JP5634291B2 - Optical spectrum measuring apparatus and optical spectrum measuring method - Google Patents

Description

  The present invention relates to an optical spectrum measuring apparatus and an optical spectrum measuring method using a wavelength tunable etalon filter.

  An optical spectrum analyzer using a wavelength tunable etalon filter is commercially available, has no moving parts, and can be downsized. However, there is a drawback that the dynamic range is narrow. In order to improve the dynamic range, a method of passing light twice through a wavelength tunable etalon filter as shown in FIG. 6 has been studied (for example, see Patent Document 1).

  The optical spectrum analyzer of Patent Document 1 reflects the measured light L14 that has passed through the tunable etalon filter 112, while the modulation mirror 113 modulates the measured light L14 to the tunable etalon filter 112, and again reflects the reflected light L15 to the tunable etalon filter 112. Then, the passing light L16 is separated by the circulator 111 and received by the light receiver 114.

  Assume that the measured light L11 as shown in FIG. 7A is input and the measured light L14 that has passed through the wavelength tunable etalon filter 112 only once has a dynamic range as shown in FIG. 7B. As shown in FIG. 7C, the passing light L16 obtained by passing the measured light L14 again through the wavelength tunable etalon filter 112 has a wide dynamic range.

  However, the light receiver 114 includes not only the passing light L16 but also the measured light L11 reflected by the wavelength variable etalon filter 112. In Patent Document 1, the measured light L14 is modulated by the modulation mirror 113 in order to remove the measured light L11 from the light reception signal of the light receiver 114. Then, the calculation unit 116 extracts the signal of the passing light L16 from the signal of the light receiver 114 using the modulation signal modulated by the modulation mirror 113.

US7391970

  The optical spectrum analyzer of Patent Document 1 does not consider polarization dependence. The PDL (Polarization-Dependent-Loss) performance of the commercially available wavelength tunable etalon filter 112 is less than about 0.2 dB, which is worse than the market requirement of ± 0.05 dB. For this reason, the optical spectrum analyzer of Patent Document 1 may not be able to accurately measure the spectrum due to the PDL performance of the wavelength tunable etalon filter 112.

  Therefore, an object of the present invention is to improve PDL performance in an optical spectrum analyzer that passes light twice through a wavelength tunable etalon filter.

In order to achieve the above object, an optical spectrum measuring apparatus according to the present invention includes a polarization controller (15) for setting input light to be measured in a predetermined polarization direction, and the polarization controller and polarization maintaining fiber. in being connected, the passing through the light of a predetermined polarization direction and the same direction of said light to be measured from the polarization controller, separating the direction of light perpendicular to the polarization direction of predetermined PBS (11) that is connected to the PBS by a polarization maintaining fiber, and extracts light of the set wavelength that is in the same direction as the predetermined polarization direction of the measured light that has passed through the PBS. to together, the wavelength tunable etalon filter polarization direction after extraction of light to extract light of the predetermined wavelength from the 90 ° rotated polarization rotation light (12), a polarization maintaining the wavelength tunable etalon filter Are connected by Aiba, said extracted by the wavelength tunable etalon filter is rotated 90 ° to the polarization direction of the measured light, the polarization to be incident on the wavelength tunable etalon filter light after the rotation as the polarization rotation light A rotation unit (13); a light receiver (14) that receives the polarization rotation light extracted by the wavelength variable etalon filter and separated by the PBS; and the light of the polarization rotation light received by the light receiver. A calculation unit (16) for storing the intensity in association with the set wavelength; and a control unit (17) for changing the wavelength extracted by the wavelength tunable etalon filter.

