JP2013239841A - High frequency oscillator and method of changing oscillation frequency of high frequency oscillator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a high frequency oscillator that implements a variable oscillation frequency without using a delayer nor a variable bandpass filter.SOLUTION: The high frequency oscillator includes an optical transmission system and an electrical transmission system, inputs a signal from the optical transmission system into the optical transmission system again as a feedback signal via the electrical transmission system to configure a feedback circuit, and starts to oscillate with a high frequency signal. The electrical transmission system includes: signal output means (9) for outputting a high frequency signal; first branch means (8) for bifurcating the high frequency signal; first signal mixing means (5) for mixing a high frequency signal converted from an optical signal to an electrical signal with the signal branching from the first branch means; and second signal mixing means (6) for mixing a high frequency signal from the first signal mixing means with the signal branching from the first branch means to generate a high frequency signal including a signal component of the feedback signal. The signal output means (9) changes an output frequency to change the oscillation frequency.

Description

  The present invention relates to a high-frequency oscillator that can oscillate high-frequency signals such as millimeter waves and microwaves, and a method for varying the oscillation frequency of a high-frequency oscillator.

  As a conventional high-frequency oscillator, for example, there is a photoelectric oscillator. FIG. 20 is a configuration diagram showing a conventional high-frequency oscillator. The conventional high-frequency oscillator shown in FIG. 20 includes a laser light source 301, an optical modulator 302, an optical fiber 303, an O / E converter 304, a bandpass filter 305, a delay device 306, and a coupler 307. The intensity of the laser light from the laser light source 301 is modulated by the optical modulator 302. The intensity-modulated laser light is converted into an electric signal by the O / E converter 304 via the optical fiber 303.

  This electric signal is input to the bandpass filter 305, and only the signal component near the center frequency of the bandpass filter 305 passes through the bandpass filter 305 and is output. The electrical signal output from the bandpass filter 305 is branched into two by the coupler 307 via the delay unit 306, one is output to the outside as a high frequency signal, and the other is input again to the optical modulator 302 to be laser light. Is used for intensity modulation, and a feedback circuit is configured.

  In this feedback circuit, by setting the feedback gain so as to be larger than the loss of the entire circuit, the high frequency oscillator starts oscillating at a predetermined frequency set by the band pass filter 305. Further, by giving a delay by the delay unit 306, the oscillation frequency can be varied (see, for example, Patent Document 1).

JP-A-2005-351951

  Since the conventional high-frequency oscillator is configured as described above, the oscillation frequency can be varied. However, there is a problem that the frequency variable amount of such a conventional high-frequency oscillator is limited to the variable amount of the provided delay device 306.

  For example, a microwave phase shifter can be considered as an application example of the delay device 306. However, the amount of phase shift of commercially available microwave phase shifters is often about 2π, and in order to obtain a phase shift amount larger than that, a plurality of microwave phase shifters are required. The disadvantage is that it leads to high costs.

  Another problem is that the frequency variable amount of such a conventional high-frequency oscillator is limited to the band of the provided bandpass filter 305. With respect to this point, for example, the frequency variable amount can be increased by using a bandpass filter that can change the passband. However, this band-pass filter is required to have a function of suppressing spurious generated at a frequency interval that is inversely proportional to the fiber length. For this purpose, it is necessary to have a narrow band.

  Therefore, although a bandpass filter that achieves both narrow band and variable passband is expected, there is a problem that the performance is degraded as compared with a filter that pursues only one of the performances. Moreover, the fault of being connected with high cost arises.

  The present invention has been made to solve the above-described problems and disadvantages, and provides a high-frequency oscillator capable of varying the oscillation frequency without using a delay device or a variable bandpass filter, and a method for varying the oscillation frequency of the high-frequency oscillator. With the goal.

  A high-frequency oscillator according to the present invention includes an optical transmission system that transmits an optical signal and an electrical transmission system that transmits an electrical signal. After a signal from the optical transmission system passes through the electrical transmission system, the optical transmission system is again connected to the optical transmission system. A feedback circuit is configured by being input as a feedback signal, and is a high-frequency oscillator that starts oscillating with a first electric signal that is a high-frequency signal and outputs a first electric signal, and an optical transmission system generates laser light Light generating means for modulating the laser light according to a high frequency signal from the electric transmission system, and outputting the modulated laser light as modulated laser light. The electrical transmission system includes a signal output means for outputting a second electrical signal, which is a high-frequency signal, and a high-frequency signal from the signal output means in two. First branching means and first light First signal mixing means for mixing the high-frequency signal converted by the gas conversion means and one of the second electric signals branched by the first branching means; the high-frequency signal from the first signal mixing means and the first branching means The second signal mixing means for generating a high frequency signal including the signal component of the feedback signal by mixing the other one of the second electric signals branched in step 1 and the first electric signal are branched into two, Second signal output means for outputting to the outside, and the signal output means changes the frequency of the first electric signal by changing the frequency of the second electric signal.

  Also, the oscillation frequency variable method of the high frequency oscillator according to the present invention includes an optical transmission system that transmits an optical signal and an electrical transmission system that transmits an electrical signal, and a signal from the optical transmission system passes through the electrical transmission system. After that, the feedback circuit is configured by inputting the signal again as a feedback signal into the optical transmission system, and starts oscillating with the first electric signal that is a high-frequency signal, and the oscillation frequency variable method of the high-frequency oscillator that outputs the first electric signal. In the optical transmission system, a light generation step for generating laser light, a light modulation step for modulating the laser light according to a high-frequency signal from the electric transmission system, and outputting the modulated laser light, And a first photoelectric conversion step for converting the modulated laser light from an optical signal to a high-frequency signal that is an electrical signal, and a signal output step for outputting a second electrical signal that is a high-frequency signal in an electrical transmission system. A first branching step for branching the high-frequency signal output in the signal output step into two, a high-frequency signal converted in the first photoelectric conversion step, and a second electrical signal branched in the first branching step A first signal mixing step for mixing one of the signals, a high-frequency signal mixed in the first signal mixing step, and the other of the second electric signals branched in the first branching step, thereby providing a signal of the feedback signal A second signal mixing step for generating a high-frequency signal including a component; and a second branching step for branching the first electric signal into two and outputting one to the outside. The frequency of the first electric signal is varied by varying the frequency.

  According to the high-frequency oscillator and the oscillation frequency variable method of the high-frequency oscillator according to the present invention, a signal output means, a first signal mixing means, and a second signal mixing means are provided in the electrical transmission system, and output from the signal output means. By changing the frequency of the harmonic signal, the oscillation frequency output from the high-frequency oscillator can be changed to a desired value. Can be obtained.

1 is a first configuration diagram showing a high-frequency oscillator according to a first embodiment of the present invention. It is a 2nd block diagram which shows the high frequency oscillator by Embodiment 1 of this invention. It is a 3rd block diagram which shows the high frequency oscillator by Embodiment 1 of this invention. It is a 4th block diagram which shows the high frequency oscillator by Embodiment 1 of this invention. It is a 5th block diagram which shows the high frequency oscillator by Embodiment 1 of this invention. It is a 6th block diagram which shows the high frequency oscillator by Embodiment 1 of this invention. It is a 7th block diagram which shows the high frequency oscillator by Embodiment 1 of this invention. It is an 8th block diagram which shows the high frequency oscillator by Embodiment 1 of this invention. It is a 9th block diagram which shows the high frequency oscillator by Embodiment 1 of this invention. It is a 10th block diagram which shows the high frequency oscillator by Embodiment 1 of this invention. It is an 11th block diagram which shows the high frequency oscillator by Embodiment 1 of this invention. It is a 12th block diagram which shows the high frequency oscillator by Embodiment 1 of this invention. It is a 1st block diagram which shows the high frequency oscillator by Embodiment 2 of this invention. It is a 2nd block diagram which shows the high frequency oscillator by Embodiment 2 of this invention. It is a 3rd block diagram which shows the high frequency oscillator by Embodiment 2 of this invention. It is a 4th block diagram which shows the high frequency oscillator by Embodiment 2 of this invention. It is a block diagram which shows the high frequency oscillator by Embodiment 3 of this invention. It is a 1st block diagram which shows the high frequency oscillator by Embodiment 4 of this invention. It is a 2nd block diagram which shows the high frequency oscillator by Embodiment 4 of this invention. It is a block diagram which shows the conventional high frequency oscillator.

