Patent Description:
Light can be modulated by a data-carrying radio frequency signal and transmitted over an optical fibre link. This is referred to as RF over fibre (or radio over fibre). There are many communications applications of RF over fibre, including transmission of mobile radio signals (<NUM>, <NUM>, <NUM> and WiFi) and cable television signals. RF over fibre is also used in satellite base station communications. Fibre optic links are advantageous because they provide lower transmission losses and reduced sensitivity to noise and electromagnetic interference compared to all-electrical signal transmission. Thus, RF over fibre can be used to transport analogue RF signals of very high bandwidth over long distances with very low loss and electromagnetic isolation from the environment. The present application aims to provide a versatile solution in terms of distribution of RF signals which provides various advantages over those of the prior art.

<CIT> discloses an optical switch. <CIT> discloses an optical bridge.

According to the present invention, there is provided a reconfigurable array for facilitating dynamic combination and distribution of RF/analogue signals. The reconfigurable array comprises: a number (Ni) of input devices for generating or supplying RF/analogue input signals; a number (No) of output devices for analysing or forwarding RF/analogue output signals; an optical switch matrix comprising a number (Np of ports; and a plurality of splitters/combiners that each have multiple uncommon ports which couple to a single common port. Each of the ports of the optical switch matrix is an optical input or an optical output. Each input device is coupled to a respective port of the optical switch matrix at an optical input, and each output device is coupled to a respective port of the optical switch matrix at an optical output. The optical switch matrix is configurable to enable optical connection of any optical input to any optical output. Each splitter/combiner enables either fan-in of optical signals from the uncommon ports to the common port or fan-out of optical signals from the common port to the uncommon ports. Each port of each splitter/combiner is coupled to a respective port of the optical switch matrix. The plurality of splitters/combiners include at least one M:<NUM> splitter/combiner, where M is a predetermined maximum number of RF/analogue signals for the reconfigurable array to fan-in or fan-out, where M ≤ Ni and M ≤ No. Each output device is coupled to the respective port of the optical switch matrix by means of a respective optical-to-electrical (O/E) converter configured to convert an optical signal received from the optical switch matrix into an RF/analogue signal for analysis or onward transmission by the output device. Each O/E converter is configured to provide automatic gain control by controlling a respective RF/analogue amplifier based on a measured light level of the received optical signal so as to adjust an output power of the respective RF/analogue signal to a predetermined level.

An alternative for achieving fan-out uses a tuneable optical filter architecture. However, such an arrangement band limits very wideband RF signals and generally has a deleterious effect on linearity. In contrast, the present reconfigurable array has no bandwidth limiting optical features.

An alternative for achieving fan-in is described below in relation to <FIG>. However, as will be discussed below, this solution is not scalable. In contrast, the present reconfigurable array is completely scalable and may be designed to enable unconstrained fan-in/fan-out for all input and output devices, or may be constrained to limit the fan-in/fan-out options by means of the number M.

The input devices may include one or more of: a receiving antenna; a software defined radio, SDR, transmitter; and an RF/analogue signal generator.

The output devices include one or more of: a transmitting antenna; an SDR receiver; and an RF/analogue signal analyser.

Each input device may be coupled to the respective port of the optical switch matrix by means of a respective electrical-to-optical (E/O) converter configured to convert the respective RF/analogue signal into a corresponding optical signal for distribution through the optical switch matrix. The E/O converters
for each of the input devices may be configured to generate optical signals having different optical wavelengths to one another.

The plurality of splitters/combiners may include duplicate splitters/combiners to provide redundancy in case of failure of one or more of the plurality of splitters/combiners.

In a first embodiment, the optical switch matrix is an any-to-any optical switch matrix, where each of the ports is reconfigurable as either an optical input or an optical
output, and where the any-to-any optical switch matrix is configurable to enable optical connection of any one of the ports to any other one of the ports.

In the first embodiment, the plurality of splitters/combiners may be defined as follows: (a) A is defined as max(Ni, No) and B is defined as min(Ni, No), (b) for i = <NUM>, <NUM>,. , the ith splitter/combiner is an Xi:<NUM> splitter/combiner, where Xi = A/i rounded down to the nearest integer, (c) if Xi < <NUM>, the ith splitter/combiner is excluded from the plurality of splitters/combiners and the number of splitters/combiners in the plurality of splitters/combiners is defined as S, and (d) the total number of ports is given by <MAT>.

In one example of the first embodiment, M = A such that the reconfigurable array is unconstrained to enable fan-in from all of the input devices or fan-out to all of the output devices if desired. Alternatively, M < A such that the reconfigurable array is constrained to enable fan-in from a maximum of M input devices or fan-out to a maximum of M output devices, wherein each Xi is constrained by Xi ≤ M.

In a second embodiment, the optical switch matrix is a CxD optical switch matrix having a number (C) of ports on one side and a number (D) of ports on the other side, where C ≤ D, and where the CxD optical switch matrix <NUM> is configurable to enable optical connection of any of the C ports on the one side to any of the D ports on the other side. In the second embodiment, the plurality of splitter/combiners comprises a first set of splitters/combiners having their uncommon ports connected to respective ones of the D ports of the optical switch matrix and having their common ports connected to respective ones of the C ports of the optical switch matrix. In the second embodiment, the plurality of splitter/combiners comprises a second set of splitters/combiners having their uncommon ports connected to respective ones of the C ports of the optical switch matrix and having their common ports connected to respective ones of the D ports of the optical switch matrix.

