WO2009027583A1 - Procédé d'alignement pour couplage entre fibre et guide d'onde optique - Google Patents

Procédé d'alignement pour couplage entre fibre et guide d'onde optique Download PDF

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Publication number
WO2009027583A1
WO2009027583A1 PCT/FI2008/050477 FI2008050477W WO2009027583A1 WO 2009027583 A1 WO2009027583 A1 WO 2009027583A1 FI 2008050477 W FI2008050477 W FI 2008050477W WO 2009027583 A1 WO2009027583 A1 WO 2009027583A1
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WIPO (PCT)
Prior art keywords
light
channel
fibre
alignment
connection
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PCT/FI2008/050477
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English (en)
Inventor
Timo Aalto
Original Assignee
Valtion Teknillinen Tutkimuskeskus
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Publication of WO2009027583A1 publication Critical patent/WO2009027583A1/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
    • G02B6/24—Coupling light guides
    • G02B6/26—Optical coupling means
    • G02B6/30—Optical coupling means for use between fibre and thin-film device
    • 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
    • G02B6/122—Basic optical elements, e.g. light-guiding paths
    • G02B6/1228—Tapered waveguides, e.g. integrated spot-size transformers
    • 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
    • G02B6/24—Coupling light guides
    • G02B6/26—Optical coupling means
    • G02B6/30—Optical coupling means for use between fibre and thin-film device
    • G02B6/305—Optical coupling means for use between fibre and thin-film device and having an integrated mode-size expanding section, e.g. tapered waveguide
    • 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
    • G02B6/24—Coupling light guides
    • G02B6/42—Coupling light guides with opto-electronic elements
    • G02B6/4201—Packages, e.g. shape, construction, internal or external details
    • G02B6/4219—Mechanical fixtures for holding or positioning the elements relative to each other in the couplings; Alignment methods for the elements, e.g. measuring or observing methods especially used therefor
    • G02B6/422—Active alignment, i.e. moving the elements in response to the detected degree of coupling or position of the elements
    • G02B6/4221—Active alignment, i.e. moving the elements in response to the detected degree of coupling or position of the elements involving a visual detection of the position of the elements, e.g. by using a microscope or a camera
    • G02B6/4222—Active alignment, i.e. moving the elements in response to the detected degree of coupling or position of the elements involving a visual detection of the position of the elements, e.g. by using a microscope or a camera by observing back-reflected light

Definitions

  • the present invention relates to a packaging technique for optical waveguide components and particularly for joining optical light channels and optical fibres to each other precisely and with low losses.
  • a fibre-light-channel connection is formed of an optical fibre and an optical light channel which are aligned and possible also permanently attached to each other, preferably as precisely as possible and with the lowest possible optical insertion attenuation.
  • a fibre- light-channel connection is intended to connect light from an optical fibre to an optical light channel or vice versa, with the lowest possible losses.
  • a fibre-light-channel connection can also be formed from a fibre array, i.e. from several parallel fibres, which are connected to a corresponding array of light channels.
  • both the optical fibre and the optical light channel are single-mode waveguides, in other words, that in them the light travels only in a single advancing waveguide mode.
  • a fibre-light-channel connection can also be implemented in cases, in which either or both of these waveguides are multimode.
  • the optical fibre has a circular cross-section with an external diameter of 100 - 300 ⁇ m and that it has a core, which is either of glass, or has optical properties similar to those of glass, and a diameter of 5 - 10 ⁇ m.
  • the fibre-light-channel connection can also be implemented with other kinds of optical fibres, for example, a fibre made from an organic substance, or a fibre with a rectangular cross-section or one that is elongated to be narrower at its point.
  • the optical light channel is an optical waveguide manufactured on a planar substrate, and which is part of an integrated optical circuit, the dimensions of the cross-section of the core of which being the same or smaller than the corresponding dimensions of the optical fibre.
  • the light channel is on a light -channel chip, which is detached from a larger planar substrate, for example, a wafer, used in the manufacture of the light channel.
  • the fibre-light-channel connection can also be implemented using some other kinds of optical light channels, for example, a light channel manufactured on a flexible substrate, or a light channel, the dimensions of the core of which are greater than the dimensions of the core of the fibre.
  • a passive alignment method is previously known, in which the optical fibre or fibre array is placed in a groove, or other corresponding structure, which is manufactured on the same planar substrate as the light channel.
  • the additional structures required by passive alignment interfere with the manufacture of the light-channel chips, and by no means always provide a sufficient alignment precision.
