JP2001050860A - Waveguide type polarization condition measuring apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize a waveguide type polarization condition measuring apparatus which is compact and superior in reliability and suited for mass production. SOLUTION: The apparatus comprises on a substrate 11 a polarized light separator element 13 for separating a light signal inputted from an input optical guide 12 into two orthogonal polarization components and outputting to two output ports, two light branching elements 14a, 14b for branching the two polarization components into two each, a polarized light changer element 15 for converting the two polarization components on second output ports of each light branching element 14a, 14b into the same polarization, and a light combining-branching element 16 for inputting the two polarized lights made into the same polarization by the polarized light changer element 15 and making them interfere. The light intensity of each polarized light is taken out on an output optical guide 12 connected to each of first output ports of the first and second light branching elements. The interfering light intensity of each polarized light is taken out on each of output optical guides 17a-17d connected to output ports of the light combining-branching element 16, and provided for measuring the polarization condition of the input light signal.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a waveguide type polarization state measuring device for measuring the polarization state of light or the polarization transmission characteristics of an optical component or an optical transmission line.

[0002]

2. Description of the Related Art Measuring the polarization state of light is important in many fields such as optical communication, optical measurement, and optical properties. In particular, in the field of optical communication, with the improvement of signal speed, the polarization dispersion of optical transmission lines and optical components (the phenomenon that the group speed varies depending on the polarization state) cannot be ignored as a factor that degrades the signal quality of light. I have. In evaluating and compensating for this polarization dispersion,
Measurement of the state of polarization has become indispensable.

(Principle of Polarization Measurement) First, a Stokes vector representing the state of polarization will be described. Now, considering monochromatic light, the z-axis is taken in the light traveling direction, and the x-axis and y-axis are taken perpendicular to this. Here, the x-polarization component of the optical electric field is represented by Ex with a complex amplitude, and the y-polarization component is represented by Ey with a complex amplitude. At this time, the Stokes vector S is

[0004]

(Equation 1) Defined by From equation (1), it can be seen that there is a relationship of S ₀ ² = S ₁ ² + S ₂ ² + S ₃ ² ... (2) between the elements of the Stokes vector in the case of monochromatic light. If not monochromatic light, typically the ^{_{S 0 2 ≧ S 1 2 +}} S 2 2 + S 3 2 ... (3).

As can be seen from equation (1), the first element S ₀ of the Stokes vector is a quantity representing the optical electric field intensity. Therefore, a Stokes vector in which the second, third, and fourth elements of the Stokes vector are normalized by the first element is often used. This normalized Stokes vector s is

[0006]

(Equation 2) Becomes From equation (3), | s ₁ | ≦ 1, | s ₂ | ≦ 1, |
s ₃ | ≦ 1. Hereinafter, a normalized Stokes vector is shown in this specification unless otherwise specified.

In order to measure the state of polarization, the Stokes vector defined by equation (4) may be obtained. For this purpose, the optical electric field intensity of x-polarized light, the optical electric field intensity of y-polarized light, and x
It can be seen that the phase difference between the optical field intensity of the polarized light and the y-polarized light may be obtained.

Conventionally, as an optical measuring instrument for measuring the polarization state, an optical measuring instrument using a polarizer and a wave plate is known (Hewlett-Packard Japan, Inc., “Optical measuring instrument catalog 1998-1999”). Pp. 80-84, 1998).

(Configuration of Conventional Optical Measuring Device) FIG. 16 shows a configuration example of a conventional polarization state measuring device. In the figure, the light to be measured is branched into four by three translucent mirrors 201a to 201c and two total reflection mirrors 202a to 202b. 4 the first light of the branched light to be measured is received by the light receiving unit 205a through the intact polarizer 204a, a light intensity I ₁ of transmitted light of the polarizer 204a is measured. Here, the polarizer 204a
The polarization transmission axis of ~204d the x-axis, taking the polarization block axis to the y-axis, the light intensity I ₁ measured by the light receiver 205a, the intensity of the x-polarization except constants | a ² | Ex.

On the other hand, the second light passes through the half-wave plate 203a inclined by 45 degrees, and passes through the polarizer 204b to receive the second light.
05b and the light intensity I of the light transmitted through the polarizer 204b.
₂ is measured. The light intensity I ₂ is the intensity | Ey | ² of y-polarized light except for a constant.

The third light passes through the half-wave plate 203b inclined by 22.5 degrees, is received by the light receiver 205c via the polarizer 204c, and the light intensity I ₃ of the transmitted light of the polarizer 204c is reduced. Measured. This light intensity I ₃ is, except for a constant, |
Ex + Ey | ² .

