JP2012088554A - High frequency oscillator and high frequency oscillation method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a high frequency oscillator with less phase noise.SOLUTION: The high frequency oscillator includes: a light source; optical modulation means; first optical transmission means; a photoelectric transducer; signal generation means for generating an electric signal; first branching means for branching the electric signal; a first mixer for mixing one of branched electric signals and an electric signal from the photoelectric transducer; a band-pass filter which allows an electric signal generated by the first mixer and having a difference frequency to pass therethrough; a second mixer which mixes the electric signal passing through the band-pass filter and the other of electric signals branched by the first branching means to generate an electric signal with which light is modulated by the optical modulation means; second branching means which branches a part of the first electric signal or the second electric signal to output a branched electric signal as an output signal; and passage time adjustment means which adjusts the passage time of one of the third electric signals, the other of the third electric signals, or the fourth electric signal.

Description

  The present invention relates to a high-frequency oscillator and a high-frequency oscillation method that oscillate a high-frequency signal such as a millimeter wave or a microwave using, for example, laser light.

  As a conventional high-frequency oscillator, for example, there is one disclosed in Patent Document 1. The high-frequency oscillator includes an optical transmission system that transmits an optical signal and an electrical transmission system that transmits an electrical signal. The optical transmission system includes a laser light source, an optical modulator, and a photoelectric converter. The electrical transmission system includes an oscillator (local oscillator), a first coupler, a first mixer, a bandpass filter, a second mixer, a signal selection unit, and a second coupler. Yes. In the optical transmission system, the laser light from the laser light source is intensity-modulated at the first frequency in the optical modulator. The intensity-modulated laser light is converted into an electric signal by a photoelectric converter. On the other hand, in the electric transmission system, a high-frequency signal from a local oscillator having a second frequency different from the first frequency is branched into two by a first coupler. The first mixer mixes the high-frequency signal from the photoelectric converter and one high-frequency signal from the first coupler to generate two high-frequency signals. The band-pass filter passes only signal components included in a predetermined pass band having the third frequency as the center frequency from the two high-frequency signals from the first mixer. The second mixer mixes the other high-frequency signal from the band-pass filter and the first coupler to generate two high-frequency signals. The signal selection means selects and passes one of the two high-frequency signals. The second coupler branches the high-frequency signal from the signal selection means into two, outputs one to the outside as a high-frequency signal having the first frequency, and outputs the other to the optical modulator. Here, the third frequency is set to a frequency lower than the first frequency output from the high-frequency oscillator.

  In this high-frequency oscillator, a high-frequency signal from an optical transmission system is down-converted by a first mixer, then passed through a bandpass filter, and up-converted again to the same frequency as an input signal from the optical transmission system by a second mixer. Thus, it is possible to use a bandpass filter having a center frequency lower than the oscillation frequency, thereby effectively suppressing spurious. (Hereinafter, this operation method is referred to as a down-up conversion method.)

JP 2009-157044 A

  In the conventional high-frequency oscillator described in Patent Document 1, spurious is effectively suppressed by the configuration using the down-up conversion method. However, since the passage time in the optical transmission system is large, the passage time in the band-pass filter arranged between the mixers is also large, so that the high-frequency signal from the local oscillator having the second frequency is the first mixer. There is a large time difference between the timing of mixing in the second mixer and the timing of mixing in the second mixer. As a result, the high-frequency signal output from the second mixer is strongly affected by the phase noise of the local oscillator having the second frequency.

  The present invention has been made to solve the above-described problems. The time required for the high-frequency signal to pass through the band-pass filter disposed between the mixers and the high-frequency signal from the local oscillator are the second. By adjusting the time difference between the time to reach the mixer and the time to reach the first mixer, the superposition of the phase noise of the local oscillator on the output signal is suppressed, and a high-frequency oscillator with lower phase noise is provided. Objective.

The high-frequency oscillator according to the present invention is
A light source that generates light;
Light modulating means for modulating light generated by the light source with a first electrical signal;
First light transmission means for transmitting light modulated by the light modulation means;
A photoelectric converter that converts the light transmitted by the first optical transmission means into a second electrical signal;
Signal generating means for generating a third electrical signal;
First branching means for branching the third electrical signal generated by the signal generating means into two;
A difference frequency between one of the third electric signals and the second electric signal is obtained by mixing one of the third electric signals branched by the first branching means and the second electric signal. A first mixer for generating a fourth electrical signal having;
A bandpass filter for passing a fourth electrical signal having the difference frequency generated by the first mixer;
By mixing the fourth electric signal that has passed through the band-pass filter and the other of the third electric signal branched by the first branching means, the second electric signal has the same frequency as the second electric signal. A second mixer for generating the first electrical signal that modulates light by a light modulation means;
A second branching unit for branching a part of the first electrical signal or the second electrical signal and outputting the branched electrical signal as an output signal;
Transit time adjusting means for adjusting the transit time of one of the third electrical signals, the other of the third electrical signals, and the fourth electrical signal;
It is characterized by comprising.

