JP2015125381A - Tunable optical filter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a tunable optical filter with an enhanced filter property capable of selectively transmitting a beam of light of predetermined wavelength.SOLUTION: A tunable optical filter 1 capable of selectively transmitting a beam of light of predetermined wavelength, includes: a frame 4; a reflector plate 2 which is supported by the frame 4 inside hereof; a reflector plate 3 which is supported by the frame 4 inside hereof being interposed by a beam 5; and a drive layer 9 composed of a piezoelectric member 8 provided to the beam 5. The reflector plate 3 is configured to be supported at the reflector plate 2 side of the beam 5.

Description

  The present invention relates to a wavelength tunable optical filter that selectively transmits a light beam having a predetermined wavelength.

  Conventionally, as this type of wavelength tunable optical filter, incident light is reflected multiple times between a pair of reflecting plates, and a technology that transmits light of a specific wavelength by interference action at that time is used. A structure is known in which the wavelength of transmitted light is varied by changing the interval.

  As examples of the use of this wavelength tunable optical filter, a multi-gas sensor that detects the type of gas using mid-infrared light or far-infrared light, or a urine sugar level or blood glucose level that uses near-infrared light. A good sugar sensor.

  In such a tunable optical filter, when controlling the minute distance between the reflecting plates, the electrostatic drive method using electrostatic force, the piezoelectric drive method using the inverse piezoelectric effect of piezoelectric material, the thermal expansion coefficient of different materials A thermal drive method using the difference between the two is used.

  Among these driving methods, when a wavelength tunable optical filter in the infrared region is handled, a temperature rise occurs due to infrared rays, so that it is difficult to perform high-precision control with the heat driving method that actively uses heat. Further, in the electrostatic drive system, when the minute interval between the reflecting plates is brought closer than 2/3 from the initial value, control at the minute interval becomes impossible due to the pull-in phenomenon. Theoretically, the control range of the minute interval and the wavelength variable region of the optical filter have a correlation, so that the restriction due to the pull-in phenomenon has a larger influence as the wavelength becomes shorter. As for the wavelength tunable optical filter corresponding to), the use area is limited.

  On the other hand, although the temperature rise due to infrared rays occurs in the piezoelectric drive method, the influence is small compared to the heat drive method, and there is no restriction due to the pull-in phenomenon, so it can cope with a wide wavelength region including the near infrared region. Suitable for tunable optical filters.

  As prior art document information related to the invention of this application, for example, Patent Document 1 is known.

JP 2005-215323 A

  However, as the detection wavelength in the wavelength tunable optical filter is widened to the short wavelength side, the distance between the pair of reflectors becomes smaller, so the wavelength tunable optical filter that uses the interference effect in multiple reflection between the reflectors In order to obtain filter characteristics, it is important to widen the displacement width of the pair of reflectors and to maintain the parallelism with higher accuracy.

  Therefore, the present invention aims to solve such problems and improve the filter characteristics of the wavelength tunable optical filter.

  In order to achieve this object, the present invention provides a frame, a first reflector supported on the inside of the frame, and a second reflector supported on the inside of the frame via a beam. In the wavelength tunable optical filter having a driving layer made of a piezoelectric body provided on the beam, the second reflecting plate is supported on the first reflecting plate side of the beam.

  With this configuration, the filter characteristics of the wavelength tunable optical filter can be improved.

