KR100264950B1 - Wavelength-variable light extraction / transmission filter for WDM communication without feedback noise - Google Patents

Abstract

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a wavelength variable light extraction / transmission filter for wavelength multiplex (WDM) communication without feedback noise in an optical communication system using a plurality of wavelengths. It is also a technology that can be used again at the next node by passing it to the next node when not in use. The system is implemented so that it is independent of the feedback of the input signal, so that an additional element such as an optical isolator can be used. By eliminating the need for use, it is possible to reduce the implementation cost and provide the advantage of making the overall system small in size. Also, because the wavelength is easy to change and the pass wavelength is narrow, the high-speed channel selection is possible and the wavelengths are different from each other. It offers the advantage of transmitting many other signals simultaneously.

Description

Wavelength-variable light extraction / transmission filter for wavelength multiplex (WDM) communication without feedback noise

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a wavelength tunable light drop / pass filter for wavelength multiplex (WDM) communication without feedback noise in an optical communication system using a plurality of wavelengths. This technology relates to a filter that can effectively separate two or more desired wavelengths and deliver all the input signals to the next stage.

In general, an optical communication system using an optical waveguide as a transmission medium has invested a lot of time and effort in carrying a lot of information in one strand of optical waveguides as technology advances, and due to the development of a light source having a narrow line width, A wide frequency band can be used efficiently.

However, it was not possible to transmit high-capacity data such as voice and moving pictures in real time.

As a solution for this, there is an increasing demand for a wavelength multiplexing method (hereinafter referred to as WDM) that modulates and multiplexes multiple wavelengths, transmits them through the same optical waveguide, and selects and demodulates only a signal having a desired wavelength at a detector. .

Therefore, the development from the current optical communication network to the all-optical communication network which minimizes the number of photoelectric conversion / electric conversion is expected to realize the all-optical communication network based on the WDM method.

Such a wavelength multiplexing transmission system typically includes a plurality of light sources emitting different wavelengths, a wavelength combiner for sending them together, an optical waveguide that is a transmission medium, a wavelength separator for separating the bundled wavelengths, and a detector for receiving the light. It is constructed.

In the WDM communication method, since a signal having a plurality of wavelengths is transmitted, an optical filter having a function of selectively extracting a specific wavelength is required.

Accordingly, an optical filter element conventionally used in the WDM communication method includes an optical add / drop filter using a Bragg diffraction grating element (US Pat. No. 5,712,717, Hamel et al.), And an additional / extraction filter. Has a function to extract a signal of a specific wavelength from the input multi-wavelength signal, and add a signal of the same wavelength as the extracted signal at the same time.

However, in the case of the add / extract filter, when one of the input signals is extracted, the extracted signal cannot be used in the next stage. Therefore, when extracting the signal, it must be added again and sent to the next stage to extract the signal required by the next node.

Currently used WDM multiplexer / demultiplexer and optical filter have a fixed wavelength that can be separated. Therefore, when the operating wavelength is changed, components must be replaced, and the signal loss is relatively large. In addition, it is inconvenient to separate the required signal wavelengths from the signal wavelengths input from one node and then add the same signals again to send all the input signals to the next node.

In order to solve the conventional problems as described above, the present invention has been made of a variable wavelength selector that can be used in the WDM method using Bragg diffraction grating elements, and the input signal is input without reinsertion of the signal extracted from the node. It aims to be configured so that all can penetrate to the next node.

In addition, since the extraction / transmission filter is miniaturized to be manufactured directly in the optical waveguide, there is almost no loss in inserting and using the optical communication system, and the period and refractive index of the Bragg diffraction grating element are changed even when the operating wavelength is changed. The purpose is to be able to change the operating wavelength by changing through.

In addition, to configure an efficient all-optical network, a node selects a required signal and transmits all input signals to the next node without additional signal insertion and photoelectric conversion / optical conversion.

