JPH10229363A - Optical transmission system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make the configuration of a slave station side the same as that of a PDS system by adopting a wavelength multiplex division multiple-access system that assigns one wavelength for each slave station to an outgoing signal from a center station to each slave station, so as to avoid the dependence of a transmission loss on a branch number. SOLUTION: A center station C sends optical signals, whose stimulated wavelength bands are λd1 -λdn in the time division multiplex system. Respective wavelength bands are used for carriers to send an outgoing signal to each subscriber. In an optical multiplexer/demultiplexer S, a guided direction of each signal differs from each wavelength and the destination of the optical signals whose stimulated wavelength bands are λd1 -λdn is distributed. Control sections CON1 - CONn of each subscriber light-emitting elements LD1 -LDn in a timing, according to a control signal as part of the outgoing signal from the center station C to send an incoming signal. In the incoming signal from each of slave stations M1 -Mn , the conditions λuk <λdmin or λuk >λdmax (where k=1, 2,...n) are satisfied, where wavelength bands are λu1 -λun and minimum and maximum wavelength bands of the wavelength bands λd1 -λdn emitted from the light-emitting elements of the center station C are λdmin and λdmax .

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is applied to an optical communication system. The present invention is particularly suitable for use in realizing an optical network of a subscriber line connecting a telephone station and a subscriber.

[0002]

2. Description of the Related Art In order to meet the demands for diversity and high-speed communication, the optical network of a subscriber line, which forms the basis of a communication infrastructure, is being promoted. All-optical subscriber system (FTTH: Fiber To
In order to realize The Home, the first step is to economically provide the INS network 64 and the analog telephone service currently provided by the existing metal line using the optical fiber.

As a method proposed for this purpose, there is a PDS (Passive Double Star) optical subscriber transmission method. In this method, as shown in FIG.
A plurality of slave stations M _{1 to} M _n having a subscriber unit (ONU: Optical Network Unit) are provided in an U: Optical Subscriber Unit via an optical star coupler (SC: Star Coupler) which is a passive component. in a manner to be accommodated, since the plurality of slave stations M ₁ ~M _n can be efficiently accommodated, active development has been promoted.

In this case, the center station C and the slave stations M _{1 to} M
The configuration of _n is, as shown in FIG.
_c , the semiconductor lasers LD _{1 to} LD _n and the light receiving element P
D _c, PD ₁ ~PD _n and an optical coupler for connecting both to a single optical fiber PC _c, which is from the PC ₁ to PC _n.

[0005]

In this conventional PDC optical subscriber transmission system, in addition to a coupling loss when a light emitting element or a light receiving element is coupled to an optical fiber, a line loss due to an optical fiber, and an optical star coupler SC. There are branch losses, and the maximum transmission station and the maximum number of branches are determined by the relationship between these losses and the optical output from the light emitting element, the minimum receiving sensitivity of the light receiving element, and the transmission speed. Currently the transmission speed is 50Mb
/ S, the maximum transmission distance is about 7 km, and the maximum number of branches is 32
However, an increase in the number of branches has been desired in order to further increase the economy.

Further, in a branch connection using an optical star coupler, an optical signal from the center station is transmitted equally to all slave stations. In actual operation, for example, by performing time-division control so that transmission and reception timings of a plurality of slave stations and the center station do not overlap, communication is performed so that signals do not collide with each other. Since it is extremely easy for another slave station to receive an optical signal transmitted from the center station to a particular slave station, the confidentiality is low.

[0007] In order to solve these problems, the applicant has disclosed in Japanese Patent Application No. 8-026827 a method of selectively changing the output port according to the wavelength of the incident light instead of the conventional optical star coupler. Using a wavelength router, which is an optical multiplexer / demultiplexer that can be used, instead of placing a light emitting element in the slave station, a modulation element is used to modulate a part of the downstream signal from the center station to the slave station to produce an upstream signal. An optical transmission scheme to send back is proposed.

In the proposed optical transmission system, the transmission loss does not depend on the number of branches, the confidentiality is high, and precise control of the wavelength in the slave station is not required, so that a low-cost optical transmission system can be realized. There are advantages.

However, according to the method of the proposed invention, the path of the upstream signal is a long path going back and forth to the center station.
When performing long-distance transmission, it is disadvantageous compared to the PDS method. Further, the configuration of the slave station is a light receiving element and a modulation element, and when changing from the PDS method to the method of the proposed invention,
There was a problem that the configuration of the slave station had to be changed.

The present invention has been made in such a background, and the transmission loss due to branching does not depend on the number of branches, and can be extended, and the configuration on the slave station side is the same as that of the PDS system. It is an object of the present invention to provide an optical transmission system.

