Abstract:
An atomic oscillator includes a light source, a first coil initiating the light source to emit light, a resonance cell having enclosed atoms absorbing light from the light source, a second coil adjusting the resonant frequency of the atoms in the resonance cell, a resonator supplying the microwave of a predetermined frequency to the resonance cell, a control circuit generating a control voltage corresponding to a light absorption amount in the resonance cell according to the microwave frequency, and an oscillator having an output signal frequency controlled to the resonant frequency by the control voltage, wherein the first and second coils and the resonator are formed of a conductor pattern on a rigid-flexible substrate having a rigid portion and a flexible portion, and the flexible portion is wound on the periphery of the light source and the resonance cell, and connected to a connector disposed on the rigid portion.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2008-151638, filed on Jun. 10, 2008, the entire contents of which are incorporated herein by reference. 
       FIELD 
       [0002]    The present invention relates to a passive atomic oscillator based on the principle of optical pumping. 
       BACKGROUND 
       [0003]    In recent years, with the advance of information digital networks, a highly accurate and highly stable clock source is essentially required. As such the clock source, an atomic oscillator such as a rubidium atomic oscillator is paid attention to, and a small-sized, low-cost oscillator is desired. In particular, from the viewpoint of mounting on an apparatus, a thin structure is an important issue. To develop a thin atomic oscillator, miniaturization of an optical microwave resonator is a key point (Patent document 1). 
         [0004]      FIG. 1  is a diagram illustrating the structure of a rubidium atomic oscillator based on the principle of optical pumping. In  FIG. 1 , a first magnetic shield structure  101  is covered with a second magnetic shield structure  102 . The respective inner sides thereof are covered with heat insulating materials  103 ,  104 . Further, in a resonance cell  105 , rubidium atoms are enclosed. Using the transition between the energy levels of the above rubidium atoms, a light of a particular wavelength is absorbed. A photodetector  106  detects light passing through the above resonance cell  105 . A cavity resonator  107  houses resonance cell  105 , and a coupling antenna  108  supplies a microwave to cavity resonator  107 . A solenoid coil  109  generates a static magnetic field to adjust the resonant frequency of the rubidium atoms enclosed in resonance cell  105 . A rubidium lamp  110  emits resonance light, and a lamp house  111  houses rubidium lamp  110 . An exciter  112  is a circuit for exciting rubidium lamp  110 . Also, a coil  113  is provided for discharging rubidium lamp  110  in an electrodeless manner. 
         [0005]    An optical microwave unit (OMU) is configured of the above resonance cell  105 , photodetector  106 , cavity resonator  107 , solenoid coil  109 , rubidium lamp  110 , lamp house  111  and exciter  112 . Further, heaters  114 ,  115  are provided for respectively maintaining resonance cell  105  and rubidium lamp  110  at a constant temperature. Further, there are provided thermistors  116 ,  117  having resistance values varied with the temperatures of resonance cell  105  and rubidium lamp  110 , respectively. 
         [0006]    Temperature control circuits  118 ,  119  are provided for controlling the temperatures of resonance cell  105  and rubidium lamp  110  to be constant. The above temperature control circuits  118 ,  119  respectively control transistors  120 ,  121  by the resistance values of thermistors  116 ,  117 , so as to control heater currents. 
         [0007]    Moreover, there are provided a preamplifier  122  for amplifying the output of photodetector  106 , a low frequency oscillator circuit  123 , a synchronous detector circuit  124  for performing synchronous detection of the output of preamplifier  122  using the output of low frequency oscillator circuit  123 , a frequency control circuit  125  for controlling a voltage controlled crystal oscillator, which will be described later, by the output of synchronous detector circuit  124 , a voltage controlled crystal oscillator  126  for stabilizing the oscillation frequency using atomic resonance produced by resonance cell  105 , a frequency modulation circuit  127  modulated by low frequency oscillator circuit  123 , and a high frequency generator circuit  128  for generating the resonant frequency (6.8346 . . . GHz) of the rubidium atoms. 
