JP5137776B2 - High frequency oscillator - Google Patents

Description

  The present invention relates to a high-frequency oscillator that generates high-frequency signals such as millimeter waves and microwaves.

Some high-frequency oscillators that extract millimeter waves and microwaves use an optoelectric oscillator. The optoelectric oscillator modulates the intensity of laser light generated from a laser light source with an optical modulator, converts the modulated laser light into a high-frequency signal, which is an electrical signal, with a photoelectric converter, and bandpasses the converted high-frequency signal. A predetermined passband component is extracted by a filter, and a high-frequency signal having the predetermined passband component is fed back to the optical modulator as a modulation signal (see, for example, Patent Document 1). Therefore, an intensity-modulated laser beam or a photoelectrically converted high-frequency signal can be obtained as the output of the oscillator.
In such an optoelectric oscillator, low-phase noise is realized by extending the distance using an optical fiber or the like in the optical path. However, thermal expansion and contraction of the fiber occurs due to fluctuations in the ambient environmental temperature. There is a problem that the signal frequency fluctuates. As a method for solving this problem, a phase lock loop (hereinafter referred to as “PLL”) is provided in the feedback path to the optical modulator, and the phase of the high-frequency signal that is an electric signal is automatically controlled. A method for stabilizing the signal frequency can be proposed. In the PLL control, by providing a reference oscillator, the signal frequency can be matched with the frequency of the reference oscillator or a frequency (or a frequency obtained by frequency division) obtained by multiplying the frequency.

Japanese Patent Laying-Open No. 2005-351951 (paragraph number [0020], FIG. 2)

  In a high-frequency oscillator using an opto-electric oscillator, by providing PLL control as described above, it is possible to cope with fluctuations in signal frequency caused by thermal expansion and contraction of an optical fiber due to a certain ambient temperature. However, in practice, the high-frequency oscillator is controlled by the PLL when the fluctuation of the environmental temperature becomes large and the thermal expansion and contraction of the optical fiber becomes remarkable, or when stress is applied to the optical fiber due to vibration or the expansion and contraction of the RF transmission path. There is a problem that oscillation is outside the possible pull-in frequency range, and stabilization of the signal frequency cannot be realized (described later with reference to FIG. 3). In addition, when the frequency of the oscillation signal is present near the boundary of the frequency range where PLL control is possible in the temperature state at the time of initial setting, the signal frequency fluctuates outside the PLL controllable range due to slight temperature fluctuations. Therefore, there is a problem that stabilization of the signal frequency cannot be realized (described later with reference to FIGS. 4 and 5).

The present invention has been made to solve the above-described problems, and performs PLL control for thermal expansion / contraction of the optical fiber due to the ambient temperature, application of stress to the optical fiber due to vibration, etc., and expansion / contraction of the RF transmission path. An object of the present invention is to obtain a high-frequency oscillator that can perform normally.
Another object of the present invention is to provide a high-frequency oscillator that can suppress fluctuations in oscillation frequency even in a configuration that does not use PLL control.

  The high-frequency oscillator according to the present invention modulates laser light generated from a laser light source by an optical modulator, converts the modulated laser light transmitted through an optical fiber into a high-frequency signal by a photoelectric converter, In a high-frequency oscillator that extracts a predetermined passband component from a high-frequency signal by a bandpass filter, feeds back the high-frequency signal of the predetermined passband component to the optical modulator as a modulation signal, and outputs it as an oscillation signal, the frequency of the high-frequency signal is constant And a phase adjusting means for adjusting the phase of the high frequency signal so that the fluctuation of the oscillation frequency of the high frequency oscillator falls within a preset frequency pulling range of the PLL controlling means. is there.

  According to the present invention, the high frequency oscillator can be used even when thermal expansion and contraction of the optical fiber becomes noticeable due to fluctuations in ambient environmental temperature, when stress is applied to the optical fiber due to vibration or the expansion and contraction of the RF transmission path occurs. Since oscillation can be performed within a frequency range in which PLL control is possible, signal frequency can be stabilized without any problem by PLL control. Further, even when the frequency of the oscillation signal is present near the boundary of the frequency range where PLL control is possible in the temperature state at the time of initial setting, the signal frequency will not fluctuate outside the PLL controllable range due to temperature fluctuation. .

Embodiment 1 FIG.
1 is a block circuit diagram showing a functional configuration of a high-frequency oscillator according to Embodiment 1 of the present invention.
In FIG. 1, this high-frequency oscillator is roughly divided into an optical transmission system 1 that transmits an optical signal and an RF signal transmission system 2 (electric transmission) that transmits a high-frequency signal that is an electrical signal (hereinafter referred to as an “RF signal”). System). The optical transmission system 1 includes a laser light source 10, an optical path (for example, an optical fiber) 11, an optical modulator 12, an optical fiber 13, and a photoelectric converter 14. The RF signal transmission system 2 includes a band pass filter 15, a PLL control system (PLL control means) 3, a phase shifter 18, an amplifier 19, and a coupler 20. The PLL control system 3 included in the RF signal transmission system 2 includes a phase shifter 16, a coupler 17, a reference oscillator 21, a frequency divider 22, and a PLL circuit 23.

Next, the overall operation of the high frequency oscillator of FIG. 1 will be described.
In the optical transmission system 1, a laser light source 10 generates laser light, and the generated laser light is connected to, for example, an optical fiber 11 and output to an optical modulator 12. The optical modulator 12 modulates the intensity of the laser light supplied from the laser light source 10 according to the RF signal supplied from the coupler 20 of the RF signal transmission system 2, and outputs the modulated laser light to the optical fiber 13. The optical fiber 13 transmits the modulated laser light output from the optical modulator 12 to the photoelectric converter 14. In the photoelectric converter 14, the modulated laser light transmitted through the optical fiber 13 is converted into an RF signal by direct detection (square detection), and the converted RF signal is converted into an RF signal via an electric cable such as a coaxial cable. The signal is transmitted to the band pass filter 15 of the signal transmission system 2.

  In the RF signal transmission system 2, the band pass filter 15 is a signal component in a frequency band other than a predetermined pass band including the center frequency of a preset band pass filter with respect to the RF signal converted by the photoelectric converter 14. Or the spurious signal is cut off, and only the signal component included in the predetermined pass band is allowed to pass through and supplied to the phase shifter 16. The phase shifter 16 adjusts the phase of the RF signal that has passed through the bandpass filter 15 according to the voltage value of the control signal output from the PLL circuit 23 described later. The coupler 17 branches the RF signal whose phase is adjusted by the phase shifter 16 into two, outputs one RF signal to the phase shifter 18, and outputs the other RF signal to the frequency divider 22.

The phase shifter 18 adjusts one of the RF signals branched by the coupler 17 to a predetermined phase set in advance and outputs the signal to the amplifier 19. The detailed function of the phase shifter 18 will be described later. An amplifier 19 that is an electric amplifier amplifies the RF signal output from the phase shifter 18 and outputs the amplified RF signal to the coupler 20. In the coupler 20, the RF signal amplified by the amplifier 19 is branched into two, and one RF signal is output to the optical modulator 12 via a cable such as a coaxial cable, for example, and the other RF signal is Output to the outside as an oscillation signal of the oscillator.
The optical modulator 12 intensity-modulates the laser beam using the other RF signal branched by the coupler 20 as a modulation signal. This high-frequency oscillator forms a feedback circuit by inputting an RF signal to the optical modulator 12, and in this feedback circuit, by setting a feedback gain so as to be larger than the loss of the entire circuit, Oscillation occurs at a predetermined frequency set by the pass filter 15.