  Since the optical spectrum measuring apparatus of the present invention includes the wavelength tunable etalon filter (12), the light receiver (14), and the control unit (17), the optical spectrum of the light to be measured can be measured. Since the optical spectrum measuring apparatus of the present invention includes the polarization rotation unit (13), the light to be measured can pass through the wavelength tunable etalon filter (12) twice. Here, in order for the polarization rotation unit (13) to make the polarization direction of the light to be measured orthogonal, the polarization direction of the polarization rotation light after passing through the wavelength tunable etalon filter (12) twice is measured. It is orthogonal to the measurement light. For this reason, only the polarization rotation light after having passed twice through the wavelength tunable etalon filter (12) using the PBS (11) can be incident on the light receiver (14). Furthermore, since the optical spectrum measuring apparatus of the present invention includes the polarization controller (15), the PBS (11), and the polarization rotation unit (13), the light in the predetermined polarization direction has a variable wavelength. It can be passed through an etalon filter (12). For this reason, the optical spectrum measuring apparatus of the present invention can improve the PDL performance.

  In the optical spectrum measuring apparatus according to the present invention, the polarization controller includes a measured light separating unit that separates the measured light into the light in the predetermined polarization direction and the light in the direction orthogonal to the polarization direction. (21), a polarization direction converter (22) for converting light in a direction orthogonal to the polarization direction separated by the measured light separation unit into light of the predetermined polarization direction, An optical switch (23) that outputs the light in the predetermined polarization direction separated by the measurement light separation unit or the light in the predetermined polarization direction converted by the polarization direction conversion unit to the PBS. The polarization rotation received by the light receiver when the light having the predetermined polarization direction separated by the measured light separation unit is output from the optical switch. The light intensity of the light and the polarization direction change A light intensity obtained by adding the light intensity of the polarization rotation light received by the light receiver when the light having the predetermined polarization direction converted by the optical unit is output from the optical switch, and the set wavelength. It may be stored in association.

  In the optical spectrum measuring apparatus according to the present invention, the polarization controller includes a measured light separating unit that separates the measured light into the light in the predetermined polarization direction and the light in the direction orthogonal to the polarization direction. (21), a polarization direction converter (22) for converting light in a direction orthogonal to the polarization direction separated by the measured light separation unit into light of the predetermined polarization direction, The light having the predetermined polarization direction separated by the measurement light separation unit and the light having the predetermined polarization direction converted by the polarization direction conversion unit are combined and output to the PBS An optical coupler (24).

In order to achieve the above object, an optical spectrum measuring method of the present invention is an optical spectrum measuring method using a wavelength tunable etalon filter (12) that extracts light of a set wavelength from measured light. and a polarization adjustment procedure for the polarization direction determined in advance by using a polarization controller (15), the measured light of the predetermined polarization direction after passing through the wavelength tunable etalon filter, The polarization polarized light obtained by rotating the polarization direction of the passing light by 90 ° using the polarization rotating unit (13) is again passed through the wavelength tunable etalon filter and is again passed through the wavelength tunable etalon filter. has a polarization rotation light receiving procedure for storing the light intensity of the polarization rotation light the in association with the set wavelength rotation light receiving, in sequence, the polarization controller in the polarization adjustment procedure The polarization direction of the measured light from the wavelength tunable etalon filter to the polarization rotating unit in the polarization rotating light receiving procedure and the polarization direction of the measured light from the wavelength tunable etalon filter in the polarization rotating light receiving procedure. The wave direction is maintained using a polarization maintaining fiber, and the polarization adjustment procedure and the polarization rotation light receiving procedure are sequentially performed while changing the set wavelength of the wavelength tunable etalon filter.

  Since the optical spectrum measurement method of the present invention sequentially performs the polarization rotation light receiving procedure while changing the set wavelength of the wavelength tunable etalon filter, the optical spectrum of the light to be measured can be measured. In the optical spectrum measuring method of the present invention, the measured light is passed through the wavelength tunable etalon filter (12) after passing the measured light through the wavelength tunable etalon filter (12). It can be passed twice through the filter (12). Here, there is a polarization adjustment procedure, and the polarization direction of the polarization rotation light after passing through the wavelength variable etalon filter (12) twice in the polarization rotation light receiving procedure is orthogonal to the light to be measured. . For this reason, only polarization rotation light can be received. Furthermore, since the optical spectrum measurement method of the present invention has a polarization adjustment procedure, light in a predetermined polarization direction can be passed through the wavelength tunable etalon filter (12). For this reason, the optical spectrum measuring apparatus of the present invention can improve the PDL performance.

