Wavelength variable interference filter and driving method thereof, optical module

Abstract

This invention relates to a wavelength-variable interference filter and its driving method, and an optical module, providing a wavelength-variable interference filter that can improve the accuracy of wavelength adjustment in a wide band. As described above, the wavelength-variable interference filter (1) includes: a first reflective film (4) and a second reflective film (5) facing each other; and an electrostatic actuator unit (6) that changes the gap amount (G) between the first reflective film (4) and the second reflective film (5). The electrostatic actuator unit (6) includes: a bias electrode (61) to which a bias voltage corresponding to a target value of the gap amount (G) (i.e., a gap target value (Gt)) is applied; a control electrode (62) to which a control voltage controlled by feedback according to the gap amount (G) is applied; and a variable electrode (63) to which the bias voltage and the control voltage can be switched.

Description

Technical Field

[0001] This invention relates to a wavelength-variable interference filter, an optical module, and a driving method for the wavelength-variable interference filter. Background Technology

[0002] Conventionally, there exist wavelength-variable interference filters (for example, see Patent Document 1) that have a pair of opposing reflective films and an electrostatic actuator that varies the gap between the pair of reflective films. In this wavelength-variable interference filter, by adjusting the gap between the pair of reflective films, light of a desired wavelength can be transmitted or reflected.

[0003] In the wavelength-variable interference filter disclosed in Patent Document 1, the electrostatic actuator section has multiple driving electrodes that are independently controlled by voltage. Specifically, the electrostatic actuator section has: a bias electrode, to which a bias voltage corresponding to a target gap value between a pair of reflective films is applied; and a control electrode, to which a control voltage is applied based on the gap amount and the target gap value and is feedback-controlled. In this wavelength-variable interference filter, by using the bias electrode for coarse adjustment of the gap amount and the control electrode for fine adjustment of the gap amount, fine wavelength adjustment over a wide wavelength range can be achieved.

[0004] Patent Document 1: Japanese Patent Application Publication No. 2018-128681

[0005] However, in the wavelength-variable interference filter disclosed in Patent Document 1, the problem of nonlinear voltage sensitivity of the electrostatic actuator to the gap between a pair of reflective films remains unresolved, resulting in insufficient accuracy in wavelength adjustment over a wide band. For example, when the gap is large, the electrostatic actuator's voltage sensitivity decreases, making it more susceptible to interference. On the other hand, when the gap is small, the electrostatic actuator's voltage sensitivity increases, making fine-tuning of the gap difficult. Summary of the Invention

[0006] The first aspect of this disclosure relates to a wavelength-variable interference filter comprising: a pair of reflective films facing each other; and an electrostatic actuator unit for changing the gap amount between the pair of reflective films, the electrostatic actuator unit comprising: a bias electrode for being applied a bias voltage corresponding to a target value of the gap amount; a control electrode for being applied a control voltage that is feedback-controlled based on the gap amount and the target value; and a variable electrode for being able to switch between applying the bias voltage and the control voltage.

[0007] The second aspect of this disclosure relates to an optical module comprising: a wavelength-variable interference filter as described above; and a filter driving unit that drives the electrostatic actuator unit, the filter driving unit comprising: a bias driving unit that applies the bias voltage to the bias electrode; a gap detection unit that detects the gap amount between the pair of reflective films; a feedback control unit that applies the control voltage to the control electrode based on the gap amount detected by the gap detection unit; and a voltage switching unit that can switchably apply the bias voltage and the control voltage to the variable electrode.

[0008] The third aspect of this disclosure relates to a driving method for a wavelength-variable interference filter, comprising the following steps: changing the gap amount by applying a bias voltage to a bias electrode corresponding to a target value of the gap amount between a pair of reflective films; adjusting the gap amount by detecting the gap amount between the pair of reflective films and applying a control voltage, which is based on the detected gap amount and the target value, to a control electrode; selecting one of the bias voltage and the control voltage as a selection voltage based on the target value; and assisting in the change or adjustment of the gap amount by applying the selection voltage to a variable electrode when a voltage is applied to the bias electrode or the control electrode. Attached Figure Description

[0009] Figure 1 This is a block diagram showing the general configuration of the spectrophotometer according to this embodiment.

[0010] Figure 2 This is a schematic cross-sectional view of the wavelength-variable interference filter according to this embodiment.

[0011] Figure 3 This is a top view schematically showing the electrode configuration in the second substrate of the wavelength-variable interference filter according to this embodiment.

[0012] Figure 4 This is a flowchart illustrating the driving method of the wavelength-variable interference filter involved in this embodiment.

[0013] Figure 5 This is a coordinate graph used to illustrate the change in voltage sensitivity of the wavelength-variable interference filter involved in this embodiment.

[0014] Figure 6 This is a coordinate graph used to illustrate the change in the bias voltage value of the wavelength-variable interference filter involved in this embodiment.

[0015] Figure 7 This is a schematic cross-sectional view of a wavelength-variable interferometric filter involved in a variant example.

[0016] Figure 8This is a schematic cross-sectional view of a wavelength-variable interferometric filter involved in other variations.

[0017] Explanation of reference numerals in the attached figures

[0018] 1. 1A~1C…wavelength variable interference filter, 2…first substrate, 21…first surface, 22…second surface, 23…groove, 24…movable part, 25…diaphragm part, 26…base, 3…second substrate, 31…third surface, 32…fourth surface, 33…recess, 34…reflective film setting part, 35…detection electrode setting part, 36…drive electrode setting part, 37…lead wiring part, 38…drive electrode terminal, 39…common electrode terminal, 4…first reflective film, 5…second reflective film, 6…electrostatic actuator part, 61…bias electrode, 610…first electrostatic actuator part, 62…control electrode, 620…the… 63… Variable electrode, 630… Third electrostatic actuator section, 631… Dividing electrode, 64… Grounding electrode, 65… Variable preparatory electrode, 7… Capacitor detection section, 71… First detection electrode, 72… Second detection electrode, 8… Third substrate, 81… Opposing surface, 9… Filter drive section, 91… Bias drive section, 92… Gap detection section, 93… Feedback control section, 94… Voltage switching section, 95… Microcomputer, 100… Spectrophotometer, 101… Optical module, 102… Light receiving section, 103… Signal processing section, 104… Spectrophotometer control section, C… Central axis, G… Gap amount. Detailed Implementation

[0019] Reference Figures 1-6 One embodiment of this disclosure will be described.

