JP2730658B2 - Polarization dependence measurement method and apparatus - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention measures a polarization dependent loss (or gain) characteristic of an optical device such as an optical amplification transmission system for relaying and transmitting an optical signal using an optical amplifier, an optical isolator, and an optical fiber coupler. And a device directly used in its implementation.

[0002]

2. Description of the Related Art A conventional technique of this kind will be described with reference to the drawings. FIG. 9 is a block diagram showing a first configuration example of a conventional apparatus for measuring polarization-dependent loss (or gain). In the figure, 1 is a light source for outputting the signal light S1, 2α is a polarization controller composed of a polarizer 2a and a π-phase element 2b such as a λ / 2 wave plate, 3 is a measured object to be measured, and 4 is a measured object. 3 is an optical receiving and measuring device that receives and measures the signal light S2 that has passed through No. 3.

FIG. 10 is a block diagram showing a second configuration example of a conventional apparatus for measuring polarization-dependent loss (or gain). In the figure, 2β is π / 2 of a λ / 4 wavelength plate or the like.
This is a polarization controller including a phase element 2c and a π phase element 2b such as a λ / 2 wavelength plate. The same members as those of the first conventional example are denoted by the same reference numerals.

FIG. 11 is a block diagram showing a third configuration example of a conventional apparatus for measuring polarization-dependent loss (or gain). In the figure, 2γ is an optical fiber type phase shifter 2d
And a fiber rotator 2e. The same members as those in the first and second conventional examples are denoted by the same reference numerals.

The concept of measurement using a conventional polarization dependence measuring device will be described with reference to FIG. Conventionally, the polarization state of the output light S1 of the light source 1 is determined by the polarization controllers 2α and 2α.
As shown in FIG. 12, the polarization plane is rotated (changed in angle) using β and 2γ to pass through the DUT 3 and the optical output power fluctuation of the DUT 3 received by the optical receiver 4. The polarization dependence was measured from the maximum value H and the minimum value L.

[0006]

However, each of the conventional polarization dependence measuring devices shown in FIGS. 9 to 11 has the following problems. In the polarization dependence measuring apparatus shown in FIG. 9, the output signal light S1 of the light source 1 is linearly polarized by the polarizer 2a and mechanically rotated by 0 to 180 ° by the π phase element 2b such as a λ / 2 wave plate. Although the optical output fluctuation is measured from the difference between the maximum value H and the minimum value L of the optical output of the device under test 3, the polarizer 2a can form only a linearly polarized state. Π phase element 2b such as λ / 2 wave plate
There is a problem that an optical output variation due to an error due to the mechanical rotation of the optical disk is included.

[0007] In the polarization dependence measuring device in FIG.
The polarization state created by rotating the output signal light S1 of the light source 1 by rotating the π / 2 phase element 2c such as a λ / 4 wavelength plate by 0 to 45 ° is converted by the π phase element 2b such as a λ / 2 wavelength plate. 0-18
This apparatus uses a method of measuring polarization-dependent loss (gain) characteristics from the difference between the maximum value H and the minimum value L of the output power of the signal light S2 of the device under test 3 by rotating by 0 °.

In an apparatus using this method, π / 2
Since there is no polarizer 2a as shown in FIG. 9 in front of the phase element 2b, all polarization states (linearly polarized light, circularly polarized light, elliptically polarized light)
In addition, there is a problem that an optical output variation due to an error caused by mechanical rotation of the π-phase element 2b is included as in the first conventional device.

In the polarization dependence measuring device shown in FIG.
Π / 2 phase element 2c and π phase element 2b in FIG.
Is replaced by an optical fiber type phase shifter 2d and an optical fiber type rotator 2e.

[0010] Therefore, there is a problem peculiar to the optical fiber type element that the phase characteristic is ambiguous and there is an uncertain element as compared with the optical device, and the polarization dependence measurement in all polarization states cannot be realized. Further, there is a problem in that the measured values may include uneven rotation due to twisting of the optical fiber type elements 2d and 2e. The present invention has been made to solve the problems of the conventional polarization dependence measuring apparatus and to provide a method and an apparatus for measuring the polarization dependence of an object under measurement in all polarization states with high accuracy. .

