JP2005191918A - Optical transmitter - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical transmitter easily constituting a radio base station together with the optical transmitter itself in an optical/radio merged communication system at a low cost. <P>SOLUTION: By using electric amplitude modulated signals for which electric carrier signals having a frequency equal to the half value of the frequency of optional intermediate frequency signals generated in an electric oscillator 7 are amplitude-modulated in an electric modulator 8 by electric digital signals m (m=1, 2 or M or the like) taking M pieces of inputted values or electric frequency modulated signals for which they are frequency-modulated, by an optical modulator 6, carrier suppression double side band optical modulation is executed to output light from an optical multiplexer 5 which multiplexes the first and second optical signals of a single spectrum for which the difference of respective center frequencies generated in first and second single spectrum light sources 3 and 4 is equal to the frequency of radio signals. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an optical transmitter in an optical-radio fusion communication system using broadband signal light, and more particularly to an optical transmitter that transmits a desired radio signal to a radio base station as an optical signal.

  1, 2, and 3 show examples of an optical transmitter, a radio base station, and a wireless subscriber terminal in a conventional optical-wireless communication system, and FIG. 4 shows a conventional optical-wireless communication. An example of the spectrum of the electrical frequency and optical frequency in a system is shown.

  An optical signal (101g) is transmitted from the optical transmitter 101 to the radio base station 109 via an optical transmission line. Here, the output signal from the electric oscillator 105 is an electric carrier signal (101c) having a frequency equal to half the frequency of the radio signal, and the optical modulator 104 is used for the output light (101b) of the single spectrum light source 103. Then, optical phase modulation is performed based on the electrical modulation signal (101c) to obtain an output optical modulation signal (101d). On the other hand, using an electric oscillator 107 and an electric modulator 108 that generate an output signal (101e) of an arbitrary intermediate frequency band based on a digital signal (101a) that can take M values inputted to the input terminal 102. The multimode light source 106 is directly modulated by the generated modulation signal (101f) in the intermediate frequency band. At the same time, the output light modulation signal (101d) is input to the multimode light source 106 and injection locking is performed. An optical signal (101g) synchronized with two modes of the output light modulation signal of the multimode light source is obtained.

  In the radio base station 109, a difference frequency component (101h) is obtained by simultaneously square-detecting such an optical signal (101g) with one light receiving element 110, but this signal is not required using the bandpass filter 111. A signal (101i) obtained by removing a simple signal is amplified as necessary and transmitted as a radio wave from the antenna 112, so that an electric signal in the millimeter wave band is not directly transmitted and the millimeter wave is transmitted to the radio base station. It is possible to transmit a millimeter-wave band radio signal without preparing a band electric oscillator.

The radio wave (101i) transmitted from the wireless base station 109 is received by the antenna 114 in the wireless subscriber terminal 113. If the optical modulator 101 performs frequency modulation or phase modulation by the electric modulator 108, Since the signal radio wave (101i) is a double sideband signal including an unmodulated carrier wave signal, square detection is performed by the multiplier 115 using a non-linear element such as a mixer diode, and the output electric signal (101j) of the multiplier 115 is further detected. Is passed through the low-pass filter 116, and an intermediate frequency band electric modulation signal (101k) can be obtained without preparing a millimeter wave band electric oscillator. In addition, since the frequency instability of the optical signal (101g) is canceled at the time of square detection in the radio base station, the electrical modulation signal (101k) in the intermediate frequency band obtained in the radio subscriber terminal 113 is very The frequency stability is high (see Non-Patent Document 1).
Masahiro Kominato, Keizo Inagaki, Takashi Ohira, “Study of Millimeter-Wave Multiplexed Signal Source Using Two-Mode Injection-Locked FP Laser”, Proceedings of the 2001 IEICE General Conference, The Institute of Electronics, Information and Communication Engineers, March 2001 7th, B-5-259