  The high-frequency oscillator according to the present invention is effective in obtaining an output signal with little phase noise.

It is a block diagram which shows the structure of the high frequency oscillator which concerns on Embodiment 1 of this invention. It is a block diagram which shows the structure of the high frequency oscillator which concerns on Embodiment 2 of this invention. It is a block diagram which shows the structure of the high frequency oscillator which concerns on Embodiment 3 of this invention. It is a block diagram which shows the structure of the high frequency oscillator which concerns on Embodiment 4 of this invention. It is a block diagram which shows the structure of the high frequency oscillator which concerns on Embodiment 5 of this invention.

  Hereinafter, preferred embodiments of the high-frequency oscillator of the present invention will be described with reference to the drawings. In addition, the same code | symbol is attached | subjected and demonstrated about the member or site | part which is the same or corresponds in each figure.

Embodiment 1 FIG.
1 is a block diagram showing a configuration of a high-frequency oscillator according to Embodiment 1 of the present invention. In FIG. 1, 1 is a high-frequency oscillator, 2 is an optical transmission system, 21 is a laser light source that is a light source, 22 is an optical modulator that is optical modulation means, and 23 is a first optical fiber that is first optical transmission means, 24 is a photoelectric converter, 3 is an electric transmission system, 31 is a local oscillator as signal generating means, 32 is a first coupler as first branching means, 33 is a first mixer, 34 is a second mixer, 35 is a band pass filter, 36 is a filter, 37 is a high frequency amplifier, 38 is a second coupler as second branch means, 4 is a transit time adjusting means, 41 is an E / O (Electrical / Optical) converter, 42 Is a second optical fiber as second optical transmission means, 43 is an O / E (Optical / Electrical) converter, and 5 is an output signal.
As shown in FIG. 1, the high-frequency oscillator 1 according to Embodiment 1 of the present invention includes an optical transmission system 2 that transmits an optical signal and an electrical transmission system 3 that transmits an electrical signal, and the oscillation frequency is the first. A high frequency signal (output signal 5) having a frequency of 1 is output.

  The optical transmission system 2 includes a laser light source 21, an optical modulator 22, a first optical fiber 23, and a photoelectric converter 24. The electric transmission system 3 includes a local oscillator 31, a first coupler 32, a first mixer 33, a second mixer 34, a bandpass filter 35, a filter 36, a high frequency amplifier 37, a second amplifier. The coupler 38 is provided, and an E / O converter 41, a second optical fiber 42, and an O / E are provided between the first coupler 32 and the second mixer 34 as the transit time adjusting means 4. And a converter 43.

Next, the operation of the high-frequency oscillator according to Embodiment 1 of the present invention will be described with reference to FIG.
First, in the optical transmission system 2, laser light from the laser light source 21 is input to the optical modulator 22. Here, the wavelength of the laser light is in the 1.5 μm band, but laser light in other wavelength bands can also be used. Further, instead of laser light using the laser light source 21, for example, emitted light generated from an LED (Light Emitting Diode) may be used, and light generated using various light sources can be used. The laser light input to the optical modulator 22 is intensity-modulated according to the first electric signal input from the second coupler 38. This electric signal becomes an electric signal having the first frequency f ₀ after the high frequency oscillator 1 oscillates in a steady state. Here, the first frequency f ₀ is set to 10 GHz. The laser light whose intensity is modulated by the optical modulator 22 is output to the first optical fiber 23. The modulated optical signal transmitted by the first optical fiber 23 is input to the photoelectric converter 24. The photoelectric converter 24 converts the modulated optical signal into a second electric signal by direct detection and outputs the second electric signal to the first mixer 33 of the electric transmission system 3. The second electric signal has the first frequency f ₀ like the first electric signal.

  Note that it is not always necessary to separately provide the optical modulator 22 outside the laser light source 21, and a direct modulation type laser light source in which the light source and the light modulation means are integrated may be used.

On the other hand, the local oscillator 31 of the electric transmission system 3 generates a third electric signal and outputs it to the first coupler 32. Frequency of the third electrical signal is a second frequency f _1. Here, 9 GHz is selected as the second frequency f ₁ . The first coupler 32 splits the third electrical signal from the local oscillator 31 into two branches, and outputs each electrical signal to the second mixer 34 via the first mixer 33 and the transit time adjusting means 4. To do.
The first mixer 33 mixes the second electrical signal from the photoelectric converter 24 and one of the third electrical signals from the first coupler 32 to generate a fourth electrical signal. The fourth electric signal has two frequency components having a sum frequency and a difference frequency of the second electric signal and the third electric signal to be mixed. The first mixer 33 outputs this fourth electric signal to the band pass filter 35. The band pass filter 35 has a preset pass band whose center frequency is a third frequency f ₂ = f ₀ −f ₁ (when f ₀ > f ₁ ), which is a frequency lower than the first frequency f _0. Only the signal component included in the signal is passed through and output to the second mixer 34. Here, since the first frequency f ₀ is 10 GHz and the second frequency f ₁ is 9 GHz, the third frequency f ₂ is 1 GHz.

