JP2013205473A - Resonator system, light source device, and frequency filter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a resonator system which achieves high temperature stability and allows a resonance frequency of a resonator to be changed.SOLUTION: The resonator system includes a resonator, an electromagnetic wave source, a first control unit, a reception unit, a second control unit, and a third control unit. The resonator is provided with first and second resonator modes having first and second resonance frequencies respectively. The first and second resonance frequencies have temperature dependencies different from each other. The electromagnetic wave source makes a first electromagnetic wave impinge on the resonator. The first control unit controls the electromagnetic wave source so that the first frequency matches the first resonance frequency. The reception unit receives a second electromagnetic wave being an electromagnetic wave emitted out of the resonator as a result of resonance of the first electromagnetic wave with the second resonator mode. The second control unit controls the temperature of the resonator so as to maximize the intensity of the second electromagnetic wave. The third control unit controls an internal refractive index of the resonator so as to change a frequency maximizing the intensity of the second electromagnetic wave.

Description

  Embodiments described herein relate generally to a resonator system, a light source device, and a frequency filter.

  The resonator has a property of transmitting only an electromagnetic wave having a frequency that matches the resonance frequency of the electromagnetic wave mode (resonator mode) unique to the resonator. For this reason, the resonator is used in a wide range of optical communication and optical measurement, such as an optical filter and a reference frequency for obtaining a frequency-stable laser beam.

  Since the resonance frequency of the resonator depends on the temperature of the resonator, the resonator cannot be used for an application that requires high frequency stability in a general environment where it is difficult to block the influence of temperature fluctuation.

Physical Review B 83, 021801R, (2011) Optics Express 19, 14495, (2011) Proceedings of SPIE-The International Society for Optical Engineering 7913, 79131G, (2011)

  In the resonator, a function capable of changing the resonance frequency may be required. For example, when the resonant frequency of an actually manufactured resonator is slightly different from the design specification frequency, or when it is desired to change the frequency of the transmission spectrum while being used as an optical filter.

  The present embodiment according to the present invention provides a resonator system that can achieve high temperature stability and can change the resonance frequency of the resonator. Moreover, the light source device and frequency filter using this resonator system are provided.

  A resonator system according to an embodiment includes a resonator, a first electromagnetic wave source, a first controller, a receiver, a second controller, and a third controller. The resonator includes a first resonator mode having a first resonance frequency and a second resonator mode having a second resonance frequency, and the first resonance frequency and the second resonance frequency are They have different temperature dependencies. The first electromagnetic wave source makes a first electromagnetic wave having a first frequency incident on the resonator. The first control unit controls the first electromagnetic wave source so that the first frequency matches the first resonance frequency. The receiving unit receives a second electromagnetic wave that is an electromagnetic wave emitted to the outside of the resonator by resonating with the second resonator mode. The second control unit controls the temperature of the resonator so that the intensity of the second electromagnetic wave is maximized. The third control unit controls the refractive index inside the resonator in order to change the frequency at which the intensity of the second electromagnetic wave becomes maximum.

1 is a block diagram schematically showing a resonator system according to a first embodiment. (A) And (b) is a figure explaining the method of temperature stabilization which concerns on 1st Embodiment. The graph explaining the temperature dependence of the resonant frequency of resonator mode. The graph which shows the change of the resonant frequency of the resonator mode when a voltage is applied to the resonator shown in FIG. The figure explaining the method to select the 1st and 2nd resonator mode based on 1st Embodiment. The block diagram which shows roughly the resonator system which concerns on 2nd Embodiment. (A) And (b) is a figure explaining the method of temperature stabilization which concerns on 2nd Embodiment. The graph explaining the temperature dependence of the resonant frequency of 1st and 2nd resonator mode, and the frequency of Stokes light. The graph which shows the change of the resonant frequency of the resonator mode when a voltage is applied to the resonator shown in FIG. 6, and the change of the frequency of Stokes light. The figure explaining the method to select the 1st and 2nd resonator mode based on 2nd Embodiment. The block diagram which shows schematically the light source device which concerns on 3rd Embodiment. The block diagram which shows schematically the light source device which concerns on 4th Embodiment. The block diagram which shows roughly the light source device which concerns on 5th Embodiment.