  Hereinafter, preferred embodiments of the high-frequency oscillator of the present invention will be described with reference to the drawings. In each drawing, the same or corresponding parts will be described with the same reference numerals.

Embodiment 1 FIG.
FIG. 1 is a first configuration diagram showing a high-frequency oscillator according to Embodiment 1 of the present invention. The high frequency oscillator oscillates and outputs a high frequency signal (hereinafter referred to as an RF signal) using laser light. This also applies to other embodiments described below.

  The high-frequency oscillator in the first embodiment includes a laser light source 1, an optical modulator 2, an optical fiber 3, an O / E converter 4, a first mixer 5, a second mixer 6, a bandpass filter 7, a first coupler 8, The frequency variable oscillator 9, the filter 10, and the second coupler 11 are configured to output an output signal 12 as a high frequency signal. Here, the laser light source 1, the optical modulator 2, the optical fiber 3, and the O / E converter 4 correspond to an optical transmission system that transmits an optical signal, and includes a first mixer 5, a second mixer 6, and a bandpass filter. 7, the first coupler 8, the variable frequency oscillator 9, the filter 10, and the second coupler 11 correspond to an electrical transmission system that transmits electrical signals.

  The laser light source 1 generates laser light. The optical modulator 2 modulates the intensity of the laser light from the laser light source 1 according to the RF signal input from the second coupler 11, and outputs the modulated laser light to the optical fiber 3. The optical fiber 3 is a transmission path that transmits the modulated laser light output from the optical modulator 2 to the O / E converter 4.

  The O / E converter 4 that is a photoelectric converter converts the laser light into an RF signal that is an electrical signal by directly detecting (square detection) the laser light transmitted through the optical fiber 3, and the first mixer. 5 is output.

  The variable frequency oscillator 9 generates an RF signal and outputs it to the first coupler 8. Further, the frequency variable oscillator 9 can continuously vary the frequency of the generated signal from the first frequency to the second frequency. The first coupler 8 branches the RF signal from the frequency variable oscillator 9 into two and outputs them to the first mixer 5 and the second mixer 6, respectively.

  The first mixer 5 mixes the RF signal from the O / E converter 4 and the RF signal from the first coupler 8, and generates two RF signals having the sum frequency and the difference frequency of these two RF signals. And output to the bandpass filter 7.

  The band pass filter 7 passes only the signal components included in a predetermined pass band set in advance from the two RF signals from the first mixer 5 and outputs them to the second mixer 6. The band pass filter 7 blocks signals and spurious signals in a frequency band other than a predetermined pass band.

  The second mixer 6 mixes the RF signal from the bandpass filter 7 and the RF signal from the first coupler 8, and generates two RF signals having the sum frequency and the difference frequency of these two RF signals. , Output to the filter 10.

  The filter 10 passes only signal components included in a predetermined pass band set in advance from the two RF signals from the second mixer 6 and outputs the signal components to the second coupler 11. Further, the filter 10 blocks signals and spurious signals in a frequency band other than a predetermined pass band.

  The second coupler 11 branches the RF signal from the filter 10 into two, and outputs one to the outside as a high frequency signal (hereinafter referred to as “output signal 12”). The second coupler 11 outputs the other RF signal to the optical modulator 2.

  Next, a series of operations will be described using specific numerical examples. In the first embodiment, the first frequency is assumed to be 9 GHz and the second frequency is assumed to be 10 GHz for easy understanding of the operation of the high frequency oscillator. Further, the center frequency of the band pass filter 7 is 1 GHz, and the filter 10 is described as a high pass filter including 10 GHz to 11 GHz in the pass band.

  These set values are examples of specific values, and are not limited to these values, and may be different values. The filter 10 may not be a high pass filter. However, in order to obtain the effect described later, the RF signal passing through the band-pass filter 7 has a difference frequency between the two RF signals at the time of mixing out of the two RF signals output from the first mixer 5 described above. Only RF signals are used.

  The RF signal passing through the filter 10 is only the RF signal having the sum frequency of the two RF signals at the time of mixing among the two RF signals output from the second mixer 6 described above.

  First, laser light is generated by the laser light source 1 and output to the optical modulator 2. The laser beam input to the optical modulator 2 is modulated according to the RF signal from the second coupler 11 and output to the optical fiber 3 as a modulated laser beam. The modulated laser light input to the optical fiber 3 is transmitted through the optical fiber 3 and output to the O / E converter 4. The modulated laser light input to the O / E converter 4 is directly detected and converted into an RF signal and output to the first mixer 5.

  Here, when the oscillation of the high-frequency oscillator has not started, signals output from the O / E converter 4 are thermal noise, shot noise, RIN (relative intensity noise) from the laser light source 1, and the like. It consists only of noise components. This also applies to the following other embodiments.

  Here, first, it is assumed that the oscillation frequency of the variable frequency oscillator 9 is set to 9 GHz. In this case, a 9 GHz RF signal is generated from the variable frequency oscillator 9 and output to the first coupler 8. The RF signal input to the first coupler 8 is branched into two RF signals with a predetermined branching ratio and output to the first mixer 5 and the second mixer 6, respectively.

  Subsequently, the RF signal from the O / E converter 4 input to the first mixer 5 (only the above-described noise component if oscillation has not started) and the RF signal from the first coupler 8 are mixed. Then, two RF signals having the sum frequency and the difference frequency of these two RF signals are generated and output to the bandpass filter 7.

  As for the two RF signals from the first mixer 5 input to the band pass filter 7, only the 1 GHz signal included in the pass band is passed and output to the second mixer 6.

  Next, the RF signal from the bandpass filter 7 input to the second mixer 6 and the RF signal from the first coupler 8 are mixed, and two signals having the sum frequency and the difference frequency of these two RF signals are mixed. An RF signal is generated and output to the filter 10. That is, a 1 GHz RF signal from the bandpass filter 7 and a 9 GHz RF signal from the first coupler 8 are mixed, and a 10 GHz RF signal having the sum frequency of these two RF signals and an 8 GHz having a difference frequency. RF signal is generated.

  As for the two RF signals from the second mixer 6 input to the filter 10, only a 10 GHz signal included in the pass band is passed and output to the second coupler 11. That is, of the two RF signals from the second mixer 6, the 8 GHz RF signal is removed, and only the 10 GHz RF signal is output to the second coupler 11.

  The RF signal input to the second coupler 11 is branched into two RF signals with a predetermined branching ratio, one RF signal is output to the outside as the output signal 12, and the other RF signal is the optical modulator. 2 is output.

  Here, when the RF signal branched by the second coupler 11 is input to the optical modulator 2 again, a feedback circuit is configured. In this feedback circuit, the high-frequency oscillator starts to oscillate at a frequency of 10 GHz by setting the feedback gain so as to be larger than the loss of the entire circuit.

  Here, it is assumed that the oscillation frequency setting value of the frequency variable oscillator 9 is changed from 9 GHz to 10 GHz. In this case, an RF signal of 10 GHz is generated from the frequency variable oscillator 9 and output to the first coupler 8. The RF signal input to the first coupler 8 is branched into two RF signals with a predetermined branching ratio and output to the first mixer 5 and the second mixer 6, respectively.

  Subsequently, the RF signal from the O / E converter 4 input to the first mixer 5 (only the above-described noise component if oscillation has not started) and the RF signal from the first coupler 8 are mixed. Then, two RF signals having the sum frequency and the difference frequency of these two RF signals are generated and output to the bandpass filter 7.

  As for the two RF signals from the first mixer 5 input to the band pass filter 7, only the 1 GHz signal included in the pass band is passed and output to the second mixer 6.

  Next, the RF signal from the bandpass filter 7 input to the second mixer 6 and the RF signal from the first coupler 8 are mixed, and two signals having the sum frequency and the difference frequency of these two RF signals are mixed. An RF signal is generated and output to the filter 10. That is, the 1 GHz RF signal from the bandpass filter 7 and the 10 GHz RF signal from the first coupler 8 are mixed, and the 11 GHz RF signal having the sum frequency of these two RF signals and the 9 GHz having the difference frequency. RF signal is generated.

