WO2004095149A2 - Procede de production d'elements optiques integres, et element optique - Google Patents

Procede de production d'elements optiques integres, et element optique Download PDF

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Publication number
WO2004095149A2
WO2004095149A2 PCT/EP2004/004193 EP2004004193W WO2004095149A2 WO 2004095149 A2 WO2004095149 A2 WO 2004095149A2 EP 2004004193 W EP2004004193 W EP 2004004193W WO 2004095149 A2 WO2004095149 A2 WO 2004095149A2
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WO
WIPO (PCT)
Prior art keywords
optical
optical element
electro
structuring
femtosecond laser
Prior art date
Application number
PCT/EP2004/004193
Other languages
German (de)
English (en)
Other versions
WO2004095149A3 (fr
Inventor
Philipp Dittrich
Germano Montemezzani
Peter Günter
Original Assignee
Eidgenössische Technische Hochschule Zürich
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
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Application filed by Eidgenössische Technische Hochschule Zürich filed Critical Eidgenössische Technische Hochschule Zürich
Publication of WO2004095149A2 publication Critical patent/WO2004095149A2/fr
Publication of WO2004095149A3 publication Critical patent/WO2004095149A3/fr

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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
    • G02B6/10—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type
    • G02B6/12—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type of the integrated circuit kind
    • G02B6/13—Integrated optical circuits characterised by the manufacturing method
    • G02B6/138—Integrated optical circuits characterised by the manufacturing method by using polymerisation
    • 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
    • G02B6/10—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type
    • G02B6/12—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type of the integrated circuit kind
    • G02B6/13—Integrated optical circuits characterised by the manufacturing method
    • 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 
    • G02F1/0102—Constructional details, 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 
    • G02F1/061—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 electro-optical organic material
    • G02F1/065—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 electro-optical organic material in an optical waveguide structure
    • 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
    • G02F2203/15—Function characteristic involving resonance effects, e.g. resonantly enhanced interaction

