JP3199507B2 - Photodetector - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for detecting an optical signal level in an optical circuit.

[0002]

2. Description of the Related Art As an example of a conventional photodetector, a connector disconnection judging circuit will be described with reference to FIG. In the figure, reference numeral 400 denotes a distributed feedback semiconductor laser (DFB-LD)
, A light source 401, an optical coupler 401, and a first
403 is a second main optical transmission line, 404 is a first connector, 405 is a second connector, and 406 is a first connector.
407 is a second sub-optical transmission line, 408 is a photoelectric conversion unit, and 409 is a comparison determination unit. The operation of the connector disconnection determination circuit configured as described above will be described below.

[0003] An optical signal output from an optical device 400 is input to a first main optical transmission line 402. This optical signal passes through the optical coupler 401, propagates through the second main optical transmission line 403, and is input to another optical device connected by the first connector 404. This optical signal is branched by the optical coupler 401, and a signal of a part of the power is transmitted to the first sub optical transmission line 4.
06 is output. The level of this split optical signal is
By monitoring with an optical device connected via the second connector 405, it is possible to know the magnitude of the optical signal propagating through the first and second main optical transmission lines.

On the other hand, the first connector 404 is opened,
Alternatively, when an optical connector in another optical device connected via the first connector 404 is disconnected and the reflected return light increases, the reflected return light is transmitted to the first connector 404 and the second connector 404.
And enters the optical coupler 401 via the main optical transmission path 403. A part of the power of the reflected return light is branched by the optical coupler 401 to the second sub optical transmission line 407, and is converted into an electric signal by the photoelectric conversion unit 408. That is, the electric signal level varies depending on the amount of reflected return light propagating through the first connector 404.

Accordingly, the comparison / determination unit 409 determines that the electric signal level has exceeded a predetermined threshold value, thereby increasing the amount of reflected return light via the first connector 404, that is, disconnection of the optical connector. Can be detected.

[0006]

However, in the connector disconnection detection circuit as described above, not only the reflected return light from the optical connector but also the reflected return light other than the optical connector, for example, from the second connector. Also enter the photoelectric conversion unit through the optical coupler. When a DFB-LD is used as a light source, its light wavelength spectrum is very narrow and has high coherence. Therefore, when a plurality of optical signals are combined in the photoelectric conversion unit, a beat occurs due to mutual interference. Therefore, also in the electric signal output by the photoelectric conversion unit, a beat is generated by a plurality of reflected return lights. As a result, the accuracy of the determination of connector disconnection decreases. Similarly, in all the photodetectors having the above-described configuration, the light branched by the optical coupler is reflected at a plurality of different places and multiplexed again by the optical coupler, thereby causing erroneous detection.

SUMMARY OF THE INVENTION The present invention solves the above-mentioned conventional problems. In an optical apparatus using a light source having a narrow light wavelength spectrum, such as a DFB-LD, it is possible to effectively prevent reflected return light outside a detection target, Alternatively, it is an object of the present invention to provide a useful photodetector capable of preventing a decrease in detection accuracy even when such reflected return light exists.

[0008]

According to a first aspect of the present invention, light is output.
And the optical power input from the first entrance / exit
An optical coupler that outputs from the third inlet / outlet and the third inlet / outlet, and outputs optical power input from the second inlet / outlet from the fourth inlet / outlet, and a photoelectric conversion unit that converts an optical signal into an electric signal. And said
Connecting a light source and a first inlet / outlet of the optical coupler;
A first main optical transmission line for guiding light output from the optical coupler , one end of which is connected to a second entrance / exit of the optical coupler , and another optical component .
A second main optical transmission line provided with a connector at the other end for mediating the connection of the optical coupler, and one end connected to a third inlet / outlet of the optical coupler.
To communicate with other light level monitoring equipment
A first sub optical transmission line having a connector at the other end, wherein a difference in length from the second main optical transmission line is equal to or longer than a coherent length;
A second sub-optical transmission line that connects the fourth input / output port of the optical coupler and the photoelectric conversion unit is compared with a predetermined threshold value of the electric signal level output from the photoelectric conversion unit. This is a light detection device including a comparison determination unit.

