WO2001048541A2 - Stabilisateur de polarisation sans fin - Google Patents

Stabilisateur de polarisation sans fin Download PDF

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Publication number
WO2001048541A2
WO2001048541A2 PCT/EP2000/012761 EP0012761W WO0148541A2 WO 2001048541 A2 WO2001048541 A2 WO 2001048541A2 EP 0012761 W EP0012761 W EP 0012761W WO 0148541 A2 WO0148541 A2 WO 0148541A2
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WIPO (PCT)
Prior art keywords
polarization
signal
optical
input
intensity
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PCT/EP2000/012761
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English (en)
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WO2001048541A3 (fr
Inventor
Mario Martinelli
Paolo Martelli
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Optical Technologies U.S.A. Corp.
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Application filed by Optical Technologies U.S.A. Corp. filed Critical Optical Technologies U.S.A. Corp.
Priority to AU26736/01A priority Critical patent/AU2673601A/en
Publication of WO2001048541A2 publication Critical patent/WO2001048541A2/fr
Publication of WO2001048541A3 publication Critical patent/WO2001048541A3/fr

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    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B27/00—Optical systems or apparatus not provided for by any of the groups G02B1/00 - G02B26/00, G02B30/00
    • G02B27/28—Optical systems or apparatus not provided for by any of the groups G02B1/00 - G02B26/00, G02B30/00 for polarising
    • G02B27/286—Optical systems or apparatus not provided for by any of the groups G02B1/00 - G02B26/00, G02B30/00 for polarising for controlling or changing the state of polarisation, e.g. transforming one polarisation state into another
    • G—PHYSICS
    • G02—OPTICS
    • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
    • G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
    • G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour 
    • G02F1/0136—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  for the control of polarisation, e.g. state of polarisation [SOP] control, polarisation scrambling, TE-TM mode conversion or separation
    • G—PHYSICS
    • G02—OPTICS
    • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
    • G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
    • G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour 
    • G02F1/0121—Operation of devices; Circuit arrangements, not otherwise provided for in this subclass

