WO2009001100A1 - A method and device for digitising an electrical signal - Google Patents

A method and device for digitising an electrical signal Download PDF

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Publication number
WO2009001100A1
WO2009001100A1 PCT/GB2008/002218 GB2008002218W WO2009001100A1 WO 2009001100 A1 WO2009001100 A1 WO 2009001100A1 GB 2008002218 W GB2008002218 W GB 2008002218W WO 2009001100 A1 WO2009001100 A1 WO 2009001100A1
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WO
WIPO (PCT)
Prior art keywords
signal
optical
modulator
wavelength dependent
modulators
Prior art date
Application number
PCT/GB2008/002218
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French (fr)
Inventor
John Heaton
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Filtronic Plc
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Publication of WO2009001100A1 publication Critical patent/WO2009001100A1/en

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Classifications

    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04J—MULTIPLEX COMMUNICATION
    • H04J14/00—Optical multiplex systems
    • H04J14/08—Time-division multiplex systems
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03M—CODING; DECODING; CODE CONVERSION IN GENERAL
    • H03M1/00—Analogue/digital conversion; Digital/analogue conversion
    • H03M1/12—Analogue/digital converters
    • H03M1/1205—Multiplexed conversion systems
    • H03M1/121—Interleaved, i.e. using multiple converters or converter parts for one channel
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B10/00—Transmission systems employing electromagnetic waves other than radio-waves, e.g. infrared, visible or ultraviolet light, or employing corpuscular radiation, e.g. quantum communication
    • H04B10/25—Arrangements specific to fibre transmission
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B10/00—Transmission systems employing electromagnetic waves other than radio-waves, e.g. infrared, visible or ultraviolet light, or employing corpuscular radiation, e.g. quantum communication
    • H04B10/40—Transceivers
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04J—MULTIPLEX COMMUNICATION
    • H04J14/00—Optical multiplex systems
    • H04J14/02—Wavelength-division multiplex systems

