JP2014211466A - Variable wavelength optical filter - Google Patents

Abstract

The present invention relates to a wavelength tunable optical filter that selectively transmits a light beam having a predetermined wavelength, and an object thereof is to improve filter characteristics.
In order to achieve this object, in a wavelength tunable optical filter 1 that adjusts the distance between a pair of reflecting plates 2 and 3 supported by a frame 4, a beam 5 that supports the reflecting plate 2 is replaced with a piezoelectric body. The driving layer 9 is composed of a laminated structure including the vibrating portion 13 and the reflecting plate 2. The plurality of beams 5 are symmetrically arranged with respect to the reflecting plate 2 and the driving layer 9 is individually controlled by the control circuit 10. .
[Selection] Figure 2

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.

  Examples of the use of this wavelength tunable optical filter include a multi-gas sensor that detects the type of gas using mid-infrared light, and a sensor that detects urine sugar level and blood glucose level using near-infrared light. can give.

  In such a wavelength tunable optical filter, when controlling the minute distance between the reflecting plates, an electrostatic driving method using an electrostatic force, a piezoelectric driving method using the inverse piezoelectric effect of a piezoelectric material, and a heat of a different material. A thermal drive system that uses the difference in expansion coefficient is used.

  However, when a wavelength tunable optical filter in the infrared region is handled, a temperature rise due to infrared rays occurs, so that it is difficult to perform high-precision control with a heat drive system 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 greater effect as the wavelength is 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 wavelength of the tunable optical filter becomes wider on the short wavelength side of the detection wavelength, the displacement width of the pair of reflecting plates widens to the minute side, so that the wavelength tunable light that uses the interference action in multiple reflection between the reflecting plates In a filter, widening the displacement width of a pair of reflectors and maintaining parallelism are important issues for obtaining filter characteristics.

  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 relates to a wavelength tunable optical filter that adjusts the distance between a pair of reflectors supported by a frame, and a beam that supports the reflectors as a driving layer made of a piezoelectric material, and a vibration. In this configuration, a plurality of beams are arranged symmetrically with respect to the reflector, and the drive layer is individually controlled by the control circuit.

  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)-(e) The schematic diagram which shows the manufacturing method of the same wavelength variable optical filter A perspective view of a wavelength tunable optical filter according to another embodiment

  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 two opposing reflectors 2 and 3 are supported by a frame body 4, and the reflector 2 arranged on the upper side is circular. The outer peripheral end portion is connected to the frame body 4 via beams 5 arranged at equal intervals in all directions.

  Each beam 5 is provided with a driving layer 9 having a laminated structure in which a piezoelectric layer 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 layer 8 is bent according to the potential difference. Due to this bending, the reflecting plate 2 can be moved in a direction facing the reflecting plate 3. 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 wavelength tunable optical filter 1, and is connected to the electrode pad 11 connected to the upper electrode 6 and the lower electrode 7 by wire bonding 12.

  The beam 5 has a laminated structure including the upper reflecting plate 2, the driving layer 9 disposed on the surface thereof, and the vibrating portion 13 disposed on the surface of the driving layer 9, and the vibrating portion 13 is formed on the surface of the driving layer 9. By joining these, the drive layer 9 is constrained and a large deflection of the beam 5 is obtained.

  In the tunable optical filter 1, a substrate 14 having a predetermined thickness is bonded to the lower surface of the lower reflecting plate 3 to ensure product strength.

