AU2009201717A1

AU2009201717A1 - A module for transforming between a RF signal and a digital multiplexed optical signal

Info

Publication number: AU2009201717A1
Application number: AU2009201717A
Authority: AU
Inventors: Kamal Alameh; Budi Juswardy; Yong Tak Lee
Original assignee: Edith Cowan University; Ytel Photonics Inc
Current assignee: Edith Cowan University; Ytel Photonics Inc
Priority date: 2008-05-12
Filing date: 2009-04-30
Publication date: 2009-12-10

Description

AUSTRALIA Patents Act 1990 COMPLETE SPECIFICATION Standard Patent Applicant (s) EDITH COWAN UNIVERSITY and GWANGJU INSTITUTE OF SCIENCE AND TECHNOLOGY Invention Title: A MODULE FOR TRANSFORMING BETWEEN A RF SIGNAL AND A DIGITAL MULTIPLEXED OPTICAL SIGNAL The following statement is a full description of this invention, including the best method for performing it known to me/us: PSAS8AU 1 Pa1_SetFilng Application 2001-4-29 doc (P) - 2 A MODULE FOR TRANSFORMING BETWEEN A RF SIGNAL AND A DIGITAL MULTIPLEXED OPTICAL SIGNAL 5 Field of the Invention The present invention broadly relates to a module for transforming between a RF signal and a digital multiplexed optical signal. 10 Background of the Invention Processing of received broadband radio frequency (RF) signals or signal processing for emission of RF signals 15 provides many technological challenges, especially if the processing is to be conducted in a commercially viable manner. Conventional RF broadband transmission systems are 20 arranged for RF signal processing using analogue circuitries. Transmission protocols often change and consequently the transmission systems should provide adaptability, which makes the transmission systems relatively complex. The transmission systems are often 25 also arranged for conversion of the analogue signals before the analogue signals are digitised. The conversion requires a large number of components including well matched mixers and filters, which add to the cost, size and power consumption of the transmission systems. 30 Smart antenna devices have recently been developed for transmission of broadband RF signals. Controlling and steering of beams emitted from smart antennas is ideally - 3 performed using suitable computer software and consequently requires conversion between digital and analogue signals. However, to date it has not been possible to produce low-cost broadband RF signal 5 converters for direct conversion between broadband RF signals and the digital signals. There is a need for technological advancement. 10 Summary of the Invention The present invention provides in a first aspect a module for transforming between a RF signal and a digital multiplexed optical signal, the RF signal comprising a 15 plurality of RF signal components, the module comprising: a plurality of guides for guiding the RF components, at least two of the RF signal components including different frequency ranges; a converter being arranged to convert between the RF 20 signal components and a plurality of digital signal components and being arranged to convert between the plurality of digital signal components and a multiplexed optical digital signal; and an optical light guide for guiding the digital 25 multiplexed optical signal. The RF signal components may each have a different frequency range. For example, the converter may be arranged to convert between N RF signal components and 30 corresponding N digital signals components, typically in parallel. At least some, typically all, of the RF signal components may have differing frequency ranges. For . example, each RF signal component may have a frequency - 4 range that is adjacent, typically directly adjacent, a frequency range of another one of the RF signal components. 5 The converter typically comprises a first converter component being arranged to convert between the RF signal components and a plurality of respective digital electrical signal components; and a second converter component being arranged to convert between the plurality 10 of digital electrical signal components and the digital multiplexed optical signal. Alternatively, the first converter component may be arranged to convert between the RF signal components and a 15 plurality of respective optical digital signal components. In this case the second converter component typically is arranged for converting between the plurality of digital optical signal components and the digital multiplexed optical signal. 20 The second converter component may be arranged to convert between N digital signal components and the digital multiplexed optical signal using time division multiplexing or time division de-multiplexing. The second 25 converter component typically is arranged for conversion in parallel. The digital multiplexed optical signal may have a frequency range that is N times higher than that of each digital signal component. For example, the module may be arranged to convert between RF signal components having 30 frequencies in the MHz range and a digital multiplexed optical signal having a frequency in the GHz range.