  In the optical spectrum measurement method of the present invention, in the polarization adjustment procedure, the measured light is separated into light in the predetermined polarization direction and light in a direction orthogonal to the polarization direction, and the separated light is separated. The light in the direction orthogonal to the polarization direction is converted into the light in the predetermined polarization direction, and the light in the predetermined polarization direction obtained by the separation or the predetermined light obtained by the conversion Any one of the lights having a predetermined polarization direction is output, and is received when the light having the predetermined polarization direction obtained by the separation is output in the polarization rotation light receiving procedure. The light intensity obtained by adding the light intensity of the polarization rotation light and the light intensity of the polarization rotation light received when the light having the predetermined polarization direction obtained by the conversion is output Store it in association with the set wavelength. Good.

  In the optical spectrum measurement method of the present invention, in the polarization adjustment procedure, the measured light is separated into light in the predetermined polarization direction and light in a direction orthogonal to the polarization direction, and the separated light is separated. The light in the direction orthogonal to the polarization direction is converted into the light in the predetermined polarization direction, the light in the predetermined polarization direction obtained by the separation and the predetermined light obtained by the conversion. You may combine with the light of the obtained polarization direction.

  According to the present invention, PDL performance can be improved in an optical spectrum analyzer that passes light through a wavelength tunable etalon filter twice.

1 shows an example of an optical spectrum measuring apparatus according to a first embodiment. The 1st example of a form of the polarization controller 15 is shown. The 2nd example of a form of the polarization controller 15 is shown. The 2nd example of a polarization rotation part 13 is shown. The 3rd example of a form of the polarization rotation part 13 is shown. The structure of the optical spectrum analyzer of patent document 1 is shown. An example of the waveform in the optical spectrum analyzer of patent document 1 is shown, (a) shows measured light L11, (b) shows measured light L14, and (c) shows passing light L16.

  Embodiments of the present invention will be described with reference to the accompanying drawings. The embodiments described below are examples of the present invention, and the present invention is not limited to the following embodiments. In the present specification and drawings, the same reference numerals denote the same components.

(Embodiment 1)
FIG. 1 shows an example of an optical spectrum measuring apparatus according to the first embodiment. The optical spectrum measurement apparatus according to this embodiment includes an optical input terminal 18, a polarization controller 15, a PBS 11, a wavelength tunable etalon filter 12, a polarization rotation unit 13, a light receiver 14, a calculation unit 16, And a control unit 17.

  The optical spectrum measurement method according to the present embodiment includes a polarization adjustment procedure and a polarization rotation light receiving procedure in order. In the polarization adjustment procedure, the measured light L1 is input to the polarization controller 15, and the polarization controller 15 passes the measured light L2 having a predetermined polarization direction. The predetermined polarization direction is, for example, a P wave or an S wave. In the following description, it is assumed that the predetermined polarization direction is a P wave, and the polarization direction obtained by rotating the predetermined polarization direction by 90 ° is an S wave.

  In the polarization rotation light receiving procedure, after passing the P-wave measured light L2 through the wavelength tunable etalon filter 12, the polarization rotation light L5 obtained by rotating the polarization direction of the passing light L4 by 90 ° is used as the wavelength tunable etalon filter. 12, the polarization rotation light L6 after passing is received, and the light intensity of the polarization rotation light L6 is stored in association with the set wavelength. Hereinafter, the polarization rotation light receiving procedure will be specifically described.

  The PBS 11 passes the P wave and separates the S wave. Since the measured light L2 from the polarization controller 15 is a P wave, it passes through the PBS 11 and is input to the wavelength tunable etalon filter 12. The wavelength tunable etalon filter 12 extracts light having a set wavelength from the light L2 to be measured that has passed through the PBS 11. As a result, the P wave in the light L1 to be measured is passed through the wavelength tunable etalon filter 12 once.

