JP2008017002A - Optical transmission system - Google Patents

Abstract

In the present invention, it is possible to provide an optical transmission system that can reduce the shift in wavelength characteristics between optical multiplexers / demultiplexers facing each other regardless of changes in the temperature environment, and that can construct an inexpensive system.
An optical transmission system according to the present invention includes two optical multiplexers / demultiplexers, an optical transmission line connecting the two optical multiplexers / demultiplexers, and two optical multiplexers / demultiplexers connected by the optical transmission line. The other optical multiplexer / demultiplexer so that the center wavelength of the pass wavelength band of the branch side port of the other optical multiplexer / demultiplexer corresponding to the branch side port matches the center wavelength of the pass wavelength band of any branch side port Wavelength characteristic control means for shifting the wavelength characteristic of the other optical multiplexer / demultiplexer while maintaining the interval between the center wavelengths of the optical multiplexer / demultiplexer.
[Selection] Figure 1

Description

  The present invention relates to an optical transmission system that multiplexes and transmits light of different wavelengths.

  A WDM-PON (Wavelength Division Multiplex-Passive Optical Network) system that multiplexes light of different wavelengths on one optical transmission line and enables communication between a plurality of users and one center is expected in the future. It is expected as a PON system in the broadband age. In the WDM-PON system, in order to multiplex light of different wavelengths, an optical multiplexer / demultiplexer such as AWG (Arrayed Waveguide Grating) is a key device for optical communication.

  However, in the optical multiplexer / demultiplexer, although the interval between the center wavelengths of the light to be demultiplexed is constant, the wavelength characteristic has temperature dependence, so the fluctuation of the center wavelength output from the optical multiplexer / demultiplexer with respect to the temperature. It is necessary to keep the absolute value constant by suppressing.

  For this reason, conventionally, for example, a wavelength control unit that controls the absolute value of the oscillation wavelength of light that is the basis of signal light output from the optical transmitter is provided in the optical transmitter, and the wavelength control unit is an optical multiplexer / demultiplexer. The oscillation wavelength has been adjusted so that the absolute value of the center wavelength output from is constant (see, for example, Patent Document 1). Also, a temperature control unit is provided to control the temperature of the optical multiplexer / demultiplexer itself, and the temperature controller controls the temperature of the optical multiplexer / demultiplexer itself so that the absolute value of the center wavelength output from the optical multiplexer / demultiplexer is constant. (For example, see Patent Document 2).

JP 2000-12949 A Japanese Patent Laid-Open No. 7-15384

  However, in the conventional optical transmission system, the wavelength is controlled for each optical transmitter as described in the cited document 1, or the temperature is controlled for each optical multiplexer / demultiplexer as described in the cited document 2. For this reason, the optical transmitter and the optical multiplexer / demultiplexer themselves are expensive, and all the optical transmitters and optical multiplexer / demultiplexers are configured with active components (components for managing the wavelength and temperature) in the optical transmission system. Therefore, enormous costs are required to construct the optical transmission system.

  In addition, when the optical multiplexer / demultiplexer is installed outdoors, it becomes an external temperature environment with a large difference between the temperature and the temperature, and the burden on the active parts is large, making it difficult to control the temperature of the optical multiplexer / demultiplexer. Furthermore, there is a risk of exposure to severe environmental conditions of high or low temperatures during the day or at night, resulting in a deviation from the wavelength characteristics of the opposing optical multiplexer / demultiplexers, and channel correspondence between the optical multiplexer / demultiplexers may be different. was there.

  In order to solve the above problems, in the present invention, the wavelength characteristic of one optical multiplexer / demultiplexer is made to follow the wavelength characteristic of the other optical multiplexer / demultiplexer among the two optical multiplexers / demultiplexers facing each other.

  Specifically, the optical transmission system according to the present invention includes a plurality of branch side ports through which light of different wavelengths are input / output and a backbone side port through which combined light in which the lights of different wavelengths are combined is input / output The two optical multiplexers / demultiplexers in which the wavelengths of the center wavelengths of the branch line side ports match each other, and the core side ports of the two optical multiplexers / demultiplexers are combined. The optical transmission line to be connected to the center wavelength of the passing wavelength band of one of the two optical multiplexers / demultiplexers, and the other optical multiplexer / demultiplexer corresponding to the branch port Wavelength characteristic control means for shifting the wavelength characteristic of the other optical multiplexer / demultiplexer while maintaining the interval of the center wavelengths of the other optical multiplexer / demultiplexer so that the center wavelengths of the passing wavelength bands of the branch side ports of the optical detector are matched And comprising. Thereby, the wavelength characteristic of the other optical multiplexer / demultiplexer can be made to follow the fluctuation of the wavelength characteristic of one optical multiplexer / demultiplexer. In addition, since the wavelength characteristics of the two optical multiplexers / demultiplexers can be matched only by controlling the wavelength characteristic of the other optical multiplexer / demultiplexer in this way, the wavelength characteristic of one optical multiplexer / demultiplexer is controlled. Therefore, it is possible to eliminate the necessity of providing active parts and to construct an inexpensive system.

