DE3932369A1 - Optical waveguide device for integrated optics - has strip waveguides at 90 degrees to one another on either side of mirrored bend - Google Patents

Abstract

The waveguide device provides an abrupt change of direction for the light fed along a strip waveguide using a bend (K) in the latter and a reflective mirror surface (Sp) across the outer edge of the bend (K). Pref. the waveguide sections on either side of the bend are formed integral with the latter as strip waveguides (Lx,Ly) extending at 90 degrees to one another, with the bend (K) having a higher refractive index (n3) than the strip waveguides. ADVANTAGE - Reduced light losses.

Description

The invention relates to an optical waveguide arrangement according to the preamble of claim 1.

An essential area of application of the invention is opti connections of integrated electronic semiconductors circuits (VLSI chips) in a circuit arrangement with several separate such circuits. This is done data transfer between the chips (for example Processor chips, memory chips) not exclusively via electrical lines, but at least partially via optical connections. Such an optical ver binding consists for example of a semiconductor laser, which is the electrical signal of a  Converts chips into an optical signal from a world of light conductor into which the light signal is fed and to the emp catching chip, and from a photodiode that the incoming optical signal back into an electrical one Signal converts and gives it to the receiving chip. Complexes Circuit arrangements with many chips require one large number of optical connections. That's what it's for partial, instead of individual laser diodes laser diode arrays and instead of individual photodiodes, ver turn. To get the closest possible pack of optical Obtaining connecting lines is the use of Optical waveguides, preferably strip waveguides in integrated optics advantageous. Optical connections ha a number of electrical connections Advantages, especially at high transmission frequencies. A principle advantage is that photons in Ge Do not interact with electrons. In contrast to electronic connections it is therefore in optical Connections in principle possible that the data streams cross in a plane without losses and without crosstalk Zen.

For complex circuit arrangements with a large number optical connections are only straightforward running waveguide not sufficient the direction of the It must be possible to change the waveguide. Change of direction can in principle be defined by curvatures with a defined Radius of curvature can be reached. From the optics of the glass fa water-optical waveguide is known for the above given data of the waveguide radii from 10 to 20 mm are required to reduce losses by just a few tenths of a dB (see, e.g., S.E. Miller, A.G. Chynoweth, "Optical  fiber telecommunications ", Academic Press, New York 1979). Such large radii are not very advantageous, however Changes in direction then require too much space exhibit. Abrupt riches are much more advantageous changes in direction via kinked light paths in light guides with mirror surfaces, such as those in the audience tion: C.T. Sullivan, "Optical waveguide circuits for principle ted wire-board interconnections ", SPIE Vol. 994, 92-100 (1988).

With such a known arrangement can be in connection with the abrupt change in direction of the light path but in Buckling range losses occur because part of the Light emerges from the optical fiber. Quantitatively these losses are equal to the losses of two axially optimally aligned fiber optic cables a gap between the end faces. From the audience tion: T.C. Chu and A.R. McCormick, "Measurements of loss due to offset, end separation, and angular misalignment in graded index fibers excited by an incoherent source ", ver published in Bell System Technical Journal Vol. 57, 1978, p.595-602, the expected losses can be found men. The losses depend on the refractive index profile and the numerical aperture of the optical waveguide and are typically in the range of 0.2 dB to 0.4 dB (5% until 10%). In circuit arrangements with a plurality of chips and connecting optical fibers, however essential, the losses as low as possible to keep. Because the optical losses from an increase the electrical driver power must be compensated and generally with a plurality of  Changes in direction are to be expected if possible Essential low-lust changes of direction.

The present invention is therefore based on the object reasons, an optical waveguide arrangement in the preamble of claim 1 specified type, in which the losses in the kink area of the light path are clearly ver are struggling.

The invention is described in claim 1. The Un Claims include advantageous refinements and Developments of the invention.

It is essential in the invention that through training of the kink area as two crossing wave guides in the directions of the fed and the reflected No beam expansion in the kink area, either with conventional training essentially the losses causes occurs.

Losses essentially only occur as reflections losses on the transverse shaft guides that are quantitatively negligible.

The invention is based on exemplary embodiments still play with reference to the pictures explained. It shows

Fig. 1 shows two types of channel waveguides in inte grated optics,

Fig. 2 shows a conventional embodiment of a strip conductor arrangement for shafts abrupt change in direction,

Fig. 3 shows a first embodiment of the invention,

Fig. 4 shows a further embodiment of the invention,

Fig. 5, 6, arrangements for cross-coupling light out of a strip waveguide by abrupt change in direction.