         [0008]      FIG. 2  is a diagram illustrating the operating principle of the rubidium atomic oscillator. As illustrated in  FIG. 2A , when the rubidium atoms enclosed in resonance cell  105  illustrated in  FIG. 1  are in a thermal equilibrium state, the rubidium atoms exist in a (5S, F1) level, which is a ground level, and a (5S, F2) level in equal probability. In the above state, when the resonant light of rubidium lamp  110  is irradiated on resonance cell  105 , only the rubidium atoms in the (5S, F1) level are excited to a 5P level, which is called optical pumping, as illustrated in  FIG. 2B . However, since the 5P level is an unstable energy level, by spontaneous emission, transition to the (5S, F1) level and the (5S, F2) level occurs with equal probability, as illustrated in  FIG. 2C . 
         [0009]    Then, after the repetition of the excitation of the rubidium atoms in the (5S, F1) level to 5P by the resonant light of rubidium lamp  110  and the spontaneous emission transition to the (5S, F1) level and the (5S, F2) level with equal probability, the rubidium atoms become existent only in the (5S, F2) level, as illustrated in  FIG. 2D . The above state is called a “negative temperature” state. In the above state, a microwave signal generated in high frequency generator circuit  128  is excited in cavity resonator  107 . When the microwave signal frequency coincides with a frequency (resonant frequency) corresponding to an energy difference between the (5S, F1) level and the (5S, F2) level, the rubidium atoms in the (5S, F2) level are transited to the (5S, F1) level by stimulated emission, as illustrated in  FIG. 2E . At this time, a light level detected by photodetector  106  decreases because resonance cell  105  absorbs light energy emitted from rubidium lamp  110 . The transition of the rubidium atoms becomes maximum when the microwave frequency coincides with a frequency (resonant frequency) corresponding to the energy difference between the (5S, F1) level and the (5S, F2) level, and becomes smaller as the difference between the microwave frequency and the resonant frequency becomes greater. 
         [0010]      FIGS. 3A and 3B  are diagrams illustrating the output of photodetector  106  caused by optical pumping. As illustrated in  FIG. 3A , the output of photodetector  106  becomes minimum when the microwave frequency coincides with the resonant frequency, and increases as the difference therebetween becomes greater. Finally, the output becomes constant because the stimulated emission does not occur any more. Additionally, a recess in the vicinity of f 0  of the curve A is called a “dip”. 
         [0011]    Now, the output of voltage controlled crystal oscillator  126  is phase modulated by low frequency oscillator circuit  123 , and a microwave signal frequency excited in cavity resonator  107  varies accordingly. This causes varied light absorption efficiency (a light absorption amount) in resonance cell  105 , and a varied light level detected by photodetector  106 . First, when the microwave frequency is equal to f 0 , the microwave signal modulated by a low frequency signal varies in the vicinity of the bottom of the dip. As a result, in the output of photodetector  106 , a frequency signal having twice as large frequency as the low-frequency modulation frequency is detected, as illustrated by B in  FIG. 3A . On the other hand, when the microwave signal is higher than f 0 , a microwave signal modulated by the low frequency signal varies in a rise portion of the right side of the dip. As a result, a microwave signal having an identical phase to the low frequency modulation signal is detected, as illustrated by C in  FIG. 3A . To the contrary, when the microwave signal is lower than f 0 , a microwave signal modulated by the low frequency signal varies in a rise portion of the left side of the dip. As a result, a microwave signal varies with an inverse phase to the low frequency modulation signal, as illustrated by D in  FIG. 3A . 
         [0012]    Such the above photodetector output is led to a synchronous detector circuit  124  via a preamplifier  122 , so that synchronous detection is carried out by means of low frequency oscillator circuit  123 . Namely, the output of photodetector  106  amplified by preamplifier  122  is supplied to frequency control circuit  125 , and a control voltage (refer to  FIG. 3B ) to be supplied to voltage controlled crystal oscillator  126  is generated through proportional control, integral control, differential control or control in combination thereof. By the above control voltage, the output of voltage controlled crystal oscillator  126  is controlled to have an identical frequency to the resonant frequency f 0  in the resonance cell. The above output is then supplied to an external circuit, as an output of the rubidium atomic oscillator. 
         [0013]      FIG. 4  is a diagram for explaining a structure to assemble an optical-microwave resonator of the rubidium atomic oscillator. The optical-microwave resonator is configured of a rubidium lamp unit P, a cavity resonator unit Q and a heat insulating material unit R. 
