JPS63171329A - Light spectrum detector - Google Patents

Abstract

PURPOSE:To enable light spectrum to be detected at high speed by deflecting light at high speed by using a diffraction grating wherein grating spacing can be controlled to be changed and changing the incident angle of light being measured to the diffraction grating for use in dispersion. CONSTITUTION:An optical system is provided with a second diffracting grating 9 newly composed of an acoustic optical light modulating element in the rear stage of an input side slit 3. Light to be measured is diffracted and deflected and the deflected light is dispersed by a first diffraction grating 5 via a first concave reflecting mirror 4. The dispersed light is reflected and converged by a second concave reflecting mirror 6 and light spectrum is produced on the surface of an output side slit 7. In case of a sine-wave-like phase grating using surface acoustic wave or the like, the light spectrum is deflected and separated to the three light beams of + or - primary light generated by diffraction and 0-th light that is not subjected to diffraction. Openings are provided in the slit 7 in coincidence with the generating positions of the three light spectrums and light passing the openings is measured by a plurality of light detectors 8.

Description

[Detailed description of the invention] [Industrial application field] This invention uses two diffraction gratings to redirect light.

The present invention relates to an optical spectrum detection device that is capable of detecting dispersed wavelength components of light at high speed.

[Conventional technology]

Methods for detecting wavelength components of light as a spectrum include dispersive spectroscopy and interference spectroscopy.

The present invention relates to dispersive spectroscopy, and there are many conventional methods for detecting optical spectra by rotating a diffraction grating.

This dispersive spectroscopy method can obtain good wavelength resolution through the development of a diffraction grating with high-density ruled lines, and is also easily realized mechanically, making it suitable for current optical spectrum detection. It is the mainstream of equipment.

[Problem that the invention seeks to solve]

However, in this method of detecting optical spectra by rotating a diffraction grating using dispersive spectroscopy, there are limits to the rotation speed of the diffraction grating due to the shape and weight of the diffraction grating, as well as the components of the three-rotation mechanism. There is a drawback that the rotational operation time required for detection is limited to several tens of milliseconds to several milliseconds.

For this reason, there is a problem in that the optical spectrum that changes rapidly (several ms to several μs) with time cannot be detected.

[Means for solving problems]

Therefore, the present invention was made to solve this problem, and a second diffraction grating is newly arranged in the middle of the measurement optical path of an optical spectrum detection device using a conventional diffraction grating. For example, the same applicant
Invention by the same inventor “Surface Acoustic Wave (SAW: 5
Light diffraction device 1i using Surface AcousticWave)! (Japanese Patent Application No. 60-234812) (hereinafter referred to as an acousto-optic light modulator), etc., to provide a function that allows variable control of the diffraction grating spacing. With this function, the second diffraction grating acts as a deflection element that changes the direction of the measured light incident on the conventional first diffraction grating, and as a result, the first diffraction grating is rotated relative to the first diffraction grating. A similar situation can be created.

In addition, since the acousto-optic light modulation element can variably control the diffraction grating spacing at high speed using an electric signal, the state is temporarily the same as that of rotating the first diffraction grating at high speed. It becomes possible to detect spectra at high speed and in a short time.

〔Example〕

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail below based on illustrated embodiments.

FIG. 1 is a diagram showing the configuration of an embodiment of the optical spectrum detection device according to the present invention, and FIG. 2 is one of the diffraction gratings, which is a component of the present invention, and whose diffraction grating spacing can be variably controlled. A diagram showing the configuration of an acousto-optic light modulator, FIG. 3 is a diagram showing a state in which the measured light is changed by the acousto-optic light modulator of FIG. 2, and FIG. 4 is an example of an embodiment of the present invention. A diagram showing an optical system in which the measurement optical system in the example is replaced with a transmission type,
FIG. 5 is a diagram showing the relationship between the tilt angle of the grating direction of the first and second diffraction gratings, which are the constituent elements of the present invention, and the generation position of the output optical spectrum, and FIG. 6 is a diagram showing the relationship between the generation position of the output optical spectrum. 1 is a diagram showing an example of the configuration of an optical system of an optical spectrum detection device using a single diffraction grating.

