JPH07120711A - Optical variable attenuator and optical output control unit using the same - Google Patents

Abstract

PURPOSE:To provide the optical variable attenuator which varies the intensity of light by electrical control and the optical output control unit using the same. CONSTITUTION:This optical variable attenuator AN 1 is installed on the optical path of an optical fiber 10. The optical variable attenuator AN 1 is composed of a lens 11 disposed to face the output face of the optical fiber 10 and a double refractive crystal 12, magneto-optical crystal 13, compensation plate 14, double refractive crystal 15 and lens 16 successively disposed on the optical path of the light passing this lens 11 and a magnetic coil 17 disposed around the magneto-optical crystal 13. The intensity of the light outputted from the optical variable attenuator AN 1 is modulated by varying the current to be supplied to the magnetic coil 17.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical variable attenuator for adjusting the output by attenuating input light to an appropriate intensity as necessary in the field of optical fiber communication and the like, and an optical output control unit using the same. Is.

[0002]

2. Description of the Related Art In optical fiber communication, a variable optical attenuator is used to adjust the optical power output from a laser diode. The variable optical attenuator stabilizes the optical power by reflecting, scattering, or absorbing a part of the power of the light transmitted therethrough. As such an optical variable attenuator, a device as shown in FIG. 6 is conventionally used. Optical fiber 210 to variable optical attenuator AN
The light incident on the beam No. 4 passes through the lens 211 provided on the front surface of the output end of the optical fiber 210 and is converted into parallel rays. Then, this light is absorbed by passing through the variable attenuating plate 200 that is provided obliquely with respect to the optical path, and the transmitted light of the variable attenuating plate 200 passes through the lens 216 and is emitted to the optical fiber 210. . Here, a metal attenuation film is vapor-deposited on the input surface of the disc-shaped variable optical attenuation plate 200, and the thickness thereof is continuously changed in the rotation direction of the optical attenuation film. The amount of light attenuation is adjusted by rotating the motor 201.

[0003]

However, in the above-mentioned variable optical attenuator, the amount of light attenuation is adjusted by the mechanical mechanism that rotates the variable optical attenuating plate 200 by the motor 201. Was very slow. Moreover, if the amount of attenuation of light is adjusted by such a mechanical mechanism, the movable part will be worn by repeated use, and there is a problem in reliability for long-term use.

The present invention has been made in view of the above problems, and an object of the present invention is to provide an optical variable attenuator which changes the intensity of light by electrical control and an optical output control unit using the same. .

[0005]

In order to solve the above problems, an optical variable attenuator of the present invention comprises a first optical polarizer that allows only polarized light of a predetermined direction of input light to pass therethrough,
A magneto-optical member arranged on the optical path of the polarized light from the first optical polariser; and a variable magnetic field applying means provided around the magneto-optical member to generate a magnetic field for rotating the polarized light in the magneto-optical member. , And a second optical polariser provided opposite to the first optical polariser via a magneto-optical member.

An optical output control unit using such an optical variable attenuator is based on an optical output monitor for detecting the intensity of output light from the optical variable attenuator and a detection signal from the optical output monitor. When the output light intensity fluctuates, the current supplied to the variable optical attenuator is changed to perform sequential feedback control,
A feedback control circuit for stabilizing the intensity of light output is provided.

[0007]

According to the variable optical attenuator of the present invention, first, the polarized light in the predetermined direction of the light input by the first optical polarizer is passed. Then, by adjusting the strength of the magnetic field generated in the magneto-optical member by the variable magnetic field applying means, the polarization plane of the magnetic field is rotated. This polarized light is
The intensity transmitted through the second optical polarizer is modulated according to the rotation angle of the plane of polarization. That is, for example, assuming that the plane of polarization that has passed through the first optical polariser is rotated by 45 degrees and the second optical polariser is tilted at 45 degrees with respect to the first optical polariser, approximately 100%. If it passes through this, but the polarization plane is rotated by 45 ± Δ degrees at this time, the intensity of light passing through the second optical polariser will decrease. As described above, the variable optical attenuator of the present invention electrically controls the intensity of light, and thus can perform intensity modulation at high speed.