  As for the two RF signals from the second mixer 6 input to the filter 10, only the 11 GHz signal included in the pass band is passed and output to the second coupler 11. That is, of the two RF signals from the second mixer 6, the 9 GHz RF signal is removed, and only the 11 GHz RF signal is output to the second coupler 11.

  The RF signal input to the second coupler 11 is branched into two RF signals with a predetermined branching ratio, one RF signal is output to the outside as the output signal 12, and the other RF signal is the optical modulator. 2 is output.

  Here, when the RF signal branched by the second coupler 11 is input to the optical modulator 2 again, a feedback circuit is configured. In this feedback circuit, the high-frequency oscillator starts to oscillate at a frequency of 11 GHz by setting the feedback gain so as to be larger than the loss of the entire circuit.

  Next, the effect of the high frequency oscillator in the first embodiment will be described. As described in the foregoing operation, in this type of high-frequency oscillator, the frequency of the RF signal generated from the variable frequency oscillator 9 can be varied to vary the frequency of the oscillation signal of the high-frequency oscillator itself. Therefore, by providing the configuration as shown in FIG. 1 in the first embodiment, an oscillation frequency can be obtained without using a delay device and a variable bandpass filter that are used to vary the frequency with this type of conventional high-frequency oscillator. Can be varied.

  Here, the conventional high frequency oscillator of this type described above has a problem that the frequency variable amount is limited to the variable amount of the provided delay device. For example, a microwave phase shifter can be considered as an application example of the delay device, but the phase shift amount of the commercially available microwave phase shifter is often about 2π, in order to obtain a phase shift amount larger than that. Requires a plurality of microwave phase shifters, resulting in disadvantages of increased size and cost.

  Further, in this type of conventional oscillator, there is a problem that the frequency variable amount is limited to the band of the provided bandpass filter. With respect to this point, for example, the frequency variable amount can be increased by using a bandpass filter that can change the passband. However, this band-pass filter is required to have a function of suppressing spurious generated at a frequency interval that is inversely proportional to the fiber length. For this purpose, it is necessary to have a narrow band.

  Therefore, although a bandpass filter that achieves both narrow band and variable passband is expected, there is a problem that the performance is degraded as compared with a filter that pursues only one of the performances. Moreover, the fault of being connected with high cost arises.

  Therefore, in the first embodiment, since the oscillation frequency can be varied by the variable frequency oscillator 9 without using a delay unit or a variable bandpass filter, the effect of reducing the size and reducing the cost compared to the conventional case is achieved. Have.

  Further, as described in the above description of the operation, in this type of high-frequency oscillator, the frequency of the RF signal generated from the frequency variable oscillator 9 is varied from 9 GHz to 10 GHz, so that the frequency of the oscillation signal of the high-frequency oscillator itself is increased. Can be varied from 10 GHz to 11 GHz.

  Therefore, when the frequency band of the mixer, the coupler, etc. sufficiently covers the frequency variable range of the RF signal generated from the frequency variable oscillator 9 and the frequency variable range of the high frequency oscillator itself, the frequency variable amount of the high frequency oscillator itself is An amount equivalent to the variable amount of the variable frequency oscillator 9 can be obtained.

  On the other hand, in the conventional high-frequency oscillator using the delay device described above, for example, when the phase shift amount is 2π, the frequency variable amount of the high-frequency oscillator by this delay device is calculated as follows. Here, the oscillation loop length of the high-frequency oscillator of the first embodiment is almost the same as the length of the optical fiber 3, and the lengths of the other parts are negligible.

When the length of the optical fiber 3 is L, the refractive index of the optical fiber is n, the speed of light is c, and the oscillation loop propagation time of the high-frequency oscillator is τ, τ is expressed by the following equation (1).
τ = nL / c (1)

Further, if the frequency at which this high-frequency oscillator can oscillate (the frequency at which the phase of the oscillation signal is an integer multiple of 2π) is f ₀ (k), f ₀ (k) can be expressed by the following equation (2) using τ: expressed.
f ₀ (k) = k / τ (2)

Here, k is a natural number. Therefore, if the frequency variable amount of the high frequency oscillator when the 2π phase is changed by the delay device described above is Δf ₀ , Δf ₀ is expressed by the following expression (3).
Δf ₀ = 1 / τ (3)

Here, for example, when L = 1000 m and n = 1.5, Δf ₀ = 200 kHz is calculated. In order to increase Δf ₀ , L may be set to a small value, but this type of high-frequency oscillator has the advantage that the phase noise of the oscillation signal can be reduced by setting L to a large value. However, if L is set to a small value, there is a problem that this advantage cannot be obtained. In order to obtain Δf ₀ of 1 GHz, it is necessary to set L = 0.2 m, and it can be said that phase noise reduction of the oscillation signal is hardly expected.

  On the other hand, in the first embodiment, the oscillation frequency can be varied without using a delay unit or a variable bandpass filter. Therefore, the frequency variable amount can be set while keeping the fiber length at a large value compared to the conventional case. It is possible to increase the phase noise and to achieve both the reduction of the phase noise and the increase of the frequency variable amount.

  However, the above-mentioned effect is obtained because the variable range of the oscillation frequency is within the usable frequency of the first mixer 5, the second mixer 6, and the second coupler 11, and the first range corresponding to the variable range of the oscillation frequency. This is limited to the case where the pass signal frequency range of the coupler 8 is within the usable frequency range of the first coupler 8.

  In the first embodiment, the laser light source 1 and the optical modulator 2, the optical modulator 2 and the optical fiber 3, and the optical fiber 3 and the O / E converter 4 are connected by optical fibers. Therefore, the oscillator can be miniaturized. In addition, high reliability is obtained, handling is easy, and effects such as high placement freedom are obtained.

  However, the optical transmission system in the high-frequency oscillator described in the first embodiment is not limited to the one that is connected by the optical fiber, and the laser light transmission path uses other things such as a space. It doesn't matter. This also applies to other embodiments described below.

  In the first embodiment, the branching ratio of the first coupler 8 is not specifically mentioned, but the RF signal output from the first coupler 8 to the first mixer 5 and the first coupler 8 to the second Any branching ratio may be used as long as the power of the RF signal output to the mixer 6 satisfies a condition that allows the first mixer 5 and the second mixer 6 to perform a desired operation. This also applies to other embodiments described below.

  In the first embodiment, the branching ratio of the second coupler 11 is not particularly mentioned, but any branching ratio may be used as long as the conditions for the high-frequency oscillator to oscillate are satisfied. This also applies to other embodiments described below.

  In the first embodiment, the second coupler 11 is disposed between the second mixer 6 and the optical modulator 2. However, the present invention is not limited to such a configuration. FIG. 2 is a second configuration diagram showing the high-frequency oscillator according to the first embodiment of the present invention. As shown in FIG. 2, the second coupler 11 may be disposed between the O / E converter 4 and the first mixer 5.

  In the first embodiment, the RF signal from the filter 10 is input to the second coupler 11. However, the present invention is not limited to such a configuration. FIG. 3 is a third configuration diagram showing the high-frequency oscillator according to the first embodiment of the present invention. As illustrated in FIG. 3, an amplifier 21 (amplifier) that amplifies an RF signal that is an electrical signal may be disposed between the filter 10 and the second coupler 11. Thus, by arranging the amplifier 21, it is possible to amplify the RF signal output to the outside, and to produce an oscillation even when the power of the laser beam is low.

  In the example of FIG. 3, the amplifier 21 is arranged between the filter 10 and the second coupler 11, but any position in the transmission path from the O / E converter 4 to the optical modulator 2 can be used. The amplifier 21 may be disposed in the stub. A plurality of amplifiers 21 may be arranged.

  However, an amplifier that amplifies a 1 GHz signal is used between the first mixer 5 and the bandpass filter 7 and between the bandpass filter 7 and the second mixer 6, and a 10 GHz signal is transmitted between them. An amplifier that amplifies is used. These also apply to other embodiments described below.

  In the first embodiment, the laser light from the optical fiber 3 is input to the O / E converter 4. However, the present invention is not limited to such a configuration. FIG. 4 is a fourth block diagram showing the high-frequency oscillator according to the first embodiment of the present invention. As shown in FIG. 4, an optical amplifier 22 that amplifies laser light may be disposed between the optical fiber 3 and the O / E converter 4. Thus, by arranging the optical amplifier 22, it is possible to amplify an RF signal output to the outside and to obtain an effect of obtaining oscillation even when the power of the laser beam is low.