  Further, when an optical transmitter is connected to the branch line side port of the optical multiplexer / demultiplexer, it is desirable to adjust the wavelength of the signal light output from the optical transmitter so that the transmission loss of the optical multiplexer / demultiplexer is minimized. . Thereby, the wavelength of the signal light output from the optical transmitter can be controlled so as to follow the fluctuation of the wavelength characteristic of the optical multiplexer / demultiplexer and fall within the wavelength band assigned to the branch line side port.

When adjusting the wavelength of the signal light output from the optical transmitter as described above, a part of the signal light output from the trunk side port of the optical multiplexer / demultiplexer to which the optical transmitter is connected is reflected to be optically combined. It is desirable to change the wavelength so that the light intensity of the signal light returning to the optical transmitter via the duplexer is maximized. Thereby, even if the wavelength characteristic of one optical multiplexer / demultiplexer changes with time, the wavelength of the signal light of the optical transmitter can be adjusted. Further, even if the optical transmitter is replaced, the wavelength of the optical transmitter can be automatically adjusted without changing other configurations, so that maintenance management is easy.

When shifting the wavelength characteristic of the other optical multiplexer / demultiplexer as described above, the monitor light is input to the main port of one optical multiplexer / demultiplexer and the branch side of one of the other optical multiplexer / demultiplexers Monitoring light output from the main port of one optical multiplexer / demultiplexer by reflecting the monitor light output from one of the branch side ports of one optical multiplexer / demultiplexer The wavelength of the monitor light is changed so that the intensity becomes maximum, and the monitor light output from the branch side port of the other optical multiplexer / demultiplexer, or the branch side port or the trunk side port of the other optical multiplexer / demultiplexer is output. The wavelength characteristic of the other optical multiplexer / demultiplexer is shifted so that the light intensity of the monitor light reflected from the monitor light output from the branch side port or the trunk side port of the other optical multiplexer / demultiplexer is maximized. Is desirable. Thereby, even if the wavelength characteristic of one optical multiplexer / demultiplexer changes with time, the wavelength characteristic of the other optical multiplexer / demultiplexer can be controlled. In addition, even if one optical multiplexer / demultiplexer is replaced, the wavelength characteristic of the other optical multiplexer / demultiplexer can be automatically controlled without changing the other configuration, so that maintenance management is easy.

  Also, when applying monitor light as described above, the monitor light is pulsed pulse monitor light, and an optical shutter is provided that conducts after a predetermined delay time in accordance with the emission timing of the pulse monitor light, It is desirable to receive pulse monitor light from the optical shutter. As a result, it is easy to take the timing of receiving the pulse monitor light, and only the pulse monitor light can be received without receiving other reflected light. Also, the reflected light from the other optical multiplexer / demultiplexer can be masked separately from the reflected light from one optical multiplexer / demultiplexer. Therefore, the control accuracy of the wavelength and wavelength characteristics can be improved.

  According to the present invention, it is possible to provide an optical transmission system capable of reducing the shift in wavelength characteristics between the optical multiplexers / demultiplexers facing each other regardless of changes in the temperature environment and capable of constructing an inexpensive system.

  Hereinafter, the present invention will be described in detail with specific embodiments, but the present invention is not construed as being limited to the following description.

(First embodiment)
FIG. 1 shows a schematic configuration diagram of an optical transmission system according to the present embodiment. FIG. 2 shows a schematic configuration diagram of a portion where an optical transceiver is connected to the optical multiplexer / demultiplexer.

  The optical transmission system 10 of FIG. 1 includes two optical multiplexers / demultiplexers 21, 22; an optical transmission line 23 that connects the trunk-side ports 33, 34 of the two optical multiplexers / demultiplexers 21, 22; Wavelength characteristic control means (to be described later) for controlling the wavelength characteristic of the wave multiplexer 22 and MC (Media) as an optical transceiver connected to the branch line side ports 31-1 to 31-n of one optical multiplexer / demultiplexer 21 Converter) 41.

