JPH02228830A - Optical network communication system - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to an optical network communication system, and particularly relates to an optical network communication system in which communication between stations is performed by optical communication using a wavelength multiplexing method, a frequency multiplexing method, etc. .

[Prior Art] In the wavelength multiplexing method, which uses light of different wavelengths for communication by multiplexing them on the same communication path, and the frequency multiplexing method in coherent optical communication, it is necessary to keep the wavelength of the signal light at a constant wavelength or to It is necessary to prevent crosstalk by controlling the wavelengths of the signal lights by maintaining them at regular intervals. For this purpose, a method is taken in which a light source with a reference wavelength is set and the operating wavelengths of other optical elements are set based on this reference wavelength. In an optical multiplex communication system of an optical network, etc., each terminal station has a light source of a reference wavelength, which makes it difficult to manage whether the wavelengths of the light sources of each reference wavelength match. In addition, since the cost of terminal stations increases, a method is used in which a center station is installed, a light source with a reference wavelength is placed there, and the reference wavelength is transmitted from the light source of the reference wavelength at the center to each terminal station on the network using a multiplex communication method. is proposed.

FIG. 7 is a schematic diagram showing an optical network communication system. Reference numeral 101 denotes an optical transmission line, which is composed of an optical fiber. A center station 102 includes a reference wavelength light source. 1031...1O34 are optical couplers. 1
04. . . 1044 is a connection line that connects each of the terminal stations 1051 to 1054 and a corresponding optical coupler, and is composed of an optical fiber or an optical waveguide. 1051
...1054 is a terminal station.

In addition to the signal light, reference wavelength light from the center station 102 is propagated through the optical transmission line 101 . The signal light or reference wavelength light in the optical transmission line 101 is transmitted through optical couplers 103+"103-
from the terminal station 105. to the terminal station 105. ... 1054 and undergoes signal processing within the terminal station.

In addition, the signal light transmitted from the terminal stations 1051...1054 passes through the connection lines 1041...1044 and connects to the optical coupler.
03+...1034 into the optical transmission line 101. The signal light multiplexed on the optical transmission line 101 is uniquely taken into the center station and subjected to signal processing. Terminal station 1' 05 t...105. Now, using the reference wavelength light transmitted from the center station 102, the optical elements in the terminal stations,
That is, control is performed to keep the wavelengths of the signal light source, light source, optical heterodyne detection local light source, etc. constant.

[Problems to be Solved by the Invention] However, in the conventional example described above, the reference wavelength light is sent from the center station to each terminal station using a multiplex communication method, and each terminal station determines the operating wavelength of its respective optical element based on the reference wavelength light. It's matching. This process for matching the wavelengths was performed when no communication was being performed between the terminal stations of the optical network communication system. Therefore, when using an optical network communication system, there is a drawback that the efficiency of network communication usage is reduced.

In addition, when transmitting long-term continuous signals using optical network transmission paths, for example when transmitting moving images, the wavelength difference between the center station and the terminal stations relative to the reference wavelength is As a result, the wavelength of the signal light may deviate from the desired position, making optical multiplex transmission between the center station and the terminal stations impossible.

The present invention has been made in view of the above conventional example, and the frequency band of signal light and the frequency band of reference wavelength light used for communication between terminal stations in an optical network communication system are set to be different, and each terminal station While communicating information between each
It is an object of the present invention to provide an optical network communication system in which the wavelength of the operating wavelength light of each optical element in each terminal station can be matched to the reference wavelength light at the same time.

[Means for Solving the Problems] In order to achieve the above object, the optical network communication system of the present invention has the following configuration.

In other words, it is an optical network communication system in which information is communicated by optical signals between a plurality of terminal stations via a transmission path, and the wavelength of the signal light for transmitting and receiving information and the wavelength of the reference wavelength light for wavelength control are different. Different from each other, each of the terminal stations includes a sending means for multiplexing the signal light and the reference wavelength light and sending the multiplexed signal light to the transmission line, and an adjusting means for adjusting the wavelength of the light source of the own station based on the reference wavelength light. and has.

[Operation] In the above configuration, the wavelength of the signal light for transmitting and receiving information and the wavelength of the reference wavelength light for wavelength control are different from each other,
The signal light and the reference wavelength light are multiplexed and sent to the transmission path. Each terminal station connected to this transmission line operates to adjust the wavelength of its own light source based on this reference wavelength light.

