KR20020026634A - A Sagnac tunable optical drop/pass filter system for WDM - Google Patents

Abstract

PURPOSE: A Sagnet-type tunable optical drop/pass filter system for WDM(Wavelength Division Multiplexing) communication is provided to pass all of the inputted signals to the next node without reinserting the signals extracted at a node by configuring a WDM tunable selector using a brag diffraction grating. CONSTITUTION: The first optical signal add/drop multiplexer(30) distributes an optical signal(s1), inputted through a fiber-optic or plane optical waveguide(21) from an optical signal generator(10) generating many wavelengths, into two optical signals(s2,s3). One(s2) of the two optical signals is outputted to the second optical signal add/drop multiplexer(60) through a fiber-optic or plane optical waveguide(23). The other distributed optical signal(s3) is outputted to a pass part(50) through a fiber-optic or plane optical waveguide(24). The optical signal(s2) inputted to the second optical signal add/drop multiplexer(60) is distributed into a clockwise optical signal(s4) and a counterclockwise optical signal(s5) again. The distributed signals(s4,s5) are inputted to a wavelength selector(80), which reflects only a specific wavelength, and fed back clockwise and counterclockwise respectively. The optical signal(s6,s7) fed back from the wavelength selector(80) are combined by the second optical signal add/drop multiplexer(60) and outputted to the second receiving part(70).

Description

A Sagnac tunable optical drop / pass filter system for WDM}

The present invention relates to a snag-type wavelength-variable optical drop / pass filter system for WDM communication. In particular, a Bragg diffraction grating is used to construct a wavelength-variable selector that can be used in the WDM method, without reinserting a signal extracted from a node. The present invention relates to a new wavelength-tunable optical drop / pass filter system for WDM communication configured to pass all the signals to the next node.

In general, conventional WDM-based systems must separate only the desired wavelengths from signals with multiple wavelengths, so the wavelength selector at the detector stage is essential, but currently used WDM multiplexer / demultiplexers and optical filters are separated. If the operating wavelength is changed due to the fixed wavelength, the additional cost is added. Also, to extract the required conversion signal wavelength from the input signal wavelength at one node, and then send all the input signals to the next node again. There was an inconvenience of having to send additional signals.

Accordingly, the present invention has been made to solve the above problems, by using a Bragg diffraction grating to configure a wavelength variable selector that can be used in the WDM method, the entire input signal without reinsertion of the signal extracted from the node The purpose is to provide a new wavelength-tunable optical drop / pass filter system for WDM communication configured to pass to the next node.

1 is a configuration example of a new wavelength type variable wavelength Drop / Pass filter system for WDM communication according to the present invention,

Figure 2 is a configuration example of the wavelength-type optical variable drop / pass filter system for the WDM communication with a path length control unit according to the present invention,

3 is a configuration example of a sack type wavelength variable optical drop / pass filter system for WDM communication for applying a signal generated by attaching a signal processor according to the present invention to a path length controller;

4 is an example of a structure of a light-wavelength variable wavelength Drop / Pass filter for WDM communication with a sample grating according to the present invention;

5 is an application example in which the cask-type wavelength variable optical Drop / Pass filter system for WDM communication according to the present invention is connected in series;

6 is an application example using ADM (Add / Drop Multiplexer) to some nodes of the configuration of FIG. 5 according to the present invention;

Figure 7 is an example showing the power ratio at each output port according to the phase difference of the Snack-type wavelength variable optical Drop / Pass filter system according to the present invention,

Figure 8 is an example showing the power ratio at each output port according to the phase difference in the case where the coupling ratio of the optical signal distribution / coupling portion in the Snack-type wavelength variable optical Drop / Pass filter system according to the present invention is 2: 8.