  The optical multiplexer / demultiplexer 21 includes a plurality of branch-side ports 31-1 to 31-n through which light having different wavelengths are input / output, and a trunk-side port through which combined light in which the light having different wavelengths is combined is input / output. 33 multiplexes and demultiplexes light having different wavelengths. In the optical multiplexers / demultiplexers 21 and 22, the intervals of the center wavelengths of the branch line side ports 33 and 34 coincide with each other. As the optical multiplexer / demultiplexer 21, an optical multiplexer / demultiplexer such as an AWG, a Mach-Zehnder interferometer, a transversal filter, a lattice filter, or the like can be applied. As shown in FIG. 1, optical transmission / reception such as ONU (Optical Network Unit), OLT (Optical Line Terminal), etc. is used for the branch line side ports 31-1 to 31- (n-1) of the optical multiplexer / demultiplexer 21. Connected. The same applies to the branch line-side ports 32-1 to 32- (n-1) of the optical multiplexer / demultiplexer 22.

  The optical transmission line 23 connects the trunk side ports 33 and 34 of the optical multiplexers / demultiplexers 21 and 22, and optically couples the multiplexed light input to and output from the trunk side ports 33 and 34 of the two optical multiplexers / demultiplexers 21 and 22. Transmit between the demultiplexers 21 and 22. Examples of the optical transmission line 23 include an optical fiber and an optical waveguide, but any optical circuit or optical line that can transmit combined light may be used.

In this embodiment, the MC 41 as an optical transmitter / receiver transmits light of wavelength λ ₁ as upstream signal light and receives light of wavelength λ ₂ as downstream signal light, as shown in FIG. Here, the optical transmission system 10 of FIG. 1 includes transmitter wavelength control means for changing the wavelength of the signal light output from the MC 41 so that the transmission loss of the optical multiplexer / demultiplexer 21 is minimized. In this embodiment, as transmitter wavelength control means, as shown in FIG. 2, the optical coupler 42 provided in the middle of the optical transmission line 23 and the light from the optical coupler 42 provided at the output end 61 of the optical coupler 42 are used. And a reflector 43 that reflects with high reflectivity. The other output end 62 of the optical coupler 42 is a reflection end 44 having a low reflectivity.

The transmitter wavelength control means reflects a part of the signal light having the wavelength λ ₁ from the MC 41 by the reflector 43 and inputs it again to the trunk side port 33 of the optical multiplexer / demultiplexer 21, and passes through the optical multiplexer / demultiplexer 21. Adjustment is made by changing the wavelength λ ₁ of the signal light from the MC 41 so that the light intensity of the signal light returning to the MC 41 is maximized. For example, the wavelength λ ₁ can be adjusted by changing the temperature of the light source (not shown) provided in the MC 41 itself by a Peltier element (not shown). As a result, even if the wavelength of the signal light output from the MC 41 varies due to the temperature dependence of the wavelength characteristic of the optical multiplexer / demultiplexer 21, the branch-side port 31 follows the variation of the wavelength characteristic of the optical multiplexer / demultiplexer 21. It is possible to control to enter the wavelength band allocated to −1 to 31- (n−1). The same applies to the optical transceivers connected to the branch line side ports 32-1 to 32- (n-1) of the other optical multiplexer / demultiplexer 22 in FIG.

  In the present embodiment, the optical coupler 42 and the reflector 43 are provided as transmitter wavelength control means, but any means may be used as long as it can obtain information on the transmission loss of the optical multiplexer / demultiplexer 21. . For example, the wavelength characteristics depending on the temperature of the branch line side ports 31-1 to 31- (n-1) of the optical multiplexer / demultiplexer 21 are measured in advance, and the operation of the optical transmission system 10 is performed based on the measured wavelength characteristics. The wavelength of the MC 41 may be changed so that the transmission loss is minimized with the temperature of the optical multiplexer / demultiplexer at the time as a control variable. On the other hand, with the configuration in which the signal light output from the trunk side port 33 is reflected as in this embodiment, the wavelength of the signal light of the MC 41 can be changed even if the wavelength characteristics of the optical multiplexer / demultiplexer 21 change over time. Can be adjusted. Further, even if the MC 41 is replaced, the wavelength of the MC 41 can be automatically adjusted without changing other configurations, so that maintenance management is easy. The same applies to the optical transceivers connected to the branch line side ports 32-1 to 32- (n-1) of the other optical multiplexer / demultiplexer 22 in FIG.

