JP2001320329A - Device and method for detecting pulse distortion, and recording medium with program recorded thereon - Google Patents

Abstract

PROBLEM TO BE SOLVED: To simply detect the distorted state of a received optical pulse signal. SOLUTION: A post-transmission optical waveform 13 is controlled by an optical amplifier 2 so that output power is a constant level, converted into an electrical signal by O/E converter 3 and controlled by an amplifier circuit 4 so that power is a constant level, and a direct current component is eliminated by an AC coupler 5. Next, the slanted line part of an in-phase electricity waveform 14 is inputted to a lowpass filter 8 by an offset adjustment circuit 6 and a rectifier 7. Next, a voltage comparison circuit 9 compares a voltage circuit output 16 decided by a variable voltage circuit 11 with a filter output 15 of the filter 8, and it can be detected whether a pulse distortion is due to pulse compression or pulse expansion, in such a manner that a voltage monitor 10 monitors the comparison output. Adverse effects due to automatic dispersion compensation and nonlinear optics by feedbacking a value detected by the monitor 10 to a dispersion compensation module 17 and by controlling the gain of the optical signal.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pulse distortion detecting device and method for detecting the state of optical pulse distortion in an optical communication system, and a recording medium on which a program used for the method is recorded.

[0002]

2. Description of the Related Art Generally, an optical fiber used as an optical transmission line in an optical fiber communication system has chromatic dispersion characteristics. The chromatic dispersion characteristic is a characteristic in which the propagation time of an optical signal varies depending on the wavelength. A digital optical signal propagating in an optical fiber having chromatic dispersion characteristics deteriorates in optical waveform after transmission as the transmission speed increases or as the transmission distance of the optical fiber increases. The chromatic dispersion characteristic of a typical single mode optical fiber is as follows: chromatic dispersion value = 17 ps
/ Nm / km ＠ wavelength 1.55 μm.

When a digital signal having a transmission speed of 10 Gbit / s, for example, is propagated in the optical fiber 80 km, the transmission characteristics are greatly affected, and the optical waveform after transmission is greatly distorted due to chromatic dispersion. As a result, in the received digital waveform, it is impossible to distinguish between a mark and a space, so that optical transmission with good quality and a sufficiently small error rate becomes impossible.

As a means for correcting the waveform distortion due to the chromatic dispersion, the dispersion of the optical fiber is compensated, that is, an optical device having a dispersion value equal to the dispersion amount of the optical fiber and opposite in sign to the optical fiber is inserted into the optical fiber. A way to do that is being considered. In general, a dispersion compensating fiber or a chirped grating having a dispersion value opposite to that of a transmission line is used for a dispersion compensating device.

[0005] When dispersion compensation is performed using these devices, it is necessary to make the total dispersion amount of the transmission line equal to the compensation amount of the dispersion compensation device. The state of the waveform distortion differs depending on the correlation between the amount of dispersion of the transmission path and the chirp characteristic of the modulator of the transmitter.

FIG. 6 shows the relationship between the chirp characteristic of the modulator and the waveform distortion due to the amount of dispersion in the transmission path. As an example, when the chirp characteristic of the modulator is positive and the amount of dispersion in the transmission path is positive, the waveform is distorted so as to expand as shown in FIG. Also,
When the chirp characteristic of the modulator is positive and the amount of dispersion of the transmission path is negative, the waveform is distorted in a compression tendency as shown in FIG. As described above, the waveform is distorted due to the dispersion of the transmission line, and the reception sensitivity is deteriorated.

On the other hand, when the dispersion compensation amount and the total dispersion amount of the transmission line match (cases of FIGS. 6 (b), (e), and (h))
The reception waveform is equivalent to the waveform of the optical transmission unit, and excellent optical transmission without deterioration in sensitivity is realized in the optical reception unit. That is, when performing dispersion compensation, it is important to make the total dispersion amount and the dispersion compensation amount of the transmission line coincide with each other.

