GB2301681A

GB2301681A - Connecting integrated optical components using inclined reflecting surfaces

Info

Publication number: GB2301681A
Application number: GB9610933A
Authority: GB
Inventors: Heinrich Hauer; Albrecht Kuke
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 1995-05-27
Filing date: 1996-05-24
Publication date: 1996-12-11
Anticipated expiration: 2016-05-24
Also published as: FR2734650A1; FR2734650B1; DE19519548A1; GB2301681B; GB9610933D0

Description

1 2301681 Arrangement for connecting integrated-optical components and use

of the arrangement

Prior art

The invention relates to an arrangement for connecting integrated-optical components which are arranged on different substrates and a use of the arrangement.

According to the prior art, integrated-optical circuits with optical waveguides and passive optical components such as beam splitters, branching points or wavelength-selective components are known. other integrated-optical circuits contain active optical components such as erbium-doped amplification waveguides. In many cases, for technological reasons it is not possible to produce very diverse optical components on the same substrate. To produce erbium-doped amplification waveguides, for example, glass substrates are required which differ from those needed to produce optical couplers, branching-points or beam splitters.

An optical arrangement which contains integrated-optical components which are produced in incompatible processes or on different substrate materials therefore requires at least two substrates with integrated- optical components, the light paths of which must be connected together. According to the prior art, an optical connection via coupled fibres or a face coupling is known for this purpose.

Connection via optical fibres is very complex because a fibre has to be coupled twice for each light path. In the case of a face coupling of two integrated-optical substrates, although 2 several light paths can indeed be jointly coupled, a highly accurate common carrier is required for both substrates to be connected in order to maintain the desired coupling tolerances and to achieve sufficient mechanical stability.

On the basis of this prior art the object of the invention is to propose an arrangement for connecting integrated-optical components which is simply constructed and achieves a high coupling efficiency, and to propose a use of the arrangement.

Claims

The object is achieved by an arrangement with the features of Claim 1.

Advantageous further developments are proposed in the sub-claims. A use of the arrangement is proposed in Claim 11.

The invention proposes an arrangement which enables at least two substrates with integrated-optical components to be connected together with high stability and low optical attenuation in the coupled light paths. An active alignment with high accuracy is permitted by means of alignment marks. Passive alignment is achieved if complementary structures or recesses for inserting alignment bodies are provided in the substrates.

With an arrangement according to the invention it is also possible to connect several substrates together and then correspondingly arrange them on top of each other.

An embodiment of the invention will be explained with the aid of the drawings which are as follows:

Fig. I shows a cross-section through an arrangement according to the invention with waveguide structures, Fig.
2 shows a top view onto the above arrangement, wherein the substrates are transparent, Figs. 3 to 5 show known arrangements with optical fibre amplifiers in bidirectional transmission systems with 3 wavelength multiplex and Figs. 6a to 6c show the use of an arrangement according to the invention in an optical fibre amplifier for bidirectional transmission systems.

The arrangement comprises a first substrate 10 with a waveguide structure 11 and a second substrate 20 with a waveguide structure 21 fitted above it. The substrates are fixed to each other on the common contact surface 40 in such a way that the sides which carry the waveguide structures face one another. In each of these substrates at least one face 12 and/or 22 is inclined at an angle a, and/or a2, wherein ol + % 9 0 0 ' The inclined faces 12 and 22_face each other and together form a right- angled convex edge 30 of the overall substrate formed of the substrates 10 and 20. The ends to be coupled of the waveguide structures 11 and 21 butt against the inclined faces 12 and 22 and lie on top of each other there if the waveguides to be coupled both run perpendicular to the substrate edge. If the waveguide structure ill in the lower part- substrate 10 runs inclined at at angle T, to the normal of the substrate edge (see Fig. 2), the waveguide structure 21, in the upper substrate 20 which is coupled to it must run at an angle T2 - -YJ. The projections of the axes of the waveguide structures ill and 211 onto the connection surface 40 between the substrates 10 and 20 then intersect in the edge 30.

The light beam guided in a waveguide structure 11 is reflected at the face 12 as a free beam 13 upwards through the connection surface 40 into the substrate 20 where it impinges on the face 22. It is reflected again there and impinges in the waveguide structure 21 where it is guided again. As the surfaces of the part-substrates 10 and 20 which carry the optical waveguide structures 11 and 21 face one another, the path of the free beam 13 is only very short. Even in the case 4 of buried waveguides in which the axes of the waveguides are up to 10 Am below the substrate surface, the light path of the free beam 13 is only 20 Am long. For a free beam with a Gaussian beam profile and a waist radius, matched to a singlemode fibre, of 5 Am, a coupling efficiency of 98.3t corresponding to a coupling loss of - 0.074 dB is calculated for a substrate refractive index of n. = 1.5 and a wavelength in air of 1.55 Am. The coupling of light paths from the upper part-substrate 20 into the lower part-substrate 10 is possible in the same way.

