JP2007194576A - Optical transmitter and its control method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical transmitter capable of promptly detecting a deterioration of a characteristic of a laser diode and having an optimal extinction ratio by using a function for detecting the deterioration of the characteristic of the laser diode, and to provide a method of controlling the optical transmitter. <P>SOLUTION: The optical transmitter is equipped with a laser diode driving circuit for driving the laser diode by a laser diode current superposed, so that pilot signals respectively having lower frequencies as compared with sending signals to different voltage levels of the sending signals may mutually become inverse phases; a monitor circuit for monitoring an optical output of the laser diode; a filter circuit for abstracting frequency components of the pilot signals from an output of the monitor circuit; a phase comparator circuit for comparing phases of the pilot signals with phases of the frequency components abstracted by the filter circuit; and a deterioration judging circuit for judging a deterioration of the laser diode according to a phase comparing result of the phase comparator circuit. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an optical transmitter, and more particularly, to an optical transmitter that controls deterioration of an optical transmitter using a laser diode (LD) and an extinction ratio based on the result of detection of the deterioration.

  An optical transmitter using an LD is used as a light source of an optical transmission system that enables long-distance transmission. The optical transmitter controls the optical transmission power to be a constant power in order to extend the optical transmission distance, and the extinction is a level ratio between the logical level “1” and the logical level “0” of the optical transmission signal. Control the ratio to a certain range.

  FIG. 12 is a diagram for explaining the direct modulation of the LD. The right side of the figure is a peripheral circuit of the LD 101, and the left side of the figure is an LD driving circuit having an amplifier (AMP) 102. The transmission signal (2) is modulated by Ip controlled by the modulation current (Ip) control signal (4), and biased to the LD threshold current (Ith) or more by Ib controlled by the bias current (Ib) control signal (5). Applied to the formed LD. Ith is the minimum current that can be oscillated by the LD.

  FIG. 13 is a diagram for explaining the modulated optical output of the transmission signal. (A) is a transmission signal, and (B) is an optical output signal in which a continuous wave (CW) oscillated by being biased by Ib is modulated by Ip that modulates the transmission signal. The optical output signal is generally shown as a waveform in which the CW that oscillates inherent to the LD is omitted as shown in FIG. In other words, the LD oscillates by being biased to Ith or more to generate CW, the amplitude of the CW is determined by applying the modulated Ip, and an optical signal whose transmission signal can be identified by the CW level. Output.

  FIG. 14 is a diagram (1) for explaining the LD conversion efficiency. (103) is an LD conversion efficiency curve showing the relationship between the LD current and the optical output power. The LD begins stimulated emission when the LD current exceeds a critical level. The critical level is the LD threshold current (Ith) in FIG. Generally, Ib and Ip are set so that the LD current exceeds the LD threshold current. (104) indicates the LD current when the transmission signal has a random pattern. (105) indicates the optical output of the LD oscillating when the LD current (104) is applied. The operating point of the LD current is determined by Ib biased to Ith or more, and the operating range of the LD current is determined by Ip. The light output is determined according to the slope of the LD conversion efficiency curve (103). Therefore, the optical output power is controlled by Ib and Ip, and the extinction ratio is controlled by Ip.

  The direct modulation of the LD will be described with reference to FIGS. The transmission signal (2) is modulated by Ip in the AMP 102 and applied to the LD 101 biased by Ib set to Ith or higher. Therefore, the LD current (104) applied to the LD101 becomes a signal having an amplitude of Ip with the operating point biased in the LD current region capable of oscillating the LD of the LD conversion efficiency curve (103) as the LD conversion efficiency. The light output (105) can be obtained by the characteristic of the curve (103). As a result, the extinction ratio is affected by the magnitude of Ip due to the slope of the LD conversion efficiency curve (103).

  FIG. 15 is a diagram for explaining the control of the optical transmitter. 111 is a photodiode (PD) that monitors the light output of the LD 101, 112 is the LD drive circuit shown in FIG. 12, and 113 is a control circuit that controls the LD drive circuit 112.

  FIG. 16 is a diagram for explaining monitoring of optical output. (106) is the PD current of the signal monitored by the PD 111. A part of the output light of the optical output (105) is received by the PD 111 and is photoelectrically converted to obtain a PD current (106).