  The polarization rotation unit 13 rotates the polarization direction of the passing light L4 extracted by the wavelength tunable etalon filter 12 by 90 °, and causes the rotated light to enter the wavelength tunable etalon filter 12 as polarization rotation light L5. The polarization rotation unit 13 is, for example, a Faraday mirror. The polarization rotation light L5 rotates the polarization direction of the P wave by 90 °. For this reason, the polarization rotation light L5 becomes an S wave. The wavelength tunable etalon filter 12 extracts light having a set wavelength from the polarization rotation light L5. As a result, the P wave in the measured light L1 is passed through the wavelength tunable etalon filter 12 twice.

  Since the polarization rotation light L6 from the wavelength tunable etalon filter 12 is an S wave, the PBS 11 separates the polarization rotation light L6. The light receiver 14 receives the polarization rotation light L6 separated by the PBS 11.

  Here, since the measured light L2 reflected by the wavelength tunable etalon filter 12 is a P wave, the measured light L2 is not incident on the light receiver 14. For this reason, the optical spectrum measuring apparatus and the optical spectrum measuring method according to the present embodiment can separate the polarization rotation light L6 and the measured light L2 without being modulated in the polarization rotation unit 13. For this reason, a structure becomes simple and an apparatus can be reduced in size.

  The calculation unit 16 stores the light intensity of the polarization rotation light L6 received by the light receiver 14 in association with the set wavelength. The control unit 17 changes the set wavelength extracted by the wavelength tunable etalon filter 12, and stores the light intensity of the polarization rotation light L6 at the changed wavelength in association with the changed set wavelength.

  The above is the polarization rotation light receiving procedure. The optical spectrum can be measured by sequentially performing the above-described polarization adjustment procedure and polarization rotation light receiving procedure while changing the set wavelength of the wavelength etalon filter 12.

  The measured light L2 and the polarization rotation light L5 input to the wavelength tunable etalon filter 12 have predetermined polarization directions such as a P wave and an S wave, respectively. For this reason, the optical spectrum measuring apparatus and the optical spectrum measuring method according to the present embodiment can improve the PDL performance. The optical arrangement of each component in the optical spectrum measuring apparatus according to the present embodiment is not limited, but it is preferable that each component is connected by a polarization maintaining fiber in order to maintain the polarization state.

(Embodiment 2)
In the present embodiment, the first form of the polarization controller 15 is used in the polarization adjustment procedure. FIG. 2 shows a first form example of the polarization controller 15. The first form of the polarization controller 15 includes a PBS 21 as a measured light separation unit, a polarization direction conversion unit 22, and an optical switch 23.

  The PBS 21 separates the measured light L1 into P wave light and S wave. The polarization direction converter 22 converts S-wave light into P-wave light. The optical switch 23 receives the P-wave light from the PBS 21 and the P-wave from the polarization direction converter 22, and outputs either of them as the measured light L2.

Here, the polarization direction converting unit 22 may use a 90 degree phase shifting device. Alternatively, the PBS 21 and the optical switch 23 may be connected by a polarization maintaining fiber so that the connection portion of the PBS 21 and the connection portion of the optical switch 23 are rotated by 90 degrees.

  In the present embodiment, the polarization rotation light L6 before and after switching of the optical switch 23 is received. For example, first, P-wave light from the PBS 21 is output to the optical switch 23, and the light receiver 14 receives the polarization rotation light L6 at this time. Then, the calculation unit 16 stores the light intensity of the polarization rotation light L6 in association with the set wavelength. Thereafter, the output port of the optical switch 23 is switched to cause the optical switch 23 to output the P-wave light from the polarization direction converter 22, and the light receiver 14 receives the polarization rotation light L6 at this time. Then, the calculation unit 16 stores the light intensity of the polarization rotation light L6 in association with the set wavelength.