Definitions

  • the present invention relates to a polarization stabilizer and to a method for stabilizing the polarization of optical signals
  • the present invention also relates to an optical telecommunication system employing such polanzation stabilizer
  • SOP state of polarization
  • optical fibers such as single-mode (SM) optical fibers perturb the SOP of propagating optical signals in a complicated and often unpredictable way, depending on many parameters such as temperature, mhomogeneities of the core structure deviations from core circularity, stresses, etc
  • a relatively short length of fiber e g , of one meter, or less, may significantly perturb in a random way the SOP of optical signals propagating in it if the fiber is exposed to stress or to temperature changes
  • polarization perturbing optical paths may be of interest for optical signal transmission or optical signal processing, such as optical planar optical waveguides biref ⁇ ngent crystals, paths comprising optical retarder waveplates or other optical birefnngent path
  • Polarization perturbation it is meant herein the fact that the SOP of an optical signal entering an optical path is not kept unaltered to the end of said path and is changed along the path, the entity of the SOP change being difficult or impossible to predict Polarization maintaininc fibers are known and available, but their loss is much higher than that of ordinary fibers, as well as their cost, so that they are of limited use for telecommunications.
  • some devices employed in optic communication systems and showing sensitivity to the SOP of the optical signal propagating in the system are the semiconductor optical amplifiers (SOA's), electro-optical modulators, wavelength division multiplex couplers and electrically controlled switches based on electro-optic crystals and liquid crystals.
  • SOA's semiconductor optical amplifiers
  • electro-optical modulators electro-optical modulators
  • wavelength division multiplex couplers wavelength division multiplex couplers
  • U.S. Patent 5,090,824 describes an electrically controlled optical switch using an electro-optic crystal of the type having at least one set of fast and slow axes.
  • a polarizer arranged at the input of said optical switch, for polarizing the light entering the switch along one of the fast or slow axes.
  • optical devices that generally polarization sensitive are the fiber optic sensors, e.g. the interferometric fiber optic sensor.
  • optical communication systems using coherent detection techniques require the matching of the state of polarization of the optical signal at the output of the transmission path to that of the local oscillator beam at the receiver.
  • a polarization stabilization technique system is needed to control the SOP of an optical signal.
  • Amplification or attenuation by a constant factor, or a constant phase shift, or a combination of the above are not here considered to be substantial signal variations
  • Any polarizer, as a linear polarizer when aligned in the path of an optical signal, does indeed produce an output signal with a constant polarization by selecting a predetermined polarization component of the signal, however, the intensity of the polarizer output signal varies in this case with the SOP of the input signal, and the SOP of the output signal is not controlled in the above sense
  • Known techniques to stabilize the SOP of optical signals include active SOP control by means of optical elements such as retarders (e g biref ⁇ gent devices) and/or rotators (e g Faraday rotators), operated by actuators under control of a feedback circuit sensing the output polarization
  • optical elements such as retarders (e g biref ⁇ gent devices) and/or rotators (e g Faraday rotators), operated by actuators under control of a feedback circuit sensing the output polarization
  • a known problem connected to the use of polarization stabilizers in optical communication systems is caused by the fact that the input polarization may vary monotonically without limit Then, the polarization stabilizer may reach an intrinsic limit related to the particular optical elements that it uses, and the polarization stabilization may be interrupted
  • polarization stabilizers that are endless in control, i e that are able to operate in a relatively continuous way for any variation of SOP of the signal to be stabilized
  • endless polarization stabilizers can be classified into two categories according to the presence or the absence of a reset procedure
  • U S Patent 5,005,952 describes a polarization controller comprising a routing device for routing an incoming optical beam, the polarization of which is sought to be controlled partly or entirely into two alternative paths Each path contains a respective stack of liquid cells that are able to change the phase retardation of the radiation passing through by means of electric or magnetic fields applied across the cells A recombining device for combining the two path are also provided When the retardation introduced by one of the two stacks approaches a limit value the routing device routes the optical beam to the other path comprising the other stack of liquid cells Alternatively it is proposed a controller comprising four liquid cells Polarization stabilizers are also known that are both endless in control and reset- free, i e , these stabilizers are able to operate in a contmuos way for any variations of SOP without the use of a reset procedure
  • a polarization controller in which an optical directional coupler combines the received signal light and a local oscillator light
  • One of the two combined output beams is used for transmission signal detection and the other for polarization detection
  • the polarization detection is achieved by means of two Wollaston prisms (WP) and two photodiodes
  • WP Wollaston prisms
  • the polarization state of the received signal is mechanically controlled by rotating a quarter- wave plate and a half-wave plate so that the signal polarization state coincides with that of the linearly pola ⁇ zed wave produced by the local oscillator
  • WP Wollaston prisms
  • a polarization control scheme using an interferomet ⁇ c configuration is described by V Napasab et al , "New Polarization-State Control Scheme Polarization Recombining", Optics Communications, Vol 66, No 2 3 (15 April 1988)
  • the system illustrated by the authors consists of a polarization beam splitter, such as a Woilaston prism, a 90° linear polarization rotator, an endless phase shifter and a beam combiner two photodetectors followed by signal processing electronics
  • the signal light is separated into two orthogonal linearly polarized components by the polarization beam splitter
  • One of the two components is converted in the orthogonal one and then recombined with the other component in the beam combiner
  • the phase shift given by the endless phase shifter is adjusted so that the output intensities detected by the two photodetectors are equal
  • the endless phase shifter proposed by the author comprises a stationary quarter-wave plate, a rotatable half-wave plate and a further stationary quarter-wave plate
  • the SOP of a the light in a generic elliptical state is completely characterized by four quantities, the azimuth ⁇ 0 , the ellipticity ⁇ , the direction of rotation, and the phase difference ⁇ between the phase angles of the electric field components
  • the azimuth & 0 is the angle formed between the major axis of the ellipse representing the polarization and a reference axis, i e the x-axis