  The frequency divider 22 divides the frequency of the other RF signal branched by the coupler 17 into a preset value and outputs the result to the PLL circuit 23. A reference oscillator 21 provided in the PLL control system 3 oscillates a reference signal (RF signal) having a predetermined frequency set in advance, and outputs this reference signal to the PLL circuit 23. The PLL circuit 23 compares the frequency of the RF signal divided by the frequency divider 22 with the frequency of the reference signal from the reference oscillator 21, generates a control signal having a voltage value corresponding to the frequency difference, and generates the phase shifter 16. Output to. In this case, if the PLL circuit 23 indicates that the frequency of the RF signal from the frequency divider 22 is higher than the frequency of the reference signal from the reference oscillator 21, the phase of the frequency of the RF signal is delayed. A voltage value control signal is generated. Therefore, the phase shifter 16 delays the phase of the RF signal input from the band pass filter 15 according to the voltage value of the control signal. On the other hand, if it indicates that the frequency of the RF signal from the frequency divider 22 is delayed from the frequency of the reference signal, the PLL circuit 23 generates a control signal having a voltage value that advances the phase of the frequency of the RF signal. The phase shifter 16 advances the phase of the RF signal in accordance with this control signal.

Next, main functions and effects of the high frequency oscillator of FIG. 1 will be described.
First, the oscillation mode will be described.
In general, in an opto-electric oscillator, an optical fiber having a smaller loss than an electric cable is used as a laser light transmission line, thereby extending the transmission line. Thereby, the Q value of the oscillation is increased, and the phase noise is reduced as compared with a normal high frequency oscillator. However, on the other hand, there is a problem that the oscillation frequency fluctuates due to fluctuations in the ambient environmental temperature. FIG. 2 is a schematic diagram showing the oscillation mode of the high-frequency oscillator and the transmission spectrum of the internal bandpass filter in the first embodiment. The oscillation mode is a mode that can oscillate in proportion to the reciprocal of the total loop length in the oscillator. As shown in FIG. 2, the oscillation signal is the mode with the highest transmittance in the transmission spectrum of the bandpass filter (BPF). can get. At this time, when the ambient environmental temperature varies, the oscillation mode frequency varies due to the change in the loop length, and the frequency of the oscillation signal varies. Therefore, phase control using a PLL is performed.

Next, the PLL control used here will be described.
FIG. 3 is a schematic diagram illustrating a frequency pull-in range of PLL control. As shown in FIG. 3, in the PLL control, an oscillation frequency setting value (frequency of the reference signal of the reference oscillator 21 × frequency division number of the frequency divider 22) is determined, and a feedback circuit for matching the oscillation frequency with this setting value. Is configured. At this time, the frequency range for drawing the oscillation frequency to the set value is proportional to the performance of the phase shift amount of the phase shifter 16 used for the PLL control. That is, it is determined only by the performance of this phase shift amount. Further, when the oscillation frequency is outside the frequency pull-in range of the PLL control, the PLL control becomes impossible.

Here, in order to explain the effect of the high-frequency oscillator in FIG. 1 in an easy-to-understand manner, a case where PLL control is performed between ambient environmental temperatures of 10 ° C. to 40 ° C. will be described. Therefore, it is assumed here that the following preconditions 1 to 3 are satisfied.
Precondition 1: It is assumed that the expansion / contraction amount of the fiber length is proportional to the fluctuation range of the ambient environmental temperature, and if the ambient environmental temperature is determined, the oscillation mode at that time is also determined.
Precondition 2: It is assumed that the amount of frequency pull-in range by the PLL is the same as the fluctuation amount of the oscillation mode between 10 ° C. and 40 ° C.
Precondition 3: It is assumed that the fiber length increases as the ambient temperature increases, and the frequency value in the oscillation mode at 40 ° C. is smaller than that at 10 ° C.
Precondition 1 and precondition 3 are conditions that hold for fibers coated with highly versatile UV resin or nylon material.

  When the relationship between the oscillation mode and the oscillation frequency setting value is as shown in FIG. 4 under the above preconditions, the frequency range between the oscillation frequency setting value and the oscillation mode at 10 ° C. is outside the frequency pull-in range by the PLL. On the other hand, when the relationship between the oscillation mode and the oscillation frequency setting value is as shown in FIG. 5, a part of the frequency range on the oscillation mode side at 40 ° C. is outside the frequency pull-in range by the PLL. In such a case, another phase shifter 18 is provided separately from the PLL phase shifter 16 as shown in FIG. 1 so that the oscillation mode and the oscillation frequency set value have the relationship shown in FIG. Adjust. As a result, the fluctuation of the oscillation frequency at 10 ° C. to 40 ° C. matches the frequency pull-in range by the PLL, and the phase shift amount performance of the phase shifter 16 for PLL control can be fully utilized. That is, the effect that the temperature range in which frequency control is possible increases can be obtained.

In addition, the above-mentioned precondition 2 was not observed, and the conventional PLL control was used by sufficiently increasing the amount of frequency pull-in range by the PLL with respect to the fluctuation amount of the oscillation mode between 10 ° C. and 40 ° C. Even with the configuration, it is considered possible to achieve frequency stabilization. However, by using the configuration shown in the present invention, it is possible to obtain an effect that frequency control is possible not only in the above-described 10 ° C. to 40 ° C. but also in a temperature range higher than that.
Further, in the above description, for the sake of simplicity, it is assumed that the ambient environmental temperature is 10 ° C. to 40 ° C. and the preconditions 1 to 3 are satisfied, but these assumptions and preconditions are satisfied. Even if not, the same effect as described above can be obtained. This also applies to other embodiments described below.

Further, in FIG. 6, the frequency pull-in range by the PLL control and the fluctuation range of the oscillation mode at 10 ° C. to 40 ° C. are matched, but the same effect as described above can be obtained even if they do not match separately. The two ranges do not necessarily match.
Even if the phase shifter 18 is not used, the same effect as described above can be obtained by adjusting the length of the coaxial cable, for example.

  Further, according to the configuration example of FIG. 1, the laser light source 10 and the optical modulator 12 in the optical transmission system 1 and the optical modulator 12 and the photoelectric converter 14 are connected by optical fibers. The transmission system 1 can be downsized. In addition, high reliability is obtained, handling is easy, and an arrangement with high flexibility is obtained. However, in the first embodiment, the entire laser light transmission path is not limited to using only an optical fiber, and other things such as a space may be used. This also applies to other embodiments described below.

In the configuration example of FIG. 1, the RF signal transmission system 2 includes a band pass filter 15, a phase shifter 16, a coupler 17, a phase shifter 18, an amplifier 19, and a coupler 20. 1 as long as it is between the photoelectric converter 14 and the optical modulator 12, it may be installed at any position. This also applies to other embodiments described below.
Further, although the branching ratio of the couplers 17 and 20 is not particularly mentioned, the coupler 17 has a condition for the high-frequency oscillator to oscillate and a condition for performing the PLL control, while the coupler 20 has a high-frequency oscillator. Any branching ratio may be used as long as the conditions for oscillation are satisfied. This also applies to other embodiments described below.

