Optical module

Abstract

To provide an optical module capable of improving mass productivity.SOLUTION: The first optical filter and the second optical filter include 2000nm or more of a common transmission band in which a transmissivity is 60% or more in a wave range of 50nm to 10000nm, and include 200nm or more of a wave range in which a difference in transmissivity is 20% or more in total outside the common transmission band, in addition, in a band closer to the common transmission band than the wave bands in which the difference between the transmittances is 20% or more on both outer sides of the common transmission band, 1000nm or more of wave bands in which the difference between the transmittances is less than 20% and the transmittances are less than 60% are included in total, and when the responsivity spectrum of the infrared optical device and the transmission spectra of the plurality of optical filters are multiplied, the responsivity of the cutoff band is 5% or less of the peak responsivity.SELECTED DRAWING: Figure 7

Description

[Technical Field]

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

[0002] Conventionally, non-dispersive infrared absorption (NDIR) gas concentration measurement devices have been known as gas concentration measurement devices for measuring the concentration of a target gas in the atmosphere. Non-dispersive infrared absorption gas concentration measurement devices utilize the fact that different types of gas absorb different wavelengths of infrared light, and measure the gas concentration by detecting the amount of absorption. For example, a non-dispersive infrared absorption gas concentration measurement device is configured with an infrared optical element and an optical filter that transmits infrared light of a specific wavelength depending on the target gas. For example, Patent Document 1 discloses a gas sensor equipped with multiple optical filters. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] U.S. Patent No. 1,149,914 Summary of the Invention [Problem to be solved by the invention]

[0004] Here, the gas to be measured is not limited to carbon dioxide, but can be varied. The optimal combination of infrared optical elements and optical filters for each gas to be measured has not yet been explored. In particular, the specifications of optical filters have not been optimized. Furthermore, high-precision optical filters tend to have thick multilayer films. This results in reduced processability and yield, which in turn reduces the mass productivity of optical modules incorporating optical filters.

[0005] In view of the above circumstances, an object of the present disclosure is to provide an optical module that enables improved mass productivity. Here, the optical module is a module that includes an infrared optical element and an optical filter and is used in, for example, a concentration measuring device, an infrared radiation thermometer (non-contact thermometer), infrared spectroscopic imaging, a human body detection sensor, etc. The optical module is an optical component in which the infrared optical element and the optical filter are arranged and packaged while maintaining a positional relationship between them so as to obtain desired characteristics. [Means for solving the problem]

[0006] (1) An optical module according to an embodiment of the present disclosure includes: a plurality of optical filters including at least a first optical filter and a second optical filter separate from the first optical filter; and an infrared optical element having peak sensitivity in a wavelength range 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 having a plurality of layers with different refractive indexes formed on at least one surface of the substrate, the first optical filter and the second optical filter include a common transmission band of 50 nm or more in which the transmittance is 60% or more in a wavelength range of 2000 nm to 10000 nm, and include a wavelength range outside the common transmission band of 200 nm or more in total in which the difference in transmittance is 20% or more, and include a wavelength range of 1000 nm or more in total in which the difference in transmittance is less than 20% and the transmittance is less than 60% in a band closer to the common transmission band than the wavelength range where the difference in transmittance is 20% or more on both sides of the common transmission band, When the sensitivity spectrum of the infrared optical element is multiplied by the transmission spectrum of the plurality of optical filters, the sensitivity in the blocking band is 5% or less of the peak sensitivity.

[0007] (2) As an embodiment of the present disclosure, in (1), At least one of the plurality of optical filters is directly stacked on the infrared optical element and shares a substrate with the infrared optical element.

[0008] (3) As one embodiment of the present disclosure, in (1), a filter substrate that is a substrate of at least one of the plurality of optical filters is a different type from an optical element substrate that is a substrate of the infrared optical element, The filter substrate and the optical element substrate are bonded together.

[0009] (4) As an embodiment of the present disclosure, in any one of (1) to (3), At least one of the plurality of optical filters has a total thickness of the multilayer film of (λp×1.5) nm or less, where λp is the center wavelength of the transmission band.

[0010] (5) As an embodiment of the present disclosure, in any one of (1) to (4), the plurality of optical filters include a first optical filter and a second optical filter; The difference between the half width of the first optical filter and the half width of the second optical filter is 1500 nm or less.

[0011] (6) As an embodiment of the present disclosure, in any one of (1) to (5), Each of the optical filters having the multilayer film has a total film thickness of 14 μm or less.

[0012] (7) As an embodiment of the present disclosure, in any one of (1) to (6), The infrared optical element has a ratio of maximum sensitivity to minimum sensitivity of 20 or more in the wavelength range of 2000 nm to 10000 nm.

