JP2005121699A - Method for manufacturing thin film filter, apparatus for manufacturing thin film filter, thin film-fixed filter and tunable filter - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method and apparatus for manufacturing thin film filter capable of manufacturing a thin film filter having a desired optical film thickness distribution over wide radial positions on a rotating base plate, and to provide a high performance thin film-fixed filter and thin film tunable filter. <P>SOLUTION: In the method and apparatus for manufacturing the thin film filter, a white light source and a spectroscope, or a tunable light source and a power meter are disposed, an optical mechanism which allows optical beams to branch to the radial positions of at least two or more of different spots on the rotating base plate and to be transmitted is disposed, a means of calculating the deposition speed and the refractive index in the radial direction on the base plate from the light quantity of the optical beams is disposed and, thereby, the deposition speed distribution or the refractive index distribution on the base plate is controlled. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a dielectric thin film filter used in an optical communication system or the like and a manufacturing method thereof. More particularly, the present invention relates to a thin film fixed filter and a thin film wavelength tunable filter.

  With the recent development of high-speed communication networks, a large amount of information has been transmitted at high speed. As one of the methods for enabling this, a wavelength division multiplexing optical communication system (DWDM: Dense Wavelength Division Multiplexing) has been actively developed. In this wavelength division multiplexing optical communication system, optical signals having a plurality of wavelengths are transmitted by being superimposed on a single glass fiber. For this purpose, it is necessary to connect an optical multiplexer / demultiplexer before and after the glass fiber. The dielectric thin film filter of the present invention is used as various thin film fixed filters used in an optical communication system including a narrow band pass filter (NBPF) constituting an optical multiplexer / demultiplexer. On the other hand, in a wavelength multiplexing optical communication system, optical add & drop multiplexing (OADM) is required to extract or add an optical signal having a desired wavelength from one glass fiber. At this time, conventionally, a fixed filter with a fixed center wavelength has been used to extract or add an optical signal having a desired wavelength. A thin film wavelength tunable filter is also a kind of narrowband filter, but differs from a fixed filter in that the center wavelength is variable. By providing a small number of wavelength tunable filters by changing the center wavelength, it becomes possible to freely change the optical communication path for only the light of the required wavelength (Reconfigurable OADM). Further, the wavelength tunable filter is widely used for optical analyzers and optical signal monitors because it can selectively extract wavelengths in addition to OADM applications. Recently, applied research in the biomedical field has also become active.

  These thin film filters form a multilayer film of several tens to three hundred layers by alternately laminating high refractive index dielectric films and low refractive index dielectric films on a glass substrate. It reaches several tens of μm. As an example of the structure of the thin film filter, there is an example of a fixed filter (for example, Patent Document 1). Further, there are examples of the film structure of the wavelength variable filter (for example, Patent Document 2 and Patent Document 3). The basic structure of the thin film filter is to provide a desired center wavelength, so that the optical film thickness is 1/4 of the center wavelength high refractive index dielectric layer and the optical film thickness is 1/4 wavelength low refractive index dielectric. It comprises a mirror layer in which body layers are alternately stacked, a spacer layer whose optical film thickness is ½ wavelength of the center wavelength or an integral multiple thereof, a film formation substrate, and an antireflection film. The wavelength tunable filter also basically has the same film configuration as that of the fixed filter, except that it is a film thickness gradient type filter whose film thickness changes in the filter plane. The film thickness of each layer constituting the thin film filter is required to have a film thickness accuracy of 1 / 10,000 to 1 / 100,000, and it is desired by adjusting the film thickness and combination of these layers according to the specifications of the thin film filter. It is possible to produce a thin film filter having a center wavelength and a steep base.

  A general method for producing a multilayer optical filter having a desired center wavelength is to transmit light having a desired wavelength to the substrate being formed, and to monitor the amount of transmitted light while determining the film thickness and replacing the deposition material. A multilayer film is formed. At this time, it is known that the amount of transmitted light repeatedly increases and decreases as the film thickness increases, and the increase and decrease in the amount of light occurs for each quarter wavelength of the optical film thickness. For example, it relates to an optical film thickness monitor, and there is a method of stopping evaporation when the transmittance or reflectance exceeds a peak (Patent Document 4). Thereby, a film having an optical film thickness of ¼ wavelength can be formed. As another method, a method of accurately detecting a peak by using curve fitting software for predicting the peak of light quantity and switching film forming materials has been proposed.

An ion-assisted vapor deposition method is employed as a general dielectric multilayer film forming method. In the ion-assisted deposition method, the high refractive index material and the low refractive index material constituting the above-described dielectric multilayer film are alternately evaporated using an EB gun (electron gun) to form a film on the substrate. At this time, the substrate is irradiated with oxygen or mixed ions of argon and oxygen using an ion gun at the same time to help the vapor deposition particles migrate on the substrate. Thereby, the multilayer film which tends to become a columnar structure can be improved to a multilayer film having a high packing density. It is also possible to adjust the degree of oxidation of the multilayer film by irradiation with oxygen ions so as to approach the stoichiometric composition. The film deposition equipment is designed to improve the film thickness distribution as much as possible. However, as described above, the film thickness of each layer constituting the thin film filter has a film thickness accuracy of 1 / 10,000 to 1 / 100,000. Therefore, it is impossible to manufacture a multilayer optical filter having a desired center wavelength, pass band, insertion loss, and the like over the entire surface of the film formation substrate. Usually, a desired thin film fixing filter can be obtained from a partial region on the substrate along the center or the outer periphery of the substrate. In addition, a thick glass substrate is generally used for film formation, but the film is finished in the shape of a thin film fixed filter by cutting and polishing operations after film formation. Normally, the wavelength of the thin film fixed filter that can be produced is only one desired wavelength in one vacuum batch. Among the thin-film filters, the wavelength tunable filter can form a desired wavelength tunable filter by forming a multilayer film having a thickness gradient in the radial direction of the substrate and cutting it out in the radial direction (for example, Patent Document 5). . Further, a method of measuring film thicknesses at two or more locations with an optical film thickness monitor has been studied (for example, Patent Document 6). The light beam related to the multilayer filter is disclosed in Non-Patent Document 1, for example.
JP-A-10-197721 (5th page, FIG. 1) Japanese Patent Laid-Open No. 06-265722 (pages 4 to 5, FIGS. 1 and 4) Japanese Patent Laid-Open No. 11-326633 (5th page, FIG. 4) JP 61-296305 A (page 2) US Pat. No. 5,872,655 (FIG. 3) JP2003-147521A (page 4) Yoshida, Yajima: “Thin Films and Optical Devices”, p. 16

When manufacturing a thin film filter by a conventional method, since the film thickness accuracy is strict, the biggest problem is that only a part of the substrate can be used. Here, the film thickness during film formation is constantly measured by a light amount monitor and fed back to the switching of the deposition material. Further, the deposition rate is measured using a crystal film thickness monitor separately from the light amount monitor, and the film can be formed at a desired deposition rate by being fed back to the emission current of the electron gun. However, it is extremely difficult to make the film thickness distribution on the substrate uniform with an accuracy of 1 / 10,000 to 1 / 100,000. Usually, the film thickness distribution of a high refractive index Ta oxide (Ta ₂ O ₅ ) or Nb oxide (Nb ₂ O ₅ ) and a low refractive index Si oxide (SiO ₂ ) is flat and the film thickness distribution of both is normal. The film forming conditions are adjusted so that the two match. However, as a result of a detailed investigation of the film thickness distribution during film formation, it has become clear that the film thickness distribution changes from moment to moment. This does not correct and suggests that the deposition rate distribution changes during film formation. Similarly, it was inferred that the refractive index of the film changed every moment during the film formation.

