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
  • G02F1/35—Non-linear optics
  • G02F1/355—Non-linear optics characterised by the materials used
  • G02F1/361—Organic materials
  • G02F1/3615—Organic materials containing polymers
  • G02F1/3617—Organic materials containing polymers having the non-linear optical group in a side chain

Definitions

• the present invention relates to the manufacture of electrooptical materials and in particular the manufacture of electrooptical components. These components can be used in optical signal processing applications, in particular the modulation, switching and coding of one or more optical carriers.
• this invention applies to components using polymers having second order nonlinearity optical properties.
• Electrooptical polymers have great potential in the telecommunications field. These are materials likely to allow the manufacture of components at low cost and to be implemented in distribution networks by otic fiber directly to the user (Y.Shi et al. "Fabrication and characterization of High-Speed Polyurethane-Disperse Red 19 Integrated Electrooptic Modulators for Analog System Applications ", IEEE J. of Selected Topics in Quantum Electronics, Vol 2 (2), 1996, 289-298) (fiber to the home, FTTH), or over the air (SA Hamilton, DR Yankelevich, A.Knoesen, RTWeverka, RAHi ⁇ l, GCBjorklund, "Polymer in-line fiber modulators for broadband radio-frequency optical links", J. Opt.
• these polymers must be oriented in a non-centro-symmetrical manner.
• an electric field (of the order of 100 V / ⁇ m or more) is applied between these electrodes. This field directs the molecules by dipolar interaction; this orientation is then fixed by cooling the polymer while maintaining the applied field.
• an electric modulation field is applied between the electrodes and makes it possible to modulate the refractive index of the polymer via the Pockels effect. This results in a phase shift of the optical wave propagating in the oriented polymer; this phase shift can be used to process the optical signal (modulation or switching).
• Another solution consists in finding polymeric matrices with a high glass transition temperature and in modifying them in order to introduce a large quantity of dyes (T. Verbiest, DM Burland, MC Jurich, VY Lee, RD Miller , W. Herbsten, "Exceptionnaly Thermally stable Polyimides for Second Order Nonlinear Optical Applications", Science, Vol 268, 1995, 1604-1606).
• a last approach consists in making interpenetrating networks combining polymers such as polyimides and a sol-gel matrix onto which the dyes are grafted (RJJen, YM Chen, AK Jain, J. Kumar, SK Tripathy, "Stable Second- Order Nonlinear Optical Polyimide / lnorganic Composite ", Chem. Mater. 1992, 4, 1141-1144).
• the first class of materials can cause problems of solubility (a good solvent must be found for the deposition of polymers) and insolubility (to allow the successive deposition of multilayers necessary for the production of waveguides) .
• Sol-gel materials are relatively difficult to control because the repeatability of their implementation, and therefore the stability of the orientation of the dyes, depends on the reproducibility of the temperature and hygrometry conditions. Furthermore, the stability of the orientation of molecules in the sol-gel matrix depends on the density of the crosslinking. Significant rigidity of the network therefore implies a lower concentration of dyes, which limits the effectiveness of the final component.
• the object of the invention is to overcome these drawbacks by proposing a process for obtaining a matrix of polymers which can be dissolved by conventional solvents and which has better rigidity.
• the invention proposes for this purpose a process for obtaining an electrooptical material characterized in that a solution of oligoimides is deposited on a substrate on which are orientable dyes, in that the crosslinking of the oligoimides is carried out by annealing and the dyes are oriented.
• polymers is meant a molecule in which a motif, the monomer is repeated a large number of times (up to several thousand).
• oligomer is meant a molecule in which the motif is repeated less than 20 times.
• oligoimides in place of the polyimides conventionally used allows better solubility of the matrix obtained, which facilitates its shaping.
• This increased solubility is due both to the presence of terminal groups and to the fact that the chains are shorter than that of polyimides. Thanks to this new structure, films of micron thickness can easily be obtained, which makes them compatible for the manufacture of waveguides. This solubility also makes it possible to dissolve them in conventional solvents which are not very toxic.
• the invention proposes to use fluorinated oligoimides.
• the use of fluorinated oligomers introduced during the polymerization makes it possible to reduce the sensitivity of the material obtained to humidity.
• the oligoimide solution used in the process is obtained by the following steps: - the synthesis of oligoimides terminated by reactive double bonds, the addition of dyes which can be oriented on the lateral OH functions of the oligoimides,
• crosslinking groups of the alkoxysilane, nadic or allylic type for example allows crosslinking and densification of the films after deposition. This crosslinking makes them insoluble while giving them optical transparency.
