KR19990020073A - Wavelength-variable optical drop / pass filter system structure for wavelength division multiple communication - Google Patents

Abstract

The present invention relates to a structure of a wavelength variable optical drop / pass filter system for wavelength division multiplexing (WDM) communication, and is one of essential functions required for constructing multiple optical networks using WDM. A wavelength variable drop / pass filter system using an optical waveguide can be selected by varying the wavelength of a desired signal and transmitting all input signals simultaneously to the next node. By changing the period and refractive index through the external signal, it is possible to change the operating wavelength, select the necessary signal at the node to construct an efficient all-optical network, and then input all input signals without additional signal insertion and photoelectric conversion / optical conversion. By allowing the transmission to the node, the overall system size can be made smaller and the wavelength can be varied. It is easy and has the advantage of fast channel selection due to the narrow pass wavelength width, and it can transmit numerous signals of different wavelengths at the same time. Due to the advantage that there is no need to perform any electrical processing on the transmitted traffic, it is possible to manufacture the whole system in a small size, which can be positioned as a base technology that enables the development of various technologies of the WDM communication network in the future.

Description

Wavelength-variable optical drop / pass filter system structure for wavelength division multiple communication

DETAILED DESCRIPTION OF THE INVENTION The present invention is a wavelength-variable optical drop / pass for wavelength division multiplexing (WDM) that can effectively separate one or two or more desired wavelengths from multiple wavelengths of a light receiver and transmit all input signals to the next stage. (drop / pass) filter system.

Optical communication systems that use optical waveguides as transmission mediums are investing a lot of time and effort in carrying a lot of information on one strand of optical waveguides.

As a result of this effort, a wavelength multiplexing system has been applied, in which different signals are transmitted to light having different wavelengths and transmitted through a single optical waveguide, and a signal having a desired wavelength is received at a receiving side.

The wavelength multiplexing transmission system consists of a plurality of light sources emitting different wavelengths, a wavelength combiner which bundles them, and an optical waveguide which is a transmission medium, a wavelength separator which separates the bundled wavelengths into respective ones, and a detector which receives these lights.

Conventionally, a method used as a WDM device includes a method of selecting frequencies using a Fabry-Perot resonator, a method using a bulk diffraction grating, and a method of selecting a desired wavelength using a thin film filter reflecting only a specific wavelength. Has been used.

In the method using the Favor-Perot resonator, a mirror having high reflectivity is formed on both sides of the resonator, and when light is incident, only the wavelength of the resonator is transmitted.

Fabry-Perot resonators can vary the wavelength transmitted by varying the length of the resonator.

The bulk diffraction grating method is a method using the principle that the incident multi-wavelength light is diffracted at different angles for each wavelength in the diffraction grating.

The method using a thin film filter is a method of separating a desired wavelength from incident multi-wavelength using a thin film filter reflecting a specific wavelength.

Then, using wavelength division add / drop multiplexer using Bragg diffraction grating, select required wavelength and add extracted signal or new signal to next node and transmit to next node without photoelectric conversion / electric conversion It was.

The Bragg diffraction grating features a reflective filter that reflects a specific stop band and passes other wavelengths.

In particular, the Bragg diffraction grating will be described in more detail. The Bragg diffraction grating is made by periodically changing the refractive index in the optical waveguide, and various methods are used to periodically change the refractive rule in the waveguide. It has a common point in 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 in the 240 nm band.

The photosensitivity affects the reflectivity of the Bragg diffraction grating, and when the photosensitivity is high, the reflectance becomes high.

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

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

In other words, the relationship between the reflected wavelength and the period of the grating is as follows.

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

The method using the Fabry-Perot resonator has the advantage of varying the operating wavelength in the incident multi-wavelength signal, but in order to maintain high wavelength selectivity, a mirror having a very high reflectance should be used.

However, making mirrors with high reflectivity is quite difficult and expensive.

The Bragg diffraction grating can select a desired wavelength by forming a grating in an optical waveguide, and can change the operating wavelength with high frequency selectivity.

The method using the bulk diffraction grating has the disadvantage that the system is bulky and therefore bulky, and the signal loss is large when connected to the optical fiber system.

The method using the thin film filter has a disadvantage that the new wavelength filter has to be used when the operating wavelength is changed because the operating wavelength of the thin film filter is broken.

In order to solve the above disadvantages, the present invention can change the operating wavelength by changing the period and refractive index of the Bragg diffraction grating through an external signal even if the operating wavelength changes using the Bragg diffraction grating.

In addition, it aims to select the necessary signal in the node to construct an efficient all-optical network, and to transmit all input signals to the next node without additional signal insertion and photoelectric conversion / electric conversion.

1 is a structure diagram of a wavelength tunable filter system for wavelength division multiplexing (WDM) communication to which the present invention is applied.

2 is an exemplary diagram of a wavelength tunable drop / pass filter system for wavelength division multiplexing (WDM) communications of the present invention.