As a result of investigating the cause of the change in the deposition rate distribution during film formation, it became clear that the shape of the raw material at the start of film formation gradually changed as the raw material was evaporated. Change in the shape of the material is particularly pronounced in the case of sublimable material, for example, Atsuta material surface in SiO ₂ first flat exhausted by evaporation with the deposition time, eventually becoming a tilted material surface in Also often occurred. Since the raw material evaporates in the inclined direction from the inclined raw material surface, the deposition rate distribution changes every moment. On the other hand, in the case of a meltable raw material such as Ta ₂ O _5, the melted surface is kept almost horizontal by gravity or surface tension, so that the surface shape does not change greatly even when the raw material is consumed. As another cause, it was found that the ion current density distribution of the ion gun also changes every moment. This is mainly because the grid that controls the ion current density distribution of the ion gun is contaminated during film formation, and it has been confirmed that the grid returns to its original state after cleaning. Therefore, depending on the contamination of the grid, not only a change during film formation but also a different ion current density distribution may be generated for each vacuum batch. Since ions blow off the vapor deposition particles to reduce the effective vapor deposition rate, the effective vapor deposition rate distribution changes when the ion current density distribution changes.

  By using an optical film thickness monitor, the film thickness at the monitor position on the substrate can be accurately measured, and a thin film filter having desired characteristics can be produced. A thin film filter having desired characteristics could not be produced at a place other than the measurement position of the thickness monitor. Conventionally, an optical film thickness monitor is installed so that the product (n × d) of the refractive index and film thickness at one radial position on the substrate can be monitored. At a distance of mm, it was difficult to obtain a thin film filter having desired characteristics. At this time, the deterioration of the optical characteristics is not limited to the shift of the center wavelength, but extends to the insertion loss, passband, and ripple. This is because the product of the refractive index and the film thickness of all the multilayer films ranging from several tens to three hundred layers does not change uniformly with respect to the substrate radius, but also changes non-uniformly in the thickness direction. Indicates that Further, it is clear that the non-uniform change in the film thickness direction is based on the temporal change in the deposition rate distribution or the refractive index.

  Accordingly, the present invention provides a method for controlling the deposition rate distribution and refractive index distribution in a thin film filter manufacturing apparatus, thereby increasing the effective area where a thin film fixed filter satisfying the characteristic specifications can be obtained with a single film formation. A filter manufacturing apparatus is provided. The present invention also provides a method of inclining the film thickness distribution in the substrate radial direction, thereby providing a method of forming a plurality of types of thin film fixed filters in a single vacuum batch. Furthermore, the method of inclining the film thickness distribution provides a method for forming a high performance thin film wavelength tunable filter and a thin film filter manufacturing apparatus. Furthermore, the present invention provides a high-performance thin film fixed filter and a thin film wavelength tunable filter formed by the above method.

  As a result of detailed studies on the thin film filter manufacturing apparatus and manufacturing method, the inventors have determined that the effective area on the substrate of the thin film fixed filter that satisfies the characteristic specifications that can be manufactured in a single film formation is the deposition rate distribution during the film formation. In addition, it has been clarified that at least one of the refractive index distributions, preferably the deposition rate distribution and the refractive index distribution, can be increased by uniformly controlling the refractive index distribution. In addition, it was clarified that in the manufacture of a thin film wavelength tunable filter, a high performance thin film wavelength tunable filter can be obtained by controlling the film thickness distribution to a predetermined gradient distribution during film formation. At this time, the deposition rate distribution and refractive index distribution during film formation are calculated from the light amount of the light beam measured at two or more radial positions on the rotating substrate using an optical film thickness monitor, and this is fed back to perform deposition. The speed mainly controls the aperture ratio of the film thickness distribution correction plate inserted between the rotating substrate and the evaporation source, the ion current of the ion gun, and the emission current of the electron gun, and the refractive index is mainly the beam voltage and oxygen partial pressure of the ion gun. It was clarified that it should be controlled.

  Conventionally, a method of measuring film thicknesses at two or more locations with an optical film thickness monitor has been disclosed (for example, Patent Document 6). In the disclosed method, white light is transmitted through a thin film, and the film thickness at two or more locations is monitored by utilizing the phenomenon that the transmittance of white light decreases as the film thickness increases due to film formation. However, with this method, the amount of light only monotonously decreases as the film thickness increases, and it is difficult to accurately measure the film thickness, and a precise film thickness distribution cannot be obtained. In the present invention, as an optical film thickness monitor, a set of a white light source, a spectroscope, a wavelength tunable light source, and a power meter is provided, and the light beam is branched to monitor the light quantity of a specific wavelength at two or more radial positions. Is different. By monitoring a specific wavelength, it is possible to observe the periodic increase and decrease of the light amount shown in FIG. 1, and this period corresponds to a quarter wavelength of the specific wavelength, so that a precise film thickness can be measured. In addition, the deposition rate and refractive index can be determined. Furthermore, by splitting the light beam, it is possible to keep the light amount difference at different radial positions constant even if the light source fluctuates, and it is possible to accurately capture the vapor deposition rate difference and refractive index difference calculated from the light amount. It becomes possible. However, if the fluctuation of the light source can be stabilized by using a feedback circuit in combination, it is possible to provide two sets of light sources and light receiving devices, which have a higher light quantity and are easier to control. On the other hand, when monitoring the amount of light using light beams of different wavelengths having a desired wavelength difference at two or more radial positions, a system having two sets of spectrometers or two sets of variable wavelength light sources is desirable. It is not limited to. The aperture ratio of the film thickness distribution correction plate corresponds to a ratio when the area is reduced with respect to a state where the area of the correction body that blocks evaporation of the vapor deposition element is maximum.

  Accordingly, the present invention provides an optical mechanism for splitting and projecting a white light beam or a specific wavelength light at two or more different radial positions of the film formed on the rotating substrate, and a light amount of a specific wavelength by the transmitted light of the film. And a thin film filter manufacturing method and apparatus for controlling the deposition rate distribution or the refractive index distribution, and a means for calculating the deposition rate and refractive index of the film based on the amount of light. To do.

  Here, it is known that the light quantity T of the light beam can be expressed by the following theoretical formula: Formula 1 (for example, Non-Patent Document 1).

Here, each has the following relationship.
n ₀ : Refractive index of medium (0)
n ₁ : Refractive index of parallel plane film (1)
n ₃ : Refractive index of substrate (3)

When the above equation is modified and expressed as a function of time, the transmitted light quantity of the monitor is expressed by Equation 3, which can be expressed by the refractive index n ₁ and the deposition rate v ₁ of the parallel plane film.

At monitor positions 1 and 2, the above transmitted light amount is measured, and n ₁ and v ₁ giving the measured transmitted light amount are always calculated by the fitting method, and the values of n ₁ and v ₁ at monitor positions 1 and 2 are obtained. In comparison, the aperture ratio, ion gun beam voltage, ion gun ion current, electron gun emission current, oxygen partial pressure, etc. of the film thickness distribution correction plate can be controlled so that the difference approaches 0. Thereby, the refractive index and the deposition rate at the monitor positions 1 and 2 can be matched, and the refractive index distribution and the film thickness distribution on the substrate can be made uniform.

