Optical module

Abstract

This invention provides an optical module that improves mass production capabilities. The optical module comprises multiple optical filters and infrared optical elements. The first and second optical filters contain a common passband with a transmittance of 60% or more and a wavelength of 50 nm or more in the 2000 nm to 10000 nm wavelength range. Outside this common passband, there are wavelength regions with a transmittance difference of 20% or more totaling 200 nm. Furthermore, in the bands closer to the common passband than the wavelength regions with a transmittance difference of 20% or more, on both outer sides of the common passband, there are wavelength regions with a transmittance difference of less than 20% and a transmittance of less than 60% and a wavelength of less than 1000 nm in total. When the sensitivity spectrum of the infrared optical element is multiplied by the transmission spectra of the multiple optical filters, the stopband sensitivity is less than 5% of the peak sensitivity.

Description

Technical Field

[0001] This disclosure relates to optical modules. Background Technology

[0002] Conventionally, non-dispersive infrared (NDIR) gas concentration measuring devices are known for measuring the concentration of a target gas in the atmosphere. NDIR gas concentration measuring devices utilize the different wavelengths of infrared light absorbed by the gas type to measure its concentration by detecting the amount of absorption. For example, an NDIR gas concentration measuring device is configured with an infrared optical element and an optical filter that transmits infrared light of a specific wavelength according to the target gas. For example, Patent Document 1 discloses a gas sensor equipped with multiple optical filters.

[0003] Existing technical documents

[0004] Patent documents

[0005] Patent Document 1: US Patent No. 11499914 Utility Model Content

[0006] The problem to be solved by the utility model

[0007] Here, the target gas is not limited to carbon dioxide, but can be a variety of gases. Currently, the optimal combination of infrared optical elements and optical filters has not been studied for each target gas. In particular, the specifications of the optical filters have not been optimized. Furthermore, high-precision optical filters tend to have thicker multilayer films. As a result, processability and yield decrease, leading to reduced mass production of optical modules containing optical filters.

[0008] The purpose of this disclosure, made in view of the above, is to provide an optical module that improves mass production capabilities. Here, the optical module includes infrared optical elements and optical filters, and is used, for example, in concentration measuring devices, infrared radiation thermometers (non-contact thermometers), infrared spectrophotometers, human body detection sensors, and the like. The optical module is an optical component that arranges and packages the infrared optical elements and optical filters in a positional relationship to obtain desired characteristics.

[0009] Methods for solving problems

[0010] (1) An optical module according to 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 peak sensitivity in the wavelength region of 2000nm to 10000nm.

[0011] At least one of the first optical filter and the second optical filter comprises: a substrate; and a multilayer film formed on at least one surface of the substrate, having multiple layers with different refractive indices.

[0012] The first optical filter and the second optical filter, in the wavelength region of 2000nm to 10000nm, include a common passband with a transmittance of 60% or more at a wavelength of 50nm or more. Outside the common passband, there are wavelength regions with a transmittance difference of 20% or more totaling 200nm or more. Furthermore, in the two outer bands of the common passband that are closer to the common passband than the wavelength regions with a transmittance difference of 20% or more, there are wavelength regions with a transmittance difference of less than 20% and a transmittance of less than 60% totaling 1000nm or more.

[0013] When the sensitivity spectrum of the infrared optical element is multiplied by the transmission spectrum of the plurality of optical filters, the stopband sensitivity is less than 5% of the peak sensitivity.

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

[0015] 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.

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

[0017] The filter substrate, which serves as the substrate for at least one of the plurality of optical filters, is a different type from the optical element substrate, which serves as the substrate for the infrared optical element.

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

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

[0020] When the center wavelength of the passband is set to λp, the total thickness of the multilayer film of at least one of the plurality of optical filters is less than (λp×1.5) nm.

[0021] (5) As one embodiment of this 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-width of the first optical filter and the half-width of the second optical filter is less than 1500 nm.

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

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

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

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

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

[0029] The plurality of optical filters include a wavelength region totaling more than 50 nm in the 2000 nm to 10000 nm range, where the difference in transmittance between at least two of the plurality of optical filters is more than 30%.

[0030] In the wavelength region of 2000nm to 10000nm, when the sensitivity spectrum of the infrared optical element is multiplied by the transmission spectrum of the plurality of optical filters, the stopband sensitivity is less than 2% of the peak sensitivity.

