JPH04932A - Wavelength multiplexing optical communication network and optical transmitter receiver using same - 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 is applicable to optical LAN (local area network)
The present invention relates to a wavelength division multiplexing optical communication network, such as a wavelength division multiplexing optical communication network, and an optical transmitter/receiver used therein.

[Conventional technology] Optical communication networks such as optical LAN have been developing rapidly in recent years, but it will be essential to support multimedia in the future, and higher functionality through wavelength multiplexing is expected as a countermeasure. ing. However, there are many problems that must be solved in order to realize a wavelength multiplexed optical LAN that is compatible with multimedia.

[Problems to be solved by the invention] First, when a system is configured with terminal stations that are passive to light, there is a limit to the number of terminal stations that can be connected to the system because attenuation is repeated at each terminal station. , the system has no development potential.

Therefore, it is highly necessary to provide a repeater in the system (although it becomes necessary to provide repeaters for each channel, 0/E (optical-electrical) and Elo (
Amplification by electrical-to-optical conversion becomes more difficult as the wavelength multiplicity increases. To solve this problem, it is considered effective to use a wideband optical amplifier that amplifies multiple channels at once.

However, in a wavelength division multiplexed LAN, the input level of such an optical amplifier varies considerably depending on the number of channels used due to multiple access, so there is a problem that it is difficult to set the output level to a desired level.

Secondly, the temperature stability of the oscillation wavelength of the semiconductor laser used as the light source is poor, and in order to prevent a decrease in error rate due to crosstalk between channels, it is necessary to provide wide channel separation. As a result, as many semiconductor lasers as there are channels and narrow-band and stable wavelength filters (e.g., dielectric thin film interference filters or diffraction gratings) are required as light sources, the cost is high (not to mention the wavelength multiplicity is high). However, it had its limitations and did not satisfy the needs of users.

Thirdly, related to the second problem, a method has been proposed in which a wavelength tunable laser is used as a light source and a semiconductor tunable wavelength filter is used as a filter in order to increase the wavelength multiplicity. In order to ensure the number of channels, both the semiconductor laser and the semiconductor wavelength tunable filter require highly accurate temperature control, resulting in an extremely expensive system.

Therefore, in view of the above-mentioned problems, an object of the present invention is to provide a configuration that is relatively inexpensive, has high reliability, can increase the wavelength multiplicity, and can further limit the number of terminal stations. An object of the present invention is to provide a high-density wavelength division multiplexing optical communication network and an optical transmitting/receiving device used therein.

[Means for Solving the Problems] A wavelength division multiplexing optical communication network according to the present invention that achieves the above object has a bus-type configuration, and a plurality of terminal stations are connected to an optical transmission line in which a plurality of lights are wavelength-multiplexed. In a coupled optical communication network, one reference station having means for constantly transmitting light (carriers) of multiple wavelengths onto an optical transmission path is located at one end of the optical transmission path, and a plurality of ordinary ends including optical transceiver devices are located at one end of the optical transmission path. A station is placed on the optical transmission line.

Furthermore, in the optical transmitter/receiver used in the wavelength division multiplexing optical communication network according to the present invention that achieves the above object, a carrier of an arbitrary wavelength is selected from light (carriers) of a plurality of wavelengths, and data superimposed on this carrier is recognized. means for selectively switching an optical path provided on an optical transmission path to the optical transmitting/receiving device according to the recognized content; and means for selecting carriers of a plurality of wavelengths and separating them from carriers of other wavelengths; A means for superimposing a data signal on the separated carriers, a means for recombining the separated carriers and the remaining carriers, a means for simultaneously amplifying all the combined light, and a means for simultaneously amplifying all the combined light. and means for sending the light back to the optical transmission line.

With this configuration, the reference station is the only light source, so
By stabilizing only the reference station, you can always maintain a stable carrier (
The wavelength is , □,...λ. ) can be sent. Normally, the terminal station splits the light on the transmission path, sweeps the wavelength, and recognizes the data superimposed on the carrier.
It can be determined whether the channel is in use.