[Embodiments] Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

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

The block diagram of FIG. 1 shows each terminal node in the optical network communication system. Reference numeral 11 denotes received light, which is light sent from another terminal station or the center station. Reference numerals 12 to 14 denote optical branching/combining devices, in which bulk beam splitters or optical waveguide type elements are used.

12 and 14 are operating as optical splitters, and 13 is operating as an optical combiner. Reference numeral 15 denotes a wavelength tunable laser, which is a semiconductor laser or the like whose emission wavelength changes depending on the amount of current injected. Reference numeral 16 denotes control light, which is a part of the light beam emitted from the wavelength tunable laser 15. 17 is a wavelength control photodetector.

18.19 is a band pass filter (BPF), 20.2
1 is an amplifier. Also, 22 is a frequency controller, 23.2
4 is a tuner. Reference numeral 25 denotes an operating signal source, which is the source of the signal to be sent out from this node. 26 is a driver. 27 is a transmission light, which is a part of the output light of the wavelength tunable laser 15 like the control light 16, and is a part of the output light of the wavelength tunable laser 15.
4, it is branched into a transmission signal light 27 and a control light 16. 2
Reference numeral 8 denotes a wavelength tunable filter, which can be produced using the same technique as the wavelength tunable laser 15. 29 is a photodetector for signal detection. An avalanche photodiode, a pin photodiode, or the like is used as the signal detection photodetector 29 and the wavelength control photodetector 31. 30 is a low pass filter (LPF), and 32 is a decoder.

31 is a frequency detector.

The node shown in FIG. 1 is for wavelength division multiplex communication.

FIG. 2 is a graph showing the frequency distribution of signals in the transmission path, and FIG. 3 is a graph showing the wavelength distribution of signals in the transmission path.

201 indicates the frequency spectrum of the signal from the terminal station,
202 to 205 indicate frequency spectra of reference wavelength light. Further, in FIG. 3, 210 to 213 are wavelength spectra of operating signals of the terminal stations, and 214 to 217 are wavelength spectra of reference wavelength light.

Figures 2 and 3 show the case of 4-wave multiplexing in an optical network communication system, where each terminal station is λ,...λ
They communicate with each other using light of one of the four wavelengths. Here, no matter what wavelength is used, the frequency band distribution of the signal light is DC
It becomes a frequency spectrum from the component to a certain frequency.

However, when looking at the wavelengths, as shown in FIG. 3, the operating signals of the terminal stations are separated into wavelength spectra 214 to 217. On the other hand, each of the reference wavelength lights 214 to 217 is sent out from the center station to a specific terminal station, and the reference light of each wavelength is modulated at a different frequency. That is, the frequency spectrum 202 to 20 of the reference wavelength light in FIG.
5 correspond to each of the wavelength spectra 214 to 217 of the reference wavelength light in FIG. In this way, for each wavelength, a set is created, for example, the operating signal wavelength spectrum 210 of each terminal station and the wavelength spectrum 214 of reference wavelength light.

The frequencies of the frequency spectra 202 to 205 of the signals from the terminal stations are on the order of several hundred MHz to several GHz. On the other hand, assuming that the interval between two adjacent wavelengths λ1...λ4 is 10 people, the frequency in the 0.8 μm wavelength band is 470 GHz% 1.
Since the 3 μm band is 180 GHz, the mutual spacing between each wavelength is actually the frequency spectrum 201 of the signal from the terminal station and the frequency spectrum 202 of the reference wavelength light shown in FIG.
It is quite large compared to the interval of ~205.

In FIG. 1, received light 11 is taken in from a transmission line in an optical network to a terminal node via a coupler connection line. The received light 11 includes frequency-multiplexed signals from each terminal station and reference wavelength light from the center station. A portion of the received light 11 passes through the optical splitter/combiner 12.13. On the other hand, a portion of the light emitted from the wavelength tunable laser 15 is reflected by the light branching/merging device 14 and reflected by the light branching/merging device 13 as control light 16, and then is transmitted to the photodetector 17 along with a portion of the signal light 11. It is incident.

FIG. 4 is a sectional view of the wavelength tunable laser 15 provided at this terminal station.

In the figure, 41 is a substrate, 42 is a leading wave layer, and 43 is a cladding layer. A grating is formed on a part of the interface between the substrate 41 and the optical waveguide layer 42 to form a DBR region. 44 is an active layer. Each of 45a, 45b, and 45c is a signal electrode, a phase control electrode, and a DBR region control electrode. 46 is a common electrode. 47a, 47b
, 47c are a signal line, a phase control line, and a DBR area control line, respectively, and are connected to the signal electrode 45a2, the phase control electrode 45b, and the DBR area control electrode 47c, respectively. 48 is emitted light. This wavelength tunable laser has G, A
,/G,AffA,,1. It can be created using materials such as P/InG, A, and P.

