JPH052407U - Reflective variable attenuator - Google Patents

Abstract

(57) [Summary] (Modified) [Purpose] To obtain a reflective variable attenuator that has a small output monitor circuit and that can feedback control the attenuation amount by the output monitor circuit even if the input and output are connected in reverse. . A laser diode 4 is attached to one port of a circulator 3, and a light receiving element 5 for converting light output from the laser diode into light / electricity is provided. Further, a detection circuit 6 for detecting the optically / electrically converted signal and a bias circuit 7 for controlling the bias current applied to the laser diode based on the output of the detection circuit are provided.

Description

[Detailed description of the device]

[0001]

[Industrial applications]

 The present invention relates to a reflective variable attenuator capable of varying the amount of high frequency attenuation.

[0002]

[Prior Art]

 FIG. 2 is a diagram showing a configuration of a conventional reflective variable attenuator. In the figure, 1 is an input terminal, 2 is an output terminal, 3 is a circulator, 6 is a detection circuit, 7 is a bias circuit, 8 is a diode, and 9 is a directional coupling circuit.

Next, the operation will be described. The high frequency input from the input terminal 1 is output to the diode 8 by the circulator 3. Here, if no voltage is applied to the diode 8 by the bias circuit 7, the diode 8 has a high impedance, the high frequency wave is totally reflected by the diode 8, passes through the circulator 3 again, and is output to the output terminal 2.

Next, when a forward current is applied to the diode 8 by the bias circuit 7, the impedance of the diode 8 is lowered and the high frequency is absorbed. Therefore, the amount of reflection of high frequencies in the diode 8 is reduced, and as a result, the high frequencies output to the output terminal 2 are attenuated. However, in general, it is difficult to determine an accurate forward current value for a desired amount of attenuation in advance because of variations in the diode's forward current-impedance characteristic. To do so, it is necessary to adjust the bias current according to the individual difference of the attenuator.

Therefore, after the output of the circulator 3 is branched by the directional coupling circuit 9, it is detected by the detection circuit 6 and the signal having information on the attenuation amount is fed back to the bias circuit 7. In the bias circuit 7, a desired attenuator output power is obtained by adjusting the bias current and changing the amount of attenuation by the diode 8 based on this feedback information.

[0006]

[Problems to be solved by the device]

 Since the conventional reflective variable attenuator is configured as described above, a directional coupling circuit is required on the output side of the attenuator to monitor the output of the attenuator. Therefore, this directional coupling circuit causes an increase in the size of the attenuator, and there is a problem in that if the input / output directions of this reflective variable attenuator are to be used in reverse, the feedback cannot be performed by the output monitor. It was

The present invention has been made to solve the above problems, and an object thereof is to obtain a reflection type variable attenuator which has a small output monitor circuit and is reversible with input and output.

[0008]

[Means for Solving the Problems]

 The reflection-type variable attenuator according to the present invention has a laser diode attached to one output terminal of a circulator, and controls the bias current to the laser diode based on a signal obtained by monitoring the output light of the laser diode. I went to.

[0009]

[Action]

 The reflective variable attenuator according to the present invention monitors the output light of the laser diode attached to the output terminal of the circulator to grasp the high-frequency attenuation of the laser diode, and to provide an appropriate feedback for setting the attenuation. Send information to the bias circuit.

[0010]

【Example】

 Example 1. An embodiment of this invention will be described below with reference to FIG. In FIG. 1, 4 is a laser diode and 5 is a light receiving element.

Next, the operation will be described. The high frequency input from the input terminal 1 is output to the laser diode 4 by the circulator 3. Here, if no voltage is applied to the laser diode 4 by the bias circuit 7, the laser diode 4 has a high impedance, the high frequency wave is totally reflected by the laser diode 4, passes through the circulator 3 again, and goes to the output terminal 2. Output.

Next, when a forward current is applied to the laser diode 4 by the bias circuit 8, the impedance of the laser diode 4 is lowered and the high frequency is absorbed. Therefore, the amount of high frequency reflection in the laser diode 4 is reduced, and as a result, the high frequency output to the output terminal 2 is attenuated with respect to the input wave.

At this time, since the forward current is applied to the laser diode 4, the laser diode 4 is oscillating the laser, and the oscillated light is subjected to light intensity modulation by the applied high frequency. The amount of change in the degree of modulation is proportional to the amount of change in the high frequency power absorbed by the laser diode.

The output light of the laser diode 4 is photo-electrically converted by the light receiving element 5, and the high frequency is demodulated. This high frequency is detected by the detection circuit 6 and is fed back to the bias circuit 7 as information regarding the amount of attenuation in the laser diode 4. The bias circuit 7 controls the bias current applied to the laser diode 4 based on this feedback information and changes the impedance of the laser diode 4 to obtain a desired attenuation amount. In this case, the attenuation is constant power attenuation that attenuates a constant power regardless of the input power. The same operation is performed even if the input and output of the attenuator are connected in reverse.

Example 2. Although the laser diode 4 is used as the light emitting element attached to the circulator in the above embodiment, an LED may be used as the light emitting element, and in this case, the same effect as that of the above embodiment is obtained. .

[0016]

EFFECTS OF THE INVENTION Since the present invention is configured as described above, the attenuation amount can be monitored without providing a directional coupling circuit, and even if the input and output are connected in reverse, the Since the same attenuation monitoring function can be added, there is an effect that a small and inexpensive reflective variable attenuator can be obtained.

[Brief description of drawings]

FIG. 1 is a diagram showing the configuration of a reflective variable attenuator according to an embodiment of the present invention.

FIG. 2 is a diagram showing a configuration of a conventional reflective variable attenuator.

[Explanation of symbols]

 3 Circulator 4 Laser diode 5 Light receiving element 6 Detection circuit 7 Bias circuit

Claims (1)

Claims for utility model registration 1. In a reflective variable attenuator using a circulator, a circulator, a laser diode connected to one point of the circulator, and an output light of the laser diode are received. A reflective variable attenuator comprising a light receiving element, a detection circuit connected to the light receiving element, and a bias circuit connected to the detection circuit for applying a bias to the laser diode.