When it is recognized that the channel (wavelength is E) is recognized as empty, the optical path switching switch on the transmission path routes all the carriers to the terminal station, and the wavelength transmission/separation filter switches the wavelength L1 to The carrier and other carriers are separated, and only the carrier with wavelength λ1 is modulated and combined with the other carriers again. This keeps the total light level approximately constant. In this way, the input levels of the optical amplifiers are made the same for each channel, so the output level can be kept constant regardless of the access state by simply performing gain control for carriers of all wavelengths.

[Embodiment] FIG. 1 is a block diagram of an embodiment of the present invention. In the figure, 1 is an optical fiber transmission line having a U-shaped bus shape;
1a is a transmission path, 1b is a reception path, 1C is a transmission path turning point, 2 is a reference station placed at one end of this transmission path l, 3 to 6
A plurality of ordinary terminal stations 7 to 10 are connected to the respective terminal stations 3 to 6 and transmit and receive signals. A terminal device 11 is an optical branching element located on the reception path 1b.12. 13
1 is an optical switch on the transmission path 1a, and 14 is the terminal end of the transmission path 1.

First, the reference station 2 will be explained. The reference station 2 is the only light emitting source in this optical communication system, and simultaneously sends continuous light of each wavelength for wavelength multiplexing l to the optical fiber transmission path 1a and reception path 1b. As a light emitting source (not shown) of this reference station 2, for example, a broadband multimode semiconductor laser (hereinafter referred to as broadband LD) is suitable.

More specifically, semiconductor lasers and light emitting diodes with the same structure have an asymmetric quantum well structure (a quantum well structure having a well layer with a bandgap of j!) in their active layer as this light emission source. It is possible to achieve a significantly wider band than one having an active layer of . Therefore, by selecting the end face reflectance of the device, Fabry-Perot modes with wavelength intervals corresponding to the cavity length appear in the emission spectrum, and each of these modes can be used as a wavelength multiplexed light source. 3
00 um and the center wavelength is 0.83 μm, the wavelength spacing, that is, the channel spacing is approximately 0.3 nm. Therefore, by appropriately biasing the above-mentioned wideband LD, continuous waves of several tens of wavelengths with uniform output levels (here, the wavelength is λ) can be generated.
1, eh 2,... eh. ) can be sent at the same time and at all times.

An example of the emission spectrum of this broadband LD is shown in FIG. 2, where 21 is the axial (longitudinal) mode and 22 is the envelope fiber of the axial mode 21. The number of channels can be determined by changing the parameters of the asymmetric quantum well structure (well depth, thickness, barrier height, thickness, etc.), the wavelength spacing can be determined by changing the cavity length, and the optical output level can be adjusted by changing the optical power level applied to the device. This can be selected by changing the bias level and end face reflectance.

The above describes a method of outputting continuous waves of multiple wavelengths with one element, but it is also possible to prepare a light emitting element individually for each channel (wavelength). In either case, the wavelength and optical output of each channel In order to stabilize the temperature of the light emitting element, a device is required to control the temperature of the light emitting element. In the former case (when only one element is required), temperature control of about ±0.1°C is sufficient, and the reference station 2
The cost of the light source section can be reduced. On the other hand, in the latter case (in which each light emitting element is used for each channel), although it is disadvantageous in terms of cost compared to the former, it has the advantage that the channel spacing and optical output can be set freely.

Next, the ordinary terminal stations 3 to 6 will be explained. FIG. 3 shows an example of the configuration of an ordinary terminal station (described as terminal station 3) in this embodiment. In the figure, 31 is an optical branching element, 32 is an optical combining element, and the already mentioned 12 and 13 are respectively , an optical switch for switching the light on the transmission path la between the transmission path 1a (light path 1) and the terminal station side (light path 15), and the terminal station side or optical path l.
Optical switch for directing side light to transmission path 1a, 33
．． 34 is a variable wavelength filter, 35 is an optical modulator, 36.3
7 is a light receiver, 38 is an optical amplifier, and 39 is a control for controlling the optical path selection of the optical switch 12.13, the wavelength selection of the variable wavelength filter 33.34, the gain control of the optical amplifier 38, and the overall communication procedure. Department.

