WO1999010761A2 - Filtre quasi rectangulaire - Google Patents

Filtre quasi rectangulaire Download PDF

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Publication number
WO1999010761A2
WO1999010761A2 PCT/DE1998/002575 DE9802575W WO9910761A2 WO 1999010761 A2 WO1999010761 A2 WO 1999010761A2 DE 9802575 W DE9802575 W DE 9802575W WO 9910761 A2 WO9910761 A2 WO 9910761A2
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WO
WIPO (PCT)
Prior art keywords
optical
coupler
filter according
filter
power coupling
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Ceased
Application number
PCT/DE1998/002575
Other languages
German (de)
English (en)
Other versions
WO1999010761A3 (fr
Inventor
Helmut BÜNNING
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Fraunhofer Institut fuer Nachrichtentechnik Heinrich Hertz Institute HHI
Original Assignee
Fraunhofer Institut fuer Nachrichtentechnik Heinrich Hertz Institute HHI
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Fraunhofer Institut fuer Nachrichtentechnik Heinrich Hertz Institute HHI filed Critical Fraunhofer Institut fuer Nachrichtentechnik Heinrich Hertz Institute HHI
Publication of WO1999010761A2 publication Critical patent/WO1999010761A2/fr
Publication of WO1999010761A3 publication Critical patent/WO1999010761A3/fr
Anticipated expiration legal-status Critical
Ceased legal-status Critical Current

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Classifications

    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
    • G02B6/24—Coupling light guides
    • G02B6/26—Optical coupling means
    • G02B6/28—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals
    • G02B6/293—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals with wavelength selective means
    • G02B6/29346—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals with wavelength selective means operating by wave or beam interference
    • G02B6/29358—Multiple beam interferometer external to a light guide, e.g. Fabry-Pérot, etalon, VIPA plate, OTDL plate, continuous interferometer, parallel plate resonator

