JP5604988B2 - Coherent optical receiver adjustment method - Google Patents

Description

  The present invention relates to a method for adjusting a coherent light receiving apparatus that receives coherent light.

  A coherent optical receiver used when performing optical coherent transmission is required to output an optical signal to be received at an appropriate signal level. Therefore, various methods have been proposed for adjusting the coherent optical receiver itself so that the received optical signal can be appropriately output.

  Patent Document 1 describes a method for adjusting a coherent optical receiver. In the adjustment method described in Patent Document 1, the amplitude value (first amplitude value) of input signal light without waveform distortion is stored in advance, and when input signal light in a distorted state is input, the first The amplitude value of the input signal light is adjusted in a direction to match the amplitude value.

  Patent Document 2 describes a transmission characteristic evaluation system that evaluates the transmission characteristics of an optical module. In the system described in Patent Document 2, by using a pseudo transmission line device capable of providing an optical path length difference of reflected return light for each incident light wavelength, by giving chromatic dispersion characteristics that an actual transmission line can have, Evaluate the transmission characteristics of optical modules.

JP 2009-212994 A (paragraphs 0032 to 0035) JP 2006-86955 A (paragraphs 0034 and 0036)

  In the adjustment method described in Patent Document 1, the optical receiver is adjusted based on signal light without waveform distortion. However, in an actual optical transmission line, it is common that distortion occurs in the light waveform. For this reason, when the optical receiver is adjusted based on signal light having no waveform distortion, there is a problem that an adjustment different from the optimum point when used in an actual environment is made.

  Therefore, the present invention adjusts a coherent light receiving apparatus capable of adjusting the coherent light receiving apparatus so that the received coherent light can be corrected to an accurate signal level even when the coherent light receiving apparatus is used in an actual environment. It aims to provide a method.

An adjustment method for a coherent light receiving device according to the present invention includes a conversion unit that performs polarization separation on received measurement light, converts the polarization-separated measurement light into an optical signal, and an optical signal converted by the conversion unit. A method for adjusting a coherent light receiving device including an amplitude correcting unit for correcting an amplitude, wherein wavelength dispersion is performed between the light transmitting device that transmits measurement light to the coherent light receiving device and the coherent light receiving device. By connecting chromatic dispersion means that gives light to the light, chromatic dispersion is given to the measurement light, the polarization of the measurement light transmitted from the optical transmitter is changed, and the amplitude of the optical signal output from the amplitude correction means Is measured according to the polarization changing process, the maximum value of the amplitude of the optical signal is detected, the amplitude correction unit is adjusted so that the maximum value of the amplitude becomes a predetermined value, and the amplitude correction unit The optical signal corrected by The maximum amplitude of the optical signal is detected by measuring the amplitude of the optical signal output from the digital signal correcting means that corrects the amplitude of the optical signal according to the polarization changing process. The digital signal correction means is adjusted so that the maximum value of the signal becomes a predetermined value .

  According to the present invention, even when a coherent light receiver is used in an actual environment, the coherent light receiver can be adjusted so that the received coherent light can be corrected to an accurate signal level.

It is explanatory drawing which shows the example of whole structure of the apparatus used for the adjustment method of the coherent optical receiver in the 1st Embodiment of this invention. It is explanatory drawing which shows the example of the optical transmission apparatus 10 used by 1st Embodiment. It is explanatory drawing which shows the example of the coherent optical receiver 40 used in 1st Embodiment. It is a flowchart which shows the example of the adjustment method of the coherent optical receiver 40 in 1st Embodiment. It is a flowchart which shows the example of the adjustment method of an amplitude correction part. It is explanatory drawing which shows the example of the whole structure which does not include the wavelength dispersion means. It is explanatory drawing which shows the structural example of the apparatus used for the adjustment method of the coherent optical receiver in the 2nd Embodiment of this invention. It is explanatory drawing which shows the example of the optical transmitter 10a used by 2nd Embodiment.

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

Embodiment 1. FIG.
FIG. 1 is an explanatory diagram illustrating a configuration example of an apparatus used in the coherent optical receiver adjustment method according to the first embodiment of the present invention. In the method for adjusting a coherent light receiving apparatus according to the present invention, the optical transmitting apparatus 10, the wavelength dispersion means 30, and the coherent light receiving apparatus 40 are used.

  The optical transmission device 10 is a device that outputs the measurement signal light 20. FIG. 2 is an explanatory diagram illustrating an example of the optical transmission device 10 used in the first embodiment. The optical transmission device 10 illustrated in FIG. 2 includes a light source 11, an optical phase modulator 12, and a polarization controller 14.