         [0014]    The rubidium lamp unit P is configured of the following component group: rubidium lamp  110 , coil  113  for electrodeless discharge, lamp house  111 , heater  115 , thermistor  117  for temperature control of the rubidium lamp, coil  113 , and rigid substrate  402  supplying necessary power to heater  115 . A flexible substrate  403  extends from rigid substrate  402 , so as to be connected to a main board. On the main board, there are mounted a variety of control circuits including high frequency generator circuit  128 , frequency modulation circuit  127 , low frequency oscillator circuit  123 , preamplifier  122 , synchronous detector circuit  124 , frequency control circuit  125  and voltage controlled crystal oscillator  126 , and a power supply circuit as well. 
         [0015]    Rubidium lamp  110  is adhesively secured inside coil  113  and included in lamp house  111  for heating. To heat lamp house  111 , a heater transistor  115  is secured by and in contact with a sheet etc. having good heat conduction. 
         [0016]    In the cavity resonator unit Q, cavity resonator  107  is configured of a metal case  405  to be the outer wall of a rectangular waveguide, a metal lid  406  and a rigid substrate  409 . Metal case  405  has a light guide hole for guiding an optical pumping light to the inside. A dielectric block  404  to miniaturize the resonator and resonance cell  105  are included inside metal case  405 . Further, a heater transistor  114  for heating resonance cell  105  is attached to metal case  405 . On the opposite face of the light guide hole, rigid substrate  409  is attached in such a manner as to close an aperture of metal case  405 . On rigid substrate  409 , there are mounted photodetector  106 , thermistor  116  for temperature control and coupling antenna  108  for exciting inside the resonator by microwave. Flexible substrate  403  extends from rigid substrate  409 , so as to be connected to the main board. 
         [0017]    The upper face of metal case  405  is closed by a metal lid  406 . Cavity resonator  107  is formed in the above closed space. On lid  406 , a tuning screw  407  is provided for adjusting the resonant frequency of the cavity resonator. By the insertion and extraction of the above tuning screw  407 , the resonant frequency is made adjustable. The rubidium lamp unit P and the cavity resonator unit Q are inserted in the heat insulating material unit R, and thereby a heat insulating effect is obtained. The heat insulating material unit R is configured of solenoid coil  109  being wound on the outer periphery of a heat insulating material  410 , so as to supply a static magnetic field to the resonance cell. A Zeeman effect produced by the above static magnetic field arranges the energy levels of the rubidium atoms in the resonance cell. Further, by adjusting the applied strength of the static magnetic field, it is possible to adjust the resonant frequency of the rubidium atoms. 
         [0018]      FIG. 5  is a top plan view of the optical-microwave resonator formed by the combination of the rubidium lamp unit, the cavity resonator unit and the heat insulating material unit. Since the atomic oscillator based on the optical pumping principle utilizes the Zeeman effect by the static magnetic field, the atomic oscillator is greatly influenced by the static magnetic field of terrestrial magnetism etc. Therefore, the resonance cell is magnetically shielded. 
         [0019]      FIG. 6  is an outer schematic view of an optical-microwave resonator covered with a shield case. The optical-microwave resonator is housed in a shield case  601  of a high permeability material. Flexible substrate  403  extending from shield case  601  is connected to a main board  603 . Main board  603  is a rigid substrate. On main board  603 , there are mounted high frequency generator circuit  128 , frequency modulation circuit  127 , low frequency oscillator circuit  123 , preamplifier  122 , synchronous detector circuit  124 , frequency control circuit  125 , voltage controlled crystal oscillator  126 , etc. illustrated in  FIG. 1 . Further, shield case  601  and main board  603  are housed in an external case (not illustrated), so that a product is completed. 
         [0020]    By using the above-mentioned structure, and by optimizing the size and the performance, a rubidium atomic oscillator having a thickness of 18 mm (75 cc in volume) has been developed today. 
         [0021]    [Patent document] the official gazette of the Japanese Unexamined Patent Publication No. 2001-308416. 
         [0022]    However, in the conventional structure described above, the rubidium atomic oscillator is configured of the combination of a plurality of units, each having a complicated structure also. Such the complicated structure is a cause of impeding further miniaturization and thinner formation. Moreover, the method of assembling each unit is also complicated (particularly, a coil winding process is intricate), and a strict rule is required for the assembly sequence. 
