JPH10148707A - Diffraction grating and spectroscope - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a diffraction grating, in which the light having a wavelength ratio of rational number mixed into diffracted light flux to be used, is fundamentally completely eliminated, and to provide a spectroscope which can fundamentally eliminate light of a wavelengths other than the wavelength to be used, without using a filter or total reflection mirror. SOLUTION: In the diffraction grating, where many recessed grooves or projecting lines 2 are disposed on the surface of substrate 1, a plenty of these recessed groves or the projecting lines are disposed so that their disposition pitches have a quasi-periodicity. Further, the diffraction grating has a first diffraction grating 5 and a second diffraction grating 6 arranged in a path of light passing through the first diffraction grating 5, and the first diffraction grating 5 comprises many recessed grooves or projecting lines disposed on the surface of the substrate so that the disposition pitch of the recessed grooves or the projecting lines has a quasi-periodicity, while the second diffraction grating 6 comprises many recessed grooves or projecting lines 2 disposed on the surface of the substrate so that the disposition pitch of the recessed grooves or the projecting lines has a periodicity.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a diffraction grating used in a spectroscopic optical system and the like, and a spectroscopic device using the same.

[0002]

2. Description of the Related Art A conventional diffraction grating is constructed by arranging a large number of rows so that the arrangement pitch of concave grooves or ridges has a periodicity in either a transmission type diffraction grating or a reflection type diffraction grating. In general, lattice grooves are arranged at equal intervals. For this reason, the optical path difference of the diffracted light passing through two adjacent grating grooves engraved on the element surface is always an integral multiple of the wavelength of the light used. Therefore, light having a wavelength ratio of an integer to the wavelength of the light to be used is mixed in the light flux diffracted in the same direction. For example, 1 of light of wavelength λ
Order diffracted light, second order diffracted light of wavelength λ / 2, wavelength λ /
Each of the third-order diffracted lights of light No. 3 is diffracted in the same direction because the optical path difference is λ. More generally, the n-th order diffracted light of the wavelength λ and the m-th order diffracted light of the wavelength n / m · λ are diffracted in the same direction because the optical path difference is nλ (n , M is a natural number). For this reason, in the light beam diffracted in the same direction, the wavelength ratio is n /
m, that is, light which is a rational number was mixed. As a result, in the above-described spectral device using the diffraction grating, light having an integer ratio of wavelength is always mixed in the diffracted light beam. Therefore, in order to remove light other than the light having the wavelength to be used, various filters, and in particular, a total reflection mirror has been used in a short wavelength region.

[0003]

As described above, in the conventional "diffraction grating", light having an integer wavelength ratio mixed in the same diffracted light beam (more precisely, light having a rational wavelength ratio).
It was impossible to eradicate the outbreak. In addition, in the conventional “spectroscopic device”, it is necessary to change a filter inserted for removing light having an integer wavelength ratio diffracted from the diffraction grating for each wavelength, and furthermore, the mixed light is completely removed in principle. I couldn't do that. Even when using a total reflection mirror,
It is necessary to change the total reflection angle with the change of the used wavelength range,
As a result, the optical path had to be changed, and a complicated optical system had to be adopted.

Accordingly, an object of the present invention is to provide a diffraction grating in which light having a ratio of a rational number mixed into a diffracted light beam having a wavelength to be used is eradicated in principle. Another object of the present invention is to provide a spectroscopic device capable of simply and in principle completely removing light other than the wavelength to be used without using a filter or a total reflection mirror which has been conventionally used.

[0005]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, that is, a transmission type or a transmission type in which a large number of grooves or projections are arranged on the surface of a transmission type or reflection type substrate. A transmission or reflection type diffraction grating, wherein a large number of the grooves or the ridges are arranged so that the arrangement pitch of the grooves or the ridges has a quasi-periodicity. With this configuration, of the light mixed in the diffracted light beam having the wavelength to be used, the light having a ratio of the ratio of the used light to the rational number is removed, and only the light having the irrational number of the wavelength ratio is obtained.

