JP2016082481A - Optical multiplexing system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical multiplexing system capable of lossless multiplexing of signal light.SOLUTION: The optical multiplexer wave system comprises: a first polarization control device which converts the polarized light of first input light to first linear polarized light and outputs the first converted light; a second polarization control device which converts the polarized light of second input light different in wavelength from the first input light to second linear polarized light orthogonal to the first linear polarized light and outputs the second converted light; and a PBC which multiplexes the first converted light and the second converted light and outputs output light.SELECTED DRAWING: Figure 4

Description

  The present invention relates to an optical multiplexing system, and more particularly to an optical multiplexing system that combines signal lights in optical communication, for example.

  In the existing optical communication system, the loss at the time of multiplexing of the signal light becomes a barrier for extending the communication distance. FIG. 1 is a schematic diagram of a configuration of a conventional optical communication system. As shown in FIG. 1, signal light is multiplexed a plurality of times using a coupler until an optical signal arrives at an OLT (Optical Line Terminal) from a home ONU (Optical Network Unit).

  Couplers include a PLC (Planer lightwave circuit) type coupler that uses light interference, a fiber type coupler that is manufactured by fusing and drawing fibers, and a polarization beam combiner (PBC) that uses the polarization dependence of reflectivity. ) Etc. exist.

Here, in order to understand the description to be described later, the polarization and the Poincare sphere will be described. First, polarized light will be described. Light is a type of electromagnetic wave, and an orthogonal electric field and magnetic field propagate while oscillating. Assuming that the horizontal component of the electromagnetic field with respect to a certain axis is E _x and the vertical component is E _y , E _x and E _y are amplitudes E _0x and E _0y , wave number k, angular frequency ω, traveling direction coordinate z, time t , And the phase difference ε, the following (Expression 1) and (Expression 2) are shown.
E _x = E _0x cos (kz−ωt) (Formula 1)
E _y = E _0y cos (kz−ωt + ε) (Formula 2)
The polarization is a vibration state of the electric field obtained by combining (Equation 1) and (Equation 2), and is determined by the amplitudes E _0x and E _0y and the phase difference ε. If the plane containing the electric field is the electric field vibration plane, the polarization with the constant electric field vibration plane is called linear polarization, and the polarization with the electric field vibration plane drawing a spiral orbit is called elliptical polarization, and is projected in the propagation direction of the electromagnetic wave. The case where is a circle is called circularly polarized light. If a plane whose horizontal axis is the major axis of the ellipse drawn by the projection of the electric field vibration plane in the propagation direction of the electromagnetic wave is a polarization plane, the plane of polarization coincides with the electric field vibration plane of the electromagnetic wave. When the plane of polarization changes, the amplitude ratio E _0x / E _{0y of} E _x and E _y changes. Linearly polarized waves can be considered as having no short axis component of elliptically polarized waves. Hereinafter, in this specification, linearly polarized light having an electric field of only E _x is a-polarized light, and linearly polarized light having only an E _y is b-polarized light.

Next, the Poincare sphere will be described with reference to FIG. The Poincare sphere is one in which the polarization is made to correspond to a point on a sphere having a radius 1 as shown in FIG. For the Stokes parameters S ₀ , S ₁ , S ₂ , S ₃ representing the polarization, when the amplitude E _0x , E _0y , and the phase difference ε are sufficiently small in time, the electromagnetic wave intensity S ₀ is constant, and the Stokes parameters S ₀ , S ₁ , S ₂ and S ₃ are represented by the following (formula 3) to (formula 6), respectively.
S ₀ = E _0x ² + E _0y ² (Formula 3)
^{_{S 1 = E 0x 2 -E 0y}} 2 ( Equation 4)
_{S 2 = 2E 0x E 0y cosε} ( Equation 5)
_{S 3 = 2E 0x E 0y sinε} ( Equation 6)
For any E _0x , E _0y , ε, S ₁ ² + S ₂ ² + S ₃ ² = S ₀ ² holds. Since S ₁ , S ₂ , and S ₃ are normalized by S ₀ , S ₁ , S ₂ , and S ₃ take values of −1 to ₁ and have (S ₁ , S ₂ , S ₃ ) as coordinates. Is on the Poincare sphere with radius 1. Each point corresponding to the Arctic and Antarctic earth represents a circularly polarized wave of clockwise-counterclockwise, equatorial represents linear polarization, that intersects the S ₁ axis, each represent a horizontal and vertical linear polarization .

Rotation of the polarization plane, as shown in FIG. 2 (b), expressed the S ₃ of the Poincare sphere in rotation trajectory around an axis. The change in the phase difference between E _x and E _y is represented by a rotational trajectory with S ₁ as an axis, as shown in FIG. As shown in FIG. 2 (d), the polarization change that repeats the constant polarization plane rotation and the constant phase difference change is the Mueller matrix shown in the following (Expression 7) that represents the polarization plane rotation and the phase difference change. Is an oblique rotation with the eigenvector v as the rotation axis. Here, θ _c and φ _c are a fixed amount of rotation of the polarization plane and a phase difference, respectively.

Converting arbitrary polarized light to a-polarized light and emitting it means collecting arbitrary points on the Poincare sphere at (S ₁ , S ₂ , S ₃ ) = (1, 0, 0).

Japanese Patent No. 3581661

  As described above, in an optical communication system, signal light is multiplexed a plurality of times using a PLC-type coupler, a fiber-type coupler, a PBC, and the like. The PLC is a device having specific optical characteristics by combining an optical waveguide manufactured on a quartz substrate using a microfabrication technique such as photolithography and etching, and one of them is a PLC type coupler. Since the PLC type coupler makes two optical waveguides close to each other and multiplexes the light using the interference of light, a loss of at least 3 dB is always generated at the time of multiplexing as in the case of demultiplexing.

