JP6167985B2 - Spectroscopic sensor - Google Patents

Description

  The present invention relates to a spectroscopic sensor for guiding light to be measured into a housing by an optical fiber and measuring a wavelength spectrum of the light to be measured by a diffraction grating and a photodiode array arranged in the housing.

  In various analyzers based on spectroscopic methods, color sensors, fruit saccharimeters, etc., in general, by irradiating a sample with measurement light, and spectroscopically measuring the transmitted light or reflected light, and measuring the light intensity for each wavelength, Spectral information of light from the sample is obtained, and components and color information included in the sample are specified.

  As a product that can be used universally by unitizing the measurement optical system and the light introduction optical system in various apparatuses using such a spectroscopic method, what is called a spectroscopic sensor or a polychromator is known. (For example, see Non-Patent Document 1 and Patent Document 1).

  The basic structure of a spectroscopic sensor is that a diffraction grating and a photodiode array are arranged in a casing, and light to be measured is guided into the casing by an optical fiber and irradiated to the diffraction grating through an entrance slit. The light after the spectrum is received by the photodiode array and converted into an electrical signal, whereby a signal representing the wavelength (energy) spectrum of the light to be measured is obtained.

  A structure in which the tip of the optical fiber that guides the light to be measured to the housing is fixed to the housing with an SMA or FC connector, and a rectangular slit is arranged as an entrance slit immediately in front of the optical fiber connector, Only light that has passed through the slit is applied to the diffraction grating. The slit shape of the entrance slit is generally a square, a circle, a rhombus, or the like in addition to the above-described rectangle, and is appropriately used depending on the NA (numerical aperture) of the optical fiber and the shape of the diffraction grating.

JP 2003-139611 A

Shimadzu Home Page> Product Information> Optical Devices / Laser Equipment> Spectroscopic Sensors [online] Search February 15, 2013 Internet <URL; http://www.shimadzu.co.jp/opt/products/optsens/index. html>

  By the way, most of the above-described spectroscopic sensors generally have a rectangular slit structure if the outer shape has a rectangular diffraction grating. However, the shape accuracy of the surface of the diffraction grating is not uniform, especially in the case of a concave diffraction grating, the shape accuracy near the four corners is lower than the center. Causes a noise level called stray light.

  In addition, the SMA and FC connector used to fix the tip of the optical fiber to the housing has a female connector attached to the housing, and the male side attached to the optical fiber end with respect to the female connector. However, due to the misalignment of the SMA connector, light does not strike the center of the diffraction grating, which also causes a decrease in resolution and an increase in noise level.

  The present invention has been made in view of such a situation, and solves the above-described problems in a spectroscopic sensor that guides light to be measured to a diffraction grating and a photodiode array in a housing by using an optical fiber. Compared to this, it is an object of the present invention to provide a spectroscopic sensor capable of improving the optical resolution and reducing the noise level.

  In order to solve the above-described problems, the spectroscopic sensor of the present invention guides the measurement target light to the diffraction grating in the housing through the optical fiber, and receives the light diffracted by the diffraction grating by the photodiode array. In the spectroscopic sensor having a concave diffraction grating as the diffraction grating, the optical fiber is a bundle fiber, and the end face shape on the emission side of the bundle fiber is a rhombus, Is characterized in that the end on the emission side is fixed to the casing so that the diagonal line of the line coincides with the direction in which the groove of the diffraction grating extends.

  Here, in the present invention, the diffraction grating having a rectangular outer shape can be used (claim 2).

  Further, in the present invention, as the photodiode array, the light receiving surface of each element has a longer dimension in a direction perpendicular to the dimension in the arrangement direction of the elements, and the emission side of the bundle fiber It is desirable that the end face shape rhombus is shaped so that the length of one diagonal along the direction in which the groove of the diffraction grating extends is longer than the length of the other diagonal.

  In the present invention, the optical fiber that guides the measurement target light to the diffraction grating in the housing is a bundle fiber, the shape of the end face of the bundle has a function as a slit, and the slit shape is a rhombus. It is intended to solve the problem.

  In other words, the concave diffraction grating does not require any other optical element such as a concave mirror as compared with the planar diffraction grating, and is useful for making the spectroscopic sensor compact and simplifying the structure, but as described above, the shape near the four corners. Although the accuracy tends to be low, the irradiation region of the measurement target light on the concave diffraction grating is limited to a rhombus according to the end face shape of the bundle fiber. Thereby, irradiation of light near the four corners having relatively low shape accuracy in the concave diffraction grating is suppressed. In addition, the light irradiation area to the concave diffraction grating is limited by the shape of the end face of the bundle fiber, and the optical fiber and the slit are substantially integrated. There is nothing. As a result, the optical resolution can be improved and the noise level can be reduced.

