JPS63115111A - Light wavelength demultiplexing detector - Google Patents

Abstract

PURPOSE:To obtain a small-sized, lightweight two-wavelength optical demultiplexing detector while reducing the number of components by providing an elliptic Fresnel lens between an optical input part and a photodetector. CONSTITUTION:Two-wavelength incident light 4 from an optical fiber part 2 is made incident on the elliptic Fresnel lens 1 and converged as branch light beams 51 and 52 on the photodetector while generating chromatic aberration. A converged light spot 71 having long wavelength is thin and long in a Y-axial direction and the other light spot 72 having short wavelength is thin and long in an X-axial direction. Four detectors 31-34 are arranged surrounding the part where the spots 7 cross each other. At this time, only the light with the wavelength lambda1 is converted and made incident on the detectors 31 and 32 and only the light with the wavelength lambda2 is converged and made incident on the detectors 32 and 34. Then a summing amplifier 8 extracts two groups of the outputs of the detectors 3, so that the light wavelengths are demultiplexed and detected.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to an optical wavelength demultiplexing detector used in a receiving terminal of optical multiplex communication.

Conventional technology Optical multiplexing technology using optical fibers is considered to be a technology that not only increases communication capacity but also increases the flexibility and freedom of communication systems, and will play an important role in the future development of optical communication systems. It fulfills the following.

Optical wavelength demultiplexing detectors are required at receiving terminals for optical multiplexing communications. The basic structure of a conventional optical wavelength demultiplexing detector using a grating is shown in FIG. (Aohaku, Minowa, Kobayashi, “Study of grating demultiplexer for 0.8pm%% WDM transmission”, Institute of Electronics and Communication Engineers/Photon Quantum Electronics Research Group Material 0QE-78-104 (1978),
) In the figure, incident light (wavelengths λ1, λ2) inputted from an optical fiber 2 serving as a light input section is converted into parallel light by a collimating lens 9, and subjected to angular dispersion according to the wavelength by a grating 10. After that, it passes through the mirror 12 and becomes the demultiplexed light that is converged by the focusing lens 11.

62 and are guided to photodetectors 31 and 32, respectively,
Wavelength λ1. Each of the incident lights of λ2 is detected.

The problem that the invention aims to solve Another problem was that alignment was troublesome.

The present invention has been made in view of the above problems, and it is an object of the present invention to provide a two-wavelength optical demultiplexing detector that has a small number of component parts, is compact, lightweight, and has excellent reliability.

Means for Solving the Problems In order to solve the above problems, the present invention uses an elliptical Fresnel lens.

Effect of the Invention According to the present invention, a single elliptical Fresnel lens functions as a grating and a lens, and furthermore, it becomes possible to create an optical wavelength demultiplexing detector that is smaller and lighter than a Fresnel lens.

Embodiment FIG. 1 (1) and (1=) are plan views showing the configuration of an optical wavelength demultiplexing detector according to an embodiment of the present invention. The figure (-) shows the elliptical Fresnel lens 1, and the figure Φ) shows the photodetector 3. Take the X and Y coordinates as shown.

FIGS. 2(-) and 2(b) are cross-sectional views of an optical wavelength demultiplexing detector according to an embodiment of the present invention. The same figure (,) is a cross-sectional view at Y=O, and the same figure (b) is a cross-sectional view at X=O. Two axes are taken as shown in Susu. FIG. 3 shows the shape of the light spot 7 focused on the photodetector 3 and the state of signal detection to explain the operation of the optical wavelength demultiplexing detector according to one embodiment of the present invention. It is. An optical wavelength demultiplexing detector according to an embodiment of the present invention will be described with reference to FIGS. 1 to 3. Two wavelengths of incident light 4 (wavelengths λ1, λ22, e.g., λ1: 0.83 μ
m.