The second mixer 34 mixes the fourth electrical signal that has passed through the bandpass filter 35 and the other of the third electrical signal that has arrived from the first coupler 32 via the transit time adjusting means 4, and 1 electrical signal is generated. This first electric signal includes two frequency components, a sum frequency (f ₀ ) and a difference frequency (| f ₂ −f ₁ |). Here, the sum frequency is 10 GHz and the difference frequency is 8 GHz. The second mixer 34 outputs this first electric signal to the filter 36. In the filter 36, the other frequency component (image signal) other than the first frequency f ₀ is removed from the two input frequency components, and only the electric signal of the first frequency f ₀ is the high frequency amplifier 37. Is output. Here, the 8 GHz image signal is removed and a 10 GHz signal is output. This signal has the same frequency as the second electric signal input to the first mixer 33. The high frequency amplifier 37 amplifies the input first electric signal with a predetermined gain and outputs it to the second coupler 38.

The first electric signal input to the second coupler 38 is branched into two at a predetermined branching ratio, one of the branched electric signals is output to the outside as an output signal 5, and the other branched electric signal is It is output to the optical modulator 22.
Here, the first electric signal branched by the second coupler 38 is input again to the optical modulator 22, thereby forming a feedback circuit. By setting the feedback gain to be larger than the loss of the entire feedback circuit, the high-frequency oscillator 1 oscillates at the first frequency f ₀ of 10 GHz in the steady state.

  The high-frequency oscillator 1 of the first embodiment uses the first optical fiber 23 as a part of the feedback circuit, and the transmission loss is very small. For example, 1.5 μm band optical fibers with a transmission loss of about 0.2 dB / km are commercially available. This is a very excellent characteristic as compared with coaxial cables and waveguides which are typical electric wire cables. For this reason, the transmission path of the feedback circuit can be extended without increasing the transmission loss by increasing the length of the first optical fiber 23. In the high-frequency oscillator 1, by increasing the length of the feedback circuit, the Q value of the oscillation is increased, and the phase noise is reduced as compared with the high-frequency oscillator in which the feedback circuit is configured using only the normal electric transmission system 3. That is, the longer the length of the first optical fiber 23, the lower the phase noise characteristic.

On the other hand, the frequency interval (hereinafter referred to as a mode) that can be oscillated by the high-frequency oscillator 1 is inversely proportional to the length of the optical fiber, and the mode interval becomes narrower as the first optical fiber 23 becomes longer. Therefore, in order to suppress spurious which is an unnecessary mode, a filter for attenuating modes other than the oscillation frequency f ₀ which is the first frequency is required in the feedback circuit. Here, the second electric signal from the photoelectric converter 24 is down-converted by the first mixer 33 and frequency-converted into a fourth electric signal, and then passed through the band-pass filter 35, and then by the second mixer 34. A down-up conversion method is used in which up-conversion is performed again to a first electric signal having the same frequency as the output from the photoelectric converter 24. Therefore, it is possible to use a band-pass filter 35 having a center frequency of the second frequency f ₂ lower than the oscillation frequency f ₀ is the first frequency f _0, in the case of not using the down-up-conversion scheme In comparison, the specific bandwidth required for the bandpass filter 35 can be increased.

However, there is no change in the bandwidth itself required for the bandpass filter regardless of whether the down-up conversion method is applied. For example, when the fiber length of the first optical fiber 23 is increased to 1 km in order to reduce the phase noise, the oscillation loop delay time is about 5 μs when the refractive index of the optical fiber material is 1.5. The mode interval is about 200 kHz which is the reciprocal of the delay time. In this high-frequency oscillator, it is necessary to oscillate only one mode by selecting one mode with the band-pass filter 35. Therefore, the band-pass filter 35 requires a small value on the order of kHz. Since the pass time of the bandpass filter is generally close to the reciprocal of the bandwidth, the pass time τ ₁ is considered to be on the order of μs.

