JPH02214806A - Optical variable attenuator - Google Patents

Abstract

PURPOSE:To accurately set the quantity of attenuation of an attenuation plate by extracting light power before the light enters the attenuation plate, and light power after the light passes through the attenuation plate by a branching coupler and processing them. CONSTITUTION:The input light passes through an optical fiber 11 and is branched by an optical branching coupler 1A into light 21 and light 22. The light 21 is collimated by a lens 12, attenuated by the attenuation plate 15, and converged by a lens 13, and the converged light is branched by an optical branching coupler 1B into light 23 and 24, the light 22 is converted photoelectrically by a photodetecting element 2A into an electric signal, and the light which is branched by the optical branching coupler 1B is converted photoelectrically by a photodetecting element 2B into an electric signal. Then the outputs of the photodetecting elements 2A and 2B are amplified by amplifying circuits 3A and 3B and inputted to an arithmetic processing circuit 4, which calculates the light power values of the light 22 and light 24; and a control circuit 5 compares the value of the quantity of attenuation indicated by an indicating circuit 6 with the quantity of attenuation found by the arithmetic processing circuit 4 to rotate the attenuation plate 15 to a necessary position. Consequently, the quantity of attenuation of the attenuation plate is accurately set.

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Technical Field of the Invention The present invention relates to a variable optical attenuator that attenuates optical power in an optical fiber by a necessary amount.

(b) Prior Art and Problems Next, the configuration of a conventional variable optical attenuator will be explained with reference to FIG.

In FIG. 3, 11 and 14 are optical fibers, 12 and 13 are lenses, 15 is an attenuation plate, 16 is a motor that moves the attenuation plate 15, 1
7 is a motor control circuit, and 18 is an instruction section.

Next, the structure of the damping plate 15 shown in FIG. 3 is shown in FIG. 4.

The attenuation plate 15 is a glass plate with metal vapor-deposited,
The deposition density is varied along the circumference.

Therefore, if the attenuation plate 15 is rotated within the light path,
The amount of attenuation given to the passing light can be changed.

Next, the operation of FIG. 3 will be explained.

Input light passes from optical fiber 11 through lens 12 and is collimated by lens 12 . The collimated light passes through an attenuation plate 15, and its optical power is attenuated.

The attenuated light is focused by a lens 13 and then connected to an optical fiber 1.
4 and becomes the output light.

In order to dampen the damping plate 15 by the necessary amount, it is necessary to control the rotation so that it stops at the required position. For this purpose, as shown in FIG. 3, a motor 16 is attached to the damping plate 15, and the rotation of the damping plate 15 is controlled by a motor control circuit 17.

An instruction unit 1 is used to instruct the attenuation amount of the attenuation plate 15 from the outside.
There are 8. Further, in order to set the attenuation amount accurately, the relationship between the set position of the attenuation plate 15 and the attenuation amount is calibrated in advance using an optical power meter or the like.

However, with the configuration shown in FIG. 3, it is difficult to maintain the attenuation amount of the damping plate 15 and the stability and reproducibility of the mechanism over a long period of time.

Therefore, in order to maintain the variable optical attenuator shown in FIG. 3 with high accuracy, it is necessary to occasionally calibrate it using an optical power meter.

Further, in the variable optical attenuator shown in FIG. 3, the amount of attenuation of the attenuation plate 15 changes depending on the wavelength of input light.

For example, when comparing light with a wavelength of 1300 nm and light with a wavelength of 1550 nm, a difference in attenuation appears, such as an attenuation of 30 dB at a wavelength of 1300 nm, but an attenuation of 29 dB at a wavelength of 1550 nm.

Furthermore, at wavelength 1330 nm, the attenuation amount is 50 dB.
At 550 nm, the attenuation is about 46 dB, and the amount of attenuation increases.

As described above, since the wavelength characteristics differ depending on the amount of attenuation, there is a problem in that in order to use the device at various wavelengths, the amount of attenuation must be calibrated at the wavelength to be used.