In one example of the second embodiment, Ni > No such that each input device is coupled to a respective one of the C ports of the optical switch matrix, and each output device is coupled to a respective one of the D ports of the optical switch matrix. Alternatively, Ni < No such that each input device is coupled to a respective one of the D ports of the optical switch matrix, and each output device is coupled to a respective one of the C ports of the optical switch matrix.

In the second embodiment, the first set of splitters/combiners may be defined as follows: (a) A is defined as max(Ni, No) and B is defined as min(Ni, No); (b) for i = <NUM>, <NUM>,. , the ith splitter/combiner in the first set of splitters/combiners is an Xi:<NUM> splitter/combiner, where Xi = A/i rounded down to the nearest integer; and (c) if Xi < <NUM>, the ith splitter/combiner is excluded from the first set of splitters/combiners and the number of splitters/combiners in the first set of splitters/combiners is S. If desired, each Xi may be constrained by Xi ≤ P, where P is a predetermined maximum number of RF/analogue signals for the first set of splitters/combiners to fan-in or fan-out, where P ≤ A.

In the second embodiment, the second set of splitters/combiners may be defined as follows: (a) for i = <NUM>, <NUM>,. , the ith splitter/combiner in the second set of splitters/combiners is an Yi:<NUM> splitter/combiner, where Yi = B/i rounded down to the nearest integer; and (b) if Yi < <NUM>, the ith splitter/combiner is excluded from the second set of splitters/combiners and the number of splitters/combiners in the second set of splitters/combiners is T. If desired, each Yi may be constrained by Yi ≤ Q, where Q is a predetermined maximum number of RF/analogue signals for the second set of splitters/combiners to fan-in or fan-out, where Q ≤ B.

In the second embodiment, the numbers C and D of ports required may be given by: <MAT>.

Other preferred features of the present invention are set out in the appended claims.

Embodiments of the present invention will now be described by way of example with reference to the accompanying drawings in which:.

For applications that require more than just point-to-point connections, where fan-in (combining) or fan-out (splitting) distribution is desired, optical solutions can support these requirements. In particular, RF over fibre can be used to multiplex many channels on a single fibre for high density, small footprint distribution using wavelength division multiplexing (WDM).

A known system <NUM> for routing RF over fibre signals is shown in <FIG>. RF over fibre refers to analogue over fibre, as opposed to digital over fibre. As mentioned in the Background section, the analogue (e.g. RF) data signal is used to modulate an optical (e.g. laser) carrier signal. In many applications, the analogue data signal is a radio frequency signal (hence the terminology 'RF over fibre'), but a lower frequency analogue data signal (e.g. a <NUM> audio signal) or a DC data signal (having high and low states) could also be used to modulate the optical carrier signal. Thus, in this application, the term 'RF over fibre' encompasses an analogue data signal (DC up to <NUM>) being modulated onto an optical carrier signal and transmitted via an optic fibre; the data signals are described herein as RF/analogue signals. <FIG> shows four RF over fibre inputs 110a-d on the left hand side, each of which provides an input signal having a different wavelength (A-D). Each of these four RF over fibre input signals is split by a respective splitter 120a-d into four separate signals. The system <NUM> further includes four switch arrays 130a-d. Each switch array <NUM> feeds into a respective combiner 140a-d. Each combiner <NUM> is associated with a respective RF over fibre output 150a-d.

The four signals output by each splitter <NUM> are fed into four switches, one from each of the four switch arrays <NUM>. For example, the split signals output by the first splitter 120a feed into (a) a first switch of the first switch array 130a, (b) a first switch of the second switch array 130b, (c) a first switch of the third switch array 130c, and (d) a first switch from the fourth switch array 130d. Thus, each switch array <NUM> receives one input signal from each of the four splitters <NUM>. In other words, each of the receivers receives a version of each input signal, regardless of the fact that they may only be interested in a single input signal. Depending on which input signals are selected using the switches of the switch arrays <NUM>, the combiners <NUM> each act to combine the selected input signals to provide an output signal to the respective output <NUM>. Thus, each switch array <NUM> and associated combiner <NUM> may be considered as a tunable filtering element. For example, the first switch array 130a may be used to select the first input signal only such that the output from the first combiner 140a is based on the first input signal only. The second switch array 130b may be used to select the second and third input signals only such that the output from the second combiner 140b is based on a combination of the second and third input signals. The third switch array 130c may be used to select the first and third input signals only such that the output from the third combiner 140c is based on a combination of the first and third input signals. The fourth switch array 130d may be used to select all of the input signals such that the output from the fourth combiner 140b is based on a combination of all of the input signals.