Here, the influence of the passage time τ ₁ in the band-pass filter 35 and the phase noise of the local oscillator 31 on the phase noise of the high-frequency oscillator 1 will be described.
Assuming that a sine wave high-frequency signal that is a second electric signal input from the photoelectric converter 24 to the first mixer 33 is s ₀ (t), s ₀ (t) is expressed by the following equation (1). .

s ₀ (t) = sin [ω ₀ t + φ ₀ (t)] (1)

Here, ω ₀ represents the oscillation angular frequency of the high-frequency oscillator 1, and φ ₀ (t) represents the phase noise of the high-frequency oscillator 1. On the other hand, assuming that a high frequency signal that is one of the third electric signals from the local oscillator 31 and input to the first mixer 33 is _sl (t), _sl (t) is expressed by the following equation (2). Is done.

s _l (t) = sin [ω _l t + φ _l (t)] (2)

Here, ω _l indicates the oscillation angular frequency of the local oscillator 31, and φ _l (t) indicates the phase noise of the local oscillator 31. Assuming that the output signal of the difference frequency component from the first mixer 33 is s _1m (t) according to equations (1) and (2), s _1m (t) is expressed by the following equation (3).

s _1m (t) = sin [(ω ₀ -ω _l ) t + φ ₀ (t) -φ _l (t)] (3)

Here, τ _{1 is} the time for the high-frequency signal to pass through the band-pass filter 35 disposed between the first and second mixers, and the time for the high-frequency signal to reach the second mixer 34 from the local oscillator 31 is Assuming that the difference from the time to reach the first mixer 33 is τ ₂ , the output signal from the second mixer 34 is s _2m (t) by considering in the same manner as in the equations (1) to (3). s _2m (t) is expressed by the following equation (4).

s _2m (t) = sin [ω ₀ (t + τ ₁ ) + ω _l (τ ₂ -τ ₁ ) + φ ₀ (t + τ ₁ ) + φ _l (t + τ ₂ ) -φ _l (t + τ ₁ )]
... (4)

Here, if τ ₁ = τ ₂ in equation (4), equation (4) can be expressed as equation (5).

s _2m (t) = sin [ω ₀ (t + τ ₁ ) + φ ₀ (t + τ ₁ )] (5)

In the equation (5), it can be seen that all the terms due to the phase noise of the local oscillator 31 are canceled. Therefore, by setting τ ₁ = τ ₂ , that is, by generating the same delay as the passing time of the band pass filter 35 between the mixers between the first coupler 32 and the second mixer 34, the local oscillator The influence of the 31 phase noise can be canceled.

Even if τ ₁ and τ ₂ do not completely match, by making τ ₁ and τ ₂ close to each other, the influence of the phase noise of the local oscillator 31 is reduced in the frequency band corresponding to the difference. be able to.

Since the high-frequency oscillator having the optical transmission system can increase the length of the feedback circuit and the oscillation Q value is large, very low phase noise can be realized if the phase noise of the local oscillator 31 is not superimposed. However, when the passing time is not adjusted in the down-up conversion method, the phase noise of the local oscillator 31 is superimposed on the output signal. For this reason, the phase noise of the output signal is likely to be dominated by the noise component of the local oscillator 31. Although a certain degree of improvement can be expected by using the local oscillator 31 having a low phase noise, it is difficult to completely cancel the phase noise. Such a low phase noise local oscillator 31 is very expensive. In the high frequency oscillator 1, by setting τ ₁ and τ ₂ to the same value, the influence of the phase noise of the local oscillator 31 can be suppressed, and a high frequency oscillator with low phase noise can be obtained.

In the high frequency oscillator 1, the other of the third electric signals output from the first coupler 32 to the second mixer 34 is input to the passage time adjusting unit 4. Then, the E / O converter 41 included in the transit time adjusting unit 4 converts the electrical signal into an optical signal and outputs it to the second optical fiber 42. Here, the E / O converter 41 may be a combination of a laser light source and an optical modulator, or may be a direct modulation type laser light source, and an optical signal obtained by modulating an electric signal with the electric signal. Anything can be used as long as it is converted to. The second optical fiber 42 is set to have a fiber length such that the passage time τ ₁ generated by the bandpass filter 35 and the passage time τ ₂ generated by the passage time adjusting means 4 are the same. The optical signal transmitted through the second optical fiber 42 is converted from an optical signal to an electrical signal by the O / E converter 43, and as a high-frequency signal having a transit time equivalent to the transit time τ ₁ generated by the bandpass filter 35, It is output to the second mixer 34.

Here, for example, a coaxial cable or a delay element may be used as the transit time adjusting means 4 of the high frequency oscillator 1. However, the passing time τ ₁ in the band pass filter 35 of the high frequency oscillator 1 is on the order of μs as described above. The distance traveled by electromagnetic waves in the order of μs is equivalent to several hundred meters, and transmission loss becomes very large when the distance is transmitted by a coaxial cable. Moreover, since the coaxial cable has a large diameter and is not excellent in flexibility, a huge arrangement space is required.