  • a typical problem is that the location of the fibre core relative to the outer edge of the fibre varies randomly, so that a precise alignment of the light channel relative to the outer edge of the fibre will not ensure a precise alignment between the cores of the fibre and the light channel. In practice, passive alignment becomes impossible, if the light should be connected to very small light channels.
  • An active alignment method is also previously known, in which the optical power travelling through the fibre-light-channel connection is measured, and the feedback signal thus obtained is exploited when actively aligning the fibre-light-channel connection.
  • active alignment is made by moving the fibre manually relative to the light channel and maximizing the optical power coming through the fibre-light-channel connection to a light detector.
  • Active alignment can also be automated, for example, by moving the fibre under computer control. Compared to the passive and automated alignment methods, manual active alignment is indeed a quite slow and expensive method. Active alignment requires the continuous measurement of the optical power going through the fibre-light-channel connection, so that, for example, a laser or detector that may be at the other end of the light channel must be switched on. In some cases, it can be very difficult to implement the measurement of the transmittance power and, as the integration density of the light-channel chips increases, it can be assumed to become increasingly difficult to manually align the fibre-light-channel connection.
  • An active alignment method is also previously known, in which the optical power that has gone through a fibre-light-channel connection implemented by means of a fibre array is measured from only the outermost fibres of the array, which are not necessarily used for anything other than making the fibre-light-channel connection.
  • the task of the outermost fibres is then to align the other fibres between them with the corresponding light channels, without the light having to be connected at all to the light channels in the middle.
  • This solution functions well only if the location of the fibres in relation to each other in the fibre array corresponds completely to the location of the light-channels in relation to each other in the light-channel array. In practice, this is often difficult to implement, due, among other things, to the aforementioned variations in the locations of the cores of the fibres as well as to even the slightest curvature in the fibre and/or light-channel array.
  • a so-called alignment light is directed to photosensitive material between the fibres, either simultaneously, or alternately from each fibre.
  • the alignment light increases the refraction index of the photosensitive material, which in turn refracts the alignment light in the direction of the higher refractive index.
  • a so-called self- aligning connection channel in which the core of the higher refractive index is created by the alignment light, arises between the cores of the fibres.
  • near-infrared light is generally used, and by no means all of the light channels developed for it will transmit the visible-wavelength range alignment light required for cold welding.
  • the light channel may be connected to a complex integrated optical circuit, or its other end may terminate, for example, in a laser or light detector. In many cases, bringing an alignment light to a fibre-light-channel connection from its both sides is either impossible, or extremely difficult.
  • the invention is intended to eliminate the defects of the prior art described above and to provide a new, accurate, low-loss, and economical method for making fibre-light-channel connections.
  • the edge of a light-channel chip is patterned and/or surfaced in such a way that, when aligning a fibre-light-channel connection, the alignment light coming from the fibre is reflected back to the fibre considerably better from the core of a light channel than from its environment.
  • a fibre can be aligned with a light channel by maximizing the alignment light reflected back to the fibre.
  • the alignment light reflected from the end of the light channel can be used when applying cold welding to a fibre-light-channel connection.
  • a thin film grown on the end of the light channel acts as a reflection reducing, so-called anti-reflection film at the operating wavelength of the light-channel chip and simultaneously reflects well alignment light of different wavelength. This simultaneously maximizes both the reflection of the alignment light from the light- channel' s end and the transparency of the fibre-light-channel connection at the actual operating wavelength of the light-channel chip.
  • the structures immediately surrounding the light-channel end are moved farther from the fibre, as the farther the reflective surface is from the fibre, the less it will reflect light back to fibre.
  • the surfaces of the structures surrounding the light-channel end are made to be such that the alignment light reflects back to the fibre from them much poorer than from the end of the light channel. In this case, it is possible, for example, to exploit the property of the thin film grown on the end of the light channel that, grown on other surfaces, its reflectivity may be much less.
  • the gap between the fibre and the light- channel chip can also be filled with a liquid (for example, a photosensitive material, or an adhesive that is hardened later), the refractive index of which is close to the refractive index of some material surrounding the light-channel end, whereby the surface of the material in question reflects practically no light.
  • the surfaces of the structures surrounding the light-channel end can also be made, or left intentionally rough, in other words they effectively scatter the alignment light and do not reflect it well back to the fibre.