Definitions

  • the present invention relates to a method and device for digitising an electrical signal, preferably a microwave signal. More particularly, but not exclusively, the present invention relates to a method of digitising a microwave signal comprising the steps of simultaneously passing continuous waves of different wavelengths through a modulator where they are modulated by a received microwave signal, splitting the continuous waves into a plurality of wavelength dependent paths, chopping the signals in each wavelength dependent path into pulses and passing the pulses to analogue to digital converters.
  • TDM time division multiplexing
  • WDM wavelength division multiplexing
  • TDM systems provide a succession of optical pulses. These are modulated by the microwave signal.
  • a high speed RF driven optical switching element sends successive pulses along different optical paths.
  • An analogue to digital converter in each path digitises the received pulses .
  • the high speed optical element is difficult and expensive to manufacture and is also difficult to drive electrically.
  • WDM systems provide a series of pulses of different wavelengths. These are modulated by the microwave signal before being split into different optical paths by an arrayed waveguide grating before being digitised. It is difficult to generate a series of pulses with different wavelengths from one pulse to the next. Such WDM systems are complex and difficult to manufacture.
  • the present invention provides a device for digitising an electrical signal comprising
  • an optical combiner having a plurality of input ports each adapted to receive the output of a laser and an output port, the optical combiner being adapted to combine the optical signal received at the plurality of input ports at the output port;
  • an optical modulator comprising an input port adapted to receive the output of the optical combiner, an output port and at least one optical path extending therebetween, the optical modulator being adapted to receive an electrical signal and to modulate the amplitude of the optical signal in the optical path in response to the electrical signal;
  • an optical splitter for splitting the signal received from the output port of the optical modulator into a plurality of wavelength dependent signal paths;
  • each wavelength dependent signal path comprising an optical signal modulator between optical splitter and analogue to digital converter
  • control circuit connected to the optical signal modulators adapted to switch the optical signal modulators between on and off states to allow a portion of the optical signal to pass through as a pulse.
  • ADC photonic analogue to digital converter
  • continuous wave lasers allow the device to sample signals with higher precision than other wavelength division multiplexed architectures.
  • Other WDM systems require a short pulsed (mode locked) laser which may not have a stable enough pulse-to-pulse power jitter to give a high enough effective number of bits (ENOB) or spurious free dynamic range (SFDR).
  • ENOB effective number of bits
  • SFDR spurious free dynamic range
  • the device according to the invention allows a complex sampling function to be achieved using simple passive photonic components.
  • the device according to the invention is reliable and lightweight and is particularly suitable for use in high performance avionic and naval electronic warfare applications. Other applications include high speed single shot oscilloscopes and spectrum analysers.
  • at least one of the wavelength dependent signal paths includes an optical delay element to delay the signal in the path relative to the signal in at least one other wavelength dependent signal path.
  • control circuit turns on at least two of the optical signal modulators at different times.
  • control circuit simultaneously turns on at least two of the optical signal modulators.
  • the device further comprises a sampling pulse modulator between the optical modulator and signal splitter adapted to split the signal received from the optical modulator into pulses.
  • the device further comprises compression means for compressing in time each of the pulses received from the sampling pulse modulator.
  • the compression means comprises a grating.
  • the optical combiner comprises an arrayed waveguide grating.
  • the optical splitter comprises an arrayed waveguide grating.
  • each wavelength dependent signal path comprises a photodetector adapted to receive the optical signal from the optical splitter and provide an electrical signal to the analogue to digital converter.
  • the electrical signal is a microwave signal.
  • a method for digitising an electrical signal comprising the steps of (a) providing a plurality of continuous wave lasers, each providing a continuous optical wave at a different wavelength;
  • the method further comprises the step of introducing a delay into the signal in at least one wavelength dependent signal path relative to the signals in the other wavelength dependent signal paths prior to chopping by the optical signal modulators.
  • At least one of the optical signal modulators chops its received signal into a pulse at a different time to at least one of the other optical signal modulators.
  • the optical signal modulators simultaneously chop their received signals into pulses.
  • the combined waves are passed through a sampling pulse modulator to split the waves into a series of pulses before splitting into the wavelength dependent signal paths.
  • the pulses from the sampling pulse modulator are compressed in time before splitting into wavelength dependent signal paths.
  • the electrical signal is a microwave signal.
  • Figure 1 shows a first embodiment of a device according to the invention
  • Figure 2 shows a second embodiment of a device according to the invention
  • Figure 3 shows a third embodiment of a device according to the invention.
  • Figure 4 shows a fourth embodiment of a device according to the invention.
  • Shown in figure 1 is a first embodiment of a device 1 for digitising an electrical signal according to the invention.
