Optical waveguides – With disengagable mechanical connector – Optical fiber to a nonfiber optical device connector
Reexamination Certificate
2000-11-06
2002-08-13
Ullah, Akm E. (Department: 2874)
Optical waveguides
With disengagable mechanical connector
Optical fiber to a nonfiber optical device connector
Reexamination Certificate
active
06431766
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to a method of alignment in an optoelectronic assembly, in particular, but not exclusively, to a method of generating an alignment feature in an optoelectronic assembly which enables another part, for example an optical fibre, to be aligned to a device within the assembly.
Conventionally, a micro fabricated optoelectronic device, for example a single chip photodetector or laser source device, is packaged within an associated hermetically sealed package for protection. An optical fibre for conveying electromagnetic radiation to or from the device is attached to the package and penetrates through the package to contact directly onto the device. Alternatively, the optical fibre penetrates through the package to align remotely to the device, a secondary structure physically connecting to the device and receiving an end of the fibre thereby securing the fibre in alignment with the device. Alignment of the optical fibre to the device can often be difficult to achieve especially when the fibre is a monomode fibre having an associated core diameter in the order of a few ricrometres. When the device is a III-V compound device, for example a gallium-indiumarsenide laser source, alignment of the fibre to the device can be critical; an alignment error in the order of 0.1 &mgr;m can adversely affect coupling efficiency of the device to the fibre. There also arises an issue of mechanical stability where the optical fibre abuts onto the device; relative movement therebetween over time of tens of nanometres can adversely effect transmission efficiency from the device into the fibre or detection efficiency of the device to incoming fibre-borne radiation.
There are a number of conventional approaches to assist with aligning optical fibres to associated devices.
In a first conventional approach, there is provided an optoelectronic device housed within a hermetically sealed package, the device having etched thereinto a channel for receiving a core of an optical fibre, the fibre passing from a region exterior to the package through the package to terminate on the device. Assembly of the fibre to the device requires considerable operator skill and damage can occur to the device if the fibre is misdirected during assembly, for example the fibre scraping and severing metal electrodes of the device. Location of the core in the channel can occur by mechanical abutment although optically transparent bonding agents, for example Norland Inc. optically transparent UV curing adhesive, can be advantageously added to obtain a robust joint.
In a second alternative approach, an epitaxial alignment structure is formed onto the device to provide lateral abutment edges onto which the core can register. However, this second approach suffers the same disadvantages of the first approach in that a skilled operator is required for manipulating the core to align it precisely to the device without causing damage thereto.
In a granted U.S. Pat. No. 4,892,377, the inventor discloses an approach to accurately align an array of optical fibres with corresponding optical components such as waveguides. The fibres are fixed in accurately etched V-grooves formed into a substrate connected to the optical components and can be secured thereto using solder. Such an approach requires skilled operators to manipulate the fibres into the V-grooves to obtain a satisfactory alignment providing acceptable matching.
The inventor has appreciated that it is desirable to accurately align fibres to devices without having to physically bond or abut the fibres to the devices. Superficially, such an approach would seem unworkable because each fibre would have to be accurately aligned to an associated intermediate region and a corresponding device would also have to be accurately aligned to the intermediate region thereby fixing the fibre spatially with respect to the device; this would result in a build up of tolerances which would be more difficult to control than the first and second conventional approaches described above.
The inventor has evolved a method of alignment in an optoelectronic assembly which addresses alignment problems associated with spatially defining a fibre's position with respect to an associated device within the assembly without having to bond the fibre directly to the device within the assembly as in the prior art.
SUMMARY OF THE INVENTION
According to a first aspect of the present invention, there is provided a method of alignment in an optoelectronic assembly, the assembly including one or more optoelectronic devices and interfacing means for interfacing from the one or more devices to one or more corresponding optoelectronic components external to the assembly, the method characterised in that it includes the steps of:
(a) defining one or more regions of the interfacing means to which the one or more devices are responsive to or emissive towards, thereby rendering the one or more regions delineated for processing purposes;
(b) processing the assembly to generate one or more alignment features at the one or more regions, the one or more features operable to assist with aligning the one or more external components relative to their respective one or more devices within the assembly;
(c) aligning the one or more components to their respective features so as to be operable to emit towards or receive radiation from their respective one or more devices; and
(d) applying attaching means for attaching the one or more external components to the assembly when aligned to their respective features, the one or more components thereby optically aligned to their corresponding one or more devices within the assembly.
The method provides the advantage that the one or more devices are capable of defining positions of their respective alignment features in the interfacing means, thereby assisting to align the one or more external components to the devices without the position of the interfacing means needing to be initially precisely defined with respect to the one or more devices.
Advantageously, in step (a), the interfacing means includes a wall of the assembly, the wall bearing a system of layers responsive to radiation emitted from the one or more devices within the assembly for defining the one or more regions in the system of layers, the layers providing a template for the formation of the alignment features in step (b). Inclusion of the system of layers enables the one or more devices to define positions of their corresponding one or more alignment features, the system of layers responsive to radiation emitted from the one or more devices.
Conveniently, the system of layers comprises:
(a) an etch resist layer through which the wall is processable to generate the one or more features therein; and
(b) a photochromic layer operable to be activated by externally applied radiation and capable of being rendered locally transmissive in response to radiation received thereat from the one or more devices,
thereby enabling the externally applied radiation to define regions in the resist layer corresponding to the one or more features, the resist layer providing a template for formation of the one or more features. Use of the photochromic layer provides a simplified method of alignment which does not need to be conducted in darkroom conditions.
Alternatively, the system of layers includes multiplying means for frequency multiplying radiation emitted from the one or more devices within the assembly, thereby generating corresponding relatively shorter wavelength radiation for defining the one or more regions in one or more layers of the system. Inclusion of the multiplying means enables one or more of the devices emitting infra-red radiation having a wavelength in the order of 1300 to 1550 nm to form a latent image in the system of layers, the latent image processable for ultimately forming a template in the system of layers through which the wall can be etched to generate the alignment features therein.
The multiplying means preferably comprises a multiplying layer including potassium ti
Bookham Technology PLC
Kirschstein et al.
Ullah Akm E.
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