JP5957857B2 - Optical transmitter - Google Patents

Description

  The present invention relates to an optical transmitter used in, for example, an optical transmission system.

  Patent Document 1 discloses an optical transmission system having a plurality of laser elements and an optical multiplexer. This optical transmission system prevents variations in the intensity of the optical signal due to variations in the loss of the optical signal of each wavelength. Specifically, a control circuit that monitors the optical signal controls the plurality of laser elements so that the intensity of the optical signal is kept constant.

JP-A-9-261205

  By the way, the optical signal multiplexed by the optical transmitter is amplified by the optical fiber amplifier and then transmitted to the receiver. The signal amplification factor of the optical signal by the optical fiber amplifier is different for each wavelength. That is, an optical signal with a certain wavelength is amplified with a large signal amplification factor, and an optical signal with another wavelength is amplified with a small signal amplification factor. Therefore, there is a problem that the intensity of the optical signal of each wavelength transmitted to the receiver cannot be made uniform. Further, when an attenuator or the like is used to make the intensity of the optical signal transmitted to the receiver uniform, there is a problem that the optical transmission system becomes large.

  The present invention has been made to solve the above-described problems. An optical transmitter capable of equalizing the intensity of an optical signal of each wavelength transmitted to a receiver without increasing the size of the optical transmission system. The purpose is to provide.

An optical transmitter according to the invention of the present application emits laser light having different wavelengths, a plurality of laser elements whose intensity of the laser light is variable, a modulator that modulates the laser light into an optical signal, A multiplexer that outputs the multiplexed optical signal multiplexed to the optical fiber amplifier, and the wavelength dependence of the intensity of the amplified optical signal that is the multiplexed optical signal amplified by the optical fiber amplifier is eliminated. A controller that changes the intensity of the laser light of the plurality of laser elements , and the controller changes the signal amplification factor of the optical fiber amplifier according to the number of optical signals constituting the multiplexed optical signal. Reflecting this, the intensity of the laser beam of the plurality of laser elements is changed .

  According to the present invention, the controller arranged in the optical transmitter adjusts the output of the laser element, so that the wavelength dependence in the intensity of the amplified optical signal can be eliminated.

It is a block diagram which shows the optical transmitter etc. which concern on Embodiment 1 of this invention. It is a figure which shows the memory content of the memory with which a controller is provided. It is a flowchart which shows control of the laser element by a controller. It is a figure which shows the output of the optical fiber amplifier before and after the laser beam intensity of a laser element is changed by a controller. It is a block diagram which shows the optical transmitter etc. which concern on Embodiment 2 of this invention. It is a flowchart which shows operation | movement of a transmitter.

Embodiment 1 FIG.
FIG. 1 is a block diagram showing an optical transmitter and the like according to Embodiment 1 of the present invention. The optical transmitter 10 according to the first embodiment of the present invention includes a laser element 12a and a laser element 12b that emit laser beams having different wavelengths. The wavelength of the laser beam of the laser element 12a is λ1, and the wavelength of the laser beam of the laser element 12b is λ2. In the laser elements 12a and 12b, the intensity and wavelength of the laser light are variable. The laser element 12a is connected to the modulator 14a. The modulator 14a modulates the laser beam into an optical signal. The laser element 12b is connected to the modulator 14b.

  The modulator 14a is connected to the light intensity monitor 16a. The modulator 14b is connected to the light intensity monitor 16b. The light intensity monitors 16a and 16b detect the intensity of the optical signal. The light intensity monitors 16 a and 16 b are connected to the multiplexer 18. The multiplexer 18 multiplexes optical signals having different wavelengths. The optical signal multiplexed by the multiplexer 18 is referred to as a “multiplexed optical signal”. The multiplexer 18 is connected to the optical fiber amplifier 20. The multiplexer 18 outputs the multiplexed optical signal to the optical fiber amplifier 20. The optical fiber amplifier 20 amplifies the multiplexed optical signal in order to extend the transmission distance of the multiplexed optical signal. The multiplexed optical signal amplified by the optical fiber amplifier 20 is referred to as “amplified optical signal”.

  The optical transmitter 10 includes a controller 17. Functionally speaking, the controller 17 changes the intensity of the laser light of the laser elements 12a and 12b so as to eliminate the wavelength dependence of the intensity of the amplified optical signal. A specific configuration of the controller 17 will be described. The controller 17 includes a memory 17a, an acquisition unit 17b, a calculation unit 17c, and an adjustment unit 17d.