Definitions

  • the invention relates to a quasi-rectangular filter for electromagnetic waves.
  • Such filters can be designed both as optical and as electrical filters.
  • optical filters With optical filters, the intensity (neutral filter such as gray filter, gray wedges), the spectral composition (absorption filter, interference filter such as line filter, edge filter, waveguide filter with reflective fiber grating, AWG - arrayed waveguide grating) or the polarization state (polarization filter) of the light can be changed.
  • These filters are key components in optical transmission systems that use the WDM (wavelength division multiplexing) or OFDM (optical frequency division multiplexing) technology.
  • WDM wavelength division multiplexing
  • OFDM optical frequency division multiplexing
  • WDM filters based on fuse couplers for low-loss separation or merging of WDM signals and in optical direct receivers are tunable filters, such as Fabry-Perot filters, for frequency selection of OFDM signals and for suppression of ASE (amplified spontaneous emission - Light noise) from optical fiber amplifiers.
  • tunable filters such as Fabry-Perot filters, for frequency selection of OFDM signals and for suppression of ASE (amplified spontaneous emission - Light noise) from optical fiber amplifiers.
  • the filters currently available are limited in their selection effect and their filter properties are largely determined by the design principle used.
  • the mirror / resonator surfaces of such filters must be of very good quality, i.e. the power reflection factor must be> 0.95.
  • the implementation of such a power reflection factor and the mechanical structure are associated with high costs.
  • optical quasi-rectangular filters consist of a
  • the transmission properties of the optical resonator are surprisingly influenced to such an extent that a changed, novel transmission behavior results.
  • the function of the optical quasi-rectangular filter according to the invention is a periodic quasi-rectangular filter with a lower equidistant with respect to the optical frequency Pass-through and high blocking attenuation in the adjacent channel with a very flat course of the attenuation in the transmission and reflection range and with a broad quasi-linearly increasing or decreasing attenuation in the frequency range between the extreme values.
  • an optical input signal (complex field size) is fed in, which is divided into two parts that are phase-shifted by 90 degrees and differently damped. These signals pass through the two waveguides of equal length to an optical resonator, which is characterized by the Fabry-Perot transfer function. Each of the two signals leads to a wave reflected by the resonator and transmitted through the resonator. These four waves then run back in pairs over the two waveguides of the same length to the pre-coupler, where they overlap constructively and in phase with the same polarization state, so that complementary power transfer functions with quasi-rectangular characteristics result at the lower and at the upper output.
  • the optical power amplitudes of the quasi-rectangular optical filter depend on the polarization state of the light, on the power losses and the reflectivity of the mirror interfaces, the power losses in the optical resonator and in the pre-coupler and also on the attenuation of the optical fibers and the optical input connectors.
  • the frequency dependence of the power transfer function is determined by the lengths and the refractive index of the optical fibers in the resonance path of the optical resonator.
  • the mirrors are either formed from dielectric layers on the end faces of the substrate (for example by vapor deposition of the end faces of the wafer) or metal mirrors, which are arranged in pre-etched slots at the ends of the resonance path, or are Bragg gratings, which are used for example in the construction of integrated technology into the waveguide.
  • a 3dB coupler with an optical fiber bridge on the output side can also be used. This has two reflective inputs that can be connected either at the ends of the longitudinal or the cross path.
  • the optical resonator with the desired Fabry-Perot transfer function can also be constructed from two 2x2 couplers bridged on the output side, which are connected in series via a bridge on the input side.
  • the last variant for a Fabry-Perot resonator consists of two 2x2 couplers connected in a Mach-Zehnder arrangement with four mirrors on conductors of the same length and a detour line between the two couplers.
  • each of the above-mentioned resonators is preceded by a 2x2 coupler with fixed power coupling factors.
  • These arrangements then form the different embodiments of the quasi-rectangular filter.
  • Two further functions can be implemented by changing the temperature and the associated change in refractive index in the optical waveguide sections: The tuning of the power spectral function as a function of the frequency with constant power amplitudes can be achieved by locally influencing the temperature of the waveguide in the resonance path.
  • the switch from reflection to transmission mode can be achieved by a temperature gradient between the two waveguides between the pre-coupler and the optical resonator with Fabry-Perot transfer function.
  • the filters according to the invention can thus also be used as an active component - and thus even more flexibly.
  • the optical filter according to the invention can be constructed from discrete optical components with extremely short optical fibers and in a compact, encapsulated construction or in an integrated optical construction.
  • a particular advantage of the integrated structure is that the optical waveguide is voltage-free
  • the lengths of the optical fibers can be determined with sufficient accuracy ( ⁇ / 2), so that the conditions of identical lengths of the optical fibers in pairs both between the pre-coupler and the Fabry-Perot coupler and in the resonance path between the Fabry-Perot coupler and the Mirroring or between the Fabry-Perot coupler and the 3dB coupler with optical fiber bridge (mirror coupler) can be fulfilled.
  • optical couplers are replaced by electrical 3 dB or directional couplers.
  • the main difference to the optical field of application is that the transmission properties of the filter due to the complex voltage Transfer function (amount, phase, group term) is given.
  • the problem of maintaining the polarization state of the wave is eliminated in the electrical field. In the optical range, the full functionality of the optical filter is only guaranteed if the interfer
  • FIG. 1 shows a first basic embodiment of the quasi-rectangular filter (QRF) according to the invention as an optical filter.
  • FIG. 2 shows the dependency of the power transmission factor on the optical frequency for a known Fabry-Perot filter and the power transfer functions (LÜF) for the quasi-rectangular filter according to the invention obtained therefrom according to FIG. 1 in comparison;
  • Fig. 3 amount and group delay (dashed) for the field size E at the output of the quasi-rectangular filter over the optical frequency;
  • FIG. 4 shows a second exemplary embodiment of the quasi-rectangular filter according to the invention with a Fabry-Perot coupler
  • 5 shows a third exemplary embodiment of the quasi-rectangular filter according to the invention with Fabry-Perot coupler and mirror coupler; 6 shows a fourth exemplary embodiment of the quasi-rectangular filter according to the invention with two optical couplers connected in series on the input side and bridged on the output side;
  • Fig. 7 shows a fifth embodiment of a steep quasi-rectangular filter consisting of a pre-coupler and two Mach-Zehnder couplers two mirrors each, over pairs of different lengths
  • Optical fibers are connected to the couplers; Fig. 8 power transmission functions (transmission dashed) in
  • FIG. 10 shows a sixth exemplary embodiment of a quasi-rectangular filter consisting of a pre-coupler and two Mach-Zehnder couplers with a total of four mirrors, which are connected to the two couplers via optical fibers of the same length;