In the above configuration, consider the case where data is transmitted from the terminal station A3 to the terminal station B4 in FIG. 1. At terminal station A3, turning point 1
The optical branching element 11 branches the wavelength-multiplexed light propagating through the reception path 11 downstream from c to the transmission path 1 side and the terminal station 3 side further downstream, and the variable wavelength filter 33 branches the wavelength-multiplexed light propagating through the reception path 11 downstream from c. From the light branched to the side (wavelength 3, 2, ... eh.),
A specific method of wavelength selection that selects only light of an arbitrary wavelength (for example, E) according to the control state is to scan the channel with a wavelength tunable filter 33 that can continuously sweep the wavelength, and then The optical output of the transmitted light is monitored by the optical receiver 36, and the occupied state of each channel is recognized based on whether or not the signals are superimposed.

As the wavelength tunable filter 33 having such a function,
Here, a distributed feedback (DFB) type transmission filter having a semiconductor structure similar to the broadband LD used in the reference station 2 is used.

Here, when it is recognized that the channel of wavelength E is vacant, the control unit 39 of the terminal station A3 controls the optical switch 12 to send all the light on the transmission path la to the terminal station A3 side. . The optical switch 12 is normally a fail-safe type that is connected to the transmission line 1 side. The light switched in this way is sent to the tunable filter 34, where the wavelength is swept by the tunable wavelength filter 33 described above, and the wavelength is the same as the wavelength recognized as vacant (in this case, E), and the wavelengths other than the wavelength are swept. The wavelength is separated into light and light.

This wavelength tunable filter 34 is the tunable filter 3 described above.
It has a structure similar to 3.

Next, the light with the wavelength λ1 separated by one is split into two directions by the optical branching element 31, one of the lights enters the light receiver 37, where the wavelength, light intensity, phase, etc. are monitored, and the other light is split into two directions. ,
Data from the terminal device 7 is superimposed by the optical modulator 35 via the control unit 39 . The modulation method in this case is a modulation method in which the optical output does not change, for example, frequency variable II (F
This modulated light (wavelength 'L1
) is multiplexed by the optical combining element 32 with light of wavelengths other than the wavelength-separated light described above.

At this time, when the modulation method is FM or PM, the light intensity of the modulated optical signal input to the optical multiplexing element 32 is adjusted to each wavelength (
If the intensity of the light of each wavelength is set to the same level as the light of other wavelengths), the intensity of the light of each wavelength is kept constant regardless of the access status of terminal stations other than the terminal station A3.

When the modulation method is AM, the specific power at 11 o'clock changes, but by selecting an encoding method (Manchester encoding method, etc.) that sets the mark rate (stream component) to 50%, the output level at any time can be changed. The time average can always be 50% of FM or PM. Therefore, by giving a gain of 3 dB to the optical modulator 35 under the control of the control section 39, the output level of each wavelength input to the optical amplifier 38 can be kept constant.

In this way, the light of each wavelength that is simultaneously amplified by the amplifier 38 is controlled by the optical switch 13 controlled by the control unit 39.
It is sent out to the transmission path 1a.

On the other hand, when receiving at the terminal station B4, the optical branching element 11 of the terminal station B4 branches the light of reception i'81b, the variable wavelength filter 33 selects the wavelength, and the optical receiver 36 receives the signal. At this time, the variable wavelength filter 33 is controlled by the control unit 39 so that the light with the wavelength tl is selected, and in this way, the signal superimposed on the light with the wavelength tl at the terminal station A3 is received at the terminal station B4. As a method of setting the selected wavelength of the wavelength tunable filter 33, for example, the wavelength can be set at the terminal station A3.

When superimposing a signal on the light of , information indicating that the signal is destined for terminal station B4 is placed at the beginning of the signal, and this is wavelength swept with the wavelength variable filter 33 of terminal station B4 to find out the header. There is a method of fixing the selected wavelength of this filter 33 to the wavelength on which the signal is loaded.

