Optical module

Abstract

The invention provides an optical module capable of improving mass production. The optical module is provided with a plurality of optical filters and an infrared optical element, and the first optical filter and the second optical filter include a common passband having a transmittance of 60% or more at 50 nm or more in a wavelength region of 2000-10000 nm, and include a wavelength region having a difference in transmittance of 20% or more at a total of 200 nm or more outside the common passband. A wavelength region in which the difference in transmittance is less than 20% and the transmittance is less than 60% is included in a wavelength band that is closer to the common passband than a wavelength region in which the difference in transmittance is 20% or more on both outer sides of the common passband. The wavelength region has a total of 1000 nm or more and has a difference in transmittance of less than 20% and a transmittance of less than 60%. When the sensitivity spectrum of the infrared optical element is multiplied by the transmission spectrum of the plurality of optical filters, the sensitivity of the stop band is 5% or less of the peak sensitivity.

Description

TECHNICAL FIELD

[0001] The present disclosure relates to an optical module. BACKGROUND

[0002] In the past, as a gas concentration measuring device that performs concentration measurement of a measurement target gas in the atmosphere, a non-dispersive infrared (NDIR) type gas concentration measuring device is known. The non-dispersive infrared type gas concentration measuring device measures the concentration of a gas by detecting the amount of absorption of infrared light whose wavelength differs depending on the type of gas, using the fact that the wavelength of the infrared light absorbed differs depending on the type of gas. For example, the non-dispersive infrared type gas concentration measuring device is configured with an infrared optical element and an optical filter that transmits infrared light of a specific wavelength depending on the measurement target gas. For example, Patent Literature 1 discloses a gas sensor that includes a plurality of optical filters.

[0003] PRIOR ART DOCUMENTS

[0004] PATENT LITERATURE

[0005] Patent Literature 1: U.S. Patent No. 11499914 Specification SUMMARY

[0006] PROBLEMS TO BE SOLVED BY THE INVENTION

[0007] Here, the measurement target gas is not limited to carbon dioxide, but is various. The current situation is that, for each measurement target gas, the optimal combination of the infrared optical element and the optical filter has not been studied. In particular, optimization of the specifications of the optical filter has not been performed. In addition, there is a tendency for the film thickness of the multilayer film of the high-precision optical filter to be thick. As a result, the processability and the yield are reduced, leading to a reduction in the mass productivity of the optical module configured to include the optical filter.

[0008] The present disclosure, which has been achieved in light of the above circumstances, aims to provide an optical module capable of improving the mass productivity. Here, the optical module is a module used in, for example, a concentration measuring device, an infrared radiation thermometer (non-contact thermometer), infrared spectroscopic imaging, a human detection sensor, or the like. The optical module is an optical component in which an infrared optical element and an optical filter are arranged so as to maintain the positional relationship and the like of the infrared optical element and the optical filter, and are packaged in order to obtain desired characteristics.

[0009] MEANS FOR SOLVING THE PROBLEMS

[0010] (1) The optical module of one embodiment of the present disclosure includes a plurality of optical filters including at least a first optical filter and a second optical filter independent of the first optical filter, and an infrared optical element having a peak sensitivity in a wavelength region of 2000 nm to 10000 nm,

[0011] At least one of the first optical filter and the second optical filter has a substrate and a multilayer film formed on at least one face of the substrate and having a plurality of layers with different refractive indexes,

[0012] The first optical filter and the second optical filter include a common passband of 60% or more in transmittance of 50 nm or more in a wavelength region of 2000 nm to 10000 nm, include a wavelength region of 20% or more in difference in transmittance of 200 nm or more in total on the outside of the common passband, and include a wavelength region of less than 20% in difference in transmittance and less than 60% in transmittance of 1000 nm or more in total in a wavelength region closer to the common passband than a wavelength region of 20% or more in difference in specific transmittance on both sides of the common passband,

[0013] In a case where the sensitivity spectrum of the infrared optical element is multiplied by the transmittance spectrum of the plurality of optical filters, the sensitivity of the stop band is 5% or less of the peak sensitivity.

[0014] (2) As one embodiment of the present disclosure, in (1),

[0015] At least one optical filter of the plurality of optical filters is directly laminated to the infrared optical element and shares a substrate with the infrared optical element.

[0016] (3) As one embodiment of the present disclosure, in (1),

[0017] A filter substrate that is a substrate of at least one optical filter of the plurality of optical filters is different in kind from an optical element substrate that is a substrate of the infrared optical element,

[0018] The filter substrate is joined to the optical element substrate.

[0019] (4) As one embodiment of the present disclosure, in any one of (1) to (3),

[0020] When a center wavelength of the passband is set as λp, a total film thickness of the multilayer film of at least one optical filter of the plurality of optical filters is (λp x 1.5) nm or less.

[0021] (5) As one embodiment of the present disclosure, in any one of (1) to (4),

[0022] The plurality of optical filters includes a first optical filter and a second optical filter,

[0023] The difference between the half-value width of the first optical filter and the half-value width of the second optical filter is 1500 nm or less.

[0024] (6) As one embodiment of the present disclosure, in any one of (1) to (5),

[0025] The total film thickness of the multilayer film of each of the plurality of optical filters having the multilayer film is 14 μm or less.