-5 The module may form a part of a receiver for receiving the RF signal. Alternatively, the module may form a part of a transmitter for emitting the RF signal. 5 In one specific embodiment the module comprises a frequency range component that is arranged to convert between a RF signal having a first frequency range and the plurality of RF signal components which each have a frequency range that is included in the first frequency 10 range. In one example the frequency range component is arranged to convert between N RF signal components and the RF signal, wherein the RF signal has a frequency range that is approximately N times wider than that of each RF signal component. In this specific embodiment the module 15 typically comprises an antenna for emitting or receiving the RF signal. The module may be arranged to convert a received RF signal having a relatively wide bandwidth into a higher frequency digital multiplexed optical signal having a narrower 20 bandwidth. Embodiments of the present invention provide a module that is arranged for high speed digitisation of a broadband RF signal by dividing the broadband RF signal into narrower bandwidth component signals, processing the component signals in parallel and converting the component 25 signals into a high speed digital multiplexed optical digital signal. The frequency range component may also be arranged to convert each first RF signal of a plurality of first RF 30 signals into a plurality of RF signal components which each have a frequency range that is included in a frequency range of a respective one of the first RF -6 signal. The frequency ranges of the first RF signals typically differ from one another. Components of the module may be provided in the form of 5 integrated devices, such as chips, or the entire module may be provided in the form of an integrated device such as a chip. Consequently, inexpensive production and low power consumption are facilitated. 10 The module typically is provided in the form of a software defined radio device and arranged so that physical properties of the module, such as frequency ranges of the RF component signals and those related to a change in a transmission protocol, are controllable via suitable 15 computer software. The module may also form a part of a transmitter or receiver for emitting or receiving a plurality of respective ones of the RF signal components. In this case 20 the module typically comprises a plurality of antennas and may form a smart antenna. The smart antenna may be arranged for beam forming and/or null steering and typically is also arranged for spatial division multiplexing, code division multiplexing or frequency 25 division multiplexing. The smart antenna typically is arranged so that emission or reception properties of the smart antenna are controlled by selecting properties of the RF signal components. 30 The second converter component typically is arranged to convert between the plurality of digital signal components and a digital multiplexed electrical signal and between the digital multiplexed electrical signal and the digital multiplexed optical signal. Alternatively, the second converter component may also be arranged to convert between the plurality of digital signal components and a plurality of respective optical signal components and 5 between the plurality of the optical signal components and the digital multiplexed optical signal. The first converter component typically comprises a plurality of delta sigma modulators. The module typically 10 is arranged so that properties of the delta sigma modulators are controllable using suitable computer software. For example, the properties may include a frequency range and a dynamic range. Each delta sigma modulator typically is arranged to convert between one of 15 the RF signal components and a respective digital electrical signal component. The second converter component may then be arranged to convert between the respective electrical signal components and the digital multiplexed optical signal. Alternatively, each delta 20 sigma modulator may be arranged to convert between one of the RF signal components and a respective optical digital signal component. In this case the second converter component may be arranged to convert between the respective optical digital signal components and the 25 digital multiplexed optical signal. The converter components of the module may be directly or indirectly coupled. For example, the first converter component may be directly or indirectly electrically 30 connected to the second converter component and the frequency range component may be directly or indirectly electrically connected to the first converter component.