  Then, the arithmetic unit 16 outputs the P wave separated by the PBS 21 from the optical switch 23 and the light intensity of the polarization rotation light L6 received by the light receiver 14 and the P converted by the polarization direction converter 22. The light intensity obtained by adding the light intensity of the polarization rotation light L6 received by the light receiver 14 when the wave light is output from the optical switch 23 is stored in association with the set wavelength. Thereby, the calculating part 16 can obtain | require the optical spectrum which added the light intensity of the P wave of the to-be-measured light L1, and the light intensity of the S wave of the to-be-measured light L1.

(Embodiment 3)
In the present embodiment, the second form of the polarization controller 15 is used in the polarization adjustment procedure. FIG. 3 shows a second embodiment of the polarization controller 15. The second form of the polarization controller 15 includes an optical coupler 24 instead of the optical switch 23 described in the second embodiment. The optical coupler 24 receives the P-wave light from the PBS 21 and the P-wave light from the polarization direction converter 22, combines them, and outputs the resultant as measured light L <b> 2.

  In the present embodiment, the optical coupler 24 can input the light obtained by combining the P wave and the S wave of the measured light L1 to the PBS 11 as the measured light L2. Thereby, the light receiver 14 can receive the polarization rotation light L6 having a light intensity obtained by adding the light intensity of the P wave of the light L1 to be measured and the light intensity of the S wave of the light L1 to be measured.

(Embodiment 4)
In the first embodiment, the Faraday mirror is exemplified as the first form of the polarization rotating unit 13. In the embodiment, another example of the polarization rotating unit 13 will be described.

  FIG. 4 shows a second example of the polarization rotation unit 13. The second form of the polarization rotation unit 13 includes a 45-degree phase shifter 34 and a mirror 32. The passing light L4 passes through the 45 degree phase shifter 34 and then enters the mirror 32, and the passing light L4 reflected by the mirror 32 passes through the 45 degree phase shifter 34 again. Thereby, the phase of the passing light L4 is rotated by 90 degrees.

  In the second embodiment of the polarization rotator 13, the input / output optical path to the mirror 32 can be shared because the 45-degree phase shifter 34 is passed through the mirror 32 both at the time of incidence and at the time of reflection. it can.

  FIG. 5 shows a third example of the polarization rotation unit 13. A third form of the polarization rotation unit 13 is configured such that the circulator 31 and the 90-degree phase shifter 33 are connected by a polarization-maintaining optical waveguide. The polarization maintaining optical waveguide is, for example, a polarization maintaining fiber. By adopting this configuration, the mirror 32 can be omitted. Furthermore, if a polarization-maintaining fiber is used for the polarization-maintaining optical waveguide and the connection angle of the polarization-maintaining fiber is rotated by 90 degrees, the 90-degree phase shifter 33 can be omitted.

  The present invention can be applied to the information communication industry.

11: PBS
12: Wavelength variable etalon filter 13: Polarization rotation unit 14: Light receiver 15: Polarization controller 16: Calculation unit 17: Control unit 18: Optical input terminal 21: PBS
22: Polarization direction conversion unit 23: Optical switch 24: Optical coupler 31: Circulator 32: Mirror 33: 90 degree phase shifter 34: 45 degree phase shifter

Claims (6)