  The control circuit 113 receives the monitor current of the PD 111 and drives the LD via the Ip control signal (4) and the Ib control signal (5) shown in FIG. 12 so that the optical output of the LD 101 becomes a predetermined constant power. Control the circuit. Further, the LD driving circuit is controlled via the Ip control signal (4) in order to control the extinction ratio of the LD 101.

  FIG. 17 is a diagram (2) for explaining the LD conversion efficiency. This is a case where Ip is increased from Ip shown in FIG. 14, and shows that the extinction ratio increases in accordance with the LD conversion efficiency curve (103). In this case, although not shown in the figure, when Ib is increased, the operating point moves and the optical output power increases.

  Since the LD conversion efficiency is easily affected by temperature changes and changes with time, the slopes of Ith and LD conversion efficiency curves are not constant. Therefore, it is necessary to perform automatic power control (APC: auto power control) for keeping the optical output power constant and automatic extinction ratio control (AMC: auto modulation control) for keeping the extinction ratio in a certain range.

  As a control technique of the APC and AMC, in order to control the optical output power and the extinction ratio to be constant with respect to the aging degradation of the laser diode, the optical output power of the laser diode before the degradation is detected, and the detected value is calculated. A technique for storing as a reference value and performing feedback control with respect to the reference value is disclosed (for example, see Patent Document 1).

Also, the Ib operating point and Ip operating range of the LD conversion efficiency curve set in advance are compared with the Ib operating point and Ip operating range of the LD conversion efficiency curve during operation, and Ib and Ip are changed. Thus, a technique for ensuring an optimum optical output power and extinction ratio is disclosed (for example, see Patent Document 2).
Japanese Patent Laid-Open No. 11-135871 US Pat. No. 6,414,974

  By the way, the LD conversion efficiency varies depending on the type of the LD, and also varies depending on the ambient temperature even in the same LD, and also varies depending on aging. Generally, deterioration occurs due to high temperature use and aging.

  FIG. 18 is a diagram for explaining LD degradation. In general, when the LD deteriorates, the LD conversion efficiency curve 103 has a small slope as shown in 103 (1), 103 (2), and 103 (3).

  FIG. 19 is a diagram for explaining the LD conversion efficiency when the LD is deteriorated. As shown in this figure, when the slope of the LD conversion efficiency curve deteriorates so as to become very small, it is possible to increase the extinction ratio by increasing both Ib and Ip, but the slope of the LD conversion efficiency curve As I becomes smaller, larger Ib and Ip are required. Further, when the slope of the LD conversion efficiency curve is degraded to about zero, it is difficult to increase the extinction ratio even if Ib and Ip are increased. However, in the control of APC and AMC, unless it can be recognized that the LD conversion efficiency is remarkably deteriorated due to LD deterioration, feedback control is performed so that Ib is increased and Ip is increased until the control limiter is applied. Unnecessary control is performed. In general, in an optical transmitter using an LD, an allowable LD bias current is set in advance, the LD bias current is monitored, and an alarm is issued when the preset LD bias current exceeds an allowable value. In addition, it is known to stop the control of the optical transmitter.

  An object of the present invention is to provide an optical transmitter that can quickly detect LD degradation in an optical transmitter using an LD. It is another object of the present invention to provide an optical transmitter and an optical transmitter control method capable of obtaining an optimum extinction ratio by using the function of detecting LD degradation.

  The first invention is an LD driving circuit for driving an LD with LD currents superimposed so that pilot signals having lower frequencies than the transmission signal are in opposite phases with respect to different voltage levels of the transmission signal. A monitor circuit for monitoring the optical output of the LD, a filter circuit for extracting the frequency component of the pilot signal from the output of the monitor circuit, the phase of the pilot signal and the phase of the frequency component extracted by the filter circuit And a deterioration determination circuit that determines deterioration of the laser diode based on a phase comparison result of the phase comparison circuit.

  According to the first invention, in the optical transmitter using the LD, it is possible to provide an optical transmitter capable of quickly detecting deterioration of the LD.

