JP2017139573A - Optical transmission device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical transmission device capable of suppressing frequency variations of an electric modulation signal obtained by performing photoelectric conversion upon an optical modulation signal on which polarization multiplexing has been performed, to be transmitted.SOLUTION: The optical transmission device comprises: a light source which generates a continuous light; means for generating from the continuous light a first optical signal including a light tone signal in a first frequency and a light tone signal in a second frequency that is different from the first frequency; means for performing polarization demultiplexing upon the first optical signal to generate a second optical signal of a first polarization plane and a third optical signal of a second polarization plane that is orthogonal with the first polarization plane; means for modulating one light tone signal of the second optical signal with transmission data, thereby generating a fourth optical signal including an optical modulation signal and a light tone signal; means for modulating one light tone signal of the third optical signal with transmission data and shifting a frequency of the other light tone signal of the third optical signal, thereby generating a fifth optical signal including an optical modulation signal and a light tone signal; and means for multiplexing the fourth optical signal and the fifth optical signal.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an optical transmission apparatus for a radio over fiber (RoF) system.

  RoF technology is used in a transmission line including an optical transmission line and a wireless transmission line. Specifically, in the RoF system, an optical signal including an optical modulation signal is transmitted to the optical transmission line, and at the conversion point to the wireless transmission line, the optical signal is photoelectrically converted into a radio frequency band signal. Radio frequency band signals are transmitted wirelessly. Non-Patent Document 1 transmits two optical modulation signals that are polarization multiplexed (PDM) in an optical transmission line and optical tone signals for each polarization plane, and these optical signals including the optical modulation signal and the optical tone signal are transmitted. A configuration is disclosed in which two electrical modulation signals having two different frequencies, that is, two electrical modulation signals that are frequency-multiplexed (FDM), are transmitted to the wireless transmission path by photoelectric conversion. .

Y. Kawaguchi et al. , “Conceptual Study on Seamless Optical and Wireless Transmission using PDM-FDM Conversion,” Proc. , OECC, paper TH10A-2, July 2014.

  The optical transmitter of Non-Patent Document 1 uses a total of three light sources: one light source for polarization-modulated optical modulation signals and two light sources for generating two optical tone signals of different frequencies. . In the photoelectric conversion, an optical modulation signal having the same polarization plane and a beat signal of the optical tone signal, that is, an electric modulation signal having the frequency difference between the optical modulation signal and the optical tone signal having the same polarization plane as the frequency is obtained. However, since the frequency variation of each light source occurs independently, in the configuration of Non-Patent Document 1, the frequency of the electrical modulation signal obtained by photoelectric conversion also varies and the quality deteriorates.

  The present invention provides an optical transmitter capable of suppressing frequency fluctuations of an electrical modulation signal obtained by photoelectric conversion of a polarization multiplexed optical modulation signal to be transmitted.

  According to an aspect of the present invention, an optical transmission device includes a light source that generates continuous light, an optical tone signal having a first frequency from the continuous light, and an optical tone signal having a second frequency different from the first frequency. A first generation means for generating one optical signal; a third optical polarization that separates the first optical signal by polarization; a second optical signal having a first polarization plane; and a third polarization plane that is orthogonal to the first polarization plane Second generation means for generating an optical signal; third generation means for modulating one optical tone signal of the second optical signal with transmission data and generating a fourth optical signal including the optical modulation signal and the optical tone signal; The first optical tone signal of the third optical signal is modulated with transmission data, the other optical tone signal of the third optical signal is frequency-shifted, and the fifth optical signal including the optical modulation signal and the optical tone signal is obtained. A fourth generation means for generating, a combination for combining the fourth optical signal and the fifth optical signal; Characterized in that it comprises a means.

  According to the present invention, it is possible to suppress frequency fluctuations of an electrical modulation signal obtained by photoelectric conversion of a polarization multiplexed optical modulation signal to be transmitted.

1 is a configuration diagram of an optical transmission device according to an embodiment. FIG. The figure which shows the spectrum of the optical signal which the functional block in the optical transmitter by one Embodiment outputs. The figure which shows the spectrum of the optical signal which the optical transmitter by one Embodiment outputs. 1 is a configuration diagram of an optical transmission device according to an embodiment. FIG. The figure which shows the spectrum of the optical signal which the functional block in the optical transmitter by one Embodiment outputs. The figure which shows the electric modulation signal obtained by carrying out photoelectric conversion of the optical signal which the optical transmitter by one Embodiment outputs.

  Hereinafter, exemplary embodiments of the present invention will be described with reference to the drawings. In addition, the following embodiment is an illustration and does not limit this invention to the content of embodiment. In the following drawings, components that are not necessary for the description of the embodiments are omitted from the drawings.

