JP3472427B2 - Optical transmission system - Google Patents

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention is used in an optical communication system. The present invention is particularly suitable for use in realizing an optical system of a subscriber line network connecting a telephone station and a subscriber.

[0002]

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

Proposed as a system for this purpose is a PDS (Passive Double Star) optical subscriber transmission system. As shown in FIG. 4, this system uses the center station C (OS
U: Optical Subscriber Unit) includes a plurality of slave stations M _{1 to} M _n equipped with subscriber side devices (ONU: Optical Network Unit) via an optical star coupler (SC: Star Coupler) that is a passive component. Since the plurality of slave stations M _{1 to} M _n can be efficiently accommodated by the accommodating method, vigorous development is underway.

In this case, the center station C and the slave stations M _{1 to} M _1
As shown in FIG. 4, the structure of _n is the light emitting element LD.
_c , the semiconductor lasers LD _{1 to} LD _n , and the light receiving element P
D _c , PD _{1 to} PD _n, and optical couplers PC _c and PC _{1 to} PC _n for connecting them with one optical fiber.

[0005]

In this conventional PDC optical subscriber transmission system, in addition to the coupling loss when coupling the light emitting element or the light receiving element to the optical fiber, the line loss due to the optical fiber, and the optical star coupler SC. There is a branch loss, and the maximum transmission station and the maximum number of branches are determined by the relationship among these losses, 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 50 Mb
/ 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 is desired for further economicization.

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

In order to solve these problems, the applicant, in Japanese Patent Application No. 08-026827, selectively changes the output port according to the wavelength of incident light instead of the optical star coupler of the conventional example. Using a wavelength router, which is an optical multiplexer / demultiplexer capable of performing the above, and instead of placing a light emitting element in the slave station, a modulation element is placed and a part of the downlink signal from the center station to the slave station is modulated to produce an uplink signal. An optical transmission method for sending back is proposed.

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

However, in the method of the proposed invention, the path of the upstream signal is a long path that goes back and forth between the center stations,
When performing long-distance transmission, it is more disadvantageous than the PDS method. Furthermore, the configuration of the slave station is a light receiving element and a modulator, 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 against such a background, and the transmission loss due to branching does not depend on the number of branches and can be extended, and the PDS system and the slave station side have the same configuration. It is an object of the present invention to provide an optical transmission system that

[0011]

The present invention SUMMARY OF] is the downstream signal toward the center station slave station, Ri split the wave for each sub-stations
With the wavelength multiplexing division multiple access scheme Ru hit, upstream signals directed from the slave station to the center station and performing the configuration of the conventional. In particular, the branch loss can be reduced and the transmission rate can be improved for a downlink signal that has a lot of information and requires a high transmission rate. In addition, the length can be extended.

That is, the present invention is an optical communication system,
The feature is that one center station (C), a plurality of n slave stations (M _{1 to} M _n ), the center station and the n stations.
An optical multiplexer / demultiplexer (S) interposed between each slave station,
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 connected by n optical fibers. The station is provided with a light emitting element and one or a plurality of light receiving elements, and each of the slave stations has a light emitting element and a light receiving element, 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. To the center station, the center station is provided with 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 includes control means for operating the respective light-receiving elements and the respective light-emitting elements 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 the station and one or a plurality of optical signals output from the light emitting elements of the respective slave stations, one end of which is connected to the input terminal of the light receiving element of the center station The wavelength λ _u1 to λ _un output by the light-emitting element of each slave station, the minimum and maximum wavelength of the wavelength λ _d1 to λ _dn output by the center station, respectively. λ
Let _min and λ _max be λ _uk <λ _min or λ _uk > λ
_max (however, k = 1, 2, ... N).

The wavelengths λ _d1 to λ _dn are 1.5
The wavelengths λ _u1 to λ _un output by the respective slave stations are between 1.25 μm and 1.
It is desirable that the thickness 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 depending on the wavelength of the incident light is used instead of the conventional optical star coupler. Therefore, the loss does not increase even if the number of branches increases, so that a multi-branch network configuration can be realized. Further, since the slave station cannot receive optical signals other than the wavelength assigned to itself, the confidentiality is improved.
Furthermore, the slave station has the same advantage as the PDS method.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, an example of an embodiment of the present invention will be described in detail with reference to the drawings.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows the overall configuration of an embodiment of the present invention.

