KR100281514B1 - Mach-Zehnder interferometer type add / extract filter in wavelength division multiple optical communication system - Google Patents

Abstract

1. TECHNICAL FIELD OF THE INVENTION

The present invention relates to a Mach-Zehnder interferometer addition / extraction filter in an optical communication system.

2. The problem to be solved by the invention

The present invention implements a Mach-Zehnder interferometer type add / extract filter in a multi-core optical fiber in a WDM optical communication system by matching the phases of two paths at both ends and arbitrarily adjusting the transition of the reflected wavelength, thereby changing the wavelength. Its purpose is to provide an add / extract filter that is easy and can simultaneously transmit numerous different signals of different wavelengths.

3. Summary of Solution to Invention

The present invention comprises: first and second optical distribution and coupling means for distributing an optical signal to be transmitted, combining and extracting and outputting an additional optical signal and a reflected optical signal; Light reflection and transmission means for reflecting and passing the transmitted optical signal; Phase adjusting means for matching the phases of the optical paths at both ends of the light reflection and transmission means; Transition amount adjusting means for controlling the wavelength shift amount of the reflected optical signal; And reflected wavelength shifting means for shifting the wavelength of the reflected optical signal.

4. Important uses of the invention

The present invention is used in a WDM optical communication system.

Description

Mach-Zehnder interferometer add / extract filter in wavelength division multiplex optical communication system

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a Mach-Zehnder interferometric add / drop filter in a Wave Division Multiple (WDM) optical communication system, in particular one or two of several wavelengths at an optical node. The present invention relates to an addition / extraction filter capable of effectively separating a desired wavelength and adding a new signal to the wavelength to deliver a signal to the next node.

In general, in the conventional method of separating the required wavelengths among the multiple wavelengths received in the wavelength division multiplexing optical communication system, a Mach-Zehnder interferometer is constructed using a single core optical fiber, and each path of the interferometer To separate wavelengths using Bragg diffraction gratings that have a refractive index periodicity of the single core optical fiber waveguides, and to polish or fuse two single core optical fibers to form an optical fiber coupler A method of separating wavelengths using Bragg diffraction gratings that have a refractive index periodicity for optical fiber cores has been used.

Here, the Bragg diffraction grating used has a function of reflecting a specific wavelength region (that is, a stop band) with a reflection filter and passing another wavelength.

In particular, Bragg diffraction gratings are described in more detail. Bragg diffraction gratings are created by periodically changing the refractive index in the optical waveguide, and various methods are used to periodically change the refractive index in the waveguide. It has a common point that the refractive index of the optical waveguide is changed by using the photosensitivity of.

The light sensitivity refers to a phenomenon in which the refractive index of the portion to which the ultraviolet light is applied to the optical waveguide increases when the ultraviolet light is irradiated with strong ultraviolet light in the 240 nm band.

In addition, the photosensitivity affects the reflectivity of the Bragg diffraction grating, and when the photosensitivity is high, the reflectivity becomes high.

The general principle of the reflection of a specific wavelength in the Bragg diffraction grating is as follows.

As light passes through the Bragg diffraction grating, it is reflected from each grating. Wavelengths in which the phase of light reflected between each grating of the reflected light is exactly 2 nπ are reflected by the constructive interference with each other.

That is, the relationship between the reflected wavelength and the period of the grating is as shown in [Equation 1].

here, Is the average refractive index between the lattice, Λ is the lattice period, m is an integer, and λ is the reflected wavelength.

As described above, by using a specific wavelength reflection characteristic of Bragg diffraction grating, a part of a specific wavelength signal is extracted and used as a reception signal, and a new signal is loaded on the same wavelength as the extracted wavelength so that the next node can be used. A tunable addition / extraction filter, which functions, was constructed using a multicore fiber.

1A and 1B are diagrams illustrating the operation of a general Mach-Zehnometer interferometer type add / extract filter.

FIG. 1A is an explanatory diagram illustrating an extraction operation of a general Mach-Zehnder interferometer type add / extract filter. When a signal having various wavelengths is input to an input terminal of a single core optical fiber 5, the input signal is a 3-dB directional coupler ( 20), the signal is divided into both paths of the addition / extraction filter and proceeds.

In this way, the divided signal proceeds with the phase difference of π / 2 between the two paths due to the characteristic of the 3-dB directional coupler 20 to the Bragg grating 11 formed in both paths. Reflected by the single core optical fiber 6 to the extraction stage, the remaining signals proceed through the Bragg grating 11 to the next 3-dB directional coupler 30 to the output stage of the single core optical fiber (8) It will exit through the outside.