[0013] (8) As an embodiment of the present disclosure, in any one of (1) to (7), the plurality of optical filters include a wavelength range 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 the wavelength range of 2000 nm to 10000 nm; In the wavelength range of 2000 nm to 10000 nm, when the sensitivity spectrum of the infrared optical element is multiplied by the transmission spectrum of the plurality of optical filters, the sensitivity in the stop band is 2% or less of the peak sensitivity.

[0014] (9) As an embodiment of the present disclosure, in any one of (1) to (8), In any 1000 nm section of the blocking band, there is a wavelength range where the difference in transmittance is 5% or less between wavelength ranges where the difference in transmittance is 20% or more for at least two of the plurality of optical filters.

[0015] (10) As an embodiment of the present disclosure, in any one of (1) to (9), At least one of the plurality of optical filters has a transmission spectrum with a slope of 3.3% or more.

[0016] (11) As an embodiment of the present disclosure, in any one of (1) to (10), All of the optical filters have a structure including a substrate and a multilayer film having a plurality of layers with different refractive indices formed on at least one surface of the substrate.

[0017] (12) As an embodiment of the present disclosure, in any one of (1) to (11), In the common transmission band, when the half width of one of the plurality of optical filters is A and the half width of the other optical filter is B, the relationship 0.5<(A / B)<2 is satisfied.

[0018] (13) As an embodiment of the present disclosure, in (12), The relationship between A and B satisfies 0.7<(A / B)<1.3.

[0019] (14) As an embodiment of the present disclosure, in any one of (1) to (13), Two or more of the optical filters have a film thickness of (center wavelength×1.5) or less.

[0020] (15) As an embodiment of the present disclosure, in any one of (1) to (14), The slope of the transmission spectrum obtained when the transmission spectra of the plurality of optical filters are multiplied together is smaller than the slope of the transmission spectrum of each of the optical filters individually. [Effects of the Invention]

[0021] According to the present disclosure, an optical module that allows for improved mass productivity can be provided. [Brief explanation of the drawings]

[0022] [Figure 1] FIG. 1 is a diagram showing an example of a cross section of an optical filter. [Figure 2] FIG. 2 is a diagram illustrating an example of a concentration measurement device including an optical module according to an embodiment of the present disclosure. [Figure 3] FIG. 3 is a diagram illustrating a comparison between an optical filter of an optical module according to an embodiment of the present disclosure and an optical filter according to a comparative example. [Figure 4] FIG. 4 is a diagram showing the difference between an optical filter according to a comparative example and the optical filter of the present disclosure. [Figure 5] FIG. 5 is a diagram illustrating the configuration of the optical filter and the infrared optical element in the optical module. [Figure 6] FIG. 6 is a diagram illustrating the transmittance of the example. [Figure 7] FIG. 7 is a diagram illustrating the characteristics of the embodiment. [Figure 8] FIG. 8 is a diagram showing a layered structure of the infrared optical element of the example. DETAILED DESCRIPTION OF THE INVENTION

[0023] An optical module according to an embodiment of the present disclosure will now be described with reference to the drawings.

[0024] (Optical module) The optical module according to this embodiment includes 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) includes a substrate and a multilayer film having a plurality of layers with different refractive indices formed on at least one surface of the substrate. However, it is sufficient that at least one of the plurality of optical filters includes a substrate and a multilayer film. The infrared optical element is an infrared light receiving element or an infrared light emitting element, and is a collective term for both. In the following, "light receiving and emitting" refers to having at least one of the functions of receiving 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 receives and emits infrared light. In other words, the optical module according to this embodiment is an infrared module. The infrared light emitting element can be realized with the structure described below (see FIG. 8), and the infrared light receiving element can be realized with the same structure. The infrared light emitting element may specifically be a light emitting diode (LED). The infrared light receiving element may specifically be a photodiode (PD). Here, the optical module according to this embodiment includes a plurality of optical filters, but in the following description, when not describing each of the plurality of optical filters individually, they may be simply referred to as optical filters.

[0025] Hereinafter, the optical module according to this embodiment will be described as being used in a concentration measuring device. As described above, the optical module is an optical component in which an infrared optical element and an optical filter are arranged and packaged while maintaining the positional relationship between them so as to obtain desired characteristics. Furthermore, the optical module is not limited to concentration measuring devices and may be used in infrared thermometers and the like.

[0026] In this embodiment, the concentration measurement device is a gas sensor that measures the concentration of a gas to be measured. The concentration measurement device may be, for example, a non-dispersive infrared (NDIR) gas sensor that has a light receiving unit that receives infrared light that has passed through the gas. Alternatively, the concentration measurement device may be, for example, a photoacoustic gas sensor that measures the gas concentration by picking up the vibrations of gas molecules that have absorbed light as sound using a high-performance microphone.