  In the configuration example of FIG. 1, the RF signal transmission system 2 mounts the amplifier 19 and the amplifier 19 amplifies the RF signal so that a desired signal can be obtained. In addition, for example, an optical amplifier that amplifies the optical signal may be mounted between the laser light source 10 and the photoelectric converter 14. Alternatively, both the amplifier 19 and the optical amplifier may be mounted. This also applies to other embodiments described below.

  In the configuration example of FIG. 1, the phase shifter 16 is mounted on the RF signal transmission system 2, and the PLL circuit 23 controls the phase shifter 16 to adjust the phase of the RF signal to a desired value. However, instead of the phase shifter 16, as shown in FIG. 7, an optical delay unit 31 for changing the length of the optical path to a desired value is mounted in the optical transmission system 1, and the voltage value of the control signal of the PLL circuit 23 By controlling the optical delay device 31 and adjusting the length of the optical path, the phase of the RF signal may be controlled to be adjusted to a desired value. In this case, the installation position of the optical delay device 31 may be any position as long as it is between the optical modulator 12 and the photoelectric converter 14.

  In the configuration example of FIG. 1, the phase shifter 18 is mounted on the RF signal transmission system 2. Instead of the phase shifter 18, the length of the optical path is set to a desired value as shown in FIG. 8. The optical delay device 32 to be changed may be mounted on the optical transmission system 1 and the phase of the RF signal may be adjusted to a desired value by adjusting the length of the optical path. In this case, the installation position of the optical delay device 32 may be any position as long as it is between the optical modulator 12 and the photoelectric converter 14.

  Further, in the configuration of FIG. 7 provided with the optical delay device 31, as shown in FIG. 9, instead of the phase shifter 18, the optical delay device 32 is mounted in the optical transmission system 1, and the length of the optical path is adjusted. Thus, the phase of the RF signal may be adjusted to a desired value. The installation positions of the optical delay device 31 and the optical delay device 32 may be any positions as long as they are between the optical modulator 12 and the photoelectric converter 14. It should be noted that the use of an optical delay device instead of the phase shifter described above also applies to other embodiments described below.

  As described above, according to the first embodiment, the phase adjustment means (phase shift means for adjusting the phase of the high-frequency signal so that the fluctuation of the oscillation frequency of the high-frequency oscillator falls within the preset frequency pull-in range of the PLL control. 18), the optical delay device 32, the coaxial cable, etc.), when the thermal expansion and contraction of the optical fiber becomes noticeable due to fluctuations in the ambient environmental temperature, the high-frequency oscillator can apply stress to the optical fiber due to vibration or the like. Even when expansion or contraction of the RF transmission path occurs, it is possible to oscillate within a frequency range in which PLL control is possible, and it is possible to realize stabilization of the signal frequency without any trouble by PLL control. Further, even when the frequency of the oscillation signal is present near the boundary of the frequency range where PLL control is possible in the temperature state at the time of initial setting, the signal frequency will not fluctuate outside the PLL controllable range due to temperature fluctuation. .

Embodiment 2. FIG.
FIG. 10 is a block circuit diagram showing a functional configuration of the high-frequency oscillator according to the second embodiment of the present invention. In the figure, parts corresponding to those in FIG. 1 are denoted by the same reference numerals, and description thereof will be omitted in principle. The configuration of FIG. 10 is different from the configuration of FIG. 1 in that a temperature detector 41, a phase shift amount determination unit 42, and a voltage generation unit 43 are provided.
Here, in order to explain the operation and effect of the high-frequency oscillator in an easy-to-understand manner, a case where PLL control is performed between ambient environmental temperatures of 10 ° C. to 40 ° C. will be described as in the first embodiment. In the following description, it is assumed that the above-described preconditions 1 to 3 are satisfied.

Next, the operation will be described.
In FIG. 10, the temperature detector 41 detects the ambient temperature around the high-frequency oscillator, and outputs a temperature information signal representing the detected temperature to the phase shift amount determination means 42. Next, when receiving the temperature information signal from the temperature detector 41, the phase shift amount determination means 42 adjusts the phase shifter 18 according to the temperature detected by the temperature detector 41 indicated by the temperature information signal. A desired phase shift amount is determined. Here, for example, when the environmental temperature detected by the temperature detector 41 is 25 ° C., the oscillation signal when the PLL control is not performed is from the oscillation mode when the ambient environmental temperature is 10 ° C. in FIG. The amount of phase shift necessary to occur at the center until the oscillation mode is determined. Then, a phase shift amount information signal representing the determined phase shift amount is output to the voltage generating means 43. When the voltage generating means 43 receives the phase shift amount information signal, it generates a control voltage value corresponding to the phase shift amount indicated by this signal and outputs it to the phase shifter 18. The phase shifter 18 shifts the phase of the RF signal from the coupler 17 in accordance with the control voltage value from the voltage generating means 43.

Next, the effect of the high frequency oscillator in FIG. 10 will be described.
In the high-frequency oscillator according to the first embodiment described above, for example, the frequency of the oscillation mode when the ambient temperature is 10 ° C. and the frequency of the oscillation mode when the ambient temperature is 40 ° C. are known. The correspondence was assumed to be known in advance. However, in the high-frequency oscillator of FIG. 10, even when the correspondence between the environmental temperature and the oscillation mode is not known, from the frequency of the oscillation signal when the PLL control is not performed and the environmental temperature detected by the temperature detector 41 at that time, The correspondence between the temperature and the oscillation mode is clarified, and the same effect as in the first embodiment can be obtained.
Further, for example, even when the oscillation mode with respect to the environmental temperature is deviated from the initial setting time and the correspondence between the environmental temperature and the oscillation mode becomes unclear, the high-frequency oscillator of FIG. 10 has a correspondence between the environmental temperature and the oscillation mode. Becomes clear, and the same effect as in the first embodiment can be obtained.

  Further, when the correspondence between the environmental temperature and the oscillation mode is known in advance, as shown in FIG. 11, the phase shift amount determination means 42 has the frequency of the oscillation signal branched by the coupler 51 provided on the output end side. Accordingly, a desired phase shift amount may be determined, and a control voltage value corresponding to the phase shift amount may be applied to the phase shifter 18 to shift the phase of the RF signal. This is because by detecting the oscillation signal frequency (corresponding to the oscillation mode) when the PLL control is not performed in the configuration of FIG. 11, the environmental temperature at the time of detection can be known from the correspondence between the oscillation mode and the environmental temperature. Is due to.

  In addition to the fact that the correspondence between the environmental temperature and the oscillation mode is known in advance, when the applied voltage value in the phase shifter 16 and the phase shift amount at that time are known, the phase shift amount and the PLL control are performed. From this frequency, the frequency of the oscillation signal when the PLL control is not performed is known, so the environmental temperature when the control signal having the voltage value is applied to the phase shifter 16 can be known. Therefore, as shown in FIG. 12, the control signal of the voltage value from the PLL circuit 23 is branched using the coupler 62, one of the branched control signals is given to the voltage value detector 61, and the voltage value detector 61 moves the control signal. The voltage value applied to the phase shifter 16 is detected. Then, the phase shift amount determination means 42 may determine a desired phase shift amount for adjustment by the phase shifter 18 from the detected voltage value.

