JP2008310118A - Variable optical attenuator - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To totally save electric power by continuously varying an optical attenuation amount and reducing a current value which needs to be always supplied to adjust the optical attenuation amount. <P>SOLUTION: A polarizer 10 and an analyzer 12 are disposed between an input collimation system and an output collimation system, and a discrete variation type optical attenuating mechanism 14 having self-holding type Faraday rotators FR1 and FR2 and a continuous variation type optical attenuating mechanism 16 having a continuous power supply type Faraday rotors FR3 are arrayed between the polarizer and analyzer linearly along an optical axis. Switching control over a current direction to a magnetic field applying means of the self-holding type Faraday rotors and power supply control over a current value to a magnetic field applying means of the continuous power supply type Faraday rotor are combined with each other to interpolate a discrete optical attenuation amount by the discrete variation type optical attenuating mechanism with a continuous optical attenuation amount by the continuous variation type optical attenuating mechanism, thereby adjusting the optical attenuation amount in detail. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a variable optical attenuator in which a discrete variable optical attenuation mechanism having a self-holding Faraday rotator and a continuously variable optical attenuation mechanism having an always energizing Faraday rotator are incorporated between a polarizer and an analyzer. More specifically, a discrete variable type can be obtained by combining the current direction switching control to the magnetic field application means of the self-holding type Faraday rotator and the current value conduction control to the magnetic field application means of the constant current type Faraday rotator. The present invention relates to a variable optical attenuator that interpolates a discrete optical attenuation amount by an optical attenuation mechanism with a continuous optical attenuation amount by a continuously variable optical attenuation mechanism and adjusts the optical attenuation amount. This variable optical attenuator is useful for adjusting the optical power level in an optical communication system, for example.

  A magneto-optic variable optical attenuator that adjusts the amount of light attenuation by controlling the rotation angle of the Faraday rotator is well known. Such a variable optical attenuator is used, for example, for adjusting an optical power level in an optical communication system.

  As a variable optical attenuator of the magneto-optical system, a polarizer, a Faraday rotator, and an analyzer are arranged between an input collimating system and an output collimating system, and the optical attenuation is controlled by controlling the Faraday rotation angle of the Faraday rotator. The configuration to adjust is common. Here, the Faraday rotation angle is controlled by the strength of the externally applied magnetic field. Here, the magnetic field applying means for generating the external magnetic field requires a current value of about several tens of mA at the maximum, and it is necessary to continuously supply the current in order to maintain the necessary light attenuation amount. At all times, considerable power is required. A typical example of the optical attenuation characteristic of the conventional variable optical attenuator is shown in FIG. In the case where the light attenuation amount in a state where current is not supplied is approximately 0 dB, a current of about 60 mA is required to obtain the maximum light attenuation amount. For example, when an optical attenuation of 20 dB is required, a current of about 45 mA must be continuously supplied.

On the other hand, as a low power consumption type optical attenuator, a polarizer, a self-holding Faraday rotator and an analyzer are arranged between an input collimating system and an output collimating system, and the Faraday rotation angle of the self-holding Faraday rotator is set. There is a configuration in which the amount of light attenuation is adjusted by controlling (see Patent Document 1). In this case, the Faraday rotation angle is controlled by switching the current direction to the magnetic field applying means. Therefore, since it is only necessary to energize instantaneously only when it is desired to change the Faraday rotation angle, although there is an advantage that power consumption can be reduced, the light attenuation that can be realized becomes discontinuous (discrete), and fine adjustment of the light attenuation is possible. Can not be performed, and therefore the application is limited.
JP 2007-114746 A

  The problem to be solved by the present invention is that the amount of light attenuation can be continuously varied, and the current value that needs to be constantly supplied to adjust the amount of light attenuation can be reduced, and overall power saving can be achieved. Is to be able to plan.

  According to the present invention, a polarizer and an analyzer are disposed between an input collimating system and an output collimating system, and a discrete variable optical attenuation mechanism having a self-holding Faraday rotator and a constant variable optical attenuation mechanism are provided between the polarizer and the analyzer. A continuously variable optical attenuating mechanism having an energizing Faraday rotator is arranged on a straight line along the optical axis, and the current direction switching control to the magnetic field applying means of the self-holding Faraday rotator and the always energizing Faraday rotation Combined with current control of the current value to the magnetic field application means of the child, the amount of light attenuation is interpolated by the amount of continuous light attenuation by the continuously variable light attenuation mechanism. The variable optical attenuator is characterized in that is adjusted.

