Gas cell, and structure for atomic clock

Abstract

This gas cell GC is provided with a plate-shaped substrate having an internal space IS filled with gas, and is provided, on a first side surface S1 of the substrate, with a laser light introduction port WIN that is optically coupled to the internal space IS. The gas cell GC is provided, on a second side surface S2 of the substrate on the reverse side to the first side surface S1, with a laser light emission port WOUT that is optically coupled to the internal space IS. In the gas cell GC, a dimension L1 in the thickness direction of the internal space IS and an optical path length L2 of laser light traveling in the internal space IS, in a plane perpendicular to the thickness direction, satisfy the relationship L1 < L2.

Description

Gas cell and atomic clock structure

[0001] The present disclosure relates to gas cells and structures for atomic clocks.

[0002] Atomic clocks are known as devices that measure time accurately. There are several types of atomic clocks. In recent years, atomic clocks that irradiate gas in a gas cell with laser light, such as CPT (Coherent Population Trapping), have been expected. Gas containing alkali metals such as rubidium (Rb) or cesium (Cs) is sealed in the gas cell. Various types of measurement methods are possible. Physical structural components of atomic clocks, i.e., atomic clock structures equipped with laser elements, photodetectors, and gas cells, are also being studied. Patent Documents 1 to 3 disclose atomic clocks equipped with gas cells.

[0003] JP 2009-273088 A JP 2019-007763 A JP 2016-171419 A

[0004] There is a desire to miniaturize gas cells and structures for atomic clocks that include gas cells.

[0005] The gas cell of the present disclosure includes a plate-shaped substrate having an internal space filled with gas, and a laser light inlet optically coupled to the internal space on a side surface of the substrate. The gas cell of the present disclosure has a thickness dimension L1 of the internal space and an optical path length L2 of the laser light traveling within the internal space in a plane perpendicular to the thickness direction, where L1<L2. The atomic clock structure includes the gas cell, a laser element optically coupled to the laser light inlet, and a photodetector optically coupled to the internal space.

[0006] FIG. 1 is an exploded perspective view of an atomic clock structure including a gas cell according to a first embodiment. FIG. 2 is a longitudinal sectional view of the gas cell according to the first embodiment. FIG. 3 is a horizontal sectional view of the gas cell according to the first embodiment. FIG. 4 is a diagram showing a longitudinal sectional configuration of an atomic clock structure including a heater. FIG. 5 is a diagram showing a longitudinal sectional configuration of an atomic clock structure including a heater. FIG. 6 is a diagram showing a longitudinal sectional configuration of an atomic clock. FIG. 7 is a block diagram of an atomic clock. FIG. 8 is a longitudinal sectional view of a gas cell according to a second embodiment. FIG. 9 is a longitudinal sectional view of a gas cell according to a third embodiment. FIG. 10 is a longitudinal sectional view of a gas cell according to a fourth embodiment. FIG. 11 is a longitudinal sectional view of a gas cell according to a fifth embodiment. FIG. 12 is a longitudinal sectional view of a gas cell according to a sixth embodiment. FIG. 13 is a longitudinal sectional view of a gas cell according to a seventh embodiment. FIG. 14 is a horizontal sectional view of a gas cell. FIG. 15 is a horizontal sectional view of a gas cell. FIG. 16 is a horizontal sectional view of a gas cell. FIG. 17 is a horizontal sectional view of a gas cell. FIG. 18 is a horizontal sectional view of a gas cell. Fig. 19 is a horizontal cross-sectional view of a gas cell. Fig. 20 is a horizontal cross-sectional view of a gas cell. Fig. 21 is a horizontal cross-sectional view of a gas cell. Fig. 22 is a horizontal cross-sectional view of a gas cell. Fig. 23 is a horizontal cross-sectional view of a gas cell.

[0007] The gas cell and atomic clock structure according to the embodiment will be described below. Note that the same elements will be denoted by the same reference numerals, and duplicated explanations will be omitted.

[0008] FIG. 1 is an exploded perspective view of an atomic clock structure including a gas cell according to a first embodiment.

[0009] The atomic clock structure 100 includes a gas cell GC and a laser light inlet W of the gas cell GC. ＩＮ a laser element 3 optically coupled to the gas cell GC, and a laser beam output port W ＯＵＴ and a photodetector 4 optically coupled thereto via a laser diode. The laser element 3 may be a vertical cavity surface emitting laser (VCSEL), and the photodetector 4 may be a photodiode, although other types of elements may also be used.

