CN1677171A - Polarization controller and use thereof - Google Patents

Abstract

The invention is a polarization controller and its application. For realizing the polarization control and the random disturbing function of polarizing state, the invention discloses a polarization controller, including an optical part and an electric control part composed of driving circuits, where the optical part is formed cascadedly and alternatively of three magnetooptical crystal-made Faraday rotators and two 1/4 wave plates along the light path, and the two wave plates are fixed and the three Faraday rotators are controlled by the electric control part at the rotating angles of plus or minus 45 degrees, plus or minus 90 degrees and plus or minus 45 degrees, respectively, so as to realize the conversion of arbitrary determined input polarizing state to arbitrary determined output polarizing state. The structure is simple, the control is accurate, the cost is low and it is easy for system integration.

Description

A kind of Polarization Controller and application thereof

Technical field

The invention belongs to fiber optic communication field.

Background technology

In optical fiber telecommunications system, often there is tangible fluctuation in light signal along its polarization state in optical fiber and the various optical device direction communication process, and the light signal that the receiving end requirement has stable polarized characteristic, particularly polarisation multiplex system requires the demultiplexing end accurately to discern polarization state, and this just need control exactly to the light signal polarization state of receiving end.In addition, the widespread use with dense wavelength division multiplexing system of improving constantly along with optical fiber telecommunications system single channel speed, the polarization mode dispersion effect is considered to limit the final obstacle of optical communication system to higher rate, high capacity, long distance development, and in the polarized mode dispersion compensation scheme, the device that any input polarization can be changed into any output polarization attitude is absolutely necessary, and also needs to use polarization state disturbance device to simulate the random law of light signal polarization characteristic in the actual fiber link in the polarization mode dispersion correlative study process.More than the function of control light signal polarization state all can realize by Polarization Controller.

Existing Polarization Controller mainly comprises optical fiber extruding/winding-type, wave plate is rotary-type and liquid crystal/electrooptical modulation type etc. is several.Wherein, the Polarization Controller of optical fiber extruding/winding-type is mainly by using devices such as piezoelectric ceramics optical fiber to be applied the external force of different directions, thereby produce the stress birefrin effect and change polarization state, its advantage is relatively simple for structure, cost is cheaper, but owing to there is factor such as physics fatigue, its unstable properties can not realize accurate control; The rotary-type Polarization Controller of wave plate is by half-wave plate and quarter-wave plate cascade more than three, and with the major axes orientation of manual or automatically controlled mode rotating wave plate, to introduce birefringence in different directions, thereby reach the purpose of Polarization Control, this method is more accurate than optical fiber extruding/winding-type, but, influenced the speed of control owing to need the mechanical rotation of wave plate; The Polarization Controller of liquid crystal/electrooptical modulation type utilizes liquid crystal or LiNO ₃Introduce the birefringence and then the control polarization state of different directions Deng the electrooptical effect of crystal, this class methods precision height, speed are fast, but complex structure, and cost is higher.

Summary of the invention

The objective of the invention is to: realize a kind of Polarization Controller that can be applicable in optical fiber telecommunications system receiving end, demultiplexing end and the polarization mode dispersion compensator spare, and can realize being applied to the polarization state random perturbation function of polarization mode dispersion correlative study simultaneously.This Polarization Controller is simpler compared to the Polarization Controller structure of liquid crystal/electrooptical modulation type, cost is cheaper, then avoided the parts mechanical motion compared to optical fiber extruding/winding-type and the rotary-type Polarization Controller of wave plate, made control more accurately with rapid.

The present invention proposes a kind of Polarization Controller, comprise opticator, and the automatically controlled part of forming by computing machine and driving circuit, it is characterized in that: the opticator of described Polarization Controller is to be formed along the alternate cascade of optical path direction by Faraday rotator and two quarter-wave plates that three magneto-optical crystals are made, described two quarter-wave plate fixed placement, described three Faraday rotators are controlled by described automatically controlled part, automatically controlled rotation angle range is respectively ± and 45 °, ± 90 °, ± 45 °, to realize determining that arbitrarily input polarization is to the conversion of determining the output polarization attitude arbitrarily.

The application of above-mentioned Polarization Controller in polarization mode dispersion random character research experiment, it is characterized in that: the Faraday rotator that three magneto-optical crystals of the automatically controlled part STOCHASTIC CONTROL by Polarization Controller are made, realize output polarization attitude random perturbation, make the output polarization attitude spread all over whole group and add ball.

The advantage of Polarization Controller of the present invention is: wave plate is a fixed placement, utilize magneto-optic effect that polarization state is rotated, avoided mechanical rotation, and can guarantee control accuracy, made it have simple in structure, accurate, with low cost, the characteristics that are easy to the system integration of control simultaneously.