Further, by disposing the ferromagnetic member between the variable magnetic field applying means and the magneto-optical member, it is possible to increase the strength of the magnetic field generated in the magneto-optical member.
Furthermore, by inserting a compensator between the magneto-optical member and the second optical polariser, it is possible to compensate for the phase shift that occurs between the two intrinsic polarizations of the polarized light.

Further, such variable magnetic field applying means can be composed of a coil, a permanent magnet movable in the optical path direction of polarized light, and a moving coil for moving the permanent magnet by supplying an electric current. . When the variable magnetic field applying means is composed of a coil, the polarization plane of the polarized light can be rotated by varying the current supplied to the coil, and when it is composed of a permanent magnet and a moving coil. Can change the current supplied to the moving coil to move the permanent magnet and adjust the rotation of the polarized light (polarization plane).

Further, according to the optical output control unit of the present invention, the optical output monitor detects the intensity of the output light from the optical variable attenuator, and the optical output attenuator is mounted on the optical variable attenuator based on the detection signal. Since the current supplied to the variable magnetic field applying means is changed to perform the sequential feedback control, it is possible to stabilize the output intensity of the light passing through the optical output control unit.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT An optical variable attenuator according to an embodiment of the present invention will be described below with reference to the accompanying drawings. In the description, the same elements will be denoted by the same reference symbols, without redundant description.

FIG. 1 is an explanatory diagram for explaining the configuration of an optical variable attenuator (attenuator) according to the first embodiment of the present invention. This variable optical attenuator AN1 is provided with an optical fiber 10
Installed on the optical path of. The variable optical attenuator AN1 is a lens 11 provided to face the output surface of the optical fiber 10.
And a birefringent crystal 12, a magneto-optical crystal 13, and a compensating plate 1 which are sequentially provided on the optical path of light passing through the lens 11.
4, birefringent crystal 15, lens 16 and magnetic coil 17 provided around the magneto-optical crystal 13 (variable magnetic field applying means)
It consists of and. The light incident on the variable optical attenuator AN1 having such a configuration has its optical output attenuated as follows.

First, the light that has entered the variable optical attenuator AN1 from the optical fiber 10 enters the birefringent crystal 12 through the lens 11. The birefringent crystal 12 is an optical polarizer and is made of a crystal such as calcite. That is, as for the light incident on the birefringent crystal 12, only polarized light in a certain direction is transmitted, and polarized light perpendicular to the polarized light is not transmitted.

Next, the polarized light transmitted through the birefringent crystal 12 is placed in the magnetic coil 17, and the magneto-optical crystal 13 is arranged.
It is incident on the (Faraday element) and its plane of polarization is rotated.

For example, if this polarized light (plane of polarization) is rotated by 45 degrees, this polarized light is generated by the magneto-optical crystal 1.
It is possible to pass through the birefringent crystal 13 which is installed at an opposite position of the birefringent crystal 12 with an inclination of 45 degrees.
As the magneto-optical crystal 13, various glasses (Faraday glass; for example, gadolinium, iron,
For garnet), various garnet type ferrites (for example, yttrium / aluminum / garnet and yttrium / iron / garnet) can be used for long wavelength. The rotation angle of this polarized light is determined by the magnetic coil 1
7 is approximately proportional to the magnitude of the magnetic field applied to the magneto-optical crystal 13 and the length of the magneto-optical crystal 13 multiplied by the Verdet constant of the magneto-optical crystal 13, so that the current supplied to the magnetic coil 17 can be varied. Thus, the rotation angle of the polarized light (polarization plane) can be controlled. By thus rotating the polarized light, the intensity of light passing through the magneto-optical crystal 13 can be changed. Then, the light that has passed through the magneto-optical crystal 13 is incident on the optical fiber 10 via the lens 16. The compensating plate 14 (for example, crystal) compensates for the phase shift between the two intrinsic polarizations of this polarized light.

Thus, according to the first embodiment of the present invention,
The light incident on the variable optical attenuator AN1 receives the magneto-optical crystal 12
Is transmitted, and the current supplied to the magnetic coil 17 is varied to appropriately rotate the polarization plane of the polarized light and vary the intensity of the light passing through the magneto-optical crystal 13. can do. As described above, the variable optical attenuator AN1 of the present embodiment changes the intensity of light by an electric control method of changing the current supplied to the magnetic coil 17, so that the response speed at the time of optical output modulation is changed. Since the optical variable attenuator AN1 is extremely fast and does not have a mechanical drive unit as in the prior art, a part of the variable optical attenuator AN1 will not be worn by long-term use.