[0010] An optical component 5 is interposed between the gas cell GC and the laser element 3. The optical component 5 is one or more optical elements selected from a group of optical elements such as a lens, an optical filter, and a quarter-wave plate. The optical component 5 may include all of a lens, an optical filter, and a quarter-wave plate, and these optical elements may be arranged in order from the laser element 3 side toward the gas cell GC.

[0011] The gas cell GC includes a plate-shaped substrate having an internal space IS filled with gas. The plate-shaped substrate is formed by combining a substrate 1 and a lid member 2. In the description, an XYZ Cartesian coordinate system is set. The thickness direction of the substrate 1 is the Z axis, the longitudinal direction of the substrate 1 is the Y axis, and the width direction of the substrate 1 is the X axis, and these axes are perpendicular to each other. A laser light introduction port W optically coupled to the internal space IS is provided on a first side surface S1 of the plate-shaped substrate. ＩＮ The laser light L emitted from the laser element 3 is ＩＮ travels in the Y-axis direction and passes through the optical component 5 through the laser light introduction port W ＩＮ The gas cell GC is connected to the laser light inlet W ＩＮ and the internal space IS. ＩＮ is one end face of the optical waveguide 1A. The optical waveguide 1A extends along the Y axis.

[0012] The laser light introduced into the optical waveguide 1A travels in the Y-axis direction within the optical waveguide 1A and is emitted from the other end face of the optical waveguide 1A. The laser light emitted from the optical waveguide 1A is irradiated onto a gas in the internal space IS. This gas contains an alkali metal such as cesium (Cs) or rubidium (Rb). This gas may also contain a rare gas.

[0013] If this gas contains an alkali metal, absorption of the laser light occurs according to its energy level. By controlling the energy level and frequency of the laser light, the absorption rate of the laser light in the gas changes. If the control signal given to the laser element 3 is feedback-controlled so that it matches the specific energy level difference of the alkali atoms that make up the gas, the frequency (clock) of the output signal from the feedback control circuit will be an accurate value.

[0014] The laser light propagates along the Y-axis in the internal space IS and passes through it. The laser light is incident on one end surface of the first window member 1B and exits from the other end surface (laser light exit port W ＯＵＴ In other words, the gas cell GC has a laser beam output port W optically coupled to the internal space IS on a second side surface S2 opposite to the first side surface S1 of the plate-like substrate. ＯＵＴ The laser beam output port W ＯＵＴ The laser light L emitted from ＯＵＴ is incident on the photodetector 4.

[0015] The gas cell GC is provided with a first auxiliary space 1D and a second auxiliary space 1E that communicate with the internal space IS and allow a portion of the gas source material in the internal space IS to remain. That is, a solid source material containing an alkali metal is placed in advance in the first auxiliary space 1D and the second auxiliary space 1E. During manufacturing, when this solid source material is heated to vaporize it and converted into gas in the internal space, some of the source material (including impurities, etc.) may remain in the first auxiliary space 1D and the second auxiliary space 1E.

[0016] The gas cell GC includes a lid member 2 fixed to the upper surface of a substrate 1. The upper surface of the substrate 1 is parallel to the XY plane. The lid member 2 is used to seal the internal space IS. An adhesive can be interposed between the lid member 2 and the substrate 1. One or both of the materials of the substrate 1 and the lid member 2 can be semiconductors or metals, respectively. One or both of the materials of the substrate 1 and the lid member 2 can also be glass or resin, respectively. If either the material of the substrate 1 or the lid member 2 is a heat-melting material, they can be bonded by applying heat and pressure to their interface. In this example, the material of the substrate 1 is silicon (Si), and the material of the lid member 2 is also silicon (Si).

[0017] FIG. 2 is a vertical cross-sectional view of the gas cell according to the first embodiment.

[0018] An optical waveguide 1A is disposed on the first side surface S1 of the plate-shaped substrate. The optical waveguide 1A can be formed by etching the top surface of the substrate 1 to form a groove, and then filling the groove with a laser light transmitting material. An example of the laser light transmitting material is glass (SiO ２ ) No optical waveguide is formed in the lid member 2. Except for the absence of an optical waveguide, the shape of the lid member 2 is the same as the shape of the substrate 1. In other words, the lid member 2 has a first auxiliary space and a second auxiliary space that are the same in shape as the first auxiliary space 1D and the second auxiliary space 1E shown in FIG.

