WO2007007073A1

WO2007007073A1 - Three dimensional optical path control by integrating rotated structures

Info

Publication number: WO2007007073A1
Application number: PCT/GB2006/002543
Authority: WO
Inventors: Robert Campbell Mcdougall; Alistair James Poustie; Graeme Douglas Maxwell
Original assignee: The Centre For Integrated Photonics Limited
Priority date: 2005-07-09
Filing date: 2006-07-10
Publication date: 2007-01-18
Also published as: GB0514120D0

Abstract

An integrated optical device (17) comprises a first optical component (5) formed from a plurality of layers of material and a second optical component (11) formed from a plurality of layers of material. A first optical path (4) is defined in the first optical component (5) and a second optical path (12) is defined in the second optical component (11). The first optical path (4) is coupled to the second optical path (12). The first optical component (5) is arranged relative to the second optical component (11) such that there is a non-zero angle, particularly a right angle, between the layers of the first optical component (5) and the layers of the second optical component (11). The second optical path (12) directs light from the first optical path (4) in a direction substantially normal to the layers of the first optical component (5) or in a direction having at least a component normal to the layers of the first optical component (5). In this way, light can be coupled out of the plane of the first optical component (5) in a relatively simple manner.

Description

THREE DIMENSIONAL OPTICAL PATH CONTROL BY INTEGRATING

ROTATED STRUCTURES

Field of the Invention This invention relates to the field of integrated optical devices and sub-systems. The invention is expected to find applications in devices, components and sub-systems required for the fields of telecommunications, computer networks, sensors, instrumentation and bio-photonics.

Background to the Invention

It is known that there are techniques available to couple light from in-plane light controlling structures to out of plane, see for example US 5,481,633 (Mayor) which describes active or passive polymer components with integrated vertical coupling features that utilise field coupling between separate vertically spaced components. Another example is that by US 5,831,752 (Bowers), which describes a vertical directional coupling technique that couples light vertically in specific wafer fusion regions. Again, US 6,859,603 (Hryniewicz) describes a multilayer evanescent coupling approach to couple integrated photonic devices. Because these approaches rely on field coupling between vertically adjacent waveguides, they are limited in the extent by which light is coupled vertically to the next successive stack level. The coupling is also dependent upon the precise vertical photonic component distance and the intermediate material separating the structures. US 6,690,845 (Yoshimura) describes methods of vertical coupling between opto-electronic stacks using vertical coupling mirrors and grating elements defined in the in plane stacks. Yoshimura uses microlenses and optical glue to aid the light control to the other layers in the stack. There are also several other techniques that use vertical light turning mirror to couple light out of plane for example K. Jackson (Journal Lightwave Technology, Vol. 12, No. 7, July 1994), M. Bazylenko (Journal Lightwave Technology, Vol. 15, No. I₅ January 1997), T. Sasaki (Optical Fibre Communication conference Vol. 3, ppWB6-l - WB6-3, 2001), H. Terui (Journal Lightwave Technology, Vol. 16, No. 9, September 1998) (Electronic Letters, Vol. 32, No. 18 29th August 1996).

In-plane light control can be achieved with high accuracy due to the ability to fabricate precise patterns (micrometer and better definition). However out of plane light controlling features incorporated in the same in plane component, although often defined by similar pattern defining techniques, have their light control complicated and restricted by the subsequent processing steps to achieve the out of plane coupling. This invention, at least in its preferred embodiments, enables high precision out of plane light control from in plane photonic components with a new approach over the prior art.

Summary of the Invention

Accordingly, this invention provides an integrated optical device comprising a first optical component formed from a plurality of layers of material and having defined therein a first optical path; and a second optical component formed from a plurality of layers of material and having defined therein a second optical path. The first optical path is coupled to the second optical path and the first optical component is arranged relative to the second optical component such that there is a non-zero angle between the layers of the first optical component and the layers of the second optical component. Preferably, the nonzero angle is substantially a right angle.

Typically, the second optical path directs light from the first optical path in a direction substantially normal to the layers of the first optical component or in a direction having at least a component normal to the layers of the first optical component. For example, the second optical path may be curved or arcuate or arranged obliquely to the first optical path. The first optical path and/or the second optical path may be defined by a waveguide. The first optical component and the second optical component may comprise interengaging physical formations for locating the first optical path relative to the second optical path. For example, the second optical component may comprise projection arranged to engage with a surface of the first optical component.

The plurality of layers of the first optical component may have a first common normal and the plurality of layers of the second optical component may have a second common normal and the angle between the first common normal and the second common normal may be non-zero, preferably substantially 90 degrees.

The first optical component and/or the second optical component may be formed by a semiconductor fabrication method. The fabrication method for each component may be different or the same.

