JPH0814510B2 - Spectroscopic device - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a spectroscopic device using the principle of Fourier spectroscopy, and more particularly, to improvement in structure and characteristics of a spectroscopic device configured to give birefringence to light. Regarding

<Prior Art> Conventionally, as this type of spectroscopic device, one shown in FIGS. 2 to 4 has been known.

In the device shown in FIG. 2, the light incident from the entrance slit 11 is converted into a parallel light flux by the concave mirror 12 and is incident on the diffraction grating 13.
The transmitted light or the diffracted light is imaged by the concave mirror 14.

The device shown in FIG. 3 is a spectroscopic device based on the principle of Fourier spectroscopy using a two-beam interferometer. The light incident from the entrance slit 21 is made into a parallel light by a lens 22, and this parallel light is made by a half mirror 23. Two ray bundles and each ray bundle is a reflecting mirror
The reflected light is reflected by 24 and 25, and these reflected lights are made incident on the slit 27 through the lens 26. In this device, when either one of the reflecting mirrors 24 and 25 is moved in the direction shown by the arrow to change the optical path difference between the two ray bundles, the signal interface obtained from the light receiving element 28 receiving the light passing through the slit 27 is changed. Since the ferrogram is the Fourier transform of the spectral distribution of the incident light, this inverse transformation is performed so that the original spectral distribution can be known.

The device shown in FIG. 4 is a Fourier spectroscopy device that utilizes the wavelength dependence of birefringence. Between the polarizer 32 and the analyzer 33, two birefringent crystal plates 31a and 31b are stacked in a wedge shape,
It is designed to give a phase difference between the ordinary ray and the extraordinary ray by sliding the layers and changing the thickness d ₁ .

<Problems to be Solved by the Invention> However, in the conventional configuration shown in FIG. 2, in order to improve the resolution, the slit on the light receiving side needs to be thin, and the resolution and the accuracy are improved at the same time. There is a problem that it is difficult to let them do it. Compared to Fig. 2, the one shown in Fig. 3 does not require an entrance slit and can simultaneously measure the whole spectrum of the light entering the light receiving element. Since the amount of light is large, the S / N ratio is good. However, on the other hand, it has advantages such as high wavelength accuracy, but it is necessary to move the reflecting mirror to change the optical path difference, mechanical accuracy is required, miniaturization is difficult, and vibration is weak. .
Further, the one shown in FIG. 4 has a drawback that it is difficult to give a large phase difference and a high resolution cannot be obtained.

The present invention has been made in view of the above-mentioned problems of the prior art. It does not require components that require mechanical precision, is resistant to vibration, and can be downsized and integrated. The spectroscopic device has good resolution and precision. The purpose is to realize.

<Means for Solving the Problems> The configuration of the present invention for solving the above problems includes a first polarization separation element for extracting output light from a reference wavelength light source and extracting a linear polarization component, A second polarization demultiplexing element that receives the light to be measured and extracts a linear polarization component, an optical multiplexer that combines the output light from the first and second polarization demultiplexing elements, and an optical fiber in a loop shape. The output light from the optical multiplexer is input to the wound optical fiber which is formed by winding a plurality of times into the wound optical fiber, and the wound portion is rotated at an arbitrary angle in a direction perpendicular to the traveling direction of the light. The birefringence amount control means for continuously changing the birefringence amount to the light, and the demultiplexing for separating the output light from the birefringence amount control means into the light from the reference wavelength light source and the light from the measured light And a third component for extracting linearly polarized components from the respective output lights from this demultiplexer And a fourth polarization separation element, and first and second photoelectric conversion elements that receive the output light from the third and fourth polarization separation elements and convert them into electric signals, respectively. Is input and the birefringence amount of the reference light is changed continuously by the birefringence control means, and the spectrum distribution is calculated from the change amount of the birefringence amount of the measured light by Fourier spectroscopy. It is characterized by comprising an arithmetic control unit for obtaining

<Embodiment> FIG. 1 is a structural explanatory view showing an embodiment of a spectroscopic device of the present invention.

In the figure, 41 is a reference wavelength light source that outputs a laser having a wavelength of λ ₀ , and 42a is a first polarization separation element (for example, a polarization beam or a splitter) that inputs the laser and extracts a linear polarization component. Reference numeral 42b is a second polarization separation element for injecting the measured wavelength A of λ ₁ to λ ₂ and extracting its linear wavelength. The output light from these first and second polarization separation elements is the optical fiber 60. It is guided to an optical multiplexer (for example, a fusion type optical coupler, a dichroic mirror, etc.) 43 via. The output from the optical multiplexer is incident on the optical demultiplexer 44 via the optical fiber 60, and the optical fiber is wound in a loop a plurality of times to form a birefringence amount control means. The loop-shaped optical fiber includes a rotation means (not shown), and is rotated in the opposite direction when the optical fiber is rotated 360 degrees from a certain position to the extent that the optical fiber is not twisted. When the optical fiber is wound in a loop shape, anisotropy occurs inside the optical fiber, and the optical fiber plays a role similar to that of the “wave plate”. By rotating this loop-shaped optical fiber in the direction of arrow BB '(right angle to the traveling direction of light), the birefringence amount of guided light changes according to the rotation angle. It is known that the degree of this change is almost inversely proportional to the wavelength of light (the theory of this birefringence control means will be described later).