  If it is attempted to perform feedback control directly on the film forming conditions from the light amount difference at the monitor positions 1 and 2, the control algorithm becomes complicated and difficult because the light amount difference greatly fluctuates in one film. In the method of the present invention, the amount of light can be obtained by converting it into a refractive index and a deposition rate. Since these values do not show a large movement in the film of one layer, it is easy to perform feedback control using the difference.

  As a result of using the method of the present invention, not only changes in the deposition rate distribution based on the surface shape change of the raw material due to evaporation, but also changes in the deposition rate distribution based on changes over time in the ion current density irradiated from the ion gun, Changes in the refractive index distribution based on gas pressure fluctuations can be controlled together. As a result, in the past, only the narrow area near the radial position where the optical film thickness monitor was installed was the effective area, and when deviating from the effective area, the center wavelength, insertion loss, passband, ripple, etc. did not satisfy the specifications. However, according to the present invention, a desired value for the center wavelength can be obtained, deterioration of insertion loss, passband, ripple, etc. can be reduced, and the effective region where a thin film fixed filter can be obtained can be expanded. In addition, as the vapor deposition rate distribution and the refractive index distribution are made uniform, the film quality is improved even when the individual thin film fixed filters are viewed. In the thin film fixed filter cut out from the wafer and having an area of 2.4 mm square or less, the peak insertion loss and the ripple are simultaneously improved.

  Conventionally, only a thin film wavelength tunable filter having a narrow passband has been obtained. However, the present invention has improved the film thickness distribution accuracy of the tilted film, and it has become possible to obtain a thin film wavelength tunable filter having a wide passband. Therefore, a high-performance and highly productive thin-film filter manufacturing method and apparatus could be developed.

  [1] The manufacturing method of the thin film filter of the present invention includes an optical mechanism that splits and transmits a white light beam or specific wavelength light at two or more different radial positions of a film formed on a rotating substrate, and the film Means for detecting the amount of light of a specific wavelength by the transmitted light, and means for calculating at least one of the deposition rate or refractive index of the film based on the amount of light, and at least of the deposition rate distribution or the refractive index distribution It is characterized by controlling one. In particular, it is desirable to calculate the deposition rate or refractive index and control the deposition rate distribution and refractive index distribution in the radial direction on the substrate.

  Here, the light amount of the light beam transmitted through the film refers to the light amount of a specific wavelength. As a light source for generating a light beam, it is desirable to include a set of white light sources and spectroscopes, or a set of variable wavelength light sources and power meters. Each set of white light source and spectroscope, or each set of wavelength variable light source and power meter is the deposition rate of high refractive index material and low refractive index material formed on the rotating substrate provided in the thin film filter manufacturing apparatus, and Used to monitor refractive index.

  In addition, in order to monitor the film thickness at two or more radial positions, the number of light sources, spectroscopes, and the like are required as many as the number of radial positions. However, by providing the light beam branching mechanism of the present invention, the light source system and spectroscope are provided. It is possible to monitor the film thickness at a plurality of radial positions by simply using a set. By this method, an error for each radial position based on the fluctuation of the light source can be reduced, and the deposition rate and the refractive index can be accurately obtained for each radius.

  [2] In the method for producing a thin film filter according to [1], the light amount of the light beam is constantly measured at two or more radial positions, the vapor deposition rate and the refractive index are calculated from the light amounts at the respective radial positions, the vapor deposition rate difference and A thin film fixed filter is formed by controlling the deposition rate distribution and the refractive index distribution in the radial direction on the substrate so as to reduce the refractive index difference.

  Here, the light amount of the light beam changes as shown in FIG. 1 as the multilayer film is formed. The numbers in the figure indicate the number of layers of the multilayer film. At this time, assuming that a desired film thickness is formed at the radius position 1 and a film thin by 6.5 / 10,000 is formed at the radius position 2, the light amount difference between the two changes as shown in FIG. Show. The numbers in the figure indicate the number of layers of the multilayer film. That is, the light amount difference once increases from 0 in one layer of film and then decreases to 0. Or, it decreases once from 0 and then increases to 0. Therefore, it is difficult to feedback control the deposition rate by using such a light amount difference that shows such a complicated change for each layer. In the present invention, in order to avoid this problem, the light amount of the light beam is converted into a deposition rate and a refractive index by a fitting method based on a theoretical formula. Since the calculated vapor deposition rate and refractive index change substantially constant during film formation, the vapor deposition rate difference and refractive index difference at different radial positions change monotonously in one layer of film. Therefore, it can be said that feedback control of the deposition rate and refractive index using this difference is suitable for more accurate film thickness control.

  [3] In the manufacturing method of the thin film filter of [2], the wavelength of the light beam at the two radial positions is set to different values having a desired wavelength difference, and the ratio of the product of the deposition rate and the refractive index at the two positions is A plurality of types of thin film fixed filters having different wavelengths are formed at a time by controlling the deposition rate distribution and the refractive index distribution so as to be equal to the wavelength ratio of the two places. In the present invention, “two places” is used as a term encompassing both cases where only two places are measured and cases where two places are selected from two or more places. ing.

  Here, by setting the wavelength of the light beam at two radial positions to different values having a desired wavelength difference, thin film filters for different wavelengths can be accurately formed at each radial position. However, because there is a wavelength difference between the two locations, it is not possible to control the deposition rate or the difference in refractive index to decrease, and the ratio of the product of the deposition rate and the refractive index is the two wavelengths. It is necessary to control the ratio. As a result, it is possible to form a filter having a thickness gradient in the radial direction of the substrate. For example, in the case of a 100 GHz filter, since the interval between adjacent wavelengths is 0.8 nm, if a wavelength difference of 3.2 nm is given in the radial direction, four types of thin film fixed filters for four channels can be obtained. become.

  [4] In the method for manufacturing a thin film filter described in [2] above, the wavelength of the light beam at the two radial positions is set to different values having a desired wavelength difference, and the product of the deposition rate and the refractive index at the two positions. A wavelength tunable filter is formed by controlling the deposition rate distribution and the refractive index distribution so that the ratio is equal to the wavelength ratio of the two places.

  Here, filters having different center wavelengths are continuously formed between the radial positions. That is, it becomes possible to form a filter having a thickness gradient in the radial direction of the substrate, and a wavelength tunable filter can be obtained.

  [5] In the method for manufacturing a thin film filter according to any one of [1] to [4], the method for calculating the deposition rate and the refractive index from the light amount of the light beam is based on the theoretical formula, and the amount of transmitted light is given. It is characterized in that the velocity and the refractive index are always calculated by the fitting method.

  It has been known that the amount of light beam transmitted through the substrate during film formation can be expressed by a theoretical formula consisting of the refractive index and film thickness of the film. However, the present invention is novel in that this theoretical formula is utilized and the amount of light is separated into a refractive index and a vapor deposition rate by a fitting method, and the refractive indexes and vapor deposition rates at two or more radial positions are obtained. As a result, it is possible to directly compare the refractive index and the deposition rate at two or more locations, and the deposition conditions can be controlled so that the difference between the refractive index and the deposition rate at each position is zero. Became.