In preferred embodiments, the invention uses lithographically defined features in an integrated structure to control out-of-plane light from a structure that originally controls light in-plane. By defining light controlling features using in-plane fabrication processes, a submount device can be made that when rotated can be integrated with other in-plane devices to provide a combined solution that simply and precisely controls the path of light in three dimensions. Overall, the precision-defined features on the rotated submounts can provide different out-of-plane light control using bulk and/or waveguide element combinations.

Viewed in broad terms, embodiments of the invention provide a technique for coupling light from in-plane optical devices to out of plane, in particular a technique that utilises high precision in-plane feature definition processes to define light controlling elements onto separate submounts/structures that when rotated and integrated with in-plane integrated optic devices provide the coupling from in-plane optical devices to out of plane. Embodiments of the invention also provide a number of rotated structures/submounts that provide different functionalities to the in-plane device. The functions may comprise vertical output coupling, coupling between stacked levels of in- plane devices and/or providing optical functions utilising the vertical space about the in- plane device.

Brief Description of the Drawings Embodiments of the invention will now be described by way of example only and with reference to the accompanying drawings, in which:

Figure 1 is a schematic diagram identifying the out of plane light control from a waveguide of a motherboard that is achievable by an embodiment of the invention;

Figure 2 is a schematic diagram illustrating the principle of making a rotated submount according to an embodiment of the invention;

Figure 3 is a schematic diagram illustrating a motherboard with a recess that accommodates rotated submounts according to an embodiment of the invention;

Figure 4 is a schematic diagram illustrating an example of a rotated submount according to an embodiment of the invention;

Figure 5 is a schematic diagram illustrating an example of a further rotated submount according to an embodiment of the invention;

Figure 6 is a schematic diagram illustrating an example of a yet further rotated submount according to an embodiment of the invention;

Figure 7 is a schematic diagram illustrating an example of another rotated submount according to an embodiment of the invention;

Figure 8 is a schematic diagram showing the integration of the rotated submount of Figure

4 in a device according to an embodiment of the invention;

Figure 9 is a schematic diagram showing the integration of the rotated submount of Figure

5 in a device according to an embodiment of the invention; Figures 10 and 11 are schematic diagrams showing the integration of the rotated submount of Figure 6 in a device according to an embodiment of the invention; and

Figure 12 is a schematic diagram showing the integration of the rotated submount of Figure 7 in a device according to an embodiment of the invention.

Detailed Description of Embodiments

This invention addresses the issues of providing out-of-plane light control of light in a device ("motherboard 5") which controls light in-plane. The invention accomplishes this using a method that gives a high degree of optical functionality and fabrication precision that is also compatible with existing fabrication techniques. Unlike known prior art, this technique firstly utilises in-plane feature-defining technology (see Figure 2) and then rotates the design to form an out-of-plane device (rotated submounts 7, 11, 13, 15) that can be integrated with other in-plane devices 5 to give complex light paths in the 'X' and Υ (in-plane) and 'Z' (out-of-plane) axes 6.

Figure 1 shows schematically the out of plane light control from a waveguide 4 of a motherboard 5 that is achievable by an embodiment of the invention. The device controlling light in-plane is hereafter referred to as the 'motherboard' 5. In this instance, the motherboard 5 consists of a substrate layer 1 covered on its top by an undercladding layer 2. Above the undercladding layer is the waveguide 4 which is covered by an overcladding layer 3.

The invention utilises a principle of the making of a rotated submount by which light control out-of-plane is achieved by lithographically defining features on a separate device (referred to hereafter as the "rotated submount" 7, 11, 13, 15) and rotating them as depicted in Figure 2. The rotated submount is then integrated with one or multiple motherboards 5 to provide additional out-of-plane optical functionality to the overall integrated device 17, 18, 20, 21, as shown in Figures 8 to 12. This rotated submount can be integrated at any point on the motherboard and along any edge.

Figure 3 shows schematically a portion 9 of motherboard 5 with a recess 10 that accommodates rotated submounts, for example the rotated submount examples 7, 11, 13, 15 shown in Figures 4 to 7. To allow light to couple from within the motherboard 5 to the rotated submount, a recess 10 is made at the desired coupling point 9 that can physically accommodate the rotated submount. The recess region or the region at the edge of the motherboard 5 where the rotated submount couples to the motherboard is known as the "integration area" 10.

The motherboard 5 and rotated submount 7, 11, 13, 15 may originate from the same material system or different material systems such as silicon and other semiconductors, glasses, polymer or free space. Different material systems may be used for the rotated submount to achieve different levels of optical functionality that are difficult or impossible to achieve with the motherboard material system. These can be aspects of:

• polarisation diversity such as polarisation selective elements;

• active control such as modulators, light sources and amplifiers; and/or

• waveguiding properties of the material system such as waveguiding devices requiring a smaller bending radius than the motherboard can provide.

Within the material system of the rotated submount, a number of different functions can be realised. Three such functions are described herein in relation to the embodiments shown in Figures 4 to 12.