FIG. 2 is an explanatory view for explaining the structure of the variable optical attenuator AN2 according to the second embodiment of the present invention, and it is between the magnetic coil 17 and the magneto-optical crystal 13 in the first embodiment. The ferromagnetic member 28 is arranged. Examples of the constituent material of the ferromagnetic member 28 include ferrite and the like. According to the present embodiment, since the ferromagnetic member 28 is used, even when the electric power supplied to the magnetic coil 17 is small, the magnetic field strength applied to the magneto-optical crystal 13 can be made sufficiently strong, which is advantageous. The power consumption of the variable optical attenuator AN2 can be reduced.

FIG. 3 is an explanatory diagram for explaining the configuration of an optical variable attenuator AN3 according to the third embodiment of the present invention. An annular magnet 39 is installed around the magneto-optical crystal 13 in the variable optical attenuator AN3 of this embodiment. The magnet 39 is regulated by the guide portion 38 so as to slide (move) only in the direction parallel to the optical axis of the light incident on the magneto-optical crystal 13. In addition, the magnet 3 of the guide portion 38
Stoppers for restricting the sliding of the magnet 39 are erected on both end surfaces of the sliding direction 9 of the magnet 9. The magnet 39 slides in the guide portion 38 by varying the magnitude and direction of the current flowing through the cylindrical magnetic coil whose end surface is provided on the extension of the guide portion 38 in the longitudinal direction. be able to. Even with such a configuration, the intensity of the magnetic field applied to the magneto-optical crystal 13 can be varied, so that the intensity of the light input to the variable optical attenuator AN3 can be modulated. Is. In particular, in the variable optical attenuator AN3 having such a configuration, since the sliding of the magnet 39 is binary-controlled by the presence of the stopper, the transmitted light can be binary ON / OFF.

FIG. 4 is an explanatory diagram for explaining the configuration of a light output control unit using the variable optical attenuator AN as in the first to third embodiments. The light output from the laser diode 100 passes through a transmission line such as an optical fiber and is input to the variable optical attenuator AN to be given an appropriate amount of attenuation. The output light from the variable optical attenuator AN is
The intensity is detected by the optical output monitor 101, and this detection signal is input to the feedback circuit 102. The feedback circuit 102 controls the power supplied to the variable optical attenuator AN on the basis of the detection signal to make the intensity of the light transmitted through the variable optical attenuator AN constant.

As such a light output control unit,
For example, the structure shown in FIG. In the optical output control unit shown in FIG. 5, the optical variable attenuator AN1 according to the first embodiment of the present invention is connected to a branching device 101a for branching output light from the optical attenuator AN1 and a part of intensity of the branched light A photodiode 101b for detecting the is provided. The optical signal detected by the photodiode 101b is sequentially feedback-controlled by the optical output automatic control circuit configured by the integrating circuit 102a, the intermediate driver 102b, and the constant current circuit 102c to control the current supplied to the magnetic coil 17. The current supplied to the magnetic coil 17 decreases when the intensity of the light detected by the photodiode 101b increases, and increases when the intensity of the light detected by the photodiode 101b decreases. When the current supplied to the magnetic coil 17 thus increases, the strength of the magnetic field applied to the magneto-optical crystal 13 decreases, and the amount of attenuation in the variable optical attenuator AN1 increases, resulting in a variable optical attenuation. The intensity of the light output from the device AN1 can be stabilized. Although the optical variable attenuator AN1 of the first embodiment is used in the present embodiment, the same operation can be achieved by using the optical variable attenuators AN2-3 of the second to third embodiments. .

As described above, according to the optical output control unit of this embodiment, the optical output monitor 101 detects the intensity of the output light from the variable optical attenuator AN, and the feedback circuit 102 uses the detected signal to detect the optical variable attenuator. Since the current supplied to the AN is modulated to control the attenuation amount of the light intensity in the variable optical attenuator AN to make the intensity of the optical output from the variable optical attenuator AN constant, the laser diode 100 This optical output can be compensated and stabilized at high speed while the output of is kept at a high level.