According to a second aspect of the present invention, an LD driving circuit that drives an LD with an LD current corresponding to a transmission signal, a monitor circuit that monitors an optical output of the LD, and a monitor current output by the monitor circuit An optical transmitter comprising a control circuit that controls either the optical output power or the extinction ratio of the optical output of the LD, or both,
The LD driving circuit generates an LD current in which pilot signals having lower frequencies than the transmission signal are superimposed on the different voltage levels of the transmission signal so as to have opposite phases to each other. A filter circuit for extracting the frequency component of the pilot signal from the output, a phase comparison circuit for comparing the phase of the pilot signal with the phase of the frequency component extracted by the filter circuit, and the phase comparison result of the phase comparison circuit A deterioration determination circuit for determining the deterioration of the LD is provided,
An optical transmitter characterized in that, when the degradation determination circuit determines degradation of the LD, the control circuit holds control of the optical output power of the LD and the extinction ratio of the optical output of the LD.

  According to the second invention, it is possible to provide an optical transmitter having an optimum extinction ratio by using the function of detecting the degradation of the LD.

The third invention drives the LD with an LD current in which a bias current is superimposed on a modulation current for modulating a transmission signal,
Monitor the optical output of the LD,
In the optical transmitter control method for controlling either or both of the optical output power of the LD and the extinction ratio of the optical output of the LD based on the monitor current output by the monitor circuit,
Modulating a transmission signal with a modulation current superimposed with a pilot signal to generate an LD current superimposed with a bias current,
Extract the frequency component of the modulated pilot signal of the optical output,
Comparing the phase of the pilot signal with the phase of the frequency component of the pilot signal;
The degradation of the LD is determined based on the phase comparison result,
In the optical transmitter control method, when the degradation of the LD is determined, control of the optical output power of the LD and the extinction ratio of the optical output of the LD is maintained.

  According to the third invention, it is possible to provide a method of controlling an optical transmitter having an optimum extinction ratio by using the function of detecting the degradation of the LD.

  The optical transmitter and the optical transmitter control method according to the present invention quickly detect the degradation of the LD provided in the optical transmitter in a state where the LD conversion efficiency has deteriorated due to degradation due to temperature rise or deterioration over time. Is possible. Further, it is possible to provide an optical transmitter that controls Ib and Ip based on the result of comparing the phase of the pilot signal and the result of detecting the amplitude of the pilot signal and operates in accordance with the optimum extinction ratio.

Hereinafter, the details of the present invention will be described with reference to the drawings. In addition, the same code | symbol is described about the same thing or similar thing in drawing.
Example 1
This will be described with reference to FIGS.

  FIG. 1 is a diagram (1) illustrating the configuration of an optical transmitter according to the present invention. 101 is an LD, 111 is a PD, 10 is an LD drive circuit, 11 is a phase comparison circuit, 12 is a filter circuit, and 13 is a deterioration determination circuit.

  FIG. 2 is a diagram for explaining direct modulation of the LD of the present invention. Corresponding to FIG. 12, pilot signal (1) is superimposed on Ip. By superimposing the generated pilot signal (1) on the Ip control signal (4), the transmission signal (2) is modulated by the Ip on which the pilot signal (1) is superimposed, and is controlled by the Ib control signal (5). Applied to the LD 101 biased by the biased Ib.

  FIG. 3 is a diagram (1) for explaining the operation of the optical transmitter of the present invention. An LD current (6) for driving the LD, an LD conversion efficiency curve (8), an LD light output (3), and a PD current (7) are shown.

  The pilot signal (1) is a signal having a sufficiently lower frequency than the transmission signal (2). For example, when the transmission signal is 2.4 GHz, the pilot signal is about 2 KHz. In this embodiment, the signal is a signal having a constant period of logical levels “1” and “0”, but a pilot having a unique specific pattern in which the opposite optical receiver in the transmission system including this optical transmitter can recognize the transmission destination. It may be a signal.

  The generated pilot signal (1) is provided to the LD driving circuit 10 and the phase comparison circuit 11. As shown in FIG. 2, the LD driving circuit 10 superimposes the generated pilot signal (1) on the Ip control signal (4), thereby superimposing the pilot signal (1) on the transmission signal (2). Modulated by Ip. The LD current (6) is applied to the LD 101 biased by Ib controlled by the Ib control signal (5).

  The Ip control signal (4) controls the amplitude value of the LD current (6). By increasing the Ip control signal (4), the amplification factor of the AMP (102) increases and the amplitude value of the LD current (6) increases. Become. The Ib control signal (5) controls the center value of the LD current (6). By increasing the Ib control signal (5), the center value of the LD current (6) increases.