The compact structure, in which no more surface is occupied for two substrates than for one, is advantageous in the arrangement according to the invention. A very stable construction is achieved by means of the full-surface fixing of the two substrates 10 and 20 to one another. The alignment of the two substrates with respect to each other can take place either actively or, more simply, passively wherein alignment marks 16 and 26, which can be seen simultaneously on both surfaces of the generally transparent substrates that are to be joined together or can be identified by an image processing system, can be used. A further method for aligning the two substrates 10 and 20 with respect to each other comprises the fitting of complementary recesses 17 and projections 27 on the surfaces or of recesses 18 and 28 on both surfaces and separate alignment bodies such as highly accurate spheres or cylinders. The two substrates 10 and 20 can be fixed to each other according to the prior art by means of adhesive bonding or anodic bonding, optionally with an intermediate layer required for this. The only matter of importance is that this connection is transparent at least in the region of the coupling free beams 13 for the wavelength used.

In optical communications technology, optical fibre amplifiers are required in order to equalize line losses and distribution losses after beam splitters. Erbium-doped amplification fibres or integrated optical erbium-doped waveguides, into which the wanted signal to be amplified and via beam splitters the pump light are coupled, are used for this. For the forward direction from the control centre to the users, corresponding systems use the wavelength X, = 1550 nm which can be pumped with the wavelengths XP = 850 nm, 980 nm or 1480 nm. The wavelength X2 m 1300 nm is provided, for example, for the reverse direction. In the reverse direction this light may not pass through the amplification fibre because it would be strongly attenuated there. For the reverse direction, therefore, either a second fibre or, if both directions are transmitted on the same fibre, a detour line round the optical amplifier, must be provided via wavelength-selective couplers. If only low bit rates for the reverse direction and a low distribution ratio with few users are provided, an amplification of the signals from the users to the control centre can be dispensed with in the reverse direction. If, however, a very large number of users with higher bit rates are to be connected in the reverse channel, an amplification of the signals is also required here. According to the prior art, optical amplifiers which are pumped at 1017 nm are also known for signals at 1300 nm. If the reverse direction is also to be optically amplified, then according to the prior art an optical amplifier of this kind must be used either in the second fibre for the reverse direction or, if one fibre is used for both directions, in a detour line round the optical amplifier for the forward direction. These solutions are shown in Figs. 3 and 4. Fig. 3 shows an amplification device for two separate fibres for the forward direction with the fibre P1 for the wavelength X, and for the reverse direction with the fibre F2 and the wavelength X2 ' The signal for the forward direction is amplified in the optical amplifier V1 in which the pump light with the wavelength Xp, is coupled. Similarly the signal for the reverse direction is amplified in the amplifier V2 in which the pump light of the wavelength Xp2 is coupled. Fig. 4 shows an amplification arrangement with only one transmission fibre F12 for the forward and reverse 6 direction. In this case the signals for the reverse direction are guided past via the two wavelength-selective couplers K1 and K2 at the amplifier V1 and amplified in the amplifier V2.

optical amplifiers can be used at the same time for the amplification in forward and reverse direction of an individual transmission fibre. Fig. 5 shows a block diagram of an arrangement of this kind. In this case the wavelengths X, for the forward and X2 for the reverse direction are so close together that they can be amplified jointly in the optical amplifier V12. In the forward direction the signal to be amplified, which comes from the control centre from the transmission fibre F12Z on the control centre side and is of wavelength Xl, reaches the amplifier arrangement via the input port E, is amplified there in the optical amplifier V12, which is pumped with the pump light of wavelength XP for this purpose, and reaches the transmission fibre F12T on the user side via the output port A. The return signal transmitted by the users from the transmission fibre F12T on the user side is fed into the input of the optical amplifier V12 from port A via a first wavelength-selective coupler KI, a first detour line U1 and a second wavelength-selective coupler K2. The return signal is amplified there jointly with the forward signal. The amplified return signal is coupled into the transmission fibre F12Z on the control centre side via the third wavelength-selective coupler K3, the second detour line U2 and the fourth wavelength-selective coupler K4. The numerous passive components that are required such as wavelength-selective couplers and detour lines are achieved by means of fibre-optic components or by means of integrated optical components. The integrated optical solution offers the advantage of being more compact, less susceptible to faults and easier to handle and, particularly where a very large number of components is integrated, being able to be produced more cheaply and in a more reproducible manner. For the achievement of the amplification part also, an integrated optical amplification waveguide on the basis of a special 7 glass with erbium-doped waveguides was proposed in addition to the known fibre-optic solution.

