JP2000059315A - Optical access network, optical transmission method and its subscriber device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To facilitate the buildup of an optical subscriber system network by simply configuring a station side receiver and a subscriber side transmitter. SOLUTION: A network of a subscriber system is configured to be a straight line network that connects a station 10 and an and light source 11 that supplies a DC light. Subscribers #1, #2 are connected in series between the station 10 and the end light source 11. A signal light that is produced by modulating a DC light supplied from the end light source 11 with an external modulator or the like is transmitted to the station 10. A time slot permitting modulation of the DC light is assigned to the subscribers #1, #2 and a signal from its own subscriber device is set to time slots assigned to itself. Since the station 10 is configured to have the end light source 11, communication from the station to a subscriber can be made by using a same transmission line with a looped network.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical subscriber network configuration and a subscriber unit thereof.
In particular, the present invention relates to a method for transmitting a signal on the subscriber side and a method for simplifying the configuration of a circuit for receiving a signal (up signal) from the subscriber on the station side.

[0002]

2. Description of the Related Art In recent years, with the development of optical communication technology, a shift from a conventional electric communication network to an optical communication network has been made.
At present, an optical communication network is used as a trunk communication network, but a line to each subscriber of the communication network is generally an electric line. In order to further promote the use of optical communication networks, it is important to replace subscriber transmission lines that branch off from the trunk communication network with optical transmission lines. In some cases, the path is formed by an optical transmission path.

The connection from the trunk communication network to the subscriber system generally includes a station that terminates the transmission path of the trunk communication network, and the transmission path is routed from this station to each subscriber. . The term "subscriber system" includes the transmission line and the communication device from the station to the subscriber. 2. Description of the Related Art Conventionally, a star network using an optical star coupler is generally used as an optical subscriber network configuration.

[0004] That is, as shown in FIG. 8 (a), one optical transmission line is routed from a station 81, which terminates a trunk communication network, to an optical star coupler 80, and an optical signal is distributed to a subscriber by the optical star coupler. And transmitted using the transmission path connected to each of the subscribers # 1 to #N. Also, subscribers # 1 to #N
Similarly, the signal from is transmitted from the optical star coupler 80 to the station by using a separate line configured in a star type.

[0005]

The first problem with the conventional star-type network is that the station-side receiver has a large optical power for each of the subscribers # 1 to #N transmitting the optical signal. That is, different optical signals must be received.
That is, when a subscriber system is actually configured, FIG.
, The optical star coupler 80 and the subscribers # 1 to #N
The distance between them differs for each of the subscribers # 1 to #N. In addition, the branch loss of the optical star coupler 80 varies. As a result, as shown in FIG. 8B, even if each of the subscribers # 1 to #N sends an optical signal having the same power to the station 81, the power loss occurs due to the length of the optical signal propagating through the transmission path. In addition to the differences, the loss occurs when the optical signals of the optical star coupler 80 are multiplexed, and it is necessary for the station-side receiver to receive signals from subscribers having greatly different optical powers. ATM (As
In the case of adopting a mode of transmitting data in packet format, such as asynchronous transfer mode),
The station-side receiver requires a circuit for resetting a threshold for identifying the amplitude of a received signal every time a burst signal such as an ATM cell arrives. However, in the future, when the tendency to increase the transmission speed of communication becomes strong, it is difficult to add a start-up bit to a burst signal of a cell or the like to make a circuit that starts up with one or two start-up bits. It is becoming. In particular, it is necessary to produce a threshold detection circuit that operates at high speed. Therefore, the device becomes complicated, a very short reset time, a very short start-up time for the receiving circuit, and the like are required.

As a second problem, in the transmitting section on the subscriber side, there is a problem that the waveform deterioration is particularly large at the first bit at the rise due to the pattern dependence of the oscillation delay time due to the LD characteristic. . This is because the light emission power of each of the subscribers # 1 to #N when the signal is not transmitted is synthesized and input to the station-side receiver, which causes deterioration of the reception sensitivity. In the case of modulation, there is a problem that the LD cannot be instantaneously started due to the operating characteristics of the LD, even though the LD completely extincts and then starts up to full power. Therefore, this is a problem peculiar to the transmission of the burst signal to which the bias-less modulation is applied.