3 is a power ratio characteristic diagram at each terminal according to the phase difference of the wavelength variable drop / pass filter of the present invention.

4 is a block diagram of a wavelength variable selector according to the present invention;

5 is a structural diagram of a directional coupler-type optical switching unit according to the present invention.

Explanation of symbols for main parts of the drawings

10: multi-wavelength signal generator 12: directional optical coupler

14 Bragg diffraction grating 16 Light path length adjuster

17: variable reflection wavelength transition unit 18: signal control unit

20: receiver 22: optical waveguide

30: pass part 40: optical switch part

50: isolator 70: variable wavelength selector

82 input signal 84 reflected signal of Bragg diffraction grating

In order to achieve the above object, the present invention provides a multi-wavelength signal generator for generating an optical signal composed of several wavelengths, an optical isolator for passing all the incident optical signals and blocking the reflected light, and incident from the optical isolator. Some of the light is sent to the pass portion, and part of the light is sent to the variable wavelength selector, and includes a light switching unit for extracting the light coming back from the variable wavelength selector, and a receiver for receiving the signal extracted from the variable wavelength selector .

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

1 is a structure diagram of a wavelength tunable filter system for wavelength division multiplexing (WDM) communication to which the present invention is applied, and shows a multi-wavelength generator 10 and a multi-wavelength signal 82 for generating a signal having a plurality of wavelengths. A wavelength selector consisting of an optical fiber or planar optical waveguide 22 which can be transmitted, an optical switch unit 40 having two optical paths, and a Bragg diffraction grating 14 capable of reflecting only a part of a signal having multiple wavelengths ( 70), a receiver 20 for receiving the signal extracted by the wavelength selector, and a pass 30 for transmitting all the input signals to the next stage.

In the multi-wavelength generator 10 generating several wavelengths Signal is generated, and propagates through the optical waveguide 22.

The input signal is divided into both paths of the optical switch unit 40 by the first 3dB directional coupler 12 constituting the optical switch unit 40.

The signal proceeding in two directions proceeds with a phase difference of π / 2 + Φ between both paths according to the characteristics of the 3dB directional coupler 12 and the degree of the signal applied to the path length adjuster 16 attached to one path. Signals 90 and 92 input through the 3 dB directional coupler 12 are output to the pass section 30 and the wavelength selector 70.

The signal 92 exiting the wavelength selector 70 applies a control signal of the control unit 18 to the variable reflection wavelength shifting unit 17 attached to the grating element 14 of the optical fiber or the planar waveguide. in Only one wavelength 94 is reflected, and the signal 98 is returned to the input terminal 10 and the receiver 20, respectively.

At this time, the magnitude and the amount of light waves coming out of the receiver 20 and the pass unit 30 can be obtained by adjusting the optical path length controller 16 attached to one path of the optical switch unit 40.

Here, the variable reflection wavelength shifter 17 constituting the wavelength selector 70 is made of a material in which strain is frequently generated due to 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 transmitted to the Bragg diffraction grating element 14 to which the material is attached, thereby changing the lattice period or refractive index of the diffraction grating element 14, and thus the reflection wavelength 94 is changed, and the receiver (drop) ( The signal wavelength 84 coming out 20 is varied.

The wavelengths passing through the pass portion are propagated through the optical waveguide and the light switching unit 40.

FIG. 2 is an exemplary diagram of a wavelength variable drop / pass filter system for wavelength division multiplexing (WDM) communication according to the present invention. As a special application of FIG. 1, the systems of FIG. 1 are connected in series to reflect multiple wavelengths. The other wavelengths represent the system passing back to the pass section.

The input wavelength may be reflected by a specific wavelength or by transmitting 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 is incident to the next system through the pass section, and the second system can reflect a specific wavelength on the same principle as the first system, and can also be transmitted to the next system by adjusting the optical path difference.

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

When a system is constructed by connecting drop / pass filters in series, light waves coming out of the pass section 30 of the first stage by the feedback of the drop / pass filter of the second stage are transmitted to the receiver of the first stage ( Since it may affect 200, the signal is isolated by preventing further progression by the isolator 50.

3 is a power ratio characteristic diagram of each terminal according to the phase difference of the wavelength-variable drop / pass filter according to the present invention. In the system of FIG. Denotes the optical power output from the input unit, the pass unit, and the signal receiving unit, respectively.

As shown in FIG. 3, when the phases of both optical path differences are changed, the optical power output to the signal receiver or the pass unit can be adjusted.

4 is a block diagram of a wavelength tunable selector according to the present invention and is a block diagram of a wavelength tunable selector using Bragg diffraction gratings.

Strain is generated by a material sensitive to signals such as current, voltage, temperature, pressure, and magnetic field from the control unit 18 so that the period or refractive index of the Bragg diffraction grating can be changed at the same time. Or coated.

