US-12618772-B2 - Optical physical quantity measuring apparatus

Abstract

An optical physical quantity measuring apparatus ( 1 ) includes a light-emitting element (L), light-receiving elements (S) including at least a first light-receiving element and a second light-receiving element, and a reflector. The light-emitting element has a different radiation spectrum depending on a radiation direction and emits light at least at a first radiation angle, a second radiation angle, and a third radiation angle into a space in which an object to be measured is located. The reflector causes light emitted from the light-emitting element in different radiation directions to reach different positions. The first light-receiving element is arranged in an optical path formed by light emitted at the first radiation angle. The second light-receiving element is arranged in an optical path formed by light emitted at the second radiation angle. An absorber or a void is provided in an optical path formed by light emitted at the third radiation angle.

Inventors

• Daiki YASUDA
• Shota ISSHIKI

Assignees

• ASAHI KASEI MICRODEVICES CORPORATION

Dates

Publication Date

20260505

Application Date

20240226

Priority Date

20230302

Claims (20)

1. 1 . An optical physical quantity measuring apparatus comprising: a light-emitting element, a plurality of light-receiving elements including at least a first light-receiving element and a second light-receiving element, and a reflector, wherein the light-emitting element has a different radiation spectrum depending on a radiation direction, and emits light at least at a first radiation angle, a second radiation angle, and a third radiation angle into a space in which an object to be measured is located, the reflector causes light emitted from the light-emitting element in different radiation directions to reach a plurality of different positions, the first light-receiving element is arranged in an optical path along which the light emitted at the first radiation angle travels, the second light-receiving element is arranged in an optical path along which the light emitted at the second radiation angle travels, and an absorber or a void is provided in an optical path along which the light emitted at the third radiation angle travels.
2. 2 . The optical physical quantity measuring apparatus according to claim 1 , wherein the plurality of light-receiving elements is formed on a same substrate.
3. 3 . The optical physical quantity measuring apparatus according to claim 2 , wherein the substrate is a semiconductor substrate, and the light-receiving elements are semiconductor elements formed on the semiconductor substrate.
4. 4 . The optical physical quantity measuring apparatus according to claim 1 , further comprising a molded resin part that seals at least a portion of the plurality of light-receiving elements.
5. 5 . The optical physical quantity measuring apparatus according to claim 4 , wherein the plurality of light-receiving elements is arranged symmetrically with respect to the molded resin part in plan view.
6. 6 . The optical physical quantity measuring apparatus according to claim 1 , wherein the light-emitting element comprises wavelength limiting means, and the light-emitting element has the different radiation spectrum depending on the radiation direction due to incident angle dependence of a wavelength transmitted by the wavelength limiting means.
7. 7 . The optical physical quantity measuring apparatus according to claim 6 , wherein the wavelength limiting means is an optical interference filter using a dielectric multilayer film.
8. 8 . The optical physical quantity measuring apparatus according to claim 7 , wherein the dielectric multilayer film is formed from a material with a refractive index of less than 2.5.
9. 9 . The optical physical quantity measuring apparatus according to claim 6 , wherein the wavelength limiting means is a diffraction grating.
10. 10 . The optical physical quantity measuring apparatus according to claim 6 , wherein the wavelength limiting means is a metamaterial.
11. 11 . The optical physical quantity measuring apparatus according to claim 6 , wherein the wavelength limiting means is provided in proximity to the light-emitting element.
12. 12 . The optical physical quantity measuring apparatus according to claim 1 , wherein a light-emitting region of the light-emitting element includes a microstructure.
13. 13 . The optical physical quantity measuring apparatus according to claim 1 , wherein the light-emitting element is a resonant-cavity light-emitting diode or a vertical cavity surface emitting laser.
14. 14 . The optical physical quantity measuring apparatus according to claim 1 , wherein the light-emitting element and the plurality of light-receiving elements have a reception and emission wavelength of 1 μm to 12 μm, and a gas concentration is calculated based on an amount of light absorption by gas molecules present in an optical path.
15. 15 . The optical physical quantity measuring apparatus according to claim 1 , further comprising a plurality of light-emitting elements, wherein at least one of the plurality of light-receiving elements is arranged at a position reached by light emitted from both of two light-emitting elements in the plurality of light-emitting elements.
16. 16 . The optical physical quantity measuring apparatus according to claim 1 , wherein the reflector has a reflective surface that is a quadratic surface.
17. 17 . The optical physical quantity measuring apparatus according to claim 1 , wherein the third radiation angle is an angle between the first radiation angle and the second radiation angle.