[0019] The main space of the internal space IS of the gas cell GC is composed of a first recess 1C formed in the substrate 1 and a second recess 2C formed in the lid member 2. The depth direction of the first recess 1C is the negative direction of the Z axis, and the depth direction of the second recess 2C is the positive direction of the Z axis. The first recess 1C is connected to the first auxiliary space 1D via a first source gas inlet 1D1. Similarly, the second recess 2C is connected to the first auxiliary space (not shown) of the lid member 2 via a second source gas inlet 2D1. Similarly, the first recess 1C is connected to the second auxiliary space 1E (see FIG. 1) via a source gas inlet (not shown). Similarly, the second recess 2C is connected to the second auxiliary space (not shown) of the lid member 2 via a source gas inlet (not shown).

[0020] A first window material 1B is embedded in the region on the second side surface S2 side of the first recess 1C. Similarly, a second window material 2B is embedded in the region on the second side surface S2 side of the second recess 2C. These window materials can be formed by embedding a laser light transmitting material in the region on the second side surface side after forming each recess. An example of the laser light transmitting material is glass (SiO ２ This may be formed by preparing a block of window material in a separate process and fixing the block within the region on the second side surface of the recess.

[0021] The dimension L1 in the thickness direction (Z-axis direction) of the internal space IS of the gas cell GC is set to be small. In a plane (XY plane) perpendicular to this thickness direction (Z-axis direction), the optical path length L2 of the laser light traveling along the Y-axis within the internal space IS is greater than the dimension L1. In other words, the relationship of dimension L1 < optical path length L2 is satisfied. In this example, the optical path length L2 within the internal space IS is also the dimension of the internal space IS in the Y-axis direction.

[0022] It is also possible to use a structure in which the laser light is reflected so that it travels back and forth inside the internal space IS along the Y-axis direction. In this structure, the relationship L1 < L2 is also satisfied. To allow the laser light to travel back and forth, the angles of the wall surfaces at both ends of the Y-axis direction that define the internal space IS may be slightly inclined from the XZ plane, and a reflective film may be provided on these wall surfaces.

[0023] The dimension L1 satisfies 0.1 μm≦L1≦1000 μm. If L1 is smaller than the lower limit, it becomes practically difficult to introduce laser light. If L1 exceeds the upper limit, the gas cell cannot be sufficiently miniaturized. More preferably, the dimension L1 satisfies 1 μm≦L1≦500 μm. This gas cell GC is thinner than existing structures, and therefore can be installed in small devices such as mobile phones.

[0024] The optical path length L2 (dimension) can be set, for example, to 100 μm≦L2≦5000 μm. If L2 is smaller than the lower limit, the amount of gas for the atomic clock will be insufficient. If L2 exceeds the upper limit, the gas cell cannot be made sufficiently small.

[0025] 3 is a horizontal cross-sectional view of the gas cell according to the first embodiment, which is an XY cross-sectional view taken along the line III-III shown in FIG.

[0026] As shown in the figure, the first auxiliary space 1D and the second auxiliary space 1E are also located in the horizontal cross section of the substrate 1 where the internal space IS exists. Since the first auxiliary space 1D and the second auxiliary space 1E are formed from recesses, these recesses can be formed simultaneously when the first recess 1C is formed. The recesses can be formed by etching or the like.

[0027] The horizontal cross-sectional shape of the optical waveguide 1A is rectangular. The optical waveguide 1A extends along the Y-axis direction. The XZ cross-sectional shape of the optical waveguide 1A is also rectangular, but it can also be trapezoidal or triangular. A rectangle is an easy shape to process and can also sufficiently transmit laser light.

[0028] The horizontal cross-sectional shape of the internal space IS includes a trapezoid. The second width X2 of the internal space IS on the photodetector side is wider than the first width X1 on the laser element side. Even if the laser light widens as it approaches the photodetector, it can still be detected sufficiently.