[0020] like Figure 1 As shown, the spectrophotometer 100 of this embodiment includes an optical module 101, a light-receiving unit 102, a signal processing unit 103, and a spectrophotometer control unit 104. The optical module 101 includes a wavelength-variable interference filter 1 and a filter drive unit 9. The spectrophotometer 100 is a device that uses the wavelength-variable interference filter 1 to disperse the measurement light incident from the measurement object and receives the light with the light-receiving unit 102 to analyze the light intensity of a specified wavelength of light reflected from the measurement object and measure the spectrophotometer spectrum. This spectrophotometer 100 can be integrated into various devices such as printers, projectors, or drones for use.

[0021] [Construction of Wavelength Variable Interference Filter 1]

[0022] Figure 2 This is a cross-sectional view showing the wavelength-variable interference filter 1 of this embodiment. The wavelength-variable interference filter 1 is a beam splitter filter that can change the transmission wavelength according to the driving voltage input from an external source.

[0023] The wavelength-variable interference filter 1 includes: a first substrate 2 and a second substrate 3, which are arranged opposite to each other; a first reflective film 4 disposed on the first substrate 2; a second reflective film 5 disposed on the second substrate 3; an electrostatic actuator 6 that changes the size (hereinafter, gap amount G) of the gap between the first reflective film 4 and the second reflective film 5; and a capacitance detection unit 7 that detects the gap amount G.

[0024] Furthermore, in the following description, the opposing directions of the first substrate 2 and the second substrate 3 (i.e., the thickness directions of the first substrate 2 and the second substrate 3) are referred to as the thickness directions of the wavelength-variable interference filter 1. Figure 2 This is equivalent to a cross-sectional view formed by cutting the wavelength-variable interference filter 1 along its thickness direction.

[0025] The first substrate 2 and the second substrate 3 are each formed of various materials that allow light to pass through, such as glass or crystal. Furthermore, the first substrate 2 and the second substrate 3 are joined together to form an integral structure with cavities between them.

[0026] The first substrate 2 has a first surface 21 opposite to the second substrate 3 and a second surface 22 that is the side opposite to the first surface 21. When the first substrate 2 is viewed along the thickness direction, an annular groove 23 is formed on the second surface 22 of the first substrate 2. Thus, the first substrate 2 includes: a movable portion 24, which is a portion surrounded by the annular groove 23; a diaphragm portion 25, which is a portion that has been thinned by the groove 23; and a base portion 26, which supports the movable portion 24 displaceably in the thickness direction via the diaphragm portion 25. The base portion 26 of the first substrate 2 is bonded to the second substrate 3 via an arbitrary bonding film.

[0027] The second substrate 3 has a third surface 31 opposite to the first substrate 2 and a fourth surface 32 that is the side opposite to the first surface 21. A recess 33 is formed in the center of the third surface 31 to form a cavity between the first substrate 2 and the second substrate 3. A reflective film setting portion 34, a detection electrode setting portion 35, and a driving electrode setting portion 36 are formed on the bottom surface of the recess 33 of the second substrate 3. The reflective film setting portion 34 is disposed in the center of the recess 33, and the detection electrode setting portion 35 and the driving electrode setting portion 36 are arranged in a ring surrounding the reflective film setting portion 34. In addition, the reflective film setting portion 34, the detection electrode setting portion 35, and the driving electrode setting portion 36 are formed according to an initial set distance from the first substrate 2, and may have a pedestal shape or a groove shape.

[0028] A first reflective film 4 is disposed on the first surface 21 of the movable portion 24 of the first substrate 2, and a second reflective film 5 is disposed on the reflective film placement portion 34 of the second substrate 3. The first reflective film 4 and the second reflective film 5 are positioned opposite each other via a gap, and the axis passing through the centers of the first reflective film 4 and the second reflective film 5 is defined as the central axis C of the wavelength-variable interference filter 1. Furthermore, when the wavelength-variable interference filter 1 is viewed along the thickness direction, the area where the first reflective film 4 and the second reflective film 5 overlap forms the filter region of the wavelength-variable interference filter 1, which has an approximately circular shape centered on the central axis C. The gap G between the first reflective film 4 and the second reflective film 5 corresponds to the wavelength of light transmitted through the filter region of the wavelength-variable interference filter 1.

[0029] Furthermore, although not particularly limited, the first reflective film 4 and the second reflective film 5 in this embodiment are dielectric multilayer films formed by alternately stacking Si (silicon layer) and SiO2 layer (silicon oxide layer).

[0030] In this embodiment, the electrostatic actuator section 6 changes the gap G between the first reflective film 4 and the second reflective film 5 by pulling the movable part 24 of the first substrate 2 closer to the second substrate 3. This electrostatic actuator section 6 has a bias electrode 61, a control electrode 62, and a variable electrode 63 as multiple drive electrodes to which a drive voltage is applied. The bias electrode 61, control electrode 62, and variable electrode 63 are provided in the drive electrode setting section 36 of the first substrate 2. Specifically, the bias electrode 61 is configured to face the movable part 24, and the variable electrode 63 and control electrode 62 are configured to face the diaphragm section 25. Furthermore, the electrostatic actuator section 6 has a ground electrode 64, which is provided on the first surface 21 of the first substrate 2, respectively, facing the bias electrode 61, the control electrode 62, and the variable electrode 63.