  • the fibre-light-channel connection is made by cold welding, in such a way that the alignment light is brought to the gap between the fibre and the light channel only through the fibre, and part of it is reflected back towards the fibre.
  • the alignment light reflected from the light-channel end thus replaces the alignment light coming separately to the connection from the other direction.
  • the alignment light coming from the fibre is reflected from the light-channel end clearly better than from the surfaces or structures surrounding it. In terms of the success of cold welding, this largely corresponds to a situation in which the alignment light is directed to the connection through the light channel.
  • the gap between the fibre and the light channel is filled with a material, the refractive index of which increases when the alignment light used in cold welding is aimed at it.
  • the refractive index first begins to increase relatively mostly directly in front of the core, where the intensity of the alignment light is greatest.
  • the refractive index begins to also increase particularly directly in front of the light-channel end, where the reflected alignment light increases the intensity of the alignment light locally.
  • the alignment light begins to be gradually directed towards the areas with the greatest refractive index, in which a so-called connection channel gradually arises through this self-controlling process. Thanks to the self-alignment, the connection channel need not necessarily be straight, but can also connect a fibre and light channel that were not originally aligned precisely against each other.
  • connection channel created in cold welding in the fibre-light- channel connection connects a light channel and a fibre, the sizes of the optical fields of which clearly differ from each other.
  • the connection channel will then form a so-called field-size converter, in which, for example, the cross-sectional area of the light beam travelling to the light channel changes significantly as the light travels along the connection channel.
  • the alignment light coming from the fibre and reflected back to the fibre from the light channel end is amplified and directed back to the fibre-light-channel connection, in which case a strong positive feedback is achieved between the strength of the alignment light and the power reflected from the light-channel end.
  • Figure 1 shows a cross-section of a previously known light channel
  • Figure 2 shows a cross-section of a previously known optical fibre
  • Figure 3 shows a three-dimensional illustration of a fibre-light-channel connection
  • Figure 4 shows a three-dimensional illustration of a connection between two fibres, in which a self-aligning connection channel has been made between the fibres, with the aid of previously known cold welding;
  • Figure 5 shows a three-dimensional illustration of a connection between a fibre and a light channel, in which a self-aligning connection channel has been made, with the aid of the cold- welding method according to the invention
  • Figure 6 shows one arrangement according to the invention, for making a fibre- light-channel connection
  • Figure 7 shows a three-dimensional illustration of a light-channel end, which can be used in one method according to the invention for making a fibre-light- channel connection;
  • Figure 8 shows the calculated reflection (R, thick line) and the transmittance spectra
  • T thin line
  • ⁇ o wavelength range corresponding to one transmittance maximum
  • % ⁇ , ⁇ 2 reflection maxima
  • Figure 9 shows the reflection spectrum of a thin titanium-oxide film grown on top of both the end of the silicon light channel (thick line) and of the silicon- dioxide layer surrounding it (thin line).
  • Figure 1 shows an illustration of one example of a cross-section of a light channel 2 and of the light-channel end 1.
  • the light channel is implemented on a planar substrate 4, on top of which is a buffer layer 5, which optically isolates the light-transmitting core layer 7 on top of it from the substrate 4.
  • a thin sheathing layer 6 At the sides and on top of the light-channel core 7 is a thin sheathing layer 6.
  • numerous other light-channel structures, to which the method according to the invention can be applied, are previously known.
  • the refractive index of the core layer 7 is clearly greater than the refractive indices of the materials (4, 5, 6) surrounding it and the light travels mainly in the core layer 7 entirely reflecting it from the boundary surfaces immediately surrounding it.
  • numerous light-channel structures are previously known, in which the light travels simultaneously in several different materials, or a significant part of the optical field extends outside the core layer 7.
  • the basic assumption is made that the light channel, or at least part of it, is single-mode, in other words the light travels through the light channel in only one advancing waveguide mode, i.e. in the so-called basic mode.
  • Figure 2 shows an illustration of a cross-section of an optical fibre 11, in which there is a light-transmitting core 12 of the fibre.
  • the refractive index of the core 12 is greater than the refractive indices of the materials surrounding it, though other kinds of optical fibre are previously known, for example, hollow fibres and so-called photon-crystal fibres.
  • optical fibres there is quite a small difference in refractive index between its core 12 and the so-called sheathing surrounding it, whereby the reflection of the light arising at the end of the fibre and its possible refraction can generally be calculated accurately by assuming that the interface is one-dimensional, i.e. that the light at the end of the fibre travels in a homogeneous medium.
