KR20090082698A - Photonics microwave filter and filtering method using the same - Google Patents

Abstract

An optical delay line, a superhigh frequency optical filter and a filtering method using the same are provided to couple two or more optical fibers with a multi-wavelength beam generator to produce an optical delay line with high Q-factor. An optical delay line and a superhigh frequency optical filter comprise a modulator(120), an optical delay line(130) and a demodulator(140). The modulator modulates a multi-channel beam pattern according to input signals. The optical delay line is formed by connecting two or more optical fibers having different dispersion characteristics and adds different time delay to the each multi-channel beam pattern. The demodulator is outputted from the optical delay line and generates output signals by demodulating the multi-channel beam pattern.

Description

Optical delay line and ultra-high frequency optical filter and filtering method using same {PHOTONICS MICROWAVE FILTER AND FILTERING METHOD USING THE SAME}

The present invention relates to an optical delay line, and an ultra-high frequency optical filter and a filtering method using the same. In particular, a multi-wavelength beam generator for generating a multi-channel beam pattern from an ultra-wideband supercontinental light and two or more optical fibers having heterogeneous dispersion characteristics are bonded. The present invention relates to an optical delay line providing a high Q factor using an optical delay line unit manufactured by the optical delay line unit, and an ultra-high frequency optical filter and a filtering method using the same.

The microwave filter according to the prior art is manufactured using a micro strip line. In the case of using a micro strip line, a design considering electromagnetic noise is required, and there is a problem in that it is not easy to manufacture an ultrahigh frequency filter having a bandwidth of several GHz or more.

In order to overcome the above problem, an ultra-high frequency filter using photonics technology, in particular microwave photonics technology, has been proposed. Microwave optical technology is commonly used in the design of transversal microwave filters.

An example of a transverse ultra-high frequency filter according to the prior art is shown in FIG. 1.

Referring to FIG. 1, a transverse ultra-high frequency filter according to the prior art includes a multi-channel light source 10, an electro-optic modulator 20, a photo delay line 30, and a photo-electric modulator 40.

The multichannel light source 10 generates and emits multichannel light, that is, light having N wavelengths (channels).

The electro-optic modulator 20 modulates the multichannel light according to the input signal x (t).

The optical delay line 30 adds a different delay to each channel of modulated multichannel light output from the electro-optic modulator 20.

The photo-electric modulator 40 extracts and outputs an output signal y (t) from multichannel light to which different delays are added.

The response of the transversal ultrahigh frequency filter according to the prior art illustrated in FIG. 1, that is, the output signal y (t) with respect to the input signal x (t) may be expressed by Equation 1.

The Q factor of the conventional ultra-high frequency filter is defined as the value of the transverse half-width of the transmission band with respect to the first resonant frequency, and the value is in a 1: 1 relationship with the number of channels of the transverse ultra-high frequency filter. have. Therefore, to have N Q factor values, N channels are required as shown in FIG. 1.

When using N lasers to generate light having N channels or using a single laser and N optical delay lines, N electro-optic modulators and N photo-electric modulators must be used. There is a problem that the manufacturing cost rises.

Figure 2 is a graph showing the frequency response curve of the transverse ultra-high frequency filter according to the prior art.

When the wavelength band of the light source is wide, the wavelength spacing between the optical channels is different. Since the conventional ultra-high frequency filter cannot compensate for the change in the wavelength spacing, the distorted shape as shown in FIG. There is a problem in that the frequency response curve has a form in which the peak of the frequency is distorted and the front half width (FWHM) is widened.

It is an object of the present invention to provide an optical delay line having a high Q factor and an ultra-high frequency optical filter and filtering method using the same by melting and connecting two or more optical fibers having heterogeneous dispersion characteristics to adjust the dispersion slope of the optical fiber.

In accordance with another aspect of the present invention, an optical filter includes: a modulator configured to modulate a multichannel beam pattern according to an input signal; An optical delay line unit formed by connecting two or more optical fibers having heterogeneous dispersion characteristics and adding different time delays to respective channels of the modulated multichannel beam pattern; And a demodulator configured to demodulate a multi-channel beam pattern output from the optical delay line unit and having different delay times to generate an output signal.

An optical filter according to the present invention comprises a light source; And a multi-wavelength beam generator for generating the multi-channel beam pattern from the light emitted from the light source.

The light source preferably comprises an ultra-wideband supercontinuum light source.