  Hereinafter, the resonator system according to the embodiment will be described with reference to the drawings as necessary. Note that, in the following embodiments, the same numbered portions are assumed to perform the same operation, and repeated description is omitted.

(First embodiment)
FIG. 1 schematically shows a resonator system according to the first embodiment. As shown in FIG. 1, the resonator system includes a resonator 100, a light source 110, a frequency control device 120, a light receiver 130, a temperature control device 140, a voltage control device 150, and a polarization beam splitter (PBS) 160. .

  The resonator 100 is a single crystal resonator made of, for example, LiNbO that is a birefringent crystal. For example, the resonator 100 is formed in a spheroid shape having a radius in the major axis direction of 500 μm and a radius in the minor axis direction parallel to the Z axis of the crystal of 10 μm. In the resonator 100 having such a shape, when light is propagated along the circumference in the major axis direction, a plurality of resonator modes called whispering gallery modes are generated.

  In the first embodiment, a light source that emits laser light will be described as an example of the first electromagnetic wave source. The light source 110 emits laser light, and this laser light is directed to the resonator 100 by an optical system (not shown), for example. In the present embodiment, the laser light emitted from the light source 110 is polarized light including both ordinary and extraordinary rays (linearly polarized light or circularly polarized light that is not parallel to both ordinary and extraordinary rays). As the light source 110, for example, a semiconductor laser, a solid-state laser, a dye laser, a gas laser, an excimer laser, a free electron laser, or the like can be used. The frequency control device 120 uses the Pound-Drever-Hall method so that the center frequency of the laser light matches the resonance frequency of one of the resonator modes of the resonator 100 (first resonator mode). To control the light source 110. Hereinafter, one resonator mode that is a target for locking the center frequency of the laser light is referred to as a first resonator mode.

  A light receiver (also referred to as a receiving unit) 130 receives the laser light (transmitted light) emitted from the resonator 100 and generates a detection signal. The detection signal indicates the intensity of the received transmitted light. As the light receiver 130, for example, a photodiode can be used. In order to examine the polarization state of the transmitted light, a polarizing beam splitter 160 may be disposed between the resonator 100 and the light receiver 130.

  The temperature control device 140 receives the detection signal from the light receiver 130 as a feedback signal, and controls the temperature of the resonator 100 according to the feedback signal. The voltage control device 150 applies a voltage to the resonator 100 in order to change the resonance frequency of the resonator 100.

  Next, the resonator system of FIG. 1 will be described in detail.

First, a method in which the temperature control device 140 controls the temperature of the resonator 100 will be described.
In general, the resonance frequency of a resonator greatly varies depending on the temperature of the resonator. For example, in a monolithic resonator made of LiNbO, the resonance frequency fluctuates several GHz at 1 ° C. In order to keep the resonance frequency of the resonator constant, it is necessary to keep the temperature of the resonator constant. As a method of keeping the temperature of the resonator constant, a method of attaching temperature sensors to a plurality of locations of the resonator and feeding back to the temperature of the resonator, or a self-reference temperature stabilization method can be used. As a self-reference type temperature stabilization method, a method of fixing the frequency of the first resonator mode to a temperature that matches the frequency of the second resonator mode (first method), and an electromagnetic wave incident on the resonator There is a method (second method) in which the frequency of the Stokes light generated by combining the mechanical mode (acoustic mode) of the resonator and the resonator is fixed at a temperature that matches the frequency of the second resonator mode. The resonator system can perform temperature control with high accuracy by using a self-reference temperature stabilization method.

  In the present embodiment, the temperature of the resonator 100 is controlled using the first method described above. Hereinafter, the temperature of the resonator is referred to as the resonator temperature. The first method uses the difference in temperature dependence of the refractive index between the ordinary ray mode and the extraordinary ray mode in the birefringent crystal, and achieves the temperature stability of nK (nanokelvin) to pK (picokelvin). .

The resonance frequency of the first resonator mode is ν _1, and the resonance frequency of the other resonator mode (referred to as the second resonator mode) is ν ₂ . These resonance frequencies ν ₁ and ν ₂ depend on the resonator temperature. When the resonator temperature T is a specific temperature T _lock , the frequency ν ₁ of the first resonator mode coincides with the frequency ν ₂ of the second resonator mode. That is, ν ₁ (T _lock ) = ν ₂ (T _lock ). In this embodiment, the resonator temperature is fixed to a temperature at which the frequency ν ₁ of the first resonator mode matches the frequency ν _{2 of} the second resonator mode by the temperature control device 140.

