JPH11205245A - Optical transmission system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical transmission system that sends an optical signal with high transmission quality independently of a type of an optical fiber used for a transmission line. SOLUTION: The optical transmission system consists of a transmitter 12 that applies electrooptic conversion to a received digital electric signal and provides an output of an optical pulse signal, a transmission line 14, and a receiver 16. The receiver 16 consists of a means 36 that detects a pulse width of a received optical pulse signal, compares it with a prescribed pulse width (an optimum optical signal pulse width of a received signal to realize a best eye pattern) and provides a difference output, and transmission means 38, 40 that send the difference output to the transmitter via other transmission line 18 as the difference output optical signal. The transmitter is made up of reception means 44, 46 that detect the difference output optical signal to provide an output of the difference output and a control means 48 that applies feedback control to a pulse width of the optical signal to be sent so that the difference output is made zero.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical transmission device, and more particularly, to a method for converting an optical pulse signal obtained by converting a digital electrical signal from light to light into a high transmission quality signal so that a received signal shows a good eye pattern. The present invention relates to an optical transmission device for transmitting light.

[0002]

2. Description of the Related Art A conventional digital optical transmission device basically includes a transmitter for transmitting a digital optical signal and an optical fiber, for example, a single mode optical fiber (hereinafter simply referred to as SMF), as shown in FIG. ), And a transmission path for transmitting the transmitted optical signal, and a receiver for receiving the optical signal transmitted by the transmission path. When the distance between the transmitting and receiving points is long, a repeater is provided between the transmitter and the receiver as needed.

A conventional digital optical transmission apparatus has a wavelength of 1.3.
The light in the μm band is used as a transmission wave, and the transmission path is 1.3.
An SMF having a dispersion of almost zero at a wavelength of μm is used. The transmitter has an electric / optical converter for converting a digital electric signal into an optical pulse signal, and converts the input digital electric signal into an optical pulse signal having a certain wavelength and outputs the signal. The receiver detects the transmitted optical pulse signal, performs optical-to-electric conversion, and obtains a digital electric signal. When a regenerative repeater is used as the repeater, the optical pulse signal is detected, the waveform for shaping is also equalized, amplified, etc., and sent out again as an optical pulse signal. When light in the 1.55 μm band is used, zero dispersion occurs at a wavelength in the 1.55 μm band.
The MF is used, and the optical intensity is increased using an optical amplifier in addition to the electric regenerative relay, and is sent to the next transmission line. In addition, there is an optical amplification method.

[0004]

SUMMARY OF THE INVENTION Quartz SM
The propagation loss of F is 1.5 μm
Since the band becomes the minimum and the 1.55 μm band can be optically relayed, the 1.55 μm band light is more suitable for long-distance transmission than the 1.3 μm band light. Therefore, attempts have been made to perform long-distance transmission between continents using light of 1.55 μm. However, when a 1.35 μm band light-dispersed SMF is used as a transmission line and a 1.55 μm band light pulse signal is transmitted over a long distance via a repeater, the waveform of the light pulse signal is deteriorated. There is a problem that the code error rate is high. Therefore, there is a demand for an optical transmission device that can use a 1.3 μm band light and zero-dispersion SMF as a transmission line and can transmit a 1.5 μm band optical pulse signal over a long distance with high transmission quality. In addition, even when an SMF having zero dispersion in the 1.55 μm band is used as a transmission line and an optical pulse signal in the 1.3 μm band is transmitted, the same pulse signal degradation occurs.

In view of the above circumstances, an object of the present invention is to provide an optical transmission apparatus for transmitting an optical signal of high transmission quality irrespective of an optical fiber used in a transmission line. is there.

[0006]

SUMMARY OF THE INVENTION The present inventor evaluates the waveform deterioration of an optical pulse signal based on the quality of an eye pattern of a received signal, and evaluates the received signal from the relationship between the eye pattern of the received signal and the pulse width of the received optical signal. The idea was to control the pulse width of the transmitted optical pulse signal to an optimal value that would maintain the signal eye pattern best. The eye pattern can be observed by displaying a random pattern as shown in FIG. 7A on an oscilloscope by triggering with a clock.
For example, the waveform triggered by the waveform shown in FIG. Next, the waveform triggered by is shown in FIG.
As shown in (c), the waveform triggered by is shown in FIG.
As shown in (d), the waveform triggered by is shown in FIG.
(E). Hereinafter, when the waveform obtained in the same manner is superimposed on the oscilloscope screen, FIG.
An eye pattern as shown in FIG. This is an eye pattern considerably close to an ideal eye pattern, and indicates that the transmission quality of the optical pulse signal is high. By the way, the dispersion of SMF is zero dispersion near 1.3 μm, but is large in the 1.55 μm band. Therefore, when an optical signal in the 1.55 μm band is transmitted through the transmission path of the SMF, the pulse width is compressed and the transmission quality of the received signal is degraded. As shown in FIG. But tend to be off center. vice versa,
SMF with zero dispersion in 1.55 μm band, ie DS
When an optical signal of 1.3 μm is input to F (Dispersion Shifted Fiber), the pulse width increases and the cross point of the eye pattern shifts.