  The fiber type coupler is a type in which a plurality of fiber cores are closely fused and combined by mode coupling between the fibers, and a coupling loss of 3 dB occurs at the time of multiplexing as in the PLC type.

  PBC uses the polarization dependence of reflectivity to combine and output two orthogonally polarized lights, and recently, combined clockwise and counterclockwise circularly polarized light using metamaterial technology. PBC has also been reported. The polarization of the signal light output from the optical fiber changes with time at random, and when averaged over time, it includes a-polarized light and b-polarized light, so that a loss of 3 dB occurs even when PBC is used in the same manner as a PLC type coupler. .

  Thus, in the conventional optical communication system as shown in FIG. 1, the signal light from the home communication device is multiplexed multiple times by the multiplexer between the communication device from the home communication device to the station building, When the optical fiber is concentrated and a PLC coupler, fiber coupler, PBC, or the like is used as a multiplexer, there is a problem that coupling loss occurs.

  FIG. 3 illustrates a method for compensating for propagation light loss in the prior art. As shown in FIG. 3, the light is multiplexed by the coupler, but a loss of about 3 dB occurs in the coupler, and the intensity of the a-polarized light and the b-polarized light in the combined light is smaller than that before the multiplexing. In the prior art shown in FIG. 3, the loss caused by the coupler is compensated by amplifying the combined light using an erbium doped fiber optical amplifier. However, the system is equivalent to adding an erbium doped fiber optical amplifier to the system. Has led to an increase in size.

  In order to solve the above-described problem, the optical multiplexing system according to claim 1 converts the polarization of the first input light into the first linearly polarized light and outputs the first converted light to the first converted light. And second polarized light that converts the polarization of the second input light having a wavelength different from that of the first input light into the second linear polarized light orthogonal to the first linear polarized light and outputs the second converted light. A control device, and the first converted light output from the first polarization control device and the second converted light output from the second polarization control device are combined to output output light. And PBC.

  The optical multiplexing system according to claim 2, wherein the first input light is divided into the first branched light composed of the first linearly polarized light and the second branched light composed of the second linearly polarized light orthogonal to the first linearly polarized light. A first polarization splitting optical system that splits and outputs light into a light; a second input light having a wavelength different from that of the first input light; a third branched light composed of a second linearly polarized light; A first polarization beam obtained by combining the first polarization beam and the third branch beam with the second polarization beam splitting optical system that outputs the beam beam after splitting it into the fourth beam beam composed of the linearly polarized light. The first PBC that outputs the second PBC, the second PBC that outputs the second combined light by combining the second branched light and the fourth branched light, and the polarization of the first combined light. A first polarization control device that converts the light into first linearly polarized light and outputs first converted light; and converts the polarization of the second combined light into second linearly polarized light. A second polarization control device that outputs a second converted light; the first converted light output from the first polarization control device; and the second conversion output from the second polarization control device. And a third PBC that combines the light and outputs the output light.

  An optical multiplexing system according to a third aspect is an optical multiplexing system that combines first to fourth input lights having different wavelengths, and the first input light is composed of a first linearly polarized light. A first polarization splitting optical system that splits and outputs a second branched light composed of a first branched light and a second linearly polarized light orthogonal to the first linearly polarized light; and A second polarization splitting optical system that splits and outputs the third branched light composed of two linearly polarized light and the fourth branched light composed of the first linearly polarized light; A third polarization separation optical system that separates and outputs the fifth branched light composed of the linearly polarized light and the sixth branched light composed of the second linearly polarized light, and outputs the fourth input light to the second The fourth split light that is separated into the seventh branched light composed of linearly polarized light and the eighth branched light composed of the first linearly polarized light is output. A light separation optical system; a first PBC that combines the first branched light and the third branched light to output a first combined light; the second branched light; and the fourth branched light. A third PBC that combines the branched light and outputs the second combined light, the fifth branched light and the seventh branched light, and outputs a third combined light. PBC, a fourth PBC that combines the sixth branched light and the eighth branched light and outputs a fourth combined light, and a polarization of the first combined light as a first linearly polarized light. A first polarization control device that converts the first combined light into a second linearly polarized light and outputs a second converted light. A control device; a third polarization control device that converts the polarization of the third combined light into a first linearly polarized light and outputs a third converted light; and a second polarization of the fourth combined light. A fourth polarization control device that converts the light into linearly polarized light and outputs a fourth converted light; and the first converted light that is output from the first polarization control device and the fourth polarization control device that are output from the first polarization control device. A fifth PBC that combines the fourth converted light and outputs a fifth combined light; and the second converted light and the third polarized light output from the second polarization control device. A sixth PBC that combines the third converted light output from the control device and outputs a sixth combined light, and converts the polarization of the fifth combined light into a first linearly polarized light. A fifth polarization control device that outputs a fifth converted light; a sixth polarization control device that converts the polarization of the sixth combined light into a second linearly polarized light and outputs a sixth converted light; The fifth converted light output from the fifth polarization control device and the sixth polarization control device And a seventh PBC that combines the sixth converted light output from the chair and outputs the output light.

  An optical multiplexing system according to a fourth aspect is the optical multiplexing system according to the second or third aspect, wherein at least one of the polarization separation optical systems is a PBS.

  An optical multiplexing system according to a fifth aspect is the optical multiplexing system according to any one of the first to fourth aspects, wherein the polarization control device is an automatic polarization controller or a PSA.