[0009]

[0010]

According to a second aspect of the present invention , a light source for outputting light and optical power input from the first input / output port are output from the second input / output port and the third input / output port, and input from the second input / output port. An optical coupler that outputs the received optical power from a fourth input / output port, a photoelectric conversion unit that converts an optical signal into an electric signal, and connects the light source and the first input / output port of the optical coupler. A first main optical transmission path for guiding the separated light, and one end connected to the second entrance / exit of the optical coupler, and a connector for mediating connection with another optical component at the other end. A first optical transmission line, one end of which is connected to the main optical transmission line of the second optical coupler and the third inlet / outlet of the optical coupler, and the other end of which is provided with a connector for mediating connection with another optical level monitoring device. A second sub-optical transmission path connecting the fourth entrance / exit of the optical coupler and the photoelectric conversion unit;
Connected to the photoelectric conversion unit, having a predetermined first threshold and a predetermined second threshold smaller than the first threshold, the electric signal level and the first and second thresholds; A comparison determination unit that performs magnitude comparison of
The ratio of the time during which the electric signal level is determined to be larger than the first threshold to the predetermined period, and the time during which the electric signal level is determined to be lower than the second threshold are within the predetermined period. This is a photodetection device including a statistical processing unit that compares the occupying ratios in magnitude.

[0012]

In the first invention, the optical path of the reflected return light generated at the optical component at the end of the second main optical transmission line and the optical path of the reflected return light generated at the optical component at the end of the first sub optical transmission line. The difference in length is considered to be equal to or greater than the coherent length. Now, the electric field intensity of the reflected return light of the second main optical transmission line is E ₁ , the electric field intensity of the reflected return light of the first auxiliary optical transmission line is E ₂ , and the second optical transmission line and the first auxiliary light are E1. Assuming that the optical path length difference of the transmission path is L, the electric field strength E (maximum value and minimum value) of the light input to the photoelectric conversion unit is expressed by the following equation.

[0013]

(Equation 1)

The third term in the above equation is a fluctuation component generated due to interference between two reflected lights. This fluctuation component decreases exponentially as the optical path length difference L increases. Generally, if the optical path length difference L is equal to or longer than the coherent length of light, there is no practical problem. Therefore, in the first invention, the first
The effect of the reflected return light on the sub optical transmission path can be prevented.

[0015]

[0016]

[0017]

[0018]

In the second invention , the beats caused by the interference of the plurality of reflected return lights are compared with a predetermined first threshold value and a predetermined second threshold value smaller than the first threshold value, and the comparison is made for a predetermined period. By comparing the total time during which the beat level is determined to be larger than the first threshold value with the total time during which the beat level is determined to be smaller than the second threshold value, By adding a statistical processing unit that determines that the amount of light has increased, even when there are a plurality of reflected return lights, the accuracy of the magnitude comparison determination of the reflected return light is improved.

When two thresholds are provided, the detection accuracy is improved as compared with the case where only one threshold is provided. Therefore, it can be said that the fourth aspect of the present invention has higher accuracy than that of the third aspect of the invention in preventing erroneous detection.

[0021]

FIG. 1 is a block diagram showing the configuration of a photodetector according to a first embodiment of the present invention. Reference numeral 101 denotes a 12 dB optical coupler having four entrances and exits, which outputs optical power input from the first entrance and exit from the second entrance and exit, and is input from the second entrance and exit. Optical power is output from the fourth inlet / outlet. Reference numeral 102 denotes a photoelectric conversion unit that converts an optical signal output from the fourth input / output port of the optical coupler 101 into an electric signal. 103 is a first connector, 104 is a second connector, 105 is an optical coupler 1
01 is a first main optical transmission line, one end of which is connected to the first entrance / exit of No. 01. Reference numeral 106 denotes a second entrance / exit of the optical coupler 101 and a first entrance / exit.
Second main optical transmission line 107 for connecting the connector 103 of FIG.
Are the third inlet / outlet of the optical coupler 101 and the second connector 10
4 is a first sub-optical transmission line connecting the first and second sub-optical transmission lines. Reference numeral 108 denotes a second sub optical transmission line that connects the fourth entrance / exit of the optical coupler 101 and the photoelectric conversion unit 102, and reference numeral 109 denotes a level between an electric signal output from the photoelectric conversion unit 102 and a predetermined threshold. This is a comparison determination unit that performs a magnitude comparison. Also, the second main optical transmission line 1
06 and the length of the first sub optical transmission line 108 have a length equal to or longer than the coherent length. Either length may be longer. An optical device 110 uses a distributed feedback semiconductor laser (DFB-LD) as a light source.
Is connected to the other end of the main optical transmission line 105.