  • the device 1 comprises a plurality of continuous wave lasers 2 each producing a different wavelength.
  • the outputs from the lasers are passed to the input ports 3 of an optical combiner 4 comprising an arrayed waveguide grating (AWG).
  • AWG arrayed waveguide grating
  • the output from the AWG is passed to the input 6 of an optical modulator 7.
  • the optical modulator 7 of this embodiment is an interferometer 7.
  • the signals passing down the arms of the interferometer 7 are altered by the incident microwave signal 9.
  • the two optical signals recombine at the output of the optical modulator 7 the resulting amplitude depends upon the amplitude of the incident microwave signal.
  • the operation of such optical modulators 7 is known in the art and will not be discussed further.
  • the signal output from the optical modulator 7 is passed to an optical splitter 10 which splits the received signal into a plurality of wavelength dependent signal paths 11.
  • the optical splitter 10 for this embodiment is an AWG.
  • each of the wavelength dependent signal paths 11 Attached to each of the wavelength dependent signal paths 11 is a photodetector 12.
  • the photodetectors 12 each output an analogue electrical signal dependent upon the amplitude of the optical signal received. This output is then converted by an electronic analogue to digital converter (not shown) to a digital output.
  • an optical signal modulator 13 Arranged in each wavelength dependent signal path 11 is an optical signal modulator 13.
  • Each optical signal modulator 13 can be switched by a control circuit (not shown) between an on configuration whereby signals pass through the optical signal modulator 13 to the photodetector 12 and an off configuration whereby signals do not pass through the optical signal modulator 13.
  • optical signal modulators 13 are rapidly switched between on and off configurations so chopping the signal received from the optical splitter 10 into pulses as shown. Each pulse corresponds to the amplitude of the modulated signal at a particular instant as it exits the optical modulator 7.
  • control circuit is arranged such that the optical signal modulators 13 which receive signals at different wavelengths are turned on and off at slightly different times to each other as shown. In this way the modulated optical signal can be sampled at a high effective frequency. Sampled pulses which are adjacent in time are sent to different photodetectors 12 and so can be processed at a lower frequency.
  • FIG 2 Shown in figure 2 is a further embodiment of a device 1 according to the invention.
  • the embodiment is similar to that of figure 1 except the wavelength dependent signal paths 11 include optical delay elements 14.
  • Each wavelength dependent signal path 11 has an optical delay element 14 which introduces a different degree of delay.
  • each of the optical signal modulators 13 is turned on and off simultaneously. Due to the delays introduced in the wavelength dependent signal paths 11 the optical signal modulators 13 sample the signal as modulated by the optical modulator 7 at different times.
  • FIG 3 Shown in figure 3 is a further embodiment of a device 1 according to the invention.
  • This embodiment is similar to that of figure 1 except it includes a sampling pulse modulator 15 between the output 8 of the optical modulator 7 and the optical splitter 10.
  • the sampling pulse modulator 15 reduces the signal from the output of the optical modulator 7 to a series of pulses as shown.
  • the optical signal modulators 13 are arranged to turn on and off such that each allows a signal pulse through.
  • the timing for the opening and closing of the optical signal modulators 13 is arranged such that a first optical signal modulator 13 turns on and off to let the first of the series of pulses presented on its associated wavelength dependent signal path 11 through to the associated photodetector 12. The remaining pulses on the wavelength dependent line 11 are blocked.
  • the same pulses are presented on the adjacent wavelength dependent signal line 11 as shown.
  • the opening and closing of the optical signal modulator 13 on this line 11 is timed to allow a different pulse through. This is repeated on all the wavelength dependent signal lines 11 such that each optical signal modulator 13 lets through one pulse, each optical signal modulator 13 letting through a different pulse.
  • sampling pulse modulator 15 reduces the requirement for the optical signal modulators 13 to be turned on and off rapidly.
  • the optical signal modulators 13 need only to turn on and off sufficiently rapidly to be able to discriminate between one pulse and the next.
  • the sampling pulse modulator 15 can be turned on and off more rapidly than optical signal modulators 13 so allowing shorter pulses to be generated. Short pulses provide a more accurate measure for the instantaneous measure of the modulated signal at a particular time. Longer pulses tend to average the signal over the length of the pulse.
  • FIG 4 A further embodiment of a device 1 according to the invention is shown in figure 4. This is similar to the embodiment of figure 3 except the wavelength dependent signal paths 11 include optical delay elements 14. Those are arranged such that by the time the pulses reach the optical signal modulators 13 different pulses on different wavelength dependent signal paths 11 are simultaneous. Accordingly, in this embodiment all of the optical signal modulators 13 open and close simultaneously.
  • the device 1 further comprises pulse compression means (for example a grating) for compressing the length for the pulses after they exit the sampling pulse modulator 15.
  • pulse compression means for example a grating
  • the optical splitters and combiners 4,10 comprise integrated optic on-chip gratings or echelle gratings.
  • the above embodiments have been described with reference to incident microwave signals.
  • the device may be adapted to digitise received signals in other regions of the electromagnetic spectrum.