Using the known system of <FIG>, any input <NUM> can be routed to any output <NUM>, with signal combination as necessary. However, if more than four inputs are required, the required number of components and the complexity of the system both increase substantially. Furthermore, as the number of inputs increases from the four shown in <FIG> to an arbitrary large number N, it will be appreciated that the splitting losses also increase since each input signal is split into N separate signals, with a consequent reduction in amplitude. In this case, optical amplification is likely to be required, which adds significant complexity in terms of the implementation. Furthermore, the architecture of <FIG> is unidirectional. Therefore, the system of <FIG> is in many ways not practical when considering a larger number of inputs and outputs. Nonetheless, from this starting point, it is desired to design a completely reconfigurable signal distribution/routing array where numerous input devices require reconfigurable access to multiple output devices, without the disadvantages described with reference to <FIG>.

A signal distribution/routing array where numerous input devices require reconfigurable access to multiple output devices is schematically illustrated in <FIG>. The example of <FIG> includes four input devices <NUM> and six output devices <NUM> with a reconfigurable distribution/routing arrangement <NUM> between them. Equally, the system of <FIG> could be used in reverse such that there are six input devices and four output devices. Of course, it will be appreciated that any number of input and output devices may be present depending on the desired use case. In general, the input devices generate or supply RF/analogue signals, so could be RF/analogue source devices such as receiving antennas, SDR transmitters (TX), or other RF/analogue signal generators. The output devices analyse or forward RF/analogue signals, so could be RF/analogue sink devices such as transmitting antennas, SDR receivers (RX), or other RF/analogue signal analysers (e.g. test devices).

As a specific example, <FIG> shows the input and output devices as six antennas <NUM> and four SDRs <NUM>. Each antenna <NUM> in <FIG> can be either an input device <NUM> (i.e. a receiving antenna) or an output device <NUM> (i.e. a transmitting antenna). In addition, each SDR <NUM> in <FIG> can be either an input device <NUM> (i.e. an SDR TX which generates RF/analogue signals) or an output device <NUM> (i.e. an SDR RX which analyses RF/analogue signals). Furthermore, single or many connections to an SDR <NUM> or antenna <NUM> may be necessary to meet the following requirements:.

Thus, a bidirectional, reconfigurable signal distribution/routing arrangement <NUM> between the input devices <NUM> and the output devices <NUM> is desirable, including options for fan-in and fan-out. Such an arrangement could be used to re-purpose communications infrastructure (e.g. antennas) to inject electronic countermeasure waveforms to block certain communications. This can be done using fan-in functionality to combine the signal-to-be-blocked with an opposing signal which can jam or obliterate the signal-to-be-blocked.

Accordingly, a suitable reconfigurable array <NUM> for facilitating dynamic combination and distribution of RF/analogue signals is schematically illustrated in <FIG>. The reconfigurable array <NUM> comprises input devices <NUM> for generating or supplying RF/analogue signals, output devices <NUM> for analysing or forwarding RF/analogue signals, an optical switch matrix <NUM>, and a plurality of splitters/combiners <NUM> to enable fan-in or fan-out of optical signals. In the exemplary arrangement of <FIG>, there are six input devices <NUM> and four output devices <NUM>, but it will be understood that any number of input and output devices could be used depending on the use case.

The optical switch matrix <NUM> comprises a number of ports <NUM>, the number designated Np. Note that most, but not all of the ports <NUM> are labelled in <FIG>. In the arrangement of <FIG> there are <NUM> ports <NUM> (i.e. Np = <NUM>), but it will be appreciated that this is exemplary such that a different number of ports <NUM> may be provided depending on the implementation requirements in a particular case. In the example of <FIG>, the optical switch matrix <NUM> is a so-called "any-to-any" optical switch matrix that is fully configurable to enable optical connection of any one of the ports <NUM> to any other one of the ports <NUM>. Each of the ports <NUM> acts as an optical input to or an optical output from the optical switch matrix <NUM>. Furthermore, each of the ports <NUM> of the any-to-any optical switch matrix <NUM> is reconfigurable from being an optical input to an optical output (or vice versa), and may switch seamlessly between the two. Thus, the optical switch matrix <NUM> is reconfigurable, fully bidirectional, and has low loss and high isolation. The optical switch matrix <NUM> is also non-blocking in that no optical connections block other optical connections therethrough. An exemplary any-to-any optical switch matrix with <NUM> ports is the Polatis Series <NUM>48xCC OSM available from Huber+Suhner (see https://www. com/switch-modules-for-oemall-optical-switch-module-solutions-original-equipment-manufactures.

The number of input devices <NUM> is designated Ni. In the arrangement of <FIG> there are six input devices <NUM> (i.e. Ni = <NUM>), but it will be appreciated that this is exemplary such that a different number of input devices <NUM> may be provided. Each input device <NUM> is coupled to a respective port <NUM> of the optical switch matrix <NUM> at an optical input.

The number of output devices <NUM> is designated No. In the arrangement of <FIG> there are four output devices <NUM> (i.e. No = <NUM>), but it will be appreciated that this is exemplary such that a different number of output devices may be provided. Each output device <NUM> is coupled to a respective port <NUM> of the optical switch matrix <NUM> at an optical output.