  • the Applicant has observed that the use of independently rotating optical elements for compensating the polanzation changing of the input signal, increases the complexity of the electronic control, the overall size and, particularly if mechanically rotating means are required, reduces the rapidity and the reliability of the polarization stabilizer operation Moreover, the interferomet ⁇ c schemes proposed in the prior art cause additional power losses of the signal to be stabilized and have performances strictly connected to the optical alignment of the used elements.
  • an endless and reset-free stabilization of the polarization of an input signal can be obtained from a conversion of the polarization of said input signal into a circular polarization.
  • this conversion can occur in a polarization transformer comprising a linear polarizer, that selects a portion of the input signal having linear polarization, and an optical element, for example a quarter-wave plate, that converts the selected linear polarization into a circular polarization.
  • This optical element may be joined to the linear polarizer in order to form a single rotatable element.
  • the stabilization of the intensity of the circular polarized optical signal emerging from the polarization transformer is achieved by changing the orientation of said transformer in response to the polarization fluctuations of the input signal.
  • an intensity of the circular polarized signal independent from the SOP of the input signal can be obtained operating on the orientation of the polarization transformer in such a way to keep the intensity of said circular polarized signal proportional to the intensity of said input signal according to a proportionality factor belonging to a suitable range comprising the value 0.5.
  • said suitable range may be comprised between the values 0.4 and 0.6.
  • the Applicant has determined that by choosing said proportionality factor substantially equal to 0.5 optimum polarization stabilization is obtained.
  • a control circuit can operate on said polarization transformer so as to keep the intensity of said circular polarized signal substantially equal to half of input intensity.
  • said Applicant has observed that said polarization stabilized signal having a circular SOP can be converted in any further state of polarization by means of suitable optical elements, e.g., ordinary wave plates, without introducing any fluctuation in the intensity.
  • the present invention has to do with a polarization stabilizer for generating from an input optical signal of intensity I and polarization A, an output signal having intensity and polarization substantially independent from the polarization A, comprising:
  • a linear polarizer optically coupled to said input and having an orientation defined by an inherent axis, for selecting a portion of said input signal having linear polarization parallel to said inherent axis; an optical element operatively coupled to said linear polarizer for converting said selected portion into said output signal having a circular polarization;
  • said optical element is structurally connected to said linear polarizer to form a single optical element.
  • said proportionality factor is comprised between 0.45 and 0.55. More preferably, said proportionality factor is equal to 0.5.
  • optical element comprises a quarter-wave plate optically coupled to said linear polarizer and provided of a principal axis oriented in such a way to form an angle of 45° with the inherent axis of the linear polarizer.
  • said polarization stabilizer comprises an output detector, optically coupled to said output port for converting at least a portion of said output signal into a feed-back signal and for feeding said feed-back signal to the control circuit.
  • said polarization stabilizer comprises an optical beam divider coupled to said output for transmitting a portion of the output optical signal towards said detector.
  • said linear polarizer comprises a polarization beam splitter.
  • said linear polarizer and said optical element are rotatable around the propagating axis of said input optical signal.
  • said polarization comprises an output optical element coupled to said output for converting the output signal having circular polarization into a signal having a pre-established polarization.
  • said polarization stabilizer comprises a further detector coupled to said input for converting at least a portion of said input signal into a reference electric signal and for feeding said reference electric signal to said control circuit.
  • said polarization stabilizer comprises a further optical beam divider coupled to said input for transmitting at least a portion of said input optical signal towards said further detector.
  • said linear polarizer and said optical element are structurally connected to at least a motor controlled by said electronic circuit.
  • said single optical element is mounted on an axis of a motor.
  • said axis of the motor is perforated in such a way to allow the passage of said input optical signal.
  • said polarization stabilizer comprises a reflecting element for sending said input signal towards said input of the polarization stabilizer.
  • said electric motor rotates of multiples of an elementary rotation step.
  • said at least one elementary rotation step is lower than about 5°. More preferably, said at least one elementary rotation is lower than about 1 °.
  • the present invention has to do with a polarization independent optical apparatus including a polarization stabilizer according to the first aspect of the invention and a polarization sensitive optical device optically coupled to the output of the polarization stabilizer.
  • the present invention has to do with a method for stabilizing the polarization of an input optical signal of intensity I, comprising the step of transforming the input optical signal by an optical device suitable for polarizing it and for converting its polarization state into a circular polarization state.
  • the method further comprises the step of controlling the orientation of the optical device so as to keep the intensity of said output signal proportional to the intensity I of said input signal according to a proportionality factor substantially comprised between 0.4 and 0.6.
  • the polarization stabilizer according to the invention is endless and reset-free and does not require a complex control circuitry Moreover it shows a reduced over-all size Moreover, since the polarization stabilizer according to the invention is based on a single rotatable optical element or on two rotatable optical elements, it requires a simple apparatus for moving these elements
  • FIG 1 shows a preferred embodiment of a polarization stabilizer 1 made according to the invention
  • FIG 2 shows schematically a polarization transformer employed in the polarization stabilizer of FIG 1 ,
  • FIG 3 illustrates, on the Pomcare sphere, the operation of the polarization stabilizer according to the invention
  • FIG 4a shows a simulated intensity variation of a non-stabilized signal corresponding to a periodically varying polarization
  • FIG 4b shows a simulated intensity behavior of a signal stabilized according to the invention and corresponding to the polarization variation of FIG 4a
  • FIG 5a shows a simulated intensity variation of a non-stabilized signal corresponding to a randomly varying polarization
  • FIG 5b shows a simulated intensity behavior of a signal stabilized according to the invention and corresponding to the polarization variation of FIG 5a
  • FIGG 6a, 6b, 6c show three simulated intensity behaviors of signals stabilized according to the invention using three different control conditions
  • FIG 7 shows a simulated intensity behavior of a signal stabilized according to the invention using a fourth control condition
  • FIG 8 shows a simulated intensity behavior of a signal exiting a polarization stabilizer according to the invention for a fifth control condition