[0031] Furthermore, in this embodiment, the distances H1 to H3 between the bias electrode 61, the control electrode 62, and the variable electrode 63 and the ground electrode 64 are equal, but they may also be different. Additionally, in this embodiment, the distances H1 to H3 between the bias electrode 61, the control electrode 62, and the variable electrode 63 and the ground electrode 64 are larger than the gap G between the first reflective film 4 and the second reflective film 5, but this is not a limitation; their relative sizes may also be reversed.

[0032] Figure 3 This is a top view of the second substrate 3 viewed along its thickness direction, and a diagram schematically showing the arrangement of the electrodes on the third surface 31 of the second substrate 3. Figure 3As shown, when the second substrate 3 is viewed along the thickness direction, the bias electrode 61, the control electrode 62, and the variable electrode 63 are arranged around the second reflective film 5 in a concentric circle centered on the central axis C. Furthermore, the electrodes of the electrostatic actuator section 6 in the second substrate 3 are arranged radially outward from the second reflective film 5 in the order of bias electrode 61, variable electrode 63, and control electrode 62.

[0033] Furthermore, in this embodiment, the area of ​​the bias electrode 61 is larger than the area of ​​each of the control electrode 62 and the variable electrode 63, and preferably larger than the total area of ​​the control electrode 62 and the variable electrode 63 combined.

[0034] Furthermore, as will be described in detail later, the bias electrode 61 and the ground electrode 64 together constitute the first electrostatic actuator section 610, which is subjected to a bias voltage. The control electrode 62 and the ground electrode 64 together constitute the second electrostatic actuator section 620, which is subjected to a control voltage. The variable electrode 63 and the ground electrode 64 together constitute the third electrostatic actuator section 630, which is subjected to either a bias voltage or a control voltage. The first electrostatic actuator section 610 and the second electrostatic actuator section 620 are driven and controlled independently of each other, and the third electrostatic actuator section 630 can switch between a bias drive mode that is driven and controlled together with the first electrostatic actuator section 610 and a feedback control mode that is driven and controlled together with the second electrostatic actuator section 620.

[0035] like Figure 2 As shown, the capacitance detection unit 7 includes: a first detection electrode 71 disposed on the first surface 21 of the first substrate 2; and a second detection electrode 72 disposed on the detection electrode placement portion 35 of the second substrate 3, and opposite to the first detection electrode 71, with a charge corresponding to the gap amount G maintained between the first detection electrode 71 and the second detection electrode 72. When the wavelength-variable interference filter 1 is observed along the thickness direction, the first detection electrode 71 and the second detection electrode 72 are respectively arranged in a ring shape centered on the central axis C, surrounding the first reflective film 4 or the second reflective film 5. In addition, the first detection electrode 71 is disposed between the first reflective film 4 and the ground electrode 64, and the second detection electrode 72 is disposed between the second reflective film 5 and the bias electrode 61.

[0036] Furthermore, although not specifically limited, in this embodiment, the bias electrode 61, control electrode 62, variable electrode 63, and ground electrode 64 are each composed of a metal oxide film such as ITO (Indium Tin Oxide) stacked relative to a dielectric multilayer film. Additionally, the first detection electrode 71 and the second detection electrode 72 are each composed of a dielectric multilayer film and a metal film such as Au stacked relative to a metal oxide film such as ITO.

[0037] like Figure 3 As shown, the bias electrode 61, control electrode 62, variable electrode 63, and second detection electrode 72 of the electrostatic actuator section 6 described above are electrically connected to each of the plurality of drive electrode terminals 38 disposed on the outside of the cavity via lead-out wiring sections 37 formed on the second substrate 3. Furthermore, in Figure 3 Although the illustration is simplified, the wiring section 37 and the drive electrode terminal 38 are configured to allow voltage to be applied independently to each of the bias electrode 61, control electrode 62, variable electrode 63, and second detection electrode 72. Furthermore, the drive electrode terminal 38 is connected to the external filter drive section 9 (see reference 9) via an arbitrary wiring structure (not shown). Figure 1 ).

[0038] The grounding electrode 64 and the first detection electrode 71 in the first substrate 2 are electrically connected to a common electrode terminal 39 disposed on the outside of the cavity via wiring (through wiring or lead-out wiring of the first substrate 2, etc., not shown in the figure). The common electrode terminal 39 is grounded.

[0039] [Filter Driver Section 9]

[0040] Refer again Figure 1 The filter drive unit 9 will be described below. The filter drive unit 9 is a circuit that drives and controls the wavelength variable interference filter 1 described above, and includes a bias drive unit 91, a gap detection unit 92, a feedback control unit 93, a voltage switching unit 94, and a microcomputer 95.

[0041] The bias drive unit 91 at least supports the first electrostatic actuator unit 610 (specifically...) Figure 2 A bias voltage is applied to the bias electrode 61. The bias voltage is a voltage corresponding to a target value of the gap amount G (hereinafter referred to as the gap target value Gt). In the bias drive unit 91, the voltage value of the bias voltage is set based on the bias signal input from the microcomputer 95. Furthermore, the bias drive unit 91 is, for example, a D / A converter having a predetermined number of bits.

[0042] The gap detection unit 92 acquires a detection signal corresponding to the gap amount G from the capacitance detection unit 7 and outputs the acquired detection signal to the feedback control unit 93.

[0043] The feedback control unit 93 controls at least the second electrostatic actuator unit 620 (specifically...) Figure 2A control voltage is applied to the control electrode 62. Specifically, the feedback control unit 93 outputs a control voltage that is feedback-controlled based on the detection signal (i.e., according to the gap amount G) input from the gap detection unit 92 and the target signal input from the microcomputer 95, so that each signal becomes the same value. Furthermore, the feedback control unit 93 can also be configured as an analog controller with a fixed gain, and the voltage variable range can be set to a predetermined width. For example, a PI controller or a PID controller can be used as this analog controller.