  As described above, according to the second embodiment, the phase adjusting unit changes the ambient temperature, or changes corresponding to the application of stress to the optical fiber due to the ambient temperature, vibration, or the like, expansion and contraction of the RF transmission path, and the like. The phase shift amount for adjusting the high frequency signal is determined based on the frequency of the oscillation signal of the high frequency oscillator to be expressed or the voltage value of the control signal in the PLL control system 3, and a control voltage value corresponding to the determined phase shift amount is generated. The phase shifter 18 adjusts the phase of the high-frequency signal based on the generated control voltage value. Therefore, as in the first embodiment, when the thermal expansion and contraction of the optical fiber becomes noticeable due to fluctuations in the ambient temperature, the high-frequency oscillator does not give stress to the optical fiber due to vibration or the like, or expand and contract the RF transmission path. Even if it occurs, it can oscillate within the frequency range in which PLL control is possible, and it is possible to realize stabilization of the signal frequency without any trouble by PLL control. Further, even when the frequency of the oscillation signal is present near the boundary of the frequency range where PLL control is possible in the temperature state at the time of initial setting, the signal frequency will not fluctuate outside the PLL controllable range due to temperature fluctuation. .

（１）式に、ｆ＝１０ＧＨｚ、Δφ＝３６０度を代入すると、ΔＬ＝２．１ｃｍが得られる。そこで、光ファイバ７５の長さをＬ_min （Ｌ_min ＞４．２ｃｍ）、光ファイバ７６の長さをＬ_min −２．１ｃｍとする。 Embodiment 3 FIG.
FIG. 13 is a block circuit diagram showing a functional configuration of the high-frequency oscillator according to the third embodiment of the present invention. In the figure, parts corresponding to those in FIG. 1 are denoted by the same reference numerals, and description thereof will be omitted in principle. FIG. 13 shows a temperature detector 41, a control signal output unit 71, a branching device 72, optical path switchers 73 and 74, and a plurality of light beams having different optical path lengths, instead of the phase shifter 18 and the optical fiber 13 configured as shown in FIG. The fibers 75 and 76 are provided.
Next, the operation will be described.
Here, in order to explain the operation and effect of the high-frequency oscillator in an easy-to-understand manner, the frequency of the high-frequency oscillation signal is 10 GHz, and the phase shift amount that can be adjusted by the phase shifter 16 is 360 degrees. Further, the fluctuation amount ΔL [cm] of the oscillator loop length when the phase of the signal of the frequency f [Hz] is shifted by Δφ [degrees] is expressed by the equation (1) in consideration of the refractive index n of the fiber. .

Substituting f = 10 GHz and Δφ = 360 degrees into equation (1) yields ΔL = 2.1 cm. Therefore, the length of the optical fiber 75 is L _min (L _min > 4.2 cm), and the length of the optical fiber 76 is L _min −2.1 cm.

  Further, as in the first and second embodiments described above, a case where PLL control is performed between ambient environmental temperatures of 10 ° C. to 40 ° C. will be described. Furthermore, in the following description, it is assumed that the above-described preconditions 1 to 3 are satisfied. At this time, generally, as the ambient temperature increases, the fiber length increases. Therefore, when the ambient temperature is 40 ° C., the fiber length is 2.1 cm longer than that when the ambient temperature is 10 ° C.

  The temperature detector 41 detects the ambient temperature around the high frequency oscillator and outputs a temperature information signal representing the detected ambient temperature to the control signal output unit 71. Next, when receiving the temperature information signal from the temperature detector 41, the control signal output unit 71 outputs a switching control signal for switching the optical fiber to the branching device 72 according to the environmental temperature indicated by the temperature information signal. To do. In this case, the control signal output unit 71 provides a threshold for the detected environmental temperature, and outputs a switching control signal when the environmental temperature detected by the temperature detector 41 is immediately before 40 ° C., for example, under the conditions described above. To do. The branching device 72 branches the switching control signal into two and outputs them to the optical path switching devices 73 and 74, respectively. Upon receiving the switching control signal, the optical path switchers 73 and 74 switch the optical fibers 75 and 76 to optical fibers having a desired optical path length and connect them between the optical modulator 12 and the photoelectric converter 14. For example, under the conditions described above, the optical path switchers 73 and 74 are connected to the optical fiber 75 of the longer optical path before receiving the switching control signal, but after receiving the switching control signal. The connection is switched to the connection of the optical fiber 76 in the shorter optical path.

Next, the effect of the high frequency oscillator of FIG. 13 will be described.
The spectrum for explaining the frequency control of this high-frequency oscillator is shown in FIG. 14. When the ambient temperature is between 10 ° C. and 40 ° C., the frequency can be pulled by PLL control. Is not retractable. At this time, the fiber length is extended by 2.1 cm or more with respect to the environmental temperature of 10 ° C. under the conditions described above. Therefore, as shown in FIG. 14, just before the ambient temperature reaches 40 ° C., by switching to the optical path with the shorter fiber length of 2.1 cm, the oscillation mode again matches the oscillation frequency setting value, and the PLL control continues. Can be implemented. Therefore, the configuration as shown in FIG. 13 provides an effect that the temperature range in which the frequency can be controlled can be increased as compared with the conventional case.

  Note that when switching to an optical path having a fiber length of 2.1 cm short as shown in FIG. 14 under the conditions described above, if the actual fiber length is not yet shortened by 2.1 cm at the moment of switching, the fiber length after switching May increase from the initial time, and PLL control may not be possible. Therefore, in such a case, if the actual fiber length difference is set slightly shorter than 2.1 cm, the possibility that PLL control cannot be performed is reduced. Thus, when setting the fiber length, it is preferable that PLL control can always be performed after switching.

Further, as shown in FIG. 15, it is possible to add one optical fiber 77 to increase the optical path as compared with the case of FIG. This further increases the temperature range. In this case, by setting the length of the optical fiber 77 L _min -4.2cm or about L _min + 2.1 cm,, Under conditions described above, that the frequency controllable temperature range is increased to about 30 ° C. become. Similarly, if the optical path is further increased, the temperature range in which the frequency can be controlled can be further increased. This also applies to other embodiments described below.

In the above description, for the sake of clarity, the frequency of the high-frequency oscillation signal is set to 10 GHz and the phase shift amount adjustable by the phase shifter 16 is set to 360 degrees. Since the same effect as described above can be obtained, it does not necessarily have to be established. This also applies to other embodiments described below.
Further, the lengths of the optical fibers 75, 76, and 77 can be increased by switching the optical path by the optical path switchers 73 and 74 without setting the length described above. Any length can be used as long as it is possible and PLL control is always possible after switching as described above. This also applies to other embodiments described below.

