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
  • H01S3/067—Fibre lasers
  • H01S3/06754—Fibre amplifiers
• • 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
  • H01S3/0632—Thin film lasers in which light propagates in the plane of the thin film
  • H01S3/0637—Integrated lateral waveguide, e.g. the active waveguide is integrated on a substrate made by Si on insulator technology (Si/SiO2)
• • 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
  • H01S3/067—Fibre lasers
  • H01S3/06708—Constructional details of the fibre, e.g. compositions, cross-section, shape or tapering

Definitions

• the present invention relates to a hybrid optical amplifier comprising at least one integrated pump filter and a matrix of such amplifiers.
• the invention finds applications in all fields requiring amplification of an optical signal and in particular in the field of optical telecommunications.
• FIG. 1a represents a block diagram of a conventional amplification structure produced in integrated optics.
• the optical amplification structures produced in integrated optics comprise two parts in which optical guides are produced.
• An optical guide is made up of a central part generally called the heart and surrounding media located all around the heart and which may be identical to each other or different.
• the guide can be a planar guide, when the light confinement is in a plane or a microguide, when the light confinement is also carried out laterally.
• the guide will be likened to its central part or core.
• all or part of the surrounding media will be called a substrate, it being understood that when the guide is not or only slightly buried, one of the surrounding media may be outside the substrate and be, for example, air.
• the substrate can be monolayer or multilayer.
• an optical guide in a substrate can be more or less buried in this substrate and in particular comprise guide portions buried at variable depths. This is especially true in ion exchange technology in glass.
• the first part of the amplification structure which is referenced 1 in FIG. La, receives at the input on the one hand the light wave E of power Pe to be amplified and on the other hand, a pump wave L generally originating from a laser source.
• the waves E and L are transported respectively in two guides 5 and 4 to a coupler 3.
• the latter is produced by the guides 5 and 4 which are separated over a given interaction length, by a distance such as the wave E is injected into the guide 4 carrying the wave L.
• the guide 4 At the outlet of the coupler 3, only the guide 4 remains which then transports the waves E and L.
• This first part has for role only the coupling of the two waves in the guide 4.
• the second part of the amplification structure receives at the input of a guide 6, the waves E and L coupled from the first part.
• the purpose of this second part is to amplify the E wave of initial power Pe from the pump wave L.
• the amplification in this second part is carried out in the guide 6.
• the light wave S at the outlet of the guide 6 then has a power Ps greater than the power Pe.
• the first part is for example silicate and the second part is for example phosphate glass doped with erbium. These two parts are usually glued together.
• the integrated amplifier structures have the advantage of being particularly compact, however they generally require high pump powers.
• FIG. 1b schematically illustrates such a structure.
• the light wave E of power Pe to be amplified is conveyed by an optical fiber referenced 15 while the pump wave L is transported by an optical fiber referenced 14.
• These two waves E and L are multiplexed by a multiplexer 13 obtained by fusion of two fibers 14 and 15.
• the output of the multiplexer is itself soldered to an amplifying fiber 16 doped for amplification; this solder is protected by a protective sleeve 11.
• the light wave S at the output of the fiber 16 has, as described above, a power Ps greater than the power Pe.
• These fiber amplifying structures present today a better amplification efficiency than the integrated structures. They can therefore use lower power pump sources. However, they have the disadvantage of being large sizes.
• a multiplexer 13 measures approximately 5 to 6 cm and a weld with its protective sleeve 11 measures approximately 3 cm.
• the mode sizes between a standard fiber and a fiber doped for amplification are quite different, which results in coupling losses at the assembly of these fibers.
• the mode size for a standard fiber 14 or 15 is approximately 10.4 ⁇ m and the mode size for a fiber 16 doped for amplification is approximately 5 ⁇ m to 8 ⁇ m.
• the smaller the mode size the more we will be able to use weak curvatures and have more compact structures, but the more we will on the other hand have significant coupling losses.
• the pump wave is not completely absorbed in the amplifying part of these structures, residual components of the pump wave can exit and create disturbances.
• the present invention aims to provide a hybrid optical amplifier combining the advantages of fiber amplifier structures and those of integrated amplifier structures while avoiding the drawbacks described above.