       SUMMARY 
       [0023]    According to an aspect of the invention, an atomic oscillator includes a light source, a first coil initiating the light source to emit light, a resonance cell having enclosed atoms absorbing light from the light source by transition between energy levels corresponding to a resonant frequency, a second coil adjusting the resonant frequency of the atoms in the resonance cell, a resonator supplying the microwave of a predetermined frequency to the resonance cell by exciting a microwave, a control circuit generating a control voltage corresponding to a light absorption amount in the resonance cell according to the microwave frequency, and an oscillator having an output signal frequency controlled to the resonant frequency by the control voltage, wherein the first coil, the second coil and the resonator are formed of a conductor pattern on a rigid-flexible substrate having a rigid portion and a flexible portion, and the flexible portion is wound on the periphery of the light source and the resonance cell, and connected to a connector disposed on the rigid portion. 
         [0024]    The object and advantages of the invention will be realized and attained by means of the elements and combinations particularly pointed out in the claims. 
         [0025]    It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are not restrictive of the invention, as claimed. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0026]      FIG. 1  is a diagram illustrating the structure of a rubidium atomic oscillator based on the principle of optical pumping; 
           [0027]      FIG. 2A-E  are diagrams illustrating the operating principle of the rubidium atomic oscillator; 
           [0028]      FIGS. 3A and 3B  are diagrams illustrating the output of photodetector  106  caused by optical pumping; 
           [0029]      FIG. 4  is a diagram for explaining a structure to assemble an optical-microwave resonator of the rubidium atomic oscillator; 
           [0030]      FIG. 5  is a top plan view of the optical-microwave resonator formed by the combination of the rubidium lamp unit, the cavity resonator unit and the heat insulating material unit; 
           [0031]      FIG. 6  is an outer schematic view of an optical-microwave resonator covered with a shield case; 
           [0032]      FIGS. 7A ,  7 B and  7 C are diagrams for explaining a structure of the rigid-flexible substrate according to the first embodiment; 
           [0033]      FIGS. 8A through 8C  are diagrams illustrating the structure of the rigid-flexible substrate according to a second embodiment; 
           [0034]      FIGS. 9A through 9C  are diagrams illustrating the structure of the rigid-flexible substrate according to the third embodiment; 
           [0035]      FIGS. 10A and 10B  are diagrams illustrating the structure of the rigid-flexible substrate according to the fourth embodiment; and 
           [0036]      FIGS. 11A through 11C  are diagrams for explaining the rigid-flexible substrate having the attached shield case. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
     First Embodiment  
       [0037]    According to a first embodiment, a solenoid coil for discharging a rubidium lamp in an electrodeless manner is formed of a conductor pattern of a rigid-flexible substrate. The rigid-flexible substrate has a flexible substrate and a rigid substrate of an integrated structure. The rigid-flexible substrate is a print substrate including a rigid portion constituted of a hard material such as glass epoxy and a flexible portion using a bendable material. In general, the rigid portion is formed by pasting a glass epoxy substrate on both sides of a portion of the flexible substrate. A portion of the flexible substrate having no glass epoxy substrate pasted thereon becomes the flexible portion intact. Electric conduction between the flexible portion and the rigid portion is secured by through holes. 
         [0038]      FIGS. 7A and 7C  are diagrams illustrating the structure of the rigid-flexible substrate according to the first embodiment. 
         [0039]      FIG. 7A  is a top plan view of the rigid-flexible substrate. As a conductor pattern, the rigid-flexible substrate includes a plurality of conductor lines  703  extending from a rigid portion  701  toward an end portion A of a flexible portion  702 . At the other end A′ of the conductor lines on rigid portion  701 , there is provided a connector  704  having each contact point to each of the one end side A of conductor lines  703  on flexible portion  702 . For electric connection, the conductor face on the one end side A of conductor lines  703  is exposed on a surface layer. 
         [0040]      FIGS. 7B and 7C  are diagrams respectively viewed from the directions Y, X illustrated in  FIG. 7A . As illustrated in  FIG. 7B , flexible portion  702  is looped in a manner to enclose rubidium lamp  110 , so that one end side A of conductor lines  703  of flexible portion  702  is connected to connector  704  disposed on the other end side A. At that time, the connection between the one end side A of conductor lines  703  and the other end side A′ thereof via connector  704  is made in a manner to be shifted by one line (refer to  FIG. 7C ). Thus, a solenoid coil is formed by the plurality of conductor lines  703 . The above solenoid coil functions as a coil for the electrodeless discharge of rubidium lamp  110 . As such, by looping and connecting to the connector the flexible substrate having the formed conductor pattern, the solenoid coil can be formed easily. 