  An optical multiplexing system according to claim 6 is the optical multiplexing system according to any one of claims 1 to 4, wherein the first polarization control device is an automatic polarization controller or a PSA, and the second The polarization control device includes a second PSA for converting the polarized light into the first linearly polarized light, and a half-wave plate or a 90 ° Faraday rotator provided at a subsequent stage of the second PSA. And

  An optical multiplexing system according to claim 7 is an optical multiplexing system including first to third optical multiplexing units configured by the optical multiplexing system according to any one of claims 1 to 6, wherein The output light output from the first optical combining unit is input to the third optical combining unit as the first input light of the third optical combining unit, and is output from the second optical combining unit. The output light is input to the third optical multiplexing unit as the second input light of the third optical multiplexing unit.

  According to the optical multiplexing system according to the present invention, before the signal light propagating through the optical fiber is multiplexed, one signal light is converted into a polarized light and the other signal light is converted into b polarized light using a polarization control device, Since the signal light is multiplexed using PBC, the signal light can be multiplexed without loss.

  In the past, it was common to use an optical amplifier to compensate for the coupling loss. However, in the present invention, in order to multiplex the light with substantially no loss, the polarization is combined before the light is combined. They are orthogonally multiplexed using PBC. Therefore, since it is not necessary to add an optical amplifier to the optical multiplexing system, it is possible to reduce the size of the optical multiplexing system.

It is the schematic of the structure of the conventional optical communication system. It is explanatory drawing of a Poincare sphere. It is a figure which illustrates the compensation method of the propagation light loss in a prior art. It is a figure which illustrates the optical multiplexing system which concerns on Example 1 of this invention. It is a figure for demonstrating the specific example of the polarization control device used by this invention. It is a figure which illustrates the optical multiplexing system which concerns on Example 2 of this invention. It is a figure which illustrates the optical multiplexing system which concerns on Example 3 of this invention. It is a figure which illustrates the other example of the optical multiplexing system which concerns on Example 3 of this invention. It is a figure which illustrates the optical multiplexing system which concerns on Example 4 of this invention. It is a figure for demonstrating the other example of the polarization control device used by this invention. It is a figure for demonstrating the other example of the polarization control device used by this invention. It is a figure which shows PSA which concerns on Example 5 which arranged several unit elements. It is a figure for demonstrating the change of the polarization when light passes PSA shown in FIG. 12 using a Poincare sphere. It is a figure which shows the optical multiplexing system which concerns on Example 5 using PSA shown in FIG. It is a figure which shows the other example of the optical multiplexing system which concerns on Example 5 using PSA shown in FIG. It is a figure which illustrates the optical multiplexing system which concerns on Example 6 of this invention. It is a figure which illustrates the other example of the optical multiplexing system which concerns on Example 6 of this invention. It is a figure which illustrates the other example of the optical multiplexing system which concerns on Example 6 of this invention. It is a figure which illustrates the other example of the optical multiplexing system which concerns on Example 6 of this invention.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

Example 1
Hereinafter, the a polarization of the signal light n wavelengths lambda _n and a _n, a b polarization and b _n, between components of the optical multiplexing system of the present invention and the polarization maintaining optical fiber so that polarization unchanged It shall be connected using.

The optical multiplexing system according to Embodiment 1 of the present invention will be described with reference to FIG. In the optical multiplexing system according to the first embodiment of the present invention, it is possible to multiplex signal light that is not polarization multiplexed without loss using the polarization control device and the PBC. In Example 1, consider the case for multiplexing the signal light and second signal light 1 and lambda ₂ wavelength lambda ₁ that has not been polarization multiplexed. Since the polarized light propagating through the optical fiber changes randomly with time, the signal lights 1 and 2 have both a-polarized light and b-polarized light components on a time average.

  In FIG. 4, the first polarization control device 401 that receives the signal light 1 and converts the polarization of the signal light 1 into a unique polarization and outputs it, and the signal light 2 and the polarization of the signal light 2 are unique. An optical multiplexing system 400 including a second polarization control device 402 that converts to and outputs the polarized light and a PBC 403 is shown.

As shown in FIG. 4, first and second polarization control devices 401 and 402 are provided in the front stage of the PBC 403, and the first polarization control device 401 converts the polarization of the signal light 1 into b ₁ polarization, The second polarization control device 402 converts the polarization of the signal light 2 into a ₂ polarized light and outputs it to the PBC 403 respectively. Here, when WDM signals that are not polarization-multiplexed are assumed as the signal lights 1 and 2, even if the polarization is uniquely converted by the first and second polarization control devices 401 and 402, the signal does not deteriorate.

The signal lights 1 and 2 converted into b ₁ polarized light and a ₂ polarized light, respectively, are multiplexed by the PBC 403. The signal light 1 is converted only to b ₁ polarized light, the signal light 2 is converted only to a ₂ polarized light, and the PBC 403 transmits the b polarized light component and reflects the a polarized light component, so that no loss occurs during multiplexing. . Since the orthogonal polarization components do not interfere with each other, the signal lights 1 and 2 after being combined by the PBC 403 can be demultiplexed for each wavelength using AWG (Arrayed-Waveguide Grating) or the like. Therefore, the signal lights 1 and 2 can be received by demultiplexing the multiplexed light output from the PBC 403, respectively.

  A specific example of the polarization control device used in the present invention will be described with reference to FIG. As shown in FIG. 5A, the polarization control device controls the polarization of the optical element unit 501 that changes the polarization of the incident signal light, the monitoring unit 502 that measures the polarization, and the optical element unit 501. And a control unit 503 for adjusting the change.

  For example, as shown in FIG. 5B, the optical element portion 501 has a structure in which a λ / 2 wavelength plate is sandwiched between λ / 4 wavelength plates, and the optical axis is set in a plane perpendicular to the light traveling direction. By rotating, incident light can be converted into arbitrary polarized light and emitted. The monitoring unit 502 measures the polarized light that has passed. For example, the control unit 503 mechanically rotates the wavelength plate of the optical element unit 501 by using an actuator or the like so as to convert the polarized light measured by the monitoring unit 502 into the desired polarized light. Can be adjusted. The polarization control device configured as described above is called an automatic polarization controller, and can convert arbitrary polarization into desired polarization.

