CA1189368A - Method for coupling or connecting an integrated optical wave-guide and a monomodal optical fibre - Google Patents
Method for coupling or connecting an integrated optical wave-guide and a monomodal optical fibreInfo
- Publication number
- CA1189368A CA1189368A CA000411890A CA411890A CA1189368A CA 1189368 A CA1189368 A CA 1189368A CA 000411890 A CA000411890 A CA 000411890A CA 411890 A CA411890 A CA 411890A CA 1189368 A CA1189368 A CA 1189368A
- Authority
- CA
- Canada
- Prior art keywords
- guide
- fibre
- wave
- distribution
- monomodal
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
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
Landscapes
- Physics & Mathematics (AREA)
- General Physics & Mathematics (AREA)
- Optics & Photonics (AREA)
- Optical Couplings Of Light Guides (AREA)
Abstract
ABSTRACT OF DISCLOSURE
This invention concerns a method for coupling or connecting an integrated optical wave-guide to a monomodal optical fibre.
In this method, the end portion of the fibre is treated, in order to alter the distribution parameter Wo of the electric field on the end surface of the fibre, the fundamental distribution mode being assumed to be Gaussian. The new parameter is approximately equal to ?WxWy, where Wx and Wy are parameters for the mode in the integrated wave-guide, also assumed to be Gaussian, with two dimensions. The treatment consists stretching of drawing the fibre or simply heating it to change its refractive index gradient.
The invention can be applied to optical telecommunications.
This invention concerns a method for coupling or connecting an integrated optical wave-guide to a monomodal optical fibre.
In this method, the end portion of the fibre is treated, in order to alter the distribution parameter Wo of the electric field on the end surface of the fibre, the fundamental distribution mode being assumed to be Gaussian. The new parameter is approximately equal to ?WxWy, where Wx and Wy are parameters for the mode in the integrated wave-guide, also assumed to be Gaussian, with two dimensions. The treatment consists stretching of drawing the fibre or simply heating it to change its refractive index gradient.
The invention can be applied to optical telecommunications.
Description
BACKGROUND OF THE INVENTION
1. Fleld of the invention.
This invention concerns the coupling between an integrated optical wave-guide and a monomodal optical fiber.
Such fibres are used for optical telecommunica-tions, because they allow signals to be propagated with pass-bands of more than 1 gigahertz.
Optical telecommunications also make use of modu-lators and switches, preferably of integrated optical cons-truction. The integrated guides for such modulators and switches have to be connected to telecommunication lines made wi-th monomodal optical fibres t with minimum transmis-sion loss caused by such connection.
1. Fleld of the invention.
This invention concerns the coupling between an integrated optical wave-guide and a monomodal optical fiber.
Such fibres are used for optical telecommunica-tions, because they allow signals to be propagated with pass-bands of more than 1 gigahertz.
Optical telecommunications also make use of modu-lators and switches, preferably of integrated optical cons-truction. The integrated guides for such modulators and switches have to be connected to telecommunication lines made wi-th monomodal optical fibres t with minimum transmis-sion loss caused by such connection.
2. Description of the prior art.
Methods for connecting a monomodal fibre and an integrated waveguide in such a way as to ensure negligible positioning errors have been described, for example, by ~.P. Hsu and A.F~ Milton, in the periodical Electronics Letters, vol. 12, no. 16 of 5th August 1976. An improved process for aligning a monomodal optical fibre and an integrated wave-guide formlng part of an integrated opti-cal circuit is characterized by the Eact the fibre is pla-ced in a straight - .
., ,.:j ~
33~
groove in a plate, which rests on one base, a second base is juxtaposed beside the first, by placing flat slip surfaces against each other, the integrated optical circuit being attached to the second base, the axes and ends of the wave-guide and fibre are aligned by moving the fibre in the groove and by sliding the first base relative to the second bases the fibre, plate and first base being clamped together, and the two bases being joined by an adhesive film covering the slip surfaces,suchadhesive being applied while fluidg at any rate during the final step of alignment operations.
However, the efficiency of connection depends on how well the modes of light energy distribution in the fibre and wave-guide sections overlap.