  1, 2, 3, and 4, an optical modulator having a frequency band of a radio signal in order to stably synchronize two modes of a multimode light source in an optical transmitter. It is necessary to prepare. In addition, in the radio base station, when square detection is performed by the light receiving element, the difference frequency component of the combination of the received optical signals is output. Since this output signal includes a plurality of signals unnecessary for signal transmission, A band-pass filter in the frequency band of the radio signal for removing unnecessary signals is required. When transmitting a wideband signal, it is expected to use the millimeter wave band that can secure a wide signal band as the frequency of the radio signal, but the optical transmitter becomes expensive because it includes an optical modulator of the millimeter wave band. In addition, since the millimeter-wave bandpass filter is difficult to design, the configuration of the base station becomes complicated.

  An object of the present invention is to provide an optical transmitter capable of making the configuration of a radio base station inexpensive and simple together with the optical transmitter itself.

  In order to achieve the above object, according to the present invention, in an optical transmitter for transmitting a desired radio signal to a radio base station as an optical signal, the difference between the respective center frequencies is simply equal to the frequency of the radio signal. A first and second single spectrum light source that generates an optical signal of one spectrum; and an optical multiplexer that combines the first and second optical signals output from the first and second single spectrum light sources. An electric oscillator that generates an electric carrier signal having a frequency equal to half the frequency of an arbitrary intermediate frequency signal, and an electric digital signal that can take M values inputted to the electric carrier signal output from the electric oscillator an electrical modulator that performs amplitude modulation or frequency modulation at m (m = 1, 2,..., M) and outputs an electrical amplitude modulation signal or an electrical frequency modulation signal; and an optical signal output from the optical multiplexer. Contrast, the optical transmitter with a solving means, characterized in that it comprises at electrical amplitude modulation signal or electrical frequency modulated signal from an electrical modulator and an optical modulator for performing double sideband suppressed carrier light modulation.

  According to the first aspect of the present invention, four optical signals can be transmitted from the optical transmitter, and an amplitude modulation signal or a frequency modulation signal is output as an output of the light receiving element of the radio base station in a desired radio signal frequency band. In addition, it is possible to obtain three radio signals having different frequency intervals by the frequency of the intermediate frequency signal.

In the first aspect of the invention, the electric field E _opt of the optical signal transmitted at the time of amplitude modulation can be expressed by the following equation.

E _opt = a _m cos {2π (f _c2 + f _IF / 2) t + φ ₂ (t)}
+ A _m cos {2π (f _c2 −f _IF / 2) t + φ ₂ (t)}
+ A _m cos {2π (f _c1 + f _IF / 2) t + φ ₁ (t)}
+ A _m cos {2π (f _c1 -f _IF / 2) t + φ ₁ (t)} (1)
However, where, a _m is a field amplitude modulation component, m is (a M is 2 n (n is a natural number), M value signal is a signal of n bits) M value input digital signal (m of = 1, 2,..., M), f _c1 and f _c2 are the optical frequencies of the first and second optical signals, f _IF is the intermediate frequency, and φ ₁ (t) and φ ₂ (t) are the first and first optical signals. Let represent the phase noise of two single spectrum light sources.

The electric field E _{RF of the} radio signal obtained by square detection of this optical signal with the light receiving element can be expressed as follows.

^{_{E RF αa m 2 cos {2π}} (f RF + f IF) t + φ 2 (t) -φ 1 (t)}
_{^{+ 2a m 2 cos {2πf RF}} t + φ 2 (t) -φ 1 (t)}
^{_{+ A m 2 cos {2π (}} f RF -f IF) t + φ 2 (t) -φ 1 (t)} ... (2)
Here, f _RF represents a radio signal frequency, and f _RF = f _{c2 −c1} .

  At the wireless subscriber terminal, after receiving these high-frequency radio signal radio waves with an antenna, square detection is performed by a non-linear element such as a diode, and a low pass filter is used to prepare a local oscillator, that is, an electric oscillator in the radio signal frequency band. Without this, electrical amplitude modulation in the low frequency band can be obtained as the intermediate frequency signal.