  That is, as shown in FIG. 3, the operating range of the LD current (6) is determined by the Ip control signal (4), and the center value of the LD current (6) is determined by the Ib control signal (5).

  In FIG. 3, since the operating point and operating range of the LD current (6) are set to be equal to or greater than Ith, the light output (3) is generated based on the slope of the light conversion efficiency curve (8).

  The PD 111 monitors a part of the output light of the optical output (3), and outputs a PD current (7) obtained by photoelectric conversion to the filter circuit 12.

  The filter circuit 12 passes the PD current (7) through a low band below the pilot signal (1). Alternatively, only the frequency component of the pilot signal (1) band is passed. Since the pilot signal included in the optical output (3) and the PD current (7) monitoring the optical output (3) is superimposed and modulated on Ip, the positive phase pilot on the logic level “1” side The signal and the pilot signal of the opposite phase on the logic level “0” side. Therefore, when the optical output (3) is converted based on the same slope of the LD conversion efficiency curve (8), the filter circuit 12 has a positive phase pilot signal on the logic level “1” side and the logic level. In order to average the pilot signals of the opposite phase on the “0” side, no pilot signal is output to the filter circuit 12.

  The phase comparison circuit 11 indicates whether the filter circuit 12 outputs a pilot signal, and when the pilot signal is output, the phase of the pilot signal is positive compared to the generated pilot signal (1). Or if they are in antiphase.

Based on the comparison result of the phase comparison circuit, the deterioration determination circuit 13 determines that the filter circuit 12 does not output a pilot signal, that is, that the LD is not deteriorated.
(Example 2)
FIG. 4 is a diagram (2) for explaining the operation of the optical transmitter of the present invention. Corresponding to FIG. 3, the operation of the optical transmitter when the LD conversion efficiency curve is degraded will be described.

  Based on the LD conversion efficiency curve (18) when the LD deteriorates, the positive output pilot signal on the logic level “1” side is completely suppressed in the optical output (13) converted from the LD current (6). End up. Similarly, the PD current (17) monitoring the optical output (13) is also a signal in which the positive phase pilot signal on the logic level “1” side is completely suppressed.

  Therefore, the filter circuit 12 filters only the pilot signal having the opposite phase on the logic level “0” side.

  The phase comparison circuit 11 compares with the generated pilot signal (1) to notify that an antiphase pilot signal has been detected.

The degradation determination circuit 13 determines that the slope of the logic level “1” side of the LD conversion efficiency curve (18) is abnormal based on the comparison result of the phase comparison circuit, and determines that degradation has occurred in the LD. .
(Example 3)
FIG. 5 is a diagram (2) illustrating the configuration of the optical transmitter of the present invention. Corresponding to FIG. 1, the control circuit 14 receives the deterioration determination result of the deterioration determination circuit 13 and the monitor signal of the PD 111 and controls the LD driving circuit 10.

  FIG. 6 is a diagram (3) for explaining the operation of the optical transmitter of the present invention. Corresponding to FIG. 3, the LD conversion efficiency curve (8) is the same, but since Ib is small, the operating point of the LD is lowered, the operating range is lowered, and a part of the operating range of the LD is Ith. It is as follows.

  Based on the LD conversion efficiency curve (8) at the LD operating point and operating range, the optical output (23) converted from the LD current (6) is an antiphase pilot signal on the logic level “0” side. Will be suppressed. Similarly, the PD current (27) monitored for the optical output (23) is the one in which the pilot signal of the opposite phase on the logic level “0” side is suppressed.

  In order to average the positive phase pilot signal on the logic level “1” side and the antiphase pilot signal on the logic level “0” side, the filter circuit 12 has the positive phase pilot signal on the logic level “1” side. Is output.

  The phase comparison circuit 11 notifies the deterioration determination circuit 13 that a positive phase pilot signal has been detected by comparing with the generated pilot signal (1).

  Based on the comparison result of the phase comparison circuit, the deterioration determination circuit 13 determines that the LD operating point and operating range are low, and determines that the LD has not deteriorated.