  Further, when the correspondence between the environmental temperature and the oscillation mode is known in advance, as shown in FIG. 16, the control signal output unit 71 has the frequency of the high-frequency oscillation signal branched by the coupler 51 provided on the output end side. On the basis of this, a switching control signal may be generated, and the switching control signal may be supplied to the optical path switching units 73 and 74 to perform the optical path switching. By detecting the oscillation signal frequency (corresponding to the oscillation mode) when the PLL control is not performed in the configuration of FIG. 16, the environmental temperature at the time of detection can be known from the correspondence between the oscillation mode and the environmental temperature. Is due to. This also applies to other embodiments described below.

  In addition to the fact that the correspondence between the environmental temperature and the oscillation mode is known in advance, when the applied voltage value in the phase shifter 16 and the phase shift amount at that time are known, the phase shift amount and the PLL control are performed. From this frequency, the frequency of the oscillation signal when the PLL control is not performed is known, so the environmental temperature when the control signal having the voltage value is applied to the phase shifter 16 can be known. Therefore, as shown in FIG. 17, the control signal of the voltage value from the PLL circuit 23 is branched using the coupler 62, one of the branched control signals is given to the voltage value detector 61, and the voltage value detector 61 moves the control signal. The voltage value applied to the phase shifter 16 is detected. Then, the control signal output unit 71 may generate a switching control signal based on the detected voltage value to switch the optical path. This also applies to other embodiments described below.

  As described above, according to the third embodiment, the phase adjusting unit includes the plurality of optical fibers having different optical path lengths and the optical path switching units 73 and 74 that selectively switch the plurality of optical fibers. The switching control signal is generated based on the environmental temperature or the frequency of the output oscillation signal representing the change corresponding to the environmental temperature or the voltage value of the control signal in the PLL control system 3, and the optical path switching units 73 and 74 perform this switching control. By selecting an optical fiber having a desired optical path length from a plurality of optical fibers according to the signal and connecting it as a part of the optical transmission path between the optical modulator 12 and the photoelectric converter 14, the phase of the high frequency signal To adjust. Therefore, as in the above embodiments, the high-frequency oscillator is capable of applying stress to the optical fiber due to vibration or the like, expanding / contracting the RF transmission line, etc. Even if it occurs, it can oscillate within the frequency range in which PLL control is possible, and it is possible to realize stabilization of the signal frequency without any trouble by PLL control. Further, even when the frequency of the oscillation signal is present near the boundary of the frequency range where PLL control is possible in the temperature state at the time of initial setting, the signal frequency will not fluctuate outside the PLL controllable range due to temperature fluctuation. .

Embodiment 4 FIG.
FIG. 18 is a block circuit diagram showing a functional configuration of the high-frequency oscillator according to the fourth embodiment of the present invention. In the figure, parts corresponding to those in FIG. 15 are denoted by the same reference numerals, and description thereof will be omitted in principle. FIG. 18 shows a configuration in which optical fibers 82, 83, and 84 are provided instead of the optical fibers 75 to 77 in the configuration of FIG. 15 and an optical fiber 81 is provided as an optical path between the optical modulator 12 and the optical path switch 73. Yes. Here, the optical fibers 82, 83, and 84 are optical fibers having different lengths. In addition, most of the length of the optical fiber used in the high-frequency oscillator is assigned to the optical fiber 81, and on the other hand, a sufficiently short fiber is assigned to the optical fiber 82, 83, 84 relative to the optical fiber 81. Configure.
In the operation of the high-frequency oscillator of FIG. 18, the laser light modulated by the optical modulator 12 is transmitted to the optical path switch 73 through the optical fiber 81. Further, when the optical path switching units 73 and 74 receive the switching control signal from the branching unit 72, the optical path switching units 73 and 74 select an optical fiber of a desired optical path from the optical fibers 82, 83, and 84 in accordance with the switching control signal and perform light. A connection is made between the fiber 81 and the photoelectric converter 14. Other operations are the same as those in the third embodiment.

Next, the effect of the high frequency oscillator of FIG. 18 will be described.
When a long optical fiber is used in this high-frequency oscillator, most of the length is assigned to the optical fiber 81, and the remaining short part is assigned to the optical fibers 82, 83, and 84 that can be switched by the optical path switchers 73 and 74. Specifically, the optical fibers 82, 83, and 84 are set to have a length corresponding to the phase shift amount of the phase shifter 16 (about 2.1 cm under the above-described conditions). As a result, the fiber length to be switched by the optical path switchers 73 and 74 can be shortened compared to the case of using the same fiber length as in FIG. 15 (the same applies to FIGS. 16 and 17). Etc. are obtained.
In the example of FIG. 18, most of the length of the optical fiber is allocated between the optical modulator 12 and the optical path switch 73, but instead the optical fiber between the optical path switch 74 and the photoelectric converter 14. The same applies to the assignment.
As described above, according to the fourth embodiment, in addition to the configuration of the third embodiment, most of the length of the optical fiber used between the optical modulator 12 and the photoelectric converter 14 is switched to a plurality of optical paths. Since a sufficiently short optical fiber is assigned to a plurality of optical fibers between a plurality of optical path switchers, in addition to the effects of the third embodiment, there are effects such as downsizing and cost reduction. can get.

Embodiment 5 FIG.
FIG. 19 is a block circuit diagram showing a functional configuration of the high-frequency oscillator according to the fifth embodiment of the present invention. In the figure, parts corresponding to those in FIG. 1 are denoted by the same reference numerals, and description thereof will be omitted in principle. 19 is provided with a temperature detector 41, a control signal output unit 71, a branching device 72, transmission line switching units 91 and 92, and RF signal transmission lines 93, 94, and 95 instead of the phase shifter 18 having the configuration shown in FIG. It has a configuration. The RF signal transmission lines 93, 94, and 95 are transmission lines having different lengths. Further, the switching control signal from the control signal output unit 71 is branched into two by the branching device 72 and supplied to the transmission line switching devices 91 and 92, and the configuration similar to that of FIG. doing.
In the operation of the high-frequency oscillator of FIG. 19, the modulated laser light from the optical modulator 12 is transmitted to the photoelectric converter 14 through the optical fiber 13 as in the case of FIG. The operations of the temperature detector 41, the control signal output unit 71, and the branching device 72 are the same as in the case of FIG. When the transmission path switching units 91 and 92 receive the switching control signal output from the control signal output unit 71 from the branching unit 72, the transmission path switching units 91 and 92 have a desired length from the RF signal transmission paths 93, 94, and 95 according to the control signal. Is selected and connected between the coupler 17 and the amplifier.

Next, the effect of the high frequency oscillator of FIG. 19 will be described.
In general, an optical switch used as an optical path switch is a commercial product, and a switching time on the order of milliseconds occurs. On the other hand, for example, a semiconductor switch that can be used as an RF signal transmission path switch is a commercially available nano switch. Those with switching times on the order of seconds are available. Therefore, the use of an RF signal transmission path switching unit for path switching can provide an effect that switching time can be shortened.

  In the high-frequency oscillator of FIG. 19, the transmission path switching units 91 and 92 are switched using a switching control signal generated by the control signal output unit 71 based on the ambient environmental temperature detected by the temperature detector 41. Similar to FIG. 16 or FIG. 17 of the third embodiment described above, the frequency or PLL of the output oscillation signal representing the change corresponding to the application of stress to the optical fiber due to the ambient temperature, vibration, etc., the expansion and contraction of the RF transmission path, etc. You may comprise so that the switching control signal generated based on the voltage value of the control signal in the control system 3 may be used.

