WO2003102675A1 - Filtres passe-bandes optiques bases sur des reseaux de guides d'ondes a induction electro-optique et effet pi - Google Patents

Filtres passe-bandes optiques bases sur des reseaux de guides d'ondes a induction electro-optique et effet pi Download PDF

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Publication number
WO2003102675A1
WO2003102675A1 PCT/CA2003/000840 CA0300840W WO03102675A1 WO 2003102675 A1 WO2003102675 A1 WO 2003102675A1 CA 0300840 W CA0300840 W CA 0300840W WO 03102675 A1 WO03102675 A1 WO 03102675A1
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WO
WIPO (PCT)
Prior art keywords
waveguide
electrodes
grating
shift
core
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/CA2003/000840
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English (en)
Inventor
Mykola Kulishow
Xavier Daxhelet
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Adtek Photomask Inc
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Adtek Photomask Inc
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Publication date
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Priority to AU2003238593A priority Critical patent/AU2003238593A1/en
Priority to CA002488510A priority patent/CA2488510A1/fr
Publication of WO2003102675A1 publication Critical patent/WO2003102675A1/fr
Anticipated expiration legal-status Critical
Ceased legal-status Critical Current

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Classifications

    • G—PHYSICS
    • G02—OPTICS
    • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
    • G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
    • G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour 
    • G02F1/011—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  in optical waveguides, not otherwise provided for in this subclass
    • G—PHYSICS
    • G02—OPTICS
    • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
    • G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
    • G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour 
    • G02F1/13—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  based on liquid crystals, e.g. single liquid crystal display cells
    • G02F1/133—Constructional arrangements; Operation of liquid crystal cells; Circuit arrangements
    • G02F1/1333—Constructional arrangements; Manufacturing methods
    • G02F1/1334—Constructional arrangements; Manufacturing methods based on polymer dispersed liquid crystals, e.g. microencapsulated liquid crystals
    • G02F1/13342—Holographic polymer dispersed liquid crystals
    • G—PHYSICS
    • G02—OPTICS
    • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
    • G02F2201/00—Constructional arrangements not provided for in groups G02F1/00 - G02F7/00
    • G02F2201/12—Constructional arrangements not provided for in groups G02F1/00 - G02F7/00 electrode
    • G02F2201/124—Constructional arrangements not provided for in groups G02F1/00 - G02F7/00 electrode interdigital
    • G—PHYSICS
    • G02—OPTICS
    • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
    • G02F2201/00—Constructional arrangements not provided for in groups G02F1/00 - G02F7/00
    • G02F2201/30—Constructional arrangements not provided for in groups G02F1/00 - G02F7/00 grating
    • G02F2201/307—Reflective grating, i.e. Bragg grating
    • G—PHYSICS
    • G02—OPTICS
    • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
    • G02F2203/00—Function characteristic
    • G02F2203/05—Function characteristic wavelength dependent
    • G02F2203/055—Function characteristic wavelength dependent wavelength filtering