[0029] In the horizontal cross section, the first and second source gas inlets 1D1 and 1E1 communicate with the hypotenuse of the trapezoidal internal space IS, respectively communicating with the first auxiliary space 1D and the second auxiliary space 1E. In the horizontal cross section, the first auxiliary space 1D is rectangular, and the first center line DX1 of the path from the first source gas inlet 1D1 to the first source gas inlet 1D1 is oriented toward the XZ plane including the end face on the exit side of the gas cell. Similarly, in the horizontal cross section, the second auxiliary space 1E is rectangular, and the second center line EX1 of the path from the second auxiliary space 1E to the second source gas inlet 1E1 is oriented toward the XZ plane including the end face on the exit side of the gas cell. The window material can also be arranged so that it is not located on the extension of these center lines. The shape of the gas introduction path can also prevent adhesion of source material to the optical waveguide and window material when introducing gas into the internal space. The shape of each auxiliary space can also be circular, elliptical, or other shapes other than rectangular.

[0030] FIG. 4 is a diagram showing a vertical cross-sectional configuration of an atomic clock structure equipped with a heater.

[0031] In the figure, the laser element 3, photodetector 4, optical components 5, and gas cell GC are shown with gaps between them to clearly explain the structure. These elements can also be placed in close contact, if necessary. The atomic clock structure 100 includes a second heater H2 attached to the upper lid member 2 that constitutes a plate-shaped substrate. The atomic clock structure 100 also includes a coil CL that surrounds the plate-shaped substrate (substrate 1 and lid member 2) along the Y-axis direction. The coil CL applies a static magnetic field to the inside of the gas cell, suppressing the influence of external magnetic fields such as geomagnetism. Heating by the second heater H2 can vaporize the raw material. Additionally, the second heater H2 can be used to control the gas pressure in the internal space IS, if necessary, or to control the temperature of the laser element 3 located nearby.

[0032] FIG. 5 is a diagram showing a vertical cross-sectional configuration of an atomic clock structure equipped with a heater.

[0033] This atomic clock structure 100 has a structure in which a first heater H1 is further attached to the lower surface of the substrate 1 in the atomic clock structure 100 shown in Fig. 4. The first heater H1 can function in the same way as the second heater H2.

[0034] FIG. 6 is a diagram showing the vertical cross-sectional structure of an atomic clock.

[0035] The atomic clock 200 includes a wiring substrate 10, an atomic clock structure 100 mounted on the wiring substrate 10, and a control circuit 20 mounted on the wiring substrate 10. The control circuit 20 processes electrical signals in the atomic clock structure 100 and outputs a clock signal. The control circuit 20 can supply a drive signal to the laser element 3, receive a signal from the photodetector 4, generate a feedback signal from the received signal, and generate a drive signal for the laser element 3 from the feedback signal. The control circuit 20 can also control the power supplied to the first heater H1 and the second heater H2 based on the feedback signal or independently of the feedback signal.

[0036] FIG. 7 is a block diagram of an atomic clock.

[0037] The control circuit 20 includes a drive circuit 20A that generates a drive signal (drive current) and a feedback control circuit 20B that receives the output signal of the photodetector 4 and performs feedback control of the drive signal. In a laser light irradiation type atomic clock, a laser light is irradiated onto a gas cell and output light from the gas cell is detected. The output light intensity changes due to the energy level transition of the gas. In an atomic clock, the output signal of the photodetector 4 is feedback controlled to generate a drive signal of a specific frequency so as to obtain the desired output light intensity that correlates with the energy level difference in the alkali atoms, and this frequency is used to measure time. The number of pulses contained in the signal of this frequency is counted to generate a clock signal S ＯＵＴ You can also output the following.

[0038] The feedback control circuit 20B detects the level of the low-frequency component of the photodetector 4 and adjusts the frequency and amplitude of the drive signal output from the drive circuit 20A so that the detection level meets the desired conditions. For example, the feedback control circuit 20B may include a synchronous detection circuit to which the output signal of the photodetector 4 is input, a loop filter to which an error signal from the synchronous detection circuit is input, a local oscillator to which a control signal output from the loop filter is input, and a high-frequency synthesizer to which the output of the local oscillator is input. The drive signal output from the high-frequency synthesizer is input to the drive circuit 20A. The feedback control circuit 20B can also obtain an accurate frequency by utilizing the phenomenon of coherent population trapping (CPT). In this case, the drive signal modulates the output frequency of the laser element, generating laser light with two sideband frequencies. When the difference frequency between these sideband frequencies matches a transition frequency corresponding to a specific energy level difference of alkali atoms, CPT resonance occurs. During CPT resonance, the intensity of the transmitted light increases, so by monitoring the level of the low frequency component of the photodetector 4, it is possible to obtain the frequency corresponding to the specific energy level difference of the atom.