Based on the determination result of the deterioration determination circuit and the determination result, the control circuit 14 controls the LD drive circuit via the Ib control signal (5) so as to increase Ib in order to increase the operating point.
Example 4
In the configuration of the optical transmitter of FIG. 5, when the LD conversion efficiency curve (18) shown in FIG. 4 is provided, the control circuit 14 is based on the determination of the deterioration of the LD of the deterioration determination circuit 13. Holds control to the LD drive circuit via the Ip control signal (4) and the Ib control signal (5). In the system in which the optical transmitter is used, if permitted, the control circuit 14 stops the control to the LD drive circuit via the Ip control signal (4) and the Ib control signal (5). Also good.
(Example 5)
FIG. 7 is a diagram (3) illustrating the configuration of the optical transmitter according to the present invention. Corresponding to FIG. 5, 15 is an amplitude comparison circuit, 16 is a deterioration determination circuit, 17 is a deterioration determination condition storage circuit, and 18 is a control circuit.

  The amplitude comparison circuit 15 is an averaged pilot signal of the pilot signal (1), the positive phase pilot signal on the logic level “1” side and the antiphase pilot signal on the logic level “0” side in the filter circuit 12. Compare the amplitude values.

  FIG. 8 is a diagram illustrating an amplitude comparison circuit. (A1), (B1), and (C1) indicate PD currents focused on a pilot signal obtained by monitoring the optical output of the PD111. (A2), (B2), and (C2) are outputs of the filter circuit 12, and are obtained by averaging the positive phase pilot signal on the logic level “1” side and the antiphase pilot signal on the logic level “0” side. The pilot signal is shown. (A3), (B3), and (C3) are comparison results of the amplitude comparison circuit 15, and the amplitude of the filtered pilot signal shown in (A2), (B2), and (C2) with respect to the pilot signal (1) is shown. The ratio and the phase of the filtered pilot signal are shown. (A1), (A2), and (A3) are cases where the LD described with reference to FIG. 3 is not deteriorated, and the comparison result of the amplitude comparison circuit 15 is 0%. In the case described with reference to FIG. 4, (B1), (B2), and (B3) do not have a slope of 0 in the LD conversion efficiency curve (18). This is a case where only half is suppressed, and the comparison result of the amplitude comparison circuit 15 is 50% and in reverse phase. In (C1), (C2), and (C3), since the LD described in FIG. 6 is not deteriorated and Ib is small, the operating point of the LD is lowered, the operating range is lowered, and the operating range of the LD is reduced. This is a case where a part of the signal is equal to or lower than Ith and the pilot signal of the opposite phase on the logic level “0” side is suppressed by 30%, and the comparison result of the amplitude comparison circuit 15 is 30% and the positive phase.

  FIG. 9 is a diagram for explaining the deterioration determination condition, which is stored in the deterioration determination condition storage circuit 17, and stores the condition for the deterioration determination circuit 16 to determine the deterioration of the LD. The pilot signal amplitude value indicates the amplitude value of the pilot signal (1), and the determination threshold value is lower than the comparison result of the amplitude comparison circuit 15 shown in (A3), (B3), and (C3) of FIG. The threshold value indicates that the degree is normal.

  FIG. 10 shows a flow of processing for determining deterioration and extinction ratio. The processing flow for determining LD deterioration and controlling extinction ratio will be described using the above phase comparison result, amplitude comparison result, and deterioration determination condition.

  S1. A phase comparison result between the pilot signal (1) of the phase comparison circuit 11 and the filtered pilot signal of the filter circuit 12 is determined. When the pilot signal does not appear in the filtered pilot signal, that is, when the positive phase pilot signal on the logical level “1” side and the negative phase pilot signal on the logical level “0” side are averaged and not output. In other cases, that is, when a pilot signal of any phase appears in the filtered pilot signal, it is determined as not normal.

  S2. This is a case where it is determined in S1 that the signal is not normal, and the amplitude comparison result between the pilot signal (1) of the amplitude comparison circuit 15 and the filtered pilot signal of the filter circuit 12 is determined. Based on the deterioration determination condition shown in FIG. 9, the ratio of the amplitude of the filtered pilot signal to the pilot signal (1) is obtained, and the ratio is determined with respect to the determination threshold corresponding to the amplitude value of the pilot signal (1). To determine whether it is in the normal range.