A third problem is stabilization of optical output power when a burst signal is transmitted in a transmission unit on the subscriber side. As a stabilization method, a high-speed APC method or an APC-free / temperature feed-forward method has been proposed. However, the high-speed APC has a problem that a rise time is long and it is difficult to realize a high-speed monitor circuit. In the APC-free temperature feed-forward method, LD sorting is required, and there is a problem of an increase in cost.

An object of the present invention is to simplify the configuration of the station-side receiver and the configuration of the subscriber-side transmitter to facilitate the supply of an optical subscriber network.

[0009]

SUMMARY OF THE INVENTION An optical access network according to the present invention comprises: a light source means for transmitting DC light to a station in an optical subscriber network connecting a station and a subscriber unit; The subscriber unit having modulation means for modulating light, wherein the station, the subscriber apparatus and the light source means are connected in series with the station and the light source means at both ends of a network, and are time-divided. According to a multiplexing method, each subscriber modulates the direct-current light by the modulation means, and performs communication from each subscriber device to the station.

An optical access network according to another aspect of the present invention is an optical subscriber network for connecting a station and a subscriber unit, wherein the light source means for transmitting DC light to the station, and an amplifier having a modulation function. The station, the subscriber unit, and the light source unit are connected in series with the station and the light source unit at both ends, and are separated from the subscriber unit by time division multiplexing. When communicating with the station, optical amplification is performed if it is not a predetermined time slot, and if it is the predetermined time slot, the direct-current light is modulated by the amplifying means so that it can be transmitted from the subscriber unit. The communication to the station is performed.

The subscriber unit of the present invention includes a light source for transmitting DC light to a station, and the station, the subscriber unit, and the light source are connected in series with the station and the light source as both ends of a network. In the above optical access network, the subscriber unit has a modulator for modulating DC light from the light source, and performs communication from each subscriber unit to a station by a time division multiplexing method.

A subscriber unit according to another aspect of the present invention includes a light source for transmitting DC light to a station, wherein the station, the subscriber unit, and the light source are connected in series with the station and the light source at both ends. In the optical access network connected to the above, the subscriber unit has a semiconductor laser amplifier, and when performing communication from the subscriber unit to the station by the time division multiplexing method, if it is not a predetermined time slot, Optical amplification is performed, and in the case of the predetermined time slot, communication from the subscriber unit to the station is performed by modulating the DC light by the semiconductor laser amplifier.

An optical signal transmission method according to the present invention is an optical signal transmission method in an optical subscriber network for performing communication between a station and a subscriber unit, comprising the steps of: providing a light source for oscillating DC light; Connecting the light source, the station, and the subscriber unit linearly with the light source and the station as both ends, and modulating the DC light transmitted from the light source to the station at the subscriber unit; And receiving, at the station, the DC light modulated by the subscriber unit.

According to the present invention, a direct-current light is supplied from the end of the subscriber network and this is modulated by the subscriber device into an optical signal, so that there is only one light source. There is no difference in the level of the optical signal sent to the station for each user device. Therefore, the receiving device of the station can be simplified and downsized.
High reliability can be obtained.

Further, since the light source is not directly modulated, it is possible to suppress the waveform deterioration of the transmission optical signal due to the characteristics of the light source, particularly, the waveform deterioration at the rising of the burst signal. Further, since there is one light source, it is not necessary to stabilize the output characteristics of the light source for each subscriber. In particular, if a light source is provided in a station, the place where monitoring and maintenance is performed is the station, so that specialists can collectively receive monitoring and maintenance in one place.

[0016] Therefore, the device for receiving the optical signal from the subscriber can be simplified, and the subscriber device can also be simplified.
An effective method can be provided when an optical subscriber system is actually installed.

[0017]

FIG. 1 is a diagram illustrating the principle of the present invention.
As shown in FIG. 1B, the station 10 and the subscribers # 1 and # 2
(The number of subscribers is not limited to two.) Connection is performed in series, and a light source 11 is provided at the end. Each subscriber device has an external modulator (right in FIG. 2B), and the signals assigned to the subscribers # 1 and # 2 by the external modulator as shown in FIG. Is modulated only in the time slot in which the signal is to be transmitted, and when the signal is not transmitted, the signal coming from the downstream is passed as it is.

