The present invention relates generally to optical components, and particularly to compact optical fiber splitters.
An embodiment of the present invention described herein provides an apparatus including one or more optical waveguides, one or more first micro-lenses, and one or more second micro-lenses. The one or more optical waveguides are formed in a substrate and are configured to convey respective optical signals between first ends and second ends of the optical waveguides. The one or more first micro-lenses are disposed on the respective first ends of the optical waveguides and are configured to couple the optical signals between the first ends and respective first optical elements. The one or more second micro-lenses are disposed on the respective second ends of the optical waveguides and are configured to couple the optical signals between the second ends and respective second optical elements.
In some embodiments, the first micro-lenses are disposed on a face of the substrate, and the first ends of the optical waveguides terminate at a predefined distance from the face of the substrate, opposite the first micro-lenses. In other embodiments, the first and second optical elements include at least one element type selected from a group of types consisting of optical fibers, optical detectors and optical emitters. In yet other embodiments, the apparatus also includes a mechanical fixture that fixes the first optical elements at a predefined distance from the respective first micro-lenses, so as to form an air gap between the first optical elements and the first micro-lenses.
In some embodiments, each optical waveguide includes a respective bending element that bends an optical signal in the optical waveguide between a first axis and a second axis. In other embodiments, the optical waveguides include first and second subsets of the optical waveguides, such that the first ends of the optical waveguides in the first subset are arranged in a first row, and the first ends of the optical waveguides in the second subset are arranged in a second row positioned above the first row. In yet other embodiments, the first and second subsets of the optical waveguides lie in first and second different parallel planes.
In some embodiments, the optical waveguides include a first subset of the optical waveguides whose second ends lie on a first face of the substrate, and a second subset of the optical waveguides whose second ends lie on a second face of the substrate, different from the first face. In other embodiments, the first face is parallel with the second face. In yet other embodiments, the first face is perpendicular to the second face.
There is additionally provided, in accordance with an embodiment of the present invention, an apparatus, which includes an optical interconnect, which includes a substrate, one or more optical waveguides, one or more first micro-lenses, one or more second micro-lenses, and first and second mechanical fixtures. The one or more optical waveguides are formed in a substrate and are configured to convey respective optical signals between first ends and second ends of the optical waveguides. The one or more first micro-lenses are disposed on the respective first ends of the optical waveguides and are configured to couple the optical signals between the first ends and respective first optical elements. The one or more second micro-lenses are disposed on the respective second ends of the optical waveguides and are configured to couple the optical signals between the second ends and respective second optical elements. The first and second mechanical fixtures are configured to fix the first and second optical elements against the first and second ends of the optical waveguides, respectively.
In some embodiments, the first optical elements include optical fibers, and the first mechanical fixture includes a ferrule that is configured to fix respective facets of the optical fibers to the respective first ends of the optical waveguides. In other embodiments, the first mechanical fixture is configured to fix the first optical elements at a predefined distance from the respective first micro-lenses, so as to form an air gap between the first optical elements and the first micro-lenses.
There is additionally provided, in accordance with an embodiment of the present invention, a method including forming one or more optical waveguides in a substrate, for conveying respective optical signals between first ends and second ends of the optical waveguides. One or more first micro-lenses are disposed on the respective first ends of the optical waveguides, for coupling the optical signals between the first ends and respective first optical elements. One or more second micro-lenses are disposed on the respective second ends of the optical waveguides, for coupling the optical signals between the second ends and respective second optical elements.
The present invention will be more fully understood from the following detailed description of the embodiments thereof, taken together with the drawings in which:
Many optical systems use optical fibers to couple light between different optical elements. In some systems, individual fibers are held in a bundle, or optical cable, and need to be separated to route the fibers to optical elements at different locations in the system. For example, an optical fiber splitter module may be used to physically separates and bend the individual fibers in the fiber cable into two or more different output fiber cables in a very small module volume, in order to route the fibers to their destination in the system. As the number of fibers in the bundle increase, the size of the splitter increases accordingly to accommodate the density of fibers. This constraint limits reducing the size of the splitter, whereas space constraints are sometimes critical and require modules with small form factors.
Embodiments of the present invention described herein provide highly compact optical interconnects, and methods for fabricating such interconnects as building block for optical splitter modules. In the disclosed embodiments, optical signals in one or more optical fibers are coupled through an optical interface with integrated micro-lenses to an array of compact waveguides formed in a substrate. The micro-lenses are configured to focus or collimate the light efficiently between the individual fiber and respective waveguides in the substrate.
Once the light is coupled into the waveguide array in the substrate, the separate waveguides are bent horizontally or vertically in the substrate. A portion of the waveguides in the array can be split and routed to any desired face of the substrate. The waveguides can be routed in a very small form factor to another micro-lens interface at the other end of the waveguide array.