Figure 4 shows schematically an example of rotated submount 11 of a first type. The rotated submount 11 provides a control of vertical light coupling via a lithographically- defined waveguide element 12. Figure 8 shows schematically the integration 17 of the rotated submount 11, which in this instance provides 90 degree out of guided wave coupling to the light diffracting from the exit aperture of the waveguide 4 into the recess 10 from one side of the motherboard 5 using a lithographically-defined waveguiding element 12.

Figure 5 shows schematically an example of a rotated submount 13 of a second type. The rotated submount 13 provides control of vertical light coupling via a lithographically- defined bulk reflecting element 14. Figure 9 shows schematically the integration 18 of the rotated submount 13 that in this instance provides 90 degree out of plane beam coupling to the light diffracting from the exit aperture of the waveguide 4 into the recess 10 from one side of the motherboard 5 using a lithographically defined upstanding reflecting element 14. The reflecting element 14 can control both direction and collimation of the output light beam.

The embodiments of Figures 4 and 8 and 5 and 9 provide the motherboard with an out of plane coupling solution (17, 18) via guided wave (waveguide element 12) or free space (bulk reflecting elementl4) features. Such an embodiment may give high precision direction (rotated submount 11, 13) and collimation (rotated submount 13) control to the output light. The light controlling features may be defined either lithographically or by directly writing the pattern. A material of choice for this embodiment would be silica features on a silicon substrate, polymer features on a substrate or semiconductor features on a semiconductor substrate.

Figure 6 shows schematically a rotated submount 7 of a second type that allows stacking of multiple motherboard device levels via a semicircular connecting waveguide 8. Figure 10 shows schematically the first integration step to integrate multiple motherboard 5 levels using a rotated submount 7 by coupling light from the waveguide 4 of the bottom motherboard 5 using an out of plane semicircular waveguide 8. Figure 11 shows schematically the stacking 20 of multiple levels of motherboards 5 using the rotated submount 7 by coupling light from the waveguide 4 of the bottom motherboard 5 using an out of plane semicircular waveguide 8 that couples to the waveguide 4 of another motherboard 5 that is vertically displaced and inverted. This embodiment provides the ability to integrate multiple levels of motherboards into stacks 20. This can be achieved using waveguides 8 or free space coupling elements 14. The preferred material and feature definition methods are the same as for the previous embodiments. To accurately align between the waveguides 4 in each stack, this embodiment would preferentially use the overcladding 3 in each motherboard 5 as the vertical reference frame.

Figure 7 shows schematically a rotated submount 15 for added guided wave optical functionality 16 that couples back into the initial planar device. Figure 12 shows schematically the integration of the rotated submount 15 that is used to provide an extra out-of-plane degree of optical functionality 16 to the motherboard 5. This embodiment provides varying levels of optical functionality to the motherboard 5 in similar or dissimilar material systems 21. This can allow the addition of long complex optical paths 16 that couple back into and out of the motherboard 5 within the in-plane dimensions of the integration area 10. This can alleviate spatial waveguide design issues such as unwanted waveguide crossings by utilising the unused space above and below the motherboard 5. The preferred feature definition processes are the same as the previous embodiments.

In summary, an integrated optical device 17 comprises a first optical component 5 formed from a plurality of layers of material and a second optical component 11 formed from a plurality of layers of material. A first optical path 4 is defined in the first optical component 5 and a second optical path 12 is defined in the second optical component 11. The first optical path 4 is coupled to the second optical path 12. The first optical component 5 is arranged relative to the second optical component 11 such that there is a non-zero angle, particularly a right angle, between the layers of the first optical component 5 and the layers of the second optical component 11. The second optical path 12 directs light from the first optical path 4 in a direction substantially normal to the layers of the first optical component 5 or in a direction having at least a component normal to the layers of the first optical component 5. In this way, light can be coupled out of the plane of the first optical component 5 in a relatively simple manner.

Claims

1. An integrated optical device comprising: a first optical component formed from a plurality of layers of material and having defined therein a first optical path; and a second optical component formed from a plurality of layers of material and having defined therein a second optical path, wherein the first optical path is coupled to the second optical path and the first optical component is arranged relative to the second optical component such that there is a non-zero angle between the layers of the first optical component and the layers of the second optical component.

2. An optical device as claimed in claim 1 , wherein the non-zero angle is substantially a right angle.

3. An optical device as claimed in claim 1 or 2, wherein the first optical path and/or the second optical path is defined by a waveguide.

4. An optical device as claimed in any preceding claim, wherein the second optical path directs light from the first optical path in a direction substantially normal to the layers of the first optical component or in a direction having at least a component normal to the layers of the first optical component.

5. An optical device as claimed in claim 4, wherein the second optical path is curved.

6. An optical device as claimed in any preceding claim, wherein the first optical component and the second optical component comprise interengaging physical formations for locating the first optical path relative to the second optical path.