* Description of the main symbols in the drawings

10: multi-wavelength optical signal generator 30: first optical signal distributor / combiner

40: first receiving unit 50: pass unit

60: second optical signal distributor / combiner 70: second receiver

80: wavelength selection unit 90: path length adjustment unit

100: signal processor 120: sample grating

In order to achieve the above object, the snag-type wavelength-variable optical drop / pass filter system for WDM communication according to the present invention is a WDM (Wavelength Division Multiplexing) -based broadband transmission network structure, generating a plurality of wavelengths of different lengths A multi-wavelength optical signal generator; A first optical signal distributor / combiner for receiving and distributing or combining optical signals generated from the generator; A first receiver comprising a light receiving element capable of receiving and receiving an optical signal from the distribution / combining unit; A pass unit for receiving an optical signal from the distribution / combining unit and transmitting the optical signal to another node; A second optical signal distributor / combiner for receiving or distributing an optical signal from the distributor / combiner; A second receiver including a light receiving element capable of receiving and receiving an optical signal from the second optical signal distributor / combiner; A wavelength selector attached to a Sangnac loop capable of receiving an optical signal from the second optical signal distributor / combiner and selecting an arbitrary signal wavelength; And a planar optical waveguide including an optical fiber capable of transmitting an optical signal between the components.

In the Snag-type wavelength variable optical drop / pass filter system for the WDM communication, the phase difference of the optical signal reflected and returned from the wavelength selector is always nπ (n: 0, 1, 2, ...) The second optical signal splitter / combiner may be set to one of the second optical signal divider to reduce noise components fed back to the input terminal of the multi-wavelength optical signal generator while maintaining maximum optical power at the second receiver. A path length regulator attached to the optical waveguide between the and the wavelength selector; And a controller for applying a control signal to the regulator.

The controller may be configured as a signal processor for converting an optical signal output from the first receiver into an electrical signal and applying a control signal to the controller.

1. A broadband transmission network structure based on Wavelength Division Multiplexing (WDM), comprising: a multi-wavelength optical signal generator for generating a plurality of wavelengths having different lengths; A first optical signal distributor / combiner for receiving and distributing or combining optical signals generated from the generator; A first receiver comprising a light receiving element capable of receiving and receiving an optical signal from the distribution / combining unit; A pass unit for receiving an optical signal from the distribution / combining unit and transmitting the optical signal to another node; A second optical signal distributor / combiner for receiving or distributing an optical signal from the distributor / combiner; A sample grating capable of receiving an optical signal from the second optical signal distributor / combiner and simultaneously reflecting various signal wavelengths; A third optical signal distributor / combiner for receiving or distributing or combining optical signals from the second optical signal distributor / combiner; A second receiver including a light receiving element capable of receiving and receiving an optical signal from the third optical signal distributor / combiner; A wavelength selector configured to receive an optical signal from the third optical signal distributor / combiner and select an arbitrary signal wavelength; And a planar optical waveguide including an optical fiber capable of transmitting an optical signal between the components.

In the Snag-type wavelength variable optical drop / pass filter system for the WDM communication, the phase difference of the optical signal reflected and returned from the wavelength selector is always nπ (n: 0, 1, 2, ...) The second optical signal splitter / combiner may be set to one of the second optical signal divider to reduce noise components fed back to the input terminal of the multi-wavelength optical signal generator while maintaining maximum optical power at the second receiver. A path length regulator attached to the optical waveguide between the sample grating and the sample grating; And a controller for applying a control signal to the regulator.

The first optical signal distributor / combiner and the second optical signal distributor / combiner may be configured such that a coupling ratio is tunable.

An optical isolator may be attached between the multi-wavelength optical signal generator and the first optical signal distributor / combiner to block an optical signal reflected and incident to the multi-wavelength optical signal generator.

The wavelength-modulated optical drop / pass filter system for the WDM communication includes a plurality of wavelength-variable optical drop / passes for selecting a plurality of wavelengths for use in operation and for protection in case of failure. ) Can be configured by connecting the filter system in series, wherein the Snack-type wavelength variable optical drop / pass filter system for WDM communication, the middle of the plurality of wavelength variable optical drop / pass filter system It can be configured by attaching a wavelength variable add / drop multiplexer (ADM) to the node.

The wavelength selection unit includes a controller for generating a control signal; A variable reflection wavelength shifter which generates a strain proportional to the magnitude or the square of the magnitude of the applied signal when the control signal generated by the controller is applied; And a diffraction grating element that receives the strain generated by the transition and changes the lattice period or refractive index.

The path length adjuster may be composed of a material whose length is changed by pressure, voltage, current or electric field, which is attached by adhesion, contact, or coating.