  Further, since the optical multiplexer / demultiplexer 21 has temperature dependence on the wavelength characteristics, the optical transmission system 10 in FIG. 1 has the wavelength of the other optical multiplexer / demultiplexer 22 out of the two optical multiplexers / demultiplexers 21 and 22. Wavelength characteristic control means for controlling the characteristics is provided. The wavelength characteristic control means sets the other optical multiplexer / demultiplexer 22 corresponding to the branch port 31-n to the center wavelength of the passing wavelength band of any one branch port 31-n of the one optical multiplexer / demultiplexer 21. The wavelength characteristic of the other optical multiplexer / demultiplexer 22 is shifted while maintaining the interval of the center wavelengths of the other optical multiplexer / demultiplexer 22 so that the center wavelengths of the passing wavelength bands of the branch line side port 32-n of the other optical multiplexer / demultiplexer 22 match. In the present embodiment, as the light input means of the wavelength characteristic suppressing means, the light source 51 that emits monitor light, the optical coupler 53 provided in the middle of the optical transmission path 23, and the light provided at the output end 63 of the optical coupler 53. And a reflector 57 that reflects the light from the coupler 53 with high reflectivity. In addition to this, the optical multiplexer / demultiplexer is provided at a specific branch line side port 31-n of one optical multiplexer / demultiplexer 21 as wavelength characteristic suppression means. Reflector 54 that reflects light from wave 21 with high reflectivity, optical circulator 52, light receiving unit 55 that receives monitor light from optical circulator 52, and light intensity of monitor light received by light receiving unit 55 , A wavelength control unit 56 that controls the wavelength of the light source, a light receiving unit 58 that receives monitor light output from a specific branch-side port 32-n of the other optical multiplexer / demultiplexer 22, and a light receiving unit 58 that receives the light. Intensity of monitored light It provided based on a temperature control unit 59 for controlling the temperature of the optical demultiplexer 22, a.

  The light source 51 emits monitor light having a wavelength λp. The monitor light is preferably pulsed pulse monitor light, but may be continuous light as long as it can be distinguished from other signal light by the light receiving portions 55 and 58. The pulsed pulse monitor light emitted from the light source 51 is input to the trunk side port 33 of one optical multiplexer / demultiplexer 21 via the optical circulator 52 and the optical coupler 53. Then, it is output from the branch line side port 31-n of the optical multiplexer / demultiplexer 21, is reflected by the reflector 54, and is input again to the branch line side port 31-n. One optical multiplexer / demultiplexer 21, the optical coupler 53, and the optical circulator 52 are reflected. Is received by the light receiving unit 55. At this time, the pulse monitor light reflected from the reflector 57 is masked, and only the pulse monitor light from the reflector 54 is received. The light receiving unit 55 outputs an electric signal corresponding to the light intensity of the received pulse monitor light toward the wavelength control unit 56. The wavelength controller 56 determines the wavelength of the pulse monitor light so that the light intensity of the pulse monitor light is maximized based on the light intensity of the monitor light received by the light receiver 55 measured from the electrical signal from the light receiver 55. Adjust by changing λp. For example, the wavelength λp can be adjusted by changing the temperature of the light source 51 itself by a Peltier element.

  On the other hand, the pulse monitor light reflected by the reflector 57 is input to the trunk side port 34 of the other optical multiplexer / demultiplexer 22. Then, the light is output from the branch line side port 32-n of the optical multiplexer / demultiplexer 22 and received by the light receiving unit 58. At this time, the pulse monitor light reflected from the reflector 54 is masked, and only the pulse monitor light from the reflector 57 is received. The light receiving unit 58 outputs an electric signal corresponding to the light intensity of the received pulse monitor light toward the temperature control unit 59. The temperature controller 59 is an optical multiplexer / demultiplexer so that the light intensity of the pulse monitor light is maximized based on the light intensity of the pulse monitor light received by the light receiver 58 measured from the electrical signal from the light receiver 58. The temperature of 22 is changed. For example, the temperature of the optical multiplexer / demultiplexer 22 itself can be changed by a Peltier element. Here, when the temperature of the optical multiplexer / demultiplexer 22 is changed, for example, when the temperature of the entire optical path of the optical multiplexer / demultiplexer 22 is controlled, the center wavelength interval can be shifted while being kept constant.

  Here, the wavelength controller 56 can control the wavelength as follows. The temperature controller 59 can control the temperature as follows. For example, the wavelength control unit 56 changes the wavelength of the light source 51 from one wavelength to either the long side or the short side, and when the transmission loss of the optical multiplexer / demultiplexer 21 increases, the wavelength of the light source 51 is changed to the opposite direction. Shift. On the other hand, when the transmission loss of the optical multiplexer / demultiplexer 21 decreases, the wavelength of the light source 51 is further shifted in the same direction. The increase / decrease in the transmission loss of the optical multiplexer / demultiplexer 21 corresponds to the increase / decrease in the received light intensity in the light receiving unit 55. By repeating this operation while detecting increase / decrease in transmission loss of the optical multiplexer / demultiplexer 21, the wavelength of the light source 51 can be set to the optimum wavelength. Then, after the wavelength of the light source 51 is set, the temperature control unit 59 changes the temperature of the optical multiplexer / demultiplexer 22 from a certain temperature to either the higher side or the lower side, and the transmission of the optical multiplexer / demultiplexer 22 is performed. When the loss increases, the temperature of the optical multiplexer / demultiplexer 22 is shifted in the opposite direction. On the other hand, when the transmission loss of the optical multiplexer / demultiplexer 22 decreases, the temperature of the optical multiplexer / demultiplexer 22 is further shifted in the same direction. The increase / decrease in the transmission loss of the optical multiplexer / demultiplexer 22 corresponds to the increase / decrease in the received light intensity in the light receiving unit 58. By repeating this operation while detecting increase / decrease in transmission loss of the optical multiplexer / demultiplexer 22, the temperature of the optical multiplexer / demultiplexer 22 can be set to the optimum temperature. When controlling the wavelength of the light source 51 and the temperature of the optical multiplexer / demultiplexer 22 in this manner, the wavelength control unit 56 controls the wavelength after the wavelength control unit 56 controls the wavelength, and the temperature control unit 59 controls the temperature. The temperature control unit 59 needs to control the wavelength or temperature by changing the control time.