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

[0032] Within any 1000nm range of the stopband, between wavelength regions where the transmittance difference between at least two of the plurality of optical filters is greater than 20%, there exists a wavelength region where the transmittance difference is less than 5%.

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

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

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

[0036] All of the optical filters have a structure with a substrate and a multilayer film. The multilayer film is formed on at least one surface of the substrate and has multiple layers with different refractive indices.

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

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

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

[0040] Regarding A and B, the relationship 0.7 < (A / B) < 1.3 is satisfied.

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

[0042] The film thickness of two or more of the plurality of optical filters is less than (center wavelength × 1.5).

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

[0044] The slope of the transmission spectrum obtained by multiplying the transmission spectra of the plurality of optical filters is smaller than the slope of the transmission spectrum of all individual optical filters.

[0045] Utility Model Effect

[0046] According to this disclosure, an optical module that can improve mass production capability can be provided. Attached Figure Description

[0047] Figure 1 This is a diagram showing an example of the cross-section of an optical filter.

[0048] Figure 2 This is a diagram illustrating an example of a concentration measuring device equipped with an optical module according to an embodiment of the present disclosure.

[0049] Figure 3 The figure illustrates a comparison between the optical filter of an optical module according to one embodiment of the present disclosure and an optical filter based on a comparative example.

[0050] Figure 4 This is a graph showing the differences between the optical filter based on the comparative example and the optical filter of this disclosure.

[0051] Figure 5 This is a diagram used to illustrate the structure of optical filters and infrared optical elements in an optical module.

[0052] Figure 6 This is a graph showing the transmittance of an exemplary embodiment.

[0053] Figure 7 This is a diagram illustrating the characteristics of an exemplary embodiment.

[0054] Figure 8 This is a diagram illustrating the stacked structure of the infrared optical element in an embodiment. Detailed Implementation

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

[0056] (Optical module)

[0057] The optical module of this embodiment includes multiple optical filters and infrared optical elements. In this embodiment, each of the multiple optical filters (i.e., all the optical filters) has a structure having a substrate and a multilayer film, which is formed on at least one surface of the substrate and has multiple layers with different refractive indices. However, it is acceptable as long as at least one of the multiple optical filters has a structure having a substrate and a multilayer film. The infrared optical element is a collective term for either an infrared light-receiving element or an infrared light-emitting element. Furthermore, hereinafter, "light-receiving" means having at least one of the functions of light-receiving and light-emitting. The infrared optical element is configured, for example, to include a first conductive semiconductor layer, an active layer, and a second conductive semiconductor layer, and performs infrared light-receiving and light-emitting. That is, the optical module of this embodiment is an infrared module. The structure described below (refer to...) Figure 8 This embodiment implements an infrared light-emitting element, and also implements an infrared light-receiving element using the same structure. Specifically, the infrared light-emitting element can be a light-emitting diode (LED). Additionally, the infrared light-receiving element can be a photodiode (PD). Here, the optical module of this embodiment includes multiple optical filters; however, hereinafter, unless otherwise described, they will sometimes be referred to simply as optical filters.

[0058] The following description explains the application of the optical module of this embodiment in a concentration measuring device. As described above, the optical module is an optical component that is configured and packaged to obtain desired characteristics and maintain the positional relationship between infrared optical elements and optical filters. Furthermore, the optical module is not limited to concentration measuring devices and can also be used in infrared radiation thermometers, etc.

[0059] In this embodiment, the concentration measuring device is a gas sensor that measures the concentration of the target gas. For example, the concentration measuring device may be a non-dispersive infrared absorption (NDIR) gas sensor with a light-receiving section that receives infrared light transmitted through the gas. Alternatively, the concentration measuring device may be a photoacoustic gas sensor that measures gas concentration by using a high-performance microphone to pick up the vibrations of light-absorbing gas molecules as sound.