  Here, it is preferable that the discrete variable optical attenuation mechanism includes a plurality of self-holding Faraday rotators and phase shifters, and the rotation angle of the self-holding Faraday rotator is offset by the phase shifters. The phaser is a (1/2) × (2n−1) wave plate (where n is a positive integer).

  The self-holding type Faraday rotator includes magnetic field applying means in which a coil is wound around a magnetic yoke made of, for example, a semi-hard magnetic material, and a Faraday element inserted between the gaps of the magnetic yoke. Or the structure which consists of a Faraday element which has the coercive force inserted between the magnetic field application means which wound the coil around the magnetic yoke which consists of soft magnetic materials, and the said magnetic yoke may be sufficient.

  The normally energized Faraday rotator includes a Faraday element, a permanent magnet that magnetically saturates the Faraday element, and variable magnetic field applying means that winds a coil around a magnetic yoke and applies a variable magnetic field to the Faraday element.

  Here, the self-holding type Faraday rotator has a combination of two types of Faraday rotation angles of ± 12.5 degrees and ± 22.5 degrees, and the normally energized Faraday rotator has a Faraday rotation angle of 35 to 60 degrees. It is preferable to cover those.

  The variable optical attenuator of the present invention incorporates a discrete variable optical attenuation mechanism having a self-holding Faraday rotator and a continuously variable optical attenuation mechanism having a normally energized Faraday rotator to apply a magnetic field to the self-holding Faraday rotator. The switching control of the current direction to the means and the current control of the current value to the magnetic field applying means of the normally energized Faraday rotator are combined, and the discrete light attenuation amount by the discrete variable optical attenuation mechanism is determined by the continuously variable optical attenuation mechanism. Since the interpolation is performed with the continuous light attenuation amount, the light attenuation amount can be finely adjusted over a wide range. In addition, the adjustment of the discrete light attenuation by the discrete variable optical attenuation mechanism may be carried out instantaneously in a predetermined direction only when the variable needs to be changed. Although the adjustment is always energized, a small current value may be used, so that the supply current can be reduced as a whole, and power saving can be achieved.

  The principal part of an example of the variable optical attenuator according to the present invention is shown in FIG. Between the polarizer 10 and the analyzer 12, a discrete variable optical attenuation mechanism 14 having a self-holding Faraday rotator and a continuously variable optical attenuation mechanism 16 having an always energizing Faraday rotator are straightened along the optical axis. Arranged on a line. FIG. 2 shows an arrangement state of each optical component in the entire variable optical attenuator. An input collimating system 20 is located on the incident side of the polarizer 10, and an output collimating system 22 is located on the exit side of the analyzer 12.

The polarizer 10 and the analyzer 12 are preferably parallel plane type (opposing input and output surfaces are parallel to each other) birefringent members, and are made of, for example, rutile (TiO ₂ ) or YVO ₄ . The discrete variable optical attenuating mechanism 14 includes two types of self-holding Faraday rotators FR1 and FR2 and a half-wave plate HWP. The rotation angle by the self-holding Faraday rotators FR1 and FR2 is a half-wave plate. In this configuration, offset is performed by HWP. The continuously variable optical attenuation mechanism 16 is composed of a constantly energized Faraday rotator FR3.

  The two types of self-holding Faraday rotators FR1 and FR2 are each composed of a magnetic field applying means in which a coil is wound around a magnetic yoke made of a semi-hard magnetic material, and a Faraday element inserted between the gaps of the magnetic yoke. An example of the structure is shown in FIG. Both Faraday elements F1 and F2 may be made of the same magneto-optical material. In this case, the difference in Faraday rotation angle can be realized by changing the thickness of the Faraday elements F1 and F2. Since the magnetic yoke 30 is made of a semi-hard magnetic material, when the magnetic yoke 30 is magnetized by energization of the coils C1 and C2, the magnetization state is maintained even when the energization is stopped, and the Faraday elements F1 and F2 in the gap are retained. Will continue to be applied with the saturation magnetic field H1. The direction of the magnetic field applied to the Faraday elements F1 and F2 can be changed by switching the energization direction to the coils C1 and C2 to the opposite direction.