         [0041]    Flexible portion  702  is required to have flexibility to the extent that the loop can be formed. Therefore, preferably, the thickness of the conductor pattern (conductor thickness) on the flexible portion of the rigid-flexible substrate is small. Though products having a variety of thicknesses are commercially sold, products having 18 μm are generally sold as thin products. However, if the conductor thickness is small, a current tolerance value of the conductor becomes small. The excitation circuit current of rubidium lamp  110  is 300 mA maximum, and 100 mA normally. By the size of the conductor thickness of 18 μm with a line width of 0.5 mm, or of that order, it is possible to satisfy both flexibility to be capable of being looped and the condition of the current tolerance value. 
         [0042]    Also, a heater (corresponding to heater  115  illustrated in  FIG. 1 ) and a thermistor (corresponding to thermistor  117  illustrated in  FIG. 1 ) required for heating to vaporize the rubidium in the rubidium lamp can be easily mounted on rigid portion  701 . Further, to secure rubidium lamp  110 , in consideration of heat conduction, it is preferable to use an adhesive agent having high heat conduction, so as to be filled between with flexible portion  702 . 
         [0043]    The structure of forming the solenoid coil by looping the flexible portion is also applicable to a solenoid coil to be wound on the periphery of the resonance cell, as will be described later. 
       Second Embodiment  
       [0044]    According to a second embodiment, a resonator for making a resonance cell resonate is formed using a rigid-flexible substrate. 
         [0045]      FIGS. 8A through 8C  are diagrams illustrating the structure of the rigid-flexible substrate according to a second embodiment. In  FIG. 8A , a microstrip line (microstrip resonator)  803  functioning as a resonator is formed on a flexible portion  802  of the rigid-flexible substrate. Microstrip resonator (which is also called patch antenna)  803  has a length L equal to λ/2 (λ is a resonant frequency). In general, the microstrip line produces small leakage of an electromagnetic field. Therefore, by widening a width W of microstrip resonator  803 , the leakage of the electromagnetic field is increased, thereby producing magnetic field coupling with the resonance cell. To avoid resonance in an unnecessary mode, preferably, the width W is λ/2 or smaller. 
         [0046]    By winding the periphery of resonance cell  105  with flexible portion  802 , microstrip resonator  803  is made to contact to the glass surface of resonance cell  105  (refer to  FIG. 8B ). At this time, microstrip resonator  803  is attached to resonance cell  105  in such a manner that a magnetic field component generated by resonant microstrip resonator  803  becomes parallel to a pumping light. 
         [0047]    To microstrip resonator  803 , a microstrip line  804  for power feeding is connected, and extends to rigid portion  801 . A microwave signal is input from microstrip line  804  on rigid portion  801 . The input level of the microwave signal is of the order of −30 dBm, by which the propagation of power through the microstrip line can be made. As such, by configuring the resonator using the conductor pattern, a cavity resonator becomes unnecessary. Thus, the miniaturization and the thin formation of the atomic oscillator can be obtained. 
         [0048]    Microstrip lines  803 ,  804  may be formed on a surface layer, an inner layer or a back surface layer of the rigid-flexible substrate. The ground plane is formed on a different layer from the layer on which microstrip lines  803 ,  804  are formed. Therefore, at least two layers are necessary. 
         [0049]    To realize a microstrip resonator having a resonant frequency of approximately 6834 MHz of the rubidium atom on the flexible portion having at least two layers, in case that a conductor thickness is 18 μm, the thickness of the flexible portion is 25 μm and the dielectric constant is 3.0, the length L of microstrip resonator  803  is L≈15 mm or of that order. Microstrip resonator  803  having the above length is applicable to a resonance cell having a size of φ10×20 mm, although a certain degree of correction is necessary because of the influence of the glass material of resonance cell  105 . 
         [0050]    Further, in  FIG. 8A , the rigid-flexible substrate includes a plurality of conductor lines  805  extending from rigid portion  801  to the end portion A of flexible portion  802 . The above plurality of conductor lines  805  are disposed respectively on the upper and lower areas of the portion in which microstrip resonator  803  is formed. Similar to connector  704  illustrated in  FIG. 7A , at the other end side A′ of the conductor lines on rigid portion  801 , there is provided a connector  806  having each contact point to each end of the one end side A of conductor lines  803  on flexible portion  802 . 