[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 detailed later. The first and second optical filters, in the wavelength region of 2000 nm to 10000 nm, include a common passband with a transmittance of 60% or more at least 50 nm, and outside the common passband, include a wavelength region totaling 200 nm or more in which the transmittance difference among at least two of the plurality of optical filters is 20% or more. Furthermore, in the bands closer to the common passband than the wavelength region with a transmittance difference of 20% or more on both sides of the common passband, the first and second optical filters include wavelength regions totaling 1000 nm or more in which the transmittance difference is less than 20% and the transmittance is less than 60%. Additionally, 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 transmission spectra of the plurality of optical filters, the stopband sensitivity is less than 5% of the peak sensitivity. In other words, when the sensitivity spectrum of the infrared optical element is multiplied by the transmission spectra of multiple optical filters, the sensitivity of the stopband is less than 5% of the peak sensitivity. Here, multiplication means multiplying the sensitivity spectrum of the infrared optical element and the transmission spectra of the multiple optical filters by each identical wavelength. Furthermore, the stopband is a wavelength region where sensitivity is not required in the design of the optical module. For example, the stopband includes at least one wavelength region in which the infrared emitting element and the infrared receiving element used with the optical filters in the optical module lack sensitivity. Additionally, the stopband may include, for example, a wavelength region with low transmittance of the optical filters. Low transmittance of the optical filters is not limited to 0% transmittance; for example, it may include a transmittance of less than 5%. On the other hand, the passband is a band that is not part of the stopband and is at least a portion of the wavelength region in which at least the infrared emitting element and the infrared receiving element have sensitivity.

[0061] According to the optical module of this embodiment, even using a simplified optical filter, it is possible to selectively receive only infrared light or emitted light in the desired wavelength band. By using a simplified optical filter, the optical module of this embodiment can be miniaturized compared to conventional modules using unsimplified optical filters. Furthermore, in the optical module of this embodiment, the optical filter is composed of multiple simplified optical filters. By distributing the function among multiple simplified optical filters and comprehensively constructing a filter with the desired characteristics, as explained below, an optical module with improved mass production capabilities can be provided. Here, each of the multiple simplified optical filters cannot individually achieve the desired characteristics. The optical module of this embodiment is constructed by combining such multiple simplified optical filters.

[0062] Figure 1 This is an example of a cross-section of an optical filter. In this embodiment, the optical filter consists of alternating layers on both sides of a Si substrate, comprising layers made of a low-refractive-index material (L) such as silicon monoxide (SiO), silicon dioxide (SiO2), titanium dioxide (TiO2), zinc sulfide (ZnS), or aluminum oxide (Al2O3), and layers made of a high-refractive-index material (H) such as Si or Ge. As the low-refractive-index material (L), a material with a refractive index of 1.2 to 2.5 is preferably selected. Furthermore, as the high-refractive-index material (H), a material with a refractive index 0.5 or more greater than that of the low-refractive-index material (L) is preferably selected. The alternatingly stacked multilayer films are formed such that the layer directly disposed on the Si substrate is a high-refractive-index material (H). However, the optical filter is not limited to this type of filter. Figure 1 The structure can also be modified so that the high refractive index material (H) is not directly placed on the substrate.

[0063] In this embodiment, the optical filter is an interferometric bandpass filter in the mid-infrared region. Typically, mid-infrared interferometric bandpass filters have a high number of layers, which can easily increase defects during film deposition. Therefore, it is preferable that the optical filter has a low number of layers. However, if simplification is achieved simply by reducing the number of layers in the optical filter, the accuracy of the gas sensor may deteriorate.

[0064] As a result of research into the optimal combination of infrared optical elements and filters, as described below, the inventors of this application have achieved an optical module whose accuracy is not degraded even when using a “simplified filter” consisting of multiple filters.

[0065] Here, the simplified optical filter refers to an optical filter that reduces the number of optical film layers required to block areas without sensor sensitivity. In this embodiment, a comprehensively simplified optical filter is further achieved by multiplying 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, the generation of breakage during cutting can be suppressed, improving mass production stability. That is, it is possible to suppress the reduction in processability and yield.

[0066] Figure 2 This diagram illustrates an example of a concentration measuring device using the optical module of this embodiment. In the optical module of this embodiment, as... Figure 2 As shown, an infrared light-receiving element (IR) is provided in the optical path of infrared light emitted from the infrared light-emitting element (light source), and an optical filter is provided before the infrared light-receiving element to selectively transmit the absorption wavelength of the gas being detected. The optical module corresponds, for example, to the portion containing the infrared light-emitting element and the optical filter, or to the portion that also includes the infrared light-receiving element.

[0067] Here, the target gas measured by the concentration measuring device is, for example, carbon dioxide (CO2), but it is not limited to this. For example, the target gas can be water vapor, carbon monoxide, nitric oxide, ammonia, sulfur dioxide, alcohol, formaldehyde, methane, propane, etc.