  As shown in FIG. 3, the wavelength tunable optical filter 1 irradiates the measurement target 17 with the parallel light beam 16 emitted from the light source 15, and transmits the transmitted light 18 to the bandpass filter 19 and the wavelength tunable optical filter. 1 is received and received by the photodiode 20. In such a configuration, the wavelength of the transmitted light 18 emitted from the reflecting plate 3 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 20. By measuring, the spectrum can be measured. The wavelength tunable optical filter 1 causes multiple reflections with the lower reflecting plate 3 after the transmitted light 18 passes through the upper reflecting plate 2, and interference determined by a minute interval between the reflecting plates 2 and 3. Only the light beam having the wavelength that matches the condition resonates, and only the light beam having the resonated wavelength can be transmitted through the reflector 3 and extracted. That is, the wavelength of the light beam to be extracted 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 18 having a mixture of wavelengths. At this time, by combining a bandpass filter 19 that removes unnecessary wavelengths extracted due to interference conditions of other orders and a photodiode 20 that is sensitive to a desired wavelength region, it can respond 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, the manufacturing method of the wavelength tunable optical filter 1 in the embodiment of the present invention will be described below.

  First, as shown in FIG. 4A, a lower reflector 3 is formed by laminating a silicon nitride layer 21 and silicon 22 on one surface of a substrate 14 made of silicon. A silicon oxide layer to be the sacrificial layer 23 is formed on the reflector 3. A silicon layer 24 and silicon nitride 25 are laminated on the sacrificial layer 23 to form the upper reflector 2. Thereafter, platinum that becomes the lower electrode 7, lead zirconate titanate that becomes the piezoelectric layer 8, and gold that becomes the upper electrode 6 are sequentially laminated by a sputtering method or the like.

  Next, an elastic resin layer having photosensitivity is used as an etching mask (not shown in particular), and the lower electrode 7, the piezoelectric layer 8, and a part of the upper electrode 6 are removed by ICP dry etching. The drive layer 9 is patterned as shown in b).

  Next, as shown in FIG. 4C, an elastic resin layer (not shown) made of an insulating material that has photosensitivity and undergoes a photocrosslinking reaction is used, and a vibrating portion is formed on the upper surface of the drive layer 9. 13 first layers 26 are formed.

  Next, as shown in FIG. 4D, a second layer 27 made of copper is formed on the upper surface of the first layer 26 by electroplating.

  Finally, the inner part of the sacrificial layer 23 located below the upper reflector 2 and the beam 5 is removed from the opening part between the adjacent beams 5 using hydrogen fluoride, and the outer peripheral part is framed. By leaving it as 4, as shown in FIG. 4E, the vibration space 28 of the pair of reflectors 2 is formed, and the upper reflector 2 can be operated.

  In addition, according to this structure, the board | substrate 14 selects the material which has translucency in a desired measurement wavelength range, for example, in the area | region of a far infrared ray from the long-wavelength side of a near infrared ray, it is transparent in this area | region. It is only necessary to select silicon or the like having a light transmittance, and silicon having low translucency in the region of visible light from the near-infrared short wavelength side may be selected.

  Although not particularly shown, the transmission region of the transmitted light 17 in the substrate 14 may be partially etched away.

  The vibration unit 13 is generally formed by processing the substrate 14 existing on the lower surface of the drive layer 9. In the case of the wavelength tunable optical filter 1, the pair of reflectors 2 is formed on the substrate 14 in advance. , 3 and a sacrificial layer 23 for maintaining a gap between them is formed in advance, so that the reflector 2 and the vibrating portion 13 on the same surface with respect to the drive layer 9 are individually processed. However, there is a problem that the process is complicated and the yield is extremely reduced. However, as described above, if the vibrating portion 13 is formed on the upper surface of the drive layer 9 and the reflector 2 is formed on the lower surface of the drive layer 9, each can be configured on a different surface, so that the manufacturing method can be simplified. , Can prevent the yield from deteriorating.

  Further, when the vibrating portion 13 is manufactured by processing the substrate 14 existing on the lower surface of the drive layer 9, the formation temperature of the drive layer 9 including the piezoelectric layer 8 made of lead zirconate titanate is high. Since the thermal stress is accumulated in the vibration part 13 and the beam 5 is warped, the minute interval between the pair of reflectors 2 and 3 is deviated from the design value, and the reflector 2 is inclined, and as a result, highly accurate filter characteristics are obtained. There arises a problem that it cannot be realized. However, since the stress can be controlled according to the formation conditions of the vibration part 13 by forming the vibration part 13 after the drive layer 9 is formed, the warp of the beam 5 on which the drive layer 9 is arranged can be suppressed. Thus, it is possible to realize a highly accurate filter characteristic.