Description of drawings

Fig. 1 is the structural representation of an embodiment of Polarization Controller of the present invention, and wherein two quarter-wave plate slow axis all become 0 ° of fixed placement with the x axle in Jones space.

Fig. 2 is the structural representation of another embodiment of Polarization Controller of the present invention, and wherein two quarter-wave plate slow axis become 0 ° and 45 ° of fixed placement respectively with the x axle in Jones space.

Fig. 3 a～Fig. 3 d utilizes Polarization Controller of the present invention to realize the synoptic diagram of Polarization Control process.

Fig. 4 utilizes Polarization Controller of the present invention to realize the synoptic diagram of polarization state random perturbation process.

Embodiment

1. utilize magneto-optical crystal to realize the principle analysis of Faraday rotator.

Magneto-optic effect is called Faraday effect again, is meant the phenomenon that produces circular birefringence when applying magnetic field in magneto-optic memory technique in the material, and promptly right-handed polarized light is experienced different refractive indexes with left-hand polarization light in medium.Magneto-optic effect makes the polarization state of light the propagated S along the Stokes space in magnet-optical medium ₃The axle rotation, its anglec of rotation is relevant with the power of magneto-optic effect, can control by the magnetic field intensity that change is applied on the magneto-optic memory technique.This rotation effect to polarization state can be represented with following Jones matrix J and Stokes matrix S:

$J=\left[\begin{array}{cc}\cos \mathrm{\α}& -\sin \mathrm{\α}\\ \sin \mathrm{\α}& \cos \mathrm{\α}\end{array}\right]---\left(1\right)$

$S=\left[\begin{array}{ccc}\mathrm{<figure-callout\; id="2"\; label="cos"\; filenames="A20051001147100085.png"\; state="\{\{state\}\}">cos</figure-callout>}2\mathrm{\&alpha;}& -\mathrm{<figure-callout\; id="2"\; label="sin"\; filenames="A20051001147100085.png"\; state="\{\{state\}\}">sin</figure-callout>}2\mathrm{\&alpha;}& 0\\ \mathrm{<figure-callout\; id="2"\; label="sin"\; filenames="A20051001147100085.png"\; state="\{\{state\}\}">sin</figure-callout>}2\mathrm{\&alpha;}& \mathrm{<figure-callout\; id="2"\; label="cos"\; filenames="A20051001147100085.png"\; state="\{\{state\}\}">cos</figure-callout>}2\mathrm{\&alpha;}& 0\\ 0& 0& 1\end{array}\right]---\left(2\right)$

Wherein α represents the angle of rotating.

Faraday rotator promptly is rotated polarization state of light based on above-mentioned magneto-optic effect.Multiple magneto-optical crystal material is available, and for example the bismuth-substituted rare earth iron garnet single crystal has the little and tangible characteristics of Faraday effect of the loss of insertion.The automatically controlled part drive coil of forming by computing machine and driving circuit produces the magnetic field of intensity controlled and direction and puts on the magneto-optical crystal, promptly the may command polarization state anglec of rotation ± 45 ° or ± 90 ° of scopes in change.For reducing the loss fluctuation of magneto-optical crystal, can apply two variable magnetic fields respectively from horizontal and vertical, total controllable magnetic field is reached capacity.

2. the parameter control principle of Polarization Controller is analyzed and example.

The present invention utilizes magneto-optical crystal and quarter-wave plate to realize Polarization Controller, and this Polarization Controller comprises opticator, and the automatically controlled part of being made up of computing machine and driving circuit, and structure as depicted in figs. 1 and 2.Faraday rotator and two alternate cascades of quarter-wave plate that opticator is made by three magneto-optical crystals form, wherein two quarter-wave plates can be selected the centre wavelength that the is suitable for optical fiber communication wave plate at 1550nm for use, or be suitable for the wave plate of other centre wavelengths of other field, two equal fixed placement of quarter-wave plate, the slow axis of quarter-wave plate can become any angle with the x axle in Jones space, preferred 0 ° of (see figure 1) or 45 ° of (see figure 2)s.The automatically controlled rotation angle range of three Faraday rotators is respectively ± 45 °, ± 90 °, ± 45 °, control by the automatically controlled part that computing machine and driving circuit are formed.Computer control algorithm in the automatically controlled part and design of drive circuit are made and can be utilized routine techniques to realize.

The principle of work of this Polarization Controller is: first Faraday rotator 1 adds S on the ball with the polarization state of any input optical signal around group ₃The angle that axle (latitude direction) rotation is suitable; Thereafter first quarter-wave plate 10 with postrotational polarization state around S ₁The axle half-twist, thus make light signal become linear polarization; Subsequently second Faraday rotator 2 with polarization state around S ₃Axle adds the ball equator along group and rotates suitable angle; Second quarter-wave plate 20 again with linear polarization around S ₁The axle half-twist makes its elliptically polarized light that becomes certain ellipsoid degree or circularly polarized light; At last, the 3rd Faraday rotator 3 with light signal around S ₃Axle rotates to the output polarization attitude of appointment.