Further, the fourth light passes through the quarter-wave plate 203c inclined by 45 degrees, is received by the light receiver 205d via the polarizer 204d, and the light intensity I ₄ of the transmitted light of the polarizer 204d is reduced. Measured. This light intensity I ₄ is, except for the constant,
Ex + jEy | ² . Here, j is an imaginary unit.

With the above configuration, the optical field intensity of each of the x-polarized light and the y-polarized light is obtained from the outputs of the light receivers 205a and 205b, and the angle between the x-polarized light and the y-polarized light is obtained from the outputs of the light receivers 205c and 205d. , Stokes vector can be calculated.

[0014]

The conventional polarization state measuring device shown in FIG. 16 has the following problems.

First, in the conventional polarization state measuring device, since the optical system is spatially configured, there is a problem that strict accuracy is required for the position of each component. If the optical coupling amount changes due to misalignment of each part, the measurement error will increase.
It is difficult to realize portability with a conventional polarization state measuring instrument.

Further, there is a problem that it is difficult to miniaturize the conventional polarization state measuring instrument. In the polarization dispersion compensation of the optical communication, if the control is performed using the result of analyzing the communication signal by the polarization state measuring device, a polarization dispersion compensation circuit excellent in accuracy and stability can be realized. However, in the conventional polarization state measuring device, since the optical system is spatially configured, it is not easy to reduce the size and incorporate the optical system in the device.

Further, the conventional polarization state measuring device is expensive. In order to manufacture a conventional polarization state measuring device, it is necessary to arrange individual components with high precision, and mass production is difficult and has to be expensive.

An object of the present invention is to provide a waveguide type polarization state measuring instrument which is small, has excellent reliability, and is suitable for mass production.

[0019]

According to a first aspect of the present invention, there is provided a waveguide type polarization state measuring device which separates an optical signal input from an input optical waveguide into two orthogonal polarization components on a substrate. A polarization splitting element that outputs to an output port, two optical branching elements that respectively split two polarization components into two, and two polarization components that are branched to a second output port of each optical splitting element are converted into the same polarization. And a light combining / branching element for inputting and interfering two polarized light components having the same polarization by the polarization replacing element, and each of the first light branching element and the first light branching element of the second light branching element. The light intensity of each polarized light is taken out to the output optical waveguide connected to the output port, the interference light intensity of each polarized light is taken out to the output optical waveguide connected to the output port of the optical coupling / branching element, and the polarization state of the input optical signal is extracted. Configuration for measurement of That.

According to a second aspect of the present invention, there is provided a waveguide type polarization state measuring device, wherein an optical branching element for splitting an optical signal input from an input optical waveguide into two and an optical signal split into two are orthogonally arranged on a substrate. Two polarization splitting elements for splitting into two polarization components and outputting to two output ports, and a polarization switching element for converting the two polarization components split to two output ports of the second polarization splitting element into the same polarization And a light combining / branching element for inputting and interfering two polarization components having the same polarization by the polarization switching element, and the first and second light branching elements of the first light branching element.
The light intensity of each polarized light is taken out to the output optical waveguide connected to the output port of the optical coupling device, the interference light intensity of each polarized light is taken out to the output optical waveguide connected to the output port of the optical coupling / branching element, and the polarization of the input optical signal is extracted. This is a configuration for measuring the state.

According to a third aspect of the present invention, there is provided a waveguide type polarization state measuring device in which an optical filter having a predetermined selected wavelength is inserted into an input optical waveguide. Further, the optical filter is configured to change the selected wavelength, and may be configured to measure the polarization dispersion from the light intensity and the interference light intensity of each polarized light at at least two selected wavelengths.

A waveguide type polarization state measuring device according to a fifth aspect of the present invention has a configuration in which an input port of a multi-input / one-output optical switch is connected to a plurality of output optical waveguides, and one output optical waveguide is selected. .

A waveguide type polarization state measuring device according to a sixth aspect of the present invention is configured such that a photodetector disposed on a substrate is connected to a plurality of output optical waveguides or an output port of a multi-input / one-output optical switch. .

[0024]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS (First Embodiment: Claim 1) FIG. 1 shows a first embodiment of a waveguide type polarization state measuring instrument according to the present invention. In the figure, on a substrate 11, an input optical waveguide 12, a polarization splitting element 13, and light splitting elements 14a, 14
b, a polarization switching element 15, an optical coupling / branching element 16, and output optical waveguides 17a to 17d. The input port of the polarization splitter 13 is connected to the input optical waveguide 12, and the optical splitters 14 a and 14 b are connected to two output ports of the polarization splitter 13.
The input ports of the optical splitter 14b are connected to each other, the output optical waveguide 17a is connected to the first output port of the optical splitter 14a, and the optical splitter is coupled to the second output port of the optical splitter 14a via the polarization switching element 15. A first input port of the element 16 is connected, and an output optical waveguide 17d is connected to a first output port of the optical branching element 14b.
The second input port of the optical coupling / branching element 16 is connected to the second output port b, and the output optical waveguides 17b and 17c are connected to the two output ports of the optical coupling / branching element 16, respectively. Note that the polarization switching element 15 is
And the second input port of the optical coupling / branching element 16.