[0011]

Means for Solving the Problems The above-mentioned conventional problems can be solved by adopting the following novel characteristic construction methods and means of the present invention. That is, a first feature of the method of the present invention is that the polarization state of an optical signal from a light source is converted into an arbitrary polarization state and rotated, and the rotated optical signal of an arbitrary polarization state is input to a measurement target. The power fluctuation of the optical signal for measurement output from the object to be measured, which is branched into the optical signal for measurement and the optical signal for reference not input to the object to be measured, and the power fluctuation of the optical signal for reference not input to the object to be measured. This is a polarization dependence measurement method in which the polarization dependence of the object to be measured is measured by comparing the components and canceling out the polarization dependence of the object to be measured.

According to a second feature of the method of the present invention, in the first feature of the method of the present invention, an optical signal from a light source is first
The optical signal in the linearly polarized state is rotated by at least 0 to 45 ° while the optical signal in the linearly polarized state is transmitted through the π / 2 phase element by transmitting the polarizer, whereby the optical signal is The polarization state is converted into an arbitrary polarization state, and then the π-phase element is transmitted through the π-phase element at least from 0 to 18 while transmitting the optical signal in the arbitrary polarization state.
This is a polarization dependence measurement method in which the polarization state of an optical signal is converted to an arbitrary polarization state and rotated by rotating by 0 °.

A third feature of the method of the present invention is that the polarization state of an optical signal from a light source is converted into an arbitrary polarization state and rotated, and the power fluctuation of the rotated optical signal in an arbitrary polarization state is calculated. First, measure and record without inserting the measuring object, then measure and record the power fluctuation of the optical signal by inserting the measuring object, and calculate the power fluctuation and the measuring object when the measuring object is inserted by the calculating means. This is a polarization dependence measuring method in which the power fluctuations when no is inserted are compared and the polarization dependence of the measurement target is measured by canceling out the polarization dependence of the measurement target.

According to a fourth aspect of the method of the present invention, in the third aspect of the method of the present invention, an optical signal from a light source is first
The optical signal in the linearly polarized state is rotated by at least 0 to 45 ° while the optical signal in the linearly polarized state is transmitted through the π / 2 phase element by transmitting the polarizer, whereby the optical signal is The polarization state is converted into an arbitrary polarization state, and then the π-phase element is transmitted through the π-phase element at least from 0 to 18 while transmitting the optical signal in the arbitrary polarization state.
This is a polarization dependence measurement method in which the polarization state of an optical signal is converted to an arbitrary polarization state and rotated by rotating by 0 °.

A first feature of the present invention is that a light source means for outputting an optical signal, and a polarization control means for converting the polarization state of the optical signal output from the light source means into an arbitrary state and rotating the polarization state Means, branching means for splitting the signal light output from the polarization control means, first reception measuring means for directly receiving and measuring the signal light output from the splitting means, and a signal output from the splitting means Second reception measuring means for receiving and measuring light by passing the light through a measurement target;
And a calculation and recording unit for comparing and calculating the measurement results of the reception measurement unit and the second reception measurement unit, and canceling and recording the polarization dependence of other than the object to be measured.

A second feature of the apparatus of the present invention is that a light source means for outputting an optical signal, and a polarization control means for converting the polarization state of the optical signal output from the light source means into an arbitrary state and rotating the polarization state Means, receiving and measuring means for receiving and measuring respective optical power fluctuations when a measuring object is inserted and not inserted, and recording, comparing and calculating the respective optical power fluctuations which are data of the receiving and measuring means. And a calculation recording means for canceling and recording the polarization dependence of the object other than the object to be measured.

A third feature of the present invention is that the polarization control means in the first or second feature of the present invention is characterized in that the polarization control means comprises a polarizer, a π / 2 phase element and a π phase element. Device.

[0018]

According to the present invention, since the above-described configuration method and means are adopted, the fluctuation power of the optical signal when no measurement target exists is measured separately from the fluctuation power of the optical signal passing through the measurement target. Then, the two are compared and calculated to cancel the power fluctuation of the optical signal other than the object to be measured, so that it is possible to provide a method and an apparatus for measuring the polarization dependency with high accuracy.

In order to control the polarization state of an optical signal,
First, the polarization state of an optical signal is changed to a linear polarization state by transmission of a polarizer, and then the π / 2 phase element is transmitted through a π / 2 phase element such as a λ / 4 wavelength plate at least from 0 to 45 °.
By rotating the optical signal, the polarization state of the optical signal is changed to an arbitrary polarization state (linearly polarized light, elliptically polarized light, or circularly polarized light). Then, at least the π phase element is transmitted while passing through a π phase element such as a λ / 2 wave plate. By rotating the optical signal by 0 to 180 °, the polarization state of the optical signal can be converted to an arbitrary polarization state and rotated. As a result, the difference between the maximum value and the minimum value of the optical output of the measurement object causes Realize the measurement.