  In the example of FIG. 4, the optical amplifier 22 is disposed between the optical fiber 3 and the O / E converter 4, but any transmission path from the laser light source 1 to the O / E converter 4 may be used. The optical amplifier 22 may be disposed at any position. A plurality of optical amplifiers 22 may be arranged.

  However, between the optical modulator 2 and the O / E converter 4, there is a modulated laser beam (a component of the laser beam from the laser light source 1 on the optical spectrum and both sidebands of this laser beam by modulation). It is assumed that an optical amplifier capable of amplifying a component of a laser beam separated by 1 GHz is used. These also apply to other embodiments described below.

  In the first embodiment, an image rejection mixer 6 b may be used as the second mixer 6. FIG. 5 is a fifth block diagram showing the high-frequency oscillator according to the first embodiment of the present invention. For example, when an image rejection mixer in which only an RF signal having the sum frequency of two RF signals input to the second mixer 6 is generated and an RF signal having a difference frequency is suppressed is used, The function of the filter 10 is also provided.

  For this reason, as shown in FIG. 5, by using an image rejection mixer 6 b instead of the second mixer 6, the same effect as described above can be obtained without using the filter 10. Thereby, compared with the case where the filter 10 is used, the effect that it becomes low cost and size reduction is acquired.

  Further, in the high frequency oscillator shown in FIG. 1, a control unit 210 that controls the frequency of the variable frequency oscillator 9 may be provided. FIG. 6 is a sixth configuration diagram showing the high-frequency oscillator according to the first embodiment of the present invention, which is a high-frequency oscillator in which the control unit 210 is applied to the high-frequency oscillator shown in FIG.

  Compared with the wet configuration shown in FIG. 1, the high frequency oscillator shown in FIG. 6 further includes a coupler 31 and a control unit 210. Here, it is assumed that the variable frequency oscillator 9 is a voltage controlled oscillator that can vary the oscillation frequency according to the input voltage. However, the frequency variable oscillator 9 is not necessarily a voltage-controlled oscillator.

  The coupler 31 branches the RF signal from the filter 10 into two, outputs one to the second coupler 11, and outputs the other to the controller 210. The control unit 210 changes the frequency of the variable frequency oscillator 9 by automatically adjusting the voltage applied to the variable frequency oscillator 9 in accordance with the RF signal from the coupler 31. Here, the control unit 210 includes, for example, a crystal oscillator 211, a frequency divider 212, a PLL circuit 213, and a loop filter 214.

  The crystal oscillator 211 has a function of generating and outputting a reference signal for changing the oscillation frequency of the high-frequency oscillator to a stable value or a desired value. The frequency divider 212 has a function of dividing and outputting the RF signal from the coupler 31 by the ratio of the desired oscillation frequency of the high frequency oscillator and the reference frequency. The PLL circuit 213 detects the frequency difference between the RF signal from the crystal oscillator 211 and the RF signal from the frequency divider 212 and outputs a signal such as a voltage value including information on the frequency difference to the loop filter 214. Has the function of

  The loop filter 214 blocks signal components and spurious signals in a frequency band other than a predetermined predetermined pass band from the signal from the PLL circuit 213 and passes only signal components included in the predetermined pass band. It has a function to make it.

  Here, for example, if the output signal frequency of the crystal oscillator 211 is 100 MHz and the frequency divider 212 is 100, the RF signal of about 10 GHz from the coupler 31 is frequency-divided by the frequency divider 212 to about 100 MHz. After that, the PLL circuit 213 detects the frequency difference with the signal of the crystal oscillator 211, and a signal such as a voltage value including information on this frequency difference is input to the frequency variable oscillator 9 via the loop filter 214. Is done.

  The variable frequency oscillator 9 changes the frequency of the output signal based on the signal from the loop filter 214 so as to correct the above-described frequency difference. Here, by configuring a feedback circuit as shown in FIG. 6 and repeating the above-described operation, the frequency of the high-frequency oscillator can be stabilized or the frequency can be changed to a desired value.

  Note that the configuration of the control unit 210 is not limited to the above, and may be other configurations. Further, the coupler 31 may be installed at an arbitrary position between the O / E converter 4 and the first mixer 5 and between the filter 10 and the optical modulator 2. This also applies to the following other embodiments.

  In the first embodiment, the phase shifter 41 that changes the phase of the input RF signal may be used to stabilize the oscillation frequency or change the oscillation frequency to a desired value. . FIG. 7 is a seventh block diagram showing the high-frequency oscillator according to Embodiment 1 of the present invention, which is a high-frequency oscillator in which a phase shifter 41 is applied to the high-frequency oscillator shown in FIG.

  In FIG. 7, the phase shifter 41 changes the phase of the RF signal to a desired value according to the applied voltage, for example, and outputs it. In the example of FIG. 7, the phase shifter 41 is arranged between the filter 10 and the optical modulator 2, but if it is a transmission path from the O / E converter 4 to the optical modulator 2, The phase shifter 41 may be arranged at any position. A plurality of phase shifters 41 may be arranged.

  However, a phase shifter that changes the phase of a signal of 1 GHz is used between the first mixer 5 and the bandpass filter 7 and between the bandpass filter 7 and the second mixer 6. A phase shifter that changes the phase of the signal is used. This also applies to the following other embodiments.

  Further, in the high-frequency oscillator shown in FIG. 7, a phase shifter control unit 220 (phase shifter control unit) that controls the operation of the phase shifter 41 may be provided. FIG. 8 is an eighth configuration diagram illustrating the high-frequency oscillator according to the first embodiment of the present invention, which is a high-frequency oscillator in which the phase shifter control unit 220 is applied to the high-frequency oscillator illustrated in FIG. The high frequency oscillator in FIG. 8 includes a coupler 51 and a phase shifter control unit 220.

  The coupler 51 branches the RF signal from the phase shifter 41 into two, outputs one to the second coupler 11, and outputs the other to the phase shifter control unit 220. The phase shifter control unit 220 controls the operation of the phase shifter 41 by automatically adjusting the voltage applied to the phase shifter 41 in accordance with the RF signal from the coupler 51, and sets the phase of the RF signal to a desired value. The value is changed. Here, similarly to the control unit 210 in FIG. 6 described above, the phase shifter control unit 220 includes, for example, a crystal oscillator 221, a frequency divider 222, a PLL circuit 223, and a loop filter 224.

  The functions of the crystal oscillator 221, frequency divider 222, PLL circuit 223, and loop filter 224 in the phase shifter control unit 220 are the same as those of the crystal oscillator 211, frequency divider 212, PLL circuit 213, and loop filter in the control unit 210 described above. This is the same as each of 214, and a description thereof will be omitted.

  Here, for example, assuming that the output signal frequency of the crystal oscillator 221 is 100 MHz and the frequency dividing number of the frequency divider 222 is 100, the RF signal of about 10 GHz from the coupler 51 is frequency-divided by the frequency divider 222 to about 100 MHz. After that, the PLL circuit 223 detects a frequency difference with the signal of the crystal oscillator 221, and a signal such as a voltage value including information on the frequency difference is input to the phase shifter 41 via the loop filter 224. Is done.

  The phase shifter 41 changes the phase of the passing RF signal of about 10 GHz so as to correct the above-described frequency difference based on the signal from the loop filter 224. Here, a feedback circuit as shown in FIG. 8 is configured, and the above-described operation is repeated, whereby the oscillation frequency can be stabilized or the oscillation frequency can be changed to a desired value.

  The configuration of the phase shifter control unit 220 is not limited to the above configuration, and may be another configuration. The coupler 51 may be installed at any position between the O / E converter 4 and the first mixer 5 and between the filter 10 and the optical modulator 2. This also applies to the following other embodiments.

  In the first embodiment, an optical delay device 61 that changes the optical path length of the input laser beam may be used to stabilize the oscillation frequency or change the oscillation frequency to a desired value. FIG. 9 is a ninth configuration diagram showing the high-frequency oscillator according to the first embodiment of the present invention, which is a high-frequency oscillator in which an optical delay device 61 is applied to the high-frequency oscillator shown in FIG.