[0039] It is also possible to change the wavelength of the laser light output from the laser element 3. The wavelength of the laser light can also be controlled by the temperature generated by the laser element 3 by the drive signal itself, the temperature of the laser element 3 controlled by the power supplied to the heater, or the pressure applied to the laser element 3 when a piezoelectric element is attached to the laser element 3. Such control can be performed as necessary. Many types of control methods are known for atomic clocks, so an appropriate one can be adopted.

[0040] FIG. 8 is a vertical cross-sectional view of a gas cell according to the second embodiment.

[0041] This gas cell GC is obtained by integrating the first window material 1B and the second window material 2B in the gas cell shown in Fig. 2, and this integration forms the first window material 1B. This gas cell has the advantage of increasing light transmittance because there are no seams between the window materials.

[0042] FIG. 9 is a vertical cross-sectional view of a gas cell according to the third embodiment.

[0043] This gas cell GC is obtained by removing the first window material 1B from the gas cell shown in Fig. 8 from the recess and attaching it as a third window material GCB to the side surfaces of the substrate 1 and the lid material 2 on the light-emitting surface side. This gas cell has the advantage of being easier to manufacture than the structure shown in Fig. 8.

[0044] FIG. 10 is a vertical cross-sectional view of a gas cell according to the fourth embodiment.

[0045] This gas cell GC is obtained by changing the lid member 2 of the gas cell shown in Fig. 9 to a simple plate. That is, the lower surface of the lid member 2 is flat. This has the advantage that the lid member 2 does not need to be processed.

[0046] FIG. 11 is a vertical cross-sectional view of a gas cell according to the fifth embodiment.

[0047] This gas cell GC is the gas cell shown in Fig. 10 with a thinner lid member 2. That is, the thickness of the lid member 2 is smaller than the thickness of the substrate 1. This structure has the advantage of enabling further miniaturization of the gas cell.

[0048] FIG. 12 is a vertical cross-sectional view of a gas cell according to the sixth embodiment.

[0049] In this gas cell GC, the depth of the first recess 1C in the substrate 1 shown in FIG. 11 is the same as the depth of the optical waveguide 1A, and the thickness of the substrate 1 is reduced. This structure has the advantage of further miniaturizing the gas cell. It is also possible to omit the formation of the first recess 1C and instead place a frame-shaped plate material of the same thickness as the optical waveguide 1A between the substrate 1 and the lid material 2. If a deeper recess is required, a structure can be adopted in which a frame-shaped plate material is placed on the substrate 1, an optical waveguide and a window material are placed on top of that, a frame-shaped plate material is further stacked on top of that, and the lid material 2 is placed on top of that. In this structure, resin, glass, or the like may be interposed between the plates as needed.

[0050] FIG. 13 is a vertical cross-sectional view of a gas cell according to the seventh embodiment.

[0051] This gas cell GC is formed by attaching a lid member 2 to the upper surface of a substrate 1 having a first recess 1C. The substrate 1 and the lid member 2 are made of a laser light transmitting material (SiO ２ ) In order to suppress light from outside, the periphery of the gas cell can be covered with a light-shielding material. It is also possible to include a light-shielding material such as carbon in the region of the laser light-transmitting material that does not transmit the laser light.

[0052] FIG. 14 is a horizontal cross-sectional view of the gas cell.

[0053] In this gas cell, the horizontal cross-sectional shape of the internal space IS in the gas cell shown in Fig. 3 is modified from a trapezoid to a rectangle. That is, the width of the internal space IS in the X-axis direction is constant (second width X2). This structure can increase the gas capacity in the horizontal plane more than the structure shown in Fig. 3.

[0054] FIG. 15 is a horizontal cross-sectional view of the gas cell.

[0055] This gas cell is an example of the gas cell shown in Figure 14, in which the position of the first auxiliary space 1D is set within the wall surface on the laser light incident surface side of the substrate 1. The first auxiliary space 1D is adjacent to the optical waveguide 1A. The first auxiliary space 1D is in communication with the inside of the first recess 1C via a first source gas inlet 1D1. As in the above example, an auxiliary space and a source gas inlet communicating with it may be provided in a position within the lid member opposite the first auxiliary space 1D and the first source gas inlet 1D1. With this structure, the thickness of the wall located outside the second width X2 of the internal space IS can be made thinner, enabling further miniaturization.