  As described above, according to the fifth embodiment, the phase adjusting means transmits a plurality of electrical signal transmission paths 93, 94, and 95 having different lengths, and transmission that selectively switches between the plurality of electrical signal transmission paths. The path switching units 91 and 92 are provided, and the frequency of the output oscillation signal or the PLL control system that represents changes in response to the ambient temperature, the stress applied to the optical fiber due to the environmental temperature, vibration, etc., and the expansion and contraction of the RF transmission path 3 generates a switching control signal based on the voltage value of the control signal in 3, and the transmission path switching units 91 and 92 select an electrical signal transmission path having a desired length from among the plurality of electrical signal transmission paths in accordance with the switching control signal. By selecting and connecting as part of the RF transmission path between the photoelectric converter 14 and the optical modulator 12, the phase of the high-frequency signal is adjusted. Therefore, as in the above embodiments, the high-frequency oscillator is capable of applying stress to the optical fiber due to vibration or the like, expanding / contracting the RF transmission line, etc. Even if it occurs, it can oscillate within a frequency range in which PLL control is possible, and stabilization of the signal frequency without any trouble by PLL control can be realized. Further, even when the frequency of the oscillation signal is present near the boundary of the frequency range where PLL control is possible in the temperature state at the time of initial setting, the signal frequency will not fluctuate outside the PLL controllable range due to temperature fluctuation. .

Embodiment 6 FIG.
FIG. 20 is a block circuit diagram showing a functional configuration of the high-frequency oscillator according to the sixth embodiment of the present invention. In the figure, parts corresponding to those in FIG. 1 are denoted by the same reference numerals, and description thereof will be omitted in principle. 20, the phase shifter 18 in the configuration of FIG. 1 is not provided, the wavelength variable laser light source 101 is provided in place of the laser light source 10, and the temperature detector 41 and the output wavelength discriminating means 111 are further provided. Yes. Therefore, the optical transmission system 1 in the case of FIG. 20 is configured by the wavelength tunable laser light source 101, the optical modulator 12, the optical fibers 11 and 13, and the photoelectric converter 14.

The operation of the high frequency oscillator of FIG. 20 will be described.
Laser light generated by the wavelength tunable laser light source 101 is output to the optical modulator 12. The temperature detector 41 detects the ambient temperature around the high frequency oscillator and outputs a temperature information signal representing the detected temperature to the output wavelength discriminating means 111. Upon receiving the temperature information signal from the temperature detector 41, the output wavelength discriminating means 111 receives a desired laser beam to be generated from the wavelength tunable laser light source 101 in accordance with the temperature detected by the temperature detector 41 indicated by the temperature information signal. The output wavelength is determined, and a wavelength information signal representing the determined wavelength is output to the wavelength tunable laser light source 101. The desired output wavelength of the laser light discriminated here is a wavelength necessary for keeping the fluctuation of the oscillation frequency of the high-frequency oscillator within the preset frequency pull-in range of the PLL control. When the wavelength tunable laser light source 101 receives the wavelength information signal from the output wavelength discriminating means 111, it generates a laser beam having a desired output wavelength indicated by the wavelength information signal. Other operations are the same as those in the first embodiment.

Next, the effect of the high frequency oscillator in FIG. 20 will be described.
Here, in order to explain the effect of the high-frequency oscillator in an easy-to-understand manner, a case where PLL control is performed between ambient environmental temperatures of 10 ° C. to 40 ° C. will be described below. In the following description, it is assumed that the above-described precondition 1 and precondition 3 are satisfied.
In general, when the above-described fluctuation of the ambient temperature occurs, the largest factor for the frequency fluctuation in this high-frequency oscillator is a fluctuation in length due to thermal expansion and contraction of the optical fiber. In addition, quartz glass, which is the main material of the optical fiber itself, has a linear expansion coefficient of 1 ppm / ° C. or less, whereas materials such as UV resin and nylon, which are often used as protective coatings for optical fibers, have a linear expansion coefficient. Since there are many that are 10 ppm / ° C. or more, the length variation due to thermal expansion and contraction of the optical fiber is generally often dominant due to the expansion and contraction of the protective coating. Here, in order to explain the effect of the high-frequency oscillator in an easy-to-understand manner, it is assumed that the fiber length used in the high-frequency oscillator is 1000 m, and the length variation due to thermal expansion and contraction of the optical fiber is 10 ppm / ° C.

  In addition, when light propagates through a material such as an optical fiber, a phenomenon occurs in which the speed of light varies depending on the wavelength (frequency) of light, which is called dispersion. The dispersion value of a general single mode fiber (hereinafter referred to as SMF) is approximately 0 near a wavelength of 1.3 μm and is approximately 17 ps / km / nm near a wavelength of 1.55 μm. The unit of “ps / km / nm” represents a difference in propagation time that occurs when two light beams having a wavelength of 1 nm are propagated through a fiber length of 1 km. In the following description, it is assumed that the laser wavelength band used in the wavelength tunable laser light source 101 is around 1.55 μm, the optical fiber to be used is a general SMF, and the dispersion value is 17 ps / km / nm.

ここで、ｃは光速、ｎはファイバの屈折率、ｄ_SMFは用いたＳＭＦの分散値である。
（３）式に、ｃ＝３．０×１０⁸ｍ／ｓ、ｎ＝１．４５、ｄ_SMF＝１７ｐｓ／ｋｍ／ｎｍおよびΔＬ（１０℃−４０℃）＝０．３ｍを代入すると、Δλ＝８５ｎｍが得られる。 At this time, if the fiber length fluctuation amount generated when the optical fiber of 1000 m fluctuates from 10 ° C. to 40 ° C. is ΔL (10 ° C.-40 ° C.), ΔL (10 ° C.-40 ° C.) is The length variation due to thermal expansion and contraction is 10 ppm / ° C. and can be calculated as in equation (2).
ΔL (10 ° C.-40 ° C.) = 1000 × 10 · 10 ⁽⁻⁶⁾ · (40−10) = 0.3 [m]
(2)
Next, assuming that the wavelength difference of light necessary to generate the propagation time difference corresponding to the fiber length fluctuation amount of ΔL (10 ° C.-40 ° C.) is Δλ, ΔL (10 ° C.-40 ° C.) is used. (3) can be expressed as follows.

Here, c is the speed of light, n is the refractive index of the fiber, and d _SMF is the dispersion value of the SMF used.
Substituting c = 3.0 × 10 ⁸ m / s, n = 1.45, d _SMF = 17 ps / km / nm and ΔL (10 ° C.−40 ° C.) = 0.3 m into the equation (3), Δλ = 85 nm is obtained.

  Therefore, even when the ambient environmental temperature varies from 10 ° C. to 40 ° C., by changing the wavelength of the laser light output from the wavelength tunable laser light source 101 by 85 nm, the fiber length variation caused by the environmental temperature variation can be reduced. Correction can be performed from the viewpoint of the optical path length in consideration of the wavelength. In an optical fiber, since the refractive index increases and the optical path length increases as the wavelength of light decreases, in the above example, the wavelength of the laser beam is 85 nm smaller than that at 40 ° C. when the ambient temperature is 10 ° C. By doing so, the above-described correction becomes possible.