The operation of the photodetector of the present embodiment configured as described above will be described below. DFB-LD
To the first main optical transmission path 105
Is transmitted through the 12 dB coupler 101 and output to the second main optical transmission line 106. Further, light having a power attenuated by 12 dB from the optical signal power is output from the second connector 104 via the first sub optical transmission line 107. By connecting an appropriate monitoring optical device to the second connector 104, it is possible to monitor the power of the light propagating through the main optical transmission line. The optical signal that has propagated through the second main optical transmission line 106 is connected to another main optical device via the first connector 103. This first connector 103
Is disconnected, the first connector 103 reflects an optical signal. This reflected light is transmitted to the second main optical transmission line 1
06 to the 12 dB coupler 101 and
The reflected light of the attenuated power propagates through the second sub optical transmission line 108 and is input to the photoelectric conversion unit 102, where the optical signal is converted into an electric signal by the photoelectric conversion unit 102, The magnitude of the signal level and a predetermined threshold are determined. In this way, by detecting the reflected light from the first connector 103 and determining the level thereof, the detachment of the first connector 103 is determined.

Here, the optical signal branched by the 12 dB optical coupler 101 and propagated through the first sub optical transmission line 107 is
Even when the second connector 104 is disconnected or when an optical connector or the like inside the optical device connected by the second connector 104 is disconnected, a part of the light is reflected, and the reflected light is the first sub light. The light propagates through the transmission line 107 and is input to the 12 dB coupler 101, passes through the 12 dB coupler 101, propagates through the second sub optical transmission line 108, and
2 is input. That is, the photoelectric conversion unit 102 includes the first
Not only the reflected light from the second main optical transmission path 106 but also the reflected light from the first auxiliary optical transmission path 107 necessary to determine the disconnection of the connector 103 is input. In the case of the present embodiment, the difference between the length of the second main optical transmission line 106 and the length of the first sub optical transmission line 107 is equal to or longer than the coherent length. And the coherence between the light beams is reduced, and no large beat occurs.

With the above-described configuration, the reflected light power is stable, and the magnitude of the electric signal detected by the photoelectric conversion unit 102 causes the comparison / determination unit 109 to determine the first main light transmission path 106 It is possible to accurately determine whether or not the connection of the connector 103 is disconnected. Note that the difference between the lengths of the second main optical transmission line 106 and the first sub optical transmission line 107 may be longer than the coherent length.

[0025]

[0026]

[0027]

( Second Embodiment) FIG. 2 is a block diagram showing the configuration of a photodetector according to a second embodiment of the present invention. In the present embodiment, a statistical processing unit 111 is used instead of making the difference between the lengths of the second main optical transmission line 106 and the first sub optical transmission line 107 equal to or longer than the coherent length in the embodiment shown in FIG. Things. Other configurations are the same as those of the embodiment shown in FIG.

[0029]

[0030]

In the case of the present embodiment, the comparison / determination section 109 compares the magnitude of the predetermined first threshold value with the output signal from the photoelectric conversion section 102 and determines the magnitude of the predetermined second threshold value smaller than the first threshold value. Is compared with the output signal from the photoelectric conversion unit 102, and the statistical processing unit 111 determines the proportion of the time occupied by the time determined to be larger than the first threshold within a predetermined time,
The percentage of time determined to be smaller than the second threshold is calculated. As a result, if the ratio of the period in which the output of the photoelectric conversion unit 102 is larger than the first threshold is larger than the ratio of the period of time smaller than the second threshold, it is determined that the first connector 103 is disconnected stochastically. .

The optimum value of the two thresholds depends on the fluctuation width of the electric signal detected by the photoelectric conversion unit.
As an example, it can be set as in the following equation.
In the equation, V _th1 is a first threshold, and V _th2 is a second threshold.

[0033]

(Equation 3)

With the above configuration, the connection / disconnection state of the first connector 103 can be determined even if a plurality of reflected lights interfere with each other and a large beat is generated in the photoelectric conversion unit 102. In the present embodiment, the difference between the lengths of the second main optical transmission line 106 and the first sub optical transmission line 107 may be equal to or longer than the coherent length as in the embodiment shown in FIG.
No.