  The normally energized Faraday rotator FR3 includes a Faraday element F3, a permanent magnet 32 for magnetically saturating the Faraday element F3, and a variable magnetic field applying means for applying a variable magnetic field to the Faraday element F3 by winding a coil C3 around a magnetic yoke. It consists of. This magnetic yoke is made of a soft magnetic material. As shown in FIG. 1A, a permanent magnet applies a fixed magnetic field H2 in the optical axis direction to the Faraday element to magnetically saturate it, and is variable by a magnetic yoke and a coil in a direction perpendicular to it (x direction perpendicular to the optical axis). A magnetic field H3 is applied. The magnitude of the variable magnetic field is changed by the energization current to the coil C3, and the combined magnetic field of the fixed magnetic field H2 and the variable magnetic field H3 is applied to the Faraday element F3, and the Faraday rotation angle depends on the component of the combined magnetic field in the optical axis direction. Be controlled.

  When the Faraday rotation angles of the two self-holding Faraday rotators FR1 and FR2 and the normally energized Faraday rotator FR3 are θF1, θF2 and θF3, respectively, the combined rotation angle θtotal of the polarization plane of the light transmitted therethrough is , ΘF1 + θF2 + θF3. The rotation angle θF1 + θF2 is offset by the half-wave plate HWP to be self-held, and the fine rotation angle θF3 is adjusted. The self-holding type Faraday rotators FR1 and FR2 require electric power only at the time of switching. However, since fine adjustment of the light attenuation amount can be performed only by the electric power of the always-on type Faraday rotator FR3, the power consumption as a whole is greatly increased. It can be reduced.

As the input collimating system 20 and the output collimating system 22, a beam waist system including an optical fiber 40, a ferrule 42, and a lens 44 is used. Setting the offset angle on the plane of polarization of light by the half-wave plate HWP can improve the wavelength characteristics and temperature characteristics within the desired range of light attenuation. The half-wave plate HWP may be incorporated at any position on the optical axis, but is preferably incorporated at the beam waist position. Therefore, here, they are arranged between the two self-holding Faraday rotators and the normally energized Faraday rotator. The half-wave plate HWP is made of, for example, quartz (SiO ₂ ).

  With such a configuration, the switching control of the current direction to the magnetic field applying means of the self-holding type Faraday rotators FR1, FR2 and the energization control of the current value to the magnetic field applying means of the constantly energizing type Faraday rotator FR3 are combined. Thus, it is possible to finely adjust the light attenuation amount by interpolating the discrete light attenuation amount by the discrete variable light attenuation mechanism 14 with the continuous light attenuation amount by the continuous variable light attenuation mechanism 16.

  As shown in FIGS. 1 and 2, an input collimating system 20, a polarizer 10, two types of self-holding Faraday rotators FR1 and FR2, and a half-wave plate HWP, a discrete variable optical attenuation mechanism 14, always The continuously variable optical attenuation mechanism 16, the analyzer 12, and the output collimating system 22 having the energization type Faraday rotator FR3 are arranged in a straight line along the optical axis in this order.

  The two types of self-holding Faraday rotators FR1 and FR2 of the discrete variable optical attenuating mechanism 14 include a Faraday element and a magnetic yoke with a coil (made of a semi-rigid magnetic material) that can individually apply an external magnetic field to the Faraday element. Become. Here, as the two Faraday elements F1 and F2, those having Faraday rotation angles of θF1: 12.5 degrees and θF2: 22.5 degrees are used. Therefore, one self-holding Faraday rotator can switch the polarization plane of light to either +12.5 degrees or -12.5 degrees depending on the direction of the external magnetic field, and the other self-holding Faraday rotator Depending on the direction of the external magnetic field, the polarization plane of light can be switched to either +22.5 degrees or −22.5 degrees. The half-wave plate HWP has its optical axis set to 0 degree (horizontal direction, that is, the x direction). The continuously energized Faraday rotator FR3 of the continuously variable optical attenuating mechanism 16 is a variable that applies a variable magnetic field to the Faraday element by winding a Faraday element, a permanent magnet that magnetically saturates the Faraday element, and a coil around a magnetic yoke. Magnetic field applying means. Here, a Faraday element F3 having a Faraday rotation angle θF3 of 60 degrees is used. Therefore, this always energized Faraday rotator FR3 can change the plane of polarization of light from 0 to 60 degrees in accordance with the energized current value.