If a frequency [nu ₁ of the first resonator mode frequency [nu ₂ of the second resonator modes are different, i.e., if the cavity temperature is not the temperature T _lock, as shown in FIG. 2 (a), the light source 110 When the laser beam having the frequency ν _{1 from} the laser beam enters the resonator 100, only the light having the same polarization as that in the first resonator mode is transmitted through the resonator 100. In contrast, if the frequency [nu ₁ of the first resonator mode and a frequency [nu ₂ of the second resonator modes are matched, i.e., if the cavity temperature is a temperature T _lock, in FIG. 2 (b) As shown, light having the same polarization as that of the first resonator mode and light having the same polarization as that of the second resonator mode are transmitted through the resonator 100. Δν (T) shown in FIGS. 2A and 2B represents a frequency difference between the first resonator mode and the second resonator mode.

In the present embodiment, as will be described later, the first resonator mode is selected from the ordinary ray mode and the second resonator mode is selected from the extraordinary ray mode, or the first resonator mode is selected. Is selected from the extraordinary ray mode, and the second resonator mode is selected from the ordinary ray mode. The polarization of light either of the ordinary ray and the extraordinary ray comprises the use as the incident light, the polarization of the light is at a temperature other than the specific temperature T _lock reflected by the resonator 100, the resonator at a specific temperature T _lock 100 is transmitted. The polarization beam splitter 160 reflects light having the same polarization as that of the first resonator mode out of the transmitted light from the resonator 100 by 90 degrees and transmits light having the same polarization as that of the second resonator mode. The temperature control device 140 adjusts the resonator temperature to a temperature at which the intensity of transmitted light indicated by the feedback signal is maximized, that is, a temperature at which the light having the same polarization as the second resonator mode is detected by the light receiver 130. To do. Examples of the temperature adjustment method include a method using a thermoelectric element such as a Peltier element and a method of heating with a modulated laser.

Here, the temperature dependence of the resonance frequency of the resonator mode will be described.
The resonator mode spectrum of the resonator has a shape in which Lorentz-type transmission regions are arranged at regular intervals, such as a comb shape, and the peak frequency (resonance frequency) and interval of the resonator mode (free spectrum range (FSR)). )) Is determined by the size of the resonator and the refractive index inside the resonator. The rate of change of the resonance frequency of the resonator mode with temperature is expressed by the following formula (1).

However, the resonance frequency of the e-th resonator mode at the resonator temperature T is ν _e (T), the thermal expansion coefficient is α, and the refractive index is n _e (T). Here, e = 1 and 2.

FIG. 3 shows the temperature dependence of the resonance frequency of two resonator modes (first and second resonator modes) of the plurality of resonator modes. As shown in FIG. 3, when the resonator temperature is the temperature T _lock , the resonance frequency ν ₁ of the first resonator mode coincides with the resonance frequency ν _{2 of} the second resonator mode. Therefore, when the resonator temperature is fixed to the temperature T _lock by the temperature control device 140, the resonance frequencies of all the resonator modes of the resonator 100 are also uniquely determined as the frequencies at the fixed temperature T _lock .

Next, a method in which the voltage control device 150 controls the resonance frequency of the resonator 100 will be described.
In the self-referencing temperature stabilization method, as described above, the resonance frequency of the resonator mode is uniquely determined. In the present embodiment, the resonance frequency of the resonator mode can be changed by changing the refractive index of the resonator 100 using the electro-optic effect. In this embodiment, as a method of changing the resonance frequency of the resonator 100, a method of applying a voltage (electrostatic field) to the resonator 100 is used. Note that the method of changing the refractive index of the resonator 100 is not limited to a method using an electric field, and may be a method using a magnetic field, for example.

In the case of a material having a finite electro-optic coefficient, the rate of change of the resonator mode frequency by the voltage V is expressed by the following formula (2).