The electric field E _IF of the intermediate frequency band signal can be expressed as:

^{_{E IF α4a m 4 cos (2πf}} IF t) ... (3)
From equation (3), the phase noise of the first and second single optical spectrum light sources is canceled during the square detection of electricity at the wireless subscriber terminal, and an intermediate frequency signal with high frequency stability can be obtained. I understand.

  According to a second aspect of the present invention, there is provided an optical transmitter for transmitting a desired radio signal as an optical signal to a radio base station. A second single-spectrum light source, an optical multiplexer that combines the first and second optical signals output from the first and second single-spectrum light sources, and half the frequency of any intermediate frequency signal An electric oscillator that generates an electric carrier signal having an equal frequency, and an electric digital signal m (m = 1, 2,..., M) that can take M values inputted to the electric carrier signal output from the electric oscillator. ) To output an electric phase modulation signal, and the phase of the output electric phase modulation signal with respect to the electric digital signal (m + 1) and the output electric power with respect to the electric digital signal m. An electrical phase modulator that performs phase modulation such that the phase difference from the phase of the phase modulation signal is π / M, and an optical phase modulation signal from the electrical modulator with respect to the optical signal output from the optical multiplexer An optical transmitter characterized by comprising an optical modulator for performing carrier wave suppression double-sideband optical modulation.

  According to the second aspect of the present invention, four optical signals can be transmitted from the optical transmitter, and the output of the light receiving element of the radio base station includes the phase modulation signal in the desired radio signal frequency band, and the frequency interval However, it is possible to obtain three-wave radio signals different from each other by the frequency of the intermediate frequency signal.

In the invention of claim 2, the electric field E _opt of the optical signal to be transmitted can be expressed by the following equation.

E _opt = A cos {2π (f _c2 + f _IF / 2) t + φ _m + φ ₂ (t)}
+ A cos {2π (f _c2 −f _IF / 2) t−φ _m + φ ₂ (t)}
+ A cos {2π (f _c1 + f _IF / 2) t + φ _m + φ ₁ (t)}
+ A cos {2π (f _c1 −f _IF / 2) t−φ _m + φ ₁ (t)} (4)
Where A is the electric field amplitude, f _c1 and f _c2 are the optical frequencies of the first and second optical signals, f _IF is the intermediate frequency, and m is the M value (M is the nth power of 2 (n is a natural number)) , M value signal is an n-bit signal), input digital signals (m = 1, 2,..., M), φ ₁ (t), φ ₂ (t) are first and second single signals. It represents the phase noise of the spectrum light source, and φ _m satisfies φ = φ _{m + 1} −φ _m = π / M.

The electric field E _{RF of the} radio signal obtained by square detection of this optical signal with the light receiving element can be expressed as follows.

E _RF ∝A ² cos {2π (f _RF + f _IF ) t + 2φ _m + φ ₂ (t) −φ ₁ (t)}
+ 2A ² cos {2πf _RF t + φ ₂ (t) −φ ₁ (t)}
+ A ² cos {2π (f _RF −f _IF ) t−2φ _m + φ ₂ (t) −φ ₁ (t)} (5)
Here, f _RF represents a radio signal frequency, and f _RF = f _c2 −f _c1 .

At the wireless subscriber terminal, after receiving these high-frequency radio signal radio waves with an antenna, square detection is performed by a non-linear element such as a diode and a low-pass filter is prepared, thereby preparing a local oscillator, that is, an electric oscillator in the radio signal frequency band. Without being performed, the electrical phase in the low frequency band where the phase difference φ ′ (= 2φ _{m + 1} −2φ _m ) with respect to the M-value signal of the electrical digital signal input to the input terminal is 2π / M as the intermediate frequency signal. A signal can be obtained.