  • the transverse refractive index structure When calculating the transverse distribution of the optical field advancing in the fibre or exiting from it, or the so-called eigenmodes of the fibre, the transverse refractive index structure must, however, be taken into account. Due to the small difference in refractive index, even a considerable part of the light advancing in the fibre, particularly of its so-called advancing modes, extends to the so-called sheathing surrounding the core 12. In the following examination, a basic assumption is made that the fibre 11 is single-mode, i.e. that it has only a single advancing eigenmode. However, this does not prevent the invention from also being applied to multimode fibres.
  • the outer edge 24 of the cross-section of the fibre 11 is typically round in shape and has a diameter of 100 - 300 ⁇ m. Because in a single-mode fibre the diameter of the intensity distribution of the advancing basic mode is typically 5 - 15 ⁇ m, so that the outer edge 24 is generally a considerable distance from the optical exit of the fibre. In addition, the shape of the outer edge generally deviates slightly from a perfect circle, and the core 12 of the fibre generally is not precisely at the centre point of the circle defined by the outer edge. Thus, the outer edge 24 is only to a limited extent suitable for the passive alignment of the core 12 of the fibre, for example, relative to the light channel 2.
  • the aim of the invention is to provide a better method than previously known methods for implementing a connection between a fibre 11 and a light channel 2.
  • the fibre-light- ch'annel connection is illustrated in Figure 3.
  • the optical light channel 2 is an optical waveguide, which is manufactured on a planar substrate 4, and which is part of an integrated optical circuit, and the transverse dimensions of the core 7 of which are the same or smaller than the corresponding dimensions of the optical fibre 11.
  • the light channel 2 is on a light-channel chip 3, which has been detached from a larger planar substrate used in the manufacture of the light channel, for example, from a wafer.
  • the fibre-light-channel connection can also be implemented using other kinds of optical channels, for example, a light channel manufactured on a flexible substrate, or a light channel with core dimensions that are larger than the dimensions of the core of the fibre.
  • the light travels along the so-called optical axis 21.
  • the optical field is not like a point, so that the optical axis is defined, for example, on the basis of the intensity maximum of the optical field, or of the position distribution weighted by the intensity.
  • the fibre 11 the light travels along a corresponding optical axis 22.
  • the transverse alignment is intended to bring the optical axes of the light channel and the fibre onto the same line.
  • the longitudinal alignment is intended to bring the light-channel end 1 to the optimal distance from the end of the fibre 11.
  • the light beam gradually begins to spread, so that generally the light-channel end is sought to be brought as close as possible to the end of the fibre.
  • the so-called cold- welding method illustrated in Figure 4 can be used to compensate for alignment errors arising in the mechanical alignment between the fibres.
  • a small transverse alignment error can thus remain between the optical axes (22, 23) of the fibres (11, 13), and the distance between the ends of the fibres need not be particularly precisely defined, nor very small.
  • a so-called alignment light is directed to the photosensitive medium 15 (not distinguished in Figure 4) between the fibres, either simultaneously or alternately from both fibres.
  • the alignment light increases the refractive index of the photosensitive material 15, which in turn refracts the alignment light in the direction of the higher refractive index.
  • the alignment light exiting from the fibre thus itself centres its own advancing. This either reduces or entirely avoids the spreading of the alignment-light beam coming from the fibre and forms a so-called alignment channel 16 in the photosensitive medium 15, in which there is a high refractive index core formed by the alignment light.
  • the alignment-light beams coming from the fibres first of all form the beginning of a small connection channel at the end of both fibres.
  • the alignment-light beams coming from the various fibres affect the connection channels formed by each other, always extending to the end of the opposite fibre. Indeed, the connection channels starting from the opposite fibres become guided gradually towards each other in the gap between the fibres, and finally connect the cores (12, 14) of the fibres (11, 13) to each other as a unified and self-aligning connection channel 16.
  • Figure 5 illustrates the application of cold welding to a fibre-light-channel connection.
  • a successful cold weld generally requires the alignment light to be brought to the connection from both the light-channel 2 and the fibre 11 sides.
  • Cold welding also generally requires an alignment light that has a precisely limited wavelength, which is typically in the range of visible light.
  • the guiding of the alignment light to the fibre-light- channel connection from the direction of the light-channel 2 side for its part requires that the alignment light is able to advance well in the light channel and that the alignment light can in some way be guided to the light channel from its other end.