[0020]

【Example】

(Embodiment 1) A first embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram showing the configuration of the present apparatus example. In the figure, 2δ is a polarizer 2a, π / 2 phase element 2
A polarization controller 3 'comprising the c and .pi. phase elements 2b is a reference optical fiber.

4a is the signal light S passing through the DUT 3.
2a ″ optical detector / receiver of synchronous detection system for receiving and measuring,
4b is an optical signal S2 passing through the reference optical fiber 3 '.
a synchronous detection type optical receiving and measuring device for receiving and measuring b, 5,
5 'is an optical isolator, 6 is an external modulator, 7 is a modulation signal generator for providing a modulation signal M to the external modulator 6, 8 is a narrow band optical filter, 9 is an optical splitter, 10 is an optical reception measuring device 4a,
4b is an operation recording device such as a computer for comparing and calculating the measurement results of 4b. The same members as those in the conventional example are denoted by the same reference numerals.

(Method Example) The method of the present invention applied to the first apparatus example will be described with reference to FIGS. 4 (a), 4 (b) and 4 (c). The signal light S1 output from the light source 1 passes through the optical isolator 5, is modulated by the external modulator 6 by the signal M from the modulation signal generator 7, and is input to the polarization controller 2δ.

The optical signal S1 'input to the polarization controller 2δ is linearly polarized by the polarizer 2a, and π /
By mechanically rotating the two-phase element 2c at least 0 to 45 ° in a plane perpendicular to the direction in which the optical signal S1 'is set to be incident, an arbitrary polarization state (linearly polarized light, circularly polarized light, elliptically polarized light) is obtained. Next, the π-phase element 2b is set to the optical signal S1 ′.
By rotating at least 0 to 180 ° in a plane perpendicular to the incident setting direction of
For example, the polarization plane of the signal light S2a incident on the DUT 3 such as an optical amplification system including the optical amplifier 3a and the optical fiber 3b can be rotated by 0 to 360 °.

Thereafter, the optical signal S2a ″ that has passed through the narrow-band optical filter 8 in order to suppress optical noise corresponding to the optical power fluctuation P1 of the output light S2a ′ of the device under test 3 is passed through the optical isolator 5 ′. Optical reception measuring device 4a of optical synchronous detection system
Measure with However, optical power fluctuation due to mechanical rotation due to backlash or the like of the π / 2 phase element 2c and the π phase element 2b may be included as an error in the measurement result.

For this reason, the optical output level P0 of the reference light S2b is monitored by another optical receiving / measuring device 4b by the optical splitter 9, and
This is subtracted from the result of the optical receiver 4a by the arithmetic recorder 10, thereby canceling the error of the π / 2 phase element 2c and the π phase element 2b as shown in FIG. It becomes possible to measure with high accuracy. When the device under test 3 is other than the optical amplification system, it is possible to measure even an unmodulated optical signal that is not modulated by the external modulator 6 and the modulation signal generator 7.

(Embodiment 2) A second embodiment of the present invention will be described with reference to the drawings. FIG. 2 is a block diagram showing the configuration of this example of the apparatus. In the figure, 9 'is a signal light S2a for measurement.
This is an optical fiber coupler for splitting the signal light S1 ″ into the signal light S2b and the reference signal light S2b.

The same members as those of the conventional example and the first apparatus are denoted by the same reference numerals. In this embodiment, since the optical fiber coupler 9 'operates in the same manner as the optical branching device 9 of the first embodiment, the operation thereof is substantially the same as that of the first embodiment, so that the description is omitted.

As in the case of the first apparatus, the measurement can be performed by using an unmodulated optical signal for the device under test 3 other than the optical amplification system. In these measuring devices, in the first device example, the optical branching device 9 and the optical receiving measuring device 4 are used.
In this example, the polarization characteristics of the optical fiber couplers 9 'and 4a and 4b are problematic.

The polarization characteristics of the optical fiber coupler 9 'are described in [Y. Namihira, T. Kawazawa, and H. Wakabaya].
shi: "Incident polarization angle and temperature
dependence of polarization and spectral response
characteristics in opticalfiber couplers "Applied
Optics, Vol. 30, No. 9, pp. 1062-1069, 1991.], an example of which is shown in the figure.