  • FIG 9 schematically shows a polarization stabilizer according to the invention employed for experimental tests
  • FIG 10a shows the oscilloscope trace of non-stabilized signal corresponding to a periodically varying polarization
  • FIG 10b shows the oscilloscope trace of signal stabilized according to the invention corresponding to the polarization variation of FIG 10a
  • FIG 1 1 shows a further embodiment of the invention
  • FIG 12 illustrates a particular electro-optical switch
  • FIG 13 shows a wavelength division multiolexing optical system according to the invention
  • FIG 1 it is schematically shown a preferred embodiment of a polarization stabilizer 1 made according to the invention
  • the polarization stabilizer 1 comprises an input optical splitter 2, a polarization transformer 5 and an output optical splitter 8
  • the input optical splitter 2 has an input port 3 and two output ports 4 and 3'
  • the input optical splitter 2 is able to send most of the signal power to port 4 and to send the remaining power to port 3'
  • 99% of the optical power is transmitted to port 4 and 1 % is deviated towards port 3', but other values e g lower are possible
  • the output optical splitter 8 has an input port 9 and two output ports 10 and 11
  • the input optical splitter 8 is able to send most of the signal power to port 10 and to reflect the remaining power to port 11
  • 99% of the optical power is transmitted to port 10 and 1% is deviated towards port 1 1 , but other values are possible
  • the ports 3, 4 of the input optical splitter 2 and the ports 9,10 of the output optical splitter 8 are aligned along an axis z
  • the output port 4 of the input optical splitter 2 is optically coupled to the polarization transformer 5 comprising a linear polarizer 6 and a quarter-wave plate 7
  • FIG 2 schematically shows said polanzation transformer 5 and the reference axes, x, y and z, used to define the orientation of the linear polarizer 6 and the quarter- wave plate 7
  • FIG 2 shows the z-axis as the propagating direction of an input optical signal
  • the linear polarizer 6 is a known optical element capable of transmitting a linear polarization from the polarization of an entering signal More in detail, the linear polarizer transmits the portion of the input signal having a linear polarization parallel to an inherent axis PP' that, in FIG 2, is parallel to the y-axis
  • the position of said inherent axis PP' is defined by an angle ⁇ (counted in anti-clockwise direction), in the following azimuth ⁇ , comprised between the inherent axis PP' and the x-axis
  • the linear polarizer 6 may be a thin glass of dichroic material, such as a Polaroid ® filter that ideally, absorbs only the optical radiation having polarization different from its inherent axis Moreover, the linear polarizer 6 may be made of a biref ⁇ ngent material that spatially divides the input optical radiation into two portions having two orthogonal states of polarization As an example, the linear polanzer 6 may be a bulk polarization beam splitter
  • a quarter-wave plate is made of birefrmgent material producing two principal axes, namely a fast axis and a slow axis, and is able to introduce a phase shift of 90° between the states of polarization of input signals coincident with the fast and
  • the quarter-wave plate 7 it perpendicular to the z-axis and its orientation is defined by the azimuth ⁇ ' (counted in anti-clockwise direction) that is the angle formed between the fast axis QQ' and the x-axis
  • the quarter wave-piate 7 is oriented in such a way that the fast axis
  • the quarter wave-plate 7 may be oriented in such a way that the slow axis forms an angle of 45° with the inherent axis PP' of the linear polarizer 6
  • This orientation of the quarter-wave plate 7 allows transforming the linear polarization of an optical signal emerging from the linear poia ⁇ zer 6 into a circular polarization
  • an exchange of the fast axis with the slow axis of the quarter-wave plate 7, for orientation in respect of the linear polarizer 6, may merely cause an inversion of the rotation direction of said circular polarization
  • the quarter-wave plate 7 may be replaced with any optical element suitable to perform said polarization conversion of the signal emerging from the linear polarizer for example two octave-wave plates can be used
  • optical splitters 2 and 8 are bulk beam splitters but, alternatively, optical fiber- fused couplers or planar couplers may be employed Moreover the optical splitters 2 and 8 may be coupled to input or output optical fibers or optical waveguides (not shown) In such cases, suitable focalizing lenses may be used
  • the linear poia ⁇ zer 6 and the quarter-wave plate 7 are structurally connected with each other in order to produce a single optical element
  • the polarization transformer 5 is suitable to convert any polarization of an entering signal into a circular polarization, independently from its orientation
  • the polarization transformer 5 can rotate in both rotation directions around the z- axis, for example by means of a motor (not shown in FIG 1 )
  • Such motor may be a DC brush-less electrical motor, as the one marketed by Deltaomega, Opera (Italy) or, preferably, a step motor, as the one made by Sonceboz (CH)
  • a DC brush-less electrical motor may be provided of a suitable device (called encoder) for measuring the angular position
  • a DC brush-less electrical motor controlled by a digital signai or a step motor rotate the polarization transformer 5 by means of a sequence of elementary rotations, "steps", each corresponding to an angle va ⁇ ations of ⁇
  • the output port 3 of the input optical splitter 2 is optically coupled to a first detector 12, for example a conventional photodiode, for converting the received optical power into an electrical reference signal of voltage V,
  • the output port 11 of the output optical splitter 8 is optically coupled to a second detector 13 for converting the optical power into an electrical feedback signal of voltage V 2
  • the electrical outputs of the detectors 12 and 13 are connected to an electronic controller 15
  • the electronic controller 15 by actuating said motor, is able to operate on the orientation of the polarization transformer 5, modifying the azimuth ⁇ , in such a way to keep the intensity l out of the output signal proportional the intensity I of the input optical signal according to a factor ⁇ substantially comprised between 0 4 and 0 6
  • said factor ⁇ is comprised between 0 45 and 0 55
  • the electronic controller 15 can operate on the orientation of the polarization transformer 5 in such a way to minimize an error E, namely to satisfy the following condition
  • the coefficient ⁇ is a corrective factor related to the losses introduced by the optical elements employed in the polarization stabilizer 1 or associated with a difference in the splitting ratios of the optical splitters 2 and 8
  • the value of ⁇ can be determined by means of a calibration
  • the value of ⁇ is set in such a way that the error £ is zero when the output optical power is half the maximum output power (achieved by varying the input polarization state), with fixed input optical power and fixed position of the linear polarizer 6
  • polarization transformer 5 in alternative to the described polarization transformer 5, another optical element or combination of optical elements that performs the functions of polarizing and of converting the input polarization state into a circular polarization state may be used for polarization transformer 5
  • the polarization controller 1 comprises a fixed quarter-wave plate 14
  • the fixed quarter-wave plate 14 may be coupled to the input port 9 of the output optical splitter 8, as shown in FIG 1 , or it may be coupled to the output port 10 of said optical splitter
