JPH03204604A - Spectroscope and optical demultiplexer - Google Patents

Abstract

PURPOSE:To obtain the small-sized, inexpensive spectroscope by providing a plane-shaped optical diffraction element which resolves incident divergent light in wavelength, and diffracts each light beams converged in different directions, and a photodetector which detects the converged light beams respectively. CONSTITUTION:This device is equipped with the plane-shaped optical diffraction element 2 which resolves the incident divergent light 3 in wavelengths, and diffracts the each converged light beams 4 converged in the different directions, and the photodetector 5 which detects the converged light beams respectively. Then when diverged light 3 is made incident on the diffraction element 2, the light is dispersed by wavelength through the diffraction and converged in the different directions and the converged light beams 4 are made incident on and detected by the photodetector 5 respectively. This optical diffraction element 2 is large in the degree in freedom of design of convergence distance, etc., as compared with a conventional concave grating, its replica is easily manufactured because of the plane shape, and the necessary area becomes small. Consequently, the small-sized, low-cost spectroscope is obtained.

Description

[Detailed Description of the Invention] [Field of Industrial Application] This invention is applicable to a spectrometer applied to the field of optical measurement and to the field of optical communication, and in particular to an optical demultiplexer that wavelength-decomposes a wavelength-multiplexed optical signal. It is related to vessels.

[Conventional technology]

A spectrometer is a device that separates light of multiple wavelengths, and occupies an important position in the field of measurement.

The configuration of a conventional spectrometer is shown in FIG. A slit 72 for limiting the exit pupil is provided near the end face of the input optical fiber 71 that guides the light to be measured.
The light diverging from the concave grating 73 is reflected by the reflecting mirror 75, enters the concave grating 73, is wavelength-resolved by the concave grating 73, and is focused on a specific surface due to the concave shape of the concave grating 73. The wavelength-resolved convergent light is then detected by an image sensor 74. 76 is a box that supports the entire optical system.

On the other hand, wavelength division multiplexing optical communication enables large-capacity optical communication, but its realization requires an optical demultiplexer for wavelength-separating light of a plurality of wavelengths. The configuration of a conventional optical demultiplexer is shown in FIG. The light emitted from the input optical fiber 81 becomes diverging light, but it becomes parallel light by the SELFOC lens 82 and enters the diffraction grating 83 made of parallel and equidistant straight lines via the prism 85. The light is diffracted by the diffraction grating 83, and since different wavelengths of light have different diffraction angles, wavelength separation is performed. The decomposed light passes through the SELFOC lens 82 again and is focused on the end face of each output optical fiber group 84, and enters each of the optical fibers.

[Problem to be solved by the invention]

In conventional spectrometers, a concave grating 73 has been used as an element for wavelength resolution. This is a linear grating formed on a concave surface of a specific shape, and serves to wavelength-resolve the light diverging from the slit 72, and also realizes a light focusing function using the concave surface of a specific shape.

However, this concave grating 73 is not easy to process, leading to high costs, and in order to focus light at a short distance, the curvature of the concave surface is large and the period of the grating becomes small, making it difficult to realize. As a result, there was a problem in that the size of the spectrometer could not be reduced.

On the other hand, in conventional full-wavelength detectors, a reflective diffraction grating 83 patterned into a group of parallel, equally spaced straight lines has been used as an element for wavelength decomposition. Optical fiber 81 for input
A SELFOC lens 82 has been used to collimate the divergent emitted light from the diffraction grating 83 and to condense the light that has been dispersed by the diffraction grating 83 and guide it to a group of optical fibers 84 for output.

However, when this SELFOC lens 82 is used, there are problems in that the optical system of the optical demultiplexer becomes complicated, making it difficult to downsize and increasing costs.

Therefore, an object of the present invention is to provide a small and inexpensive spectrometer and optical demultiplexer.

[Means to solve the problem]

The spectrometer according to claim 11 is provided with a planar optical diffraction element that wavelength-decomposes incident diverging light and diffracts convergent light that converges in different directions, and a photodetector that detects each of the convergent lights. It is something.