         [0051]    Further, as illustrated in  FIG. 8B , by looping flexible portion  802 , the one end side A of conductor lines  805  of flexible portion  802  is connected to connector  806 . At that time, the connection between the one end side A of conductor lines  805  and the other end side A′ of the conductor lines via connector  806  is made in a manner to be shifted by one line. Thus, solenoid coils by conductor lines  805  are formed respectively on the upper and lower areas of microstrip resonator  803  in a manner to sandwich microstrip resonator  803 . A static magnetic field for inducing the Zeeman effect onto the resonance cell is applied by the solenoid coil formed of conductor lines  805 . Additionally, a circuit for applying the static magnetic field using divided solenoid coils is described in the official gazette of the Japanese Unexamined Patent Publication No. 2005-175221, as an example. Also, as described earlier, by looping flexible portion  802  in a manner to enclose the resonance cell, microstrip resonator  803  is made to contact to the glass surface of resonance cell  105 . 
         [0052]      FIG. 8C  is a diagram illustrating the back surface of the rigid-flexible substrate, on which heater  114  and thermistor  116  are mounted. By heating the ground pattern using heater  114 , the periphery of resonance cell  105  can be heated effectively. Further, preferably, adhesion between resonance cell  105  and flexible substrate  802  is made by use of an adhesive agent having high heat conduction. 
       Third Embodiment  
       [0053]    According to a third embodiment, a resonator for making a resonance cell resonate is formed using a rigid-flexible substrate, similar to the second embodiment. In the third embodiment, in place of the microstrip line in the second embodiment, the resonator is formed of a microstrip line. 
         [0054]      FIGS. 9A through 9C  are diagrams illustrating the structure of the rigid-flexible substrate according to the third embodiment. In  FIG. 9A , a microslot line (microslot resonator)  903  functioning as a resonator is formed on the surface layer of a flexible portion  902  of the rigid-flexible substrate. The plane on which microslot line  903  is formed becomes a ground plane. 
         [0055]    On a layer (inner layer or back surface layer) which is different from the layer having microslot line  903  formed thereon, a microstrip line  904  for power feeding is formed. A microwave signal is input from microstrip line  904 , and supplied to microslot line  903 .  FIG. 9C  illustrates a back surface layer of the rigid-flexible substrate, illustrating an example of the formation of microstrip line  904 . 
         [0056]    Similar to the second embodiment, the periphery of resonance cell  105  is wound with flexible portion  802  so as to make microslot line  903  contact to the glass surface of resonance cell  105  (refer to  FIG. 9B ). At this time, microslot resonator  903  is attached to resonance cell  105  in such a manner that a magnetic field component generated by resonant microslot resonator  903  becomes parallel to a pumping light. 
         [0057]    To realize a microstrip resonator having a resonant frequency of approximately 6834 MHz of the rubidium atom, in case that a conductor thickness is 18 μm, the thickness of the flexible portion is 25 μm, and the dielectric constant is 3.0, the length L of microslot resonator  903  is L≈14 mm or of that order. Microslot resonator  903  having the above length is applicable to a resonance cell having a size of φ10×20 mm, although a certain degree of correction is necessary because of the influence of the glass material of resonance cell  105 . 
         [0058]    Further, in  FIG. 9A , similarly to  FIG. 8A , a plurality of conductor lines  905  extending from rigid portion  901  to the end portion A of flexible portion  902  are patterned respectively on the upper and lower areas of the portion of the rigid-flexible substrate in which microstrip resonator  903  is patterned. At the other end side A′ of the conductor lines on rigid portion  901 , there is provided a connector  906  having contact points each connected to each end of the one end side A of conductor lines  905  on flexible portion  902 . 
         [0059]    Further, as illustrated in  FIG. 9B , by looping flexible portion  902 , the one end side A of conductor lines  905  of flexible portion  902  is connected to connector  906 . At that time, the connection between the one end side A of conductor lines  805  and the other end side A′ thereof via connector  906  is made in a manner to be shifted by one line. Thus, solenoid coils by conductor lines  905  are formed respectively on the upper and lower areas of microslot resonator  903  in a manner to sandwich microslot resonator  903 . A static magnetic field for inducing the Zeeman effect onto the resonance cell is applied by the solenoid coil. Additionally, as described earlier, by looping flexible portion  902  in a manner to enclose the resonance cell, microslot resonator  903  is made to contact to the glass surface of resonance cell  105 . 