At the input of the station-side receiving section, since all the losses of the respective subscribers are added up, the optical input is at a certain level. That is, in FIG. 3B, assuming that the loss of the subscriber # 2 is l (2) and the loss of the subscriber # 1 is l (1), the loss on the receiving side is l (1) + l ( 2). However, since the light from the terminal light source 11 all receives the same loss and attenuates, the station 10 receives a different loss for each subscriber and receives a loss.
Is never entered. Further, the extinction ratio of the signal modulated by each subscriber is stored as it is. Although it depends on the characteristics of the external modulator in each subscriber, if 10 dB or more can be ensured, the power penalty in the receiver is negligible even if there is variation among the subscribers.
Therefore, unlike the conventional star-type configuration, it is not necessary to receive a signal having a large difference in optical power level, and the station-side receiver can be configured with a simple circuit. Further, since the reset signal and the high-speed burst reception function of the receiver are not required, the speeding up of the network can be easily realized. In this configuration, the signal input to the station-side receiver has negative logic (low level indicates “1” and high level indicates “0”), but this is easily performed by logic processing in the apparatus. Can be resolved.

Also, as the second and third problems,
The problem of the oscillation delay of the LD, which is a problem in realizing a high-speed burst transmission unit, can be solved by using an external modulator, and similarly, the problem of stabilizing the optical output power can be avoided. That is, the LD emits only DC light as the terminal light source 11, and the problem of delay in starting the LD is avoided.

Further, an external modulator using an electro-optic effect such as an LN modulator (Mach-Zehnder modulator) is used as the external modulator, and when no voltage is applied to this modulator, a terminal light source is used. By allowing the light from 11 to pass through as it is, it is possible for the subscriber to turn off the power when no signal is emitted, and to reduce the power consumption of the subscriber device.

Alternatively, an electroabsorption modulator using the Frank Keldysh effect can be used as the external modulator. In this case, since the size can be reduced as compared with the LN modulator, the size of the subscriber device can be reduced. In order to increase the transmission distance of the network, it is also possible to adopt a configuration in which an optical amplifier is installed between the subscriber units, between the terminal light source and the subscriber unit, or between the station and the subscriber unit. An optical fiber amplifier or a semiconductor laser amplifier can be used as the optical amplifier for that purpose.

It is also possible to use a semiconductor laser amplifier instead of an external modulator. Each subscriber supplies a DC current to the semiconductor laser amplifier when the signal is not emitted, amplifies the optical power, and at the time of the signal emission, modulates the supplied current to reduce the amplifying effect and give intensity modulation to the signal. . This facilitates an increase in the transmission distance of the network.

It is also possible to adopt a configuration in which the subscriber unit has a semiconductor laser amplifier and an external modulator together. If an external modulator of an electroabsorption type is used, the semiconductor process can be performed in the same manner as the semiconductor laser amplifier. Since it can be manufactured, the size of the subscriber device can be reduced by integrating it.

FIG. 2 is a diagram for explaining a configuration in which a station is provided with a terminal light source and a receiver, and subscribers are connected by a loop transmission line. As shown in FIG. 1A, in this embodiment, a terminal 20 is provided with a terminal light source 21 and a receiver 22, and subscribers # 1 to #N are connected by a loop-shaped transmission path. By doing so, the subscribers # 1 to #N can transmit information to the station 20 by modulating the light from the terminal light source 21, and when transmitting the terminal light source 21 from the station 20, If modulated and transmitted, each subscriber # 1
To #N. Subscriber # 1 to #
N receives the signal transmitted from the station 20 by a receiver provided in the subscriber unit, and the station 20 causes the receiver 22 to receive the signals from the subscribers # 1 to #N. I do.

The light emitted from the terminal light source 21 of the station 20 is modulated by the subscriber units # 1 to #N. Each subscriber has a time slot assigned to it, as shown in FIG. 2B, and the communication time between the station and the subscriber is divided by time division. On the other hand, this time slot is also provided with a time slot used for communication from the station to each of the subscribers # 1 to #N. The station modulates this time slot portion with a modulator, and Subscriber # 1 to #N
Send to Communication from the station to the subscriber is performed by the terminal light source 21 placed in the station 20, and the communication time from the subscriber to the station is:
DC light emission is performed, and the subscriber modulates the external light modulator at the time of the DC light emission. In this configuration, only one light source is required, and the cost of the entire network can be reduced. In addition, when a semiconductor laser is used as the terminal light source, the use of a laser having lower reliability than other components is generally limited to the terminal light source. Thus, the reliability of the entire network can be improved. In addition, the terminal light source 21 and the receiver 22 can be maintained in the station 20 by arranging the terminal light source 21 in the station 20 and adopting a ring-type configuration.
Maintenance problems can be simplified compared to conventional star networks.