The optical signal input to the input optical waveguide 12 is separated into an x-polarized component and a y-polarized component by a polarization separating element 13. Here, it is assumed that the x-polarized light component is guided to the light branching element 14a and the y-polarized light component is guided to the light branching element 14b. The x-polarized light component input to the light splitting element 14a is further split into two, one of which is taken out to the output optical waveguide 17a, and the other is converted to y-polarized light by the polarization switching means 15 and input to the light splitting element 16. You. Optical branch element 1
The y-polarized light component input to 4b is further split into two, one of which is input to the optical coupling / branching element 16, and the other is output to the output optical waveguide 17d. In the optical coupling / branching element 16, 2
The two y-polarized light components (the original x-polarized light component and the y-polarized light component) interfere with each other and are output to the output optical waveguides 17b and 17c.

As a result, x is output from the output optical waveguide 17a.
The intensity | Ex | ² of the polarized light is obtained, and the intensity | Ey | ² of the y-polarized light is obtained from the output optical waveguide 17d.
The interference light intensities of x-polarized light and y-polarized light are obtained from 7b and 17c. Therefore, by observing the light intensity extracted to each of the output optical waveguides 17a to 17d, the polarization state of the input optical signal can be known.

In the configuration shown in FIG.
2 (output optical waveguides 17b, 17c)
However, this number may be 1, 2, 3, or 4 depending on the configuration of the optical coupling / branching element 16. However, by using an optical coupling / branching element having n inputs and m outputs (n is 2 or more and m is an integer of 3 or more), the polarization state of the optical signal can be completely obtained by observing the light intensity extracted to two or more output ports. It is possible to obtain information for identifying

That is, when a two-input two-output directional coupler or a two-input two-output multimode interference optical coupler is used as the optical coupling / branching element 16, the position between the x polarization component and the y polarization component is used. Although the absolute value of the phase difference is known, it is not possible to determine which phase of the x-polarized light component or the y-polarized light component is advanced. Hereinafter, a configuration example of an optical coupling / branching element having n inputs and m outputs to solve the problem will be described.

(Example of Structure of Optical Coupling / Branching Element 16: Claim 7,
8) FIG. 2 shows a first configuration example (n =
4, m = 4). Referring to FIG.
Are input optical waveguides 21a and 21b and four 2-input 2
Output optical couplers 22a to 22d and output optical waveguide 23
a, 23b (17b, 17c). The first input port of the optical coupler 22a is connected to the input optical waveguide 21a, and the first input port of the optical coupler 22b is connected to the input optical waveguide 21b. First output ports of the optical couplers 22c and 22d are respectively connected to two output ports of the optical coupler 22a, and second input ports of the optical couplers 22c and 22d are connected to two output ports of the optical coupler 22b. Connected respectively. The output optical waveguide 23a is connected to the first output port of the optical coupler 22c, and the output optical waveguide 23b is connected to the first output port of the optical coupler 22d.

Here, the optical coupler 22a to the optical coupler 22
an optical path leading to c, and the phase difference between the optical path from the optical coupler 22b to the optical coupler 22c and theta _1, an optical path to the optical coupler 22d from the optical coupler 22a, position of the optical path from the optical coupler 22b to the optical coupler 22d Let the phase difference be θ ₂ . At this time, assuming that the optical electric fields input to the input optical waveguides 21a and 21b are E ₁ and E ₂ , the light intensity I ₁ output to the output optical waveguide 23a is | E ₁ + E ₂ exp ( jθ ₁ ) | ² , and the light intensity I ₂ output to the output optical waveguide 23b
Is | E ₁ + E ₂ exp (jθ ₂ ) | ² except for the constant. Therefore, if the parameters are set so that θ ₁ ≠ θ ₂ , the output optical waveguides 23 a and 23 b (FIG. 1)
Output optical waveguide 17b in the configuration of the light intensity observed at 17c), it is possible to determine the phase difference between E ₁ and E _2, which of whether the phase is advanced.
It is also possible to observe the light intensity extracted to two output ports, two each of the optical couplers 22c and 22d.