  Further, the wavelength control unit 56 may control the wavelength as follows. The temperature controller 59 may control the temperature as follows. For example, the wavelength control unit 56 changes the wavelength of the light source 51 with a certain period centered on a certain wavelength (center wavelength). In this case, the transmission loss of the optical multiplexer / demultiplexer 21 also changes with a certain period. Here, since the phase of the change in the transmission loss of the optical multiplexer / demultiplexer 21 is reversed when the transmission loss of the optical multiplexer / demultiplexer 21 becomes the minimum, the wavelength control unit 56 transmits the transmission of the optical multiplexer / demultiplexer 21. The phase of the loss change is detected, and the center wavelength of the light source 51 is shifted in the direction in which the phase is opposite. At this time, the closer the transmission loss of the optical multiplexer / demultiplexer 21 is to the minimum, the smaller the amplitude of the change in the transmission loss of the optical multiplexer / demultiplexer 21 becomes. Therefore, the wavelength control unit 56 determines the shift amount of the center wavelength of the light source 51 by detecting and feeding back the amplitude of the transmission loss change of the optical multiplexer / demultiplexer 21, and sets the wavelength of the light source 51 to the optimum wavelength. can do. On the other hand, similarly, the temperature control unit 59 detects the phase of the transmission loss change of the optical multiplexer / demultiplexer 22 and shifts the center temperature of the optical multiplexer / demultiplexer 22 in the direction in which the phase becomes an opposite phase. The temperature of the waver 22 can be set to the optimum temperature. Note that the cycle of changing the temperature in the temperature control unit 59 needs to be appropriately determined according to the response speed of the transmission loss with respect to the temperature change in the temperature control unit 59. In this way, when controlling the wavelength of the light source 51 and the temperature of the optical multiplexer / demultiplexer 22, if the light having the frequency of the wavelength change in the wavelength control unit 56 is filtered in the light receiving unit 58, only the center wavelength of the light source 51 is obtained. Since it can be detected, the wavelength control unit 56 and the temperature control unit 59 can simultaneously control the wavelength or temperature.

  Here, the pulse monitor light uses the center wavelength of the branch line side port 31-n (outermost side) of the optical multiplexer / demultiplexer 21 and the branch line side ports 31-1 to 31- (n of the optical multiplexer / demultiplexer 21). It is applicable to any case of using light in the vicinity of any one of the center wavelengths of -1). However, when using light in the vicinity of the center wavelength of the branch side ports 31-1 to 31- (n-1) of the optical multiplexer / demultiplexer 21, pulse monitor light passes through the optical multiplexer / demultiplexer 21 in advance. A channel (monitor channel) must be installed. The monitor channel is determined according to the wavelength of the pulse monitor light.

  Further, in order to mask the pulse monitor light from the reflector 57 in the light receiving unit 55, the pulse monitor light output from the trunk side port 33 via the one optical multiplexer / demultiplexer 21 is cut off from the reflector 54, and the light source. It is desirable to provide an optical shutter (not shown) that is turned on after a predetermined delay time has elapsed in accordance with the emission timing of the pulse monitor light. In this case, the optical shutter is provided in front of the light receiving unit 55, for example. The predetermined delay time is set to, for example, a propagation delay time from when the pulse monitor light is emitted from the light source 51 to when the pulse monitor light is reflected by the reflector 54 and returns to the optical shutter. When the optical shutter is provided in front of the light receiving unit 55, the optical shutter blocks light incident on the light receiving unit 55, and a predetermined delay time elapses when the pulse monitor light is emitted from the light source 51 as a trigger. Later, the shutter is opened to allow the pulse monitor light to pass through. Then, after the elapse of the time when the pulse of the pulse monitor light rises, the shutter is closed again to block the light incident on the light receiving unit 55. Thus, when the monitor light is pulsed, the light receiving unit 55 can easily take the light reception timing of the pulse monitor light, and can receive only the pulse monitor light from the reflector 54. Also, the reflected light from the optical multiplexer / demultiplexer 22 can be masked separately from the reflected light from the optical multiplexer / demultiplexer 21. Therefore, in the optical transmission system 10, the control accuracy in the wavelength control unit 56 can be improved. The same applies to the light receiving unit 58. The predetermined delay time of the optical shutter (not shown) in the light receiving unit 58 is a propagation delay from when the pulse monitor light is emitted from the light source 51 until the pulse monitor light is reflected by the reflector 57 and returns to the optical shutter. Set to time.