[0026] (7) As one embodiment of the present disclosure, in any one of (1) to (6),

[0027] In a wavelength region of 2000 nm to 10000 nm, the ratio of the maximum sensitivity to the minimum sensitivity of the infrared optical element is 20 or more.

[0028] (8) As one embodiment of the present disclosure, in any one of (1) to (7),

[0029] The plurality of optical filters includes, in a wavelength region of 2000 nm to 10000 nm, a wavelength region in which the difference in transmittance between at least two of the plurality of optical filters is 30% or more,

[0030] In a wavelength region of 2000 nm to 10000 nm, in a case where the sensitivity spectrum of the infrared optical element is multiplied by the transmittance spectrum of the plurality of optical filters, the sensitivity of the stop band is 2% or less of the peak sensitivity.

[0031] (9) As one embodiment of the present disclosure, in any one of (1) to (8),

[0032] In any 1000 nm interval of the stop band, between wavelength regions in which the difference in transmittance between at least two of the plurality of optical filters is 20% or more, there is a wavelength region in which the difference in transmittance is 5% or less.

[0033] (10) As one embodiment of the present disclosure, in any one of (1) to (9),

[0034] The slope of the transmittance spectrum of at least one of the plurality of optical filters is 3.3% or more.

[0035] (11) As one embodiment of the present disclosure, in any one of (1) to (10),

[0036] The plurality of optical filters are all structured to have a substrate and a multilayer film formed on at least one face of the substrate and having a plurality of layers having different refractive indexes.

[0037] (12) As one embodiment of the present disclosure, in any one of (1) to (11),

[0038] In the common passband, when a half-value width of one of the plurality of optical filters is set to A and a half-value width of the other optical filter is set to B, a relationship of 0.5 < (A / B) < 2 is satisfied.

[0039] (13) As one embodiment of the present disclosure, in (12),

[0040] With respect to the A and the B, a relationship of 0.7 < (A / B) < 1.3 is satisfied.

[0041] (14) As one embodiment of the present disclosure, in any one of (1) to (13),

[0042] A film thickness of two or more of the plurality of optical filters is 1.5 times or less of the center wavelength.

[0043] (15) As one embodiment of the present disclosure, in any one of (1) to (14),

[0044] A slope of a transmission spectrum obtained when the transmission spectra of the plurality of optical filters are multiplied is smaller than a slope of a transmission spectrum of an individual optical filter.

[0045] Effects of Invention

[0046] According to the present disclosure, an optical module capable of improving productivity can be provided. BRIEF DESCRIPTION OF DRAWINGS

[0047] Figure 1 is a drawing showing an example of a cross section of an optical filter.

[0048] Figure 2 is a drawing showing an example of a concentration measuring device provided with an optical module of one embodiment of the present disclosure.

[0049] Figure 3 is a drawing for explaining an optical filter of an optical module of one embodiment of the present disclosure in comparison with an optical filter based on a comparative example.

[0050] Figure 4 is a drawing showing a difference between an optical filter based on a comparative example and an optical filter of the present disclosure.

[0051] Figure 5 is a drawing for explaining a structure of an optical filter and an infrared optical element in an optical module.

[0052] Figure 6 is a graph illustrating transmittance of an example embodiment.

[0053] Figure 7 is a graph illustrating characteristics of an example embodiment.

[0054] Figure 8 is a graph showing a layer structure of an infrared optical element of an example embodiment. DETAILED DESCRIPTION

[0055] Hereinafter, an optical module of one embodiment of the present disclosure is described with reference to the drawings.

[0056] (Optical Module)

[0057] The optical module of this embodiment has a plurality of optical filters and an infrared optical element. In this embodiment, each of the plurality of optical filters (i.e., all of the optical filters) has a structure of a substrate and a multilayer film formed on at least one surface of the substrate and having a plurality of layers with different refractive indexes. However, it is only necessary that at least one of the plurality of optical filters has a structure of a substrate and a multilayer film. The infrared optical element is an infrared light-receiving element or an infrared light-emitting element, which is a collective name of them. Note that hereinafter, receiving and emitting mean at least one of receiving light and emitting light. The infrared optical element includes, for example, a first-conductivity-type semiconductor layer, an active layer, and a second-conductivity-type semiconductor layer, and is configured to receive and emit infrared light. That is, the optical module of this embodiment is an infrared module. The infrared light-emitting element is realized by the structure described below (see FIG. 1), and the infrared light-receiving element is also realized by the same structure. The infrared light-emitting element can be a light-emitting diode (LED) in particular. The infrared light-receiving element can be a photodiode (PD) in particular. Here, the optical module of this embodiment has a plurality of optical filters, but hereinafter, in the case of description other than that of each of the plurality of optical filters, the optical filter is sometimes simply referred to as an optical filter. Figure 8

[0058] Hereinafter, a case in which the optical module of this embodiment is used for a concentration measuring device is described. As described above, the optical module is an optical component in which an infrared optical element and an optical filter are arranged and packaged so that a desired characteristic is obtained and the positional relationship between the infrared optical element and the optical filter is maintained. Note that the optical module is not limited to the concentration measuring device and can be used for an infrared radiation thermometer or the like.