  • Optical fibres generally transmit light well over a very wide wavelength range, but light channels in no way always transmit light over an equally wide wavelength range.
  • near-infrared light is generally used in optical telecommunications technology and the light channels developed for it in no way always transmits the alignment light in the visible wavelength range required in cold welding.
  • the silicon light channels well suited to optical telecommunications technology are transparent only at a wavelength of more than 1.2 ⁇ m.
  • the light channel can be connected to a complex integrated optical circuit manufactured on the same light-channel chip, or its other end can terminate in, for example, a laser or a light detector. In several cases, it is either impossible or very difficult to bring the alignment light to the fibre-light-channel connection from its both sides.
  • the edge of the light-channel chip 3 is manufactured, patterned, and/or coated in such a way that the alignment light coming from the fibre 11 when aligning a fibre-light-channel connection is reflected back to the fibre 11 considerably better from the light-channel end 1 than from its immediate surroundings, and this is exploited when implementing a fibre-light-channel connection.
  • the term light-channel end 1 refers by default to the part of the core material 7 of the light channel, visible from the edge of the light-channel chip 3, from which the light (not the alignment light) advancing in the light channel essentially exits.
  • the light- channel end 1 is formed of a homogeneous material, which is surrounded by another material preferably with clearly different optical properties. More generally, it can also be stated that the light-channel end 1 is an area immediately surrounding the optical axis 21 in the exit plane of the light channel 2, the optical properties of which differ in some way from those of the areas surrounding it.
  • the fibre-light-channel connection is aligned by moving the fibre 11 and the light channel 2 transversely relative to each other, until the amount of alignment light coming from the fibre 11 and reflected back to the fibre 11 through the light-channel end 1 is as great as possible.
  • the fibre-light-channel connection is formed by cold welding, in such a way that the alignment light is brought to the gap between the fibre 11 and the light channel 2 only through the fibre 11 and part of it is reflected back from the light-channel end 1 towards the fibre.
  • the alignment light reflected from the light-channel end 1 thus replaces the alignment light coming separately from the other direction of the connection.
  • the alignment light coming from the fibre 11 is reflected from the light-channel end 1 clearly better than form the other surfaces or structures immediately surrounding it. In terms of the success of the cold welding, this corresponds largely to a situation, in which alignment light would be directed through the light channel 2.
  • the gap between the fibre 11 and the light channel 2 is filled with a material 15 (not shown in the figure), the refractive index of which increases when the alignment light used in the cold welding is aimed at it.
  • the refractive index first increases relatively most directly in front of the core 12 of the fibre, where the alignment light is most intense.
  • the alignment light also begins to increase in particular directly in front of the light-channel end 1, where the reflected alignment light increases the intensity of the alignment light locally. After this, the alignment light begins to gradually become directed towards the areas of the greatest refractive index, in which, through this self-controlling process, a connection channel 16 gradually arises.
  • connection channel 16 need not necessarily be straight, but instead it can also connect a fibre 11 and a light channel 2, which were not originally aligned precisely against each other. After the cold welding, if necessary, the photosensitive material 15 can be removed chemically from around the connection channel 16.
  • connection channel 16 that arises in a fibre-light-channel connection during cold welding connects a fibre 11 and a light channel 2, the sizes of the optical fields of which clearly differ from each other.
  • the connection channel 16 can form a so-called field-size converter, in which, for example, the cross-sectional area of the light beam travelling from the fibre to the light channel changes significantly as the light travels along the connection channel.
  • the surface area of the reflective light-channel end 1 that reflects the alignment light well can be considerably smaller than the effective cross-sectional area at the end of the fibre of the alignment light coming from the fibre 11.
  • field-size converter based on a connection channel of this kind can clearly reduce the optical connection loss and significantly ease the precision requirements of a mechanical fibre-light-channel connection.
  • Figure 6 shows an embodiment of the invention, in which the amount of alignment light coming to a fibre-light-channel connection increases strongly if the fibre 11 and the light channel 2 are brought precisely against each other.
  • the alignment light coming from the light source 17 is first guided to a power divider 18, the end 19 of one exit fibre reflects as little light as possible.
  • the alignment light from the other exit fibre 11 is guided towards the light-channel end 1 , from where it is reflected back to the fibre 11.
  • the reflection back to the fibre 11 is the greater, the better the core 12 of the fibre and the light-channel end 1 are aligned with each other.
  • the light reflected back to the fibre 11 (and only it) is amplified by an optical amplifier 20.