  [6] The method for manufacturing a thin film filter according to any one of [1] to [5], wherein the method for controlling the radial deposition rate distribution on the substrate changes the aperture ratio of the film thickness distribution correction plate. The method is characterized in that it is at least one method selected from a method of changing an ion current of an ion gun or a method of changing an emission current of an electron gun.

  Here, the width of the correction plate is adjusted in advance so that the required film thickness distribution before film formation is obtained in the conventional film thickness distribution correction plate, and the width is fixed during film formation. The width of the correction plate can always be changed, and can be controlled by a signal fed back from the film thickness monitor even during film formation. The aperture ratio can also be changed by changing the width.

  On the other hand, a method of controlling the deposition rate distribution by changing the emission current of the electron gun and changing the evaporation rate of the deposition source, or a method of controlling the deposition rate distribution by changing the ion current of the ion gun can be used. Generally, increasing the evaporation rate of the evaporation source increases the evaporation rate at the center of the substrate, and increasing the ion current of the ion gun tends to increase the evaporation rate at the periphery of the substrate.

  [7] The method for manufacturing a thin film filter according to any one of [1] to [5], wherein the method for controlling the refractive index distribution in the radial direction on the substrate is a method for changing the beam voltage of an ion gun, or an oxygen content. It is at least one method selected from methods for changing pressure. Here, the refractive index of the film and its distribution can be changed by changing the beam voltage of the ion gun. Further, the refractive index can be controlled by changing the oxygen partial pressure.

  [8] The thin film fixed filter of the present invention is a multilayer optical filter including a dielectric multilayer film in which a plurality of high refractive index films and low refractive index films are alternately stacked, and has a dimension of 1.5 × 1.5. The peak insertion loss corresponding to 100 GHz is 0.1 dB or less, the ripple is 0.1 dB or less, and the passband is −0.5 dB or 0.6 nm or more. More preferably, the thin film filter manufactured by the method for manufacturing a thin film filter according to any one of the above [1], [2], [3], [5], [6] or [7], which is compatible with 100 GHz The fixed filter has a peak insertion loss of 0.1 dB or less, a ripple of 0.1 dB or less, and a passband of −0.5 dB at 0.6 nm or more.

  Here, the characteristics of the thin film filter can be obtained only when the film thickness and refractive index of each layer constituting the filter are controlled with high accuracy. The thin film fixed filter produced by the method of the present invention is controlled by the deposition rate and the refractive index between different radial positions from the first layer directly above the substrate to the outermost surface layer, and can be formed with extremely high accuracy. is there. As a result, the above high characteristics can be obtained.

  For example, the thin film fixed filter can be configured to correspond to a wavelength pitch of 100 GHz or less for DWDM and include a multilayer film of 4 cavities or more and 100 layers or more. A cavity is an optical resonator composed of a spacer made of a laminated body having a half wavelength or an integral multiple of the laminated film and a pair of mirrors made of a laminated body having a quarter wavelength. A four-cavity multi-layer film is formed by stacking four cavities. More specifically, a multilayer optical filter comprising a dielectric multilayer film in which a plurality of high refractive index films and low refractive index films are alternately laminated, wherein the dielectric multilayer film is silicon oxide and tantalum pentoxide or niobium pentoxide. It is comprised with the material chosen from at least one of these. By mounting the thin film fixed filter, it is possible to configure an optical multiplexer / demultiplexer with suppressed loss.

  [9] A wavelength tunable filter according to the present invention is a wavelength tunable filter having a dielectric multilayer film formed with an inclined film thickness, and has a size of 10 × 30 × 5.0 mm or less and a path corresponding to 100 GHz. A band is 0.4 nm or more at −0.5 dB. More preferably, it is a thin film filter manufactured by the method for manufacturing a thin film filter according to any one of [1], [4], [5], [6], and [7], and the passband of the wavelength tunable filter for 100 GHz is − It is characterized by being 0.4 nm or more at 0.5 dB.

  Here, a general wavelength tunable filter is a thin film filter formed on a strip-shaped substrate having a length of about 20 mm with a film thickness inclined. It was difficult to improve the -0.5 dB passband to 0.3 nm or more due to the film thickness gradient and the long strip shape. According to the present invention, it is possible to precisely control the film thickness distribution of the gradient film, and it is possible to set the pass band of −0.5 dB to 0.4 nm or more.

  A wavelength tunable filter having a dielectric multilayer film formed with an inclined film thickness can be configured to have a reflecting mirror adjacent to the dielectric multilayer film. The reflecting mirror can be used as an optical path when a light beam transmitting a signal passes when moving from an initial light beam position to a variable light beam position.

  [10] Another thin film fixed filter of the present invention is a multilayer optical filter including a dielectric multilayer film in which a plurality of high refractive index films and low refractive index films are alternately laminated, and has a dimension of 2.4 × 2. .4 × 2.4 mm or less, more preferably, the peak insertion loss corresponding to 50 GHz is 0.1 dB or less, the ripple is 0.1 dB or less, and the passband is −0.5 dB and 0.28 nm or more. To do. More preferably, it is a thin film filter manufactured by the method for manufacturing a thin film filter according to any one of [1], [2], [3], [5], [6] or [7], and is compatible with 50 GHz. The fixed filter has a peak insertion loss of 0.1 dB or less, a ripple of 0.1 dB or less, and a passband of −0.5 dB, which is 0.28 nm or more.

  Here, the thin film fixed filter manufactured by the method of the present invention is controlled by the deposition rate and the refractive index between different radial positions from the first layer directly above the substrate to the outermost surface layer, so that the film can be formed with extremely high accuracy. Is possible. By using this film forming method, it is possible to remarkably improve the characteristics of a fixed filter for 50 GHz, which has particularly strict film thickness accuracy.

  [11] Another wavelength tunable filter of the present invention is a wavelength tunable filter having a dielectric multilayer film formed with an inclined film thickness, and has a size of 10 × 30 × 5.0 mm or less, and is compatible with 50 GHz. The pass band of −0.5 dB is 0.2 nm or more. More preferably, it is a thin film filter manufactured by the method for manufacturing a thin film filter according to any one of [1], [4], [5], [6] or [7] above, and the path of the wavelength tunable filter corresponding to 50 GHz. A band is 0.2 nm or more at −0.5 dB.

  Here, a general wavelength tunable filter is a thin film filter formed on a strip-shaped substrate having a length of about 20 mm with a film thickness inclined. It is almost impossible to form a wavelength tunable filter corresponding to 50 GHz by the conventional film forming method, and it is difficult to improve the pass band of −0.5 dB to 0.1 nm or more. According to the present invention, it is possible for the first time to precisely control the film thickness distribution of the gradient film, and it becomes possible to set the pass band of −0.5 dB to 0.2 nm or more.

  As described above, the thin film filter manufacturing method and apparatus according to the present invention provide a thin film fixed filter with high performance and uniform center wavelength over a wide radial position of the filter substrate. As a result, the yield per vacuum batch was significantly increased compared to the conventional method. Furthermore, the present invention provides a method of producing a thin film fixed filter having a plurality of channels in one vacuum batch by using a desired different monitor wavelength to produce a thin film filter having a thickness gradient in the radial direction. Further, the thin film filter having the thickness gradient becomes a thin film wavelength tunable filter, and provides a high performance thin film wavelength tunable filter having a flat-top characteristic with a wide pass band.