  In FIG. 9, the optical delay device 61 changes the optical path length of the laser light to a desired value and outputs it, for example, according to the applied voltage. In the example of FIG. 9, the optical delay device 61 is disposed between the optical fiber 3 and the O / E converter 4. However, in the transmission path from the optical modulator 2 to the O / E converter 4. If so, the optical delay device 61 may be arranged at any position. This also applies to the following other embodiments.

  In the high-frequency oscillator shown in FIG. 9, an optical delay control unit 230 (optical delay control means) that controls the operation of the optical delay 61 may be provided. FIG. 10 is a tenth configuration diagram showing the high frequency oscillator according to the first embodiment of the present invention, which is a high frequency oscillator in which an optical delay control unit 230 is applied to the high frequency oscillator shown in FIG.

  The high frequency oscillator in FIG. 10 includes a coupler 71 and an optical delay controller 230. The coupler 71 branches the RF signal from the filter 10 into two, outputs one to the second coupler 11, and outputs the other to the optical delay controller 230. The optical delay control unit 230 automatically adjusts the voltage applied to the optical delay 61 in accordance with the RF signal from the coupler 71, thereby controlling the operation of the optical delay 61 and determining the optical path length of the laser light. The value is changed.

  Here, the optical delay unit control unit 230 is, for example, the crystal oscillator 231, the frequency divider 232, and the optical delay unit application, similarly to the control unit 210 in FIG. 6 or the phase shifter control unit 220 in FIG. 8 described above. The voltage control means 233 and the loop filter 234 are configured. The functions of the crystal oscillator 231, the frequency divider 232, the optical delay device applied voltage control means 233, and the loop filter 234 in the optical delay unit control unit 230 are the same as those of the crystal oscillator 211, the frequency divider 212, and the PLL in the control unit 210 described above. This is the same as each of the circuit 213 and the loop filter 214, and description thereof is omitted.

  Here, for example, assuming that the output signal frequency of the crystal oscillator 231 is 100 MHz and the frequency dividing number of the frequency divider 232 is 100, the RF signal of about 10 GHz from the coupler 71 is frequency-divided by the frequency divider 232 to about 100 MHz. Thereafter, the optical delay device applied voltage control means 233 detects a frequency difference with the signal of the crystal oscillator 231, and a signal such as a voltage value including information on the frequency difference is transmitted through the loop filter 234. Input to the delay device 61.

  Based on the signal from the loop filter 234, the optical delay device 61 changes the optical path length of the passing laser light so as to correct the above-described frequency difference. Here, a feedback circuit as shown in FIG. 10 is configured, and the above-described operation is repeated, whereby the oscillation frequency can be stabilized or the oscillation frequency can be changed to a desired value.

  Note that the configuration of the optical delay device controller 230 is not limited to the above configuration, and may be other configurations. The coupler 71 may be installed at any position between the O / E converter 4 and the first mixer 5 and between the filter 10 and the optical modulator 2. In the first embodiment, the phase shifter 41 and the optical delay device 61 may be used simultaneously. This also applies to the following other embodiments.

  In the first embodiment, when it is possible to perform intensity modulation at the oscillation frequency with the laser light source and output the modulated laser light, another configuration can be employed. FIG. 11 is an eleventh configuration diagram showing the high-frequency oscillator according to the first embodiment of the present invention. As shown in FIG. 11, the RF signal from the second coupler 11 may be directly input to the laser light source and the optical modulator 2 may not be used. As a result, it is possible to obtain an effect that the cost is reduced and the size is reduced as compared with the case where the optical modulator 2 is used. This also applies to the following other embodiments.

  In the first embodiment, the RF signal from the filter 10 is input to the second coupler 11, but other configurations may be adopted. FIG. 12 is a twelfth configuration diagram showing the high-frequency oscillator according to the first embodiment of the present invention. As shown in FIG. 12, an amplifier 81 (amplifier) that amplifies an RF signal that is an electrical signal may be disposed between the first coupler 8 and the frequency variable oscillator 9.

  As described above, by arranging the amplifier 81, the local signal power (output signal power from the frequency variable oscillator 9) necessary for performing a desired operation in the first mixer 5 and the second mixer 6 is actually increased. Even if the output signal power from the frequency variable oscillator 9 is low, the desired operation can be performed.

  In the example of FIG. 12, the amplifier 81 is arranged between the first coupler 8 and the frequency variable oscillator 9, but between the first coupler 8 and the first mixer 5 and between the first coupler 8 and the second mixer 6. You may arrange | position between. A plurality of amplifiers 81 may be arranged in these sections. These also apply to other embodiments described below.

  As described above, according to the first embodiment, it is possible to realize a high-frequency oscillator that can vary the oscillation frequency without using a delay device or a variable bandpass filter, and achieve both reduction in phase noise and increase in frequency variable amount. Can do.

Embodiment 2. FIG.
FIG. 13 is a first block diagram showing a high-frequency oscillator according to the second embodiment of the present invention. In the figure, the same reference numerals as those in FIG. The high-frequency oscillator shown in FIG. 13 further includes an E / O converter 91, an optical fiber 92, and an O / E converter 93 with respect to the configuration of FIG. Corresponds to the passage time adjusting means.

  The E / O converter 91 generates laser light, modulates the intensity according to the RF signal from the first coupler 8, and outputs the modulated laser light to the optical fiber 92. The optical fiber 92 is a transmission path that transmits the modulated laser light output from the E / O converter 91 to the O / E converter 93. The O / E converter 93 directly detects the laser light transmitted by the optical fiber 92 (square detection), thereby converting the laser light into an RF signal that is an electric signal and outputs the RF signal to the second mixer 6. Other configurations are the same as those of the first embodiment, and the description thereof is omitted.

  Hereinafter, the operation of the high-frequency oscillator configured as described above will be described with reference to FIG. The description of the same operation as that of the first embodiment will be omitted.

  The RF signal input to the first coupler 8 is branched into two RF signals with a predetermined branching ratio, and one RF signal is output to the first mixer 5. The operation of the RF signal output to the first mixer 5 is the same as that in the first embodiment.

  The other RF signal output from the first coupler 8 is input to the E / O converter 91, where a laser beam whose intensity is modulated is generated and output to the optical fiber 92. The laser beam transmitted through the optical fiber 92 is input to the O / E converter 93, converted from the laser beam to an RF signal, and output to the second mixer 6. Others are the same as in the first embodiment.

  In the configuration of FIG. 1 in the first embodiment, for example, when the passage time delay of the bandpass filter 7 is large, the timing at which the RF signal from the frequency variable oscillator 9 is mixed by the first mixer 5 and the first A large time difference occurs in the timing of mixing by the two mixers 6. As a result, there is a problem that the phase noise of the output signal of the high-frequency oscillator is strongly influenced by the phase noise of the output signal from the variable frequency oscillator 9.

  Therefore, in the configuration shown in FIG. 13, the first time until the RF signal from the first mixer 5 reaches the second mixer 6 after passing through the bandpass filter 7, and the RF signal from the frequency variable oscillator 9. The optical fiber length of the optical fiber 92 is set so as to match the second time obtained by subtracting the time until it reaches the first mixer 5 from the time until it reaches the second mixer 6.

  Thereby, it is possible to suppress the superposition of the phase noise of the output signal from the frequency variable oscillator 9 on the output signal of the high-frequency oscillator, and to obtain a high-frequency oscillator with a lower phase noise. This also applies to the following other embodiments.

  In FIG. 13, a phase shifter 94 that changes the phase of the input RF signal may be used in order to more accurately match the matching time. FIG. 14 is a second block diagram showing the high frequency oscillator according to the second embodiment of the present invention, which is a high frequency oscillator in which a phase shifter 94 is applied to the high frequency oscillator shown in FIG.

  In FIG. 14, the phase shifter 94 changes the phase of the RF signal to a desired value according to the applied voltage, for example, and outputs it. In the example of FIG. 14, the phase shifter 94 is disposed between the first coupler 8 and the E / O converter 91, but is disposed between the O / E converter 93 and the second mixer 6. Also good. A plurality of phase shifters 94 may be arranged. This also applies to the following other embodiments.