• alkoxysilane groups it is also possible to envisage the preparation of oligoimides terminated by maleimide, acetylenic, benzocyclobutenes or cyanate groups which crosslink by thermal autocondensation.
• the oligoimides can be self-crosslinkable (via the alkoxysilane, nadic or allylic functions) or crosslinkable via an additional crosslinking agent (for example 1, 1, 1-tris (4-hydroxyphenyl) ethane or oxalic acid).
• the crosslinkable oligoimides can therefore be in the form of a monocomponent material, that is to say having the two functions crosslinkable on the oligoimide chain, or bicomponent, that is to say resulting from a reaction between two components.
• crosslinking can be done by reaction of alkoxysilane with hydroxylated crosslinking agents, but it can be envisaged in the form of a reaction of a compound carrying at least three functions capable of react with the double bonds located at the end of the chain.
• crosslinking can be envisaged by radical addition to the nadic double bonds of a multifunctional compound of the tri or tetrathiol type such as pentaerythitol tetrakis (3-mercaptopropionate).
• crosslinking can be carried out by hydrosilylation reaction with functional tetra or penta compounds such as tetramethylcyclotetrasiloxane.
• Cross-linking reactions can be elementary: a simple annealing is enough. This annealing also makes it possible to evaporate the residual solvents. Crosslinking makes the material insoluble, which allows it to be easily used in multilayer deposits since the lower layers are not altered during the deposition of additional layers. Furthermore, this insolubility does not prevent a subsequent orientation of the dyes, which allows it to be effectively used as a technological step without prejudice to the non-linear efficiency of the material if the latter is oriented after crosslinking.
• This family of materials implements synthesis reactions of soluble polyimides which are well controlled and which are carried out with good yields. Their synthesis and implementation can take place at relatively low temperatures (below 300 ° C). Thanks to their high glass transition temperature due to the imide groups in the main chain, the matrices obtained remain stable at temperatures above the temperatures envisaged for their uses (below 85 ° C.). These polyimides can easily lend themselves to mixing operations because their chemical structures are close. One can thus finely adjust, at the time of use and shaping, by mixing different synthesis batches, specific properties such as the refractive index, the resistivity or the dielectric constant of the material. We can therefore obtain products suitable for a specific use.
• the refractive indices of the various layers making up a waveguide can be adjusted to optimize their thicknesses.
• the dielectric constant of the material can be adapted to adapt phase speeds in very high frequency electrooptical modulation.
• the non-linear optical properties of the materials made up of a matrix of oligoimides are comparable or superior to that obtained using the corresponding model polyimides.
• the dyes used must be hyperpolarizable to ensure their orientation, that is to say that they must preferably have a tensor of quadratic optical hyperpolarisability of which at least one coefficient is greater than 10 ⁇ 30 esu
• the orientational stability of organic dyes can be characterized by the measurement of the non-linear optical coefficient as a function of the temperature by measurement during its heating of the variation of the intensity of second harmonic generated by a film of the compound .
• FIGS. 5 to 7 are reaction diagrams illustrating the different stages of the process for manufacturing an electrooptical material, in which the oligoimide is oligohydroxyimide, the grafted dye is Disperse Red One, and the crosslinking agent is a derivative mercaptosilane.
• FIGS. 8a and 8b represent two chemical structures of crosslinkable oligoimides on which stability measurements have been made,
• FIG. 9 represents the relaxation curves of the signals obtained for the two types of electrooptical material of FIGS. 8a and 8b,
• FIG. 10 combines the resistivity measurement curves of different electrooptical materials as a function of the applied electric field.
• the first step represented in FIG. 1 consists in synthesizing an oligohydroxyimide 1 having reactive double bonds 2 at its ends and lateral OH functions.
• chromophores 3 are added to the lateral OH functions via the Mitsunobu reaction.
• crosslinking groups 4 of trialcoxysilane type are added to the double bonds 2 at the chain end.
• the oligohydroxyimides are crosslinked by thermal voice, which leads to the formation of bonds 5 between the crosslinking groups 4.
• oligohydroxyimides are synthesized with 4,4'-hexafluoroisopropylidene biphtalic anhydride (6FDA).
• 6FDA 4,4'-hexafluoroisopropylidene biphtalic anhydride
• Three families of oligoimides which differ in the hydroxydiamine used were prepared. The three types of hydroxydiamine are:
• nadic anhydride recrystallized from acetic acid
• DR1 chromophore Dispersed Red One
• Step 1 Synthesis of oligohydroxyimides (OIA) terminated by nadic and allylic double bonds.