[0059] ​In the present embodiment, the concentration measuring device is a gas sensor that measures the concentration of a measurement target gas. The concentration measuring device can be, for example, a non-dispersive infrared absorption (NDIR) type gas sensor that has a light-receiving portion that receives infrared light that has passed through a gas. Alternatively, the concentration measuring device can be a photoacoustic type gas sensor that measures the concentration of a gas by picking up the vibration of a gas molecule that has absorbed light as sound using a high-performance microphone.

[0060] The plurality of optical filters includes at least a first optical filter and a second optical filter independent of the first optical filter, as will be described in detail later. The first optical filter and the second optical filter include, in a wavelength region of 2000 nm to 10000 nm, a common passband in which the transmittance is 60% or more over 50 nm or more, and, outside the common passband, a wavelength region in which the difference in transmittance between at least two of the plurality of optical filters is 20% or more over 200 nm or more in total. Furthermore, the first optical filter and the second optical filter include, in a wavelength region closer to the common passband than the wavelength region in which the difference in transmittance is 20% or more on both sides of the common passband, a wavelength region in which the difference in transmittance is less than 20% and the transmittance is less than 60% over 1000 nm or more in total. In addition, in the wavelength region of 2000 nm to 10000 nm, the infrared optical element has a peak sensitivity, and as a result of multiplying the sensitivity spectrum of the infrared optical element by the transmittance spectrum of the plurality of optical filters, the sensitivity in the stop band is 5% or less of the peak sensitivity. In other words, in the case where the sensitivity spectrum of the infrared optical element is multiplied by the transmittance spectrum of the plurality of optical filters, the sensitivity in the stop band is 5% or less of the peak sensitivity. Here, the multiplication means that the sensitivity spectrum of the infrared optical element and the transmittance spectrum of the plurality of optical filters are multiplied for each identical wavelength. In addition, the stop band is a wavelength region in which the sensitivity is not required on the design of the optical module. For example, the stop band includes a wavelength region in which at least one of an infrared light-emitting element and an infrared light-receiving element used together with the optical filter in the optical module does not have sensitivity. In addition, for example, the stop band includes a wavelength region in which the transmittance of the optical filter is low. The low transmittance of the optical filter is not limited to the case where the transmittance is 0%, and for example, can include the case where the transmittance is 5% or less. On the other hand, the passband is a wavelength region that does not belong to the stop band, and is at least a part of a wavelength region in which at least the infrared light-emitting element and the infrared light-receiving element have sensitivity.

[0061] According to the optical module of the present embodiment, even if a simplified optical filter is used, infrared rays or light of only a desired wavelength band can be selectively received. By using a simplified optical filter, the optical module of the present embodiment can be downsized compared to a conventional module using an unsimplified optical filter. In addition, in the optical module of the present embodiment, the optical filter is composed of a plurality of simplified optical filters. By sharing the functions of the plurality of simplified optical filters and integrally configuring a filter having a desired characteristic, as described below, an optical module that can improve productivity can be provided. Here, the plurality of simplified optical filters cannot individually achieve the desired characteristic. The optical module of the present embodiment is configured by combining such a plurality of simplified optical filters.

[0062] Figure 1 An example of a cross section of an optical filter. In the present embodiment, the optical filter alternately stacks layers composed of a low refractive index material (L) using silicon monoxide (SiO), silicon dioxide (SiO2), titanium dioxide (TiO2), zinc sulfide (ZnS), or aluminum oxide (Al2O3), or the like as a material and layers composed of a high refractive index material (H) using Si or Ge, or the like as a material on both surfaces of a Si substrate. As the low refractive index material (L), a material having a refractive index of 1.2 to 2.5 is preferably selected. In addition, as the high refractive index material (H), a material having a refractive index that is greater than that of the low refractive index material (L) by 0.5 or more is preferably selected. The multilayer film that is alternately stacked is formed as a layer directly provided on the Si substrate as the high refractive index material (H). However, the optical filter is not limited to the structure of Figure 1 , and, for example, the high refractive index material (H) can not be directly provided on the substrate.

[0063] In the present embodiment, the optical filter is an interference type bandpass filter in the mid-infrared region. In general, an interference type bandpass filter in the mid-infrared region has a large number of layers, and defects during film formation are likely to increase. Therefore, it is preferable that the optical filter have a small number of layers. However, if the optical filter is simply simplified by merely reducing the number of layers, the accuracy of the gas sensor can deteriorate.

[0064] As a result of studying the optimal combination of an infrared optical element and a filter, as described below, the inventors of the present application have achieved an optical module in which the accuracy does not deteriorate even when a "simplified filter" composed of a plurality of filters is used.

[0065] Here, the so-called simplified optical filter refers to an optical filter in which the number of layers of optical films required for blocking the region having no sensor sensitivity is reduced by not blocking the region. In the present embodiment, a synthetically simplified optical filter is realized by multiplying the transmittance spectra of a plurality of optical filters. Thus, the number of layers of each optical filter can be further reduced, and the defects at the time of film formation can be reduced. For example, by reducing the warping due to the multilayer, the generation of chipping at the time of cutting can be suppressed, and the mass production stability can be improved. That is, the reduction in workability and yield can be suppressed.