  In response to the above problem, the transit time adjusting means 4 of the high-frequency oscillator 1 transmits in the low-loss optical fiber to generate the transit time. Therefore, even if there is a delay of the order of μs, it is transmitted with almost no loss. Can be made. In addition, since the optical fiber is light and excellent in flexibility, it leads to a reduction in size and weight of the apparatus. In addition, the optical fiber is generally broadband with respect to the coaxial cable, and is hardly affected by the high frequency of the local oscillator 31. Furthermore, by using an optical fiber that suppresses the expansion and contraction of the fiber due to a change in the external environment, the passage time can be stabilized. As described above, a coaxial cable, a delay element, or the like can be used for the transit time adjusting means 4, but by using an optical fiber, it is possible to obtain a high-frequency oscillator 1 that is smaller and can easily cope with a high frequency.

  As described above, the high-frequency oscillator 1 according to the first embodiment of the present invention includes the first mixer 33 and the second mixer in order to suppress unnecessary spurious generated as the first optical fiber 23 becomes longer. The E / O converter 41 provided between the first coupler 32 and the second mixer 34 with respect to the passage time of μs order generated in the bandpass filter 35 inserted between The passage time adjusting means 4 including the optical fiber 42 and the O / E converter 43 adjusts the other passage time of the third electric signal, compensates for the passage time of the bandpass filter 35, and performs the same passage. Since time is generated, the influence of the phase noise of the local oscillator 31 generated on the output signal can be canceled, and a high-frequency oscillator with low phase noise can be obtained.

  In the present embodiment, the E / O converter 41, the second optical fiber 42, and the O / E converter 43 are used as the transit time adjusting means 4, but the present invention is not limited to this. Not only this but all the circuits etc. which can adjust the other passage time of the 3rd electric signal can be used.

In the present embodiment, the second coupler 38 is inserted between the high-frequency amplifier 37 and the optical modulator 22 and the output signal 5 is extracted. However, the present invention is not limited to this. The coupler 38 can be inserted anywhere between the second mixer 34 and the optical modulator 22. Further, it can be inserted between the photoelectric converter 24 and the first mixer 33. A high frequency signal having the first frequency f ₀ is transmitted in common to these portions, and the output signal 5 having the first frequency f ₀ can be extracted with low phase noise.

Furthermore, in the present embodiment, the case where the second frequency f ₁ that is the frequency of the third electric signal generated by the local oscillator 31 is made lower than the first frequency f ₀ that is the oscillation frequency of the high-frequency oscillator. It has been described, not only limited to this but also the second frequency f ₁ higher than the first frequency f _0. For example, f ₀ can be 10 GHz and f ₁ can be 11 GHz. The third frequency _{f 2} in the case _f 1 -f ₀ becomes again the 1 GHz. By using a band-pass filter 35 to the f ₂ as the center frequency, it is possible to remove the spurious is likewise unnecessary mode. The second mixer 34 generates a high-frequency signal having a sum frequency of 12 GHz and a difference frequency of 10 GHz. By selecting a high-frequency signal having a difference frequency of 10 GHz by the filter 36, the high-frequency oscillator is similarly connected to the first frequency f. Oscillation can be performed at ₀ , and the effect of this embodiment can be obtained in the same manner.

Embodiment 2. FIG.
FIG. 2 is a block diagram showing the configuration of the high-frequency oscillator according to Embodiment 2 of the present invention. In FIG. 2, 34b is an image rejection mixer which is a mixer for suppressing an image signal which is an unnecessary signal among the sum frequency signal and the difference frequency signal generated at the output.
The high-frequency oscillator 1 according to the second embodiment of the present invention is different from the high-frequency oscillator 1 according to the first embodiment in that the second mixer 34 of the high-frequency oscillator 1 according to the first embodiment is an image rejection mixer 34b, and the filter 36 is removed. Since other than that is the same as that of Embodiment 1, it attaches | subjects the same code | symbol to the same or corresponding part, and abbreviate | omits description.
The image rejection mixer 34 b of the high-frequency oscillator 1 has the other of the fourth electric signal that has passed through the bandpass filter 35 and the third electric signal that has been transmitted from the first coupler 32 via the passage time adjusting means 4. Are entered. The first electrical signal output from the image rejection mixer 34 b is output to the high frequency amplifier 37.

Next, the operation of the high frequency oscillator 1 according to Embodiment 2 of the present invention will be described.
In the first embodiment, two high-frequency signals input to the second mixer 34 are mixed to generate two high-frequency signals having a sum frequency and a difference frequency, and an image which is one unnecessary high-frequency signal by the filter 36. The signal is being removed. On the other hand, in the second embodiment, one of the sum frequency and difference frequency obtained by mixing is suppressed, and only the signal having the other desired oscillation frequency f ₀ is output. An image rejection mixer 34b is provided. That is, the first role of the filter 36 as a signal selecting means image rejection mixer 34b has both in form, only the image rejection mixer 34b are possible suppression of unwanted image signals other than the oscillation frequency f ₀ .
As described above, the use of the image rejection mixer 34b as the second mixer eliminates the need for the image signal suppression filter 36, so that the high-frequency oscillator 1 can be further reduced in size.

