JPH11127120A - Coding in optical network and optical switch control system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To control an optical switch, so that a mark rate of a coded signal due to signal interruption through optical switch changeover and a consecutive same bit number are not changed. SOLUTION: Optical transmitters 1, 101 consist of coding sections 11-111 and electrooptic conversion sections 12-112 through DFB-LD direct modulation at 1.55 μm band, and optical receivers 3, 103 constituted of photoelectric conversion sections 31-131 and decoding sections 32-132. Since the photoelectric conversion sections 31, 131 are configured with a PIN-PD, a Si preamplifier and AC coupled identification circuit and a mean identification level is adopted, a mark rate in data in average is 1/2. The coding sections 11-111 encode a signal to be sent so that the mark rate of the sent signal and the consecutive same code bit number are within a prescribed range and an optical switch 4 is controlled, so that a mark rate of a coded signal due to signal interrupt by optical switch changeover and a consecutive same bit number are not changed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to transmission line coding and an optical switch control method in an optical network using an optical switch.

[0002]

2. Description of the Related Art In an optical network using an optical switch, a network having a large capacity, a small size, and a low delay can be realized as compared with a case using an electric switch. Conventionally, optical networks using various optical switches have been researched and developed.
There has not been much studied on optical switch elements and network configurations, and optical data link units such as optical transmitters, optical receivers and transmission line codes.

[0003] Regarding transmission line codes, see, for example,
Japanese Patent Application Laid-Open No. 207139/1992 “Cell signal processing circuit and optical switch using the same” describes that a mark rate is 1 /
2, the optical switch switching is performed by the "0" bit of the dummy data so that the mark rate is not changed by the optical switch switching. , And the same code continuation is not particularly considered.

[0004]

However, when an optical network is actually constructed using an optical data link and an optical switch, the network cannot be realized unless the optical data link unit operates normally. Since many optical data links are used in an optical network, an optical data link using an inexpensive AC-coupled optical receiver is desired.
In the case of AC coupling, in order to maintain DC balance, the mark ratio of a signal to be transmitted needs to be approximately 、, and the number of consecutive bits of the same code needs to be within the range satisfying the low cutoff frequency of the receiver. .

[0005] Further, in an optical network using an optical switch, when the optical switch is switched, the signal is temporarily interrupted on the receiving side. Therefore, in an optical receiver,
Possibility of receiving a signal whose mark rate is not 1/2 even if the mark rate of the transmitted signal is 1/2, or a signal in which 0 consecutive bits are greater than the number of consecutive bits of the same sign of the transmitted signal Could be received.

For this reason, when the optical receiver is AC-coupled, the DC balance may be lost, or the signal may include a component having a frequency lower than the low cutoff frequency, and the signal may not be accurately received. there were.

Further, when the size of the optical network is increased and the number of nodes is increased, it is difficult to accurately control the switching timing of each node.

[0008]

SUMMARY OF THE INVENTION The present invention encodes a signal to be transmitted so that the mark rate and the number of consecutive bits of the same code of the signal to be transmitted are within predetermined ranges, and codes the signal by signal disconnection by switching an optical switch. By controlling the optical switch so that the mark rate and the number of consecutive bits of the same code of the converted signal do not change, the signal can be accurately received even by a low-cost AC-coupled optical receiver. It is characterized by: That is, the encoding and optical switch control method in the optical network according to the present invention has the following configuration and method.

A first invention comprises a plurality of nodes comprising an optical transmitter and an optical receiver, an optical switch connecting the plurality of nodes, and an optical switch control unit for controlling the optical switch. In an optical network, the signal to be transmitted is encoded so that the mark rate and the number of consecutive bits of the same code within a predetermined range are within a predetermined range, and the mark rate and the signal rate of the signal encoded by the signal disconnection due to the switching of the optical switch. An encoding and optical switch control method characterized by controlling an optical switch so that the number of code consecutive bits does not change.

[0010] In the embodiment, as the switching timing of the optical switch, a guard time constituted by "0" continuous bits is used.

