FR2849015A1 - Optical telecommunications switching having five optical switch connections providing input intermediate outputs from four switches and fifth connection providing remaining outputs - Google Patents

Abstract

The optical microswitch connects 4N optical inputs (I1n to I4n) with 4N optical outputs (O1n to O4n). There are five optical switch connections (S1 to S5) with 2N outputs. A group of four switches are connected together to generate 2N intermediate outputs and to a final output whilst a fifth structure provides the remaining outputs.

Description

OPTICAL MICROSWITCH

  Technical field The invention relates to the field of microelectronics applied to telecommunications by optical means. It relates more precisely to microelectronic optical components ensuring switching functions, commonly called "switch". Among these components, we can mainly mention brewers optics, also called "optical cross connect OXC", as well as extraction / insertion multiplexers, also called "add drop 10 multiplexer".

  The invention relates more specifically to a new architecture of this type of component, intended to limit the insertion losses as well as the optical path, by reducing the number of necessary mirrors. BACKGROUND ART In general, an optical switch is connected to a set of optical inputs and outputs. A set of movable mirrors, and more generally of reflecting structures, is arranged in alignment with the various optical inputs and outputs. so that when the mirrors are moved appropriately, any optical input can be connected to any of the optical outputs.

  Conventionally, these different mirrors are arranged in a matrix organization, which is square when the number of inputs is equal to the number of optical outputs. An example of such a matrix is described in document US 2002/0102045.

  However, this type of matrix structure has drawbacks, in particular in terms of insertion losses. In fact, the larger the size of the matrix, the greater the optical paths that the rays can travel inside the matrix. In addition, these optical paths are staged in a wide range. This range goes from a very small value, corresponding to the path for connecting the input and the output closest to a corner of the matrix, up to a value the highest corresponding substantially to twice the dimension of this matrix. An objective of the invention is to reduce the optical path within the switch, in order to reduce the insertion losses.

  Another object of the invention, by reducing this optical path, is also to reduce the distance over which the mirror must move, moving to a blocking state, and therefore thus improve the efficiency of the actuators used.

  The importance of the longest optical path within a matrix is a consequence of the fact that it is necessary to have a sufficient number of mirrors to allow the combination of any input with any optical output Thus, for example, for a matrix making it possible to combine four inputs with four outputs, a number of sixteen mirrors is necessary to ensure the twenty-four combinations between the four optical inputs and the four outputs.

  Another objective of the invention is to reduce the number of mirrors in order to limit the optical path traveled by the different beams propagating within the switch.

  DESCRIPTION OF THE INVENTION The invention therefore relates first of all to an optical microswitch, making it possible to interconnect four optical inputs with four optical outputs. According to the invention, this microswitch comprises five mirrors 30 divided into two groups A first group of four mirrors is arranged in two lines and two columns These mirrors are arranged opposite four optical inputs, which are each aligned with a line or a column These mirrors are also arranged opposite two of the optical outputs of the microswitch, as well as two intermediate optical outputs These different outputs, global or intermediate, are each aligned with a line or a column, and are in alignment with a optical inputs The microswitch also includes a second group of mirrors, limited to the fifth mirror, which acts as a crossover switch The inputs of this fifth mirror are formed by the two intermediate outputs from the group of four mirrors, and the outputs of this patch switch are formed by the two remaining optical outputs, which are not not connected to the group of four 10 mirrors.

  In other words, the invention consists in no longer using a fully matrix structure, but in constructing a switch from two zones operating in a complementary manner, and of a different structure. It should be noted that the number 15 of mirrors for a switch 4 x 4 according to the invention, amounts to five, while it is sixteen for a conventional 4 × 4 switch matrix, comprising four rows and four columns The reduction in the number of mirrors therefore inevitably results in a reduction in the optical path of the different beams propagating within the switch, and therefore a reduction in optical losses It should also be noted that the number of five mirrors for a 4 x 4 switch corresponds to the minimum number to allow the twenty four combinations of 'entry and exit, since it therefore authorizes thirty-two different states. In practice, the two groups of mirrors can be installed either on the same substrate, or preferably, on two different substrates. In the latter case, it is possible to optimize each of the groups, using identical or different technologies.

  In practice, the connections between the different groups, that is to say the way in which the intermediate outputs are routed from the first group of four mirrors to the fifth mirror, can be carried out either by fixed mirrors, or by preferred way by waveguides Indeed, in the latter case, the optical losses for the transmission between two groups of mirrors are very limited, and it is therefore not necessary to have the two groups of mirrors with the lowest possible distance This solution is therefore recommended when the two groups of mirrors are produced on different substrates.