  The present invention will be described in detail based on examples. In addition, this invention is not necessarily limited by these Examples.

(Example 1)
The thin film filter was manufactured by the following process. A cleaning glass substrate having a thickness of 7 mm on which an antireflection film 4 is formed on the back surface is loaded as a film formation substrate 3 in a film formation apparatus, and the degree of vacuum is 6.7 × 10 ⁻⁴ Pa (≈about 5 × 10 ⁻⁶ Torr). ) After evacuating to the following, film formation was started. The plate | board thickness of a glass substrate can use the thing within the range of 5-12 mm, for example. The thin film filter produced in this example is a narrowband filter (NBPF) for DWDM shown in FIG. 3, and its basic structure is a quarter wavelength laminate 1 serving as a mirror and a half wavelength or an integer thereof serving as a spacer. The double layer 2 was laminated with the number of laminated layers = 164 layers. Note that the number of stacked layers can be changed in the range of hundreds to tens of layers.

Here, the quarter wavelength laminated body 1 which becomes a mirror is a high refractive index dielectric layer having a quarter wavelength optical film thickness made of Ta oxide (Ta ₂ O ₅ ) or Nb oxide (Nb ₂ O ₅ ). And low refractive index dielectric layers having an optical film thickness of ¼ wavelength made of Si oxide (SiO ₂ ) are alternately laminated. Also, the 1/2 wavelength or integer multiple layer 2 serving as a spacer is made of a low refractive index dielectric layer having an optical film thickness of Si wavelength of 1/2 wavelength or an integral multiple thereof, or Ta oxide or Nb oxide. A high refractive index dielectric layer having an optical film thickness of ½ wavelength or an integral multiple thereof. In the cross-sectional view of FIG. 3, since the number of continuous laminations is large, illustration of a laminated state in the middle is omitted.

  For forming the dielectric multilayer film, an ion-assisted vapor deposition apparatus shown in the cross-sectional view of FIG. 4 was used as a thin film filter manufacturing apparatus. In the ion-assisted deposition apparatus, a high refractive index material and a low refractive index material constituting the dielectric multilayer film are loaded in a ring-shaped deposition source hearth 6 in a chamber, and an electron beam is irradiated from an electron gun 5. Then, both raw materials were alternately evaporated, the deposition source shutter 7 and the substrate shutter 9 were opened, and a film was formed on the glass substrate 8. At this time, the glass substrate 8 was irradiated with oxygen ions or mixed ions of argon and oxygen using the assisting ion gun 12 at the same time to help the vapor deposition particles migrate on the glass substrate 8. As a result, it was possible to improve a multilayer film that tends to have a columnar structure into a multilayer film having a high packing density. In this example, the acceleration voltage of the ion gun 12 was set to 500 to 900 V, and a uniform thin film filter film having a high packing density could be obtained.

  In FIG. 4, the trajectory of the electron beam is represented by a thick dotted line, and the direction of evaporation of the raw material is represented by a thin dotted line. The member that holds the glass substrate 8 was rotated by a high-speed substrate rotation motor 11. The thickness of each dielectric film constituting the dielectric multilayer film was measured with a crystal film thickness monitor 10. The thickness of the multilayer film formed on the glass substrate 8 is such that the light irradiated from the optical film thickness monitor light projecting unit 13 is transmitted through the glass substrate on which the multilayer film is formed, and the transmitted light is transmitted through the optical film thickness. Measurement was performed by receiving the light at the monitor light receiving unit 14. A vacuum exhaust device is connected to the right side of the chamber in FIG. 4 (the side indicated by the white arrow), but the illustration thereof is omitted.

  FIG. 5 is a schematic view showing an optical film thickness monitor used in the thin film filter manufacturing apparatus. The optical film thickness monitor is a configuration example using a white light source and a spectroscope. As shown in FIG. 5, the film thickness during film formation is in the process of forming white light from the halogen lamp 22 through the light beam branching mechanism 23-1 and the optical film thickness monitor light projecting units 13-1 and 13-2. Are transmitted through the multilayer film and the glass substrate 8 rotating at high speed, and the transmitted light is transmitted through the optical film thickness monitor light receiving units 14-1 and 14-2 and the light beam combining mechanism 23-2 and further through the optical fiber 18. Then, monitoring was performed by measuring with a spectroscope 19 (one that splits light, converts light intensity for each wavelength into an electric signal, and detects the amount of light). Here, when the light beam branching mechanism is used, it is possible to project a light beam to two or more radial positions even if a single light source or spectroscope is set, and it is possible to monitor the amount of light at different radial positions. The light quantity calculation / control computer 20 inputs the electric signal of the spectroscope 19 and performs monitoring, and controls the lamp power source 21 connected to the halogen lamp to suppress fluctuations in the light quantity.

  Further, the light quantity calculation / control computer 20 controls the ring-shaped vapor deposition source hearth, the electron gun, the shutter, and the ion gun in the vapor deposition source 16, but the connection state with these is not shown. In addition to the combination of a white light source and a spectroscope, the combination of a wavelength tunable light source and a power meter similarly transmits a light beam to the multilayer film being formed and the glass substrate 8 rotating at high speed, thereby reducing the amount of transmitted light. Can be detected. Here, the method of providing a set of light sources and light receiving systems and branching the light beam is advantageous when canceling fluctuations of the light sources and light receiving systems and comparing signals at different radial positions. However, since the amount of light decreases due to branching, there is a concern that the amount of light in the multilayer film near the spacer is insufficient. In this case, it is desirable that the branching of the light beam is stopped only for the layer having a small amount of light, and the light beam is transmitted only to the main radial position, so that the deposition material exchange control is performed with high accuracy. Of course, it is also possible to provide two or more light sources and light receiving systems, measure the amount of light respectively, and calculate the deposition rate and refractive index from the amount of light. In this case, a sufficient amount of light can be obtained, so film thickness control becomes easy. However, fluctuations may occur for each light beam, and fluctuations or noise is removed when comparing the signals obtained from each light beam. Need to be considered.

  Specifically, as shown in FIG. 1, since the optical film thickness of one layer of the multilayer film repeats transmission and reflection every quarter wavelength, the transmitted light is monitored by monitoring the amount of transmitted light. By detecting the end point of the film of one layer from the local maximum value or the local minimum value, and changing the deposition raw material, a high refractive index film and a low refractive index film were alternately formed. In general, the time when the maximum value or the minimum value is obtained from the change in the amount of light is obtained by the curve fitting method, and the deposition material is replaced at this time. On the other hand, in the present invention, the light amount is decomposed into a deposition rate and a refractive index based on a theoretical formula, and the maximum or minimum value of the light amount is recalculated from the theoretical formula to determine the replacement time of the deposition source. As a result, the film thickness of each layer could be formed with high accuracy, and a desired thin film filter could be produced.