  The memory 17 a stores the wavelength dependence of the signal amplification factor of the optical fiber amplifier 20. FIG. 2 is a diagram illustrating the contents stored in the memory 17 a included in the controller 17. The memory 17a stores the signal amplification factor in digital information for each wavelength that the laser elements 12a and 12b can take.

  The acquisition unit 17b is a unit that acquires the detection results of the light intensity monitors 16a and 16b. The computing unit 17c is a unit that obtains a predicted value of the intensity of the amplified optical signal by multiplying the signal amplification factor by the detection result of the intensity monitor for each wavelength. The adjusting unit 17d is a unit that changes the intensity of the laser light of the laser elements 12a and 12b so that the wavelength dependence of the intensity of the amplified optical signal in the predicted value is eliminated. The acquisition unit 17b, the calculation unit 17c, and the adjustment unit 17d are configured by, for example, a microcomputer.

  FIG. 3 is a flowchart showing control of the laser element by the controller. The operation of the optical transmitter 10 according to the first embodiment of the present invention will be described with reference to FIG. First, the controller 17 reads out signal amplification factors of optical signals of wavelengths λ1 and λ2 by the optical fiber amplifier 20 from the memory 17a (step 21). The signal amplification factor for the optical signal with wavelength λ1 is A1, and the signal amplification factor for the optical signal with wavelength λ2 is A2. Next, the intensity of the optical signal detected by the light intensity monitors 16a and 16b is acquired by the acquisition means 17b (step 22). The light intensity of the optical signal having the wavelength λ1 is S1, and the intensity of the optical signal having the wavelength λ2 is S2.

  Next, the predicted value of the intensity of the amplified optical signal is calculated by the calculating means 17c (step 23). The calculation result is referred to as “predicted value”. The predicted value is calculated for each wavelength. The predicted value (P1) of the wavelength λ1 is obtained by multiplying A1 and S1. The predicted value (P2) of the wavelength λ2 is obtained by multiplying A2 and S2.

  Here, since the signal amplification factor by the optical fiber amplifier 20 has wavelength dependency, P1 and P2 have different values. Therefore, the adjusting means 17d changes the intensity of the laser light of the laser elements 12a and 12b so that P1 and P2 are equal (step 24). Specifically, the adjusting means 17d is configured so that the laser light intensity (optimum laser light intensity O1) of the laser element 12a and the laser light intensity of the laser element 12b (optimum laser light intensity O2) for making P1 and P2 equal. Is calculated. Then, the laser elements 12a and 12b are controlled so that the intensity of the laser light from the laser element 12a becomes O1 and the intensity of the laser light from the laser element 12b becomes O2.

  FIG. 4 is a diagram illustrating the output of the optical fiber amplifier before and after the controller changes the intensity of the laser light of the laser element. FIG. 4A shows the output of the optical fiber amplifier 20 after the controller 17 controls the laser elements 12a and 12b. FIG. 4B shows the output of the optical fiber amplifier 20 before the control by the controller 17. As a result of changing the intensity of the laser beams of the laser elements 12a and 12b by the controller 17, the intensity of the amplified optical signal can be made uniform between the wavelengths. 4 indicates that the intensity of optical signals having wavelengths other than λ1 and λ2 can be made uniform.

  As described above, according to the optical transmitter 10 according to the first embodiment of the present invention, the amplified optical signal transmitted to the receiver is wavelength-dependent by adjusting the intensity of the laser light of the laser elements 12a and 12b. Can be made uniform. Further, since the controller 17 and the light intensity monitors 16a and 16b necessary for controlling the laser elements 12a and 12b described above are formed inside the optical transmitter 10, the optical transmitter 10 and the optical fiber amplifier 20 are included. The configuration of the optical transmission system can be simplified. Since all the processes for obtaining the above-described effects are completed inside the optical transmitter 10, it is not necessary to incorporate a measuring means such as a spectrum monitor for measuring the optical output of the optical transmitter 10 in the optical transmission system. Can be manufactured at low cost.