The splitters/combiners <NUM> are used to address requirements (a)-(f) listed above. The splitters/combiners <NUM> are reconfigurable and bidirectional. Thus, each splitter/combiner <NUM> has multiple uncommon ports which couple to a single common port. Each splitter/combiner <NUM> enables either fan-in of optical signals from the uncommon ports to the common port, or fan-out of optical signals from the common port to the uncommon ports, depending on the direction in which the splitter/combiner <NUM> is connected. in particular, when connected in one direction, a splitter/combiner <NUM> acts as a combiner where inputs to the uncommon ports are fanned-in to the common port (i.e. there is a many-to-one configuration of splitter/combiner inputs to splitter/combiner outputs). When connected in the opposite direction, a splitter/combiner <NUM> acts as a splitter where an input to the common port is fanned-out to the uncommon ports (i.e. there is a one-to-many configuration of splitter/combiner inputs to splitter/combiner outputs). Each port (common/uncommon) of each splitter/combiner <NUM> is coupled to a respective port <NUM> of the optical switch matrix <NUM>. The plurality of splitters/combiners include at least one M:<NUM> splitter/combiner, where M is a predetermined maximum number of RF/analogue signals for the reconfigurable array to fan-in or fan-out, where M ≤ Ni and M ≤ No. In the example of <FIG>, M = <NUM>. Thus, the <NUM>:<NUM> splitter/combiner may be used to fan-in all of the signals from the six input devices <NUM>. Equally, the <NUM>:<NUM> splitter/combiner may be used to fan-out a single input signal to all of the four output devices <NUM>. The plurality of splitters/combiners <NUM> in the reconfigurable array <NUM> of <FIG> further include a <NUM>:<NUM> splitter/combiner and a <NUM>:<NUM> splitter/combiner <NUM>.

Notably, each port <NUM> of the optical switch matrix <NUM> is configured to connect to a single optical input or output. Thus, if an optical switch matrix port <NUM> is coupled to an input device <NUM>, it cannot also be coupled to an output device <NUM> or to a common/uncommon port of a splitter/combiner <NUM> or even to another input device <NUM>.

Regarding inputs into the optical switch matrix <NUM>, each input signal should be an optical input signal. Thus, an RF/analogue input signal from an input device <NUM> is converted to an optical signal prior to its presentation at a port <NUM> of the optical switch matrix <NUM>. Equally, outputs from the optical switch matrix <NUM> will all be optical output signals. Thus, it is also necessary to convert such output signals back to RF/analogue for onward transmission or processing by the output devices <NUM>. For this reason, each input device <NUM> may be coupled to its respective port <NUM> of the optical switch matrix <NUM> by means of a respective electrical-to-optical (E/O) converter (not shown). Each E/O converter is configured to convert an incoming RF/analogue signal into a corresponding optical signal for distribution/routing through the optical switch matrix <NUM>. As is known, this may be achieved by modulating a light source intensity with the RF/analogue signal to generate a corresponding optical signal. In addition, each output device is coupled to the respective port of the optical switch matrix <NUM> by means of a respective optical-to-electrical (O/E) converter (not shown). Each O/E converter is configured to convert an optical signal from the optical switch matrix <NUM> into an RF/analogue signal for analysis or onward transmission by the relevant output device <NUM>. As is also known, this may be achieved by demodulation of the optical signal. If an input device <NUM> or output device <NUM> is remote from the optical switch matrix <NUM>, an optical fibre (of up to several kilometres in length) may extend between the relevant E/O or O/E converter and the associated port <NUM> of the optical switch matrix <NUM>.

When generating optical inputs into the optical switch matrix <NUM>, it is important that any optical inputs destined to be combined by one of the splitters/combiners <NUM> have different wavelengths assigned to enable wavelength-division multiplexing (WDM). This can be achieved if the E/O converters for each of the input devices <NUM> are configured to generate optical signals having different optical wavelengths (or wavelength bands) to one another. Of course, if signals from one or more of the input devices <NUM> are never required to be combined with signals from any of the other input devices <NUM>, it will be understood that those input devices <NUM> need not have distinct wavelengths (or wavelength bands) associated with them. Note that the use of an optical switch matrix <NUM> enables fan-in of signals in a highly linear manner for frequency stacking each of the generated optical signals, and this is clearly advantageous.

Each of the O/E converters includes an optical receiver configured to receive an optical signal from the optical switch matrix <NUM> for subsequent conversion into an RF/analogue signal for onward transmission to the relevant output device <NUM>. Notably, optical receivers are by their nature wideband and will respond to any wavelengths present.

In cases where optical signals are split by one or more of the splitters/combiners <NUM> as they pass through the optical switch matrix <NUM>, there will be a consequent reduction in amplitude of the optical signal. In addition, the optical loss of the splitters/combiners <NUM> can be different (e.g. there will generally be a greater optical loss when using a <NUM>:<NUM> splitter/combiner as compared to using a <NUM>:<NUM> splitter/combiner). Thus, the O/E converters are configured to provide automatic gain control to compensate for this. In this case, each O/E converter includes a respective RF/analogue amplifier, and the automatic gain control is achieved by controlling the RF/analogue amplifier based on a measured light level of the received optical signal so as to adjust an RF/analogue output power to a predetermined level. In this way, the different optical paths can be gain balanced if deemed necessary.

<FIG> shows the optimal unconstrained arrangement of splitters/combiners <NUM> for the 6x4 example (which has six input devices <NUM> and four output devices <NUM>). With this arrangement, all requirements can be met without restriction/constraint on fan-in or fan-out. In other words, the unconstrained example of <FIG> enables fan-in of all six input devices <NUM> or fan-in of any subgroups of input devices <NUM>. Similarly, the unconstrained example of <FIG> enables fan-out to all four output devices <NUM> or fan-out to any subgroups of output devices <NUM>. The full configuration options are set out in Table <NUM> below:.