-8 In one specific example the module is provided in the form of a receiver module. In this example the converter typically comprises at least one optical light source, such as a solid state laser, that is arranged to provide 5 the digital optical signal in response to the corresponding electrical signal. The optical component may comprise a vertical cavity surface emitting laser (VCSEL) with driver electronics. Alternatively, the optical component may comprise an electro-optical modulator that 10 is arranged to provide the optical signal in response to the corresponding electrical signal. In another specific example the module is provided in the form of a transmitter module. In this example the 15 converter comprises at least one receiver component, such a suitable photo-detector, which is arranged to provide the digital electrical signal in response to the corresponding received optical signal. The receiver component typically is provided in the form of a resonance 20 cavity enhanced photo-detector (RCE-PD). The optical light guide may be a planar optical light guide, but typically is an optical fibre. 25 The present invention provides in a second aspect a system for converting between a RF signal and at least one digital electrical signal, the RF signal comprising a plurality of RF signal components, the system comprising: the module in accordance with the first aspect of the 30 present invention, wherein the module is provided in the form of a receiver module and comprises at least one optical light source for emission of the digital multiplexed optical signal; and - 9 a converter being arranged to convert between the digital multiplexed optical signal and the at least one digital electrical signal. 5 The converter for converting between the digital multiplexed optical signal and the at least one digital electrical signal may comprise a photo-detector for converting between the digital multiplexed optical signal and a digital multiplexed electrical signal. 10 Further, the converter may comprise a de-multiplexer for converting the digital multiplexed electrical digital signal into a plurality of digital electrical signal components that typically are not multiplexed. 15 The at least one photo-detector may be a resonance cavity enhanced photo-detector (RCE-PD). The system may also comprise a combiner for combining the 20 plurality of digital electrical signals into the at least one (combined) digital electrical signal. The present invention provides in a third aspect a system for converting between a RF signal and at least one 25 digital electrical signal, the RF signal comprising a plurality of RF signal components, the system comprising: the module in accordance with the first aspect of the present invention, wherein the module is provided in the form of a transmitter module and comprises at least one 30 photo-detector for receiving the digital multiplexed optical signal; and - 10 a converter being arranged to convert between the digital multiplexed optical signal and the at least one digital electrical signal. The present invention provides in a fourth aspect a method 5 of transforming between a RF signal having RF signal components and a digital multiplexed optical signal, the method comprising: guiding the RF signal components, at least two of the RF signal components including different frequency ranges; 10 converting between the RF signal components and a plurality of respective digital signal components; converting between the plurality of digital signal components and a digital multiplexed optical signal; and guiding the digital multiplexed optical signal. 15 The method typically comprises converting between the RF signal components and a plurality of respective digital electrical signal components; and converting between the plurality of digital 20 electrical signal components and the digital multiplexed optical signal. The method typically also comprises the step of converting between a RF signal having a first frequency range and the 25 plurality of RF signal components which may each have a frequency range that is included in the first frequency range. The invention will be more fully understood from the following description of specific embodiments of the 30 invention. The description is provided with reference to the accompanying drawings. Brief Description of the Drawings - 11 Figure 1 shows a schematic representation of a smart antenna system including a module for transforming between a RF signal and a digital multiplexed optical signal in 5 accordance with a first embodiment of the present invention; Figure 2 shows a schematic representation of a system including a module for transforming between an RF signal 10 and a digital multiplexed optical signal in accordance with the second embodiment of the present invention; Figure 3 shows a schematic representation of a transmitter including a module for transforming between an RF signal 15 and a digital multiplexed optical signal in accordance with a third embodiment of the present invention; Figure 4 shows a schematic representation of a receiver including a module for transforming between an RF signal 20 and a digital multiplexed optical signal in accordance with a fourth embodiment of the present invention; Figure 5 shows a schematic representation of a receiver array including a module for transforming between an RF 25 signal and a digital multiplexed optical signal in accordance with a fifth embodiment of the present invention; Figure 6 shows a schematic representation of a transmitter 30 array including a module for transforming between an RF signal and a digital multiplexed optical signal in accordance with a sixth embodiment of the present invention; - 12 Figure 7 shows a schematic representation of a smart antenna including a module for transforming between an RF signal and a digital multiplexed optical signal in 5 accordance with a seventh embodiment of the present invention; and Figure 8 shows a schematic representation of a smart antenna including a module for transforming between an RF 10 signal and a digital multiplexed optical signal in accordance with an eighth embodiment of the present invention. 15 Detailed Description of Specific Embodiments Embodiments of the present invention provide a module that is arranged to transform between a broadband radio frequency (RF) signal and a higher frequency digital 20 multiplexed optical signal. The module may function as a receiver and/or as a transmitter. When the module operates as a receiver, a broadband RF signal is received and converted to a digital multiplexed optical signal for transmission through an optical light guide to achieve 25 cost effective high-speed data transmission and signal processing. When the module operates as a transmitter, a digital optical signal is received through an optical light guide and then converted to a broadband RF signal for subsequent transmission. 30 Referring initially to Figure 1 there is shown a smart antenna system 100 including a plurality of modules 102 in accordance with a first embodiment of the present - 13 invention. Each module 102 is arranged for converting between a RF signal and a digital multiplexed optical signal. Each module 102 is arranged to receive a broadband RF signal and split the broadband RF signal into 5 component RF signals having different component frequency ranges that are each included in the broadband RF signal. These RF signal components are converted in parallel into respective digital signal components which are in turn combined to form a digital multiplexed optical signal. 10 The smart antenna system 100 comprises radio frequency (RF) antennas 106. Broadband RF signals are received by the antennas 106 and amplified by amplifier 107 before being directed to other components of the modules 102. 15 Further, the antenna system 100 comprises an optical fibre 103 for optical connection with the base station 104. The modules 102 and the base station 104 form together a transmission system in which the base station 104 is 20 arranged for converting between the multiplexed optical digital signal and an electrical signal, such as a digital electrical signal. Each module 102 comprises in this embodiment a RF splitter 25 110 arranged to split the incoming broadband RF signal into a plurality of narrow band RF signals. The RF splitter 110 is connected to a plurality of band pass filters 112 such that each narrow band RF signal passes through a respective band pass filter 112. Each of the 30 band pass filters 112 is connected in series with a respective low noise amplifier 114. Each low noise amplifier 114 is arranged to increase the signal strength of each narrow band RF signal while minimizing the amount - 14 of added noise. Each low noise amplifier 114 is connected in series with a respective delta sigma modulator 116 arranged to convert each of the narrow band RF signals to a respective digital signal. The outputs of the delta 5 sigma modulators 116 are connected to a multiplexer 118 which is arranged to combine and synchronise the digital signals into a high-rate digital signal. The antenna system 100 comprises in this embodiment one 10 vertical cavity surface emitting laser (VCSEL) 120 that is arranged to receive the multiplexed digital electrical signal from each module 120 and to convert the combined multiplexed signal into the high-rate digital multiplexed optical signal. The output of the VCSEL 120 is connected 15 to an optical fiber 103 arranged to transmit the optical signal to the base station 104. It will be appreciated that in an alternative embodiment the digital signal outputs from the delta sigma modulators 20 116 may be converted to optical signals before being combined in an optical multiplexer (not shown). The base station 104 comprises in this embodiment a photo detector for receiving the digital multiplexed optical 25 signal and for converting the digital multiplexed optical signal into a digital multiplexed electrical signal. Further, the base station comprises a converter for parallel converting the digital multiplexed electrical signals into a plurality of digital electrical signals 30 that are not multiplexed. The plurality of digital electrical signals are then combined and/or processed by a digital signal processor.