Definitions

  • the present invention relates to a method for producing integrated optical elements for guiding and manipulating light waves, in particular waveguides and microresonators, from organic and inorganic crystals and optical polymers, in particular from organic single crystals, which have nonlinear-optical or electro-optical properties, through direct structuring using femtosecond laser ablation. Furthermore, the invention relates to optical elements that can be produced using such a method.
  • Essential elements that are required for this are electro-optical modulators, electrically and optically controllable switching distributors (cross connect) and wavelength-selective optocouplers or filters.
  • electro-optical modulators electrically and optically controllable switching distributors (cross connect) and wavelength-selective optocouplers or filters.
  • cross connect electrically and optically controllable switching distributors
  • wavelength-selective optocouplers or filters In order to meet the requirements of future ultra-fast networks with a wide bandwidth, it is therefore very important and of great interest to manufacture materials with large optical non-linearities and electro-optical properties in order to optimize the properties of these optical elements.
  • specially developed organic materials can be far superior to the most commonly used inorganic materials today, such as the standard lithium niobate (LiNbO), because of their large and fast non-linear properties, which are a consequence of the purely electronic nature of the non-linearities.
  • LiNbO lithium niobate
  • the organic crystal DAST (4-N, N-dimethylamino-4'N'-methyl stibazolim tysolate) is one of the most interesting materials for integrated optical applications due to its large nonlinear and electro-optical properties in the telecommunications wavelength range [1].
  • the structuring of DAST is very difficult, however, because standard photolithographic processes cannot be used due to the solubility of the crystal in water or common organic solvents. All previously known and used methods for structuring DAST have disadvantages. Waveguides have recently been structured in DAST, on the one hand by a "serially-graft" process [2] and on the other hand by bleaching [3].
  • the "serially-graft" process is very complex and consists of many different manufacturing steps, which makes it particularly suitable for the production of more complex structures, e.g. Microresonators, seems unsuitable.
  • the refractive index of DAST is changed locally by illumination with visible or ultraviolet light so that a waveguide structure is created.
  • bleaching also changes the crystal composition, which also changes the nonlinear optical properties.
  • the aim of this invention is to provide a method with which integrated-optical elements made of electro-optical materials, in particular of organic crystals, such as DAST, can be microstructured precisely without the Damage or destroy the crystal structure or the substrate material under the structured microstructures.
  • a method for the direct, contactless structuring of integrated-optical elements made of electro-optical materials, in particular organic crystals, which have nonlinear-optical or electro-optical properties is presented by means of femtosecond laser ablation.
  • Ablation 'here means structuring by means of irradiation with laser light to such an intensity that ablation processes are brought about.
  • Laser light with pulse lengths of less than 500 fs is preferred, For example, even less than 300 fs, 250 fs, 200 fs, 100 fs or even 10 fs pulse length used.
  • Another advantage of the method according to the invention is the precise production of optical elements with smooth surfaces, which are necessary for coupling in and for guiding light waves as losslessly as possible.
  • the invention relates to optical elements which can be produced in this way and can be used, for example, for guiding and manipulating light waves, in particular waveguides for guiding and manipulating light waves and microresonators for filtering and coupling simultaneously guided light waves of different wavelengths.
  • the method according to the invention is particularly advantageous for the structuring of nonlinear-optical, organic crystals.
  • the structuring of such crystals is difficult to do with conventional methods, as mentioned at the beginning. It has now surprisingly been found that the method according to the invention enables the precise production of fine and smooth structures of such crystals, that is to say that if the radiation only interacts briefly with the material, the material is only leached without crystal lattice vibrations occurring, for example, with a time delay which could locally damage the crystal structure.
  • the deposited energy therefore remains essentially limited to the volume element defined by the focus area of the laser beam.
  • the method according to the invention uses a focused femtosecond laser beam for structuring electro-optical materials, in particular non-linear-optical, organic crystals.
  • the short interaction time of, for example, less than 250 femtoseconds of the laser pulse with the material to be structured, defines the entire energy of the pulse by exciting electronic states of the organic molecules and by ionizing electrons in one that is well defined by the laser focus and small volume element deposited. It was found that it is not important whether the wavelength used is strongly or only weakly absorbed by the material.
  • the intensity of the light pulse in the focus is so strong that electronic states can be excited very effectively by multiphoton absorption or atoms and molecules can be ionized several times.
  • Good ablation results have been achieved with a wavelength of at least 400 nm and at most 1500 nm, preferably in the ranges from 500 nm to 620 nm or from 750 to 800 nm. If the energy density now exceeds a certain limit within this volume element, the volume is leached , ie its molecular components separate from the crystal lattice.
  • the physical mechanisms for this ablation are on the one hand breaking chemical bonds and the strong excitation of electronic states up to the generation of a local high temperature plasma, which leads to the evaporation of the material.
  • optical or electro-optical can be obtained on the surface of organic crystals by scanning the laser beam or by scanning the crystal under the fixed focus of the laser beam Precisely create structures that can be used to guide and manipulate light waves.
  • these are waveguides for loss-free guidance of light waves, electro-optical modulators for phase or amplitude modulation of these light waves, and microresonators for filtering and coupling simultaneously guided light waves of different wavelengths, as well as combinations of all these elements.
  • the method according to the invention can be used to produce precise optical elements with smooth surfaces, which are necessary for coupling in and for guiding light waves with as little loss as possible.
