; said switching device having a first state for causing said at least one selected signal propagated from said selective wavelength filter to propagate to said output port by means of said second optical path, and a second state in which said at least one selected signal propagated from said selective wavelength filter is extracted so that it does not propagate to said output port. 18. The apparatus according to claim 17, further characterized in that said switching device comprises a non-selective wavelength optical switch. 19. The apparatus according to claim 18, further characterized in that said 4-port switch has a first and fourth port respectively coupled to said input port and said output port in said first state, a second port coupled to said port exit through said fourth port and a third port coupled to said entry port by said first port in said second state, and said second and fourth ports constitute the ports of addition and extraction, respectively. 20. The apparatus according to claim 17, which includes a first optical circulator and a second optical circulator, each having first, second and third ports, the first port of said first circulator being said entry port, constituting the third said second circulator port said output port, said selective wavelength filter including a reflective grid connected between the second ports of said first and second circulators, and said switching device being connected between the third port of said first circular and the first port of said second circulator. 21. The apparatus according to claim 17, including a first optical coupler and a second optical coupler, each having first, second and third port, the first port of said first coupler being said entry port, constituting the second said second coupling port said output port, said selective wavelength filter including a reflecting grid connected between the second port of said first coupler and the first port of said second coupler, and said switching device being connected between the third ports of said first and second couplers. 22. The apparatus according to claim 17, which includes a 4-port filter device having a thin film notch filter constituting said selective wavelength filter and coupled to a first port, a second port , a third port and a fourth port, said first port and fourth port constituting said input port and said output port, respectively, said switching device being connected between said second port and said third port, and said notch filter being constructed of thin film to reflect said remnant of said signals to propagate them to said fourth port and to transmit said at least one selected signal to propagate it to said optical switching device by said second port. 23. - The apparatus according to claim 17, including a Mach-Zehnder filter assembly that incorporates said selective wavelength filter, said Mach-Zehnder filter assembly comprising: first and second optical couplers 2x2, each having first , second, third and fourth ports; the first port of said first coupler constituting said input port, the third and fourth ports of said first coupler being connected by the first and second optical phase shift paths with the first and second ports, respectively, of said second coupler, and the fourth port of said second coupler constituting said output port; and a portion of reflecting grid disposed in said first and second optical phase shift paths; said switching device being connected between the second port of said first coupler and the third port of said second coupler. 24. The apparatus according to claim 23, further characterized in that said reflecting grid portion comprises the first and second reflecting grids in said first and second optical phase shift paths, respectively, said first and second reflecting grids being tuned to the channel of said selected signal. 25. The apparatus according to claim 17, further characterized in that said selective wavelength filter is a thin film filter transmissive to said signal and reflector to the rest of said signals, and said switching device includes an element that can to be switched between a first position to intercept said one signal to cause the signal to propagate back to said thin film filter towards said output port, and a second position to allow the signal to be extracted. 26. The switching device for optical communications WDM comprising: an input port; a first selective optical wavelength switching assembly; and an output port and an extraction port optically coupled to said input port by said optical switching assembly; said optical switching assembly including a thin film filter and a switching device; said thin film filter being transmissive in light of a first communication wavelength and reflector in light of a second communication wavelength, and being arranged in a light path that propagates from said input port to reflect the light of said second wavelength to propagate it to said output port and to transmit the light of said first wavelength; said switching device having an element that can be switched between a first position to intercept the light of said first wavelength transmitted by said thin film filter and to cause the light to propagate to said output port, and a second position to allow light of said first wavelength transmitted by said thin film filter to propagate to said extraction port. 27. - The apparatus according to claim 26, further characterized in that said switchable element has a first reflecting surface that intercepts the light of said first wavelength transmitted by said thin film filter in said first position. 28. The apparatus according to claim 27, further characterized in that said switching device has a second reflecting surface, and said first reflecting surface reflects the intercepted light towards said second reflecting surface to propagate it towards said exit port. 29. The apparatus according to claim 28, further characterized in that said second reflecting surface reflects the intercepted light back to said thin film filter. 30. The apparatus according to claim 28, further characterized in that said first and second reflecting surfaces are fixedly positioned on a common mobile support element. 31. The apparatus according to claim 30, further characterized in that said support element is a prism. 32. The apparatus according to claim 26, further characterized in that it comprises a pulse mechanism for moving said switchable element between said first and second positions. 