  In order to stably produce a thin film filter, it is preferable to use two or more light beams that pass through the glass substrate 8 as shown in FIG. That is, even when a thin film filter is produced by uniformly controlling the film thickness of the dielectric multilayer film in the radial direction of the glass substrate 8, the film wavelength can be varied by controlling the film thickness of the dielectric multilayer film to be inclined in the radial direction. When producing a filter, it is desirable to monitor the film thickness at two or more radial positions. Furthermore, the signals output from the two or more optical film thickness monitors are fed back, and the aperture ratio of the film thickness distribution correction plate 17 inserted between the glass substrate 8 and the vapor deposition source 16 is changed. It is possible to form a uniform film or a gradient film on the substrate.

  In the thin film filter manufacturing apparatus of this example, the light beam of the optical film thickness monitor was transmitted at two or more radial positions during film formation, and the amount of transmitted light was measured. FIG. 6 is a schematic diagram showing an example of the film thickness distribution when the conventional light beam is one system. FIG. 7 is a schematic diagram showing the film thickness distribution when the two light beams of the present invention are used. The amount of transmitted light at each radial position was monitored at all times or as needed using a light beam branching mechanism. At this time, one of the light quantity monitors, for example, the light quantity monitor 1 is a monitor for vapor deposition source replacement control, always monitors the light quantity, and calculates the time when the light quantity at this radial position reaches the maximum value or the minimum value from the light quantity change. , Predicted that time. When this predicted time was reached, the deposition raw material was switched to form a dielectric multilayer film. Further, the other light quantity monitor, for example, the light quantity monitor 2 is a monitor for controlling the deposition rate distribution and the refractive index distribution, obtains a difference from the monitor value of the deposition source exchange control monitor, and reduces the difference in the deposition rate distribution and The refractive index profile was controlled.

  FIG. 1 shows the result of the change in the amount of light indicated by the light amount monitor. The figure shows the change in the amount of light when the filter in the first half of one cavity is formed. When the optical film thickness of each multilayer film reaches ¼ of the monitor wavelength, the light amount takes a maximum value or a minimum value. More specifically, at this time, the deposition raw material is switched and the formation of the next layer is started. When the light quantity reaches the maximum value or the minimum value again, the deposition material is switched again, and the next layer is formed. In the case of multiple cavities, the light quantity change of this one cavity is repeated. The multi-cavity thin film filter thus formed has a center wavelength equivalent to the monitor wavelength.

  The control algorithm when radius position 1 is a monitor for vapor deposition source exchange control and radius position 2 is a monitor for vapor deposition rate distribution and refractive index distribution control is explained assuming that there are monitors at two radial positions for simplicity. To do. In this embodiment, the radius position 1 is set to a radius of 50 mm, and the radius position 2 is set to a radius of 120 mm. At the radial position 1, the time at which the light quantity reaches the maximum value or the minimum value is always predicted using the polynomial approximation or the differential value of the light quantity change from the change in the light quantity, and an instruction for the time to switch the deposition material is issued.

  Further, it is more desirable to always predict the time when the light quantity reaches the maximum value or the minimum value from the deposition rate, the refractive index and the film formation time based on the theoretical formula, and to give the instruction of the time for switching the deposition material. In parallel, the light amount of the light beam is also monitored at the radial position 2 and the deposition rate and refractive index calculated from the light amount are always compared with the values at the radial position 1 to correct the distribution in a direction to reduce the deposition rate difference or the refractive index difference. An instruction is given to adjust the aperture ratio of the plate, the ion current of the ion gun, the emission current of the electron gun, the beam voltage of the ion gun, and the oxygen partial pressure, and the vapor deposition rate and the refractive index of the radial position 1 and the radial position 2 are made equal. Was controlled as follows.

  FIG. 8 shows a measurement example of the deposition rate difference and the refractive index difference between the radial position 1 and the radial position 2. This figure shows the difference before controlling the deposition rate distribution and the refractive index distribution. As is apparent from the figure, unlike the light amount difference shown in FIG. 2, the deposition rate difference and the refractive index difference show a monotone increase or a monotone decrease, and it is easy to reduce each value by feedback control. In this example, control of the aperture ratio of the distribution correction plate, the ion current of the ion gun, and the emission current of the electron gun was mainly effective in improving the deposition rate distribution. The distribution correction plate increases the deposition rate at the radial position where the aperture ratio is increased, increasing the ion current of the ion gun decreases the deposition rate at the inner periphery of the substrate, and increasing the emission current of the electron gun increases the deposition rate at the inner periphery of the substrate. There was a tendency to increase.

  Control of the beam voltage and oxygen partial pressure of the ion gun was effective for improving the refractive index distribution. Increasing the ion gun beam voltage increased the refractive index of the inner periphery of the substrate, and increasing the oxygen partial pressure tended to decrease the refractive index of the entire substrate. As a result, a uniform optical film thickness (product of refractive index and film thickness) distribution was obtained at the radius between radius position 1 and radius position 2. As a result, as shown in FIG. 9, the obtained filter substrate has a change range of the center wavelength between the radial position 1 (radius 50 mm) and the radial position 2 (radius 120 mm) and 0.5 nm or less over a radius 70 mm or more. Moreover, it was 0.1 nm or less over a radius of 10 mm or more. At this time, it is desirable to detect the light quantity at each radial position at least once per second even if the process of suppressing the fluctuation of the light quantity is performed.

  After the film formation was completed, the back surface was polished to a plate thickness of 1 mm, an antireflection film was formed on the back surface, and cut into 1.4 mm square filter chips. As a result of evaluating the spectral characteristics of the obtained 100 GHz thin film fixed filter consisting of 5 cavities using an optical characteristic inspection apparatus, a flat top spectral waveform as shown in FIG. 10 is shown, and the peak insertion loss is 0.1 dB or less. The ripple was 0.1 dB or less, and the passband was excellent spectral characteristics of 0.6 nm or more. In addition, as a result of examining the in-plane spectral characteristics of the filter chip in detail, the insertion loss has a tendency to increase from the center of the chip to the outside, but the change is a gradual monotonic increase, and the film thickness of the multilayer film And the refractive index showed that the film was formed very uniformly in the chip surface. The same applies to the center wavelength, and the center wavelength showed a gradual monotonic decrease from the center of the chip toward the outside. These gradual changes occur when the chip is processed to release internal stress from the outside of the chip (around the chip) and the film thickness changes, but the film thickness and refractive index of the multilayer film are within the chip plane. It is a gradual change due to being extremely uniform. Conventional non-uniform multilayer films often show steep changes or characteristic changes that are asymmetric with respect to the center of the chip, but the filter chip of the present invention is improved. As a result, by using the method and apparatus of the present invention, the deposition rate and refractive index can be stably controlled even in a long-day film formation from the layer immediately above the substrate to the surface layer. Suggests that the film thickness and refractive index were exactly as expected. Further, in this embodiment, a thin film fixed filter having a desired center wavelength can be formed, and the yield thereof is more than doubled as compared with a conventional method in which a light amount monitor is set.