[0011]

SUMMARY OF THE INVENTION The present invention provides a wavelength division multiplexing multiple access system in which a downstream signal from a center station to a slave station is divided by one wavelength for each slave station.
The uplink signal from the slave station to the center station is performed in a conventional configuration. In particular, for a downlink signal that has a lot of information and requires a high transmission speed, the branch loss can be reduced, and the transmission speed can be improved. In addition, it can be extended.

That is, the present invention relates to an optical communication system,
It is characterized by one center station (C), a plurality of n slave stations (M _{1 to} M _n ), the center station and the n
An optical multiplexer / demultiplexer (S) interposed between the slave stations.
The center station and the optical multiplexer / demultiplexer are connected by two or more optical fibers less than n, the n slave stations and the optical multiplexer / demultiplexer are connected by n optical fibers, The station is provided with a light emitting element and one or more light receiving elements, and each of the slave stations is provided with a light emitting element and a light receiving element, and an output end of the light emitting element and an input end of the light receiving element, respectively, at one end of the optical fiber. The center station includes control means for operating the light emitting element and the light receiving element in a time-division manner, and the slave station is synchronized with the control means of the center station. The center station is provided with control means for operating each light receiving element and each light emitting element in a time-division manner, and the center station outputs a wave output from the light emitting element to the optical multiplexer / demultiplexer through an optical fiber connected to an output end. Lambda _d1 without comprising means for selectively outputting the optical signals of lambda _dn, the optical demultiplexer, said to no wavelength lambda _d1 output from the center station selects the optical signal of lambda _dn respectively of n child Means for coupling to n optical fibers connected to a station, one or more optical signals having one end connected to the input end of the light receiving element of the center station, Means for coupling to the optical fiber of each of the slave stations, wherein the wavelengths λ _u1 to λ _un output by the light emitting elements of the respective slave stations are the minimum and maximum wavelengths of the wavelengths λ _d1 to λ _dn output by the center station, respectively. λ
λ _uk <λ _min or λ _uk > λ, where _min and λ _max
max (where k = 1, 2,... n).

The wavelengths λ _d1 to λ _dn are 1.5
Located between μm of 1.6 [mu] m, the wavelength lambda _u1 to lambda _un the respective slave station to output 1 from 1.25 .mu.m.
Desirably it is between 4 μm.

Thus, in the downstream direction, a wavelength router, which is an optical multiplexer / demultiplexer capable of selectively changing the output port according to the wavelength of the incident light, is used instead of the conventional optical star coupler. Therefore, even if the number of branches increases, the loss does not increase, so that a multi-branch network configuration can be realized. Further, since the slave station cannot receive an optical signal other than the wavelength assigned to the slave station, the confidentiality is improved.
Further, there is an advantage that the slave station may have the same configuration as the PDS system.

[0015]

Embodiments of the present invention will be described below in detail with reference to the drawings.

[0016]

FIG. 1 shows an overall configuration diagram of an embodiment of the present invention.

The present invention relates to an optical transmission system, which is characterized by one center station C and a plurality of n slave stations M _{1 to} M _1.
comprising a _n, and a demultiplexer S interposed between the central station C and n-number of the slave station M ₁ ~M _n, central station C and the optical demultiplexer S
Is connected by two or more optical fibers less than n,
The n number of the slave station M ₁ ~M _n and the optical demultiplexer S are connected by n optical fibers, the central station C includes a light-emitting element LD _c and one or a plurality of light receiving elements PD _c, each Slave station M ₁
Each light emitting element LD ₁ to Ld _n and the light receiving element PD ₁ -PD _n to M _n, one end of each said optical fiber input end of the output end and the light-receiving element PD ₁ -PD _n of the light-emitting element LD ₁ to Ld _n includes the optical coupler PC ₁ to PC _n as coupling means for coupling to a common, the central station C the center station controller CON as a control means for operating a time division manner and the light-emitting element LD _c and the light-receiving element PD _{c c,} and each of the slave stations M _{1 to} M _n has a center station control unit CON _c of the center station C.
Each comprise controller CON ₁ ~CON _n as control means when causing divisionally operate the respective light receiving elements PD ₁ -PD _n and the respective light emitting elements LD ₁ to Ld _n in synchronism with, the center station C is It is no wavelength lambda _d1 output from the light-emitting element LD _c to demultiplexer S through connected to an output end the optical fiber comprises a wavelength conversion portion F as a means for selectively outputting the optical signals of lambda _dn, optical demultiplexing The unit S selects the optical signals of the wavelengths λ _d1 to λ _dn output from the center station C and couples them to n optical fibers connected to the n slave stations M _{1 to} M _n , respectively. station M ₁ ~M _n of the light-emitting element LD ₁ ~LD _{n 1} or a plurality of means for coupling to an optical fiber one end of the optical signal output is connected to the input end of the light-receiving element PD _c of the center station C from with bets, each child station M ₁ ~M _n of the light emitting element D ₁ wavelength lambda _u1 which to Ld _n outputs, λ _u2, ··· λ _un is the minimum wavelength lambda _d1 to lambda _dn center station C is output, the maximum wavelength respectively lambda _min, when the lambda _max , Λ _uk <λ _min or λ _uk >
λ _max (where k = 1, 2,... n).