• an object of the invention is an optical amplifier which can be compact while being capable of attenuating pump residues, easy to produce, good amplification efficiency and if possible low cost.
• Another object of the invention is also to propose a matrix of such amplifiers.
• the invention provides a hybrid optical amplifier comprising:
• a support comprising at least a first optical guide capable of receiving from a first end of the support, a light wave E of power Pe to be amplified, a second optical guide capable of receiving from a second end of the support, a first pump wave L, a first multiplexer connected to the first and second optical guides and capable of transmitting the E and L waves to a third optical guide, the third optical guide being connected to a third end of the support, a fourth optical guide connected on the one hand to a filtering element and on the other hand at a fifth end of the support capable of delivering an S wave of power Ps greater than the power Pe and a last optical guide connected to the fourth end of the support and to the filtering element,
• an amplifying fiber comprising a first end connected to the third end of the support and a second end capable of delivering an S wave of power Ps greater than the power Pe.
• the amplifying part uses an amplifying fiber which allows to have a good optical efficiency and which allows to use a large number of fibers existing on the market.
• optical guides, the multiplexer and the filtering element described above which are the basic elements necessary, in association with the amplifying fiber, to perform an optical amplification function, are integrated on a support, which allows to have a compact package.
• the support can of course be produced by a single integrated optical block or several blocks which may be independent.
• other functions can of course also be integrated on the support.
• the support further comprises one or more guided mode adapters, respectively at one or more ends of the support.
• a mode adapter is produced at the third end of the support.
• This adapter located at the third end of the support, makes it possible to adapt the mode between the third guide and the first end of the fiber.
• a mode adapter is located at the first end of the support, this adapter makes it possible to adapt the guided mode between the first guide and the means for introducing the E wave.
• the support advantageously further comprises at least one mode adapter produced at the fourth and / or at the fifth end of the support.
• an adapter When an adapter is located at the fourth end of the support, it makes it possible to adapt the mode between the guide connected to said end and the second end of the fiber.
• an adapter When an adapter is located at the fifth end of the support, it makes it possible to adapt the guided mode between the fourth guide and the means for recovering the S wave.
• the association of optical guides integrated on a support and of an amplifying fiber makes it possible to simply carry out an adaptation of the modes on the support between the guides and the fiber.
• the filtering element implemented by the invention makes it possible to attenuate the pump residues.
• the term “attenuation of pump residues” means a reduction for example greater than 30 dB of these residues, it being understood that some traces of said residues may persist.
• this reduction is such that the remaining residues are sufficiently small so as not to disturb the operation of the amplifier.
• the filtering element comprises at least one pump filter capable of absorbing pump residues and a so-called second amplifier multiplexer connected to the pump filter by a fifth optical guide, said multiplexer being connected on the one hand to the fourth and to the fifth optical guide and on the other hand to the last optical guide.
• the fourth optical guide is therefore connected to the fourth end of the support via the second multiplexer and the last optical guide.
• the multiplexer is produced for example by a coupler formed by the bringing together of the fourth and the fifth optical guide.
• the fifth and the last optical guide form a single optical guide and the fourth optical guide has a free end.
• the pump filter can be produced by stopping the fifth optical guide in the support, the pump residues are then no longer guided and are absorbed in the support; the pump filter can also be produced by one end of the support, the pump residues are then removed from the support.
• This pump filter is called in English terminology: "kill filter”.
• the coupler is produced by bringing the two guides closer to a distance and over an interaction length such that the signal amplified by the amplifying fiber and injected into the last guide passes to the level of the coupler in the fourth guide while the residues of the pump wave, leaving the amplifying fiber and injected into the last guide, remain at the level of the coupler, in the last guide (which coincides with the fifth guide), the end of this guide being free.
• the filter element of the invention comprises a Mach-Zehnder element (corresponding to two Y junctions mounted head to tail connected by guides), said Mach-Zehnder element being connected between the fourth and the last light guide.
• This filter element is designed to allow filtering of pump residues without disturbing the signal.
• the difference in length between the two arms of the Mach-Zehnder is calculated to obtain said filtering.
• the filter element comprises an absorbent element placed above this optical guide.