The present invention is an optical transmission system, which is characterized by one center station C and a plurality of n slave stations M _{1 to} M.
_n and an optical multiplexer / demultiplexer S interposed between the center station C and the n slave stations M _{1 to} M _n, and the center station C and the optical multiplexer / demultiplexer S are provided.
Is connected with two or more optical fibers less than n,
The n slave stations M _{1 to} M _n and the optical multiplexer / demultiplexer S are connected by n optical fibers, and the center station C includes a light emitting element LD _c and one or a plurality of light receiving elements PD _c. 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 Is provided with optical couplers PC _{1 to} PC _n as coupling means commonly coupled to each other, and the center station C has a center station control unit CON as a control means for operating the light emitting element LD _c and the light receiving element PD _c in a time division manner. comprising a _c, the slave station M ₁ ~M to _n of the center station C center station controller CON _c
The center station C includes control units CON _{1 to} CON _n as control means for operating the light receiving elements PD _{1 to} PD _n and the light emitting elements LD _{1 to} LD _n in a time division manner in synchronization with each other. The optical multiplexer / demultiplexer is provided with a wavelength conversion unit F as means for selectively outputting the optical signal of the wavelengths λ _d1 to λ _dn output from the light emitting element LD _{c to} the optical multiplexer / demultiplexer S through the optical fiber connected to the output end. The device S selects the optical signals of the wavelengths λ _d1 to λ _dn output from the center station C and connects them to the n optical fibers respectively connected to the n slave stations M _{1 to} M _n , and the respective slaves. 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 to λ _un output by the respective slave stations M _{1 to} M _n are
It is set between 1.25 μm and 1.4 μm.

Embodiments of the present invention will be described in detail. In the center station C, the white light emitted from the light emitting element LD _c passes through the wavelength conversion element provided in the wavelength conversion section F, thereby changing the wavelength of the optical signal to be transmitted to the wavelength of λ _d1 to λ _dn .
As the light emitting element LD _c , the light emitting element LD _c itself may be a wavelength tunable element such as a wavelength tunable semiconductor laser capable of variably controlling the wavelength.

First, a downlink signal from the center station C to each subscriber will be described. The center station C time-division-multiplexes (TDM) the optical signals whose emission wavelengths are λ _d1 to λ _dn.
ultiplexing) method. Each wavelength is used as a carrier to transmit a downlink signal to each subscriber. As a signal system, for example, an NRZ (Non Retu
rn to Zero) signal. In the optical multiplexer / demultiplexer S, since the waveguiding 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. The downlink signals reaching each subscriber are received by the light receiving elements PD _{1 to} PD _n.
Will be received at. In this way, the downlink signal is transmitted.

Next, an upstream signal from each subscriber to the center station C will be described. Control units CON _{1 to} CON of each subscriber
_In accordance with the instruction of the control signal sent from the center station C as a part of the downlink signal, _n makes each of the light emitting elements LD _{1 to} LD _n emit light at a certain timing and transmits the uplink signal.
Here, the control signal on the center side refers to instructing the timing of sending an optical signal so that the upstream signals from the respective subscribers do not overlap in time and are not received by the light receiving element PD _c of the center station C. By doing so, so-called time division multiple access (TDMA) is performed.
) System, the center station C can receive an upstream signal from each subscriber.

In this system, the construction of the optical multiplexer / demultiplexer S is important. FIG. 2 and FIG. 3 each show a configuration example of the optical multiplexer / demultiplexer S.

In the example shown in FIG. 2, the optical multiplexer / demultiplexer S is played.
Structured with a PLC (Planar Lightwave Circuit)
Array Waveguide Lattice Type Optical Multiplexer / Demultiplexer (AWG: Arra)
yedWaveguide Grating Multi / demultiplexer) and 1
Xn optical star coupler SC, 1x2 optical star coupler
Or WDM (Wavelength Division Multiplexing)
It is composed of 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 from λ_d1From λ_dnLight of each wavelength
Since the direction of waveguiding differs for each_d1From λ_dnLight of
As for the signal, each destination M₁~ M_nDistributed to
You can Next, each slave station M₁~ M_n Upstream signal from
Is the wavelength λ_u1From λ_unEmits light from the light emitting element of the center station
Wavelength λ_d1~ Λ_dnThe minimum and maximum wavelengths of_dmin,
λ_dmaxAnd then λ_uk<Λ_dminOr λ_uk> Λ
_dmax(However, k = 1, 2, ... N) is satisfied,
The downlink signal and wavelength are separated, and each slave station and array
WDM filter provided between the waveguide grating type optical multiplexer / demultiplexer AWG
Filter bypasses the arrayed-waveguide-grating optical multiplexer / demultiplexer AWG.
It is possible to turn. Or alternative to WDM filter
Even if a 1 × 2 star coupler is used instead, one of the upstream signals
The power of the part is input to the arrayed waveguide grating type optical multiplexer / demultiplexer AWG.
Power, but the rest of the power cannot be bypassed
It Upstream signals or uplink signals bypassed in this way
A part of the power of the signal is transmitted from the center station C by the optical star coupler.
Light receiving element PD_cIs received and received.