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

1 is a configuration example of a new wavelength type variable wavelength drop / pass filter system for WDM communication according to the present invention, using a wavelength division multiplexing (WDM) using a wavelength selector 80 of a new type drop / pass filter. It is a system for communication. First, a multi-wavelength optical signal generator 10 for generating a plurality of wavelengths λ ₁ , λ ₂ to λ _m and an optical fiber or a planar optical waveguide 21 for transmitting the generated multi-wavelength optical signal s ₁ . ) And the optical signal s ₁ input from the multi-wavelength optical signal generator 10 are distributed by the first optical signal distributor / combiner 30 into the optical signals s ₂ and s ₃ . The distributed one optical signal s ₂ is output to the second optical signal distribution / combining unit 60 through the optical fiber or the planar optical waveguide 23, and the other distributed optical signal s ₃ is the optical fiber or the planar optical wave. It is output to the pass section 50 through the waveguide 24.

The optical signal s ₂ input from the second optical signal distributor / combiner 60 is distributed again, proceeds to the optical signal s _{4 in the} clockwise direction and the optical signal s _{5 in the} counterclockwise direction, and then multi-wavelength. Λ ₁ to the wavelength selection unit 80 composed of a Bragg diffraction grating element 81 capable of reflecting only a part of the signal, a variable reflection wavelength shifter 82, and a controller 83 generating a control signal. By reflecting only a specific wavelength among the λ _m wavelengths, the optical signal s ₇ fed back clockwise and the optical signal s ₆ fed back counterclockwise are combined by the second optical signal distributor / combiner 60. The light signals s ₆ and s ₇ distributed again are output to the second receiver 70 including the light receiving element. In addition, the remaining non-reflected optical signals s _{8 and} s ₉ continue in the same direction to be combined by the second optical signal splitter / combiner 60, and the divided optical signals s _{8 and} s ₉ are zero. 1 is input to the input terminal of the optical signal distributor / combiner 30 and then distributed again and output to the first receiver 40.

Here, the variable reflection wavelength shifter 82 constituting the wavelength selector 80 is made of a material in which strain is frequently generated due to temperature, pressure, voltage, electric field, magnetic field, and the like. Applying Strain generates strain proportional to the magnitude of the applied signal or the square of the magnitude of the applied signal. The strain generated in this way is transmitted to the Bragg diffraction grating element 81 to which the material is attached, thereby changing the lattice period or refractive index, so that the optical signals s ₆ and s ₇ of the reflected wavelength are changed so that the second receiver ( The optical signals s ₆ and s ₇ of the wavelength output to 70 are varied. The wavelengths passing through the pass part 50 propagate to other nodes through the optical waveguide. In addition, the coupling ratio of the first optical signal distribution / coupling unit 30 may be tuned to appropriately adjust the optical power of the pass unit 50, and the power fed back to the input terminal may be very small. In the figure, 21 to 27 represent an optical fiber or a planar optical waveguide. The second optical signal distributor / combiner 60 and the wavelength selector 80 are connected in a simple loop manner.

2 is an example of a structure of a wavelength-varying optical drop / pass filter for WDM communication with a path length adjusting unit according to the present invention, and is provided between the second optical signal distribution / combining unit 60 and the Bragg diffraction grating 80. Path length adjustment unit 90 is attached. When the control signal is applied by the controller 92 connected to the path length regulator 91, the optical signals s ₆ and s ₇ reflected by the Bragg diffraction grating element 81 are different in phase according to the degree of the signal. Will proceed with. That is, the optical signal s ₇ fed back clockwise proceeds with a phase difference of 2 ψ than the optical signal s ₆ fed back counterclockwise. The mathematical analysis of the operating characteristics of the wavelength-variable Sagnac-type Drop / Pass filter system is as follows. The phase difference caused by the path length regulator 91 between the second optical signal distribution / coupling unit 60 and the Bragg diffraction grating element 81 is referred to as ψ (or ㅿ φ ), and the Snack interferometer and Bragg diffraction grating are Considering the characteristics of the element 81, the feedback signal (input stage = E ₁ ), the output signal (output stage = E ₂ ), the pass signal (pass stage = E ₃ ), and the drop signal from each terminal of the drop / pass filter are considered. (Drop end = E ₄ ) can be expressed as follows.