[0068] Figure 3 This diagram compares and explains the optical filter of the optical module of this embodiment with the optical filter of the comparative example. In the sensor (infrared light-receiving element) of the comparative example, the spectral sensitivity lacks wavelength selectivity (sensitivity change based on wavelength). On the other hand, the sensor provided with the optical module of this embodiment (or the sensor provided with the concentration measuring device using the optical module of this embodiment) has wavelength selectivity. Therefore, in this embodiment, the optical filter does not need to cut off wavelengths with no sensitivity, simplifying the optical filter. Similarly, in the case of an infrared light-emitting element with wavelength selectivity in emission intensity, the optical filter does not need to cut off non-emitting wavelengths, simplifying the optical filter. Here, in Figure 3 The above-mentioned wavelengths with no sensitivity and non-emitting wavelengths are shown on both the side longer than the peak wavelength (high wavelength side) and the side shorter than the peak wavelength (short wavelength side), but this is only an example as a concept. The cutoff specification of the mildened optical filter can be applied to at least one of the high wavelength side and the short wavelength side.

[0069] Figure 4This is a diagram showing the differences between the optical filter of the comparative example and the optical filter of this disclosure. In the optical filter of the optical module of this embodiment, the function can be divided using multiple optical filters, reducing the number of layers for each optical filter. The multiple optical filters included in the optical module of this embodiment are described below as two or three as examples, but may also be four or more. That is, the optical module has N optical filters (refer to...). Figure 5 N can be any integer greater than 2.

[0070] Figure 5 This diagram illustrates the structure of optical filters and infrared optical elements in an optical module. The optical filters are positioned in the optical path after the infrared optical element, which serves as a light-emitting element. Additionally, the optical filters are positioned in the optical path before the infrared optical element, which serves as a light-receiving element. The optical filters are arranged with gaps between them and other optical filters. Here, da is the distance between the infrared light-emitting element and the nearest optical filter. Furthermore, 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 multiple 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 multiple optical filters can be directly stacked on the infrared optical element. In this case, the directly stacked optical filters can share a substrate with the infrared optical element. By sharing the substrate, miniaturization of the optical module can be achieved. However, in cases where design freedom is more important than miniaturization, the substrate may not be shared. For example, the filter substrate, which serves as the substrate of at least one of the multiple optical filters, can be a different type of optical element substrate than the substrate of the infrared optical element. Furthermore, it can be a structure where the filter substrate and the optical element substrate are joined together. Additionally, the optical module is not limited to... Figure 5 The structure shown can also be a structure in which other optical components such as lenses or mirrors are arranged in the optical path.

[0071] The following describes in detail the constituent elements of the optical module according to this embodiment. 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 luminous intensity of the infrared light-emitting element are referred to as "sensitivity". That is, if the optical module has a structure with an infrared light-receiving element, the sensitivity can be replaced by the light-receiving sensitivity; if the optical module has a structure with an infrared light-emitting element, the sensitivity can be replaced by the luminous intensity.

[0072] (Optical filter)

[0073] As described above, the optical filter comprises a substrate and a multilayer film formed on the substrate, having multiple layers with different refractive indices. The multilayer film may be formed on only one side of the substrate or on both sides. In a concentration measuring device, the optical filter is positioned in the optical path from the infrared light emitted by the infrared emitting element to the infrared light receiving element. The optical filter can be fabricated by forming a first layer and a second layer on the substrate using 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. In the wavelength region of 2000 nm to 10000 nm, the first and second optical filters include a common passband with a transmittance of 60% or more of 50 nm or more, and outside the common passband, they include a wavelength region totaling 200 nm or more in which the transmittance difference among at least two of the plurality of optical filters is 20% or more. Furthermore, in the wavelength bands closer to the common passband than the wavelength region with a transmittance difference of 20% or more, both outside the common passband, the first and second optical filters include a wavelength region totaling 1000 nm or more in which the transmittance difference is less than 20% and the transmittance is less than 60%. More preferably, the plurality of optical filters include a wavelength region in the wavelength region of 2000 nm to 10000 nm in which the transmittance difference among at least two of the plurality of optical filters is 30% or more of 50 nm or more. Furthermore, in the wavelength region of 2000 nm to 10000 nm, the infrared optical element exhibits peak sensitivity, and when the sensitivity spectrum of the infrared optical element is multiplied by the transmission spectra of multiple optical filters, the stopband sensitivity is less than 5% of the peak sensitivity. Here, in the wavelength region of 2000 nm to 10000 nm, when the sensitivity spectrum of the infrared optical element is multiplied by the transmission spectra of multiple optical filters, it is more preferable that the stopband sensitivity is less than 2% of the peak sensitivity.