  In the optical transmitter 10 according to Embodiment 1 of the present invention, the number of laser elements is two, but the present invention is not limited to this. The present invention eliminates the wavelength dependence of the intensity of an amplified optical signal when a plurality of laser elements emit laser beams having different wavelengths. Therefore, the number of laser elements is not particularly limited as long as it is plural. By the way, when the total number of laser elements, that is, the number of inputs to the optical fiber amplifier is changed, the signal amplification factor of the optical fiber amplifier changes. Therefore, it is desirable to store in the memory 17a a signal amplification factor table that is distinguished for each number of inputs to the optical fiber amplifier (total number of laser elements). If the laser element is controlled using a table corresponding to the number of inputs to the optical fiber amplifier, control with higher accuracy can be performed. Instead of storing the aforementioned table in the memory, the signal amplification factor corresponding to the number of inputs may be calculated using the number of inputs to the optical fiber as a variable in the controller. In this way, it is not necessary to incorporate an optical passband filter or peak value detection means in the optical transmission system in order to cope with a change in the number of inputs, so that the configuration of the optical transmission system can be simplified.

  The memory 17a according to the first embodiment of the present invention stores a table in which the wavelength dependence of the signal amplification factor is converted into digital information. You may remember.

Embodiment 2. FIG.
The transmitter according to Embodiment 2 of the present invention will be described focusing on the differences from the transmitter according to Embodiment 1 described above. FIG. 5 is a block diagram showing an optical transmitter and the like according to Embodiment 2 of the present invention. The optical transmitter 30 includes a main controller 32 and sub-controllers 34 and 35. The sub-controllers 34 and 35 are connected to the main controller 32 and are connected to the laser elements 12a and 12b, respectively. The sub-controller 34, the laser element 12a, the modulator 14a, and the light intensity monitor 16a constitute an assembly 36a. The sub-controller 35, the laser element 12b, the modulator 14b, and the light intensity monitor 16b constitute an assembly 36b.

  The main controller 32 has a memory 32 a that stores the wavelength dependence of the signal amplification factor of the optical fiber amplifier 20. And it has the correction amount calculating means 32b which reads the memory | storage of the memory 32a and calculates the correction amount of the intensity | strength of an optical signal required in order to eliminate the wavelength dependence of the intensity | strength of an optical signal after amplification. Furthermore, it has a notification means 32c for notifying the correction amounts to the sub-controllers 34 and 35.

  The sub-controller 34 has an acquisition unit 34a that acquires the detection result of the light intensity monitor 16a. And it has the target intensity | strength calculating means 34b which calculates a target intensity | strength of the laser beam of the laser element 12a by multiplying a detection result and a correction amount. The target intensity is the intensity of the laser beam that can eliminate the wavelength dependence of the intensity of the amplified optical signal. Furthermore, it has the adjustment means 34c which changes the intensity | strength of a laser beam so that the intensity | strength of the laser beam of the laser element 12a may become target intensity | strength. Similarly to the sub-controller 34, the sub-controller 35 obtains the detection result of the light intensity monitor 16b, and the target intensity for calculating the target intensity of the laser beam of the laser element 12b by multiplying the detection result by the correction amount. The calculation unit 35b and the adjustment unit 35c for changing the intensity of the laser beam so that the intensity of the laser beam of the laser element 12b becomes the target intensity. The adjusting means 34c and 35c can change not only the intensity of the laser beam but also the wavelength. Thus, the target intensity is calculated for each wavelength.

  FIG. 6 is a flowchart showing the operation of the transmitter. The operation of the optical transmitter 30 according to the second embodiment of the present invention will be described with reference to FIG. First, the correction amount calculation means 32b reads the memory 32a, and calculates the correction amount of the intensity of the optical signal necessary to eliminate the wavelength dependence of the intensity of the amplified optical signal (step 41). The correction amount is calculated for each wavelength. That is, the correction amount of the intensity of the optical signal having the wavelength λ1 and the correction amount of the intensity of the optical signal having the wavelength λ2 are obtained.

  Next, the notification unit 32c notifies the correction amounts to the sub-controllers 34 and 35 (step 42). The correction amount notified to the sub controller 34 and the correction amount notified to the sub controller 35 are different. Next, the acquisition unit 34a of the sub-controller 34 acquires information on the intensity of the optical signal output from the modulator 14a. Further, the acquisition means 35a of the sub-controller 35 acquires information on the intensity of the optical signal output from the modulator 14b (step 43).

  Next, the target intensity calculation means 34b multiplies the detection result and the correction amount to calculate the target intensity of the laser beam of the laser element 12a. Similarly, the target intensity of the laser beam of the laser element 12b is calculated by the target intensity calculator 35b (step 44). Next, the intensity of the laser beam is changed by the adjusting unit 34c so that the laser beam intensity of the laser element 12a becomes the target intensity. Similarly, the adjustment means 35c changes the intensity of the laser beam so that the intensity of the laser beam of the laser element 12b becomes the target intensity (step 45).