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  • Engineering & Computer Science (AREA)
  • Computer Networks & Wireless Communication (AREA)
  • Signal Processing (AREA)
  • Physics & Mathematics (AREA)
  • Electromagnetism (AREA)
  • Theoretical Computer Science (AREA)
  • Optical Communication System (AREA)

Abstract

A device for digitising an electrical signal comprising (a) at least two continuous wave lasers each being adapted to produce light at a different wavelength; (b) an optical combiner having a plurality of input ports each adapted to receive the output of a laser and an output port, the optical combiner being adapted to combine the optical signal received at the plurality of input ports at the output port; (c) an optical modulator comprising an input port adapted to receive the output of the optical combiner, an output port and at least one optical path extending therebetween, the modulator being adapted to receive an electrical signal and to modulate the amplitude of the optical signal in the optical path in response to the electrical signal; (d) an optical splitter for splitting the signal received from the output port of the optical modulator into a plurality of wavelength dependent signal paths; (e) a plurality of analogue to digital converters each connected to at least one wavelength dependent signal path and being adapted to convert the received ', optical signal to a digital signal; (f) each wavelength dependent signal path comprising an optical signal modulator between optical splitter and analogue to digital converter; and, (g) a control circuit connected to the optical signal modulators adapted to switch the optical signal modulators between on and off states to allow a portion of the optical signal to pass through as a pulse.