In Table <NUM>, S/C is shorthand for "splitter/combiner". The number of uncommon ports for each splitter/combiner <NUM> is shown, as well as the total number of optical switch matrix ports <NUM> that are required for each splitter/combiner <NUM>. In each case, the number of optical switch matrix ports <NUM> required for each splitter/combiner <NUM> is equal to the number of uncommon ports plus one (for the common port). This is clearly depicted for the splitters/combiners <NUM> in <FIG> (e.g. the <NUM>:<NUM> splitter/combiner <NUM> is connected to <NUM> ports <NUM> of the optical switch matrix <NUM>). Note that, for each configuration, there are only entries in four columns at most, since, in this example, there are only four output devices <NUM> to which the input devices may ultimately be connected.

Configurations A-J in Table <NUM> depict all possible required configurations for fan-in of the six input devices <NUM>. For example, configuration A involves all six input devices <NUM> being connected to a single output device <NUM> by means of the <NUM>:<NUM> splitter/combiner <NUM>. If the input devices <NUM> were antennas and the single output device <NUM> was an SDR, this arrangement could be used for requirement (d) listed above. If the input devices <NUM> were SDRs and the single output device <NUM> was an antenna, this arrangement could be used for requirement (b) listed above. It is clear that any one-to-one mapping of any input device <NUM> to any output device <NUM> is possible, bypassing all splitters/combiners <NUM>. This is used to some extent in all of configurations B, D, F, G, I and J. For example, configuration D connects four of the input devices <NUM> to one output device <NUM> by means of the <NUM>:<NUM> splitter/combiner <NUM>, with the other two input devices <NUM> being directly connected to respective output devices <NUM> without the need for splitting/combining. Configuration E involves connecting three input devices <NUM> to one output device <NUM> by means of the <NUM>:<NUM> splitter/combiner <NUM>, and connecting the other three input devices <NUM> to another output device <NUM> by means of the <NUM>:<NUM> splitter/combiner <NUM>. The <NUM>:<NUM> splitter/combiner <NUM> is only required for configuration H where the input ports <NUM> are separated into three pairs. Nonetheless, it will be appreciated that the <NUM>:<NUM> splitter/combiner <NUM> could be used instead of the <NUM>:<NUM> splitter/combiner <NUM> in configurations C, F, I and J. Equally, the <NUM>:<NUM> splitter/combiner <NUM> could be used instead of the <NUM>:<NUM> splitter/combiner <NUM> in configurations F, G and I. This may be desirable to reduce splitting losses. Notably, one of the input devices <NUM> is not used in configuration J, so this is an unlikely scenario in the 6x4 example.

An example of the configurability of the reconfigurable array <NUM> to meet the different distribution requirements is shown in <FIG>. In this example, the <NUM>:<NUM> splitter/combiner is not used. Input device <NUM> is directly connected to output device <NUM> without passing through a splitter/combiner. In addition, input devices <NUM>, <NUM>, <NUM> and <NUM> are all connected to uncommon ports of the <NUM>:<NUM> splitter/combiner for onward connection to output device <NUM>. Also, input device <NUM> is connected to the common port of the <NUM>:<NUM> splitter/combiner for onward connection to output devices <NUM> and <NUM>. This corresponds to configuration D in Table <NUM>. Importantly, if the distribution requirements change, then the optical switch matrix <NUM> may be reconfigured to provide different connections as desired.

A further example of the configurability of the reconfigurable array <NUM> to meet the different distribution requirements is shown in <FIG>. In this example, input devices <NUM>, <NUM>, <NUM>, and <NUM> are connected to four of the six uncommon ports of the <NUM>:<NUM> splitter/combiner so as to combine the four signals. The common ports of the <NUM>:<NUM> and <NUM>:<NUM> splitters/combiners are then connected such that the combined signal is split into two to provide output signals to output devices <NUM> and <NUM>. Again, the <NUM>:<NUM> splitter/combiner is not used in this example.

Whilst a 6x4 example of the reconfigurable array <NUM> is described above, it will be understood that the reconfigurable array <NUM> may be expanded to account for larger distribution requirements. As the size of the system increases (in terms of the numbers Ni, No of input and output devices <NUM>, <NUM>), it may not be feasible to support an unconstrained system due to the number of splitters/combiners <NUM> required, and the consequent size of the optical switch matrix <NUM>. Constraining the array in terms of fan-in/fan-out requirements can significantly reduce the optical switch matrix size (i.e. Np) by altering or dropping some of the splitter/combiner options. Furthermore, a typical deployment will not generally require unconstrained flexibility as not all input and output devices <NUM>, <NUM> will be the same and there is often a known set of input and output devices <NUM>, <NUM> that require support for fan-in/fan-out, and this can be designed into the reconfigurable array <NUM>.