[0056] FIG. 16 is a horizontal cross-sectional view of the gas cell.

[0057] This gas cell is an example of the gas cell shown in Figure 15, in which the second auxiliary space 1E is set within the wall surface on the laser light incident surface side of the substrate 1. The second auxiliary space 1E is adjacent to the optical waveguide 1A. The second auxiliary space 1E is connected to the inside of the first recess 1C via the second source gas inlet 1E1. As in the above example, an auxiliary space and a source gas inlet communicating with it may be provided in a position within the lid member opposite the second auxiliary space 1E and the second source gas inlet 1E1. With this structure, the gas cell has multiple auxiliary spaces, so the volume of each auxiliary space can be reduced, and the thickness of the wall surface on the light incident surface side can also be reduced, allowing for further miniaturization.

[0058] FIG. 17 is a horizontal cross-sectional view of the gas cell.

[0059] This gas cell is similar to the gas cell shown in FIG. 15 except that the number of first auxiliary spaces 1D is increased, and each first auxiliary space 1D is connected to the inside of the first recess 1C via a first source gas inlet 1D1. The positions of these first auxiliary spaces 1D do not have to be on the same horizontal plane, and they may be distributed along the thickness direction. As in the above example, auxiliary spaces and source gas inlets connected thereto may be provided in positions within the lid opposite the first auxiliary spaces 1D and the first source gas inlet 1D1. With this structure, the gas cell has multiple distributed auxiliary spaces, which can increase the uniformity of the source gas flow during gas introduction.

[0060] FIG. 18 is a horizontal cross-sectional view of the gas cell.

[0061] This gas cell is an example in which the positions of the first auxiliary space 1D and the second auxiliary space 1E in the gas cell shown in FIG. 16 have been moved to within the wall surface on the laser light emission surface side of the substrate 1. The first auxiliary space 1D is in communication with the first recess 1C via a first source gas inlet 1D1. The second auxiliary space 1E is in communication with the first recess 1C via a second source gas inlet 1E1. As in the above example, an auxiliary space and a source gas inlet communicating therewith may be provided in a position within the lid member opposite the auxiliary space and source gas inlet formed in the substrate 1. This gas cell can achieve the same effects as the gas cell shown in FIG. 16. The horizontal shape of the auxiliary space is not limited to a circle and can be various shapes such as an ellipse.

[0062] FIG. 19 is a horizontal cross-sectional view of the gas cell.

[0063] Although the auxiliary space is not shown in the figure, the auxiliary space described above can be used. The gas cell of this example is an example in which the second width X2 of the internal space IS is set small in the gas cell of Figure 14. The auxiliary space can also be provided in the wall surfaces located at both ends in the width direction. In this case, the gas cell can be made smaller.

[0064] FIG. 20 is a horizontal cross-sectional view of the gas cell.

[0065] Although the auxiliary space is not shown in the figure, an auxiliary space such as that described above can be employed. The gas cell of this example is an example in which the longitudinal direction of the optical waveguide 1A is tilted with respect to the Y-axis in the gas cell of FIG. 15 . The second width X2 of the first window member 1B on the laser light emission side can be set to the second width X2 of the internal space IS. In this gas cell, the optical path length L2 of the laser light traveling within the internal space IS can be set to be longer than the dimension of the internal space IS in the Y-axis direction. The laser light within the internal space IS can be configured to be reflected by the inner wall surface of the substrate 1. A reflective film may be provided on this inner wall surface. In this case, the gas cell can be made smaller.

[0066] FIG. 21 is a horizontal cross-sectional view of the gas cell.

[0067] Although the auxiliary space is not shown in the figure, an auxiliary space such as that described above can be employed. The gas cell of this example is an example in which, in the gas cell of Figure 20, multiple optical waveguides 1A are provided in the wall surface on the laser light incident surface side, and the longitudinal direction of each optical waveguide 1A is parallel to the Y axis. This structure, which includes multiple optical waveguides 1A, can increase the amount of incident laser light.

[0068] FIG. 22 is a horizontal cross-sectional view of the gas cell.