[0066] Figure 2 is a view showing an example of a concentration measuring apparatus using the optical module of the present embodiment. In the optical module of the present embodiment, as shown in Figure 2 , an infrared light receiving element (IR) is provided in the optical path of infrared light output from an infrared light emitting element (light source), and an optical filter that selectively transmits the absorption wavelength of a gas to be detected is provided before the infrared light receiving element. The optical module corresponds to, for example, a portion of the infrared light emitting element and the optical filter, or a portion further including the infrared light receiving element.

[0067] Here, the gas to be detected by the concentration measuring apparatus is, for example, carbon dioxide (CO2), but is not limited thereto. For example, the gas to be detected can be, for example, water vapor, carbon monoxide, nitrogen monoxide, ammonia, sulfur dioxide, alcohol, formaldehyde, methane, propane, or the like.

[0068] Figure 3 is a view for comparing the optical filter of the optical module of the present embodiment with the optical filter of a comparative example. In the sensor (infrared light receiving element) of the comparative example, the spectral sensitivity has no wavelength selectivity (wavelength-based change in sensitivity). On the other hand, the sensor provided in the optical module of the present embodiment (or provided in the concentration measuring apparatus using the optical module of the present embodiment) has wavelength selectivity. Thus, in the present embodiment, the optical filter does not need to cut the wavelength having no sensitivity, and the optical filter can be simplified. In addition, in the case of an infrared light emitting element in which the emission intensity has wavelength selectivity, the optical filter does not need to cut the wavelength that does not emit light, and the optical filter can be simplified. Here, in Figure 3 , the wavelength having no sensitivity and the wavelength that does not emit light are shown on both the long wavelength side (high wavelength side) and the short wavelength side (short wavelength side) from the peak wavelength, but this is an example as a concept. The object of relaxing the cutoff specification of the optical filter can be at least one of the high wavelength side and the short wavelength side.

[0069] Figure 4is a diagram indicating the difference between the optical filter of the comparative example and the optical filter of the present disclosure. In the optical filter of the optical module of the present embodiment, the function of the optical filter can be divided with a plurality of optical filters, and the number of layers of each optical filter can be reduced. The plurality of optical filters provided in the optical module of the present embodiment are explained as two or three in the following as an example, but can be four or more. That is, the optical module is provided with N optical filters (refer to Figure 5 ), N being an integer of two or more.

[0070] Figure 5 is a diagram for explaining the structure of the optical filter and the infrared optical element in the optical module. The optical filter is disposed on the optical path at the rear stage of the infrared optical element that is a light-emitting element. In addition, the optical filter is disposed on the optical path at the front stage of the infrared optical element that is a light-receiving element. The optical filters are disposed apart from each other by a gap. Here, da is the distance between the infrared light-emitting element and the nearest optical filter. In addition, db is the distance between the infrared light-receiving element and the nearest optical filter. At least one of da and db can be zero. That is, at least one of the plurality of optical filters can be integrated with the infrared optical element (at least one of the light-emitting element and the light-receiving element). For example, at least one of the plurality of optical filters can be directly laminated on the infrared optical element. At this time, the directly laminated optical filter can share a substrate with the infrared optical element. By sharing the substrate, miniaturization of the optical module can be achieved. However, in a case where the degree of freedom of design is more important than miniaturization, or the like, the substrates can not be shared. For example, the filter substrate that is the substrate of at least one of the plurality of optical filters can be a different kind from the optical element substrate that is the substrate of the infrared optical element. Also, it can be a structure in which the filter substrate and the optical element substrate are joined. In addition, the optical module is not limited to the structure shown in Figure 5 , for example, can be a structure in which other optical members such as a lens or a mirror are further disposed on the optical path.

[0071] The following describes the details of the constituent elements of the optical module of the present embodiment. Here, the optical module is provided with at least one of an infrared light-receiving element and an infrared light-emitting element, and the light-receiving sensitivity of the infrared light-receiving element and the light-emitting intensity of the infrared light-emitting element are explained as "sensitivity". That is, if the optical module is a structure provided with an infrared light-receiving element, the sensitivity can be replaced with the light-receiving sensitivity, and if the optical module is a structure provided with an infrared light-emitting element, the sensitivity can be replaced with the light-emitting intensity.

[0072] (Optical filter)

[0073] As described above, the optical filter includes a substrate and a multilayer film formed on the substrate and having a plurality of layers with different refractive indexes. The multilayer film can be formed on only one surface of the substrate, or can be formed on both surfaces. The optical filter is disposed in the light path of infrared light emitted from the infrared light emitting element to the infrared light receiving element in the concentration measuring device. The optical filter can be manufactured by forming the first layer and the second layer on the substrate by a vapor deposition method.