The present invention also relates to a first diffraction grating and the first diffraction grating.
And a second diffraction grating arranged in the optical path of the light that has passed through the diffraction grating, wherein the first diffraction grating is disposed on the surface of the substrate.
The grooves or the ridges are arranged in a large number of rows so that the arrangement pitch of the grooves or the ridges has a quasi-periodicity. The second diffraction grating has a groove or a ridge on the surface of the substrate. Is a spectroscopic device configured by arranging a large number of the concave grooves or convex stripes such that the arrangement pitch has periodicity. At this time, the first diffraction grating and the second diffraction grating may be replaced with each other. With this configuration, of the light mixed in the diffracted light beam of the wavelength to be used, the diffraction grating arranged so that the arrangement pitch of the concave grooves or the ridges has a quasi-periodicity causes the wavelength ratio with the light to be used to be a rational number. The light is removed, leaving only the light with an irrational wavelength ratio. On the other hand, of the light mixed in the diffracted light beam, the diffraction grating arranged so that the arrangement pitch of the concave grooves or the ridges has periodicity, the light having an irrational wavelength ratio to the light used is removed, The wavelength ratio is only rational light. Therefore, by passing through both diffraction gratings in series, only the light of the wavelength to be used is selected and separated.

[0007] The present invention also relates to a first diffraction grating and the first diffraction grating.
And a second diffraction grating arranged in the optical path of the light that has passed through the diffraction grating, wherein the first diffraction grating is disposed on the surface of the substrate.
The grooves or the ridges are arranged in a large number of rows so that the arrangement pitch of the grooves or the ridges has a quasi-periodicity. The second diffraction grating has a groove or a ridge on the surface of the substrate. Is a spectroscopic device configured by arranging a large number of the concave grooves or the ridges such that the arrangement pitch has a quasi-periodicity different from the quasi-periodicity of the first diffraction grating. With this configuration, of the light mixed in the diffracted light beam having the wavelength to be used, the light having a ratio of the ratio of the light to be used to the light having a rational number is removed by both diffraction gratings, and the light having the ratio of the wavelength to the light to be used being irrational to the light , Are removed by any of the diffraction gratings. Therefore, by passing through both diffraction gratings in series, only the light of the wavelength to be used is selected and separated.

[0008]

Embodiments of the present invention will be described below. First, the diffraction grating will be described. 1 and 2 show an embodiment of a reflection type diffraction grating according to the present invention. This diffraction grating has a linear grating groove 2 formed on a surface of a planar substrate 1.
Are arranged in a large number of rows. The arrangement pitch of each lattice groove 2 is determined using an arbitrary irrational number: τ. There are two types, d ₁ and d ₂ , which have the following relationship, and the two types of pitches d ₁ and d ₂ are arranged so as to form a Fibonacci sequence. For _{example, A 1 = d 1, A} 2 = d 2, A n = A n-1 When _{A n-2 (n ≧ 3} ), A 3 = d 2 d 1 A 4 = d 2 d 1 d 2 A _{5 = d 2 d 1 d 2} d 2 d 1 A 6 = d 2 d 1 d 2 d 2 d 1 d 2 d 1 d 2 A 7 = d 2 d 1 d 2 d 2 d 1 d 2 d 1 d 2 d ₂ d ₁ d ₂ d ₂ d ₁ }, but the two types of pitches d ₁ and d ₂ are arranged in this manner.

As is well known in solid state physics and crystallography, a Fibonacci sequence generates a quasi-periodic sequence, and its Fourier spectrum also forms a quasi-periodic sequence having an irrational ratio with each other. The spectrum of the Fibonacci sequence will be described. The coordinates X _n of the n-th grid point of the Fibonacci sequence are dimensionless and normalized using the reference length d, Here, τ is an arbitrary irrational number, and α and β are arbitrary real numbers. or Is a function that gives the largest integer. From equation (1), the interval between each grid point is Two lattice intervals having an irrational ratio (1 + τ) / τ are quasi-periodically arranged.