[0022]

As described above, according to the optical variable attenuator of the present invention, the polarized light in only a predetermined direction of the light input by the first optical polarizer is rotated and supplied to the variable magnetic field applying means. By adjusting the intensity of the magnetic field generated in the magneto-optical member by changing the, the intensity of the light transmitted through the second optical polarizer is modulated, so that the light output is electrically controlled. Thus, it is possible to perform high speed modulation of the light intensity. Further, since the variable optical attenuator of the present invention does not have a mechanical drive unit as in the conventional case, it is possible to prevent the life of the device from being shortened and the reliability from being deteriorated due to abrasion or the like. Further, since the drive device such as the motor is not provided, the entire device can be downsized.

According to the optical output control unit of the present invention, the intensity of the output light from the variable optical attenuator is detected by the optical output monitor, and the current supplied to the variable magnetic field applying means based on the detection signal. Since it was decided to vary the value and perform sequential feedback control, it is possible to stabilize the intensity of light passing through this. As a result, the laser light input to the light output control unit can be used in the output saturation region, so that high-power light can be transmitted.

[Brief description of drawings]

FIG. 1 is an explanatory diagram illustrating an optical variable attenuator according to a first embodiment of the present invention.

FIG. 2 is an explanatory diagram for explaining an optical variable attenuator according to a second embodiment of the present invention.

FIG. 3 is an explanatory diagram for explaining an optical variable attenuator according to a third embodiment of the present invention.

FIG. 4 is an explanatory diagram illustrating a light output control unit according to an embodiment of the present invention.

5 is an explanatory diagram for explaining an example of the light output control unit shown in FIG.

FIG. 6 is an explanatory diagram for explaining a conventional variable optical attenuator.

[Explanation of symbols]

10, 210 ... Optical fiber, 11, 16, 211, 21
6 ... Lens, 12 ... Birefringent crystal, 13 ... Magneto-optical crystal,
14 ... Compensation plate, 15 ... Birefringent crystal, 17, 37 ... Magnetic coil, 28 ... Ferromagnetic member, 38 ... Guide part, 39 ... Magnet, 100 ... Laser diode, 101 ... Optical output monitor, 101a ... Divider, 101b …Photodiode,
102 ... Feedback circuit, AN, AN1 to 4 ... Optical variable attenuator, 102a ... Integrating circuit, 102b ... Intermediate driver, 102c ... Constant current circuit, 200 ... Optical variable attenuating plate,
201 ... Motor.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Oi Oi, 1 Taya-cho, Sakae-ku, Yokohama-shi, Kanagawa Sumitomo Electric Industries, Ltd. Yokohama Works (72) Inventor Masayuki Nishimura, 1 Taya-cho, Sakae-ku, Yokohama, Kanagawa Sumitomo Electric Ki Industry Co., Ltd. Yokohama Works

Claims (6)

[Claims] 1. A first optical polarizer that allows only polarized light of a predetermined direction of input light to pass therethrough, and a magneto-optical member arranged on an optical path of polarized light from the first optical polarizer. A variable magnetic field applying unit that is provided around the magneto-optical member and that generates a magnetic field that rotates the polarized light in the magneto-optical member; and a variable magnetic field applying unit that faces the first optical polariser and that includes the magneto-optical member. An optical variable attenuator comprising: a second optical polarizer provided. 2. The variable optical attenuator according to claim 1, wherein a ferromagnetic member is arranged between the variable magnetic field applying unit and the magneto-optical member. 3. The compensating plate for compensating for the phase difference of the polarized light is inserted between the magneto-optical member and the second optical polarizer. Optical variable attenuator. 4. The variable optical attenuator according to claim 1, wherein the variable magnetic field applying means is composed of a coil. 5. The permanent magnet, wherein the variable magnetic field applying unit is provided in the vicinity of the permanent magnet and is movable near the permanent magnet, the permanent magnet being movable in the optical path direction of the polarized light of the magneto-optical member. 4. A moving coil for moving the moving coil as claimed in claim 1.
An optical variable attenuator according to the item. 6. An optical variable attenuator according to claim 1, an optical output monitor for detecting the intensity of output light from the optical variable attenuator, and detection by the optical output monitor. A feedback control circuit that stabilizes the intensity of the optical output by varying the current supplied to the variable optical attenuator to perform sequential feedback control when the intensity of the output light changes based on a signal. A light output control unit characterized by.