FIG. 1B is an explanatory diagram illustrating a further operation of a general Mach-Zehnder interferometer type add / extract filter, and illustrates a function of adding a signal of a specific wavelength.

As shown in the figure, a signal of several wavelengths is input to an input terminal, and this time, a signal of a wavelength to be added is input to an additional stage of a single core optical fiber 7.

The signal entering the input stage is divided into two paths through the 3-dB directional coupler 20, passes through the Bragg grating 11, and passes through the 3-dB directional coupler 30 of the next stage to the output stage.

On the other hand, the signal added to the additional stage is divided into both paths through the 3-dB directional coupler 30, and then proceeds to be reflected by the Bragg grating 11 is reflected to the output terminal.

As a result, both the signal coming into the input terminal and the signal coming into the additional stage come out to the output stage, so the two signals are added.

As an optical fiber type add / extract filter using Bragg grating in the conventional WDM communication system, a circulater type add / extract filter shown in FIG. 2A, a Mach-Zehnder interferometer type add / extract filter shown in FIG. 1A, and shown in FIG. 2B Polished coupler type add / extract filter, and a fused coupler type add / extract filter shown in FIG. 2C.

As illustrated in FIG. 2A, the circulator type add / extract filter may be configured by forming a Bragg grating reflecting a specific wavelength in a single core optical fiber between two circulators.

As described above, the circulator shape shows a stable operation characteristic, but the cost and overall volume between the circulators are too large.

In addition, the Mach-Zehnder interferometer type add / extract filter of FIG. 1B is implemented in a fully optical fiber type, so that connection loss is improved and the price is low. However, in order to operate correctly, the same Bragg grating has the same length of each single core fiber. Since it has to be in the same position, it is very difficult to implement, and as the length of the optical fiber used in the configuration increases, it is very sensitive to the external environment and has not been stable.

In the polish coupler type and the fuse coupler type shown in FIGS. 2B and 2C, respectively, two single core optical fibers are bonded using two single core optical fibers as described in US Pat. No. 5,457,758 to form two waveguides in the coupling region. In this way, the coupler is formed to couple the signal so that the Bragg grating is engraved in the coupling area to perform the addition / extraction function.

Such a shape is a good method for miniaturization and low cost, but there are the following problems depending on the manufacturing method of the coupler.

First, the polish coupler type add / extract filter is difficult to manufacture, it is difficult to ensure long-term reliability and there is a problem that the wavelength can not be changed.

Secondly, the fuse coupler type add / extract filter is extremely small when each single core optical fiber is pulled and glued together, and the germanium (Ge) component remaining in the core disappears, making the Bragg grating hard to be engraved. There is a drawback, since it is difficult to break Bragg grating after manufacture of the coupler, there is a problem that it is difficult to prepare a set-up for improving productivity.

Accordingly, the present invention has been made to solve the above problems, and in implementing the Mach-Zehnder interferometer type add / extract filter using a multicore fiber in a WDM optical communication system, the phase of the two paths from both ends from the outside It is an object of the present invention to provide an add / extract filter that can easily change wavelengths and transmit a large number of different signals at the same time by matching and arbitrarily adjusting the transition of reflected wavelengths.

1A and 1B are diagrams illustrating the operation of a typical Mach-Zehnder interferometer type add / extract filter.

2A to 2C are schematic diagrams showing the configuration of a conventional Mach-Zehnder interferometer type add / extract filter.

Figure 3 is a structure diagram of an embodiment of a Mach-Zehnder interferometer addition / extraction filter in a wavelength division multiple optical communication system according to the present invention.

Figure 4 is an example of implementing a multi-core optical fiber applied to the present invention.

Figure 5a is an enlarged illustrative view of the Mach-Zehnder interferometric addition / extraction filter in accordance with the present invention.

Figure 5b is an illustration of implementing a number of Mach-Zehnder interferometer type add / extract filters of the present invention using one multicore optical fiber.

5c and 5d are exemplary views of a complex implementation of the Mach-Zehnder interferometer type add / extract filter according to the present invention.

Explanation of symbols on the main parts of the drawings

310: multicore fiber 320, 330: 3-dB directional coupler

340, 350: waveguide connection 360, 370: phase adjuster

380: variable reflection wavelength transition unit 390: transition amount adjustment unit

In order to achieve the above object, the present invention provides a Mach-Zehnder interferometer type add / drop filter in a Wave Division Multiple (WDM) optical communication system. First optical distribution and coupling means for distributing at a predetermined ratio and for combining and dropping the additional optical signal and the reflected optical signal; It consists of a multi-core optical fiber having a Bragg grating, the signal transmitted through the first optical distribution and coupling means by dividing by a predetermined ratio to reflect and pass, and the additional optical signal is distributed and transmitted at a predetermined ratio Light reflection and transmission means for transmitting to the first light distribution and coupling means; Second light distribution and coupling means for combining and outputting the optical signal transmitted through the light reflection and transmission means, and distributing the additional optical signal at a predetermined ratio to the light reflection and transmission means; Phase adjusting means for matching the phases of the optical paths at both ends of the light reflecting and transmitting means; Transition amount adjusting means for providing a control signal for controlling the wavelength transition amount of the optical signal reflected by the light reflection and transmission means; And reflected wavelength shifting means for shifting the wavelength of the optical signal reflected by the light reflection and transmission means in accordance with the control signal.