A second invention comprises a plurality of nodes comprising an optical transmitter and an optical receiver, an optical switch for connecting the plurality of nodes, and an optical switch control unit for controlling the optical switch. In an optical network, a signal to be transmitted is encoded so that the mark rate and the number of consecutive bits of the same code within a predetermined range are within a predetermined range, the mark rate of the optical switch switching time is increased, and the signal by optical switch switching is increased. The encoding and optical switch control method is characterized in that the optical switch is controlled so that the mark ratio and the number of consecutive bits of the same code of the signal encoded by the interruption fall within predetermined ranges.

In the embodiment, the switching timing of the optical switch is performed by a guard time composed of bits having a mark ratio of 1/2 or more. It is set to 1/2.

According to a third aspect of the present invention, there is provided an encoding section for performing encoding for controlling the mark rate and the number of consecutive bits of the same code of a signal to be transmitted to fall within predetermined ranges, and an encoder for converting the encoded signal into an electric signal. It comprises an optical transmitter comprising an electrical / optical converter for performing optical / optical conversion, and an optical receiver comprising an optical / electrical converter for optically / electrically converting a received optical signal and a decoding unit for decoding the electrical signal. A plurality of nodes, an optical switch connecting the plurality of nodes, and controlling the optical switch so that the mark rate and the number of consecutive bits of the same code of the encoded signal do not change due to a signal interruption due to the optical switch switching. And an optical switch control unit.

According to a fourth aspect of the present invention, there is provided an encoding section for performing encoding for controlling the mark rate and the number of consecutive bits of the same code of a parallel signal to be transmitted to fall within predetermined ranges, and an encoded parallel signal. An optical transmitter comprising a parallel / serial conversion unit for parallel / serial conversion and an electrical / optical conversion unit for electrical / optical conversion of a serial signal, an optical / electric conversion unit for optical / electrical conversion of a received serial optical signal, and light A plurality of nodes including an optical receiver including a serial / parallel converter for serially / parallel-converting the converted serial signal and a decoding unit for decoding the parallel signal subjected to serial / parallel conversion; And a mark ratio of a signal encoded by signal interruption by switching the optical switch and the same sign An optical network, characterized in that it is composed of an optical switch control section for controlling so as not to count continue bit changes.

According to a fifth aspect of the present invention, there is provided an encoding unit for performing encoding for increasing the mark rate of the optical switch switching time so that the mark rate and the number of consecutive bits of the same code of a signal to be transmitted fall within predetermined ranges. An optical transmitter comprising an electrical / optical converter for electrical / optical conversion of a coded signal, an optical / electrical converter for optical / electrical conversion of a received optical signal, and a decoding unit for decoding an electrical signal A plurality of nodes comprising an optical receiver, an optical switch connecting the plurality of nodes, and a mark ratio and a continuation of the same code of the encoded signal even if there is a signal interruption due to switching of the optical switch. An optical switch control unit for controlling the number of bits to be within a predetermined range.

According to the present invention, in an optical receiver of an optical network using an optical switch, the DC balance does not collapse due to a signal interruption state when the optical switch is switched, and a low cutoff frequency is included in the signal. Since the following components do not occur, an inexpensive AC-coupled optical receiver can be employed.

[0017]

Next, a first embodiment of the present invention will be described with reference to FIGS. In this example, the number of nodes is 4, and a combination code of 7-stage PN scramble and 16B1MS is used as a transmission line code. In FIG. 1, optical transmitters 1 to 101 include encoding units 11 to 11
1, 1.55 μm band composed of DFB-LD direct modulation electrical / optical converters 12 to 112, output -3 dBm
Of 2.5 Gb / s is transmitted.

The optical receivers 3 to 103 include an optical / electrical converter 3
1 to 131, and decoding units 32 to 132. The optical / electrical conversion units 31 to 131 are provided with a PIN-PD and an S
The i-preamplifier and the identification circuit are configured by AC coupling. The reception sensitivity is -24 dBm, the continuity of the same code is 20 bits, and the average level is used for the identification level. Therefore, the average mark rate in the data is 1/2. It is necessary to be.