For technological reasons, glasses which are different from those required for producing erbium-doped amplification waveguides are required for producing integrated optical passive components such as branching points, beam splitters, tapers and wavelength-selective couplers, and so the per se desirable combination of all passive and active components on a single glass substrate is not technically possible. According to the invention a solution for an optical amplifier is proposed in which two different glass substrates are indeed used but which offers the same compactness as if all active and passive components were integrated on one substrate only. In cross-section Fig. 6 shows the two substrates S1 with the waveguide structure WL1 for passive optical components and S2 with the active amplification waveguide structure WL2. The two substrates are joined to one another in such a way that the upper sides with the waveguide structures face each other. The ports for the input E, the outputs Al and An and the pump light source P are on at least one lateral surface Sp of the substrate S1. At least one lateral surface Ski of the substrate S1 and at least one lateral surface Sk2 of the substrate S2 are polished so as to be inclined and face each other so that the two inclined lateral surfaces Ski and Sk2 together include a right angle. Fig. 4b shows a passive waveguide structure WL1 in the substrate S1 and Fig. 4c the active amplification waveguide structure WL2 in the substrate S2. The overcoupling of the light between the waveguide structures WL1 and WL2 takes place by means of two-fold total reflection or optionally by means of reflection on mirror coatings at the inclined lateral surfaces Ski and Sk2 in the connection ports VA1 and VE1 and/or VA2 and VE2 which are aligned with respect to each other. The waveguide structure WL1 in Fig. 6 contains all passive coupling and connection elements required for the optical amplifier in the form of integrated optical elements, the purpose of which was 8 explained with the aid of Fig. 3. In addition, a 1:n beam splitter Tn with n output ports Al to An is further integrated. By way of example an active amplification wave(guide) structure is shown as a coil in Fig. 6c. Similarly, other waveguide structures are suitable which make it possible to achieve the desired wavelength without falling below the minimum waveguide curvature, wherein crossings of light paths and reflections at suitable reflection surfaces, including substrate side edges, are permissible.

9 Claims 1. Arrangement for connecting integrated-optical components which are arranged on different substrates, characterized in that the substrates (10, 20) with the integratedoptical components (11, 21) to be connected lie on top of each other, that the integrated-optical components (11, 21) have facing inclined lateral surfaces (12, 22) at the ends to be connected in the light path and that the lateral surfaces (12, 22) are inclined in such a way that light in the first integrated-optical component (11) radiates as far as the first inclined lateral surface (12), is reflected there, impinges on the second inclined surface (22) and is reflected from there into the second integrated-optical component (12).

Arrangement according to Claim 1, characterized in that at least one of the inclined lateral surfaces (12, 22) is mirrored.
3. Arrangement according to Claim 1, characterized in that the lateral surfaces (12, 22) are inclined in such a way that light from the integrated-optical components (11, 21) experiences total reflection.
Arrangement according to one of Claims 1 to 3, characterized in that the light paths of the integratedoptical components run in parallel planes at the ends to be connected and the sum of the angles of inclination of the inclined lateral surfaces (12) with respect to one of the parallel surfaces is 900.
5. Arrangement according to one of Claims 1 to 4, characterized in that alignment marks (16, 26) are provided on the transparent substrates (10, 20) for active alignment.
6. Arrangement according to one of Claims 1 to 4, characterized in that complementary recesses (17) and projections (27) are provided on the substrates (10, 20) for passive alignment.
Arrangement according to one of Claims 1 to 4, characterized in that recesses (18, 28) for inserting alignment bodies (19) into the substrates (10, 20) are provided for passive alignment.
8. Arrangement according to one of Claims 1 to 7, characterized in that the substrates (10, 20) lie on top of each other.
9. Arrangement according to one of Claims 1 to 7, characterized in that the substrates (10, 20) are fixed over each other by sticking or bonding.
10. Arrangement according to one of Claims 1 to 7, characterized in that the substrates (10, 20) are fixed over each other by means of an intermediate layer.

Use of an arrangement according to one of Claims 1 to 10 for an optical amplifier for bidirectional transmission systems, characterized in that passive integrated-optical components (WLI) (are provided) on the first substrate (51) and an active integrated-optical waveguide structure (WL2) which is connected to the passive components is provided on the second substrate (52).
11
12. An arrangement substantially as herein described with reference to the accompanying drawings.
13. Use of an arrangement substantially as herein described with reference to the accompanying drawings.