λ2=0.78 μm) enters the elliptical Fresnel lens 1 and is focused on the photodetector 3 with a chromatic aberration of 5° with respect to the demultiplexed light 51. Optical fiber 2. Oval Fresnel lens 1. By appropriately arranging the positional relationship of the photodetector 3, the light spot 7 is focused due to the chromatic aberration of the lens.
The λ1 side 71 having a longer wavelength is elongated in the Y-axis direction, and the λ2 side 72 having a shorter wavelength is elongated in the X-axis direction. The photodetector 3 is arranged so as to surround the intersection of the light spots 7.
Four pieces were arranged using l-C34 ma. At this time, the photodetector 31
Only the light with wavelength λ1 is focused on and 33, and only the light with wavelength λ2 is focused on the photodetectors 32 and 34. By extracting them in pairs, it was possible to separate the wavelengths of light and perform detection. The elliptical Fresnel lens 1 is composed of a concentric elliptical grating whose period becomes shorter toward the outside, and is an astigmatic lens having individual focal lengths in the X-axis direction and the Y-axis direction. The elliptical Fresnel lens 1 has a large chromatic aberration, and the product of focal length and wavelength has a constant relationship. In this example, the lens 1 is formed using an 0MS electron beam resist on a glass substrate e by electron beam lithography, and has a size of, for example, 2+m in the X-axis direction and 1.9m in the Y-axis direction. By making the cross section into a sawtooth shape with an optimum film thickness, the light collection efficiency can be improved to approximately 10% at a single wavelength. In this example, the wavelength of the incident light 4 is λ1=0.83 μm, λ2=
Since there are two wavelengths such as 0.78 μm, the maximum film thickness of Fresnel lens 1 is the average value of the two wavelengths λ = (λ1 + λ2) /
2: Set according to 0.805 μm, and considering the refractive index n = 1.6 of the 0MS resist, the maximum film thickness (maximum depth of the grating groove) d is λm/(n-1) = 1.34 μm.
And so. At this time, a high efficiency of 90 or more was achieved for both wavelengths λ1 and λ2. In this way, the maximum film thickness d of the elliptical Fresnel lens 1 is determined by the wavelengths λ1 and λ
Considering that the average value of Efficiency was also high for wavelengths of light. Moreover, the sensitivity of the photodetector 3 used is
When the wavelength differs, it was possible to correct the sensitivity dispersion of the photodetector by changing the maximum film thickness d of the elliptical Fresnel lens 1 from λm/(n-1). For example, 40 wavelengths of incident light λ, = 0.83 μm, λ2 = 0.6328
S on the photodetector 3 in μm, 7. When using a Si photodiode, the sensitivity of the Si photodiode is λ1=0.83μ
Since m is better, the maximum film thickness d of the elliptical Fresnel lens 1 is changed from λm/(n-1)=1.22μm to λ2/(n
-1) = 1.06 μm, it was possible to correct the sensitivity with a certain value. The same effect was obtained in the opposite case. In addition, the elliptical Fresnel lens 1 is manufactured by electron beam lithography, and a replica is formed using it as a master.
Mass production can be easily achieved by manufacturing by a replication method using synthetic resin such as MA or ultraviolet curing resin.

In this embodiment, two sets of four photodetectors 3, 31 to 34''&, were arranged;
It is also possible to use one each, but in this case the sensitivity will be approximately halved. Further, when performing demultiplexing detection of only one wavelength out of two wavelengths, only one set of photodetectors 3 is sufficient. Furthermore, in this embodiment, the photodetector 3 was not placed at the intersection of the light spots 7, but this enabled good demultiplexing detection with low crosstalk.

Effects of the Invention As described above, according to the present invention, optical wavelength division detection is possible using only a thin and lightweight elliptical Fresnel lens and a photodetector, and therefore, it is inexpensive, easy to align, and reliable. This has the advantage that a compact optical wavelength demultiplexing detector with excellent performance can be constructed.

[Brief explanation of the drawing]

FIGS. 1(a) and (n) are a plan view and a sectional view of an optical wavelength demultiplexing detector in an embodiment of the present invention, and FIG. 2(a) is a
), (b) is a configuration diagram of the optical wavelength demultiplexing detector, and FIG. FIG. 4 is a schematic diagram showing the state of output, and is a configuration diagram of a conventional optical wavelength demultiplexing detector. 1... elliptical 7 renel lens, 2...
Optical fiber, 3...Photodetector, 4...
・Incoming light. Name of agent: Patent attorney Toshio Nakao and 1 other person No. 1
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Claims (1)

[Scope of Claims] (1) It has a light input section, an elliptical Fresnel lens, and a photodetector, and the elliptical Fresnel lens is provided between the light input section and the photodetector. Optical wavelength demultiplexing detector. (2) The optical wavelength demultiplexing detector according to claim 1, wherein the grating constituting the elliptical Fresnel lens has a sawtooth cross section. (3) The optical wavelength demultiplexing detector according to claim 1, wherein the photodetector is arranged around the optical axis except at the center. (4) The optical wavelength demultiplexing detector according to claim 3, characterized in that at least four photodetectors are provided. (5) The maximum film thickness (d) of the elliptical Fresnel lens is 0.8·[λ_1+λ_2/2( n-1)]≦d≦1.
2. The optical wavelength demultiplexing detector according to claim 1, which satisfies [λ_1+λ_2/2(n-1]). (5) The maximum film thickness (d) of the elliptical Fresnel lens is: The used wavelength (λ_1, λ_2; λ_1>λ_2), the refractive index (n) of the constituent material of the elliptical Fresnel lens, the sensitivity of the photodetector (S(λ) to the used wavelength (λ_1, λ_2)
_1), S(λ_2)), when S(λ_1)>S(λ_2), [λ_1+λ_2/2(n-1)]≧d≧[λ_2/(
n-1)] When S(λ_1)≦S(λ_2), [λ_1/(n-1)]≧d≧[λ_1+λ_2/2(
The optical wavelength demultiplexing detector according to claim 1, which satisfies [n-1)].