As a method of allocating the time slots to the transmissions from the subscribers # 1 to #N and the station 20, the station 20 allocates the time slots using an appropriate clock. Station 2
0 and the length of each time slot assigned to each of the subscribers # 1 to #N depends on the type of service provided from the station 20 to each of the subscribers # 1 to #N and the actual number of the subscribers # 1 to #N. It depends on the number.

FIG. 3 is a diagram for explaining a station-side reception method in the subscriber unit in the configuration of FIG. FIG. 1A shows the principle. An optical coupler 30 is provided on the input side in the subscriber unit, and a signal is branched to enable reception. Also, FIG. 2B shows the case where the optical waveguide technology is used.
Miniaturization by integrating optical components and low cost by passive alignment can be realized.

When the light from the terminal light source is received as the light input, the optical signal is branched by the optical coupler 30 and received by the light receiver 33. The received optical signal is converted into an electric signal, and a signal processing unit (not shown) extracts only a signal of a time slot including a signal from the station and receives a service or the like from the station.

The other optical signal split by the optical coupler 30 is input to the external modulator 32. The drive circuit 31
According to the information obtained from the signal from the station, the external modulator 32 is driven only during the time slot assigned to it, and the DC light is modulated and transmitted to the next subscriber. In this way,
The optical signal modulated by the subscriber unit passes through each subscriber, is received by a receiver in the station, and transmits information from the subscriber to the station.

FIG. 2B shows a configuration in the case where the principle configuration shown in FIG. 1A is actually manufactured. As shown in FIG. 2B, for example, an optical waveguide 39 is formed on a substrate of Si, plastic, glass, lithium niobate, or the like.
The optical signal from the optical fiber 34 is input. The optical waveguide 39 is provided with an optical coupler 35, and is configured to branch an input optical signal. The optical coupler 35 is, for example, a Y-branch waveguide. Optical coupler 35
The optical signal split by the PD is one with the PD mounted on the substrate
While being received by 40, it is converted into an electric signal and transmitted to a receiving circuit (not shown). The other optical signal is the Mach-Zehnder type external modulator 3 in the case of FIG.
7 and is modulated by the driving circuit 36 in the DC light emitting portion, that is, the portion of the time slot allocated to the own subscriber device. The modulated optical signal propagates through the optical waveguide 39, enters the optical fiber 38, and is transmitted to the next subscriber.

As shown in FIG. 1B, by integrating the optical receiving unit and the optical modulation unit of the subscriber unit on one substrate, the subscriber unit can be downsized. The reliability of the device can also be increased.

FIG. 4 shows a configuration in which the external modulator of the subscriber unit is replaced by a semiconductor laser chip. In the figure, a station and a terminal light source are separately provided, and the configuration of a subscriber device when the station and the subscriber are connected linearly is shown. In the case where the subscriber system is configured linearly, the subscriber device 41 is provided with a separate configuration for transmitting a signal from the station to the subscriber. Therefore, the configuration shown in the figure is a configuration for transmitting a signal from a subscriber to a station.

The light transmitted from the terminal light source is input to the semiconductor laser amplifier 42 of the subscriber unit 41. The semiconductor laser amplifier 42 is driven by the modulation circuit 43. The semiconductor laser amplifier 42 has its own subscriber device 41.
When it is not a time slot for transmitting a signal from the optical input, the optical input is amplified by the control signal Ip applied from the modulation circuit. The right side of the figure shows the power of the optical input, the power of the amplified optical output, and the state of the control signal Ip output from the modulation circuit 43. The control signal Ip from the modulation circuit 43 applied to the semiconductor laser amplifier 42 is
This is a drive current of the semiconductor laser amplifier 42. When the current value is increased, a large amplification effect is obtained, and when the current value is reduced, the amplification effect is suppressed. The optical input has a low optical power level due to losses through many subscriber units and transmission lines. The portion between the dotted lines on the right side of the figure is the time to which a time slot in which a signal can be transmitted from the own subscriber device is allocated. During this time slot, the modulation circuit 43 controls the semiconductor laser amplifier 42. By changing the current value of the control signal Ip applied to
The gain of the semiconductor laser amplifier 42 is changed. As a result, the optical power in the portion of the time slot to which the optical input is assigned changes, and it becomes as if amplitude modulation was applied to the DC light. In this way, an optical signal is generated from the subscriber unit 41 to the station to transmit information.