[0035]

As described above, the present invention provides a DFB-LD
For an optical device using a light source with a narrow light wavelength spectrum as described above, it is possible to provide a photodetector that does not cause a decrease in detection accuracy even when reflected return light that is not a detection target exists.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a photodetector according to a first embodiment of the present invention.

FIG. 2 is a configuration diagram of a photodetector according to a second embodiment of the present invention.

FIG. 3 is a configuration diagram of a conventional photodetector.

[Explanation of symbols]

 101 12bB coupler 102 photoelectric conversion unit 103 first connector 104, 104a second connector 105 first main light transmission line 106 second main light transmission line 107 first sub light transmission line 108 second sub light Transmission line 109 Comparison / determination unit 110 Optical device using DFB-LD as a light source 111 Statistical processing unit

──────────────────────────────────────────────────の Continued on the front page (72) Inventor Hiroaki Yamamoto 1006 Kazuma Kadoma, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. (56) References JP-A-63-61132 (JP, A) JP-A-2-52536 (JP, A) JP-A-55-149034 (JP, A) JP-A-63-279205 (JP, A) JP-A-4-248434 (JP, A) JP-A-6-204951 (JP, A) JP-A-5-327622 (JP, A) JP-A-6-268596 (JP, A) (JP, U) Hiroaki Yamamoto, Manabu Tanabe, Hiroaki Nakata, Katsuyuki Fujito, Yasushi Matsui, "Investigation of distortion caused by multiple reflections in optical fibers", Proc. Of the 1992 IEICE Spring Conference, Japan Association IEICE Issued March 15, 1992, Volume 4, p4-192 (58) Fields surveyed (Int. Cl. ⁷ , DB name) H04B 10/00-10/28 H04J 14/00-14/08 G01M 11 / 00-11/08 G02B 6/28

Claims (2)

(57) [Claims] 1. A light source for outputting light, and optical power input from a first input / output port, output from a second input / output port and a third input / output port, and optical power input from a second input / output port. An optical coupler that outputs an optical signal from a fourth input / output port, an opto-electrical conversion unit that converts an optical signal into an electric signal, and a light source that connects the light source and the first input / output port of the optical coupler and outputs light from the light source. A first main optical transmission line that guides the optical coupler, a second end having a connector for connecting one end to the second entrance / exit of the optical coupler, and a connector for mediating connection with another optical component at the other end.
And a connector for connecting one end to a third entrance / exit of the optical coupler, and a connector for mediating connection with another optical level monitoring device, the other end of which is provided with the second main light. A first sub optical transmission line whose difference in length from the transmission line is equal to or longer than the coherent length, a second sub optical transmission line connecting a fourth entrance / exit of the optical coupler and the photoelectric conversion unit, A photodetector, comprising: a comparison / determination unit that performs a magnitude comparison between the electric signal level output from the photoelectric conversion unit and a predetermined threshold. 2. A light source for outputting light and optical power input from a first input / output port are output from a second input / output port and a third input / output port, and optical power input from a second input / output port is output. An optical coupler that outputs from a fourth input / output port, an opto-electrical conversion unit that converts an optical signal into an electrical signal, and connects the light source and the first input / output port of the optical coupler to output light output from the light source. A first main optical transmission line that guides light; a second main light that has one end connected to the second entrance / exit of the optical coupler and the other end provided with a connector for mediating connection with another optical component. a transmission line, one end connected to the third inlet and outlet of said optical coupler, a first sub optical transmission path Ru with a connector other end to mediate a connection with another optical level monitoring device, A second sub-optical transmission line that connects a fourth entrance / exit of the optical coupler and the photoelectric conversion unit, and a second auxiliary optical transmission line that connects to the photoelectric conversion unit; A comparison determination unit that has a fixed first threshold value and a predetermined second threshold value that is smaller than the first threshold value, and performs a magnitude comparison between the electric signal level and the first and second threshold values; A ratio of the time during which the electric signal level is determined to be higher than the first threshold to be occupied in a predetermined period, and the electric signal level being lower than the second threshold. A photodetecting device, comprising: a statistical processing unit that compares the ratio of the determined time within a predetermined period with the statistical processing unit.