JPH04221723A - Photodetecting mechanism - Google Patents

Abstract

PURPOSE:To provide a photodetector which can detect the power of light of low level which enters from a light directly or through an optical fiber cable with good accuracy. CONSTITUTION:In order to remove an influence of heat of an optical fiber cable 2 where measured light enters, a temperature compensating optical fiber 4 is provided. In order to make the temperature compensating optical fiber 4 reach the same temperature of the optical fiber cable 2, the optical fiber 4 is thermally connected to the optical fiber cable 2 by a holder 9. Further, the radiation heat from each optical fiber is detected by the respective photodetecting elements 3, 5. A difference between the respective output is obtained by an electric processing to detect a light level of light from the optical fiber 2 to be found.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a photodetection device capable of detecting the power of light incident from a light source, particularly the power of low-level, wide dynamic range light incident through an optical fiber.

0002

2. Description of the Related Art A photodetector for detecting the power of light from a light source includes a light receiving element that converts incident light into an electrical signal. After the light incident from the light source is converted into an electrical signal, it is amplified to a predetermined level and output to, for example, an optical power meter, which is a testing device, and its value is indicated.

Furthermore, this type of photodetector is used, for example, as a standard photodetector in a calibrator for general-purpose equipment. in this case,
There are two types of standard photodetectors: parallel light is incident directly from a light source, and parallel light is incident through an optical fiber.
As shown in FIG. 2, the value of the standard detector 24 is determined using the optical power from the collimated light source 23 using the standard optical power meter 25.

Furthermore, as shown in FIG.
The fiber light source 28
The optical power from the detector is adjusted by an optical attenuator 29, and in this state, the device to be calibrated is replaced with a general-purpose detector 30, and calibration is performed by a general-purpose power meter 31.

[0005]

By the way, when this type of device is used in combination with other devices, each device is generally connected by a connector, and this operation is performed manually by the user.

However, in the above-mentioned photodetection device,
Since thermoelectric elements are used as elements for detecting light, they are susceptible to changes in ambient temperature, and it takes a long time for these temperature changes to settle down. Therefore, it is necessary to suppress heat transfer to the inside of the device as much as possible through the optical fibers, which have different ambient temperatures and individual heat conduction characteristics.

As a method of suppressing the ambient temperature and heat transfer from the optical fiber as much as possible, as shown in the cross-sectional view of FIG.
A structure has been considered in which the light-receiving element is covered with a heat insulating material and, at the same time, the connector fastening holder is rotated at a position sufficiently far from the light-detecting element (Reference: Kenji Kuroda et al., "High-speed, high-precision optical power meter" (Institute of Electrical Engineers of Japan) Study group materials IM-90-57))
.

However, even with the structure shown in FIG. 5, the influence of heat through the optical fiber cannot be ignored for very low light levels, and specifically, the lowest detection level is about -20d.
This can only be achieved up to Bm, and there is a need for optical measurement technology.
It was not possible to cope with the need for higher precision in optical power measurement. In addition, as shown in Fig. 6, two light receiving elements of the same shape are used.
Attempts have been made to reduce noise from surrounding radiant heat and improve the minimum detection level by arranging them close together and using one for detection and the other for compensation, but they had the same problem. (Reference: Yasuyuki Suzuki et al. “Calorimeter for optical fiber output light” (IEEJ study group material IM-90
-56)).

In other words, in order to improve measurement accuracy in low-level measurements, it is essential to reduce noise factors. Figure 7 as a noise factor in the photodetector
The following three factors are considered. N1 is noise generated by the operating resistance (600 ohms) of the photodetector, and N2 is noise generated by the on-resistance (approximately 200 ohms) of the chopper. N1 and N2 are calculated using Equation 1.

0010

[Math 1]

By calculation, N1=1.7nV, N2=1
．． 0nV, and furthermore, the noise generated by the preamplifier N3
As a result of actual measurements, a result of N2=1.7 nV has been obtained. Therefore, the total noise Ns is expressed by Equation 2.