However, the resonance frequency of the e-th resonator mode when the voltage is 0 is ν _e (0), the primary electro-optic coefficient of the e-th resonator mode is r _e , and the distance between the electrodes is d. FIG. 4 shows the temperature dependence of the resonance frequency of the first and second resonator modes when a certain voltage V is applied to the resonator 100. In FIG. 4, ν ₁ ′ (T) represents the resonance frequency of the first resonator mode when the voltage V is applied to the resonator 100, and ν ₂ ′ (T) represents the voltage V applied to the resonator 100. The resonance frequency of the 2nd resonator mode at the time of applying is shown. Thus, when the voltage V is applied to the resonator 100, the resonance frequency of the resonator mode changes by a different amount due to the electro-optic effect. As a result, the fixed temperature at which the resonance frequency of the first resonator mode coincides with the resonance frequency of the second resonator mode is shifted to the temperature T _lock ′. As a result, the resonance frequency of the resonator mode at a fixed temperature is shifted.

By applying a voltage, the resonance frequency of the resonator mode is shifted, and the temperature is stabilized under a new frequency matching condition (fixed temperature T _lock ′), whereby the resonance frequency at the time of temperature stabilization is made variable. That is, a self-reference type temperature stabilization method can achieve high temperature stability and a resonator system with a variable resonance frequency. Furthermore, since the electrostatic field is used to set the frequency, it is easy to set with high accuracy and high stability, and the temperature is stabilized from nK (nanokelvin) to pK (picokelvin) by the self-reference temperature stabilization method. The frequency at a fixed temperature can be shifted without impairing the performance. In this way, the resonator system of the present embodiment uses the electro-optic effect to change the “frequency when a signal used for temperature stabilization (transmitted light from the resonator 100) is strongly emitted”. ing.

  In order to widen the settable resonance frequency range, a crystal material having a large difference in electro-optic coefficient between the two resonator modes is preferably used as the material of the resonator 100. Further, as shown in Equation (2), the resonance mode frequency changes greatly as the distance between the electrodes decreases. Therefore, by reducing the size of the resonator 100 so as to reduce the distance between the electrodes, the resonance frequency can be greatly shifted even with the same voltage.

Next, a method for selecting the first resonator mode and the second resonator mode will be described with reference to FIG.
When the first method is used, the resonance frequencies of the two resonator modes need to match at a specific temperature. For this reason, it is impossible to use two ordinary ray modes that are separated by FSR and are adjacent to each other like the j-th ordinary ray mode and the j + 1th (or j−1) th ordinary ray mode in FIG. . As shown in FIG. 5, when the j-th ordinary ray mode is selected as the first resonator mode, among the extraordinary ray modes of polarized light orthogonal to the ordinary ray mode, the anomaly that can match the resonance frequency. The light beam mode (kth extraordinary light beam mode) can be selected as the second resonator mode. Here, j and k are integers. Instead of the above-described example, the first resonator mode may be selected from the extraordinary ray mode, and the second resonator mode may be selected from the ordinary ray mode.

Next, an operation example of the resonator system according to the present embodiment will be specifically described.
In the resonator 100 of this embodiment, when the resonator temperature is 25.0 ° C., the resonance frequency ν ₁ of the first resonator mode and the resonance frequency ν _{2 of} the second resonator mode are both 280 THz. Shall. Further, it is assumed that the first resonator mode is selected from the ordinary ray mode, and the second resonator mode is selected from the extraordinary ray mode. At 25.0 ° C., the refractive index n ₁ of the first resonator mode is 2.2, and the refractive index n ₂ of the second resonator mode is 2.1. That is, n ₁ (25.0 ° C.) = 2.2 and n ₂ (25.0 ° C.) = 2.1. The temperature dependence n ₁ (T) and n ₂ (T) of the refractive index is expressed by the following mathematical formula (3).

Here, e = 1 and 2. ^{_{Furthermore, X 1 = 1.41 × 10 -6}} , Y 1 = 2.14 × 10 -8, X 2 = 3.85 × 10 -5, a Y 2 = 1.15 × ^{10 -7.} The thermal expansion coefficient α is 2.9 × 10 ⁻⁶ .

The frequency control device 120 controls the light source 110 so that the center frequency of the laser light from the light source 110 matches the resonance frequency ν ₁ of the first resonator mode. The temperature control device 140 applies a feedback to the temperature at which the light having the same polarization state as that in the extraordinary light mode is detected by the light receiver 130, that is, the intensity of the light indicated in the feedback signal is maximized. As a result, the resonator temperature is fixed at 25.0 ° C.