In the spectrometer according to claim (2), in claim (1), the optical diffraction element forms a diffraction grating by an electron beam drawing method.

The optical demultiplexer according to claim (3) includes an input optical fiber that outputs wavelength-multiplexed diverging light, and an optical diffraction element that wavelength-decomposes the diverging light and diffracts convergent light that is converged in different directions. and a group of output optical fibers into which the convergent light enters, respectively.

In the optical demultiplexer according to claim (4), in claim (3), the optical diffraction element forms a diffraction grating by an electron beam drawing method.

[Effect]

Claim! According to the spectrometer No. 11, when diverging light enters the optical diffraction element, it is dispersed into wavelengths by diffraction and converged in different directions, and each convergent light enters a photodetector and is detected. Compared to conventional concave gratings, this optical diffraction element has a greater degree of freedom in design such as focusing distance, and because of its planar shape, it is easy to manufacture replicas, and the area required is small, so it is extremely compact and low cost. A spectrometer is realized.

According to the spectrometer of claim (2), since the diffraction grating of the optical diffraction element is formed by electron beam lithography, a pattern with a small period and a large curvature can be easily formed. Since the distance between elements can be reduced, the spectrometer can be further downsized.

According to the optical demultiplexer of claim (3), when the wavelength-multiplexed diverging light emitted from the input optical fiber enters the optical diffraction element, the diffraction causes it to be dispersed into wavelengths and converged in different directions. Then, each convergent light enters a group of output optical fibers. Therefore, since a conventional SELFOC lens or the like is not used, a compact and low-cost optical demultiplexer can be realized.

According to the optical demultiplexer of claim (4), since the diffraction grating of the optical diffraction element is formed by electron beam lithography, a pattern with a small period and a large curvature can be easily formed.
Therefore, since the distance between each component of the optical demultiplexer can be reduced, the optical demultiplexer can be further downsized.

〔Example〕

A first embodiment of the present invention will be described based on FIGS. 1 to 4. That is, in FIG. 1, 1 is an input optical fiber, and 2 is a reflective optical diffraction element arranged obliquely with respect to the optical axis of the input optical fiber 1 in the radiation direction. For example, white diverging light 3 emitted from the end face of the input optical fiber l is diffracted by the optical diffraction element 2,
The light is converted into convergent light 4 and detected by an image sensor 5 which is a photodetector. Since the convergent light beams 4 having different wavelengths have different diffraction angles, the convergent light beams 4 are separated into wavelengths and are detected at different positions on the surface of the image sensor 5. 6 is a box that supports the entire optical system.

The design principle of this optical diffraction element 2 will be explained using FIG.

That is, the optical diffraction element 2 is composed of a diffraction grating having a structure in which the curvature and period change continuously, and the curve shape of the diffraction grating is represented by a part of a group of quartic curves. Assuming an orthogonal coordinate system of x and y on the planar optical diffraction element 2, the axis connecting the point P at the center of the end face of the input optical fiber l, which is the divergence point of light, and the origin 0 of the coordinates is The angle between the light diffraction element 2 and the vertical direction is θ1, and the distance between the point P and the origin 0 is rl. In addition, the center point Q of the detection position of the image sensor 5 that detects light with the center wavelength λ of the wavelength range to be separated is located at a distance llff2 from the origin O, and the axis connecting the point Q and the origin 0 is the optical diffraction element 2. The angle made with the perpendicular direction is 02. However, the directions of θ1 and θ2 are defined to be opposite directions.

The shape of the diffraction grating is set so that the phase of light emitted from point P, reaching point G, which is one point of the diffraction grating formed on optical diffraction element 2, and reflected and reaching point Q, is aligned. In this case, this diffraction grating acts as a lens.

That is, if the point G (x, y) is considered as the equiphase point of the diffraction grating, the shape of the diffraction grating is given by the following equation.

PC+QG=mλ+ (constant) ・−・・−・−+11 Here, λ is the center wavelength of the demultiplexing region, and m is an integer.

