JP2006333257A - Method and device for rejecting noise - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reject an AM modulation component caused by a Raman effect of an optical analog signal. <P>SOLUTION: The optical analog signal is made incident on an optical multiplexer 24 through a WDM (wavelength division multiplexing) optical coupler 20. A laser beam for reducing an AM modulation component from a laser diode (LD) 26 is made incident on the optical multiplexer 24. A photoelectric converter 30 converts output light of the multiplexer 24 into an electrical signal. A separator 32, electrical filters 34-1 to n and power meters 36-1 to n measure the power of a prescribed frequency component. Comparison circuits 38-1 to n output differences between measured results of the power meters 36-1 to n and thresholds Ref1 to Refn. Respective amplitude/phase/frequency controllers 42-1 to n sweep amplitude and phases of generators 44-1 to n of central frequencies f1 to fn so as to make an output difference value of a corresponding comparator 38-1 to n small. A multiplexer 46 multiplexes outputs of the generators 44-1 to n and applies the outputs to a driving circuit 48 of the LD 26. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a noise removal method and apparatus, and more specifically, a method and apparatus for removing AM modulation noise superimposed on an analog signal in an optical transmission system that transmits a digital signal and an analog signal by wavelength division multiplexing (WDM). About.

Optical fibers are being used not only for metro networks but also for access lines. On the other hand, it has been proposed to use the optical fiber not only for data communication but also for broadcasting. For example, as described in Patent Document 1, a WDM optical transmission system that transmits digital signals and analog signals at different wavelengths on the same optical fiber is known. The digital signal is data such as the Internet, and the analog signal is a broadcast signal such as a television signal.
JP 2004-166300 A

  When a digital signal light and an optical analog broadcast signal are transmitted by WDM in a metro core network or a PON (Passive Optical network) system of Gigabit Ethernet ("Ethernet" is a registered trademark), the optical analog signal is converted to digital by the Raman effect. The intensity is modulated by the signal light. The modulation component due to the Raman effect is superimposed on the optical analog signal as noise. This noise component interferes with a video carrier in an optical analog signal optical receiver, and appears as stripe noise on the screen. As a result, there is a great reception failure.

  An object of the present invention is to provide a noise removal method and apparatus for reducing AM modulation noise due to such a Raman effect.

  According to an embodiment of the present invention, a method for removing AM modulation noise from analog signal light is provided. In this noise removal method, the output light of the laser light source is combined with the analog signal light by an optical multiplexer. The output light of the optical multiplexer is converted into an electric signal. A component having one or a plurality of predetermined frequencies corresponding to the AM modulation noise is separated from the electrical signal. A laser with a drive signal including the plurality of predetermined frequencies having such amplitude and phase that the power of each of the separated components of one or a plurality of predetermined frequencies falls within a threshold value indicating a level at which the presence of noise is not sensed on the television receiver screen. Drive the light source.

  According to an embodiment of the present invention, an apparatus for removing AM modulation noise from analog signal light is provided. The noise removing device includes a laser light source, an optical multiplexer that combines the analog signal light with the output light of the laser light source, a photoelectric converter that converts the output light of the optical multiplexer into an electrical signal, and the photoelectric converter. A separation device that extracts a first predetermined frequency component from the output electric signal of the converter; a first power measurement device that measures the power of the first predetermined frequency component separated by the separation device; In order to determine whether or not the measured power level at the first predetermined frequency is equal to or lower than a threshold value indicating a level at which the presence of noise is not detected on the television receiver screen, the power level measured by the power meter and the power level measured by the power measuring instrument A first comparator that compares the two and outputs a difference value, a first oscillator that oscillates at the first predetermined frequency, and a drive that drives the laser light source in accordance with the output of the first oscillator And road, measurement result of the first power meter is characterized by comprising an amplitude-phase control device for controlling the amplitude and phase of the first oscillator to fit below the threshold value.

  According to an embodiment of the present invention, an apparatus for removing AM modulation noise from analog signal light is provided. The noise removing device includes a laser light source, an optical multiplexer that combines the analog signal light with the output light of the laser light source, and a photoelectric converter that converts the output light of the optical multiplexer (24) into an electrical signal. A separation device that separates a plurality of components of a predetermined frequency corresponding to the AM modulation noise included in the output electric signal of the photoelectric converter, and a power of each component of the predetermined frequency separated by the separation device And a feedback control device that drives the laser light source with a drive signal including the plurality of predetermined frequencies having amplitudes and phases that fall within a threshold value indicating a level at which noise is not detected on the screen.