It is also an object of the present invention to implement a system so as to be independent of the feedback of an input signal so that an additional element such as an optical isolator does not have to be used, thereby enabling a low cost configuration.

1 is a block diagram showing a wavelength tunable extraction / transmission filter for WDM communication according to the present invention;

FIG. 2 is a detailed block diagram of the variable wavelength extraction unit of FIG. 1. FIG.

3 is a detailed block diagram of the wavelength selector of FIG.

4 is a graph showing the power ratio at each terminal according to the phase difference of the wavelength tunable extraction / transmission filter of FIG.

5 is a block diagram illustrating another embodiment of the optical switching unit of FIG. 1.

6 is a block diagram illustrating a system block in which the wavelength tunable extraction / transmission filter of FIG. 1 is actually applied.

<Description of Symbols for Major Parts of Drawings>

10: multi-wavelength generator 12, 13, 15, 50: directional optical coupler

14 Bragg diffraction grating element 16 Optical path length regulator

17: reflection wavelength transition unit 18: control unit

20: receiver 22: optical waveguide

30: pass 40, 80 light switching unit

60: variable wavelength extraction unit 70: wavelength selector

82: input signal

94: signal reflected from Bragg diffraction grating element

The configuration of the present invention for achieving the above object is an optical switching unit for distributing the optical signal transmitted from the multi-wavelength generation unit for generating an optical signal consisting of a plurality of wavelengths in a desired ratio by having a plurality of optical paths; ;

A variable wavelength extracting unit extracting a specific wavelength from the signal distributed through the optical switching unit;

A receiver which receives a signal extracted by the variable wavelength extractor; And

Including a pass portion for transmitting all the input signals other than the signal extracted by the variable wave extraction unit to the next stage without loss,

It extracts some or all of the selected wavelength signal without passing the input signal to the input terminal or passes all the signals to the next node when not in use, so that it can be used again at the next node.

The above objects, features, and advantages will become more apparent from the following detailed description taken in conjunction with the accompanying drawings. Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

First, in order to find out the principle of the wavelength separation method to be implemented in the present invention, a conventional method for separating the required wavelengths from a plurality of received wavelengths, the method using a wavelength separation optical coupler, 'Fabry-Perot', 'Michelson' and Mach-Zehnder interferometers have been used to separate wavelengths using Bragg diffraction gratings that have a periodicity of refractive index in the waveguide.

The Bragg diffraction grating element used herein has a function of reflecting a specific stop band and passing other wavelengths through a reflection filter.

In particular, the Bragg diffraction grating element will be described in more detail. The Bragg diffraction grating element is produced 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 it uses photosensitivity to change the refractive index of an optical waveguide.

Photosensitivity refers to a phenomenon in which the refractive index of the portion where ultraviolet light is applied to the optical waveguide increases when irradiated with strong ultraviolet rays of 240 nm in the optical waveguide, and affects the reflectivity of the Bragg diffraction grating element. If the photosensitivity is high, the reflectivity is high.

The general principle that the specific wavelength is reflected in Bragg diffraction grating element is as follows. Light is reflected from each grating as it passes through the Bragg diffraction grating element, of which the phase of light reflected between each grating 2nπ The added wavelengths cause constructive interference with each other and are reflected. That is, the relationship between the reflected wavelength and the period of the grating is shown in Equation 1 below.

here, Indicates.

As described above, a part of a specific wavelength signal is extracted and used as a reception signal by using a specific wavelength reflection characteristic of the Bragg diffraction grating element, and a signal having a wavelength different from that of the rest of the extracted part can be used at the next node. The extraction / transmission filter is configured to function.

As for the function of the extraction / transmission filter, a signal having a plurality of wavelengths is input to the input stage, and the intensity of the signal is divided by the desired ratio of the input multi-wavelength signal. One of the divided multi-wavelength signals is extracted using the Bragg diffraction grating element and then received by the receiver, and the multi-wavelength signal of the other part is sent to the next node so that it is not necessary to add the same signal in multiple nodes. It can be characterized.