1 is a perspective view of a wavelength tunable optical filter according to an embodiment of the present invention. Cross-sectional view of the same wavelength tunable optical filter Schematic showing the measurement principle of the same wavelength tunable optical filter (A)-(c) The schematic diagram which shows the manufacturing method of the 1st block which comprises the same wavelength variable optical filter. (A)-(d) The schematic diagram which shows the manufacturing method of the 2nd block which comprises the same wavelength variable optical filter. The schematic diagram which shows the joining method of the 1st block and the 2nd block Cross-sectional view of another tunable optical filter Cross-sectional view of another tunable optical filter Cross-sectional view of another tunable optical filter Perspective view of another wavelength tunable optical filter

  Hereinafter, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a perspective view of the wavelength tunable optical filter 1, and FIG. 2 is a sectional view thereof. The basic structure of the wavelength tunable optical filter 1 is a structure in which the outer peripheral portions of the two reflecting plates 2 and 3 that are arranged opposite to each other are supported by a frame body 4. The lower reflecting plate 2 is directly supported by the frame 4, but the upper reflecting plate 3 is supported by the frame 4 via four beams 5 having outer peripheral portions arranged at equal intervals. .

  Each beam 5 is provided with a driving layer 9 having a laminated structure in which a piezoelectric body 8 is provided between the upper electrode 6 and the lower electrode 7. The drive layer 9 applies a drive signal from the control circuit 10 to the upper electrode 6, thereby generating a potential difference between the upper electrode 6 and the lower electrode 7, and the piezoelectric body 8 bends according to the potential difference. By this bending, the reflecting plate 3 can be moved in a direction facing the reflecting plate 2. That is, by adjusting the voltage of the drive signal applied to the drive layer 9 disposed on the beam 5, the distance between the pair of reflectors 2 and 3 can be freely adjusted. The control circuit 10 is mounted on the upper surface outside the beam 5 in the tunable optical filter 1 and is connected to the terminal electrode 11 connected to the upper electrode 6 and the lower electrode 7 by wire bonding 12. ing. In this wavelength tunable optical filter 1, the control circuit 10 is mounted on the extended portion of the frame body 4. However, a terminal electrode 11 that is electrically connected to the control circuit 10 is disposed on the wavelength tunable optical filter 1, and the control circuit 10 can also be arranged on a base material on which the wavelength tunable optical filter 1 is mounted.

  Further, the reflecting plate 3 disposed on the upper side in FIG. 2 is disposed on the inner end portion of the beam 5 and on the lower reflecting plate 2 side. An intermediate layer 13 is provided between the beam 5 and the reflector 3.

  As shown in FIG. 3, the wavelength tunable optical filter 1 irradiates the measurement object 16 with the parallel light beam 15 emitted from the light source 14, and transmits the transmitted light 17 to the bandpass filter 18 and the wavelength tunable optical filter. 1 is received and received by the photodiode 19. In such a configuration, the wavelength of the transmitted light 17 emitted from the reflecting plate 2 is selected by sequentially changing the minute interval between the reflecting plates 2 and 3 in the wavelength tunable optical filter 1, and the transmitted light amount is selected by the photodiode 19. By measuring, the spectrum can be measured. Note that the wavelength tunable optical filter 1 causes multiple reflections with the lower reflection plate 2 after the transmitted light 17 passes through the reflection plate 3, and interference conditions determined by a minute interval between the reflection plates 2 and 3. Only the light having the same wavelength resonates, and only the light having the resonated wavelength passes through the reflector 2. That is, the wavelength of the transmitted light 17 emitted from the reflecting plate 2 is determined by the interval between the pair of reflecting plates 2 and 3, and the detection wavelength can be selected by displacing the interval.

  More specifically, by applying a drive signal from the control circuit 10 to the drive layer 9 and controlling the distance between the reflectors 2 and 3 in the range of 350 nm to 1.5 μm, various control conditions can be used depending on the primary interference conditions. It becomes possible to extract a light beam having an arbitrary wavelength in the near-infrared region (700 nm to 3.0 μm) from the transmitted light 17 having a mixture of wavelengths. At this time, by combining a band-pass filter 18 that removes unnecessary wavelengths extracted by interference conditions of other orders and a photodiode 19 that is sensitive to a desired wavelength region, it can be adapted to the near infrared region with a simple component configuration. Spectroscopic spectra can be measured. As for the interference condition, the primary interference condition is used as an example, but interference orders of other orders may be used.