As described above, the resonance frequency of the resonator mode depends on the refractive index of the resonator mode. In the present embodiment, the refractive index is changed by applying a voltage to the resonator 100 by the voltage control device 150. A pair of electrodes for applying a voltage to the resonator 100 are provided facing the minor axis direction of the resonator 100, and the distance between the electrodes is 10 μm. When a voltage of 2 V is applied to the resonator 100, at 25.0 ° C., the resonance frequencies of the first and second resonator modes are shifted to the higher frequency side by 1.3 GHz and 4 GHz, respectively. Here, the primary electro-optic coefficients r ₁ and r ₂ of LiNbO are 9.6 × 10 ⁻¹² and 3.09 × 10 ⁻¹¹ , respectively. Thus, since the electro-optic coefficients of the first and second resonator modes are different, the fixed temperature at which the resonance frequency of the first resonator mode and the resonance frequency of the second resonator mode coincide with each other under a voltage of 2V. T _lock ′ shifts. In this example, the fixed temperature T _lock ′ is shifted from 25.0 ° C. to 25.3 ° C., and the resonance frequency of the first and second resonator modes at the fixed temperature T _lock ′ is 280 THz to 2.7 GHz. Just shift. That is, ν ₁ (25.3 ° C.) = Ν ₂ (25.3 ° C.) = 280.0027 THz. The temperature control device 140 fixes the light intensity indicated by the feedback signal to a new fixed temperature T _lock ′ that maximizes the light intensity. By applying a voltage to the resonator 100 in this way, the resonance frequency of the resonator can be changed.

  As described above, the resonator system according to the first embodiment includes the temperature control device that controls the temperature of the resonator using the self-reference temperature stabilization method, and the voltage control device that applies a voltage to the resonator. In addition to achieving high temperature stability, the resonance frequency of the resonator can be changed.

(Second Embodiment)
In the second embodiment, a method of fixing the frequency of the Stokes light generated by combining the electromagnetic wave incident on the resonator and the mechanical mode (acoustic mode) of the resonator to a temperature that matches the frequency of the second resonator mode. The temperature control of the resonator is performed using (second method) as a self-reference type temperature stabilization method. In the second embodiment, parts and operations different from those in the first embodiment will be mainly described, and descriptions of parts and operations similar to those in the first embodiment will be omitted as appropriate.

  FIG. 6 schematically shows a resonator system according to the second embodiment. The resonator system shown in FIG. 6 has substantially the same configuration as the resonator system shown in FIG. More specifically, the polarization beam splitter 160 is removed from the resonator system shown in FIG.

First, a method for controlling the temperature of the resonator 100 according to the present embodiment will be described.
The resonance frequency of the first resonator mode is ν ₁ . When laser light of frequency [nu ₁ from the light source 110 is incident on the resonator 100, the laser light is coupled with the mechanical mode of the resonator 100, thereby, as shown in FIG. 7 (a), a mechanical mode from the frequency [nu ₁ The light (Stokes light) shifted to the lower frequency side by the natural frequency ν _m is emitted from the resonator 100. When the resonator temperature is a specific temperature T _lock , as shown in FIG. 7B, the frequency of the Stokes light is set to another resonator mode (second resonator mode) such as the adjacent resonator mode. ) of matching the resonant frequency [nu _2, Stokes light is strongly emitted by resonance effect. That is, the condition under which the Stokes light is strongly emitted is that the frequency difference Δν (T) between the first resonator mode and the second resonator mode matches the natural frequency ν _m (T) of the mechanical mode. That is, Δν (T _lock ) = ν _m (T _lock ) is satisfied. The light receiver 130 receives the Stokes light (transmitted light) emitted from the resonator 100 and sends a detection signal indicating the intensity of the received light to the temperature control device 140 as a feedback signal. The temperature control device 140 fixes the resonator temperature at a temperature at which the intensity indicated by the feedback signal is maximized.

Since the frequency difference Δν between the first resonator mode and the second resonator mode and the natural frequency ν _m of the mechanical mode are different in temperature, the condition is satisfied only at a predetermined temperature T _lock . By utilizing this characteristic, the resonator temperature can be stabilized with high accuracy. The amount of change in the frequency of the mechanical mode depending on the temperature is expressed by the following mathematical formula (4).

  However, the resonance frequency of the mechanical mode at a certain temperature T is νm (T), and the sound speed is νs (T).