The electric field E _IF of the intermediate frequency band signal can be expressed as:

E _IF ∝4A ⁴ cos (2πf _IF t + 2φ _m ) (6)
From the equation (6), the phase noise of the first and second single optical spectrum light sources is canceled during the square detection of electricity at the wireless subscriber terminal, and an intermediate frequency signal with high frequency stability can be obtained. I understand.

  According to a third aspect of the present invention, there is provided an optical transmitter for transmitting a desired radio signal as an optical signal to a radio base station. A second single-spectrum light source, an optical multiplexer for combining the first and second optical signals output from the first and second single-spectrum light sources, and a frequency equal to the frequency of any intermediate frequency signal And an electric digital signal m (m = 1, 2,..., M) that can take M values with respect to the electric carrier signal output from the electric oscillator. An electric modulator that performs amplitude modulation, frequency modulation, or phase modulation and outputs an electric amplitude modulation signal, electric frequency modulation signal, or electric phase modulation signal, and an optical signal output from the optical multiplexer An optical transmitter comprising: an optical single sideband modulator that performs single sideband optical modulation with an electric amplitude modulation signal, electric frequency modulation signal, or electric phase modulation signal from an electric modulator Is the solution.

  According to the third aspect of the present invention, four optical signals can be transmitted from the optical transmitter, and the output of the light receiving element of the wireless base station is an amplitude modulated signal or a frequency modulated signal in the desired wireless signal frequency band. It is possible to obtain three-wave radio signals including the phase modulation signal and having different frequency intervals by the frequency of the intermediate frequency signal.

In the invention of claim 3, the electric field E _opt of the optical signal transmitted when _performing phase modulation by the electric modulator and single sideband optical modulation in which the upper sideband remains by the optical single sideband modulator is given by Can be expressed as:

E _opt = A cos {2π (f _c2 + f _IF ) t + φ _m + φ ₂ (t)}
+ Acos {2π (f _c2 ) t + φ ₂ (t)}
+ A cos {2π (f _c1 + f _IF ) t + φ _m + φ ₁ (t)}
+ Acos {2π (f _c1 ) t + φ ₁ (t)} (7)
Where A is the electric field amplitude, f _c1 and f _c2 are the optical frequencies of the first and second optical signals, f _IF is the intermediate frequency, and m is the M value (M is the nth power of 2 (n is a natural number)) , M value signal is an n-bit signal), input digital signals (m = 1, 2,..., M), φ ₁ (t), φ ₂ (t) are first and second single signals. It represents the phase noise of the spectrum light source, and φ _m satisfies φ = φ _{m + 1} −φ _m = 2π / M.

The electric field E _{RF of the} radio signal obtained by square detection of this optical signal with the light receiving element can be expressed as follows.

E _RF ∝A ² cos {2π (f _RF + f _IF ) t + φ _m + φ ₂ (t) −φ ₁ (t)}
+ 2A ² cos {2πf _RF t + φ ₂ (t) −φ ₁ (t)}
+ A ² cos {2π (f _RF −f _IF ) t−φ _m + φ ₂ (t) −φ ₁ (t)} (8)
Here, f _RF represents a radio signal frequency, and f _RF = f _c2 −f _c1 .

  At the wireless subscriber terminal, after receiving these high-frequency radio signal radio waves with an antenna, square detection is performed by a non-linear element such as a diode, and a low pass filter is used to prepare a local oscillator, that is, an electric oscillator in the radio signal frequency band. Without doing so, an electrical phase signal in a low frequency band can be obtained as the intermediate frequency signal.

The electric field E _IF of the intermediate frequency band signal can be expressed as:

E _IF ∝4A ⁴ cos (2πf _IF t + φ _m ) (9)
From the equation (9), the phase noise of the first and second single optical spectrum light sources is canceled during the square detection of electricity at the wireless subscriber terminal, and an intermediate frequency signal with high frequency stability can be obtained. I understand.