  The light source 11 outputs measurement signal light 20 having a constant amplitude.

  The optical phase modulator 12 phase-modulates the measurement signal light 20 by applying a modulation signal 13 to the measurement signal light 20 output from the light source 11. Examples of a method in which the optical phase modulator 12 performs phase modulation include a BPSK (Binary Phase Shift Keying) method and a QPSK (Quadrature Phase Shift Keying) method.

  The polarization controller 14 arbitrarily sets the polarization state of the measurement signal light 20 output from the optical phase modulator 12. Specifically, for example, the polarization controller 14 changes the polarization of the measurement signal light 20 in an arbitrary direction in accordance with a user operation.

  The wavelength dispersion means 30 gives wavelength dispersion to the measurement signal light 20 received from the optical transmitter 10. Specifically, the measurement signal light 20 is transmitted through the wavelength dispersion means 30, so that the measurement signal light 20 is given chromatic dispersion. The wavelength dispersion means 30 is a medium used when transmitting coherent light, and is realized by, for example, a dispersion shifted fiber. Thus, by providing the wavelength dispersion means 30 between the optical transmitter 10 and the coherent optical receiver 40, it is possible to make the measurement signal light 20 into a waveform having a random amplitude close to an actual transmission signal. become. Therefore, the coherent optical receiver can be adjusted in a state closer to the actual communication environment.

  The coherent light receiver 40 illustrated in FIG. 1 includes a coherent light detector 50, amplitude adjusting units 70 a to 70 d (hereinafter, referred to as amplitude adjusting unit 70), and a signal processing unit 80. The coherent optical detector 50 converts the received measurement signal light 20 into received signals 60a to 60d.

  The amplitude adjusting unit 70 adjusts the amplitude of each of the converted reception signals 60a to 60d. As the amplitude adjusting means 70, for example, an electric signal amplifier is used. The amplitude of each received signal 60a-60d is adjusted by adjusting this amplifier and changing the amplitude value of the electrical signal. Examples of the electric signal amplifier (that is, the amplitude adjusting unit 70) include a variable gain amplifier, but the amplitude adjusting unit 70 is not limited to the variable gain amplifier. The amplitude adjusting unit 70 transmits the adjusted reception signals 60 a to 60 d to the signal processing unit 80.

  The signal processing unit 80 generates an output signal 90 by performing various processes on the received signals 60a to 60d adjusted by the amplitude adjusting unit 70, and outputs the output signal 90 to an external device.

  FIG. 3 is an explanatory diagram showing an example of the coherent optical receiver 40 used in the present embodiment. A coherent optical detector 50 illustrated in FIG. 3 includes a local light source 51, a 90-degree optical hybrid 53, and optical receivers 54a to 54d (hereinafter referred to as an optical receiver 54). The signal processing unit 80 illustrated in FIG. 3 includes AD converters 81a to 81d (hereinafter referred to as AD converter 81) and a digital signal processing circuit 82. Furthermore, the digital signal processing circuit 82 includes amplitude detection units 83a to 83d (hereinafter referred to as amplitude detection unit 83), amplitude correction units 84a to 84d (hereinafter referred to as amplitude correction unit 84), and a reception processing unit. 85.

  The local light source 51 outputs local light 52 that is light for causing the measurement signal light 20 received by the 90-degree optical hybrid 53 to interfere with the 90-degree optical hybrid 53.

  The 90-degree optical hybrid 53 causes the received measurement signal light 20 and the local light 52 to interfere with each other, and separates the light wave by polarization. Then, the 90-degree optical hybrid 53 outputs the polarization-separated light waves to the optical receiver 54, respectively.

  The optical receiver 54 converts the light received from the 90-degree optical hybrid 53 into received signals 60a to 60d. Then, the optical receiver 54 outputs the converted received signals 60 a to 60 d to the amplitude adjusting unit 70.

  The AD converter 81 digitizes the received signals 60 a to 60 d whose amplitude has been adjusted by the amplitude adjusting means 70. Hereinafter, the digitized received signals 60a to 60d may be referred to as digitized received signals 60a to 60d. Then, the AD converter 81 outputs the digitized reception signals 60 a to 60 d to the digital signal processing circuit 82.

  The amplitude detector 83 detects the amplitude of the digitized received signals 60a to 60d.