  The vibrating portion 13 includes a first layer 26 formed of an elastic resin having photosensitivity and allowing a photocrosslinking reaction to proceed, and a second layer 27 formed of an electroplating method using a coating layer for plating. With the stacked structure, miniaturization is facilitated, so that the device can be miniaturized.

  Further, like the wavelength tunable optical filter 1, the first layer 26 of the vibration part 13 is an elastic resin layer and the second layer 27 is a copper plating layer, so that the longitudinal elastic modulus of the first layer 26 is the second layer. 27, the distance from the neutral plane of deflection to the drive layer 9 can be increased, and the force generated in the drive layer 9 can be efficiently converted into deflection. As a result, a large displacement can be obtained, and the tunable optical filter 1 that can cope with a wide wavelength region can be realized. Moreover, since the rigidity of the vibration part 13 can be increased without reducing the displacement, the wavelength tunable optical filter 1 with improved resistance to disturbance vibration can be realized.

  In the wavelength tunable optical filter 1 that requires high-precision control even at a minute interval corresponding to the near-infrared region, in order to increase the accuracy of the spectral spectrum, the parallelism of the pair of reflectors 2 and 3 at the minute interval It is important to increase Therefore, it is effective to individually control the drive layer 9 provided on each beam 5.

  This is because, when the movements of the plurality of beams 5 are the same, the control from the control circuit 10 is usually the same control using the same drive signal. When the parallelism of the pair of reflectors 2 and 3 is desired, the beam 5 including fluctuation elements such as the material variation and the machining accuracy variation of the reflector 5, the drive layer 9, the vibration part 13, and the like related to the deflection of the beam 5 Since it is necessary to match the bending accuracy, it is effective to individually control the bending amount of each beam 5. In particular, by arranging the beam 5 at a symmetrical position with respect to the center of the reflector 2, the inclination of the reflector 2 can be highly corrected. The number of beams 5 that support the reflector 2 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 is four. It is preferable.

  In the wavelength tunable optical filter 1, a portion where the reflecting plate 2 extends to the outer peripheral side and is exposed is interposed between the beam 5 and the reflecting plate 2, and this exposed portion is used as the auxiliary beam 29. . This is because the auxiliary plate 29 composed of the reflecting plate 2 having lower elasticity than that of the beam 5 is provided at the tip of the beam 5 having a large amplitude, whereby the reflecting plate 2 can obtain a larger displacement.

  Although not particularly shown, two or more drive layers 9 may be provided on each beam 5 that supports the reflector 2. By individually controlling different driving layers 9 arranged on the same beam 5, the parallelism with the lower reflector 3 can be controlled with higher accuracy. In addition, the piezoelectric layer 8 and the lower electrode 7 constituting the driving layer 9 are single, and only the upper electrode 6 is separated into two or more. An effect 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 wavelength tunable optical filter is selected depending on the measurement environment. The minute interval of 1 may fluctuate, and the absolute value of the measurement wavelength may vary. In this case, for example, as shown in FIG. 3, another light source 30 having a known wavelength and another photodiode 31 corresponding to the other light source 30 are connected to the optical path of the transmitted light 18 for measuring the spectrum. Can be corrected by providing them in different optical paths 32.

  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 2 so that the amount of light received by another photodiode 31 is maximized. Since the known distance is selected as the minute interval between the pair of reflectors 2 and 3 when the amount of light received by the separate photodiode 31 is maximized, the absolute value of the measurement wavelength can be corrected.