An example of a constrained 6x4 reconfigurable array <NUM> is shown in Table <NUM> where the predetermined maximum number of RF/analogue signals for the reconfigurable array to fan-in or fan-out is M = <NUM>. As can be seen, this means that a <NUM>:<NUM> splitter/combiner may be used in place of the <NUM>:<NUM> splitter/combiner <NUM> of <FIG>, which reduces the total number Np of required ports <NUM> from <NUM> to <NUM>. This is a relatively small saving in terms of the number Np of ports <NUM>, but the savings can be very significant when constraining a larger reconfigurable array <NUM>.

The described reconfigurable array <NUM> could be used in many communications applications, such as the distribution requirements (a)-(f) listed above.

For a general Ni x No unconstrained reconfigurable array <NUM>, it is possible to calculate the splitter/combiner requirements as follows:.

The total number of ports required is given by: <MAT>.

Then, consider constraining the Ni x No reconfigurable array <NUM> such that there is a predetermined maximum number (M) of RF/analogue signals for the reconfigurable array to fan-in or fan-out. In this case, the unconstrained splitter/combiner requirements (as calculated above) should be modified as follows:.

In each case (constrained/unconstrained), note that the system is symmetric. In other words, the same splitter/combiner requirements and the same number of optical switch matrix ports occur regardless of whether you have, e.g., <NUM> input devices and <NUM> output devices, or <NUM> input devices and <NUM> output devices.

Consider an exemplary reconfigurable array <NUM> having Ni = <NUM> and No = <NUM> (i.e. A = <NUM> and B = <NUM>). In this case, the splitters/combiners <NUM> required to provide an unconstrained system (M = <NUM>) would be as follows: <NUM>:<NUM>, <NUM>:<NUM>, <NUM>:<NUM>, <NUM>:<NUM>, <NUM>:<NUM>, <NUM>:<NUM>. Thus, the total number Np of ports <NUM> required for the optical switch matrix <NUM> would be <NUM>. If the 16x6 (or 6x16) reconfigurable array <NUM> were constrained such that the predetermined maximum number of RF/analogue signals for the reconfigurable array to fan-in or fan-out is M = <NUM>, the splitters/combiners <NUM> required would be as follows: <NUM>:<NUM>, <NUM>:<NUM>, <NUM>:<NUM>, <NUM>:<NUM>, <NUM>:<NUM>, <NUM>:<NUM>. This reduces the total number Np of required ports to <NUM>.

As another example, consider a reconfigurable array <NUM> having Ni = <NUM> and No = <NUM> (i.e. A = <NUM> and B = <NUM>). In this case, the splitters/combiners <NUM> required to provide an unconstrained system (M = <NUM>) would be as follows: <NUM>:<NUM>, <NUM>:<NUM>, <NUM>:<NUM>, <NUM>:<NUM>, <NUM>:<NUM>, <NUM>:<NUM>. Thus, the total number Np of ports <NUM> required for the optical switch matrix <NUM> would be <NUM>. If the 32x6 reconfigurable array <NUM> were constrained to M = <NUM>, the splitters/combiners <NUM> required would be as follows: <NUM>:<NUM>, <NUM>:<NUM>, <NUM>:<NUM>, <NUM>:<NUM>, <NUM>:<NUM>, <NUM>:<NUM>. this reduces the total number Np of required ports <NUM> to <NUM>. If the 32x6 reconfigurable array <NUM> were further constrained to M = <NUM>, the splitters/combiners <NUM> required would be as follows: <NUM>:<NUM>, <NUM>:<NUM>, <NUM>:<NUM>, <NUM>:<NUM>, <NUM>:<NUM>, <NUM>:<NUM>. This further reduces the total number Np of required ports <NUM> to <NUM>.

The M-constrained system described above is just one example of the sort of constraint that may be applied to the reconfigurable array <NUM> when deciding which splitter/combiners <NUM> should be included. Other types of constraint are possible to meet system requirements. For example, a 16x6 system could be constrained to provide fan-in for up to <NUM> input devices <NUM>, with the remaining input devices <NUM> only requiring a maximum of <NUM> to be fanned-in. This would require the following splitters/combiners: <NUM>:<NUM>, <NUM>:<NUM>, <NUM>:<NUM>, <NUM>:<NUM>, <NUM>:<NUM>, <NUM>:<NUM>. Thus, it will be appreciated that the system is fully configurable to provide any required signal routing/distribution requirements with the minimum number of optical components and optical ports. Given size, weight and power constraints, an array of optical components can be added to the optical switch matrix <NUM> to provide the functionality required.

Any-to-any optical switch matrices are available to buy with a number of ports that is a multiple of <NUM> (i.e. Np = <NUM>n, where n is an integer). This is because the switches tend to be built in slices of <NUM> ports per slice. Thus, in cases where the constrained or unconstrained system has spare optical ports <NUM>, additional splitters/combiners <NUM> may be included for redundancy purposes in order to cope with any component failures or to maximise availability. For example, in the unconstrained 6x4 example of <FIG>, if it were not possible to obtain a <NUM>-port optical switch matrix <NUM>, then a <NUM>-slice, <NUM>-port optical switch matrix <NUM> could be used, leaving <NUM> spare ports. These could be used to provide an additional (redundant) <NUM>:<NUM> splitter/combiner, or additional (redundant) <NUM>:<NUM> and <NUM>:<NUM> splitters/combiners, as desired. An important aspect of constraining the signal routing/distribution requirements is to reduce the number of ports required since costs go up considerably with each additional slice added to the optical switch matrix.

