KR101013030B1 - Dual wavelength optical fiber laser, photonic microwave notch filter and methods for notch frequency turning - Google Patents

Abstract

The present invention relates to a double-wavelength fiber laser, a photonic microwave notch filter, and a method for varying the notch frequency, wherein the photonic microwave notch filter applies different strains to each of the mounted first and second optical fiber gratings by rotation. Optically coupled to a transducer, the first optical fiber grating reflecting light of the first wavelength by strain of the transducer, the second optical fiber grating reflecting light of the second wavelength by strain of the transducer, and A bi-wavelength optical fiber comprising a resonator for oscillating the light of the first wavelength and the second wavelength reflected, and the electrical power to modulate the light of the first wavelength and the light of the second wavelength output from the bi-wavelength optical fiber laser to the RF wave To provide different time delays to the light modulator, the light of the first wavelength and the light of the second wavelength modulated by the electro-optic modulator. And a photodetector for detecting the optical fiber spool and the light having a first wavelength and the second wavelength having passed through the optical fiber spool with microwaves.

Photonic microwave, double wavelength fiber laser, fiber optic grating

Description

DUAL WAVELENGTH OPTICAL FIBER LASER, PHOTONIC MICROWAVE NOTCH FILTER AND METHODS FOR NOTCH FREQUENCY TURNING}

The present invention relates to a double-wavelength fiber laser, a photonic microwave notch filter, and a method of varying the notch frequency. The present invention relates to a frequency response by varying the wavelength spacing of two lights oscillating according to the degree of deformation of a transducer and adjusting the time delay of the two lights. A device is capable of varying the frequency of a microwave notch in a characteristic.

Recently, the use of a wireless subscriber network, a phased array antenna, and a radio over fiber (ROF) system based on the optical technology, the microwave signal generation has attracted a lot of attention. The technique using the light has many advantages, such as the use of an optical fiber with no interference phenomenon due to electromagnetic waves, a large bandwidth, and low loss.

Microwave notch filters are the main components of RF signal processing and are implemented in various ways. Conventional microwave notch filter technology using light waves modulates optical signals of different wavelengths into RF signals, passes through a dispersion medium (ex. Chirped FBG, optical fiber), and then detects the beating signals of the two light sources. The frequency response of the notches was changed by detecting the RF signal of the notch.

However, the above-described prior art is complicated in structure because the dispersion value has to be adjusted for changing the notch frequency of microwaves. In addition, when the optical fiber Bragg grating is used, there is a limit in the variation of the dispersion value, and there is a problem in that the variable frequency range is limited.

The present invention is to solve the above problems, by using a specially designed transducer to implement a double-wavelength fiber laser light source of varying the oscillation wavelength according to the degree of deformation of the transducer, and to adjust the time delay to the two light output Accordingly, an object of the present invention is to provide a bi-wavelength fiber laser, a photonic microwave notch filter, and a notch filter frequency variable method capable of varying frequency response characteristics.

According to an embodiment of the present invention, a bi-wavelength fiber laser includes a transducer for applying different strains to a mounted first optical fiber grating and a second optical fiber grating by rotation, and a first strain by the strain of the transducer. A first optical fiber lattice that reflects light of a wavelength, a second optical fiber lattice that reflects light of a second wavelength by strain of the transducer, and optically coupled to the transducer and having a reflected light and a second wavelength And a resonator for oscillating light.

The transducer may further include a first optical fiber grid and a second optical fiber mounted as the shape of the first disk, the circumference of the first disk, and a shape change in response to rotation of the second and second rotatable disks. It further includes a plate for applying different strains to the grating.

In addition, the photonic microwave notch filter according to an embodiment of the present invention for achieving the above object is RF of the light of the first wavelength and the light of the second wavelength and the wavelength of the second wavelength that is output from the double wavelength fiber laser An electro-optic modulator for modulating with a wave, an optical fiber spool that gives a different time delay to light of a first wavelength and a light of a second wavelength modulated by the electro-optic modulator, and light and a second wavelength of a first wavelength passing through the optical fiber spool It includes a photodetector for detecting the light of the microwave.

In addition, the method of varying the frequency of the photonic microwave notch filter according to an embodiment of the present invention for achieving the above object, the step of applying different strains to the first optical fiber grating and the second optical fiber grid by the rotation of the transducer, Reflecting light of a first wavelength by a first optical fiber grid; reflecting light of a second wavelength by a second optical fiber grid; resonating light of the first wavelength and light of a second wavelength; resonance Modulating the light of the first wavelength and the light of the second wavelength into RF waves, imparting different time delays to the modulated light of the first wavelength and light of the second wavelength, and giving the first different time delays. Detecting the light of the wavelength and the light of the second wavelength with microwaves.