  S3. In S2, the amplitude ratio is not in the normal range, and it is determined that the LD is in a deteriorated state, so an alarm is issued. Then, the control circuit 18 may perform control so as to maintain control of the optical output power of the LD and the extinction ratio of the optical output of the LD. Further, the control circuit 18 may be controlled to stop the optical output of the LD.

  S4. Whether the phase comparison result is normal in S1 or the amplitude comparison result is normal in S2, it is determined whether or not to control the extinction ratio of the optical output of the LD. When the current extinction ratio satisfies the characteristics of the optical transmission system including the optical transmitter to be controlled, it is determined that the extinction ratio control is not performed. When the extinction ratio is improved, it is determined that the extinction ratio control is performed.

  S5. This is a case where the extinction ratio is not improved in S4, and the control circuit 18 performs control so as to maintain Ib and Ip at their current values.

  S6. In the case where the extinction ratio is improved in S4, whether the phase comparison result between the pilot signal (1) of the phase comparison circuit 11 and the filtered pilot signal of the filter circuit 12 is a positive phase or the filtered pilot signal It is determined whether the pilot signal does not appear in FIG.

  S7. In S6, the phase comparison result is a positive phase, and the control circuit 18 decreases Ip. This control improves that the anti-phase pilot signal on the logic level “0” side is operating below Ith by decreasing Ip. The amount of change in Ip is determined based on control information stored in a control table (not shown) provided in advance in the control circuit 18.

  S8. This is a case where the phase comparison result is the opposite phase in S6, and the control circuit 18 decreases Ib or Ip. In this control, the operating point of the LD conversion efficiency curve is moved to the smaller LD current by decreasing Ib, and the slope of the LD conversion efficiency curve of the positive phase pilot signal on the logic level “1” side is the logic level. It is improved that the operation is performed at a curve point smaller than the slope of the LD conversion efficiency curve of the pilot signal having the opposite phase on the “0” side. The amount of decrease in Ip or Ib is determined based on control information stored in a control table (not shown) provided in advance in the control circuit 18.

  S9. In S6, the phase comparison result is a case where no pilot signal appears in the filtered pilot signal, and the control circuit 18 increases Ip. This control is improved to increase the extinction ratio by increasing the operating range of the LD conversion efficiency curve by increasing Ip.

S10. After processing any of S7, S8, or S9, a pilot signal (1) is transmitted to determine whether the extinction ratio has been improved by the processing. This process is necessary for an optical transmitter that transmits the pilot signal (1) in a timely manner, and is unnecessary when the pilot signal (1) is constantly transmitted. By transmitting the pilot signal (1), the processing flow from S1 is performed, whereby an extinction ratio that satisfies the characteristics of the optical transmission system can be obtained.
(Example 6)
FIG. 11 is a diagram (4) for explaining the configuration of the optical transmitter of the present invention. Corresponding to FIG. 7, reference numeral 19 denotes a pilot generation circuit. A pilot signal whose pilot signal pattern, pilot signal generation period, emission timing, and pilot signal amplitude value are controlled by the control circuit 20 is generated.

  Regarding the embodiment including the above Examples 1 to 6, the following additional notes are disclosed.

(Supplementary note 1) Laser diode drive for driving a laser diode with a laser diode current superimposed so that pilot signals having lower frequencies than the transmission signal are in opposite phases with respect to different voltage levels of the transmission signal Circuit,
A monitor circuit for monitoring the optical output of the laser diode;
A filter circuit for extracting the frequency component of the pilot signal from the output of the monitor circuit;
A phase comparison circuit that compares the phase of the pilot signal with the phase of the frequency component extracted by the filter circuit;
A deterioration determination circuit for determining deterioration of the laser diode based on a phase comparison result of the phase comparison circuit;
An optical transmitter comprising:

(Supplementary note 2) a laser diode driving circuit for driving a laser diode with a laser diode current according to a transmission signal;
A monitor circuit for monitoring the optical output of the laser diode;
An optical transmitter comprising a control circuit for controlling either or both of the optical output power of the laser diode or the extinction ratio of the optical output of the laser diode based on the monitor current output by the monitor circuit,
The laser diode driving circuit generates laser diode currents superimposed such that pilot signals having lower frequencies than the transmission signals are in opposite phases with respect to different voltage levels of the transmission signals,
A filter circuit for extracting the frequency component of the pilot signal from the output of the monitor circuit;
A phase comparison circuit that compares the phase of the pilot signal with the phase of the frequency component extracted by the filter circuit;
A deterioration determination circuit for determining deterioration of the laser diode based on a phase comparison result of the phase comparison circuit;
When the deterioration determination circuit determines deterioration of the laser diode, the control circuit holds control of the optical output power of the laser diode and the extinction ratio of the optical output of the laser diode. .

