JP2000324061A - Two-way optical multiplex method and two-way optical multiplex communication system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a two-way optical multiplex communication unit that is configured only with optical filters without the need for an optical wavelength converter or an optical demultiplexer because a master-slave relation is always fixed for the exchange optical transmission interfaces. SOLUTION: In the two-way optical multiplex system provided with a host unit 10 and a subordinate unit 20 interconnected by an optical transmission line, the host unit 10 consists of photocouplers 31, 32 that are used for interfacing the optical transmission line 60, an optical transmitter that transmits an optical signal with a 1st wavelength to the optical transmission line 60 via the photocouplers 31, 32, a 1st optical filter 41 that passes through the optical signal with a 2nd wavelength and stops the optical signal with the 1st wavelength from the optical signal through the optical transmission line 60 via the photocouplers 31, 32 and an optical receiver 21 that receives the optical signal passing through the optical filter 41. The subordinate unit 20 has a similar configuration.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a bidirectional optical multiplexing system used for a line between exchanges, a public line, a dedicated line, a CATV line and the like, and a bidirectional optical multiplexing system.

[0002]

2. Description of the Related Art The optical two-way transmission system can double the transmission capacity, so that it is an effective optical communication transmission system not only for optical communication but also for optical measurement and in automobiles. Various types of optical bidirectional transmission systems have been developed in the past. As one conventional example, a communication light generation unit and a communication light reception unit are provided at both ends of an optical fiber transmission line via a multiplexer / demultiplexer. It is connected to a fiber transmission line, uses light of different wavelengths for an upstream signal and a downstream signal, and separates both signals by the multiplexer / demultiplexer.

In addition, an optical coupler is used in place of the multiplexer / demultiplexer of the conventional example, and a communication light generator and a communication light receiver are arranged at both ends of an optical fiber transmission line. An optical receiver is connected to an optical fiber transmission line via an optical coupler, and the same signal or different wavelength light is used for an upstream signal and a downstream signal, and both signals are separated by the optical coupler.

However, in a transmission system using different optical wavelengths for the upper and lower signals, it is necessary to take a large difference between the wavelengths of the two signal lights in order to separate the two signals. High-performance optical transmission or wavelength multiplexing becomes difficult. Further, in the method using the optical coupler, at least half of the transmitted light is wasted by the optical coupler, and light in the opposite direction is mixed into the laser, so that the operation of the laser becomes unstable.

Therefore, as a conventional example, Japanese Patent Application Laid-Open No.
Japanese Patent No. 2549 describes that an optical circulator is used for multiplexing / demultiplexing an upstream signal and a downstream signal. This optical circulator is connected to the optical fiber transmission line, enters from the input port to the optical fiber transmission line, and is connected from the optical fiber transmission line to the output port. It is described as a high-performance multi-directional transmission system with low loss.

As a conventional example, an exchange optical transmission interface circuit will be described with reference to FIG. In the figure, an optical transmitter 61 of a higher-level device 65 and an optical transmitter 62 of a lower-level device 66 transmit an optical signal of the same wavelength λ1
66, without passing through another device. Optical transmitter 6
1 is received by the optical receiver 72 and demodulated. The optical signal of wavelength λ1 transmitted from the optical transmitter 62 is received by the optical receiver 71 and demodulated.
Here, the higher-level device 65 and the lower-level device 66 do not have a relation of a higher order or a lower order, but are simply referred to to distinguish parallel operations.

[0007]

However, the conventional exchange optical transmission interface circuit has the following problems.

A first problem is that since signals having the same optical wavelength are used for transmission, multiplexing cannot be performed on an optical transmission line, and the number of cables to be laid cannot be reduced.

In the above publication, although the loss of the optical demultiplexer can be reduced by the optical circulator,
Due to the characteristics of optical circulators, it is necessary to increase the degree of separation between wavelengths.Compared to single-wavelength transmission, it is not possible to employ a transmission path that satisfies both optical wavelengths separated by a specific optical fiber, and the transmitter / receiver is also used. However, it requires a transceiver corresponding to each optical wavelength, and is not efficient.

[0010] An object of the present invention is to provide a bidirectional optical communication system using only an optical filter without using an optical wavelength converter or an optical demultiplexer, since the exchange optical transmission interface always has an upper and lower relationship determined. It is to provide a multiplex communication system.