(C) Purpose of the Invention This invention accurately sets the attenuation amount of the attenuation plate by extracting the optical power before entering the attenuation plate and the optical power after passing through the attenuation plate using a branching coupler and calculating it. The purpose of the present invention is to provide a variable optical attenuator that can perform

(d) Examples of the invention Next, a block diagram of an embodiment according to the present invention is shown in FIG.

In FIG. 1, IA and IB are optical branching couplers, 2A and 2B are light receiving elements, 3A and 3B are amplifiers, 4 is an arithmetic processing circuit, 5 is a control circuit, 6 is an instruction circuit, and 7 is a motor control circuit. Other parts are the same as in FIG.

Input light passes through an optical fiber 11 and is branched into light 21 and light 22 by an optical splitter/coupler IA.

The light 21 is collimated by the lens 12 and attenuated by the attenuation plate 15 . Then, the light is condensed by the lens 13 and branched into light 23 and light 24 by 6 parts by the optical splitter/coupler IB. The light 23 passes through the optical fiber 14 and becomes output light.

The light 22 branched by the optical branching coupler IA is sent to the light receiving element 2A.
It is photoelectrically converted into an electrical signal.

Further, the light component #t, the light 24 branched by the coupler IB, is photoelectrically converted by the light receiving element 2B and converted into an electric signal.

The output of the light-receiving element 2A is amplified by an amplifier circuit 3A and input to an arithmetic processing circuit 4, where the optical power of the light 22 is calculated.

Further, the output of the light receiving element 2B is amplified by the amplifier circuit 3B,
The light enters an arithmetic processing circuit 4, where the optical power of the light 24 is calculated.

The actual amount of attenuation is determined as follows.

The actual attenuation amount ATT (dB) is ATT--10Xlog, where Pi is the optical input power and Po is the optical output power.
It is expressed as (Po/Pi)-(1).

In addition, the transmittance of the optical branching coupler IA is n%, the optical power of the light 21 is P2□, the optical power of the light 22 is P2□, the optical power of the light 23 of the optical branching coupler IB is P23, and the optical power of the light 24 is P23. If the optical power is P24, then p i -(1/n) x
(P21+P22) ・=----(2) Po=P23
・・・・・・・・・・・・・・・・・・・・・・・・
It is represented by (3).

On the other hand, the degree of coupling of optical branching couplers IA and IB is
If Y, then x=p2□/(P21+P2□)・・・・・・・・・・・・
・・・・・・・・・・・・(4)Y=P24'/(
P 230 P 24 )・・・・・・・・・・・・・・・
...... Since (5), P 21 = (I X ) X P 22/ X...
・・・・・・・・・・・・・・・ (6) P 23=
(i y) x P 24/Y・・・・・・・・・
...... It is expressed as (7).

From this, Pi and Po can be expressed as follows.

P 1 ” (1/n)
zt+P 2z)P 22/n X・・・・・・・・・
・・・・・・・・・・・・・・・・・・・・・・・・
(8) P O- (I Y ) X P 24/ Y-
...... Old... (9) Attenuation amount ATT (
dB) is ATT=-10X log((P22/IIX)/
(1-Y) P24/1 10X too (YP, □ / n X (I Y ) P z4) ---
−(10).

Here, n, X, and Y are constants.

The actual amount of attenuation can be measured from the optical power P2□ and the optical power P24.

The arithmetic processing circuit 4 calculates the actual attenuation amount by calculating the equation (10).

The control circuit 5 compares the attenuation amount instructed by the instruction circuit 6 with the attenuation amount determined by the arithmetic processing circuit 4, and as a result, sends the necessary data to the motor control circuit 7 to start the motor 6. Damping plate 1 rotated and coupled to a motor 16
Rotate 5 to the required position.

In FIG. 1, since the optical powers P2□ and P24 are always measured in terms of conversion, the attenuation plate 15 can be set at a position with an accurate amount of attenuation.

Furthermore, since the actual attenuation amount is obtained by measuring the optical powers P22 and P24, there is no need to consider the wavelength stability of the attenuation plate 15 itself.