On the one band, in the fibre, the core radius of which is only a few microns for monomodal fibres, the electric field is distributed accord-ing to a substantially Gaussian and circular pattern. The distance WO, (distribution parameter) from the fibre axis at which the electric field drops to 1/e of its value at the axis is also a few microns.
On the other hand, the electric field of a wave-guide with lateral confinement, realised in integrated optics follows substantially a Gaussian elliptical distribution, along two rectangular axes of the cross-sectional plane. For a guide with rectangular cross-section, there are two distribution parameters Wx and Wy, i.e. the distances along the rectangular axes x and y at which the electric field drops tol/e of its value at the centre of the guide.
This invention offers a method -to improve the coupling by adapting such distribution modes in order to increase their mutual overlapping, when (as is generally the case) WO is greater than ~ .
SUMMARY OF THE INVENTION
The invention concerns a method for coupling or connecting an integrated optical wave-guide and a monomodal optical fibre, the monomodal fibre propagating a ma;nly Gaussian distribution of the electric field with a distribution parameter WO, and the integrated optical wave-guide with lateral confinement propagating a mode of distribution of the electric field with two separate parameters Wx and Wy on the cross-sectional plane of the guide, this method being characterized by the fact that it comprises a preliminary step during which the end portion of the fibre and/or wave-guide is treated, in order to reduce the diFference between WO and ~WxWy at the coupling section.
This preliminary treatment consists in stretching the end portion of the fibre. Experience shows that if the fibre is heated for long enough, doping agents will migrate, producing the necessary adaptation.
BRIEF DESCRIPTION OF THE DRAWINGS
Other features and advantages of the invention will ~ppear from the following description, with reference to the accompanying figures:
- figure 1, showing a diagrammatical view of the junction of an optical fibre and an integrated wave-guide;
- figure 2, showing electric field distributions in the wave-guide and fibre;
- figure 3, showing an explanatory graph.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Figure 1 shows an integrated wave-guide G on a blade L, produced, for example, by diffusing titanium on a lithium niobate substrate.
r - ~
Methods for connecting a monomodal fibre and an integrated waveguide in such a way as to ensure negligible positioning errors have been described, for example, by ~.P. Hsu and A.F~ Milton, in the periodical Electronics Letters, vol. 12, no. 16 of 5th August 1976. An improved process for aligning a monomodal optical fibre and an integrated wave-guide formlng part of an integrated opti-cal circuit is characterized by the Eact the fibre is pla-ced in a straight - .
., ,.:j ~
33~
groove in a plate, which rests on one base, a second base is juxtaposed beside the first, by placing flat slip surfaces against each other, the integrated optical circuit being attached to the second base, the axes and ends of the wave-guide and fibre are aligned by moving the fibre in the groove and by sliding the first base relative to the second bases the fibre, plate and first base being clamped together, and the two bases being joined by an adhesive film covering the slip surfaces,suchadhesive being applied while fluidg at any rate during the final step of alignment operations.
However, the efficiency of connection depends on how well the modes of light energy distribution in the fibre and wave-guide sections overlap.
On the one band, in the fibre, the core radius of which is only a few microns for monomodal fibres, the electric field is distributed accord-ing to a substantially Gaussian and circular pattern. The distance WO, (distribution parameter) from the fibre axis at which the electric field drops to 1/e of its value at the axis is also a few microns.
On the other hand, the electric field of a wave-guide with lateral confinement, realised in integrated optics follows substantially a Gaussian elliptical distribution, along two rectangular axes of the cross-sectional plane. For a guide with rectangular cross-section, there are two distribution parameters Wx and Wy, i.e. the distances along the rectangular axes x and y at which the electric field drops tol/e of its value at the centre of the guide.
This invention offers a method -to improve the coupling by adapting such distribution modes in order to increase their mutual overlapping, when (as is generally the case) WO is greater than ~ .