[0075] Here, the 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 25°C. Furthermore, depending on the design of the concentration measuring device, the angle of incidence of light can be, for example, 0°, 10°, 20°, 30°, 40°, 45°, etc., but it is acceptable as long as the aforementioned characteristics are satisfied at any given angle of incidence. For example, an optical filter only needs to satisfy the above characteristics with at least one of the angles of incidence that can be set in the design (30° as an example). Here, it is further preferable that the optical filter satisfies the above characteristics with all the angles of incidence that can be set in the design.

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

[0077] Multiple optical filters may include a first optical filter and a second optical filter, wherein the difference between the half-width at half-maximum (WWHM) of the first optical filter and the WWHM of the second optical filter is less than 1500 nm. Here, the wavelength-dependent variation of the transmittance of the multiple optical filters (transmission spectrum, see reference) is discussed. Figure 6 When the slopes before and after the center wavelength exhibit the following relationship, the transmission spectrum, as a comprehensive characteristic, can be made steeper. First, the slope is determined by dividing the wavelength width (bandwidth) from the point of 10% transmittance (transmission point) to the 80% transmittance point, i.e., Δλ1, by the center wavelength, i.e., λp, by (Δλ1 / λp). Alternatively, the slope can be defined as the wavelength width from the 80% transmittance point to the 10% transmittance point, Δλ2, and determined by (Δλ2 / λp). (Δλ1 / λp) and (Δλ2 / λp) can be calculated using the method described in Table 1 below, and the larger 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 multiple optical filters is 3.3% or greater, the transmission spectrum, as a comprehensive characteristic, can be made steeper, and the film thickness of the optical filter can be reduced. If the slope of the transmission spectrum of at least one of the multiple optical filters is greater than 4.2%, the transmission spectrum, as a comprehensive characteristic, can be made steeper, and the film thickness of the optical filter can be further reduced, thus simplifying the optical filter.

[0078] Furthermore, within any 1000 nm range of the stopband, it is preferable that there exist wavelength regions where the transmittance difference between at least two of the multiple optical filters is 20% or more, and the transmittance difference is 5% or less. For example, it is preferable that within any 1000 nm range of the stopband, at least two of the multiple optical filters have regions where the maxima of the transmission spectra do not overlap (see reference). 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 materials and film thicknesses of the multiple first layers stacked together can be the same or different. Similarly, the materials and film thicknesses of the multiple second layers stacked together can be the same or different. The multilayer film may also include layers different from the first and second layers.

[0091] Furthermore, the total thickness of the multilayer film is the sum of the thickness of the cutoff surface and the bandpass surface. By reducing the total thickness, manufacturing time is shortened and yield is improved in optical filter manufacturing. The film thickness can be measured by cross-sectional SEM observation. Preferably, the total thickness of the multilayer films of each of the multiple optical filters is less than 14 μm.

[0092] (Infrared optical element)

[0093] Infrared optical elements can have a structure having a first conductive semiconductor layer, an active layer, and a second conductive semiconductor layer. Specifically, infrared optical elements are infrared light-emitting diodes (LEDs) or infrared photodiodes.

[0094] The active layer is either a light-absorbing layer or a light-emitting layer (see reference). Figure 8 In this embodiment, the active layer is made of Al. y In 1-y Sb(0.04≤y≤0.14) or InAs y Sb 1-y (0.1≤y≤0.2) constitutes the condition. "Al y In 1-y "Sb(0.04≤y≤0.14)" refers to a layer containing Al, In, and Sb, but the presence of other elements is also included in this description. Specifically, the addition of small amounts of other elements (e.g., less than a few percent of As, P, Ga, N, etc.) that slightly alter the composition of the layer is also included in this description. The same applies to the description of other components.

[0095] Here, the Al or As components can be determined, for example, by secondary ion mass spectrometry (SIMS). The determination can be performed using, for example, a magnetic field type SIMS device, the IMS7f, manufactured by CAMECA.

[0096] The second conductivity type is a conductivity type different from the first conductivity type. The first and second conductivity types can be any of the following: n-type (containing n-type impurities), i-type (not containing impurities), and p-type (containing p-type impurities). The first conductivity type semiconductor layer can, for example, be made of n-type InSb (see reference). Figure 8 It is composed of, for example, p-type InSb (see reference). Additionally, the second conductivity type semiconductor layer can be composed of, for example, p-type InSb (see reference). Figure 8It is composed of ( ). In this embodiment, the first conductivity type is n-type and the second conductivity type is p-type.