The prior art will be explained below with reference to FIG.

In the figure, the light to be measured 1 enters a lens 2 and is converged, and an input side slit 3 is placed at the focal point of the lens 2.
The name that passes through the opening.

The light that has passed through the input slit 3 is incident on the first concave reflecting mirror 4 while expanding in a fan shape, and is reflected as a parallel beam and guided to the nine diffraction gratings 5. This diffraction grating 5 is often a rectangular optical diffraction grating with hundreds to thousands of evenly spaced scored lines between each dragon, and the side length of about 2 to 4C11. There is. The measured light 1 incident on the diffraction grating by these high-density ruled lines is reflected while undergoing dispersion according to its wavelength, and proceeds toward the second concave reflection &1!6. The dispersed light to be measured 1 reflected by the concave reflector 6 of No. 2 toward the output side slit 7 converges on the surface of the output side slit 7 at a position corresponding to each wavelength of light, and the aperture of the long lift. photodetector 8
The light intensity is measured by In this measurement, it is necessary to arrange the measured light intensities in the order of the wavelengths included in the light to be measured, that is, according to the optical spectrum, so the position of the output side slit 7 is fixed and the diffraction grating 5 is It is rotated and the intensity distribution of the dispersed light is continuously measured by the photodetector 8. In addition, when measuring dispersed light in a narrow range, the diffraction grating may be fixed and the output side slit 7 and the photodetector 8
may be moved.

In either case, while the diffraction grating 5 is rotating or the output side slit 7 and photodetector 8 are moving, an accurate optical spectrum cannot be detected unless the spectrum of the light to be measured is constant. However, in actual light, most of the spectrum constantly changes over time, and the intervals between these changes are short. Therefore, attempts have been made to shorten the measurement time by rotating the diffraction grating at high speed.

In the present invention, instead of rotating the diffraction grating at high speed, the optical path of the measured light incident on the diffraction grating is deflected by an acousto-optic light modulation element, and the same effect as when the diffraction grating is rotated can be obtained. This is what I was trying to make happen.

Here, the diffraction grating is the first diffraction grating in the present invention.

Since the acousto-optic light modulation element can electrically change the direction of light at high speed, the detection time of the optical spectrum is significantly shortened, making it suitable as an optical spectrum detection device suitable for measuring a fluctuating spectrum. Configurable.

As shown in FIG. 1, the optical system according to the present invention basically looks the same as the conventional device, but a second diffraction element newly constructed from an acousto-optic light modulation element is added after the input side slit 3. A grating 9 is provided to diffract and redirect the light to be measured, and the redirected light is dispersed by the first diffraction grating 5 as in the conventional example. Then, the dispersed light is reflected and converged by the second concave reflecting mirror 6 to produce a light spectrum on the surface of the output side slit 7.

This optical spectrum includes each deflected light of the measured light deflected by the second diffraction grating. The output side slit Three light spectra occur simultaneously on the surface. It is known that these light spectra differ in light quantity but have the same spectrum distribution shape. In the present invention, it is necessary to spatially separate these three light spectra and measure them independently. , the output side slit 7 is provided with openings corresponding to the generation locations of the three light spectra, and a plurality of photodetectors 8 are provided for measuring the light passing through each of the entrances. It has become.

Next, the deflection of the measured light by the second diffraction grating and the generation of a plurality of optical spectra will be explained with reference to FIG. FIG. 2 shows a configuration example of a SAW tunable grating that can be used as a diffraction grating whose grating spacing can be variably controlled. It has a three-layer structure. The substrate 11 and the electrically insulating pedestal 12 are each provided with a light transmitting window aligned with each other at the center thereof, and light passes through this window. , the phase changes due to the SAW propagating on the substrate 11. SA on the surface of the piezoelectric substrate 13
A first interdigital electrode 14a having a structure in which two comb teeth are intertwined to generate W, and this electrode 14a.
The SA generated by the SA and propagated on the piezoelectric substrate 13
A pair of second interdigital electrodes 14b for monitoring W is provided.