SUMMARY OF THE INVENTION
The invention concerns a method for coupling or connecting an integrated optical wave-guide and a monomodal optical fibre, the monomodal fibre propagating a ma;nly Gaussian distribution of the electric field with a distribution parameter WO, and the integrated optical wave-guide with lateral confinement propagating a mode of distribution of the electric field with two separate parameters Wx and Wy on the cross-sectional plane of the guide, this method being characterized by the fact that it comprises a preliminary step during which the end portion of the fibre and/or wave-guide is treated, in order to reduce the diFference between WO and ~WxWy at the coupling section.
This preliminary treatment consists in stretching the end portion of the fibre. Experience shows that if the fibre is heated for long enough, doping agents will migrate, producing the necessary adaptation.
BRIEF DESCRIPTION OF THE DRAWINGS
Other features and advantages of the invention will ~ppear from the following description, with reference to the accompanying figures:
- figure 1, showing a diagrammatical view of the junction of an optical fibre and an integrated wave-guide;
- figure 2, showing electric field distributions in the wave-guide and fibre;
- figure 3, showing an explanatory graph.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Figure 1 shows an integrated wave-guide G on a blade L, produced, for example, by diffusing titanium on a lithium niobate substrate.
r - ~
3~
The core C of the monomotlal optical fibre F to be connected to the guide G has a radius a.
Taking co-ordinates x and y in the input section of the guide G, the electric field E1 (x~y) in the guide cross section can be generally represented by the following equation:
E~(x,Y) = exp ( X2 + y2 ~
4WxWy Wx~ Wy2 ( 1 ) where Wx and Wy depend on the dimensions and refraction indexes of the guide.
A distinction may be made between monomodal fibres in which the refraction index varies continously and those in which it is subject to abrupt variations.
For abruptly varying refractive indexes, if r is the distance to the fibre axis z and n(r) is the refraction index:
n(r) = n(g) where r exceeds a n(r) = n(g) + ~n where r is less than a and ~n = n(c) - n(g) (2) where n(g) and n(c) are the refraction indexes of the sheath and core, and a the core radius; An is also known as the "index jump".
For continously-varying refraction indexes, n(r) is given by the following equation, where it is assumed to be Gaussian:
n(r) = n(g) + ~n exp (~r2~a2) (3) To simplify matters, the core radius will be referred to as a ! and the index variation as ~n for both types of fibres, since the same laws of propagation apply for practical purposes to equations 2 and 3 above.
3~3 If the index variation is discontinous, it can be shown that, for a fibre to be monomodal, V must be less than 2.4 (4) with V = a2~ ~ 2n~n (5) where ~ = is the wavelength.
The fundamental mode, which can be propagated only if equation 4 applies, is in practice such that:
E2(r) = 1l exp(-r2/W02) (6) where E2(r) is the electric field, and WO, for Gaussian dlstribution, is generally given by the equation:
~0 = a/(V~ (7) where V is given by equation 5.
For an abrupt index variation, on the other hand, WO is given by the equation: -Wo = a Ln(V2) If it is assumed that the axis z of the fibre F is properly centred relative to the guide Gi with negligible angular error, and also that the end of the fibre F is more or less in contact with the guide input, the coupling y between fibre and guide is given by the equation:
y = {I~E1(x~y)E2(x,y) dxdy}2 (8) where E1(x,y) and E2(x,y) are standardized values for electric fields of modes in the integrated guide G and fibre F, with integration on the 25 plane ~ in figure 1.
Equations 1, 6 and 8 above show that y is maximum where:
~0 = \/ WxWy Figure 2 shows, in diagrammatical form, the curves CG and CF
5 corresponding to the points at which E~(x,y) and E2(x9y) are equal to 1/e of the maximum.
In this invention, the end portion of a monomodal optical fibre with a given Wo(i) is treated in order to obtain a new distribution parameter W to on the end surface such that:
W to = \/ WxWy In one embodiment9 the increase in WO at the fibre end is obtained by drawing a length 11, normally greater than 100um, of the end portionT.
Figure 3 shows the variation in W to . at the fibre end in relation to $he radius of the core end a t , where the refraction index is subject to Gaussian variation in accordance with equation 7.
In another embodiment, at the output WO is brought to W-to by heating, which causes doping agents to migrate. For Gaussian distribution of the index, this operation produces an increase in the core radius and a reduction in An.