The inventor has also paid attention to the following facts. First, from the above-described correlation between the eye pattern of the received signal and the pulse width of the received optical signal, the optimum pulse width of the received optical signal that can realize the best bit error rate characteristic is determined. Is to exist. Second,
Since there is a certain correlation between the pulse width of the transmission optical signal transmitted from the transmitter and the pulse width of the reception optical signal, the transmission light that can realize the best eye pattern of the reception signal can be realized. There is an optimum pulse width of the signal. Based on the first and second facts described above, the pulse width of the received optical signal is detected, and the pulse width of the transmitted optical signal is feedback-controlled so that the obtained pulse width detection value becomes the optimum pulse width of the received optical signal. The present invention focuses on improving the quality of a received signal, thereby completing the present invention.

[0008] To achieve the above object, an optical transmission device according to the present invention has an electro-optical converter for converting a digital electric signal into an optical pulse signal, and converts an input digital electric signal into an optical signal. A transmitter for outputting as a pulse signal, and a transmission line configured by an optical fiber for transmitting an optical pulse signal from the transmitter, and detecting the transmitted optical pulse signal,
In an optical transmission device having a receiver for performing optical-to-electrical conversion, a detecting means for detecting a pulse width of a transmitted optical pulse signal, and a pulse width detection value detected by the detecting means may be a predetermined pulse width. Control means for feedback-controlling the pulse width of the optical pulse signal from the transmitter.

The present invention is applicable regardless of the wavelength of an optical signal, the type of optical fiber, and the configuration. In particular, when the pulse width is compressed during transmission, for example, when the light in the 1.55 μm wavelength band is used in an optical transmission device using a 1.3 μm wavelength and zero dispersion SMF as the transmission path, Also, when the pulse width is increased during transmission, for example, when the light having a wavelength of 1.3 μm is used in an optical transmission apparatus using a DSF which has a zero dispersion at a wavelength of 1.55 μm as a transmission path, etc. is there. In a preferred embodiment of the present invention, the detecting means includes a detector for detecting the pulse width, and a comparison amplifier for comparing the detected pulse width with a predetermined pulse width to output a difference signal, The means is a controller that feedback controls the pulse width of the optical pulse signal transmitted from the transmitter so that the difference signal becomes zero. Here, the predetermined pulse width means an optimum pulse width of a received optical signal that can realize the best bit error rate, and is obtained in advance by an experiment or the like. The same applies to the following description.

[0010] In a further preferred embodiment of the present invention,
The transmitter includes a semiconductor laser element as an electric-optical converter and a drive circuit for driving the semiconductor laser element, and a threshold value control circuit of the drive circuit as control means. , The feedback control of the pulse width of the optical pulse signal from the transmitter is performed so that the pulse width detection value becomes a predetermined pulse width. In another preferred embodiment of the present invention, the transmitter includes, as an electric-to-optical converter, a semiconductor laser device that emits continuous laser light, and a continuous laser beam emitted from the semiconductor laser device that receives the input digital electric signal. And a threshold value control circuit for controlling the converter as a control means to adjust the pulse width of the output optical pulse signal, and the pulse width detection value is predetermined. The feedback control of the pulse width of the optical pulse signal transmitted from the transmitter is performed so that the pulse width becomes the following pulse width.

In a wavelength division multiplexing (WDM) optical transmission apparatus, a transmitter uses a plurality of different wavelengths to convert a digital electric signal into an optical pulse signal using different wavelengths. An optical conversion unit, which is connected to the electric-optical conversion unit, includes a wavelength multiplexing unit that performs wavelength multiplexing, and the control unit provided in each electric-optical conversion unit, and a receiver, a wavelength separation unit, A plurality of optical-to-electrical converters corresponding to the respective electrical-to-optical converters of the transmitter, and the detection means provided in each of the optical-to-electrical converters, and a light pulse signal Feedback control of pulse width.