FIG. 3 shows how light is deflected when a SAW is used as a phase grating. It has a spatial period d corresponding to the lattice constant, and moves at a speed V in the direction of the arrow. The piezoelectric substrate 1
3 is transparent to light, and when light incident from the left direction in the figure passes through this piezoelectric substrate 13, the incident light is SA
The phase shift is caused by the sinusoidal unevenness of the surface of the piezoelectric substrate 13 caused by W and the change in the density directly under the surface of the piezoelectric substrate 13, that is, the change in the refractive index.

Since this phase modulation is periodic due to the repetition of the spatial period d, when these lights are focused on the focal plane 16 of the lens by the lens 15, they form a diffraction image, just like those transmitted through a normal phase grating. arise.

If the incident light is monochromatic light with wavelength λ, the diffraction image will be
A diffraction bright spot of the ±1st order determined by the lattice constant d is generated.

The generation position of this diffraction bright spot is a distance α' from the optical axis of the focal plane 16, and its direction is equal to the propagation direction of the SAW.

The value of the distance α is expressed as follows, where F is the focal length of the lens 15. Here, the frequency of the sine wave electrical signal is f6
If it changes by ±Δf/2 around , then the focal plane 16
The displacement amount Δα of the ±1st-order diffraction bright spot above is Δ′fFλ Δα−−□−−−(21) As is clear from equation (2), the SAW transmission speed is slow, and the above-mentioned The longer the focal length of the lens 15 and the longer the wavelength λ of the light, the larger the displacement Δα.

If such a SAW tuner puller is placed in the middle of the measurement optical path of the optical spectrum detector, the above-mentioned ±
Three light spectra centered on the first-order diffraction bright spot and the three bright spots of zero-order light that does not undergo diffraction are generated simultaneously, and FIG. 4 shows the optical system according to the present invention shown in FIG. In other words, a convex lens 17.1B is used in place of the first and second concave reflecting mirrors 4.6 in FIG. The optical system replaced with the grating 19 changes the angle of the diffracted light beams generated by the SAW chainable grading, and
It is shown that the light enters the diffraction grating 5 and connects three bright spots again. The dotted line shown in Figure 2 indicates the optical axis of the light beam deflected by the SAW. It can be seen that it has an angle with the optical axis of the folded light. Actually, the first
Since the diffraction grating is of a reflective type, a change in the angle of incidence of the incident light ray produces an effect similar to a rotation of the diffraction grating itself.

Now, if the grating directions of the first and second diffraction gratings 5.9 are the same, the three simultaneously generated spectra described above are as follows.
The spectra are arranged on a straight line, making it difficult to separate each spectrum. In addition, when the grating directions are perpendicular, each spectrum is arranged in a vertical relationship and separation is easy, but by sweeping the SAW frequency and changing the grating spacing of the second diffraction grating, Even if the light spectrum is spatially scanned, there is no effect because it does not move in the direction in which the light spectrum is arranged. Therefore, the grating directions of the first and second diffraction gratings must be oblique.

Figure 5 shows this situation, where the grating direction of the first diffraction grating is the y-axis direction, and the direction perpendicular to the grating direction is the x-direction, and the second diffraction grating (S AW tunable grating) is Figure (a) shows the arrangement of the first diffraction grating, Figure (b) shows the state of the first diffraction grating and its incident light flux, and Figure (C) shows the output distribution lines of the optical spectrum due to these arrangements.
This is shown below. The angle θ is the angle IIJi of the second diffraction grating, but in the present invention, the SA forming the second diffraction grating
SAW is a method that sweeps the frequency of W to move the optical spectrum of the ±1st-order diffracted light on the output side slit 7 surface in the direction in which the spectra are arranged, and performs high-speed scanning photometry using the fixed aperture of the slit. It is necessary to shift UJ of the optical spectrum more effectively with respect to the frequency change of , and for this reason, the angle θ needs to be minimized within a range in which the three optical spectra can be spatially separated on the slit. The part surrounded by the dotted line in FIG.
2 shows an optical spectrum 21 for normal photometry, which is measured by rotating the diffraction grating. In the present invention, an output side slit 7 having an opening at an appropriate portion within this dotted line is used, and if necessary, a plurality of photodetectors 8 are used to detect the optical spectrum. Regarding the display of the optical spectrum, in addition to the conventional method of displaying the wavelength axis by the rotation angle of the first diffraction grating, the wavelength axis can be displayed by the frequency of the SAW generation electric signal applied to the second diffraction grating. Use display methods together.