0012

[Math 2]

[0013] In other words, the noise from the three factors is 2.6
Since it is nV, if there are no other noise factors, -30
This means that dBm (300 nV) can be detected with an accuracy of 1%. However, in reality, it is possible to detect only -20 dBm with an accuracy of 1%. This is because the conventional configurations shown in FIGS. 5 and 6 do not sufficiently eliminate the influence of other factors than the above three factors, that is, the influence of thermal radiation propagated from the optical fiber cable. In order to eliminate these problems, it is an object of the present invention to provide a photodetection device that does not affect measurement accuracy even if there is a change in ambient temperature.

[0014]

[Means for Solving the Problems] In order to solve the above problems, the present invention eliminates the influence of heat on the optical fiber cable 2 through which the light to be measured is incident, so that the temperature becomes the same as that of the optical fiber cable 2. A temperature compensation optical fiber 4 is provided. Furthermore, a light receiving element 3 for detecting the amount of light and radiant heat from the optical fiber cable 2 and a light receiving element 5 for detecting radiant heat from the temperature compensating optical fiber 4 were provided. Furthermore, the difference between each output is calculated by electrical processing,
Detects the radiant heat due to the desired amount of light, that is, the light level. Specifically, the following configurations (a) to (e) were adopted.

(a) a first light receiving element 3 that receives light incident through the optical fiber cable 2; and (b) a temperature compensating optical fiber 4 for removing the influence of heat on the optical fiber cable 2. (c) means 9 for thermally contacting the temperature compensating optical fiber 4 with the optical fiber cable 2; and (d)
a second light receiving element 5 receiving radiant heat from the temperature compensation optical fiber 4; and (e) means 6 for detecting the difference in output signals of the first light receiving element 3 and the second light receiving element 5 (hereinafter referred to as (simply referred to as "detecting means 6").

[0016]

[Operation] According to the photodetecting device configured as described above, the first light receiving element 3 detects the radiant heat P1 of the light incident through the optical fiber cable 2 and the radiant heat P2 due to the heat of the optical fiber cable 2 itself. It receives the sum and outputs the detection voltage V1.

Further, the second light-receiving element 5 receives radiant heat P3 due to the heat of the temperature-compensating optical fiber 4, and outputs a detection voltage V2. Here, since the optical fiber cable 2 and the temperature compensation optical fiber 4 are thermally connected, P
2 and P3 are equal. P1+P2=V1...(3) P3=P2=V2...(4) P1=V1-V2...(5) From equation 5, it is not affected by the radiant heat P2 due to the heat of the optical fiber cable 2 itself. In addition, the radiant heat P1 of the light can be detected by the means 6 for detecting it.

Here, in order to equalize the radiant heat output of the first light receiving element 3 and the second light receiving element 5 at the same temperature, the detecting means 6 is calibrated in advance.

[0019]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. 1 and 2 are block diagrams of an embodiment of the present invention, with FIG. 1 being a schematic cross-sectional view of a photodetector, and FIG. 2 being a schematic diagram of a light-receiving element.

[0020] A photodetection device for detecting light incident through the optical fiber cable 2 equipped with the connector 1A includes a first light receiving element 3 for detecting the amount of light incident through the optical fiber cable 2, and a light receiving element 3 for detecting the amount of light incident through the optical fiber cable 2. A temperature-compensating optical fiber 4 that is in thermal contact with the fiber cable 2, a second light-receiving element 5 that detects the radiant heat of the temperature-compensating optical fiber 4, the first light-receiving element 3, and the second light-receiving element 3. Each light receiving element and the tip of the optical fiber are covered with heat insulating jackets 7 and 8, as shown in FIG. 1, so that they are not susceptible to surrounding thermal disturbances.

The first light receiving element 3 and the second light receiving element 5 are
As shown in FIG. 2, a light absorber 11A having the same characteristics,
11B, each cascaded thin film thermocouple 12A-1
2B, 13A-13B, 14A-14B, 15A-16
B and electrodes 16A, 16B, 16C, 16D, 16E
and are integrated on the same substrate 10.