[0008]

In order to make the total amount of dispersion in the transmission line equal to the amount of dispersion compensation as described above, it is necessary to know the amount of dispersion in the transmission line. For this purpose, it is necessary to detect the state of the received pulse distortion. In an optical transmission system, pulse distortion is also caused by the influence of the nonlinear optical effect, thereby limiting the transmission distance.
From the above, in order to correct pulse distortion, it is an important subject to detect distortion of an optical signal propagated through an optical line.

Incidentally, techniques for performing dispersion compensation are disclosed in, for example, JP-A-8-256106, JP-A-8-265256, JP-A-10-213714, and JP-A-11-127.
No. 136186 discloses this.

The present invention has been made in view of the above circumstances, and has as its object to enable easy detection of a distortion state of an optical pulse signal.

[0011]

In order to achieve the above object, a pulse distortion detecting device according to the present invention comprises a converting means for converting an input optical pulse signal into an electric pulse signal, and a converted pulse signal. A detection unit that detects whether the state of signal distortion is pulse compression or pulse expansion and outputs a signal of a level corresponding to the state.

In the pulse distortion detecting method according to the present invention, a conversion procedure for converting an input optical pulse signal into an electric pulse signal, and a step of determining whether the distortion state of the converted pulse signal is pulse compression or not. Detects spread,
And a detection procedure for outputting a signal of a level corresponding to the state.

In a recording medium on which a program according to the present invention is recorded, a conversion process for converting an input optical pulse signal into an electrical pulse signal and a state of distortion of the converted pulse signal is pulse compression. And a program for executing a detection process of detecting whether or not the pulse is spread and outputting a signal of a level corresponding to the state.

[0014]

Embodiments of the present invention will be described below with reference to the drawings. The present embodiment is applied to an optical communication system, and detects a state of distortion of an optical pulse received by an optical receiver. As shown in FIG. 2, the pulse distortion causes pulse compression or pulse spread. These distortions are caused by the influence of the dispersion of the optical fiber and the influence of the nonlinear optical effect in the optical communication system.

In this embodiment, as shown in FIG. 5, a pulse distortion occurs in an optical transmission waveform 12 propagated through an optical fiber 1, and when the optical transmission waveform 12 is input to an optical amplifier 2, an optical pulse is output by an optical / electrical converter 3. Are converted into electric pulses, the pulse distortion is detected by the pulse distortion detection circuit 18, and the detected value can be monitored by the voltage monitor 10. At this time, the pulse distortion can be detected regardless of the dispersion or the nonlinear optical effect. Automatic dispersion compensation can also be performed by feeding back and controlling the value detected by the voltage monitor 10 to the dispersion compensation module 17.

FIG. 1 is a block diagram showing a pulse distortion detecting device according to a first embodiment of the present invention. In FIG. 1, a pulse distortion detecting device includes an optical fiber 1 and an optical amplifier 2.
It comprises an optical / electrical converter 3, an amplifier circuit 4, an AC coupler 5, an offset adjusting circuit 6, a rectifier 7, a low-pass filter 8, a voltage comparing circuit 9, a voltage monitor 10, and a variable voltage circuit 11.

Next, the outline of the operation will be described. Optical fiber 1
The following describes an example in which the optical transmission waveform 12 propagated through the optical communication apparatus has a pulse distortion like the optical waveform 13 after transmission due to the influence of dispersion and nonlinear optical effects. Optical waveform after transmission 13
Is controlled by the optical amplifier 2 so that the output power is constant, is converted into an electric signal by the optical / electrical converter 3, is controlled by the amplifier circuit 4 so that the power is constant, and is controlled by the AC coupler 5. The components are removed. Next, the shaded portion of the in-phase electric waveform 14 is input to the low-pass filter 8 by the offset adjustment circuit 6 and the rectifier 7.