At this time, the optical switch 12 of the terminal station B4 is on the optical path 1 side, and the light on the transmission path 1a only passes through the terminal station B4. In other words, the terminal station B4 functions only as a receiving section. However, it is also possible to transmit using other channels while receiving. For example, the wavelength tunable filter 3
When the wavelength is raised in step 3, an empty carrier or channel is found, and this carrier is used to transmit the signal to optical modulator 3.
Such control is performed by the control unit 39, and the communication procedure is performed by the terminal station A described above.
As seen from the user's point of view, the normal terminal stations 3 to 6 of this embodiment have all the functions of a normal passive terminal station. or access method (e.g. C8MA/CD (ca
rr i er 5ense multiple
aCCeSs with collision
For example, an optical amplifier may be installed as a repeater at any position on the transmission path if necessary for system expansion, etc., where the detection can be used almost as is.

[Effects of the Invention] As explained above (1) According to the present invention, since the light emitting source is only the reference station, temperature control basically only needs to be installed in the reference station, and a wavelength division multiplexing optical communication network can be established at an extremely low cost. In addition, since the input signal level of the optical amplifier of the optical transmitter/receiver can be aligned for each channel, level adjustment can be easily made by amplifying all wavelengths with a constant gain, making the system extremely simple. This eliminates the limitation on the number of terminal stations, which was a drawback of networks.

Furthermore, from the point of view of the user of a normal terminal station, it has all the functions of a passive terminal station, so the commonly used communication methods can be applied almost as is, and system design becomes easy.

On the other hand, in the above embodiment, a specific example of the wavelength band of 0.8 μm was shown, but it goes without saying that other wavelength bands, such as the 1.3 μm band, the 1.55 μm band, etc., may also be used.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of one embodiment of the optical communication system of the present invention, FIG. 2 is a diagram of an example of the emission spectrum of a broadband semiconductor laser of a reference station, and FIG. 3 is a diagram of an example of the emission spectrum of a broadband semiconductor laser of a reference station. FIG. 3 is a block diagram of a terminal station. 1... Optical path, 1a... Transmission path, 1b...
...Reception path, 1c...Fiber turning point, 2...
...Reference station, 3-6...8i! i terminal, 7-1
0...terminal device, 11.31...optical branching element, 12.13...optical switch, 33.34...-
... Tunable wavelength filter, 35 ... Optical modulator, 3
6.37... Light receiver, 38... Optical amplifier,
39...Control unit Fig. 3 h

Claims (1)

[Claims] 1. In an optical communication network having a bus-type configuration in which a plurality of terminal stations are coupled to an optical transmission line in which a plurality of lights are wavelength-multiplexed, the light beams of a plurality of wavelengths are Wavelength multiplexing characterized in that one reference station having means for constantly transmitting data to the transmission line is located at one end of the optical transmission line, and a plurality of terminal stations including optical receivers are arranged on the optical transmission line. Optical communication network. 2. The optical transmitting/receiving device includes means for selecting light of an arbitrary wavelength from the plurality of wavelengths and recognizing data superimposed on this light, and a means provided on the optical transmission path according to the recognized content. means for selectively switching the optical path to the optical transmitter/receiver; means for newly selecting light of an arbitrary wavelength from the light of the plurality of wavelengths and separating it from light of other wavelengths; and means for adding data to the sorted and separated light. A means for superimposing the signals, a means for recombining this separated light and the remaining light, a means for simultaneously amplifying all of the combined light, and a means for transmitting the amplified light back into the optical transmission line. 2. The optical communication network according to claim 1, further comprising means for transmitting. 3. In an optical transmitter/receiver that is included in a terminal station connected to an optical communication network that has a bus type configuration and has an optical transmission line in which a plurality of lights are wavelength-multiplexed, an optical transmitter/receiver that transmits light of any wavelength from among the plurality of wavelengths mentioned above. means for selecting the light and recognizing the data superimposed on the light; means for selectively switching the optical path provided on the optical transmission path to the optical transmitting/receiving device according to the recognized content; A means for newly selecting light of an arbitrary wavelength from the light of the light and separating it from light of other wavelengths, a means for superimposing a data signal on this sorted and separated light, and a means for recombining this separated light and the remaining light. An optical transmitting/receiving device comprising means for multiplexing, means for simultaneously amplifying all of the multiplexed light, and means for sending the amplified light back to the optical transmission path.