[0027] The multiple optical filters include at least a first optical filter and a second optical filter separate from the first optical filter. The first and second optical filters include a common transmission band of 50 nm or more in a wavelength range of 2000 nm to 10,000 nm where the transmittance is 60% or more, and a wavelength range outside the common transmission band where the difference in transmittance between at least two of the multiple optical filters is 20% or more, for a total of 200 nm or more. Furthermore, the first and second optical filters include a wavelength range where the difference in transmittance is less than 20% and the transmittance is less than 60%, for a total of 1,000 nm or more, in a band closer to the common transmission band than the wavelength range where the difference in transmittance is 20% or more outside the common transmission band. Furthermore, the infrared optical element has a peak sensitivity in the wavelength range of 2000 nm to 10,000 nm, and when the sensitivity spectrum of the infrared optical element is multiplied by the transmission spectrum of the multiple optical filters, the sensitivity in the stop band is 5% or less of the peak sensitivity. Here, "multiplying" refers to multiplying the sensitivity spectrum of the infrared optical element by the transmission spectra of multiple optical filters for each wavelength. The stop band is a wavelength range for which sensitivity is not required in the design of the optical module. For example, the stop band includes a wavelength range for which at least one of the infrared light emitting element and the infrared light receiving element used together with the optical filter in the optical module has no sensitivity. The stop band also includes a wavelength range for which the optical filter has low transmittance. The low transmittance of the optical filter is not limited to a transmittance of 0% and may include, for example, a transmittance of 5% or less. On the other hand, the transmission band is a band that does not fall under the stop band and is at least a portion of the wavelength range for which at least the infrared light emitting element and the infrared receiving element have sensitivity.

[0028] The optical module according to this embodiment is capable of selectively receiving or emitting only infrared light in a desired wavelength band while using a simplified optical filter. By using a simplified optical filter, the optical module according to this embodiment can be made smaller than conventional modules that use non-simplified optical filters. Furthermore, in the optical module according to this embodiment, the optical filter is composed of multiple simplified optical filters. By configuring a filter with desired overall characteristics while sharing functions among the multiple simplified optical filters, an optical module can be provided that can improve mass productivity, as described below. However, each of the multiple simplified optical filters alone cannot achieve the desired characteristics. The optical module according to this embodiment is configured by combining multiple such simplified optical filters.

[0029] FIG. 1 shows an example of a cross section of an optical filter. In this embodiment, the optical filter is formed by alternately stacking layers of low-refractive-index materials (L) such as silicon monoxide (SiO), silicon dioxide (SiO), titanium dioxide (TiO), zinc sulfide (ZnS), or aluminum oxide (AlO) on both sides of a Si substrate, and layers of high-refractive-index materials (H) such as Si or Ge. The low-refractive-index materials (L) are preferably selected from materials with a refractive index of 1.2 to 2.5. The high-refractive-index materials (H) are preferably selected from materials with a refractive index 0.5 or more higher than that of the low-refractive-index materials (L). The alternately stacked multilayer film is formed such that the layer directly disposed on the Si substrate is the high-refractive-index material (H). However, the optical filter is not limited to the configuration shown in FIG. 1. For example, the high-refractive-index material (H) does not have to be disposed directly on the substrate.

[0030] In this embodiment, the optical filter is a mid-infrared interference bandpass filter. In general, mid-infrared interference bandpass filters have a large number of layers, which makes them prone to defects during film formation. Therefore, it is preferable to have a small number of layers in the optical filter. However, simply reducing the number of layers in the optical filter to simplify it may result in a deterioration in the accuracy of the gas sensor.

[0031] As a result of examining the optimal combination of infrared optical elements and optical filters, the inventors have realized an optical module in which accuracy does not deteriorate even when a "simplified optical filter" consisting of multiple optical filters is used, as described below.

[0032] Here, a simplified optical filter is an optical filter that does not block areas where the sensor is not sensitive, thereby reducing the number of optical thin film layers required to block those areas. In this embodiment, a comprehensively simplified optical filter is realized by further combining the transmission spectra of multiple optical filters. Therefore, the number of layers for each optical filter can be further reduced, reducing defects during film formation. For example, by reducing warpage caused by multiple layers, chipping that occurs during dicing can be suppressed, improving mass production stability. In other words, it is possible to suppress decreases in processability and yield.

[0033] Fig. 2 is a diagram showing an example of a concentration measurement device using the optical module according to this embodiment. In the optical module according to this embodiment, as shown in Fig. 2, an infrared receiving element (IR) is installed 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 the gas to be detected is installed in front of the infrared receiving element. The optical module corresponds to, for example, the portion of the infrared light emitting element and the optical filter, or a portion that further includes the infrared receiving element.