FIG. 3 shows a second configuration example of the optical coupling / branching element 16 (Reference: M. Bachmann et al., "General self-i").
maging properties in N × N multimode interference
couplers including phase relations ", OSA Applied
Optics, vol.33, no.18, pp.3905-3911, 1994). The optical coupling / branching element 16 of this configuration has three input ports 31a to 31a.
1c, the multimode interference region 32, and three output ports 3
This is a configuration using a three-input three-output multimode interference optical coupler having 3a to 33c. Here, the input ports 31a and 31c at both ends of the three input ports are used for input, and one of the three output ports and the central output ports 33a and 33b are used for output. May be other combinations as long as they are asymmetric.

At this time, assuming that the optical electric fields input to the input ports 31a and 31c are E ₁ and E ₂ , the output port 33
The light intensity I ₁ output to a is | E ₁ + E ₂ exp (j2π / 3) | ² except for the constant, and the light intensity I ₂ output to the output port 33b is | E ₁ + E ₂ except for the constant. | ^two. Therefore, it is possible to determine the phase difference between E ₁ and E ₂ and which phase is advanced from the light intensity observed at the output ports 33 a and 33 _b .

The multi-mode interference optical coupler is not limited to the three-input three-output type, but may be a four-input four-output type, a two-input four-output type, or the like.
The same function can be realized by using the n-input / m-output multimode interference optical coupler.

(Configuration Example of Optical Dividing Elements 14a and 14b) As the optical branching elements 14a and 14b, a directional coupler, a multi-mode interference optical coupler, or another optical coupler can be used.

(Structural Example of Polarization Separating Element 13: Claim 9)
FIG. 4 shows a configuration example of the polarization beam splitter 13. In the figure, a polarization separating element 13 includes an input optical waveguide 41, two optical couplers 42a and 42b having two inputs and two outputs, two arm waveguides 43a and 43b connecting them, and one arm waveguide. Amorphous silicon thin film (stress applying film) 44 for adjusting birefringence formed on 43a, thin film heaters 45a and 45b for operating point adjustment formed on both arm waveguides 43a and 43b, and output optical waveguide 46a, 4
6b.

By irradiating the amorphous silicon thin film 44 with a laser to perform so-called laser trimming, a phase difference of π is generated between the phase difference φ _x of the interferometer for x-polarized light and the phase difference φ _y of the interferometer for y-polarized light. A phase difference can be provided. Therefore, by adjusting the operating point by the thin film heaters 45a and 45b, a polarization separation function is realized in which, for example, y-polarized light is output from one output port and x-polarized light is output from the other output port.

Here, as the polarization splitting element 13,
A configuration using a Mach-Zehnder interferometer using a silica-based optical waveguide, an amorphous silicon thin film, and a thin film heater has been shown, because this combination has excellent matching with an optical fiber and good controllability. However, the waveguide-type polarization splitter 1 in the waveguide-type polarization state measuring device of the present invention.
3 is not limited to this, and another waveguide type polarization splitting element such as a semiconductor optical waveguide structure or a waveguide type polarization splitting element using proton exchange of a LiNbO ₃ waveguide may be used.

(Structural Example of Polarization Swapping Element 15: Claim 10) FIG. 5 shows a structural example of the polarization swapping element 15.
In the figure, the polarization switching element 15 has a groove 52 provided so as to traverse the optical waveguide 51 almost perpendicularly to the optical waveguide 51, and the main axis direction is 45 ° with respect to the birefringent axis of the optical waveguide 51. In this configuration, a half-wave plate 53 tilted in the direction is inserted.

As the half-wave plate 53, a polyimide-based wave plate or a quartz-based wave plate can be used. Further, the polarization switching element 15 is not limited to the configuration using the half-wave plate 53, and may use a polarization switching element by another method such as, for example, using polarization coupling of a LiNbO ₃ optical waveguide. .

(Second Embodiment: Claim 2) FIG. 6 shows a second embodiment of the waveguide type polarization state measuring device of the present invention. Here, components functionally corresponding to the components of the first embodiment shown in FIG. 1 are denoted by the same reference numerals, but the number and arrangement of the components are different from those of the first embodiment.

In the figure, an input optical waveguide 12, an optical branching element 14, and polarization splitting elements 13a and 13 are provided on a substrate 11.
b, a polarization switching element 15, an optical coupling / branching element 16, and output optical waveguides 17a to 17d. The input port of the optical splitter 14 is connected to the input optical waveguide 12, and the polarization splitters 13 a and 1 are connected to two output ports of the optical splitter 14.
3b are connected to the respective output ports, and the output optical waveguides 17a and 17a are connected to the two output ports of the polarization separation element 13a.
7d are connected to each other, two output ports of the polarization splitting element 13b are connected to two input ports of the optical coupling / branching element 16, and output optical waveguides 17b and 17c are connected to two output ports of the optical coupling / branching element 16, respectively. Is done. Further, the polarization switching element 15 is
It is inserted into one of two optical paths connecting b and the optical coupling / branching element 16.