ㅿ φ is equal to 2 π ㅿ ln _eff / λ by the phase difference by the path difference ㅿ ℓ, and n _eff is the effective refractive index of the optical fiber core. E ₀ is the state of the incident beam, and k _{m, t,} k _{m, c} are the coupling indices of the directional coupler. In addition, r and t are reflection coefficients and pass coefficients of the optical fiber grating, respectively, and can be expressed as elements S _jj of the S matrix as follows.

Positioning the Bragg diffraction grating element 81 attached to the roof loop in the middle of the loop can cause some errors, so this error can be obtained by using the path length regulator 91, thereby making Phase difference of light reflected and fed back clockwise and counterclockwise 2ψAlways nπ( n: 0, 1, 2, ..) can be set to one of the best possible design. In addition, the optical signal s reflected from the Bragg diffraction grating element 81 of the Snack interferometer due to external environmental changes, that is, factors such as temperature, vibration, bending and twisting₆, s₇), The phase difference between the light running clockwise and the light running counterclockwise is different from the initial value. Therefore, the change in power in the second receiver 70 causes a phase difference to always be n again using the path length adjuster 91.π( n: 0, 1, 2, ..) can be set to one of the following to reduce the noise component fed back to the input terminal of the multi-wavelength optical signal generator 10 and at the same time to maximize the power of the second receiver 70 Can be maintained.

3 is a diagram illustrating an example of a structure of a sack type wavelength variable optical drop / pass filter system for WDM communication that applies a signal generated by attaching a signal processing unit 100 according to the present invention to a path length controller 91. We show a tunable drop / pass filter system controlled using the feedback principle. The optical signals s _{8 and} s ₉ output to the first receiving unit 40 are converted into electric signals, and the electric signals are forwarded to the signal processing unit 100 again. The output of the signal processing unit 100 is fed back through the electric signal transmission path 110 to the path length controller 91 to automatically reduce the noise fed back to the input terminal of the multi-wavelength optical signal generator 10 and at the same time, The power ratio at the receiver 70 may be adjusted.

4 is a configuration example of a Snack-type wavelength-varying optical Drop / Pass filter system for WDM communication with a sample grating 120 according to the present invention. In FIG. 1, the Bragg diffraction grating element 81 attached to the Snack loop is a single unit. While only the wavelength can be reflected, the sample grating 120 is an optical device capable of simultaneously reflecting several wavelengths. In FIG. 1, in order to change the reflection wavelength, a separate variable reflection wavelength shifter 82 and a controller 83 are attached to the Bragg diffraction grating element 81. However, in FIG. 4, the sample grating 120 is constructed using the multi-wavelength reflecting system, so other additional devices do not need to be attached to the sacks loop. Instead, in the second receiver 70, a separate Bragg diffraction grating element 81 and a variable reflection for selecting an optical signal s ₁₄ having a desired wavelength from among the reflected optical signals s ₁₀ and s ₁₁ having multiple wavelengths. There is a need for a variable wavelength selector 80 composed of a wavelength shifter 82 and a signal controller 83. That is, the optical signal s14 reflected by the Bragg diffraction grating element 81 receives such light because part of the optical signal distributed by the third optical signal distribution / combining unit 130 may enter the sank loop again. There is a need for a separate blocking device, such as an optical isolator for blocking. In addition, the path length controller 91 is attached between the second optical signal distribution / coupling unit 60 and the sample grating 120 as shown in FIG. 2 and FIG. Can be configured.

5 is an application example in which the Snack-type wavelength variable optical Drop / Pass filter system for WDM communication according to the present invention is connected in series, and the several wavelengths are connected in series as if the Snack-type wavelength variable drop / pass filter system is used for several nodes. And reflects the other wavelengths back to the pass section 50. The clockwise light indicates the working state and the counterclockwise light indicates the protection state. The input wavelength may be reflected by the wavelength selector 80 in the first system to reflect a specific wavelength and transmit all wavelengths to the next system. That is, the transmitted wavelength is incident to the next node through the pass unit 50, and the second system can reflect the specific wavelength in the same principle, and also can transmit to the next node as in the previous node. In such a system, when the desired wavelength is connected in series, the optical signal coming out of the first stage pass section 50 by the feedback optical signal of the second stage drop / pass filter is transmitted to the first stage receiver section. 20), an optimal system can be realized by reducing the noise component fed back to the input stage by using the path length controller 91 as shown in FIGS. 2 and 3. There is also a method of attaching an optical isolator to the input to isolate the returned noise component.