[0044] The voltage switching unit 94 pairs with the third electrostatic actuator unit 630 (specifically...) Figure 2 The variable electrode 63 can be switched between applying either a bias voltage or a control voltage. That is, the voltage switching unit 94 can switch the third electrostatic actuator unit 630 between a bias drive mode and a feedback control mode. For example, in this embodiment, the voltage switching unit 94 can switch the connection destination of the variable electrode 63 between the bias drive unit 91 and the feedback control unit 93 based on a switching signal input from the microcomputer 95.

[0045] The microcomputer 95 controls the bias drive unit 91, the feedback control unit 93, and the voltage switching unit 94 according to the target wavelength indicated by the spectral control unit 104.

[0046] [Spectrophotometer 100]

[0047] The configuration of the spectrophotometer 100, excluding the optical module 101, will be described.

[0048] The light-receiving unit 102 is a sensor that receives light transmitted through the wavelength-variable interference filter 1. For example, an image sensor such as a CCD or CMOS can be used as the light-receiving unit 102. When the light-receiving unit 102 receives light transmitted through the wavelength-variable interference filter 1, it outputs a light-receiving signal corresponding to the amount of light received to the beam splitting control unit 104.

[0049] The signal processing unit 103 includes a sampling circuit for sampling the light-receiving signal output from the light-receiving unit 102, an amplification circuit for amplifying the light-receiving signal, and an A / D conversion circuit for converting the light-receiving signal into a digital signal. The signal processing unit 103 performs signal processing on the light-receiving signal through these circuits and inputs the signal-processed light-receiving signal to the beam splitting control unit 104.

[0050] The spectrophotometer control unit 104 is configured, for example, by combining a CPU or a memory, and controls the overall operation of the spectrophotometer 100. The spectrophotometer control unit 104 commands the filter drive unit 9 to start the spectrophotometer based on input information from the outside, and performs spectrophotometer measurement on the target object based on the light-receiving signal input from the signal processing unit 103.

[0051] [Driving method of wavelength-variable interference filter 1]

[0052] Next, regarding the driving method of the wavelength-variable interference filter 1 in this embodiment, please refer to... Figure 4 The flowchart is explained below. Furthermore, the following example illustrates the case where a spectrophotometer is performed with any single wavelength as the target wavelength.

[0053] The beam splitting control unit 104 outputs a control signal indicating the target wavelength to the filter drive unit 9 based on user operations, etc. When the control signal is input from the beam splitting control unit 104, the microcomputer 95 calculates the target value (gap target value Gt) of the gap amount G required to extract light of the target wavelength from the wavelength variable interference filter 1 (step S1).

[0054] The microcomputer 95 determines whether the gap target value Gt is smaller than a predetermined first threshold (step S2). Based on this comparison result, it selects either the bias voltage or the control voltage as the selection voltage applied to the variable electrode 63. For example, if the gap target value Gt is smaller than the predetermined first threshold (step S2; "Yes"), the microcomputer 95 selects the bias voltage as the selection voltage applied to the variable electrode 63 (step S3). On the other hand, if the gap target value Gt is greater than or equal to the predetermined first threshold (step S2; "No"), the microcomputer 95 selects the control voltage as the selection voltage applied to the variable electrode 63 (step S4). Then, the microcomputer 95 outputs a switching signal corresponding to the selection voltage to the voltage switching unit 94. As a result, the switching connection destination of the voltage switching unit 94 is set, and the third electrostatic actuator unit 630 is set to either bias drive mode or feedback control mode (step S5).

[0055] In addition, the microcomputer 95 calculates the bias voltage value corresponding to the gap target value Gt (hereinafter referred to as the bias voltage value V). b (Step S6). At this time, the microcomputer 95 can calculate the bias voltage value V corresponding to the gap target value Gt by referring to the mathematical formula or drive table stored in the memory (not shown). b Then, the microcomputer 95 will indicate the bias voltage value V. b The bias signal is output to the bias drive unit 91.

[0056] Here, the bias voltage value V is used to calculate. b The mathematical formula can be referred to, for example, the following formula (1) disclosed in Japanese Patent Application Publication No. 2018-128681.

[0057] [Mathematical Expression 1]

[0058] In the above equation (1), k is the spring constant of the second substrate 3, ε is the dielectric constant of the gap between the first reflective film 4 and the second reflective film 5, and S b S is the area of ​​the electrode region to which a bias voltage is applied, viewed from above when observing the wavelength-variable interference filter 1 in the thickness direction. c d is the area of ​​the electrode region to which the control voltage is applied, viewed from above when observing the wavelength-variable interference filter 1 in the thickness direction. max R is the initial clearance amount, d is the target displacement amount representing the difference between the initial clearance amount and the target clearance value Gt. c It is the sensitivity of the electrode to which a control voltage is applied.

[0059] Furthermore, the area S of the electrode region to which the bias voltage is applied c and the area S of the electrode region to which the control voltage is applied c The value varies depending on the setting of the voltage switching unit 94 (i.e., whether the third electrostatic actuator unit 630 is in bias drive mode or feedback control mode). When the third electrostatic actuator unit 630 is in bias drive mode, the area S of the electrode region to which the bias voltage is applied... c The area S of the electrode region to which the control voltage is applied is the sum of the areas of the bias electrode 61 and the variable electrode 63. c This corresponds to the area of ​​the control electrode 62. On the other hand, when the third electrostatic actuator section 630 is in feedback control mode, the area S of the electrode region to which the bias voltage is applied... c The area S of the electrode region to which the control voltage is applied is equivalent to the area of ​​the bias electrode 61. c This is equivalent to the sum of the areas of the control electrode 62 and the variable electrode 63. Therefore, it is preferable that the microcomputer 95 calculates the area S of the electrode region to which the bias voltage is applied based on the setting of the voltage switching unit 94 set in step S5. c and the area S of the electrode region to which the control voltage is applied c The bias voltage V is calculated using the calculated areas. b .

[0060] Next, the bias drive unit 91 begins to apply a bias voltage based on the bias signal input from the microcomputer 95 (step S7).