  The amplitude correction unit 84 corrects the amplitudes of the reception signals 60a to 60d detected by the amplitude detection unit 83. As a method for adjusting the amplitude by the amplitude correcting unit 84, a general method for correcting the amplitude of the digital signal is used. For example, when a multiplication circuit is used as the amplitude correction unit 84, the amplitude correction unit 84 corrects the amplitude by multiplying the digitized reception signals 60 a to 60 d by a certain coefficient. Accordingly, the amplitude correction unit 84 is adjusted by setting various information used by the amplitude correction unit 84 to correct the amplitude. For example, in the above example, the amplitude correction unit 84 is adjusted by setting a constant used when the amplitude correction unit 84 corrects the amplitude.

  The reception processing unit 85 performs dispersion compensation, polarization separation, and phase detection on the reception signals 60 a to 60 d whose amplitude is corrected by the amplitude correction unit 84. However, the processing performed by the reception processing unit 85 is not limited to dispersion compensation, polarization separation, and phase detection.

  By the way, the input levels of the reception signals 60a to 60d input to the AD converters 81a to 81d and the input levels of the reception signals 60a to 60d input to the digital signal processing circuit 82 are equal to each other. Need to be. However, in practice, there may be a difference in amplitude between the received signals 60a to 60d due to variations in the characteristics of the 90-degree optical hybrid 53 and the characteristics of the AD converters 81a to 81d that occur during manufacturing. .

  In order to correct this, the coherent optical receiver 40 includes amplitude adjusting units 70a to 70d that adjust the input levels of the received signals 60a to 60d to the AD converters 81a to 81d. Similarly, the coherent optical receiver 40 includes amplitude correction units 84 a to 84 d that adjust the input levels of the received signals 60 a to 60 d to the digital signal processing circuit 82.

  Next, a method for adjusting the coherent light receiving device 40 will be described. FIG. 4 is a flowchart illustrating an example of a method for adjusting the coherent optical receiver 40 according to this embodiment. As illustrated in FIG. 1, the optical transmitter 10 illustrated in FIG. 2 is connected to the coherent optical receiver 40 illustrated in FIG. 3 via the wavelength dispersion unit 30. Thus, the wavelength dispersion is given to the measurement signal light 20 by connecting the wavelength dispersion means 30 between the optical transmission device 10 and the coherent light reception device 40 (step S1).

  That is, the measurement signal light 20 output from the light source 11 and whose phase is modulated by the optical phase modulator 12 reaches the coherent light receiving device 40 via the wavelength dispersion means 30. At this time, the measurement signal light 20 is wavelength-dispersed by the wavelength dispersion means 30 to have a waveform having a random amplitude close to an actual transmission signal.

  Then, while adjusting the polarization controller 14 of the optical transmission device 10, the amplitude adjusting means 70a to 70d are adjusted so that the maximum values of the input levels of the received signals 60a to 60d to the AD converters 81a to 81d are the same. Set.

  Specifically, the polarization of the measurement signal light 20 transmitted from the optical transmitter 10 is changed while adjusting the polarization controller 14 (step S2). Then, by measuring the amplitude of the reception signal output from the amplitude adjusting means 70 (that is, the reception signals 60a to 60d input to the AD converter 81) according to the change of the polarization, the amplitude of the reception signal is measured. The maximum value is detected (step S3). Thereafter, the amplitude adjusting means 70 is adjusted so that the maximum value of the amplitude becomes a predetermined value (specifically, the optimum input level by the AD converter 81) (step S4).

  For example, in the case of the coherent optical receiver illustrated in FIG. 3, the input amplitude in every polarization state is traced with respect to the received signal 60a input to the AD converter 81a, and the peak value of the input amplitude is detected. Then, the amplitude adjusting unit 70a is adjusted so that the peak value of the input amplitude input to the AD converter 81a becomes a predetermined value. Hereinafter, the same adjustment is performed on the amplitude adjusting units 70b, 70c, and 70d that receive the reception signals 60b, 60c, and 60d.

  FIG. 5 is a flowchart illustrating an example of an adjustment method of the amplitude correction unit. By measuring the amplitude of the received signal output from the AD converter 81 according to the change of the polarization, the maximum value of the amplitude of the received signal is detected (step S5). Then, the amplitude is set so that the maximum value of the amplitude becomes a predetermined value (specifically, a value that is assumed to be output from the AD converter 81 when a reception signal of the optimum level is input to the AD converter 81). The correction unit 84 is adjusted (step S6).

  For example, in the case of the coherent optical receiver illustrated in FIG. 3, after the AD converter 81 digitizes each of the adjusted reception signals 60 a to 60 d, the amplitude correction unit 81 corrects when the AD converter 81 performs AD conversion. Adjust the value that did not fit. Specifically, after adjusting the amplitude adjusting means 70 to adjust the amplitudes of the received signals 60a to 60d, the amplitude detector 83a further converts the amplitude of the received signal 60a in any polarization state output from the AD converter 81a. Trace and detect its peak value. Then, the amplitude correction unit 84a is adjusted so that the peak value of the amplitude becomes a predetermined value. Hereinafter, the same adjustment is performed on the amplitude correction units 84b, 84c, and 84d that output the reception signals 60b, 60c, and 60d.