  Next, a manufacturing method of the wavelength tunable optical filter 1 will be described. In this manufacturing method, the step of forming the first block 20 with the lower part including the reflector 2, the step of forming the second block 21 with the upper part including the reflector 3 and the beam 5, It consists of the process of joining.

  In the step of forming the first block 20, first, as shown in FIG. 4A, a recess 23 is formed on the Si substrate 22. Next, as shown in FIG. 4B, the SiN layer 24 and the Au layer 25 are sequentially stacked on the main surface side including the recess 23 in the Si substrate 22. Next, as shown in FIG. 4C, the first block 20 is formed by forming the recess 26 in the portion that becomes the optical path of the transmitted light 17 on the back side of the Si substrate 22 and exposing the SiN layer 24. The Note that the Au layer 25 forms a reflection surface of the reflection plate 2.

  As shown in FIG. 5 (a), the second block 21 is formed by preparing an SOI (Si on Insulator) substrate 30 in which an SiO2 layer 28 and an Si layer 29 are laminated in this order on an Si substrate 27. Forms a Pt layer 31 that forms the lower electrode 7, a PZT layer 32 that forms the piezoelectric body 8, and an Au layer 33 that forms the upper electrode 6. Further, a SiN layer 34 and an Au layer 35 are stacked on the back surface. Next, as shown in FIG. 5B, the Au layer 33, the PZT layer 32, and the Pt layer 31 are sequentially processed to form the drive layer 9. In this patterning, although not particularly shown, wiring electrodes and terminal electrodes 11 for the drive layer 9 are also formed. Then, as shown in FIG. 5C, a recess 36 is formed on the lower surface side of the SOI substrate 30 to expose the SiO 2 layer 28 and form the beam 5. Further, as shown in FIG. 5D, the second block 21 is formed by forming the concave portion 37 in the portion that becomes the optical path of the transmitted light 17 and forming the reflecting plate 3 with the SiN layer 34 exposed. . Further, the intermediate layer 13 interposed between the beam 5 and the reflecting plate 3 is formed by the Si layer 27.

  As shown in FIG. 6, the bonding process between the first block 20 and the second block 21 includes an Au layer 25 positioned on the outer peripheral portion of the upper surface of the first block 20 and an outer peripheral portion of the lower surface of the second block 21. The wavelength tunable optical filter 1 can be configured by bonding the Au layer 35 located at the position. In the joined body of the first block 20 and the second block 21, the frame body 4 includes the Si substrate 27, the SiO 2 layer 28, the Si layer 29, the SiN layer 34, and the second block located outside the beam 5. The Au layer 35 is composed of a multilayer structure including the Si substrate 22, the SiN layer 24, and the Au layer 25 constituting the first block.

  Further, as described above, when the Au layer 25 forming the reflecting plate 2 in the first block 20 and the Au layer 35 forming the reflecting plate 3 in the second block 21 are provided, the first, second blocks 20 and 21 are provided. Since the Au layers 25 and 35 can be used as the joining members of the first and second blocks 20 and 21, the step of separately forming the members necessary for the joining is omitted.

  As described above, such a wavelength tunable optical filter 1 is multiplexed by oscillating the inner end portion of the beam 5 in the vertical direction, displacing the reflecting plate 3 in the opposite direction to the reflecting plate 2, and changing the interval. Since the resonance wavelength in reflection is variable, the variable width of the transmitted light 17 can be broadened by increasing the amplitude of the beam 5, and the detection accuracy is ensured by ensuring the parallelism of the opposing reflectors 2 and 3. It can be enhanced. In addition, since the range of the transmission wavelength determined by the interval between the reflecting plates 2 and 3 facing each other is a minute range as described above, the reflecting plate 3 is supported on the side of the reflecting plate 2 facing the beam 5. It is said. Further, as shown in FIG. 1, the drive layer 9 provided on the beam 5 has a part of the drive layer 9 used as a wiring electrode (not shown in particular) or a terminal electrode 11, so It is preferable to dispose on the surface or the vicinity thereof.