- 15 It is to be appreciated that the module 102 and the base station 104 may be separated by any distance, such as a distance of a few meters, kilometres or even hundred of kilometres and linked by the optical fibre 103 over that 5 distance. Alternatively, the base station 104 may also be provided in a form similar to that of the module 102. In this case the VCSEL 120 is replaced by a suitable photo-detector and 10 the RF signal components may not necessarily be provided by antennas 106, but may be provided by any other means. A person skilled in the art will appreciate that many components of the module 102 may function in a direction that is reverse to that of the module 102. 15 Figure 2 shows an example of a receiver 200 in accordance with a second embodiment of the present invention. The receiver is arranged to receive and convert a RF signal to a digital optical signal whereupon it is transmitted 20 through an optical light guide and then converted back to a digital signal for processing. The receiver 200 comprises an antenna 106 connected in series to a band pass filter 112 which is in turn 25 connected in series to a low noise amplifier 114. A RF signal is received by the antenna 106 and converted to a narrow band RF signal through the band pass filter 112. This narrow band RF signal is then amplified through the low noise amplifier 114. The output signal from the low 30 noise amplifier 114 is passed through a delta sigma modulator 116 arranged to digitize the narrow band RF signal. This digitized signal is then amplified through a VCSEL driver 202 before being converted into an optical - 16 signal by the VSCEL 120. This optical signal is then transmitted over an optical fibre 103 before being converted back into a digital 5 signal through a photodiode 204. This digital signal is then passed through a transimpedance and limiting amplifier 206 which amplifies the digital signal before it is passed through a decimation filter 208. The decimation filter 208 down-converts and filters the digital signal 10 through the use of digital filtering and decimation filtering. The output of the decimation filter may then be processed in a digital signal processor 210. In the above example, the decimation filter 208 may be 15 integrated with the digital signal processor 210, or implemented by software through DSP / FPGA or ASIC, while the low noise amplifier 114, the delta sigma modulator 116 and the VCSEL driver 202 may be integrated into a single integrated circuit. It will be appreciated however that 20 the dissemination filter 208 may be placed between the delta sigma modulator 116 and the VCSEL driver 202. Figure 3 shows an example of a transmitter in accordance with a third embodiment of the present invention. The 25 transmitter is arranged to convert a digital signal to a digital optical signal for transmission through an optical light guide. This digital optical signal is converted back to a digital signal and then converted to a RF signal for transmission from an antenna. 30 Referring to Figure 3 there is shown an example of a transmitter 300. In this example a digital signal from the digital signal processor 210 is conditioned by the - 17 VCSEL driver 202 before being converted to an optical signal by the VCSEL 120. This optical signal is then transmitted via an optical fibre 103 to a photodiode 204 where the optical signal is converted back to a digital 5 signal. This digital signal is then amplified by a transimpedance and limiting amplifier 206 before being converted into a radio frequency signal by the delta sigma modulator 116. This radio frequency signal is then be amplified by a power amplifier 302 and filtered by the 10 band pass filter 112 before it is transmitted by the radio frequency transceiver 106. For both of the examples illustrated in Figures 2 and 3, the delta sigma modulator 116, VCSEL driver 202 and VCSEL 15 120 may be replaced by a photonic delta sigma modulator (not shown). For a receiver configuration in this embodiment the photonic delta sigma modulator is arranged to sample the radio frequency signal and convert the digital signal to an optical signal through an optical 20 modulator. The optical modulator incorporates the VCSEL and driver circuitry. The optical modulator may be integrated in a photonic integrated circuit. In a transmitter arrangement, a digital signal is converted to a digital optical signal through an electro optical 25 modulator (not shown) before being transmitted to a photonic delta sigma modulator for conversion of the digital optical signal to a RF signal. The photodiode 204 may be arranged as part of the photonic delta sigma modulator (not shown). 30 Figure 4 shows an example of a receiver 400 in accordance with a fourth embodiment of the present invention. The receiver of this embodiment receives a RF signal which is - 18 then split into component RF signals for parallel conversion into respective component digital signals. These component digital signals are then combined and converted into a digital optical signal for transmission 5 through an optical light guide. The optical signal is then converted back to a digital signal for processing. The receiver 400 is arranged to receive and split a RF signal into N equal range RF signals before digitization. 10 In this embodiment the broadband RF signal is received by antenna 106 after which it is filtered into a narrow band signal by the band pass filter 112 and amplified by the low noise amplifier 114. The narrow band RF signal is then split into N equal range radio frequency signals by a 1:N 15 splitter 402. Each of these N radio frequency signals is then converted into a respective digital signal through a respective delta sigma modulator 116. The N digital signals are then combined in a N:1 serialiser 404 or a multiplexer 118. The output from the N:1 serialiser 404 or 20 the multiplexer 118 is then converted to an optical signal and transmitted via the optical fibre 103 and converted back to a digital signal and processed by the digital signal processor 210 in a manner similar to that described previously. 25 The configuration shown in Figure 4 may be arranged to increase the sampling rate or to increase the bandwidth of the digital signal. If the configuration is arranged to increase the sampling rate then each delta sigma modulator 30 116 typically is arranged to provide an output at the same sample rate f,. The outputs from each of the delta sigma modulators 116 are then input into a multiplexer 118. The multiplexer 118 then samples each of these inputs at a - 19 higher sampling rate, the higher sampling rate being a multiple of f.. If the configuration is arranged to increase the bandwidth then at least some delta sigma modulator 116 are arranged to provide an output at 5 different sample rates. These outputs are then input into a N:l serialiser 404 where the signals are time interleaved and serialized into a single digital output. For the above example it will be appreciated that the decimation filter 208 may be located at different 10 positions in the signal chain. It will also be appreciated that the 1:N serialiser 404 and the multiplexer 118 may be integrated into a single circuit such that a selection can be made between the desired function of either increasing the sampling rate or increasing the bandwidth. 