The optical switch 2 has a 4 × 4 configuration having four optical inputs and four optical outputs as shown in FIG.
It comprises a 4:16 splitter 21, an SOAG (semiconductor optical amplifier gate) switch 22, and a 16: 4 multiplexer 23. The 4:16 splitter 21 has four 1: 4 splitters.
The demultiplexer, and the SOAG switch 22 is provided by 16 switches of the 1.55 μm band, and 16:
The four multiplexers 23 are each constituted by four 4: 1 multiplexers.

This optical switch has a configuration capable of broadcasting and multicasting. The optical losses of the 4:16 splitter 21 and the 16: 4 multiplexer 23 are 13 dB in total. On the other hand, since the gain of the SOAG switch 22 is 5 dB, the optical loss of the entire optical switch 2 is 8 dB. The switching of the switch is performed by the switch control unit 4, and the switching time of the optical switch is 1 ns.

PN 7-stage scramble code and 16B1M
The encoding units 11 to 111 that perform S-combination encoding include:
The configuration is as shown in the encoding unit 5 in FIG. 2, and the decoding units 32 to 132 are in the configuration as shown in the decoding unit 6 in FIG.

The encoding section 5 includes a pseudo random signal generation section 52 having seven stages of PN and an exclusive OR section 53 for obtaining an exclusive OR of the pseudo random code generated by the pseudo random signal generation section 52 and the input data. Become a scrambler 51
And a Pulse unit 54 for generating a “10” pattern;
An MS insertion unit 55 for inserting a “10” pattern for every 16 bits of data output from the scramble unit 51, a 1.5 ns guard time bit “000000” for switching an optical switch, and synchronization for synchronizing data. The header “00000” including the pattern “11011101”
010101110111 ″ header section 56
And a header insertion unit 57 for inserting a header at the head of the data frame.

The decoding unit 6 has a synchronization pattern "110111".
A sync section 64 which detects "01" and removes a header other than data and a "10" pattern inserted every 16 bits of data, and a PN7-stage pseudo-random stage which descrambles data and outputs the original input data It comprises a descrambling unit 61 comprising a signal generating unit 62 and an exclusive OR unit 63. The configuration of the descrambling unit 61 is the same as that of the scrambling unit 51.

According to this configuration, the mark ratio of the optical signal to be transmitted is １ ／, and the maximum number of consecutive bits of the same sign is 17. Further, as shown in the reception waveform 70 of FIG. 5, the switching of the optical switch is performed with the guard time bit “0000” of 1.5 ns.
Since the optical switch 2 is controlled by the switch control unit 4 so as to be performed at the timing of "00", the optical receivers 3, 10
The mark ratio of the optical signal received by the optical / electrical conversion units 31 and 131 of No. 3 remains unchanged at 1/2, and the maximum number of consecutive bits of the same code is 17 in 16B1MS.
The optical / electrical conversion unit using the AC coupling as shown in FIGS.

If the guard time is 1.5 ns and the switching of the optical switch is about 1 ns, there is a margin of 0.5 ns in the timing of the switching of the optical switch, so that control is possible.

Next, a second embodiment of the present invention will be described with reference to FIGS. According to the present invention, the guard time bit for switching the optical switch among the headers generated in the header section 56 in the encoding section in FIG. The configuration "11101" in which the mark ratio becomes 1/2 or more
1101110 ".

In the optical switch control unit 4, the optical switch is:
If control is performed so as to switch within the guard time of 3 ns, the switch switching time is 1 ns, so that the reception signal after passing through the optical switch has a mark rate of 1/2 during the guard time as shown by a waveform 72 in FIG. Since the mark rate of the entire signal can be reduced to 、, the maximum number of consecutive bits of the same code becomes 17, and AC
Even the optical / electrical conversion unit using the coupling can sufficiently receive the signal.