  In addition, by correcting with another optical path 32 as described above, the reflecting plate 2 can be controlled in parallel to the reflecting plate 3. 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. By utilizing this fact, the parallelism of the reflectors 2 and 3 can be adjusted by varying the voltage applied individually and sequentially in the plurality of drive layers 9 so that the amount of light received by another photodiode 31 is maximized. Improvement, high-precision filter characteristics are realized, and a spectral spectrum with a small spectrum half-value width can be measured. Note that the optical path 32 used for correction is transmitted through the wavelength tunable optical filter 1, but the same correction can be performed by reflected light from the wavelength tunable optical filter 1. Further, the wall 33 provided so as to surround the outer peripheral portion of the upper reflecting plate 2 shown in FIG. 1 is provided in order to increase the bending strength of the upper reflecting plate 2, and the above-described FIG. 4 (c). In the stage of formation with the vibration part 13 in FIG. 4D, it is formed in the same manner as the vibration part 13.

  Next, another embodiment of the present invention will be described with reference to FIG. The difference from the embodiment described above is that the shape of the auxiliary beam 29 is a meandering shape whose width is narrower than the tip of the beam 5, and the elasticity of a region with a large amplitude in the vicinity of the reflector 2 is reduced. As a result, the amount of displacement of the reflecting plate 2 with respect to the amount of bending of the beam 5 can be increased. In FIG. 5, a portion for mounting the control circuit 10 shown in FIG. 1 is omitted, and the beam 5 and its inner portion are extracted.

  The auxiliary beam 29 has a meandering shape including a first extending portion 34 that coincides with the extending direction of the beam 5 and a second extending portion 35 that is orthogonal to the first extending portion 34. The driving layer 36 is provided on the surface of the first extending portion 34, and by controlling the amount of bending of this portion, a large amount of bending is secured by the driving layer 9 having a large area provided on the beam 5, and the auxiliary beam 29 is provided. Since the amount of bending can be finely adjusted with the small driving layer 36 provided on the upper side, the parallelism with the lower reflector 3 can be maintained with high accuracy while ensuring the amount of displacement of the upper reflector 2.

  Further, a driving layer 37 is provided on the surface of the second extending portion 35 extending in a direction orthogonal to the extending direction of the beam 5, and by controlling the amount of bending of the driving layer 37, the driving layer 37 is orthogonal to the extending direction. Since the amount of displacement of the reflecting plate 2 in the direction can be finely adjusted, the parallelism can be controlled with higher accuracy.

  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.

DESCRIPTION OF SYMBOLS 1 Wavelength variable optical filter 2 2nd reflecting plate 3 1st reflecting plate 4 Frame 5 Beam 9, 36, 37 Drive layer 10 Control circuit 13 Vibrating part 29 Auxiliary beam 34 1st extending part 35 2nd extending part

Claims (5)

A frame, a first reflector supported by the frame, and a second reflector supported by the frame via a beam and disposed opposite to the first reflector with a predetermined interval; A drive layer made of a piezoelectric body provided on the beam, and a control circuit for controlling the deflection of the drive layer,
The beam has a laminated structure including the driving layer, a vibration part joined to the driving layer, and the second reflecting plate, and a plurality of the beams are provided, and the plurality of beams are provided to the second reflecting plate. The wavelength tunable optical filter is characterized in that the drive layer provided on each of the plurality of beams is individually controlled by the control circuit. The wavelength tunable optical filter according to claim 1, wherein an auxiliary beam having lower elasticity than the beam is provided between the beam and the second reflecting plate. The wavelength tunable optical filter according to claim 2, wherein the second reflecting plate is extended to the outer periphery, and the extended portion is used as an auxiliary beam. The auxiliary beam has a first extending portion extending in the extending direction of the beam and a second extending portion extending in a direction orthogonal to the extending direction, and a drive layer is provided in the first extending portion. The tunable optical filter according to claim 3. The wavelength tunable optical filter according to claim 4, wherein a driving layer is provided in the second extending portion.

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