However, in the configuration shown in Figure 1, the transmittance and coupling degree of the optical branching couplers IA and IB usually have different wavelength characteristics, and the sensitivities of the light receiving elements 2A and 2B also have different wavelength characteristics.
It is necessary to calibrate each wavelength characteristic.

However, since these characteristics are constant regardless of the optical power, it is only necessary to calibrate the characteristics when a certain optical power is input.

Next, a block diagram of another embodiment according to the present invention is shown in FIG.

8 in FIG. 2 is an optical switch, and the other parts are the same as in FIG. 1.

That is, in FIG. 2, the light receiving element 3A and the amplifier circuit 3A are shared, and the optical switch 8 switches between the light 22 of the optical branch/coupler IAO and the light 24 of the optical branch/coupler IB.

Therefore, the wavelength characteristics of the light receiving element 2A can be ignored.

Even though the optical switch 8 has wavelength dependence, in the configuration shown in Fig. 2, the difference in characteristics between terminals 8A and 80 and between terminals 8B and 8C poses a problem. Therefore, the wavelength characteristics of the optical switch 8 can be ignored.

(e) Effects of the Invention According to this invention, the optical power before entering the attenuation plate and the optical power after passing through the attenuation plate are taken out by the branching coupler and calculated, thereby controlling the position of the attenuation plate. Therefore, the amount of attenuation of the attenuation plate can be set accurately.

Furthermore, when calibrating the attenuation amount, it is only necessary to calibrate one point for one wavelength, which simplifies the calibration.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of an embodiment according to the present invention, FIG. 2 is a block diagram of another embodiment according to the present invention, FIG. 3 is a block diagram of a variable optical attenuator according to the prior art, and FIG. 4 is a block diagram of an attenuation plate 15. FIG. IA/IB... Optical branching coupler, 2A/2B...
...Photodetector, 3A/3B...Amplification circuit,
4... Arithmetic processing circuit, 5... Control circuit, 6... Instruction circuit, 7... Motor control circuit, 11/100. Optical fiber, 12/13...
...Lens, 14...Optical fiber, 15...
...Dampening plate, 16...Motor. Agent Patent Attorney Kinji Komata

Claims (1)

[Claims] 1. Input light is collimated from a first optical fiber (11) by a first lens (12) and attenuated by an attenuation plate (15) whose rotational position is controlled by a motor (16). receiving, second
The light is focused by the lens (13) and sent to the second optical fiber (14).
), a first optical branching coupler (1A) disposed between a first optical fiber (11) and a first lens (12); A first light-receiving element (2A) which receives the branched output of the optical splitter/coupler (IA) as an input, and a second light disposed between the second lens (13) and the second optical fiber (14). A branching coupler (1B), a second light receiving element (2B) that receives the branched output of the second optical branching coupler (1B), and a first light receiving element (2B) that receives the first light from the output of the first light receiving element (2A). fiber(
an arithmetic processing circuit (4) that converts and calculates the optical power passing through the second optical fiber (11) and calculates the optical power that passes through the second optical fiber (14) from the output of the second light receiving element (2B);
); and a motor control circuit (7) whose input is the output of the arithmetic processing circuit (4). 2. The input light is collimated from the first optical fiber (11) by the first lens (12), is attenuated by the attenuation plate (15) whose rotational position is controlled by the motor (16), and is collimated by the first optical fiber (11).
The light is focused by the lens (13) and sent to the second optical fiber (14).
), the variable optical attenuator extracts output light from the optical fiber (11) and the first lens (12). A second optical branch/coupler (1B) disposed between the lens (13) and the second optical fiber (14), and a branch output of the first optical branch/coupler (1A) and the second optical branch. An optical switch (8) that switches the branch output of the coupler (1B), and a light receiving element (2A) that receives the output of the optical switch (8) as an input.
And, from the output of the light receiving element (2A) to the first optical fiber (11)
an arithmetic processing circuit (4) that converts and calculates the optical power passing through the second optical fiber (14) and the optical power passing through the second optical fiber (14);
); and a motor control circuit (7) whose input is the output of the arithmetic processing circuit (4).