First embodiment with Polarization Controller shown in Figure 1 is an example, and the slow axis of two quarter-wave plates is 0 ° with the angle of the x axle in Jones space all.If the input optical signal polarization state is [a, b, c] ', specify output polarization attitude be [x, y, z] ', the automatically controlled anglec of rotation of three Faraday rotators then ₁, ₂, ₃Be respectively:

Wherein, fix is to 0 direction bracket function,

$\mathrm{\&Delta;\&theta;}=\left(\frac{1-\mathrm{sgn}\left(a\right)}{2}\right)\mathrm{\&pi;}+\arctan \frac{-c}{\mathrm{sgn}\left(a\right)\sqrt{a^2+b^2}}-\left(\frac{1-\mathrm{sgn}\left(x\right)}{2}\right)\mathrm{\&pi;}+\arctan \frac{z}{\mathrm{sgn}\left(x\right)\sqrt{x^2+y^2}}---\left(6\right)$

Wherein, sgn is a sign function.

Write computer-controlled program according to above-mentioned control algolithm, and the control Driver Circuit drive coil, change is applied to the magnetic field on the Faraday rotator in the opticator, can realize the Spin Control to polarization state.

Place as if the x axle in two quarter-wave plate slow axis and Jones space other fixed angle that wait at 45, then need make corresponding modify above-mentioned control algolithm.

Fig. 3 a～Fig. 3 d is depicted as once control and determines that arbitrarily input polarization changes the example procedure of determining the output polarization attitude arbitrarily into.Whole transition process added on the ball in group represents that wherein input polarization is [0.6000,0.3000 ,-0.7416] ', the output polarization attitude of requirement is [0.5000 ,-0.5000,0.7071] '.First Faraday rotator 1 adds S on the ball with the polarization state of input optical signal around group ₃-26.5651 ° of axle (latitude direction) rotations, polarization state is changed to [0.6708,0 ,-0.7416] '; First quarter-wave plate 10 with postrotational polarization state around S ₁The axle half-twist, thereby make light signal become linear polarization [0.6708,0.7416,0] '; Second Faraday rotator 2 with polarization state around S ₃Axle adds 87.1304 ° of ball equator rotations along group, and polarization state is changed to [0.7071,0.7071,0] '; Second quarter-wave plate 20 again with linear polarization around S ₁The axle half-twist makes it become elliptically polarized light [0.7071,0,0.7071] '; At last, the 3rd Faraday rotator 3 with light signal around S ₃45.0000 ° of output polarization attitudes [0.5000 ,-0.5000,0.7071] of axle rotation ' to appointment.

Because Polarization Controller of the present invention can be realized the output of random polarization state, therefore can in polarization mode dispersion random character research experiment, use, realize polarization state random perturbation function.When specifying any input polarization, if utilize three Faraday rotators of automatically controlled part control to make its random value in angle variation range separately, then the output polarization attitude adds appearance at random on the ball in whole group, the output polarization attitude that Figure 4 shows that 5000 independent samples distributes, and visible output polarization attitude spreads all over whole group and adds ball.On the other hand, if input polarization is the unknown-value of fluctuation, need control output polarization attitude constant in a certain value, then can use the analyzing instrument to detect the output polarization attitude at output terminal, and three controlled variable by optimized Algorithm FEEDBACK CONTROL Polarization Controller, thereby reach the effect of stablizing the output polarization attitude.

Claims (3)

1. Polarization Controller, comprise opticator, and the automatically controlled part of forming by computing machine and driving circuit, it is characterized in that: the opticator of described Polarization Controller is to be formed along the alternate cascade of optical path direction by Faraday rotator and two quarter-wave plates that three magneto-optical crystals are made, described two quarter-wave plate fixed placement, described three Faraday rotators are controlled by described automatically controlled part, automatically controlled rotation angle range is respectively ± and 45 °, ± 90 °, ± 45 °, to realize determining that arbitrarily input polarization is to the conversion of determining the output polarization attitude arbitrarily.

2. Polarization Controller according to claim 1 is characterized in that: the slow axis of described quarter-wave plate becomes 0 ° or 45 ° with the x axle in Jones space.

3. the application of the described Polarization Controller of claim 1 in polarization mode dispersion random character research experiment, it is characterized in that: the Faraday rotator that three magneto-optical crystals of the automatically controlled part STOCHASTIC CONTROL by Polarization Controller are made, realize output polarization attitude random perturbation, make the output polarization attitude spread all over whole group and add ball.

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