[0069] Although the auxiliary space is not shown in the figure, the auxiliary space described above can be used. The gas cell of this example is an example in which the position of the internal space IS is asymmetric with respect to the X-axis position of the optical waveguide 1A in the gas cell of Figure 15. This structure also makes it possible to reduce the size of the gas cell.

[0070] FIG. 23 is a horizontal cross-sectional view of the gas cell.

[0071] Although the auxiliary space is not shown in the figure, an auxiliary space such as that described above can be employed. The gas cell of this example is an example in which the position of the first window material 1B in the gas cell shown in FIG. 15 has been moved to within the wall surface on the laser light incident surface side. If necessary, a reflective film M1 may be provided on the inner wall surface located at the end of the internal space IS in the Y-axis direction. Examples of materials for the reflective film M1 include metals such as aluminum. Laser light introduced from the optical waveguide 1A into the internal space IS is reflected by the reflective film M1, output to the outside through the first window material 1B, and introduced to the photodetector. Since the optical path length L2 of the laser light within the internal space IS is lengthened by reflection, the dimension of the gas cell in the Y-axis direction is reduced. In this structure, the laser element and the photodetector are arranged adjacent to each other along the X-axis direction.

[0072] As described above, the auxiliary space that serves as the supply source of the gas raw material can have various positions, shapes, dimensions, and quantities as long as it is in communication with the internal space, and is not limited to the above examples. In any case, the gas generated by decomposition of the raw material in the auxiliary space is supplied to the internal space. Note that, although it is preferable that the substrate has an optical waveguide, a structure in which laser light is introduced using a simple through-hole without an optical waveguide is also possible.

[0073] As described above, the gas cell and atomic clock structure described above can be miniaturized. If an atomic clock can be miniaturized sufficiently, it can be mounted in a variety of devices. For example, a miniaturized atomic clock can be mounted in a mobile phone, an automobile, a robot, a drone, a global positioning system (GPS), a security system, or the like.

[0074] Although various exemplary embodiments have been described above, various omissions, substitutions, and modifications may be made without being limited to the above-described exemplary embodiments. Furthermore, elements from different embodiments may be combined to form other embodiments. It will be understood from the above description that various embodiments of the present disclosure have been described herein for illustrative purposes, and that various modifications may be made without departing from the scope and spirit of the present disclosure. Accordingly, the various embodiments disclosed herein are not intended to be limiting, with the true scope and spirit being indicated by the appended claims.

[0075] 1...substrate, 1A...optical waveguide, 2...lid material, 3...laser element, 4...photodetector, 100...atomic clock structure, GC...gas cell, IS...internal space, L ＩＮ , L ＯＵＴ ...laser light, W ＩＮ ...laser light introduction port, W ＯＵＴ ...Laser light exit port.

Claims

1. A gas cell comprising: a plate-shaped substrate having an internal space filled with a gas; and a laser light inlet optically coupled to the internal space on a side surface of the substrate.

2. The gas cell according to claim 1, further comprising a laser light emission port optically coupled to said internal space on a side surface of said substrate opposite said side surface.

3. The gas cell according to claim 1, wherein a dimension L1 in a thickness direction of the internal space and an optical path length L2 of the laser light traveling within the internal space in a plane perpendicular to the thickness direction satisfy the relationship L1<L2.

4. The gas cell according to claim 3, wherein the dimension L1 satisfies 0.1 μm≦L1≦1000 μm.

5. The gas cell according to claim 1, further comprising an auxiliary space communicating with the internal space and capable of allowing a portion of the gas source to remain.

6. The gas cell according to claim 5, wherein the auxiliary space is also located within a horizontal cross section of the substrate in which the internal space exists.

7. The gas cell of claim 1, wherein the gas comprises an alkali metal.

8. The gas cell according to claim 1, further comprising an optical waveguide disposed between the laser light inlet and the internal space.

9. The gas cell according to claim 8, wherein the horizontal cross-sectional shape of the optical waveguide is rectangular.

10. The gas cell according to claim 1, wherein the horizontal cross-sectional shape of the internal space includes a trapezoid.

11. The gas cell according to claim 1, wherein the horizontal cross-sectional shape of the internal space includes a rectangle.

12. The gas cell of claim 1, further comprising a heater attached to the substrate.

13. An atomic clock structure comprising: a gas cell according to any one of claims 1 to 12; a laser element optically coupled to the laser light inlet; and a photodetector optically coupled to the internal space.

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