  The optical element unit 501 and the control unit 503 are of a type that controls the polarization by mechanically driving a crystal material having a uniaxial anisotropy of refractive index, such as calcite, or an optical fiber, There are types that control polarization by changing the voltage applied to LN and liquid crystal, etc., but the automatic polarization controller used in the present invention is not limited by the type of optical element unit, monitoring unit, or control unit Needless to say.

(Example 2)
An optical multiplexing system according to Embodiment 2 of the present invention will be described with reference to FIG. In the optical multiplexing system according to the second embodiment of the present invention, the polarization control device, the PBC, and the polarization that is an element that demultiplexes the light into the a-polarized light and the b-polarized light when the light mixed with the a-polarized light and the b-polarized light is input. Using a beam splitter (PBS: Polarization Beam Splitter), it is possible to multiplex polarization multiplexed signal light without loss. In the second embodiment, a case is considered where the signal light 3 having the wavelength λ ₃ and the signal light ₄ having the wavelength λ 4 are multiplexed. Since both the a-polarized component and the b-polarized component have information in the polarization multiplexed signal light, the polarization multiplexed signal cannot be demodulated if the polarization is converted as it is as in the first embodiment.

6 includes a first PBS601 branching to input signal light 3 with a _3-polarized light and b ₃ polarized light into a _3-polarized light and the b ₃ polarization, signal light 4 having a ₄ polarization and b ₄ polarization And the second PBS 602 branched into the a ₄ polarized light and the b ₄ polarized light, the b ₃ polarized light branched by the first PBS 601 and the a ₄ polarized light branched by the second PBS 602 are combined. The first PBC 603 that outputs the first combined light, the a ₃ polarized light branched by the first PBS 601 and the b ₄ polarized light branched by the second PBS 602 are combined to output the second combined light. The second PBC 604, the first polarization control device 605 that inputs the first combined light, converts the polarization of the first combined light into a unique polarization, and outputs it, and inputs the second combined light. The second polarization control device 606 that converts the polarization of the second combined light into a unique polarization and outputs it. , And the third optical multiplexing system 600 and a PBC607 of multiplexing the outputs from the first and second polarization control device 605 and 606 are shown.

As shown in FIG. 6, the signal light 3 input to the first PBS 601 is branched into two when the b ₃ polarized light is transmitted and the a ₃ polarized light is reflected. The signal light 4 input to the second PBS 602 is split into two when the b ₄ polarized light is transmitted and the a ₄ polarized light is reflected.

The b ₃ polarized light branched by the first PBS 601 and the a ₄ polarized light branched by the second PBS 602 are input to the first PBC 603, the b ₃ polarized light is transmitted, and the a ₄ polarized light is reflected. And output as first combined light including a ₄ polarized light and b ₃ polarized light. The a ₃ polarized light branched by the first PBS 601 and the b ₄ polarized light branched by the second PBS 602 are input to the second PBC 604, the b ₄ polarized light is transmitted, and the a ₃ polarized light is reflected. And output as a second combined light including a ₃ polarized light and b ₄ polarized light.

First multiplexing light by the first polarization control device 605 a _4-polarized light is output as it is converted to b ₄ polarization b _{3, 4} polarization, the second combined light by the second polarization control device 606 b _4-polarized light is outputted as converted into a ₄ polarization a _{3, 4} polarization. Since the a ₃ polarized light and the b ₄ polarized light and the a ₄ polarized light and the b ₃ polarized light are signals having different wavelengths, even if the polarization is uniquely converted by the polarization control device, the signal is not destroyed.

The b ₃ and ₄ polarizations and the a ₃ and ₄ polarizations output from the first and second polarization control devices 605 and 606, respectively, are input to the third PBC 607, and the b _{3 and 4} polarizations are transmitted _{. The four} polarized lights are combined by being reflected. The signal light incident on the third PBC 607 has been converted into only a-polarized light or b-polarized light, and the third PBC 607 transmits the b-polarized component and reflects the a-polarized component. Therefore, at the time of multiplexing by the third PBC 607 There is no loss.

  The signal lights 3 and 4 after being combined by the third PBC 607 can be demultiplexed for each wavelength by using AWG or the like without orthogonal polarization components interfering with each other. Therefore, the signal lights 3 and 4 can be received by demultiplexing the multiplexed light output from the third PBC 607, respectively.

  In the second embodiment, the automatic polarization controller illustrated in FIG. 5 can be used as the polarization control device.

  In the second embodiment, an example using PBS is shown. However, an optical multiplexing system may be configured by using an arbitrary polarization separation optical system that performs polarization separation on input light. The same applies to the following embodiments.

(Example 3)
The optical multiplexing system according to Embodiment 3 of the present invention will be described using FIG. In the optical multiplexing system according to Embodiment 3 of the present invention, four or more WDM signal lights can be multiplexed without loss. In Figure 7, the signal light 5 having a wavelength lambda _5, the signal light 6 having a lambda _6, the signal light 7 having a wavelength lambda _7, is polarization multiplexing different wavelengths and a signal light 8 which has a lambda ₈ Consider a case in which four signal lights that have not been combined are combined.

FIG. 7 shows a first optical multiplexing unit 400 ₁ for inputting signal lights 5 and 6, a second optical multiplexing unit 400 ₂ for inputting signal lights 7 and 8, and first and second optical multiplexing units. An optical multiplexing system is shown that includes a _third optical multiplexing unit 400 ₃ that inputs and combines the multiplexed lights output from 400 ₁ and 400 ₂ , respectively. The configurations of the first, second, and third optical multiplexing units 400 ₁ , 400 _2, and 400 ₃ are the same as the configuration of the optical multiplexing system according to the first embodiment, and the first polarization control device 401, respectively, A second polarization control device 402 and a PBC 403 are included. The process and principle of multiplexing light in the first, second, and third optical multiplexing units 400 ₁ , 400 _2, and 400 ₃ are the same as those in the optical multiplexing system described in the first embodiment. Description of is omitted.