  ADVANTAGE OF THE INVENTION According to this invention, AM modulation noise received by a Raman effect etc. while analog signal light, such as broadcast signal light, transmits an optical transmission line can be reduced. As a result, it is possible to reduce image quality degradation of the analog broadcast signal when the optical transmission path is shared for digital transmission of data communication and analog transmission of the broadcast signal.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  FIG. 1 shows a schematic block diagram of an embodiment of the present invention. The data transmission / reception device 10 transmits / receives data to / from the data transmission / reception device 14 via the optical fiber transmission line 12. The optical fiber transmission line is, for example, an optical transmission line of a PON system, the data transmission / reception device 10 corresponds to an optical terminal device OLT (Optical Line terminal) disposed in the center station, and the data transmission / reception device 14 is a user home. Corresponds to an optical network unit ONU (Optical Network Unit). The optical analog signal generator 16 generates an optical analog signal having a wavelength of 1.55 μm from the electrical RF signal. The optical analog signal is, for example, an optical signal that carries a television broadcast signal. This optical analog signal is input to the optical fiber transmission line 12 via the WDM optical coupler 18. The optical analog signal propagated through the optical fiber transmission line 12 is separated by the WDM optical coupler 20 at the user's home and input to the optical analog signal signal receiving device 22. As described above, the optical analog signal is AM-modulated by the Raman effect by the data signal light communicated between the data transmitting / receiving apparatuses 10 and 14 while being transmitted through the optical fiber transmission line 12.

  The configuration and operation of the optical analog signal receiver 22 will be described in detail. The optical analog signal from the WDM optical coupler 20 enters the optical multiplexer 24. Laser light having a wavelength of 1.55 μm from the laser diode 26 is incident on the optical multiplexer 24. As will be described later, the output laser light of the laser diode 26 is used to reduce the AM modulation component due to the Raman effect on the optical fiber transmission line 12. The photoelectric converter 30 converts the output light of the multiplexer 24 into an electrical signal. Although the output signal of the photoelectric converter 30 is an RF signal, it contains not a few AM modulation components due to the Raman effect.

  The separation device 52 divides the output signal of the photoelectric converter 30 into two, supplies one to the separation device 32, and supplies the other to the television 50. The separation device 32 separates the output electric signal of the separation device 52 into each channel of the broadcast wave. The electric filters 34-1 to 34-n extract carrier wave components from the broadcast signals of the respective channels separated by the separation device 32. The power meters 36-1 to 36-n measure the output power of the electric filters 34-1 to 34-n, and the comparison circuits 38-1 to 38-n measure the power meters 36-1 to 36-n. A result is compared with each threshold value Ref1-Refn, and the difference is output. The outputs of the comparison circuits 38-1 to 38-n are applied to the control circuit 40 and the amplitude / phase / frequency control devices 42-1 to 42-n.

  Each of the amplitude / phase / frequency control devices 42-1 to 42-n sets the oscillation frequency of the oscillators 44-1 to 44-n to the center frequencies f1 to fn of the electric filters 34-1 to 34-n. Each of the amplitude / phase / frequency control devices 42-1 to 42-n is also controlled by the oscillator 44- so that the difference value output from the corresponding comparator 38-1 to 38-n is reduced according to the control of the control circuit 40. The amplitude and phase of 1 to 44-n are swept and locked to the amplitude and phase at the time point instructed by the control device 40. A method of sweeping the amplitude and phase will be described later. The multiplexing device 46 multiplexes the outputs of the oscillators 44-1 to 44-n and applies them to the drive circuit 48 of the laser diode 26. The drive circuit 48 drives the laser diode 26 according to the output of the multiplexing device 46.

  The optical multiplexer 24 combines the optical analog signal including the AM modulation component from the WDM optical coupler 20 and the output laser light of the laser diode 26, and supplies the combined light to the photoelectric converter 30. The output laser light of the laser diode 26 is modulated with an amplitude and a phase so that noise components of the respective frequencies f1 to fn of the output electric signal of the photoelectric converter 30 are reduced. Therefore, the AM modulation component due to the Raman effect can be reduced at the optical stage by multiplexing in the optical multiplexer 24.

  That is, the laser diode 26, the optical multiplexer 24, the separation device 52, the separation device 32, the electric filters 34-1 to 34-n, the power meters 36-1 to 36-n, and the comparators 38-1 to 38-3 of the present embodiment. 38-n, the control device 40, each amplitude / phase / frequency control device 42-1 to 42-n, the oscillator 44-1 to 44-n, the multiplexer 46, and the drive circuit 48 are AM modulated by the Raman effect. An apparatus for reducing a component, that is, a Raman crosstalk component, that is, a noise removing apparatus is configured. Separation device 52, separation device 32, electrical filters 34-1 to 34-n, power meters 36-1 to 36-n, comparators 38-1 to 38-n, control device 40, amplitude / phase / frequency control devices 42-1 to 42-n, the oscillators 44-1 to 44-n, the multiplexing device 46, and the drive circuit 48 function as a device for feedback control of the laser diode 26, that is, a feedback control device.