Embodiment 3 FIG.
FIG. 3 is a block diagram showing the configuration of the high-frequency oscillator according to Embodiment 3 of the present invention. In FIG. 3, reference numeral 44 denotes an optical path length varying means, which is a fiber stretcher capable of varying the optical path length of the optical fiber by applying mechanical stress to the optical fiber. Reference numeral 45 denotes a variable delay element that is a circuit element that can change the passage delay time of the electric signal.
The high-frequency oscillator 1 according to the third embodiment of the present invention is different in that a fiber stretcher 44 and a variable delay element 45 are added to the passage time adjusting means 4 of the high-frequency oscillator 1 according to the first embodiment of the present invention. Since the rest is the same, the same or corresponding parts are denoted by the same reference numerals, and the description will be simplified.
In the high frequency oscillator 1 according to the third embodiment, a variable delay element 45 is provided between the first coupler 32 and the E / O converter 41. A fiber stretcher 44 is provided adjacent to the second optical fiber 42 between the E / O converter 41 and the O / E converter 43.

Next, the operation of the high frequency oscillator 1 according to Embodiment 3 of the present invention will be described.
In the first embodiment, the transit time adjusting means 4 includes an E / O converter 41, a second optical fiber 42, and an O / E converter 43, so that the transit time equivalent to that of the bandpass filter 35 is obtained. Is occurring. However, in the first embodiment, since the passage time is adjusted only by the fiber length of the second optical fiber 42, fine adjustment of the passage time is not always easy.

  Therefore, in the high-frequency oscillator 1 according to the third embodiment, the other of the third electrical signals output from the first coupler 32 to the second mixer 34 side is passed through the variable delay element 45 included in the transit time adjusting means 4. Input to the E / O converter 41. The E / O converter 41 converts the electrical signal into a modulated optical signal and outputs it to the second optical fiber 42. The modulated optical signal input to the second optical fiber 42 is output to the O / E converter 43 via the fiber stretcher 44. The O / E converter 43 converts the modulated optical signal into an electric signal and outputs it to the second mixer 34.

  In the above configuration, since the passage time can be finely adjusted by the variable delay element 45 or the fiber stretcher 44, the passage time of the passage time adjusting means 4 can be accurately adjusted to the passage time of the bandpass filter 35. Therefore, it is possible to suppress the superposition of the phase noise of the local oscillator 31 on the output signal 5 in a more nearly complete state. In addition, readjustment can be easily performed when the passage time changes due to a change in the external environment, or when the setting conditions to be used are changed.

  In the third embodiment, it is sufficient that at least one of the variable delay element 45 and the fiber stretcher 44 is provided. In addition, the variable delay element 45 is not necessarily between the first coupler 32 and the E / O converter 41 described above, and between the first coupler 32 and the E / O converter 41, Between the O / E converter 43 and the second mixer 34, between the first coupler 32 and the first mixer 33, between the first mixer 33 and the band pass filter 35, and the band pass filter 35. And at least one location between the second mixer 34 and the second mixer 34. The variable delay element 45 is not limited to a delay element having a positive passage time, and may be a delay element having a negative passage time (group delay time).

  As described above, the transit time adjusting means 4 includes either the fiber stretcher 44, the variable delay element 45, or both, so that the superposition of the phase noise of the local oscillator 31 on the output signal 5 is more nearly complete. It can be suppressed by the state. In addition, it is possible to adjust the change of the passage time with respect to the environmental change or the like, and an effect that a flexible response is possible is obtained.

Embodiment 4 FIG.
4 is a block diagram showing a configuration of a high-frequency oscillator according to Embodiment 4 of the present invention. In FIG. 4, 25 is an optical coupler which is an optical branching means, 46 is a second optical modulator which is an E / O converter, and 6 is a third optical fiber.
The high-frequency oscillator 1 according to the fourth embodiment of the present invention is the same as the high-frequency oscillator 1 according to the first embodiment of the present invention, except that the E / O converter 41 includes only the second optical modulator 46 and the laser light source 21. The optical coupler 25 for branching the laser light from the second optical fiber 25 and the third optical fiber 6 for connecting the optical coupler 25 and the second optical modulator 46 are different, and the others are the same. Corresponding parts are denoted by the same reference numerals, and the description will be simplified.
In the high frequency oscillator 1, an optical coupler 25 that splits the laser light from the laser light source 21 into two branches, and a third laser light that is transmitted to the second optical modulator 46 included in the transit time adjusting means 4. An optical fiber 6 is provided.