15 Figure 5 shows an example of a receiver array 500 in accordance with a fifth embodiment of the present invention. The receiver array 500 in this embodiment is arranged to receive and convert a plurality of RF signals 20 into a plurality of respective digital signals to be combined into a serial digital signal. The serial digital signal is then converted to a digital optical signal for transmission through an optical light guide before being converted back to a digital signal for processing. 25 The receiver array 500 may have multiple receiver elements 502 connected to the N:1 serialiser 404. In this example each receiver element 502 comprises an antenna 106, band pass filter 112, low noise amplifier 114, delta sigma 30 modulator 116 and decimation filter 208 for receiving a RF signal and converting it into a digital signal in a manner similar to that described previously. Preferably, the digital signal is a serial digital signal. The digital - 20 outputs from the decimation filter 208 are combined into a higher-rate serial digital signal by the N:l serialiser 404. This serial digital signal is then converted to an optical signal for transmission to the digital signal 5 processor 210 in a manner similar to that described previously. In this example the output rate of the decimation filter 208 is selected such that it matches the output rate of 10 the N:1 serialiser 404. For example if the N:1 serialiser 404 output rate is 10Gbps then the serial output rate of each decimation filter 208 is 10Gbps/N. N may be selected such that integration of the delta sigma modulator 116, N:1 serialiser 404 and VCSEL driver 202 into a single 15 integrated circuit is still possible. The VCSEL may be a single, matrix or 2-D array type. Figure 6 shows an example of a transmitter array 600 in accordance with a sixth embodiment of the present 20 invention. The receiver array in this embodiment is arranged to receive a digital signal which is converted to a digital optical signal for transmission through an optical light guide. The digital optical signal is then converted to a digital signal which is split into 25 component digital signals. The component digital signals are then converted to respective RF signals which are then transmitted from respective antennas. The transmitter array shown in Figure 6 is analogous to 30 the example shown in Figure 5 however it is arranged to transmit a broadband radio frequency signal from a high rate digital signal input. In this example, a high-rate digital signal is converted into an optical signal and - 21 transmitted over the optical fibre 103 before being converted back into a digital signal. After this process, the digital signal is split into N digital signals through a 1:N deserialiser 602. Each of these N digital signals is 5 then converted to a RF signal after passing in series through a respective delta sigma modulator 116, power amplifier 302 and band pass filter 112. Each RF signal may then be transmitted through a respective antenna 106. 10 In each of the examples illustrated by Figures 5 and 6, each of the delta sigma modulators 116 may be of the parallel array type described in Figure 4 to provide wideband high-resolution sampling of the RF signal. In other alternatives, the location of the decimation filter 15 208 in the signal chain may be altered. Figure 7 shows a smart antenna system 700 in accordance with a seventh embodiment of the present invention. A plurality of RF signals are received by a plurality of 20 antennas. Each RF signal is then converted into a digital optical signal for processing through a spatial light modulator before being converted to digital signals and combined for digital processing. 25 The smart antenna system 700 comprises in this example an antenna array 702 for receiving RF signals. Each of these RF signals is converted into a respective digital signal in a manner similar to that described previously where the RF signals are transmitted in series through a band pass 30 filter 112, a low noise amplifier 116 and a delta sigma modulator 116. Each of the digital outputs from each of the delta sigma modulators 116 are then converted into optical signals through a VCSEL array 704. These optical - 22 signals are then routed to a respective spatial light modulator 706. The spatial light modulator 706 may be employed to perform optical matrix vector multiplication, optical discrete Fourier transforms or optical neural 5 network functions on the optical signals. The spatial light modulator 706 may be a one-dimensional, two dimensional or three-dimensional modulator and implemented using a liquid crystal or magneto-optic material. Further, the spatial light modulator 706 may comprise a micro 10 channel, a deformable mirror, a Pockels read-out modulator, a Preobrasovatel Izobrazheniy system, and may also comprise a micro-electro mechanical system or multiple quantum wells. 15 Figure 8 shows a smart antenna system 800 in accordance with an eighth embodiment of the present invention. In this example, an array of antennas 801, for example an array of three groups of two antennas, are arranged to receive RF signals. Each group of two antennas 801 20 transmits the received RF signals to a respective module 802 arranged to convert the two received RF signals into a single digital multiplexed electrical signal. In this example there would be three modules 802, each receiving two RF signals from the antennas 801 and converting each 25 group of two RF signals into a single digital multiplexed electrical signal. A total of three digital multiplexed electrical signals would therefore be output from the three modules 802. 