[0034] Here, the gas to be measured by the concentration measuring device is, for example, carbon dioxide (CO2), but is not limited to this. For example, the gas to be measured may be water vapor, carbon monoxide, nitric oxide, ammonia, sulfur dioxide, alcohol, formaldehyde, methane, propane, etc.

[0035] FIG. 3 is a diagram illustrating a comparison between the optical filter of the optical module according to this embodiment and an optical filter according to a comparative example. The sensor (infrared light receiving element) in the comparative example does not have wavelength selectivity (sensitivity change due to wavelength) in its spectral sensitivity. On the other hand, the sensor included in the optical module according to this embodiment (or included in a concentration measuring device using the optical module according to this embodiment) has wavelength selectivity. Therefore, in this embodiment, it is not necessary to use an optical filter to cut wavelengths for which the optical filter is insensitive, and the optical filter can be simplified. Similarly, in the case of an infrared light emitting element having wavelength selectivity in its emission intensity, it is not necessary to use an optical filter to cut wavelengths for which no light is emitted, and the optical filter can be simplified. Here, FIG. 3 shows the above-mentioned wavelengths for which no sensitivity and no light are emitted on both the wavelength side (high wavelength side) and the wavelength side (short wavelength side) longer than the peak wavelength, but this is a conceptual example. The cutoff specifications of the optical filter may be relaxed on at least one of the high wavelength side and the short wavelength side.

[0036] FIG. 4 is a diagram showing the difference between an optical filter according to a comparative example and the optical filter of the present disclosure. In the optical filter of the optical module according to this embodiment, functions are divided among multiple optical filters, making it possible to reduce the number of layers per optical filter. The optical module according to this embodiment is described below as including two or three optical filters in the examples, but the number may be four or more. In other words, the optical module includes N optical filters (see FIG. 5), where N is an integer equal to or greater than 2.

[0037] FIG. 5 is a diagram illustrating the configuration of an optical filter and an infrared optical element in an optical module. The optical filter is arranged on the optical path after the infrared optical element, which is a light-emitting element. The optical filter is also arranged on the optical path before the infrared optical element, which is a light-receiving element. The optical filter is arranged with a gap between it and another optical filter. Here, da is the distance between the infrared light-emitting element and the nearest optical filter. db is the distance between the infrared light-receiving element and the nearest optical filter. At least one of da and db may be zero. That is, at least one of the multiple optical filters may 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 multiple optical filters may be stacked directly on the infrared optical element. In this case, the directly stacked optical filter may share a substrate with the infrared optical element. Sharing a substrate enables the optical module to be miniaturized. However, sharing a substrate is not necessary when design freedom is more important than miniaturization. For example, a filter substrate, which is a substrate of at least one of the multiple optical filters, may be a different type from the optical element substrate, which is a substrate of the infrared optical element. The filter substrate and the optical element substrate may be bonded together. Furthermore, the optical module is not limited to the configuration shown in FIG. 5, and may have a configuration in which other optical members, such as lenses or mirrors, are further disposed on the optical path.

[0038] The components of the optical module according to this embodiment are described in detail below. Here, the optical module includes 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 emission intensity of the infrared light emitting element are referred to as "sensitivity." That is, sensitivity can be interpreted as light receiving sensitivity if the optical module includes an infrared light receiving element, and as light emission intensity if the optical module includes an infrared light emitting element.

[0039] (optical filter) As described above, the optical filter includes a substrate and a multilayer film formed on the substrate and having multiple layers with different refractive indices. The multilayer film may be formed on only one surface of the substrate, or on both surfaces. The optical filter is installed on an optical path in a concentration measuring device, through which infrared rays emitted from an infrared emitting element reach an infrared receiving element. The optical filter can be produced by depositing a first layer and a second layer on the substrate by vapor deposition.

[0040] The plurality of optical filters includes at least a first optical filter and a second optical filter separate from the first optical filter. The first and second optical filters include a common transmission band of 50 nm or more in a wavelength range of 2000 nm to 10,000 nm where the transmittance is 60% or more, and a wavelength range outside the common transmission band where the difference in transmittance between at least two of the plurality of optical filters is 20% or more, for a total of 200 nm or more. Furthermore, the first and second optical filters include a wavelength range of 1000 nm or more in a band closer to the common transmission band than the wavelength range where the difference in transmittance between both sides of the common transmission band is 20% or more, where the difference in transmittance is less than 20% and less than 60%. More preferably, the plurality of optical filters include a wavelength range of 50 nm or more in a wavelength range of 2000 nm to 10,000 nm where the difference in transmittance between at least two of the plurality of optical filters is 30% or more, for a total of 50 nm or more. Furthermore, the infrared optical element has a peak sensitivity in the wavelength range of 2000 nm to 10000 nm, and when the sensitivity spectrum of the infrared optical element is multiplied by the transmission spectrum of multiple optical filters, the sensitivity in the stop band is 5% or less of the peak sensitivity.Here, it is more preferable that when the sensitivity spectrum of the infrared optical element is multiplied by the transmission spectrum of multiple optical filters in the wavelength range of 2000 nm to 10000 nm, the sensitivity in the stop band is 2% or less of the peak sensitivity.