[0011]

According to the present invention, there is provided a bidirectional optical multiplexing system having a first device and a second device connected by an optical transmission line, wherein the first device is connected to the optical transmission line. An optical coupler for use as an interface with the optical coupler, an optical transmitter for transmitting an optical signal having a first wavelength to the optical transmission path via the optical coupler, and a second optical signal from the optical coupler on the optical transmission path. A first optical filter that transmits an optical signal having a wavelength of the first wavelength and makes the optical signal having the first wavelength outside the pass band; and an optical receiver that receives the optical signal transmitted from the optical filter. An optical coupler used for interfacing with the optical transmission line, an optical transmitter for transmitting an optical signal having a second wavelength to the optical transmission line via the optical coupler,
A second optical filter that transmits an optical signal of a first wavelength from an optical signal on the optical transmission path from the optical coupler and makes the optical signal of the second wavelength out of a pass band; and transmission from the optical filter. And an optical receiver for receiving the optical signal.

In the above-mentioned bidirectional optical multiplexing system, an optical signal of a second wavelength is transmitted from an optical signal on the optical transmission line instead of the first optical filter, and the optical signal of the first wavelength is blocked. A second optical filter that transmits a first wavelength optical signal from the optical signal on the optical transmission line and blocks the second wavelength optical signal instead of the second optical filter. It is characterized by using an optical isolator.

Further, the present invention provides a bidirectional optical multiplexing system having a first device and a second device connected by an optical transmission line, wherein the first device has an interface with the optical transmission line. An optical coupler to be used, an optical transmitter for transmitting an optical signal having a first wavelength to the optical transmission line via the optical coupler, and light of a second wavelength from the optical signal on the optical transmission line from the optical coupler. A first optical filter that transmits a signal and makes the optical signal of the first wavelength outside the pass band; and an optical receiver that receives the optical signal transmitted from the optical filter,
The first device uses the same device as the first device in terms of mass production effect of the optical coupler, the optical transmitter, and the optical receiver, and the first device faces the first optical filter. A second optical filter that transmits an optical signal of a wavelength and makes the optical signal of the second wavelength out of a pass band.

Further, according to the present invention, in an interface circuit of a first device and a second device by optical transmission used in an exchange system, an optical coupler and an optical filter are provided in a transmission line portion after electrical / optical conversion in the device. In systems where the relationship between the upper and lower levels is not fixed, the wavelength multiplexing transmission method requires wavelength conversion and separation of optical signals by a demultiplexer. Is established, the amount of optical fiber used for the transmission line between the devices can be reduced to half without using an optical demultiplexer.

Further, the bidirectional optical multiplexing system of the present invention is similar to that of FIG.
The optical couplers 31 and 32 multiplex an optical signal transmitted from a device onto an optical fiber 60 used for transmission between the devices. The optical filters 41 and 42 input only the optical signal transmitted from the opposing device to the optical receivers 21 and 22. Each of the optical transmitters 11 and 12 sends an optical signal to the opposing device at a different wavelength λ1, λ2.

As described above, according to the present invention, transmission between devices in which the relationship between the higher-order device and the lower-order device is always determined, for example, the upper-lower relationship between the first repeater and the sub-second repeater in the relay transmission path. Since signals of different optical wavelengths are used for transmission, the amount of optical fiber used for a transmission path between devices can be reduced to half without using an optical demultiplexer.

[0017]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments according to the present invention will be described.
This will be described in detail with reference to the drawings.

[First Embodiment] FIG. 1 shows a first embodiment of the present invention.
1 is a block diagram of a bidirectional optical multiplex communication system using a bidirectional optical multiplex communication system as an embodiment of the present invention. In the figure, the relationship between a higher-level device 10 as a first device and a lower-level device 20 as a second device is based on a case where a first relay device and a second relay device, which are often used when forming a public line network, are installed. It is similar to the same relationship as.

In FIG. 1, a higher-level device 10 includes an optical coupler 31 having a function as an exchange optical transmission interface of a higher-level device connected to a transmission line 60 of an optical fiber;
An optical transmitter 11 for transmitting an optical wavelength λ1 to the optical coupler 31;
The optical filter 41 includes an optical filter 41 that transmits only necessary light of optical signals of wavelengths λ1 and λ2 from the optical coupler 31 and an optical receiver 21 that receives an optical signal of optical wavelength λ2 transmitted by the optical filter 41. . And 32 multiplex an optical signal transmitted from each device to an optical transmission line 60 of an optical fiber used for transmission between the devices.

