JP2011102920A - Optical filter - Google Patents

Abstract

An optical filter capable of significantly reducing the dependence of optical characteristics on an incident angle is configured by simple means.
An optical filter, which is a UVIR cut filter for limiting transmission of light in a predetermined wavelength region, is formed by uniformly depositing a physical film thickness on a sheet-like resin substrate by vapor deposition. The periphery of the optical filter 12 is fixed to a curved frame 21 so as to have a convex shape such as a cylindrical surface, thereby forming a convex shape.
[Selection] Figure 5

Description

  The present invention relates to an optical filter such as an edge filter or a bandpass filter that limits transmission in a predetermined wavelength region.

  A solid-state imaging device used in an imaging apparatus such as a video camera is often used in combination with an optical filter that adjusts a transmission wavelength in order to correspond to the sensitivity characteristics of human eyes. More specifically, there are edge filters such as UV (ultraviolet) cut filters and IR (near infrared) cut filters, or bandpass filters such as UVIR cut filters in which these are realized by a single filter.

  In order to limit the transmission of light in a desired wavelength region, an optical filter such as an edge filter or a band-pass filter is kneaded with an absorbent material in a filter material in a region where transmission is limited or is applied onto a substrate. Absorption types are known. Further, a reflective type is also known in which a vapor deposition film composed of a plurality of layers is laminated on a substrate to reflect using the interference of the vapor deposition film.

  However, an absorption type optical filter requires a suitable thickness in order to obtain a desired absorptance. In recent years, particularly from the viewpoint of cost factors and reduction in the thickness of the optical system, a reflection type optical filter is required. Is more preferred.

  FIG. 12 shows a spectral characteristic graph of a reflection type IR cut filter in which a plurality of vapor-deposited films are laminated, and FIG. 13 is a spectral characteristic graph showing an enlarged partial wavelength of FIG. As shown in FIGS. 12 and 13, the reflection type IR cut filter has a principle problem that the spectral characteristic shifts depending on the incident angle of incident light. As a reference for determining the shift amount, the change amount of the half-value wavelength on the IR side is used.

  For example, in FIG. 13, when the incident angle is 0 degree, the IR half-value wavelength is about 662 nm, whereas when the incident angle is 15 degrees, the IR half-value wavelength is about 655 nm, and the incident angle is 0 to 15 degrees and half-value. The wavelength changes by about 7 nm. As described above, when the half-value wavelength greatly changes depending on the incident angle, the color of the photographed image changes depending on the incident angle, and there is a problem that a practical incident angle region is limited.

  In particular, reflection-type edge filters and bandpass filters that use interference are inevitably generated in principle and are greatly affected.

  On the other hand, Patent Documents 1 and 2 propose a method of reducing a change in optical characteristics with respect to an incident angle by devising a configuration of a laminated film even in a reflection type optical filter.

JP-A-7-27907 JP 2008-020563 A

  However, in the case of the configuration shown in Patent Documents 1 and 2, the film configuration becomes complicated, or the refractive index difference between the alternating layers becomes small. As a result, a larger number of layers is required, which increases the product cost and sacrifices some of the optical characteristics. Furthermore, it is possible to reduce the problem of angle dependence, but from a fundamental point of view, it is not a fundamental solution, and it is difficult to ideally solve the problem of angle dependence.

  As another method, it is conceivable to form an IR cut film on a substrate having a curved shape from the beginning. However, it is extremely difficult to form a uniform thin film on a substrate having a curved shape. In addition, it is necessary to provide a film deposition apparatus with a special mechanism for depositing a thin film on a substrate having a curved shape, which greatly reduces productivity and increases product costs. is doing.

  An object of the present invention is to provide a reflection-type optical filter that eliminates the above-described problems and easily reduces the dependence of optical characteristics on the incident angle.

  In order to achieve the above object, an optical filter according to the present invention is an optical filter comprising an edge filter or a band-pass filter that limits the transmission of light in a predetermined wavelength region by laminating a thin film on a sheet-like resin substrate. The laminated thin film has a uniform physical film thickness and is deformed into a convex shape by an external force.