Next, the voltage circuit output 16 determined by the variable voltage circuit 11 and the filter output 15 of the low-pass filter 8 are compared by the voltage comparison circuit 9, and the difference output is monitored by the voltage monitor 10. The state of pulse distortion can be detected. Further, by feeding back the value detected by the voltage monitor 10 to the dispersion compensation module 17 and controlling the gain of the input optical signal, it is possible to reduce the effects of the automatic dispersion compensation and the nonlinear optical effect.

Next, a more detailed operation will be described. When the optical waveform 13 after transmission through the optical fiber 1 is distorted due to the influence of dispersion, nonlinear optical effect, or the like, it appears as pulse compression or pulse expansion as shown in FIGS. When an ideal optical pulse signal having a mark rate of 1/2 and a duty ratio of 50% is transmitted, as shown in FIG. 2A, the mark component increases in pulse compression, and conversely, in FIG.
As shown in (c), the mark component decreases in the pulse spread.

The operation of this embodiment will be described for each case. In FIG. 1, first, as shown in FIG.
To enter. The optical pulse signal whose output power is controlled to be constant by the optical amplifier 2 is converted into an electric pulse signal by the optical / electrical converter 3 and becomes an electric pulse signal whose output power is controlled by the amplifier circuit 4 to be constant. Removes the DC component. Next, the turn-on voltage of the rectifier 7 is applied from the offset adjustment circuit 6, a half-wave rectified signal is obtained from the rectifier 7, and the low-pass filter 8 converts the signal into a DC voltage filter output 15.

Here, the voltage circuit output 16 is set so that the voltage value of the filter output 15 and the voltage value of the variable voltage circuit 11 become equal. This state is referred to as an initial setting state. When the optical waveform input to the amplifier 2 is the pulse compression shown in FIG. 2A, the mark component increases, so that the filter output 15 becomes larger than the voltage circuit output 16. Figure 2
In the case of the pulse spread shown in (c), since the mark component decreases, the filter output 15 becomes smaller than the voltage circuit output 16.

By detecting this relationship as a voltage value by the voltage monitor 10 via the voltage comparison circuit 9, the state of the pulse distortion can be detected. Further, by controlling the value detected by the voltage monitor 10 by feeding it back to the dispersion compensation module 17, the influence of the automatic dispersion compensation and the nonlinear optical effect can be reduced.

FIG. 3 is a block diagram showing a pulse distortion detecting device according to a second embodiment of the present invention. 3, the pulse distortion detecting device according to the present embodiment includes an optical amplifier 2, an optical / electrical converter 3, an amplifier circuit 4, and an AC coupler 5
a, 5b, an offset adjusting circuit 6, rectifiers 7a, 7b, low-pass filters 8a, 8b, a voltage comparing circuit 9, and a voltage monitor 10.

Next, the operation will be described. The optical pulse signal whose output power is controlled to be constant by the optical amplifier 2 is an optical / optical signal.
The signal is converted into an electric pulse signal by the electric converter 3 and is amplified by the amplifier circuit 4.
As a result, an in-phase and an opposite-phase electric pulse signal whose output power is controlled to be constant is obtained. Subsequently, the DC components are removed by the AC couplers 5a and 5b. Next, the turn-on voltages of the rectifiers 7a and 7b are applied from the offset adjustment circuit 6, and the hatched portions of the in-phase electric waveform 14a and the anti-phase electric waveform 14b are
Half-wave rectified signals are obtained at a and 7b, and are converted into DC voltages at the low-pass filters 8a and 8b.

The optical pulse input to the optical amplifier 2 is shown in FIG.
If there is no distortion shown in FIG.
The voltage value of “a” becomes equal to the voltage value of the negative-phase filter output 15b. When the optical waveform input to the optical amplifier 2 is the pulse compression shown in FIG. 2A, the mark component increases, so that the in-phase filter output 15a becomes larger than the anti-phase filter output 15b. Conversely, in the case of the pulse spread shown in FIG. 2C, since the mark component is reduced, the in-phase filter output 15
a becomes smaller than the output 15b of the negative phase filter.