33. The apparatus according to claim 26, further characterized in that it comprises: a second extraction door; and a second selective wavelength optical switching assembly that includes a second thin film filter and a second switching device; said thin film filter being transmissive in light of said second wavelength and reflector to the light of said first wavelength and being placed in a path of light propagated from said thin film filter of said first optical switching assembly to reflect the light of said first wavelength to propagate it to said output port and to transmit the light of said wavelength; said second switching device including an element that can be switched between a first position to intercept the light of said second wavelength transmitted by said second thin film filter to cause light to propagate towards said outlet port; and a second position to allow light of said second wavelength transmitted by said second thin film filter to propagate to said second extraction port. 34. The apparatus according to claim 26, further characterized in that it comprises: an addition port coupled to said output port by said first optical switching assembly; wherein said thin film filter is placed in a light path that propagates from said addition port, and said light path is blocked when said switchable element is in said first position and is not blocked when said switchable element is in said location. second position. 35. - The apparatus according to claim 26, further characterized in that said input port is coupled to said first optical switching assembly by a first lens, and said extraction port is coupled to said first optical switching assembly by a second lens substantially optically aligned with said first lens through said thin film filter. The apparatus according to claim 26, further characterized in that it comprises: an addition port coupled to said output port by said first optical switching assembly, said addition port being coupled to said first optical switching assembly by means of a first lens and said output port being coupled to said first optical switching assembly by a second slow motion substantially aligned optically with said first lens through said thin film filter. 37.- The apparatus according to claim 26, further characterized in that said first optical switching assembly further comprises a plurality of reflector elements arranged to define, together with said thin film filter, a zigzag optical path that is coupled with said port of entry and said exit port, said thin film filter being positioned at a vertex of said optical path in a zigzag manner. 38.- The apparatus according to claim 37, further characterized in that at least one of said reflector elements is an additional thin film filter transmissive to the light of said first wavelength and reflector in light of said second length of wave, and said switchable element in said first position causes the intercepted light of said first wavelength to propagate through said additional thin film filter and towards said zigzag optical path. 39.- The apparatus according to claim 38, further characterized in that said second thin film filter is coupled to an add port to add a signal to be transmitted to said output port on a portion of said optical path in zig Zag. 40.- A switching device arrangement according to claim 26 connected in series, the first wavelengths being associated with the respective thin film filters which are different. 41 .- The switching device for optical communications WDM comprising: an input port built to receive a plurality of wavelength channels; a selective wavelength optical switching assembly; and an output port optically coupled to said input port by said switching assembly; said switching assembly being constructed to switch a wavelength channel selected between a step state and an extraction or addition / extraction state without switching another wavelength channel present in said switching assembly, all the optical components being said switching assembly of free optics components. 42. - The apparatus according to claim 41, further characterized in that said free optics components include a thin film filter and a switchable element, said thin film filter being transmissive to the light of a first communication wavelength and reflector to the light of a second communication wavelength and being placed in a light path that propagates from said input port to reflect the light of said second wavelength to propagate it to said output port and to transmit the light of said first wavelength, said element being switchable between a first position to intercept the light of said first wavelength transmitted by said thin film filter and to cause it to propagate to said output port, and a second position to allow the light of said first wavelength transmitted by said thin film filter is propagated towards a extraction. 43.- The apparatus according to claim 42, further characterized in that said free optical components include respective lenses that couple said input, output and extraction ports with said thin film filter. The apparatus according to claim 43, further characterized in that the lenses for said inlet port are substantially aligned optically with the lenses for said extraction port through said thin film filter. 45. - The apparatus according to claim 43, further characterized in that said lenses are GRIN lenses. 46.- A signal addition / extraction apparatus for an optical communication system WDM, comprising: a plurality of selective wavelength addition / extraction switches coupled in series, each of the switches being constructed to switch a channel of corresponding wavelength between a step state and an addition / extraction state without switching another wavelength channel present in that switch. 47. The apparatus according to claim 46, further characterized in that said switch is constructed to only switch the corresponding wavelength channel. 48. The apparatus according to claim 46, further characterized in that at least one of said switches comprises: a wavelength selective optical switching assembly that includes an input port constructed to receive multiple channels of optical wavelength , an output port, a selective optical wavelength filter and an optical switching device; said selective wavelength filter being arranged and being functional to direct signals on a plurality of the received wavelength channels to propagate them to said output port and to direct a signal on another of the received wavelength channels towards said optical switching device; said optical switching device being arranged and being functional to switch said other wavelength channel between a step state and an extraction state or addition / extraction state without switching said plurality of wavelength channels. 