  According to the optical filter of the present invention, it is possible to reduce the problem of the dependence of the optical characteristics on the incident angle without greatly increasing the cost, and when using the imaging device in an imaging apparatus, it is possible to prevent defects such as color changes in images. It can be significantly reduced.

3 is a plan view of a state in which a mask is overlaid on the resin substrate of Example 1. FIG. It is a top view of the state where an optical filter was cut out after forming a vapor deposition film. It is a film | membrane structural drawing of a UVIR cut filter. It is a spectral transmittance characteristic graph figure of the design UVIR cut filter. It is explanatory drawing which deform | transforms an optical filter with a frame. It is explanatory drawing of arrangement | positioning with a frame and an optical filter. It is a top view of the state which attached the piezoelectric material of Example 2 to the optical filter. It is explanatory drawing of the electrode of a piezoelectric material. It is a perspective view of a state where an optical filter is deformed by a piezoelectric body. It is explanatory drawing of the imaging optical system which has arrange | positioned the optical filter. It is a spectral characteristic graph figure of a UVIR cut filter. It is a spectral characteristic graph figure of IR cut filter. It is a spectral characteristic graph figure which expanded the wavelength of FIG.

  The present invention will be described in detail based on the embodiment shown in FIGS.

  The optical filter of this embodiment is a UVIR cut filter that is a band-pass filter that restricts transmission of light in a predetermined wavelength region in the near infrared light region and ultraviolet light region, or a predetermined light beam in the near infrared light region. It is an IR cut filter that is an edge filter that limits transmission.

  For the resin substrate 1 shown in FIG. 1, a sheet-like Arton (product name) film made of norbornene having a thickness of 0.1 mm is used. On the resin substrate 1, a mask 3 having a plurality of square holes 2 of 10 mm both vertically and horizontally is stacked, and a vapor deposition film composed of a plurality of layers is laminated in the range of the holes 2 of the resin substrate 1.

  As shown in FIG. 2, the optical filter 12 which is a UVIR cut filter is formed by depositing a plurality of deposited films 11 on the resin substrate 1, and then removing the mask 3 to form a deposited film 11. Manufactured by cutting into shapes.

  In this embodiment, since it is necessary to deform the optical filter 12 using some means after the vapor deposition film 11 is formed on the resin substrate 1, the resin substrate 1 is a sheet-like sheet having a thickness of 0.1 mm. Resin-made Arton film is selected. This Arton film has a glass transition temperature of 100 ° C. or higher and a flexural modulus of about 3000 MPa, which is relatively high, and is selected because it can reduce cracks and waviness of the substrate. In this embodiment, Arton, which is a norbornene-based material, is used, but a polyimide-based resin film or the like is also a suitable substrate, and is not limited to these substrates, and PET, PEN, PC, etc. May be used.

  In the optical filter 12 of the present embodiment, the vapor deposition film 11 which is a thin film having a plurality of layers is formed on the resin substrate 1 by vapor deposition, but may be formed by a physical film formation method other than vapor deposition, or a spin coater. You may use the painting method using etc.

Figure 3 shows a film structure view of an optical filter 12 is a UVIR cut filter, TiO _2, the low refractive index material is SiO ₂ is used for the high refractive index material. On the planar resin substrate 1, SiO ₂ films 11a and TiO ₂ films 11b are alternately laminated, and 21 layers / 29 layers are laminated on both surfaces of the resin substrate 1, respectively, and a total of 50 layers are formed on both surfaces. It is said that.

TiO ₂ is used because it has a high refractive index and is an advantageous material for film design. Of course, SiO ₂ slightly differs depending on the film formation conditions, but in the film formation conditions by ion plating, the generation direction of the film stress is opposite to that of TiO ₂ , and the refractive index is low and the material is advantageous for the film design. Has been selected to be.

  In the film forming process, first, a mask 3 is stacked on the surface of a square resin substrate 1 having a length and width of 100 mm, and a vapor deposition film 11 composed of 21 layers is stacked. Thereafter, the front and back of the resin substrate 1 are changed, and a mask 3 similar to that used for vapor deposition of the surface is overlaid, and a vapor deposition film 11 consisting of 29 layers is laminated on the back surface.