  Here, in the present invention, the outer shape of the concave diffraction grating is not particularly limited. However, by using a diffraction grating having an outer shape based on a rectangle, it is possible to disperse light during assembly to the housing. There is an advantage that it is easy to match the arrangement direction of the grooves that determine the direction with the arrangement direction of the elements of the photodiode array. The invention according to claim 2 can realize the improvement in optical resolution and the reduction of noise by suppressing the light irradiation to the vicinity of the four corners while exhibiting the advantages in the assembling.

  In addition, the light receiving surface shape of each element of the photodiode array is considered so as to increase the amount of incident light by lengthening in the direction orthogonal to the light dispersion direction, and the light dispersed by the diffraction grating is It is desirable to have a spread (thickness) that irradiates the entire longitudinal direction of the element. The invention according to claim 3 takes this point into consideration, and the rhombus formed by the end face of the bundle fiber has a diagonal line extending in the direction of the grooves of the diffraction grating, that is, a direction perpendicular to the light dispersion direction, as the other diagonal line. Thus, the dispersed light is irradiated to the entire longitudinal direction of the elements of the photodiode array, and the amount of light received by each element is sufficiently combined with the shape of the light receiving surface of each element of the photodiode array. Can be bigger.

  According to the present invention, using a concave diffraction grating that can make the optical system compact and simple, the measurement target light is guided to the concave diffraction grating by the bundle fiber, and the end face shape of the bundle fiber is changed. The one diagonal is a rhombus along the direction in which the grooves of the diffraction grating extend, and the bundle fiber and slit are substantially integrated, so there is no risk of deterioration in assembly accuracy due to misalignment of the optical fiber, As a result of reliably irradiating the measurement target light to the region excluding the four corners of the concave diffraction grating, a wavelength (energy) spectrum of the measurement target light can be obtained with high resolution and low noise level.

It is explanatory drawing of embodiment of this invention, Comprising: (a) is a typical block diagram, (b) shows the B arrow enlarged view which shows the end surface shape by the side of bundle fiber. The embodiment of the present invention and a graph showing a simulation result of the light amount distribution on the photodiode array of diffracted light of a specific wavelength when the slit shape is rectangular as a comparative example, (a) is the result of the comparative example, (B) shows the result in the embodiment of the present invention. It is a graph which shows the simulation result of the wavelength distribution of the light which injected into the theoretical micro area | region of the light of the specific wavelength on the photodiode array, when the slit shape is a rectangle as an embodiment of the present invention, and a comparative example. (A) is a result of a comparative example, (b) shows a result in an embodiment of the present invention.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
First, FIG. 1A shows a schematic configuration diagram of the embodiment, and FIG. 1B shows an end face shape on the emission side of the bundle fiber in an enlarged view as viewed from the arrow B. As shown in FIG. 1 (a), a diffraction grating 2 and a photodiode array 3 are arranged in the housing 1, and the measurement target light is guided into the housing 1 through the bundle fiber 4. Irradiated.

  The diffraction grating 2 is a concave diffraction grating in which a large number of grooves parallel to each other are formed on a spherical concave surface, and each groove is formed in a direction perpendicular to the paper surface in FIG. When light is irradiated, the light becomes diffracted light wavelength-dispersed in a direction parallel to the paper surface. In this example, the outer shape of the diffraction grating 2 is a rectangle.

  The arrangement direction of each element of the photodiode array 3 is the same as the wavelength dispersion direction by the diffraction grating 2, and the light receiving surface of each element has a dimension in a direction perpendicular to the arrangement direction of the elements. Is a longer rectangle.

  The bundle end surface 4a on the emission side of the bundle fiber 4 is bundled by a terminal fitting 5, and this terminal fitting 5 is fixed to the housing 1 by a screw (not shown) at a flange 5a formed on the outer periphery thereof, for example. The shape of the bundle end face 4a is a rhombus as shown in FIG. In the rhombus, the terminal fitting 5 is fixed to the housing 1 so that one diagonal line is along the direction in which the groove of the diffraction grating 2 extends. The bundle end face 4a directly faces the diffraction grating 2 at a required angle, and has a function as a slit that restricts an irradiation area of the transmitted measurement target light to the diffraction grating 2, and substantially includes an optical fiber. It can be said that the slit is integrated. The rhombus is formed so that the diagonal line along the direction in which the groove of the diffraction grating 2 extends is longer than the other diagonal line.