30 Each digital multiplexed electrical signal is then transmitted to a VCSEL array 803 where each of the digital multiplexed electrical signals is converted into a respective digital multiplexed optical signal. In this - 23 example, three digital multiplexed electrical signals are converted into three digital multiplexed optical signals. The three digital multiplexed optical signals are then transmitted via optical fibre cables 804 to a photodiode 5 array 805. The photodiode array 805 is arranged to convert the three digital multiplexed optical signals back into respective digital multiplexed electrical signals. Each of these three digital multiplexed electrical signals are then transmitted to a respective converter 806 arranged to 10 de-multiplex each of the three digital multiplexed electrical signals back into two digital electrical signals. In this example, a total of six digital electrical signals will be output from the converters 806. Each of these six digital electrical signals is then 15 transmitted to a DSP 807 for signal processing. In a specific embodiment, there are twelve groups of sixteen antennas 801. Twelve modules 802 are arranged to convert the twelve groups of sixteen received RF signals 20 into twelve digital multiplexed signals. The twelve digital multiplexed signals are converted by the VCSEL array 803 to twelve respective digital multiplexed optical signals. The twelve digital multiplexed optical signals are guided through twelve respective optical fibre cables 25 804 to photodiode array 805. The photodiode array 805 is arranged to convert the twelve digital multiplexed optical signals back into twelve respective digital multiplexed electrical signals. These 30 twelve digital multiplexed electrical signals are each converted by a respective converter 806 into sixteen digital electrical signals. In this example, there would therefore be a total of 192 digital electrical signals - 24 output from the twelve converters 806. These 192 digital electrical signals are then transmitted to the DSP 807 for signal processing. 5 In addition to the above examples, it is envisaged that any number of antennas and components could be adapted for use is the smart antennas system 800. 10 The transmitter and receiver may be implemented in one circuit in full duplex or half duplex configuration. A full duplex configuration may be realized by combining each full circuit of each of the transmitter and receiver such that the configuration is able to transmit and 15 receive simultaneously. A half duplex configuration is arranged to operate either in transmit or receive mode wherein parts of the common circuit are shared. In a particular embodiment, parallel software defined 20 radio (SDR) RF to digital delta sigma converters may be employed. These may be arranged for example to allow the instantaneous conversion of 400MHz signal bandwidth (for 16-bit resolution with a data rate of 40Mbps for each converter), in conjunction with a 16:1 time-division 25 multiplexer and 10Gbps optical interconnects such that a smart antenna beamformer of more than 5.5GHz radio frequency bandwidth operating over a frequency range of 0.05-6.0GHz is realized. The multiplexer could be any combination of 4:1, 8:1, 16:1 etc. depending on the design 30 and needs of the communication system. A benefit of using a SDR system is that the physical-layer characteristics of the smart antenna system can be altered - 25 by reconfiguring software without the need to change hardware. This type of smart antenna could be used in broadband wireless networks, remotely controlled phased array microwave radar, MIMO smart antenna and is 5 applicable to radio astronomy projects where a high performance and cost-effective receiver solution is important. Particular embodiments also allow for high-speed broadband 10 communication systems that operate efficiently over a large frequency spectrum and may be arranged to operate for any type of protocol/coding scheme such as UHF and VHF radio, GSM, CDMA, 3G Network, WiFi, Bluetooth and WiMax amongst others. 15 The module in accordance with embodiments of the present invention may be fabricated using CMOS technologies and may comprise integrated device or may be provided in the form of an integrated device. 20 The delta sigma modulators described in the various embodiments may utilize a locally generated clock for the delta sigma modulator's sampler. This may be produced by a digital frequency synthesizer, or analogue/digital PLL 25 with internal VCO, or external local or remote VCO where the signal needed to control the VCO/PLL may be transmitted via a digital optical fiber link. The antenna arrays described may be used in a software 30 defined phased array transceiver/smart antenna for wideband interference mitigation. In embodiments where optical processing is desired, the - 26 delta sigma modulator may be implemented using electronic means or optical means. If electronic delta sigma modulators are used, then the 5 outputs from the electronic delta sigma modulators are typically connected to VCSEL driver circuits to generate digitized optical beams. These optical beams may then be routed to achieve optical true-time delay generation, for example by using a multi-cavity optical substrate arranged 10 to generate multiple delayed reflections of the optical signal. If optical delta sigma modulators are used, then true-time delay generation can be achieved using devices such as 8 15 bit programmable integrated optical spiral planar light guide circuits, InP based optical IC time-delays, White cell based free space true-time delay generators, optical true-time delay using fibre Bragg gratings and metal-film reflectors, moveable mirror true-time delays or moveable 20 waveguide channels. After the true-time delay generation of outputs from the electronic or optical delta sigma modulators, a photodiode array may provide the FIR-type tapped true-time delay 25 generation required for wideband interference mitigation, for example by using space-time adaptive processing, or any type of processing where digital filtering using tapped delay line is required. The outputs from the photodiode arrays are then routed into a register so that 30 the delay can be dynamically selected and added on a bit to-bit basis to generate the weight for the desired focused signal. After the digital weight generation, the output is routed into a decimation filter for low pass - 27 filtering and down-conversion for digital processing. The output may then be routed to a processor or adaptive controller to give feedback to adjust parameters such as the sampling rate of the delta sigma modulators, the 5 filtering and decimation rate and the weight generation. Although the invention has been described with reference to particular examples, it will be appreciated by those skilled in the art that the invention may be embodied in 10 many other forms. For example, the module for transforming between a RF signal and a digital multiplexed optical signal may be used to convert from any type of RF signal to any type of optical digital signal and is not necessarily restricted to the use of broadband 15 communication systems.