  The wavelength tunable optical filter 1 has a structure in which the reflection plate 3 is supported by the inner end portion of the beam 5 on which the drive layer 9 is disposed. According to this configuration, the characteristics of the wavelength tunable optical filter 1 can be enhanced.

  In other words, the drive layer 9 has a laminated structure in which the piezoelectric body 8 is sandwiched between the upper electrode 6 and the lower electrode 7, but due to the application of stress and the difference in thermal expansion to enhance the orientation of the piezoelectric body 8 in these formation stages. The generated stress remains as internal stress in the drive layer 9 and causes distortion in the beam 5 on which the drive layer 9 is disposed. For this reason, if the reflecting plate 3 is formed on the back surface of the beam 5 in which this distortion occurs, the flatness and inclination of the reflecting plate 3 cannot be maintained. Further, if the thickness of the beam 5 is increased to eliminate the influence of the strain, the vibration property of the beam 5 is deteriorated. Therefore, the beam 5 and the reflector 3 on which the drive layer 9 is provided have different structures, and the separate structure of the reflector 3 is supported by the inner portion of the beam 5 so that the internal stress of the drive layer 9 on the reflector 3 is affected. As a result, the characteristics of the wavelength tunable optical filter 1 can be improved. Furthermore, when the drive layer 9 and the reflector 3 are formed, the drive layer 9 and the reflector 3 can be formed under optimum conditions without being restricted by manufacturing. As a result, it is possible to contribute to improving the characteristics of the wavelength tunable optical filter 1.

  When setting the interval between the reflecting plates 2 and 3 facing each other, by providing the intermediate layer 13 between the beam 5 and the reflecting plate 3, it is possible to suppress the distortion generated in the beam 5 from being transmitted to the reflecting plate 3. The flatness of the reflecting plate 3 can be increased and the inclination can be suppressed. The intermediate layer 13 is made of the same material as the material for forming the frame 4, particularly the Si substrate 27 for forming the second block 21 described above, and therefore, a separate process is provided as described with reference to FIG. 5. Thus, the intermediate layer 13 can be formed.

  In addition, as a configuration for reducing the internal stress of the driving layer 9, the inner end of the driving layer 9 is positioned outside the inner end of the beam 5, so that the inner end portion of the beam 5 that supports the reflector 3 is This is a portion that is not formed, and the influence of internal stress on the reflecting plate 3 in this portion is alleviated, the inclination of the reflecting plate 3 is suppressed, and the parallelism between the reflecting plates 2 and 3 can be controlled with high accuracy.

  As shown in FIG. 7, the intermediate layer 13 is provided so as to cover the entire surface of the reflecting plate 3, whereby the strength of the reflecting plate 3 can be further increased and the flatness of the reflecting plate 3 can be increased. it can. However, when the intermediate layer 13 is provided on the entire surface, the intermediate layer 13 is in the incident optical path, and therefore, a material that matches the wavelength of the transmitted light 17 must be selected as the material of the intermediate layer 13. For example, if the wavelength of the transmitted light 17 is 1.1 μm or more, the material of the intermediate layer 13 can be Si to cover the transmitted light band.

  Further, as a configuration for relaxing the internal stress of the drive layer 9 with respect to the reflecting plate 3, as shown in FIG. 8, an upper layer 38 having an internal stress opposite to the internal stress of the drive layer 9 is provided on the drive layer 9. It is preferable to arrange in. The upper layer 38 having an internal stress opposite to the internal stress of the drive layer 9 may be formed of a metal film such as Ni. However, since it is necessary to ensure insulation with the upper electrode 6 constituting the surface of the drive layer 9, the surface of the beam 5 including the drive layer 9 is covered with an insulating layer 39 such as an epoxy-based photoeffect resin, and the surface In this structure, an upper layer 38 is formed. As a result, the inclination of the reflecting plate 3 can be suppressed, and the parallelism between the reflecting plates 2 and 3 can be controlled with high accuracy.