[0061] Here, when the third electrostatic actuator section 630 is in bias drive mode, the bias voltage output from the bias drive section 91 is applied to both the bias electrode 61 and the variable electrode 63. On the other hand, when the third electrostatic actuator section 630 is in feedback control mode, the bias voltage output from the bias drive section 91 is applied to the bias electrode 61.

[0062] As a result, in the first electrostatic actuator section 610 (and the third electrostatic actuator section 630), the electrostatic attraction based on the bias voltage is activated, and the movable part 24 is displaced toward the second substrate 3, thereby changing the gap amount G.

[0063] The feedback control unit 93 outputs a control voltage so that the detection signal input from the gap detection unit 92 and the target signal input from the microcomputer 95 become the same value (step S8).

[0064] Here, when the third electrostatic actuator unit 630 is in bias drive mode, the control voltage output from the feedback control unit 93 is applied to the control electrode 62. On the other hand, when the third electrostatic actuator unit 630 is in feedback control mode, the control voltage output from the bias drive unit 91 is applied to both the control electrode 62 and the variable electrode 63.

[0065] Therefore, in the second electrostatic actuator section 620 (and the third electrostatic actuator section 630), the electrostatic attraction based on the control voltage is activated, and the displacement (i.e., the gap amount G) of the movable section 24 is finely adjusted.

[0066] After step S8, before receiving the end instruction, the filter drive unit 9 applies a bias voltage and a control voltage to control the gap amount G, so that the light of the target wavelength passes through the wavelength variable interference filter 1 (step S9).

[0067] Furthermore, while the gap amount G of the wavelength-variable interference filter 1 is controlled, the light-receiving unit 102 detects the light transmitted through the wavelength-variable interference filter 1, and the beam splitting control unit 104 acquires the received light signal from the light-receiving unit 102 via the signal processing unit 103. Then, based on the acquired received light signal, the beam splitting control unit 104 calculates the optical characteristic value of the measured object relative to the target wavelength.

[0068] Furthermore, when measuring the spectroscopic spectrum corresponding to each wavelength set at predetermined intervals within the measurement wavelength range, steps S1 to S9 described above can be repeated for each wavelength. For example, when changing the gap target value Gt at predetermined intervals, the third electrostatic actuator unit 630 can be set to bias drive mode when the gap target value Gt is smaller than the first threshold, and set to feedback control mode when the gap target value Gt is greater than or equal to the first threshold.

[0069] [Operation of electrostatic actuator section 6]

[0070] Reference Figure 5 and Figure 6 The changes in voltage sensitivity and bias voltage of the electrostatic actuator section 6 will be explained. Furthermore, in the following description, examples, Reference Example 1, Reference Example 2, and comparative examples will be used.

[0071] In this embodiment, the wavelength-variable interference filter 1 of this embodiment is used to obtain the voltage sensitivity and bias voltage when the gap target value Gt is changed at predetermined intervals. Furthermore, in this embodiment, when the gap target value Gt becomes a first threshold or higher, the third electrostatic actuator unit 630 is switched from bias drive mode to feedback control mode.

[0072] In Reference Example 1, using the wavelength-variable interference filter 1 of this embodiment, the voltage sensitivity and bias voltage were obtained when the gap target value Gt was changed at predetermined intervals, with the third electrostatic actuator section 630 fixed in the bias drive mode.

[0073] In Reference Example 2, using the wavelength-variable interference filter 1 of this embodiment, the voltage sensitivity and bias voltage were obtained when the gap target value Gt was changed at predetermined intervals, with the third electrostatic actuator section 630 fixed in the feedback control mode.

[0074] The comparative example omits the third electrostatic actuator section 630 and the voltage switching section 94 from the wavelength-variable interference filter 1 of this embodiment. Furthermore, the area of ​​the bias electrode 61 in the comparative example is approximately equal to the area of ​​the bias electrode 61 in the embodiment. Additionally, the area of ​​the control electrode 62 in the comparative example is larger than the areas of each electrode of the control electrode 62 and the variable electrode 63 in the embodiment, and is less than the combined area of ​​each electrode of the control electrode 62 and the variable electrode 63 in the embodiment. In this comparative example, the voltage sensitivity and bias voltage were obtained when the gap target value Gt was changed at predetermined intervals.

[0075] Figure 5 and Figure 6 The changes in voltage sensitivity and bias voltage are shown for each of the embodiments, Reference Example 1, Reference Example 2, and Comparative Examples, when the target gap value Gt is changed at predetermined intervals. Furthermore, Figure 5 and Figure 6 The horizontal axis in each coordinate graph shows the displacement of the gap (gap displacement) when the gap amount G is changed according to the gap target value Gt. Figure 5 The vertical axis shows the voltage sensitivity of the electrostatic actuator section 6. Figure 6 The vertical axis shows the bias voltage value. Additionally, in Figure 5 and Figure 6 The figure shows the value of the gap displacement (threshold Th) corresponding to the first threshold of the gap target value Gt.

[0076] like Figure 5 As shown, in Reference Examples 1 and 2 and Comparative Examples, the larger the gap displacement, the greater the voltage sensitivity.

[0077] On the other hand, in the embodiments, when the gap displacement is less than the threshold Th, the voltage sensitivity is ensured to be higher than that of the comparative example, and when the gap displacement is greater than or equal to the threshold Th, the voltage sensitivity is suppressed to be lower than that of the comparative example. Specifically, the voltage sensitivity when the gap displacement is greater than or equal to the voltage sensitivity when the gap displacement is less than the threshold Th is suppressed to the same degree.

[0078] Therefore, in the embodiment, it is obvious that the voltage sensitivity of the electrostatic actuator section 6 can be adjusted according to the gap displacement.

[0079] like Figure 6 As shown, in Reference Examples 1 and 2 and Comparative Examples, the larger the gap displacement, the greater the bias voltage V required to achieve the target gap value Gt. b The larger.