Next, the operation of the high-frequency oscillator 1 according to Embodiment 4 of the present invention will be described.
In the first embodiment, since the optical transmission system 2 and the transit time adjusting means 4 are completely independent, when the transit time adjusting means 4 is configured to use an optical fiber, at least two laser light sources are used. Etc. are necessary. Therefore, in the high-frequency oscillator 1 of the fourth embodiment, the laser light from the laser light source 21 is branched into two by the optical coupler 25, one is output to the optical modulator 22, and the other is passed through the third optical fiber 6. This is output to the second optical modulator 46 included in the passage time adjusting means 4. The second optical modulator 46 generates a laser beam input from the third optical fiber 6 according to the other of the third electrical signals generated by the local oscillator 31 and input via the first coupler 32. Modulation is performed, and this modulated optical signal is output to the O / E converter 43 via the second optical fiber 42. In the first embodiment, a light source such as a laser light source is required in the E / O converter 41 of the transit time adjusting means 4. In the transit time adjusting means 4 of the fourth embodiment, the laser light from the laser light source 21 is used. Therefore, the same effects as those of the first embodiment can be obtained without newly providing a laser light source or the like.

  As described above, one laser beam branched by the optical coupler 25 is input to the second optical modulator 46 via the third optical fiber 6, so that the laser light from the laser light source 21 passes through the time adjustment means 4. However, since it can be used, the high-frequency oscillator 1 can be operated with a single laser light source or the like, and the effect that the high-frequency oscillator can be reduced in size, cost, and power consumption can be obtained.

Embodiment 5 FIG.
5 is a block diagram showing a configuration of a high-frequency oscillator according to Embodiment 5 of the present invention. In FIG. 5, 47 is a negative group delay time generating means which is a passage time adjusting means.
In the high-frequency oscillator 1 according to the fifth embodiment of the present invention, the passage time adjusting means 4 of the high-frequency oscillator 1 according to the first embodiment of the present invention is used as the negative group delay time generating means 47, and this passage time adjusting means 4 Is not inserted between the first coupler 32 and the second mixer 34, but between the first coupler 32 and the first mixer 33, and the rest is the same. The same or corresponding parts are denoted by the same reference numerals, and the description will be simplified.
In the high frequency oscillator 1, a negative group delay time generation unit 47 is provided between the first coupler 32 and the first mixer 33.

Next, the operation of the high frequency oscillator 1 according to the fifth embodiment of the present invention will be described.
In the first embodiment, the passage time adjusting means 4 includes an E / O converter 41, a second optical fiber 42, and an O / E converter 43, and the passage time is a positive delay time. . On the other hand, in the fifth embodiment, as the passing time adjusting means 4, a negative delay time generating means 47 for generating a negative group delay time at a specific frequency is provided. Such means can be realized, for example, by generating a negative group delay time in a certain frequency region centered on the resonance frequency by a circuit using series resonance and parallel resonance having a periodic structure.

  The first coupler 32 splits the third electrical signal from the local oscillator 31 into two branches, outputs the other of the branched third electrical signals to the second mixer 34, and splits the third electrical signal. Is output to the negative group delay time generation means 47. The negative group delay time generation means 47 gives one of the third electrical signals a negative delay time equivalent to the positive delay time generated by the bandpass filter 35 that passes later, and outputs it to the first mixer 33. The first mixer 33 mixes one of the third electrical signals having a negative delay time from the negative group delay time generating means 47 and the second electrical signal from the photoelectric converter 24, and these two A high-frequency signal having a sum frequency and a difference frequency of the electric signal is output to the band pass filter 35. The band pass filter 35 passes only the signal component included in a predetermined pass band having the third frequency as the center frequency, and outputs the signal component to the second mixer 34.

At this time, a delay time is generated in the bandpass filter 35, but since a negative delay time corresponding to the delay time of the bandpass filter 35 is given by the negative group delay time generation means 47, these delay times are Canceled. Therefore, the other of the third electrical signals directly input from the first coupler 32 to the second mixer 34, the negative group delay time generating means 47, the first mixer 33, the band pass from the first coupler 32 There is no time difference from the fourth electrical signal that passes through the filter 35 and is input to the second mixer 34. For this reason, the superposition of the phase noise of the local oscillator 31 on the output signal 5 can be canceled, and a high-frequency oscillator with low phase noise can be obtained.
In the first embodiment, the transit time adjusting means 4 is composed of an E / O converter 41, a second optical fiber 42, and an O / E converter 43, and many elements. In the fifth embodiment, since the simple configuration of only the negative group delay time generating means 47 is sufficient, the effect of reducing the size and reducing the power consumption of the high frequency oscillator can be obtained.

  As described above, by giving a negative delay time by the negative group delay time generating means 47, the other one of the third electric signals input directly from the first coupler 32 to the second mixer 34, and the first The time difference of the fourth electrical signal input to the second mixer 34 through the negative group delay time generating means 47, the first mixer 33, and the band pass filter 35 from the coupler 32 can be canceled. A high-frequency oscillator with low phase noise can be obtained. Further, since the transit time adjusting means 4 has a simple configuration, an effect that the high-frequency oscillator can be reduced in size and power consumption can be obtained.