  As described above, the optical transmitter of the present invention can be used in an optical transmitter of a broadband optical-radio fusion communication system that transmits an optical signal to a radio base station without preparing an optical modulator in the frequency band of the radio signal. In addition, it is possible to obtain an intermediate frequency modulation signal with high frequency stability without preparing a filter in the frequency band of the radio signal in the radio base station. Thereby, it becomes possible to make a wireless base station into an inexpensive and simple hardware configuration together with an optical transmitter.

<Embodiment 1>
The first embodiment of the present invention will be described with reference to the block diagrams of FIGS. 5, 6, and 7, and the spectrum diagrams of the electrical frequency and optical frequency in FIG.

  FIG. 5 is a block diagram showing the configuration of the optical transmitter 1 according to the first embodiment of the present invention, in which 2 is an input terminal for inputting an electric digital signal (1a) to be transmitted, 3 and 4 are first and The second single spectrum light source 5 is an optical multiplexer that combines the first and second output optical signals (1b, 1c) from the first single spectrum light source 3 and the second single spectrum light source 4. , 6 is the output light (1f) of the optical multiplexer 5 by the electric modulation signal (1f) obtained by amplitude-modulating or frequency-modulating the output signal (1e) from the electric oscillator 7 by the electric modulator 8 based on the input electric digital signal (1a). 1d) is an optical modulator that performs optical modulation on both sides of a carrier wave.

In this optical transmitter 1, the optical frequency (f _c1 ) of the output optical signal (1 b) from the first single spectrum light source 3 and the optical frequency of the output optical signal (1 c) from the second single spectrum light source 4. the difference between _{(f c2) (f c2 -f} c1) is set to be equal to the radio signal frequency such as a millimeter wave band (f _RF), the output signal from the electric generator 7 (1e) of the intermediate frequency signal frequency made to be an electrical carrier wave signal having half the frequency (f _IF / 2) of (f _IF). Further, the occupied frequency band (B) of the output electric modulation signal (1f) of the electric modulator 8 is made smaller than the frequency (f _IF ) of the intermediate frequency signal.

  The optical signal (1g) transmitted from the optical transmitter 1 as described above is received by the radio base station 9 shown in FIG.

  The radio base station 9 includes a light receiving element 10 that squarely detects an optical signal (1g) and converts it into an electric signal, and an antenna that transmits a millimeter wave band radio signal that is an output electric signal (1h) of the light receiving element 10 as a radio wave. 11.

In the optical transmitter 1, the optical frequency (f _c1 ) of the output optical signal (1b) from the first single spectrum light source 3 and the optical frequency (f 1) of the output optical signal (1c) from the second single spectrum light source 4 the difference between _{f c2) (f c2 -f c1} ) is set to be equal to the radio signal frequency such as a millimeter wave band (f _RF), further, the output signal from the electrical oscillator 8 (1e) of the intermediate frequency signals by such that the electric carrier signal having a frequency half the frequency of _{(f IF) (f IF /} 2), the radio base station 9, the frequency of the intermediate frequency signal frequency intervals, respectively by (f _IF) different Three millimeter-wave band radio signals (1h: f _RF + f _IF , f _RF , f _RF −f _IF ) can be obtained.

  FIG. 7 is a block diagram showing the configuration of the wireless subscriber terminal 12 according to the first embodiment of this invention. The millimeter-wave band radio signal (1h) transmitted from the radio base station 9 is received by the antenna 13 and then square-detected by a multiplier 14 using a non-linear element such as a mixer diode. By passing the signal (1i) through the low-pass filter 15, an intermediate frequency band electric modulation signal (1j) having high frequency stability can be obtained without preparing a millimeter wave band electric oscillator.

<Embodiment 2>
The second embodiment of the present invention will be described with reference to the block diagrams of FIGS. 9, 10, and 11 and the spectrum diagrams of the electrical frequency and the optical frequency in FIG.