[0041] Here, transmittance varies depending on the measurement conditions. Specifically, it varies depending on the temperature and the angle of incidence of light. In this embodiment, the temperature is assumed to be 25°C. The angle of incidence of light can be, for example, 0°, 10°, 20°, 30°, 40°, 45°, etc., depending on the design of the concentration measurement device, and it is sufficient that the above characteristics are satisfied at any angle of incidence. For example, the optical filter only needs to satisfy the above characteristics at at least one of the angles of incidence that can be set in the design (e.g., 30°). Here, it is more preferable that the optical filter satisfy the above characteristics at all angles of incidence that can be set in the design.

[0042] At least one of the optical filters preferably has a total multilayer film thickness of (λp × 1.5) nm or less, where λp is the central wavelength of the transmission band. Here, the central wavelength is a wavelength in the wavelength range of 2000 nm to 10000 nm, which is the center of the half-width of the transmission band having the maximum transmittance. The half-width is the wavelength range where the transmittance is half of the maximum transmittance (i.e., the difference between the maximum wavelength and the minimum wavelength).

[0043] The multiple optical filters may include a first optical filter and a second optical filter, and the difference between the half-width of the first optical filter and the half-width of the second optical filter may be 1500 nm or less. Regarding the wavelength-dependent change in transmittance of the multiple optical filters (transmission spectrum, see FIG. 6), the transmission spectrum as an overall characteristic can be sharpened if the following relationship exists between the slopes around the center wavelength: First, the slope is determined by dividing Δλ1, which is the wavelength width (bandwidth) from the 10% transmittance point (transmission point) to the 80% transmittance point, by λp, which is the center wavelength (Δλ1 / λp). Alternatively, the slope can be determined by Δλ2, which is the wavelength width from the 80% transmittance point to the 10% transmittance point, as (Δλ2 / λp). As shown in Table 1 below, (Δλ1 / λp) and (Δλ2 / λp) may be calculated, and the larger of the two values ​​may be determined as the slope of the transmission spectrum. If the slope of the transmission spectrum of at least one of the multiple optical filters is 3.3% or more, the film thickness of the optical filter can be reduced while the transmission spectrum as an overall characteristic is sharp.If the slope of the transmission spectrum of at least one of the multiple optical filters is 4.2% or more, the film thickness of the optical filter can be further reduced while the transmission spectrum as an overall characteristic is sharp, and the optical filter can be simplified.

[0044] Furthermore, in any 1000-nm section of the stop band, it is preferable that there be a wavelength range where the difference in transmittance between at least two of the multiple optical filters is 20% or more, and there be a wavelength range where the difference in transmittance is 5% or less. For example, it is preferable that there be a region where the maximum values ​​of the transmission spectra of at least two of the multiple optical filters do not overlap in any 1000-nm section of the stop band (see the region from 2000 nm to 3000 nm in the left diagram of FIG. 7). Here, in the common transmission band, when the half-width of one of the multiple optical filters is A and the half-width of the other optical filter is B, the relationship 0.5<(A / B)<2 may be satisfied. Furthermore, the relationship 0.7<(A / B)<1.3 may be satisfied for A and B. Furthermore, the film thickness of two or more of the multiple optical filters may be (center wavelength × 1.5) or less. Furthermore, the slope of the transmission spectrum obtained by multiplying the transmission spectra of the multiple optical filters may be smaller than the slope of the transmission spectra of all the optical filters individually.

[0045] (substrate) The substrate may be any suitable substrate as long as it is suitable for forming each layer constituting the multilayer film, and examples thereof include, but are not limited to, a silicon substrate, a germanium substrate, a sapphire substrate, or a glass substrate.

[0046] (Multilayer film) The multilayer film is a film having multiple layers with different refractive indices. In this embodiment, the multilayer film has a structure in which first layers having a refractive index of 1.2 or more and 2.5 or less in the wavelength range of 6 μm to 10 μm and second layers having a refractive index of 3.2 or more and 4.3 or less in the wavelength range of 6 μm to 10 μm are alternately stacked. The first layers are made of the low refractive index material (L) described above. The second layers are made of the high refractive index material (H) described above.