  On the other hand, when the two groups of mirrors are produced on the same substrate, it may be practical to redirect the intermediate outputs of the first group of four mirrors to the fifth mirror by means of a fixed mirror 10, which must on the other hand be relatively precisely oriented.

  It is easy to understand that this principle can be reproduced on a larger scale, and transposed to an optical switch making it possible to connect 4 N optical inputs with 4 N optical outputs. In this case, the switch has five structures forming switches of smaller size, with 2 N inputs and 2 N outputs. These structures are arranged so that they form a group of four structures which are connected to 4 N optical inputs and with 2 N optical outputs These four structures are interconnected to generate 2 N intermediate outputs A fifth switch structure 2 N x 2 N is connected to these 2 N intermediate outputs, to ensure mixing with the 2 N outputs remaining optics.

  In practice, this architecture therefore makes it possible to produce 8 x 8 switches 25 from 4 x 4 switch structures as described above. Such a switch therefore comprises 5 times 5 mirrors, ie a total number of 25, to be compared with a number of 64 mirrors for a switch produced according to a square matrix of eight columns and eight rows Similarly, for a 16 x 16 switch, the number of mirrors with a construction according to the invention is 30,125, to be compared with the number of 256 in the case of a conventional matrix.

  Brief description of the figures The manner of carrying out the invention as well as the advantages which ensue therefrom, will emerge clearly from the description of the embodiments which follow, with the support of the appended figures in which: 'a 4 x 4 switch produced in accordance with the invention, with mirrors moving parallel to the plane containing the input and output optical fibers; * Figures 2 and 3 are block diagrams of alternative embodiments using mirrors moving perpendicular to the plane of the optical fibers; 10 * Figure 4 is a general diagram illustrating the embodiment of a switch on two separate chips; * Figures 5 and 6 are block diagrams illustrating the generalization of the invention to switches 4 Nx 4 N. Way of carrying out the invention The switch (1) 4 x 4 illustrated in Figure 1 has four optical inputs, illustrated by the arrows (Il, I 2, I 3 and I 4) It also has four optical outputs represented by the arrows (01, 02, 03 and 04) The four inputs Il, I 2, I 3, I 4 are connected to a set of four mirrors (M 1, M 2, M 3, M 4) which are arranged in two rows and two columns defined by the entrances (II to I 4) In the illustrated form, each mirror has a reflecting zone ( 3) which can be moved in its main direction by an actuator (2) which, for example, is an interdigitated comb network. Thus, the reflecting structure of the mirror (M 4) can be moved to intercept the entry. (13) in order to redirect it to the exit (O 1) At the same time, the inlet (I 4) is then directed towards the outlet (04).

  When, on the contrary, the mirror (M 4) is in the rest state, the entry (I 3) propagates freely until the exit (04), the entry (14) then propagating also and freely towards the output (01), or more precisely towards the mirror M 3 The mirror M 4 therefore acts as a 2 x 2 switch.

  According to the invention, the switch (1) also includes a fifth mirror (Ms), which can intercept beams forming the intermediate outputs (O '3) and (O' 4) of the group of four mirrors (MI-M 4 ).

  These intermediate outputs are reflected by two fixed mirrors (7,8) The mirror (5) therefore also acts as a 2 x 2 switch to blend the two intermediate outputs (O '2) and (O' 3) with the outputs of the switch (02) and (03).

  Appropriate control of each of the mirrors (M 1-Ms) therefore makes it possible to connect each of the outputs (Il-I 4) to any of the outputs (0104).

  In practice, the mirrors illustrated in FIG. 1 can be produced on different types of substrates, and in particular SOI substrates. 10 An alternative embodiment is illustrated in FIG. 2, in which the mirrors (Mll, M 12, M 13, M 14, M 15) do not move parallel to the plane defined by the optical fibers, but perpendicular to the latter De such mirrors can for example be produced according to the technique described by the Applicant in document WO 02/44781 This technology makes it possible in particular to achieve alignment between the optical fibers and the faces of the mirrors very precisely, for etching operations chemical.

  Another variant is illustrated in FIG. 3, in which the four mirrors 20 (M 21, M 22, M 23, M 24) have orientations that are not convergent as in FIG. 2, but parallel, with a distribution of the different inputs and different exits.