• the absorbent element is able to selectively absorb pump residues without absorbing the amplified signal.
• the filter element comprises a Bragg grating, capable of reflecting the pump residues .
• This network is formed for example by etching the substrate, or by an appropriate ion exchange in the substrate.
• the filter element comprises a network long period formed in the substrate for example by ion exchange so as to couple the pump residues out of the guide.
• the support may also include at least one element for taking a portion of the light wave carried by one of the optical guides of the support in order to allow control of said wave by means of control means which may be external to the support.
• a sampling element is placed on the first guide to sample a part of the E wave and another sampling element is arranged on the fourth guide to sample a part of the wave S.
• the sampled parts of the waves allow control of said waves.
• the sampling element of the invention is for example a divider (called “tap" in English terminology) capable of sampling a small percentage of the wave, for example 1%.
• the first and / or the second multiplexer are respectively produced for example by a coupler also called proximity coupler.
• the fiber amplifier is for example a fiber doped with erbium.
• the support is glass and the guides are formed by the ion exchange technique.
• the support and the guides could also be produced for example from Si / Si0 2 or LiNb0 3 etc ...
• the pump wave L can come from a pump source such as for example a laser diode, fiber-optic or not, optically connected to the second end of the support.
• the ends of the support are connected to the ends of the fiber by connection elements.
• the pump source the means for introducing the wave to be amplified and / or for recovering the amplified wave or else the control means and in general all the elements connected to the support by optical fibers, are by
• the invention also applies to a matrix of n hybrid optical amplifiers as described above, this matrix comprising:
• an amplifier assembly comprising at least a first optical guide capable of receiving from a first end of the support, a light wave E of power Pe to be amplified, a second optical guide capable of receiving from a second end of the support, a first pump wave L, a first multiplexer connected to the first and to the second optical guide and capable of transmitting to a third optical guide the waves E and L, the third optical guide being connected to a third end of the support, a fourth optical guide connected on the one hand to a filtering element and on the other hand to a fifth end of the support capable of delivering an S wave of power Ps greater than the power Pe, and a last optical guide connected to the fourth end of the support and to the filter element,
• each amplifying fiber comprising a first end connected to the third end of the support corresponding to this assembly and a second end capable of delivering an S wave of power Ps from the amplified E wave.
• FIG. 1b already described schematically represents a fiber amplifier structure also known.
• FIG. 2 schematically represents a first exemplary embodiment of a hybrid amplifier according to the invention.
• FIG. 3 schematically represents a variant of the hybrid amplifier of FIG. 2.
• FIG. 4 schematically represents another variant of the hybrid amplifier of FIG. 2.
• FIG. 5 schematically illustrates a second exemplary embodiment of a hybrid amplifier according to the invention.
• FIG. 6 schematically illustrates a third embodiment of a hybrid amplifier according to the invention.
• FIG. 7 schematically represents an example of a matrix of hybrid amplifiers according to the invention.
• FIG. 2 schematically represents a first embodiment of a hybrid optical amplifier according to the invention.
• This amplifier comprises a support 30 containing elements made of integrated optics and an amplifier fiber 31 such as a doped fiber.
• the elements produced in integrated optics are the following: - a first optical guide 32 connected by one end of the support referenced 35 to means for introducing (not shown) a light wave E of power Pe to be amplified,
• a second optical guide 34 connected by one end of the support referenced 33 to a pump source
• a multiplexer produced in this example by a coupler 36 connected on the one hand to the guides 32 and 34 and on the other hand to a third optical guide 37, the latter being connected by one end referenced 39 to one of the ends of the fiber 31, - an optical guide 50, said last guide, connected to the second end of the fiber 31 and to a filter residue element of the pump, and
• a fourth optical guide 41 connected to the filtering element and, by one end referenced 43 of the support, to recovery means (not shown) of the amplified light wave S.
• FIG. 2 and the following figures are cross-sections of the support in planes containing the optical guides, it being understood that, depending on the technologies used, these guides are not necessarily in practice contained in the same plane.
• the light wave E is introduced into the guide 32 through the end 35 of the support.
