Coherent light generators – Particular active media – Semiconductor
Reexamination Certificate
1999-07-15
2002-01-08
Davie, James W. (Department: 2881)
Coherent light generators
Particular active media
Semiconductor
C372S096000, C372S102000, C372S043010
Reexamination Certificate
active
06337871
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to multiple edge-emitting lasers manufactured on a single wafer and also relates to testing of the lasers while still located on the wafer. This is called “on-wafer” testing.
BACKGROUND OF THE INVENTION
Edge-emitting lasers are lasers that emit outputs in a horizontal direction through the edges of a laser. When manufacturing edge-emitting lasers, multiple laser cavities (resonators) are usually formed in parallel strips on the surface of a single wafer using a first order grating. Each strip is divided into multiple segments to form multiple coaxial lasers on the wafer so that each edge of the lasers can be exposed horizontally for testing.
On-wafer testing is critical for achieving low cost production of edge-emitting lasers or Distributed Feedback (DFB) lasers by avoiding the testing of each individual die. Assuming the cost of labor is $20 per hour, a worker can only spend minutes testing each individual device to achieve a goal of $20 per die. Any time spent on testing an individual device will add significant cost to the final product. However, if an entire wafer containing 25,000 dies could be automatically tested in even an hour, the cost per die will be dramatically reduced.
For the traditional edge-emitting laser fabrication process, laser testing has to be done after bar cleaving when the length of the laser cavity is determined. Bar cleaving is a process which breaks the wafer into multiple individual pieces defining the length of each laser cavity.
For telecommunications lasers such as a Distributed Feedback laser (DFB), the testing of the laser cannot be done until after the bar cleaving step. Therefore, a large portion of the manufacturing costs occurs during laser testing.
On-wafer testing will reduce the cost of production of edge-emitting lasers and more particularly DFB lasers due to the reduction of testing cost.
Conventional testing of each edge-emitting laser requires emitting and measuring the outputs emitted through the edges of the laser. However, this is not possible to do on a single wafer because the edges from which the outputs are emitted are too close to one another. Therefore, the wafer must be subjected to a cleaving process which breaks the wafer into multiple individual pieces, each individual piece being a single edge emitting laser. The output of each individual laser which is emitted through the edges of the laser is then tested for quality assurance.
SUMMARY OF THE INVENTION
The present invention improves upon the present testing of edge-emitting lasers by allowing for on-wafer testing of edge-emitting lasers located on a single wafer. On-wafer testing is an improvement over the current method of testing because it eliminates the cleaving process which breaks the wafer into multiple individual pieces. The cleaving process is eliminated by substituting a high order grating for the first order grating typically used in edge-emitting lasers. By substituting a high order grating for the typical first order grating, an output is not only emitted through the edges of the laser but outputs are also emitted through the surface of the laser. Measurements can therefore be easily taken from the surface of the wafer without cleaving or breaking the wafer into multiple pieces.
An edge-emitting laser of the present invention comprises a substrate; an insulating layer located on said substrate defining a first channel having insulating layers located on either side of said first channel; a high order grating layer located in said first channel wherein said high order grating layer has an order greater than a first order grating layer; a waveguide located on top of said grating layer; and a cap layer located on top of said waveguide and said insulating layers.
In an alternate embodiment, a component of an edge-emitting laser comprises a first resonator; a grating located in said first resonator having a grating order greater than one; a waveguide located in said first resonator; a cap layer located above said waveguide and said grating wherein said first resonator has an edge-emitting component being transmitted through said first resonator and a surface-emitting component being transmitted in a different direction than said edge-emitting component.
An edge-emitting laser of the present invention may further comprise a high order grating layer that is a second order grating layer located in a first channel and also comprises a second channel that is co-axial to said first channel. A cap layer may have an opening located above said waveguide and also comprises metal slabs located on either side of said opening.
A method for fabricating an edge-emitting laser cavity of the present invention comprises the steps of providing a substrate; forming an insulating layer on said substrate defining a first channel having insulating layers located on either side of said first channel; forming a high order grating layer in said first channel wherein said high order grating layer is greater than a first order grating layer; forming a waveguide over said grating layer; and forming a cap layer over said waveguide and said insulating layers.
In an alternate embodiment, a method for the fabrication of a component of an edge-emitting laser comprises the steps of forming a first resonator; forming a high order grating layer in said first resonator wherein said high order grating layer is of an order greater than one; forming a waveguide in said first resonator; and forming a cap layer over said waveguide and said first resonator.
The method of for the fabrication of an edge-emitting laser cavity in accordance with the present invention may further comprise forming said high order grating layer as a second order high order grating layer and also comprises forming a second channel being co-axial to said first channel. The method further comprises etching across said insulating layer and said first channel forming two or more channels and also comprises forming an opening in said cap layer above said waveguide. In addition, the method further comprises forming metal slabs on either side of said opening and also etching an opening above said waveguide in said cap layer.
A method for testing edge emitting-lasers located on a single substrate comprises the step of taking measurements from each surface-emitting component of said lasers.
In an alternate embodiment, the method for testing edge-emitting lasers located on a single substrate further comprises the step of taking said measurements using a lensed fiber and an electrode.
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patent: 6121634 (2000-09-01), Saito et al.
Davie James W.
Fleshner & Kim LLP
Menefee James
University of Maryland Baltimore County (UMBC)
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