  • the quarter-wave plate 14 is oriented so as to convert the circular polarization of the signal coming from the polarization transformer 5 into a linear polarization
  • a further linear polarizer may be used
  • two quarter-wave plates of suitable orientation may be employed
  • one of the parameters used for defining the state of polarization of an optical signal is the azimuth, i.e , the angle formed between the major axis of the ellipse representing the polarization and a reference axis, i e , the x-axis
  • An input signal of intensity I and generic state of polarization A having an azimuth ⁇ 0 enters the device 1 at the input port 3.
  • the input optical splitter 2 splits the input signal into a main signal and a reference signal.
  • the main signal propagates, along the z-axis, from the output port 4 of the input optical splitter 2, to the output splitter 8.
  • Said main input signal passing through the polarization transformer 5, undergoes a polarization conversion and emerges with a circular polarization P.
  • FIG. 3 shows the projection of the Poincare sphere on the equatorial plane.
  • the equator of the sphere, circle EQ, represents the linear states of polarization
  • the poles P of the sphere represent circular states of polarization.
  • Two circular SOP's having different rotation directions correspond to the two poles of the Poincare sphere.
  • the input signal having polarization A and azimuth ⁇ 0 is represented in FIG. 3 by a point A having longitude 2 ⁇ 0 -
  • the axis OO' is a reference axis from which the longitudes are counted.
  • the longitudes are counted in an anti-clockwise direction.
  • the effect of the linear polarizer 6, included in the polarization transformer 5, is to project the polarization state A on the equator EQ and at a point B having longitude 2 ⁇ , where ⁇ is the above-defined azimuth of the linear polarizer 6.
  • the point B represents the linear SOP selected by the linear polarizer 6. This selection has been indicated by means of an arrow in FIG. 3.
  • the quarter-wave plate 14 having azimuth ⁇ " causes a second rotation of 90° around an axis passing through the sphere center (not shown in figure 3) and an equatorial point of longitude 2 ⁇ "
  • the quarter-wave plate 14 having azimuth ⁇ " transforms the signal having a circular state of polarization P into an output signal having iinear state of polarization L
  • the signal having circular state of polarization P passes through the output beam splitter 8
  • the input optical beam splitter 2 sends, through port 3', a portion of the input optical signal towards the first detector 12 that converts the received optical power into an electrical reference signal of voltage V-i
  • the first detector 12 is advantageously used when the intensity of the input optical signal may change during the operation of the polarization stabilizer 1
  • the detector 12 and the input optical splitter 2 can be omitted
  • a portion of the circularly polarized optical signal exiting from polarization transformer 5 is deviated by the output optical splitter 8 towards the second detector 13
  • the second detector 13 converts the received optical power into an electrical feedback signal of voltage V 2
  • the voltages V and V 2 are proportional to the intensities of the input and optical signals
  • the electric reference and control signals are fed to the electronic controller 15
  • the electronic controller 15 determines the error E, defined above and acts on the motor rotating the polarization transformer 5 in order to minimize said error By the consequent rotation of the polarization transformer 5 the intensity variations due to the variation of the state of polarization of the input signal are stabilized
  • the polarization stabilizer according to the invention allows to obtain an intensity variation ⁇ U A lower than 25%
  • the intensity variation ⁇ l % is lower than 15% More preferably, ⁇ l % is lower than 5%
  • the electronic controller 15 computes the error E, determines the rotation direction that causes a decreasing of said error and sends a corresponding electric signal to the motor Consequently the motor performs a rotation equal to ⁇ and then, the electronic controller 15 repeats the above mentioned operations
  • the circuit control 15 when the condition [1] is achieved the circuit control 15 provides an electric signal to the motor that causes a permanent oscillation of the polarization transformer 5 around the reached position The amplitude of this oscillation is equal to the rotation step ⁇
  • the rotation of the polarization transformer 5 can be interrupted when the error E is lower than a pre-established value
  • the effect of polarizing devices can be represented as a matrix operator which, using the standard rules of matrix algebra, can be combined with the vector representing the incident light to give the resultant vector
  • the state of polarization may be represented by a vector representation, namely Stokes vector
  • the Stokes vector consists of a set of four quantities, the so-called Stokes parameters, all of which have the dimension of time- averaged intensity
  • the Mueller matrix M of the polarizer transformer 5 comprising the linear polarizer 6 followed by the quarter-wave plate 7, is given by the following product
  • the matrix M, resulting by the product [4], is the following 4x4 matrix
  • This matrix M has been expressed as function of the sole azimuth ⁇ .
  • S', n1 and S',m are two Stokes parameters of the input signal s, n .
  • the output signal s out is a column vector 4x1 of the type representing a signal having a circular state of polarization.
  • the signal emerging from the polarization transformer 5, expressed by [6] is in a constant circular polarization state, whereas the intensity depends on the linear polarizer azimuth 3 respect to the input state of polarization.
  • the output optical signal will have intensity constant and independent from the state of polarization of the input signal.
  • the intensity of a signal represented by a Stokes vector is given by the first Stokes parameter
  • the Applicant observes that if condition [7] is satisfied, the normalized intensity of the output signal s ou , is equal to ⁇ A
  • the rotation step ⁇ influences the rapidity and the precision of the polarization stabilizer
  • the speed of the polarization stabilizer represents the maximum variation rate of the input state of polarization that the polarization stabilizer is suitable to compensate The speed is limited by the time necessary to rotate, by means of more rotating steps the polanzation transformer 5 until the right orientation is reached
  • the precision of the polarization stabilizer represents the capability of giving to the polarization transformer 5 an actual azimuth ⁇ close to the pre-established theoretical angle, i e the angle determined by the relations [1] or [2]
  • the design of the polarization controller according to the invention performs a trade-off between precision and rapidity
  • the Applicant has simulated the behavior of the polanzation stabilizer according to the invention by considering several values of the rotation step ⁇ For this simulation the Applicant has developed a software that reproduces the behavior of the optical components described with reference to figure 1 and represented by means of the above-discussed matrix formalism
  • the Applicant has observed that satisfactory performances can be achieved choosing a rotation step ⁇ lower than 5°
  • the rotation step ⁇ may be lower than or equal to1 °