Substrate 41. Optical waveguide N42. The cladding layer 43 forms an optical waveguide, through which light can propagate.

Light is generated by current injection in the active layer 44, and laser oscillation occurs by reciprocating within the resonator formed by the grating and the cleavage plane. A current injected from the signal lines 47a to 47c between the signal electrode 45a and the common electrode 46 can control laser oscillation, turn on/off the emitted light 48, and carry a signal.

On the other hand, DBR area control voltage %45c and common electrode 4
The current injected from the DBR region control line 47c between the two regions changes the wavelength of the emitted light 48 by changing the refractive index of this region by carrier injection and changing the optical path length. The wavelength change caused by the current injection change in the DBR region control line 47c is relatively large. Control means for finely adjusting the wavelength is provided by a two-phase control electrode 45b and a phase control line 47b. When a current is passed between the phase control electrode 45b and the common electrode 46 through the phase control line 47b,
As expected, changes in refractive index and optical path length occur due to the effect of carrier injection. The wavelength change of the emitted light 48 caused by this is small, and when combined with the wavelength change using the DBR region control line 47c described above, a semiconductor laser whose wavelength can be smoothly changed can be obtained.

In FIG. 1, a photodetector 17 is used to perform heterodyne detection of two beams. The BPF 18 extracts only those generated from the wavelength of the control light 16 from the tunable laser 15 and the wavelength components of the received light 11 that are close to the wavelength of the beat signal. The frequency controller 22 further receives the reference wavelength light and control light 1 from the center station out of the beat signal.
6 and tuner 2 based on that frequency.
Send a control signal to 4. This signal is, for example, a signal that makes the emission wavelength of the wavelength tunable laser 15 lower than the wavelength of the reference wavelength light by the modulation frequency of the reference wavelength light, ie, fl...f4. The signal from the tuner 24 is sent to the wavelength change control line of the wavelength tunable laser 15.

That is, in the case of the wavelength tunable semiconductor laser 15 shown in FIG. 4, the signal is sent to the phase control line 47b and the DBR area control line 47C.

The driver 26 drives the wavelength tunable laser 15 based on the signal from the signal source 25 .

A signal from the driver 26 is sent to a signal line 47a in the wavelength tunable semiconductor laser shown in FIG.

As described above, part of the light emitted from the wavelength tunable laser 15 becomes the control light 16, and the rest passes through the optical branch/combiner 14 and becomes the transmitted light 27. This transmitted light 27 is sent out to a transmission path through a connection line and a coupler (not shown).

Next, the case of reception will be explained.

A portion of the received light 11 is reflected by the optical splitter/combiner 12 and enters the variable wavelength filter 28 . Various types of wavelength tunable filters are known, such as those that mechanically rotate a grating-type spectrometer, and those that configure an interferometer using materials with electro-optic effects, and change the optical path length by applying an electric voltage. There are some that change the transmitted wavelength. There is also a device which has a structure similar to the wavelength tunable semiconductor laser 15 shown in FIG. 4, but does not have an active layer and uses a DBR or DFB type grating structure element to change the transmission wavelength.

The signal detected by the photodetector 29 is amplified by the amplifier 20 and then sent to the LPF 30 and the BPF 19. LPF
30 has the function of extracting only the signal component from the terminal station.

The signal from LPF 30 is decoded by decoder 32,
Read by this node. From the signal sent to the BPF 19, only the component generated by the reference wavelength light from the center station is extracted by the action of the BPF 19. The signal component is further sent to a frequency detector 31.

As shown in FIG. 2, the reference wavelength light from the center station has a different modulation frequency for each wavelength of the reference light, so the frequency detector 31 can easily identify which wavelength the reference light is. . The frequency detector 31 sends a signal to the tuner 23 to control the variable wavelength filter 28 so that the detected value of the desired reference wavelength light becomes large. Tunable wavelength filter 2
In step 8, one set of wavelengths of signals from the terminal station and reference wavelength light from the center station is transmitted. That is, the third
In the figure, for example, the wavelength spectrum 21 of the signal from the terminal station
0 and the reference wavelength light 214 from the center station are transmitted.

In wavelength control on the transmitting side, since the frequency of the beat signal obtained from the photodetector 17 fluctuates, it may be difficult to determine which reference wavelength light is being tracked based only on this signal. In such cases, the following measures are effective.