[0080] On the other hand, in the embodiment, when the gap displacement is smaller than the threshold Th, similar to Reference Example 1, the larger the gap displacement, the greater the bias voltage V required to achieve the gap target value Gt. b The larger the gap displacement, the greater the bias voltage V required to achieve the target gap value Gt. However, when the gap displacement is above the threshold Th, the bias voltage V required to achieve the target gap value Gt will be reduced. b The suppression was smaller than that of Reference Example 1 or the Comparative Example.

[0081] Therefore, in the embodiments, when the gap displacement is large, it is obviously possible to drive it with a low voltage.

[0082] [Effects of this implementation method]

[0083] (1) As described above, the wavelength variable interference filter 1 of this embodiment includes: a first reflective film 4 and a second reflective film 5, which are opposite to each other; and an electrostatic actuator 6, which changes the gap amount G between the first reflective film 4 and the second reflective film 5. The electrostatic actuator 6 includes: a bias electrode 61, which is subjected to a bias voltage corresponding to a target value of the gap amount G (i.e., the gap target value Gt); a control electrode 62, which is subjected to a control voltage that is feedback controlled based on the gap amount G and the gap target value Gt; and a variable electrode 63, which can be switched between being subjected to a bias voltage and a control voltage.

[0084] In this configuration, by using the bias electrode 61 to which a bias voltage is applied and the control electrode 62 to which a control voltage is applied as the electrostatic actuator section 6, coarse and fine adjustments of the gap amount G can be made, and fine wavelength adjustment in a wide band can be achieved with a simple configuration.

[0085] Furthermore, in the wavelength-variable interference filter 1 of this embodiment, by utilizing a variable electrode 63 that can be switched between bias voltage and control voltage as an electrostatic actuator section 6, the ratio between the area of ​​the electrode region to which the bias voltage is applied and the area of ​​the electrode region to which the control voltage is applied can be changed within the electrostatic actuator section 6. For example, when the target gap value Gt is large, by ensuring a larger ratio of the area of ​​the electrode region to which the bias voltage is applied within the electrostatic actuator section 6, the voltage sensitivity of the electrostatic actuator section 6 can be suppressed from decreasing, resulting in the suppression of interference effects. Conversely, when the target gap value Gt is small, by reducing the ratio of the area of ​​the electrode region to which the bias voltage is applied within the electrostatic actuator section 6, the voltage sensitivity of the electrostatic actuator section 6 can be suppressed from increasing, resulting in easier fine-tuning of the gap amount G.

[0086] Therefore, the wavelength-variable interference filter 1 according to this embodiment can perform coarse and fine adjustments to the gap amount G through the electrostatic actuator section 6, and can adjust the voltage sensitivity of the electrostatic actuator section 6 according to the gap target value Gt, thereby improving the accuracy of wavelength adjustment in a wide band.

[0087] Furthermore, in the wavelength-variable interference filter 1 of this embodiment, when the target gap value Gt is large, by ensuring a larger proportion of the area of ​​the electrode to which the bias voltage is applied in the electrostatic actuator section 6, the maximum voltage value required for the bias voltage can be reduced. That is, according to the wavelength-variable interference filter 1 of this embodiment, even when the target gap value Gt is large, it can be driven with a low voltage, and the accuracy of wavelength adjustment can also be improved. Alternatively, according to the wavelength-variable interference filter 1 of this embodiment, the range in which wavelength adjustment can be performed can be set to a wider band.

[0088] (2) When the wavelength variable interference filter 1 of this embodiment is viewed along the thickness direction, the bias electrode 61, the control electrode 62 and the variable electrode 63 are arranged in a concentric circle with the first reflective film 4 or the second reflective film 5 as the center.

[0089] In this configuration, the balance of electrostatic forces generated in the bias electrode 61, control electrode 62 and variable electrode 63 can be improved, and the gap G between the first reflective film 4 and the second reflective film 5 can be adjusted uniformly.

[0090] (3) When the electrostatic actuator section 6 of this embodiment is viewed along the thickness direction, it is arranged in the order of bias electrode 61, variable electrode 63 and control electrode 62 from the first reflective film 4 or the second reflective film 5 toward the radially outward direction.

[0091] With this configuration, the sensitivity of the electrostatic actuator section 6 to the bias voltage can be appropriately improved when a bias voltage is applied to the variable electrode 63.

[0092] (4) The area of ​​the bias electrode 61 in this embodiment is larger than the area of ​​the control electrode 62 and the variable electrode 63.

[0093] With this configuration, the coarse and fine adjustments of the gap amount G can be made in a good balance.

[0094] (5) The optical module 101 of this embodiment includes: the wavelength variable interference filter 1 described above; and a filter driving unit 9 that drives the electrostatic actuator unit 6. The filter driving unit 9 includes: a bias driving unit 91 that applies a bias voltage to the bias electrode 61; a gap detection unit 92 that detects the gap amount G between the first reflective film 4 and the second reflective film 5; a feedback control unit 93 that applies a control voltage to the control electrode 62 according to the gap amount G detected by the gap detection unit 92; and a voltage switching unit 94 that can switch between applying a bias voltage and a control voltage to the variable electrode 63.

[0095] In this configuration, the wavelength-variable interference filter 1 described above can be appropriately implemented.

[0096] (6) In this embodiment, the voltage switching unit 94 switches the voltage applied to the variable electrode 63 between the bias voltage and the control voltage based on the comparison result between the gap target value Gt, which is the target value of the gap amount G, and the first threshold.

[0097] In this configuration, the voltage sensitivity of the electrostatic actuator section 6 can be appropriately adjusted.

[0098] (7) The driving method of the wavelength variable interference filter 1 in this embodiment includes: a step of changing the gap amount G by applying a bias voltage to the bias electrode 61 according to the target value of the gap amount G between each first reflective film 4 and second reflective film 5, namely the gap target value Gt (step S7); a step of adjusting the gap amount G by detecting the gap amount G between the first reflective film 4 and second reflective film 5 and applying a control voltage based on the detected gap amount G and the gap target value Gt to the control electrode 62 (step S8); a step of selecting one of the bias voltage and the control voltage as the selection voltage applied to the variable electrode 63 based on the target value of the gap amount G (steps S2 to S5); and a step of assisting the change or adjustment of the gap amount G by applying the selection voltage to the variable electrode 63 when a voltage is applied to the bias electrode 61 or the control electrode 62.