Further, in addition to the above-described precondition 1 and precondition 3, it is assumed that the following precondition 4 is satisfied.
Precondition 4: One-to-one correspondence between the propagation time difference of light of two wavelengths due to dispersion, that is, the converted amount to the fiber length fluctuation obtained from this difference and the fiber length fluctuation amount caused by the ambient temperature fluctuation In the case where the ambient environmental temperature fluctuates, it is assumed that the output wavelength discriminating means 111 can discriminate the amount of change in the wavelength of the laser beam necessary for correcting the fiber length fluctuation amount caused by the fluctuation.
At this time, from the formulas (2) and (3) and the precondition 4, even if the ambient environmental temperature fluctuates not only in a range of 10 ° C. to 40 ° C. but also in an arbitrary range, the fiber length variation amount caused by the variation is calculated. The wavelength change amount of the laser beam necessary for correction can be discriminated by the output wavelength discriminating means 111. Therefore, the high-frequency oscillator in FIG. 20 has an effect that the frequency can be stabilized even when the ambient environmental temperature fluctuates.

  Further, for example, in the high-frequency oscillators in the third, fourth, and fifth embodiments, an optical path switch or a transmission path switch, a plurality of optical fibers or RF signal transmission paths are required. In the case of the high-frequency oscillator in FIG. This can be implemented with a single optical fiber, and the effect of shortening the fiber length can be obtained. Therefore, there are advantages such as downsizing and cost reduction as compared with the high-frequency oscillators in the third, fourth, and fifth embodiments described above.

Note that the fiber length described above and the length variation due to thermal expansion and contraction of the optical fiber may not be assumed separately as long as the above-described effect can be obtained.
Further, although the optical fiber used is assumed to be SMF, it may not be SMF.
Moreover, although the dispersion value of the optical fiber is assumed to be a constant value of 17 ps / nm / km, the dispersion value may vary depending on the wavelength depending on the optical fiber. However, if the dispersion value at each wavelength is known, the wavelength change amount of the desired laser beam in the wavelength tunable laser light source 101 can be derived by using the equations (2) and (3). As described above, it does not have to be a constant value.

In the above-mentioned precondition 4, the difference in propagation time of light of two wavelengths due to dispersion, that is, the conversion amount to the fiber length fluctuation obtained from this difference and the fiber length fluctuation amount caused by the fluctuation of the ambient temperature are 1 Although it is assumed that there is a one-to-one correspondence, when the ambient temperature changes, the output wavelength discrimination means 111 determines the wavelength change amount of the laser light necessary to correct the fiber length fluctuation amount caused by the fluctuation. As long as it can be determined, the above-described one-to-one correspondence may not be necessary.
The output wavelength discriminating means 111 discriminates the desired output wavelength of the laser beam from the environmental temperature detected by the temperature detector 41. However, the present invention is not limited to this. You may make it discriminate | determine a desired output wavelength based on the voltage value of the control signal used for a phase shift with a frequency or PLL control means.

  As described above, according to the sixth embodiment, the wavelength tunable laser light source 101 is used as a laser light source, and stress is applied to the optical fiber due to the ambient environment temperature or the environment temperature, vibration, etc. In order to keep the fluctuation of the oscillation frequency of the high-frequency oscillator within the preset frequency pull-in range of the PLL control based on the frequency of the output oscillation signal representing the change corresponding to expansion or contraction or the voltage value of the control signal in the PLL control system 3 The desired output wavelength of the necessary laser light is discriminated, and the laser light having the discriminated desired output wavelength is generated from the wavelength tunable laser light source 101. Therefore, the same effects as those of the above-described embodiments can be obtained. In addition, as compared with the high-frequency oscillators in the third, fourth, and fifth embodiments, the size and cost can be reduced.

  Similar to the high-frequency oscillator shown in FIG. 20, by changing the wavelength of the laser light output from the wavelength tunable laser light source 101, the fiber length variation caused by the ambient temperature variation can be sufficiently corrected. When the frequency of the oscillation signal can be stabilized without performing PLL control, a high frequency oscillator having a configuration excluding the PLL control system from the configuration of FIG. 20 may be used as shown in FIG. This makes it possible to further simplify the high-frequency oscillator.

It is a block circuit diagram which shows the function structure of the high frequency oscillator by Embodiment 1 of this invention. It is a schematic diagram showing the oscillation mode of the high frequency oscillator concerning Embodiment 1 of this invention, and the transmission spectrum of an internal band pass filter. It is a schematic diagram showing the frequency pull-in range of PLL control. It is a schematic diagram which shows the example from which the relationship between the oscillation mode of ambient temperature and an oscillation frequency setting value becomes out of a frequency drawing range. It is a schematic diagram which shows the other example from which the relationship between the oscillation mode of ambient environment temperature and an oscillation frequency setting value is out of a frequency drawing range. It is a schematic diagram which shows the state with which the relationship between the oscillation mode of ambient environment temperature and the oscillation frequency setting value, and the frequency pull-in range corresponded by Embodiment 1 of this invention. It is a block circuit diagram which shows the other structural example of the high frequency oscillator by Embodiment 1 of this invention. It is a block circuit diagram which shows the further another structural example of the high frequency oscillator by Embodiment 1 of this invention. It is a block circuit diagram which shows the further another structural example of the high frequency oscillator by Embodiment 1 of this invention. It is a block circuit diagram which shows the function structure of the high frequency oscillator by Embodiment 2 of this invention. It is a block circuit diagram which shows the other structural example of the high frequency oscillator by Embodiment 2 of this invention. It is a block circuit diagram which shows the further another structural example of the high frequency oscillator by Embodiment 2 of this invention. It is a block circuit diagram which shows the function structure of the high frequency oscillator by Embodiment 3 of this invention. It is a schematic diagram which shows the spectrum for demonstrating the frequency control which concerns on Embodiment 3 of this invention. It is a block circuit diagram which shows the other structural example of the high frequency oscillator by Embodiment 3 of this invention. It is a block circuit diagram which shows the further another structural example of the high frequency oscillator by Embodiment 3 of this invention. It is a block circuit diagram which shows the further another structural example of the high frequency oscillator by Embodiment 3 of this invention. It is a block circuit diagram which shows the function structure of the high frequency oscillator by Embodiment 4 of this invention. It is a block circuit diagram which shows the function structure of the high frequency oscillator by Embodiment 5 of this invention. It is a block circuit diagram which shows the function structure of the high frequency oscillator by Embodiment 6 of this invention. It is a block circuit diagram which shows the other structural example of the high frequency oscillator by Embodiment 6 of this invention.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 Optical transmission system, 2 RF signal transmission system, 3 PLL control system, 10 Laser light source, 11 Optical path (optical fiber), 12 Optical modulator, 13, 75-77, 81-84 Optical fiber, 14 Photoelectric converter, 15 band pass filter, 16, 18 phase shifter, 17, 20, 51, 62 coupler, 19 amplifier, 22 frequency divider, 23 PLL circuit, 31, 32 optical delay device, 41 temperature detector, 42 phase shift amount discrimination Means, 43 Voltage generating means, 61 Voltage value detector, 71 Control signal output unit, 72 Branching device, 73, 74 Optical path switch, 91, 92 Transmission path switch, 93-95 RF signal transmission path, 101 Wavelength variable laser Light source, 111 output wavelength discrimination means.