FIG. 5 is a graph showing another example of the frequency distribution of signals in the transmission path.

51.52 is the frequency spectrum of the reference wavelength light of the first wavelength λ1, and when compared with the frequency spectrum shown in FIG. 2, it can be considered that the spectrum of the reference wavelength light has become two. Similarly, 53.54 is the second wavelength λ2, 55.
56 is the third wavelength λ, 57.58 is the fourth wavelength λ4
The frequency spectrum of the reference wavelength light 203 in FIG.
．． 204.205. 2 of the reference light of each wavelength
The intervals of the actual frequency spectrum are set to be different for each wavelength.

As can be seen from FIG. 5, the frequency intervals between the frequency spectra 51, 52.53, 54.55, 56°, 57, and 58 of the reference wavelength light gradually become larger.

As a result, when heterodyne detection is performed by wavelength control on the transmitting side, it becomes possible to easily determine which wavelength the reference signal is by reading the frequency interval of the beat signal generated from the reference wavelength light.

Alternatively, different modulation signals may be given to the reference wavelength signals for identification. You can use analog to apply different modulations, or you can use digital to give different codes.

[Other Embodiments (FIG. 6)] FIG. 6 is a block diagram showing a second embodiment of the present invention. FIG. 6 illustrates a receiving section of a terminal node. Note that the transmitter is the same as that shown in FIG. 1, so it is omitted for simplicity. In the second embodiment, the communication method is coherent optical communication, and the signal is detected by heterodyne detection.

Reference numeral 61 designates a received light, and 62 a light branching/combining device, which is used here as a light combining device. 63 is a photodetector.

64 is a local oscillator, and a laser whose oscillation frequency can be controlled is used. Further, the local oscillator 64 may be a wavelength tunable semiconductor laser shown in FIG. 4. Reference numeral 65 denotes local light, which is a luminous flux emitted from the local oscillator 64.

66 is an amplifier. 67 and 68 are both band pass filters (BPF), and their respective transmission bands are different. 69 is a demodulator, and 70 is a frequency controller.

The received light 61 is reflected by a light branching/merging device 62 and sent to a photodetector 6.
3. On the other hand, the local light 65 emitted from the local oscillator 64 passes through the optical branching/merging device 62 and enters the photodetector 63 as well. The wavelengths of the received light 61 and the local light 65 are close to each other, and the photodetector 63 obtains a beat signal. The signal from the photodetector 63 is amplified by an amplifier 66. B.P.
The F67 has a band that allows the beat signal generated by the local light 65 and the signal component of the received light 61 from the terminal station to pass through.

In the wavelength spectrum of the signal in Fig. 3, for example, the wavelength λ
, when transmitting using the channel, the local light 65 and the beat signal of the wavelength spectrum 210 of the signal from the terminal station pass through the BPF 67. The signal that has passed through the BPF 67 is converted into FSK, ASK, and PS by a demodulator 69.
It is demodulated according to the modulation method of the signal such as K. On the other hand, the beat signal amplified by the amplifier 66 is also sent to the BPF 68. In the BPF 68, among the local light 65 and the received light 61,
The light generated between the light and the reference wavelength light from the center station is transmitted.

If the channel of wavelength λ1 is used in FIG. 3, the wavelength spectrum 214 of the reference wavelength light and the local light 65
The beat signal between the two passes through the BPF 68. Note that when performing optical communication by frequency multiplexing using a coherent optical communication method, the interval between the wavelengths of each channel is usually very narrow compared to the case of wavelength multiplexing. If so, wavelengths are assigned so that the interval between λ1 and λ4 becomes narrower.

The frequency controller 70 controls the tuner 71 based on the signal transmitted through the BPF 68. That is, since the reference wavelength light from the center station and the beat signal of the local light 65 from the local oscillator 64 are obtained, a signal is sent to the tuner 71 so that the beat signal has a constant frequency, and the local oscillator 64
control the oscillation wavelength. In order to easily identify which wavelength the reference wavelength light corresponds to, the means described in connection with the wavelength control on the transmitting side of the node of the terminal station in the first embodiment, that is, the method shown in FIG. The means shown may be added.

In Example 1.2, the wavelength control on the transmitting side of the terminal node uses heterodyne detection.
A method may also be used in which the variable wavelength filter is controlled so as to increase the signal of a specific wavelength, as used for wavelength control on the receiving side in the first embodiment. At this time, a variable wavelength filter and a photodetector are prepared on the transmitting side. The received light is made incident on a photodetector through a wavelength tunable filter, and the wavelength tunable filter is adjusted so that the detection signal of the reference wavelength light of the channel used by the transmitted light becomes large. A part of the light emitted from the wavelength tunable laser for transmission is branched, and is made to enter a photodetector through a wavelength tunable filter.