By detecting this relationship with the voltage monitor 10, the state of pulse distortion can be detected. Further, by controlling the value detected by the voltage monitor 10 by feeding it back to the dispersion compensation module 17, the influence of the automatic dispersion compensation and the nonlinear optical effect can be reduced. According to the present embodiment, the variable voltage circuit 1 shown in FIG.
There is an effect that the adjustment by 1 can be omitted.

FIG. 4 is a block diagram showing a pulse distortion detecting device according to a third embodiment of the present invention.

The pulse distortion detecting device according to the present embodiment comprises an optical amplifier 2, an optical / electrical converter 3, an amplifying circuit 4,
It comprises a coupler 5, an offset adjusting circuit 6, rectifiers 7a and 7b, low-pass filters 8a and 8b, an inverting circuit 19, a voltage comparing circuit 9, and a voltage monitor 10.

Next, the operation will be described. The optical pulse signal whose output power is controlled to be constant by the optical amplifier 2 is converted into an electric pulse signal by the optical / electrical converter 3, and becomes an in-phase electric pulse signal whose output power is controlled to be constant by the amplifier circuit 4. The DC component is removed by the AC coupler 5. The turn-on voltages of the rectifiers 7a and 7b are respectively applied from the offset adjustment circuit 6, and the hatched portions of the in-phase electric waveform 14a and the anti-phase electric waveform 14b are half-wave rectified by the rectifiers 7a and 7b, and the rectification directions are different. The obtained signal is obtained and is converted into a DC voltage by the low-pass filters 8a and 8b. The signal output from the rectifier 7b is inverted by an inverting circuit 18.
Is inverted. This inverted output and the rectified output of the rectifier 7a are compared by the voltage comparison circuit 9.

The optical waveform input to the optical amplifier 2 is shown in FIG.
When there is no distortion shown in (b), the in-phase filter output 15a
Is equal to the voltage value of the common-mode filter output 15b. When the optical waveform input to the amplifier 2 is the pulse compression shown in FIG. 2A, the mark component increases, so that the in-phase filter 15a becomes larger than the in-phase filter output 15b. Conversely, in the case of the pulse spread shown in FIG. 2C, since the mark component is reduced, the in-phase filter output 15a becomes smaller than the in-phase filter output 15b.

By detecting this relationship with the voltage monitor 10, pulse distortion can be detected. Further, by controlling the value detected by the voltage value monitor 10 by feeding it back to the dispersion compensation module 18, the influence of the automatic dispersion compensation and the nonlinear optical effect can be reduced. According to the present embodiment, the variable voltage circuit 1 shown in FIG.
1 can be omitted, and there is an effect that detection can be performed using only the in-phase electric signal.

In each of the embodiments described above, when compensating the dispersion of the transmission line in the optical transmission system, it is necessary to make the total dispersion amount and the dispersion compensation amount of the transmission line coincide with each other. After the transmission, it is determined whether the distortion state of the optical waveform is pulse compression or pulse expansion, and a voltage value corresponding to the determined state is obtained from the voltage comparison circuit 9.

FIG. 5 is a diagram schematically showing each embodiment of FIGS. 1, 3 and 4, and portions corresponding to the respective drawings are denoted by the same reference numerals and redundant description is omitted. In FIG.
The pulse distortion detection circuit 18 is provided with the AC
It comprises a coupler 5, an offset adjusting circuit 6, a rectifier 7, a low-pass filter 8, a voltage comparing circuit 9, and the like, and determines whether the state of the waveform distortion after transmission is pulse compression or pulse expansion. , To obtain a voltage value of a level corresponding to the determined state.