  The function of the above feedback control device will be specifically described. An example of reducing the AM modulation component of the frequency f1 component will be described. When the AM modulation component of frequency f1 is superimposed on the optical analog signal, the electric filter 34-1 outputs an electric signal corresponding to the amplitude of the AM modulation component, and the power meter 36-1 outputs the electric signal. Measure power. The comparator 38-1 compares the power measured by the power meter 36-1 with the allowable threshold value Ref1 of the component of the frequency f1, and outputs the difference. At this time, the output of the power meter 36-1 is assumed to be larger than the allowable threshold value Ref1.

  When the control circuit 40 detects that the comparator 38-1 is larger than the allowable value, the control circuit 40 activates the amplitude / phase / frequency control device 42-1. When the amplitude / phase / frequency control device 42-1 is started, first, the oscillation frequency of the oscillator 44-1 is set to f1 in the amplitude / phase / frequency control device 42-1, and then the comparator 38-1 The amplitude and phase of the oscillator 44-1 are swept so that the output value becomes smaller, and the oscillator 44-1 is fixed at the amplitude and phase at which the output value of the comparator 38-1 becomes less than a predetermined value.

  For example, the control device 42-1 first detects the phase at which the output value of the comparator 38-1 is minimized with a certain amplitude value. This time, the amplitude is swept with the detected phase, and the amplitude at which the output value of the comparator 38-1 is minimized is determined. The phase is swept again with the determined amplitude, and the phase at which the output value of the comparator 38-1 is minimized is determined. In this way, the amplitude and phase are swept alternately so that the output value of the comparator 38-1 becomes smaller. When the output value of the comparator 38-1 falls below a certain value, the amplitude / phase / frequency control device 42-1 fixes the oscillator 44-1 at the current amplitude and phase according to an instruction from the control circuit 40.

  The comparators 38-2 to 39-n, the amplitude / phase / frequency control devices 42-2 to 42-n, and the oscillators 44-2 to 44-n execute the same processing for the frequencies f2 to fn. Thereby, the AM modulation components of the frequencies f1 to fn in the output of the photoelectric converter 30 are controlled to be less than a predetermined value.

  The frequencies f1 to fn extracted by the electrical filters 34-1 to 34-n are any one of, for example, the carrier frequency of the video signal and the frequency of the sideband, the carrier frequency of the audio signal, and the frequency within the broadcast signal band of 6 MHz. It is.

  Although the invention has been described with reference to specific illustrative embodiments, various modifications and alterations may be made to the above-described embodiments without departing from the scope of the invention as defined in the claims. This is obvious to an engineer in the field to which the present invention belongs, and such changes and modifications are also included in the technical scope of the present invention.

It is a schematic block diagram of one Example of this invention.

Explanation of symbols

10: data transmitter / receiver 12: optical fiber transmission line 14: data transmitter / receiver 16: optical analog signal generator 18: WDM optical coupler 20: WDM optical coupler 22: optical analog signal receiver 24: optical multiplexer 26: laser diode 30 : Photoelectric converter 32: Separating devices 34-1 to 34-n: Electric filters 36-1 to 36-n: Power meters 38-1 to 38-n: Comparison circuit 40: Control circuits 42-1 to 42-n: Amplitude / phase / frequency control devices 44-1 to 44-n: oscillator 46: multiplexing device 48: drive circuit 50: television 52: separation device

Claims (13)