  FIG. 9 is a block diagram showing the configuration of the optical transmitter 18 according to the second embodiment of the present invention. In FIG. 9, 19 is an input terminal for inputting an electric digital signal (2a) to be transmitted, 20 and 21 are first and second input terminals. An optical multiplexer 22, which combines the first and second output optical signals (2 b, 2 c) from the first single spectrum light source 20 and the second single spectrum light source 21. , 23 indicates the output light (2d) of the optical multiplexer 5 by the electric phase modulation signal (2f) obtained by phase-modulating the output signal (2e) from the electric oscillator 24 by the electric phase modulator 25 based on the input electric digital signal (2a). ) Is an optical modulator that performs optical modulation on both sides of the carrier wave.

In this optical transmitter 18, the optical frequency (f _c1 ) of the output optical signal (2 b) from the first single spectrum light source 20 and the optical frequency of the output optical signal (2 c) from the second single spectrum light source 21. the difference between _{(f c2) (f c2 -f} c1) is set to be equal to the radio signal frequency such as a millimeter wave band (f _RF), the output signal from the electric oscillator 24 (2e) of the intermediate frequency signal frequency made to be an electrical carrier wave signal having half the frequency (f _IF / 2) of (f _IF). Further, in the electrical phase modulator 25, an output electrical phase modulation signal for the electrical digital signal (m + 1) with respect to the electrical digital signal m (m = 1, 2,..., M) that can take M values. Phase modulation is performed so that the phase difference between the phase of (2f) and the phase of the output electrical phase modulation signal (2f) with respect to the electrical digital signal m is π / M, and the output electrical phase of the electrical phase modulator 25 The occupied frequency band (B) of the modulation signal (2f) is made smaller than the frequency (f _IF ) of the intermediate frequency signal.

  The optical signal (2g) transmitted from the optical transmitter 18 as described above is received by the radio base station 26 shown in FIG.

  The radio base station 26 squarely detects the optical signal (2g) and converts it into an electric signal, and an antenna that transmits a millimeter-wave band radio signal that is an output electric signal (2h) of the light receiving element 27 as a radio wave. 28.

In the optical transmitter 18, the optical frequency (f _c1 ) of the output optical signal (2 b) from the first single spectrum light source 20 and the optical frequency (2 _c ) of the output optical signal (2 c) from the second single spectrum light source 21. the difference between _{f c2) (f c2 -f c1} ) is set to be equal to the radio signal frequency such as a millimeter wave band (f _RF), further, the output signal from the electric oscillator 24 (2e) of the intermediate frequency signals by such that the electric carrier signal having a frequency half the frequency of _{(f IF) (f IF /} 2), the radio base station 26, the frequency of the intermediate frequency signal frequency intervals, respectively by (f _IF) different Three millimeter-wave band radio signals (2h: f _RF + f _IF , f _RF , f _RF −f _IF ) can be obtained.

  FIG. 11 is a block diagram showing a configuration of the wireless subscriber terminal 29 according to the second embodiment of this invention. The millimeter-wave band radio signal (2h) transmitted from the radio base station 26 is received by the antenna 30 and then square-detected by a multiplier 31 using a non-linear element such as a mixer diode. By passing the signal (2i) through the low-pass filter 32, it is possible to obtain an electric modulation signal (2j) in the intermediate frequency band of frequency stability without preparing a millimeter wave band electric oscillator.

  Further, in the present invention, in the optical transmitter, the phase difference φ with respect to the M-value signal of the input electrical digital signal is modulated to be π / M. Therefore, as an intermediate frequency band signal in the wireless subscriber terminal 29, It is possible to obtain a modulation signal (2j) in which the phase difference φ ′ of the input electric digital signal with respect to the M value signal is 2π / M, and the SN characteristic of detection is optimal.

<Embodiment 3>
The third embodiment of the present invention will be described with reference to the block diagrams of FIGS. 13, 14, and 15 and the spectrum diagrams of the electrical frequency and the optical frequency in FIG.