In addition, if there is no need to extract the signal component from a specific node, it transmits to the next node by transmitting all of it to the next node without loss of signal.

Hereinafter, referring to the drawings, FIG. 1 is a configuration diagram of a system for applying to WDM communication using a variable wavelength selector according to the present invention, and a signal having a plurality of wavelengths (λ ₁ , λ ₂ to λ _m ) Generating a multi-wavelength generator 10;

An optical fiber or a planar optical waveguide 22 which transmits a multi-wavelength signal 82 generated by the multi-wavelength generator 10;

An optical switching unit 40 having two optical paths, for distributing the transmitted optical signal at a desired ratio;

A variable wavelength extraction unit 60 for extracting a specific wavelength from the signal distributed through the optical switching unit 40;

A receiver 20 for receiving a signal extracted by the variable wavelength extractor 60; And

It comprises a pass portion (30) that all the input signal is transmitted to the next stage.

The optical switching unit 40 includes a directional optical coupler 12 for distributing incident beams 82 to travel through different paths;

An optical path length controller 16 attached to one path or both paths distributed through the directional optical coupler 12 to adjust the transmission power to extraction power ratio;

The optical switch part of the Mach-Zehnder interferometer type | mold which consists of the optical waveguides which comprise the directional optical coupler 13 which interrupts the optical signal which propagated by both paths, and advances one part or all to the next stage.

The variable wavelength extractor 60 includes a directional optical coupler 15 for distributing light input from the optical switch 40, as shown in FIG. 2;

A wavelength selector (70) connected to both paths through the directional optical coupler (15) to reflect only a signal of a specific wavelength of the input light;

The wavelength selector 70 includes a Bragg diffraction grating element 14 for reflecting only a part of the signals of multiple wavelengths input through the directional optical coupler 15;

A reflection wavelength transition unit (17) for changing the lattice period and refractive index of the diffraction grating element (14);

And a control unit 18 for inputting a control signal for determining the magnitude of the strain to be generated by the reflected wavelength transition unit 17.

The operation of the wavelength tunable extraction / transmission filter configured as described above will be described.

When a signal of λ ₁ , λ ₂ to λ _m is generated in the multi-wavelength generator 10 generating the various wavelengths, it is propagated through the optical waveguide 22 to constitute the first switching unit 40. The directional optical coupler 12 is divided into two paths of the optical switching unit 40 to proceed.

The signal proceeding divided into both sides proceeds with a phase difference of π / 2 + ø between both paths according to the characteristics of the directional optical coupler 12 and the degree of the signal applied to the path length regulator 16 attached to one path. Signals 90 and 92 input through the directional optical coupler 13 exit to the pass section 30 and the variable wavelength extraction section 60.

The signal 92 composed of a plurality of wavelengths input to the variable wavelength extraction unit 60 by the light switching unit 40 is input to the directional optical coupler 12, and is divided into the following stages.

The divided signals are inputted to the wavelength selector 70 and reflected by the variable reflection wavelength shifter 17 attached to the diffraction grating element 14 of the optical fiber or the planar waveguide, which is controlled by the controller 18. The signal is applied to reflect only one particular wavelength 94 out of the wavelengths λ ₁ to λ _m .

The reflected signal 94 proceeds through the directional optical coupler 13 again, and the signal fed back to the input terminal due to the phase characteristic of the directional optical coupler cancels and disappears, and the signal reflected toward the signal receiver 20 only. 94 proceeds.

As the signal fed back to the input stage is canceled and eliminated, when configuring the whole system, the system does not need additional devices such as an optical isolator at the input stage.

In this case, the variable reflection wavelength shifter 17 constituting the wavelength selector 70 is made of a material in which strain is frequently generated by temperature, stress, voltage, light, and the like, and applies a control signal to the controller 18. In principal, strain is generated that is proportional to the magnitude of the applied signal or the square of the magnitude.