  On the other hand, a thin film filter comprising 6 cavities was similarly formed, the back surface was polished to a plate thickness of 1.9 mm, an antireflection film was formed on the back surface, and cut into 2.3 mm square filter chips. As a result of evaluating the spectral characteristics of the obtained 50 GHz thin film fixed filter using an optical characteristic inspection apparatus, it shows a flat top spectral waveform similar to the 100 GHz filter, the peak insertion loss is 0.1 dB or less, and the ripple is 0. A pass band of 1 dB or less and -0.5 dB showed excellent spectral characteristics of 0.28 nm or more. Moreover, as a result of examining the in-plane spectral characteristics of the filter chip in detail, the insertion loss shows a gradual monotonic increase from the center of the chip to the outside, and the center wavelength gradually decreases from the center of the chip to the outside. It showed a monotonic decrease. These gradual changes occur when the internal stress is released and the film thickness changes, but in the filter chip of the present invention, the film thickness and refractive index of the multilayer film are extremely uniform in the chip surface. Is. As a result, by using the method and apparatus of the present invention, the deposition rate and the refractive index can be controlled stably even in a long-time film formation ranging from the layer immediately above the substrate to the surface layer, all day and night. This suggests that the layer has exactly the theoretical film thickness and refractive index. Further, in this embodiment, a thin film fixed filter having a desired center wavelength can be formed, and the yield thereof is more than doubled as compared with a conventional method in which a light amount monitor is set.

(Example 2)
In Example 1, a thin film filter was produced by the following method and apparatus. In the method for controlling the deposition rate distribution and the refractive index distribution, the wavelength of the light beam monitored at the radial position 1 and the wavelength of the light beam monitored at the radial position 2 were set to different values having a wavelength difference of 10 nm or less. That is, the change in the amount of light is measured at the radial position 1, the time when the amount of light reaches the maximum value or the minimum value is always predicted from the deposition rate, the refractive index and the film formation time based on the theoretical formula, and an indication of the time for switching the deposition material is given. put out. In parallel, the light amount is monitored at a wavelength different from that at the radial position 1 at the radial position 2, and the vapor deposition rate and the refractive index are calculated from the light amount. The aperture ratio of the distribution correction plate, the ion current of the ion gun, the emission current of the electron gun, the beam voltage of the ion gun, the oxygen content so that the ratio of the product of the deposition rate and the refractive index at these two locations is equivalent to the wavelength ratio at the two locations. The pressure was controlled. As shown in FIG. 11, the center wavelength of the obtained filter substrate was changed by 3.8 nm between the radius position 1 and the radius position 2 and the radius 70 mm. This result includes 4 channels of 100 GHz filters with an interval of 0.8 nm between adjacent wavelengths. By cutting the substrate and processing it into 1.4 mm square chips, four types of thin film fixed filters can be obtained. It was possible to produce in a single vacuum batch.

(Example 3)
In Example 1, a thin film filter was produced by the following method and apparatus. In the method for controlling the deposition rate distribution and the refractive index distribution, the wavelength of the light beam monitored at the radial position 1 and the wavelength of the light beam monitored at the radial position 2 are different values having a wavelength difference of 10 nm or more, and preferably 30 nm or more. did. That is, the change in the amount of light is measured at the radial position 1, the time when the amount of light reaches the maximum value or the minimum value is always predicted from the deposition rate, the refractive index and the film formation time based on the theoretical formula, and an indication of the time for switching the deposition material is given. put out. In parallel, the light amount is monitored at a wavelength different from that at the radial position 1 at the radial position 2, and the vapor deposition rate and the refractive index are calculated from the light amount. Distribution ratio plate aperture ratio, ion gun ion current, electron gun emission current, ion gun beam voltage, oxygen content, so that the ratio of the product of deposition rate and refractive index at these two locations is equivalent to the wavelength ratio at the two locations. The pressure was controlled.

  A thin film filter substrate prepared with a monitor wavelength difference of 35 nm at a radius of 90 mm and a radius of 120 mm is polished on the back surface to a plate thickness of 3 mm, and then an antireflection film is formed on the back surface, and a strip filter having a width of 5 mm and a length of 35 mm Cut into pieces. Here, cutting was performed so that the radial direction was the longitudinal direction of the filter. The obtained thin film filter is a wavelength tunable filter corresponding to 100 GHz, and has a center wavelength difference of 35 nm between 30 mm in length. FIG. 12 shows a side view of the wavelength tunable filter thus manufactured. In this figure, the film thicknesses of the wavelength tunable filter 26 and the antireflection film 25 are enlarged and shown in comparison with the glass substrate 24. In the spectral characteristics of the light beam transmitted through the wavelength tunable filter, the center wavelength continuously changes in proportion to the thickness of the thin film. As a result, as shown in the figure, a thin film filter having the monitor wavelength at the radial position 1 as the center wavelength is obtained at the radial position 1, and a thin film filter having the monitor wavelength at the radial position 2 as the center wavelength is obtained at the radial position 2. It was. In addition, a thin film filter having a center wavelength between the radial position 1 and the radial position 2 was obtained continuously at the radial position between the radial position 1 and the radial position 2. Therefore, a channel having a desired center wavelength can be selected by selecting a desired radial position. In the figure, arrows indicate the transmission directions of the light beams 27 and 28 of the light quantity monitors 1 and 2.

  FIG. 13 shows an example of spectral characteristics of the obtained wavelength tunable filter. The figure shows a 100 GHz wavelength tunable filter consisting of 5 cavities, and a flat top wavelength tunable filter having a passband of −0.5 dB of 0.4 nm or more was obtained. It can be inferred that the reason why the pass band of −0.5 dB is reduced as compared with the fixed filter is that the filter film thickness is inclined in the beam spot, so that the narrow band characteristics having different center wavelengths overlap and are averaged. Even so, this is a significant improvement compared to the spectral characteristics of conventional wavelength tunable filters. FIG. 14 shows an example of a wavelength tunable filter module manufactured using this thin film wavelength tunable filter. The wavelength tunable filter module includes an input port 29, a drop port 30, a reflected light output port 31, a stepping motor 32, a wavelength tunable filter 33, and a drive system 34. A light beam incident from the input port 29 passes through the wavelength tunable filter 33. The desired channel (wavelength) is output to the drop port 30 through the network. On the other hand, all light beams having wavelengths other than the desired channel are reflected by the wavelength variable filter 33 and emitted to the output port 31 of the reflected light. At this time, the channel can be switched by operating the stepping motor 32 and moving the wavelength tunable filter 33 via the drive system 34. Here, a so-called three-port tunable filter module is shown.

  FIG. 15 shows an example in which the spectral characteristic of the light beam emitted from the drop port 30 of the wavelength tunable filter module of this embodiment is measured and the center wavelength is plotted against the voltage of the potentiometer that operates the stepping motor 32. As can be seen from the figure, as the potentiometer voltage increases, the center wavelength monotonously increases, indicating that the center wavelength of the light beam output from the drop port 30, that is, the channel is continuously switched. .

  Similarly, a thin film filter consisting of 6 cavities was produced at a radius of 90 mm and a radius of 120 mm with a monitor wavelength difference of 20 nm. The thin film filter substrate was polished on the back surface to a plate thickness of 3 mm, an antireflection film was formed on the back surface, and cut into a strip filter having a width of 5 mm and a length of 35 mm. Here, cutting was performed so that the radial direction was the longitudinal direction of the filter. The obtained thin film filter is a wavelength tunable filter corresponding to 50 GHz, and has a center wavelength difference of 20 nm between lengths of 30 mm. As a result of evaluating the 50 GHz wavelength tunable filter comprising 6 cavities using an optical characteristic inspection apparatus, it showed a flat-top wavelength tunable filter characteristic having a passband of −0.5 dB of 0.2 nm or more. Conventionally, it has been particularly difficult to produce a wavelength tunable filter for 50 GHz, but by using the method of the present invention, it has become possible to obtain a flat-top wavelength tunable characteristic.