<First Embodiment>
FIG. 1 is a configuration diagram of an optical transmission apparatus according to the present embodiment. The light source 1 generates a continuous light having a frequency f _0. The two-tone generator 2 amplitude-modulates the continuous light output from the light source 1 with a sine wave having a frequency f ₁ received from the oscillator 12, and generates an optical signal including an upper sideband and a lower sideband obtained by the amplitude modulation. . FIG. 2A shows the spectrum of the optical signal generated by the two-tone generator 2. As shown in FIG. 2 (A), the two-tone generator 2 suppresses the frequency f ₀ that is the carrier component, and 2 of the upper side band of the frequency f ₀ + f _{1 and} the lower side band of the frequency f ₀ -f _1. An optical signal including two optical tone signals is output.

  The polarization separation unit 3 separates the optical signal output from the two-tone generation unit 2 into an optical signal having a first polarization plane and an optical signal having a second polarization plane orthogonal to the first polarization plane. For example, the polarization separation unit 3 has an angle between the first polarization plane and the second polarization plane of 45 so that the amplitudes of the components of the first polarization plane optical signal and the second polarization plane optical signal are equal. The optical signal is polarization-separated with reference to the polarization plane (reference polarization plane) that becomes °. For this reason, the two-tone generator 2 is adjusted so as to output the optical signal of the reference polarization plane of the polarization separator 3.

The demultiplexing unit 4 wavelength-separates the optical signal of the first polarization plane output from the polarization demultiplexing unit 3, outputs an optical tone signal having a frequency f ₀ -f ₁ to the modulation unit 6, and has a frequency f ₀ + f ₁ . The optical tone signal is output to the multiplexing unit 9. The optical tone signal output to the modulation unit 6 and the optical tone signal output to the multiplexing unit 9 may be reversed. Similarly, the demultiplexing unit 5 wavelength-separates the optical signal of the second polarization plane output from the polarization demultiplexing unit 3, outputs the optical tone signal of frequency f ₀ -f ₁ to the modulation unit 7, and outputs the frequency f _0. The optical tone signal of + f ₁ is output to the frequency shift unit 8. The optical tone signal output to the modulation unit 7 and the optical tone signal output to the frequency shift unit 8 may be reversed. 2B is a spectrum of one optical tone signal output from the demultiplexing unit 4 and the demultiplexing unit 5, and FIG. 2C is the other spectrum output from the demultiplexing unit 4 and the demultiplexing unit 5. It is a spectrum of an optical tone signal. The polarization planes of the optical signals output from the demultiplexing unit 4 and the demultiplexing unit 5 are orthogonal to each other as described above.

The modulation unit 6 modulates the input optical signal with the transmission data, and outputs the optical modulation signal to the multiplexing unit 9. The multiplexing unit 9 receives the optical modulation signal and the optical tone signal having the frequency f ₀ + f _1. Combine and output. FIG. 2D shows the spectrum of the optical modulation signal output from the modulation unit 6, and FIG. 2E shows the spectrum of the optical signal output from the multiplexing unit 9.

The modulation unit 7 modulates the input optical signal with the transmission data, and outputs the optical modulation signal to the multiplexing unit 10. Frequency shifter 8, the sine wave of frequency f ₂ to be received from the oscillator 13, the frequency of the light tone signal from the demultiplexing unit 5 is shifted by f _2, if the light tone signal having a frequency f _{0 +} f 1 ₊ f ₂ Output to the wave unit 10. The frequency shift unit 8 can be configured by, for example, a Mahahendender interferometer. In the present embodiment, it is assumed to be shifted higher frequency by f _2, it may be shifted lower frequency by f _2. More specifically, the frequency of the optical tone signal output from the frequency shift unit 8 may not be within the band of the optical modulation signal output from the modulation unit 7. FIG. 2D shows the spectrum of the optical modulation signal output from the modulation unit 7, and FIG. 2F shows the spectrum of the optical signal output from the multiplexing unit 10.