[0097] The first conductive semiconductor layer, the active layer, and the second conductive semiconductor layer can be formed on a semiconductor substrate such as a gallium arsenide (GaAs) substrate or a silicon substrate. In this embodiment, the infrared optical element has each layer arranged in a manner that, starting from the substrate, the first conductive semiconductor layer, the active layer, and the second conductive semiconductor layer are arranged sequentially. As another example, the infrared optical element can have each layer arranged in a manner that, starting from the substrate, the second conductive semiconductor layer, the active layer, and the first conductive semiconductor layer are arranged sequentially.

[0098] One or more barrier layers can be disposed between the first conductive semiconductor layer and the active layer. Additionally, one or more barrier layers can be disposed between the active layer and the second conductive semiconductor layer. In this embodiment, an n-type barrier layer is disposed between the first conductive semiconductor layer and the active layer, and a p-type barrier layer is disposed between the active layer and the second conductive semiconductor layer. The n-type barrier layer is, for example, made of n-type Al. x In 1-x Sb(0.15≤x≤0.35) constitutes (refer to) Figure 8 The p-type barrier layer consists of p-type Al. z In 1-z Sb (0.15≤z≤0.35) constitutes (refer to) Figure 8 ).

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

[0100] (Example)

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

[0102] Examples 1-4 and Comparative Examples 1-3 shown in Table 1 were evaluated. Examples 1-4 are optical modules of this embodiment, with characteristics specified as in Table 1. Comparative Examples 1-3 are unsimplified filter units. Figure 8 This diagram illustrates the stacked structure of the infrared optical elements of Examples 1-4. The center wavelength of the optical filters in Examples 1, 4, and Comparative Example 1 is 4.3 μm. The center wavelength of the optical filters in Examples 2 and Comparative Example 2 is 3.4 μm. The center wavelength of the optical filters in Examples 3 and Comparative Example 3 is 8.5 μm. The optical modules of Examples 1, 2, and 4 include both infrared emitting elements and infrared receiving elements. The optical module of Example 3 only includes an infrared emitting element. The active layer of the infrared emitting elements in Examples 1, 2, and 4 is made of Al. y In1-y The composition is Sb, with y = 0.057 in Example 1, 0.089 in Example 2, and 0.057 in Example 4. The active layer of the infrared light-receiving element in Examples 1, 2, and 4 is composed of Al. y In 1-y The composition is Sb, with y = 0.048 in Example 1, 0.089 in Example 2, and 0.048 in Example 4. The active layer of the infrared light-emitting element in Example 3 is composed of InAs. y Sb 1-y The composition is y = 0.13.

[0103] [Table 1]

[0104]

[0105] The PIN diode structures of the infrared optical elements in Examples 1-4 were fabricated using the MBE method. n-type and p-type blocking layers were sandwiched between active layers. A positive photoresist for i-rays was coated onto the surface of a semiconductor wafer, and exposure was performed using i-rays via a shrink-projection exposure machine. Development followed, regularly forming multiple photoresist patterns on the surface of the semiconductor stack. Next, multiple mesa were formed by dry etching. After depositing a silicon dioxide film as a hard mask on the mesa-shaped elements, the elements were separated by dry etching, and a silicon nitride (SiN) film was deposited as a protective film. Contact holes were formed by photolithography and dry etching. Then, the multiple mesa were connected in series by photolithography and sputtering, and the element surface was covered with a polyimide resin as a protective film. The wafer thus fabricated was diced and monolithized, Au wires were bonded and connected to a lead frame, and sealed with epoxy molding resin to expose the light-receiving surface. Infrared light-receiving elements made in this way are sensitive to infrared light near λp, but other bands become stopbands with almost no sensitivity.

[0106] The design of the optical filters is implemented using simulation. The optical filters in Examples 1-4 incorporate multiple simplified optical filters, achieving the desired wavelength selectivity as a combined feature. Figure 6 This is a graph of transmittance illustrating an example embodiment, specifically showing 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 at the stopband was confirmed to be less than 5% of the peak sensitivity.