Claims

1. A module for transforming between a RF signal and a 5 digital multiplexed optical signal, the RF signal comprising a plurality of RF signal components, the module comprising: a plurality of guides for guiding the RF components, at least two of the RF signal components including 10 different frequency ranges; a converter being arranged to convert between the RF signal components and a plurality of digital signal components and being arranged to convert between the plurality of digital signal components and a digital 15 multiplexed optical digital signal; and an optical light guide for guiding the digital multiplexed optical signal.

2. The module of claim 1 wherein at least some of the RF 20 signal components have differing frequency ranges.

3. The module of claim 1 or 2 wherein the RF signal components each have a different frequency range. 25 4. The module of any one of the preceding claims wherein the converter is arranged to convert between N RF signal components and corresponding N digital signals components.

5. The module of claim 4 wherein the converter is 30 arranged to convert in parallel between N RF signal components and corresponding N digital signals components. - 29 6. The module of any one of the preceding claims wherein each RF signal component has a frequency range that is directly adjacent a frequency range of another one of the 5 RF signal components.

7. The module of any one of the preceding claims wherein the converter comprises a first converter component being arranged to convert between the RF signal components and a 10 plurality of respective digital electrical signal components; and a second converter component being arranged to convert between the plurality of digital electrical signal components and the digital multiplexed optical signal. 15

8. The module of any one of claims 1 to 6 wherein the converter comprises a first converter component being arranged to convert between the RF signal components and a plurality of respective optical digital signal components; 20 and a second converter component being arranged for converting between the plurality of digital optical signal components and the digital multiplexed optical signal.

