Classifications

• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
  • H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
  • H01S3/05—Construction or shape of optical resonators; Accommodation of active medium therein; Shape of active medium
  • H01S3/06—Construction or shape of active medium
  • H01S3/063—Waveguide lasers, i.e. whereby the dimensions of the waveguide are of the order of the light wavelength
• • 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
  • G02B2006/12035—Materials
  • G02B2006/12038—Glass (SiO2 based materials)
• • 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
  • G02B2006/12035—Materials
  • G02B2006/12069—Organic material
• • 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
  • G02B2006/12035—Materials
  • G02B2006/1208—Rare earths
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
  • H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
  • H01S3/14—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range characterised by the material used as the active medium
  • H01S3/16—Solid materials
  • H01S3/17—Solid materials amorphous, e.g. glass
  • H01S3/178—Solid materials amorphous, e.g. glass plastic

Definitions

• the invention pertains to an optical amplifier comprising a waveguiding component doped with a laser active substance.
• EP 511 069 discloses a waveguiding component comprising a massive substrate of praseodymium-doped fluorinated glass in which a mono ode waveguide is realised by a treatment, e.g., localized diffusion of lead, to create a channel having a refractive index different from the untreated fluorinated glass.
• the substrate containing the channel is covered with a layer of fluorinated glass not doped with praseodymium.
• an optical amplifier which comprises a thin glass slab waveguide provided onto a laser substrate.
• Optical amplifiers are mostly known in the form of glass fibre doped with a lanthanide ion such as Er 3+ .
• An optical amplifier of this type has been disclosed in EP-A2-0437935.
• the erbium ions are excited with the aid of a laser, giving a fibre containing a large number of excited Er 3+ ions.
• optical beams (photons) having the same wavelength as the emission wavelength of the excited Er 3+ ions propagate through the fibre, they effect the transition of the ions from the excited state to a lower energy level with transmission of light. This light thus has the same wavelength and phase as the photons propagating through the fibre. This process is called stimulated emission, and by this stimulated emission the light beams are amplified, with the optical fibre acting as amplifier.
• optical amplifiers as specified in the aforementioned publications are made of glass.
• Optical polymeric waveguides have several advantages over optical glass waveguides, such as the favourable processability, the relatively low price, the possibility of producing larger area devices, and the manifold options that molecular tailoring provides.
• a lanthanide-doped optical polymeric waveguide cannot be expected to perform the above-indicated amplification, or will display it in insufficient degree, unless further measures are taken.
• Doping of Er 3+ ions in glass fibres ordinarily is carried out using Er2 ⁇ 3- While this erbium oxide is not hygroscopic, it fails to dissolve in polymeric material, and so cannot simply be used in polymeric waveguides.
• one of the invention's objects is to provide an optical amplifier in which the favourable properties and numerous options of organic polymers are combined with the unaffected amplifying action of appropriately doped glass. It is a further object of the invention to provide an optical amplifier in which the ampliflying action of a laser active substance is used in conjunction with a polymeric waveguide without the functionality and activity of the polymer being affected, and in which additions or alterations to the polymer can be refrained from. In particular, it is an object of the present invention to provide a polymeric waveguide which includes an optical amplifier.
• optical amplifiers have previously been combined with polymeric materials. However, these combinations were of a totally different kind and for different purposes then in the case of the present invention.
• the all-glass waveguide disclosed in EP 511 069 may be covered or not by a supplementary coating in the form of a resin that is non-polluting to the fluoride glass.
• JP 02/300727 discloses an optical amplifier comprising a single-mode optical fibre with a laser amplifier medium, and a light source to excite the laser active substance. To allow ultra low temperature cooling, and thus give low noise levels and high amplification, the amplifier is equipped with a cooling means, and the optical fibre is provided with a secondary covering material which has a coefficient of thermal expansion below about 10 ⁇ 5 .
• GB 2244 595 discloses an optical amplifier comprising a length of doped fibre provided with a signal beam and a pump beam input, and on the signal output fibre a sampling device which comprises a plastic waveguide.
• This document describes, int.al., a dielectric waveguide comprising two glass plates which are applied onto each other with spacers in between.