The light source may also include an optical amplifier for generating a seed ASE beam; An Er-Yb amplifier for amplifying the seed ASE beam; A nonlinear optical fiber unit converting the amplified seed ASE beam into a nonpolar wideband beam; And a spectral flattening filter for flattening the nonpolar wideband beam output from the nonlinear optical fiber unit.

The multi-wavelength beam generator preferably includes any one of a Fabry-Perot filter, an AWG, a Lyot-Sagnac filter, and a multi-wavelength optical fiber grating filter.

Preferably, the two or more optical fibers are fusion-connected.

The two or more optical fibers may be a combination of single mode optical fiber and distributed compensation optical fiber or a combination of distributed transition optical fiber and distributed compensation optical fiber.

에 의해 결정되는 것이 바람직하다(단, L₁, D₁, S₁은 각각 제1 광섬유의 길이, 분산 및 분산 기울기이며, L₂, D₂, S₂는 각각 제2 광섬유의 길이, 분산 및 분산 기울기이며, D 및 S는 각각 상기 광지연 선로부의 분산 및 분산 기울기임).In the case where the two or more optical fibers include a first optical fiber and a second optical fiber, dispersion characteristics of the optical delay line part may be

It is preferable to determine that L ₁ , D ₁ , S ₁ are the length, dispersion, and dispersion slope of the first optical fiber, respectively, and L ₂ , D ₂ , S ₂ are the length, dispersion, and Dispersion slope, and D and S are the dispersion and dispersion slopes of the optical delay line portion, respectively).

The modulator preferably includes a LiNbO ₃ modulator.

The demodulator preferably includes a photo detector.

The filtering method according to the present invention comprises the steps of: (a) modulating a multichannel beam pattern according to an input signal; (b) a different time for each channel of the multichannel beam pattern modulated by applying the multichannel beam pattern modulated in step (a) to the optical delay line formed by connecting two or more optical fibers having heterogeneous dispersion characteristics; Adding a delay; And (c) generating an output signal from the multi-channel beam pattern having different delay times obtained in step (b).

The filtering method according to the present invention comprises the steps of: generating light before performing step (a); And generating the multichannel beam pattern from the light.

The optical delay line part according to the present invention is formed by connecting two or more optical fibers having heterogeneous dispersion characteristics, and adds a different time delay to each channel of the multichannel beam pattern.

The optical delay line and the ultra-high frequency optical filter and filtering method using the same according to the present invention are manufactured by joining a multi-wavelength beam generator for generating a multi-channel beam pattern from an ultra-wideband supercontinuum light and two or more optical fibers having heterogeneous dispersion characteristics. There is an advantage of having a high Q factor (Q factor) using the optical delay line portion.

In addition, the ultra-high frequency optical filter and filtering method has an advantage that the manufacturing cost can be lowered by using the optical delay line portion manufactured by bonding two or more optical fibers having heterogeneous dispersion characteristics.

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

3 is a schematic diagram illustrating an ultra-high frequency optical filter according to an exemplary embodiment of the present invention.

Referring to FIG. 3, the ultra-high frequency optical filter according to the exemplary embodiment of the present invention includes a light source 100, a multi-wavelength beam generator 110, a modulator 120, an optical delay line unit 130, and a demodulator 140. It includes.

The light source 100 generates and emits ultra-wideband supercontinuum light.

The detailed configuration of the light source 100 will be described with reference to FIG. 4.

4 is a schematic diagram illustrating a light source 100 of an ultra-high frequency optical filter according to an exemplary embodiment of the present invention.

Referring to FIG. 4, the light source 100 includes an optical amplifier 200, an Er-Yb amplifier 210, a nonlinear optical fiber unit 220, and a spectral flattening filter 230.

The optical amplifier 200 produces a seeded spontaneous emission (ASE) beam. The optical amplifier 200 is preferably an erbium doped fiber amplifier.

The Er-Yb amplifier 210 amplifies the seed ASE beam output from the optical amplifier 200. The seed ASE beam may be amplified up to 29 dBm by the Er-Yb amplifier 210.

The nonlinear optical fiber unit 220 converts the amplified seed ASE beam into a nonpolar wideband beam. The nonlinear optical fiber unit 220 preferably includes about 2 km of highly nonlinear dispersion-shifted fiber (HNL-DSF). The amplified seed ASE beam may be converted into a nonpolar wideband beam having a bandwidth of 130 nm by the nonlinear optical fiber unit 220.

The spectral flattening filter 230 flattens the non-polar broadband beam output from the nonlinear optical fiber unit 220 to generate a rectangular continuous-wave super-continuum beam. As the spectral flattening filter 230, an optical fiber long period grating or a spatial light modulator may be used.