[0074] The plurality of optical filters includes at least a first optical filter and a second optical filter independent of the first optical filter. The first optical filter and the second optical filter include, in a wavelength region of 2000 nm to 10000 nm, a common passband of 50 nm or more in which the transmittance is 60% or more, and, outside the common passband, a wavelength region of 200 nm or more in total in which the difference in transmittance between at least two of the plurality of optical filters is 20% or more. Further, the first optical filter and the second optical filter include, in a wavelength region closer to the common passband than the wavelength region in which the difference in transmittance is 20% or more on both sides of the common passband, a wavelength region of 1000 nm or more in total in which the difference in transmittance is less than 20% and the transmittance is less than 60%. The plurality of optical filters more preferably includes, in the wavelength region of 2000 nm to 10000 nm, a wavelength region of 50 nm or more in total in which the difference in transmittance between at least two of the plurality of optical filters is 30% or more. In addition, in the wavelength region of 2000 nm to 10000 nm, the infrared optical element has a peak sensitivity, and in a case where the sensitivity spectrum of the infrared optical element is multiplied by the transmittance spectrum of the plurality of optical filters, the sensitivity of the stopband is 5% or less of the peak sensitivity. Here, in the wavelength region of 2000 nm to 10000 nm, in a case where the sensitivity spectrum of the infrared optical element is multiplied by the transmittance spectrum of the plurality of optical filters, the sensitivity of the stopband is more preferably 2% or less of the peak sensitivity.

[0075] Here, the transmittance varies depending on the measurement conditions. Specifically, it varies depending on the temperature and the incident angle of light. In the present embodiment, the temperature is 25°C. In addition, depending on the design of the concentration measuring device and the like, the incident angle of light can be, for example, 0°, 10°, 20°, 30°, 40°, 45°, or the like, but as long as the characteristics described above are satisfied at any incident angle. For example, the optical filter can satisfy the characteristics described above at at least one of the incident angles that can be set by design (30° as an example). Here, the optical filter is further preferably designed to satisfy the characteristics described above at all of the incident angles that can be set by design.

[0076] At least one of the plurality of optical filters preferably sets the center wavelength of the passband to λp, and the total film thickness of the multilayer film is (λp x 1.5) nm or less. Here, the center wavelength is a wavelength region of 2000 nm to 10000 nm, and is a wavelength that is the center of the half-value width of the passband having the maximum transmittance. In addition, the half-value width is the width of the wavelength (i.e., the difference between the maximum wavelength and the minimum wavelength) of the transmittance that is half of the maximum transmittance.

[0077] The plurality of optical filters can include a first optical filter and a second optical filter, and the difference between the half-value width of the first optical filter and the half-value width of the second optical filter is 1500 nm or less. Here, regarding the change in the transmittance of the plurality of optical filters with respect to the wavelength (transmission spectrum, refer to Figure 6 ), the transmission spectrum as a comprehensive characteristic can be steep in a case where the slopes before and after the center wavelength have the following relationship. First, the slope is determined by the value (Δλ1 / λp) obtained by dividing the wavelength width (bandwidth) from the point at which the transmittance is 10% (transmission point) to the transmission point at which the transmittance is 80% by the center wavelength λp. In addition, the slope can also be determined by (Δλ2 / λp) by setting the wavelength width from the transmission point at which the transmittance is 80% to the transmission point at which the transmittance is 10% to Δλ2. (Δλ1 / λp) and (Δλ2 / λp) can be calculated as in the calculation method in Table 1 described later, and the larger one of the two values is determined as the slope of the transmission spectrum. If the slope of the transmission spectrum of at least one of the plurality of optical filters is 3.3% or more, the transmission spectrum as a comprehensive characteristic can be steep, and the film thickness of the optical filter can be reduced. If the slope of the transmission spectrum of at least one of the plurality of optical filters is 4.2% or more, the transmission spectrum as a comprehensive characteristic can be steep, and the film thickness of the optical filter can be further reduced, and the optical filter can be simplified.

[0078] In addition, in any 1000 nm interval of the stop band, it is preferable that there be a wavelength region in which the difference in the transmittance is 5% or less between wavelength regions in which the difference in the transmittance is 20% or more in at least two of the plurality of optical filters. For example, it is preferable to be configured such that, in any 1000 nm interval of the stop band, there is a region in which the maximum values of the transmission spectrum do not overlap each other in at least two of the plurality of optical filters (refer to Figure 7(The region from 2000nm to 3000nm in the left figure). Here, in the common passband, when the half-width of one optical filter among multiple optical filters is set as A and the half-width of the other optical filter is set as B, the relationship 0.5 < (A / B) < 2 can be satisfied. Furthermore, with respect to A and B, the relationship 0.7 < (A / B) < 1.3 can be satisfied. In addition, the film thickness of two or more of the multiple optical filters can be (center wavelength × 1.5) or less. Furthermore, the slope of the transmission spectrum obtained by multiplying the transmission spectra of multiple optical filters can be smaller than the slope of the transmission spectrum of all individual optical filters.

[0079] (Substrate)

[0080] The substrate can be any material suitable for forming the layers of a multilayer film. Examples include silicon substrates, germanium substrates, sapphire substrates, or glass substrates, but it is not limited to these.

[0081] (Multilayer film)

[0082] A multilayer film is a film having multiple layers with different refractive indices. In this embodiment, the multilayer film includes a structure in which a first layer with a refractive index of 1.2 or higher and 2.5 or lower in the wavelength region of 6 μm to 10 μm and a second layer with a refractive index of 3.2 or higher and 4.3 or lower in the wavelength region of 6 μm to 10 μm are alternately stacked. The first layer is made of the aforementioned low refractive index material (L). The second layer is made of the aforementioned high refractive index material (H).

[0083] (First layer)

[0084] Specific materials for the first layer include titanium dioxide, zinc sulfide, silicon monoxide, and silicon dioxide.