[0047] (1st layer) Specific materials for the first layer include titanium dioxide, zinc sulfide, silicon monoxide, silicon dioxide, and the like.

[0048] (2nd layer) Specific examples of the material for the second layer include silicon (Si) and germanium (Ge).

[0049] (Method for measuring refractive index) The refractive index of the first layer and the second layer can be measured by an ellipsometer in accordance with "JIS K7142".

[0050] The sensitivity range of an infrared optical element affects the density of states and the Boltzmann distribution. For example, by optimizing the band gap energy, it is possible to realize an infrared optical element that has high sensitivity in a specific absorption wavelength range corresponding to the target gas and low sensitivity in other wavelength ranges. As a result, for example, the cutoff wavelengths of 2000 nm to 3500 nm and 4800 nm to 10000 nm (see Figure 7) become less important, which simplifies the optical filter design.

[0051] Here, the materials and thicknesses of the first layers may be the same or different, and the materials and thicknesses of the second layers may be the same or different. The multilayer film may further include a layer different from the first and second layers.

[0052] The total thickness of the multilayer film is the sum of the thicknesses of the cut surface and the bandpass surface. By reducing the total thickness, the manufacturing time is shortened and the yield is improved in the manufacture of optical filters. The film thickness can be measured by cross-sectional SEM observation. It is preferable that each of the multiple optical filters has a total multilayer film thickness of 14 μm or less.

[0053] (infrared optical element) The infrared optical element may have a configuration including a first conductivity type semiconductor layer, an active layer, and a second conductivity type semiconductor layer. Specifically, the infrared optical element is an infrared light emitting diode or an infrared photodiode.

[0054] The active layer is a light absorbing layer or a light emitting layer (see FIG. 8). In this embodiment, the active layer is Al y In 1-ySb(0.04≦y≦0.14) or InAs y Sb 1-y (0.1≦y≦0.2) y In 1-y "Sb (0.04≦y≦0.14)" means that the layer contains Al, In, and Sb, but this expression also includes cases where other elements are contained. Specifically, this expression also includes cases where the composition of this layer is slightly changed by adding small amounts of other elements (for example, elements such as As, P, Ga, N, etc., in amounts of a few percent or less). This also applies to expressions of other compositions.

[0055] The Al composition or As composition can be determined by, for example, secondary ion mass spectrometry (SIMS), using, for example, a magnetic field type SIMS device IMS 7f manufactured by CAMECA Corporation.

[0056] The second conductivity type is a conductivity type different from the first conductivity type. The first conductivity type and the second conductivity type may each be any of n-type (containing n-type impurities), i-type (containing no impurities), and p-type (containing p-type impurities). The first conductivity type semiconductor layer may be made of, for example, n-type InSb (see FIG. 8). The second conductivity type semiconductor layer may be made of, for example, p-type InSb (see FIG. 8). In this embodiment, the first conductivity type is n-type, and the second conductivity type is p-type.

[0057] The first conductivity type semiconductor layer, the active layer, and the second conductivity type semiconductor layer may be formed on a semiconductor substrate such as a gallium arsenide (GaAs) substrate or a silicon substrate. In this embodiment, the infrared optical element is provided with the first conductivity type semiconductor layer, the active layer, and the second conductivity type semiconductor layer in this order from the substrate. As another example, the infrared optical element may be provided with the second conductivity type semiconductor layer, the active layer, and the first conductivity type semiconductor layer in this order from the substrate.

[0058] One or more barrier layers may be provided between the first conductivity type semiconductor layer and the active layer. Also, one or more barrier layers may be provided between the active layer and the second conductivity type semiconductor layer. In this embodiment, an n-type barrier layer is provided between the first conductivity type semiconductor layer and the active layer, and a p-type barrier layer is provided between the active layer and the second conductivity type semiconductor layer. The n-type barrier layer is, for example, n-type Al x In 1-x The p-type barrier layer is made of Sb (0.15≦x≦0.35) (see Figure 8). z In 1-z It is composed of Sb (0.15≦z≦0.35) (see Figure 8).

[0059] The infrared optical element preferably has a ratio of maximum sensitivity to minimum sensitivity of 20 or more in the wavelength range of 2000 nm to 10000 nm.

[0060] (Example) The effects of the present disclosure will be specifically described below based on examples, but the present disclosure is not limited to these examples.