The space-optic modulator inputs the light output from the optical fiber to the diffraction grating using a collimation lens, decomposes the wavelength by wavelength with respect to the space, and then inputs the decomposed light into a digital mirror device for flattening. To perform.

5A and 5B are graphs showing the spectrum of light before and after planarization. When the light having the spectrum shown in FIG. 5A passes through the spectral planarization filter 230, the planarization is performed as shown in FIG. 5B.

The multi-wavelength beam generator 110 generates a multi-channel beam pattern from the square spectral beam emitted from the light source 100.

6A and 6B are graphs showing spectra of multichannel beam patterns of a multi-wavelength beam generator used in an ultrahigh frequency optical filter according to an exemplary embodiment of the present invention, and show spectrums having spectral bandwidths of 28 nm and 50 nm, respectively. .

The multi-wavelength beam generator 110 preferably includes any one of a Fabry-Perot filter, an AWG, a Lyot-Sagnac filter, and a multi-wavelength fiber grating filter.

In an embodiment in which the Fabry-Perot filter is used as the multi-wavelength beam generator 110, the relationship between the wavelength and the frequency is expressed by Equation 2 below.

(단, c는 진공에서의 광속)

(Where c is the luminous flux under vacuum)

The Fabry-Perot filter is a filter utilizing the interference effect of multiple reflections of etalon, and the light output from the Fabry-Perot filter has a constant frequency interval Δf in the optical frequency domain. When a constant frequency interval is converted into a wavelength interval Δλ, the wavelength interval Δλ is proportional to the square of the wavelength λ, as shown in Equation 2. Equation 2 means that when the wavelength band of the light source is wide, the wavelength spacing between each optical channel changes. In this case, the time delay of each optical channel is expressed as the product of the center wavelength of each optical channel and the dispersion of the optical time delay line at that wavelength.

Ultrahigh frequency filters with high Q factors require that a number of optical channels have a constant time delay. Since the wavelength spacing of the optical channels is invariant, the dispersion of optical time delay lines should be controlled. The optical delay line unit 130 is used to adjust the dispersion of the optical time delay line. The optical delay line unit 130 will be described later.

The modulator 120, which is an electro-optical converter, modulates the multi-channel beam pattern, which is the output of the multi-wavelength beam generator 110, according to the RF input signal x (t).

The optical delay line unit 130 is formed by connecting two or more optical fibers having heterogeneous dispersion characteristics in order to control the dispersion of the optical time delay line, and for each channel of the multi-channel beam pattern modulated by the modulator 120. Add different time delays.

The magnitude of the time delay of each channel is given by the product of the wavelength interval and the dispersion. The dispersion curve of the optical fiber may be approximated as a linear function of the wavelength, and the slope may be defined as the dispersion slope. At this time, in order to make the time delay difference between adjacent optical channels and the time delay calculated at the center wavelength of each channel constant, the specific dispersion D and dispersion slope S of the optical delay line unit 130 should be obtained.

When the optical delay line unit 130 is formed by melting and connecting the first optical fiber and the second optical fiber having heterogeneous dispersion characteristics, the specific dispersion D and the dispersion slope S of the optical delay line unit 130 are obtained from Equation 3 below. Can be.

Here, L ₁ , D ₁ , and S ₁ are the length, dispersion, and dispersion slope of the first optical fiber, respectively, and L ₂ , D ₂ , S ₂ are the length, dispersion, and dispersion slope of the second optical fiber, respectively.

That is, the dispersion characteristics of the optical delay line unit 130 are determined by the length, dispersion, and dispersion slope of the first optical fiber and the second optical fiber. Therefore, when the first optical fiber and the second optical fiber having a predetermined dispersion and dispersion slope are cut and connected to a predetermined length, the line part 130 having the desired optical delay dispersion characteristics can be manufactured.

는 역행렬을 가져야 한다. 역행렬이 존재하는 광섬유의 조합으로는 단일 모드 광섬유(single-mode fiber) 및 분산 보상 광섬유(dispersion-compensated fiber)의 조합 또는 분산 천이 광섬유(dispersion-shifted fiber) 및 분산 보상 광섬유의 조합이 있다.procession

Must have an inverse matrix. Combinations of optical fibers with inverse matrix include a combination of single-mode fibers and dispersion-compensated fibers or a combination of dispersion-shifted and dispersion compensation fibers.