  Thereafter, the reception processing unit 85 performs dispersion compensation, polarization separation, and phase detection on each of the received signals 60a to 60d, and outputs the processed output signal 90 to the outside.

  As described above, in the present embodiment, when level adjustment is performed on the above-described received signals 60a to 60d, the wavelength dispersion unit 30 is provided between the optical transmitter 10 and the coherent optical receiver 40 as illustrated in FIG. Insert. By inserting the wavelength dispersion means 30, the measurement signal light 20 becomes a waveform having a random amplitude close to an actual transmission signal. In this way, by using the measurement signal light 20 having a random amplitude for adjustment, the levels of the received signals 60a to 60d can be adjusted more accurately.

  For example, as illustrated in FIG. 6, when the coherent light receiving device 40 is adjusted in a state where the wavelength dispersion unit 30 is not inserted between the light transmitting device 10 and the coherent light receiving device 40, the coherent light receiving device 40. The light received by has a waveform with a constant amplitude. Even if the level of the received signal is adjusted using such measurement signal light, it will be adjusted differently from the optimum point for use in the actual optical transmission line, resulting in deterioration in reception sensitivity and stability. There is a risk of deteriorating the sex.

  However, in this embodiment, the measurement signal light 20 can be brought close to the light state in the actual environment by giving the measurement signal light 20 wavelength dispersion by the wavelength dispersion means 30. Therefore, even when the coherent light receiver 40 is used in an actual environment, the coherent light receiver 40 can be adjusted so that the received coherent light can be corrected to an accurate signal level.

  Furthermore, by adjusting the amplitude adjusting unit 70 and the amplitude correcting unit 84 while changing the polarization state, it becomes possible to perform more accurate level adjustment.

Embodiment 2. FIG.
FIG. 7 is an explanatory diagram showing a configuration example of an apparatus used for the coherent optical receiver adjustment method according to the second embodiment of the present invention. In addition, about the structure similar to 1st Embodiment, the code | symbol same as FIG. 1 is attached | subjected and description is abbreviate | omitted. In the method for adjusting a coherent light receiving apparatus according to the present invention, an optical transmitting apparatus 10a, a wavelength dispersion means 30, and a coherent light receiving apparatus 40 are used.

  The optical transmission device 10a used in the present embodiment is also a device that outputs the measurement signal light 20. FIG. 8 is an explanatory diagram illustrating an example of the optical transmission device 10a used in the present embodiment. The optical transmission device 10a illustrated in FIG. 8 includes a light source 11, optical phase modulators 12a and 12b, and a polarization multiplexer 15. In the example illustrated in FIG. 8, the case where the optical transmission device 10 a includes two optical phase modulators is described, but the number of optical phase modulators is not limited to two.

  The optical phase modulators 12a and 12b receive the measurement signal light 20 output from the light source 11 and branched into two, and give the modulation signal 13a and 13b to the received measurement signal light 20, respectively. The measurement signal light 20 is phase-modulated. Note that the method in which the optical phase modulators 12a and 12b phase-modulate the measurement signal light 20 is the same as the method in which the optical phase modulator 12 performs phase modulation in the first embodiment.

  The polarization multiplexer 15 polarization-multiplexes the measurement signal light 20 output from the optical phase modulators 12a and 12b. In the present embodiment, the polarization multiplexer 15 is adjusted to have a plurality of polarization states by polarization multiplexing the measurement signal light 20. About another structure, it is the same as that of 1st Embodiment.

  Next, the operation will be described. First, as illustrated in FIG. 7, the optical transmission device 10 a illustrated in FIG. 8 is connected to the coherent light receiving device 40 illustrated in FIG. 3 via the wavelength dispersion unit 30. In the present embodiment, the polarization-multiplexed measurement signal light 20 is transmitted from the optical transmitter 10a. Then, the amplitude adjusting means 70a to 70d are adjusted so that the maximum values of the input levels of the received signals 60a to 60d to the AD converters 81a to 81d are the same. In this embodiment, since the measurement signal light is polarization multiplexed, there is no need to adjust the polarization controller 14. About subsequent operation | movement, it is the same as that of 1st Embodiment.