Here, the wavelengths λ _{d1 to} λ _dn of the downlink signal are 1.
When the wavelength λ _{u1 to} λ _un of the wavelength of the upstream signal is between 1.25 μm and 1.4 μm when it is between 5 μm and 1.6 μm, two low transmission loss regions of the optical fiber can be used. Therefore, it is possible to extend the subscriber line by separating it into two wavelength regions to reduce the transmission loss. Further, the system can be constructed by using the conventional light emitting element for light transmission, the light receiving element and the optical fiber as they are.

In the case of the optical multiplexer / demultiplexer of FIG. 2, since n inputs are aggregated into one output by using an optical star coupler,
One optical fiber may be used to connect the center station and the optical multiplexer / demultiplexer S, and one light receiving element PD _c may be used in the center station C, but branch loss occurs. In this case, the upstream branch loss is the same as that of the PDS method, and although the upstream signal transmission rate cannot be improved, the arrayed-waveguide grating optical multiplexer / demultiplexer A is used.
Since the branch loss of the WG is smaller than the branch loss of the optical star coupler, it is possible to increase the transmission speed of the downlink signal.

A configuration without the optical star coupler as shown in FIG. 3 is also possible. In this case, since branching loss does not occur in the upstream direction, the transmission speed can be improved, but n optical fibers connecting the center station C and the optical multiplexer / demultiplexer S are required, and the center station C N light receiving elements PD _c are also required.

In the present invention, the branch ratio of the optical star coupler used for upstream aggregation can be arbitrarily selected from n: 1 to 1: 1 in consideration of the required transmission rate and the degree of facility aggregation. Various configurations are possible.

[0028]

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

[Brief description of drawings]

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

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

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

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

[Explanation of symbols]

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 converter SC star coupler CON _c Center station control unit CON _{1 to} CON _n control unit

Continuation of front page (58) Fields surveyed (Int.Cl. ⁷ , DB name) H04B 10/00-10/28 H04J 14/00-14/08

Claims (2)

(57) [Claims] 1. A center station (C), a plurality of n slave stations (M _{1 to} M _n ), and an optical multiplexer / demultiplexer (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 have n optical fibers. The center station includes a light emitting element and one or a plurality of light receiving elements, and each of the slave stations includes a light emitting element and a light receiving element, an output end of the light emitting element and an input end of the light receiving element. Each of the optical fibers is provided with a coupling means commonly coupled to one end thereof, the center station is provided with control means for operating the light emitting element and the light receiving element thereof in a time division manner, and the slave station is provided with the center station. Each light receiving element and each light emission in synchronization with the control means Each of the control means for operating the elements in a time-division manner, the center station, through the optical fiber connected to the output end to the optical multiplexer / demultiplexer optical signal of the wavelength λ _d1 to λ _dn output from the light emitting element The optical multiplexer / demultiplexer includes means for selectively outputting the wavelength λ output from the center station.
Means for selecting optical signals of _d1 to λ _dn and coupling them to n optical fibers respectively connected to the n slave stations, and one end of the optical signals output from the light emitting elements of the slave stations Means for coupling to one or more optical fibers connected to the input terminals of the light receiving elements of the station, and the wavelengths λ _u1 to λ _un output by the light emitting elements of the respective slave stations are set by the center station. Output wavelength λ _d1 to λ _dn
Minimum, maximum wavelength respectively lambda _min, when a λ _max, λ _uk <λ _min or λ _uk> λ _max (where k = 1,
2 .... n) is an optical transmission system. 2. The wavelengths λ _d1 to λ _dn are 1.5 μm
From 1.6 μm to 1.6 μm, and the wavelengths λ _u1 to λ _un output by the respective slave stations are 1.25 μm to 1.4 μm.
The optical transmission system according to claim 1, wherein the optical transmission system is between m.