As shown in FIG. 7, the signal light 5 and 6 is output after being multiplexed by the first optical multiplexer 400 ₁ as a first multiplexed light including a _6-polarized light and b ₅ polarized signal light 7 and 8 It is multiplexed by the second optical multiplexer 400 ₂ is outputted as a second multiplexed light including a ₈ polarization and b ₇ polarization. By combining the first and second combined light as input light of the _third optical combining unit 4003, it is possible to combine four signal lights having different wavelengths without being multiplexed. Can do.

Moreover, the other example of the optical multiplexing system which concerns on Example 3 of this invention is demonstrated using FIG. In Figure 8, the signal light 9 having a wavelength lambda _9, the signal light 10 having a lambda _10, the signal light 11 having a wavelength lambda _11, the polarization multiplexing different wavelengths and a signal light 12 that has a lambda ₁₂ Consider a case where four signal lights are multiplexed.

FIG. 8 shows a first optical multiplexing unit 600 ₁ for inputting signal lights 9 and 10, a second optical multiplexing unit 600 ₂ for inputting signal lights 11 and 12, and first and second optical multiplexing parts. 600 ₁ and 600 optical multiplexing system including a third optical multiplexer 600 ₃ for multiplexing enter the multiplexed light output from each of ₂ is shown. The configurations of the first, second, and third optical multiplexing units 600 ₁ , 600 _2, and 600 ₃ are the same as the configuration of the optical multiplexing system according to the second embodiment, and the first PBS 601 and the second optical multiplexing unit respectively It includes a PBS 602, a first PBC 603, a second PBC 604, a first polarization control device 605, a second polarization control device 606, and a second PBC 607. The process and principle of multiplexing light in the first, second, and third optical multiplexing units 600 ₁ , 600 _2, and 600 ₃ are the same as those in the optical multiplexing system described in the second embodiment. Description of is omitted.

As shown in FIG. 8, the signal light 9 and 10 is output after being multiplexed by the first optical multiplexer 600 ₁ as a first combined beam comprising a _{9, 10} polarization and b _{9, 10} polarized signal light 11 and 12 are output after being multiplexed by the second optical multiplexer 600 ₂ as a second multiplexed light including a _{11, 12} polarization and b _{11, 12} polarization. By combining the first and second combined lights using the input light of the _third optical combining unit 6003, it is possible to multiplex four polarization multiplexed signal lights having different wavelengths without loss. it can.

Further, by repeating the optical multiplexing system shown in FIGS. 7 and 8 in a similar manner, 2 ⁿ signal lights can be multiplexed without loss. n is the number of repetitions.

  In Example 3, the automatic polarization controller exemplified in FIG. 5 can be used as the polarization control device.

Example 4
An optical multiplexing system according to Embodiment 4 of the present invention will be described with reference to FIG. In the optical multiplexing system according to the fourth embodiment of the present invention, it is possible to multiplex four or more polarization multiplexed signal lights without loss. 9, as in the case shown in FIG. 8, the signal light 9 having a wavelength lambda _9, the signal light 10 having a lambda _10, the signal light 11 having a wavelength lambda _11, signal light having a lambda ₁₂ 12 Consider a case where four polarization multiplexed signal lights having different wavelengths are combined.

9, the first PBS 901 that branches the signal light 9 into a ₉ polarized light and b ₉ polarized light, the second PBS 902 that branches the signal light 10 into a ₁₀ polarized light and b ₁₀ polarized light, The first PBC 903 that outputs the first combined light by combining the b ₉ polarized light and the a ₁₀ polarized light branched by the second PBS 901 and 902 respectively, and branched by the first and second PBS 901 and 902, respectively. The second PBC 904 that outputs the second combined light by combining the a ₉ polarized light and the b ₁₀ polarized light, and the first polarized light that converts the polarized light of the first combined light into a unique polarized light and outputs it. A control device 905; a second polarization control device 906 that converts the polarization of the second combined light into a unique polarization and outputs the same; and a third PBS 907 that branches the signal light 11 into a ₁₁ polarization and b ₁₁ polarization When a fourth for branching the signal light 12 to the a _{12-polarization} and b ₁₂ polarization And BS908, and third PBC909 for outputting the third and fourth multiplexes the PBS907 and b ₁₁ polarization branched respectively 908 and a ₁₂ polarization third multiplexed light, the third and fourth The fourth PBC 910 that outputs the fourth combined light by combining the a ₁₁ polarized light and the b ₁₂ polarized light branched by the PBSs 907 and 908 respectively, and converts the polarized light of the third combined light into a unique polarized light. From the third polarization control device 911 that outputs, the fourth polarization control device 912 that converts the polarization of the fourth combined light into a unique polarization, and outputs, and the first and fourth polarization control devices 905 and 912 The fifth PBC 913 for outputting the fifth combined light and the outputs from the second and third polarization control devices 906 and 911 to output the sixth combined light. 6 PBC914 and the fifth combined light A fifth polarization control device 915 that converts the polarized light into a unique polarization and outputs it, a sixth polarization control device 916 that converts the polarization of the sixth combined light into a unique polarization and outputs the same, An optical multiplexing system 900 comprising a seventh PBC 917 that combines and outputs the outputs from the sixth polarization control devices 915 and 916 is shown.

As shown in FIG. 6, the signal light 9 input to the first PBS 901 is branched into two when the b ₉ polarized light is transmitted and the a ₉ polarized light is reflected. The signal light 10 input to the second PBS 902 is branched into two when the b ₁₀ polarized light is transmitted and the a ₁₀ polarized light is reflected.