18. 18 . The optical physical quantity measuring apparatus according to claim 1 , wherein the absorber is provided in the optical path along which the light emitted at the third radiation angle travels, and the absorber is a portion of a molded resin part that seals at least a portion of the plurality of light-receiving elements or the absorber is a portion of the molded resin part that forms the reflector.
19. 19 . The optical physical quantity measuring apparatus according to claim 1 , wherein the absorber or the void is provided at a position in the reflector between a reflection position of the light emitted at the first radiation angle and a reflection position of the light emitted at the second radiation angle.
20. 20 . The optical physical quantity measuring apparatus according to claim 19 , wherein the absorber is provided in the optical path along which the light emitted at the third radiation angle travels, and the absorber is a portion of uncoated resin forming the reflector.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS The present application claims priority to Japanese Patent Application No. 2023-032266 filed on Mar. 2, 2023 and Japanese Patent Application No. 2024-004727 filed on Jan. 16, 2024, the entire contents of which are incorporated herein by reference. TECHNICAL FIELD The present disclosure relates to an optical physical quantity measuring apparatus. BACKGROUND As an optical physical quantity measuring apparatus, a non-dispersive infrared absorption type gas concentration measuring apparatus is known, for example. The non-dispersive infrared absorption type gas concentration measuring apparatus is known as a highly accurate gas sensor that is based on how gas molecules have a unique absorption band for mid-infrared light. This gas sensor operates as follows. First, infrared light is irradiated from an infrared light source onto gas in the optical path. Infrared light transmitted through the gas is guided by the optical path to an infrared detector, and the amount of light reaching the detector is measured. In this case, provision of a bandpass filter in the optical path before the light enters the infrared detector can restrict the light reaching the infrared detector to the infrared light in the absorption band specific to the gas molecules. The amount of light reaching the detector diminishes according to the concentration of gas in the optical path in accordance with the Beer-Lambert law. The gas concentration can be calculated based on the amount of light reaching the detector. Therefore, in a case of fluctuations in the intensity of light irradiated from the light source, fluctuations in the reflectance of the optical path, fluctuations in the characteristics of the infrared detector, or the like, large errors occur in the gas concentration calculation, making it difficult to measure the gas concentration accurately. Factors that cause such fluctuations include, for example, temperature changes, the effect of stress associated with humidity, an unclean optical path, and the effect of interfering gases. A method using a reference signal is known as a method to suppress the effects of such fluctuations. This method uses a main signal obtained by detecting only light, irradiated from a light source, in the absorption band sensitive to the gas concentration and a reference signal obtained by detecting light, irradiated from the same light source, with less sensitivity to changes in gas concentration. For example, by taking the ratio of these signals, the effect of fluctuations in the intensity of the light source and the like can be suppressed. Here, the main signal is obtained by detecting, with an infrared detector, light transmitted through a bandpass filter that transmits wavelengths specific to the gas to be detected. On the other hand, various methods for obtaining the reference signal are known. Patent Literature (PTL) 1 discloses a method of detecting light of all wavelengths emitted by a light source using an infrared detector formed on the same substrate as the light source. PTL 2 discloses a method of detection using an infrared detector with a bandpass filter that, unlike the main signal bandpass filter, transmits wavelengths that are not sensitive to the gas to be detected. CITATION LIST Patent Literature PTL 1: WO2015/045411PTL 2: JP H9-318528 A SUMMARY The method of detecting all wavelengths as a reference signal has the problem, however, of not being able to fully compensate for changes in spectral shape due to fluctuations in characteristics. The method of detecting all wavelengths as a reference signal is a method in which a signal obtained by integrating the product of the emission intensity of the emission spectrum and the spectral sensitivity of the detector over all wavelengths is used as the reference signal, and a signal obtained by integrating the product of a portion of the emission spectrum and the spectral sensitivity of the detector over all wavelengths is used as the main signal. The method using a plurality of optical filters corresponding to a plurality of wavelengths is superior in terms of suppressing fluctuations in characteristics but has the problem of increasing the size of the apparatus. It would be helpful to provide a compact yet highly accurate optical physical quantity measuring apparatus. (1) An optical physical quantity measuring apparatus according to an embodiment of the present disclosure includes: a light-emitting element, a plurality of light-receiving elements including at least a first light-receiving element and a second light-receiving element, and a reflector, whereinthe light-emitting element has a different radiation spectrum depending on a radiation direction, andemits light at least at a first radiation angle, a second radiation angle, and a third radiation angle into a space in which an object to be measured is located, the reflector causes light emitted from the light-emitting element in differen