Therefore, the detecting means 6 should be wired so that the output signals (V1, V2) from the thin film thermocouples provided on each of the first and second light receiving elements 3, 5 are in opposite directions. It is possible to detect the difference (V1-V2) between the output signals.

The means 9 for thermally contacting the optical fiber cable 2 and the temperature-compensating optical fiber 4 can be easily realized by using a holder 9 made of a material with good thermal conductivity, for example, metal. At this time, by covering the surface of the holder with a heat insulating material such as glass or an organic substance, thermal disturbance during handling can be further reduced.

It should be noted that the above-mentioned light receiving elements 3 and 5 can be manufactured relatively easily by using a normal semiconductor process. Therefore, the light receiving elements 3 and 5 have the same characteristics.

In addition to the above-mentioned embodiments, there are also detection means 6 such as (1) and (2). ■Means for detecting the output signals of the light receiving elements 3 and 5 using an analog differential amplifier. (2) Means for converting the output signals of the light receiving elements 3 and 5 into digital signals and then detecting them by software calculation. In particular, when using the method (2) to detect a light amount that is not at a low level, it is possible to detect the amount of light incident simultaneously via two optical fiber cables by switching the software processing. Further, two or more photodetecting devices can be easily constructed using similar means.

Further, in the embodiment, an example was explained in which the amount of light transmitted through an optical fiber cable is detected, but even when the light source is a beam, the present invention can remove thermal radiation other than the beam incident from the surroundings. Therefore, it goes without saying that similar effects can be obtained.

Furthermore, in order to equalize the radiant heat outputs of the light receiving elements 3 and 5 at the same temperature, including the circuit system, a method for calibrating the detecting means 6 in advance includes the optical fiber cable 2 and temperature compensation. The connectors 1A and 1B into which the optical fiber 4 is inserted can be interchanged to calibrate the outputs to be the same. Further, each of the light receiving elements 3 and 5 has a built-in DC heater, and by supplying accurate known DC power, the detected voltages of the light receiving elements 3 and 5 can be calibrated.

[0028]

As described above, according to the photodetecting device of the present invention, the temperature-compensating optical fiber 4 which has the same temperature as the optical fiber cable 2 is provided, and the radiant heat of each optical fiber is transferred to each received light. Means 6 is provided for detecting the difference between the output signals received by the elements. Therefore, the means 6 for detecting the radiant heat P1 of light can be detected without being affected by the radiant heat P2 due to the heat of the optical fiber cable 2 itself. Specifically, it has become possible to detect light levels down to -30 dBm with high accuracy of 1% or less without waiting for the level to stabilize due to temperature.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram of the present invention.

[Fig. 2] Configuration diagram of the light receiving element of the present invention

FIG. 3 is a diagram showing an apparatus configuration when calibrating general-purpose equipment.

FIG. 4 is a diagram showing an apparatus configuration when calibrating general-purpose equipment.

FIG. 5 is a cross-sectional view of a conventional optical sensor.

FIG. 6 is a cross-sectional view of a conventional optical sensor.

FIG. 7: Noise factors in the photodetector.

[Explanation of symbols]

1A connector. 1B connector. 2. Optical fiber cable. 3 First light receiving element. 4. Optical fiber for temperature compensation. 5 Second light receiving element. 6. Means for detecting the difference in output signals. 9. Means for thermal contact (holder).

Claims (1)

[Claims] 1. A photodetector for detecting light incident through an optical fiber cable (2) equipped with a connector (1), which detects the amount of light incident through the optical fiber cable (2). A first light-receiving element (3), a temperature-compensating optical fiber (4) for removing the influence of heat on the optical fiber cable (2), and a temperature-compensating optical fiber (4) connected to the optical fiber cable. (2), a means (9) for thermally contacting the temperature-compensating optical fiber (4);
a second light receiving element (5) that detects the radiant heat of the first light receiving element (5);
A photodetection device comprising means (6) for detecting a difference in output signals between the light receiving element (3) and the second light receiving element (5).