The b ₉ polarized light branched by the first PBS 901 and the a ₁₀ polarized light branched by the second PBS 902 are input to the first PBC 903, the b ₉ polarized light is transmitted, and the a ₁₀ polarized light is reflected. And is output as a first combined light including a ₁₀ polarized light and b ₉ polarized light. The a ₉ polarized light branched by the first PBS 901 and the b ₁₀ polarized light branched by the second PBS 902 are input to the second PBC 904, the b ₁₀ polarized light is transmitted, and the a ₉ polarized light is reflected. And output as a second combined light including a ₉ polarized light and b ₁₀ polarized light.

The first combined light is output as b _9,10 polarized light by converting the a ₁₀ polarized light into b ₁₀ polarized light by the first polarization control device 905. The second combined light is output as a _9,10 polarized light by converting the b ₁₀ polarized light into a ₁₀ polarized light by the second polarization control device 906. Since the a ₉ polarized light, the b ₁₀ polarized light, and the a ₁₀ polarized light and the b ₉ polarized light are signals having different wavelengths, even if the polarization is uniquely converted by the polarization control device, the signal is not destroyed.

Similarly, the signal light 11 and the signal light 12 are the third and fourth combined lights as the third and fourth combined lights via the third and fourth PBSs 907 and 908 and the third and fourth PBCs 909 and 910, respectively. Are output to the polarization control devices 911 and 912. The third and fourth combined lights are converted in polarization through the third and fourth polarization control devices 911 and 912, and output from the third polarization control device 911 as _b11,12 polarization, Output from the polarization control device 912 as a _11,12 polarized light.

The b _9,10 polarized light output from the first polarization control device 905 and the a _11,12 polarized light output from the fourth polarization control device 912 are input to the fifth PBC 913 and multiplexed to be a _11, The fifth combined light including ₁₂ polarized light and b _9,10 polarized light is output to the fifth polarization control device 915. The a _9,10 polarized light output from the second polarization control device 906 and the b _11,12 polarized light output from the third polarization control device 911 are input to the sixth PBC 914 and combined to be a 9,9 _{. The} light is output to the sixth polarization control device 916 as the sixth combined light including ₁₀ polarized light and b _11,12 polarized light.

Multiplexed light of the fifth, a _{11, 12} polarization is output as it is converted to b _{11, 12} polarization b _{9, 10, 11, 12} polarization by the polarization control device 915 of the fifth. The sixth combined light is output as a _9,10,11,12 polarized light by converting the b _11,12 polarized light into the a _11,12 polarized light by the sixth polarization control device 916. Since the a _9,10 polarized light and the b _11,12 polarized light, and the a _11,12 polarized light and the b _9,10 polarized light are signals having different wavelengths, even if the polarization is uniquely converted by the polarization control device, the signal is not destroyed.

Fifth and 6 b _{9, 10, 11, 12} and a _{9, 10, 11, 12} polarized respectively output from the polarization control device 915 and 916 are input to the seventh _PBC917, b _{9,10, 11,12} is transmitted and a _9,10,11,12 polarized light is reflected and combined.

As shown in FIG. 9, in the fourth embodiment, unlike the configuration shown in FIG. 8, a _9,10 polarized light, b _9,10 polarized light, and a _11,12 polarized light converted into unique polarized light by the polarization control device. The a _9,10 polarized light and the b _11,1 polarized light ₂ and the a _11,12 polarized light and the b _9,10 polarized light are multiplexed using the PBC without multiplexing the b _11,12 polarized light by the PBC. Multiplexed light of the fifth and sixth, are respectively converted into fifth and sixth polarization control device in a _{9, 10, 11, 12} polarization and b _{9, 10, 11, 12} polarization, using PBC917 seventh Are combined without loss.

In the present embodiment, the number of necessary PBCs and PBSs can be reduced as compared with the optical multiplexing system shown in FIG. 8, and the system can be downsized. Further, by repeating the optical multiplexing system according to the fourth embodiment with a _9,10,11,12 polarized light and b _9,10,11,12 polarized light as the next input, 2 ⁿ signal lights can be combined without loss. Can wave.

  In Example 4, the automatic polarization controller exemplified in FIG. 5 can be used as the polarization control device.

(Example 5)
An optical multiplexing system using a small polarization control device according to the fifth embodiment that does not require an external power supply will be described with reference to FIGS. In the first to fourth embodiments, the automatic polarization controller shown in FIG. 5 is used as the polarization control device. However, a PSA (Polarization Self-Aligner) that automatically converts arbitrary polarization into unique polarization shown in this embodiment is used. You can also.

  FIG. 10 shows a medium 1001, a sensing / current generating unit 1002 that changes a current generated according to polarization, and a magnetic field generating unit that is connected to the sensing / current generating unit 1002 and generates a magnetic field proportional to the generated current. A unit element 1000 including 1003 and a phase difference generation unit 1004 that generates a phase difference between polarized light is shown. The sensing / current generating unit 1002 and the magnetic field generating unit 1003 are provided on or in the surface of the medium 1001, and the phase difference generating unit 1004 is provided in or near the medium 1001.

  The PSA according to the present embodiment has a configuration in which two or more unit elements 1000 are arranged in the light traveling direction. The rotation of the polarization plane is converted into a specific state by the sensing / current generation unit 1002 and the magnetic field generation unit 1003, and the phase difference is converted into a specific state by the phase difference generation unit 1004. Can be converted.

  A specific example will be described with reference to FIG. As shown in FIG. 11A, a PSA unit element 1100 is directly connected to a magnetic field generation unit 1103 using a ring-shaped conductor provided on a plane perpendicular to the light traveling direction, and the magnetic field generation unit 1103. The sensing / current generating unit 1102 is arranged on the surface or inside of the medium 1101, and the phase difference generating unit 1104 is arranged behind the medium 1101 in the light traveling direction.

