Optical waveguides – With optical coupler – Particular coupling structure
Reexamination Certificate
1999-09-13
2001-06-19
Schuberg, Darren (Department: 2872)
Optical waveguides
With optical coupler
Particular coupling structure
C385S052000, C385S050000, C385S131000, C372S108000
Reexamination Certificate
active
06249627
ABSTRACT:
TECHNICAL FIELD
The present invention relates to an arrangement for aligning a communication fiber to a surface emitting laser and, more particularly, to an arrangement that provides self-alignment between an array of surface emitting lasers and an array of optical fibers.
BACKGROUND OF THE INVENTION
A vertical cavity surface emitting laser has a configuration of a cavity comprising an active layer made of GaAs and GaInAs sandwiched by a mirror above the active layer and an underlayer mirror on the substrate side beneath the active layer. In comparison with an edge emitter semiconductor laser, the length of the cavity is extremely short. It is thus necessary to make laser oscillation easy to generate by setting the reflectivity of each of the mirrors at a very high value of equal to or greater than 99%. For this reason, a distributed Bragg reflector (DBR) is normally used as a mirror. The distributed Bragg reflector is created from layers of low-refractivity materials made of AlAs and layers of high-refractivity materials made of GaAs. The low-refractivity and high-refractivity materials are stacked on each other alternately with a period of ¼ of the wavelength.
The vertical cavity surface emitting laser is expected to be a key device for realizing large capacity optical communication by transmitting optical information in parallel through a plurality of laser devices arranged in an array. A mounting technology for interconnecting an array of these surface emitting lasers with a suitable array of optical fibers has become an area of study and development. One exemplary mounting arrangement is disclosed in U.S. Pat. No. 5,912,913 issued to M. Kondow et al. on Jun. 15, 1999. In this arrangement an array of surface emitting lasers are disposed on a first module and an array of optical fibers are positioned within a single large opening formed through a second module. There is no attempt to provide individual fiber-to-device alignment in the Kondow et al. arrangement, and it is presumed that the fiber array disposed within the opening will generally align with the laser array upon attachment of the two modules. In the case of an optical fiber having a core diameter of 50 &mgr;m and a device also having an optical emission diameter on the order of 50 &mgr;m, by setting the gap between the optical fiber and the laser at a value less than or equal to 10 &mgr;m, the Kondow et al. arrangement provides a coupling efficiency of only 50%.
An alternative arrangement that provides for improved alignment between an individual surface emitting laser and optical fiber is disclosed in U.S. Pat. No. 5,796,714 issued to T. Chino et al. on Aug. 18, 1998. In this arrangement, the laser substrate itself is etched through on the backside to create an opening (i.e., etch a via through a portion of the substrate material) for the optical fiber. While it is possible to provide improved alignment with this configuration, such an arrangement becomes problematic when utilized with an array of surface emitting lasers. In particular, any mismatch in forming the array of optical fiber vias not only results in misalignment between the lasers and the fibers, but since the vias are formed through the actual optical substrate, requires the entire array to be discarded, a costly and time-consuming result in a large volume manufacturing environment.
Thus, a need remains in the art for a packaging arrangement capable of providing an efficient and accurate alignment between an array of surface emitting lasers and an array of optical communication fibers.
SUMMARY OF THE INVENTION
The need remaining in the prior art is addressed by the present invention, which relates to an arrangement for aligning a communication fiber to a surface emitting laser and, more particularly, to an arrangement that provides self-alignment between an array of surface emitting lasers and an array of optical fibers.
In accordance with the present invention, an array of surface emitting lasers are formed upon (or subsequently attached to) a first substrate (for example, an InP substrate). A second, separate substrate (for example, a silicon substrate) is processed to form apertures for an array of optical fibers. In particular, the second substrate (also referred to below as the “fiber substrate”) is etched through on both major surfaces to form vias from either side that meet to form the fiber apertures. The apertures are formed so as to accommodate the diameter of a typical communication fiber (for example, 125 &mgr;m). Advantageously, the use of conventional photolithographic techniques in forming the aperture array allows for the placement of the apertures on the second substrate to coincide precisely with the position of the lasers in the array on the first substrate. It is a feature of the present invention that any modification in the laser array (for example, decreasing the inter-laser spacing, changing the dimension of the array, etc.) can be easily accommodated by changing the mask used to define the locations of the fiber apertures on the second substrate.
In accordance with an aspect of the present invention, a self-aligning epoxy can be used to attach the substrates together, thus aiding in providing optimal alignment between the device array and fiber array. Alternatively, alignment fiducials can be formed on the both substrates so that the fiber substrate will “self-align” with the laser substrate upon attachment. In instances where the joined substrates are subsequently “diced” to form separate device/fiber subassemblies, a protective coating layer (such as a photoresist) may be used to prevent contamination of the substrates during sawing.
Other and further aspects of the invention will become apparent during the course of the following discussion and by reference to the accompanying drawings.
REFERENCES:
patent: 5247597 (1993-09-01), Blacha et al.
patent: 5796714 (1998-09-01), Chino et al.
Bond Aaron Eugene
Dautartas Mindaugas Fernand
Przybylek George John
Assaf Fayez
Koba Esq. Wendy W.
Lucent Technologies - Inc.
Schuberg Darren
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