Although the circuits shown in FIGS. 1, 3 and 4 may have a hardware configuration, they may be configured as a computer system including a CPU and a memory. When configured as a computer system, the memory constitutes a recording medium on which the program according to the present invention is recorded. This recording medium stores a program for executing a process based on the above-described operation. In addition, as such a recording medium, a semiconductor storage device, an optical disk, a magneto-optical disk, a magnetic recording medium, or the like can be used.

[0035]

As described above, according to the present invention, it is determined whether the state of distortion of the optical waveform after transmission is pulse compression or pulse expansion, and a signal having a level corresponding to the determined state is obtained. Therefore, the state of distortion can be easily detected with a simple configuration, and a signal from which distortion has been removed can be obtained by controlling the gain of an input optical signal based on the detected signal. The transmission quality of the system can be improved.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a pulse distortion detection device according to a first embodiment of the present invention.

FIG. 2 is a waveform diagram showing an optical waveform after transmission.

FIG. 3 is a block diagram showing a pulse distortion detection device according to a second embodiment of the present invention.

FIG. 4 is a block diagram illustrating a pulse distortion detection device according to a third embodiment of the present invention.

FIG. 5 is a block diagram schematically showing each embodiment.

FIG. 6 is a waveform chart showing waveform distortion due to chirp characteristics of a modulator and the amount of dispersion in a transmission path.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Optical fiber 2 Optical amplifier 3 Optical / electrical converter 4 Amplification circuit 5 AC coupler 6 Offset adjustment circuit 7 Rectifier 8 Low-pass filter 9 Voltage comparison circuit 10 Voltage monitor 11 Variable voltage circuit 12 Optical transmission waveform 13 Optical waveform after transmission 14 In-phase electrical waveform 14 Negative-phase electrical waveform 15 Filter output 15a In-phase filter output 15b Negative-phase filter output 16 Voltage circuit output 17 Dispersion compensation module 18 Pulse distortion detection circuit 19 Inverting circuit

Claims (15)