The sensing / current generation unit 1102 is, for example, a light receiving surface of a photoelectric conversion element 1106 covered with a polarizer 1105 as shown in FIG. The polarizer 1105 transmits the vertical component E _y out of the electric field component of the electromagnetic wave and blocks the horizontal component E _x, and thus converts the electromagnetic wave into a direct current in proportion to the vertical component E _oy ² of the electromagnetic wave. As shown in FIG. 11A, consider a case where an electromagnetic wave 1110 having a traveling direction parallel to the z-axis and having the same diameter as the ring-type conductor is incident on the unit element 1100. As shown in FIG. 11C, a part of the electromagnetic wave 1110 incident on the unit element 1100 is incident on the sensing / current generation unit 1102 and generates a direct current 1111 proportional to the vertical component E _oy ² of the electromagnetic wave. As shown in FIG. 11D, the direct current 1111 generates a magnetic field 1112 in the traveling direction of the electromagnetic wave in the magnetic field generator 1103, and the polarization plane of the incident light rotates in proportion to the magnetic field 1112 (Faraday effect).

The phase difference generation unit 1104 is configured, for example, by arranging calcite or the like so that the optical axis is horizontal to the x axis or the y axis. As a result, a phase difference occurs between the electric field vertical component and the horizontal component of polarized light. Therefore, the unit element 1100 generates θ = p · E _oy ² and φ = φ _c (φ _c : constant), where p is the proportionality coefficient, θ is the polarization plane rotation amount, and φ is the phase difference change amount. .

A change in polarization by the unit element 1100 will be described using a Poincare sphere. E _oy ^2, which is a vertical component of the electric field, is expressed as (Equation 8) below using the values of S ₀ and S ₁ of the Poincare sphere.

Since S ₁ is normalized by S ₀ , the polarization plane rotation amount θ generated in the unit element is expressed as (Equation 9) below.

From the above (Equation 9), it can be seen that the larger the polarization plane rotation is, the closer to S ₁ = −1 which is vertical polarization, and the smaller the polarization plane rotation is, the closer to S ₁ = 1, which is horizontal polarization.

FIG. 12 illustrates a PSA 1200 according to this embodiment in which a plurality of unit elements 1100 are arranged. A change in polarization when light passes through the PSA 1200 shown in FIG. 12 will be described using the Poincare sphere shown in FIG. As shown in FIG. 13, the change of the polarization state is based on the vector v obtained by substituting the polarization plane rotation θ given in (Equation 9) and the constant phase difference φ _c into (Equation 7). Represented by rotation. Since the amount of rotation of the polarization plane generated in the unit element 1100 is not constant, unlike the case shown in FIG. The rotation axis changes every time the unit element 1100 is passed. The polarized light moves toward S ₁ = 1 where θ gradually decreases, and converges to one point. For this reason, PSA1200 can convert arbitrary polarized light into a-polarized light and emit it. However, when the phase difference φ generated by the phase difference generator 1104 is φ = 2π × n (n = 0, 1, 2,...), The polarized light makes one turn on the Poincare sphere and comes to the same point. Therefore, it is necessary not to make the phase difference φ = 2π × n generated in the phase difference generator 1104.

When the polarizer 1105 shown in FIG. 11 is rotated by 90 degrees and disposed on the light receiving surface of the photoelectric conversion element 1106, the sensing / current generating unit 1102 generates a rotation of the polarization plane proportional to the electric field horizontal component E _ox ² . The PSA 1200 can convert arbitrary polarized light into b-polarized light and emit it. Hereinafter, the PSA emitted by converting the arbitrary polarization to a polarization PSA _a, a PSA that rotates the polarizer 1105 90 degrees and emits converts any polarization in b polarization and PSA _b.

14 and 15 show an optical multiplexing system according to the present embodiment in which PSA _a and PSA _b are applied as polarization control devices. The optical multiplexing system shown in FIG. 14 corresponds to the configuration using PSA _a and PSA _b as the polarization control device of the optical multiplexing system according to the first embodiment, and the optical multiplexing system shown in FIG. 15 is the optical multiplexing system according to the second embodiment. This corresponds to a configuration using PSA _a and PSA _b as the polarization control device. By disposing PSA _a and PSA _b as polarization control devices as shown in FIGS. 14 and 15, polarization can be multiplexed by PBC without loss as in the case of the first and second embodiments. By using such a PSA, the monitoring unit and the control unit that are necessary in the automatic polarization controller are not required, and the system can be downsized.

(Example 6)
The optical multiplexing system according to the sixth embodiment will be described with reference to FIGS. 16 to 19. Optical multiplexing system illustrated in FIGS. 16 and 17, using the PSA _b as the first polarization control device of an optical multiplexing system according to Example 1 and 2, lambda the PSA _b and its subsequent stage as a second polarization control device Each corresponds to the configuration using a / 2 wavelength plate connected. 18 and the optical multiplexing system shown in FIG. 19, Example using PSA _b as the first polarization control device of an optical multiplexing system according to 1 and 2, 90 PSA _b and its subsequent stage as a second polarization control device ° Corresponds to each configuration using a Faraday rotator connected.

In Example 5 described above, the polarization of light that passed through the PSA was converted into b-polarized light and a-polarized light by changing the direction of the PSA polarizer. In the sixth embodiment, as shown in FIGS. 16 to 19, a λ / 2 wavelength plate or a 90 ° Faraday rotator can be connected to the subsequent stage of PSA _b to convert b-polarized light into a-polarized light.

  Needless to say, the λ / 2 wavelength plate and the 90 ° Faraday rotator do not matter.