49. The apparatus according to claim 46, further characterized in that at least one of said switches comprises: an input port constructed to receive a plurality of optical signals multiplexed each on a different wavelength channel; an exit port; a first optical path from said port of entry to said port of entry to said port of exit; and a second optical path from said port of entry to said exit port; said second optical path including an optical switching device and said first optical path including a selective wavelength filter which is constructed to cause at least one of said selected signals to propagate to said switching device and to cause the rest of said signals propagate to said exit port by means of a track including said first optical path; said switching device having a first state for causing said at least one signal propagated from said selective wavelength filter to propagate to said output port by means of said second optical path, and a second state in which said at least one selected signal propagated from said selective wavelength filter is disconnected, so as not to propagate to said output port. 50.- The apparatus according to claim 46, characterized in that at least one of said switches comprises: an input port; a first selective optical wavelength switching assembly; and an output port and an extraction port optically coupled to said input port by said optical switching assembly; said optical switching assembly including a thin film filter and a switching device; said transmissive thin film filter being in the light of a first communication wavelength and reflector in the light of a second communication wavelength, and being placed in a light path that propagates from said input port to reflect the light of said second wavelength to propagate it to said output port and to transmit the light of said first wavelength; said switching device having an element that can be switched between a first position to intercept the light of said first wavelength transmitted by said thin film filter and to cause the light to propagate to said output port, and a second position to allowing light of said first wavelength transmitted by said thin film filter to propagate to said extraction port. 51. The apparatus according to claim 46, further characterized in that at least one of said switches comprises: an input port constructed to receive a plurality of wavelength channels; a selective wavelength optical switching assembly; and an output port optically coupled to said input port by said switching assembly; said switching assembly being constructed to switch a selected wavelength channel between a step state and an extraction or addition / extraction state without switching another wavelength channel present in said switching assembly, all the optical components being of said optical-free switching assembly. 52. The apparatus according to claim 46, further characterized in that each switch is a module having an input port, an output port, an extraction port and an addition port, and the ports of entry and exit of the ports. respective switches are connected so that they couple the modules in series. 53. The apparatus according to claim 46, further characterized in that at least one of said switches comprises: a wavelength selective optical switching assembly that includes an input port constructed to receive multiple optical wavelength channels , an output port, a first optical circulator, a second optical circulator, a selective optical wavelength filter, and an optical switching device; each of said first and second circulators have first, second and third ports, the first port of said first circulator constituting said entrance port, the third port of said second circulator constituting said exit port; said selective wavelength filter including a reflecting grid connected between the second ports of said first and second circulators and constructed to direct signals on a plurality of wavelength channels received to propagate them to said output port by said second circulator and to direct a signal on another of the received wavelength channels towards said optical switching device; said optical switching device being connected between the third port of said first circulator and the first port of said second circulator and being functional to switch said other wavelength channel between a state of passage and a state of extraction or addition / extraction without switching said plurality of wavelength channels. 54. The apparatus according to claim 46, further characterized in that at least one of said switches comprises: a wavelength selective optical switching assembly that includes an input port constructed to receive multiple optical wavelength channels , an output port, a first optical coupler, a second optical coupler, a selective optical wavelength filter and an optical switching device; each of said first and second couplers having first, second and third ports, the first port of said first coupler constituting said input port, the second port of said second coupler constituting said output port; said selective wavelength filter including a reflecting grid connected between the second port of said first coupler and the first port of said second coupler and constructed to direct signals on a plurality of received wavelength channels to propagate them to said port of output by said second coupler and to direct a signal on another one of the received wavelength channels tds said optical switching device; said optical switching device being connected between the third ports of said first and second couplers and being functional to switch said other wavelength channel between a step state and an extraction or addition / extraction state without switching said plurality of channels wavelength. The apparatus according to claim 46, further characterized in that at least one of said switches comprises: a wavelength selective optical switching assembly that includes an input port constructed to receive multiple optical wavelength channels , an output port, a selective optical wavelength filter and an optical switching device; said selective wavelength optical filter comprising a 4-port notch filter device having a thin film notch filter coupled to a first port, a second port, a third port and a fourth port, constituting said first port and fourth port said inlet port and said outlet port respectively; said notch filter being constructed to reflect signals on a plurality of received wavelength channels to propagate them to said fourth output port and to transmit a signal on another of the received wavelength channels to propagate it to said switching device optics by said second port; said optical switching device being connected between said second port and said third port and being functional to switch said other wavelength channel between a step state and an extraction or addition / extraction state without switching said plurality of channels of length of wave. 56.