Claims (16)

The laser light generated from the laser light source is modulated by an optical modulator, the modulated laser light transmitted through an optical fiber is converted into a high-frequency signal by a photoelectric converter, and the converted high-frequency signal is predetermined by a bandpass filter. In the high-frequency oscillator that takes out the passband component of the output and feeds back the high-frequency signal of the predetermined passband component to the optical modulator as a modulation signal and outputs it as an oscillation signal,
PLL control means for controlling the frequency of the high-frequency signal to be constant;
A high-frequency oscillator comprising phase adjusting means for adjusting the phase of the high-frequency signal so that the fluctuation of the oscillation frequency of the high-frequency oscillator falls within a preset frequency pull-in range of the PLL control means.   2. The high frequency oscillator according to claim 1, wherein the phase adjusting means includes a phase shifter that is provided between the photoelectric converter and the optical modulator and directly changes the phase of the high frequency signal.   2. The high-frequency oscillator according to claim 1, wherein the phase adjusting means includes an optical delay unit that is provided between the optical modulator and the photoelectric converter and sets a length of an optical path for adjusting a phase of the high-frequency signal. . The phase adjustment means is
A temperature detector for detecting the ambient temperature around the high-frequency oscillator;
A phase shift amount determining means for determining a desired phase shift amount to be adjusted by the phase adjusting means based on the detected environmental temperature;
Voltage generating means for generating a control voltage value according to the determined desired phase shift amount;
3. The high frequency oscillator according to claim 2, wherein the phase of the high frequency signal is adjusted in accordance with the generated control voltage value. The phase adjustment means is
A phase shift amount determining means for determining a desired phase shift amount to be adjusted by the phase adjusting means based on the frequency of the oscillation signal of the high frequency oscillator;
Voltage generating means for generating a control voltage value according to the determined desired phase shift amount;
3. The high frequency oscillator according to claim 2, wherein the phase of the high frequency signal is adjusted in accordance with the generated control voltage value. The phase adjustment means is
A voltage detector for detecting a voltage value of a control signal used for phase shift by the PLL control means;
A phase shift amount determining means for determining a desired phase shift amount to be adjusted by the phase adjusting means based on the voltage value of the detected control signal;
Voltage generating means for generating a control voltage value according to the determined desired phase shift amount;
3. The high frequency oscillator according to claim 2, wherein the phase of the high frequency signal is adjusted in accordance with the generated control voltage value. The phase adjustment means is
A temperature detector for detecting the ambient temperature around the high-frequency oscillator;
A control signal output unit that outputs a switching control signal based on the detected ambient temperature;
A plurality of optical fibers each having a different optical path length;
An optical path switch that selects an optical fiber having a desired optical path length from the plurality of optical fibers according to the switching control signal and connects the optical fiber as a part of an optical transmission path between the optical modulator and the photoelectric converter; The high frequency oscillator according to claim 1, wherein The phase adjustment means is
A control signal output unit that outputs a switching control signal based on the frequency of the oscillation signal of the high-frequency oscillator;
A plurality of optical fibers each having a different optical path length;
An optical path switch that selects an optical fiber having a desired optical path length from the plurality of optical fibers according to the switching control signal and connects the optical fiber as a part of an optical transmission path between the optical modulator and the photoelectric converter; The high-frequency oscillator according to claim 1. The phase adjustment means is
A voltage detector for detecting a voltage value of a control signal used for phase shift by the PLL control means;
A control signal output unit that outputs a switching control signal based on a voltage value detected by the voltage detector;
A plurality of optical fibers each having a different optical path length;
An optical path switch that selects an optical fiber having a desired optical path length from the plurality of optical fibers according to the switching control signal and connects the optical fiber as a part of an optical transmission path between the optical modulator and the photoelectric converter; The high frequency oscillator according to claim 1, wherein   Almost all of the length of the optical fiber used between the optical modulator and the photoelectric converter is allocated to an optical path other than between the optical path switches, and the remaining short part is allocated to the optical fibers switched by the optical path switch. The high-frequency oscillator according to claim 7, wherein the high-frequency oscillator is provided. The phase adjustment means is
A temperature detector for detecting the ambient temperature around the high-frequency oscillator;
A control signal output unit that outputs a switching control signal based on the detected ambient temperature;
A plurality of electrical signal transmission lines each having a different length;
Transmission in which an electrical signal transmission path having a desired length is selected from the plurality of electrical signal transmission paths in accordance with the switching control signal and connected as a part of an RF transmission path between the photoelectric converter and the optical modulator. The high-frequency oscillator according to claim 1, further comprising a path switch. The phase adjustment means is
A control signal output unit that outputs a switching control signal based on the frequency of the oscillation signal of the high-frequency oscillator;
A plurality of electrical signal transmission lines each having a different length;
Transmission in which an electrical signal transmission path having a desired length is selected from the plurality of electrical signal transmission paths in accordance with the switching control signal and connected as a part of an RF transmission path between the photoelectric converter and the optical modulator. The high-frequency oscillator according to claim 1, further comprising a path switch. The phase adjustment means is
A voltage detector for detecting a voltage value of a control signal used for phase shift by the PLL control means;
A control signal output unit that outputs a switching control signal based on a voltage value detected by the voltage detector;
A plurality of electrical signal transmission lines each having a different length;
Transmission path switching for selecting an electrical signal transmission path having a desired length from the plurality of electrical signal transmission paths in accordance with the switching control signal and connecting to an RF transmission path between the photoelectric converter and the light modulator. The high frequency oscillator according to claim 1, further comprising: The laser light generated from the laser light source is modulated by an optical modulator, the modulated laser light transmitted through an optical fiber is converted into a high-frequency signal by a photoelectric converter, and the converted high-frequency signal is predetermined by a bandpass filter. In the high-frequency oscillator that takes out the passband component of the predetermined frequency and returns the frequency of the high-frequency signal of the predetermined passband component to the optical modulator as a modulation signal and outputs it as an oscillation signal,
PLL control means for controlling the frequency of the high-frequency signal of the predetermined passband component to be constant;
A temperature detector for detecting the ambient temperature around the high-frequency oscillator;
Output wavelength discrimination for discriminating a desired output wavelength of the laser beam necessary for keeping the fluctuation of the oscillation frequency of the high frequency oscillator within the preset frequency pull-in range of the PLL control means based on the detected ambient temperature With means,
2. The high frequency oscillator according to claim 1 , wherein a tunable laser light source that generates laser light having the determined desired output wavelength is used as the laser light source.   The output wavelength discriminating unit discriminates a desired output wavelength of the laser beam based on the frequency of the oscillation signal of the high frequency oscillator instead of the environmental temperature detected by the temperature detector. 14. The high frequency oscillator according to 14.   The output wavelength discrimination means discriminates the desired output wavelength of the laser based on the voltage value of the control signal used for the phase shift by the PLL control means instead of the environmental temperature detected by the temperature detector. The high frequency oscillator according to claim 14.

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