[0061] Evaluations were carried out for Examples 1 to 4 and Comparative Examples 1 to 3 shown in Table 1. Examples 1 to 4 are optical modules of this embodiment, and the characteristics are defined as shown in Table 1. Comparative Examples 1 to 3 are single filters that are not simplified. FIG. 8 is a diagram showing the layered structure of the infrared optical elements of Examples 1 to 4. The central wavelength of the optical filters of Examples 1, 4, and Comparative Example 1 is 4.3 μm. The central wavelength of the optical filters of Example 2 and Comparative Example 2 is 3.4 μm. The central wavelength of the optical filters of Example 3 and Comparative Example 3 is 8.5 μm. The optical modules of Examples 1, 2, and 4 include an infrared light emitting element and an infrared light receiving element. The optical module of Example 3 includes only an infrared light emitting element. The active layers of the infrared light emitting elements of Examples 1, 2, and 4 are Al y In 1-y The active layer of the infrared receiving element of Example 1, Example 2 and Example 4 is made of Sb, and y is 0.057 in Example 1, 0.089 in Example 2 and 0.057 in Example 4. yIn 1-y The active layer of the infrared light emitting device of Example 3 is made of InAs, and y is 0.048 in Example 1, 0.089 in Example 2, and 0.048 in Example 4. y Sb 1-y and y is 0.13.

[0062] [Table 1]

[0063] The PIN diode structure of the infrared optical element of Examples 1 to 4 was fabricated by MBE. N-type and p-type barrier layers were provided on either side of the active layer. A positive i-line photoresist was applied to the surface of the semiconductor wafer, and exposure was performed using i-line light using a reduced projection exposure machine. Development was then performed, and multiple regular resist patterns were formed on the surface of the semiconductor laminate. Next, multiple mesas were formed by dry etching. A silicon dioxide film was formed as a hard mask on the mesa-shaped element, followed by element isolation using dry etching. A silicon nitride (SiN) film was formed as a protective film, and contact holes were formed by photolithography and dry etching. Subsequently, multiple mesas were connected in series using photolithography and sputtering, and the element surface was covered with a polyimide resin protective film. The wafer fabricated in this way was diced into individual pieces, and Au wires were bonded to lead frames, and the pieces were sealed with an epoxy-based molding resin so that the light-receiving surface was exposed. The infrared receiving element thus fabricated has sensitivity to infrared rays in the vicinity of λp, but has almost no sensitivity to other bands, which are cutoff bands.

[0064] The optical filters were designed using simulations. The optical filters of Examples 1 to 4 are composed of multiple simplified optical filters, achieving the desired wavelength selectivity as a comprehensive characteristic. FIG. 6 is a diagram illustrating the transmittance of the examples, specifically Example 1. The left diagram of FIG. 7 shows the difference in transmittance between two optical filters for Example 1. Example 1 uses two simplified optical filters, and the desired wavelength selectivity is achieved by multiplying the transmission spectrum of the first optical filter by the transmission spectrum of the second optical filter. Similarly, Examples 2 to 4 achieve the desired wavelength selectivity by combining multiple simplified optical filters. The optical filters of Examples 1 to 4 include a common transmission band of 50 nm or more in which the transmittance is 60% or more in the wavelength range of 2000 nm to 10,000 nm, and include a wavelength range of 200 nm or more in which the difference in transmittance between at least two of the multiple optical filters is 20% or more. As shown in Table 1, the common transmission band is 440 nm for Example 1, 400 nm for Example 2, 620 nm for Example 3, and 310 nm for Example 4, all of which correspond to 50 nm or more. Furthermore, the difference in transmittance of 20% or more is 900 nm for Example 1, 630 nm for Example 2, 3140 nm for Example 3, and 3370 nm for Example 4, all of which correspond to 200 nm or more. Furthermore, the optical filters of Examples 1 to 4 include wavelength ranges in the wavelength range of 2000 nm to 10,000 nm where the difference in transmittance between at least two of the multiple optical filters is 30% or more, totaling 50 nm or more. As shown in Table 1, the difference in transmittance of 30% or more is 620 nm for Example 1, 270 nm for Example 2, 1880 nm for Example 3, and 2450 nm for Example 4, all of which correspond to 50 nm or more. Furthermore, the optical filters of Examples 1 to 4 include a total of wavelength ranges of 1000 nm or more where the difference in transmittance is less than 20% and the transmittance is less than 60% in bands on both sides of the transmission band and closer to the common transmission band than the wavelength range where the difference in transmittance is 20% or more. As shown in Table 1, Example 1 has a wavelength range of 3240 nm, Example 2 has a wavelength range of 2920 nm, Example 3 has a wavelength range of 1460 nm, and Example 4 has a wavelength range of 1080 nm, all of which fall within the range of 1000 nm or more.Furthermore, in the optical filters of Examples 1 to 4, when the half width of one optical filter is A and the half width of the other optical filter is B, the half width of the other optical filter is 0.5