Definitions

  • the present invention relates to optical filters and more particularly concerns reconfigurable and multi-functional pi-shifted filters based on electro- optically induced waveguide gratings.
  • the transmission characteristics of a fiber grating are really the wrong way around: it is a band-stop rather than a band-pass.
  • tuning a radio enables the selection of a channel, not the rejection of it from a broad frequency spectrum.
  • traditional fiber gratings, short period (Bragg) as well as long period ones work quite in reverse, and therefore cannot be easily used for channel selection.
  • Several band-pass filter designs using fiber gratings have been constructed.
  • optical circulators can turn a reflection-type filter into a transmission-type filter, but optical circulators can be costly and cause serious additional losses.
  • FIG. 1 PRIOR ART
  • FIG. 1 demonstrates an example of ⁇ -shift in harmonic distribution. It is believed that this idea was first proposed in 1976.
  • a ⁇ -shift in a grating may be introduced in several ways. Post-processing of the uniform grating in a certain region creates a permanent phase-shifted region ( ⁇ -shift). This occurs because an extra exposition to ultraviolet (UV) light changes the refractive index in that region, creating an additional phase step. However, post-processing may be difficult to execute in practice, especially in short gratings. A better procedure is to use phase-shifted phase masks to introduce the desired ⁇ -shift in a grating. All these techniques are however time consuming and once phase shift is introduced, little can be done to change its position, magnitude or eliminate it at all.
  • ⁇ -shift phase-shifted region
  • a waveguide having at least one selectively actuated ⁇ -shifted grating therein comprising: a core and a cladding, wherein said core or cladding is made of an electro- optic material; a plurality of electrodes on one side of said waveguide; at least one electrode on another side of said waveguide opposite said one side; means for selectively applying a voltage pattern to said electrodes so that said pattern induces at least one ⁇ -shifted grating when said pattern is applied.
  • a pi-shifted optical grating device based on electro-optically (EO) induced waveguide gratings.
  • the electro-optically induced gratings are of the type shown in FIG. 2, but the scope of the invention is not limited thereto.
  • the applied voltage polarity for a portion of the electrode fingers is simply reversed. In this manner, the ⁇ -shift(s) can be conveniently induced or removed at will in any portion of the grating.
  • FIGs. 3a, 3b, 3c and 3d there are shown examples of structures illustrating the principles of the present invention. FIG.
  • FIG. 3a shows the central portion of an EO grating without any ⁇ -shift
  • FIG. 3b shows the same structure in the center of which the electrodes polarities have been reversed to introduce the ⁇ -shift
  • FIGs. 3b and 3c show a similar before and after scheme, with the difference that in the former case constant and variable components of electric field are induced inside the waveguide with a variable with periodicity I, whereas in the latter case only a variable component of the electric field distribution with periodicity 21 is created.
  • Figure 1 is a schematic representation of a uniform grating and one with a pi-shift
  • Figures 2a) and 2b) are a representation of two preferred embodiments of the present invention, a) where both top and bottom electrodes are discrete and b) where the bottom electrode is continuous;
  • Figures 3a)-3d) are representations of the introduction of a ⁇ -shift into EO superimposed gratings, (a,b) where the central part of the structures is without the ⁇ -shift and (c, d) where the central part of the structures is with the ⁇ -shift;
  • Figures 4a) and 4b) show the transmission spectra of the EO-induced LPG without ⁇ -shift (solid) and with ⁇ -shift (dashed) for a) equal ⁇ -product value 0.5 ⁇ and b) for ⁇ -product value 0.5 ⁇ for the uniform grating and ⁇ -product value 0.706 ⁇ for the ⁇ -shifted grating;
  • Figure 5 shows the transmission spectra for the ⁇ -shifted grating with ⁇ _- product value 0.706 ⁇ (solid) and ⁇ L-product value 2.118 ⁇ (dashed);
  • Figures 6a) and 6b) show two different schemes of the electric potential application to the IDE for effective coupling between the modes with different symmetry;
  • Figures 9a), 9b) and 9c) show the layout of EO reconfigurable grating-filter structure: (a) single grating; (b) grating with single ⁇ -shift; and (c) multiple ⁇ -shifted gratings;
  • Figure 1 1 shows the creation of a Mach-Zender interferometric filter by grounding M IDE finger pairs in the middle of the structure