Whilst the optical switch matrix described above was an any-to-any optical switch matrix <NUM>, this is not an essential feature. Alternative embodiments are envisaged using a CxD optical switch matrix <NUM>, as described below with reference to <FIG>. A CxD optical switch matrix comprises a number (C) of ports on one side and a number (D) of ports on the other side, where we will assume C ≤ D. CxD optical switch matrix matrices are bidirectional, so that a CxD optical switch matrix may be operated with the C ports as input ports and the D ports as output ports, or the other way around with the C ports as output ports and the D ports as input ports. A CxD optical switch matrix <NUM> is configurable to enable optical connection of any of the C ports on the one side to any of the D ports on the other side. Thus, any optical input may be connected to any optical output. Such optical switch matrices allow simultaneous connection between optical inputs and outputs in a fully non-blocking, all-optical, cross-connect configuration. Exemplary CxD optical switch matrices are the MEMS Matrix Optical Switches available from DiCon Fiberoptics, Inc. (see https://www. diconfiberoptics. com/products/mems_matrix_optical_switches. Features of the CxD optical switch matrix embodiment described below should be considered to be similar to those of the any-to-any optical switch matrix embodiments described above, except where described differently below.

The reconfigurable array <NUM> of <FIG> comprises input devices <NUM>, output devices <NUM>, a CxD optical switch matrix <NUM>, and a plurality of splitters/combiners <NUM> to enable fan-in or fan-out of optical signals. To enable a direct comparison to <FIG>, there are six input devices <NUM> (i.e. Ni = <NUM>) and four output devices <NUM> (i.e. No = <NUM>) shown in <FIG>. In particular, <FIG> shows the same 6x4 connection configuration as is shown in <FIG>, but using the CxD optical switch matrix <NUM> rather than the any-to-any optical switch matrix <NUM>. However, it will be understood that any number of input and output devices could be used depending on the use case.

In the arrangement of <FIG>, Ni > No. Since we have assumed that C ≤ D by definition), each input device <NUM> is coupled to a respective one of the C ports of the optical switch matrix <NUM>, and each output device <NUM> is coupled to a respective one of the D ports of the optical switch matrix <NUM>. Thus, the C ports are input ports and the D ports are output ports. If Ni < No, then the C ports would be output ports and the D ports would be input ports. In other words, the input/output devices that are greater in number should be connected to the side of the optical switch matrix <NUM> with fewer ports (i.e. the side having C ports).

In <FIG>, there are <NUM> input ports shown at the top of the optical switch matrix <NUM> (i.e. C = <NUM>), and there are <NUM> output ports shown at the bottom of the optical switch matrix <NUM> (i.e. D = <NUM>). Thus, the CxD optical switch matrix <NUM> in this example is a 15x17 optical switch matrix. Of course, it will be appreciated that this is exemplary such that different numbers of input and output ports may be provided depending on the implementation requirements in a particular case.

The plurality of splitters/combiners <NUM> comprise two sets of splitters/combiners. A first set 640a of splitters/combiners has their uncommon ports connected to respective ones of the D ports of the optical switch matrix <NUM> and has their common ports connected to respective ones of the C ports of the optical switch matrix <NUM>. Thus, since the input devices <NUM> are connected on the opposite side of the optical switch matrix <NUM> to the uncommon ports of the first set 640a of splitters/combiners (which enables the input devices <NUM> to be connected to these uncommon ports), each of the first set 640a of splitters/combiners enables fan-in of optical signals. A second set 640b of splitters/combiners has their uncommon ports connected to respective ones of the C ports of the optical switch matrix <NUM> and has their common ports connected to respective ones of the D ports of the optical switch matrix <NUM>. Thus, since the input devices <NUM> are connected on the opposite side of the optical switch matrix <NUM> to the common ports of the second set 640b of splitters/combiners (which enables the input devices <NUM> to be connected to these common ports), each of the second set 640b of splitters/combiners enables fan-out of optical signals. Note that if Ni < No, then the input and output devices would be the other way around such that each of the first set 640a of splitters/combiners enables fan-out of optical signals, and each of the second set 640b of splitters/combiners enables fan-in of optical signals.

As for the any-to-any optical switch matrix embodiment, the plurality of splitters/combiners include at least one M:<NUM> splitter/combiner, where M is a predetermined maximum number of RF/analogue signals for the reconfigurable array to fan-in or fan-out, where M ≤ Ni and M ≤ No. In the example of <FIG>, M = <NUM>, and the <NUM>:<NUM> splitter/combiner is in the first set 640b of splitters/combiners. In fact, the M:<NUM> splitter/combiner is always in the first set 640a of splitters/combiners that is opposite the larger number of input/output devices <NUM>, <NUM> (i.e. the set that has their uncommon ports connected to respective ones of the D ports of the optical switch matrix <NUM> and has their common ports connected to respective ones of the C ports of the optical switch matrix <NUM>). In <FIG>, the <NUM>:<NUM> splitter combiner may be used to fan-in all of the signals from the six input devices <NUM>. The first set 640a of splitters/combiners in the reconfigurable array <NUM> of <FIG> further includes a <NUM>:<NUM> splitter/combiner and a <NUM>:<NUM> splitter/combiner. Thus, the first set 640a of splitters/combiners is identical to the plurality of splitters/combiners <NUM> used in the any-to-any optical switch matrix embodiment of <FIG>.