The lower-level device 10 includes an optical coupler 32 having a function as an exchange optical transmission interface of the lower-level device connected to the transmission line 60 of the optical fiber, and an optical transmitter for transmitting the optical wavelength λ2 to the optical coupler 32. The optical filter 42 transmits only the necessary light to the optical signal of the wavelength λ1 and λ2 from the optical coupler 32, and the optical receiver 22 receives the optical signal of the optical wavelength λ1 transmitted through the optical filter 42. It is configured.

The optical couplers 31 and 32 are connected to each device 1
The optical signals transmitted from 0 and 20 are multiplexed on an optical transmission line 60 of an optical fiber used for transmission between devices. The optical couplers 31 and 32 are basically of a one-input / two-output type or a two-input / one-output type. For example, there are a Y-shaped plywood, an arrayed waveguide type, and a fused fiber type which are often used for a star coupler. However, in the case of the present embodiment, the optical coupler 3
Array waveguide couplers 1 and 32 are preferred because they have two inputs and two outputs. Further, since the wavelengths λ1 and λ2 of the optical signals transmitted through the optical transmission line 60 use detuned wavelengths of about 0.01 nm, a common product can be used for the optical couplers 31 and 32.

The optical filters 41 and 42 input only the optical signal transmitted from the opposing device to the optical receivers 21 and 22. Each of the optical transmitters 11 and 12 sends an optical signal to the opposing device at a different wavelength λ1, λ2. The optical filters 41 and 42 include Fabry /
A Perot interferometer-type filter, a tunable filter capable of returning a mirror interval by a piezoelectric element, a dielectric multilayer filter in which a film having a different refractive index is formed by a plurality of layers, and the like are used for an optical transmission line. A low-loss dielectric multilayer filter that has a reflectance of 95% or more when the transmission wavelength is fixed is preferable.

In FIG. 1, the optical filter 41 inputs only the optical signal λ2 from the lower order device 20 to the optical receiver 11.
The optical filter 42 is provided with an optical signal λ1 from the host device 10.
Is input to the optical receiver 22.

In the figure, the optical transmitter 11 is
The optical signal of the wavelength λ1 is transmitted. Also, the optical transmitter 12
Sends an optical signal of wavelength λ2 to the host device 10. The optical transmitters 11 and 12 modulate the original signal and apply QPSK or 16
A baseband signal such as QAM is output to an optical coupler via an EO converter that converts an electric signal of the baseband signal into an optical signal.

The optical receivers 21 and 22 receive only the desired optical wavelength from the optical filter, convert the electrical signal into an electric signal using an OE converter, and convert the electric signal into a baseband signal such as QPSK or 16QAM. The baseband signal is demodulated into the original signal.

In the above embodiment, the same optical filters 41 and 42 are not used. However, the optical couplers 31 and 32, the optical transmitters 11 and 12, and the optical receivers 21 and 22 are common. It may be used, and in this case, high quality and less variation can be obtained due to mass production effects.

Although the configuration of the embodiment has been described in detail above, the optical receivers 21 and 22 shown in FIG.
And 32 are well known to those skilled in the art and are not directly related to the present invention;

Next, the operation of the bidirectional optical multiplex communication apparatus of FIG. 1 will be described. In the figure, a signal λ1
Is supplied to the optical coupler 31, the optical coupler 31 passes the signal λ1 of the higher-level device 10 and the signal λ1 of the higher-level device 10.
And a signal multiplexed from the lower order device 20 and the signal λ2 is supplied to the transmission line 60. The optical coupler 32 passes the signal λ2 from the lower order device 20 and supplies the multiplexed signal of the signal λ1 of the higher order device 10 and the signal λ2 from the lower order device 20 to the upper order device 10.

Further, in FIG.
When the multiplexed signal of the signal 1 and the signal λ2 from the lower order device 20 is given to the optical filter 41, the optical filter 41 converts the multiplexed signal of the signal λ1 of the higher order device 10 and the signal λ2 from the lower order device 20. After filtering, only the signal λ2 from the lower-level device 20 is supplied to the optical receiver 21.

On the other hand, the optical filter 42 supplies only the signal λ1 from the host device 10 to the optical receiver 42.

In the above embodiment, an example is shown in which the optical couplers 31 and 32 transmit and receive two optical wavelengths λ1 and λ2 in the transmission path. However, the effects similar to those described above can be obtained if the interfaces of the transmission paths are respectively corresponded by optical couplers. In this case, optical signals of a plurality of wavelengths are exchanged in the transmission path, but if there is a wavelength difference of about 0.01 nm, the desired reception wavelength of each optical receiver can be separated by each optical filter.