(Supplementary note 3) The optical transmitter according to supplementary note 2, wherein
An amplitude comparison circuit that detects the amplitude of the frequency component extracted by the filter circuit and compares it with the amplitude of the pilot signal;
The deterioration determination circuit determines a deterioration state of the laser diode based on a comparison result of the phase comparison circuit, a comparison result of the amplitude comparison circuit, and a laser diode deterioration determination condition registered in advance.
The optical transmitter is characterized in that the control circuit controls an extinction ratio of the optical output of the laser diode based on a determination result of the deterioration determination circuit.

(Supplementary note 4) The optical transmitter according to supplementary note 3, wherein
The laser diode deterioration determination condition is determined for each laser diode solid identification number for identifying the group grouped according to the characteristics of the laser diode, a pilot signal amplitude value indicating the amplitude value of the pilot signal, and each laser diode solid identification number. An optical transmitter comprising a determination threshold value for determining the deterioration of the laser diode with respect to the amplitude value of the pilot signal, and registered in advance.

(Supplementary Note 5) A laser diode is driven by a laser diode current obtained by superimposing a bias current on a modulation current for modulating a transmission signal,
Monitoring the light output of the laser diode;
In an optical transmitter control method for controlling either or both of the optical output power of the laser diode or the extinction ratio of the optical output of the laser diode based on the monitor current output by the monitor circuit,
Modulating a transmission signal with a modulation current superimposed with a pilot signal to generate a laser diode current superimposed with a bias current,
Extract the frequency component of the modulated pilot signal of the optical output,
Comparing the phase of the pilot signal with the phase of the frequency component of the pilot signal;
The deterioration of the laser diode is determined by the phase comparison result,
An optical transmitter control method characterized by maintaining control of the optical output power of the laser diode and the extinction ratio of the optical output of the laser diode when the deterioration of the laser diode is determined.

(Supplementary note 6) The optical transmitter control method according to supplementary note 5, wherein
Detecting the amplitude of the frequency component of the pilot signal and comparing it with the amplitude of the pilot signal;
As a result of the phase comparison, determine the state of deterioration of the laser diode based on the comparison result and a laser diode deterioration determination condition registered in advance,
An optical transmitter control method, comprising: controlling an extinction ratio of an optical output of the laser diode based on a determination result of the deterioration determination circuit.

(Supplementary note 7) The optical transmitter control method according to supplementary note 6, wherein
When the phase comparison result is in a normal range and the amplitude comparison result is in a normal range, and extinction ratio control is performed,
In the state where the phase comparison result is a positive phase, the modulation current is decreased,
When the phase comparison result is in the opposite phase, the bias current or the modulation current is decreased,
An optical transmitter control method, wherein the modulation current is controlled to increase in a state where the phase comparison result is neither a positive phase nor a reverse phase.

(Supplementary note 8) The optical transmitter according to supplementary note 2,
An optical transmitter comprising a pilot generation circuit that generates a pilot signal having a specific pattern.

(Supplementary note 9) The optical transmitter according to supplementary note 1, wherein
The optical transmitter is characterized in that the filter circuit is either a low-pass filter or a band-pass filter.

FIG. 1 illustrates the configuration of an optical transmitter according to the present invention. The figure explaining the direct modulation of LD of this invention FIG. (1) explaining operation | movement of the optical transmitter of this invention FIG. 2 explains the operation of the optical transmitter of the present invention (2). FIG. 2 illustrates the configuration of the optical transmitter according to the present invention. FIG. 3 illustrates the operation of the optical transmitter according to the present invention. FIG. 3 illustrates the configuration of the optical transmitter according to the present invention. The figure explaining an amplitude comparison circuit A diagram for explaining deterioration judgment conditions Deterioration judgment and extinction ratio control processing flow FIG. 4 illustrates the configuration of the optical transmitter according to the present invention. Diagram explaining direct modulation of LD The figure explaining the modulated optical output of a transmission signal Diagram explaining LD conversion efficiency (1) The figure explaining control of an optical transmitter Diagram explaining optical output monitor Diagram explaining LD conversion efficiency (2) Diagram explaining LD degradation The figure explaining LD conversion efficiency at the time of LD degradation