  • the amplified light is guided back to the light- channel end 1, from there again to the amplifier 20, etc., in which case a powerful positive feedback is achieved between the strength of the alignment light and the power reflected from the light-channel end 1.
  • connection channel 16 between the fibre 11 and the light- channel end 1 increases the back reflection and through it the amplification of the alignment light.
  • this arrangement can be used to detect a powerful positive connection between the intensity of the alignment light and the alignment of the fibre-light-channel connection.
  • Figure 7 shows one example, illustrating the method in general, of the edge of a light- channel chip 3 suitable for the alignment according to the invention of a fibre-light- channel connection.
  • a core layer 7 on top of an insulating layer 5 is a core layer 7, in which a light channel 2 is formed by etching grooves 8.
  • the core layer 7 is patterned in such a way that an alignment light coming from a fibre 11 (not shown in Figure 7) is reflected from the edge of the core layer 7 back to the fibre 11 mainly from the light- channel end 1, and only weakly from the other edges of the core layer 7 surrounding it.
  • the core layer 7 is further patterned with patterns 9 like a focussing mirror, in such a way that, with their aid, the alignment light coming from the fibre 11 and passing the light-channel end 1 is reflected between the fibre and the light-channel end 1.
  • the surface of the edge of the substrate 4 of the light-channel chip is considerably rougher than the surface of the end 1 of the light- channel chip and, in addition, is farther from the fibre 11 than the light-channel end 1.
  • Figure 7 also illustrates a so-called ridge-rectangular converter 10, which in this embodiment connects with low loss, from a multimode rectangular light channel 2 connected directly to the light-channel end 1, to a single-mode ridge light channel farther from the edge of the light-channel chip 3.
  • This example shows the possibility that the cross-section of a light channel 2 connected directly to the light-channel end 1 can be optimized for a fibre-light-channel connection, and need not, for example in single-mode light-channel components, necessarily be a single-mode light channel.
  • a thin film grown on the light-channel end 1 acts as a reflection reducing so-called anti-reflection film at the operating wavelength ⁇ o of the light-channel chip 3 and simultaneously reflects well alignment light, the wavelength ⁇ ⁇ of which differs from the operating wavelength ⁇ o. This simultaneously maximizes both the reflection of the alignment light from the light-channel end 1 and the transparency of the fibre-light-channel connection at the actual operating wavelength of the light-channel chip.
  • a thin film can be grown locally only on the light- channel end 1, or it can be grown on a wider area at the edge of the light-channel chip 3.
  • Figure 8 shows an example of the application of the aforementioned thin-film coating to the end 1 of a silicon light channel.
  • a thin film of titanium oxide has been grown on the end of a silicon light channel, which acts as an interferometric thin-film filter.
  • Figure 8 shows the reflection (R, thick line) and transmittance (T, thin line) spectra calculated for this thin-film filter.
  • a wavelength range ( ⁇ o ⁇ 1550 nm) corresponding to one transmittance maximum is separately marked in Figure 8, which in this embodiment according to the invention can be used in the actual operation of the light channel 2).
  • the light-channel end 1 reflects as little light as possible and makes possible a very low-loss fibre-light-channel connection.
  • the wavelength ranges (X 1 ⁇ 440 nm, ⁇ 2 ⁇ 800 nm), corresponding to two reflection maxima, are also marked in Figure 8.
  • the alignment light wavelength XA used in making the fibre-light-channel connection is close to either of these reflection spectrum maxima, in such a way that at least part of the alignment light is reflected back from the light-channel end 1 towards the fibre 11.
  • the thin film grown on the light-channel end 1 is optimized in such a way that its transmittance at the wavelength ⁇ o ⁇ 1550 nm is as great as possible.
  • the thin film can, however, be optimized in such a way that its transmittance is good at any wavelength ⁇ o and at the same time its reflection is sufficiently great at the wavelength ⁇ A of the alignment light, as long as it differs sufficiently from the wavelength ⁇ o.
  • Figure 9 shows a second example of the application of thin-film coating to the light- channel end 1 and particularly of a method, by means of which the alignment light will be more effectively reflected from the coated light-channel end 1 than from the structures immediately surrounding it.
  • the same titanium-oxide film as in the previous example is grown on the end of the silicon-light channel.
  • the refractive index of the core 7 of the silicon-light channel is about 3.5 and that both the optically isolating layer 5 underneath it and the sheathing layer 6 on top of it are of silicon oxide, the refractive index of which is about 1.5.