9. The module of claim 7 or 8 wherein the second 25 converter component is arranged to convert between N digital signal components and the digital multiplexed optical signal using time division multiplexing or time division de-multiplexing. 30 10. The module of claim 9 wherein the second converter component is arranged for parallel conversion. - 30 11. The module of any one of the preceding claims wherein the module forms a part of a receiver for receiving the RF signal or a transmitter for emitting the RF signal. 5 12. The module of any one of the preceding claims comprising a frequency range component that is arranged to convert between a RF signal having a first frequency range and the plurality of RF signal components which each have a frequency range that is included in the first frequency 10 range.

13. The module of claim 12 wherein the frequency range component is arranged to convert between N RF signal components and the RF signal, wherein the RF signal has a 15 frequency range that is approximately N times wider than that of each RF signal component.

14. The module of any one of claims 1 to 11 comprising a frequency range component that is arranged to convert each 20 first RF signal of a plurality of first RF signals into a plurality of RF signal components which each have a frequency range that is included in a frequency range of a respective one of the first RF signal. 25 15. The module of any one of the preceding claims wherein the module comprises an integrated device.

16. The module of any one of the preceding claims wherein the module is provided in the form of a software defined 30 radio device and arranged so that physical properties of the module are controllable via suitable computer software. - 31 17. The module of any one of the preceding claims wherein the module forms a part of a transmitter or receiver for emitting or receiving a plurality of respective ones of the RF signal components. 5

18. The module of claim 17 wherein the module comprises a plurality of antennas and forms a smart antenna.

19. The module of any one of the preceding claims wherein 10 the converter comprises a first converter component and wherein the first converter component comprises a plurality of delta sigma modulators.

20. The module of claim 19 wherein the module is arranged 15 so that properties of the delta sigma modulators are controllable using suitable computer software.

21. The module of claim 19 or 20 wherein each delta sigma modulator is arranged to convert between one of the RF 20 signal components and a respective digital electrical signal component.

22. The module of claim 19 or 20 wherein each delta sigma modulator is arranged to convert between one of the RF 25 signal components and a respective optical digital signal component.

23. The module of any one of the preceding claims wherein the module is provided in the form of a receiver module 30 and wherein the converter comprises at least one optical light source for emitting the digital multiplexed optical signal. - 32 26. The module of claim 23 wherein the at least one optical light source comprises a vertical cavity surface emitting laser (VCSEL). 5 25. The module of any one of claims 1 - 22 wherein the module is provided in the form of a transmitter module and wherein the converter comprises at least one photo detector for receiving the digital multiplexed optical signal. 10

26. The method of claim 25 wherein the at least one photo-detector is a resonance cavity enhanced photo detector (RCE-PD). 15 27. A method of transforming between a RF signal having RF signal components and a digital multiplexed optical signal, the method comprising: guiding the RF signal components, at least two of the RF signal components including different frequency ranges; 20 converting between the RF signal components and a plurality of respective digital signal components; converting between the plurality of digital signal components and a digital multiplexed optical signal; and guiding the digital multiplexed optical signal. 25

28. The method of claim 27 comprising converting between the RF signal components and a plurality of respective digital electrical signal components; and converting between the plurality of digital 30 electrical signal components and the digital multiplexed optical signal.

29. The method of claim 27 or 28 comprising step of - 33 converting between a RF signal having a first frequency range and the plurality of RF signal components which each have a frequency range that is included in the first frequency range. 5

30. A system for converting between a RF signal and at least one digital electrical signal, the RF signal comprising a plurality of RF signal components, the system comprising: 10 the module of claim 23 or 24; a converter being arranged to convert between the digital multiplexed optical signal and the at least one digital electrical signal. 15 31. The system of claim 30 wherein the converter for converting between the digital multiplexed optical signal and the at least one digital electrical signal comprises a photo-detector for converting between the digital multiplexed optical signal and a digital multiplexed 20 electrical signal.

32. The system of claim 30 or 31 wherein comprising a de multiplexer for converting the digital multiplexed electrical digital signal into a plurality of digital 25 electrical signal components.

33. The system of any one of claim 30 to 32 wherein the at least one photo-detector is a resonance cavity enhanced photo-detector (RCE-PD). 30

34. The system of any one of claims 30 to 33 comprising a combiner for combining the plurality of digital electrical signals into the at least one (combined) digital - 34 electrical signal.

35. A system for converting between a RF signal and at least one digital electrical signal, the RF signal 5 comprising a plurality of RF signal components, the system comprising: the module of claim 25; and a converter being arranged to convert between the digital multiplexed optical signal and the at least one 10 digital electrical signal.