[Second Embodiment] As a second embodiment of the present invention, the basic configuration is the same as that of the first embodiment, but the light separating function is different.

FIG. 2 shows the configuration. In the figure, the optical isolators 51 and 52 pass only optical signals in the direction input to the optical receivers 21 and 22. Host device 3
When a multiplexed signal of the signal λ1 of 0 and the signal λ2 from the lower order device 40 is given to the optical isolator 51, the optical isolator 51 passes the signal λ2 from the lower order device 40 and supplies it to the optical receiver 21. . In addition, the optical isolator 5
2 passes the signal λ1 from the host device 30 and supplies it to the optical receiver 21 of the host device 30.

Here, the optical isolators 51 and 52 are provided from the optical fiber connection point or the like in order to suppress the wavelength dispersion of the speed of light propagating in the optical fiber and the optical wavelength dispersion which restricts the speed-up and long-distance communication. To prevent reflected light from returning, pass only certain wavelengths and block other wavelength bands,
For example, a rutile crystal is arranged on both end faces of a YIG crystal, and this is achieved by its propagation path and reflection characteristics.

As described above, in the present embodiment, since the optical isolators 51 and 52 are used, the effect of suppressing the influence of Fresnel reflection occurring at the optical cable connection end face or the like can be obtained.

[0036]

As described above, the present invention has the following effects. The first effect is that the number of optical fibers can be reduced because optical wavelength multiplexing is performed in transmission between devices.

The second effect is that a signal can be separated by using only an optical filter without using an optical demultiplexer or an optical wavelength converter because the system is used in a system in which the relationship between the upper and lower devices is determined. is there.

[Brief description of the drawings]

FIG. 1 is a configuration block diagram of a bidirectional communication system using optical wavelength multiplexing according to the present invention.

FIG. 2 is a configuration block diagram of a bidirectional communication system using optical wavelength division multiplexing according to the present invention.

FIG. 3 is a configuration block diagram of a conventional bidirectional communication system using optical wavelength multiplexing.

[Explanation of symbols]

 10, 30 Upper device 11, 12, 61, 62 Optical transmitter 20, 40 Lower device 21, 22, 71, 72 Optical receiver 31, 32 Optical coupler 41, 42 Optical filter 51, 52 Optical isolator 60, 63, 64 Optical transmission path

Claims (3)

[Claims] 1. A bidirectional optical multiplexing system comprising a first device and a second device connected by an optical transmission line, wherein the first device includes an optical coupler used for an interface with the optical transmission line. An optical transmitter for transmitting an optical signal of a first wavelength to the optical transmission line via the optical coupler; and transmitting an optical signal of a second wavelength from the optical signal on the optical transmission line from the optical coupler. A first optical filter that makes the optical signal of the first wavelength outside the pass band; and an optical receiver that receives an optical signal transmitted from the optical filter, wherein the second device is an optical transmission line. An optical coupler for use as an interface with the optical coupler, an optical transmitter for transmitting an optical signal having the second wavelength to the optical transmission path via the optical coupler, and an optical signal on the optical transmission path from the optical coupler. First
A second optical filter that transmits an optical signal of the second wavelength and makes the optical signal of the second wavelength out of the pass band; and an optical receiver that receives the optical signal transmitted from the optical filter. Bidirectional optical multiplexing. 2. The bidirectional optical multiplexing system according to claim 1, wherein said first optical filter is replaced by an optical signal of said second wavelength from an optical signal on said optical transmission line. Using a first optical isolator that blocks optical signals of wavelengths,
In place of the second optical filter, a second optical isolator that transmits the optical signal of the first wavelength from the optical signal on the optical transmission line and blocks the optical signal of the second wavelength is used. Bidirectional optical multiplexing. 3. A bidirectional optical multiplexing system including a first device and a second device connected by an optical transmission line, wherein the first device includes an optical coupler used for an interface with the optical transmission line. An optical transmitter for transmitting an optical signal of a first wavelength to the optical transmission line via the optical coupler; and transmitting an optical signal of a second wavelength from the optical signal on the optical transmission line from the optical coupler. A first optical filter for making the optical signal of the first wavelength out of the pass band; and an optical receiver for receiving an optical signal transmitted from the optical filter, wherein the second device comprises the optical coupler and The optical transmitter and the optical receiver use the same device as the first device in terms of mass production effect, and transmit the optical signal of the first wavelength facing the first optical filter and transmit the second signal. A second optical filter that makes an optical signal having a wavelength outside the pass band Bidirectional optical multiplexing system according to claim and.