  In this embodiment, since a synthetic resin, which is a norbornene-based material, is used for the resin substrate 1, a problem due to heat occurs in the film forming process. Synthetic resin has an extremely low glass transition temperature compared to glass, irregular warpage of the substrate due to the difference in linear expansion coefficient between the substrate and the deposited film, and wrinkles and cracks on the surface of the deposited film due to this warpage. There is a possibility of causing the occurrence of. Therefore, it is necessary to take measures against heat generated during film formation, and it is necessary to select a substrate material having a high heat-resistant temperature or to consider a method of forming a film by a low-temperature process.

  In this embodiment, a heat absorption mechanism is provided in the film forming apparatus, and a method of forcibly removing heat generated in the resin substrate 1 during film formation is employed. Therefore, it is necessary to measure in advance the maximum temperature on the resin substrate 1 reached in the film formation process and select a substrate material that can withstand the temperature. In the present embodiment, in consideration of the stability of the film forming process, a certain allowable value is added to the highest temperature reached in advance, and the glass transition temperature is used as a parameter for determining suitability. A norbornene-based material having a transition temperature is selected.

  During film formation, temperature control is performed by performing vapor deposition while cooling the back surface of the resin substrate 1 from the start of film formation to the end of film formation using cooling water having a water temperature of 10 ° C. As a result, the maximum temperature during film formation was 60 ° C. or lower on both sides, and was about 50 ° C. or less when measured with a dedicated thermo-label in vacuum previously set on the surface of the resin substrate 1.

  As a film forming method in this embodiment, the DC pulse superposition type RF ion plating method is used because the stress caused by the film can be controlled to a relatively small value as compared with other film forming methods to which assistance is added. Selected.

  However, since the temperature during film formation is lower than that in normal film formation, it is preferable to select a process in which some assistance is added or a film is formed with relatively high energy, such as sputtering, to increase the film density. Specifically, a sputtering method, an IAD method, an ion plating method, an IBS method, a cluster deposition method, or the like is used. Any film forming method can be used as long as the film thickness can be controlled relatively accurately and a film with high reproducibility can be obtained. The required film properties and the constraints of each material including the substrate An optimal method may be selected from the above.

  As a result of performing a high temperature and high humidity environmental test on the UVIR cut optical filter 12 manufactured by the above-described method, the transmittance change at the half-value wavelength on the IR side after 1000 hours is a shift amount compared to before the start of the environmental test. Was 2 nm or less. Similar environmental tests were performed on several samples, but similar results were obtained for all samples.

  Further, the appearance of the optical filter 12 was also good, and no warpage, unevenness, wrinkles or cracks were generated, and generation of wrinkles or cracks could not be confirmed after the environmental test. In another sample produced in the same manner, a high temperature test was carried out, but generation of wrinkles and cracks could not be confirmed even after 1000 hours. Furthermore, although the thermal shock test was implemented, generation | occurrence | production of a wrinkle, a crack, etc. was not able to be confirmed even after 1000 cycles progress.

  FIG. 4 is a graph showing spectral transmittance characteristics of the designed UVIR cut optical filter 12 in the first embodiment. The optical filter 12 which is a UVIR cut filter manufactured by the above-described method was able to obtain spectral transmittance characteristics substantially the same as the design values shown in FIG.

  In the case of the optical filter 12 which is a general UVIR cut filter, as shown in FIG. 4, it has a first blocking wavelength region in a desired wavelength region from the visible wavelength region to the ultraviolet wavelength region. Further, the second blocking wavelength region in a desired wavelength region from the visible wavelength region to the near infrared wavelength region, and the third blocking wavelength region in the desired wavelength region from the second blocking wavelength region to the further near infrared wavelength region. And has three blocking wavelength regions.