  • Figures 12a) to 12f) show the transmission spectra of the MZ filter with M grounded IDE finger pairs (solid line) for the grating with the period 21 as against the spectrum with the uniform grating (dashed line) with the same coupling coefficient and the number of activated IDE fingers;
  • Figures 14a) and 14b) show the transmission spectra for the two superimposed gratings of Figure 15 without (dashed line) and with ⁇ -shift (solid line) and (b) demonstration how contribution for the ⁇ -shift superimposed gratings can be controlled through ⁇ V voltage.
  • Figures 20 a) and b) show the electrode structure and potential application scheme to provide a ⁇ -shift according to another preferred embodiment of the invention, where (a) the electrodes are interdigitalized and symmetrical and (b) the bottom electrode is solid.
  • An optical fiber (waveguide) grating is generally used as a filter for selecting an optical signal at a specific wavelength(s) from multiple wavelengths propagating along a core.
  • the optical grating can eliminate or reflect light at a specific wavelength by inducing a periodic change in the refractive index of a waveguide.
  • the optical grating is categorized into short (Bragg) period gratings (FBG) and long period gratings (LPG).
  • a FBG reflect light at a specific wavelength in the filtering process
  • a LPG or transmission grating removes light without reflection by converting the optical signal component which must be removed from the core mode into the cladding mode.
  • LPGs which includes a plurality of refractive index perturbations spaced along the waveguide by a predetermined distance that ranges from tens of microns to several hundreds of microns.
  • the present invention concerns the inducement of gratings into an electro- optic sensitive medium in an optical waveguide structure, but it should be recognized that the present invention can also find application in optical fibers.
  • the present invention is directed to a method and apparatus for inducing the ⁇ -shift into a waveguide, the waveguide comprising a core and a cladding (Fig. 2), preferably mounted on a substrate (on a bottom portion thereof) and a superstrate (top portion thereof). It will also be apparent to a person skilled in the art that the words "top” and “bottom” are for ease of comprehension only.
  • a plurality of electrodes 9 is placed on one side of the top cladding.
  • the electrodes 9 are placed on the top cladding on the side of the superstrate and will be referred to a "top electrodes" for ease of description.
  • At least one electrode 11 is placed on the other side of the core (i.e. in Fig. 2, on the side of the substrate).
  • the present invention also contemplates using a plurality of electrodes 11 on the other side, where the electrodes 9, 11 are symmetrical about a longitudinal axis.
  • the at least one electrode (Fig. 2b) and the plurality of electrodes (Fig. 2a) will be hereinafter referred to as "bottom electrodes”.
  • the grating can be induced in top or bottom cladding, i.e. the top cladding can be electro-optic, and the core and the bottom cladding are not, or the bottom cladding can be made from an electro-optic material and the core and the top cladding are from non-electro-optic one(s), or finally the core can be electro-optic, and the top and bottom claddings are not.
  • the top and bottom claddings can only be included in the core or the cladding.
  • the top and bottom electrodes are interdigitated electrodes (IDE).
  • the solid curves in Fig.4 give an example of transmission spectra (solid) of the electro-optically (EO) induced waveguide grating without ⁇ -shift (Fig.3b) and with ⁇ -shift, when fingers of interdigitated electrode (IDE) along the second half of the structure length are inversely biased in respect to the first half (see Fig.3d). Because the grating is induced electro-optically, it is always possible to switch between two types of spectra presented in Fig.4. The grating also can be switched OFF if the electric potential difference between the electrodes is equal to zero and behaves as a low-loss waveguide.
  • KL 0.5 ⁇ , where is the grating full length, and K is the coupling coefficient.
  • KL- value should be increased to 0.706 ⁇ , which can be done in our design just by increasing difference of potential, Vo, 1.4 times or by increasing the grating length L through activating additional number of IDE fingers. Therefore special attenuation in the dips around the bandpass gap can be controlled electronically.
  • the structure design should be optimized for proper external electric field distribution to maximize the overlap integral for core-cladding mode interaction.
  • the electric potential application pattern in Fig.6a is more suitable for coupling the fundamental core mode into the odd (asymmetric) cladding modes