  • Figure 9 shows the reflective spectra of both the silicon light-channel end (thick line) and of the thin titanium oxide film grown on top of the silicon-dioxide material surrounding it immediately on all sides (thin line).
  • a suitable alignment-light wavelength for example, when X A ⁇ X 1 ⁇ 440 nm, or ⁇ A ⁇ ⁇ 2 ⁇ 800 nm, (c.f. also Figure 8), the alignment light is reflected considerably better from the light-channel end 1 than from the silicon oxide surrounding it. Thanks to this property, the thin film need not be grown only on the light-channel end 1, which may be technically difficult, but it can be grown on a wider area in the environment of the light-channel end 1.
  • the contrast between the alignment light reflected from the light-channel end 1 and from its environment can be increased relative to a case in which the light-channel end 1 is completely uncoated.
  • this embodiment exploits the property of the thin film that its reflection spectrum depends essentially on the substrate on which it is grown.
  • the gap between the fibre 11 and the light-channel chip 3 is filled with a liquid, for example, a so-called matching liquid to be removed later, a photosensitive material, or an adhesive to be hardened later. If the refractive index of this liquid is close to that of some material surrounding the light- channel end 1, then the surface of the material in question reflects practically no light, because there is a very small difference in refractive index in the interface in question, at least compared to the light-channel end 1. This is one effective way to minimize the reflection of the alignment light from the surfaces surrounding the light-channel end 1.
  • a liquid for example, a so-called matching liquid to be removed later, a photosensitive material, or an adhesive to be hardened later.
  • the refractive index of the liquid suitably, it can also be used to advantageously affect the thin film grown on the light-channel end 1 and/or on the surface of the materials surrounding it, as well as the reflection and transmittance spectra. If the refractive index of the liquid is close to those of the fibre 11 and particularly of its core 12, then it will additionally directly reduce the reflection arising at the end of the fibre, which might otherwise interfere with the alignment of the fibre-light-channel connection and increase its connection attenuation.
  • At least some of the structures immediately surrounding the light-channel end 1 are moved farther from the fibre 11, as the farther the reflective surface is from the fibre, the less it reflects light back to the fibre 11 and particularly to the core 12 of the fibre.
  • the moving of the reflective structures farther from the fibre 11 is illustrated in Figure 7.
  • At least some of the surfaces, reflecting the alignment light, of the structures immediately surrounding the light channel end 1 are rotated to an angle such that the alignment light is not well reflected from them towards the fibre 11 and particularly towards the core 12 of the fibre.
  • the rotation of the reflective surfaces is illustrated in Figure 7, though in this particular case the surfaces are patterned and moved farther from the fibre 11, so that the reflection to the fibre 11 is not necessarily reduced, as will be apparent from the following example.
  • some of the alignment-light reflecting surfaces of the structures immediately surrounding the light- channel end 1 are implemented to form curved mirrors, so that the alignment light striking them is focussed towards the light-channel end 1 or between the light-channel end 1 and the core 12 of the fibre.
  • This arrangement can be used in connection with cold welding to increase the intensity of the alignment light either immediately in front of the light- channel end 1, or on a line between the light-channel end 1 and the core 12 of the fibre.
  • the alignment-light reflecting surfaces of the structures immediately surrounding the light-channel end 1 are implemented in such a way that their surface roughness is clearly greater than the surface roughness of the light-channel end 1, so that the alignment light coming from the fibre is effectively scattered from them, and only a small part of the alignment light is reflected from them back towards the fibre 11 and particularly towards the core 12 of the fibre.
  • the edge of the substrate 4 can be sawn or etched very roughly, in which case the light will be effectively scattered from it.
  • the alignment light can be scattered, for example, using patterning of the structures surrounding the light-channel end 1, similar to that in Figure 7 but finer.
  • the fibre-light-channel connection is implemented between a fibre array and a light-channel array, in such a way that, in the alignment between them, only part of the alignment light reflected from the light-channel ends is exploited, for example, the alignment light reflected from the outermost light-channel ends of the array.
  • the fibre-light-channel connection is implemented between a fibre array and a light-channel array, in such a way that, in the alignment between them, only part of the alignment light reflected from the fibres is exploited, and the alignment light is reflected to these fibres from such light-channel ends as are not used at all in the actual operation of the light-channel chip 3.
  • These 'light-channel ends' which are only manufactured for the fibre-light-channel alignment, need not necessarily even be operational light-channel ends, but can also be structures only intended to reflect the alignment light.