The wavelengths λ _d1 to λ output from the center station C
_dn is between 1.5 μm and 1.6 μm, and the wavelengths λ _u1 through λ _un output by the respective slave stations M ₁ -M _n are:
It is set between 1.25 μm and 1.4 μm.

An embodiment of the present invention will be described in detail. In the center station C, by the white light emitting element LD _c emits light passes through the wavelength conversion element provided in the wavelength conversion unit F, changing the wavelength of the optical signal to be sent to the wavelength of λ _d1 ~λ _dn.
It is also possible to use a wavelength variable element such as a wavelength tunable semiconductor laser capable variably controls the light-emitting element LD _c itself wavelengths as the light emitting element LD _c.

First, a down signal from the center station C to each subscriber will be described. The center station C time-division multiplexes (TDM: Time Division M) optical signals having emission wavelengths from λ _d1 to λ _dn.
ultiplexing) method. Using each wavelength as a carrier, a downstream signal is transmitted to each subscriber. As a signal system, for example, NRZ (Non Retu
rn to Zero) signal. In the optical multiplexer / demultiplexer S, since the guided direction is different for each wavelength, λ _d1 to λ
The optical signal of _dn is distributed to the destination. In this way, one wavelength can be assigned to one subscriber. Downlink signal reaching each subscriber, the light-receiving element PD ₁ -PD _n
Received at. Thus, the downstream signal is transmitted.

Next, an uplink signal from each subscriber to the center station C will be described. Control unit CON _{1 to} CON of each subscriber
_n causes each of the light emitting elements LD _{1 to} LD _n to emit light at a certain timing according to the instruction of the control signal sent from the center station C as a part of the downlink signal, and transmits the uplink signal.
Here, the control signal of the center side refers to the upstream signals from each subscriber so as not to be received by the light receiving element PD _c of the center station C overlap in time, to indicate the timing for sending the optical signal. By doing so, a so-called TDMA (Time Division Multiple Access) is used.
2), the center station C can receive uplink signals from each subscriber.

In this system, the configuration of the optical multiplexer / demultiplexer S is important. 2 and 3 show examples of the configuration of the optical multiplexer / demultiplexer S, respectively.

In the example shown in FIG. 2, the optical multiplexer / demultiplexer S
A lightwave circuit (PLC: Planar Lightwave Circuit)
Array waveguide grating type optical multiplexer / demultiplexer (AWG: Arra
yedWaveguide Grating Multi / demultiplexer) and 1
× n optical star coupler SC, 1 × 2 optical star coupler
Or WDM (Wavelength Division Multiplexing)
It consists of ruta. In the case of the configuration of FIG.
Of the center station C input to the waveguide grating type optical multiplexer / demultiplexer AWG
Light emitting element LD_cWavelength λ from_d1To λ_dnThe light of each wavelength
Λ is different for each direction._d1To λ_dnLight of
The signal indicates the destination of each slave station M₁~ M_nAssigned to
Can be Next, each slave station M₁~ M_n Up signal from
Is the wavelength λ_u1To λ_unEmits light from the light emitting element of the center station
Wavelength λ_d1~ Λ_dnThe minimum and maximum wavelength of_dmin,
λ_dmaxWhere λ_uk<Λ_dminOr λ_uk> Λ
_dmax(Where k = 1, 2,... N)
The wavelength is separated from the downstream signal, and the
WDM filter provided between a waveguide grating type optical multiplexer / demultiplexer AWG
Filter bypasses the AWG optical multiplexer / demultiplexer AWG
It is possible to turn. Or a WDM filter
Instead of using a 1 × 2 star coupler, one
The power of the section enters the arrayed waveguide grating type optical multiplexer / demultiplexer AWG.
Power, but the rest of the power can be bypassed
You. The upstream signal detoured in this way, or the upstream signal
A part of the power of the signal is transmitted to the center station C by the optical star coupler.
Light receiving element PD_cAnd is received.