         [0060]      FIG. 9C  is a diagram illustrating the back surface of the rigid-flexible substrate, on which a heater  907  (which corresponds to heater  114  in  FIG. 1 ) and a thermistor  908  (which corresponds to thermistor  116  in  FIG. 1 ) are mounted. By means of heater  907 , the ground pattern is heated. Further, preferably, adhesion between resonance cell  105  and flexible substrate  902  is made by use of an adhesive agent having high heat conduction. 
       Fourth Embodiment  
       [0061]    A fourth embodiment illustrates a structure in which the aforementioned first embodiment and the second embodiment are realized using a single flexible substrate. A solenoid coil for the electrodeless discharge of rubidium lamp  110 , a resonator for exciting resonance cell  105 , a solenoid coil for supplying a static magnetic field to resonance cell  105  and a peripheral circuit group are formed in an integrated manner. Thus, a simplified structure and easy assembly can be obtained. 
         [0062]      FIGS. 10A and 10B  illustrate diagrams illustrating the structure of a rigid-flexible substrate according to the fourth embodiment.  FIG. 10A  illustrates the surface of the rigid-flexible substrate. The rigid-flexible substrate includes one rigid portion  1001 , and two independent flexible portions  1002 ,  1003  respectively extending from rigid portion  1001 . Flexible portion  1002  corresponds to flexible portion  702  in the first embodiment (refer to  FIGS. 7A to 7C ), and has a plurality of conductor lines  1004  formed in parallel. By looping flexible portion  1002  in a manner to enclose rubidium lamp  110 , the end portion of flexible portion  1002  is connected to connector  1005  formed on rigid portion  1001 . Thus, a solenoid coil for the rubidium lamp is formed. 
         [0063]    Flexible portion  1003  corresponds to flexible portion  802  in the second embodiment (refer to  FIGS. 8A to 8C ), and has a patterned microstrip resonator  1006 . Further, on each of the upper and lower sides thereof, a plurality of conductor lines  1007  are formed in parallel. By looping flexible portion  1003  in a manner to wind resonance cell  105  around, the end portion of flexible portion  1003  is connected to a connector  1008  formed on rigid portion  1001 . By this, microstrip resonator  1006  is made to contact to the glass surface of resonance cell  105 , and also, solenoid coils for generating static magnetic fields to be applied to resonance cell  105  are formed. 
         [0064]    To obtain efficient thermal coupling with rigid portion  1001  and flexible portions  1002 ,  1003 , both rubidium lamp  110  and resonance cell  105  are secured and filled with an adhesive agent having high heat conduction. 
         [0065]    Further, rigid portion  1001  includes an area (circuit group mounting area) for mounting a variety of circuit group disposed on the opposite side of an area having the mounted rubidium lamp  110  and resonance cell  105 , across sandwich connectors  1005 ,  1008 . Circuits to be mounted include oscillator circuit  112  for high frequency excitation of rubidium lamp  110 , high frequency generator circuit  128 , preamplifier  122 , frequency modulation circuit  127 , voltage controlled crystal oscillator  126 , low frequency oscillator circuit  123 , synchronous detector circuit  124 , etc. illustrated in  FIG. 1 . Instead of the conventional structure having a plurality of rigid substrates connected by flexible substrates, the circuit group can be concentrated on a single rigid-flexible substrate. This contributes to device miniaturization and simplification. 
         [0066]    Further, on the back surface of rigid portion  1001 , there are mounted heater  115  for heating rubidium lamp  110 , thermistor  117  for detecting the temperature of rubidium lamp  110 , temperature control circuit  119  of heater  115 , heater  114  for heating resonance cell  105 , thermistor  116  for detecting the temperature of resonance cell  105 , and temperature control circuit  118  for heater  114 , as illustrated in  FIG. 10B . 
         [0067]    Moreover, a photodetector  106  is connected to flexible portion  1009  extending downward from the mounting position of resonance cell  105  on rigid portion  1001 . At the time of assembly, photodetector  106  is adhesively secured on the bottom face of resonance cell  105  after flexible portion  1009  is bent. 
