JP2012029058A - Optical transmitter and control method of the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical transmitter for detecting stop or extinction of a data signal with the same structure even if the inputted data signal is encoded by an NRZ system or an RZ system and to provide a control method of the optical transmitter.SOLUTION: An optical transmitter 1a includes: a multistage amplifier 3 which includes an initial stage amplifier 11 and a final stage amplifier 12, which are connected in series, and amplifies the data signal inputted from an MUX 2; an external modulator 5 modulating non-modulation continuous light inputted from a laser light source 4 based on the data signal amplified by the multistage amplifier 3; a consumption current monitor unit 19 obtaining a monitor value showing current consumed by the initial stage amplifier 11; and a determining unit 23 outputting an alarm when the monitor value obtained by the consumption current monitoring unit 19 is smaller than a threshold which is previously decided.

Description

  The present invention relates to an optical transmitter and a control method thereof.

  In general, an optical transmitter used in an optical communication system detects anomalies such as fluctuations in optical output level, fluctuations in oscillation wavelength, asynchronization of modulation signals, no modulation, and fluctuations in bias voltage applied to external modulators. , It has a function to issue an alarm to the outside.

  When an abnormality occurs during the operation of the optical transmitter, it is required to specify the abnormality occurrence location more accurately in order to recover from the abnormal state to the normal state as quickly as possible.

  In this connection, Patent Document 1 includes a frequency component that is twice the pilot signal frequency in the output light from the external modulator that modulates the continuous light using the data signal on which the pilot signal is superimposed. There is described an optical transmission apparatus that monitors whether or not the frequency signal is detected and determines that the data signal has stopped or disappeared if such a frequency component is not detected and outputs an alarm.

JP 2004-56187 A

  However, when using the method described in Patent Document 1, there are the following problems.

  That is, when the data signal is a signal (RZ signal) encoded by the RZ (Return-to-Zero) method, the number of bits representing “0” and the number of bits representing “1” in the data signal sequence. Are equal to each other, the probability that the data signal becomes “H level” is 25%, whereas the probability that it becomes “L level” is 75% (see FIG. 4B). In this case, if the data signal is normally input to the external modulator, a frequency component twice the pilot signal frequency is detected in the output light from the external modulator (paragraphs 53-60 of Patent Document 1). reference).

  On the other hand, when the data signal is a signal (NRZ signal) encoded by the NRZ (Non-Return-to-Zero) method, the number of bits representing “0” and the bit representing “1” in the data signal sequence Are equal to each other, the probability of the data signal becoming “H level” and the probability of becoming “L level” is 50%, respectively (see FIG. 4A). In this case, even if the data signal is normally input to the external modulator, a frequency component twice the pilot signal frequency cannot be detected from the output light from the external modulator (paragraph 68 of Patent Document 1). -70).

  Therefore, when the data signal is an NRZ signal, the duty of the data signal input to the external modulator is a means for intentionally differentiating the probability that the data signal becomes “H level” and the probability that it becomes “L level”. And a waveform shaping unit (for example, dispersion compensating fiber) that restores the duty of the optical signal output from the external modulator must be added to the optical transmission device (paragraph 71- of Patent Document 1). 76).

  The present invention has been made in view of the above problems, and even if an input data signal is encoded by either the NRZ system or the RZ system, the data signal is stopped or extinguished with the same configuration. An object of the present invention is to provide an optical transmitter that can be detected and a control method thereof.

  In order to solve the above problems, an optical transmitter according to the present invention includes two or more amplifiers connected in series, a multistage amplifier that amplifies an input data signal by the two or more amplifiers, and the multistage amplifier. A monitor value indicating current consumed by at least one of the two or more amplifiers included in the multistage amplifier, and a modulation unit that modulates unmodulated continuous light input from the laser light source based on the amplified data signal Current consumption monitor unit, and a determination unit that outputs an alarm when a monitor value acquired by the current consumption monitor unit is smaller than a predetermined threshold value.

  According to the present invention, it is possible to detect a stop or disappearance of a data signal with the same configuration regardless of whether the input data signal is encoded by either the NRZ method or the RZ method.

  In one aspect of the present invention, the modulation means is an external modulator that modulates unmodulated continuous light input from a laser light source based on the data signal amplified by the multistage amplifier, and the optical transmitter A bias voltage control unit that controls a bias voltage applied to the external modulator so that a driving operation point voltage of the external modulator becomes an optimum point voltage on an input voltage-optical output characteristic curve of the external modulator. Further, it may be included.