Description

A METHOD AND DEVICE FOR DIGITISING AN ELECTRICAL SIGNAL
The present invention relates to a method and device for digitising an electrical signal, preferably a microwave signal. More particularly, but not exclusively, the present invention relates to a method of digitising a microwave signal comprising the steps of simultaneously passing continuous waves of different wavelengths through a modulator where they are modulated by a received microwave signal, splitting the continuous waves into a plurality of wavelength dependent paths, chopping the signals in each wavelength dependent path into pulses and passing the pulses to analogue to digital converters.
Devices for digitising microwave signals are known. Such devices use either time division multiplexing (TDM) or wavelength division multiplexing (WDM). TDM systems provide a succession of optical pulses. These are modulated by the microwave signal. A high speed RF driven optical switching element sends successive pulses along different optical paths. An analogue to digital converter in each path digitises the received pulses . The high speed optical element is difficult and expensive to manufacture and is also difficult to drive electrically.
WDM systems provide a series of pulses of different wavelengths. These are modulated by the microwave signal before being split into different optical paths by an arrayed waveguide grating before being digitised. It is difficult to generate a series of pulses with different wavelengths from one pulse to the next. Such WDM systems are complex and difficult to manufacture.
Accordingly, in a first aspect, the present invention provides a device for digitising an electrical signal comprising
(a) at least two continuous wave lasers each being adapted to produce light at a different wavelength;
(b) an optical combiner having a plurality of input ports each adapted to receive the output of a laser and an output port, the optical combiner being adapted to combine the optical signal received at the plurality of input ports at the output port; (c) an optical modulator comprising an input port adapted to receive the output of the optical combiner, an output port and at least one optical path extending therebetween, the optical modulator being adapted to receive an electrical signal and to modulate the amplitude of the optical signal in the optical path in response to the electrical signal; (d) an optical splitter for splitting the signal received from the output port of the optical modulator into a plurality of wavelength dependent signal paths;
(e) a plurality of analogue to digital converters each connected to at least one wavelength dependent signal path and being adapted to convert the received optical signal to a digital signal; (f) each wavelength dependent signal path comprising an optical signal modulator between optical splitter and analogue to digital converter; and,
(g) a control circuit connected to the optical signal modulators adapted to switch the optical signal modulators between on and off states to allow a portion of the optical signal to pass through as a pulse.
Using this approach to make a photonic analogue to digital converter (ADC) enables sampling and digitisation at significantly higher sampling rates and electrical (preferably microwave) signal bandwidths than can be achieved with purely electronic ADCs.
The use of continuous wave lasers allows the device to sample signals with higher precision than other wavelength division multiplexed architectures. Other WDM systems require a short pulsed (mode locked) laser which may not have a stable enough pulse-to-pulse power jitter to give a high enough effective number of bits (ENOB) or spurious free dynamic range (SFDR).
In addition the device according to the invention allows a complex sampling function to be achieved using simple passive photonic components. The device according to the invention is reliable and lightweight and is particularly suitable for use in high performance avionic and naval electronic warfare applications. Other applications include high speed single shot oscilloscopes and spectrum analysers. Preferably, at least one of the wavelength dependent signal paths includes an optical delay element to delay the signal in the path relative to the signal in at least one other wavelength dependent signal path.
Preferably, the control circuit turns on at least two of the optical signal modulators at different times.
Alternatively, the control circuit simultaneously turns on at least two of the optical signal modulators.
Preferably, the device further comprises a sampling pulse modulator between the optical modulator and signal splitter adapted to split the signal received from the optical modulator into pulses.
Preferably, the device further comprises compression means for compressing in time each of the pulses received from the sampling pulse modulator.
Preferably, the compression means comprises a grating.
Preferably, the optical combiner comprises an arrayed waveguide grating.
Preferably, the optical splitter comprises an arrayed waveguide grating.
Preferably, each wavelength dependent signal path comprises a photodetector adapted to receive the optical signal from the optical splitter and provide an electrical signal to the analogue to digital converter.
Preferably, the electrical signal is a microwave signal.
In an alternative aspect of the invention there is provided a method for digitising an electrical signal comprising the steps of (a) providing a plurality of continuous wave lasers, each providing a continuous optical wave at a different wavelength;
(b) combining each of the continuous optical waves into a single optical path;
(c) passing the combined waves through an optical modulator where they are modulated by a received electrical signal;
(d) splitting the combined waves into a plurality of wavelength dependent signal paths;
(e) passing the signals in each of the wavelength dependent signal paths to optical signal modulators to chop the signals into signal pulses;
(f) passing the signal pulses to analogue to digital converters.
Preferably, the method further comprises the step of introducing a delay into the signal in at least one wavelength dependent signal path relative to the signals in the other wavelength dependent signal paths prior to chopping by the optical signal modulators.
Preferably, at least one of the optical signal modulators chops its received signal into a pulse at a different time to at least one of the other optical signal modulators.
Alternatively, the optical signal modulators simultaneously chop their received signals into pulses.
Preferably, the combined waves are passed through a sampling pulse modulator to split the waves into a series of pulses before splitting into the wavelength dependent signal paths.
Preferably, the pulses from the sampling pulse modulator are compressed in time before splitting into wavelength dependent signal paths.