7 is a graph showing group delay according to the wavelength of the optical delay line unit 130 used in the ultra-high frequency optical filter according to the exemplary embodiment of the present invention. As shown in Fig. 7, it can be seen that the time delay difference between the adjacent optical channels and the time delay calculated at the center wavelength of each channel is constant.

The demodulator 140, an opto-electric converter, outputs the RF output signal y (t) by demodulating a multi-channel beam pattern output from the optical delay line unit 130 and having different delay times. The demodulator 140 may include a photo-detector.

8A and 8B are graphs showing the frequency response of an ultrahigh frequency optical filter according to an exemplary embodiment of the present invention, which are frequency response curves when a multichannel beam pattern having a spectrum shown in FIGS. 6A and 6B is applied, respectively. . It can be seen that the frequency response is not distorted, unlike the frequency response curve of the transversal ultrahigh frequency filter shown in FIG. 2.

9 is a graph showing the Q factor of the conventional ultra-high frequency filter and the ultra-high optical filter according to the embodiment of the present invention.

9, it can be seen that the ultrahigh frequency filter according to the present invention has a high Q factor compared to the ultra high frequency filter using only a single mode optical fiber or a dispersion compensation optical fiber.

10 is a flowchart illustrating a filtering method according to the present invention.

Referring to FIG. 10, an ultra-wideband supercontinuum light is generated (S100).

The process of generating the ultra-wideband supercontinuum light is as follows.

First, the seed ASE beam is amplified and the amplified seed ASE beam is passed through a nonlinear optical fiber to be converted into a nonpolar wideband beam. Next, the non-polar wideband beam is passed through the space-light modulator and flattened.

Next, the ultra-wideband supercontinuum light is passed through a multi-wavelength beam generator such as a Fabry-Perot filter, an AWG, a Lyot-Sagnac filter, or a multi-wavelength fiber grating filter to generate a multichannel beam pattern (S110).

Next, the multi-channel beam pattern and the input signal is input to the electro-optic modulator to modulate the multi-channel beam pattern in accordance with the input signal (S120).

Next, the modulated multi-channel beam pattern is applied to the optical delay line formed by connecting two or more optical fibers having heterogeneous dispersion characteristics to add a different time delay for each channel of the modulated multi-channel beam pattern (S130). ).

Next, an output signal is generated by applying a multi-channel beam pattern having different delay times to the photo-electric modulator (S140).

1 is a schematic diagram showing a transverse ultra-high frequency filter according to the prior art;

Figure 2 is a graph showing the frequency response curve of the transverse ultra-high frequency filter according to the prior art.

3 is a schematic diagram illustrating an ultrahigh frequency optical filter according to an embodiment of the present invention;

4 is a schematic view showing a light source of the ultra-high frequency optical filter according to the embodiment of the present invention;

5A and 5B are graphs showing the spectrum of light before and after planarization.

6A and 6B are graphs showing spectra of multichannel beam patterns of a multiwavelength beam generator used in an ultrahigh frequency optical filter according to an exemplary embodiment of the present invention.

FIG. 7 is a graph showing group delay according to wavelength of an optical delay line part used in an ultrahigh frequency optical filter according to an exemplary embodiment of the present invention. FIG.

8A and 8B are graphs showing the frequency response of an ultrahigh frequency optical filter according to an embodiment of the present invention.

9 is a graph showing the Q factor of the conventional ultra-high frequency filter and the ultra-high optical filter according to the embodiment of the present invention.

10 is a flowchart illustrating a filtering method according to the present invention.

Claims (30)

A modulator for modulating the multichannel beam pattern according to an input signal; An optical delay line unit formed by connecting two or more optical fibers having heterogeneous dispersion characteristics and adding different time delays to respective channels of the modulated multichannel beam pattern; And A demodulator configured to demodulate a multi-channel beam pattern having a different delay time from the optical delay line unit to generate an output signal Optical filter comprising a. The method of claim 1, Light source; And A multi-wavelength beam generator for generating the multi-channel beam pattern from the light emitted from the light source Optical filter, characterized in that it further comprises. The method of claim 2, The light source comprises an ultra-wideband supercontinuum light source. The method of claim 2, The light source is An optical amplifier for generating a seed ASE beam; An Er-Yb amplifier for amplifying the seed ASE beam; A nonlinear optical fiber unit converting the amplified seed ASE beam into a nonpolar wideband beam; And A spectral flattening filter for flattening the nonpolar wideband beam output from the nonlinear optical fiber part. Optical filter comprising a. The method of claim 4, wherein And the optical amplifier comprises an erbium-doped optical amplifier. The method of claim 4, wherein The nonlinear optical fiber unit comprises a highly nonlinear dispersion-shifted fiber (HNL-DSF). The method of claim 4, wherein The spectral flattening filter comprises a spatial-light modulator. The method of claim 2, The multi-wavelength beam generator comprises any one of a Fabry-Perot filter, an AWG, a Lyot-Sagnac filter, and a multi-wavelength optical fiber grating filter. The method of claim 1, And said at least two optical fibers are fusion-connected. The method of claim 1, Wherein said two or more optical fibers comprise a single mode optical fiber and a dispersion compensation optical fiber. The method of claim 1, Wherein said at least two optical fibers comprise a dispersion transition optical fiber and a dispersion compensation optical fiber. The method of claim 1, In the case where the two or more optical fibers include a first optical fiber and a second optical fiber, dispersion characteristics of the optical delay line part may be