When it is not the time slot of the own subscriber unit, the gain of the semiconductor laser amplifier 42 is kept constant, and the optical power level of the optical input is amplified. By doing so, it is possible to compensate for the loss caused by passing through the transmission path or the subscriber unit, and transmit the optical signal over a longer distance.

Although FIG. 2 has been described on the premise that the terminal light source is provided separately from the station, as shown in FIG.
It is also possible to adopt a configuration in which a terminal is provided with a terminal light source and a subscriber is connected to a loop network. In this case, the semiconductor laser amplifier and the photodetector can be provided on one substrate. In this case, the waveguide is formed in the shape of a substrate, an optical coupler is provided, the photodetector is provided on one side, and the photoreceptor is provided on the other side. The configuration is such that a semiconductor laser amplifier is provided. In such a case, the time slot for modulating the DC light from the terminal light source is divided into one for communication from the station and one for communication from the subscriber, and further, the time slot for communication from the subscriber is divided into each subscriber. Assigned to. The time slot for communication from the station and the time slot for communication from the subscriber vary depending on the service provided by the station, but it is sufficient to set them approximately one-to-one.

FIG. 5 is an explanatory diagram of a configuration in which light of different wavelengths is used for transmission from the station side to the subscriber and transmission from the subscriber to the station. Although FIG. 2 illustrates a configuration in which a station has a terminal light source and subscribers are connected in a loop by a transmission line, a similar network configuration is adopted in FIG. However, in FIG. 2, the time division multiplexing method is used for communication from the station to the subscriber and for transmission from the subscriber to the station, whereas in FIG. 2, the wavelength division multiplexing method is used.

In the figure, the communication from the station to the subscriber and the communication from the subscriber to the station are performed by wavelength division to improve the transmission efficiency and to provide the configuration of the subscriber unit at that time. Also, communication from the station to the subscriber is performed from the terminal light source side, and the wavelength of the light source for communication from the station and the wavelength of the light source for communication from the subscriber are brought close to each other, so that optical fibers installed between subscribers etc. By amplifying both wavelengths by the amplifier, both the upstream and downstream signals are amplified as light, and the transmission distance of the network can be increased.

FIG. 3A is a diagram showing an optical transmission configuration on the station side, which comprises a terminal light source 50 for transmitting DC light and a signal light source 51 from the station to the subscriber. Terminal light source 50
Is a DC light having a wavelength λ1, which is a light that a subscriber modulates with an external modulator or the like. As a method of allocating the DC light of wavelength λ1 to each subscriber, a time division multiplexing method as shown in FIG. 2 is used.

Since the signal of the optical signal of wavelength λ2 output from the signal light source 51 from the station to the subscriber must be specified depending on which subscriber is to be transmitted, a time division multiplexing method is adopted. According to this, the subscriber extracts the signal of the time slot assigned to him, and obtains the information on the signal directed to him from the station. Alternatively, an ID is assigned to each subscriber, and when a signal is transmitted from a station to a specific subscriber, this ID is added to the signal. In this way, the subscriber can detect the ID and determine whether or not the signal is directed to itself without performing time division multiplexing.

As a method of allocating a time slot, a method is generally used in which a subscriber obtains a synchronization signal from a station and searches for a time slot assigned to the subscriber. Any scheme used is applicable to this configuration. Also, instead of assigning time slots to all subscribers in advance, it is also possible to put a signal in an open time slot when transmission from a subscriber to a station is required. In this case, the own subscriber ID is added to the signal so that the station can know from which subscriber the signal is sent.

The DC light of wavelength λ1 output from the terminal light source 50 and the wavelength λ2 of the signal light source 51 from the station to the subscriber.
Is wavelength-multiplexed by the WDM coupler 52 with the signal light of
Sent to subscriber.

FIG. 4B shows the configuration on the subscriber side. The optical signal transmitted from the previous subscriber (subscriber closer to the terminal light source) connected to the subscriber system is composed of an optical signal of wavelength λ1 and an optical signal of wavelength λ2. The WDM coupler 53 branches the optical signal into each wavelength of the optical signal, and the optical signal of the wavelength λ1 used for communication from the subscriber to the station is input to the external modulator 56. When it is necessary to send information from the subscriber to the station, of the optical signal of the wavelength λ1, the DC light in the time slot assigned to itself is modulated by the external modulator 56 and transmitted to the next subscriber. Send out.