If the constant at the origin ○ is set to 0, and the shape of the diffraction grating is expressed by x and y coordinates, it is expressed by the following equation.

= mλ+'I" f 2 --(21 Fig. 3 shows a cross section of the optical diffraction element 2 formed by electronic computer-controlled electron beam lithography, and Fig. 3A shows its surface pattern (overall size). is the l-angle, and there are actually 30 patterns between the curves.), that is, about 0
．． A 3 μm positive type electron beam resist 8 is irradiated with an electron beam in the curved shape expressed by the above equation (2), and the portion irradiated with the electron beam is removed by immersing it in a developer. A thin film (film thickness 0.03 μm) and a thin gold film (IIIO 216 μm) 9 are formed in this order to form a diffraction grating with high reflectance. The layer of ROM is intended to increase the adhesion between the gold and the silicon substrate 7. Also 3rd B
The figure shows the spectral spectrum when light from an ultra-high pressure mercury lamp is incident on this optical diffraction element 2 from the optical fiber 1 ((a) in the same figure).
) and when He-Ne laser light is incident ((b) in the same figure).
)) (The absolute value of the horizontal axis is fa
) and (different in bl).

As a result of configuring the spectrometer shown in FIG. 1 using this optical diffraction element 2, the wavelength band is 0.4 μm to 0.8 μm, and the resolution is 2.
A 0 nm spectrometer was obtained. The shape of the concave portion of the optical diffraction element 2 used in this spectrometer is expressed by the above equation (2), and the parameters are 'I = 2.6 m, θ1 = 65.4'' f2 = 40 m, θ2
−0°, λ=0.62 μm, and the size of the region where the diffraction grating is formed is 1×1 crane 1.

FIG. 4 shows the calculation results of the spectral characteristics of this optical diffraction element 2. This shows a geometric optical image corresponding to the aperture of the diffraction grating in a plane parallel to the optical diffraction element 2, with a wavelength interval of 20 nm. An image of light from 0.4 μm to 0.8 μm was displayed (one trapezoid corresponds to one wavelength). The wavelength is 0.
It can be seen that when the distance changes from 62 μm, the image spreads and the position changes. Furthermore, since images of adjacent wavelengths do not overlap, the resolution of 20 μm is satisfied. A CCD image sensor with a size of 25fi (wavelength dispersion direction) x 5n was used as the image sensor 5, and its output was processed by a personal computer.

A second embodiment of the invention will be described based on FIGS. 5 and 6. That is, in FIG. 5, 10 is an optical fiber for manual use, 11 is a reflective optical diffraction element arranged obliquely with respect to the optical axis in the radiation direction of the input optical fiber 10, and It has the same configuration as the optical diffraction element. Divergent light 13 emitted from the end face 12 of the input optical fiber 10 reaches the optical diffraction element 11 . The light is converted into convergent light 14 due to the diffraction phenomenon, but due to the optical dispersion effect, the light is focused at different specific positions for each wavelength, and enters the end faces 16 of the output optical fiber group 15, respectively.

In this example, the center wavelength is 1.3 μm, and the wavelength interval is 2 nm.
We obtained a 5-wavelength optical demultiplexer. The shape of the concave portion of the optical diffraction element 11 used in this optical demultiplexer is expressed by the above equation (2), and the parameters are f+=3.4vs, θ,=42″, r2=47
．． 8 cranes, θ2=-33', λ-1, 3 μm, the size of the area where the diffraction grating is formed is 1.2 (x direction) xt
, s (y direction) is dragon 2.

FIG. 6 shows the calculation results of the spectral characteristics of this optical diffraction element 11. The figure shows a geometric optical image corresponding to the aperture of the diffraction grating in a plane parallel to the planar optical diffraction element 11, and the wavelength is 2 nm and 1 gI interval from 1.296 μm to 1.304 μm.
(One square corresponds to one wavelength)
. The double concentric circle indicates one optical fiber of the output optical fiber group 15, and the inner circle indicates the core. The optical fiber is a multimode Gl fiber with a core diameter of 80 μm, and
They are arranged at intervals of 25 μm. In addition, 1.296 μm
Using five 1.3 μm band external cavity semiconductor lasers whose wavelengths are controlled at lnm intervals from 1.304 μm to 1.304 μm,
Input light is obtained by wavelength multiplexing.