  • the Applicant has simulated the behavior of the polarization stabilizer according to the invention for three different types of polarization variations of the input signal For these simulations the Applicant has considered a rotation step ⁇ equal to about
  • FIG 4a shows the intensity variation exiting the polarization stabilizer when no control of the azimuth was employed and for an input signal having a periodically varying linear state of polarization
  • the intensity expressed in arbitrary units, is represented versus the "step time" unit, i e , the time necessary to perform the above defined rotation step
  • the intensity of the input signal has been considered having unitary intensity
  • FIG 4b shows the intensity va ⁇ ation exiting the polarization stabilizer employing the electronic control of the azimuth of the polarization transformer 5 for the same input signal considered with reference to FIG 4a
  • the electronic control of the azimuth of the polarization transformer was programmed to carry out a stabilization of the intensity of the output signal at a value equal to 0 5, corresponding to the optimum condition expressed by [1]
  • the Applicant has evaluated the intensity variation ⁇ l , above defined With reference to FIG 4b the intensity variation ⁇ lo /o was lower than 5%
  • the Applicant has also simulated the behavior of the polarization stabilizer for an input signal having a randomly fluctuating state of polarization
  • FIG 5a illustrates the intensity exiting the simulated polarization stabilizer when no control of the azimuth of the polarization transformer 5 was employed
  • FIG 5b shows the intensity variation exiting the polarization stabilizer when the electronic control according to the invention was employed for the same input signal considered with reference to Fig 5a
  • the electronic control of the azimuth of the polarization transformer was programmed to carry out a stabilization of the power of the output signal at a value equal to 0 5
  • the intensity variation ⁇ l % corresponding to the simulation shown in FIG 5b was lower than 10%
  • the Applicant simulated the behavior of the polarization stabilizer for an input signal having a variable elliptic polarization Particularly, according to this simulation, the ellipticity of an elliptic state of polarization, having principal semi-axes placed at 45°, was periodically changed
  • FIG 6a shows the behavior of the intensity exiting the polarization stabilizer
  • the controlled output showed an intensity variation ⁇ l % lower than 5%
  • FIG. 6b shows the behavior of the intensity exiting the polarization stabilizer of the type 1 and utilizing an electric control programmed for keeping the output intensity equal to 0.55.
  • the output intensity shows a first periodical oscillation, comprised about between the values 0.55 and 0.45, and a second oscillation around the value 0.55, of lower amplitude.
  • the Applicant has noted that the first oscillation occurs at a frequency proportional to the variation frequency of the input polarization.
  • the first oscillation causes an intensity variation ⁇ l % lower than 10%.
  • the second oscillation shows an intensity variation ⁇ l % lower than 5% as the variation previously found for a control performed in the optimum condition.
  • the intensity variation ⁇ l % is lower than 15%.
  • FIG. 6c shows the behavior of the intensity exiting the polarization stabilizer of the type 1 and utilizing an electric control programmed for keeping the output intensity equal to 0.45.
  • FIG. 7 shows the behavior of the intensity exiting the polarization stabilizer of the type 1 and utilizing an electric control programmed for keeping the output intensity equal to 0.6.
  • the output intensity shows a first periodical oscillation, comprised about between the values 0.6 and 0.4, and a second oscillation around the value 0.6, of lower amplitude, lower than 5%.
  • the first oscillation causes an intensity variation ⁇ l % lower than 20%.
  • the intensity variation ⁇ l % was lower than 25%.
  • FIG 8 it is plotted the behavior of the intensity obtained utilizing an electric control programmed for keeping the output intensity equal to 0 8
  • the intensity shown a first oscillation having an variation ⁇ l % lower 30% and the second oscillation lower than the 5%
  • the Applicant has observed that the maximum amplitude of the first oscillation was about equal to the per cent difference between the value of 0 5, corresponding to the optimum condition, and the value corresponding to the particularly used control condition As an example, by using a control condition around the value 0 6, corresponding to a per cent difference from the optimum value 0 5 of 20%, the oscillation was increased of 20%, as can be deduced from FIG 7
  • the optical beam splitter 2 and 8 were bulk components having splitting ratio of 3dB and were made by Quantum Optic (USA)
  • the quarter-wave plates 7 14 were made by Bernard Halle (DE) and the linear polarizer 6 was a POLARCOR® made by Corning (USA)
  • FIG 9 schematically shows a polarization stabilizer according to the invention employed for these experimental tests
  • the motor used for this experiment comprised a stator 16 having a rotatable axis 17
  • the axis 17 was perforated to allow the passage of the input signal to be stabilized
  • One end of the axis 17 comprised a mandrel 18 for holding the polarization transformer 5
  • the polarization transformer 5 was obtained by attaching the linear polarizer 6 to a perforated aluminum disk and sticking the quarter wave plate 7 on this disk
  • the polarization transformer 5 was introduced in the mandrel 18 and suitably blocked
  • the control algorithm developed by the Applicant performed a rotation step of the motor of 1 °
  • the optical input signal to be stabilized was an optical beam at a wavelength of 1550 nm having linear state of polarization and was generated by a diode laser
  • the optical signal exiting the polarization stabilizer was converted in an electrical signal by a conventional photodiode and this electric signal was observed by means of an oscilloscope made by Tektronix
  • FIG 10a shows the corresponding oscilloscope trace of the oscillating non- stabilized output Then, the Applicant has observed the intensity of the signal exiting the polarization controller 1 employing the electronic control 15
  • the corresponding oscilloscope trace, plotted in FIG 10b, has an intensity variation ⁇ l % lower than 15% Moreover, this oscilloscope trace shows some localized narrow peaks of the intensity These peaks of the intensity may be due to a mechanical instability of the employed motor The Applicant observes that if said intensity peaks are reduced, e g by using a mechanically stable motor, the intensity variation ⁇ l % can be lower than 5%, corresponding to the theoretical value determined by means of numerical simulation
  • FIG 11 another embodiment of the invention is shown. This embodiment does not require the use of a perforate axis 17 for the motor
  • the polarization transformer 5 is fixed at an end of the axis 17 in such a way that a suitable portion of the said transformer juts out of the axis 17 This jutting out portion can be passed through by the input signal
  • mirrors 19 and 20 are suitably placed in order to reflect the input optical signal towards the input optical splitter 2 of the polarization stabilizer 1
  • polarization stabilizer can be advantageously employed for controlling the state of polarization of optical signals entering polarization sensitive devices
  • a polarization sensitive device is an electro-optical switch
  • FIG 12 illustrates a particular electro-optical switch 1000
  • Switch 1000 comprises an electro-optical crystal, such as a crystal chosen from the crystal classes 4 3m, 42m, and 23 These crystals become biref ⁇ ngent when subjected to an electric field, and the indices of refraction of the crystals vary according to variations in the strength of the field