  In FIG. 13, an optical delay device 95 that changes the optical path length of the input laser beam may be used in order to more accurately match the matching time. FIG. 15 is a third block diagram showing the high-frequency oscillator according to the second embodiment of the present invention, which is a high-frequency oscillator in which an optical delay device 95 is applied to the high-frequency oscillator shown in FIG.

  In FIG. 15, the optical delay device 95 changes the optical path length of the laser light to a desired value according to the applied voltage, for example, and outputs it. In the example of FIG. 15, the optical delay device 95 is disposed between the E / O converter 91 and the optical fiber 92, but may be disposed between the optical fiber 92 and the O / E converter 93. . A plurality of optical delay devices 95 may be arranged. In the first embodiment, the phase shifter 94 and the optical delay device 95 may be used simultaneously. This also applies to the following other embodiments.

  FIG. 16 is a fourth block diagram showing the high-frequency oscillator according to the second embodiment of the present invention. As shown in FIG. 16, the optical modulator 96 that modulates the intensity of the laser light input via the optical coupler 97 according to the input RF signal and outputs the modulated laser light is converted into an E / O converter. It is provided instead of 91. By adopting such a configuration, the laser light generation function included in the E / O converter 91 becomes unnecessary, and the effects of low cost, size reduction, and low power consumption can be obtained. . This also applies to the following other embodiments.

  As described above, according to the second embodiment, by providing the transit time adjusting means, the timing when the RF signal from the variable frequency oscillator is mixed by the first mixer and the timing when the second mixer is mixed is large. It is possible to prevent a time difference from occurring. As a result, in addition to the effect of the first embodiment, a high-frequency oscillator with low phase noise can be realized.

Embodiment 3 FIG.
In the third embodiment, a passage time adjusting unit different from the second embodiment will be described. FIG. 17 is a block diagram showing a high-frequency oscillator according to Embodiment 3 of the present invention. In the figure, the same reference numerals as those in FIG. The high-frequency oscillator shown in FIG. 17 includes negative group delay time generating means 101 as a transit time adjusting means different from that in the second embodiment, compared to the configuration in FIG. 1 in the first embodiment. .

  The negative group delay time generation means 101 applies a negative group delay time to the RF signal from the first coupler 8 and outputs it to the first mixer 5. Other configurations are the same as those of the first embodiment, and the description thereof is omitted.

  Hereinafter, the operation of the high-frequency oscillator configured as described above will be described with reference to FIG. The description of the same operation as that of the first embodiment will be omitted.

  The RF signal input to the first coupler 8 is branched into two RF signals at a predetermined branching ratio, and one RF signal is output to the second mixer 6. The operation of the RF signal output to the second mixer 6 is the same as that in the first embodiment.

  The other RF signal output from the first coupler 8 is input to the negative group delay time generation unit 101, subjected to a negative group delay time, and output to the second mixer 6. Others are the same as in the first embodiment.

  As described in the second embodiment, in the configuration of FIG. 13, the first mixer 5 is provided by providing a positive delay time between the first coupler 8 and the second mixer 6 as the passage time adjusting means. From the first time until the RF signal from the frequency variable oscillator 9 passes through the bandpass filter 7 and reaches the second mixer 6 and from the time until the RF signal from the frequency variable oscillator 9 reaches the second mixer 6. The second time obtained by subtracting the time to reach the mixer 5 was matched. The method of matching the times can also be realized by giving a negative delay time between the first coupler 8 and the first mixer 5.

  Therefore, as shown in FIG. 17, the first time until the RF signal from the first mixer 5 reaches the second mixer 6 through the bandpass filter 7 and the RF signal from the frequency variable oscillator 9 is the first time. By setting the delay time of the negative group delay time generating means 101 so as to match the second time obtained by subtracting the time until the first mixer 5 is reached from the time until the second mixer 6 is reached The same effect as that described in the second embodiment is obtained, which is an effect that a high-frequency oscillator with lower phase noise can be obtained.

  In addition, the configuration of FIG. 13 in the second embodiment is configured with many elements compared to the configuration of FIG. 17 in the third embodiment. For this reason, by adopting the configuration of FIG. 17, it is possible to obtain the effects of low cost, size reduction, and low power consumption. This also applies to the following other embodiments.

  As described above, according to the third embodiment, by providing the negative group delay time generating means as the passing time adjusting means, the timing at which the RF signal from the frequency variable oscillator is mixed by the first mixer, and the second It is possible to prevent a large time difference from occurring in the timing of mixing by the mixer. As a result, the same effect as in the second embodiment can be obtained. Further, compared with the second embodiment, cost reduction, size reduction, and power consumption can be achieved.

Embodiment 4 FIG.
FIG. 18 is a first block diagram showing a high-frequency oscillator according to the fourth embodiment of the present invention. In the figure, the same reference numerals as those in FIG.

  The high frequency oscillator in the fourth embodiment shown in FIG. 18 is different from the configuration in FIG. 1 in the first embodiment in the first mixer 5, the second mixer 6, the band pass filter 7, the first coupler 8, and the frequency. Instead of including the variable oscillator 9, the filter 10, and the second coupler 11, a third mixer 111, a fourth mixer 112, a band pass filter 113, a third coupler 114, a frequency variable oscillator 115, a filter 116, and a fourth coupler 117 are provided. Contains.

  The variable frequency oscillator 115 generates an RF signal and outputs it to the third coupler 114. Furthermore, the frequency variable oscillator 115 can continuously vary the frequency of the generated signal from the third frequency to the fourth frequency. The third coupler 114 branches the RF signal from the frequency variable oscillator 115 into two, and outputs them to the third mixer 111 and the fourth mixer 112, respectively.

  The third mixer 111 mixes the RF signal from the O / E converter 4 and the RF signal from the third coupler 114, and generates two RF signals having the sum frequency and the difference frequency of these two RF signals. And output to the filter 116.

  The filter 116 passes only the signal component included in the predetermined pass band set in advance from the two RF signals from the third mixer 111 and outputs the signal component to the fourth coupler 117. Further, the filter 116 blocks signals and spurious signals in a frequency band other than a predetermined pass band.

  The fourth coupler 117 branches the RF signal from the filter 116 into two, and outputs one as an output signal 12 to the outside. The fourth coupler 117 outputs the other RF signal to the fourth mixer 112.

  The fourth mixer 112 mixes the RF signal from the fourth coupler 117 and the RF signal from the third coupler 114, and generates two RF signals having the sum frequency and the difference frequency of these two RF signals. And output to the bandpass filter 113.

  The band-pass filter 113 passes only the signal components included in the predetermined pass band set in advance from the two RF signals from the fourth mixer 112 and outputs them to the optical modulator 2. The band pass filter 113 blocks signals and spurious signals in a frequency band other than a predetermined pass band. Other configurations are the same as those of the first embodiment, and the description thereof is omitted.

  Hereinafter, the operation of the high-frequency oscillator configured as described above will be described with reference to FIG. The description of the same operation as that of the first embodiment will be omitted.

  Next, a series of operations will be described using specific numerical examples. In the fourth embodiment, the third frequency is 9 GHz and the fourth frequency is 10 GHz for easy understanding of the operation of the high-frequency oscillator. Further, the center frequency of the band pass filter 113 is 1 GHz, and the filter 116 is described as a high pass filter including 10 GHz to 11 GHz in the pass band.

  These set values are examples of specific values, and are not limited to these values, and may be different values. Further, the filter 116 may not be a high-pass filter. However, in order to obtain the effect described later, the RF signal passing through the filter 116 is an RF signal having the sum frequency of the two RF signals at the time of mixing out of the two RF signals output from the third mixer 111 described above. Only.

  The RF signal passing through the bandpass filter 113 is only the RF signal having the difference frequency between the two RF signals at the time of mixing, out of the two RF signals output from the fourth mixer 112 described above.

  The operations of the laser light source 1, the optical modulator 2, the optical fiber 3, and the O / E converter 4 are the same as those in the first embodiment.

  Here, first, it is assumed that the oscillation frequency of the frequency variable oscillator 115 is set to 9 GHz. In this case, a 9 GHz RF signal is generated from the variable frequency oscillator 115 and output to the third coupler 114. The RF signal input to the third coupler 114 is branched into two RF signals with a predetermined branching ratio and output to the third mixer 111 and the fourth mixer 112, respectively.