The resonator 100 also emits light (anti-Stokes light) shifted to the higher frequency side by the natural frequency ν _m of the mechanical mode together with the Stokes light. The resonator system can also perform temperature control using anti-Stokes light instead of Stokes light. In this embodiment, a case where Stokes light is used will be described.

FIG. 8 shows the temperature dependence of the resonance frequency of the first and second resonator modes and the frequency of the Stokes light. As shown in FIG. 8, the resonator temperature fixed by the second method is a temperature T _lock at which the frequency of the Stokes light and the resonance frequency of the second resonator mode coincide. When the resonator temperature is fixed to the temperature T _lock by the temperature control device 140, the resonance frequencies of all the resonator modes of the resonator 100 are also uniquely determined as the frequencies at the fixed temperature T _lock .

Next, a method for controlling the resonance frequency of the resonator 100 according to the present embodiment will be described.
In the second embodiment, similarly to the first embodiment, the resonance frequency of the resonator mode can be changed by changing the refractive index of the resonator 100 using the electro-optic effect. . It is known that the frequency of the mechanical mode hardly changes with the application of voltage (electric field). Therefore, when using the second method, as shown in FIG. 9, the frequency of the resonator mode and the frequency of the Stokes light at the fixed temperature T _lock ′ under application of an electric field are substantially equal to the frequency of the resonator mode. It is possible to shift by the shift amount. In FIG. 9, ν ₁ ′ (T) represents the resonance frequency of the first resonator mode when a certain voltage V is applied to the resonator 100, and ν ₂ ′ (T) represents the voltage V applied to the resonator 100. The resonance frequency of the second resonator mode when applied to is shown.

  Next, a method of selecting the first resonator mode and the second resonator mode according to the present embodiment will be described with reference to FIG.

  As shown in FIG. 10, when the jth ordinary ray mode is selected as the first resonator mode, the jth Stokes light is generated by the coupling of the mechanical mode. At this time, an ordinary ray mode other than the j-th or any extraordinary ray mode (k-th in FIG. 10) is selected as the second resonator mode. Alternatively, the jth extraordinary ray mode may be selected as the first resonator mode, and the extraordinary ray mode other than the jth or any ordinary ray mode may be selected as the second resonator mode.

Next, an operation example of the resonator system according to the present embodiment will be specifically described.
In the present embodiment, the ordinary ray mode is used as the first resonator mode, and the extraordinary ray mode is used as the second resonator mode. Furthermore, when the resonator temperature is 25.0 ° C., the resonance frequency ν _{1 of} the first resonator mode is 280 THz, and the resonance frequency ν _{2 of} the second resonator mode is reduced by 280 THz to 0.1 GHz. When it is on the frequency side and the resonator temperature is 25.0 ° C., the natural frequency of the mechanical mode is assumed to be 0.1 GHz. That is, when the resonator temperature is 25.0 ° C., the frequency of the Stokes light matches the resonance frequency ν ₂ of the second resonator mode. At 25.0 ° C., the refractive index n ₁ of the first resonator mode is 2.2, and the refractive index n ₂ of the second resonator mode is 2.1. That is, n ₁ (25.0 ° C.) = 2.2 and n ₂ (25.0 ° C.) = 2.1. The temperature dependence of the refractive index n ₁ (T) and n ₂ (T) is expressed by the above mathematical formula (3).

The frequency control device 120 controls the light source 110 using the Pound-Drever-Hall method so that the center frequency of the laser light from the light source 110 matches the resonance frequency ν ₁ of the first resonator mode. The temperature control device 140 applies feedback to the temperature such that the Stokes light is detected by the light receiver 130, that is, the intensity of the light indicated in the feedback signal is maximized. As a result, the resonator temperature is fixed at 25.0 ° C.

When the voltage controller 150 applies a voltage of 2V to the resonator 100, at 25.0 ° C., the resonance frequencies of the first and second resonator modes shift to the higher frequency side by 1.3 GHz and 4 GHz, respectively. As a result, the fixed temperature T _lock ′ at which the difference between the resonance frequency of the first resonator mode and the resonance frequency of the second resonator mode matches the natural frequency of the mechanical mode at a voltage of 2 V is 25.3 ° C. The resonance frequency is shifted by 2.7 GHz. The temperature control device 140 fixes the light intensity indicated by the feedback signal to a new fixed temperature T _lock ′ that maximizes the light intensity.