  According to the optical transmitter 30 according to the second embodiment of the present invention, the intensity of the amplified optical signal can be made uniform without wavelength dependence, as in the transmitter according to the first embodiment. In the case of the transmitter according to Embodiment 1, the predicted value of the intensity of the amplified optical signal is calculated by the calculation means, and then the optimum laser beam intensity that eliminates the wavelength dependence of the intensity of the amplified optical signal is calculated. However, the optical transmitter 30 according to the second embodiment calculates the correction amount of the intensity of the laser light necessary to eliminate the wavelength dependence of the intensity of the amplified optical signal. Based on this correction amount, a target intensity for eliminating the wavelength dependence of the intensity of the amplified optical signal is calculated.

  As described above, the configuration of the transmitter different from that of the optical transmitter 10 according to the first embodiment can have the same function as that of the optical transmitter 10 according to the first embodiment. The present invention adjusts the output of the transmitter so that the intensity of the amplified optical signal is made uniform without wavelength dependence, assuming that the signal amplification factor of the optical fiber amplifier 20 depends on the wavelength. Therefore, various modifications other than the modes shown in the first and second embodiments can be made without departing from the characteristics of the present invention.

  The optical transmitter 30 according to the second embodiment of the present invention can be modified at least as much as the optical transmitter 10 according to the first embodiment. Since the same number of sub-controllers as the number of laser elements are supplied, the number of sub-controllers changes according to the number of laser elements.

  10 optical transmitter, 12a, 12b laser element, 14a, 14b modulator, 16a, 16b light intensity monitor, 17 controller, 17a memory, 17b acquisition means, 17c calculation means, 17d adjustment means, 18 multiplexer, 20 optical fiber Amplifier, 30 optical transmitter, 32 main controller, 32a memory, 32b correction amount calculation means, 32c notification means, 34,35 sub-controller, 34a, 35a acquisition means, 34b, 35b target intensity calculation means, 34c, 35c adjustment means, 36a, 36b assembly

Claims (4)

A plurality of laser elements each emitting laser light having different wavelengths, and the intensity of the laser light being variable;
A modulator that modulates the laser light into an optical signal;
A multiplexer that outputs a multiplexed optical signal obtained by multiplexing the optical signal to an optical fiber amplifier;
A controller that changes the intensity of the laser light of the plurality of laser elements so as to eliminate the wavelength dependence of the intensity of the amplified optical signal that is the multiplexed optical signal amplified by the optical fiber amplifier ,
The controller reflects the change of the signal amplification factor of the optical fiber amplifier according to the number of optical signals constituting the multiplexed optical signal, and changes the intensity of the laser light of the plurality of laser elements. A featured optical transmitter. A light intensity monitor for detecting the intensity of the optical signal;
The controller is
A memory storing the wavelength dependence of the signal amplification factor of the optical fiber amplifier for each number of optical signals constituting the multiplexed optical signal ;
Obtaining means for obtaining a detection result of the light intensity monitor;
Multiplying the signal amplification factor and the detection result for each wavelength to calculate a predicted value of the intensity of the amplified optical signal;
The optical transmitter according to claim 1, further comprising: an adjusting unit that changes the intensity of the laser light of the plurality of laser elements so that the wavelength dependence in the predicted value is eliminated. A light intensity monitor for detecting the intensity of the optical signal;
The controller includes a main controller and a plurality of sub-controllers connected to the main controller and connected to each of the plurality of laser elements,
The main controller reads out the wavelength dependence of the signal amplification factor of the optical fiber amplifier for each number of optical signals constituting the multiplexed optical signal , reads out the memory, and stores the memory of the amplified optical signal. Correction amount calculation means for calculating the correction amount of the intensity of the optical signal necessary for eliminating the wavelength dependence of intensity, and notification means for notifying the correction amounts to the plurality of sub-controllers,
A plurality of sub-controllers for obtaining a detection result of the light intensity monitor; a target for calculating a target intensity of the laser light of the laser element by multiplying the detection result and the correction amount for each wavelength; 2. The apparatus according to claim 1, further comprising: an intensity calculating unit; and an adjusting unit that changes the intensity of the laser beam so that the intensity of the laser beam of the plurality of laser elements becomes the target intensity. Optical transmitter.   The controller calculates a signal amplification factor according to the input number using the number of inputs to the optical fiber amplifier as a variable, and uses the calculated signal amplification factor to calculate the intensity of the laser light of the plurality of laser elements. The optical transmitter according to claim 1, wherein the optical transmitter is changed.

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