In this CxD optical switch matrix embodiment, the plurality of splitters/combiner <NUM> further comprise additional splitters/combiners from those used in the any-to-any optical switch matrix embodiment of <FIG>. In particular, the second set 640b of splitters/combiners in <FIG> are additional to those used in <FIG>. This (additional) second set 640b of splitters/combiners includes an L:<NUM> splitter/combiner, where L = min(Ni, No) = B in the unconstrained case. In the example of <FIG>, L = <NUM> such that the second set 640b of splitters/combiners comprises a <NUM>:<NUM> splitter/combiner. The second set 640b of splitters/combiners in the reconfigurable array <NUM> of <FIG> further includes a <NUM>:<NUM> splitter/combiner.

As for <FIG>, <FIG> shows the optimal unconstrained arrangement of splitters/combiners <NUM> for the 6x4 example. With this arrangement, all requirements can be met without restriction/constraint on fan-in or fan-out. In other words, the unconstrained example of <FIG> enables fan-in of all six input devices <NUM> or fan-in of any subgroups of input devices <NUM>. Similarly, the unconstrained example of <FIG> enables fan-out to all four output devices <NUM> or fan-out to any subgroups of output devices <NUM>.

For a general Ni x No unconstrained reconfigurable array <NUM>, it is possible to calculate the splitter/combiner requirements for the CxD optical switch matrix embodiments as follows.

Let us initially consider the first set 640a of splitters/combiners having their common ports connected on the same side of the optical switch matrix <NUM> as the larger number of input/output devices <NUM>, <NUM> (i.e. the six input devices <NUM> in <FIG>), and having their uncommon ports connected on the same side of the optical switch matrix <NUM> as the smaller number of input/output devices <NUM>, <NUM> (i.e. the four output devices <NUM> in <FIG>). The first set 640a of splitters/combiners in the unconstrained CxD optical switch matrix embodiments are determined in a corresponding manner to the set of splitters/combiners <NUM> used in the any-to-any optical switch matrix embodiments:.

Let us now consider the second set 640b of splitters/combiners having their common ports connected on the same side of the optical switch matrix <NUM> as the smaller number of input/output devices <NUM>, <NUM> (i.e. the four output devices <NUM> in <FIG>), and having their uncommon ports connected on the same side of the optical switch matrix <NUM> as the larger number of input/output devices <NUM>, <NUM> (i.e. the six input devices <NUM> in <FIG>). The second set 640b of splitters/combiners in the unconstrained CxD optical switch matrix embodiments are determined as follows:.

The numbers C and D of ports required are given by: <MAT> <MAT>.

As for the any-to-any optical switch matrix embodiments, it is possible to apply constraints to the CxD optical switch matrix embodiments. Rather than using a single constraint M (as in the any-to-any optical switch matrix embodiments), two constraints are required (one on fan-in and one on fan-out) due to the separate sets 640a,b of splitters/combiners used for fan-in and fan-out:.

The CxD optical switch matrix embodiment may be preferable in some cases since CxD optical switch matrices are generally less expensive that any-to-any optical switch matrices.

Claim 1:
A reconfigurable array (<NUM>) for facilitating dynamic combination and distribution of RF/analogue signals, the reconfigurable array comprising:
a number, Ni, of input devices (<NUM>) for generating or supplying RF/analogue input signals;
a number, No, of output devices (<NUM>) for analysing or forwarding RF/analogue output signals;
an optical switch matrix (<NUM>) comprising a number, Np, of ports (<NUM>), wherein each of the ports (<NUM>) is an optical input or an optical output, wherein each input device is coupled to a respective port of the optical switch matrix (<NUM>) at an optical input, wherein each output device is coupled to a respective port of the optical switch matrix (<NUM>) at an optical output, and wherein the optical switch matrix (<NUM>) is configurable to enable optical connection of any optical input to any optical output; and
a plurality of splitters/combiners (<NUM>) that each have multiple uncommon ports which couple to a single common port, wherein each splitter/combiner (<NUM>) enables either fan-in of optical signals from the uncommon ports to the common port or fan-out of optical signals from the common port to the uncommon ports, and wherein each port of each splitter/combiner (<NUM>) is coupled to a respective port of the optical switch matrix (<NUM>);
wherein the plurality of splitters/combiners (<NUM>) include at least one M:<NUM> splitter/combiner, where M is a predetermined maximum number of RF/analogue signals for the reconfigurable array to fan-in or fan-out, where M ≤ Ni and M ≤ No;
wherein each output device (<NUM>) is coupled to the respective port of the optical switch matrix (<NUM>) by means of a respective optical-to-electrical, O/E, converter configured to convert an optical signal received from the optical switch matrix (<NUM>) into an RF/analogue signal for analysis or onward transmission by the output device; and
characterised in that each O/E converter is configured to provide automatic gain control by controlling a respective RF/analogue amplifier based on a measured light level of the received optical signal so as to adjust an output power of the respective RF/analogue signal to a predetermined level.