Wavelength λ2 used for communication from the station to the subscriber
Is split by the optical coupler 54, a part thereof is taken out, received by the receiver 55, and the signal transmitted to itself is received. Others are WDM coupler 5
7 and is wavelength-multiplexed with the optical signal from the external modulator 56 and transmitted to the next subscriber. The receiver 55 extracts the signal of the time slot assigned to itself or the signal including its own ID from the transmitted signals, and acquires the communication content from the station.

As described above, if wavelength division multiplexing is used,
Since the communication from the station to the subscriber can be an optical signal of another wavelength, all the light used for the communication from the subscriber to the station can be allocated to the subscriber. That is, as described with reference to FIG. 2, there is no need to allocate a time slot from a station to a subscriber, so if the same time interval as in FIG. Can be incorporated into the subscriber system.

FIG. 6 is a diagram showing an example in which the components of the subscriber unit are integrally formed in the configuration of FIG.
As shown in the figure, the subscriber device uses the optical waveguide technology to
Miniaturization by integrating optical components and cost reduction by passive alignment can be realized.

As described above, various materials such as Si, glass, plastic, and lithium niobate can be used for the substrate. An optical waveguide 64 is formed on these substrates, and optical signals from the optical fiber 60 are coupled. This optical signal has been described with reference to FIG. 5, and optical signals having different wavelengths are wavelength-multiplexed. Accordingly, the wavelength λ2 for communication from the station to the subscriber and the wavelength λ1 for communication from the subscriber to the station are demultiplexed by the WDM coupler 61, and the optical signal of the wavelength λ2 for communication from the station to the subscriber is transmitted to the PD 63 side. , An optical signal having a wavelength λ1 for communication from a subscriber to a station is transmitted to a Mach-Zehnder type external modulator 6.
Guide to the 6 side. In the figure, a Mach-Zehnder type external modulator 66 is described as an example of the external modulator, but the external modulator is not limited to this, and an electric absorption type external modulator, a semiconductor laser amplifier, or the like can be used. The Mach-Zehnder external modulator 66 is driven by a drive circuit 67, and generates an optical signal subjected to intensity modulation by changing the power of light.

On the other hand, the optical signal (wavelength λ2) guided to the PD 63 is branched by the optical coupler 62, and a part thereof is
The signal is converted by 63 into an electric signal. This electric signal is sent to a receiving circuit (not shown), and a signal addressed to itself is extracted. The optical signal branched by the optical coupler 62 and not guided to the PD 63 propagates through the optical waveguide 64 and the WDM coupler 65
Is wavelength-multiplexed with the optical signal (wavelength λ1) from the Mach-Zehnder type external modulator 66, and input to the optical fiber 68,
It is transmitted to the next subscriber device.

The subscriber unit is connected to a loop-shaped transmission line having a station as a start point and an end point. The station side receiving unit terminates an optical signal of wavelength λ2 and receives an optical signal of wavelength λ1. To obtain the information sent from the subscriber to the station.

FIG. 7 shows a configuration in which a transmission line for communication from the station to the subscriber and a transmission line for communication from the subscriber to the station are separately provided. As shown in FIG. 1A, two transmission lines from a station or a previous subscriber are connected, one for communication from the station to the subscriber, and the other for communication from the subscriber to the station. is there. Also in this configuration, it is assumed that a loop transmission line in which the station also serves as a start point and an end point of the transmission line is configured as a subscriber system.

An optical coupler 70 is provided on one transmission line (optical fiber). The optical coupler 70 splits the optical signal, guides a part of the optical signal to the optical receiver 72, and transmits the other to the next-stage subscriber or station.

An external modulator 71 is provided on the other transmission line, modulates DC light, carries information for transmission to the station on a signal, and transmits the signal to the next subscriber or station. FIG.
Is an example of a subscriber unit having such a configuration in which optical components are integrated using optical waveguide technology. By performing such integration, downsizing and cost reduction by passive alignment can be realized.