  In the present embodiment, the pulse monitor light output from the branch line side port 32-n is received by the light receiving unit 58. However, the pulse monitor light output from the branch line side port 32-n is further reflected to be on the branch line side. Returning to the port 32-n, the pulse monitor light output from the trunk side port 34 of the optical multiplexer / demultiplexer 22 may be received on the output end 63 side of the optical coupler 53 in which the reflector 57 is provided. Further, as in the present embodiment, the pulse monitor light is not input from the trunk side port 34 of the optical multiplexer / demultiplexer 22 but is further input from the branch side port 32-n and output from the trunk side port 34. It may be reflected and returned to the trunk side port 34 to receive the pulse monitor light output from the branch line side port 32-n of the optical multiplexer / demultiplexer 22.

  In this embodiment, an example in which pulse monitor light is applied as the wavelength characteristic control unit is described. However, the wavelength characteristic control unit is connected to one of the branch side ports 31-n of one optical multiplexer / demultiplexer 21. Any means may be used as long as it is a means for controlling the center wavelength of the pass wavelength band of the branch side port 32-n of the other optical multiplexer / demultiplexer 22 from the information on the center wavelength of the pass wavelength band. For example, a wavelength characteristic depending on the temperature of the branch line side port 31-n of one optical multiplexer / demultiplexer 21 is measured in advance, and one optical multiplexing / demultiplexing operation of the optical transmission system 10 is performed based on the measured wavelength characteristic. The temperature of the other optical multiplexer / demultiplexer 22 may be controlled using the temperature of the duplexer 21 as a control variable. In this case, it is necessary to transmit the temperature information of one optical multiplexer / demultiplexer 21 to the other optical multiplexer / demultiplexer 22. On the other hand, by adopting a configuration in which monitor light (pulse monitor light in this embodiment) is emitted as in this embodiment, even if the wavelength characteristics of the optical multiplexer / demultiplexer 21 change over time, the other optical multiplexer / demultiplexer is used. The 22 wavelength characteristics can be controlled. Further, even if one optical multiplexer / demultiplexer 21 is replaced, the wavelength characteristic of the other optical multiplexer / demultiplexer 22 can be automatically controlled without changing the other configuration, so that maintenance management is easy.

  Further, in the present embodiment, an example is described in which the temperature of the optical multiplexer / demultiplexer 22 itself is controlled as means for controlling the center wavelength of the passing wavelength band of the branch line side port 32-n of the other optical multiplexer / demultiplexer 22. However, the means may be any means as long as the means shifts the wavelength characteristic of the other optical multiplexer / demultiplexer while maintaining the interval of the center wavelength of the other optical multiplexer / demultiplexer 22. For example, when a wavelength filter such as AWG is applied as the optical multiplexer / demultiplexer 22, a resin is inserted in the middle of the waveguide path of the wavelength filter, and the temperature of the resin is changed. The wavelength characteristic of the optical multiplexer / demultiplexer 22 can be shifted while maintaining. Further, even when the filter surface of the AWG is pressed, the wavelength characteristics of the optical multiplexer / demultiplexer 22 can be shifted while maintaining the center wavelength interval. In AWG, by changing the refractive index of the entire optical waveguide in the same direction at the same time, it is possible to shift the central wavelength while keeping the interval constant. When AWG is applied as the other optical multiplexer / demultiplexer 22, the wavelength of the other optical multiplexer / demultiplexer 22 is controlled using information on the center wavelength of the passing wavelength band of the branch line side port 31-n of one optical multiplexer / demultiplexer 21 as a control variable. The characteristics can be shifted. Further, when controlling the wavelength characteristic of the optical multiplexer / demultiplexer 22, as described above, the wavelength characteristic of the optical multiplexer / demultiplexer 22 is shifted in either direction, and the branch line side port 32-n of the optical multiplexer / demultiplexer 22 is shifted. The center wavelength of the branch-side port 31-n of the optical multiplexer / demultiplexer 21 and the optical multiplexer / demultiplexer 22 are detected by detecting the light intensity of the center wavelength of the optical multiplexer / demultiplexer and detecting the increase / decrease of the light intensity or the phase of the change of the light intensity. The wavelength characteristic can be shifted to an optimum position by shifting the wavelength characteristic in a direction in which the shift amount of the center wavelength of the branch line side port 32-n is reduced.