Photonic microwave notch filter according to an embodiment of the present invention, by varying the wavelength interval of the light output from a double-wavelength fiber laser using a low-cost semiconductor optical amplifier and a fiber grating using a specially designed transducer, the frequency of the notch filter There is an advantage that can be easily changed.

In addition, by implementing a microwave notch filter using light, there is no interference phenomenon caused by electromagnetic waves, and the optical fiber with low loss can be used, which can be usefully used for optical communication and ROF systems.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the following description of the present invention, it will be omitted if the description of related known functions or configurations may unnecessarily obscure the subject matter of the present invention.

1 is a block diagram of a photonic microwave notch filter according to an embodiment of the present invention.

Referring to FIG. 1, the photonic microwave notch filter according to an exemplary embodiment includes a resonator 110, 112, and 114, a semiconductor optical amplifier 120, a circulator 130, a polarization controller 140, 142, and a light splitter ( 150), couplers 152 and 154, an electro-optic modulator 160, an optical amplifier 170, an optical fiber spool 180, a photodetector 190, and a transducer 200. In addition, the bi-wavelength optical fiber laser according to an embodiment of the present invention, the resonator (110, 112, 114), semiconductor optical amplifier 120, circulator 130, polarization controllers 140, 142, light Divider 150, coupler 152, 154 and transducer 200. In addition, the transducer includes an optical fiber grating 210, 212, a flat plate 220, a first disc 230, and a second disc 240.

The resonator includes a main resonator 110, a first auxiliary resonator 112, and a second auxiliary resonator 114. The number of the auxiliary resonators may be two or more. The main resonator 110, the first auxiliary resonator 112 and the second auxiliary resonator 114 are optically connected to the transducer, resonating the light of the first and second wavelengths reflected from the transducer. Resonance conditions of the main resonator 110, the first sub-resonator 112 and the second sub-resonator 114 are different, respectively, so oscillation is the main resonator 110 and the first and second sub-resonators 112, 114 Is possible when the resonance condition of Therefore, a bi-wavelength laser light source of a single longitudinal mode can be obtained through the plurality of resonators.

The semiconductor optical amplifier (SOA) 120 amplifies a plurality of lights simultaneously. The semiconductor optical amplifier may amplify light of two wavelengths or more differently from an erbium doped fiber amplifier (EDFA) due to non-uniform gene broadening.

The circulator 130 optically connects the transducer and the resonator. The circulator 130 may be connected to the main resonator 110. When the circulator 130 is connected to the main resonator 110, the first port and the third port of the circulator 130 are connected to both ends of the main resonator 110 and the first port of the circulator 130 is formed. Two ports are connected to the transducer. Specifically, the optical signal input to the first port of the circulator 130 is output to the second port, the light output from the second port is reflected by the first optical fiber grid and the second optical fiber grid at a different wavelength, respectively, and again It is input to the second port and is output through the third port of the circulator.

Polarization controllers (PCs) 140 and 142 are optically connected to the resonator and control polarization to minimize differences in light intensity of two different wavelengths so that the light of the two wavelengths can be stably Make it oscillate. The polarization controller may be included in each resonator. Polarization control apparatus according to an embodiment of the present invention is composed of a first polarization controller 140 connected to the first auxiliary resonator and a second polarization controller 142 connected to the second auxiliary resonator.

The light splitter 150 is optically connected to the resonator, allows a part of the light to circulate in the resonator, and emits the rest of the light to the outside of the resonator. The light splitter 150 according to an embodiment of the present invention may be connected to the main resonator 110. In addition, the optical splitter 150 may use a 9: 1 optical fiber coupler. In this case, 90% of the light is circulated into the resonator while only the remaining 10% of the light is emitted out of the resonator. In addition, when the photonic microwave notch filter includes a main resonator 110, a first auxiliary resonator 112, and a second auxiliary resonator 114, optically connected between the resonators through couplers 152 and 154. do. That is, the first coupler 152 may connect the main resonator 110 and the first auxiliary resonator 112, and the second coupler 154 may connect the main resonator 110 and the second auxiliary resonator 114. The coupler according to an embodiment of the present invention may use a 1: 1 coupler in the form of a 2 * 2 output terminal. In this case, the ratio of light is divided into 50:50, and some of the couplers circulate inside the coupler. Emits out.

An electro-optic modulator (EOM) 160 modulates the light of the first wavelength and the light of the second wavelength that are output from the light source with RF. Specifically, the electro-optic modulator 160 receives two lights having different wavelengths, and modulates the two lights into RF signals by the RF signal of the network analyzer. Examples of the RF signal may include microwaves.