  In each of the above embodiments, the PBC and PBS are configured to transmit b-polarized light and reflect a-polarized light. However, the PBC and PBS are configured to transmit a-polarized light and reflect b-polarized light. May be.

  In each of the above-described embodiments, an example in which only one of the automatic polarization controller and the PSA is used as the polarization control device has been described.

Further, in each of the above embodiments, the configuration in which polarized light orthogonal to each other is combined in the PBC is shown. However, if it is between 45 ° and 135 °, a coupling loss occurs, but since it is a loss of 3 dB or less, it is more than conventional. Also, the effect of reducing the coupling loss can be obtained. From the viewpoint of reducing coupling loss, it is not necessary to use linearly polarized light, and it is sufficient that two signal light polarizations exist on each side of a hemisphere obtained by dividing the Poincare sphere into _{two by} the plane of S ₂ = 0.

Optical multiplexing system 400, 600, 900
Polarization control device 401, 402, 605, 606, 905, 906, 911, 912, 915, 916
PBC 403, 603, 604, 607, 903, 904, 909, 910, 913, 914, 917
Optical element portion 501
Monitoring unit 502
Control unit 503
PBS 601, 602, 901, 902, 907, 908
Unit element 1000, 1100
Medium 1001, 1101
Sensing / current generator 1002, 1102
Magnetic field generator 1003, 1103
Phase difference generator 1004, 1104
PSA 1200

Claims (7)

A first polarization control device that converts the polarization of the first input light into first linearly polarized light and outputs the first converted light to the first converted light;
A second polarization control device that converts the polarization of second input light having a wavelength different from that of the first input light into second linearly polarized light that is orthogonal to the first linearly polarized light and outputs the second converted light. When,
A PBC that combines the first converted light output from the first polarization control device and the second converted light output from the second polarization control device to output output light;
An optical multiplexing system comprising: The first input light is polarized and separated into a first branched light composed of a first linearly polarized light and a second branched light composed of a second linearly polarized light orthogonal to the first linearly polarized light. A polarization separation optical system;
The second input light having a wavelength different from that of the first input light is polarized and separated into the third branched light composed of the second linearly polarized light and the fourth branched light composed of the first linearly polarized light, and output. A second polarization separation optical system;
A first PBC that combines the first branched light and the third branched light to output the first combined light;
A second PBC that combines the second branched light and the fourth branched light to output a second combined light;
A first polarization control device that converts the polarization of the first combined light into first linearly polarized light and outputs the first converted light;
A second polarization control device for converting the polarization of the second combined light into a second linearly polarized light and outputting the second converted light;
A third PBC that combines the first converted light output from the first polarization control device and the second converted light output from the second polarization control device to output output light. When,
An optical multiplexing system comprising: An optical multiplexing system that combines first to fourth input lights having different wavelengths,
The first input light is polarized and separated into a first branched light composed of a first linearly polarized light and a second branched light composed of a second linearly polarized light orthogonal to the first linearly polarized light, and then output. A polarization separation optical system of
A second polarization separation optical system that separates and outputs the second input light into a third branched light composed of a second linearly polarized light and a fourth branched light composed of a first linearly polarized light;
A third polarization separation optical system that separates and outputs the third input light into a fifth branched light composed of a first linearly polarized light and a sixth branched light composed of a second linearly polarized light;
A fourth polarization separation optical system that separates and outputs the fourth input light into a seventh branched light composed of a second linearly polarized light and an eighth branched light composed of a first linearly polarized light;
A first PBC that combines the first branched light and the third branched light to output the first combined light;
A second PBC that combines the second branched light and the fourth branched light to output a second combined light;
A third PBC that combines the fifth branched light and the seventh branched light and outputs a third combined light;
A fourth PBC that combines the sixth branched light and the eighth branched light and outputs a fourth combined light;
A first polarization control device that converts the polarization of the first combined light into first linearly polarized light and outputs the first converted light;
A second polarization control device for converting the polarization of the second combined light into a second linearly polarized light and outputting the second converted light;
A third polarization control device that converts the polarization of the third combined light into a first linearly polarized light and outputs a third converted light;
A fourth polarization control device that converts the polarization of the fourth combined light into a second linearly polarized light and outputs a fourth converted light;
The first converted light output from the first polarization control device and the fourth converted light output from the fourth polarization control device are combined to output a fifth combined light. 5 PBCs,
The second converted light output from the second polarization control device and the third converted light output from the third polarization control device are combined to output a sixth combined light. 6 PBCs,
A fifth polarization control device for converting the polarization of the fifth combined light into a first linearly polarized light and outputting a fifth converted light;
A sixth polarization control device that converts the polarization of the sixth combined light into a second linearly polarized light and outputs a sixth converted light;
A seventh PBC that combines the fifth converted light output from the fifth polarization control device and the sixth converted light output from the sixth polarization control device to output output light. When,
An optical multiplexing system comprising:   4. The optical multiplexing system according to claim 2, wherein at least one of the polarization separation optical systems is PBS.   5. The optical multiplexing system according to claim 1, wherein the polarization control device is an automatic polarization controller or a PSA. The first polarization control device is an automatic polarization controller or PSA;
The second polarization control device includes a second PSA that converts polarized light into first linearly polarized light, and a half-wave plate or a 90 ° Faraday rotator provided at a subsequent stage of the second PSA. The optical multiplexing system according to claim 1, wherein the optical multiplexing system is included. An optical multiplexing system including first to third optical multiplexing units configured by the optical multiplexing system according to any one of claims 1 to 6,
The output light output from the first optical multiplexing unit is input to the third optical multiplexing unit as the first input light of the third optical multiplexing unit,
The output light output from the second optical multiplexing unit is input to the third optical multiplexing unit as the second input light of the third optical multiplexing unit.