[0010] The Fourier vector f of this lattice sequence X _n
(K): Is already well known in solid state physics and crystallography, Becomes

Here, p and q are initial values; F ₁ = 1, F ₀ =
Using 1 becomes Fibonacci sequence F _n (the initial value is the Fibonacci sequence; F _1, F ₀ is known, n> 2 becomes F _n is,
_{F n = F n-1 +} F n-2 sequence determined by), (p, q) = (F n + 1, F n); n takes only positive integer ‥‥ (5) becomes set. To name the first few terms, (1,
1), (2,1), (3,2), (5,3), (8,
5), (13, 8),... Are the (p, q) pairs allowed in equation (4). For these p and q, Becomes From equation (4), the Fourier spectrum f (k) of the lattice sequence X _n has a spectrum only in the above k _{p, q} ,
From the expressions (5) and (6), the ratio between the spectra becomes an irrational number. Therefore, it is concluded that there is no integral multiple of harmonic components in each spectrum value.

Here, it will be described that the wavelength ratio of light diffracted in the same direction becomes an irrational number. As shown in FIG. 2, a light beam having a wide spectrum is separated by a quasi-periodic diffraction grating. At this time, the m-th Fourier spectrum of the structure extending in the direction perpendicular to the groove, counted in the direction in which the frequency increases, is q _m , the unit vector in the same direction is e, and the wave number vectors of the incident light and the diffracted light are q _in , Q _out , the incident light and the diffracted light on the quasi-periodic diffraction grating are Satisfy the relationship Further rewriting equation (9), Becomes The ratio of the Fourier spectra q _i , q _{j to} any integer i, j is irrational, ie, _Therefore , the wavelengths λ _i , λ _j of the light corresponding to the Fourier spectra q _i , q _j for the same diffraction angle are given by the following equations (10) and (11). Becomes

That is, the parallel light beam incident at the incident angle θ _in is diffracted by the grating groove 2, and the mutual ratio of the wavelength of the light in the diffracted light beam emitted at the diffraction angle θ _out is always an irrational number.
Light whose wavelength ratio becomes a rational number can be removed. In this embodiment, the reflection type diffraction grating is used. However, the present invention can be equally applied to a transmission type diffraction grating. Further, in the present embodiment, the concave groove is formed on the surface of the substrate, but a ridge may be formed on the surface of the substrate. In the present embodiment, two types of arrangement pitches d ₁ and d ₂ are used, but three or more types of arrangement pitches may be used.

Next, the spectrometer will be described. FIG. 3 shows an embodiment of the spectroscopic device according to the present invention, in which the minimum wavelength λ _min
The light beam having a wide spectrum width from to the maximum wavelength λ _max enters the entrance slit 3 of the spectroscope, is converted into a parallel light beam by the collimator lens 4, and enters the quasi-periodic reflection diffraction grating 5. The light beam diffracted from the quasi-periodic diffraction grating 5 then enters a normal periodic reflection diffraction grating 6. The light beam diffracted by the periodic diffraction grating 6 is condensed by an exit slit 8 by a condenser lens 7 and exits from the exit slit 8.

Assuming that the wavelength of light to be extracted from the exit slit 8 of the spectrometer is λ and the wavelength of other light incident on the entrance slit 3 is λ ′ (λ ′ ≠ λ), a quasi-periodic diffraction grating From the light diffracted in the same direction as the light of the desired wavelength λ from 5, there is no light whose wavelength ratio λ ′ / λ is a rational number. Therefore, only light having an irrational wavelength ratio λ ′ / λ enters the periodic diffraction grating 6 together with light having a desired wavelength λ. Subsequently, the light diffracted from the periodic diffraction grating 6 in the same direction as the light having the desired wavelength λ does not include light having an irrational wavelength ratio λ ′ / λ. Therefore, only light having a desired wavelength λ enters the exit slit 8. That is, the light continuously diffracted by the two diffraction gratings 5 and 6 is only light having a desired wavelength λ. Thus, in principle, only light of a single wavelength is spectrally separated and high-order diffracted light is prevented from being mixed. can do.