Preferably, the electrical signal is a microwave signal.
The present invention will now be described by way of example only, and not in any limitative sense, with reference to the accompanying drawings hi which
Figure 1 shows a first embodiment of a device according to the invention; Figure 2 shows a second embodiment of a device according to the invention;
Figure 3 shows a third embodiment of a device according to the invention; and
Figure 4 shows a fourth embodiment of a device according to the invention.
Shown in figure 1 is a first embodiment of a device 1 for digitising an electrical signal according to the invention. The device 1 comprises a plurality of continuous wave lasers 2 each producing a different wavelength. The outputs from the lasers are passed to the input ports 3 of an optical combiner 4 comprising an arrayed waveguide grating (AWG). The AWG combines the signals from the lasers 2 received at the input ports 3 at an output port 5.
The output from the AWG is passed to the input 6 of an optical modulator 7. As the optical signal passes through the optical modulator 7 to the output port 8, it is modulated by a received electrical (preferably microwave) signal 9. The optical modulator 7 of this embodiment is an interferometer 7. The signals passing down the arms of the interferometer 7 are altered by the incident microwave signal 9. When the two optical signals recombine at the output of the optical modulator 7 the resulting amplitude depends upon the amplitude of the incident microwave signal. The operation of such optical modulators 7 is known in the art and will not be discussed further.
The signal output from the optical modulator 7 is passed to an optical splitter 10 which splits the received signal into a plurality of wavelength dependent signal paths 11. The optical splitter 10 for this embodiment is an AWG.
Attached to each of the wavelength dependent signal paths 11 is a photodetector 12. The photodetectors 12 each output an analogue electrical signal dependent upon the amplitude of the optical signal received. This output is then converted by an electronic analogue to digital converter (not shown) to a digital output. Arranged in each wavelength dependent signal path 11 is an optical signal modulator 13. Each optical signal modulator 13 can be switched by a control circuit (not shown) between an on configuration whereby signals pass through the optical signal modulator 13 to the photodetector 12 and an off configuration whereby signals do not pass through the optical signal modulator 13.
In use the optical signal modulators 13 are rapidly switched between on and off configurations so chopping the signal received from the optical splitter 10 into pulses as shown. Each pulse corresponds to the amplitude of the modulated signal at a particular instant as it exits the optical modulator 7.
In this embodiment the control circuit is arranged such that the optical signal modulators 13 which receive signals at different wavelengths are turned on and off at slightly different times to each other as shown. In this way the modulated optical signal can be sampled at a high effective frequency. Sampled pulses which are adjacent in time are sent to different photodetectors 12 and so can be processed at a lower frequency.
Shown in figure 2 is a further embodiment of a device 1 according to the invention. The embodiment is similar to that of figure 1 except the wavelength dependent signal paths 11 include optical delay elements 14. Each wavelength dependent signal path 11 has an optical delay element 14 which introduces a different degree of delay. In this embodiment, each of the optical signal modulators 13 is turned on and off simultaneously. Due to the delays introduced in the wavelength dependent signal paths 11 the optical signal modulators 13 sample the signal as modulated by the optical modulator 7 at different times.
Shown in figure 3 is a further embodiment of a device 1 according to the invention. This embodiment is similar to that of figure 1 except it includes a sampling pulse modulator 15 between the output 8 of the optical modulator 7 and the optical splitter 10. The sampling pulse modulator 15 reduces the signal from the output of the optical modulator 7 to a series of pulses as shown. The optical signal modulators 13 are arranged to turn on and off such that each allows a signal pulse through. The timing for the opening and closing of the optical signal modulators 13 is arranged such that a first optical signal modulator 13 turns on and off to let the first of the series of pulses presented on its associated wavelength dependent signal path 11 through to the associated photodetector 12. The remaining pulses on the wavelength dependent line 11 are blocked.
The same pulses are presented on the adjacent wavelength dependent signal line 11 as shown. The opening and closing of the optical signal modulator 13 on this line 11 is timed to allow a different pulse through. This is repeated on all the wavelength dependent signal lines 11 such that each optical signal modulator 13 lets through one pulse, each optical signal modulator 13 letting through a different pulse.
The use of a sampling pulse modulator 15 reduces the requirement for the optical signal modulators 13 to be turned on and off rapidly. The optical signal modulators 13 need only to turn on and off sufficiently rapidly to be able to discriminate between one pulse and the next. In addition, the sampling pulse modulator 15 can be turned on and off more rapidly than optical signal modulators 13 so allowing shorter pulses to be generated. Short pulses provide a more accurate measure for the instantaneous measure of the modulated signal at a particular time. Longer pulses tend to average the signal over the length of the pulse.
A further embodiment of a device 1 according to the invention is shown in figure 4. This is similar to the embodiment of figure 3 except the wavelength dependent signal paths 11 include optical delay elements 14. Those are arranged such that by the time the pulses reach the optical signal modulators 13 different pulses on different wavelength dependent signal paths 11 are simultaneous. Accordingly, in this embodiment all of the optical signal modulators 13 open and close simultaneously.
In a further embodiment of the invention (not shown) the device 1 further comprises pulse compression means (for example a grating) for compressing the length for the pulses after they exit the sampling pulse modulator 15.
In an alternative embodiment of the invention (not shown) the optical splitters and combiners 4,10 comprise integrated optic on-chip gratings or echelle gratings. The above embodiments have been described with reference to incident microwave signals. In alternative embodiments the device may be adapted to digitise received signals in other regions of the electromagnetic spectrum.