         [0068]    Holes  1010 ,  1011  are holes made in rigid portion  1001 . As will be described later, hole  1010  is used as an attachment hole for a shield case. Also, because rubidium lamp  110  and resonance cell  105  are normally controlled to different temperatures, hole  1011  is provided to prevent heat conduction therebetween. The reason for separately providing flexible portions  1002 ,  1003 , instead of a single flexible substrate, is to separate thermal coupling also. 
         [0069]    In the fourth embodiment illustrated in  FIGS. 10A ,  10 B, an exemplary structure of the first embodiment in combination with the second embodiment has been illustrated. However, it is also possible to configure using the third embodiment (resonator by microslot line), instead of the second embodiment (resonator by microstrip line). 
         [0070]      FIGS. 11A through 11C  are diagrams for explaining a rigid-flexible substrate on which a shield case is attached.  FIGS. 11A-11C  illustrate an example in which a shield case  1100  is attached to the rigid-flexible substrate according to the fourth embodiment illustrated in  FIGS. 10A ,  10 B.  FIG. 11A  is a top plan view of the rigid-flexible substrate having the attached shield case  1100 , and  FIG. 11B  is a section view thereof. 
         [0071]    Shield case  1100  is attached in a manner to enclose the disposition portion of the rubidium lamp and the resonance cell on which the flexible portion is wound. With this, shield case  1100  functions as a magnetic shield covering rubidium lamp  110  and resonance cell  105 . 
         [0072]      FIG. 11C  is a development view of shield case  1100 . Shield case  1100  is a metal plate of permalloy material. On the inner side of the side face, a resilient heat insulating material  1101  such as urethane is pasted. Heat insulating material  1101  prevents rubidium lamp  110  and resonance cell  105  from directly contacting to the metal plate of shield case  1100 , so as to produce loose thermal coupling to the outside. 
         [0073]    Further, a protrusion  1102  engages with a recess  1103  at the time of bending to a box shape. Another protrusion  1104  engages with a recess  1105  by being passed through a hole  1011  illustrated in  FIG. 10A , at the time of bending to the box shape. 
         [0074]    Using the aforementioned structure, basically, an assembly process is completed simply by securing rubidium lamp  110  and resonance cell  105  on predetermined positions of rigid portion  1001 , looping flexible portions  1002 ,  1103  in a manner to be wound on rubidium lamp  110  and resonance cell  105 , so as to be connected to connectors  1005 ,  1008 , and covering with shield case  1100 . A time and labor consuming wire winding work and a strict assembly rule become unnecessary, and the assembly is completed with an extremely easy work. 
         [0075]    According to an aspect of the embodiments, an atomic oscillator has an integrated configuration of a solenoid coil for emitting a rubidium lamp, a solenoid coil for adjusting the resonant frequency of a resonance cell, and a resonator for making the resonance cell resonate, using a conductive pattern formed on a rigid-flexible substrate. 
         [0076]    A plurality of conductor lines are formed in parallel on a flexible portion of the rigid-flexible substrate. By looping the flexible portion in a manner to be wound on the rubidium lamp, and by connecting one end of the conductor lines to the other end thereof in a manner to be shifted by one line, there is configured a solenoid coil for the electrodeless discharge of the rubidium lamp. 
         [0077]    On the flexible portion of the rigid-flexible substrate, a resonator is formed by a conductor pattern. The flexible portion is looped in a manner to be wound on the resonance cell. The resonator is made to contact to the resonance cell. The conductor pattern is formed of either a microstrip line or a microslot line. 
         [0078]    A plurality of conductor lines are formed in parallel respectively on the upper and lower areas of the resonator disposed on the flexible portion. By looping the flexible portion in a manner to be wound on the resonance cell, and by connecting one end of the conductor lines to the other end with a shift by one line, there is configured a solenoid coil for adjusting a resonant frequency of the resonance cell. 
         [0079]    By configuring the solenoid coil and the resonator using the conductor pattern formed on the rigid-flexible substrate, an easy-to-assemble atomic oscillator having a simplified structure can be achieved. 
         [0080]    All examples and conditional language recited herein are intended for pedagogical purposes to aid the reader in understanding the invention and the concepts contributed by the inventor to furthering the art, and are to be construed as being without limitation to such specifically recited examples and conditions, nor does the organization of such examples in the specification relate to a showing of the superiority and inferiority of the invention. Although the embodiment(s) of the present inventions have been described in detail, it should be understood that the various changes, substitutions, and alterations could be made hereto without departing from the spirit and scope of the invention.