The optical signal input to the input optical waveguide 12 is split into two by an optical splitter 14,
a and 13b. The polarization separation element 13a,
The optical signals input to 13b are respectively an x-polarization component and y
It is separated into polarized light components. Here, the polarization separation element 13a
The x-polarized component separated by the above is guided to the output optical waveguide 17a, and the y-polarized component is guided to the output optical waveguide 17d. The x-polarized light component separated by the polarization splitting device 13b is converted into y-polarized light by the polarization switching means 15 and input to the light splitting element 16, and the y-polarized light component is input to the light splitting element 16 as it is. In the optical coupling / branching element 16, two y
Causing the polarized light components (the original x-polarized light component and the y-polarized light component) to interfere,
The light is output to the output optical waveguides 17b and 17c.

Thus, x is output from the output optical waveguide 17a.
The intensity | Ex | ² of the polarized light is obtained, and the intensity | Ey | ² of the y-polarized light is obtained from the output optical waveguide 17d.
The interference light intensities of x-polarized light and y-polarized light are obtained from 7b and 17c. Therefore, by observing the light intensity extracted to each of the output optical waveguides 17a to 17d, the polarization state of the input optical signal can be known.

(Third Embodiment: Claims 3 and 4) FIG.
Shows a third embodiment of the waveguide type polarization state measuring instrument of the present invention. The feature of this embodiment lies in that a wavelength tunable optical filter 60 is inserted into the input optical waveguide 12 in addition to the configuration of the first embodiment shown in FIG. This embodiment can be similarly applied to the second embodiment shown in FIG.

Now, the optical signal input to the input optical waveguide 12 is continuously or discretely divided into a plurality of optical frequencies (wavelengths).
Components. FIG. 8 shows a case where the spectrum is continuously spread by signal modulation, using an optical communication signal as an example.

Here, a predetermined optical communication signal is selected from a plurality of optical communication signals by the wavelength variable optical filter 60 inserted into the input optical waveguide 12. Further, by changing the passing wavelength of the tunable optical filter 60, the polarization dispersion can be measured. Hereinafter, a method of measuring the polarization dispersion will be described.

[0047] First, when the transmission center angular frequency of the tunable optical filter 60 is set to omega _1, the Stokes vector s (omega ₁₎ by the polarization analyzer 10 in the angular frequency omega ₁ is measured. Next, when the transmission center angular frequency of the wavelength tunable optical filter 60 is set to ω ₂ , similarly, the Stokes vector s (ω ₂ ) at the angular frequency ω ₂ is measured by the polarization analyzer 10. At this time, if δω = | ω ₁ −ω ₂ | is sufficiently small, the first-order polarization dispersion vector Ω is Ω · δω = δs × s (5)

[0048]

(Equation 3) Is required. Note that x is an operator representing the cross product of vectors.

The polarization dispersion vector Ω obtained by equation (6)
Is a vector whose length represents the polarization dispersion and whose direction represents the eigenpolarization state. Here, the intrinsic polarization state is a set of orthogonal polarization states that are fundamental when defining the polarization dispersion, and the group delay time difference between the two polarization states is the polarization dispersion. As described above, it can be seen that the polarization dispersion can be measured by the waveguide type polarization state measuring device of the third embodiment shown in FIG.

FIG. 9 shows a configuration example of the wavelength tunable optical filter 60. In the figure, a tunable optical filter 60 is formed on an input optical waveguide 61, two optical couplers 62a and 62b, two arm waveguides 63a and 63b connecting them, and one arm waveguide 63a. It has a thin film heater 64 as a phase adjusting means and an output optical waveguide 65, and has an asymmetric Mach-Zehnder interferometer type optical filter. Here, by driving the thin-film heater 64 to adjust the optical phase of one arm waveguide 63a,
The transmission center wavelength can be adjusted.

Although the phase adjustment is performed using the thin film heater 64 in the configuration of FIG. 9, other means such as the electro-optic effect of LiNbO ₃ may be used. Further, the present invention is not limited to the configuration of the Mach-Zehnder interferometer type optical filter, and other optical filters such as a ring resonator and an arrayed waveguide diffraction grating type optical filter may be used.

(Example of use of waveguide type polarization state measuring instrument) FIG.
0 indicates a usage example of the waveguide type polarization state measuring device of the present invention. Here, an example is shown in which the waveguide type polarization state measuring device of the third embodiment shown in FIG. 7 is used for controlling a polarization dispersion compensation circuit.