  The present invention can be used for a dielectric thin film filter used in an optical communication system or the like and a manufacturing method thereof. More specifically, it can be used for a thin film fixed filter and a thin film wavelength tunable filter.

It is a figure which shows the light quantity change which a light quantity monitor shows when forming a multicavity filter. It is a figure which shows the light quantity difference of the light beam in the radial position 1 and the radial position 2. FIG. It is sectional drawing which shows the dielectric multilayer structure which comprises the multipass band pass filter. It is sectional drawing which shows the multilayer optical filter formation apparatus used by the present Example. It is the schematic which shows the structure of the optical film thickness monitor used in the present Example. It is a schematic diagram which shows the film thickness distribution at the time of installing a light quantity monitor in one radial position in the conventional method, and controlling film thickness. It is a schematic diagram which shows the film thickness distribution at the time of setting a light quantity monitor in two radial positions used by the present Example, and controlling film thickness. When forming a multicavity filter, it is the figure which calculated the vapor deposition rate and the refractive index from the light quantity change which a light quantity monitor shows by a fitting method, and displayed the vapor deposition rate difference and refractive index difference of two radial positions. It is a figure which shows an example of the center wavelength change of the radial direction of the thin film filter board | substrate produced in the present Example. It is a figure which shows the spectral waveform of the thin film fixed filter which consists of 5 cavities produced in the present Example. It is a figure which shows an example of the center wavelength change of the radial direction of the other thin film filter board | substrate produced in the present Example. This wavelength range includes four channels. It is a side view which shows the thin film filter with the film thickness gradient produced in the present Example. It is a figure which shows an example of the spectral characteristic of the thin film wavelength variable filter which consists of 5 cavities produced in the present Example. It is a top view which shows the structure of the 3 port type | mold wavelength variable filter module produced in the present Example. It is a figure which shows the relationship between the center wavelength calculated | required from the spectral characteristic of the light beam output from the drop port of the wavelength variable filter module produced in the present Example, and the voltage of the potentiometer which operates a stepping motor.

Explanation of symbols

1 1/4 wavelength laminate to be a mirror,
2 1/2 wavelength to be a spacer or its integral multiple layer,
3 deposition substrate, 4 anti-reflection film, 5 electron gun, 6 deposition source hearth,
7 Deposition source shutter, 8 Glass substrate, 9 Substrate shutter,
10 Crystal-type film thickness monitor, 11 High-speed substrate rotation motor,
12 ion gun,
13, 13-1, 13-2 Optical film thickness monitor light projecting unit,
14, 14-1, 14-2 Optical film thickness monitor light receiving part,
15 chamber wall, 16 evaporation source, 17 film thickness distribution correction plate,
18 optical fiber, 19 spectrometer,
20 Computer for light intensity calculation and control,
21 Lamp power supply, 22 White light source,
23-1 Optical beam branching mechanism,
23-2 Light beam coalescence mechanism,
24 glass substrate,
25 anti-reflective film, 26 film thickness gradient filter film,
27 light beam at radial position 1 28 light beam at radial position 2
29 input ports, 30 drop ports, 31 reflected light output ports,
32 stepping motors, 33 tunable filters,
34 drive system, 35 fixed distribution correction plate, 36 variable distribution correction plate,
37 Distribution correction plate rotation shaft, 38 Ball gear,
39 Stepping motor

Claims (11)

An optical mechanism for branching and projecting a white light beam or specific wavelength light at two or more different radial positions of the film formed on the rotating substrate, and means for detecting the light amount of the specific wavelength by the transmitted light of the film A thin film filter comprising: means for calculating at least one of a deposition rate or a refractive index of the film based on the light amount; and controlling at least one of the deposition rate distribution or the refractive index distribution. Production method. 2. The method of manufacturing a thin film filter according to claim 1, wherein the light amount of the light beam is constantly measured at two or more radial positions, the deposition rate and the refractive index are calculated from the light amounts at the respective radial positions, and the deposition rate difference and the refractive index difference are calculated. A method of manufacturing a thin film filter, comprising forming a thin film fixed filter by controlling a deposition rate distribution and a refractive index distribution in a radial direction on a substrate so as to decrease. 3. The method of manufacturing a thin film filter according to claim 2, wherein the wavelengths of the light beams at the two radial positions are set to different values having a desired wavelength difference, and the ratio of the product of the deposition rate and the refractive index at the two locations is the two locations. A method of manufacturing a thin film filter, wherein a plurality of types of thin film fixed filters having different wavelengths are formed at a time by controlling a deposition rate distribution and a refractive index distribution so as to be equal to a wavelength ratio. 3. The method of manufacturing a thin film filter according to claim 2, wherein the wavelengths of the light beams at the two radial positions are set to different values having a desired wavelength difference, and the ratio of the product of the deposition rate and the refractive index at the two locations is the two locations. A method of manufacturing a thin film filter, comprising forming a wavelength tunable filter by controlling a deposition rate distribution and a refractive index distribution so as to be equal to a wavelength ratio. 5. The method of manufacturing a thin film filter according to claim 1, wherein the method of calculating the deposition rate and the refractive index from the light amount of the light beam always sets the deposition rate and the refractive index to give the transmitted light amount based on a theoretical formula. A method for producing a thin film filter, wherein the thin film filter is obtained by calculation using a fitting method. 6. The method of manufacturing a thin film filter according to claim 1, wherein a method of controlling a radial deposition rate distribution on the substrate is a method of changing an aperture ratio of a film thickness distribution correction plate, and an ion current of an ion gun. A method for producing a thin film filter, characterized in that it is at least one method selected from a method for changing or a method for changing an emission current of an electron gun. 6. The method of manufacturing a thin film filter according to claim 1, wherein the method of controlling the refractive index distribution in the radial direction on the substrate is a method of changing a beam voltage of an ion gun or a method of changing an oxygen partial pressure. A method for producing a thin film filter, which is at least one selected method. A multilayer optical filter comprising a dielectric multilayer film in which a plurality of high-refractive index films and low-refractive index films are alternately stacked, and has a dimension of 1.5 × 1.5 × 1.5 mm or less and is compatible with 100 GHz A thin film fixed filter having a peak insertion loss of 0.1 dB or less, a ripple of 0.1 dB or less, and a passband of −0.5 dB and 0.6 nm or more. A wavelength tunable filter having a dielectric multilayer film formed by tilting the film thickness, having a size of 10 × 30 × 5.0 mm or less, and a passband corresponding to 100 GHz of 0.4 nm or more at −0.5 dB A tunable filter characterized by being. A multilayer optical filter comprising a dielectric multilayer film in which a plurality of high-refractive index films and low-refractive index films are alternately laminated, and has a size of 2.4 × 2.4 × 2.4 mm or less and is compatible with 50 GHz A thin film fixed filter having a peak insertion loss of 0.1 dB or less, a ripple of 0.1 dB or less, and a passband of −0.5 dB of 0.28 nm or more. A wavelength tunable filter having a dielectric multilayer film formed by tilting the film thickness, having a size of 10 × 30 × 5.0 mm or less, and a passband corresponding to 50 GHz is 0.2 nm at −0.5 dB. A wavelength tunable filter characterized by the above.

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