A polarization controller (15) for changing the input measured light to a predetermined polarization direction;
The polarization controller is connected to the polarization controller fiber and passes the light in the same direction as the predetermined polarization direction of the measured light from the polarization controller, and the predetermined polarization PBS (11) for separating light in a direction perpendicular to the direction;
The extracted light that is connected to the PBS by a polarization maintaining fiber and that is in the same direction as the predetermined polarization direction and that has passed through the PBS and that has a set wavelength is extracted. A tunable etalon filter (12) for extracting light of the set wavelength from the polarization rotation light whose polarization direction is rotated by 90 °;
The tunable etalon filter is connected with a polarization maintaining fiber, the polarization direction of the light to be measured extracted by the tunable etalon filter is rotated by 90 °, and the rotated light is used as the polarization rotation light. A polarization rotation unit (13) that is incident on the wavelength tunable etalon filter;
A light receiver (14) for receiving the polarization rotation light extracted by the wavelength tunable etalon filter and separated by the PBS;
A calculation unit (16) for storing the light intensity of the polarization rotation light received by the light receiver in association with the set wavelength;
A control unit (17) for changing the wavelength extracted by the wavelength tunable etalon filter;
An optical spectrum measuring apparatus comprising: The polarization controller
A measured light separating unit (21) that separates the measured light into light of the predetermined polarization direction and light of a direction orthogonal to the polarization direction;
A polarization direction converter (22) for converting light in a direction orthogonal to the polarization direction separated by the measured light separation unit into light in the predetermined polarization direction;
An optical switch that outputs the light of the predetermined polarization direction separated by the measured light separation unit or the light of the predetermined polarization direction converted by the polarization direction conversion unit to the PBS (23)
The arithmetic unit is a light intensity of the polarization rotation light received by the light receiver when the light having the predetermined polarization direction separated by the measured light separation unit is output from the optical switch; The light intensity obtained by adding the light intensity of the polarization rotation light received by the light receiver when the light having the predetermined polarization direction converted by the polarization direction conversion unit is output from the optical switch. The optical spectrum measuring device according to claim 1, wherein the optical spectrum measuring device is stored in association with the set wavelength. The polarization controller
A measured light separating unit (21) that separates the measured light into light of the predetermined polarization direction and light of a direction orthogonal to the polarization direction;
A polarization direction converter (22) for converting light in a direction orthogonal to the polarization direction separated by the measured light separation unit into light in the predetermined polarization direction;
The PBS of the predetermined polarization direction separated by the measured light separation unit and the light of the predetermined polarization direction converted by the polarization direction conversion unit are combined, and the PBS An optical coupler (24) that outputs to
The optical spectrum measuring apparatus according to claim 1, further comprising: In an optical spectrum measurement method using a wavelength tunable etalon filter (12) for extracting light of a set wavelength from light to be measured,
A polarization adjustment procedure for changing the input light to be measured into a polarization direction determined in advance using the polarization controller (15) ;
The measured light of the predetermined polarization direction after passing through the wavelength tunable etalon filter, polarization rotation light the polarization direction of transmitted light is rotated 90 ° with the polarization rotating unit (13) Rotation that passes through the wavelength tunable etalon filter again, receives the polarization rotation light that has passed again through the wavelength tunable etalon filter, and stores the light intensity of the polarization rotation light in association with the set wavelength. Light reception procedure;
In order,
The polarization direction of measured light from the polarization controller in the polarization adjustment procedure to the wavelength tunable etalon filter in the polarization rotation light reception procedure, and the polarization direction from the wavelength variable etalon filter in the polarization rotation light reception procedure. Maintain the polarization direction of the light to be measured up to the wave rotation part using a polarization maintaining fiber,
An optical spectrum measurement method for sequentially performing the polarization adjustment procedure and the polarization rotation light receiving procedure while changing the set wavelength of the wavelength etalon filter. In the polarization adjustment procedure, the light to be measured is separated into light in the predetermined polarization direction and light in a direction orthogonal to the polarization direction, and separated light in a direction orthogonal to the polarization direction Is converted into light of the predetermined polarization direction, and the light of the predetermined polarization direction obtained by the separation or the light of the predetermined polarization direction obtained by the conversion Output one of them,
In the polarization rotation light receiving procedure, the light intensity of the polarization rotation light received when the light having the predetermined polarization direction obtained by the separation is output, and the advance obtained by the conversion Storing the light intensity obtained by adding the light intensity of the polarization rotation light received when outputting light of a predetermined polarization direction in association with the set wavelength;
The optical spectrum measurement method according to claim 4. In the polarization adjustment procedure, the light to be measured is separated into light in the predetermined polarization direction and light in a direction orthogonal to the polarization direction, and separated light in a direction orthogonal to the polarization direction Is converted into light of the predetermined polarization direction, the light of the predetermined polarization direction obtained by the separation and the light of the predetermined polarization direction obtained by the conversion Combine,
The optical spectrum measurement method according to claim 4.

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