As shown in FIG. 7B, optical fibers 73 and 79 for communication from the subscriber to the station are coupled to an optical waveguide 76 formed on an appropriate substrate, and the optical fiber is connected via an optical coupler 77. One is guided to the optical fiber 79 as it is, and the other is guided to the PD 78 and received by a receiving circuit (not shown). Optical fibers 74, 82 for communication from stations to subscribers
Are coupled to the optical waveguide 75. The optical signal from the optical fiber 74 is guided to a Mach-Zehnder type external modulator 80, and the DC light in a predetermined time slot is intensity-modulated and output to the optical fiber 82. The Mach-Zehnder external modulator 80 is controlled by a drive current of a drive circuit 81.

As described above, the external modulator is not limited to an electro-optic effect type such as a Mach-Zehnder type external modulator, but may be an electro-absorption type or a semiconductor laser amplifier. When a semiconductor laser amplifier is used, the power of an optical signal transmitted from a station can be amplified, so that it is suitable for transmission of a subscriber system having a longer transmission distance.

[0054]

As described above, according to the present invention,
The station-side receiver and the subscriber-side transmitter can be easily configured, and an optical subscriber network can be easily realized. In addition, it is possible to easily improve the transmission efficiency and speed of the network.

[Brief description of the drawings]

FIG. 1 is a principle diagram of the present invention.

FIG. 2 is a diagram illustrating a configuration in which a terminal is provided with a terminal light source and a receiver, and subscribers are connected by a loop transmission line.

FIG. 3 is a diagram illustrating a station-side reception method in a subscriber device in the configuration of FIG. 2;

FIG. 4 is a diagram in which an external modulator of a subscriber device is replaced by a semiconductor laser chip.

FIG. 5 is an explanatory diagram of a configuration in which light of different wavelengths is used for transmission from the station side to the subscriber and transmission from the subscriber to the station.

FIG. 6 is a diagram showing an example of a case where each component of the subscriber device is integrally formed in the configuration of FIG. 5;

FIG. 7 shows a configuration in which a transmission path for communication from the station to the subscriber and a transmission path for communication from the subscriber to the station are separately provided.

FIG. 8 is a diagram illustrating a conventional technique.

[Explanation of symbols]

10, 20 stations 11, 21, 50 Terminal light source 22, 55 Receiver 30, 35, 54, 62, 70, 77 Optical coupler 31, 36, 67, 81 Drive circuit 32, 56, 71 External modulator 33, 72 Light reception Containers 34, 38, 60, 68, 73, 74, 79, 82
Optical fiber 37, 66, 80 Mach-Zehnder type external modulator 39, 64, 75, 76 Optical waveguide 41 Subscriber device 42 Semiconductor laser amplifier 43 Modulator circuit 51 Light source for signal from station to subscriber 52, 53, 57, 61, 65 WDM coupler 40, 63, 78 PD

Claims (30)

