JPS60213830A - Photodiode array - Google Patents

Abstract

PURPOSE:To make it possible to perform spectrum measurement with high resolution, by forming BPFs in a window, arranging an optical fiber, thereby preventing the inclusion of high-order light, stray light and unnecessary light. CONSTITUTION:A transparent optical fiber 3 having a desired wavelength region is arranged in the vicinity of or in close contact with a window 6 and a light receiving surface 2 of a light receiving element. In the window 6, a stray removing filter 4 and a high-order-light removing filter 5, which have desired transmitting characteristics in correspondence with the desired wavelength region of the light receiving element, are constituted. As a result, the effect of the high-order light, the stray light, which is imparted by the sensitivity difference due to the wavelengths of the photodiode, and the unnecessary light due to the repeating reflections between the light receiving surface 2 and the window 6 can be removed.

Description

[Detailed Description of the Invention] [Field of Application of the Invention] Used as a photodetector for a spectrophotometer, by purely electronically scanning photodiodes arranged in an array in the dispersion direction of the measurement wavelength using a shift register. , to perform wavelength scanning without using a mechanical system.

[Background of the invention]

Spectrophotometers using photodiode arrays have attracted attention in recent years as spectrophotometers because they do not require mechanical wavelength scanning and can perform high-speed wavelength scanning purely electronically. However, when a photodiode array is used in a spectrophotometer, the following problems arise because the entire wavelength range used by the photodiode array is constantly irradiated with light dispersed by folded gratings, prisms, etc. That is, (1)
Contamination with higher-order light with a short wavelength corresponding to the measurement wavelength position.

(2) Stray light due to scattered light from a dispersion element such as a diffraction grating and reflected light inside the spectrometer mixes into the measurement wavelength light.

(3) Unwanted light that is repeatedly reflected by the window and the light-receiving surface and mixed into the measured wavelength light.

etc.

In order to eliminate the above problems, (1) a method of arranging bandpass filters with transmission characteristics that vary depending on the location on a single substrate in contact with the light-receiving surface; (2) a method of using a monochromatic glass filter with a transmission band that varies depending on the wavelength; A method has been considered to prevent stray light by forming a protective member by arranging and bonding along the direction of light dispersion, but method (1) realistically requires wire bonding between the light receiving element and the wiring pattern of the protective member. etc., a considerable gap is required between the light-receiving surface and the filter surface, which is generally 0.
A gap of 5 mm or more is required. Although it is effective in removing stray light and high-order light, it is difficult to remove unnecessary light due to repeated reflections between the substrate and the light-receiving surface. In addition, in method (2), if one element of the photodiode array is made to correspond to a unit wavelength difference, the width of the spectral image becomes narrow, and if a glass filter is placed in front of the photodiode array, the light at the end of the filter becomes Disturbance of the spectral image due to refraction and reflection could not be ignored.

[Purpose of the invention]

The purpose of the present invention is to solve problems that occur when using a photodiode array in a spectrophotometer: (1) mixing of higher order light;
) Stray light due to scattered light from the diffraction grating and reflected light inside the spectrometer; (3) Mixture of unnecessary light due to repeated reflections between the window and the light receiving surface. An object of the present invention is to provide a photodiode array in which the

[Summary of the invention]

When the photodiode array is applied to a spectrophotometer, it is possible to perform purely electronic wavelength scanning, and thus a mechanical system for wavelength scanning is completely unnecessary. Instead of adopting a mechanical system for removing stray light and high-order light by switching color glass filters, we devised a static method to eliminate the problems and maximize the benefits of using an array photometer.

[Embodiments of the invention]

An embodiment of the present invention will be described below with reference to FIG. The figure is a cross-sectional view of a photodiode array cut in the direction in which the light-receiving surfaces are arranged.

In the figure, l is a photodiode array, 2 is a light receiving surface, 3 is an optical fiber, 4 is a bandpass filter for removing stray light, 5 is a bandpass filter for removing high-order light, and 6
is the window, 7 is the protective member, 6 photodiode arrays are 4
512 photodiodes are arranged at a pitch of 0 μm, of which 5'01 photodiodes are used, and the range of the photodiodes is 300n+ to 800n+.
It is designed to be measured by setting o&-. Figure 2 shows how high-order light overlaps in the wavelength range. When a tungsten lamp is used as the 6 light sources, the
There is no light with wavelengths less than m. Therefore, when reading spectral data in the wavelength range of 300nm to 800nw+ from a photodiode array, the E
On the window surface corresponding to the photodiode in the range of i00nm to 800n+n, a bandpass filter (Fig. 3) which is opaque in the wavelength range of 40On+n or less is made by vacuum evaporation using cerium oxide as a high refractive index film and magnesium fluoride as a low refractive index film. A multilayer interference filter is formed on the window to remove high-order light.