  In the above embodiment, the measurement target light is transmitted light obtained by irradiating the sample with light from a light source, for example, and the transmitted light is applied to the incident side end surface 4b of the bundle fiber 4 by a condenser lens or the like. The light is collected and taken into the bundle fiber 4.

  The measurement target light guided into the housing 1 by the bundle fiber 4 is irradiated to a rhombus region corresponding to the shape of the bundle end surface 4a on the emission side in the surface of the rectangular diffraction grating 2, and is dispersed for each wavelength. The light is received by each element of the photodiode array 3 and converted into a signal representing a wavelength spectrum. In this measurement operation, the irradiation area of the measurement target light onto the rectangular diffraction grating 2 is an area excluding the rhombus, that is, the area near the four corners with relatively low shape accuracy, and thus the spatial resolution of the wavelength in the obtained diffracted light Is high and the noise level is low. Further, since the shape of the bundle end face 4a is a rhombus that is long in the same direction as the groove extending in the diffraction grating 2, and the light receiving surface of each element of the photodiode array 3 is long in the same direction, it is sufficient for each element. A quantity of light is incident, and the sensitivity is not lowered while being high resolution and low noise.

  FIGS. 2 and 3 show simulation results when the rhombus bundle end surface of the present invention is used and when a bundle fiber is used as a comparative example, but the bundle end surface is an elongated rectangle along the groove direction of the diffraction grating. . In each of these drawings, (a) shows a comparative example, and (b) shows the result of the embodiment of the present invention.

  FIG. 2 is a graph showing a simulation result of a spatial concentration (light quantity) distribution on the light receiving surface of the photodiode array 3 of light having a wavelength of 400 nm out of diffracted light by the diffraction grating 2, and FIG. 6 is a graph showing the wavelength distribution of light incident on a theoretical minute region on the light receiving surface of the photodiode array 3 where light having a wavelength of 400 nm is to be incident.

  As is clear from these figures, it was confirmed that by making the shape of the end face of the bundle a rhombus, the resolution for each wavelength of the diffracted light by the diffraction grating 2 is improved as compared with the rectangular shape. It can be estimated that this is a result that can reliably suppress the incidence of the measurement target light on the four corner portions having relatively low shape accuracy on the diffraction grating 2.

  Here, in the above embodiment, an example in which the rectangular outer shape is used as the diffraction grating 2 has been shown. However, if such a rectangular diffraction grating 2 is used, the arrangement direction of the grooves is correctly assembled. This is preferable because the operation for this is facilitated. However, in the present invention, the outer shape of the diffraction grating is not particularly limited, and for example, a substantially octagonal shape having a rectangular shape with four corners cut out can be equally used. Furthermore, although the example using the concave diffraction grating which formed many groove | channels mutually parallel on the spherical concave surface as the diffraction grating 2 was shown, in this invention, the concave surface where a groove | channel is formed is not limited to a spherical surface. It may be an aspherical surface.

DESCRIPTION OF SYMBOLS 1 Case 2 Diffraction grating 3 Photodiode array 4 Bundle fiber 4a Outgoing bundle end face 4b Incident side bundle end face 5 End fitting 5a Flange

Claims (3)

The measurement target light is guided to the diffraction grating in the housing through the optical fiber, and the light diffracted by the diffraction grating is received by the photodiode array, so that the wavelength spectrum information of the measurement target light is obtained and the concave diffraction is used as the diffraction grating. In a spectroscopic sensor equipped with a grating,
The optical fiber is a bundle fiber, and the shape of the end face on the exit side of the bundle fiber is rhombus, and the end on the exit side is aligned so that one of the diagonals coincides with the direction in which the groove of the diffraction grating extends. A spectral sensor fixed to the housing.   The spectroscopic sensor according to claim 1, wherein an outer shape of the diffraction grating is rectangular.   The light receiving surface of each element of the photodiode array has a dimension in a direction perpendicular to the dimension in the arrangement direction of the elements, and the rhombus of the end face shape on the emission side of the bundle fiber is a groove of the diffraction grating. 3. The spectroscopic sensor according to claim 1, wherein the length of one diagonal along the extending direction is longer than the length of the other diagonal.