  • Figure 1 1 an optical muxer / demuxer using two quasi-rectangular filters according to the invention.
  • Fig. 12 is an optical circuit with two over an optical fiber bridge in
  • Fig. 13 shows the curve of the power transmission factor of the optical
  • Fig. 15 shows the curve of the power transmission factor of the optical
  • 16 shows an exemplary embodiment of an electrical quasi-rectangular filter analogous to the optical quasi-rectangular filter according to FIG. 4 using microstrip technology;
  • FIG. 17 shows an exemplary embodiment of an electrical quasi-rectangular filter analogous to the optical quasi-rectangular filter according to FIG. 7 in microstrip
  • the filter according to the invention is a periodic quasi-rectangular filter which is equidistant with respect to the optical frequency.
  • the relatively large linear turning point range allows low-distortion FM-AM conversion (frequency modulation, amplitude modulation) of modulated signals.
  • the optical filter according to the invention can be used for the periodic suppression of light noise.
  • FIG. 3 shows the magnitude of the optical field size E and the group delay before the power is formed by a photodiode.
  • the edges of the amount of the field size E do not run as steeply over the optical frequency as those of the optical power.
  • the distortion of the phase curve over the optical frequency leads to distortion of the mean group delay (GLZ), which is decisive for the distortion-free transmission of narrow frequency groups.
  • the mean group delay is determined by the wave velocity in the waveguides and their total length. 4 shows a further embodiment of the optical filter according to the invention.
  • the upstream 2x2 coupler VK responsible for the transformation of the field size transfer functions of the Fabry-Perot coupler FPK must already have the above
  • the refractive index and the length of the waveguides can be influenced by locally heating the waveguides in the resonance path. This allows the power spectral function to be tuned slightly over the wavelength.
  • FIG. 5 shows a variant of the optical filter according to the invention, in which a mirror coupler SK with a right-hand optical fiber bridge B r is arranged instead of the technically complex mirror.
  • the “free spectral range” is reduced by increasing the effective resonator length; this filter is suitable for a “free spectral range” ⁇ 50 GHz.
  • the optical fiber bridge B r can be used to control the "free spectral range” by changing the temperature (changing the optically effective length of the resonance path).
  • FIG. 6 shows an embodiment of the invention, in which the Fabry-Perot filter is replaced by two optical 2x2 couplers Ki and K 2 , the input side with an optical fiber bridge B ⁇ (length b) connected in series and the output side with one Optical fibers are bridged.
  • the upstream 2x2 coupler VK also brings about the transformation of the field sizes and thus the generation of the power spectral function of the quasi-rectangular filter according to the invention.
  • the temperature of the bridges B r and B can be changed, as a result of which the power spectral function can be tuned slightly over the wavelength.
  • the filter consists of four coupled resonators, three of which differ from one another in pairs (pair LA, pair LB) of mirror lines of equal length. The "free spectral range" results from the lengths in the shortest resonance path.
  • FIG. 9 shows the amount and the group delay for the field size E of the quasi-rectangular filter according to FIG. 7 over the optical frequency.
  • the group delay shows distortions that are symmetrical to the center of the transmission range.
  • the filter according to FIG. 10 has the same structure as the filter according to FIG. 7.
  • the power transfer function is identical to that of the filter according to FIG. 4.
  • the "free spectral range" is determined by the identical lengths of the four coupled resonators.
  • the four mirror feed lines are of the same length, they can be guided to one side of the waveguide by means of suitable alignment of the two couplers without curvatures of the conductors, and there at one interface at one interface.
  • the “free spectral range” can be determined by selecting the detour line length LU and, if necessary, fine-tuned by influencing the temperature without affecting the symmetry of the resonators.
  • a disadvantage is the higher effort compared to the structure according to FIG. 4 (one coupler, two mirrors).
  • FIG. 11 Two identical quasi-rectangular filters QRF according to the invention according to FIG. 1 are shown in FIG. 11 as part of a Muxer / Demuxer arrangement.
  • An optical filter QRF is arranged in each case in a connection path between two 3dB couplers K 3d B. If, for example, a wave in the transmission range of the power spectral function T and a wave in the reflection range R are now applied to the upper input shown, the T signal and the R signal appear lossless at separate outputs (demuxers).
  • the Muxer function is implemented by swapping inputs and outputs.
  • the spectral functions for transmission and reflection are identical to those of the quasi-rectangular filter QRF according to the invention.
  • the R component is reflected at the input, the T component reaches the lower output.
  • the described arrangement of two optical filters according to the invention has the property of an optical attenuator when a temperature gradient is generated between the upper and lower connection path and the associated change in refractive index, the T-wave due to the optical path length difference between the upper and lower optical waveguide from the lower transmission output T 1 can be continuously faded to the upper transmission output T 2.
  • the R wave In the event of a corresponding temperature change, this is faded from the lower left output R to input E (mirror function).
  • FIG. 12 shows two identical quasi-rectangular filters QRF according to FIG. 1, which are connected in series on the input side via an optical waveguide bridge Br of length Ib.
  • This bridge Br forms a new resonance circuit via both quasi-rectangular filters QRF, which distorts the QRF power transfer function, in particular on the flanks, so that steeper flanks are created.
  • the curve of the power transmission factor of the optical circuit described as a function of the optical wavelength is shown in FIG. 13 in comparison to that of an individual filter.
  • There are two types of steep wall filters if the condition lb m ⁇ / 4 (m even or odd) is met. This condition can be realized by influencing the temperature of the bridge Br.
  • 14 shows an optical circuit with two quasi-rectangular filters QRF according to the invention connected in series via an optical isolator Iso. This optical isolator Iso, which has increased attenuation, decouples both filters QRF from one another, so that stable filter shapes are formed regardless of the length of the optical waveguide.
  • the curve shown in Fig. 12 optical circuitry also allows the creation of comb filters, but the filter curves on the flanks are distorted.
  • the exemplary embodiments for electrical quasi-rectangular filters described below each have a structure analogous to corresponding optical filters.
  • the two directional couplers are arranged orthogonally in two layers with a “ground plane” in between.
  • k 0.854 or 0.146
  • FIG. 10 Another embodiment (not shown) of an electrical quasi-rectangular filter has a structure analogous to the structure of the optical filter according to FIG. 10.
  • the termination leads of the resonator are of the same length.
  • the voltage transmission properties of the quasi-rectangular filter shown in FIG. 17 are characterized by the amount of the voltage transmission and the group delay over the electrical frequency.
  • the group delay distortions run symmetrically to the center of the transmission area (see Fig. 18).