One or more micro-lens based optical interfaces can be located on any face of the substrate to couple light between a first cable to any number of fiber in one or more cables using a multi-level waveguide substrate. Thus in additional embodiments described herein, a variety low-loss optical splitter module configurations and topologies with highly compact form factors, are shown based on the micro-lens based optical interconnect building block.
Waveguides 20 have an orientation vector that is perpendicular to the cross-section of waveguides 20. An optical interface 30 is formed on a face 35 of substrate as shown in the dashed region in
As shown in the first inset for optical interface 30, waveguides 20 terminate on a waveguide end 50 positioned at a distance D from a trench face 47 formed in face 35 of the substrate 15. The trench causes the light to traverse a distance of D through the substrate material, between ends 50 of waveguides 20 and face 47. An optical material is disposed on trench face 47 at faces 35 and 40 at a distance D from end 50 of each waveguide 20 to form an array of integrated micro-lenses 13. Each micro-lens 13 in the array is configured to focus a light ray 52 diverging from waveguide end 50 onto an optical element, such an optical fiber facet 55 of an optical fiber 60, as shown both in the first and second insets of
In some embodiments, substrate 15 may comprise one or more layers of optical materials, such as polycarbonate (PC), polystyrene (PS), silica, and poly-methyl methacrylate (PMMA). Waveguides are formed by etching grooves in the one or more layers, filling the etched grooves with a second optical material with a higher index of refraction than that of the one or more layers, and bonding the one or more layers together to form substrate 15. In the exemplary configuration of eight parallel waveguides 20 shown in
Any suitable cross-sectional shape of waveguide 20 can be created in this manner, which depends on the etching process that determines the shape of the etched grooves. Moreover, one or more layers of stacked waveguides can be formed in this manner as will be shown further below. In other embodiments, the waveguides can be directly formed with conventional lithography processes used, for example, in silicon complementary metal oxide semiconductor (CMOS) processes or processes to form Si Micromechanical Systems (MEMS) devices.
Micro-lenses 13 can be formed opposite waveguide ends 50 on trench face 47 using fabrication techniques, such as injection molding of polyetherimide (PEI), or other techniques that are known in the art for disposing suitable material on trench face 47 to form micro-lenses 13.
Optical fibers 60 are typically held in micro-channels formed in a ferrule 70, which is shown in a dotted outline in the first inset of
In some embodiments, guide pins 80 are formed on face 35 and face 40 to hold ferrule 70 at each face by inserting guide pins 80 into guide pin channels 85 formed in the body of ferrule 70. An array of fiber facets 55 can then be placed precisely at a gap distance G from an array of respective micro-lens 13, i.e., so as to form an air gap of width G between the fiber ends and the corresponding micro-lenses.
Typically an optical fiber cable is connected and supported at a first end of the ferrule. The individual fibers from the cable are thread through and held in separate micro-channels formed in the body of the ferrule. At a second (opposite) end of the ferrule, the ends of the fibers coupling light into optical interface 30 are typically cleaved or polished fiber facets 55 that are aligned with the edge of ferrule 70 as shown in the first inset of
Examples of ferrules are MT Ferrules produced by Connected Fibers, Inc. (Roswell, Ga.). A datasheet of such MT ferrules, entitled “MT ferrules,” January, 2009, is incorporated herein by reference. International Electrotechnical Commission (IEC) document number IEC61754-5, entitled “Fiber Optic Connector Interfaces—Part 5: Type MT Connector Ferrules,” January, 1996, which is incorporated herein for reference, specifies such ferrule designs. Fiber facets 55 align with the second end of ferrule 70 which connects to the module. The arrangement of the fiber facets at the edge of the ferrules can have different footprints. For example, a ferrule holding twenty-four fibers can be arranged in a footprint of two rows of twelve fibers separated by a predefined distance.
The coupling efficiency of light between waveguide 20 and fiber 60 at both faces 35 and 40 of interconnect 10 may be optimized empirically, or by simulation. This optimization is done by varying parameters, such as gap distance G, distance D, the shape of micro-lens 13, the shape of waveguide bends 45, and any other suitable geometrical or material parameter in optical interconnect 10. Stated differently, light exiting the waveguide should be matched into the fiber core with a given numerical aperture by varying the above parameters so as to focus the light diverging from waveguide end 50 onto fiber facet 55. The precision positioning of fiber facets 55 relative to trench face 47 using ferrule guide pins 85 is also an important parameter affecting the overall optical loss in interconnect 10.