FIG. 6 is an application example in which an ADM (Add / Drop Multiplexer) is used in some nodes of FIG. 5 according to the present invention. As shown in FIG. Ongoing light indicates protection in case of failure. The input wavelength is reflected by the wavelength selector 80 at the first node, and the specific wavelength is reflected, and all wavelengths may be transmitted to the next system. The transmitted wavelength passes through the pass unit 50 and enters into the next system. If a specific node transmits other information, it is added using ADM so that the next node can reflect the specific wavelength in the same principle as the first system. Like the previous node, all of them can be transmitted to the next node including the new additional signal. Such a system can select all the desired wavelengths by connecting the desired wavelengths in series as in FIG. 5. The method of reducing the noise component fed back to the input terminal is also the same as the method used in the configuration of FIG.

Figure 7 is an example showing the power ratio at each output port according to the phase difference of the Snack-type wavelength variable optical Drop / Pass filter system according to the present invention, the phase using the path length regulator 91 is always nπ( n: 0, 1, 2,... so that the optical power in the second receiver 70 maintains the same maximum as in the pass section 50 while the multiple optical signal generator 10 ) Enables optimal drop / pass filter systems by keeping the returned optical power to a minimum.

8 illustrates an example of a power ratio at each output port according to a phase difference when a coupling ratio of an optical signal distribution / coupling unit is 2: 8 in the Snack-type wavelength-variable optical drop / pass filter system according to the present invention. That is, in the case of changing the phase by adjusting the path length adjuster 91 in the system of FIG. 2 as in the case of FIG. 7, the optical power and the first receiver 40 fed back to the multi-wavelength optical signal generator 10 are respectively. , Optical power outputted to the pass section 50 and the second receiving section 70. The optical power in the pass section 50 is relatively large, so that the number of optical amplifiers can be reduced when propagating to the next node, and the second receiver 70 also outputs optical power above the reception sensitivity range. In addition, the optical power fed back to the input terminal of the multi-wavelength optical signal generator 10 is very small to implement an optimal wavelength variable drop / pass filter system.

As described above, the Snack-type wavelength-variable optical drop / pass filter system for WDM communication can reduce the overall size of the system, and it is easy to change the wavelength and narrow the pass wavelength to enable high-speed channel selection as well as many different wavelengths. The advantage is that signals can be obtained simultaneously. In addition, since it can transmit to the next node without photoelectric / optical conversion, there is an advantage in that intermediate nodes do not need to perform any processing at least electrically for traffic transmitted between other nodes.

Claims (11)