A method of removing AM modulation noise from analog signal light,
(A) The output light of the laser light source is combined with the analog signal light by an optical multiplexer,
(B) converting the output light of the optical multiplexer into an electrical signal;
(C) separating one or more components of a predetermined frequency corresponding to the AM modulation noise from the electrical signal;
(D) Drive including the plurality of predetermined frequencies having such amplitude and phase that the power of each component of the one or more predetermined frequencies separated is within a threshold value indicating a level at which no presence of noise is detected on the television receiver screen. A method for removing noise, wherein the laser light source is driven by a signal. The step (D)
(E) measuring the power of each component of the one or more predetermined frequencies separated by the separation device;
(F) generating an amplitude and phase signal of the one or more predetermined frequencies such that each measured power falls below the threshold value;
(G) The noise removing method according to claim 1, comprising the steps of driving the laser light source with each generated signal. The step (D)
(E) measuring the power of each component of the one or more predetermined frequencies separated by the separation device;
(F) At each predetermined frequency, in order to determine whether the measured power level is equal to or lower than the threshold value, the power level of the threshold value is compared with the power level measured by the measuring instrument, and a difference value between the two is output.
(G) According to the difference value, generate a signal having the amplitude and phase of the one or more predetermined frequencies so that the difference value becomes small;
The noise removal method according to claim 1, comprising (H) each step of driving the laser light source with each generated signal.   The noise removal method according to claim 1, wherein the analog signal light is broadcast signal light.   The noise removal method according to claim 1, wherein the wavelength of the analog signal light is equal to the wavelength of the laser light source. An apparatus for removing AM modulation noise from analog signal light,
A laser light source (26);
An optical multiplexer (24) for multiplexing the output light of the laser light source with the analog signal light;
A photoelectric converter (30) for converting the output light of the optical multiplexer (24) into an electrical signal;
A separation device (32, 34-1) for extracting a component of a first predetermined frequency from the output electric signal of the photoelectric converter (30);
A first power measuring device (36-1) for measuring the power of the first predetermined frequency component separated by the separation device;
In order to determine whether the measured power level at the first predetermined frequency is equal to or lower than a threshold value indicating a level at which noise is not detected on the television receiver screen, the power level of the threshold value and the power meter (36-1) are determined. A first comparator (38-1) that compares the power level measured in step) and outputs a difference value;
A first oscillator (44-1) that oscillates at the first predetermined frequency;
A drive circuit (48) for driving the laser light source (26) in accordance with the output of the first oscillator (44-1);
Amplitude / phase control device (42-1) for controlling the amplitude and phase of the first oscillator so that the measurement result of the first power measuring instrument (36-1) falls below the threshold value.
The noise removal apparatus characterized by comprising. The separation device separates a component of the second predetermined frequency different from the first predetermined frequency;
The noise removal device further includes
A second power measuring device (36-2) for measuring the power of the second predetermined frequency component separated by the separation device;
In order to determine whether the measured power level is equal to or lower than the threshold at the second predetermined frequency, the power level measured by the power meter (36-2) is compared with the power level of the threshold. A second comparator (38-2) for outputting;
A second oscillator (44-2) that oscillates at the second predetermined frequency;
A multiplexer (46) that multiplexes the outputs of the first and second oscillators and applies them to the drive circuit (48);
A second amplitude / phase control device (42) for controlling the amplitude and phase of the second oscillator (44-2) so that the measurement result of the second power measuring device (36-2) falls below the threshold value. -2)
The noise removal device according to claim 6, further comprising:   The noise removing apparatus according to claim 6, wherein the analog signal light is broadcast signal light.   The noise removing apparatus according to claim 6, wherein the wavelength of the analog signal light is equal to the wavelength of the laser light source. An apparatus for removing AM modulation noise from analog signal light,
A laser light source (26);
An optical multiplexer (24) for multiplexing the output light of the laser light source with the analog signal light;
A photoelectric converter (30) for converting the output light of the optical multiplexer (24) into an electrical signal;
A separation device (32, 34-1 to 34-n) for separating a plurality of components of a predetermined frequency corresponding to the AM modulation noise, contained in the output electric signal of the photoelectric converter (30);
The laser with a drive signal including the plurality of predetermined frequencies having an amplitude and a phase such that the power of each component of the predetermined frequency separated by the separation device falls within a threshold value indicating a level at which the presence of noise is not sensed on the television receiving screen. Feedback control device for driving the light source (36-1 to 36-n, 38-1 to 38-n, 42-1 to 42-n, 44-1 to 44-n, 46, 48)
The noise removal apparatus characterized by comprising. The feedback control device
A plurality of oscillators (44-1 to 44-n) each oscillating at any one of the plurality of predetermined frequencies;
A multiplexer (46) for multiplexing the outputs of the plurality of oscillators;
A drive circuit (48) for driving the laser light source according to the output of the multiplexer (46);
A plurality of power measuring devices (36-1 to 36-n) for measuring power for each of the plurality of components of the predetermined frequency separated by the separation device;
According to the measurement results of the plurality of power measuring devices, a plurality of amplitude / phase control devices (42-1 to 42-1) that control the amplitude and phase of the corresponding oscillator among the plurality of oscillators so that the power falls below the threshold value. 42-n)
The noise removal device according to claim 10, comprising:   The noise removing apparatus according to claim 10, wherein the analog signal light is broadcast signal light.   The noise removing device according to claim 10, wherein the wavelength of the analog signal light is equal to the wavelength of the laser light source.

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