[0099] In this method, the accuracy of wavelength adjustment in a wide band can be improved in the same way as the wavelength-variable interference filter 1 described above.

[0100] [Variation Example]

[0101] This invention is not limited to the aforementioned embodiments; variations and improvements that achieve the objectives of this invention are included in this invention.

[0102] [Variation Example 1]

[0103] like Figure 7 As shown, the wavelength-variable interference filter 1A in the modified example may also include: a variable electrode 63, configured in the same manner as in the first embodiment; and a variable preparatory electrode 65, which is a different electrode from the variable electrode 63. The variable preparatory electrode 65 can be arranged in a concentric circle centered on the central axis C between the variable electrode 63 and the control electrode 6. Alternatively, the variable preparatory electrode 65 is not limited to the region between the bias electrode 61 and the control electrode 62, but may be the inner region of the bias electrode 61 or the outer region of the control electrode 62.

[0104] Like the variable electrode 63, the variable preparatory electrode 65 can be switched between a bias voltage and a control voltage. The variable preparatory electrode 65 can also be controlled independently of the variable electrode 63. For example, the voltage switching unit 94 can be configured to switch the voltage applied to the variable preparatory electrode 65 between the bias voltage and the control voltage based on a second threshold different from the first threshold corresponding to the variable electrode 63. That is, when the gap target value Gt is smaller than the second threshold (e.g., the second threshold > the first threshold), the voltage switching unit 94 can apply a bias voltage to the variable preparatory electrode 65; when the gap target value Gt is greater than or equal to the second threshold, it can apply a control voltage to the variable preparatory electrode 65.

[0105] In this modified example, the voltage sensitivity of the electrostatic actuator section 6 can be adjusted more precisely.

[0106] [Variation Example 2]

[0107] like Figure 7 As shown, in the modified example of the wavelength-variable interference filter 1A, the bias electrode 61, control electrode 62, and variable electrode 63 may be disposed on the first substrate 2, and the ground electrode 64 may be disposed on the second substrate 3. In this case, the bias electrode 61 may be disposed on the movable portion 24 of the first substrate 2, and the control electrode 62 may be disposed on the diaphragm portion 25 of the first substrate 2. The variable electrode 63 or the variable reserve electrode 65 may also be disposed on either the movable portion 24 or the diaphragm portion 25 of the first substrate 2.

[0108] [Variation Example 3]

[0109] like Figure 7As shown, in the modified example of the wavelength-variable interference filter 1A, the first reflective film 4 and the second reflective film 5 may not be composed of a dielectric multilayer film, but rather of, for example, a metal film such as Ag, an alloy film such as Ag alloy, or the like. In this case, the first detection electrode 71 may be disposed on the first reflective film 4, and the second detection electrode 72 may be disposed on the second reflective film 5.

[0110] [Variation Example 4]

[0111] In the above embodiments, the variable electrode 63 can also be divided into multiple electrodes. For example, as in... Figure 7 As indicated by the reference numerals in the accompanying drawings, in the wavelength-variable interference filter 1B of the modified example, the variable electrode 63 may also have multiple segmented electrodes 631. The multiple segmented electrodes 631 are arranged in concentric circles centered on the central axis C and can be switched between bias voltage and control voltage. Alternatively, the multiple segmented electrodes 631 are not limited to the region between the bias electrode 61 and the control electrode 62; they may be the inner region of the bias electrode 61, the outer region of the control electrode 62, or different regions from each other.

[0112] [Variation Example 5]

[0113] In the above embodiment, when viewed along the thickness direction of the wavelength-variable interference filter 1, the electrostatic actuator section 6 is arranged radially outward from the first reflective film 4 or the second reflective film 5 in the order of bias electrode 61, variable electrode 63 and control electrode 62, but the arrangement order of each electrode can also be changed.

[0114] [Variation Example 6]

[0115] In the above embodiments, the preferred size relationship of the areas of the bias electrode 61, the variable electrode 63 and the control electrode 62 is described, but the size relationship of each area can also be changed according to the structure used to change the gap amount G between the first substrate 2 and the second substrate 3.

[0116] [Variation Example 7]

[0117] In the above embodiments, the voltage switching unit 94 is a switch that can switch the connection of the variable electrode 63 between the bias driving unit 91 and the feedback control unit 93 based on the switching signal input from the microcomputer 95, but the present invention is not limited thereto.

[0118] For example, the voltage switching unit 94 may also be configured to include: a circuit structure capable of outputting a bias voltage and a control voltage separately from the bias drive unit 91 and the feedback control unit 93 described above; and a switch capable of switching either the bias voltage or the control voltage onto the variable electrode 63 based on a switching signal input from the microcomputer 95. In this case, the value of the bias voltage applied to the bias electrode 61 may be different from the value of the bias voltage applied to the variable electrode 63 in the bias drive mode.

[0119] [Variation Example 8]

[0120] like Figure 8 As shown, the wavelength-variable interference filter 1C according to the modified example may also include: a first substrate 2; a second substrate 3, facing the first surface 21 of the first substrate 2; and a third substrate 8, facing the second surface 22 of the first substrate 2. In this wavelength-variable interference filter 1C, a first reflective film 4 is disposed on the second surface 22 of the first substrate 2, and a second reflective film 5 is disposed on the side opposite to the second substrate 3 side of the first substrate 2, that is, on the opposing surface 81 of the third substrate 8 facing the first substrate 2. Thus, the first reflective film 4 and the second reflective film 5 are arranged in a mutually opposing manner.

[0121] In the wavelength-variable interference filter 1C of the modified example, the first substrate 2 is pulled closer to the second substrate 3 by electrostatic attraction through the electrostatic actuator 6, and the gap G between the first reflective film 4 and the second reflective film 5 can be adjusted.