The multiplexing unit 11 multiplexes and outputs the optical signals output from the multiplexing unit 9 and the multiplexing unit 10. 2E and the polarization plane of the optical signal output from the multiplexing section 9 and the polarization plane of the optical signal output from the multiplexing section 10 shown in FIG. 2F are orthogonal to each other. Therefore, the spectrum of the optical signal output from the multiplexing unit 11 is as shown in FIG. Specifically, the optical signal output from the multiplexing unit 11 includes two optical modulation signals having polarizations orthogonal to each other with the frequency f ₀ -f ₁ as the center frequency and the first polarization plane having the frequency f ₀ + f ₁ . And an optical tone signal of the second polarization plane having the frequency f ₀ + f ₁ + f ₂ . When this optical signal is photoelectrically converted, an electric modulation signal having a frequency difference between the optical modulation signal and the optical tone signal having the same polarization plane is obtained. That is, when the optical signal output from the multiplexing unit 11 is photoelectrically converted, two frequency-multiplexed electric modulation signals shown in FIG. 6 can be obtained. By selecting the frequency f ₁ and the frequency f _{2 so} that the frequencies 2f ₁ and 2f ₁ + f ₂ become the frequencies of the radio frequency band (RF band), at the conversion point from the optical signal to the radio signal in the RoF system, A simple configuration that performs only photoelectric conversion and amplification can be achieved. Incidentally, the difference between the center frequencies of the two electrical modulation signal shown in FIG. 6 is a f _2. Therefore, the frequency f ₂ is set to a value larger than half of the total bandwidth of the two electric modulation signals. That is, the frequency f ₂ is set to a value larger than half the sum of the bandwidth of the optical modulation signal output from the modulation unit 6 and the bandwidth of the optical modulation signal output from the modulation unit 7.

  In the present embodiment, since only one light source 1 is used, even if frequency fluctuation occurs in the continuous light output from the light source 1, the optical modulation signal and the optical tone signal included in the optical signal output from the multiplexing unit 11 are used. It does not affect the frequency difference and can prevent deterioration of the quality of the electrical modulation signal after photoelectric conversion.

Second Embodiment
In the first embodiment, the modulation units 6 and 7 modulate the optical tone signal with different transmission data, respectively. That is, in the first embodiment, different transmission data is transmitted with two optical modulation signals. In the present embodiment, the same transmission data is transmitted using two optical modulation signals because of frequency diversity in the wireless section.

FIG. 4 is a configuration diagram of the optical transmission apparatus of this embodiment. The light source 1 generates a continuous light having a frequency f _0. The two-tone generator 2 amplitude-modulates the continuous light output from the light source 1 with a sine wave having a frequency f ₁ received from the oscillator 12, and generates an optical signal including an upper sideband and a lower sideband obtained by the amplitude modulation. . FIG. 2A shows the spectrum of the optical signal generated by the two-tone generator 2. As shown in FIG. 2 (A), the two-tone generator 2 suppresses the frequency f ₀ that is the carrier component, and 2 of the upper side band of the frequency f ₀ + f _{1 and} the lower side band of the frequency f ₀ -f _1. Outputs an optical signal containing two optical tones.

The demultiplexing unit 14 wavelength-separates the optical signal output from the two-tone generation unit 2, outputs the optical tone signal of frequency f ₀ -f ₁ to the modulation unit 15, and polarizes the optical tone signal of frequency f ₀ + f ₁ Output to the separator 16. Note that the optical tone signal output to the modulation unit 15 and the optical tone signal output to the polarization separation unit 16 may be opposite to each other. The modulation unit 15 modulates the optical tone signal of the frequency f ₀ -f ₁ with the transmission data, and outputs the optical modulation signal to the multiplexing unit 19. FIG. 2D shows a spectrum of an optical modulation signal output from the modulation unit 15. The polarization separation unit 16 outputs the optical tone signal of the frequency f ₀ + f ₁ output from the demultiplexing unit 14, the optical tone signal of the first polarization plane, and the optical tone signal of the second polarization plane orthogonal to the first polarization plane. The optical tone signal of the first polarization plane is output to the multiplexing unit 18, and the optical tone signal of the second polarization plane is output to the frequency shift unit 17. For example, the angle between the first polarization plane and the second polarization plane is 45 ° so that the amplitude of the optical tone signal of the first polarization plane is equal to the amplitude of the optical tone signal of the second polarization plane. The optical signal is polarized and separated with reference to the polarization plane (reference polarization plane). For this reason, the demultiplexing unit 14 is adjusted so as to output the optical signal of the reference polarization plane of the polarization separation unit 16. In other words, the polarization plane of the optical tone signal of frequency f ₀ -f ₁ output from the demultiplexing unit 14 to the modulation unit 15 and the optical tone of frequency f ₀ + f ₁ output from the demultiplexing unit 14 to the polarization separation unit 16. The polarization plane of the signal is the same, and the angle between each of the first polarization plane and the second polarization plane is 45 °.