The strain generated in this way is transferred to the Bragg diffraction grating element 14 to which the material is attached, thereby changing the lattice period and or refractive index of the diffraction grating element 14, so that the reflection wavelength 94 is changed and the drop is extracted. The signal wavelength 94 coming out (the receiver 20) is varied. The wavelengths passing through the pass are propagated through the optical waveguide and the light switching unit 40.

At this time, the magnitude of the light waves exiting the receiver (drop) 20 and the pass 30 is adjusted to a desired ratio by adjusting the optical path length adjuster 16 attached to one path of the optical switch 40. Can be.

3 is a configuration diagram of the wavelength selector 70 using the Bragg diffraction grating element 14, the strain of which is sensitive to the signal (current, voltage, temperature, pressure, magnetic field, etc.) from the control unit 18. The whole or part of the region is contacted, adhered or coated so that it can be generated to simultaneously change the period or refractive index of the Bragg diffraction grating element 14.

In detail, the strain generating material 17 whose length is changed by the voltage, current, and magnetic field applied by the controller 18 is deposited on the Bragg diffraction grating element 14 as a means for changing the wavelength. The Bragg diffraction grating element 14 may be formed by attaching, contacting, or coating to change a wavelength and simultaneously changing a refractive index or refractive index and length by an ultrasonic wave or pressure applied by the controller 18. The wavelength can be changed by adhering to, contacting or coating.

In addition, bonding or contacting the material 17 of which the refractive index or the refractive index and the length thereof are simultaneously changed by the heat applied by the controller 18, and the material 17 whose refractive index is changed by the intensity of light are attached to the Bragg diffraction grating element 18. The wavelength can be changed by coating, and it is preferable to change the wavelength by selecting an appropriate means among the wavelength changing means including the above method.

The Bragg diffraction grating element 14 is fabricated on an optical fiber or a planar wave and has a characteristic of reflecting only a specific wavelength. In this case, the reflectance is expressed by Equation 2 below.

here S _12, S ₂₂ Is given by Equations 3 and 4 below.

Where h is the length of Bragg diffraction grating element 14, q, r, δβ, k, λ _B Is as follows.

: Coupling coefficient

λ _B : Bragg wavelength

δn : Difference in refractive index of Bragg diffraction grating element

FIG. 4 is a graph showing the optical power output to the pass 30 and the signal receiver 20 when the phase is changed by adjusting the optical path difference of both optical switching units 40 in the system of FIG. As shown in the graph, by changing the phases due to the optical path difference, the optical power output to the signal receiver 20 or the pass 30 can be adjusted.

FIG. 5 is a diagram illustrating a configuration of an optical switching unit 80 according to an embodiment having a structure different from that of the optical switching unit 40 described in FIG. 1, which may be manufactured using a planar optical waveguide or an optical fiber, and adjusts an optical path difference of one or both paths. It consists of a directional optical coupler 50 which is made of a light path length adjuster 16, which can cause signal interference as the optical signal progresses.

Here, various methods of distributing a signal at a desired ratio with respect to the signal input from the optical coupler 40 shown in FIG. 1 and the optical coupler 80 shown in FIG. 5 will be described.

This means that a material whose length or length and refractive index are simultaneously changed by voltage, current, and magnetic field applied to the optical path length adjuster 16 in the optical switch units 40 and 80 is transferred to the optical waveguide 22 in one path or both paths. By depositing, adhering, contacting or coating, the optical path difference can be generated between the two paths so as to distribute the signal, and also the ultrasonic, pressure, heat and light applied to the optical path length adjuster 16 in the optical switch unit 40. The input signal can be distributed at a desired ratio by depositing, adhering, contacting or coating a material having a refractive index or a material whose refractive index and length are simultaneously changed by one or both paths.

It is preferable to implement a filter by selecting an appropriate method among various methods of distributing a signal including the above method.