A waveform 72 is a reception waveform when the phase of the signal from node i and the phase of the signal from node j are the same, as shown in FIG.
There is no problem even when the phases of the signals from are not aligned. FIG. 7 illustrates a state where the received signal is switched from the node i to the node j, and then switched from the node j to the node i. When switching from the node i to the node j, the DC balance slightly collapses and “1” slightly increases at the time of the switching, but the reverse occurs when switching from the node j to the node i, and the DC balance can be obtained on average. .

Although the embodiment focuses on switching only between two nodes, the same applies to the case where a large number of nodes are switched since finite nodes are switched. Further, in this configuration, it is not necessary to prepare a long “0” bit continuation for switch switching with respect to the switch switching time, and a receiver having a long tolerance for the same code continuity is not required, and a sufficient margin of the switching time is provided. And the switching control becomes easy.

Next, a third embodiment of the present invention will be described with reference to FIGS. In this example, the number of nodes is 4, and an 8B10B code is used as a transmission code. In FIG. 8, optical transmitters 301 to 401 include encoding units 311 to 411, and parallel / serial conversion units 313 to 313.
413, 1.55 μm band DFB-LD and electro-optical conversion unit 3 by light source integrating electroabsorption (EA) modulator
4.25 with an output of -3 dBm
Gb / s data is transmitted.

The optical receivers 303 to 403 include optical / electrical converters 331 to 431 and serial / parallel converters 333 to 331.
433, and decoding units 332 to 432.
The optical / electrical conversion units 331 to 431 are composed of a PIN-PD and a Si
With the configuration by AC coupling of the preamplifier and the identification circuit, the receiving sensitivity is -20 dBm, the continuity with the same code is 30 bits,
Since the discrimination level uses an average value, the average mark rate in the data needs to be 1/2.

The optical switch 2 has the configuration shown in FIG. 4 similarly to the first embodiment, and the switching time of the optical switch is 1 ns.

The encoding units 301 to 401 have a configuration as shown in the encoding unit 350 of FIG.
2 to 432 have a configuration as shown in the decoding unit 360 in FIG. The parallel / serial conversion unit 31
3 to 413 are the parallel / serial conversion units 38 in FIG.
0, and the serial / parallel converters 333 to 433 have a configuration as shown in the serial / parallel converter 390 in FIG.

In this example, in the optical transmitters 301 to 401, the encoding units 311 to 411 as shown in the encoding unit 350 and the parallel / serial conversion unit 380 in FIGS.
4B of 106.25 Mb / s data is 8B10B encoded in byte units, and the parallel / serial conversion unit 31
The signal obtained by performing the 10: 1 parallel / serial conversion in 3 to 413 is converted into 4.25 Gb / s by 4: 1 parallel / serial conversion, and the electric / optical converters 312 to 412 perform electric / optical conversion and transmit.

In the 8B10B code, the mark rate is 1/2,
The maximum number of consecutive bits of the same code is 5, but in this example, 8B
Since the 10B encoded data is subjected to 4: 1 parallel / serial conversion, the mark rate is 、 and the maximum number of consecutive bits of the same code is 20. On the other hand, the optical / electrical conversion units 331 to 43
1 can be received without any problem since the continuation tolerance of the same code is 30 bits.

In the optical receivers 303 to 403, first, the received optical signal is optically / electrically converted by the optical / electrical conversion units 331 to 431. Next, serial / parallel conversion units 333 to 433
11, as shown in FIG. 11, 1: 4 serial / parallel conversion is performed by a 1: 4 serial / parallel conversion circuit 393, frame synchronization is performed by a synchronization section 394, and 1: 1 serial / parallel conversion circuits 391-392 are used. : 10 Performs serial / parallel conversion. Then, the decoding units 332-4
32 10B8B decoding units 361 to 362
Decode and output 4 bytes of 106.25 Mb / s data.

The switching of the optical switch is performed by outputting a special character K28.5 (+) "1" of 8B10B for all 4 bytes.
100000101 ". That is, the head of output data from each node is K28.5 (+)" 1 ".
100000101 "is 4: 1 parallel / serial converted. K28.5 (+)" 11000001
01 is converted to 4: 1 parallel / serial to obtain “111”.
111110000000000000000000000
111100001111 "and 20 bits (4.
7 ns), a sufficient time can be secured for the switching time of 1 ns.
The control unit 4 controls the optical switch so as to perform switching in s. The signal received on the receiving side has a mark rate of 1/2 and a maximum of 20 consecutive bits of the same sign and can be received without any problem.