The one bury NEN waveguide (buried waveguide) and has a Annae hernd round core as an optical waveguide L of material having a refractive index in Fig. 1 (a) outlined embodiment of a light wave is guide in integrated optics of the type n ₂ which is surrounded by support material S with a lower refractive index n ₁ ′ (n ₁ <n ₂ ). The sketch in Fig. 1 (b) shows, as another embodiment, a bar-shaped strip waveguide, in which the light-conducting layer L with refractive index n _{2 is} delimited by two layers D 1 , D 2 with a lower refractive index n ' ₁ (n' ₁ < n ₂ ) and laterally surrounded by a medium with refractive index n ′ ′ ₁ <n ₂ ). The constructed from D 1, L and D 2 Wel lenleiter-beam is firmly connected to a carrier S.

The production of such waveguides can be achieved, for example, either by ion exchange in glass, by depositing doped SiO ₂ layers on Si substrate with flame hydrolysis or by spinning a polyimide layer onto a glass substrate. In all cases, the stripe waveguides can be structured photolithographically. Burying can be achieved by an additional exchange step in ion exchange and by applying additional layers in the other methods. Exemplary data of such strip waveguides are: refractive index profile step-shaped, core diameter 0.03 to 0.05 mm, numerical aperture NA = 0.2, distance between adjacent waveguides 0.05 to 0.25 mm.

Fig. 2 shows a schematic diagram of a conventional Anord voltage for changing the direction of the light path in a Strei fen waveguide with a feeding strip waveguide Lx and a leading strip waveguide Ly in plan view of the plane of the strip waveguide. The light-conducting layer has a refractive index n ₂ throughout, and the outer regions have a refractive index n ₁ <n ₂ . Three light rays B 1 , B 2 and B 3 are entered in the wave guide Lx. Beam B 1 strikes the mirror surface Sp of the kink region and is reflected without loss in the waveguide Ly leading away. Beam B 2, on the other hand, does not hit the leading waveguide Ly after reflection on the mirror surface Sp, but strikes the lateral waveguide of the waveguide Lx at a steep angle and emerges into the outside area. Finally, beam B 3 does not hit the mirror surface Sp at all, but is lost in the outside area.

In contrast, in the present invention, a Di embellish the kink area from an optical fiber supplied light avoided by the kink area for both optical fibers continue the wave guide up to the mirror surface.  

The mirror surface can, for example, by ion beam zen perpendicular to the surface of the light-guiding layer getting produced. The mirror effect can e.g. B. by evaporated metallic or dielectric layers or through total reflection at the transition to an optically thinner one Medium can be set.

In Fig. 3, a kink area for two strip wave guide with a step-shaped refractive index profile is outlined. The Wel lenleiter Lx, Ly each have a refractive index n ₂ , which is higher than the refractive index n _{1 of} the surrounding areas. In the central triangular kink region K, which is delimited by the mirror surface Sp and the extension of the interfaces of the strip waveguides, the refractive index n _{3 is} increased to such an extent that the interfaces Fx, Fy due to the transition from a higher (n ₃ ) to a lower (n ₂ ) refractive index than the waveguides Lx or Ly, which leads to all waveguides in the full aperture of the strip waveguide Lx, Ly. The transitions (Fx) which act as waveguides for the light from a waveguide (e.g. Lx) are almost losslessly permeable to light guided in the other waveguide (Ly) and the associated waveguide (Fy). The remaining losses in the abrupt change in direction occur only as reflection losses due to the index jump during the transition from n ₂ to n ₃ and n ₃ to n ₂ . These losses are, for example, about 1.5 × 10 ^-4 dB (= 0.004%) for incoherent light and between 0 and 3 × 10 ^-4 dB (= 0.008%) for coherent light and are therefore like a change of direction without wave guides sketched in Fig. 2 reduced by around a factor of 1000.

The refractive indices are preferably set such that the same numerical apertures are obtained for the strip waveguides and for the waveguides in the kink region. In an example with a refractive index n ₁ = 1.46 and a numerical aperture NA = 0.2, the optimal refractive indices for the same numerical aperture are calculated as n ₂ = 1.4736 and n ₃ = 1'4871.

If waveguides with gradient profiles are used instead of step profiles, it is also possible to maintain the profile shape in the kink area. For example, for a parabolic refractive index profile with n _2, the maximum value of the refractive index on the central axes of two mutually perpendicular strip waveguides of width applies

| x | a: n² (x, y) = n₂² - (n₂²-n₁²) (y / a) ²
| y | a: n² (x, y) = n₂² - (n₂²-n₁²) (x / a) ²

Refractive index profile in the kink area:

| x |, | y | <a: n² (x, y) = n₂² + (n₂²-n₁²) - (n₂²-n₁²) (x / a) ² - (n₂²-n₁²) (y / a) ²

with x, y as coordinates in the direction of the waveguide Coordinate origin 0 lies on the mirror surface Sp the intersection of the optical axes of the two waves ladder.  