  In one aspect of the present invention, the optical transmitter resets the driving operating point voltage of the external modulator to a predetermined bias voltage initial value in response to an alarm output from the determining unit. May further be included.

  According to this aspect, once the data signal enters the non-modulation state, the drive operating point voltage of the external modulator remains shifted to the upper limit or lower limit of the voltage range even if the data signal returns to the normal state thereafter. Can be prevented from returning to the optimum value.

  In the aspect of the invention, the data signal input to the multistage amplifier may be a signal obtained by multiplexing a plurality of data signals input from a data signal source.

  The method for controlling an optical transmitter according to the present invention includes two or more amplifiers connected in series, a multistage amplifier that amplifies an input data signal by the two or more amplifiers, and the multistage amplifier that is amplified by the multistage amplifier. Modulation means for modulating unmodulated continuous light input from a laser light source based on a data signal, and a method for controlling the optical transmitter, wherein at least one of the two or more amplifiers included in the multistage amplifier And a step of obtaining a monitor value indicating the current consumed in step (b), and outputting an alarm when the obtained monitor value is smaller than a predetermined threshold value.

  According to the present invention, an optical transmitter that detects the stop or disappearance of a data signal with the same configuration, regardless of whether the input data signal is encoded by either the NRZ method or the RZ method, and a control method therefor Can be provided.

It is a block diagram of the optical transmitter which concerns on Embodiment 1 of this invention. It is a figure which shows the input voltage-light output characteristic of an external modulator, and its operation | movement. It is a figure which shows the result of having measured the consumption current monitor value with respect to atmospheric temperature for every bit rate of a data signal. It is a figure which shows the data signal (NRZ signal) encoded by the NRZ system. It is a figure which shows the data signal (RZ signal) encoded by the RZ system. It is a figure which shows the result of having measured the consumption current monitor value with respect to the probability that a data signal will become "H level." It is a block diagram of the optical transmitter which concerns on Embodiment 2 of this invention.

  Hereinafter, Embodiments 1 and 2 of the present invention will be described in detail with reference to the drawings. In addition, the same code | symbol is attached | subjected to the same component and duplication description is abbreviate | omitted.

[Embodiment 1]
FIG. 1 is a block diagram of an optical transmitter 1a according to Embodiment 1 of the present invention. As shown in FIG. 1, an optical transmitter 1a includes a MUX (Multiplexer) 2, a multistage amplifier 3, a laser light source 4, an external modulator 5, a PD (Photodiode) 6, a current-voltage converter 7, a bias. A voltage control unit 8, a gain adjustment unit 13, an amplitude adjustment unit 14, a power supply 15, a detection resistor 16, a detection voltage amplification unit 17, an ADC (Analog to Digital Converter) 18, a current consumption monitor unit 19, and a determination unit 23 are included. Composed.

  The MUX 2 multiplexes a plurality of low-speed data signals input from an external device (not shown), converts them into a single high-speed data signal, and then outputs them to the multistage amplifier 3.

  The multistage amplifier 3 has a structure in which two or more amplifiers including at least a first stage amplifier 11 and a final stage amplifier 12 (in this embodiment, only the first stage amplifier 11 and the final stage amplifier 12) are connected in series. The multistage amplifier 3 amplifies the high-speed data signal input from the MUX 2 and outputs it to the electrode 22 inside the external modulator 5 as a drive data signal (drive voltage) for the external modulator 5.

  The power supply 15 supplies power to the first stage amplifier 11 and the final stage amplifier 12. The consumption current of the first stage amplifier 11 is converted into a voltage by the detection resistor 16, then gain-multiplied by the detection voltage amplification unit 17, and converted into a digital value by the ADC 18. The consumption current monitor unit 19 takes in the digital value obtained by the ADC 18 and generates a consumption current monitor value indicating the current consumed by the first stage amplifier 11.

  Note that the gain of the first stage amplifier 11 is set by adjusting the output voltage of the gain adjustment unit 13 so that the current consumption of the first stage amplifier 11 becomes a specified value. For example, the gain of the first stage amplifier 11 is set to a required value based on the current consumption monitor value generated by the current consumption monitor unit 19 in the manufacturing process of the optical transmitter 1a.