In the above description, the wavelength band used is 1.55 μm.
Although the m band is used, any other wavelength band can be used. The light source is not limited to the DFB laser, but may be a DBR laser or another laser such as an external cavity laser. The optical switch is not limited to the SOAG switch, but may be, for example, an EA gate switch or a LiNbO ₃ switch.

The code used is also scrambled + 16B1MS
Not only codes and 8B10B codes, but also 4B5B codes + NRZ
An I code or the like may be used. As described above, in the above configuration, as long as the above function is satisfied, the material and code format of the element used are free, and the above description does not limit the present invention.

[0040]

By using the present invention, in an optical receiver of an optical network using an optical switch, a DC balance collapse caused by a signal cutoff state due to an optical switch switching or a component having a frequency lower than a low cutoff frequency is included in a signal. The problem that the inclusion thereof makes it impossible to receive a signal accurately with a low-cost AC-coupled optical receiver can be solved by a simple configuration.

Further, according to the present invention, a margin can be provided in the timing of switching the optical switch, so that when the scale of the optical network becomes large, the timing of switching the switch must be accurately controlled for each node. Can solve the problem.

Further, according to the present invention, it is possible to realize a large-capacity, small-sized, low-delay optical network having a simple configuration and a low price.

[0043]

[Brief description of the drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention.

FIG. 2 is a block diagram illustrating a configuration of an encoding unit.

FIG. 3 is a block diagram illustrating a configuration of a decoding unit.

FIG. 4 is a block diagram illustrating a configuration of an optical switch.

FIG. 5 is an optical reception waveform for explaining the operation of the present invention.

FIG. 6 is an optical transmission / reception waveform illustrating the operation of the present invention.

FIG. 7 is an optical transmission waveform illustrating the operation of the present invention.

FIG. 8 is a block diagram showing one embodiment of the present invention.

FIG. 9 is a block diagram illustrating a configuration of an encoding unit.

FIG. 10 is a block diagram illustrating a configuration of a parallel / serial conversion unit.

FIG. 11 is a block diagram illustrating a configuration of a serial / parallel conversion unit.

FIG. 12 is a block diagram illustrating a configuration of a decoding unit.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1, 101 Optical transmitter 2 Optical switch 3, 103 Optical receiver 4 Optical switch control part 5 Encoding part 6 Decoding part 11, 111 Encoding part 12, 112 Electric / optical conversion part 21 4:16 demultiplexer 22 SOA gate switch 23 16: 4 multiplexer 31, 131 optical / electrical conversion unit 32, 132 decoding unit 51 scramble unit 52 PN pattern generation unit 53 exclusive OR unit 54 MS generation unit 55 MS insertion unit 56 header Generation unit 57 Header insertion unit 61 Descramble unit 62 PN pattern generation unit 63 Exclusive OR unit 64 Synchronization unit 70 Received waveform 71 Transmitted waveform 72 Received waveform 73 Transmitted packet 74 Transmitted packet 75 Received waveform 301, 401 Optical transmitter 303, 403 Optical receiver 311, 411 Encoding unit 312, 412 Electric / optical conversion unit 313, 413 / Serial converter 331, 431 Optical / electrical converter 332, 432 Decoder 333, 433 Serial / parallel converter 350 Encoder 351, 352 8B10B encoder 360 Decoder 361, 362 10B8B decoder 380 Parallel / Serial converters 381, 382 10: 1 parallel / serial converter 383 4: 1 parallel / serial converter 390 serial / parallel converters 391, 392 1:10 serial / parallel converter 393 1: 4 serial / parallel converter 394 Synchronization unit