In the figure, an optical signal distorted by the polarization dispersion of an optical fiber transmission line 71 is input to an optical tap circuit 72, a part of which is supplied to a polarization dispersion measuring circuit 73, and the remaining part is subjected to polarization dispersion compensation. The circuit branches to a circuit 74. Here, as the polarization dispersion measuring circuit 73, the waveguide type polarization state measuring device of the third embodiment shown in FIG. 7 is used. Since the spectrum of the optical signal is broadened by the signal component, the amount of polarization dispersion and the unique polarization state are measured based on the principle described above. The polarization dispersion compensation circuit 74 controls the polarization dispersion compensation using the amount of the polarization dispersion and the eigenpolarization state, so that the polarization dispersion can be compensated reliably and promptly.

In the ordinary polarization dispersion compensating circuit, a control method of searching for an optimum point by changing a compensation parameter is used. However, this method has a problem that the parameter is captured by a local peak. In addition, there is a possibility that signal quality degradation due to constantly changing parameters may occur. On the other hand, the waveguide-type polarization state measuring device of the present invention can quantitatively measure the polarization dispersion and provide control of the polarization dispersion compensation, so that stable and high-quality polarization dispersion compensation can be performed. It becomes possible.

(Fourth Embodiment: Claim 5) FIG.
9 shows a fourth embodiment of the waveguide type polarization state measuring instrument of the present invention. This embodiment is characterized in that, in addition to the configuration of the first embodiment shown in FIG. 1 (here, referred to as the polarization analyzer 10), an N × 1 optical switch 81 and an output are provided at the subsequent stage of the output optical waveguides 17a to 17d. At the point where the optical waveguide 82 is connected. Here, N is a positive integer, and corresponds to the number of output optical waveguides 17 of the polarization analyzer 10 (N = 4 in this case). This embodiment can be similarly applied to the second embodiment shown in FIG. 6 or the third embodiment shown in FIG.

The optical signal input to the input optical waveguide 12 is subjected to signal processing by the polarization analyzer 10 and the light intensity of the x-polarized light component, the light intensity of the y-polarized light component, and the x-polarized light component and the y-polarized light component are calculated. The interference light intensity is input to the N × 1 optical switch 81 via the output optical waveguides 17a to 17d. Here, N × 1
One of them is sequentially selected by the optical switch 81 and connected to the output optical waveguide 82. Thus, the light intensity of the x-polarized light component, the light intensity of the y-polarized light component, and the interference light intensity of the x-polarized light component and the y-polarized light component can be extracted to one output optical waveguide 82 and measured.

(Configuration Example of N × 1 Optical Switch 81: Claims 12 and 13) FIG. 12 shows a first configuration example of the N × 1 optical switch 81. In the figure, the 4 × 1 optical switches are two-input, two-output Mach-Zehnder interferometer type optical switches 83a to 83a.
83c are connected in a tree shape. Each Mach-Zehnder interferometer type optical switch includes two optical couplers 84a and 84
b and two arm waveguides 85a, 85 connecting them.
5b and a thin film heater 86 as a phase adjusting means formed on one arm waveguide 85a.
Here, by driving the thin film heater 86 to adjust the optical phase of one arm waveguide 85a, one of the two inputs is selected and output. By repeating it two steps,
One of the four inputs can be selected and output.

FIG. 13 shows a second configuration example of the N × 1 optical switch 81 (N = 4). In the figure, the 4 × 1 optical switch includes a 4 × 4 multimode interference optical coupler 87, a 4 × 1 multimode interference optical coupler 88, four arm waveguides 85a to 85d connecting them, and at least three optical waveguides. And thin film heaters 86a to 86d as phase adjusting means formed on each arm waveguide. Here, by driving the thin film heaters 86a to 86d to adjust the optical phase of each arm waveguide, one of the four inputs can be selected and output.

(Fifth Embodiment: Claim 6) FIG.
9 shows a fifth embodiment of the waveguide type polarization state measuring instrument of the present invention. The feature of this embodiment is that, in addition to the configuration of the first embodiment shown in FIG.
91d is connected. In addition, the present embodiment
The same can be applied to the second embodiment shown in FIG. 6 or the third embodiment shown in FIG.

The optical signal input to the input optical waveguide 12 is subjected to signal processing by the polarization analyzer 10, and the light intensity of the x-polarized light component, the light intensity of the y-polarized light component, and the x-polarized light component and the y-polarized light component are compared. The interference light intensity is measured by the light receivers 91a to 91d via the output optical waveguides 17a to 17d.