In this embodiment, a quasi-periodic diffraction grating 5 is arranged at the front stage to exclude light having a ratio of wavelength λ '/ λ from the light of wavelength λ' other than the desired wavelength λ. A periodic diffraction grating 6 is arranged at the subsequent stage, and a wavelength λ ′ other than the desired wavelength λ is provided.
Out of the light, the light whose wavelength ratio λ '/ λ is irrational is excluded, but the periodic diffraction grating is arranged at the front stage to exclude the light whose wavelength ratio is irrational, and the quasi-periodic diffraction grating is installed at the latter stage. It is also possible to dispose the light whose ratio of wavelengths is rational number by disposing. Also, quasi-periodic diffraction gratings may be arranged in both the former stage and the latter stage. However, in this case, it is necessary to change, for example, the arrangement pitch of the lattice grooves between the front stage and the rear stage so that the two have different quasi-periodicity.

[0017]

As described above, since the diffraction grating of the present invention contains only light having an irrational ratio wavelength in a diffracted light beam in the same direction, it is possible to remove light having a rational number wavelength. it can. Also, by combining the diffraction grating according to the present invention in series with a normal diffraction grating, light having a wavelength having an irrational ratio and light having a wavelength having a rational ratio with respect to desired light are removed. In principle, it is possible to realize a spectroscopic device that disperses only light of a single wavelength without using a mirror.

[Brief description of the drawings]

FIG. 1 is a plan view showing an embodiment of a diffraction grating according to the present invention.

FIG. 2 is an explanatory view showing the operation principle of the diffraction grating according to the present invention.

FIG. 3 is a configuration diagram showing one embodiment of a spectroscopic device according to the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Substrate 2 ... Lattice groove 3 ... Entrance slit 4 ... Collimating lens 5 ... Quasi-periodic diffraction grating 6 ... Periodic diffraction grating 7 ... Condensing lens 8 ... Exit slit

Claims (5)

[Claims] 1. A transmission type diffraction grating having a plurality of rows of grooves or ridges arranged on a surface of a transmission type substrate, wherein the grooves or ridges are arranged so as to have a quasi-periodic pitch. A transmission type diffraction grating comprising a large number of rows of ridges. 2. A reflection type diffraction grating in which a large number of grooves or ridges are arranged on the surface of a reflection type substrate, wherein the grooves or ridges have a quasi-periodic arrangement pitch. A reflection type diffraction grating comprising a large number of rows of ridges. 3. A semiconductor device comprising: a first diffraction grating; and a second diffraction grating arranged in an optical path of light passing through the first diffraction grating, wherein the first diffraction grating is provided on a surface of a substrate. A plurality of the grooves or the ridges are arranged in rows so that the arrangement pitch of the grooves or the ridges has a quasi-periodicity. The second diffraction grating has a groove or a protrusion on the surface of the substrate. A spectroscopic device comprising a large number of rows of the concave grooves or convex stripes arranged so that the arrangement pitch of the stripes is periodic. 4. A semiconductor device comprising: a first diffraction grating; and a second diffraction grating disposed in an optical path of light passing through the first diffraction grating, wherein the first diffraction grating is provided on a surface of a substrate. A plurality of grooves or protrusions are arranged in a row so that the arrangement pitch of the grooves or protrusions has a periodicity. The second diffraction grating has a groove or protrusion on the surface of the substrate. A spectroscopic device comprising a large number of rows of the concave grooves or convex stripes arranged so that the arrangement pitch has a quasi-periodicity. 5. A semiconductor device comprising: a first diffraction grating; and a second diffraction grating disposed in an optical path of light passing through the first diffraction grating, wherein the first diffraction grating is provided on a surface of a substrate. A plurality of the grooves or the ridges are arranged in rows so that the arrangement pitch of the grooves or the ridges has a quasi-periodicity. The second diffraction grating has a groove or a protrusion on the surface of the substrate. A spectroscopic device comprising a large number of rows of the concave grooves or convex lines arranged so that the arrangement pitch of the stripes has a quasi-periodicity different from the quasi-periodicity of the first diffraction grating.