[Claims] 1. An optical subscriber network for connecting a station and a subscriber unit, comprising: a light source means for transmitting DC light to the station; and a modulation means for modulating the DC light. The station, the subscriber unit, and the light source means are connected in series with the station and the light source means at both ends of the network, and each subscriber is controlled by the modulation means by time division multiplexing. An optical access network, which modulates the DC light and performs communication from each subscriber device to the station. 2. The optical access network according to claim 1, wherein said light source means is located in said station. 3. The optical access network according to claim 1, wherein said modulation means is a light intensity modulator based on an electro-optic effect. 4. The optical access network according to claim 1, wherein said modulating means does not extinguish when no voltage is applied, but extinguishes when a voltage is applied. 5. The optical access network according to claim 1, wherein said modulating means is an electro-absorption type optical intensity modulator. 6. The optical access network according to claim 1, wherein an optical amplifier is provided between the subscriber units connected in series, between the subscriber unit and the terminal light source, or between the office and the subscriber unit. 7. The optical access network according to claim 6, wherein said optical amplifier is an optical fiber amplifier. 8. The optical access network according to claim 6, wherein said optical amplifier is a semiconductor laser amplifier. 9. An optical subscriber network for connecting a station to a subscriber unit, comprising: a light source means for transmitting DC light to the station; and the subscriber unit provided with amplifying means having a modulation function. The station, the subscriber unit, and the light source unit are connected in series with the station and the light source unit at both ends, and when the subscriber unit communicates with the station by a time division multiplex method, If the time slot is not a predetermined time slot, optical amplification is performed, and if the time slot is the predetermined time slot, communication from the subscriber unit to the station is performed by modulating the DC light by the amplifying means. And optical access network. 10. The optical access network according to claim 9, wherein said light source means is arranged in said station. 11. The optical access network according to claim 9, wherein said amplification means is a semiconductor laser amplifier. 12. The subscriber unit comprises a semiconductor laser amplifier on the input side from the light source means and a modulator on the output side, the semiconductor laser amplifier controlling the intensity of the DC light from the light source means. The optical access network according to claim 11, wherein the DC light is amplified and the DC light is modulated in the modulator. 13. The modulator according to claim 1, wherein the modulator is an electro-absorption type optical intensity modulator, and the semiconductor laser amplifier and the electro-absorption type optical intensity modulator are integrally formed.
3. The optical access network according to item 2. 14. A signal transmission time from said station to said subscriber unit, and a signal transmission time from said subscriber unit to said station, wherein said light source means installed in said station comprises: The signal transmission time to the subscriber unit modulates the DC light to transmit a signal, and the signal transmission time from the subscriber unit to the station emits DC light. 11. The optical access network according to claim 2, wherein a signal transmitted from the subscriber unit to the station is modulated. 15. The subscriber unit is provided on the side of the light source means.
The optical access network according to claim 14, comprising an optical coupler, wherein one of the outputs of the optical coupler is input to a receiver for receiving a signal from the station, and the other is modulated. 16. The subscriber unit comprises an optical coupler, a receiver, an external modulator, or a semiconductor laser amplifier, and is integrally formed using optical waveguide technology. 16. The optical access network according to claim 15. 17. The method according to claim 1, wherein the signal transmission from the station to the subscriber unit uses light having a wavelength different from the wavelength for signal transmission from the subscriber unit to the station. Optical access network as described. 18. The gain band of an optical amplifier provided in a transmission line, wherein both a wavelength used for transmitting a signal from the subscriber unit to the station and a wavelength used for transmitting a signal from the station to the subscriber are provided. The optical access network according to claim 17, wherein: 19. The subscriber unit according to claim 17, wherein the subscriber unit comprises a WDM coupler, an external modulator, an optical coupler, and a light receiving element, and is integrally formed by using an optical waveguide technology.
An optical access network according to claim 1. 20. The optical access network according to claim 1, further comprising an optical fiber for communication from said station to said subscriber unit and for communication from said subscriber unit to said station. . 21. The optical access network according to claim 20, wherein said subscriber unit comprises an external modulator, an optical coupler, and a light receiving element, and is integrally formed by using an optical waveguide technology. 22. An optical access network comprising a light source for transmitting DC light to a station, wherein the station, the subscriber unit, and the light source are connected in series with the station and the light source as both ends of the network. The subscriber unit has a modulator for modulating DC light from the light source, and performs communication from each subscriber unit to a station by a time division multiplexing method. 23. The subscriber unit according to claim 22, wherein said modulator is a light intensity modulator based on an electro-optic effect. 24. The subscriber unit according to claim 22, wherein said modulator is an electro-absorption type optical intensity modulator. 25. An optical access network comprising a light source for transmitting direct current light to a station, wherein the station, the subscriber unit, and the light source are connected in series with the station and the light source at both ends. The subscriber unit has a semiconductor laser amplifier, and when performing communication from the subscriber unit to the station by the time division multiplexing method, performs optical amplification when the time slot is not a predetermined time slot, and performs the optical amplification in the predetermined time slot. In some cases, the subscriber device performs communication from the subscriber device to the station by modulating the DC light with the semiconductor laser amplifier. 26. A semiconductor laser amplifier on the light source side and a modulator on the station side, wherein the semiconductor laser amplifier steadily amplifies the light intensity, and the modulator modulates the direct-current light to produce the light. The subscriber unit according to claim 25, wherein the subscriber unit transmits a signal light to a station. 27. The semiconductor laser amplifier and the electro-absorption light intensity modulator are formed integrally as an electro-absorption light intensity modulator as the modulator.
7. The subscriber device according to 6. 28. A method for transmitting an optical signal in an optical subscriber network for performing communication between a station and a subscriber unit, comprising the steps of: providing a light source for oscillating a DC light; Linearly connecting the light source, the station, and the subscriber unit; modulating the DC light transmitted from the light source to the station at the subscriber unit; Receiving the DC light modulated by the subscriber unit. 29. The optical signal transmission method according to claim 28, wherein said light source is provided in said station. 30. The optical signal transmission method according to claim 28, wherein the subscriber unit amplifies and modulates the DC light.