The optical demultiplexer 44 separates the light from the birefringence amount control means 45 into the light of the laser λ _{0 and} the light of the measured light λ _{1 to} λ ₂ from the reference wavelength light source, and the separated output light is the first light. Only the linearly polarized component is extracted by being incident on the third and fourth polarization separation elements 42c and 42d. The output light from this polarization separation element is incident on the first and second photoelectric conversion elements 46a and 46b, respectively, and after being converted into an electric signal, an operation including an amplifier 50a, an A / D converter 50b, a computer 50c, etc. Input to the control unit 50. The amplifier 50a amplifies the electric signal of the measured light from the second photoelectric conversion element 46b, and
Output to D converter 50b. Usually, in the birefringence control means, the birefringence amount and the rotation angle (B-
Reproducibility with B'direction) is not guaranteed. Here, the first
The signal of the photoelectric conversion element 46a is used as a reference signal. That is, when the measured light is converted into a digital signal by the A / D converter 50b, a signal of a reference wavelength whose wavelength is known is used as a sampling (clock) signal. This means that the light of the wavelength to be measured is measured with the birefringence amount of the reference signal having a known wavelength as a reference, so that the above problem does not occur. The signal of the measured light sampled by this clock signal is sent to the computer, and the computer performs spectrum calculation.

Next, the operation of the birefringence control means in which the optical fiber is wound in a loop will be described.

Birefringence δ _η (ra
d) is given by the following equation.

δ _η = (2π) ² ar ² N / (Rλ) ... r; radius of optical fiber N; number of turns R; bending radius of optical fiber λ; wavelength a; constant determined by material and structure of optical fiber The ceremony is the magazine "ELECTRONICS LETTERS 25th S
eptember 1980 Vol. 16 ”is a known formula.

As can be seen from the equation, the birefringence δ _η is inversely proportional to the wavelength λ. However, in practice, the birefringence δ _η may not be exactly inversely proportional to the wavelength λ, so the relationship between δ _η and λ should be determined experimentally.

Here, by modifying the equation as _{Δ = λδ η = {(2π} ) 2 ar 2 N} / R, is (upsilon and the spectral distribution of the light to be measured B _upsilon is the reciprocal of the wavelength shows the wavenumber ). Light obtained the [delta] _eta by continuously changing the output (photoelectric conversion element of lambda ₁ to [lambda] ₂ side) is given by the following equation using the δ η = _υΔ.

(In this equation, the polarization separation elements on the incident side and the output side are in the same direction. In the case of the opposite direction, the same is true although the values in {} of the two equations change.) If Δ = 0 in the equation The change amount obtained by subtracting the direct current component from the formula using these three formulas can get. As is clear from the equation, I (Δ) is the Fourier transform of the spectral distribution B (υ). Therefore, from the relationship of the inverse Fourier transform Becomes Therefore, the Fourier distribution of I (Δ) can be used to obtain the spectral distribution of the light source.

Since it is impossible to take Δ to infinity, the integral interval of the equation is finite. However, for these, it is possible to execute operations with few errors by processing such as "multiply window function" that is generally performed in FFT operations. I can. Note that the reference light λ ₀ is outside the range of the measured light in terms of wavelength.

<Effects of the Invention> According to the present invention as specifically described above with reference to the embodiments, (1) a component such as a Fourier spectrometer using an interferometer that requires mechanical accuracy is not required, and the light is It is strong against vibration because it reaches the photoelectric conversion element without exiting the fiber or other components.

(2) Since the interferometer is not required, the structure is simple and can be downsized.

(3) The birefringence amount can be freely selected by appropriately selecting the number of windings and the winding diameter of the fiber loop, and there is no restriction as compared with the one using the crystal shown in FIG. .

(4) The S / N is good and the wavelength is accurate, so the advantages of Fourier spectroscopy can be fully utilized.

[Brief description of drawings]

FIG. 1 is a structural explanatory view showing one embodiment of the present invention, FIG. 2 is a front view showing another embodiment of the birefringence amount control means, and FIGS.
FIG. 4 is a diagram showing a conventional example. 41 ... Reference wavelength light source, 42a to 42d ... First to fourth polarization separation elements, 43 ... Optical multiplexer, 44 ... Optical demultiplexer, 45 ... Birefringence amount control means, 46a, 46b ...... First and second photoelectric conversion elements, 47 ...
… Collimator lens, 50… Calculation controller.

Claims (1)

[Claims] 1. A first polarization demultiplexing element for injecting output light from a reference wavelength light source to extract a linear polarization component, and a second polarization demultiplexing element for injecting light to be measured and extracting a linear polarization component. An element, an optical multiplexer for merging output light from the first and second polarization separation elements, and an optical multiplexer formed by winding an optical fiber a plurality of times in a loop shape, and the optical multiplexer on the wound optical fiber. Birefringence amount control means for continuously changing the birefringence amount of light by inputting the output light from the device and rotating the wound portion at an arbitrary angle in a direction perpendicular to the traveling direction of the light. And a demultiplexer for separating the output light from the birefringence control means into light from the reference wavelength light source and light from the measured light, and a linear polarization component from each output light from this demultiplexer. The third and fourth polarization separation elements to be extracted and the outputs from these third and fourth polarization separation elements The first and second photoelectric conversion elements that receive the incident light and convert them into electric signals, and the outputs of these photoelectric conversion elements are input, and the reference light of the reference light when continuously changed by the birefringence control means is input. A spectroscopic device comprising an arithmetic control unit that obtains a spectral distribution by Fourier spectroscopy from the change amount of the birefringence amount of the light to be measured based on the change amount of the birefringence amount.