  As described above, the resonator system according to the second embodiment is similar to the first embodiment in that the temperature control device that performs temperature control of the resonator using the self-reference temperature stabilization method, By providing a voltage control device that applies a voltage to the resonator, it is possible to achieve high temperature stability and to change the resonance frequency of the resonator.

(Third embodiment)
FIG. 11 schematically shows a light source device according to the third embodiment. The light source device shown in FIG. 11 includes a laser light source 1170 and a frequency control device 1180 in addition to the configuration of the resonator system shown in FIG. In the present embodiment, an example in which the light source device includes the resonator system (FIG. 1) according to the first embodiment will be described. However, the light source device is replaced with the resonator system according to the first embodiment. The resonator system according to the second embodiment (FIG. 6) may be provided.

  In the third embodiment, a laser light source will be described as an example of the second electromagnetic wave source. The laser light source 1170 emits laser light, and this laser light is directed to the resonator 100 by an optical system (not shown). The frequency control device 1180 controls the laser light source 1170 so that the center frequency of the laser light source 1170 matches the resonance frequency of the first resonator mode of the resonator 100. Specifically, the frequency control device 1180 detects the laser beam reflected by the resonator 100 and adjusts the center frequency of the laser light source 1170 based on the detection result. Note that the center frequency of the laser light source 1170 is not limited to the example controlled to match the resonance frequency of the first resonator mode of the resonator 100, but matches the resonance frequency of the other resonator modes of the resonator 100. It may be controlled to do.

  The resonance frequency of the first resonator mode is stabilized by performing the temperature control described in the first embodiment. Therefore, the laser light source 1170 whose frequency is locked in the first resonator mode can obtain very high frequency stability. Further, a beam splitter 1190 is provided between the resonator 100 and the light receiver 130 in order to extract laser light generated by the laser light source 1170 and transmitted through the resonator 100 as output light of the light source device.

  Furthermore, as described in the first embodiment, the resonance frequency of the resonator mode can be adjusted by applying a voltage to the resonator 100. In this way, by adjusting the resonance frequency of the resonator mode by applying a voltage, the frequency of the output light can be adjusted.

  As described above, the light source device according to the third embodiment uses the resonator system according to the first embodiment so that the frequency of the output light is variable and high frequency stability is realized. Can do.

(Fourth embodiment)
In the fourth embodiment, an example in which the resonator system according to the first embodiment is used as an optical filter will be described.
FIG. 12 schematically shows a light source device according to the fourth embodiment. This light source device uses the resonator system shown in FIG. 1 as an optical frequency filter. Specifically, the light source device of FIG. 12 includes a white light source 1270 and a beam splitter 1290 in addition to the configuration of the resonator system shown in FIG. In the present embodiment, an example in which the light source device includes the resonator system (FIG. 1) according to the first embodiment will be described. However, the light source device is replaced with the resonator system according to the first embodiment. The resonator system according to the second embodiment (FIG. 6) may be provided.

  The white light source 1270 emits white light, and the white light is directed to the resonator 100 by an optical system (not shown). When white light is incident on the resonator 100, a spectrum having a shape (for example, a comb shape) in which Lorentz-type transmission regions separated from each of the first and second resonator modes by a free spectral range (FSR) are arranged. The transmitted light having is obtained. The beam splitter 1290 is disposed between the resonator 100 and the light receiver 130 in order to extract light generated by the white light source 1270 and transmitted through the resonator 100 as output light of the light source device.

  Since the resonance frequency of the resonator mode is stabilized by performing the temperature control described in the first embodiment, the frequency stability of the transmission spectrum is also high. That is, the resonator system can be used as an optical frequency filter having very high frequency stability.

  Furthermore, when a voltage is applied to the resonator 100 to change the frequency of the resonator mode, the spectrum of the transmitted light that has entered the resonator 100 from the white light source 1270 and passed through the resonator 100 is also shifted.

  As described above, according to the fourth embodiment, by controlling the voltage applied to the resonator 100, the resonator system can be used as an optical frequency filter having a variable frequency and high frequency stability of the transmission spectrum. Can do.

(Fifth embodiment)
In the fifth embodiment, another example in which the resonator system according to the first embodiment is used as an optical filter will be described.