  Also by the method as described above, when the coherent light receiving device 40 is used in an actual environment, the coherent light receiving device 40 can be adjusted so that the received coherent light can be corrected to an accurate signal level.

  In addition, although a part or all of said embodiment can be described also as the following additional remarks, it is not restricted to the following.

(Additional remark 1) Polarization separation of the received measurement light, conversion means for converting the polarization-separated measurement light into an optical signal, and amplitude correction means for correcting the amplitude of the optical signal converted by the conversion means A coherent optical receiver adjustment method comprising: an optical transmitter that transmits measurement light to the coherent optical receiver; and a chromatic dispersion that imparts chromatic dispersion to the light between the coherent optical receiver By connecting the means, chromatic dispersion is given to the measurement light, the polarization of the measurement light transmitted from the optical transmitter is changed, and the amplitude of the optical signal output from the amplitude correction means is By measuring according to the polarization changing process, the maximum value of the amplitude of the optical signal is detected, and the amplitude correction means is adjusted so that the maximum value of the amplitude becomes a predetermined value. Coherent optical receiver Adjustment method.

(Supplementary Note 2) By measuring the amplitude of the optical signal output by the digital signal correcting unit that digitizes the optical signal corrected by the amplitude correcting unit and corrects the amplitude of the optical signal according to the polarization changing process, The adjustment method of the coherent optical receiver according to appendix 1, wherein the maximum value of the amplitude of the optical signal is detected and the digital signal correction unit is adjusted so that the maximum value of the amplitude becomes a predetermined value.

(Additional remark 3) The adjustment method of the coherent optical receiver of Additional remark 1 or Additional remark 2 which changes the polarization of the measurement light transmitted from an optical transmitter using a polarization controller.

(Additional remark 4) The adjustment method of the coherent optical receiver of Additional remark 1 or Additional remark 2 which changes the polarization of the measurement light transmitted from an optical transmitter using a polarization multiplexer.

(Supplementary Note 5) Any one of Supplementary Notes 1 to 4 that provides chromatic dispersion to the measurement light by connecting a dispersion-shifted fiber as a chromatic dispersion unit between the optical transmission device and the coherent light reception device. A method for adjusting a coherent light receiving device according to claim 1.

  The present invention is preferably applied when adjusting a coherent optical receiver.

DESCRIPTION OF SYMBOLS 10 Optical transmitter 11 Light source 12, 12a, 12b Optical phase modulator 13, 13a, 13b Modulated signal 14 Polarization controller 15 Polarization multiplexer 20 Measurement signal light 30 Wavelength dispersion means 40 Coherent optical receiver 50 Coherent optical detector 51 local light source 52 local light 53 90-degree optical hybrid 54a-54d optical receiver 60a-60d received signal 70a-70d amplitude adjusting means 80 signal processing unit 81a-81d AD converter 82 digital signal processing circuit 83a-83d amplitude detection unit 84a- 84d Amplitude correction section 85 Reception processing section 90 Output signal

Claims (4)

Conversion means for polarization-polarizing the received measurement light, converting the polarization-separated measurement light into an optical signal, and an amplitude correction means for correcting the amplitude of the optical signal converted by the conversion means A method for adjusting a coherent optical receiver,
By connecting wavelength dispersion means for giving chromatic dispersion to light between the optical transmission device that transmits the measurement light to the coherent light reception device and the coherent light reception device, chromatic dispersion is applied to the measurement light. Give,
Change the polarization of the measurement light transmitted from the optical transmitter,
By measuring the amplitude of the optical signal output from the amplitude correction means according to the polarization changing process, the maximum value of the amplitude of the optical signal is detected,
Adjust the amplitude correction means so that the maximum value of the amplitude becomes a predetermined value ,
By measuring the amplitude of the optical signal output by the digital signal correcting unit that digitizes the optical signal corrected by the amplitude correcting unit and correcting the amplitude of the optical signal in accordance with the polarization changing process, the optical signal is obtained. Detects the maximum amplitude of
An adjustment method for a coherent optical receiver , wherein the digital signal correction unit is adjusted so that the maximum value of the amplitude becomes a predetermined value . The polarization of the measuring light transmitted from the optical transmission device, adjusting method of the coherent light receiver according to claim 1, wherein the change with polarization controller. The polarization of the measuring light transmitted from the optical transmission device, adjusting method of the coherent light receiver according to claim 1, wherein the change with the polarization multiplexer. Between the optical transmitter and the coherent optical receiver, by connecting the dispersion shifted fiber as a wavelength dispersion unit, claimed in any one of claims 1 to 3 to provide a wavelength dispersion measuring light Adjustment method for coherent optical receivers.

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