Adhesive bonding and miscellaneous chemical manufacture – Methods – Surface bonding and/or assembly therefor
Reexamination Certificate
1999-12-23
2001-09-11
Ball, Michael W. (Department: 1733)
Adhesive bonding and miscellaneous chemical manufacture
Methods
Surface bonding and/or assembly therefor
C156S275700, C156S297000, C029S407100, C029S464000, C359S107000, C359S199200
Reexamination Certificate
active
06287401
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to optical alignment and, more particularly, to a method and apparatus for aligning semiconductor optical devices and fixing them in place.
BACKGROUND OF THE INVENTION
One of the most expensive components in any optical communications system is the optical transmitter module which may, for example, be comprised of a continuous wave (CW) distributed feedback (DFB) laser and an external Mach-Zender (MZ) intensity modulator, plus associated driving and stabilization electronics. For optical communication systems, it is natural to use optical components as much as possible if conditions permit. Traditionally, the alignment of semiconductor optical devices to one another has been carried out using conventional optics. The precise alignment of the DFB laser diode to an external MZ modulator may, for example, employ a pair of aspherical lenses with an optical isolator placed in between. An optical isolator is a device used to prevent light in a system from reflecting back to the source which could deteriorate its operation. As is well known, isolators are fairly complex devices and, as such, are generally quite expensive. Indeed, then, the precise optical alignment and packaging requirements for such transmitter modules will account for a considerable proportion of the cost for each unit.
In the past, discrete devices have been aligned with other discrete devices or with integrated devices by methods which include some form of active positioning. For example, some systems employ a feedback control loop to monitor light intensity as the devices are being aligned, the devices being fixed in place when the intensity is optimum. Alignment in such a manner has proven to be very difficult and time consuming. In addition to the high costs associated with the required complex components, such techniques necessarily demand very skilled and experienced operators.
While losses within an optical element can be reduced by appropriate component design, it is difficult to factor in the losses associated with coupling between optical elements. Connection losses are inherently variable and this forces the designer to consider the effect of both the maximum and minimum optical signal power levels on the system. Any new method of minimizing coupling losses between active or passive optical elements, minimizing the variability of such losses, or enhancing robustness and manufacturability, will be of tremendous value to the realization of cost-effective optical modules.
SUMMARY OF THE INVENTION
The present invention provides a more efficient and cost-effective means to align semiconductor optical devices to one another and fix them in place. In so doing, the complex, labour intensive, low-yield alignment process traditionally employed is eliminated.
The inventive concept is based on a chip-on-carrier model and delivers many of the benefits of a monolithically produced configuration. Specifically, a semiconductor optical device is mounted on a flat ceramic carrier while the device it is to be aligned with is mounted on a separate ceramic ‘wedged’ carrier. A ceramic wedge of similar size and proportions to the wedged carrier is also provided having been lapped to the same angle as the wedged carrier. The above device carriers are supported by a ceramic baseplate. A thin layer of liquid adhesive, applied to the top surface of both the baseplate and ceramic wedge, acts as a lubricant allowing for easy sliding of the carriers for subsequent alignment. By sliding the wedged carrier such that it slides up or down the incline of the ceramic wedge allows for adjustment in the vertical axis. The resulting configuration enables precise alignment of semiconductor optical devices with four degrees of freedom. Accordingly, the devices can be align-butted to sub-micron tolerances. Once alignment is achieved, the devices can be fixed in place by exposing the assembly to ultraviolet light or heat, depending on the adhesive used.
The invention results in approximately a ninety per cent reduction in alignment time over previous methods enabling a higher volume throughput per station. Advantageously, relatively little device development is needed since suitable independent components already exist. Furthermore, elimination of the optics presently used to couple light between respective semiconductor optical devices will make manufacture of modules more manageable and cheaper. Without the expensive optical components normally required, a lower capital value alignment station can also be realized.
Other aspects and features of the present invention will become apparent to those ordinarily skilled in the art upon review of the following description of specific embodiments of the invention in conjunction with the accompanying drawings.
REFERENCES:
patent: 6098264 (2000-08-01), Harrigan et al.
Anderson Keith D.
Ertl Paul S.
Hughes Richard P.
Ball Michael W.
Nortel Networks Limited
Tolin Michael A.
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