• the spacers which are made of manganese fluoride or silicon dioxide, leave a void, which is filled with a dielectric that consists of a laser active substance in the form of a solution of Rhodamin B in benzyl alcohol.
• a liquid-containing core-layer is highly impractical .
• EP 442 796 As background art to all-polymeric waveguides comprising a guiding layer sandwiched between two deflection layers of lower refractive index and with a waveguide channel (wave confinement) formed therein, is mentioned EP 442 796. This document does not pertain to optical amplification.
• the waveguiding component has a layered structure comprising a core layer and two cladding layers sandwiching the core layer and having a refractive index lower than that of the core layer, wherein the core layer and at least one of the cladding layers comprise an optical polymer material, and at least one cladding layer comprises an optical glass doped with the laser active substance.
• the term cladding is known in the field of waveguides.
• waveguides - whether optical fibres, slab waveguides, or channel waveguides - generally comprise a core and a cladding surrounding the core, the cladding material having a refractive index lower than that of the core material.
• the optical amplifier of the present invention exhibits both the benefits of the polymeric waveguide and those of glass doped with a laser-active substance.
• the construction of the optical amplifier according to the invention may be such that, e.g., one cladding layer consists essentially of the doped glass and the other cladding layer consists essentially of polymeric material.
• the following layers can then be identified: a substrate layer (S), a doped glass layer (G), a polymeric core layer (waveguiding layer W), and a polymeric cladding layer (C). These layers can be positioned on top of each other, e.g. as schematically indicated below (cross-section).
• the doped glass cladding may simultaneously serve to support the waveguiding structure instead of the substrate, i.e., as follows:
• one cladding layer consists essentially of polymeric material and the other cladding layer comprises polymeric material in which a piece of doped glass has been inserted.
• This can be schematically indicated as follows: CCCCCCGGGGGGCCC CCCCCCccccccCCC
• the substrate will usually be of the order of several millimeters, while the waveguiding layer will have a thickness of the order of about 1 ⁇ m to about 10 ⁇ m. It is preferred that the refractive index contrasts and the thicknesses of the waveguiding and cladding layers be chosen so as to create an asymmetric mode-profile, the asymmetry being such that when light propagates through the waveguide, a large evanescent tail is present in the cladding which comprises the doped glass. It is desired that a considerable percentage of both the pump beam and the signal beam propagate through the laser active cladding.
• the refractive index contrast ( ⁇ ) between core and doped-glass cladding is as low as possible (the lower limit being determined by the possibility of propagating monomodal light, the preferred ⁇ being about 0.02). While both cladding layers may comprise doped glass, this is not preferred.
• an asymmetric waveguide with an asymmetric mode-profile is much more effective when only one cladding layer comprises the laser active substance, and the more portions of the waveguide are made of polymer, the greater the possibilities of tailoring properties such as refractive index and ⁇ are.
• the optical amplifiers of the invention such as the structures schematically illustrated above, can advantageously be manufactured in a relatively simple and straightforward manner.
• the consecutive polymer layers can be applied onto the substrate in a known fashion, e.g., by spincoating the polymer from a solution, followed by evaporation of the solvent.
• the desired polymeric layer structure it is also possible to shape the desired polymeric layer structure by moulding, injection moulding, or any other technique known in itself.
• the doped glass materials can be employed, e.g., by providing the glass as a substrate and applying the polymer by known techniques, e.g., coating techniques such as spincoating.
• coating techniques such as spincoating.
• Suitable substrate materials include silicon wafers or synthetic laminates, such as those based on epoxy resin, which may be reinforced or not. Suitable substrates are known to the person of ordinary skill in the art, and the choice of the substrate is not essential for practising the present invention, except in the embodiment in which the doped glass layer functions as the substrate.
• ther osetting material for making the polymeric optical waveguide or a portion thereof (e.g., one of the layers). If at least the lower cladding is made from a freestanding thermoset material, it is possible to refrain from using a separate substrate if so desired, as the lower cladding will perform this function.