  • the configuration of the electric field from IDE in Fig.6b is more effective for interaction between the fundamental mode and even (symmetric) cladding modes.
  • ⁇ -shifted EO induced grating produces transmission gap in the stop-band which can be switched ON and OFF.
  • This can be achieved with a cascade of ⁇ -shifts sandwiched between sub-gratings.
  • This concept was used for filter design with the help of ultraviolet imprinted sort-period (Bragg) cascaded gratings. Depending on the length of the sub-gratings, many peaks may appear or they may coalesce into one.
  • M3 M-1
  • the bias voltage V 0 has to be adjusted when transmission is reconfigured between different band-pass windows in Fig.8.
  • the bias voltage should maintain proper values of the KL product that corresponds to the filter rejection level -35 dB.
  • the bias voltage is the only parameter to adjust. For the above example it has to be increased 1.58 times.
  • the coupling in our EO induced grating does not occur without the presence of the voltage at IDE fingers. That creates another opportunity to split our superimposed gratings into two sections by disabling (grounding) a number of IDE fingers in the middle of the structure.
  • Two sequential long period gratings with a space between them act as a Mach-Zehnder (MZ) interferometer for the range of wavelengths for which coupling is enabled.
  • the first grating (the section in our case) couples part of the core mode intensity into the cladding mode, and the second grating (section) recombines them.
  • M 1 , 2, 151, 152, 1000, and 1001 grounded finger pairs.
  • All spectra are plotted as against the spectrum of the uniform grating (without IDE finger grounding, dashed curve).
  • side-lobe suppression can be also easily done by modulating the voltage Vo along the grating length using Gaussian, raised-cosine or any other apodization profiles.
  • Fig.14a demonstrates the double-dip spectra (dash) of the superimposed gratings and appearance of band-pass gaps in the middle of the dips (solid) when the ⁇ -shift is introduced by the electric field reversing and it also demonstrates control over transmission losses of the ⁇ -shifted gratings by ⁇ V -voltage in Fig.14b.
  • EO induced grating can be used for contra propagating interaction of guided modes that reflects light at a specific wavelength based on Bragg diffraction.
  • the refractive index change is proportional to the normal component of the electric field, E z (x, z), therefore the fundamental spatial harmonic has the period of 21.
  • the refractive index change is proportional to Ez (x, z) squared.
  • the ⁇ -shift opens very narrow transmission gap with a Lorentzian line shape. This gap can be switched ON and OFF in our design or the spectrum itself can be reshaped by changing coupling coefficient ⁇ (V 0 ), or through grating length variation by enabling or disabling the IDE fingers.
  • disabling (enabling) a certain amount of IDE fingers in the sub- gratings from their inner cavity ends we simultaneously enable (disable) the same amount of IDE fingers in the sub-gratings from their outer ends; and 2) the total number of enabled IDE fingers in each sub-grating, (N-M)/2, increases (decreases) as we enable (disable) the IDE fingers of the sub-gratings from their inner (cavity) ends.
  • H-PDLC holographic polymer dispersed liquid crystals
  • the H-PDLC material comprises a transparent polymer material populated by periodical distribution of liquid crystal micro-droplets. Such droplet distribution forms holographic fringes, or, in the case of a waveguide, it can be short or long period gratings.
  • the H-PDLC has two optical states corresponding to the electrical stimulus being ON or OFF, these being equivalent respectively to the grating being disabled or activated.
  • the liquid crystal droplets In its normal or rest state the liquid crystal droplets tend to be randomly aligned. When the external electric field is applied the droplets tend to re-orient such that that liquid crystal molecules become aligned with the direction of the applied electric field. This property is widely known in the art and is used to switch ON and OFF the hologram or waveguide grating(s).
  • a structured electrode to selectively disable a fringe or a number of fringes within H-PDLC waveguide grating by applying an electric potential to a finger pair or a group of finger pairs keeping the rest of electrode grounded. This allows us to dynamically split the grating into arbitrary amount of subgratings (or Fabry-Perot resonators) with the same transmission spectrum manipulation freedom over the transmission spectrum as was described above, and shown in Fig. 20.
  • subgratings or Fabry-Perot resonators