[0085] (Second layer)

[0086] Examples of specific materials for the second layer include silicon (Si) and germanium (Ge).

[0087] (Methods for determining refractive index)

[0088] The refractive indices of the first and second layers can be determined using an ellipsometer according to "JISK7142".

[0089] Here, the sensitivity region of an infrared optical element affects the density of states and Boltzmann distribution. For example, by optimally designing the bandgap energy, it is possible to achieve an infrared optical element with high sensitivity in the inherent absorption wavelength region corresponding to the target gas and low sensitivity in other wavelength regions. The result is, for example, sensitivity in the 2000 nm–3500 nm and 4800 nm–10000 nm range (see reference). Figure 7 The blocking of ) becomes less important, which simplifies the design of optical filters.

[0090] Here, the material and the film thickness of each of the first layers laminated multiple times can be the same or different. Also, the material and the film thickness of each of the second layers laminated multiple times can be the same or different. The multilayer film can further include a layer different from the first and second layers.

[0091] Also, the total film thickness of the multilayer film is the film thickness of the sum of the cross section and the band surface. By reducing the total film thickness, the manufacturing time is shortened and the yield is improved in the manufacturing of the optical filter. The film thickness can be measured by cross section SEM observation. It is preferable that the total film thickness of each of the multilayer films of the plurality of optical filters be 14 μm or less.

[0092] (Infrared optical element)

[0093] The infrared optical element can have a structure of a first conductive type semiconductor layer, an active layer, and a second conductive type semiconductor layer. The infrared optical element is specifically an infrared light emitting diode or an infrared photodiode.

[0094] The active layer is a light absorbing layer or a light emitting layer (see Figure 8 ). In the present embodiment, the active layer is composed of Al y In 1-y Sb (0.04 ≤ y ≤ 0.14) or InAs y Sb 1-y (0.1 ≤ y ≤ 0.2). "Al y In 1-y Sb (0.04 ≤ y ≤ 0.14)" means that Al, In, and Sb are contained in the layer, but cases where other elements are contained are also included in the expression. Specifically, cases where a small amount (for example, several % or less of elements such as As, P, Ga, N, and the like) of other elements or the like is added to slightly change the composition of the layer are also included in the expression. The same is true for the expression of other compositions.

[0095] Here, the Al composition or the As composition can be found by, for example, a secondary ion mass spectrometry (SIMS) method. The measurement can use, for example, a magnetic field type SIMS device IMS7f manufactured by CAMECA Corporation.

[0096] The second conductive type is a conductive type different from the first conductive type. The first conductive type and the second conductive type can each be any one of an n-type (including an n-type impurity), an i-type (not including an impurity), and a p-type (including a p-type impurity). The first conductive type semiconductor layer can be composed of, for example, an n-type InSb (see Figure 8 ). Also, the second conductive type semiconductor layer can be composed of, for example, a p-type InSb (see Figure 8) is constituted. In the present embodiment, the first conductive type is n-type, and the second conductive type is p-type.

[0097] The first conductive type semiconductor layer, the active layer, and the second conductive type semiconductor layer can be formed on a semiconductor substrate such as a gallium arsenide (GaAs) substrate or a silicon substrate. In the present embodiment, the infrared optical element is provided with the layers in the order of the first conductive type semiconductor layer, the active layer, and the second conductive type semiconductor layer from the substrate. As another example, the infrared optical element can be provided with the layers in the order of the second conductive type semiconductor layer, the active layer, and the first conductive type semiconductor layer from the substrate.

[0098] One or more barrier layers can be provided between the first conductive type semiconductor layer and the active layer. In addition, one or more barrier layers can be provided between the active layer and the second conductive type semiconductor layer. In the present embodiment, an n-type barrier layer is provided between the first conductive type semiconductor layer and the active layer, and a p-type barrier layer is provided between the active layer and the second conductive type semiconductor layer. The n-type barrier layer is, for example, composed of n-type AlxInySb(1-x-y) (0 < x < 1, 0 < y < 1, 0 < x + y < 1). x In 1-x Sb (0.15 ≤ x ≤ 0.35) (see Figure 8 ). The p-type barrier layer is, for example, composed of p-type AlxInySb(1-x-y) (0 < x < 1, 0 < y < 1, 0 < x + y < 1). z In 1-z Sb (0.15 ≤ z ≤ 0.35) (see Figure 8 ).

[0099] The infrared optical element preferably has a ratio of the maximum sensitivity to the minimum sensitivity of 20 or more in a wavelength region of 2000 nm to 10000 nm.

[0100] (Embodiments)

[0101] Hereinafter, the effects of the present disclosure will be specifically described based on the embodiments, but the present disclosure is not limited to these embodiments.