  The gain of the final stage amplifier 12 is set by adjusting the output voltage of the amplitude adjustment unit 14 so that the waveform of the optical signal output from the external modulator 5 satisfies a predetermined standard. For example, the gain of the final amplifier 12 is set to a required value based on the waveform of the optical signal output from the external modulator 5 in the manufacturing process of the optical transmitter 1a.

  Then, by setting the gain of the first stage amplifier 11 and the gain of the final stage amplifier 12 to required values, it is possible to obtain an appropriate high-speed data signal waveform for driving the external modulator 5. During the operation of the optical transmitter 1a, the gain of the first stage amplifier 11 and the gain of the final stage amplifier 12 are fixed, so that the current consumption in each is also constant.

  Here, when the gain of the first stage amplifier 11 and the gain of the final stage amplifier 12 have been set and the high speed data signal output from the MUX 2 is normally input to the multistage amplifier 3, the high speed data is output from the first stage amplifier 11. The signal is amplified, and the current consumption of the first stage amplifier 11 and the monitor value in the current consumption monitor unit 19 become fixed values according to the set gain of the first stage amplifier 11.

  On the other hand, when the high-speed data signal input from the MUX 2 to the multi-stage amplifier 3 is stopped or extinguished, the high-speed data signal is not amplified by the first-stage amplifier 11, so the current consumption of the first-stage amplifier 11 is greatly reduced. The monitor value in the current consumption monitor unit 19 is also greatly reduced.

  The determination unit 23 compares the current consumption monitor value generated by the current consumption monitor unit 19 with a preset threshold value. When the current consumption monitor value is smaller than the threshold value, the determination unit 23 determines that the high-speed data signal input from the MUX 2 to the multistage amplifier 3 has stopped or disappeared, and issues an alarm.

  The external modulator 5 modulates the unmodulated continuous light input from the laser light source 4 based on the high-speed data signal input from the multistage amplifier 3, and outputs the modulated optical signal.

In the external modulator 5, the unmodulated continuous light input from the laser light source 4 is branched into the optical path 20 and the optical path 21 and then multiplexed on the output side. The optical paths 20 and 21 are made of LiNbO ₃ , and when a voltage is applied to the electrode 22, the propagation speed of light in the optical paths 20 and 21 changes due to the electrooptic effect. For this reason, when the voltage (high-speed data signal) applied to the electrode 22 changes, the phase relationship of the light at the output ends of the optical paths 20 and 21 changes. For example, if the phase of the light at the output end of the optical path 20 is the same as the phase of the light at the output end of the optical path 21, the output of the combined light is maximized, and if the phases are inverted, the output is minimized.

  FIG. 2 is a diagram showing the input voltage-optical output characteristic of the external modulator 5 and its operation. As shown in FIG. 2, the relationship between the voltage (data signal) input to the electrode 22 of the external modulator 5 and the optical output of the external modulator 5 is a sine curve that changes periodically. Therefore, when a voltage signal (data signal) based on the driving operation point voltage is input to the external modulator 5, an optical signal having a waveform corresponding to the waveform is output from the external modulator 5. That is, the external modulator 5 can modulate the unmodulated continuous light input from the laser light source 4 based on the voltage signal applied to the electrode 22.

  The PD 6 receives a part of the optical signal output from the external modulator 5 and outputs an electrical signal corresponding to the intensity of the received optical signal. The current-voltage conversion unit 7 converts an electrical signal (output current) output from the PD 6 into a voltage. The bias voltage control unit 8 controls the bias voltage applied to the electrode 22 of the external modulator 5 based on the output voltage of the current-voltage conversion unit 7 so that the driving operation point voltage of the external modulator 5 becomes an optimum value. To do.

  FIG. 3 is a diagram showing the results of measuring the consumption current monitor value with respect to the ambient temperature for each bit rate of the data signal (horizontal axis: ambient temperature Ta, vertical axis: consumption current monitor value). The results shown in FIG. 3 indicate that the high-speed data signal (NRZ signal) encoded by the NRZ method is consumed for each of the case where it is normally input to the multistage amplifier 3 output from the MUX 2 and the case where it is not normally input. The current monitor value was measured. As shown in FIG. 3, the current consumption monitor value is substantially constant regardless of the ambient temperature Ta, regardless of whether the high-speed data signal is normally input to the multistage amplifier 3 or not. Further, the difference between the current consumption monitor values when the high-speed data signal is normally input to the multistage amplifier 3 and when the high-speed data signal is not input is sufficiently large with respect to the temperature fluctuation. On the other hand, when a high-speed data signal is normally input to the multistage amplifier 3, the current consumption monitor value is substantially the same regardless of the transmission rate.