Bragg diffraction gratings are fabricated on an optical fiber or a planar waveguide, and have a characteristic of reflecting only a specific wavelength, where the reflectance is given by the following equation (1).

here Are given by the following formulas (2) and (3).

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

: coupling coefficient

Bragg wavelength

: The refractive index difference of Bragg diffraction grating is shown.

5 is a structural diagram of a directional coupler-type optical switching unit according to the present invention, and shows an optical switching unit 40 having a structure different from that of the optical switching unit 40 described above.

The optical switching unit 40 may be manufactured using a planar optical waveguide or an optical fiber, and an optical path length adjuster 16 that may adjust the optical path difference of one path, and a directional optical coupler 60 that may cause signal interference while the optical signal proceeds. It consists of).

As described above, the wavelength-variable drop / pass filter system using the optical waveguide for WDM of the present invention can make the overall system small in size, easy to change the wavelength, and has a narrow pass wavelength so that high-speed channel selection is possible. Not only is this possible, it also has the advantage of being able to transmit numerous signals of different wavelengths simultaneously.

In addition, it is possible to transmit to the next node without photoelectric conversion / electric conversion, so that the intermediate system does not need to perform at least electrical processing on traffic transmitted between other nodes, thus making the whole system compact. Therefore, it can be positioned as a foundation technology that enables the development of various technologies of the WDM communication network, which has a ripple effect.

Claims (11)

A wavelength variable drop / pass filter system using an optical waveguide, A multi-wavelength signal generator for generating an optical signal composed of several wavelengths; An optical isolator which passes all the incident optical signals and blocks the reflected light; A part of the light incident from the optical isolator is a pass part, a part of which is sent to a variable wavelength selector, and an optical switching part which extracts light returned from the variable wavelength selector; A wavelength tunable optical drop / pass filter system structure for wavelength division multiple communication comprising a receiver for receiving a signal extracted by a variable wavelength selector. The method of claim 1, wherein the optical switching unit An optical splitter for distributing incident beams to travel through different paths; An optical path length adjuster attached to one or both paths to adjust the pass power to drop power ratio; A wavelength tunable optical drop / pass filter system structure for a wavelength division multiple communication, comprising: an optical splitter for interfering an optical signal traveling in both paths to advance to the next stage. The method of claim 1, wherein the variable wavelength selector Bragg diffraction grating consisting of an optical fiber or an optical waveguide having a structure capable of reflecting a specific wavelength; A variable reflection wavelength shift unit attached to a Bragg diffraction grating capable of applying strain by an applied control signal; And a signal control unit for applying a control signal to the variable reflection wavelength transition unit attached to the Bragg diffraction grating and the diffraction grating. The method of claim 1, A wavelength-variable optical drop / pass filter system structure for wavelength division multiple communication, in which multiple wavelengths can be selected by connecting a wavelength variable drop / pass filter in series. The method of claim 2, wherein the optical path length adjuster A wavelength-variable optical drop / pass filter system structure for wavelength division multiple communication, wherein a material whose length is changed by an applied voltage, a current, or a magnetic field is adhered and contact-coated by an optical waveguide of one or both paths. The method of claim 2, wherein the optical path length adjuster A wavelength-variable optical drop / pass filter system structure for wavelength division multiple communication, comprising: adhering, contacting, and coating a material having a refractive index or a refractive index and a length changed by an applied ultrasonic wave or pressure to an optical waveguide in one or both paths. The method of claim 2, wherein the optical path length adjuster Wavelength division multiple communication wavelengths, characterized in that the adhesion, contact, or coating of a material that changes the refractive index or the refractive index and length at the same time, ultrasonic waves or pressure, the refractive rule and the length is changed by the applied heat to the optical waveguides in one or both paths Variable light drop / pass filter system structure. The optical switch of claim 2, wherein the light switching unit A wavelength characterized by bonding a material whose length is changed by voltage, current, or magnetic field applied to the optical path controller between two paths or a material whose refractive index and length are changed by ultrasonic waves, pressure and heat to an optical waveguide between one path or both paths. Wavelength variable optical drop / pass filter system structure for split multiple communication. 4. The variable wavelength selector of claim 3 A wavelength variable optical drop / pass filter system structure for a wavelength division multiple communication, comprising: bonding and contact-coating a material whose length is changed by a voltage, current, or magnetic field applied by a signal controller to a Bragg diffraction grating. The method of claim 3, wherein the variable wavelength selector A wavelength-variable optical drop / pass filter system structure for wavelength division multiple communication, comprising: adhering, contacting, and coating a refractive index or a material whose refractive index and length are simultaneously changed by Bragg diffraction gratings by an applied ultrasonic wave and pressure. The method of claim 3, wherein the variable wavelength selector Wavelength-variable multi-wavelength wavelength communication light, characterized in that the material applied to the refractive index or the refractive index and the length is changed at the same time by the heat applied by the signal control unit, the material that the refractive index is changed by the intensity of light to the Bragg diffraction grating Drop / pass filter system structure.