[0102] Examples 1 to 4 and Comparative Examples 1 to 3 shown in Table 1 were evaluated. Examples 1 to 4 are optical modules of the present embodiment, and the characteristics were defined as in Table 1. Comparative Examples 1 to 3 are filter monomers that are not simplified. Figure 8 is a diagram showing the layer structure of the infrared optical element of Examples 1 to 4. The center wavelengths of the optical filters of Example 1, Example 4, and Comparative Example 1 are 4.3 μm. The center wavelengths of the optical filters of Example 2 and Comparative Example 2 are 3.4 μm. The center wavelengths of the optical filters of Example 3 and Comparative Example 3 are 8.5 μm. The optical modules of Example 1, Example 2, and Example 4 are provided with an infrared light emitting element and an infrared light receiving element. The optical module of Example 3 is provided only with an infrared light emitting element. The active layer of the infrared light emitting element of Example 1, Example 2, and Example 4 is composed of Al y In1-y Sb, y is 0.057 in Example 1, y is 0.089 in Example 2, and y is 0.057 in Example 4. The active layer of the infrared light receiving element of Example 1, Example 2, and Example 4 is composed of Al y In 1-y Sb, y is 0.048 in Example 1, y is 0.089 in Example 2, and y is 0.048 in Example 4. The active layer of the infrared light emitting element of Example 3 is composed of InAs y Sb 1-y Sb, y is 0.13.

[0103] [Table 1]

[0104]

[0105] The PIN diode structure of the infrared optical element of Examples 1 to 4 is fabricated by the MBE method. The barrier layer of n-type and p-type is provided in a manner sandwiching the active layer. The i-ray positive type photoresist is applied to the surface of the semiconductor wafer, and exposure is performed using the i-ray by a reduction projection exposure machine. Then, development is performed, and a plurality of resist patterns are regularly formed on the surface of the semiconductor layer stack. Next, a plurality of mesas are formed by dry etching treatment. After the silicon dioxide is deposited as a hard mask on the element having the mesa shape, element separation is performed by dry etching, silicon nitride (SiN) is deposited as a protective film, and a contact hole is formed by photolithography and dry etching. Then, a plurality of mesas are connected in series by photolithography and sputtering, the element surface is covered with a protective film of polyimide resin. The wafer thus fabricated is cut and singulated, Au wires are bonded and connected to a lead frame, and the wafer is sealed in a manner in which the light receiving surface is exposed using an epoxy-based molding resin. The infrared light receiving element thus fabricated has sensitivity to infrared light around λp, but other bands become a stop band in which there is almost no sensitivity.

[0106] The design of the optical filter is implemented using simulation. The optical filter of Examples 1 to 4 includes a plurality of simplified optical filters, and the required wavelength selectivity is achieved as a comprehensive characteristic. Figure 6 is a graph illustrating the transmittance of the example embodiment, and specifically represents Example 1. Figure 7The left figure shows the transmittance difference between the two optical filters in Example 1. In Example 1, two simplified optical filters were used, and the desired wavelength selectivity was obtained by multiplying the transmittance spectra of the first optical filter and the second optical filter. Similarly, Examples 2 to 4 also utilize combinations of multiple simplified optical filters to achieve the desired wavelength selectivity. The optical filters of Examples 1 to 4 contain a common passband with a transmittance of 50 nm or more and 60% or more in the wavelength region of 2000 nm to 10000 nm, and contain a wavelength region of 200 nm or more in which the transmittance difference between at least two of the multiple optical filters is 20% or more. As shown in Table 1, regarding the common passband, Example 1 has 440 nm, Example 2 has 400 nm, Example 3 has 620 nm, and Example 4 has 310 nm, all of which meet the requirement of 50 nm or more. In addition, regarding the transmittance difference of 20% or more, Example 1 has 900 nm, Example 2 has 630 nm, Example 3 has 3140 nm, and Example 4 has 3370 nm, all of which meet the requirement of 200 nm or more. Furthermore, the optical filters of Examples 1-4, in the wavelength region of 2000nm to 10000nm, include a total of 50nm or more in a wavelength region where the difference in transmittance between at least two of the multiple optical filters is 30% or more. As shown in Table 1, regarding the difference in transmittance of 30% or more, Example 1 is 620nm, Example 2 is 270nm, Example 3 is 1880nm, and Example 4 is 2450nm, all of which meet the requirement of 50nm or more. Furthermore, the optical filters of Examples 1-4, in the bands on both outer sides of the passband and closer to the common passband than the wavelength region where the difference in transmittance is 20% or more, include a total of wavelength regions with a transmittance difference of less than 20% and a transmittance of less than 60% of 1000nm or more. As shown in Table 1, Example 1 is 3240nm, Example 2 is 2920nm, Example 3 is 1460nm, and Example 4 is 1080nm, all of which are 1000nm or more. Furthermore, the optical filters in Examples 1-4 satisfy the relationship 0.5 < A / B < 2 when the half-width of one optical filter is set to A and the half-width of the other optical filter is set to B. As shown in Table 1, in Examples 1-3, the first optical filter and the second optical filter satisfy the relationship 0.5 < A / B < 2. Additionally, in Example 4, the second optical filter and the third optical filter satisfy the relationship 0.5 < A / B < 2. Figure 7 The right figure shows the sensitivity obtained by multiplying the transmission spectra of the two optical filters in Example 1 by the sensitivity spectrum of the infrared optical element. Furthermore, the stopband sensitivity is also obtained in Examples 2-4. That is, in the optical modules of Examples 1-4, when the sensitivity spectrum of the infrared optical element is multiplied by the transmission spectra of multiple optical filters, as shown in the figure... Figure 7As shown, the sensitivity to the stop band is 5% or less of the peak sensitivity.