[0012]

Embodiments of the present invention will be described below in detail with reference to the accompanying drawings. Embodiment 1 This embodiment is an example of an embodiment of an optical transmission device according to the present invention, and FIG. 1 is a schematic block diagram showing a configuration of the optical transmission device of this embodiment. is there. The optical transmission device 10 of this embodiment converts an input digital electric signal into an optical pulse signal having a predetermined pulse width and a wavelength of 1.5 μm band on the transmitting side, and generates a single dispersion having a zero dispersion with light of a 1.3 μm band. This is an optical transmission device that transmits a signal through a transmission line composed of a mode and an optical fiber, detects an optical pulse signal on the receiving side, performs optical-electrical conversion, and obtains a digital electric signal. The optical transmission device 10 includes:
A transmitter 12 for transmitting an optical pulse signal, a transmission line 14 for transmitting the optical pulse signal transmitted from the transmitter 12, and receiving the optical pulse signal transmitted by the transmission line 14 and detecting the pulse width of the received signal The receiver 16 includes a receiver 16 that compares the difference output with a predetermined pulse width and transmits the difference output as an optical signal, and a transmission line 18 that transmits the difference output optical signal from the receiver 16 to the transmitter 12. Note that the transmission path 14 and the transmission path 18
By setting the wavelength of the LD 20 and the wavelength of the LD 38 to be different from each other, it is possible to unify them as a common transmission path.

The transmitter 12 includes a semiconductor laser 20 and an LD drive circuit 22 for driving the semiconductor laser 20 based on the input digital electric signal, and outputs the digital electric signal as an optical pulse signal. Transmission line 14 is SMF
And, if necessary, a repeater in the middle of the route.

The receiver 16 includes a photodiode 24 provided as a photodetector, a preamplifier 26 for amplifying a signal output from the photodiode 24, a low-frequency pass filter 28, and an amplifier for limiting the amplitude of the amplified signal. A limit amplifier 30 for converting the signal to 0 or 1 and a retiming circuit 34 for decoding and separating the signal into a data signal and a clock signal are provided. Further, the receiver 16 includes a differential amplifier 36 as means for detecting the pulse width of the received optical signal. The differential amplifier 36 extracts the inverted signal from the limit amplifier 30, detects the pulse width from the inverted signal as a pulse width detection value of the DC signal, and determines a predetermined pulse width (a received optical signal that can realize the best eye pattern). And outputs the difference between the detected pulse width value and the predetermined pulse width as a difference output. The receiver 16 further includes a semiconductor laser 38 and an LD drive circuit 40 for driving the semiconductor laser 38, and transmits a difference output as a difference output optical signal. The difference output optical signal transmitted from the semiconductor laser 38 is
The transmitter 1 passes through a pulse width transmission line 18 composed of SMF.
2 is transmitted.

The transmitter 12 includes a photodetector 44 composed of a photodiode as a means for receiving the differential output optical signal, a preamplifier 46 for amplifying the differential output of the electric signal output from the photodiode 44, and an amplified differential signal. L based on
A threshold control circuit 48 for controlling the threshold of the D drive circuit 22 is provided. Thereby, the transmitter 12
Controls the emission time of the semiconductor laser 20 by the LD drive circuit 22 and feedback-controls the pulse width of the transmission optical signal of the transmitter 12 so that the difference output becomes zero.

With the above configuration, the optical transmission apparatus 10 of the first embodiment controls the pulse width of the transmission optical signal so that the pulse width of the reception optical signal is set to a predetermined pulse so that the best eye pattern can be obtained. The width (the optimum pulse width of the received optical signal that produces the best eye pattern) is maintained. In particular, the configuration of the present embodiment is particularly applicable to the mark ratio of the limit amplifier 30 (average ratio of 0 and 1 of the binarized signal over a long period).
Is about 1/2.

As a modification of the first embodiment, the portion A of FIG. 1 of the transmitter 12 of the optical transmission device 10 may be configured as shown in FIG. In this example, as shown in FIG. 2, a portion A in FIG. 1 modulates a semiconductor laser 20 that emits continuous laser light and a continuous laser light emitted from the semiconductor laser 20 by an input digital electric signal. An external modulator 23 that outputs the optical pulse signal as a converted optical pulse signal, and a threshold control circuit 48 that controls the pulse width of the optical pulse signal of the external modulator 23 by a threshold value. Except for the portion A in FIG. 1, the other configuration is the same as the configuration of the first embodiment.