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  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Optics & Photonics (AREA)
  • Optical Integrated Circuits (AREA)
  • Control Of Motors That Do Not Use Commutators (AREA)

Abstract

L'invention concerne un filtre quasi rectangulaire pour ondes électromagnétiques. Un tel filtre quasi rectangulaire doit présenter une caractéristique de bande passante plate, des flancs de filtre raides et une bonne suppression de signal dans le canal voisin. Le filtre quasi rectangulaire selon l'invention est constitué d'un élément de couplage présentant un facteur de couplage de puissance de kV1,2 = (1/2)(1±1/∑2) ou de kV = 0,5, cet élément de couplage étant relié à un élément de résonance par l'intermédiaire de deux lignes de même longueur.
PCT/DE1998/002575 1997-08-22 1998-08-21 Filtre quasi rectangulaire Ceased WO1999010761A2 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
DE19737450.6 1997-08-22
DE19737450 1997-08-22

Publications (2)

Publication Number Publication Date
WO1999010761A2 true WO1999010761A2 (fr) 1999-03-04
WO1999010761A3 WO1999010761A3 (fr) 1999-05-06

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PCT/DE1998/002575 Ceased WO1999010761A2 (fr) 1997-08-22 1998-08-21 Filtre quasi rectangulaire

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WO (1) WO1999010761A2 (fr)

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* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE10239690A1 (de) * 2002-08-25 2004-03-11 Fraunhofer-Gesellschaft zur Förderung der angewandten Forschung e.V. Optisches Filter und Anwendungen davon

Family Cites Families (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3589794A (en) * 1968-08-07 1971-06-29 Bell Telephone Labor Inc Optical circuits
GB8825481D0 (en) * 1988-11-01 1988-12-07 British Telecomm Interferrometer
IT1272081B (it) * 1993-12-16 1997-06-11 Cselt Centro Studi Lab Telecom Filtro risonante per sistemi di comunicazione ottica a divisione di lunghezza d'onda
JP3794730B2 (ja) * 1995-03-31 2006-07-12 住友大阪セメント株式会社 半導体レーザダイオードモジュールにおける出力光波長の制御方法

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DE19840697A1 (de) 1999-02-25
WO1999010761A3 (fr) 1999-05-06

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