Such a structure can be seen that the structure is considerably compact compared with the light switching portion 4 of FIG.

FIG. 6 is a block diagram illustrating a configuration in which the wavelength tunable extraction / transmission filter system proposed in the present invention is actually applied. The system of FIG. 1 is connected in series to reflect several wavelengths, and the other wavelengths are transmitted again. A system to pass through 30 is shown.

The input wavelength may reflect a specific wavelength or transmit all wavelengths to the next system by adjusting the optical path difference between both sides of the light switching unit 40 in the first system.

The transmitted wavelength passes through the pass 30 and is incident to the next system, and the second system can reflect a specific wavelength in the same principle as the first system, and by adjusting the optical path difference, it is also transmitted to the next system. It is possible.

By connecting these systems in series as many times as you want to select the desired wavelength, you can select any desired wavelength.

When the system is constructed by connecting the extraction / transmission filter in series like this, in the conventional system, since there is a signal fed back to the input stage, an additional element such as an isolator is needed, but in the proposed system, the signal returned to the input stage is There is no need for an isolator for the overall system configuration.

Therefore, an economical and simple system can be constructed. Of course, the isolator may be mounted between the input terminal 10 and the optical switching unit 40 to form a more stable system.

As described in detail above, the wavelength tunable extraction / transmission filter system using the optical waveguide for WDM of the present invention can reduce the size of the overall system, easily change the wavelength, and narrow the pass wavelength, thereby enabling high-speed channel selection. The advantage is that many signals of different wavelengths can be transmitted simultaneously.

In addition, since it can transmit to the next node without photoelectric conversion / optical conversion, it is difficult to make the whole system small due to the advantage that intermediate nodes do not need to at least electrically handle the traffic transmitted between other nodes. As it is possible, it can be positioned as a base technology that enables the development of various technologies of the WDM network in the future, and its ripple effect is great.

In addition, the proposed extraction / transmission filter is particularly useful in optical CATV networks, distributed optical sensors, broadcasting networks, and WDM communication networks, since it is more stable than simple feedback systems because it is independent of feedback signals. It can be used as an element.

In addition, preferred embodiments of the present invention are disclosed for the purpose of illustration, those skilled in the art will be able to various modifications, changes, additions, etc. within the spirit and scope of the present invention, such modifications and modifications belong to the following claims You will have to look.

Claims (15)