Embodiment 2 In this embodiment, an optical transmission apparatus according to the present invention is used for wavelength division multiplexing.
It is an embodiment example applied to an optical amplification repeater transmission system.
FIG. 3 is a schematic diagram showing a configuration of the present embodiment, and FIGS. 4 and 5 are schematic diagrams showing configurations of a transmitter and a receiver, respectively. The optical transmission device 50 of the present embodiment is an optical transmission device constructed as a wavelength division multiplexing / optical amplifying repeater transmission system, in which two remote bases A and B have transmitters 52A and B and receivers 52A and B, respectively. 54A and 54B, and is a system capable of bidirectional transmission and reception via transmission lines 56 and 58 made of SMF. In the transmission lines 56 and 58, m repeaters 60 and m repeaters 62 are sequentially provided at appropriate places. Further, the optical transmission device 50 includes the transmitter 5
It has a monitoring and control system 64 for monitoring and controlling the operations of 2A, B, receivers 54A, B and repeaters 60, 62. The monitoring and control system 64 includes central monitoring and control rooms 66A and B provided at the bases A and B, respectively,
A and B, a monitoring station (SV) 68 provided in each of the receivers 54A and B, and the repeaters 60 and 62. Control is performed by sending necessary instructions from the control rooms 66A and 66B.

In this optical transmission device 50, transmitters 52A and 52B
Is composed of an O / E converter and a transmitter, as shown in FIG. 4, uses a plurality of mutually different wavelengths, converts an input digital electrical output into an optical pulse signal, and outputs it.
It has a transmission system and a wavelength multiplexing unit that wavelength-multiplexes optical pulse signals of a plurality of electrical / optical conversion-transmission systems. Further, each electric-optical conversion-transmission system controls a threshold value of an LD drive circuit as a pulse width control circuit, and has a threshold control circuit (not shown) having the same configuration as that of the first embodiment. It has. As shown in FIG. 5, the receivers 54A and 54B each include a preamplifier, a wavelength demultiplexing unit that divides the wavelength multiplexed signal into individual optical pulse signals, and a transmitter including a receiver and an E / O converter. A plurality of optical-to-electrical conversion systems corresponding to the respective electrical-to-optical conversion-transmission systems.
And a pulse width detecting means (not shown) having the same configuration as that of FIG. The transmission lines 56 and 58 are used in common with the main signal as transmission lines for transmitting the difference output between the pulse width detection value and the predetermined pulse width as an optical signal.

For example, when the transmitter 52A transmits an optical pulse signal to the receiver 54B via the transmission path 56, the receiver 54B detects the pulse width of the transmitted optical pulse signal,
The pulse width is compared with a predetermined pulse width (the optimum pulse width of the received optical signal that causes the best eye pattern to appear), and the difference between the detected pulse width and the predetermined pulse width is output as a difference output. Receiver 5
4B further transmits the difference output as a difference output optical signal to one wavelength of the wavelength division multiplex communication from the transmitter 52B to the transmission path 58.
Through the receiver 54A. The receiver 54A transmits the received difference output to the transmitter 5 via the monitoring station 68.
Send to 4A. Thus, the transmitter 52A performs feedback control of the pulse width of the transmission optical signal so that the difference output becomes zero, as in the first embodiment. Regarding the transmission of the optical pulse signal between the transmitter 52B and the receiver 54A,
This is the same as the above description.

A threshold control circuit having the same configuration as that of the first embodiment provided in the transmitter 52 may be provided in each of the repeaters 60 and 62. As a result, the optical signal is amplified by each of the repeaters 60 and 62, and the pulse width of the optical signal to be relayed is feedback-controlled so that the difference output becomes zero, similarly to the transmitter 52. The transmission quality to the receiver and the transmission quality from the repeater to the receiver can be improved.

[0022]

According to the present invention, detection means for detecting the pulse width of a transmitted optical pulse signal, and control means for controlling the pulse width of an optical pulse signal from a transmitter are provided. Feedback control of the pulse width of the optical pulse signal from the transmitter so that the pulse width detection value becomes a predetermined pulse width, to provide an optical transmission device that transmits an optical pulse signal with high transmission quality, that is, a low bit error rate. Has been realized. By using the optical transmission device according to the present invention, it is possible to transmit an optical signal with high transmission quality while compensating for differences in the characteristics of optical fibers. Further, in a wavelength division multiplexing / optical amplification relay transmission system, a plurality of electrical / optical conversion-transmission systems using different wavelengths are provided with respective pulse width control means, and each electrical / optical conversion of a transmitter is provided. A pulse width detecting means is provided in each of the reception-optical-electrical conversion systems provided corresponding to the transmission systems, and feedback control of the pulse width of the optical pulse signal is performed for each of the electric-optical conversion-transmission systems, so that each channel is controlled. In addition, the transmission quality can be accurately controlled regardless of the length of the transmission distance, the number of optical amplifiers, and the length of the interval.