  As described above, in the optical transmission system 10, on the assumption that the grid wavelength interval is fixed, the optical wavelength is independent of the width of the grid wavelength interval defined in the so-called ITU (International Telecommunication Union). The wavelength characteristics of the duplexers 21 and 22 can be matched. Thereby, the optical transmission system 10 can make the wavelength characteristic of the other optical multiplexer / demultiplexer 22 follow the fluctuation of the wavelength characteristic of one optical multiplexer / demultiplexer 21. In addition, since the wavelength characteristics of the two optical multiplexers / demultiplexers 21 and 22 can be matched only by controlling the wavelength characteristic of the other optical multiplexer / demultiplexer 22 in this way, the one optical multiplexer / demultiplexer 21 is controlled. Therefore, it is possible to eliminate the necessity of providing an active component for the purpose and to construct an inexpensive system.

(Second embodiment)
FIG. 3 shows a schematic configuration diagram when the optical transmission system according to the present embodiment is specifically applied to the WDM-PON system. FIG. 3 shows an example of triple play in which three lines of Internet connection, IP phone, and video signal are combined on one line. Here, the components having the same reference numerals as the components described in FIG.

  In the optical transmission system 11 of FIG. 3, a video network 71, a communication business station 72 to which the IP network and the telephone network are connected, and a customer connected to the video network 71 and the communication business station 72 via the optical multiplexer / demultiplexer 21. Homes 73-1 to 73- (n-1).

  In the video network 71, an analog video source 81 and a digital video source 82 are connected to an electrical stage multiplex conversion unit 83 by a coaxial cable, output as a video signal, and connected to an optical modulator 87. Also, light of a plurality of wavelengths output from the light sources 85-1 to 85- (n-1) is multiplexed via the optical multiplexer 86, modulated by the video signal in the optical modulator 87, and output as a video light signal. Is done. The video light signal from the modulator 87 is amplified by the optical amplifier 88, coupled to the optical transmission line 23 by the optical coupler 89, and transmitted toward the optical multiplexer / demultiplexer 21. Further, the IP network and the telephone network are connected to the customer homes 73-1 to 73- (n-1) via the optical multiplexers / demultiplexers 22 and 21 by the OLT 91 and MCs 92-1 to 92-4 provided in the communication business station 72. Is done. In the customer premises 73-1 to 73- (n-1), a PC 96 that enables Internet connection and IP telephone connection for each of the customer premises 73-1 to 73- (n-1) and digital that can receive digital video signals. Communication equipment such as the TV 97 is connected via the MC 94 and the ONU 95. The MC 94 and the ONU 95 are connected to the optical splitter 93 and receive the signal light transmitted through the optical transmission path 23.

  In the optical transmission system 11 according to the present embodiment, the optical multiplexer / demultiplexer 21 on the normal customer homes 73-1 to 73- (n-1) side is installed outdoors, and the other optical multiplexer / demultiplexer on the communication business station 72 side. The device 22 is installed in the communication business station 72. In this case, the temperature environment of the optical multiplexer / demultiplexer 22 installed in the communication business station 72 is more constant than the temperature environment of the optical multiplexer / demultiplexer 22 installed outdoors. Therefore, the burden on the active component is reduced, and the temperature control of the optical multiplexer / demultiplexer 22 becomes easy. Therefore, by adopting such a configuration, the optical transmission system 11 follows the wavelength characteristic of the optical multiplexer / demultiplexer 22 installed in the communication business station 72 to the fluctuation of the wavelength characteristic of the optical multiplexer / demultiplexer 21 installed outdoors. Can be made. That is, a system that follows the wavelength characteristics of each component of the entire optical transmission system 11 with reference to the wavelength characteristics of the optical multiplexer / demultiplexer 21 that is installed outdoors, which varies mainly with temperature, can be provided. Therefore, no matter how the wavelength characteristic of the optical multiplexer / demultiplexer 21 installed outdoors varies, the possibility of a discrepancy between the branch line side ports of the optical multiplexer / demultiplexer 22 facing each other can be reduced. In addition, the optical multiplexer / demultiplexer 21 installed outdoors can be constructed with only passive elements because a temperature control circuit is not required, so that an inexpensive and high-performance access network configuration is possible. Further, since the transmission wavelength can be automatically set by connecting an optical transceiver such as an ONU installed in the customer premises 73-1 to 73- (n-1), for example, an optical transceiver such as an ONU when moving. This can contribute to the reduction of the amount of use and maintenance equipment.

    The optical transmission system of the present invention can be applied to an access network or a LAN (Local Area Network).