An optical switching unit for distributing the optical signal transmitted from the multiple wavelength generation unit for generating the optical signal having a plurality of wavelengths in a desired ratio by having a plurality of optical paths; A variable wavelength extracting unit extracting a specific wavelength from the signal distributed through the optical switching unit; A receiver which receives a signal extracted by the variable wavelength extractor; And Including a pass portion for transmitting all the input signals other than the signal extracted by the variable wave extraction unit to the next stage without loss, Wavelength multiplexing without trace noise, characterized by extracting some or all of the selected wavelength signals without passing the input signal to the input terminal, or passing all of them to the next node when not in use. (WDM) wavelength tunable light extraction / transmission filter for communication. The method of claim 1, The optical switching unit and the directional optical coupler for distributing the incident beam to proceed through different paths; An optical path length controller attached to one path or both paths to adjust the transmission power to extraction power ratio; Wavelength-variable light extraction / transmission filter for feedback multiplexing (WDM) communication, comprising a directional optical coupler for interfering part or all of the optical signal traveling through both paths to the next stage . The method of claim 1, The optical switching unit is made of an optical waveguide or an optical fiber, and consists of an optical path length adjuster for adjusting an optical path difference of one or both paths of the optical waveguide, and includes a directional optical coupler for causing an optical signal to cause signal interference. A wavelength tunable light extraction / transmission filter for wavelength multiplex (WDM) communication without feedback noise. The method of claim 2 or 3, Both paths are formed by depositing, adhering, contacting or coating a material of which the length or length and refractive index are simultaneously changed by the voltage, current, and magnetic field applied to the optical path length controller in the optical switch unit in the optical waveguides in one path or both paths. A variable wavelength light extraction / transmission filter for wavelength multiplex (WDM) communication without feedback noise, characterized by distributing an input signal at a desired ratio by causing an optical path difference to occur. The method of claim 2 or 3, The optical path between the two paths is deposited, attached, contacted or coated on the optical waveguide of one path or both paths by simultaneously changing the refractive index or the refractive index and the length by the ultrasonic wave or pressure applied to the optical path length controller in the optical switch unit. A wavelength tunable light extraction / transmission filter for wavelength multiplex (WDM) communication without feedback noise, characterized in that a difference is generated so as to distribute a signal input at a desired ratio. The method of claim 2 or 3, By depositing, adhering, contacting or coating a material of which refractive index or refractive index and length are simultaneously changed by the heat applied to the optical path length controller in the optical switch unit, the optical path difference is generated between the two paths. A wavelength tunable light extraction / transmission filter for wavelength multiplex (WDM) communication without feedback noise, wherein the signal is input at a desired ratio. The method of claim 2 or 3, By depositing, adhering, contacting or coating a material whose refractive index is changed by the intensity of light applied to the optical path length controller in the optical switch unit to an optical waveguide in one or both paths, an optical path difference is generated between the two paths. A wavelength tunable light extraction / transmission filter for wavelength multiplex (WDM) communication without feedback noise, wherein the signal is input at a desired ratio. The method of claim 1, The tunable wavelength extracting unit includes a directional optical coupler for distributing light input from the light switching unit; Wavelength-variable light extraction for wavelength multiplex (WDM) communication, characterized in that it comprises a wavelength selector connected to both paths through the directional optical coupler, and reflecting only a signal of a specific wavelength among the input light. Permeate filter. The method of claim 8, The wavelength selector is composed of an optical fiber or an optical waveguide, Bragg diffraction grating element for reflecting only a portion of the signal of the multi-wavelength input through the directional optical coupler; A reflection wavelength shift unit for changing a lattice period and a refractive index of the diffraction grating element; And a control unit for inputting a control signal for determining the magnitude of strain to be generated in the reflected wavelength shifting unit. The method of claim 9, The reflection wavelength shift unit is a strain generating material whose length is changed by voltage, current, or magnetic field applied from the controller, and changes the wavelength by depositing, attaching, contacting, or coating the Bragg diffraction grating device. Wavelength-variable light extraction / transmission filter for wavelength multiplex (WDM) communication without feedback noise. The method of claim 9, The reflective wavelength shifting unit is a material in which the refractive index or the refractive index and the length thereof are changed at the same time by ultrasonic waves or pressure applied from the controller, and the wavelength is changed by adhering, contacting or coating the Bragg diffraction grating element. Wavelength-variable light extraction / transmission filter for WDM communication without feedback noise. The method of claim 9, The reflection wavelength shift unit is a material in which the refractive index or the refractive index and the length thereof are simultaneously changed by the heat applied from the controller, and the feedback noise is characterized by changing the wavelength by adhering, contacting or coating the Bragg diffraction grating element. Wavelength-variable light extraction / transmission filter for wavelength multiplex (WDM) communications. The method of claim 9, The reflective wavelength shifting part is a material whose refractive index is changed by the intensity of light applied from the control unit. The wavelength of feedback noise is characterized by changing the wavelength by adhering, contacting or coating the Bragg diffraction grating element. Wavelength-variable light extraction / transmission filter for multiple mode (WDM) communications. The method of claim 1, The tunable wavelength extraction unit is a wavelength-variable light extraction / transmission filter for feedback multiplexing (WDM) communication, characterized in that it further comprises an isolator in order to remove the noise is partially returned to the input stage. The method of claim 1, The variable wavelength extraction / transmission filter for wavelength multiplex (WDM) communication without feedback noise, wherein the wavelength-variable extraction / transmission filter is connected and driven in series.