  Subsequently, the RF signal from the O / E converter 4 input to the third mixer 111 and the RF signal from the third coupler 114 are mixed and have a sum frequency and a difference frequency of these two RF signals. Two RF signals are generated and output to the filter 116.

  Here, as shown in FIG. 18, since the RF signal from the O / E converter 4 passes through the bandpass filter 113, it may be considered that only a signal in the vicinity of 1 GHz is included. That is, in the third mixer 111, the 1 GHz RF signal from the O / E converter 4 and the 9 GHz RF signal from the third coupler 114 are mixed, and the 10 GHz RF signal having the sum frequency of these two RF signals is mixed. A signal and an 8 GHz RF signal having a difference frequency are generated.

  As for the two RF signals from the third mixer 111 inputted to the filter 116, only the 10 GHz signal included in the pass band is passed and outputted to the fourth coupler 117. That is, of the two RF signals from the third mixer 111, the 8 GHz RF signal is removed, and only the 10 GHz RF signal is output to the fourth coupler 117.

  The RF signal input to the fourth coupler 117 is branched into two RF signals with a predetermined branching ratio, one RF signal is output to the outside as the output signal 12, and the other RF signal is the fourth mixer. 112 is output.

  Next, the RF signal from the fourth coupler 117 and the RF signal from the third coupler 114 input to the fourth mixer 112 are mixed, and two signals having the sum frequency and the difference frequency of these two RF signals are mixed. An RF signal is generated and output to the bandpass filter 113.

  That is, a 10 GHz RF signal from the fourth coupler 117 and a 9 GHz RF signal from the third coupler 114 are mixed, and a 19 GHz RF signal having the sum frequency of these two RF signals and a 1 GHz having a difference frequency. RF signal is generated.

  As described above, only the 1 GHz signal included in the pass band is passed through the two RF signals input to the band pass filter 113 from the fourth mixer 112 and output to the optical modulator 2.

  Here, the RF signal from the bandpass filter 113 is input again to the optical modulator 2 to constitute a feedback circuit. In this feedback circuit, the high-frequency oscillator starts to oscillate at a frequency of 10 GHz by setting the feedback gain so as to be larger than the loss of the entire circuit.

  Here, it is assumed that the oscillation frequency setting value of the frequency variable oscillator 115 is changed from 9 GHz to 10 GHz. In this case, an RF signal of 10 GHz is generated from the frequency variable oscillator 115 and output to the third coupler 114. The RF signal input to the third coupler 114 is branched into two RF signals with a predetermined branching ratio and output to the third mixer 111 and the fourth mixer 112, respectively.

  Subsequently, the RF signal from the O / E converter 4 input to the third mixer 111 and the RF signal from the third coupler 114 are mixed and have a sum frequency and a difference frequency of these two RF signals. Two RF signals are generated and output to the filter 116. Here, as shown in FIG. 18, since the RF signal from the O / E converter 4 passes through the bandpass filter 113, it may be considered that only a signal in the vicinity of 1 GHz is included.

  That is, in the third mixer 111, the 1 GHz RF signal from the O / E converter 4 and the 10 GHz RF signal from the third coupler 114 are mixed, and the 11 GHz RF signal having the sum frequency of these two RF signals is mixed. A signal and a 9 GHz RF signal having a difference frequency are generated.

  Of the two RF signals from the third mixer 111 input to the filter 116, only the 11 GHz signal included in the pass band is passed and output to the fourth coupler 117. That is, the 9 GHz RF signal is removed from the two RF signals from the third mixer 111, and only the 11 GHz RF signal is output to the fourth coupler 117.

  The RF signal input to the fourth coupler 117 is branched into two RF signals with a predetermined branching ratio, one RF signal is output to the outside as the output signal 12, and the other RF signal is the fourth mixer. 112 is output.

  Next, the RF signal from the fourth coupler 117 and the RF signal from the third coupler 114 input to the fourth mixer 112 are mixed, and two signals having the sum frequency and the difference frequency of these two RF signals are mixed. An RF signal is generated and output to the bandpass filter 113. That is, the 11 GHz RF signal from the fourth coupler 117 and the 10 GHz RF signal from the third coupler 114 are mixed, and a 21 GHz RF signal having the sum frequency of these two RF signals and a 1 GHz having a difference frequency. RF signal is generated.

  As described above, only the 1 GHz signal included in the pass band is passed through the two RF signals input to the band pass filter 113 from the fourth mixer 112 and output to the optical modulator 2.

  Here, the RF signal from the bandpass filter 113 is input again to the optical modulator 2 to constitute a feedback circuit. In this feedback circuit, the high-frequency oscillator starts to oscillate at a frequency of 11 GHz by setting the feedback gain so as to be larger than the loss of the entire circuit.

  Therefore, similarly to the first embodiment described above, the oscillation frequency can be varied without using a delay device or a variable bandpass filter. This has the effect of reducing the size and cost compared to the conventional one.

  Further, as compared with the prior art, the frequency variable amount can be increased while the fiber length is set to a large value, and there is an effect that both phase noise reduction and frequency variable amount increase can be achieved.

  However, the above-described effect is obtained because the variable range of the oscillation frequency is within the usable frequency of the third mixer 111, the fourth mixer 112, and the fourth coupler 117, and the third coupler corresponding to the variable range of the oscillation frequency. The pass signal frequency range of 114 is limited to be within the usable frequency range of the third coupler 114.

  In the fourth embodiment, an image rejection mixer 111 b may be used as the third mixer 111. FIG. 19 is a second block diagram showing the high-frequency oscillator according to the fourth embodiment of the present invention. For example, instead of the third mixer 111, an image rejection mixer 111b in which only an RF signal having a sum frequency of two input RF signals is generated and an RF signal having a difference frequency is suppressed is used. This mixer also has the function of the filter 116.

  For this reason, as shown in FIG. 19, by using an image rejection mixer 111 b instead of the third mixer 111, the same effect as described above can be obtained without using the filter 116. Thereby, compared with the case where the filter 116 is used, an effect that the cost is reduced and the size is reduced can be obtained.

  As described above, according to the fourth embodiment, as in the first embodiment, a high-frequency oscillator that can vary the oscillation frequency without using a delay device or a variable bandpass filter can be realized, and phase noise can be reduced. It is possible to achieve both increased frequency variable amount.

  In the first to fourth embodiments described above, the bandpass filters 7 and 113 are used as the bandpass means. However, since the oscillation frequency is limited by components having frequency selectivity in the oscillation feedback circuit, the bandpass filter is used. The filters 7 and 113 are not necessarily used.

  Further, in the present invention, within the scope of the invention, a free combination of each embodiment, a modification of an arbitrary component of each embodiment, or an omission of any component in each embodiment is possible. is there.

  DESCRIPTION OF SYMBOLS 1 Laser light source (light generation means), 2 Optical modulator (light modulation means), 3 Optical fiber, 4 O / E converter (1st photoelectric conversion means), 5 Mixer (1st signal mixing means), 6 Mixer (Second signal mixing means), 6b image rejection mixer (second signal mixing means), 7 bandpass filter (first bandpass means), 8 coupler (first branching means), 9 frequency variable oscillator (signal) (Output means), 10 filter (first signal selection means), 11 coupler (second branch means), 12 output signal, 21 amplifier (electric signal amplification means), 22 optical amplifier (optical signal amplification means), 31 coupler (branch) Means), 41 phase shifter (electric signal phase adjusting means), 51 coupler (branching means), 61 optical delay device (second optical path length adjusting means), 71 coupler (branching means), 81 amplifier (electric signal amplifying means) ), 91 E / O converter (electrical / optical conversion means), 92 optical fiber, 93 O / E converter (second optical / electrical conversion means), 94 phase shifter (electrical signal phase adjusting means), 95 optical delay device (First optical path length adjusting means), 96 optical modulator, 97 optical coupler (first optical branching means), 101 negative group delay time generating means (passing time adjusting means), 111 mixer (first signal mixing means), 111b Image rejection mixer (first signal mixing means), 112 mixer (second signal mixing means), 113 bandpass filter (second bandpass means), 114 coupler (first branching means), 115 frequency variable oscillator (Signal output means), 116 filter (second signal selection means), 117 coupler (second branch means), 210 control section (signal output frequency control means), 211 crystal oscillator, 212 Frequency divider, 213 PLL circuit, 214 loop filter, 220 phase shifter control unit (electric signal phase adjustment amount control means), 221 crystal oscillator, 222 frequency divider, 223 PLL circuit, 224 loop filter, 230 Optical delay device control (Second optical path length adjustment amount control means), 231 crystal oscillator, 232 frequency divider, 233 optical delay device applied voltage control means, 234 loop filter.