  Here, when the thin film laminated structure constituting one blocking wavelength region is considered as one block, it is formed by three blocks forming the first to third blocking wavelength regions. Each of these three blocks has a different central wavelength, and when the wavelength is λ, basically, a high refractive index material and a low refractive index material are alternately stacked by λ / 4. In order to obtain desired optical characteristics, a laminated structure or the like is generally added by adding a fine adjustment of about 0.7 to 1.3 times to the film thickness of each layer.

  UVIR cut filters and IR cut filters have a relatively large number of films to be laminated, and are likely to cause a problem of warping due to film stress. Particularly, when the resin substrate 1 is a synthetic resin, it becomes a significant problem. Therefore, in order to reduce this problem, it is preferable to laminate the same material and the same film thickness on both surfaces of the resin substrate 1 because the film stress can be reduced most.

  However, in this case, the structural design of the vapor deposition film 11 becomes difficult, and the optical characteristics may be greatly sacrificed when the film design is performed so that the number of stacked layers is the same as that when the resin substrate 1 is designed on one side. Is expensive. In addition, the number of laminated layers increases to satisfy the relaxation of the optical characteristics and the film stress at the same time, which increases the number of steps for manufacturing the optical filter 12. Therefore, it is optimal to divide the thin film laminated structure having a certain blocking wavelength region on both surfaces of the resin substrate 1.

  In this way, since the thin film laminate is formed on the normal flat resin substrate 1, the film formation can be easily managed, the flatness of the optical filter 12 can be maintained, and uniform characteristics can be obtained. Note that the uniform characteristics referred to here include variations such as changes in transmittance due to unintended elements during manufacture.

  In the case of the optical filter 12 configured to form the film on both the front and back surfaces of the resin substrate 1 as in the present embodiment, the film stress of the vapor deposition film 11 on both surfaces of the resin substrate 1 is intentionally varied to thereby change the optical filter. It is also possible to deform 12 into an arbitrary shape.

  However, in such a case, waviness may occur during the film forming process due to the fact that the film stress on one side becomes strong. Further, depending on the conditions of humidity and thermal atmosphere, there is a possibility that the initial shape changes due to the change of the film stress. Then, the optical filter 12 manufactured by the above-described method is fixed by being deformed by an external force so that the incident angle of the incident light to the optical filter 12 becomes smaller than that before the deformation.

  Therefore, in the first embodiment, as shown in FIG. 5, the periphery of the optical filter 12 that is a UVIR cut filter is fixed to the curved frame body 21 so as to have a convex shape like a cylindrical surface. As a method of deforming, there is a method of attaching a piezoelectric body as will be described later, but there is no particular limitation as long as a stably deformed shape can be maintained.

  Further, in the case of a double-sided film configuration like the UVIR cut filter in the present embodiment, it is difficult to make the film stress completely coincide on both sides, and the optical filter 12 itself is totally in the plane direction. It has a concave shape or a convex shape.

  Considering the stress applied to the optical filter 12 at the time of fixing to the frame body 21, it is desirable to arrange and fix it in a shape closer to the shape of the frame body 21, for example, as shown in FIG.

  The frame body 21 needs to be made of a material and a structure that do not deform even when the ambient temperature or humidity changes. In some cases, a certain level of strength is required, but an optimal material and shape may be determined according to product specifications.

  In Example 2, as shown in FIG. 7, a rectangular piezoelectric body (PZT) 31 is attached along the upper side and the lower side of the optical filter 12 and fixed with an adhesive. At this time, as shown in FIG. 8, electrodes 33a and 33b are previously formed on the piezoelectric body 31 via an insulating layer 32, and an element having an electrode structure is selected for the convenience of electrode wiring. By applying a voltage to the electrodes 33a and 33b of the piezoelectric body 31 and displacing the piezoelectric body 31, the optical filter 12 can be deformed as shown in FIG. Further, by adjusting this voltage, the optical filter 12 can be deformed into an arbitrary curvature shape.

  Furthermore, if a feedback mechanism is provided for this, it is also possible to realize a mechanism that automatically adjusts so that the influence of ghost light can be reduced as a whole system in response to changes in the shape over time. Various methods can be considered for this feedback mechanism.