The wavelength of the wavelength tunable laser is controlled so that the photodetection signal generated by this signal light becomes large.

Thereby, the wavelength tracking of the wavelength tunable laser for transmission is performed with respect to the reference wavelength light from the center station via the wavelength tunable filter photodetector. Since the reference wavelength light from the center station is modulated at a specific frequency, it is easy to determine which wavelength the reference light corresponds to, and the frequency bands of the transmitted light and the reference wavelength light are separated. Therefore, when controlling wavelengths, each can be handled simultaneously, and wavelength control can be continued at all times during transmission.

In the above description of the embodiment, the frequency spectrum of the communication signal between terminal stations is shifted to the lower frequency side as shown in FIG.
Although the frequency spectrum of the reference wavelength light from the center station is arranged on the high frequency side, various other frequency arrangement methods are possible as long as they are separated on the frequency axis.

As explained above, according to this embodiment, the frequency spectrum of the signal used for terminal open signal transmission of the optical network communication system and the frequency spectrum of the reference wavelength light are separated, so that continuous wavelength control is possible. Become.

Furthermore, when transmitting continuous signals over a long period of time, since the reference wavelength light is transmitted simultaneously, the reference wavelength within the terminal station is stabilized, and there is an effect that stable network communication transmission is always possible.

Furthermore, there is no need to temporarily suspend other communications for wavelength control. Therefore, continuous signal transmission over a long period of time becomes possible, which has the effect of improving the utilization efficiency of the network communication system.

Furthermore, since it is a frequency multiplexed communication system, there is no need to draw a dedicated transmission line for transmitting the reference wavelength light, so there is an effect that a more economical network communication system can be realized.

[Effects of the Invention] As explained above, according to the present invention, the frequency band of signal light and the frequency band of reference wavelength light used for communication between terminal stations in an optical network communication system are set to be different,
There is an effect that while information communication is executed between each terminal station, the wavelength of the operating wavelength light of each optical element in each terminal station can be simultaneously adjusted to the reference wavelength light.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the first embodiment of the present invention, FIG. 2 is a diagram showing the frequency distribution of signals in the transmission path, FIG. 3 is a diagram showing the wavelength distribution of signals in the transmission path, and FIG. FIG. 4 is a front cross-sectional view of a wavelength tunable laser, FIG. 5 is a diagram showing another example of the frequency distribution of a signal in a transmission path, FIG. 6 is a block diagram showing a second embodiment of the present invention, and FIG. 7 is a schematic diagram showing an optical network. In the figure, 11...Received light, 12-14... Optical branching/merging unit, 15... Tunable wavelength laser, 16... Control light, 1
7.29... Photodetector, 18.19... Bandpass filter (BPF), 20: 21... Amplifier, 22...
・Frequency controller, 23.24...Tuner, 25...
- Operating signal source, 26... Driver, 27... Transmission light, 28... Tunable wavelength filter, 31... Frequency detector, 32... Decoder, 201... Signal from terminal station Frequency spectrum of 202-205... Frequency spectrum of reference wavelength light from the center station, 210-213...
・Wavelength spectrum of the signal from the terminal station, 214 to 217・
...Wavelength spectrum of reference wavelength light from the center station, 41
... Substrate, 42 ... Optical waveguide layer, 43 ... Cladding layer, 44 ... Active layer, 51.52 ... First wavelength λ
Frequency spectrum of reference wavelength light of 1, 53.54...
Frequency spectrum of reference wavelength light of second wavelength λ2, 55
56... Frequency spectrum of the reference wavelength light of the third wavelength λ3, 57.58... Frequency spectrum of the reference wavelength light of the fourth wavelength λ4. Figure 2, Fl length (finger set) Figure 3 Figure 4 Number of waves (relative 1) Figure 5 A Figure 6 Figure 7

Claims (1)

[Claims] An optical network communication system that communicates information using optical signals between a plurality of terminal stations via a transmission path, comprising: a wavelength of signal light for transmitting and receiving information; and a reference wavelength for wavelength control. sending means for multiplexing the signal light and the reference wavelength light and sending the light to the transmission path, each of which has a different wavelength of light; and each of the terminal stations determines the wavelength of its own light source based on the reference wavelength light. An optical network communication system comprising: adjustment means for adjusting; and an optical network communication system.