The optical amplifier 170 amplifies the light of the first wavelength and the light of the second wavelength modulated by the electro-optic modulator 160. The optical amplifier according to an embodiment of the present invention may be an Erbium Doped Fiber Amplifier (EDFA).

Synthetic Mineral Fiber (SMF) 180 imparts different time delays to light of a first wavelength and light of a second wavelength that are modulated in the electro-optic modulator 160 or amplified in the optical amplifier 170. do. The optical fiber spool 180 has two light of different wavelengths passing through different time delays to form a two-tap notch filter.

A photonic detector (PD) 190 detects light of two wavelengths having a time delay as the microwave passes through the optical fiber spool 180. The photodetector 190 preferably has a fast response speed and a wider bandwidth than the microwave frequency of the desired RF signal. The frequency of the stop band of the notch detected by the photodetector 190 is controlled according to the wavelength interval of the light reflected from the first optical fiber grating and the second optical fiber grating through the transducer.

는 아래의 [수학식 1]을 통해 표현된다.Output of the photodetector 190

Is expressed through Equation 1 below.

Here, f is a frequency used when modulating the light of the first wavelength and the light of the second wavelength by the RF wave in the electro-optic modulator, and Δτ is a relative time delay difference between the two light of different wavelengths Corresponding. That is, the microwave detected by the photodetector has a stop band that varies with the time delay of the light of the first wavelength and the light of the second wavelength.

In [Equation 1], the notch position is given by [Equation 2] below.

Where N corresponds to 0, 1, 2 ..., D corresponds to the dispersion value of the optical fiber spool, and λλ represents the wavelength difference between the two lights.

That is, through [Equation 1] and [Equation 2], it can be seen that the frequency position of the stop band of the notch filter can be changed by adjusting the wavelength gap between the two lights. The wavelength gap between the two lights may be changed while changing the rotation angle of the transducer 200.

The transducer 200 is optically connected to the resonator and exerts different strains on the first and second fiber gratings mounted by rotation. The transducer 200 includes a first optical fiber grating 210, a second optical fiber grating 212, a flat plate 220, a first disc 230, and a second disc 240. The configuration of the specific transducer will be described in more detail with reference to FIG. 2.

2 is a perspective view of a transducer according to an embodiment of the present invention.

Referring to FIG. 2, the transducer 200 includes a first optical fiber grating 210, a second optical fiber grating 212, a flat plate 220, a first disc 230, a second disc 240, and a support 250. 252), and fixing screws 260, 262, 264, and 266.

The first and second optical fiber grids 210 and 212 reflect light of different wavelengths by the strain of the transducer. That is, the first and second optical fiber grids 210 and 212 serve as band filters for selecting and passing two wavelengths. The first, second, and optical fiber grids 210 and 212 receive two lights through the second port of the circulator 130, reflect the light of the first wavelength and the light of the second wavelength, and again the circulator 130 Input through the second port.

The flat plate 220 is mounted with the first and second optical fiber grids 210 and 212, and applies different strains to the first and second optical fiber grids 210 and 212 as the shape of the flat plate is deformed.

The first disc 230 is a fixed disc, the second disc 240 is open in the form of a ring, it is rotatable in a form surrounding the first disc 230. The rotation angle of the second disc 240 can be precisely controlled by a stage (not shown in FIG. 2).

The supports 250 and 252 have long grooves and are connected to the first disc 230 and the second disc 240 through fixing screws 260, 262, 264, and 266, respectively.

When the second disc 240 is rotated while the first disc 230 is fixed, the fixing screws 260 and 264 located on the second disc 240 together with the second disc 240. While rotating, the fixing screws 262 and 266 positioned on the first disc 230 do not move, and thus the flat plate 220 is deformed into an S shape.

As a result, a strain applied to the first optical fiber grid 210 attached to the flat plate 220 is applied, and a strain applied to the second optical fiber grid 212 is applied. As a result, the reflection wavelengths of the first optical fiber lattice 210 and the second optical fiber lattice 212 which have received different strains are shifted in different directions. The degree of movement is approximately proportional to the rotation angle θ of the second disc 240. Through the above method, it is possible to change the wavelength spacing of the two wavelengths oscillating by changing the shape of the transducer, and as a result, the notch frequency of the notch filter can be changed.

According to an embodiment of the present disclosure, a method of changing a frequency through a notch filter may include applying different strains to first and second optical fiber grids by rotating a transducer, reflecting light of a first wavelength by the first optical fiber grids, A second optical fiber grating reflects light of a second wavelength, the light of the first and second wavelengths is resonated, the light of the resonated first and second wavelengths is modulated into an RF wave, and the modulated first and second Imparting different time delays to light of wavelengths and detecting microwaves of light of the first and second wavelengths due to the different time delays. The frequency interval of the microwaves detected by the photodetector is controlled using the angle of rotation of the transducer and has a stop band that varies with the time delayed.