[0107] Furthermore, as shown in Table 1, in Examples 1-4, the slope of the combined transmission spectrum is steeper than the slope of the individual transmission spectra of each optical filter. Additionally, in Examples 1-4, the total thickness of the multilayer films of each optical filter is 14 μm or less. Furthermore, in Examples 1-3, a comparison with Comparative Examples 1-3 shows that even using two optical filters can reduce the total thickness of all optical filters. In Example 4, although three optical filters are used, the total thickness of all optical filters is thinner compared to Comparative Example 1 and Example 1. In other words, the examples have the same sensitivity as the comparative examples, and the thickness of the multilayer films of the multiple optical filters is reduced.

[0108] As described above, the optical module of this embodiment can improve the yield of each optical filter and enhance mass production by using simplified multiple optical filters.

[0109] The embodiments of this disclosure have been described with reference to the accompanying drawings and examples. However, it should be noted that those skilled in the art can readily make various modifications or alterations based on this disclosure. Therefore, it should be understood that these modifications or alterations are included within the scope of this disclosure.

Claims

1. An optical module, characterized in that, The optical module includes: multiple 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 peak sensitivity in the wavelength region of 2000nm to 10000nm. At least one of the first optical filter and the second optical filter comprises: a substrate; and a multilayer film formed on at least one surface of the substrate, having multiple layers with different refractive indices. The first optical filter and the second optical filter, in the wavelength region of 2000nm to 10000nm, include a common passband with a transmittance of 60% or more at a wavelength of 50nm or more. Outside the common passband, there are wavelength regions with a transmittance difference of 20% or more totaling 200nm or more. Furthermore, in the two outer bands of the common passband that are closer to the common passband than the wavelength regions with a transmittance difference of 20% or more, there are wavelength regions with a transmittance difference of less than 20% and a transmittance of less than 60% totaling 1000nm or more. When the sensitivity spectrum of the infrared optical element is multiplied by the transmission spectrum of the plurality of optical filters, the stopband sensitivity is less than 5% of the peak sensitivity.

2. The optical module according to claim 1, characterized in that, 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. The optical module according to claim 1, characterized in that, The filter substrate, which serves as the substrate for at least one of the plurality of optical filters, is a different type from the optical element substrate, which serves as the substrate for the infrared optical element. The filter substrate is bonded to the optical element substrate.

4. The optical module according to any one of claims 1 to 3, characterized in that, When the center wavelength of the passband is set to λp, the total thickness of the multilayer film of at least one of the plurality of optical filters is less than (λp×1.5) nm.

5. The optical module according to any one of claims 1 to 3, characterized in that, The plurality of optical filters includes 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 less than 1500 nm.

6. The optical module according to any one of claims 1 to 3, characterized in that, The total thickness of the multilayer films of each of the plurality of optical filters having the multilayer films is less than 14 μm.

7. The optical module according to any one of claims 1 to 3, characterized in that, In the wavelength region of 2000nm to 10000nm, the ratio of the maximum sensitivity to the minimum sensitivity of the infrared optical element is greater than 20.

8. The optical module according to any one of claims 1 to 3, characterized in that, The plurality of optical filters include a wavelength region totaling more than 50 nm in the 2000 nm to 10000 nm range, where the difference in transmittance between at least two of the plurality of optical filters is more than 30%. In the wavelength region of 2000nm to 10000nm, when the sensitivity spectrum of the infrared optical element is multiplied by the transmission spectrum of the plurality of optical filters, the stopband sensitivity is less than 2% of the peak sensitivity.

9. The optical module according to any one of claims 1 to 3, characterized in that, Within any 1000nm range of the stopband, between wavelength regions where the transmittance difference between at least two of the plurality of optical filters is greater than 20%, there exists a wavelength region where the transmittance difference is less than 5%.

10. The optical module according to any one of claims 1 to 3, characterized in that, The slope of the transmission 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, characterized in that, All of the optical filters have a structure with a substrate and a multilayer film. The multilayer film is formed on at least one surface of the substrate and has multiple layers with different refractive indices.

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

13. The optical module according to claim 12, characterized in that, Regarding A and B, the relationship 0.7 < (A / B) < 1.3 is satisfied.

14. The optical module according to any one of claims 1 to 3, characterized in that, The film thickness of two or more of the plurality of optical filters is less than (center wavelength × 1.5).

15. The optical module according to any one of claims 1 to 3, characterized in that, The slope of the transmission spectrum obtained by multiplying the transmission spectra of the plurality of optical filters is smaller than the slope of the transmission spectrum of all individual optical filters.

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