  Light input from the input collimating system 20 is polarized and separated into a horizontal component and a vertical component by the polarizer 10. The polarization of each of the separated lights becomes a polarization having a predetermined rotation angle by the two self-holding Faraday rotators FR1 and FR2 and the half-wave plate HWP, and is further arbitrarily determined by the always energizing Faraday rotator FR3. The polarization is synthesized by the analyzer 12. The two polarized waves are divided into a component coupled by the analyzer 12 and a component diverging. Here, if there is a diverging component, the combined component is attenuated compared to the power level at the time of input.

  This constant energization type Faraday rotator FR3 can change the plane of polarization of the light within a Faraday rotation angle range of 35 to 60 degrees when the value of the current energized to the coil C3 is varied within the range of 0 to 10 mA. Table 1 shows the current direction to the coils C1 and C2 of the self-holding type Faraday rotators FR1 and FR2, the Faraday rotation angles of the Faraday rotators F1 to F3, the variable range of the combined rotation angle, and the variable range of optical attenuation. Show.

  The light attenuation characteristic is shown in FIG. If a constant current type Faraday rotator FR3 having a Faraday rotation angle of 35 to 60 degrees is used, the light attenuation characteristic curve is continuous. # 1 to # 4 correspond to the combinations in Table 1. In order to cover the Faraday rotation angle of 35 to 60 degrees, the coil current only needs to be variable in the range of 0 to 10 mA. Therefore, a desired light attenuation is obtained by controlling the direction of the coil current of the self-holding type Faraday rotators FR1 and FR2 and controlling the coil current to the normally energized Faraday rotator FR3 (control in the range of 0 to 10 mA). Can be adjusted freely.

  For example, if the applied magnetic field directions of both magnetic gaps of the first and second self-holding Faraday rotators are both positive, the Faraday rotation angle of the light transmitted through both Faraday elements is θF1 + θF2 + 12.5 + 22.5 = +35 degrees and -35 degrees with a half-wave plate. Since the Faraday rotation angle by the normally energized Faraday rotator is +35 to +60 degrees, the combined rotation angle is 0 to +25 degrees. When only the applied magnetic field direction of the magnetic gap of the first self-holding type Faraday rotator is switched to the negative direction, the Faraday rotation angle of the light transmitted through both Faraday elements is −12.5 + 22.5 = + 10 degrees at θF1 + θF2. / 10 degrees with a two-wavelength plate. Since the Faraday rotation angle by the normally energized Faraday rotator is +35 to +60 degrees, the combined rotation angle is +25 to +50 degrees. When the applied magnetic field direction of the magnetic gap of the first self-holding type Faraday rotator is switched to the positive direction and the applied magnetic field direction of the magnetic gap of the second self-holding type Faraday rotator is switched to the negative direction, both Faraday elements are transmitted. The Faraday rotation angle of light is + 12.5-22.5 = −10 degrees at θF1 + θF2, and +10 degrees at a half-wave plate. Since the Faraday rotation angle by the normally energized Faraday rotator is +35 to +60 degrees, the combined rotation angle is +45 to +70 degrees. If the applied magnetic field directions of both magnetic gaps of the first and second self-holding Faraday rotators are both negative, the Faraday rotation angle of the light transmitted through both Faraday elements is θF1 + θF2, which is −12.5-22.5. = -35 degrees, and +35 degrees with a half-wave plate. Since the Faraday rotation angle by the normally energized Faraday rotator is +35 to +60 degrees, the combined rotation angle is +70 to +95 degrees. Thus, by adjusting the combination of the magnetization directions of the first and second self-holding Faraday rotators and adjusting the variable magnetic field of the constantly energizing Faraday rotator, the combined rotation angle variable region becomes 0 to +95 degrees, and light attenuation The amount variable region is 0 to the maximum.