Explanation of symbols

10, 112 LD drive circuit
11 Phase comparison circuit
12 Filter circuit
13, 16 Degradation judgment circuit
14, 18, 20, 113 Control circuit
19 Pilot generation circuit
15 Amplitude comparison circuit
17 Degradation condition storage circuit
101 Laser diode (LD)
102 Amplifier (AMP)
111 Photodiode (PD)
(1) Pilot signal
(2) Transmission signal
(3), (13), (23), (105) Optical output
(4) Ip control signal
(5) Ib control signal
(6), (104) LD current
(7), (17), (27), (106) PD current
(8), (18), (103) LD conversion efficiency curve

Claims (5)

A laser diode driving circuit for driving a laser diode with a laser diode current superimposed so that pilot signals having lower frequencies than the transmission signal are in opposite phases with respect to different voltage levels of the transmission signal;
A monitor circuit for monitoring the optical output of the laser diode;
A filter circuit for extracting the frequency component of the pilot signal from the output of the monitor circuit;
A phase comparison circuit that compares the phase of the pilot signal with the phase of the frequency component extracted by the filter circuit;
A deterioration determination circuit for determining deterioration of the laser diode based on a phase comparison result of the phase comparison circuit;
An optical transmitter comprising: A laser diode driving circuit for driving the laser diode by a laser diode current corresponding to the transmission signal;
A monitor circuit for monitoring the optical output of the laser diode;
An optical transmitter comprising a control circuit for controlling either or both of the optical output power of the laser diode or the extinction ratio of the optical output of the laser diode based on the monitor current output by the monitor circuit,
The laser diode driving circuit generates laser diode currents superimposed such that pilot signals having lower frequencies than the transmission signals are in opposite phases with respect to different voltage levels of the transmission signals,
A filter circuit for extracting the frequency component of the pilot signal from the output of the monitor circuit;
A phase comparison circuit that compares the phase of the pilot signal with the phase of the frequency component extracted by the filter circuit;
A deterioration determination circuit for determining deterioration of the laser diode based on a phase comparison result of the phase comparison circuit;
When the deterioration determination circuit determines deterioration of the laser diode, the control circuit holds control of the optical output power of the laser diode and the extinction ratio of the optical output of the laser diode. . The optical transmitter according to claim 2, wherein
An amplitude comparison circuit that detects the amplitude of the frequency component extracted by the filter circuit and compares it with the amplitude of the pilot signal;
The deterioration determination circuit determines a deterioration state of the laser diode based on a comparison result of the phase comparison circuit, a comparison result of the amplitude comparison circuit, and a laser diode deterioration determination condition registered in advance.
The optical transmitter is characterized in that the control circuit controls an extinction ratio of the optical output of the laser diode based on a determination result of the deterioration determination circuit. A laser diode is driven by a laser diode current in which a bias current is superimposed on a modulation current that modulates a transmission signal,
Monitoring the light output of the laser diode;
In an optical transmitter control method for controlling either or both of the optical output power of the laser diode or the extinction ratio of the optical output of the laser diode based on the monitor current output by the monitor circuit,
Modulating a transmission signal with a modulation current superimposed with a pilot signal to generate a laser diode current superimposed with a bias current,
Extract the frequency component of the modulated pilot signal of the optical output,
Comparing the phase of the pilot signal with the phase of the frequency component of the pilot signal;
The deterioration of the laser diode is determined by the phase comparison result,
An optical transmitter control method characterized by maintaining control of the optical output power of the laser diode and the extinction ratio of the optical output of the laser diode when the deterioration of the laser diode is determined. The optical transmitter control method according to claim 4,
Detecting the amplitude of the frequency component of the pilot signal and comparing it with the amplitude of the pilot signal;
As a result of the phase comparison, determine the state of deterioration of the laser diode based on the comparison result and a laser diode deterioration determination condition registered in advance,
An optical transmitter control method, comprising: controlling an extinction ratio of an optical output of the laser diode based on a determination result of the deterioration determination circuit.

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