  • the polarization components of a light beam propagating in such crystals have different phase velocities and thus produce a phase shift
  • the aforementioned effect is commonly called the "electro-optical effect "
  • the electro-optical switch 1000 operates for optical signals (i e , beams) having, for example, wavelengths in the range of 1480 nm to 1610 nm
  • the wavelengths of the optical signals are in the 1510 nm to 1610 nm range, which corresponds to the so-called "third windows" of optical communication
  • the electro- optical switch 1000 may alternatively employ optical signals having wavelengths in the 1300 nm to 1350 nm range
  • the optical switch 1000 depicted in FIG 12 is a bidirectional 2x2 optical switch that can be employed as a cross-connect device
  • First and second input optical fibers 1002 and 1004 affiliated with switch 1000 transmit optical signals to and from the switch via first and second collimators 1006 and 1008
  • Switch 1000 also includes first ana second optical elements 1028 and 1030, crystal element 1014, third and fourth collimators 1022 and 1020, and first and second output optical fibers 1024 and 1026
  • First optical element 1028 comprises a first polarization beam splitter 1012 and a conventional right angle reflecting prism 1010
  • the second optical element 1030 comprises a second polarization beam splitter 1018 and a second conventional right angle reflecting prism 1016
  • Right angle reflecting prism 1010 reflects the collimated signal TE emerging from collimator 1006 to the first polarization beam splitter 1012
  • the first polarization beam splitter 1012 is oriented so as to direct the signal TE along crystal element 1014
  • Signal TE is then directed by second polarization beam splitter 1018 and right angle reflecting prism 1016 to collimator 1020 and first output optical fiber 1024
  • signal TE is converted into a "signal TM," i e , a signal in a linear state of polarization orthogonal to the state of polarization TE
  • the signal TM is transmitted by second polarization beam splitter 1018 to second output optical fiber 1026
  • references 1206, 1208, 1210, 1212 may represent another optical waveguides, or polarization perturbing optical paths of other types, such as free space paths Along the optical fiber 1206 and along the optical fiber 1208 at the corresponding input ports of the optical switch 1000 the polarization stabilizers 100 and 200 of the types described with reference to figure 1 are placed
  • the polarization stabilizer 100 is able to provide at its output port an optical signal having a linear state of polarization TE and having intensity proportional to the intensity of the input signal
  • the polarization stabilizer 200 is able to provide at its output port, an optical signal having a linear sate of polarization TM, orthogonal to the state TE, and having an intensity proportional to the intensity of the input signal
  • the orthogonal sates TE and TM can be obtained from the polarization stabilizers 100 and 200 by suitably adjusting the quarter wave-plate 14 included in each stabilizer
  • Transmitter stations 1202 and 1204 comprise respectively one or more optical sources, as laser sources, capable of generating optical signals
  • the optical sources are semiconductor lasers, such as a diode laser
  • the optical sources are, preferably, able to emit polarized light which may have any predetermined SOP
  • transmitter stations 1202 and 1204 each include a conventional multiplexer for sending the generated optical signals to fiber 1206 and fiber 1208, respectively
  • multiplexers are passive optical devices comprising fused fibers coupler, or planar and microoptic couplers
  • polarization stabilizers 300 and 400 are placed at the output of the amplifier 1218 and 1220 to stabilize the polarization of the optical signals exiting said amplifiers and successively reaching the receiving stations 1214 and 1216
  • the polarization stabilizers 300 and 400 produce output signal having a linear state of polarization but they may also provide a polarization stabilized output signal having a circular polanzation
  • Receiving stations 1214 and 1216 may detect and process the optical information traveling through system 1200 on individual wavelength channels
  • Each station represented by 1214 and 1216 may in a WDM configuration include a demultiplexer for separating the combined WDM channels onto discrete paths These paths from the demultiplexer are then connected to corresponding receiving devices
  • multiplexers are passive optical devices comprising fibers, or planar or microoptic devices, including fiber gratings, AWG and the like
  • preamplifiers 1218 and 1220 may boost the optical signals provided from crystal 1000 before the respective receiving stations 1214 and 1216
  • amplifiers 1222 and 1224 serve to boost the optical signals provided from transmitting stations 202 and 1204 in a known manner to offset attenuation in the optical paths
  • line amplifiers 1222', 1224', 1210', 1212' are placed along the optical fibers 1206, 1218 and 1210, 1212 for providing the necessary power to the optical signals for propagating along the corresponding optical fibers
  • Preamplifiers 1218 and 1220 and amplifiers 1222 and 1224 and the line amplifiers 1222', 1224', 1210', 1212' may be conventional fiber optic amplifiers, e g , erbium doped fiber amplifiers or may comprise a known semiconductor optical amplifier SOA If semiconductor optical amplifiers are employed, a polarization stabilization of the signal to be amplified, by means of a polarization stabilizer of the type described above is preferable before each line amplifier and preamplifier
  • optical signals emitted by the transmitter stations 1202 and 1222 are amplified by amplifiers 1222 and 1224 and by the line amplifiers 1222' and 1224' Optical signals propagating along optical fibers 1206 and 1208 undergo a polarization perturbation This polarization perturbation causes a changing of the SOP of the said optical signals and the entity of the SOP change being difficult or impossible to predict
  • the polarization stabilizers 100 and 200 stabilize the SOP of the optical signals and provide output signals having respectively states of polarization equal to the state TE and to the state TM
  • optical signals transmitted by transmitter station 1202 are switched to optical fiber 1210
  • Analogously optical signals transmitted by transmitter station 1204 are switched to optical fiber 1212
  • electro-optical switch 1000 When electro-optical switch 1000 is in the cross state, optical signals emitted from transmitter station 1202 (or 1204) are switched to the opposite output fibers 1212 (or 1210)
  • the polarization stabilizers 100 and 200 allows the correct operation of the electro- optical switch 1000 without causing fluctuations of the intensity of the optical signals depending on the variations of their the state of polarization
  • optical signals switched from the switch 1000, propagate along optical fibers 1210 and 1212 and are amplified by means of line amplifiers 1210' and 1212'
  • optical fibers 1210 and 1212 can causes a further polarization perturbation
  • the optical signals propagated along said optical fibers 1210 and 1212 enters the polarization stabilizers 300 and 400 and emerge with a fixed state of polarization
  • the polarization stabilized signals after a suitable amplification by means of preamplifiers 1218 and 1220, enter the receiving stations 1214 and 1216
  • optical couplers employed in the demultiplexers/multiplexers, show polarization sensitivity that is, advantageously, overcome by the above-described control of the polarization.