  In the embodiment, the case where the negative group delay time generating means 47 as the passage time adjusting means is inserted between the first coupler 32 and the first mixer 33 is shown, but the present invention is not limited to this. Obviously, the negative group delay time generating means 47 may be inserted either between the first mixer 33 and the bandpass filter 35 or between the bandpass filter 35 and the second mixer 34. In these cases, the same effect can be obtained.

DESCRIPTION OF SYMBOLS 1 High frequency oscillator, 2 Optical transmission system, 21 Laser light source, 22 Optical modulator, 23 1st optical fiber, 24 Photoelectric converter, 25 Optical coupler, 3 Electrical transmission system, 31 Local oscillator, 32 1st coupler, 33 1st mixer, 34 2nd mixer, 34b Image rejection mixer, 35 band pass filter, 36 filter, 37 high frequency amplifier, 38 2nd coupler, 4 transit time adjusting means, 41 E / O converter, 42 1st 2 optical fibers, 43 O / E converter, 44 fiber stretcher, 45 variable delay element, 46 second optical modulator, 47 negative group delay time generating means, 5 output signal, 6 third optical fiber.

Claims (9)

A light source that generates light;
Light modulating means for modulating light generated by the light source with a first electrical signal;
First light transmission means for transmitting light modulated by the light modulation means;
A photoelectric converter that converts the light transmitted by the first optical transmission means into a second electrical signal;
Signal generating means for generating a third electrical signal;
First branching means for branching the third electrical signal generated by the signal generating means into two;
A difference frequency between one of the third electric signals and the second electric signal is obtained by mixing one of the third electric signals branched by the first branching means and the second electric signal. A first mixer for generating a fourth electrical signal having;
A bandpass filter for passing a fourth electrical signal having the difference frequency generated by the first mixer;
By mixing the fourth electric signal that has passed through the band-pass filter and the other of the third electric signal branched by the first branching means, the second electric signal has the same frequency as the second electric signal. A second mixer for generating the first electrical signal that modulates light by a light modulation means;
A second branching unit for branching a part of the first electrical signal or the second electrical signal and outputting the branched electrical signal as an output signal;
Transit time adjusting means for adjusting the transit time of one of the third electrical signals, the other of the third electrical signals, and the fourth electrical signal;
A high-frequency oscillator comprising:   2. The high-frequency oscillator according to claim 1, wherein the passage time adjusting unit compensates a passage time of a fourth electric signal having the difference frequency in the band-pass filter. The transit time adjusting means is
An E / O (Electrical / Optical) converter that outputs light modulated in accordance with the other of the third electric signals branched by the first branching unit;
Second optical transmission means for transmitting light output from the E / O converter;
An O / E (Optical / Electrical) converter that converts the light transmitted by the second optical transmission means into an electrical signal and outputs the converted electrical signal to the second mixer;
The high frequency oscillator according to claim 1, further comprising:   4. The high frequency oscillator according to claim 3, further comprising optical path length varying means for varying an optical path length between the E / O converter and the O / E converter.   5. The high frequency oscillator according to claim 3, wherein the second optical transmission means is an optical fiber.   It comprises light branching means for branching light generated by the light source into two, outputting one of the branched lights to the light modulating means, and outputting the other to the E / O converter. The high frequency oscillator according to any one of claims 3 to 5.   The high frequency oscillator according to claim 1, wherein the second mixer is an image rejection mixer that suppresses an image signal that is an unnecessary signal generated by mixing.   3. The high-frequency oscillator according to claim 1, wherein the transit time adjusting unit gives a negative group delay time to one of the third electric signals or the fourth electric signal. 4. A light generation step for generating light;
A light modulation step of modulating the light generated in the light generation step with a first electrical signal;
An optical transmission step of transmitting the light modulated in the optical modulation step;
A photoelectric conversion step of converting the light transmitted in the light transmission step into a second electrical signal;
A signal generating step for generating a third electrical signal;
A first branching step for branching the third electrical signal generated in the signal generating step into two;
By mixing one of the third electric signals branched in the first branching step with the second electric signal, a difference frequency between one of the third electric signals and the second electric signal is obtained. A first mixing step for generating a fourth electrical signal comprising:
A filtering step of passing a fourth electrical signal having the difference frequency generated in the first mixing step;
The optical modulation having the same frequency as the second electric signal by mixing the fourth electric signal passed in the filtering step and the other of the third electric signal branched in the first branching step A second mixing step for generating the first electrical signal that modulates light in steps;
A second branching step of branching a part of the first electrical signal or the second electrical signal and outputting the branched electrical signal as an output signal;
A transit time adjusting step for adjusting a transit time of one of the third electrical signals, the other of the third electrical signals, and the fourth electrical signal;
A high-frequency oscillation method comprising:

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