These two operations, which match the parameters by treating the fibre, can be transposed to the integrated wave-guide, in order to obtain the equation WO = ~ WxWy~ This may be done, for example, by migration of doping agent on the end portion of a guide of uniform width, or by gradual modification of the width of the end part of an integrated wave-guide.
The core C of the monomotlal optical fibre F to be connected to the guide G has a radius a.
Taking co-ordinates x and y in the input section of the guide G, the electric field E1 (x~y) in the guide cross section can be generally represented by the following equation:
E~(x,Y) = exp ( X2 + y2 ~
4WxWy Wx~ Wy2 ( 1 ) where Wx and Wy depend on the dimensions and refraction indexes of the guide.
A distinction may be made between monomodal fibres in which the refraction index varies continously and those in which it is subject to abrupt variations.
For abruptly varying refractive indexes, if r is the distance to the fibre axis z and n(r) is the refraction index:
n(r) = n(g) where r exceeds a n(r) = n(g) + ~n where r is less than a and ~n = n(c) - n(g) (2) where n(g) and n(c) are the refraction indexes of the sheath and core, and a the core radius; An is also known as the "index jump".
For continously-varying refraction indexes, n(r) is given by the following equation, where it is assumed to be Gaussian:
n(r) = n(g) + ~n exp (~r2~a2) (3) To simplify matters, the core radius will be referred to as a ! and the index variation as ~n for both types of fibres, since the same laws of propagation apply for practical purposes to equations 2 and 3 above.
3~3 If the index variation is discontinous, it can be shown that, for a fibre to be monomodal, V must be less than 2.4 (4) with V = a2~ ~ 2n~n (5) where ~ = is the wavelength.
The fundamental mode, which can be propagated only if equation 4 applies, is in practice such that:
E2(r) = 1l exp(-r2/W02) (6) where E2(r) is the electric field, and WO, for Gaussian dlstribution, is generally given by the equation:
~0 = a/(V~ (7) where V is given by equation 5.
For an abrupt index variation, on the other hand, WO is given by the equation: -Wo = a Ln(V2) If it is assumed that the axis z of the fibre F is properly centred relative to the guide Gi with negligible angular error, and also that the end of the fibre F is more or less in contact with the guide input, the coupling y between fibre and guide is given by the equation:
y = {I~E1(x~y)E2(x,y) dxdy}2 (8) where E1(x,y) and E2(x,y) are standardized values for electric fields of modes in the integrated guide G and fibre F, with integration on the 25 plane ~ in figure 1.
Equations 1, 6 and 8 above show that y is maximum where:
~0 = \/ WxWy Figure 2 shows, in diagrammatical form, the curves CG and CF
5 corresponding to the points at which E~(x,y) and E2(x9y) are equal to 1/e of the maximum.
In this invention, the end portion of a monomodal optical fibre with a given Wo(i) is treated in order to obtain a new distribution parameter W to on the end surface such that:
W to = \/ WxWy In one embodiment9 the increase in WO at the fibre end is obtained by drawing a length 11, normally greater than 100um, of the end portionT.
Figure 3 shows the variation in W to . at the fibre end in relation to $he radius of the core end a t , where the refraction index is subject to Gaussian variation in accordance with equation 7.
In another embodiment, at the output WO is brought to W-to by heating, which causes doping agents to migrate. For Gaussian distribution of the index, this operation produces an increase in the core radius and a reduction in An.
These two operations, which match the parameters by treating the fibre, can be transposed to the integrated wave-guide, in order to obtain the equation WO = ~ WxWy~ This may be done, for example, by migration of doping agent on the end portion of a guide of uniform width, or by gradual modification of the width of the end part of an integrated wave-guide.
Claims (4)
1. A method for coupling or connecting an integrated optical wave-guide and a monomodal optical fibre, the monomodal fibre propagating mainly according to Gaussian distribution pattern of the electric field, with a distribution parameter WO, and the integrated optical wave-guide with lateral confinement propagating a mode of distribution of the electric field with two separate distribution parameters Wx and Wy on the cross-sectional plane of the guide, this method being characterized by the fact that it comprises a prelimi-nary step during which the end portion of the fibre and/or wave-guide is treated, in order to reduce the difference between Wo and ?WxWy in the end coupling section, said preliminary treatment comprises drawing the fibre so as to obtain a predetermined core radius a t in the coupling section.