[0107] In addition, as shown in Table 1, in Examples 1 to 4, the slope of the overall transmission spectrum is steeper than the slope of the respective transmission spectra of the plurality of optical filters. In addition, in Examples 1 to 4, the total film thickness of the multilayer films of the plurality of optical filters is each 14 μm or less. In addition, in Examples 1 to 3, it is understood from the comparison with Comparative Examples 1 to 3 that even if two optical filters are used, the total film thickness of all of the optical filters can be made thinner. In Example 4, although three optical filters are used, the total film thickness of all of the optical filters is made thinner compared with Comparative Example 1 and Example 1. That is, the Examples have the same sensitivity as the Comparative Examples, and the film thickness of the multilayer films of the plurality of optical filters is made thinner.

[0108] As described above, the optical module of the present embodiment can improve the yield of each optical filter and improve the mass productivity by using a plurality of optical filters that are simplified.

[0109] The embodiments of the present disclosure are described based on the respective drawings and examples, but it should be noted that various modifications or corrections can be easily made by those skilled in the art based on the present disclosure. Therefore, it should be noted that these modifications or corrections are included in the scope of the present disclosure.

Claims

1. An optical module, wherein the optical module comprises: a plurality of optical filters including at least a first optical filter and a second optical filter independent of the first optical filter; and an infrared optical element having a peak sensitivity in a wavelength region of 2000 nm to 10000 nm, at least one of the first optical filter and the second optical filter has: a substrate; and a multilayer film formed on at least one surface of the substrate and having a plurality of layers having different refractive indexes, the first optical filter and the second optical filter include, in the wavelength region of 2000 nm to 10000 nm, a common passband of 50 nm or more in which a transmittance is 60% or more, a wavelength region of 200 nm or more in total in which a difference in transmittance is 20% or more outside the common passband, and a wavelength region in which a difference in transmittance is less than 20% and a transmittance is less than 60% in a wavelength band closer to the common passband than a wavelength region in which a difference in transmittance is 20% or more on both sides of the common passband, in a case where a sensitivity spectrum of the infrared optical element is multiplied by transmittance spectra of the plurality of optical filters, a sensitivity of a stop band is 5% or less of the peak sensitivity.

2. The optical module according to claim 1, wherein at least one of the plurality of optical filters is directly laminated to the infrared optical element, and shares a substrate with the infrared optical element.

3. The optical module according to claim 1, wherein a filter substrate that is a substrate of at least one of the plurality of optical filters is a different kind from an optical element substrate that is a substrate of the infrared optical element, the filter substrate is joined to the optical element substrate.

4. The optical module according to any one of claims 1 to 3, wherein when a center wavelength of the passband is set as λp, a total film thickness of the multilayer film of at least one of the plurality of optical filters is (λp x 1.5) nm or less.

5. The optical module according to any one of claims 1 to 3, wherein the plurality of optical filters include a first optical filter and a second optical filter, a difference between a half-value width of the first optical filter and a half-value width of the second optical filter is 1500 nm or less.

6. The optical module according to any one of claims 1 to 3, wherein a total film thickness of the multilayer film of each of the plurality of optical filters having the multilayer film is 14 μm or less.

7. The optical module according to any one of claims 1 to 3, wherein in the wavelength region of 2000 nm to 10000 nm, a ratio of a maximum sensitivity to a minimum sensitivity of the infrared optical element is 20 or more.

8. The optical module according to any one of claims 1 to 3, wherein The plurality of optical filters includes a wavelength region in which a difference in transmittance between at least two of the plurality of optical filters is 30% or more, over a wavelength region of 2000 nm to 10000 nm, In a case where a sensitivity spectrum of the infrared optical element is multiplied by the transmittance spectrum of the plurality of optical filters, a sensitivity of a stop band is 2% or less of the peak sensitivity, over a wavelength region of 2000 nm to 10000 nm.

9. The optical module according to any one of claims 1 to 3, wherein In any 1000 nm interval of the stop band, there is a wavelength region in which a difference in transmittance is 5% or less, between wavelength regions in which a difference in transmittance between at least two of the plurality of optical filters is 20% or more.

10. The optical module according to any one of claims 1 to 3, wherein A slope of a transmittance spectrum of at least one of the plurality of optical filters is 3.3% or more.

11. The optical module according to any one of claims 1 to 3, wherein All of the plurality of optical filters are of a structure having a substrate and a multilayer film formed on at least one face of the substrate, and having a plurality of layers having different refractive indexes.

12. The optical module according to any one of claims 1 to 3, wherein In the common pass band, when a half-value width of one of the plurality of optical filters is set to A and a half-value width of the other optical filter is set to B, a relationship of 0.5 < (A / B) < 2 is satisfied.

13. The optical module according to claim 12, wherein With respect to the A and the B, a relationship of 0.7 < (A / B) < 1.3 is satisfied.

14. The optical module according to any one of claims 1 to 3, wherein A film thickness of two or more of the plurality of optical filters is (center wavelength x 1.5) or less.

15. The optical module according to any one of claims 1 to 3, wherein A slope of a transmittance spectrum obtained in a case where the transmittance spectra of the plurality of optical filters are multiplied is smaller than a slope of a transmittance spectrum of each of the optical filters alone.

Images