[0065] Furthermore, as shown in Table 1, in Examples 1 to 4, the slope of the overall transmission spectrum is sharper than the slope of the transmission spectrum of each of the multiple optical filters. Furthermore, in Examples 1 to 4, the total thickness of the multilayer film of each of the multiple optical filters is 14 μm or less. Furthermore, as is clear from comparison with Comparative Examples 1 to 3, in Examples 1 to 3, even though two optical filters are used, the total total thickness of all the optical filters can be made thinner. In Example 4, even though three optical filters are used, the total total thickness of all the optical filters is thinner than in Comparative Example 1 and Example 1. In other words, the Examples have sensitivity equivalent to that of the Comparative Examples, but the thickness of the multilayer film of the multiple optical filters is thinner.

[0066] As described above, the optical module according to this embodiment uses a plurality of simplified optical filters, thereby increasing the yield of each optical filter and enabling improvement in mass productivity.

[0067] Although the embodiments of the present disclosure have been described based on the drawings and examples, it should be noted that those skilled in the art can easily make various modifications or alterations based on the present disclosure, and therefore, it should be noted that these modifications and alterations are included within the scope of the present disclosure.​

Claims

1. a plurality of optical filters including at least a first optical filter and a second optical filter separate from the first optical filter; and an infrared optical element having peak sensitivity in a wavelength range 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 having a plurality of layers with different refractive indexes formed on at least one surface of the substrate, the first optical filter and the second optical filter include a common transmission band of 50 nm or more in which the transmittance is 60% or more in a wavelength range of 2000 nm to 10000 nm, and include a wavelength range outside the common transmission band of 200 nm or more in total in which the difference in transmittance is 20% or more, and include a wavelength range of 1000 nm or more in total in which the difference in transmittance is less than 20% and the transmittance is less than 60% in a band closer to the common transmission band than the wavelength range where the difference in transmittance is 20% or more on both sides of the common transmission band, An optical module in which, when the sensitivity spectrum of the infrared optical element is multiplied by the transmission spectrum of the plurality of optical filters, the sensitivity in the 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 stacked on the infrared optical element and shares a substrate with the infrared optical element.

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

4. 4. The optical module according to claim 1, wherein at least one of the plurality of optical filters has a total thickness of the multilayer film of (λp × 1.5) nm or less, where λp is the center wavelength of the transmission band.

5. the plurality of optical filters include a first optical filter and a second optical filter; 4. The optical module according to claim 1, wherein a difference between a half width of the first optical filter and a half width of the second optical filter is 1500 nm or less.

6. 4. The optical module according to claim 1, wherein each of the plurality of optical filters having the multilayer film has a total film thickness of 14 [mu]m or less.

7. 4. The optical module according to claim 1, wherein the infrared optical element has a ratio of maximum sensitivity to minimum sensitivity of 20 or more in a wavelength range of 2000 nm to 10000 nm.

8. the plurality of optical filters include wavelength ranges in which the difference in transmittance between at least two of the plurality of optical filters is 30% or more, the wavelength range being 50 nm or more in total, in a wavelength range of 2000 nm to 10000 nm; 4. An optical module according to claim 1, wherein when the sensitivity spectrum of the infrared optical element is multiplied by the transmission spectrum of the plurality of optical filters in the wavelength range of 2000 nm to 10000 nm, the sensitivity of the stop band is 2% or less of the peak sensitivity.

9. 4. The optical module according to claim 1, wherein, in any 1000 nm section of the blocking band, there is a wavelength range in which the difference in transmittance is 5% or less between wavelength ranges in which the difference in transmittance is 20% or more for at least two of the plurality of optical filters.

10. 4. The optical module according to claim 1, wherein a slope of the transmission spectrum of at least one of the plurality of optical filters is 3.3% or more.

11. 4. The optical module according to claim 1, wherein all of the plurality of optical filters have a configuration including a substrate and a multilayer film having a plurality of layers with different refractive indices formed on at least one surface of the substrate.

12. 4. The optical module according to claim 1, wherein, in the common transmission band, when a half-value width of one of the plurality of optical filters is A and a half-value width of the other of the plurality of optical filters is B, a relationship of 0.5<(A / B)<2 is satisfied.

13. The optical module according to claim 12 , wherein A and B satisfy the relationship 0.7<(A / B)<1.

3.

14. 4. The optical module according to claim 1, wherein the thickness of two or more of the plurality of optical filters is equal to or less than (center wavelength x 1.5).

15. 4. The optical module according to claim 1, wherein a slope of a transmission spectrum obtained by multiplying the transmission spectra of the plurality of optical filters is smaller than a slope of a transmission spectrum of each of the optical filters individually.

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