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Takehiko Suemura 5-7-1 Shiba, Minato-ku, Tokyo Inside NEC Corporation (72) Inventor Yoshiharu Maeno 5-7-1 Shiba, Minato-ku, Tokyo Within NEC Corporation (72) Inventor Naoya Hemi 5-7-1 Shiba, Minato-ku, Tokyo Inside NEC Corporation

Claims (7)

[Claims] 1. An optical network comprising: a plurality of nodes each including an optical transmitter and an optical receiver; an optical switch that connects the plurality of nodes; and an optical switch control unit that controls the optical switch. The signal to be transmitted is encoded so that the mark rate and the same code continuous bit number of the signal to be transmitted are within a predetermined range, and the mark rate and the same code of the signal encoded by the signal interruption due to the switching of the optical switch. An encoding and optical switch control method for controlling an optical switch so that the number of continuous bits does not change. 2. The encoding and optical switch control method according to claim 1, wherein said optical switch is switched during a guard time period constituted by continuous "0" bits. 3. An optical network comprising: a plurality of nodes each including an optical transmitter and an optical receiver; an optical switch that connects the plurality of nodes; and an optical switch control unit that controls the optical switch. The signal to be transmitted is encoded so that the mark rate and the number of consecutive bits of the same code within the predetermined range are within a predetermined range, and the mark rate in the optical switch switching period is increased, and the signal is cut by the optical switch switching. An encoding and optical switch control method, wherein an optical switch is controlled so that a mark rate and a number of consecutive bits of the same code of an encoded signal fall within predetermined ranges. 4. An optical switch is switched during a guard time period in which a mark rate is a bit having a value equal to or more than 1/2 value, and a signal cutoff state due to the optical switch switching is included, so that a mark rate of a received signal is reduced. 4. The coding and optical switch control method according to claim 3, wherein the ratio is set to 1/2. 5. An encoding unit for performing encoding for controlling a mark ratio and a number of consecutive bits of the same code of a signal to be transmitted to fall within a predetermined range, and an electric / electrical unit for encoding the encoded signal.
An optical transmitter comprising an electric / optical conversion unit for performing optical conversion, an optical / electrical conversion unit for performing optical / electrical conversion of a received optical signal, and an optical receiver comprising a decoding unit for decoding the converted electric signal. A plurality of nodes to be configured, an optical switch connecting the plurality of nodes, and a change in mark ratio and number of consecutive bits of the same code of an encoded signal due to signal disconnection caused by switching the optical switch. An optical network, comprising: an optical switch control unit that performs control so that the optical network does not exist. 6. An encoding unit for performing encoding for controlling a mark rate and the number of consecutive bits of the same code of a parallel signal to be transmitted to be within a predetermined range, and a parallel / serial conversion of the encoded parallel signal. An optical transmitter comprising a parallel / serial converter for converting a serial signal and an electrical / optical converter for electrical / optical conversion of a serial signal;
From an optical receiver comprising an optical / electrical conversion unit for electrical conversion, a serial / parallel conversion unit for serial / parallel conversion of the optical / electrically converted serial signal, and a decoding unit for decoding the serial / parallel converted parallel signal A plurality of nodes to be configured, an optical switch connecting the plurality of nodes, and a mark rate and a number of consecutive bits of the same code of the encoded signal are not changed by a signal interruption due to the optical switch switching of the optical switch. And an optical switch control unit for controlling the optical network. 7. An encoding unit that performs encoding for increasing a mark rate and a mark rate during an optical switch switching period so that a mark rate and a number of consecutive bits of the same code of a signal to be transmitted fall within predetermined ranges. Optical transmitter comprising an electrical / optical converter for electrical / optical conversion of the received signal, an optical / electrical converter for optical / electrical conversion of the received optical signal, and an optical receiver comprising a decoder for decoding the electrical signal A plurality of nodes composed of a plurality of nodes, an optical switch connecting the plurality of nodes, and a mark rate and a number of consecutive bits of the same sign of the signal received by the optical receiver due to a signal interruption by switching the optical switch. An optical network, comprising: an optical switch control unit configured to perform control so as to be within a predetermined range.