  In this example, the current value energized to the coil by the always-on type Faraday rotator is varied in the range of 0 to 10 mA. However, if the current value can be varied in the range of 0 to 20 mA, the Faraday rotation angle is 20 to 60 degrees. The polarization plane of light can be changed within a range. In that case, by combining the direction of the coil current to the two types of self-holding Faraday rotators and adjusting the variable magnetic field of the constantly energizing Faraday rotator, the combined rotation angle variable region becomes 0 to +95 degrees, and two types Since there is a considerable overlap in the combined rotation angle variable region by adjusting the variable magnetic field of the always-on type Faraday rotator with respect to the combination of the direction of the coil current to the self-holding Faraday rotator, the coil current increases slightly, but the light The amount of attenuation can be changed more smoothly.

  In the above example, the self-holding type Faraday rotator is composed of a magnetic field applying means in which a coil is wound around a magnetic yoke made of a semi-hard magnetic material, and a Faraday element inserted between the gaps of the magnetic yoke. The magnetic field applying means may be a magnetic yoke made of a soft magnetic material, and a Faraday element having a coercive force inserted between the gaps of the magnetic yoke. In that case, the Faraday rotation angle can be self-maintained by utilizing the coercive force of the Faraday element itself.

  In the above example, two types of self-holding Faraday rotators are combined with the discrete variable optical attenuation mechanism, but three or more types of self-holding Faraday rotators may be combined. If the number of self-holding Faraday rotators is increased, the structure becomes complicated and there is a problem that the size of the Faraday rotator is increased, but the coil current value of the constantly energizing Faraday rotator can be made smaller.

Explanatory drawing which shows an example of the variable optical attenuator which concerns on this invention. Explanatory drawing which shows the arrangement | sequence state of the optical component. Explanatory drawing which shows the structural example of a self-holding type Faraday rotator. The graph which shows an example of the optical attenuation characteristic of the variable optical attenuator which concerns on this invention. The graph which shows the typical example of the optical attenuation characteristic of the conventional variable optical attenuator.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Polarizer 12 Analyzer 14 Discrete variable optical attenuation mechanism 16 Continuous variable optical attenuation mechanism 20 Input collimating system 22 Output collimating system 30 Magnetic yoke 32 Permanent magnet

Claims (7)

  A discrete variable optical attenuation mechanism with a self-holding Faraday rotator and a normally energized Faraday rotation between the input collimator system and the output collimator system. A continuously variable optical attenuating mechanism having a magnetic element arranged in a straight line along the optical axis, switching control of the current direction to the magnetic field applying means of the self-holding Faraday rotator, and the magnetic field of the normally energized Faraday rotator Combined with current control of the current value to the application means, the optical attenuation is adjusted by interpolating the discrete optical attenuation by the discrete variable optical attenuation mechanism with the continuous optical attenuation by the continuous variable optical attenuation mechanism. A variable optical attenuator characterized by that.   2. The variable optical attenuator according to claim 1, wherein the discrete variable optical attenuation mechanism includes a plurality of self-holding Faraday rotators and phase shifters, and the rotation angle of the self-holding Faraday rotator is offset by the phase shifters.   The variable optical attenuator according to claim 2, wherein the phase shifter is a (1/2) x (2n-1) wave plate (where n is a positive integer).   4. The variable light according to claim 2, wherein the self-holding type Faraday rotator comprises magnetic field applying means in which a coil is wound around a magnetic yoke made of a semi-hard magnetic material, and a Faraday element inserted between the gaps of the magnetic yoke. Attenuator.   4. The self-holding type Faraday rotator comprises magnetic field applying means in which a coil is wound around a magnetic yoke made of a soft magnetic material, and a Faraday element having a coercive force inserted between the gaps of the magnetic yoke. Variable optical attenuator.   The normally energized Faraday rotator comprises a Faraday element, a permanent magnet for magnetically saturating the Faraday element, and variable magnetic field applying means for applying a variable magnetic field to the Faraday element by winding a coil around a magnetic yoke. The variable optical attenuator according to any one of 5 to 5.   The self-holding type Faraday rotator is a combination of two types of Faraday rotation angles of ± 12.5 degrees and ± 22.5 degrees, and the normally energized Faraday rotator covers a Faraday rotation angle of 35 to 60 degrees. The variable optical attenuator according to claim 1, wherein the variable optical attenuator is one.

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