FIG. 4 shows the spectral sensitivity characteristics of the photodiode.

The output difference in the short wavelength range is large compared to the long wavelength range. Therefore, when measuring the short wavelength range, especially at wavelengths of 400 nm or less, the long wavelength light will be scattered, and if it enters the measurement diode due to reflection etc., the long wavelength light will be Due to its high sensitivity, even a small amount of light can greatly affect measurements. Therefore, 300ruw~400nm
40On+ on the window surface corresponding to the photodiode in the wavelength range
Stray light of long wavelengths is prevented by forming a bandpass filter (FIG. 5) that is opaque in the wavelength range of n or more by the vacuum evaporation method.

FIG. 6 is a conceptual diagram showing the generation of unnecessary light due to repeated reflections between the photodiode array light receiving surface and the window. In the figure, 1 is a photodiode array, 2 is a light receiving surface, and 6 is a window. L, -L, 4 are measurement lights L4~Lrl are L1~L3
This is part of the component that becomes unnecessary light at the time of measurement. The measurement wavelength light receiving surface 2 has measurement wavelength light, ~L3 and L4.
Unnecessary light in a wavelength range longer than the measurement light of ~Lrl also enters at the same time due to repeated reflections between the window and the light receiving surface. Although the front end of unnecessary light is extremely small compared to that of the measurement wavelength light, the spectral sensitivity of the photodiode is extremely high in the long wavelength range compared to short wavelength as shown in Figure 4, so the output due to unnecessary light is 10 at the measurement wavelength of 340 nm. % or more, which causes a large error in measurement.

FIG. 7 shows a conceptual diagram in which mixing of the above-mentioned unnecessary light is prevented by optical fibers. In the figure, 1 is a photodiode array, 2 is a light receiving surface, 6 is a window, 3 is an optical fiber, L, ~L8 is a measurement light, L4 ~ wrinkles,
-L, indicates a component that becomes unnecessary light during the measurement time. In the figure, an optical fiber 3 is bonded to a window 6 and placed close to the light receiving surface 2. By bringing the light-receiving surface and one end surface of the optical fiber close to each other, it is possible to reduce the amount of movement of unnecessary light due to repeated reflections between the light-receiving surface and the end surface, thereby reducing errors in measurement data. In addition, the gaps between the optical fibers are filled with an adhesive that is opaque to light to eliminate interference caused by unnecessary light going around.

According to the above embodiment, the bandpass filter and optical fiber formed in the window remove the influence of higher-order light, stray light caused by sensitivity differences depending on the wavelength of the photodiode, and unnecessary light caused by repeated reflections between the light receiving surface and the window. This provides a photodiode array capable of high-resolution spectrum measurement.

〔Effect of the invention〕

According to the present invention, 1. Wavelength range 60 where higher order light becomes a problem
Since a bandpass filter is provided on the photodiode corresponding to the wavelength range from 0 nm to 800 nm to remove high-order light, measurement errors due to contamination of high-order light can be prevented. 2. Short wavelength range 300
Since the photodiode corresponding to the wavelength range from nm to 400 nm is equipped with a bandpass filter that cuts off the long wavelength range, it is possible to prevent measurement errors due to stray light in the wavelength range63.
．． Since the incident light is guided to the light-receiving surface by the optical fiber after passing through the window, it is possible to prevent unnecessary light from being mixed into the measurement light due to repeated reflections between the window and the light-receiving surface.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view of the photodiode array according to the present invention, FIG. 2 is a diagram showing how secondary light overlaps with respect to the measurement wavelength range, FIG. 3 is a spectral characteristic diagram of a secondary light removal filter, and FIG.
FIG. 5 is a spectral sensitivity characteristic diagram of a photodiode, FIG. 5 is a spectral characteristic diagram of a stray light removal filter, FIG. 6 is an explanatory diagram of unnecessary light due to repeated reflection, and FIG. 7 is an explanatory diagram of removal of repeatedly reflected light. 1... Photodiode array, 2... Light receiving surface, 3...
...Optical fiber, 4...Stray light removal filter,
5...High-order light removal filter. Agent Patent Attorney Akio Takahashi 170-

Claims (1)

[Claims] 1. In a photodiode array consisting of a light-receiving element and a large window that protects the light-receiving element, an optical fiber that is transparent in a desired wavelength band is disposed close to or in close contact with the window and the light-receiving surface. . A photodiode array, characterized in that the window comprises a filter corresponding to a desired wavelength band of the element and having desired transmission characteristics. 2. A photodiode array according to claim 1, characterized in that the optical fiber is filled with a property that is clearly opaque to light.