• This light wave has one or more wavelengths
• the pump wave L introduced by the end 33 of the support in the guide 34 also has one or more wavelengths
• the coupler 36 is produced by the guides 32 and 34 which are brought together by a sufficient distance and over a sufficient interaction length to allow the E wave alone to be transferred from the guide 32 to the guide 34 without the L wave undergoing propagation modification in the coupler; at the output of the coupler, only the guide 37 which is an extension of the guide 34 carries the L and E waves which are grouped together.
• the L and E waves are then introduced into the amplifying fiber 31 which amplifies the light power of the E wave from the pump wave.
• the S wave resulting from this amplification is then available at the output of the fiber 31.
• the amplified wave is reintroduced into the support 30, by the end 45 of the latter, then transported by the guide 50 to 'to the filter element, then through the. guide 41 to the end 43 of the support connected to recovery means (not shown).
• the means for introducing a light wave, the pump source, the recovery means, in all of the embodiments of the invention, are optically connected to the ends of the support either by optical fibers via connection means such as that blocks of "V" or ferrules is directly by transferring said means to the support, or even by a free space.
• the filter element is capable of absorbing the residues of the pump L after amplification.
• this filtering element comprises a fifth optical guide 49 connected on the one hand to a pump filter F and on the other hand to a second multiplexer 44; this multiplexer is connected on the one hand to the optical guides 41 and 49 and on the other hand to a seventh optical guide 50 called the last guide.
• the optical guide 41 is connected at the end 45 of the support via the multiplexer 44 and the optical guide 50.
• the multiplexer 44 is also formed by a proximity coupler.
• the pump filter F is produced by stopping the optical guide 49 in the support, the pump residues are then no longer guided and are absorbed in the support. This stopping of the guide can also be carried out on a side wall of the support so as to eject the pump residues from the support (see the amplification assemblies in FIG. 7).
• the ends 39 and 45 of the support are connected to the ends of the amplifying fiber by ferrules or as shown in this figure by a block of "V" referenced in dashed lines by V 2 .
• the pump wave when it is emitted by a fiber laser diode, it is connected to the end 33 by a ferrule or as shown in this figure by block of "V" referenced by Vi.
• the wave E to be amplified can be introduced by introduction means connected to the end 35 of the support by a ferrule or as shown in this figure by the block V x .
• the amplified wave S is recovered by recovery means which can also be connected to the end 43 of the support by a ferrule or as shown in this figure by the block Vi.
• control means the introduction means, the recovery means, the pump source can also be connected to the corresponding ends of the support directly, for example by bonding.
• FIG. 3 precisely represents a hybrid amplifier according to the invention , of the same type as that of FIG. 2, the support of which comprises a first and a second mode adapter referenced 46 and 47.
• the mode adapter 46 is situated at the end 39 of the support, between the optical guide 37 and one of the ends of the amplifying fiber and the mode adapter 47 is located on the end 45 of the support, between an optical guide 50 and the other end of the amplifying fiber.
• FIG. 3 is also shown the use of two sampling elements referenced 42 and 45.
• the element 42 makes it possible to sample a part Mi of the light wave E conveyed by the optical guide 32 and to transport the signal sampled Mi towards control means (not shown) which may be external to the support or integrated into the support.
• This element 42 is produced by an optical guide connected to the guide 32 by an asymmetrical divider produced for example by an asymmetrical Y junction.
• the element 45 makes it possible to take a part M 2 of the light wave S conveyed by the optical guide 41 and to transport the sampled signal M 2 to control means (not shown) which may be external to the support or integrated into the support.
• This element 45 is produced as previously by an optical guide connected to the guide 41 by an asymmetrical divider produced for example by an asymmetrical Y junction.
• the sampled waves Mi and M 2 can also be connected to control means also by connection elements of the ferrule type or by the blocks of "V", V a and / or V 2 .
• FIG. 4 schematically illustrates another variant of a hybrid amplifier of the type of that of FIG. 2.
• the support includes 2 mode adapters referenced 46 'and 47'.
• the mode adapter 46 ' is located at the end 35 of the support, between the optical guide 32 and the input of the E wave; the mode adapter 47 'is located on the end 43 of the support, between the optical guide 41 and the output of the S wave of the support.
• mode adapters respectively make it possible to adapt the guided modes of the corresponding guides, to the modes of the means for introducing the E wave and the means for recovering the S wave.