2. A method for coupling or connecting an integrated optical wave-guide and a monomodal optical fibre, the monomodal fibre propagating mainly according to Gaussian distribution pattern of the electric field, with a distribution parameter Wo, and the integrated optical wave-guide with lateral confinement propagating a mode of distribution of the electric field with two separate distribution parameters Wx and Wy on the cross-sectional plane of the guide, this method being characterized by the fact that it comprises a preliminary step during which the end portion of the fibre and/or wave-guide is treated, in order to reduce the difference between Wo and ?WxWy in the end coupling section, said preliminary treatment comprises heating the end portion, to cause migration of doping agents, thereby producing a predetermined alteration in the core radius.
3. A method as defined in claims 1 or 2, in which the coupling section core radius a t is such that = ?WxWy where is the distribution parameter of the coupling section of the fibre in plane .pi..
4. A method as defined in claim 1 or 2, in which the end part of the integrated wave-guide is heated in order to adapt fibre/guide distribution parameters.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| FR8118041A FR2513393A1 (en) | 1981-09-24 | 1981-09-24 | METHOD OF COUPLING BETWEEN AN OPTICAL GUIDE REALIZED IN INTEGRATED OPTICS AND AN OPTICAL FIBER MONOMODE |
| FR8118041 | 1981-09-24 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1189368A true CA1189368A (en) | 1985-06-25 |
Family
ID=9262439
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000411890A Expired CA1189368A (en) | 1981-09-24 | 1982-09-21 | Method for coupling or connecting an integrated optical wave-guide and a monomodal optical fibre |
Country Status (4)
| Country | Link |
|---|---|
| EP (1) | EP0076187A1 (en) |
| JP (1) | JPS5866906A (en) |
| CA (1) | CA1189368A (en) |
| FR (1) | FR2513393A1 (en) |
Families Citing this family (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB8522704D0 (en) * | 1985-09-13 | 1985-10-16 | British Telecomm | Optical waveguide devices |
Family Cites Families (8)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US3819249A (en) * | 1970-10-02 | 1974-06-25 | Licentia Gmbh | Optical coupling arrangement |
| FR2110190B1 (en) * | 1970-10-02 | 1973-06-29 | Licentia Gmbh | |
| US3802761A (en) * | 1972-12-07 | 1974-04-09 | Us Navy | Optical waveguide edge coupler using graded index profile |
| US3825319A (en) * | 1973-02-26 | 1974-07-23 | Bell Telephone Labor Inc | Butt-joined optical fibers |
| US3864019A (en) * | 1973-11-15 | 1975-02-04 | Bell Telephone Labor Inc | Optical film-fiber coupler |
| JPS5226240A (en) * | 1975-08-22 | 1977-02-26 | Nippon Telegr & Teleph Corp <Ntt> | Device for a light wave-guiding path |
| JPS5646205A (en) * | 1979-09-20 | 1981-04-27 | Fujitsu Ltd | Optical fiber coupler and its manufacture |
| JPS57100409A (en) * | 1980-12-15 | 1982-06-22 | Toshiba Corp | Optical coupler |
-
1981
- 1981-09-24 FR FR8118041A patent/FR2513393A1/en active Granted
-
1982
- 1982-09-14 EP EP82401669A patent/EP0076187A1/en not_active Withdrawn
- 1982-09-21 CA CA000411890A patent/CA1189368A/en not_active Expired
- 1982-09-22 JP JP16596782A patent/JPS5866906A/en active Granted
Also Published As
| Publication number | Publication date |
|---|---|
| JPH0552483B2 (en) | 1993-08-05 |
| EP0076187A1 (en) | 1983-04-06 |
| FR2513393B1 (en) | 1984-04-06 |
| JPS5866906A (en) | 1983-04-21 |
| FR2513393A1 (en) | 1983-03-25 |
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Legal Events
| Date | Code | Title | Description |
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| MKEC | Expiry (correction) | ||
| MKEX | Expiry |