  • the advantages of the invention become apparent particularly in mass production, whereby the purchase costs of automatic alignment devices and/or cold- welding devices do not form a significant part of the total cost of a product.
  • the products being manufactured need not, however, be identical, as long as there is a structure that reflects light in the desired manner in all of the light-channel ends 1 used in alignment.
  • a particular advantage of the invention is that the light channels 2 need not be transparent at the wavelength of the alignment light, not need the alignment light be connected at all through the fibre-light-channel connection. It is sufficient if the light is reflected from the light-channel end 1. This is a great advantage in the automatic alignment of a fibre-light- channel connection. Compared to the cold-welding methods known at present, the invention offers unique possibilities for applications.
  • the limitation of the invention are the additional manufacturing stages required at the end of the light-channel chip 3 and the requirements concerning the wavelength of the alignment light.
  • the anti-reflective film to possibly be grown at the light-channel end 1 should minimize the reflection at the operating wavelength and simultaneously produce sufficient reflection at the wavelength of the alignment light.

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  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Optics & Photonics (AREA)
  • Engineering & Computer Science (AREA)
  • Power Engineering (AREA)
  • Microelectronics & Electronic Packaging (AREA)
  • Optical Couplings Of Light Guides (AREA)

Abstract

La présente invention concerne un procédé d'intégration en boîtiers pour des composants de guides d'ondes optiques et en particulier pour connecter entre eux avec précision et sans pertes des guides d'ondes optiques (2) et des fibres optiques (11, 12). L'invention cherche à éliminer les inconvénients des procédés connus et de proposer un nouveau procédé économique, précis et à faibles pertes pour faire une connexion entre fibre optique et guide d'ondes optiques. Le procédé selon l'invention consiste à tracer et/ou revêtir le bord du microcircuit du guide d'ondes (1) de façon que, lorsqu'on fait l'alignement de la connexion entre fibre optique et guide d'onde optique, la lumière d'alignement provenant de la fibre soit renvoyée par reflet dans la fibre considérablement mieux depuis l'emplacement du cœur du guide d'onde optique que depuis la zone périphérique. Ainsi, pour aligner la fibre avec le guide d'ondes optique, il suffit de maximiser la lumière d'alignement renvoyée vers la fibre. Selon un autre mode de réalisation, pour réaliser le soudage à froid entre la fibre optique et le guide d'ondes optique, on utilise la lumière d'alignement renvoyée depuis l'extrémité du guide d'onde optique.
PCT/FI2008/050477 2007-08-31 2008-08-29 Procédé d'alignement pour couplage entre fibre et guide d'onde optique WO2009027583A1 (fr)

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Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2023095278A1 (fr) * 2021-11-26 2023-06-01 日本電信電話株式会社 Élément optique, élément optique intégré et procédé de fabrication d'un élément optique

Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4770529A (en) * 1986-09-08 1988-09-13 Raychem Corp. Alignment of optical waveguides
JPH02251916A (ja) * 1989-03-27 1990-10-09 Nippon Telegr & Teleph Corp <Ntt> 石英系光導波回路と光ファイバの接続方法
US6654523B1 (en) * 2001-08-10 2003-11-25 Lightwave Microsystems Corporation Optical alignment guide and method for aligning an optical fiber array with an optical integrated circuit
EP1503231A1 (fr) * 2002-04-26 2005-02-02 Ibiden Co., Ltd. Structure de transmission optique, guide optique, procede de fabrication d'un guide d'ondes optique et coupleur d'interconnexion optique

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4770529A (en) * 1986-09-08 1988-09-13 Raychem Corp. Alignment of optical waveguides
JPH02251916A (ja) * 1989-03-27 1990-10-09 Nippon Telegr & Teleph Corp <Ntt> 石英系光導波回路と光ファイバの接続方法
US6654523B1 (en) * 2001-08-10 2003-11-25 Lightwave Microsystems Corporation Optical alignment guide and method for aligning an optical fiber array with an optical integrated circuit
EP1503231A1 (fr) * 2002-04-26 2005-02-02 Ibiden Co., Ltd. Structure de transmission optique, guide optique, procede de fabrication d'un guide d'ondes optique et coupleur d'interconnexion optique

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2023095278A1 (fr) * 2021-11-26 2023-06-01 日本電信電話株式会社 Élément optique, élément optique intégré et procédé de fabrication d'un élément optique

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