• the diamine (HODA, 6-FAP or DHB) and the dianhydride 6FDA are dissolved in a solution of 1-methyl-2-pyrrolidinone ( NMP) with a mass concentration of 20%.
• NMP 1-methyl-2-pyrrolidinone
• the solution is stirred at room temperature for 18 hours under a stream of nitrogen, then it is gradually heated to 160 ° C. and is left for 3 hours at this temperature.
• the solution is cooled to room temperature and the terminating agent (either allylamine AA or nadic anhydride AN) is added.
• the solution undergoes the same temperature cycle as above, then it is cooled and precipitated in a liter of a 1: 1 mixture of methanol-water.
• the white product is filtered then washed several times with methanol and dried.
• the physicochemical characteristics of each oligomer are given in table 2.
• Step 2 Addition of the chromophore DR1 on the oligohydroxyimides (OIA).
• the polymer is purified by Soxhlet extraction with methanol until elimination of the residual chromophore (TLC monitoring) and is finally dried under vacuum at 100 ° C.
• An assay in UV-visible spectrometry makes it possible to determine the grafting rates. The characteristics of the UV-visible assay are given in Table 4.
• Step 3 Synthesis of ⁇ , ⁇ -alkoxysilane oligoimides grafted with DR1.
• the reaction scheme for the synthesis of oligoimide ⁇ , ⁇ -trialcoxysilanes based on HODA and 6FDA is given in FIG. 7.
• An example of synthesis and characterization is described below for the radical addition of mercaptosilane derivative on nadic double bonds. It is applicable to all other ⁇ , ⁇ - trialcoxysilane oligoimides.
• Step 4 Crosslinking thermally.
• the DR1 grafted trialkoxysilane-terminated oligoimide is dissolved in a deposition solvent such as 1,1,2-trichloroethane.
• a deposition solvent such as 1,1,2-trichloroethane.
• Step 5 Orientation and measurement of the stability of the electrooptical properties
• the polymer film previously oriented under a 5kV electric field for 2 hours at 150 ° C is heated with a temperature ramp of 3 ° C / min.
• the relaxation curves of the signal l 2 ⁇ (intensity of the second harmonic generated by the film when it is irradiated by a pulsed laser of wavelength 1.34 ⁇ m and detected by a photomultiplier at 670 nm) of the oligoimides OIA-6FAP3- DR1-TMS and OIA-6FAP3-DR1 -TES are given in Figure 5.
• FIG. 9 is the superposition of the relaxation curves of the l 2 ⁇ signals of OIA-6FAP3-DR1-TES, of OIA-6FAP3-DR1-TMS crosslinked for 2 h at 150 ° C.
• the measured relaxation temperatures (l 2 ⁇ / 2) are 147 ° C for cross-linked OIA-6FAP3-DR1-TMS and 155 ° C for cross-linked OIA-6FAP3-DR1-TES.
• the resistivity of the materials studied decreases with temperature.
• the resistivities of the reference materials are measured at lower temperature (120 ° C) and have lower resistivities.
• the resistivity is calculated from the isochronous value (measured 10 minutes after the application of the voltage across the terminals of the sample) of the current passing through a cell with a thickness close to 1 micrometer of polymer comprised between two gold electrodes and thermostatically controlled at 120 ° C or 150 ° C.
• NOA65 and NOA61 are crosslinkable optical adhesives from commercial sources (Norland Optical Adhesives).
• AVO01 is a crosslinkable fluoropolymer based on methacrylic base (Liang, J., Toussaere E., Hierle R., Levenson R., Zyss
• OIP11 and OIP14 are crosslinked passive oligoimides described in this memo.
• PIA4-95 is a model polyimide substituted with DR1 (grafting rate 95%).
• OIP11 and OIP14 are crosslinkable passive oligoimides (without crosslinking site for grafting a dye). They are obtained by copolymerization of 6FDA and of fluorinated diamine 2,2'-bis (trifluoromethyl) -4,4'-diaminobiphenyl (BTDB). The crosslinking groups are of the nadic type.
• Tg of the starting oligoimides ⁇ , ⁇ -dienes b) TES: triethoxysiiane, TMS: trimethoxysilane and DMS: dimethoxysilane, c) Tg of the oligoimides ⁇ , ⁇ -trialcoxysilanes measured during the second temperature rise from 50 to 240 ° C to 20 ° C. min "1 , d) 1, 1, 2-trichloroethane.

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• Optics & Photonics (AREA)
• Macromolecular Compounds Obtained By Forming Nitrogen-Containing Linkages In General (AREA)

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  • 2001-01-22 FR FR0100801A patent/FR2819892B1/fr not_active Expired - Fee Related
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