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  • Physics & Mathematics (AREA)
  • Nonlinear Science (AREA)
  • General Physics & Mathematics (AREA)
  • Optics & Photonics (AREA)
  • Optical Integrated Circuits (AREA)

Abstract

L'invention concerne un dispositif de réseaux optiques à effet pi, basé sur des réseaux de guides d'ondes à induction électro-optique. Le guide d'ondes a une âme (1) et une enveloppe (3), ces deux éléments étant en matériau électro-optique. Une pluralité d'électrodes (9) est située sur une face du guide d'ondes et au moins une électrode (11, 11') est disposée sur l'autre face dudit guide d'ondes. Un modèle de tension est sélectivement appliqué à l'électrode, de sorte qu'il induit au moins un réseau à effet pi dans le guide d'ondes.
PCT/CA2003/000840 2002-06-03 2003-06-03 Filtres passe-bandes optiques bases sur des reseaux de guides d'ondes a induction electro-optique et effet pi Ceased WO2003102675A1 (fr)

Priority Applications (2)

Application Number Priority Date Filing Date Title
AU2003238593A AU2003238593A1 (en) 2002-06-03 2003-06-03 Optical bandpass filters based on electro-optically induced waveguide gratings with pi-shift
CA002488510A CA2488510A1 (fr) 2002-06-03 2003-06-03 Filtres passe-bandes optiques bases sur des reseaux de guides d'ondes a induction electro-optique et effet pi

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
CA2,388,746 2002-06-03
CA 2388746 CA2388746A1 (fr) 2002-06-03 2002-06-03 Filtres decales en pi utilisant des reseaux de guides d'ondes a induction electro-optique

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WO2003102675A1 true WO2003102675A1 (fr) 2003-12-11

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US9813474B2 (en) * 2014-03-07 2017-11-07 Ericsson Ab ABR video white spot coverage system and method

Citations (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO1999009440A1 (fr) * 1997-08-13 1999-02-25 Foster-Miller, Inc. Composants optiques commutables

Patent Citations (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO1999009440A1 (fr) * 1997-08-13 1999-02-25 Foster-Miller, Inc. Composants optiques commutables

Non-Patent Citations (5)

* Cited by examiner, † Cited by third party
Title
BARBOSA C L ET AL: "Grating structures with symmetric fractionally organized gaps", MICROWAVE AND OPTICAL TECHNOLOGY LETTERS, WILEY, USA, vol. 31, no. 3, 5 November 2001 (2001-11-05), pages 223 - 229, XP009016079, ISSN: 0895-2477 *
CHEN L R: "Design of flat-top bandpass filters based on symmetric multiple phase-shifted long-period fiber gratings", OPTICS COMMUNICATIONS, NORTH-HOLLAND PUBLISHING CO. AMSTERDAM, NL, vol. 205, no. 4-6, 1 May 2002 (2002-05-01), pages 271 - 276, XP004353446, ISSN: 0030-4018 *
DEPARIS O ET AL: "BANDPASS FILTERS BASED ON PI-SHIFTED LONG-PERIOD FIBER GRATINGS FOR ACTIVELY MODE-LOCKED ERBIUM FIBER LASERS", OPTICS LETTERS, OPTICAL SOCIETY OF AMERICA, WASHINGTON, US, vol. 26, no. 16, 15 August 2001 (2001-08-15), pages 1239 - 1241, XP001110599, ISSN: 0146-9592 *
KULISHOV M ET AL: "Electro-optically reconfigurable waveguide superimposed gratings", OPTICS EXPRESS, OPT. SOC. AMERICA, USA, vol. 9, no. 10, 5 November 2001 (2001-11-05), pages 483 - 489, XP002252138, ISSN: 1094-4087 *
KULISHOV M ET AL: "Reconfigurable pi -shifted and Mach-Zehnder bandpass filters on the basis of electrooptically induced long-period gratings in a planar waveguide", JOURNAL OF LIGHTWAVE TECHNOLOGY, IEEE, USA, vol. 21, no. 3, March 2003 (2003-03-01), pages 854 - 861, XP002252139, ISSN: 0733-8724 *

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CA2388746A1 (fr) 2003-12-03
AU2003238593A1 (en) 2003-12-19

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