  FIG. 13 is a block diagram showing a configuration of an optical transmitter 35 according to the third embodiment of the present invention. 36 is an input terminal for inputting an electric digital signal (3a) to be transmitted, 37 and 38 are first and A second single spectrum light source 39 is an optical multiplexer for combining the first and second output optical signals (3b, 3c) from the first single spectrum light source 37 and the second single spectrum light source 38. , 40 is an output of the optical combiner 39 by an electric modulation signal (3f) obtained by amplitude-modulating, frequency-modulating or phase-modulating the output signal (3e) from the electric oscillator 41 by the electric modulator 42 based on the input electric digital signal (3a). This is an optical single sideband modulator that modulates output light (3d) with single sideband light.

In this optical transmitter 35, the optical frequency (f _c1 ) of the output optical signal (3 b) from the first single spectrum light source 37 and the optical frequency of the output optical signal (3 _c ) from the second single spectrum light source 38. the difference between _{(f c2) (f c2 -f} c1) is set to be equal to the radio signal frequency such as a millimeter wave band (f _RF), the output signal from the electric oscillator 41 (3e) of the intermediate frequency signal frequency The electric carrier wave signal has (f _IF ). Further, the occupied frequency band (B) of the output electric modulation signal (3f) of the electric modulator 42 is set to be smaller than twice the frequency (f _IF ) of the intermediate frequency signal.

  The optical signal (3g) transmitted from the optical transmitter 35 as described above is received by the radio base station 43 shown in FIG.

  The radio base station 43 squarely detects the optical signal (3g) and converts it into an electric signal, and an antenna that transmits a millimeter-wave band radio signal as an electric signal (3h) output from the light receiving element 44 as a radio wave. 45.

In the optical transmitter 35, the optical frequency (f _c1 ) of the output optical signal (3b) from the first single-spectrum light source 37 and the optical frequency (3c) of the output optical signal (3c) from the second single-spectrum light source 38 the difference between _{f c2) (f c2 -f c1} ) is set to be equal to the radio signal frequency such as a millimeter wave band (f _RF), further, the output signal from the electric oscillator 41 (3e) of the intermediate frequency signals By making the electric carrier wave signal having the frequency (f _IF ), the radio base station 43 has three millimeter-wave band radio signals (3h) whose frequency intervals differ from each other by the frequency of the intermediate frequency signal (f _IF ). : F _RF + f _IF , f _RF , f _RF −f _IF ).

  FIG. 15 is a block diagram showing the configuration of the wireless subscriber terminal 46 according to the third embodiment of this invention. The millimeter-wave band radio signal (3h) transmitted from the radio base station 43 is received by the antenna 47, and then square-detected by a multiplier 48 using a non-linear element such as a mixer diode. By passing the signal (3i) through the low-pass filter 49, it is possible to obtain an intermediate frequency band electric modulation signal (3j) with high frequency stability without preparing a millimeter wave band electric oscillator.

Block configuration diagram showing an example of a conventional optical transmitter Block configuration diagram showing an example of a conventional radio base station Block configuration diagram showing an example of a conventional wireless subscriber terminal The figure which shows an example of the signal spectrum in the conventional optical-wireless fusion communication system The block block diagram which shows the optical transmitter which concerns on the 1st Embodiment of this invention The block block diagram which shows the radio base station which concerns on the 1st Embodiment of this invention The block block diagram which shows the radio | wireless subscriber terminal which concerns on the 1st Embodiment of this invention The figure which shows the signal spectrum in the 1st Embodiment of this invention The block block diagram which shows the optical transmitter which concerns on the 2nd Embodiment of this invention The block block diagram which shows the radio base station which concerns on the 2nd Embodiment of this invention The block block diagram which shows the wireless subscriber terminal which concerns on the 2nd Embodiment of this invention The figure which shows the signal spectrum in the 2nd Embodiment of this invention The block block diagram which shows the optical transmitter which concerns on the 3rd Embodiment of this invention The block block diagram which shows the radio base station which concerns on the 3rd Embodiment of this invention The block block diagram which shows the wireless subscriber terminal which concerns on the 3rd Embodiment of this invention The figure which shows the signal spectrum in the 3rd Embodiment of this invention