[0122] Furthermore, in the wavelength-variable interference filter 1C of the modified example, the relationship between the magnitude of the voltage applied to each electrode of the electrostatic actuator section 6 and the magnitude of the gap G between the first reflective film 4 and the second reflective film 5 is reversed compared to the above embodiment. Therefore, in the driving method of the wavelength-variable interference filter 1C, it is only necessary to reverse the relationship between the first threshold and the gap target value Gt in the driving method described in the first embodiment.

[0123] [Summary of this disclosure]

[0124] The first aspect of this disclosure relates to a wavelength-variable interference filter comprising: a pair of reflective films facing each other; and an electrostatic actuator unit for changing the gap amount between the pair of reflective films, the electrostatic actuator unit comprising: a bias electrode for being applied a bias voltage corresponding to a target value of the gap amount; a control electrode for being applied a control voltage that is feedback-controlled based on the gap amount and the target value; and a variable electrode for being able to switch between applying the bias voltage and the control voltage.

[0125] In the first embodiment described above, preferably, when viewed along the thickness direction of the reflective film, the bias electrode, the control electrode, and the variable electrode are configured in a concentric circle centered on the reflective film.

[0126] In the first embodiment described above, preferably, when viewed along the thickness direction, the electrostatic actuator section is arranged radially outward from the pair of reflective films in the order of the bias electrode, the variable electrode, and the control electrode.

[0127] In the first embodiment described above, preferably, the area of ​​the bias electrode is larger than the areas of the control electrode and the variable electrode.

[0128] The second aspect of this disclosure relates to an optical module comprising: a wavelength-variable interference filter as described above; and a filter driving unit that drives the electrostatic actuator unit, the filter driving unit comprising: a bias driving unit that applies the bias voltage to the bias electrode; a gap detection unit that detects the gap amount between the pair of reflective films; a feedback control unit that applies the control voltage to the control electrode based on the gap amount detected by the gap detection unit; and a voltage switching unit that can switchably apply the bias voltage and the control voltage to the variable electrode.

[0129] In the second scheme described above, preferably, the voltage switching unit switches the voltage applied to the variable electrode between the bias voltage and the control voltage based on the comparison result between the target value of the gap amount and the first threshold.

[0130] In the second embodiment described above, preferably, the electrostatic actuator section further includes a variable preparatory electrode to which the bias voltage and the control voltage can be switched, and the voltage switching section switches the voltage applied to the variable preparatory electrode between the bias voltage and the control voltage based on a comparison result between the target value of the gap amount and a second threshold different from the first threshold.

[0131] The third aspect of this disclosure relates to a driving method for a wavelength-variable interference filter, comprising: a step of varying the gap amount by applying a bias voltage to a bias electrode, the bias voltage being determined according to each target value of the gap amount between a pair of reflective films; a step of adjusting the gap amount by detecting the gap amount between the pair of reflective films and applying a control voltage, which is feedback-controlled based on the detected gap amount and the target value of the gap amount, to a control electrode; a step of selecting one of the bias voltage and the control voltage as a selection voltage to be applied to a variable electrode based on the target value of the gap amount; and a step of assisting in the variation or adjustment of the gap amount by applying the selection voltage to the variable electrode when a voltage is applied to the bias electrode or the control electrode.

Claims

1. A wavelength-variable interference filter, characterized in that, have: A pair of reflective films, facing each other; and The electrostatic actuator section changes the gap between the pair of reflective films. The electrostatic actuator section has: The bias electrode is subjected to a bias voltage corresponding to a target value of the gap amount; The control electrode is subjected to a control voltage that is feedback-controlled based on the gap amount and the target value; as well as The variable electrode can be switched between the bias voltage and the control voltage.

2. The wavelength-variable interference filter according to claim 1, wherein, When viewed along the thickness direction of the reflective film, the bias electrode, the control electrode, and the variable electrode are arranged in a concentric circle centered on the reflective film.

3. The wavelength-variable interference filter according to claim 2, wherein, When viewed along the thickness direction, in the electrostatic actuator section, the bias electrode, the variable electrode, and the control electrode are arranged radially outward from the pair of reflective films in that order.

4. The wavelength-variable interference filter according to claim 1, wherein, The area of ​​the bias electrode is larger than the areas of the control electrode and the variable electrode.

5. An optical module, characterized in that, have: The wavelength-variable interference filter according to claim 1; and The filter drive unit drives the electrostatic actuator unit. The filter driving unit has: The bias drive unit applies the bias voltage to the bias electrode; The gap detection unit detects the amount of gap between the pair of reflective films; The feedback control unit applies the control voltage to the control electrode based on the gap amount detected by the gap detection unit; as well as The voltage switching unit can switch between applying the bias voltage and the control voltage to the variable electrode.

6. The optical module according to claim 5, wherein, The voltage switching unit switches the voltage applied to the variable electrode between the bias voltage and the control voltage based on a comparison between the target value of the gap amount and the first threshold.

7. The optical module according to claim 6, wherein, The electrostatic actuator section also includes a variable pre-electrode that can be switched between applying the bias voltage and the control voltage. The voltage switching unit switches the voltage applied to the variable preparatory electrode between the bias voltage and the control voltage based on a comparison result between the target value of the gap amount and a second threshold different from the first threshold.

8. A driving method for a wavelength-variable interference filter, characterized in that, It includes the following steps: The gap amount is varied by applying a bias voltage to the bias electrode corresponding to a target value of the gap amount between a pair of reflective films; The gap amount is adjusted by detecting the gap amount between the pair of reflective films and applying a control voltage, which is based on the detected gap amount and the target value, to the control electrode for feedback control. Based on the target value, one of the bias voltage and the control voltage is selected as the selection voltage; as well as When a voltage is applied to the bias electrode or the control electrode, the selection voltage is applied to the variable electrode to assist in the change or adjustment of the gap amount.

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