In addition, the present invention uses the same operation principle using the optical fiber having multiple cores to solve the problem of Mach-Zehnder interferometer type manufactured using a single core optical fiber in the implementation of the addition / extraction filter used in the existing WDM communication network To be applied. Until now, multicore fiber has many questions about usability due to the difficulty of multicore fabrication and the connectivity with singlecore fiber.However, in 1994, Telecom published a paper on the method of manufacturing multicore fiber in IWCS'4 (International In the Wire & Cable Symposium Proceedings, Alcarel, France, demonstrates the feasibility of the fabrication method and characteristics by presenting them in IWCS'97 and EC'98 (see Figure 4).

In addition, the present invention is to easily implement the addition / extraction filter by applying this new concept of optical fiber, when using a multi-core fiber to form a plurality of single-mode waveguides in one optical fiber Mach-Zehnder interferometer type / Since two paths of the extraction filter can be solved within one optical fiber, the lengths of the two paths are the same and it is easy to engrave the same fiber grating at the same point at the same time, thereby improving the operation characteristics of the addition / extraction filter.

Hereinafter, with reference to the accompanying drawings will be described in detail a preferred embodiment of the present invention.

3 is a schematic diagram of a Mach-Zehnder interferometer type add / extract filter in a wavelength division multiple optical communication system according to an embodiment of the present invention.

As shown in FIG. 3, the Mach-Zehnder interferometer type add / extract filter of the present invention includes a multicore optical fiber 310 and a planar wave type 3-dB directional coupler 320 connected to both ends of the multicore optical fiber 310, respectively. , 330, a waveguide connection 340 for connecting between the input and extraction terminals and the 3-dB directional coupler 320, and a waveguide connection for connecting between the output and additional terminals, and the 3-dB directional coupler 330. 350, a phase adjuster 360 connected between the multicore optical fiber 310 and the 3-dB directional coupler 320, and a phase adjuster connected between the multicore optical fiber 310 and the 3-dB directional coupler 330. The unit 370 includes a variable reflection wavelength transition unit 380 connected to the multicore optical fiber 310, and a transition amount control unit 380 connected to the variable reflection wavelength transition unit 380.

The 3-dB directional couplers 320 and 330 transmit the power of signals of various wavelengths input through the single core fiber to the two cores of the multi-core fiber 310 in a 3-dB ratio while transmitting the single core and the multi core. It is configured to allow connection.

The multi-core optical fiber 310 composed of two cores is configured so that the gap between the two cores is sufficiently spaced apart so that there is no coupling between signals. Doing.

The variable reflection wavelength transition unit 380 is engraved with the same Bragg grating 311 in two cores of the multi-core optical fiber 310, the transition to the Bragg grating 311 so as to change the operating wavelength of the Bragg grating 311 It is possible to manufacture by bonding and coating the material generating the strain by the control signal (for example, voltage, current and light, etc.) transmitted from the transfer control unit 390.

Alternatively, the reflection wavelength can be shifted by using a material capable of changing the refractive index or the period of the Bragg grating 311.

The operation of the Mach-Zehnder interferometer type add / extract filter of the present invention having the structure as described above will be described in detail as follows.

First, the extraction operation will be described.

When a signal having a plurality of wavelengths is input to the input terminal, the input signal is divided into both paths of the add / extract filter by the 3-dB directional coupler 320 to proceed.

In this way, the signal proceeding divided into both sides proceeds with a phase difference of π / 2 between the two paths by the characteristic of the 3-dB directional coupler 320 is reflected by the Bragg grating 311 formed in both paths and extracted The signal is reflected to the stage, and the remaining signals proceed to the next 3-dB directional coupler 330 through the Bragg grating 311 and exit through the output stage.

The phase adjuster 360 may control the refractive index or the length of both paths of the waveguide connector 340, and match the phase of the add / extract filter using voltage, temperature, and light.

The variable reflection wavelength shifter 380 may be controlled by the shift amount control unit 390 to reflect only one wavelength among the wavelengths λ ₁ to λ _m .