FIG. 15 shows a modification of the fifth embodiment of the waveguide type polarization state measuring device of the present invention. This embodiment is characterized in that a photodetector 91 is connected to an output optical waveguide 82 in addition to the configuration of the fourth embodiment shown in FIG. 11 (here, referred to as a polarization analyzer 80).

The optical signal input to the input optical waveguide 12 is subjected to signal processing by the polarization analyzer 80, and the light intensity of the x-polarized light component, the light intensity of the y-polarized light component, and the x-polarized light component and the y-polarized light component are calculated. The intensity of the interference light is sequentially selected by the N × 1 optical switch 81, taken out to the output optical waveguide 82, and output to one optical receiver 9
1 can be measured.

[0063]

As described above, according to the present invention, since the main members can be constituted by optical waveguides, a compact, highly reliable waveguide type polarization state measuring instrument suitable for mass production is realized. be able to. This makes it possible to realize a control device that is excellent in stability and reliability in polarization dispersion compensation and the like of an optical communication system, and can improve communication quality and achieve economic efficiency.

[Brief description of the drawings]

FIG. 1 is a diagram showing a first embodiment of a waveguide type polarization state measuring instrument according to the present invention.

FIG. 2 is a diagram showing a first configuration example of an optical coupling / branching element 16;

FIG. 3 is a diagram showing a second configuration example of the optical coupling / branching element.

FIG. 4 is a diagram showing a configuration example of a polarization separation element 13;

FIG. 5 is a diagram showing a configuration example of a polarization switching element 15;

FIG. 6 is a diagram showing a second embodiment of the waveguide-type polarization state measuring instrument of the present invention.

FIG. 7 is a diagram showing a third embodiment of the waveguide-type polarization state measuring device of the present invention.

FIG. 8 is a view for explaining the principle of measurement of polarization dispersion in the third embodiment.

FIG. 9 is a diagram showing a configuration example of a wavelength tunable optical filter 60.

FIG. 10 is a diagram illustrating a usage example of the waveguide type polarization state measuring device of the present invention.

FIG. 11 is a diagram showing a fourth embodiment of the waveguide-type polarization state measuring instrument of the present invention.

FIG. 12 is a diagram showing a first configuration example of an N × 1 optical switch 81.

FIG. 13 is a diagram showing a second configuration example of the N × 1 optical switch 81.

FIG. 14 is a diagram showing a fifth embodiment of the waveguide type polarization state measuring instrument of the present invention.

FIG. 15 is a diagram showing a modification of the fifth embodiment of the waveguide type polarization state measuring instrument of the present invention.

FIG. 16 is a diagram showing a configuration example of a conventional polarization state measuring device.

[Explanation of symbols]

 10, 80 Polarization analysis unit 11 Substrate 12 Input optical waveguide 13 Polarization separation element 14 Optical branching element 15 Polarization switching element 16 Optical coupling / branching element 17 Output optical waveguide 21 Input optical waveguide 22 Optical coupler 23 Output optical waveguide 31 Input port Reference Signs List 32 Multimode interference region 33 Output port 41 Input optical waveguide 42 Optical coupler 43 Arm waveguide 44 Amorphous silicon thin film (stress applying film) 45 Thin film heater 46 Output optical waveguide 51 Optical waveguide 52 Groove 53 Half wavelength plate 60 Wavelength variable light Filter 61 Input optical waveguide 62 Optical coupler 63 Arm waveguide 64 Thin film heater 65 Output optical waveguide 71 Optical fiber transmission line 72 Optical tap 73 Polarization dispersion measurement circuit 74 Polarization dispersion compensation circuit 81 N × 1 optical switch (4 × 1 Optical switch) 82 Output optical waveguide 83 Machze Da interferometer type optical switch 84 the optical coupler 85 arm waveguides 86 thin film heater 87 4 × 4 multimode interference optical coupler 88 4 × 1 multimode interference optical coupler 91 photodetector

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Takashi Go 2-3-1 Otemachi, Chiyoda-ku, Tokyo Within Nippon Telegraph and Telephone Corporation (72) Inventor Katsutoshi Okamoto 2-chome, Otemachi, Chiyoda-ku, Tokyo No. 1 Nippon Telegraph and Telephone Corporation F term (reference) 2G086 EE12 2H047 KA04 KB04 LA12 MA05 RA01 TA05 TA11 2K002 AA02 AB01 AB02 AB04 AB13 AB40 BA06 BA13 CA03 CA15 DA07 DA08 EA16 GA10 HA03 HA05 HA11

Claims (15)