  For example, when incorporated in an imaging device, the captured image is analyzed in software and the applied voltage of the piezoelectric body 31 is adjusted to adjust the deformation amount of the optical filter 12 and automatically correct, or the captured image From this, it is conceivable that the photographer makes a judgment and manually corrects by external input. Further, instead of laminating the piezoelectric body 31 on the optical filter 12, a piezoelectric film may be directly attached to the surface of the optical filter 12.

  FIG. 10 is an explanatory diagram in the case where an optical filter 12 that is a UVIR cut filter is arranged on the front surface of a CIS (contact image sensor) 41 of an imaging unit used in an imaging apparatus such as an image reading apparatus. A light source 42 is built in the imaging apparatus and is not shown in FIG. 10, but the light source 42 also includes an imaging optical system that forms incident light on the imaging surface of the CIS 41. In such an image reading apparatus, the light beam generated from the light source 42 is incident on the optical filter 12 at an angle.

  FIG. 10A shows a schematic diagram of the imaging optical system when the optical filter 12 is not deformed and is arranged on the optical path while maintaining a shape close to a plane. Within the effective area of the filter surface, the incident angle of the incident light emitted from the light source 42 to the optical filter 12 varies from 0 degree to a maximum of 25 degrees, and is different in each light passing area on the optical filter 12.

  Points A and B in FIG. 11 are graphs of spectral characteristics of the optical filter 12 that is the UVIR cut filter in the state of FIG. 10A, and show the shift amount of the IR-side half-value wavelength. The IR half-value wavelength is about 662 nm at the center A of the optical filter 12 where the incident light is vertically incident, whereas the IR half-value wavelength is about 642 nm at the point B that is the maximum incident angle. A shift of about 20 nm occurs in the region.

  On the other hand, when the optical filter 12 is deformed into a convex shape and the convex surface is directed to the CIS 41 as shown in FIG. 10B, the optical filter 12 for incident light is compared in the effective area of the filter surface. The incident angle to is greatly reduced from 0 degree to a maximum of 5 degrees. At this time, as shown in a point C in FIG. 11, the IR half-value wavelength shift amount is such that the IR half-value wavelength is at a point A in the central portion shown in FIG. About 662 nm. On the other hand, at point C which is the maximum incident angle, the IR half-value wavelength is about 661 nm, and the shift amount is about 1 nm within the effective region of the optical filter 12.

  As described above, the optical filter 12 deformed into a convex shape as shown in FIG. 10B is about 19 nm as compared with a flat type that does not particularly deform the shape of the optical filter 12 shown in FIG. Also, the shift amount can be reduced.

  Ideally, the difference in incident angle can be made zero, and the change in optical characteristics with respect to the incident angle can be significantly reduced. Thus, by producing the optical filter 12 by the above-described method, the dependence of the optical characteristics on the incident angle of the light beam to the optical filter 12 can be reduced with a uniform physical film thickness.

  In addition, although the convex shape in an Example was made into the cylindrical surface shape, it can also be made into a spherical shape or an ellipsoid.

1 resin substrate 2 holes 3 mask 11 deposited film 11a SiO ₂ film 11b TiO ₂ film 12 an optical filter 21 frame 31 piezoelectric

Claims (5)

  An optical filter comprising an edge filter or a band-pass filter that limits the transmission of light in a predetermined wavelength region by laminating a thin film on a sheet-like resin substrate, wherein the laminated thin film has a uniform physical film thickness. An optical filter that is deformed into a convex shape by an external force.   The optical filter according to claim 1, wherein the optical filter is deformed by applying an external force after laminating a plurality of different films on the resin substrate.   The optical filter according to claim 1, wherein the optical filter is deformed by fixing the periphery to a curved frame.   The optical filter according to claim 1, wherein a piezoelectric body or a piezoelectric film is attached to a surface, and the optical filter is deformed by displacement by the piezoelectric body or the piezoelectric film.   An imaging apparatus comprising the optical filter according to any one of claims 1 to 4 incorporated in an optical system.

Images