• any optical polymeric material suitable for use in waveguides may be employed for forming the cladding and core layers of the present waveguide structures, and the general viability of the present invention does not hinge on the choice of polymer. Suitable optical polymers are known, and include polyurethanes, polyesters, polyacrylates, polycarbonates, polyimides, polyarylates, and polymers derived from epoxides.
• optical waveguides While in optical waveguides it is preferred to use polymers exhibiting low optical loss, such as deuterated, fluorinated, and/or chlorinated polymers, in waveguides incorporating an optical amplifying structure in accordance with the present invention the adverse effect of optical loss can be neutralized advantageously by amplification.
• the cladding layers have a refractive index lower than that of the core layer, in order for propagating light waves to be confined to the waveguide.
• the waveguide be asymmetric, the refractive index contrast with the cladding layer comprising the doped glass being as low as possible.
• passive and active optical polymers may be employed, the latter being preferred.
• active polymers are meant those that can be rendered electro-optically active. They are generally referred to as NLO polymers.
• NLO non-linear optical
• Non-linear electric polarisation occurs under the influence of an external field of force (such as an electric field).
• Non-linear electric polarisation may give rise to several optically non-linear phenomena, such as frequency doubling, Pockels effect, and Kerr effect.
• NLO effects can be generated opto-optically or acousto-optically.
• the groups present in such a material usually hyperpolarisable sidegroups, first have to be aligned (poled).
• NLO polymers are described in, int. al., EP 350 112, EP 350 113, EP 358476, EP 445864, EP 378 185, and EP 359648. In the context of the present invention NLO polymers also include conventional optical polymers doped with NLO active substances.
• the present waveguides may be used as active units in optical circuits.
• the combination of an amplifier and a circuit in a single waveguide makes it possible to have small-size intricate circuits. Also, loss of optical signal incurred when light is coupled to and from an optical switch or other active unit can be compensated for in this way.
• the design of the layered polymeric waveguide comprised in the optical amplifiers according to the present invention generally depends on the device's exact function in an optical network. Whichever design is required in the layered (slab) waveguide structure where a waveguiding layer is sandwiched between cladding layers having a lower index of refraction, a pattern of laterally defined waveguide channels will usually have to be introduced, i.e. portions of the core layer that are vertically and laterally adjacent to material having a lower index of refraction.
• a waveguide can be provided with a pattern of waveguide channels in various manners. Methods of achieving this are known in the art.
• such a pattern by removing portions of the slab waveguide, e.g., by means of wet- chemical or dry etching techniques, and to fill the gaps formed with a material having a lower index of refraction.
• such gaps to be filled for the formation of waveguide channels are formed by shaping a polymer via known moulding techniques, such as injection moulding.
• Use may also be made of photosensitive material that can be developed after irradiation. In the case of a negative photoresist the photosensitive material is resistant to the developer after irradiation, and the portions of material not subjected to irradiation can be removed.
• a positive photoresist it is preferred to use a positive photoresist, and to define the channels by means of an irradiation mask covering the waveguide portions that will form the channels.
• the irradiated material is removed using developer, after which a material of lower refractive index is applied.
• a core material that makes it possible to define a waveguide pattern without material having to be removed.
• Materials of this nature exist, e.g., those that will undergo chemical or physical conversion into a material having a different refractive index when subjected to heat, light, or UV radiation.
• the treated material will be employed as core material for the waveguide channels. This can be carried through by employing a mask in which the openings are identical with the desired waveguide pattern.
• the treated material is suitable as a cladding material.
• a mask as mentioned above is used, i.e. one that covers the desired waveguide channels.
• a particular, and preferred, embodiment of this type of core material is formed by polymers that can be bleached, i.e., of which the refractive index is lowered by irradiation with visible light or UV, without the mechanical properties being substantially affected.
• polymers that can be bleached, i.e., of which the refractive index is lowered by irradiation with visible light or UV, without the mechanical properties being substantially affected.
• Bleachable polymers have been described in EP 358476 among others.
• Optical glass materials, and the laser active substances with which these are doped for the purpose of producing an optical amplifier, are known in the art.