1 is a schematic configuration diagram illustrating an optical transmission system according to an embodiment. It is the schematic block diagram which showed the part by which the optical transmitter / receiver was connected to the optical multiplexer / demultiplexer. It is the schematic block diagram which showed the case where the optical transmission system which concerns on one Embodiment is applied concretely to a WDM-PON system.

Explanation of symbols

10, 11: Optical transmission systems 21, 22: Optical multiplexer / demultiplexer 23: Optical transmission paths 31-1 to 31-n, 32-1 to 32-n: Branch line side ports 33, 34: Main side port 41: MC
42: Optical couplers 43, 54, 57: Reflector 44: Reflecting end 51: Light source 52: Optical circulator 53: Optical coupler 55, 58: Light receiving unit 56: Wavelength control unit 59: Temperature control units 61, 62, 63: Output Terminal 71: Video network 72: Communication business station 73-1 to 73- (n-1): Customer home 81: Analog video source 82: Digital video source 83: Electrical stage multiplex conversion unit 85-1 to 85- (n- 1): Light source 86: Optical multiplexer 87: Optical modulator 88: Optical amplifier 89: Optical coupler 91: OLT
92-1 to 92-4, 94: MC
93: Optical splitter 95: ONU
96: PC
97: Digital TV

Claims (5)

The light of different wavelengths is multiplexed / demultiplexed between a plurality of branch side ports to / from which light of different wavelengths is input / output and the trunk side port to / from which multiplexed light of combined light of different wavelengths is input / output Two optical multiplexers / demultiplexers in which the distances between the center wavelengths of the branch line side ports coincide with each other;
An optical transmission line that connects the fundamental ports of the two optical multiplexers / demultiplexers;
One of the two optical multiplexers / demultiplexers passes through the branch side port of the other optical multiplexer / demultiplexer corresponding to the branch side port at the center wavelength of the pass wavelength band of one of the branch side ports of one of the optical multiplexers / demultiplexers Wavelength characteristic control means for shifting the wavelength characteristic of the other optical multiplexer / demultiplexer while maintaining the interval of the central wavelengths of the other optical multiplexer / demultiplexer so as to match the center wavelength of the wavelength band;
An optical transmission system comprising: An optical transmitter connected to the branch line side port of the optical multiplexer / demultiplexer;
The signal light output from the optical transmitter so that the transmission loss between the branch side port of the optical multiplexer / demultiplexer to which the optical transmitter is connected and the trunk side port of the optical multiplexer / demultiplexer is minimized. Transmitter wavelength control means for changing the wavelength;
The optical transmission system according to claim 1, further comprising:   The transmitter wavelength control means reflects a part of the signal light output from the basic port of the optical multiplexer / demultiplexer to which the optical transmitter is connected, and inputs the reflected light again to the basic port, so that the optical transmission is performed. Receiving the signal light returning to the optical transmitter via the optical multiplexer / demultiplexer to which the optical signal is connected, and changing the wavelength of the signal light so that the light intensity of the received signal light is maximized. The optical transmission system according to claim 2. The wavelength characteristic control means is an optical input means for emitting monitor light, inputting the monitor light to the trunk side port of the one optical multiplexer / demultiplexer, and inputting it to the branch line side port or the trunk side port of the other optical multiplexer / demultiplexer. With
Reflecting the monitor light output from any branch side port of the one optical multiplexer / demultiplexer via the one optical multiplexer / demultiplexer from the optical input means, and inputting the reflected light again to the branch side port, The monitor light output from the main port of the one optical multiplexer / demultiplexer via the one optical multiplexer / demultiplexer is received, and the light input means is configured to maximize the light intensity of the received monitor light. The monitor light that changes the wavelength of the emitted monitor light and that is output from the branch-side port of the other optical multiplexer / demultiplexer from the optical input means via the other optical multiplexer / demultiplexer, or the light The monitor light output from the main port or branch side port of the other optical multiplexer / demultiplexer via the other optical multiplexer / demultiplexer from the input means is reflected again to the main port or branch side port. Enter the above The monitor light output from the main port or branch line side port of the other optical multiplexer / demultiplexer via the other optical multiplexer / demultiplexer is received, and the light intensity of the received monitor light is maximized. 4. The optical transmission system according to claim 1, wherein the wavelength characteristic of the other optical multiplexer / demultiplexer is shifted. The light input means emits pulsed pulse monitor light,
The wavelength characteristic control unit is configured to output the pulse monitor light output from the trunk side port of the one optical multiplexer / demultiplexer, and / or the trunk side port or branch line side port of the other optical multiplexer / demultiplexer. An optical shutter that cuts off the pulse monitor light and conducts after a predetermined delay time in accordance with the emission timing of the pulse monitor light from the light input means,
The optical transmission system according to claim 4, wherein the pulse monitor light from the optical shutter is received.

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