  Since the upper layer 38 has internal stress like the driving layer 9, the inner end portion of the beam 5, that is, the inner portion including the portion supporting the reflecting plate 3, as in the driving layer 9. The non-formed portion where the upper layer 38 is not formed is preferable. Thereby, the inclination of the reflecting plate 3 and the distance between the reflecting plates 2 and 3 can be controlled with higher accuracy.

  Further, in the initial state where the wavelength tunable optical filter 1 is not operating, the beam 5 is warped upward so that the interval between the reflectors 2 and 3 can be secured during non-operation, and the wavelength tunable optical filter It is possible to prevent damage and sticking caused by contact due to impact during transportation. The beam 5 can be warped upward by using the internal stress of the upper layer 38 described above.

  Further, since the upper layer 38 is made of a metal material, the upper layer 38 can have an appropriate strength, and this portion can function as the beam 5. Therefore, as shown in FIG. 5 is partially removed from the portion facing the upper layer 38 to the connection portion with the intermediate layer 13 in FIG.

  When the parallelism of the reflecting plates 2 and 3 is controlled with higher accuracy, a plurality of counter electrodes 40 are arranged on the reflecting plates 2 and 3 as shown in FIG. 2, and the detection signals obtained here are controlled. The parallelism can be further increased by inputting to the circuit 10 and determining the balance and change of the capacitance formed by each counter electrode 40 and performing feedback control.

  Further, when the reflector 3 is supported via the plurality of beams 5 as in the wavelength tunable optical filter 1 according to this embodiment, the variation in the material and processing variations of the beams 5 and the drive layer 9 is varied. Since it is necessary to match the deflection accuracy of the beams 5 including the elements, it is effective to individually control the deflection amount of each beam 5. In particular, by arranging the beam 5 at a symmetrical position with respect to the center of the reflecting plate 3, the tilt correction of the reflecting plate 3 can be performed at a high level. The number of beams 5 that support the reflector 3 is not limited to four as long as they are symmetrically arranged at equal intervals. However, considering the complexity of the control circuit 10 and the routing of wiring, the number of beams 5 should be four. Is preferred.

  Although not particularly illustrated, two or more drive layers 9 may be provided on each beam 5 that supports the reflector 3. By individually controlling different driving layers 9 arranged on the same beam 5, the parallelism with the lower reflector 2 can be controlled with higher accuracy. Further, the piezoelectric body 8 and the lower electrode 7 constituting the drive layer 9 are single, and by separating only the upper electrode 6 into two or more, the same effect can be achieved while simplifying the manufacturing process. Is obtained.

  Next, a method for adjusting the wavelength tunable optical filter 1 will be described. When a desired wavelength is selected by sequentially changing the minute interval between the pair of reflectors 2 and 3 as in the wavelength tunable optical filter 1 and the spectrum is measured at that time, the reflectors 2 and 2 are selected depending on the measurement environment. 3 may vary, and the absolute value of the measurement wavelength may vary. In that case, for example, as shown in FIG. 3, another light source 42 having a known wavelength and another photodiode 43 corresponding to the other light source 42 are connected to the optical path of the transmitted light 17 for measuring the spectrum. Can be corrected by providing a different optical path 44.

  That is, the same voltage is applied to all the drive layers 9 of the wavelength tunable optical filter 1 to displace the upper reflector 3 so that the amount of light received by the separate photodiode 43 is maximized. Since the known distance is selected as the minute distance between the pair of reflectors 2 and 3 when the amount of light received by the separate photodiode 43 is maximized, the absolute value of the measurement wavelength can be corrected.