A second embodiment is sketched in Fig. 4 for a Strei fen waveguide with a stepped refractive index profile. This embodiment is particularly suitable for balkenför shaped waveguides with a step-shaped refractive index profile. The refractive index n ₂ in the inner region K is the same as in the waveguides Lx, Ly. The wave guidance is achieved by narrow trenches Gx, Gy with a refractive index of n ₁ . The trenches have perpendicular walls parallel to one another, the inner walls Wx, Wy being flush with the walls of the individual waveguides. The Zusatzver losses in this embodiment are only twice as high as in the first embodiment of FIG. 3 and thus also negligible.

The refractive index curves given above represent optima len solutions. However, the improvements achieved are so large that even for non-optimal refractive index curves a significant reduction in losses can be achieved can.

The manufacture of arrangements according to the invention can be carried out with different techniques can be achieved, for example:

• - When ion exchange in glass is the number of in ions introduced into the central kink area increase; this can be achieved by an extension the exchange time for this area (covering the remaining area by masking) or by an increase in the non-masked area in the Kink area.  
• - Narrow, vertical trenches can be caused by ions beam etching are produced; these trenches can with glass or organic material such as poly imid to be replenished.

The strip waveguide can be at an angle of 90 ° or meet at a different angle. The one specified by the numerical aperture may be used Angles must not be exceeded.

In Fig. 5 and Fig. 6 sketched embodiments are special cases of the embodiments of Fig. 3 and Fig. 4 shows in the sense that the change of direction not in a by a feeding and a wegfüh leaders optical waveguide (Lx, Ly in Fig. 3 , 4) spanned plane, but one of the optical fibers (e.g. Ly) is omitted and the light supplied via an optical fiber Lx is decoupled from the light-guiding layer, preferably perpendicular to the surface of a substrate carrying the optical waveguide, for example to an over the substrate arranged optoelectric component or another optical waveguide arrangement. The light path is of course reversible, ie the same arrangement is equally suitable for coupling light into the optical waveguide Lx. In particular, this significantly reduces losses when coupling active components such as lasers or photodiodes. FIGS. 5 and 6 are shown as sectional views in a plane through the longitudinal axis of a strip waveguide and perpendicular to the substrate. A step-shaped refractive index profile is assumed for the waveguide. The optical waveguide Lx runs on the surface of the substrate S. A coating layer V can also be applied to the surface of the light-guiding layer of the strip waveguide.

In the embodiment according to FIG. 5, as in the example of FIG. 3, the refractive index n is in a central prismatic kink region K, which is limited by the mirror surface Sp, the extension of the interfaces of the waveguide Lx and a flat surface Fy perpendicular to the strip waveguide ₃ so far increased that there is also a wave guide up to the surface of the light-guiding layer for the surface Sp reflected in direction a of the intended light exit. Wave guidance for light arriving from an incident direction e in the strip waveguide Lx is given by the continuous interface of light-guiding layer and coating layer V or air (n = 1) in this arrangement anyway. The quantitative information on exemplary refractive indices and losses can be taken from the explanation of FIG. 3.

The embodiment according to FIG. 6 differs from that according to FIG. 5 essentially in that the wave guidance in direction a is achieved similar to the example in FIG. 4 by a narrow trench Gx with parallel walls perpendicular to the strip waveguide Lx. The trench is filled with material with a refractive index n ₁ .

Claims (7)

1. Optical waveguide arrangement in integrated optics for the abrupt change of direction in a strip waveguide led light over a kink area of the light waveguide with a mirror surface, characterized in that the kink area (K) for the directions of the supplied and the reflected light to the mirror surface ( Sp) is designed as a shaft guide. 2. Arrangement according to claim 1, characterized in that the wave guidance in one direction through a transition from a higher refractive index in the kink area to one lower refractive index in the other direction is formed.   3. Arrangement according to claim 1 or claim 2, characterized in that incoming and outgoing strip waveguides and the kink region are made in one piece and the kink region has a higher refractive index (n ₃ ) than the strip waveguide. 4. Arrangement according to claim 3, characterized in that the wave guides have the same numerical apertures point like the strip waveguide. 5. Arrangement according to claim 1 or 2, characterized net that the kink area has the same refractive index points like the strip waveguide and from these through in Comparison to the transverse dimensions of the strip waveguide narrow trenches with lower refractive index separated is, the boundaries formed by the trenches of the kink area with the limits of the feed and discharge Strip waveguides are aligned. 6. Arrangement according to claim 5, characterized in that the trenches are filled with optically permeable material are. 7. Arrangement according to one of the preceding claims, since characterized in that it is an arrangement for Cross coupling of light from an optical fiber han delt.