Optical filters (wherein L ₁ , D ₁ , and S ₁ are the length, dispersion, and dispersion slope of the first optical fiber, respectively, and L ₂ , D ₂ , and S ₂ are the lengths of the second optical fiber, respectively). , Dispersion and dispersion slope, D and S are the dispersion and dispersion slope of the optical delay line portion, respectively). The method of claim 1, The modulator comprises an LiNbO ₃ modulator. The method of claim 1, The demodulation unit includes a photo detector. (a) modulating the multichannel beam pattern according to the input signal; (b) a different time for each channel of the multichannel beam pattern modulated by applying the multichannel beam pattern modulated in step (a) to the optical delay line formed by connecting two or more optical fibers having heterogeneous dispersion characteristics; Adding a delay; And (c) generating an output signal from the multi-channel beam pattern having different delay times obtained in step (b) Filtering method comprising a. The method of claim 15, Before performing step (a) above, Generating light; And Generating the multichannel beam pattern from the light. The method of claim 16, And the light is ultra-wideband supercontinuum light. The method of claim 16, Generating the light, Amplifying the seed ASE beam; Converting the amplified seed ASE beam into a nonpolar wideband beam; And Planarizing the nonpolar broadband beam Filtering method comprising a. The method of claim 18, Converting the amplified seed ASE beam into a nonpolar wideband beam comprising passing the amplified seed ASE beam through a nonlinear optical fiber. The method of claim 18, Planarizing the nonpolar wideband beam comprises passing the nonpolar wideband beam through a spatial-light modulator. The method of claim 16, Generating the multichannel beam pattern from the light may include passing the light through any one of a Fabry-Perot filter, an AWG, a Lyot-Sagnac filter, and a multi-wavelength fiber grating filter to generate the multichannel beam pattern. Filtering method comprising a. The method of claim 15, And the at least two optical fibers are fusion-connected. The method of claim 15, Wherein said at least two optical fibers comprise a single mode optical fiber and a dispersion compensation optical fiber. The method of claim 15, Wherein said at least two optical fibers comprise a distributed transition optical fiber and a distributed compensation optical fiber. The method of claim 15, In the case where the two or more optical fibers include a first optical fiber and a second optical fiber, dispersion characteristics of the optical delay line part may be

Filtering method, characterized in that (L ₁ , D ₁ , S ₁ are the length, dispersion and dispersion slope of the first optical fiber, respectively, L ₂ , D ₂ , S ₂ are the length of the second optical fiber, respectively) , Dispersion and dispersion slope, D and S are the dispersion and dispersion slope of the optical delay line portion, respectively). The optical delay line unit is formed by connecting two or more optical fibers having heterogeneous dispersion characteristics, and adding different time delays to each channel of the multichannel beam pattern. The method of claim 26, And the two or more optical fibers are fusion-connected. The method of claim 26, And the two or more optical fibers include a single mode optical fiber and a dispersion compensation optical fiber. The method of claim 26, And the two or more optical fibers include a dispersion transition optical fiber and a dispersion compensation optical fiber. The method of claim 26, In the case where the two or more optical fibers include a first optical fiber and a second optical fiber, dispersion characteristics of the optical delay line part may be

The optical delay line portion, wherein L ₁ , D ₁ , and S ₁ are the length, dispersion, and dispersion slope of the first optical fiber, respectively, and L ₂ , D ₂ , and S ₂ are each the second optical fiber. Is the length, the dispersion and the dispersion slope of D, and S and S are the dispersion and dispersion slope of the optical delay line portion, respectively).

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