[Claims] A converting means for converting an input optical pulse signal into an electrical pulse signal; detecting whether the distortion state of the converted pulse signal is pulse compression or pulse expansion, and detecting the distortion. And a detecting means for outputting a signal of a level corresponding to the pulse distortion detecting device. 2. The detecting unit includes: a removing unit that removes a DC component of the converted pulse signal; a rectifying unit that rectifies the pulse signal from which the DC component has been removed; and a turn-off voltage of the rectifying unit. Adjusting means for performing the operation; low-pass filter means for passing the rectified signal; variable voltage output means for outputting a desired voltage; output voltage of the variable voltage output means and output voltage of the low-pass filter means 2. The pulse distortion detecting device according to claim 1, further comprising a voltage comparing means for comparing the pulse distortion with the voltage. 3. The conversion means outputs a pulse signal having the same phase as the input optical pulse signal and a pulse signal having a phase opposite to that of the input optical pulse signal. Remove DC component 2
Two rectifying means for rectifying each pulse signal from which the DC component has been removed; adjusting means for adjusting a turn-off voltage of each rectifying means; and two low-level signals through which the rectified signals pass. 2. The pulse distortion detection device according to claim 1, further comprising: a band-pass filter unit; and a voltage comparison unit that compares output voltages of the low-pass filter units. 4. The detecting means includes: removing means for removing a DC component of the converted pulse signal; two rectifying means for rectifying the pulse signal from which the DC component has been removed; and turning off each of the rectifying means. Adjusting means for adjusting a voltage; two low-pass filter means through which the rectified signals pass; an inverting means for inverting an output of one of the low-pass filter means; an inverted output of the inverting means; 2. A pulse distortion detecting apparatus according to claim 1, further comprising a voltage comparing means for comparing an output voltage of said low-pass filter means with an output voltage of said low-pass filter means. 5. The pulse distortion detection device according to claim 1, further comprising control means for controlling a gain of the input optical pulse signal in accordance with a detection output of the detection means. 6. A conversion procedure for converting an input optical pulse signal into an electrical pulse signal, and detecting whether the distortion state of the converted pulse signal is pulse compression or pulse expansion, and according to the state. And a detection step of outputting a signal of a different level. 7. The detecting procedure includes: a removing procedure for removing a DC component of the converted pulse signal; a rectifying procedure for rectifying the pulse signal from which the DC component has been removed; and adjusting a turn-off voltage in the rectifying procedure. An adjusting procedure, a low-pass procedure for passing a low-frequency component of the rectified signal, a voltage output procedure for outputting a desired voltage, an output voltage according to the voltage output procedure, and an output voltage according to the low-pass procedure. 7. A pulse distortion detecting method according to claim 6, comprising: a comparing step of comparing the pulse distortion with the pulse distortion. 8. A pulse signal having the same phase as the input optical pulse signal and a pulse signal having the opposite phase to the input optical pulse signal according to the conversion procedure, and the detecting step includes: A removing procedure, a rectifying procedure for rectifying each pulse signal from which the DC component has been removed, an adjusting procedure for adjusting a turn-off voltage in the rectifying procedure, and a low-pass component of each of the rectified signals, respectively. 7. The pulse distortion detection method according to claim 6, comprising: a low-pass procedure to be performed; and a comparing procedure for comparing each output voltage of the low-pass procedure. 9. The detecting step includes: removing a DC component of the converted pulse signal; rectifying the pulse signal from which the DC component has been removed to obtain two rectified outputs; An adjustment procedure for adjusting a turn-off voltage in each rectification procedure; a low-pass procedure for passing a low-frequency component of each of the rectified signals; an inversion procedure for inverting one of the low-pass outputs; 7. The pulse distortion detecting method according to claim 6, further comprising a comparing step of comparing the output voltage with the other low-pass output voltage. 10. The pulse distortion detection method according to claim 6, further comprising a control step of controlling a gain of the input optical pulse signal according to a detection output of the detection step. 11. A conversion process for converting an input optical pulse signal into an electrical pulse signal, and detecting whether a state of distortion of the converted pulse signal is pulse compression or pulse expansion, and according to the state. Recording medium for recording a program for executing a detection process of outputting a signal of a predetermined level. 12. The detection process includes: a removal process for removing a DC component of the converted pulse signal; a rectification process for rectifying the pulse signal from which the DC component has been removed; and adjusting a turn-off voltage in the rectification process. Adjustment processing, low-pass processing for passing a low-frequency component of the rectified signal, voltage output processing for outputting a desired voltage, output voltage for the voltage output processing and output voltage for the low-pass processing 12. A recording medium on which the program according to claim 11, comprising a comparison process for comparing the program. 13. The conversion processing outputs a pulse signal having the same phase as the input optical pulse signal and a pulse signal having the opposite phase to the input optical pulse signal. The detection processing includes: converting DC components of the pulse signals having the same phase and the opposite phase, respectively. Removing processing, rectifying each pulse signal from which the DC component has been removed, adjusting processing to adjust a turn-off voltage in the rectifying processing, and passing low-frequency components of the rectified signals, respectively. 12. The recording medium according to claim 11, further comprising: a low-pass process for performing the low-pass process; and a comparison process for comparing each output voltage in the low-pass procedure. 14. The detection process includes: a removal process for removing a DC component of the converted pulse signal; a rectification process for rectifying the pulse signal from which the DC component has been removed to obtain two rectified outputs; An adjustment process for adjusting a turn-off voltage in each rectification process; a low-pass process for passing a low-frequency component of each of the rectified signals; an inversion process for inverting one of the low-pass outputs; 12. The recording medium according to claim 11, further comprising a comparison process of comparing the output voltage with the other low-pass output voltage. 15. A program according to claim 11, wherein a program for executing a control process for controlling a gain of said input optical pulse signal in accordance with a detection output by said detection process is recorded. Recording medium.