FIGS. 5 (a) (b) to 6 (a) (b)
Is a measurement example of the polarization dependence of the optical fiber coupler 9 '. The horizontal axis represents the rotation angle of the incident polarization, and the vertical axis represents the change in the polarization state of the optical signal [1.0 = linear polarization]. , 0 = circularly polarized light, all of which are elliptically polarized light], and (b) shows the change in the principal axis angle of the polarization plane. FIG. 5 shows an example of the optical fiber coupler 9 'having a large polarization dependency, and FIG. 6 shows a small example. It can be seen that the optical fiber coupler 9 'in FIG. 5 has a large polarization dependence with respect to the incident polarized light when the temperature is changed, so that the polarization dependence is large.

On the other hand, the optical fiber coupler 9 'shown in FIG.
Shows an example in which the polarization dependence is small. Although the optical fiber coupler 9 'as shown in FIG. 6 is more suitable for the measurement of the polarization dependence, even when the optical fiber coupler 9' having a large polarization dependence as shown in FIG. After (after), the polarization-dependent initial characteristics are recorded in advance in the operation recording device 10 such as a computer, and the result of the device under test 3 is subtracted, whereby highly accurate polarization-dependent measurement is possible.

(Apparatus Example 3) However, another apparatus of the present invention for eliminating the problem of power fluctuation due to the polarization characteristics of the optical splitter 9 or the optical fiber coupler 9 'in the first and second apparatus examples. An example is shown in FIG. In the figure, 4 '
Is a synchronous detection type optical receiving and measuring device. The same members as those in the conventional example and the first and second device examples are denoted by the same reference numerals.

In FIG. 3, the light output level P0 of the reference optical fiber 3 'is measured in advance (after) and stored in the comparison operation recording device 10 such as a computer. By subtracting the data P0 of the reference optical fiber 3 ', highly accurate measurement of polarization dependence is realized.

Further, since the present example uses the same optical receiving and measuring device 4, errors due to the polarization characteristics of the optical detectors in the optical receiving and measuring devices 4a and 4b in the first and second examples are cancelled. It also has the advantage of being able to.

FIGS. 7 and 8 show measurement examples in which polarization dependence measurement is performed using the apparatus according to the present invention. (Measurement Example 1) FIG. 7 shows a polarization dependence measurement example in which the DUT 3 is a polarization-maintaining optical fiber coupler.

In the figure, the black circle of A represents the polarization-dependent loss characteristic of the through port of the polarization-maintaining optical fiber coupler, and the white circle of B represents the polarization-dependent loss characteristic of the splitting port of the polarization-maintaining optical fiber coupler. It can be seen that there is no change in the optical power due to the rotation of the π-phase element 2b such as the λ / 2 wave plate due to backlash or the like, because the sine wave is shifted by π / 2.

(Measurement Example 2) FIG. 8 shows a polarization dependence measurement example in which the device under test 3 is a normal 3 dB optical fiber coupler. From the figure, it can be seen that a small polarization dependence measurement of 0.1 dB or less when the temperature is changed is possible. From the above measurement results, the usefulness of the polarization-dependent loss (gain) measuring method of the embodiment of the present invention is demonstrated.

[0038]

Thus, according to the present invention, the polarizer, λ
Π / 2 phase element such as / 4 wavelength plate and π such as λ / 2 wavelength plate
The use of the phase element makes it possible to measure the polarization fluctuation in the principal axis angle change of all the polarization planes in all the polarization states (linear polarization, elliptical polarization, circular polarization) of the optical signal.

Also, by canceling the optical power fluctuation when the π / 2 phase element or π phase element is mechanically rotated, a highly accurate polarization dependent loss (or gain) measuring method can be realized. As a result, excellent usefulness is exhibited, such as the achievement of an optical amplifier, an optical device, and a long-distance optical amplification repeater transmission system with small polarization-dependent loss (gain).

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration of a first device example of the present invention.

FIG. 2 is a diagram showing a configuration of a second example of the apparatus.

FIG. 3 is a diagram showing a configuration of a third example of the apparatus.

FIG. 4 is a graph illustrating the concept of measuring polarization dependent loss (or gain) in the method of the present invention.

FIG. 5 is a graph showing an example of measuring the polarization dependence of an optical fiber coupler having a large polarization dependence, which is used in the second apparatus example of the present invention.

FIG. 6 is a graph showing a measurement example of the polarization dependence of the optical fiber coupler although the polarization dependence is small.

FIG. 7 is an example of polarization dependence measurement according to the present invention in which a device under test is a polarization-maintaining optical fiber coupler.