  In addition, by correcting with another optical path 44 in this way, the reflecting plate 3 can be controlled in parallel to the reflecting plate 2. The parallelism of the reflectors 2 and 3 is closely related to the half-value width of the spectral spectrum. When the reflectors 2 and 3 are arranged in parallel, the half-value width is reduced and the amount of light is increased. Utilizing this fact, the parallelism of the reflectors 2 and 3 is improved by varying the voltage applied sequentially in the plurality of drive layers 9 so that the amount of light received by the separate photodiode 43 is maximized. Thus, a highly accurate filter characteristic is realized, and a spectrum having a small spectrum half width can be measured. Although the optical path used for correction is transmitted through the wavelength tunable optical filter 1, the same correction can be performed by the reflected light of the wavelength tunable optical filter 1.

  Further, as shown in FIG. 10, the inner portion of the beam 5 has a narrow meandering shape, so that the inner portion having a large amplitude in the beam 5 has low elasticity, and the amount of displacement of the reflector 3 with respect to the deflection amount of the beam 5. Can be made larger.

  Although not shown in particular, a drive layer is also provided on the side that coincides with the extending direction of the beam 5 in this meandering portion and on the side that is orthogonal to the extending direction of the beam, and the amount of bending of each of these is controlled. Therefore, the deflection amount can be finely adjusted with the small driving layer provided in the meandering portion while the large deflection amount is secured by the driving layer 9 provided on the beam 5 with a large area. The parallelism with the lower reflector 2 can be maintained with high accuracy while securing the amount.

  The wavelength tunable optical filter according to the present invention can increase the displacement width of the distance between the pair of reflectors and maintain the parallelism to improve the filter characteristics, and in particular, the wavelength that can correspond to a wide wavelength region including the near infrared region. Useful in variable optical filters.

2 First Reflector 3 Second Reflector 4 Frame 5 Beam 8 Piezoelectric 9 Drive Layer 10 Control Circuit 11 Terminal Electrode 13 Intermediate Layer 38 Upper Layer 39 Insulating Layer

Claims (10)

A frame and a first reflector supported on the inside of the frame;
A beam supported at one end inside the frame;
A second reflector supported by the other end of the beam and facing the first reflector;
A driving layer made of a piezoelectric body provided on the beam;
A control circuit for controlling the deflection of the driving layer or a terminal electrode for connecting the control circuit,
The wavelength tunable optical filter, wherein the second reflecting plate is connected to the beam on the first reflecting plate side. The tunable optical filter according to claim 1, wherein a driving layer is provided on a surface of the beam opposite to the first reflecting plate. The frame body has a multilayer structure, an intermediate layer is provided between the second reflector and the beam, and the intermediate layer is formed of the same material as at least one layer constituting the frame body. The tunable optical filter according to claim 2. 4. The wavelength tunable optical filter according to claim 3, wherein an intermediate layer is provided on the entire surface of the second reflecting plate. 4. The wavelength tunable optical filter according to claim 3, wherein an inner end of the driving layer is located outside an inner end of the beam. The upper layer having an internal stress opposite to the internal stress of the driving layer is provided on the surface of the insulating layer while covering the surface of the driving layer from the inner end of the beam with an insulating layer. 5. The wavelength tunable optical filter according to 5. 7. The wavelength tunable optical filter according to claim 6, wherein a portion between the inner end of the driving layer and the inner end of the beam on the surface of the insulating layer is a non-formation portion of the upper layer. The wavelength tunable optical filter according to claim 1, wherein a plurality of beams are provided on the second reflecting plate, and driving layers provided on the plurality of beams are individually controlled by a control circuit. 2. The wavelength tunable optical filter according to claim 1, wherein an inner end portion of the beam is bent to the opposite side of the first reflecting plate. A detection unit for detecting parallelism between the first reflection plate and the second reflection plate is provided, and a detection signal output from the detection unit is input to a control circuit to control the deflection of the drive layer. The tunable optical filter according to claim 1.

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