- The apparatus according to claim 46, further characterized in that at least one of said switches comprises: a wavelength selective optical switching assembly that includes an input port built to receive multiple optical wavelength channels , an output port, a Mach-Zehnder selective optical wavelength filter device and an optical switching device; said Mach-Zehnder device filter being constructed and arranged to direct signals over a plurality of received wavelength channels to propagate them to said output port and to direct a signal over another of the received wavelength channels tds said device Optical switching; said optical switching device being positioned and being functional to switch said other wavelength channel between a step state and an extraction or addition / extraction state without switching said plurality of wavelength channels. 57. - The apparatus according to claim 56, further characterized in that at least one of said switches comprises: said Mach-Zehnder filter device comprising first and second optical couplers 2x2, each having a first port, a second port, a third port and a fourth port, the first port of said first coupler constituting said input port, the third and fourth port of said first coupler being connected by the first and second optical paths of phase shift to the ports, respectively, of said second coupler, a reflective grid portion is disposed in said first and second optical phase shift paths, and said optical switching device is connected between the second port of said first coupler and the third port of said second coupler, and the fourth The port of said second coupler constitutes said output port. 58.- The apparatus according to any of claims 1, 6, 8, 11, 13 and 17, further characterized in that said optical switching device includes a plurality of optical switches connected together that operate collectively to perform the switching between the state of step and the state of addition / extraction. 59. The apparatus according to claim 58, further characterized in that said plurality of optical switches consists of 2 optical switches 1x2. 60. - A wavelength selective addition / extraction switching device having redundant addition / extraction switching capability comprising: a signal processing device constructed to receive and transmit optical signals; and a pair of selective addition / extraction wave switches, each of the addition / extraction switches arranged to receive and output signals over a plurality of optical wavelength channels in an optical transmission line different from that of the other switch, and having an add port connected to receive an optical signal on one of said selected wavelength channels from said signal processing device and a connected extraction port to disconnect an optical signal on the wavelength channel selected to said signal processing device, each addition / extraction switch being further constructed to switch the selected wavelength channel between a step state and an addition / extraction state without switching another wavelength channel present in that switch . 61.- A device according to claim 60, further characterized in that at least one of said selective wavelength addition / extraction switches constitutes an apparatus according to any of claims 1, 6, 8, 11, 13, 17, 26 and 41. 62.- The optical communication apparatus comprising a plurality of selective wavelength addition / extraction switching devices according to claim 60, further characterized by the first addition / extraction switches. of the respective pairs are connected to each other in a first series and the second addition / extraction switches of the respective pairs are connected to each other in a second series. 63.- A method for accommodating at least one new wavelength channel and / or a new wavelength plan in an optical communication network WDM, comprising: providing a network node that includes an optical communications device in accordance with claim 62; and modifying said optical communication apparatus by means of one or more of the following: a) replacing at least one of the addition / extraction switching devices, each with a similar device operating on a new wavelength channel respective; b) reorder the serial order of the addition / extraction switching devices; c) replacing the pair of switches of at least one addition / extraction switching device with a switching pair tuned to a different wavelength channel in order to operate that addition / extraction switching device in the switching channel. different wavelength; d) providing another one of said addition / extraction switching devices operative on a new wavelength channel and connecting the first addition / extraction switch and the second addition / extraction switch of said other switching device to said first series and said second series, respectively.64. - The signal addition / extraction apparatus for an optical communication system WDM, comprising: a plurality of selective wavelength addition / extraction switching assemblies coupled in series, each assembly being constructed to switch a length channel of corresponding wave between a passing state and an addition / extraction state without switching another wavelength channel present in that assembly. The apparatus according to claim 64, further characterized in that said switching assemblies define a zigzag optical path through the series. 66.- The apparatus according to claim 42, further characterized in that said switchable element in said first position causes the intercepted light to propagate back to said thin film filter.