[Claims] 1. A polarization separation element for separating an optical signal input from an input optical waveguide into two orthogonal polarization components on a substrate and outputting the resultant signals to two output ports, and two outputs of the polarization separation element. Two optical splitters for splitting the two polarized light components split into two ports, respectively; and a polarization switching element for converting the two polarized light components split to the second output ports of the respective light splitters into the same polarization. And a light combining / branching element for inputting and interfering two polarization components having the same polarization by the polarization switching element, and a first output of each of the first light branching element and the second light branching element. The light intensity of each polarized light is taken out to the output optical waveguide connected to the port, the interference light intensity of each polarized light is taken out to the output optical waveguide connected to the output port of the optical coupling / branching element, and the polarization state of the input optical signal is extracted. of Waveguide polarization state measuring device, characterized in that the structure subjected to constant. 2. An optical splitting element for splitting an optical signal input from an input optical waveguide into two on a substrate, and an optical signal split by the optical splitting element into two orthogonal polarization components. Polarization splitters that output the two polarization components separated by the two output ports of the second polarization splitter to the same polarization, and the polarization swapping element. And an optical combining / branching element for inputting and interfering two polarized components having the same polarization in the first and second output ports of the first optical branching element. Is taken out, the interference light intensity of each polarized light is taken out to the output optical waveguide connected to the output port of the optical multiplexing / branching element, and it is provided for measurement of the polarization state of the input optical signal. Waveguide type Wave state measuring instrument. 3. The waveguide type polarization state measuring device according to claim 1, wherein an optical filter having a predetermined selected wavelength is inserted into the input optical waveguide. 4. The optical filter according to claim 1, wherein the selected wavelength is variable, and the polarization dispersion is measured from the light intensity and the interference light intensity of each polarized light at at least two selected wavelengths. 4. The waveguide type polarization state measuring device according to 3. 5. The multi-input, one-output optical switch input port is connected to the plurality of output optical waveguides, and one output optical waveguide is selected.
5. The waveguide type polarization state measuring device according to any one of items 1 to 4. 6. A light receiving device arranged on the substrate is connected to the plurality of output optical waveguides or an output port of the multi-input / one-output optical switch. 6. The waveguide type polarization state measuring device according to any one of 5. 7. The optical coupling / branching element includes four two-input two-output optical couplers, and two output ports of the first optical coupler are connected to respective first input ports of the third and fourth optical couplers. Connecting the second input ports of the third and fourth optical couplers to the two output ports of the second optical coupler, and connecting the optical path from the first optical coupler to the third optical coupler to the second optical coupler. The phase difference θ ₁ from the optical path from the first optical coupler to the fourth optical coupler
And the optical path from the second optical coupler to the third optical coupler and the optical path from the second optical coupler to the fourth optical coupler are set to have a phase difference θ ₂ different from each other. Each of the first input ports of the second optical coupler is used as an input port of the optical coupler, and at least one of the output ports of the third optical coupler and the fourth optical coupler is used as an output port of the optical coupler. The waveguide-type polarization state measuring device according to any one of claims 1 to 6, having a configuration. 8. The waveguide type polarization state measuring device according to claim 1, wherein said optical coupling / branching element is a multi-mode interference optical coupler having at least three output ports. 9. The polarization separation element has two inputs and two outputs.
Forming a Mach-Zehnder interferometer with two optical couplers and two waveguide arms connecting them, forming a means for adjusting birefringence on at least one waveguide arm,
7. The waveguide type polarization state measuring device according to claim 1, wherein a phase adjusting means is formed on at least one of the waveguide arms. 10. The polarization switching element according to claim 1, wherein a half-wave plate or a Faraday rotator is arranged so as to cross the optical waveguide on the substrate.
7. The waveguide type polarization state measuring device according to any one of 6. 11. The optical filter includes two inputs and two outputs.
4. A Mach-Zehnder interferometer comprising two optical couplers and two waveguide arms connecting these optical couplers, wherein at least one waveguide arm is provided with a phase adjusting means. A waveguide type polarization state measuring device according to claim 4. 12. The multi-input one-output optical switch according to claim 5, wherein a plurality of two-input one-output optical switches formed on a substrate are connected on a tree. 7. The waveguide type polarization state measuring device according to 6. 13. The multi-input, one-output optical switch, comprising:
Is an integer of 3 or more, an N-input / N-output multimode interference optical coupler, an N-input / one-output multimode interference optical coupler, and N arm waveguides connecting them, at least (N− 1) The waveguide type polarization state measuring device according to claim 5 or 6, wherein a phase adjusting means is formed on the arm waveguides. 14. The apparatus according to claim 9, wherein said phase adjusting means is a thin film heater formed on an optical waveguide.
A waveguide type polarization state measuring device according to any one of claims 11 and 13. 15. The waveguide-type polarization state measuring device according to claim 1, wherein the optical waveguide constituting the waveguide-type polarization state measuring device is a silica-based optical waveguide.