  FIG. 13 schematically shows a light source device according to the fifth embodiment. This light source device uses the resonator system shown in FIG. 1 as an optical frequency filter. Specifically, the light source device of FIG. 13 includes a two-color light source 1370 and a beam splitter 1390 in addition to the configuration of the resonator system shown in FIG. In the present embodiment, an example in which the light source device includes the resonator system (FIG. 1) according to the first embodiment will be described. However, the light source device is replaced with the resonator system according to the first embodiment. The resonator system according to the second embodiment (FIG. 6) may be provided.

  The two-color light source 1370 emits laser light including first light and second light, and this laser light is directed to the resonator 100 by an optical system (not shown). Here, it is assumed that the frequency of the first light is 280 THz and the frequency of the second light is 280 THz + 2.7 GHz. When no voltage is applied to the resonator, when the laser light from the two-color light source 1370 enters the resonator 100, the resonator system reflects the second light and transmits the first light. Function as. On the other hand, when a voltage of 2 V is applied to the resonator, the resonator system functions as an optical selection filter that reflects the first light and transmits the second light. The beam splitter 1390 is disposed between the resonator 100 and the light receiver 130 in order to extract light generated by the two-color light source 1370 and transmitted through the resonator 100 as output light of the light source device.

  Since the resonance frequency of the resonator mode is stabilized by performing the temperature control described in the first embodiment, the frequency stability of the transmission spectrum is also high. That is, the resonator system can be used as an optical frequency filter having very high frequency stability.

  As described above, according to the fifth embodiment, by controlling the voltage applied to the resonator 100, the resonator system can be used as an optical frequency filter having a variable frequency and a high frequency stability of the transmission spectrum. Can do.

  In addition, the arrangement | positioning and shape demonstrated by each embodiment are examples, and the different arrangement | positioning and shape from which the same effect is acquired can be used. Furthermore, the material of the resonator 100 is not limited to the example of LiNbO, and different materials having an electro-optic effect such as LiTaO, KDP, and MgF can be used.

  Although several embodiments of the present invention have been described, these embodiments are presented by way of example and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the scope of the invention. These embodiments and modifications thereof are included in the scope and gist of the invention, and are included in the invention described in the claims and the equivalents thereof.

DESCRIPTION OF SYMBOLS 100 ... Resonator, 110 ... Light source, 120 ... Frequency control device, 130 ... Light receiver, 140 ... Temperature control device, 150 ... Voltage control device, 160 ... Polarizing beam splitter, 1170 ... Laser light source, 1180 ... Frequency control device, 1190 , 1290, 1390 ... beam splitter, 1270 ... white light source, 1370 ... two-color light source.

Claims (7)

A first resonator mode having a first resonance frequency and a second resonator mode having a second resonance frequency, wherein the first resonance frequency and the second resonance frequency are different from each other. Having a resonator,
A first electromagnetic wave source that inputs a first electromagnetic wave having a first frequency to the resonator;
A first controller that controls the first electromagnetic wave source so that the first frequency matches the first resonance frequency;
A receiving unit that receives a second electromagnetic wave that is an electromagnetic wave resonated with the second resonator mode and emitted to the outside of the resonator;
A second control unit for controlling the temperature of the resonator so that the intensity of the second electromagnetic wave is maximized;
A third control unit for controlling the refractive index inside the resonator in order to change the frequency at which the intensity of the second electromagnetic wave becomes maximum;
A resonator system comprising:   2. The resonator system according to claim 1, wherein the second electromagnetic wave is an electromagnetic wave that is transmitted through the resonator after the first electromagnetic wave resonates with the second resonator mode.   The second electromagnetic wave is an electromagnetic wave generated by combining the first electromagnetic wave with a mechanical mode of the resonator, and is emitted to the outside of the resonator by resonating with the second resonator mode. The resonator system according to claim 1, wherein:   4. The resonator system according to claim 1, wherein the third control unit applies an electric field or a magnetic field to the resonator in order to control the refractive index. 5.   The resonator system according to claim 1, wherein the first electromagnetic wave source is a semiconductor laser. A resonator system according to any one of claims 1 to 5;
A second electromagnetic wave source whose frequency is locked to one of a plurality of resonator modes including the first resonator mode;
A light source device comprising:   A frequency filter comprising the resonator system according to claim 1.

Images