[Brief description of the drawings]

FIG. 1 is a schematic block diagram illustrating a configuration of an optical transmission device according to a first embodiment of the present invention.

FIG. 2 is a schematic block diagram of a main part of a modification of the first embodiment.

FIG. 3 is a schematic block diagram illustrating a configuration of an optical transmission device according to a second embodiment of the present invention.

FIG. 4 is a conceptual diagram illustrating a configuration of a transmitter according to a second embodiment.

FIG. 5 is a conceptual diagram illustrating a configuration of a receiver according to a second embodiment.

FIG. 6 is a schematic diagram illustrating a configuration of a conventional optical transmission device.

FIGS. 7A to 7G are diagrams illustrating an eye pattern, respectively.

[Explanation of symbols]

 Reference Signs List 10 Optical transmission apparatus of first embodiment 12 Transmitter 14 Transmission path 16 Receiver 18 Transmission path 20 Semiconductor laser 22 LD drive circuit 23 External modulator 24 Photodiode 26 Preamplifier 28 Low frequency pass filter 30 Limit amplifier 34 Retiming circuit 36 Differential amplifier 38 Semiconductor laser 40 LD drive circuit 44 Photodiode 46 Preamplifier 48 Threshold control circuit 50 Optical transmission device of Embodiment 2 52 Transmitter 54 Receiver 56, 58 Transmission path 60, 62 Repeater 64 Monitoring / control System 66 Central monitoring and control room 68 Monitoring station (SV)

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification code FI H04B 10/08 17/00

Claims (5)

[Claims] A transmitter for converting a digital electric signal into an optical pulse signal, the transmitter converting an input digital electric signal to output as an optical pulse signal, and an optical fiber; A transmission path for transmitting the optical pulse signal from the transmitter, and detecting the transmitted optical pulse signal,
In an optical transmission device including a receiver for performing optical-to-electrical conversion, a detecting means for detecting a pulse width of a transmitted optical pulse signal, and a pulse width detection value detected by the detecting means may be a predetermined pulse width. Control means for performing feedback control of the pulse width of the optical pulse signal from the transmitter. 2. The detecting means comprises a detector for detecting a pulse width, and a comparison amplifier for comparing a detected pulse width value with a predetermined pulse width to output a difference signal. The optical transmission device according to claim 1, wherein the controller is a controller that performs feedback control of a pulse width of an optical pulse signal transmitted from the transmitter such that: 3. The transmitter includes a semiconductor laser device as an electric / optical converter and a drive circuit for driving the semiconductor laser device, and a control circuit includes a threshold control circuit of the drive circuit, and the semiconductor device is connected to the semiconductor laser device via the drive circuit. 3. The pulse width of an optical pulse signal from a transmitter is feedback-controlled by controlling a light emission time of a laser element so that a pulse width detection value has a predetermined pulse width. Optical transmission equipment. 4. A transmitter, as an electric / optical converter, converts a continuous laser light emitted from the semiconductor laser element into an optical pulse signal corresponding to an input digital electric signal. A converter for controlling the converter as a control means and a threshold control circuit for adjusting the pulse width of the output optical pulse signal, and transmitting the detected pulse width so that the detected pulse width becomes a predetermined pulse width. 3. The optical transmission device according to claim 1, wherein the pulse width of the optical pulse signal transmitted from the transmitter is feedback-controlled. 5. A wavelength-division multiplexing device, wherein the transmitter is connected to a plurality of electrical-optical converters for converting digital electrical signals into optical pulse signals using different wavelengths, and to an electrical-optical converter. A wavelength multiplexing unit to be converted, and the control unit provided in each of the electrical / optical conversion units, wherein the receiver comprises: a wavelength separation unit; and a plurality of optical / optical conversion units corresponding to the electrical / optical conversion units of the transmitter. 5. The apparatus according to claim 1, further comprising an electric conversion unit, and the detection unit provided in each of the light-to-electric conversion units, wherein the pulse width of the light pulse signal is feedback-controlled for each electric-to-light conversion unit. The optical transmission device according to any one of the above.