• all the ends of the support which are connected to external elements may include mode adapters of the same type as those described above to adapt the mode of these external elements to that of the guides connected to said ends.
• FIGS 5 and 6 schematically illustrate two other embodiments of a hybrid optical amplifier with an integrated filter element. For the sake of simplification, these figures have not depicted sampling means and adapters although these elements can also be used in these embodiments.
• Figure 5 differs from Figure 2 by a filter element 60 connected between the guides 41 and 50, of another type. All the other elements being the same as those in FIG. 2 have the same references.
• This element 60 comprises a Mach-Zehnder element integrated in the substrate 30. It is produced by two head-to-tail Y junctions Jl and J2 connected by two optical guides 61 and 62, the junction Jl being optically connected to the guide 50 and the junction J2 being optically connected to the guide 42.
• This filtering element 60 is made so as to allow filtering of the pump residues without disturbing the signal. In particular, the difference in length between the two arms of the Mach-Zehnder is calculated to obtain said filtering.
• the light wave arriving from the amplifying fiber 31 and composed of the amplified signal and the residues of the pump wave L is introduced in guide 50 then separated by the junction J1 into two light waves. These two waves then propagate respectively in the guides 61 and 62 then they recombine at the junction J2.
• the lengths of the guides 61 and 62 respectively are chosen so that the recombination of the light waves in the junction J2 results in destructive interference for the wavelength of the pump wave L and constructive for that of the amplified signal. In this way, the residues of the pump wave L are very strongly attenuated at the junction J2.
• phase shift between the two waves must be equal to ⁇ , and for the interference to be constructive, the phase shift between the two waves must be 2 ⁇ .
• a pump wave L of wavelength about 980 nm and an amplified signal of wavelength of the order of 1550 nm one can choose for one of the guides (for example 61) a length of 100 ⁇ m and for the other guide (for example 62) a length of 1000 ⁇ m.
• FIG. 6 differs from FIG. 2 by a filtering element 70 connected between the guides 41 and 50, of another type also. As before, all the other elements being the same as those in FIG. 2 have the same references.
• the guide 41 is coincident with the guide 50.
• the filtering element 70 can be composed of either a layer absorbent 71, either from a Bragg grating, or even from a long period grating, these grids being represented very schematically also by the reference 71.
• a layer absorbent 71 this is advantageously carried out on the substrate 30 above the guide 41. It is composed for example of a film of single material or of a superposition of films of materials. The material or materials making up said layer must have absorption bands at the wavelength (s) of the pump wave L but not at the length (s) of the amplified signal.
• At least the part of the guide 41 located under the layer 71 must be at a depth relative to said layer such that the evanescent part of the pump wave can interact with this layer.
• the dimensions of the absorbent layer are determined so as to obtain as much absorption as possible at the wavelength or wavelengths of the pump wave L.
• the part of the guide 41 located under said layer 71 may be non-linear and have coils or loops, to increase the length of interaction between the guide and the absorbent layer.
• the absorbent layer 71 is glass doped with ytterbium, of so as to attenuate the waves propagating at 980 nm but not those propagating at 1550 nm.
• This absorbent layer can be deposited on the substrate 30 by all the conventional deposition techniques and for example by vacuum evaporation or by sol-gel deposition.
• This network is formed for example by etching the substrate, above the guide 41 or by an appropriate ion exchange in or in the vicinity of a part of the guide 41.
• this is formed in the substrate for example by an ion exchange in or in the vicinity of a part of the guide 41 so as to couple the pump residues out of the guide.
• FIG. 7 schematically represents an example of a matrix of hybrid amplifiers according to the invention comprising n hybrid optical amplifiers as described above. More precisely, this matrix comprises in a support 60, n amplifier assembly Ni with i integer ranging from 1 to n, each assembly comprising for example, the same integrated elements as those described with reference to FIG. 4. Furthermore, each together Ni is connected to an amplifying fiber 31.
• mode adapters may or may not be used in a hybrid amplifier of the invention independently of each other.
• additional sampling elements may or may not be used in a hybrid amplifier of the invention independently of each other.

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• 2001
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• 2002
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