Various methods can be considered depending on the type or property of the light to be measured, but the most common and simple method is to perform broadband scanning by rotating the first diffraction grating at a low speed, and perform narrow-band high-speed scanning of a specific portion by rotating the first diffraction grating at a low speed. This seems to be a method that can be carried out in a timely manner using the second diffraction grating.

Further, even if the order of the first diffraction grating and the second diffraction grating is changed, the same operation can be performed in principle.

〔effect〕

As described above, according to the present invention, light is deflected at high speed using a diffraction grating whose grating spacing can be variably controlled, and the diffraction grating used for dispersion, similar to that used in conventional devices, is exposed to light. By changing the incident angle of the measurement light, we obtained an effect similar to that achieved by rapidly rotating a diffraction grating for dispersion, and it became possible to significantly shorten the measurement time required for optical spectrum detection. This has made it possible to detect light spectral fluctuations with short fluctuation periods, making it possible to observe changes in the optical spectrum.

[Brief explanation of the drawing]

FIG. 1 shows the configuration of a measurement optical system in an embodiment of the optical spectrum detection device using the second diffraction grating of the present invention. FIG. 2 shows an acousto-optic light variable element (S
This figure shows the configuration of AW Tunable Dating. FIG. 3 shows a state in which the direction of light is changed by the SAW chain puller rating shown in FIG. 2. FIG. 4 shows an optical system diagram in which the measuring optical system in one embodiment of the present invention is rewritten as a transmission type. FIG. 5 shows the relationship between the grating direction inclination θ of the first and second diffraction gratings, which are the constituent elements of the present invention, and the generation position of the output optical spectrum. FIG. 6 shows an example of a measurement optical system of a conventional optical spectrum detection device. In the figure, ■ is the light to be measured, 2 is the lens, 3 is the input side slit, 4 is the first concave reflecting mirror, 5 is the first diffraction grating,
6 is a second concave reflecting mirror, 7 is an output side slit, 8 is a photodetector, and 9 is a second diffraction grating. 11 is a substrate, 12 is an electrically insulating pedestal, 13 is a piezoelectric substrate, 14a is a first interdigital electrode, 14b is a second interdigital electrode, 15 is a lens, 16 is a focal plane, 17 and 18 19 is a convex lens, 19 is a transmission type diffraction grating, 20 is a light spectrum capable of high-speed scanning photometry, and 21 is a light spectrum for normal photometry.Patent applicant Ryuta Koike, Patent attorney, Anri Co., Ltd. Figure 1 1... Light to be measured 2... Lens 3...-Input end slit 4... First concave reflecting mirror 5... First diffraction grating 6... First concave reflecting mirror 7. ... Output side slit 8 ... Photodetector 9 ... First diffraction grating Fig. 2 11 ... Substrate 12 ... Electrically insulating pedestal 13 ... Piezoelectric substrate

Claims (1)

[Claims] In an optical spectrum detection device that emits incident light via first and second diffraction gratings; one of the first and second diffraction gratings is The diffraction grating has a fixed diffraction grating interval and is used to disperse incident light to obtain an optical spectrum. A diffraction grating for spatially changing the optical path of light incident on the diffraction grating, the diffraction grating being deflected by the other diffraction grating having a variable spacing, and one having a fixed diffraction grating spacing. An optical spectrum detection device characterized by comprising a spatial filter for passing only the optical spectrum dispersed by the diffraction grating.