FIG. 8 is an example of polarization dependence measurement according to the present invention in which a device under test is a normal 3 dB optical fiber coupler.

FIG. 9 is a block diagram illustrating a configuration example of a conventional polarization-dependent loss (gain) measuring device.

FIG. 10 is a block diagram showing a configuration example of a conventional polarization-dependent loss (gain) measuring apparatus.

FIG. 11 is a block diagram showing a configuration example of a conventional polarization-dependent loss (gain) measuring apparatus.

FIG. 12 is a graph illustrating a conventional concept of measuring polarization dependent loss.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Light source 2 (alpha), 2 (beta), 2 (gamma), 2 (delta) ... Polarization controller 2a ... Polarizer 2b ... (pi) phase element 2c ... (pi) / 2 phase element 2d ... Optical fiber type phase shifter 2e ... Optical fiber type rotator 3 ... DUT 3 ' Reference optical fibers 4, 4 ', 4a, 4b Optical receiving and measuring device 5, 5' Optical isolator 6 External modulator 7 Modulated signal generator 8 Narrow band optical filter 9 Optical splitter 9 ' Optical fiber coupler 10… Operation recorder

Claims (7)

(57) [Claims] An optical signal from a light source converts a polarization state of an optical signal into an arbitrary polarization state, rotates the optical signal, and inputs the rotated optical signal of an arbitrary polarization state to a measurement object. Is branched into a reference optical signal that is not input to the measurement target, and the power fluctuation of the measurement optical signal output from the measurement target is compared with the power fluctuation of the reference optical signal that is not input to the measurement target. A polarization dependence measurement method, wherein the polarization dependence of a measurement target is measured by canceling the polarization dependence of the measurement target. 2. An optical signal from a light source is first converted into a linearly polarized state by transmission of a polarizer, and then the optical signal in the linearly polarized state is transmitted through a π / 2 phase element while the π / 2 phase element is transmitted. At least 0-45
By rotating the optical signal into an arbitrary polarization state by rotating the optical signal, the optical signal in the arbitrary polarization state is transmitted through the π-phase element and the π-phase element is at least 0 to 180 °.
2. The polarization dependency measuring method according to claim 1, wherein by rotating the optical signal, the polarization state of the optical signal is converted into an arbitrary polarization state and rotated. 3. The method according to claim 1, wherein the polarization state of the light source is converted into an arbitrary polarization state and the light source is rotated, and the power fluctuation of the rotating optical signal in the arbitrary polarization state is measured and recorded without first inserting the measurement object. Next, the measured object is inserted and the power fluctuation of the optical signal is measured and recorded, and the calculating means compares and calculates the power fluctuation when the measuring object is inserted and the power fluctuation when the measuring object is not inserted. And measuring the polarization dependence of the object to be measured by canceling out the polarization dependence of the object other than the object to be measured. 4. An optical signal from a light source is first converted into a linearly polarized state by transmission of a polarizer, and then, while the optical signal in the linearly polarized state is transmitted through a π / 2 phase element, the π / 2 phase element is transmitted. At least 0-45
By rotating the optical signal into an arbitrary polarization state by rotating the optical signal, the optical signal in the arbitrary polarization state is transmitted through the π-phase element and the π-phase element is at least 0 to 180 °.
4. The polarization dependence measuring method according to claim 3, wherein by rotating the optical signal, the polarization state of the optical signal is converted into an arbitrary polarization state and rotated. 5. A light source means for outputting an optical signal; a polarization control means for converting a polarization state of an optical signal output from the light source means into an arbitrary state and rotating the polarization state; Branching means for splitting the output signal light; first reception measuring means for directly receiving and measuring the signal light output from the splitting means; and passing the signal light output from the splitting means through a measurement target. A second reception measurement unit for performing reception measurement, and a calculation recording unit for comparing and calculating the measurement results of the first reception measurement unit and the second reception measurement unit, and canceling and recording polarization dependence other than the measurement target. And a polarization dependence measuring device. 6. A light source means for outputting an optical signal, a polarization control means for converting the polarization state of the optical signal output from the light source means into an arbitrary state and rotating the polarization state, and inserting an object to be measured. Receiving and measuring means for receiving and measuring the respective optical power fluctuations, and recording, comparing and calculating the respective optical power fluctuations, which are data of the receiving and measuring means, to determine the polarization dependence other than the measurement object. And a calculation recording means for canceling and recording the polarization. 7. An apparatus according to claim 5, wherein said polarization control means comprises a polarizer, a π / 2 phase element and a π phase element.