A third embodiment of the invention is shown in FIG. That is, the transmission type optical diffraction element 1 is used instead of the reflection type optical diffraction element 11.
1' is used. The shape of the diffraction grating is exactly the same as that of the reflective type, but the substrate is a transparent quartz substrate, and a thin gold film as shown in FIG. 3 is not formed on the resist surface.

It should be noted that the optical diffraction element 2.11 may be produced using an electronic computer-controlled electron beam lithography method as a master, and may be reproduced by a replica process.

〔Effect of the invention〕

The spectrometer of claim +11 separates the diverging light into wavelengths using a flat optical diffraction element and converges them in different directions, so compared to conventional concave gratings, the spectrometer has greater freedom in design such as focusing distance. Because of its large size and planar shape, it is easy to make a replica, and the area required is small, so it has the effect of realizing a spectrometer that is extremely compact and low cost.

In the spectrometer of claim (2), since the diffraction grating of the optical diffraction element is formed by an electron beam writing method, a pattern with a small period and a large curvature can be easily formed, and the distance between each component of the spectrometer can be reduced. This allows the spectrometer to be further miniaturized.

The optical demultiplexer of claim (3) separates the wavelength-multiplexed diverging light into individual wavelengths using a flat optical diffraction element and converges them in different directions, so it does not use a conventional Selfoc lens or the like. This has the effect of realizing a small, low-cost optical demultiplexer.

In the optical demultiplexer of claim (4), since the diffraction grating of the optical diffraction element is formed by electron beam lithography, a pattern with a small period and a large curvature can be easily formed, and a pattern between each component of the optical demultiplexer can be easily formed. Since the distance can be reduced, the optical demultiplexer can be further downsized.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram of a spectrometer according to a first embodiment of the present invention, FIG. 2 is an explanatory diagram explaining the principle of an optical diffraction element, FIG. 3 is an explanatory diagram of the cross-sectional structure of an optical diffraction element, Figure 3A is an enlarged view of the surface pattern, Figure 3B is a spectrum diagram of the optical diffraction element, Figure 4 is a diagram showing an example of the spectral characteristics of the optical diffraction element used in this spectrometer, and Figure 5 is the second FIG. 6 is a diagram showing the spectral characteristics of the optical diffraction element used in this optical demultiplexer, FIG. 7 is an explanatory diagram of the third embodiment, and FIG. 9 is an explanatory diagram of a conventional spectrometer, and FIG. 9 is an explanatory diagram of a conventional optical demultiplexer. 2... Optical diffraction element, 3... Divergent light, 4... Convergent light, 5... Image sensor as a photodetector (Figure 3A) Figure 3B (a) (b) Figure Figure ↓ One wave k (nm) Procedurally published (self-published) Specification page 9, lines 5 to 7, August 31, 1990=mλ+f1 +f2 ・・・・・・・・・(2 )” 1990 Patent Application No. 000835 2mλ+f. +f2 ・・・・・・・・・(2)” and the person who makes the correction by 3 degrees. Relationship with Hanyu

Claims (4)

[Claims] (1) A spectrometer comprising a planar optical diffraction element that wavelength-resolves incident diverging light and diffracts convergent light that converges in different directions, and a photodetector that detects each of the convergent lights. (2) The spectrometer according to claim 1, wherein the optical diffraction element has a diffraction grating formed by an electron beam lithography method. (3) An input optical fiber that outputs the wavelength-multiplexed diverging light, an optical diffraction element that wavelength-decomposes the diverging light and diffracts the convergent light that is converged in different directions, and the convergent light is input to each of them. Optical demultiplexer with a group of optical fibers for output. (4) The optical demultiplexer according to claim 3, wherein the optical diffraction element forms a diffraction grating using an electron beam lithography method.