In the WDM (Wavelength Division Multiplexing) based broadband transport network structure, A multi-wavelength optical signal generator for generating a plurality of wavelengths different in length from each other; A first optical signal distributor / combiner for receiving and distributing or combining optical signals generated from the generator; A first receiver comprising a light receiving element capable of receiving and receiving an optical signal from the distribution / combining unit; A pass unit for receiving an optical signal from the distribution / combining unit and transmitting the optical signal to another node; A second optical signal distributor / combiner for receiving or distributing an optical signal from the distributor / combiner; A second receiver including a light receiving element capable of receiving and receiving an optical signal from the second optical signal distributor / combiner; A wavelength selector attached to a Sangnac loop capable of receiving an optical signal from the second optical signal distributor / combiner and selecting an arbitrary signal wavelength; And And a planar optical waveguide for a WDM communication, characterized in that it comprises a planar optical waveguide including an optical fiber capable of transmitting an optical signal between the components. The method of claim 1, wherein the snag-type wavelength variable optical drop / pass filter system for WDM communication, Noise returned to the input terminal of the multi-wavelength optical signal generator by allowing the phase difference of the optical signal reflected and returned from the wavelength selector to be always set to one of n π (n: 0, 1, 2, ...) In order to reduce the components and at the same time maintain the maximum optical power at the second receiver, A path length adjuster attached to an optical waveguide between the second optical signal splitter / combiner and a wavelength selector; And And a controller for applying a control signal to the regulator. The Snack-type wavelength-variable optical drop / pass filter system for WDM communication. The method of claim 2, wherein the controller, A signal processing unit for converting an optical signal output from the first receiver into an electrical signal and applying a control signal to the controller, wherein the Snack-type wavelength variable optical drop / pass filter for WDM communication is provided. system. In the WDM (Wavelength Division Multiplexing) based broadband transport network structure, A multi-wavelength optical signal generator for generating a plurality of wavelengths different in length from each other; A first optical signal distributor / combiner for receiving and distributing or combining optical signals generated from the generator; A first receiver comprising a light receiving element capable of receiving and receiving an optical signal from the distribution / combining unit; A pass unit for receiving an optical signal from the distribution / combining unit and transmitting the optical signal to another node; A second optical signal distributor / combiner for receiving or distributing an optical signal from the distributor / combiner; A sample grating capable of receiving an optical signal from the second optical signal distributor / combiner and simultaneously reflecting various signal wavelengths; A third optical signal distributor / combiner for receiving or distributing or combining optical signals from the second optical signal distributor / combiner; A second receiver including a light receiving element capable of receiving and receiving an optical signal from the third optical signal distributor / combiner; A wavelength selector configured to receive an optical signal from the third optical signal distributor / combiner and select an arbitrary signal wavelength; And And a planar optical waveguide drop / pass filter system for WDM communication, comprising: a planar optical waveguide including an optical fiber capable of transmitting an optical signal between the components. The method of claim 4, wherein the snag-type wavelength variable optical drop / pass filter system for WDM communication, Noise returned to the input terminal of the multi-wavelength optical signal generator by allowing the phase difference of the optical signal reflected and returned from the wavelength selector to be always set to one of n π (n: 0, 1, 2, ...) In order to reduce the components and at the same time maintain the maximum optical power at the second receiver, A path length adjuster attached to an optical waveguide between the second optical signal splitter / combiner and a sample grating; And And a controller for applying a control signal to the regulator. The Snack-type wavelength-variable optical drop / pass filter system for WDM communication. The method according to claim 1 or 4, wherein the first optical signal distribution / combination unit and the second optical signal distribution / combination unit, A Snack-type wavelength-variable optical drop / pass filter system for WDM communications, characterized in that the coupling rate is tunable. The method according to claim 1 or 4, wherein between the multi-wavelength optical signal generator and the first optical signal distributor / combiner, An optical isolator type wavelength variable optical drop / pass filter system for WDM communication, comprising: an optical isolator attached to block an optical signal reflected and reflected by the multi-wavelength optical signal generator. The method of claim 1 or 4, wherein the Snack-type wavelength-variable optical drop / pass filter system for WDM communication, A new wavelength-tunable light for WDM communication, comprising a series of wavelength-variable light drop / pass filter systems connected in series to select a plurality of wavelengths for use in operation and in case of failure protection. Drop / Pass Filter System. The method of claim 8, wherein the snag-type wavelength variable optical drop / pass filter system for WDM communication, Wavelength variable ADM (Add / Drop Multiplexer) attached to the intermediate node of the plurality of wavelength variable optical drop / pass (Drop / Pass) filter system is configured by the new wavelength type wavelength variable optical drop / pass (Drop) for WDM communication / Pass) filter system. The method of claim 1 or 4, wherein the wavelength selection unit, A controller for generating a control signal; A variable reflection wavelength shifter which generates a strain proportional to the magnitude or the square of the magnitude of the applied signal when the control signal generated by the controller is applied; And And a diffraction grating element for varying the lattice period or the refractive index by receiving the strain generated by the shifter. The Snack-type wavelength-variable optical drop / pass filter system for WDM communication, characterized in that it comprises a diffraction grating element. The method of claim 2 or 5, wherein the path length adjuster, A snag-type wavelength-variable optical drop / pass filter system for WDM communications, comprising a material whose length varies by pressure, voltage, current, or electric field attached by means of adhesion, contact, or coating.