• all doped optical glasses such as known laser glasses, can be employed in principle, such as fluoride glasses, zirconium glasses, phosphate glasses.
• Preferred laser-active substances are lanthanides, such as erbium, ytterbium, praseodymium, the most preferred being erbium.
• the present optical amplifier is integrated with a waveguiding device. Hence, amplification should occur within a relatively short distance (about 5 to 100 mm).
• suitable glass hosts are laser glasses ex Kigre Inc., such as QE-7 (erbium doped phosphate glass, which contains ytterbium as a sensitizer at 980 nm), Q-246 (neodymium doped silicate glass), and Q-98 (neodymium doped phosphate glass).
• QE-7 erbium doped phosphate glass, which contains ytterbium as a sensitizer at 980 nm
• Q-246 neodymium doped silicate glass
• Q-98 neodymium doped phosphate glass
• Co- dopants can be added to improve the solubility and to prevent clustering of the ions.
• the doped glass have a lower refractive index than the polymer in the waveguiding layer.
• the refractive index of most polymers is tunable within a range of from about 1.4 to 1.8 (at a wavelength of 1.5 ⁇ m), this does not present a problem to the man skilled in the art.
• the optical amplifiers according to the present invention can be used basically in a known manner. This usually involves a laser or a flash light input serving as a pump beam exciting the laser active substance. A signal beam of appropriate wavelength is then amplified by means of stimulated emission, as referred to hereinbefore. It is an essential advantage of the optical amplifiers in accordance with the present invention that the desired properties of both the polymer waveguides and the doped glass are used without one affecting the other.
• optical amplifiers according to the invention can be incorporated into devices comprising structural elements, such as coupling elements for the coupling of light into and from the waveguide, such as usually found in optical waveguiding devices.
• devices incorporating an optical amplifier according to the invention will generally also comprise the structural features required or desired for the active functioning of the NLO polymer, such as a heating element (used during poling) and electrodes (for poling and for performing functions such as switching).
• a heating element used during poling
• electrodes for poling and for performing functions such as switching
• An optical amplifier as shown in Figure 1 is made on the basis of an injection moulded polymethyl methacrylate (PMMA) substrate (1) containing a 5*5 ⁇ m groove (2).
• the groove (2) is filled with a Nouryset ® optical polymer having a refractive index of 1.55 at a wavelength of 1.5 ⁇ m, to form a waveguiding channel (3).
• Substrate (1) simultaneously functions as the lower cladding.
• the upper cladding (4) is inactive in part and made of a polished microscope glass slide (5).
• the active part (6) of the upper cladding (4) - covering the waveguiding channel over a length of about 1 cm and having a thickness of about 2 mm - is a doped optical glass, in this case QE-7 ex Kigre Inc. (an erbium and ytterbium-containing glass having a refractive index of 1.53 at a wavelength of 1.5 ⁇ m) .
• Favourable optical amplification can be attained by coupling a pump beam and a signal beam simultaneously into the waveguide channel, either on the same side (copropagating) , or on opposite sides (counterpropragating) .
• the optical amplifier on the basis of the above injection moulded substrate can suitably be provided with more grooves, e.g., so as to create a 1*2 or 1*4 splitter.
• An optical amplifier as shown in Figure 2 is made on the basis of a glass substrate (7) coated with a layer (8) of a bleachable polymer, the layer having a thickness of about 4 mm, in which a waveguide channel (9) is created having a width of about 6 ⁇ m.
• the latter is done by irradiating the bleachable polymer layer (8) with UV irradiation while a mask covers the shape of the waveguide channel (9).
• Part of the waveguide channel - having a length of about 1 cm and a thickness of about 2 mm - is covered with a doped optical glass cladding (10), in this case QE-7 ex Kigre Inc. (an erbium and ytterbium-containing glass having a refractive index of 1.53 at a wavelength of 1.5 ⁇ ) .
• Favourable optical amplification can be attained by coupling a pump beam and a signal beam simultaneously into the waveguide channel, either on the same side (copropagating), or on opposite sides (counterpropragating) .
• the optical amplifier on the basis of the above bleachable polymer can suitably be provided with more grooves as desired.

Landscapes

• Physics & Mathematics (AREA)
• Electromagnetism (AREA)
• Engineering & Computer Science (AREA)
• Plasma & Fusion (AREA)
• Optics & Photonics (AREA)
• Optical Integrated Circuits (AREA)
• Lasers (AREA)

Applications Claiming Priority (2)

Publications (1)

Family

ID=8214076

Family Applications (1)

Country Status (2)

Cited By (1)

Citations (3)

• 1993
  • 1993-12-17 TW TW82110706A patent/TW245843B/zh active
• 1994
  • 1994-08-17 WO PCT/EP1994/002766 patent/WO1995006967A1/en not_active Ceased

Patent Citations (3)

Non-Patent Citations (1)

Also Published As

Similar Documents

Legal Events