The optical reflector configurations shown in
A variety of optical splitter module configurations can be fabricated using optical interface 30 as a basic building block as shown in
To realize an optical splitter module, two or more arrays of waveguides 20 shown in optical interconnect 30 may be stacked vertically. The input optical interface may comprise one or more rows of waveguides in the XY plane but stacked vertically at different heights along the Z-axis as shown in
The exemplary embodiments of the optical splitters shown in the following figures below have a first array of micro-lenses (e.g., micro-lenses arranged in two rows) on a first edge of substrate 15 that are configured to couple light into a first and a second level of vertically stacked waveguides in the substrate. The first level of the vertically stacked waveguides is routed to a second array of respective micro-lenses formed on a second edge of the substrate, and the second level is routed to a third array of respective micro-lenses on the third edge of substrate 15.
The exemplary embodiments shown herein with eight or sixteen fibers 60 carrying light which are coupled between respective waveguides in substrate 15 through an arrays of micro-lenses 13 are shown merely for conceptual clarity and not by way of limitation whatsoever of the embodiments of the present invention. Typically, any number of fibers M*N arranged with N fibers in M rows, where M and N are integers, may be used so long as the footprint of the ferrule is configured to support the M*N fibers.
Moreover, light carried in the M*N fibers arranged in N rows and held in the ferrule should be coupled precisely to a corresponding waveguide array comprising N levels of M waveguides using a suitable multilayered substrate as described previously. However, in accordance with the embodiments of the present invention described herein, any number of fibers may be held in any suitable housing and is not limited to ferrules, which are coupled to any number of waveguides in any arrangement through respective micro-lenses.
Individual fibers 60 are held in optical cables. A first optical cable 160 is configured to connect to the footprint of ferrule 165. Cavities 150 and 151 are configured to support multi-fiber ferrule 70 holding eight optical fibers with a footprint of one row of eight fibers within the ferrule housing. A second optical cable 170 is configured to connect to the footprint of ferrule 70 in cavity 150 at face 152 and in cavity 151 at face 158 of substrate 15.
In some embodiments, T-shaped optical splitter module 168 shown in
In
For the embodiment shown in
In some embodiments, L-shaped optical splitter module 190 as shown in
For optical fiber splitter module 190 shown in
Vertical waveguide 187 can be formed by filled waveguides in substrate 15 by etching vertical vias in the substrate material layers that are filled with an suitable optical material with a higher index of refraction than the substrate material. Similarly the vertical to horizontal waveguide bend which rotates vertical portion 187 of waveguide 20 into waveguides 20 oriented in the X-Y plane can be formed using any of the reflectors shown in the embodiments of
In the first embodiment shown in
In the second embodiment shown in
Finally in the third embodiment shown in
For the embodiments shown in
In the exemplary embodiments shown in the foregoing figures, optical interface 30 and the ferrules are oriented along Cartesian axes. This orientation is shown merely for the sake of visual clarity and not by way of limitation of the embodiments of the present invention. Optical interface 30 may alternatively be configured at any suitable angle relative to substrate 15. The optical interface may be configured to couple light between a waveguide in the substrate and a fiber in the ferrule at any desired angle, for example, by cutting substrate 15 at an appropriate bevel angle, forming micro-lenses 13 on the beveled edge of the substrate, and positioning the ferrule on the bevel. Any suitable fabrication technique and materials may be used to form a beveled optical interface so as to support a ferrule mounted at any suitable angle relative to the body of the optical fiber splitter module.
Optical interface 30 as described in the embodiments of the present invention is not limited to optical fiber splitter modules. The light in the array of waveguides 20 may be directed by optical interface 30 in interconnect 10 into any suitable optical element in accordance with the embodiments of the present invention shown in
An exemplary configuration to illustrate this embodiment may comprise, for example, the light in sixteen fibers held in a ferrule 165 are coupled into two levels of waveguide 20 in substrate 15 and are split into two stacked levels of eight waveguides in substrate 15 as shown in
Similarly the waveguide may terminate at a distance D from the edge of the substrate faces where the PD and VCSEL array chips are mounted in substrate 15 (in place of ferrule 70 in cavities 150 and 151). The optical interface is designed in accordance with the embodiments of the present invention shown in
Although the embodiments described herein mainly address a low loss optical interface for coupling light in fibers between fiber bundles in input/output ferrules in an optical splitter module, the optical interface described herein can also be used in other applications, for precision coupling light in a fiber to any suitable optical element through a micro-lens array.
It will thus be appreciated that the embodiments described above are cited by way of example, and that the present invention is not limited to what has been particularly shown and described hereinabove. Rather, the scope of the present invention includes both combinations and sub-combinations of the various features described hereinabove, as well as variations and modifications thereof which would occur to persons skilled in the art upon reading the foregoing description and which are not disclosed in the prior art. Documents incorporated by reference in the present patent application are to be considered an integral part of the application except that to the extent any terms are defined in these incorporated documents in a manner that conflicts with the definitions made explicitly or implicitly in the present specification, only the definitions in the present specification should be considered.