  According to another characteristic of the invention, the different groups of 25 mirrors can be produced on different chips or substrates, as illustrated diagrammatically in FIG. 4 Thus, the four mirrors associated with the four inputs (Il-I 4), are brought together on a first chip (10) produced according to a first technology, that is to say for example on an SOI substrate as illustrated in FIG. 1, or even with the mirrors moving perpendicularly between the optical fibers as illustrated in Figure 2 This first group of four mirrors is therefore also connected to two outputs (01.02) It also generates two intermediate outputs (O'2, O'3) which are connected to a second chip (11) containing a single mirror, therefore acting as a 2 x 2 switch This second chip can be produced using the same technology or a technology different from the first (10) The transmission of these intermediate outputs (O '2,0 '3) can advantageously be done by waveguides, such as optical fibers, in which the losses are particularly reduced This connection can for example be carried out by so-called "splicing" methods which are on the one hand reduced while providing excellent results in terms of quality.

  This embodiment in two separate chips as illustrated in FIG. 4, 10 has the advantage of not involving constraints on the alignments of the mirrors of the two groups. In addition, the optical path traveled by the different beams in the free space, that is to say near the mirror, is relatively reduced, since it is limited to the zones of direct proximity of the mirror These values are to be compared with the sum of the dimensions of a matrix in the case of a conventional switch.

  As already mentioned, the principle illustrated by a 4 x 4 switch can be generalized to 4 Nx 4 N switches, as illustrated in Figures 5 and 6 In this case, 4 N inputs (I 1 N, I 2 N, I 3 N , 14 N) are assigned to a first group (15) of four switches (51-54), each represented by a block illustrating a 2 Nx 2 N switch These different 2 Nx 2 N switches (SI-54) are interconnected between them.

  They are also connected to two sets 2 N of intermediate outputs (O'2 N, Ot 3 N) of the first group (15) of switches 2 Nx 2 N, which are routed to a fifth switch 2 Nx 2 N ( 55), itself connected to 2 N outputs 25 (O 2 N, O 3 N) The interconnection of the 2 Nx 2 N switches (SI-Ss) between them can be carried out in a different form than that of FIG. 5 , as for example illustrated in FIG. 6.

  This same structure of a 2 N × 2 N switch can be produced by the same architecture from five N × N switches, the same decomposition being able to be carried out until arriving at 4 × 4 switches, as described above.

  Of course, the switches according to the invention are symmetrical, and the optical inputs and outputs described above can be reversed without departing from the scope of the invention.

  It appears from the above that the new switch architecture in accordance with the invention makes it possible to very greatly reduce the number of mirrors required compared to conventional matrix structures This reduction in the number of mirrors results in a reduction in the optical path 10 traversed by the beams propagating within the switch, with therefore consequently, a reduction of the insertion losses In the case where the decomposition of the switch according to the architecture of the invention is done on two different chips or substrates, one benefits in addition to an equalization of the optical path in the free space which is very advantageous as regards the performance of collimation required.

Claims (6)

  1 / Optical microswitch, allowing to connect 4 N optical inputs 5 (I 1 N, I 2 N, I 3 N, I 4 N) with 4 N optical outputs (ISO, 02 N, 03 N, 04 N), characterized in what it comprises five structures forming optical switching switches (SI, 52, 53, 54, 55) of 2 N inputs with 2 N outputs, in which: * a group of four (51-54) of these five structures are connected to the 4 N optical inputs (IIN-I 4 N), and to 2 N optical outputs (OIN, O 4 N), these four 10 structures being interconnected to generate 2 N intermediate outputs (O'2 N, O'3 NOT); the fifth structure (55) is connected to these 2 N intermediate outputs (O'2 N, O'3 N) to ensure mixing with the 2 N remaining optical outputs (O 2 N, O 3 N) .   2 / optical microswitch according to claim 1, characterized in that the group of four structures (Sl-54) and the fifth structure (55) are produced on the same substrate.   3 / optical microswitch according to claim 1, characterized in that the group of four structures (Sl-54) and the fifth structure (55) are produced on different substrates.   4 / optical microswitch according to claim 1, characterized in that the intermediate outputs (O '3, O'4) are connected to the fifth structure (55) by a set of fixed mirrors (7,8).   5 / optical microswitch according to claim 1, characterized in that the intermediate outputs are connected to the fifth structure by waveguides 30.   6 / optical microswitch according to claim 1, in which N is equal to 1, making it possible to connect four optical inputs (11-I 4) with four optical outputs (01.04), characterized in that it comprises five mirrors (M 1-Ms) divided into two groups, namely: a first group of four mirrors (M 1-M 4) arranged in two rows and two columns, the four mirrors being arranged: opposite four optical inputs (Il-I 4 ), each with a row or a column, and opposite two optical outputs (01-04), and two intermediate optical outputs (O '2,0' 3), also aligned each with a row or a column, and in alignment with an optical input 10 (11-I 4); * a fifth mirror (M 5), playing the role of switch, whose inputs are formed by the two intermediate outputs (O '2,0' 3), and whose outputs are the two remaining optical outputs (02,03) .