Here, the wavelengths λ _{d1 to} λ _dn of the downlink signal are as follows.
If 5μm~1.6μm is between, that wavelength lambda _u1 to [lambda] _un wavelength of the upstream signal to utilize two low transmission loss region of an optical fiber to be in between 1.25μm~1.4μm It is possible to separate the wavelength band into two wavelength regions, reduce the transmission loss, and extend the length of the subscriber line. Further, a system can be constructed by using a conventional light emitting element for light transmission, a light receiving element and an optical fiber as they are.

In the case of the optical multiplexer / demultiplexer shown in FIG. 2, since n inputs are integrated into one output by using an optical star coupler,
Optical fibers connecting the central station and a demultiplexer S may be a single, also the light receiving element PD _c of the center station C it is may be one, branching loss. In this case, the upstream branch loss is the same as that of the PDS system, and although the transmission speed of the upstream signal cannot be improved, the arrayed waveguide grating type optical multiplexer / demultiplexer A
Since the branch loss of the WG is smaller than the branch loss of the optical star coupler, the transmission speed of the downstream signal can be increased.

A configuration without using an optical star coupler as shown in FIG. 3 is also possible. In this case, since no branch loss occurs in the upstream direction, the transmission speed can be improved. However, n optical fibers for connecting the center station C and the optical multiplexer / demultiplexer S are required, and the center station C also a n-number required for the light receiving element PD _c.

In the present invention, the branching ratio of the optical star coupler used for the aggregation in the up direction is selected arbitrarily from n: 1 to 1: 1 in consideration of the required transmission speed and the degree of integration of the equipment. Configuration is possible.

[0028]

As described above, according to the present invention,
The number of branches can be increased, the subscriber line can be lengthened, and an optical transmission system in which the configuration on the slave station side is the same as that of the PDS system becomes possible. It is extremely effective in realizing.

[Brief description of the drawings]

FIG. 1 is a diagram showing an overall configuration of an optical transmission system according to the present invention.

FIG. 2 is a diagram illustrating a configuration example of an optical multiplexer / demultiplexer.

FIG. 3 is a diagram illustrating a configuration example of an optical multiplexer / demultiplexer.

FIG. 4 is a diagram showing a configuration of a conventional PDS system.

[Description of Signs] C center station LD _c , LD _{1 to} LD _n light emitting element PD _c , PD _{1 to} PD _n light receiving element PC _{1 to} PC _n optical coupler M _{1 to} M _n slave station S optical multiplexer / demultiplexer F wavelength conversion Unit SC star coupler CON _c center station control unit CON _{1 to} CON _n control unit

Claims (2)

[Claims] 1. A center station (C), a plurality of n slave stations (M _{1 to} M _n ), and an optical multiplexer / demultiplexer interposed between the center station and the n slave stations. S), the center station and the optical multiplexer / demultiplexer are connected by two or more optical fibers less than n, and the n slave stations and the optical multiplexer / demultiplexer are n optical fibers. The center station includes a light emitting element and one or a plurality of light receiving elements. Each of the slave stations includes a light emitting element and a light receiving element, and an output end of the light emitting element and an input end of the light receiving element. Coupling means commonly coupled to one end of the optical fiber, the center station includes control means for operating its light emitting element and light receiving element in a time division manner, and Each light receiving element and each light emission synchronized with the control means The center station is provided with control means for operating the elements in a time-division manner.The center station transmits an optical signal of a wavelength λ _d1 to λ _dn output from the light emitting element to the optical multiplexer / demultiplexer through an optical fiber connected to an output terminal. Means for selectively outputting, the optical multiplexer / demultiplexer has a wavelength λ output from the center station.
means for selecting optical signals of _d1 to _λdn and coupling them to n optical fibers respectively connected to the n slave stations, and an optical signal output from a light-emitting element of each slave station having one end connected to the center. Means for coupling to one or more optical fibers connected to the input end of the light receiving element of the station, wherein the wavelengths λ _u1 to λ _un output by the light emitting elements of the respective slave stations are determined by the center station. Output wavelength λ _d1 to λ _dn
Where λ _min and λ _max are the minimum and maximum wavelengths, respectively, λ _uk <λ _min or λ _uk > λ _max (where k = 1,
2,... N). 2. The wavelengths λ _d1 to λ _dn are 1.5 μm
And 1.6 μm, and the wavelengths λ _u1 to λ _un output by the respective slave stations are from 1.25 μm to 1.4 μm.
The optical transmission system according to claim 1, wherein the distance is between m and m.