Frequency shifting unit 17, the sine wave of frequency _{f 2} to be received from the oscillator 13, the frequency of the light tone signal from the polarization splitter 16 is shifted by _{f 2,} a light tone signal having a frequency _f 0 _{+ f} 1 _{+ f 2} The signal is output to the multiplexing unit 18. In the present embodiment, it is assumed to be shifted higher frequency by f _2, it may be shifted lower frequency by f _2. More specifically, the frequency of the optical tone signal output from the frequency shift unit 13 may not be within the band of the optical modulation signal output from the modulation unit 15. The multiplexing unit 18 has a frequency from the polarization separation unit 16 of f ₀ + f ₁ , an optical tone signal of the first polarization plane, and a frequency from the frequency shift unit 17 of f ₀ + f ₁ + f ₂ . In addition, the optical tone signal of the second polarization plane is multiplexed and output to the multiplexing unit 19. FIG. 5 shows an optical signal output from the multiplexing unit 18.

  The multiplexing unit 19 combines the optical signal including the two optical tone signals output from the multiplexing unit 18 and the optical modulation signal output from the modulation unit 15 and outputs the combined signal. As already described, the polarization plane of the optical tone signal output from the demultiplexing section 14 to the modulation section 15 is inclined by 45 ° with respect to each of the first polarization plane and the second polarization plane. Therefore, the polarization plane of the optical modulation signal output from the modulation unit 15 is also inclined by 45 ° with respect to each of the first polarization plane and the second polarization plane. When the optical modulation signal output from the modulation unit 15 is divided into a first polarization plane component and a second polarization plane component, the spectrum of the optical signal output from the multiplexing unit 19 is the same as that in FIG. Therefore, two optical modulation signals frequency-multiplexed as shown in FIG. 6 can be obtained by photoelectrically converting the optical signal output from the multiplexing unit 19.

Therefore, similarly to the first embodiment, by selecting the frequency f ₁ and the frequency f ₂ so that the frequencies 2f ₁ and 2f ₁ + f ₂ become the frequencies of the radio frequency band (RF band), the light in the RoF system At a conversion point from a signal to a radio signal, a simple configuration that performs only photoelectric conversion and amplification can be employed. Also in this embodiment, since only one light source 1 is used, even if frequency fluctuation occurs in the continuous light output from the light source 1, the optical modulation signal and the light included in the optical signal output from the multiplexing unit 19 are used. The quality difference of the electric modulation signal after photoelectric conversion can be prevented without affecting the frequency difference of the tone signal.

  1: Light source, 2: Two-tone generator, 3: Polarization separator, 6, 7: Modulator, 8: Frequency shifter, 11: Multiplexer

Claims (6)

A light source that generates continuous light;
First generation means for generating a first optical signal including an optical tone signal of a first frequency and an optical tone signal of a second frequency different from the first frequency from the continuous light;
A second generating means for splitting the first optical signal to generate a second optical signal having a first polarization plane and a third optical signal having a second polarization plane orthogonal to the first polarization plane;
Third generation means for modulating one optical tone signal of the second optical signal with transmission data and generating a fourth optical signal including the optical modulation signal and the optical tone signal;
One optical tone signal of the third optical signal is modulated with transmission data, and the other optical tone signal of the third optical signal is frequency-shifted to generate a fifth optical signal including the optical modulation signal and the optical tone signal. Fourth generation means for
A multiplexing means for multiplexing the fourth optical signal and the fifth optical signal;
An optical transmission device comprising:   The first value, which is the difference between the frequency of the optical modulation signal and the optical tone signal included in the fifth optical signal, is the second difference between the frequency of the optical modulation signal and the optical tone signal included in the fourth optical signal. The optical transmission device according to claim 1, wherein the optical transmission device is different from the value of.   The difference between the first value and the second value is greater than half of the total bandwidth of the optical modulation signal and the fifth optical signal included in the fourth optical signal. An optical transmitter according to claim 1. A light source that generates continuous light;
First generation means for generating a first optical signal including an optical tone signal of a first frequency and an optical tone signal of a second frequency different from the first frequency from the continuous light;
Modulation means for modulating an optical tone signal of the first frequency with transmission data to generate an optical modulation signal;
A second generation means for performing polarization separation of the optical tone signal of the second frequency, generating an optical tone signal of a first polarization plane, and an optical tone signal of a second polarization plane orthogonal to the first polarization plane;
A third generation means for generating an optical tone signal having a third frequency different from the first frequency and the second frequency by frequency shifting the optical tone signal of the second polarization plane;
Multiplexing means for multiplexing the optical modulation signal, the optical tone signal of the second frequency on the first polarization plane, and the optical tone signal of the third frequency on the second polarization plane;
An optical transmission device comprising:   The optical transmission device according to claim 4, wherein a polarization plane of the optical modulation signal is a polarization plane different from the first polarization plane and the second polarization plane.   The angle difference between the polarization plane of the optical modulation signal and the first polarization plane is 45 °, and the angle difference between the polarization plane of the optical modulation signal and the second polarization plane is 45 °. The optical transmission device according to claim 5.

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