  That is, according to the actual measurement result shown in FIG. 3, when the data signal is NRZ, the current consumption monitor value depends only on whether or not the high-speed data signal from the MUX 2 is normally input to the multistage amplifier 3, It can be considered that it does not depend on the ambient temperature or the bit rate of the data signal. Therefore, the determination unit 23 determines that the high-speed data signal input from the MUX 2 to the multistage amplifier 3 has stopped or disappeared when the current consumption monitor value generated by the current consumption monitor unit 19 is smaller than the threshold value. When it is larger than the threshold value, it can be determined that the high-speed data signal output from the MUX 2 is normally input to the multistage amplifier 3.

  Next, it will be described that this determination method can be applied to a data signal encoded by either the NRZ method or the RZ method.

  4A is a diagram illustrating a data signal (NRZ signal) encoded by the NRZ method, and FIG. 4B is a diagram illustrating a data signal (RZ signal) encoded by the RZ method. As shown in FIG. 4A, in the NRZ signal, “1” in the data signal sequence is represented by “H level”, and “0” is represented by “L level”. If the number of bits representing “0” and the number of bits representing “1” in the data signal series are equal, the probability that the data signal will be “H level” and “L level” is 50%, respectively. It becomes. On the other hand, as shown in FIG. 4B, in the RZ signal, “1” in the data signal series is represented by a combination of “H level” and “L level”. Therefore, if the number of bits representing “0” and the number of bits representing “1” in the data signal series are equal, the probability that the data signal becomes “H level” is 25%, and the data signal “ The probability of “L level” is 75%.

  FIG. 5 is a diagram showing a result of measuring a current consumption monitor value with respect to a probability that the data signal becomes “H level” using a data signal having a fixed pattern (horizontal axis: probability, vertical axis: current consumption monitor). value). As shown in FIG. 5, even when the probability that the data signal becomes “H level” is reduced to about 10%, the case where the high-speed data signal is normally input to the multistage amplifier 3 and the case where the data signal is not normally input It can be seen that there is a difference between the current consumption monitor values sufficient to set the threshold.

  For this reason, according to the optical transmitter 1a, even if the data signal input to the external modulator 5 is encoded by either the NRZ system or the RZ system, the data signal is stopped or extinguished with the same configuration. Can be detected.

[Embodiment 2]
FIG. 6 is a block diagram of an optical transmitter 1b according to Embodiment 2 of the present invention, which is a modification of Embodiment 1 described above. As shown in FIG. 6, the optical transmitter 1b includes a MUX 2, a multistage amplifier 3, a laser light source 4, an external modulator 5, a PD 6, a current-voltage conversion unit 7, a bias voltage control unit 8, an operating point reset unit 10, a gain. The adjustment unit 13, the amplitude adjustment unit 14, the power supply 15, the detection resistor 16, the detection voltage amplification unit 17, the ADC 18, the current consumption monitor unit 19, the determination unit 23, and the signal generation unit 24 are configured.

  In the optical transmitter 1b, the detection resistor 16 is disposed between the final stage amplifier 12 and the power source 15 constituting the multistage amplifier 3, and the current consumption of the final stage amplifier 12 is monitored.

  In addition, a signal generation unit 24 is disposed after the determination unit 23. The signal generation unit 24 issues a reset signal to the operating point reset unit 10 in response to the alarm output from the determination unit 23.

  The operating point resetting unit 10 compulsorily sets the driving operating point voltage of the external modulator 5 when receiving a reset signal from the signal generating unit 24 or turning off the control of the driving operating point voltage by the bias voltage control unit 8. To a predetermined bias voltage initial value. As a result, once the data signal is in the non-modulated state, the drive operating point voltage of the external modulator 5 remains at the upper or lower limit of the voltage range even if the data signal is restored to the normal state. The problem that the value cannot be restored can be prevented.

  Even in the optical transmitter 1b, the data signal having the same configuration is used regardless of whether the data signal input to the external modulator 5 is encoded by either the NRZ system or the RZ system, as in the optical transmitter 1a. Can be detected.