Claims

1. A device for digitising an electrical signal comprising
(a) at least two continuous wave lasers each being adapted to produce light at a different wavelength;
(b) an optical combiner having a plurality of input ports each adapted to receive the output of a laser and an output port, the optical combiner being adapted to combine the optical signal received at the plurality of input ports at the output port;
(c) an optical modulator comprising an input port adapted to receive the output of the optical combiner, an output port and at least one optical path extending therebetween, the modulator being adapted to receive the electrical signal and to modulate the amplitude of the optical signal in the optical path in response to the electrical signal;
(d) an optical splitter for splitting the signal received from the output port of the optical modulator into a plurality of wavelength dependent signal paths;
(e) a plurality of analogue to digital converters each connected to at least one wavelength dependent signal path and being adapted to convert the received optical signal to a digital signal.
(f) each wavelength dependent signal path comprising an optical signal modulator between optical splitter and analogue to digital converter; and,
(g) a control circuit connected to the optical signal modulators adapted to switch the optical signal modulators between on and off states to allow a portion of the optical signal to pass through as a pulse.
2. A device as claimed in claim 1, wherein at least one of the wavelength dependent signal paths includes an optical delay element to delay the signal in the path relative to the signal in at least one other wavelength dependent signal path.
3. A device as claimed in either of claims 1 or 2, wherein the control circuit turns on at least two of the optical signal modulators at different times.
4. A device as claimed in any one of claims 1 to 3, wherein the control circuit turns on at least two of the optical signal modulators at the same time.
5. A device as claimed in any one of claims 1 to 4, comprising a sampling pulse modulator between the optical modulator and optical splitter adapted to split the signal received from the optical modulator into pulses.
6. A device as claimed in claim 5, further comprising compression means for compressing in time each of the pulses received from the sampling pulse modulator
7. A device as claimed in claim 6, wherein the compression means comprises a grating.
8. A device as claimed in any one of claims 1 to 7, wherein the optical combiner comprises an arrayed waveguide grating
9. A device as claimed in any one of claims 1 to 8, wherein the optical splitter comprises an arrayed waveguide grating
10. A device as claimed in any one of claims 1 to 9, wherein each wavelength dependent signal path comprises a photodetector adapted to receive the optical signal from the optical splitter and provide an electrical signal to the analogue to digital converter.
11. A device as claimed in any one of claims 1 to 10, wherein the electrical signal is a microwave signal.
12. A method of digitising an electrical signal comprising the steps of
(a) providing a plurality of continuous wave lasers, each providing a continuous optical wave at a different wavelength; (b) combining each of the continuous optical waves into a single optical path;
(c) passing the combined waves through an optical modulator where they are modulated by a received electrical signal;
(d) splitting the combined waves into a plurality of wavelength dependent signal paths;
(e) passing the signals in each of the wavelength dependent signal paths to optical signal modulators to chop the signals into signal pulses;
(f) passing the signal pulses to analogue to digital converters.
13. A method as claimed in claim 12, further comprising the step of introducing a delay into the signal in at least one wavelength dependent signal path relative to the signals in the other wavelength dependent signal paths prior to chopping by the optical signal modulators.
14. A method as claimed in either of claims 12 or 13, wherein at least one of the optical signal modulators chops its received signal into a pulse at a different time to at least one of the other optical signal modulators.
15. A method as claimed in either of claims 12 or 13, wherein the optical signal modulators simultaneously chop their received signals into pulses.
16. A method as claimed in any one of claims 12 to 15, wherein the combined waves are passed through a sampling pulse modulator to split the waves into a series of pulses before splitting into the wavelength dependent signal paths.
17. A method as claimed in claim 16, wherein the pulses from the sampling pulse modulator are compressed in time before splitting into wavelength dependent signal paths.
18. A methods as claimed in any one of claims 12 to 17, wherein the electrical signal is a microwave signal.
19. A device substantially as hereinbefore described.
20. A device substantially as hereinbefore described with reference to the drawings.
21. A method substantially as hereinbefore described.
22. A method substantially as hereinbefore described with reference to the drawings.
PCT/GB2008/002218 2007-06-27 2008-06-26 A method and device for digitising an electrical signal WO2009001100A1 (en)

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GB0712438.1A GB2450509B (en) 2007-06-27 2007-06-27 Method and device for digitising an electrical signal

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