3 is a diagram illustrating a frequency response characteristic of a photonic microwave notch filter according to an exemplary embodiment of the present invention. When the optical fiber spool used in the above embodiment is 5 km, that is, when the dispersion value D is 85 ps / nm (17 ps / nm / km * 5 km = 85 ps / nm), the wavelength interval between the two lights is 2 nm (310) and 3 nm. At 320, the frequency response characteristics of the notch filter are shown.

Referring to FIG. 3, it can be seen that as the wavelength spacing of the two lights changes to 2 nm 310 and 3 nm 320, the frequency spacing of the stop band of the notch filter is varied.

4 is a diagram illustrating a frequency response characteristic according to a rotation angle of a transducer in a photonic microwave notch filter using a double wavelength fiber laser according to an exemplary embodiment of the present invention.

Referring to FIG. 4, the frequency response characteristic is that light having different wavelengths resonates according to the rotation angle of the transducer, and thus stop bands of the notch filter as the interval of the wavelength is changed through the transducer. Different characteristics appear at the frequency of. In the embodiment of FIG. 4, the wavelength spacing of each of the double-wavelength fiber lasers corresponds to 5.0 nm (410), 3.1 nm (420), 2,1 nm (430), 1.3 nm (440), and 0.85 nm (450).

While specific embodiments of the present invention have been illustrated and described, the technical idea of the present invention is not limited to the accompanying drawings and the above description, and various modifications can be made without departing from the spirit of the present invention. It is obvious to those skilled in the art, and such modifications will be regarded as belonging to the claims of the present invention without departing from the spirit of the present invention.

1 is a block diagram of a photonic microwave notch filter according to an embodiment of the present invention.

2 is a perspective view of a transducer according to an embodiment of the present invention.

3 is a diagram illustrating a frequency response characteristic of a photonic microwave notch filter according to an exemplary embodiment of the present invention.

4 is a diagram illustrating a frequency response characteristic according to a rotation angle of a transducer in a photonic microwave notch filter using a double wavelength fiber laser according to an exemplary embodiment of the present invention.

Claims (10)

A transducer that applies strain to the mounted first optical fiber grating and the second optical fiber grating different from each other by rotation; The first optical fiber grating reflecting light of a first wavelength by strain of the transducer; The second optical fiber grating reflecting light of a second wavelength by strain of the transducer; And And a resonator optically coupled to the transducer, the resonator oscillating light of a reflected first wavelength and light of a second wavelength. The method of claim 1, wherein the transducer, First disc; A second disc rotatable surrounding the circumference of the first disc and And a flat plate for applying different strain to the mounted first optical fiber grating and the second optical fiber grating as the shape of the second disc changes as the second disc rotates. The method of claim 2, The plate is bent in an S shape in response to the rotation of the second disc in a state where the first disc is fixed, Applying a strain to the first optical fiber grating, and applying a strain to the second optical fiber grating. The method of claim 1, wherein the resonator, Main resonator; And And a plurality of auxiliary resonators optically coupled to the main resonator, each having a different resonance condition. The method of claim 1, And a semiconductor optical amplifier optically coupled to the resonator and simultaneously amplifying a plurality of lights. A bi-wavelength fiber laser according to any one of claims 1 to 5; An electro-optic modulator for modulating the light of the first wavelength and the light of the second wavelength output by the double wavelength fiber laser into RF waves; An optical fiber spool for imparting different time delays to light of a first wavelength and light of a second wavelength modulated by the electro-optic modulator; And A photonic microwave notch filter comprising a photodetector for detecting light of a first wavelength and a light of a second wavelength that have passed through the optical fiber spool with microwaves. The method of claim 6, And controlling the microwave frequency spacing of the light of the first wavelength and the light of the second wavelength detected by the photodetector using the rotation angle of the transducer. The method of claim 6, The photonic microwave notch filter characterized in that the microwave detected by the photodetector has a stop band which varies with the time delay applied to the light of the first wavelength and the light of the second wavelength. Applying different strains to the first optical fiber grating and the second optical fiber grating by rotation of the transducer; Reflecting light of a first wavelength by the first optical fiber grating; Reflecting light of a second wavelength by the second optical fiber grating; Resonating the light of the first wavelength and the light of the second wavelength; Modulating the resonated light of the first wavelength and the light of the second wavelength into RF waves; Imparting different time delays to the modulated light of the first wavelength and the second wavelength of light; And Detecting the light of the first wavelength and the light of the second wavelength with the different time delays with a microwave. The method of claim 9, And a frequency interval of the detected microwaves by using the rotation angle of the transducer.

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