The variable reflection wavelength transition unit 380 is made of a material in which strain is often generated by temperature, stress, voltage, light, and the like, and controls the amount of transition transmitted from the transition amount control unit 390. It generates a strain proportional to the magnitude of the control signal or the square of the magnitude.

In this way, the generated strain changes the lattice period and refractive index of the Bragg grating 311 of the multicore optical fiber 310 to which the material is attached, thereby shifting the reflected wavelength so that the wavelength of the signal extracted to the extraction stage is shifted.

At this time, to adjust the transition amount adjusting unit 390 to determine the amount of transition of the half-wavelength wavelength, the user is used for controlling the amount of transition, such as voltage, current and light.

Next, the additional operation will be described.

When the input signal of several wavelengths is input to the input terminal and this time the signal of the wavelength to be added is input to the additional stage, the signal input to the input terminal is divided into both paths through the 3-dB directional coupler 320 and proceeds to Bragg grating ( 311) through the 3-dB directional coupler 330 of the next stage and exit to the output stage.

Meanwhile, the signal added as an additional stage is divided into both paths through the 3-dB directional coupler 330, and then is reflected by the Bragg grating 311 to be reflected to the output stage.

As a result, both the signal coming into the input terminal and the signal coming into the additional stage are output to the output stage, so that the two signals are added.

4 is a cross-sectional view of a multi-core optical fiber actually applied to the present invention.

FIG. 5A extends the Mach-Zehnder interferometer type add / extract filter in series so that multiple wavelengths can be selected.

FIG. 5B illustrates the implementation of several Mach-Zehnometer interferometer type add / extract filters using one multicore fiber.

5C and 5D show an example in which the addition / extraction filter of the present invention can be combined by engraving a Bragg grating by combining a waveguide-type connection to form a coupler function or a Michallson interferometer.

Although the technical idea of the present invention has been described in detail according to the above preferred embodiment, it should be noted that the above-described embodiment is for the purpose of description and not of limitation. In addition, those skilled in the art will understand that various embodiments are possible within the scope of the technical idea of the present invention.

As described above, the present invention, by matching the phase of the two paths of the both ends of the filter through the phase adjustment unit, and arbitrarily adjust the transition of the reflected wavelength through the variable reflection wavelength transition unit to transmit a number of different signals of different wavelengths at the same time By improving the operating characteristics, the narrow pass wavelength allows high-speed channel selection, and transmits the signal to the next node without converting the electrical signal into the optical signal or the optical signal into the electrical signal. There is no need to perform any electrical processing on the traffic transmitted between them, and since the product can be manufactured in a small size, there is an effect that enables the development of various technologies of the WDM communication network.

Claims (4)

In a Mach-Zehnder interferometer type add / drop filter in a Wave Division Multiple (WDM) optical communication system, First optical distribution and coupling means for distributing the input optical signal at a predetermined ratio and for combining and dropping the additional optical signal and the reflected optical signal; It consists of a multi-core optical fiber having a Bragg grating, the signal transmitted through the first optical distribution and coupling means by dividing by a predetermined ratio to reflect and pass, and the additional optical signal is distributed and transmitted at a predetermined ratio Light reflection and transmission means for transmitting to the first light distribution and coupling means; Second light distribution and coupling means for combining and outputting the optical signal transmitted through the light reflection and transmission means, and distributing the additional optical signal at a predetermined ratio to the light reflection and transmission means; First and second phase adjusting means for matching the phases of the optical paths at both ends of the light reflecting and transmitting means; Transition amount adjusting means for providing a control signal for controlling the wavelength transition amount of the optical signal reflected by the light reflection and transmission means; And Reflected wavelength shifting means for shifting the wavelength of the optical signal reflected by the light reflection and transmission means in accordance with the control signal A Mach-Zehnder interferometer type add / extract filter in a wavelength division multiple optical communication system comprising a. The method of claim 1, The first phase shifting means, Connected between the first light distribution and coupling means and the light reflection and transmission means to provide a current, voltage and light to adjust a phase, The second phase shifting means, A Mach-Zehnder interferometer type add / extract filter in a wavelength division multiple optical communication system characterized in that it is connected between the second light distribution and coupling means and the light reflection and transmission means to adjust the phase by providing current, voltage and light. . The method of claim 1, The control signal, A Mach-Zehnder interferometer type add / extract filter in a wavelength division multiple optical communication system, characterized in that it is voltage, current or light. The method according to any one of claims 1 to 3, The first and second light distribution and coupling means, respectively A Mach-Zehnder interferometric add / extract filter in a wavelength division multiple optical communication system, characterized in that it is a 3-dB directional coupler that distributes the transmitted signal at a 3-dB ratio.