  • FIG. 1 The representation of an embodiment of the inventive method. 2 shows an embodiment of the method according to the invention using the specific example of the structuring of a linear waveguide.
  • Fig. 3 The representation of an embodiment of the inventive method using the specific example of the structuring of a microresonator.
  • Fig. 4 The representation of an embodiment of the inventive method using the specific example of the structuring of a microresonator which has two linear
  • Waveguide couples together.
  • Fig. 5 coupling of two linear waveguides by several connected in series
  • Microresonators as a special example of an integrated optical element produced according to the invention.
  • Fig. 6 filter for several simultaneously guided wavelengths as a special example of an integrated optical element produced according to the invention.
  • Fig. 7 Optical coupler as a special example of an integrated optical element produced according to the invention.
  • 8 Mach-Zehnder interferometer as a special example of an integrated optical element for optical signal modulation produced according to the invention.
  • FIG. 1A The principle of the method according to the invention is shown in FIG. 1A.
  • a femtosecond laser beam 1 with a suitable wavelength and with a suitable energy density required for non-destructive ablation is transmitted through a lens or a lens 2 focused 3 and the focus 4 itself adjusted so that it comes to lie just below the surface 5 of the organic crystal 6 to be structured.
  • the organic crystal 6 is then moved in one or more of the three spatial axes, ie the x-axis 7, the y-axis 8 and the z-axis 9, with respect to the focus 4 with a suitable scanning speed.
  • Such a translation can be carried out, for example, using a computer-controlled XYZ displacement table with sub-micrometer accuracy. This is not shown in the picture.
  • the laser beam or the focus 4 can also be shifted with respect to the crystal 6 by suitable deflection.
  • suitable scanning - if necessary several times to generate structure depths - and suitable ablation of material, any structures can be formed on the surface of the organic crystal.
  • IB shows the principle of ablation in detail using an exemplary embodiment of the method according to the invention.
  • FIG. 2 shows an embodiment of the method according to the invention using the specific example of the structuring of a linear waveguide.
  • FIG. 3 shows the application of the method according to the invention using the specific example of the structuring of a microresonator.
  • material 13 originally present is ablated or removed from the crystal 6 in such a way that a microresonator 18 on the ablated surface 15 stop.
  • the wall thickness of the microresonator is typically a few micrometers, the diameter is on the order of approximately 10 to 50 micrometers.
  • 4 shows the application of the method according to the invention using the specific example of the structuring of two waveguides 19 and 20 which are coupled to one another by a microresonator 18. The structuring takes place analogously to the arrangements shown in FIGS. 2 and 3.
  • the wavelength of the light guided in the waveguide 20 corresponds to a wavelength for which the microresonator fulfills a constructive resonance condition
  • part of the energy of the light wave from the waveguide 20 via the microresonator 18 into the second waveguide 23 is coupled through the evanescent fields transmitted and exits at 23.
  • the resonance condition of the microresonator is ideally only fulfilled for a very narrow-band wavelength range
  • a wavelength filter can be implemented in this way.
  • the resonance condition for example by electro-optically changing the refractive index in the microresonator, the central wavelength of the resonance condition can be variably set in a certain wavelength range.
  • the arrangement shown in FIG. 4 is therefore suitable for selecting a specific wavelength from a band of simultaneously guided wavelengths, provided that the resonance condition of the microresonator is narrower than the distance between two adjacent wavelengths from the band of simultaneously guided waves.
  • FIG. 5 shows a top view of two linear waveguides 24 and 25 which are coupled to one another via a plurality of identical microresonators connected in series. This coupling of several microresonators makes the resonance condition for the transmissible wavelength much sharper and the bandwidth of the filter much narrower.
  • 6 shows a top view of a possible arrangement for the simultaneous and selective filtering of different wavelengths from a band of simultaneously guided wavelengths.
  • Several microresonators 29 are coupled to a linear waveguide, which have different dimensions and thus also different resonance conditions for different wavelengths.
  • a microresonator is a suitable resonance condition for a wavelength from a band of simultaneously guided wavelengths 30, which are in the linear Waveguide 28 are coupled, so the individual wavelengths by electro-optically detuning the resonance condition of the resonators (e.g. by applying an electric field across the resonators and the associated change in the refractive index, which is not shown in Fig. 6) individually and simultaneously filtered, transmitted in waveguide 31 and coupled out at 32.
  • an optical coupler is shown in a top view in FIG. 7.
  • Two waveguides 33 and 34 run side by side in a certain area at a very close distance, so that energy can be transmitted from one waveguide to the other. Whether and how much energy is transferred depends on the phase mismatch between the two waveguides, which are changed, for example, as shown in FIG. 7, by applying an electric field across electrodes 39 and 40 and the change in the refractive index induced thereby in one or in both waveguides can. For example, it is possible to couple light 35 or 36 into one of the outputs 37 and 38 depending on the phase mismatch.
  • a Mach-Zehnder interferometer is shown in supervision in FIG. 8.
  • a waveguide 41 is split into two arms 42 and 43, which are brought together again after a certain distance. If light 44 enters the waveguide, constructive or destructive interference occurs at point 45 depending on the phase difference between the two arms 42 and 43, and accordingly light 45 can be coupled out of the waveguide or not.
  • the phase difference between the two waveguide arms can now be set as desired, e.g. as shown in Fig. 8, by applying an electric field across electrodes 47 and 48 and thereby causing the change in refractive index in one or both waveguides.
  • the present invention offers a simple method for the precise structuring of electro-optical elements from organic crystals and polymers which have large and, above all, fast, non-linear and electro-optical properties. Such elements are indispensable for the further development and improvement of integrated optics and optical data transmission, which is why the present invention represents a particular enrichment in the relevant technical field. Credentials:

Abstract

L'invention concerne un procédé permettant de produire et de structurer des éléments électro-optiques à partir de matériaux électro-optiques, par exemple de cristaux organiques optiques non linéaires, en particulier à partir du sel organique DAST, par ablation au laser femtoseconde. Cette invention se rapporte en outre à des utilisations d'éléments électro-optiques produits au moyen dudit procédé.
PCT/EP2004/004193 2003-04-24 2004-04-21 Procede de production d'elements optiques integres, et element optique WO2004095149A2 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
CH730/03 2003-04-24
CH7302003 2003-04-24

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WO2004095149A2 true WO2004095149A2 (fr) 2004-11-04
WO2004095149A3 WO2004095149A3 (fr) 2004-12-23

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Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4871223A (en) * 1987-08-25 1989-10-03 Siemens Aktiengesellschaft Arrangement comprising at least one integrated optical waveguide on a substrate of electro-optical material and comprising at least one electrode
EP1176438A1 (fr) * 1999-02-09 2002-01-30 Kanagawa Academy Of Science And Technology FILTRE DE LONGUEUR D'ONDE POUR GUIDE D'ONDES OPTIQUES AVEC RESONATEUR EN ANNEAU ET FILTRE 1xN DE LONGUEUR D'ONDE POUR GUIDE D'ONDES OPTIQUES
WO2002090036A1 (fr) * 2001-05-10 2002-11-14 Vanderbilt University Procede et appareil de modification de surfaces dielectriques par ablation au laser

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4871223A (en) * 1987-08-25 1989-10-03 Siemens Aktiengesellschaft Arrangement comprising at least one integrated optical waveguide on a substrate of electro-optical material and comprising at least one electrode
EP1176438A1 (fr) * 1999-02-09 2002-01-30 Kanagawa Academy Of Science And Technology FILTRE DE LONGUEUR D'ONDE POUR GUIDE D'ONDES OPTIQUES AVEC RESONATEUR EN ANNEAU ET FILTRE 1xN DE LONGUEUR D'ONDE POUR GUIDE D'ONDES OPTIQUES
WO2002090036A1 (fr) * 2001-05-10 2002-11-14 Vanderbilt University Procede et appareil de modification de surfaces dielectriques par ablation au laser

Non-Patent Citations (4)

* Cited by examiner, † Cited by third party
Title
CHON J C ET AL: "LASER ABLATION OF NONLINEAR-OPTICAL POLYMERS TO DEFINE LOW-LOSS OPTICAL CHANNEL WAVEGUIDES" OPTICS LETTERS, Bd. 19, Nr. 22, 15. November 1994 (1994-11-15), Seiten 1840-1842, XP000475130 ISSN: 0146-9592 *
DITTRICH P ET AL: "Femtosecond laser ablation of DAST" APPLIED SURFACE SCIENCE ELSEVIER NETHERLANDS, Bd. 220, Nr. 1-4, 30. Dezember 2003 (2003-12-30), Seiten 88-95, XP002297552 ISSN: 0169-4332 *
KITANO R ET AL: "Femtosecond laser ablation processing of x-cut LiNbO3 substrates for optical communication devices" PHOTON PROCESSING IN MICROELECTRONICS AND PHOTONICS II , PROCEEDINGS OF THE SPIE, Bd. 4977, 27. Januar 2003 (2003-01-27), Seiten 386-393, XP002297532 ISSN: 0277-786X *
YOUNG-MOK SON ET AL: "A reproducible method for growing nonlinear optical organic crystals (DAST) and excimer laser processing of DAST" CONFERENCE ON LASERS AND ELECTRO-OPTICS. (CLEO 2001). TECHNICAL DIGEST., Bd. 56, 6. Mai 2001 (2001-05-06), Seiten 59-60, XP010559556 ISBN: 1-55752-662-1 *

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