Explanation of symbols

  1, 18, 35: Optical transmitter, 2, 19, 36: Input terminal, 3, 4, 20, 21, 37, 38: Single spectrum light source, 5, 22, 39: Optical multiplexer, 6, 23,. Optical modulator, 40 ... optical single sideband modulator, 7, 24, 41 ... electric oscillator, 8, 42: electric modulator, 25 ... electric phase modulator, 9, 26, 43: radio base station, 10, 27, 44: light receiving element, 11, 13, 28, 30, 45, 47 ... antenna, 12, 29, 46: wireless subscriber terminal, 14, 31, 48 ... multiplier, 15, 32, 49: low-pass filter, 16, 33, 50: detector, 17, 34, 51... Output terminal.

Claims (3)

In an optical transmitter that transmits a desired radio signal as an optical signal to a radio base station,
First and second single-spectrum light sources that generate single-spectrum optical signals each having a difference in center frequency equal to the frequency of the wireless signal;
An optical multiplexer that combines the first and second optical signals output from the first and second single spectrum light sources;
An electrical oscillator that generates an electrical carrier signal having a frequency equal to half the frequency of any intermediate frequency signal;
The electric carrier wave signal outputted from the electric oscillator is subjected to amplitude modulation or frequency modulation by an electric digital signal m (m = 1, 2,..., M) that can take M values, and electric amplitude modulation is performed. An electrical modulator for outputting a signal or an electrical frequency modulation signal;
An optical modulator for performing carrier-suppressed double-sideband optical modulation on an optical signal output from the optical multiplexer with an electric amplitude modulation signal or an electric frequency modulation signal from the electric modulator. Optical transmitter. In an optical transmitter that transmits a desired radio signal as an optical signal to a radio base station,
First and second single-spectrum light sources that generate single-spectrum optical signals each having a difference in center frequency equal to the frequency of the wireless signal;
An optical multiplexer that combines the first and second optical signals output from the first and second single spectrum light sources;
An electrical oscillator that generates an electrical carrier signal having a frequency equal to half the frequency of any intermediate frequency signal;
The electric carrier wave signal output from the electric oscillator is subjected to phase modulation by an electric digital signal m (m = 1, 2,..., M) that can take M values, and an electric phase modulation signal is output. And a phase difference between the phase of the output electrical phase modulation signal with respect to the electrical digital signal (m + 1) and the phase of the output electrical phase modulation signal with respect to the electrical digital signal m is π / M. An electrical phase modulator for modulation;
An optical transmitter comprising: an optical modulator that subjects the optical signal output from the optical multiplexer to carrier-suppressed double-sideband optical modulation with an electrical phase modulation signal from the electrical modulator. In an optical transmitter that transmits a desired radio signal as an optical signal to a radio base station,
First and second single-spectrum light sources that generate single-spectrum optical signals each having a difference in center frequency equal to the frequency of the wireless signal;
An optical multiplexer that combines the first and second optical signals output from the first and second single spectrum light sources;
An electrical oscillator that generates an electrical carrier signal having a frequency equal to the frequency of any intermediate frequency signal;
The electric carrier wave signal output from the electric oscillator is subjected to amplitude modulation, frequency modulation, or phase modulation by an electric digital signal m (m = 1, 2,..., M) that can take M values. An electrical modulator that outputs an electrical amplitude modulation signal or electrical frequency modulation signal or electrical phase modulation signal;
An optical single sideband modulator that performs single sideband optical modulation on an optical signal output from the optical multiplexer with an electric amplitude modulation signal, electric frequency modulation signal, or electric phase modulation signal from an electric modulator; An optical transmitter characterized by comprising:

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