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  • Physics & Mathematics (AREA)
  • Nonlinear Science (AREA)
  • General Physics & Mathematics (AREA)
  • Optics & Photonics (AREA)
  • Optical Communication System (AREA)
  • Mechanical Light Control Or Optical Switches (AREA)

Abstract

L'invention concerne un stabilisateur de polarisation (1) permettant de générer, à partir d'un signal optique d'entrée d'intensité I et de polarisation A, un signal de sortie d'intensité et de polarisation sensiblement indépendant de la polarisation A. Ledit stabilisateur de polarisation comprend une entrée (3) permettant d'entrer un signal d'entrée; un polariseur linéaire (6) éventuellement couplé à ladite entrée, et dont l'orientation est définie par un axe inhérent (PP') permettant de sélectionner une partie du signal d'entrée dont la polarisation linéaire est parallèle audit axe inhérent; un élément optique (7) fonctionnellement couplé au polariseur linéaire de façon à convertir la partie sélectionnée en signal de sortie à polarisation circulaire; une sortie (9) permettant d'émettre en sortie un signal de sortie; un circuit de commande (15) qui, en fonction d'un signal électrique correspondant à l'intensité du signal de sortie, commande l'orientation dudit polariseur linéaire.
PCT/EP2000/012761 1999-12-23 2000-12-13 Stabilisateur de polarisation sans fin WO2001048541A2 (fr)

Priority Applications (1)

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AU26736/01A AU2673601A (en) 1999-12-23 2000-12-13 Endless polarization stabilizer

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EP99125746 1999-12-23
EP99125746.0 1999-12-23
US17328899P 1999-12-28 1999-12-28
US60/173,288 1999-12-28

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Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2003050983A1 (fr) * 2001-12-12 2003-06-19 Marconi Uk Intellectual Property Ltd Appareil et procede de transmission de signaux
FR2841003A1 (fr) * 2002-06-14 2003-12-19 Thales Sa Systeme de controle de polarisation sans butee dans une liaison optique
EP1637912A2 (fr) * 2004-08-26 2006-03-22 Fujinon Corporation Système autofocus

Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3701042A (en) * 1970-02-03 1972-10-24 Hewlett Packard Co D. c. motor circuit for rotating a polarizer and providing a detector synchronizer signal for a laser stabilizing system
US4559546A (en) * 1984-09-04 1985-12-17 Xerox Corporation Intensity control for the imaging beam of a raster scanner
US5754571A (en) * 1994-12-15 1998-05-19 Anritsu Corporation Tunable wavelength light source apparatus for stabilizing power intensity by using external auto-power control

Family Cites Families (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPH06103769B2 (ja) * 1987-09-17 1994-12-14 富士通株式会社 レーザ出射光の偏光特性制御法

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3701042A (en) * 1970-02-03 1972-10-24 Hewlett Packard Co D. c. motor circuit for rotating a polarizer and providing a detector synchronizer signal for a laser stabilizing system
US4559546A (en) * 1984-09-04 1985-12-17 Xerox Corporation Intensity control for the imaging beam of a raster scanner
US5754571A (en) * 1994-12-15 1998-05-19 Anritsu Corporation Tunable wavelength light source apparatus for stabilizing power intensity by using external auto-power control

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
PATENT ABSTRACTS OF JAPAN vol. 013, no. 295 (E-783), 7 July 1989 (1989-07-07) & JP 01 074781 A (FUJITSU LTD), 20 March 1989 (1989-03-20) *

Cited By (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2003050983A1 (fr) * 2001-12-12 2003-06-19 Marconi Uk Intellectual Property Ltd Appareil et procede de transmission de signaux
CN100409598C (zh) * 2001-12-12 2008-08-06 爱立信股份有限公司 信号传输设备及信号传输方法
US7447441B2 (en) 2001-12-12 2008-11-04 Ericsson Ab Signal transmission apparatus and a method of signal transmission
FR2841003A1 (fr) * 2002-06-14 2003-12-19 Thales Sa Systeme de controle de polarisation sans butee dans une liaison optique
EP1637912A2 (fr) * 2004-08-26 2006-03-22 Fujinon Corporation Système autofocus

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WO2001048541A3 (fr) 2001-12-20

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