Claims (22)

An optical transmission system that transmits an optical signal, and an electrical transmission system that transmits an electrical signal,
After the signal from the optical transmission system passes through the electrical transmission system, a feedback circuit is configured by being input again as a feedback signal to the optical transmission system, and oscillation starts with the first electrical signal that is a high-frequency signal, A high-frequency oscillator that outputs the first electrical signal,
The optical transmission system is
Light generating means for generating the laser light;
Optical modulation means for modulating the laser light according to a high frequency signal from the electric transmission system and outputting the modulated laser light,
A first photoelectric conversion means for converting the modulated laser light from an optical signal to a high-frequency signal that is an electrical signal;
The electrical transmission system is
Signal output means for outputting a second electrical signal which is a high-frequency signal;
First branching means for branching the high-frequency signal from the signal output means into two;
First signal mixing means for mixing the high-frequency signal converted by the first photoelectric conversion means and one of the second electric signals branched by the first branching means;
A second signal for generating a high-frequency signal including a signal component of the feedback signal by mixing the high-frequency signal from the first signal mixing unit and the other of the second electric signals branched by the first branching unit. Mixing means;
Branching the first electrical signal into two and outputting one to the outside; and
The signal output means varies the frequency of the first electric signal by varying the frequency of the second electric signal. The high frequency oscillator according to claim 1,
The electrical transmission system further includes first band passing means for passing a predetermined band including a third electrical signal between the first signal mixing means and the second signal mixing means, and the third electrical signal The frequency is a difference frequency between the high-frequency signal converted by the first photoelectric conversion means and the second electric signal. The high frequency oscillator according to claim 2,
The electric transmission system outputs a fourth electric signal having a sum frequency of two mixed high frequency signals output from the second signal mixing means and a fifth electric signal having a difference frequency between the two mixed high frequency signals. A high-frequency oscillator characterized by further comprising first signal selection means having a function of passing the fourth electric signal out of the signal and suppressing the fifth electric signal. The high frequency oscillator according to claim 2,
The second signal mixing means outputs a fourth electric signal having the sum frequency of the two mixed high-frequency signals and suppresses a fifth electric signal having a difference frequency between the two mixed high-frequency signals. A high frequency oscillator characterized by being a mixer. The high frequency oscillator according to any one of claims 2 to 4,
The electrical transmission system includes the first branching unit and the first signal mixing unit, the first signal mixing unit and the first band passing unit, the first band passing unit and the second signal. A high-frequency oscillator characterized by further comprising a passage time adjusting means for adjusting a passage time delay at least at one place between the mixing means and between the first branching means and the second signal mixing means. The high frequency oscillator according to claim 5,
The transit time adjusting means is
Electro-optical conversion means for outputting as modulated laser light in response to a high-frequency signal from the first branching means;
A high frequency oscillator comprising: a second photoelectric conversion means for converting the modulated laser light from the electrical light conversion means into a high frequency signal which is an electrical signal from an optical signal. The high frequency oscillator according to claim 6,
The transit time adjusting unit further includes a first optical path length adjusting unit that adjusts an optical path length of an optical signal to be transmitted on a path from the electro-optical conversion unit to the second photoelectric conversion unit. High frequency oscillator. The high frequency oscillator according to claim 6 or 7,
The high-frequency oscillator, wherein the transit time adjusting means includes the electro-optic converting means and the second opto-electric converting means being connected to each other by an optical fiber. The high frequency oscillator according to any one of claims 6 to 8,
The optical transmission system branches a laser beam from the light generation means, outputs one to the light modulation means, and outputs the other to the second photoelectric conversion means in the transit time adjusting means. Further comprising means,
The transit time adjusting means in the electrical transmission system modulates the intensity of the laser branched by the first optical branching means according to a high frequency signal from the first branching means, and outputs the modulated laser light. A high-frequency oscillator comprising an optical modulator instead of the electro-optical conversion means. The high frequency oscillator according to claim 5,
The high-frequency oscillator, wherein the transit time adjusting means is means for generating a negative group delay time at a specific frequency. The high frequency oscillator according to claim 1,
The electrical transmission system includes a predetermined band including a sixth electrical signal between the first photoelectric conversion unit and the first signal mixing unit or between the second signal mixing unit and the optical modulation unit. The high-frequency oscillator further includes a second band-pass means for passing the signal, wherein the frequency of the sixth electric signal is a difference frequency between the first electric signal and the second electric signal. The high frequency oscillator according to claim 11,
The electric transmission system outputs a seventh electric signal having a sum frequency of two mixed high frequency signals output from the first signal mixing means and an eighth electric signal having a difference frequency between the two mixed high frequency signals. A high-frequency oscillator characterized by further comprising second signal selection means having a function of passing the seventh electric signal and suppressing the eighth electric signal among the signals. The high frequency oscillator according to claim 11,
The first signal mixing means passes through the seventh electric signal among a seventh electric signal having a sum frequency of the two mixed high frequency signals and an eighth electric signal having a difference frequency between the two mixed high frequency signals. And an image rejection mixer having a function of suppressing the eighth electric signal. The high frequency oscillator according to any one of claims 1 to 13,
In the optical transmission system, at least one point between the light generation unit and the light modulation unit and between the light modulation unit and the first photoelectric conversion unit is connected to each other by an optical fiber. A high-frequency oscillator characterized by The high frequency oscillator according to any one of claims 1 to 14,
The electric transmission system further includes at least one electric signal amplifying means in an electric signal transmission path. The high frequency oscillator according to any one of claims 1 to 15,
The optical transmission system further includes at least one optical signal amplifying means in an optical signal transmission path. The high-frequency oscillator according to any one of claims 1 to 16,
The electrical transmission system further includes signal output frequency control means for controlling the frequency of the high frequency signal output from the signal output means. The high frequency oscillator according to any one of claims 1 to 17,
The electric transmission system further includes an electric signal phase adjusting means for changing at least one phase in an electric signal transmission path. The high frequency oscillator according to claim 18,
The electrical transmission system further includes electrical signal phase adjustment amount control means for controlling the operation of the electrical signal phase adjustment means. The high frequency oscillator according to any one of claims 1 to 19,
The optical transmission system further includes second optical path length adjusting means for adjusting an optical path length of the laser light modulated by the optical modulation means in an optical signal transmission path. The high frequency oscillator according to claim 20,
The optical transmission system further includes second optical path length adjustment amount control means for controlling the operation of the second optical path length adjustment means. An optical transmission system that transmits an optical signal, and an electrical transmission system that transmits an electrical signal,
After the signal from the optical transmission system passes through the electrical transmission system, a feedback circuit is configured by being input again as a feedback signal to the optical transmission system, and oscillation starts with the first electrical signal that is a high-frequency signal, A method of varying an oscillation frequency of a high-frequency oscillator that outputs the first electric signal,
In the optical transmission system,
A light generating step for generating the laser light;
A light modulation step of modulating the laser light according to a high-frequency signal from the electrical transmission system and outputting the modulated laser light;
A first photoelectric conversion step of converting the modulated laser beam from an optical signal into a high-frequency signal that is an electrical signal;
In the electric transmission system,
A signal output step of outputting a second electric signal which is a high-frequency signal;
A first branching step for branching the high-frequency signal output in the signal output step into two;
A first signal mixing step of mixing the high-frequency signal converted in the first photoelectric conversion step and one of the second electric signals branched in the first branching step;
A high-frequency signal including a signal component of the feedback signal is generated by mixing the high-frequency signal mixed in the first signal mixing step and the other of the second electric signal branched in the first branching step. A two-signal mixing step;
A second branching step of branching the first electrical signal into two and outputting one to the outside,
In the signal output step, the frequency of the first electrical signal is varied by varying the frequency of the second electrical signal.

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