[Modification]
In addition, this invention is not limited to the said embodiment, A various deformation | transformation is possible. In addition, the configuration described in the above embodiment can be replaced with a configuration that is substantially the same, a configuration that exhibits the same operational effects, or a configuration that can achieve the same purpose.

  For example, during operation of the optical transmitter, the gain of the first stage amplifier 11 as well as the final stage amplifier 12 is constant, so that the current consumption of the final stage amplifier 12 is substantially constant. Therefore, the total value of the current consumption of the first stage amplifier 11 and the current consumption of the final stage amplifier 12 may be monitored. That is, the current consumption of the entire multistage amplifier 3 may be monitored, or may be monitored separately.

  Further, when changing the extinction ratio of the optical signal in consideration of the transmission characteristics, the amplitude of the data signal is changed. In this case, since the current consumption of the final stage amplifier 12 constituting the multistage amplifier 3 also changes, it may be necessary to change the threshold value in the determination unit 23. In order to deal with such a case, the threshold value in the determination unit 23 may be adjustable.

  Similarly, when the data signal to be handled is changed from the NRZ signal to the RZ signal, or when the data signal is changed from the RZ signal to the NRZ signal, the threshold value in the determination unit 23 may be adjustable.

  In the above embodiment, the transmission rate of the high-speed data signal is assumed to be on the order of 10 [Gbit / s]. However, the present invention can also be applied to an optical transmitter that handles a data signal having a different transmission rate. It is.

  Further, not only an optical transmitter that employs a method of modulating unmodulated continuous light by an external modulator, but optical transmission that employs a method of amplifying a high-speed data signal from the MUX with an amplifier and modulating the unmodulated continuous light. Similarly, the present invention is applicable to a container. Of course, the present invention can be applied not only to an optical transmitter, but also to an optical transceiver substantially including an optical transmitter.

  1a, 1b Optical transmitter, 2 MUX, 3 multistage amplifier, 4 laser light source, 5 external modulator, 6 PD, 7 current-voltage conversion unit, 8 bias voltage control unit, 10 operating point reset unit, 11 first stage amplifier, 12 Final stage amplifier, 13 gain adjustment unit, 14 amplitude adjustment unit, 15 power supply, 16 detection resistor, 17 detection voltage amplification unit, 18 ADC, 19 current consumption monitor unit, 20, 21 optical path, 22 electrode, 23 determination unit, 24 signal Generation part.

Claims (5)

A multi-stage amplifier including two or more amplifiers connected in series, and amplifying an input data signal by the two or more amplifiers;
Modulation means for modulating unmodulated continuous light input from a laser light source based on the data signal amplified by the multistage amplifier;
A current consumption monitor unit for obtaining a monitor value indicating a current consumed by at least one of the two or more amplifiers included in the multistage amplifier;
A determination unit that outputs an alarm when a monitor value acquired by the current consumption monitor unit is smaller than a predetermined threshold;
An optical transmitter comprising: The optical transmitter according to claim 1,
The modulation means is an external modulator that modulates unmodulated continuous light input from a laser light source based on the data signal amplified by the multistage amplifier,
The optical transmitter is configured to control a bias voltage applied to the external modulator so that a driving operation point voltage of the external modulator becomes an optimum point voltage on an input voltage-optical output characteristic curve of the external modulator. A voltage control unit;
An optical transmitter characterized by that. The optical transmitter according to claim 2, wherein
An operating point resetting unit for resetting a driving operating point voltage of the external modulator to a predetermined bias voltage initial value in response to an alarm output by the determination unit;
An optical transmitter characterized by that. The optical transmitter according to claim 1,
The data signal input to the multistage amplifier is a signal obtained by multiplexing a plurality of data signals input from a data signal source.
An optical transmitter characterized by that. A multi-stage amplifier including two or more amplifiers connected in series, and amplifying an input data signal by the two or more amplifiers;
Modulation means for modulating unmodulated continuous light input from a laser light source based on the data signal amplified by the multistage amplifier;
An optical transmitter control method including:
Obtaining a monitor value indicating a current consumed by at least one of the two or more amplifiers included in the multistage amplifier;
Outputting an alarm when the acquired monitor value is smaller than a predetermined threshold;
An optical transmitter control method comprising:

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