Optical system active alignment process including alignment...

Details Optical system active alignment process including alignment... Optical system active alignment process including alignment...

2000-08-25

2003-05-06

Le, Que T. (Department: 2878)

Radiant energy

Photocells; circuits and apparatus

Photocell controls its own optical systems

C250S559300

Reexamination Certificate

active

06559464

ABSTRACT:

This application also claims the benefit of the filing date of U.S. Provisional Application No. 60/186,925, filed Mar. 3, 2000, which is incorporated herein by this reference in its entirety.
BACKGROUND OF THE INVENTION
Component alignment is of critical importance in semiconductor and/or MEMS (micro electro-mechanical systems) based optical system manufacturing. The basic nature of light requires that light generating, transmitting, and modifying components must be positioned accurately with respect to one another, especially in the context of free-space-optical systems, in order to function properly and effectively in electro-optical or all optical systems. Scales characteristic of semiconductor and MEMS necessitate sub-micron alignment accuracy.
Consider the specific example of coupling a semiconductor diode laser, such as a pump laser, to a fiber core of a single mode fiber. Only the power that is coupled into the fiber core is usable to optically pump a subsequent gain fiber, such as a rare-earth doped fiber or regular fiber, in a Raman pumping scheme. The coupling efficiency is highly dependent on accurate alignment between the laser output facet and the core; inaccurate alignment can result in partial or complete loss of signal transmission through the optical system.
Moreover, such optical systems require mechanically robust mounting and alignment configurations. During manufacturing, the systems are exposed to wide temperature ranges and purchaser specifications can explicitly require temperature cycle testing. After delivery, the systems can be further exposed to long-term temperature cycling and mechanical shock.
Solder joining and laser welding are two common mounting techniques. Solder attachment of optical elements can be accomplished by performing alignment with a molten solder joint between the element to be aligned and the platform or substrate to which it is being attached. The solder is then solidified to “lock-in” the alignment. In some cases, an intentional offset is added to the alignment position prior to solder solidification to compensate for subsequent alignment shifts due to solidification shrinkage of the solder. In the case of laser welding, the fiber, for example, is held in a clip that is then aligned to the semiconductor laser and welded in place. The fiber may then also be further welded to the clip to yield alignment along other axes. Secondary welds are often employed to compensate for alignment shifts due to the weld itself, but as with solder systems, absolute compensation is not possible.
Further, there are two general classes of alignment strategies: active and passive. Typically in passive alignment of the optical components, registration or alignment features are fabricated directly on the components or component carriers as well as on the platform to which the components are to be mounted. The components are then mounted and bonded directly to the platform using the alignment features. In active alignment, an optical signal is transmitted through the components and detected. The alignment is performed based on the transmission characteristics to enable the highest possible performance level for the system.
SUMMARY OF THE INVENTION
The problem with conventional alignment processes is that they require very specialized machines to implement. Even then, the alignment process is typically slow.
It has been suggested to utilize plastic deformation of optical component structures during alignment processes. The problem, however, with these proposed systems, it that they only provided limited range of motion during the alignment process, which, even under optimal conditions, resulted in sub-optimal alignment.
In general, according to one aspect, the invention features an optical system active alignment process. It comprises activating an optical link in the optical system and detecting an optical signal after transmission through the optical link. An optical component is positioned on a deformable structure relative to the active optical link by moving the optical component in a plane that is orthogonal to a propagation direction of the optical signal at the optical component. This positioning is performed, while maintaining a position of the optical component along an axis that is parallel to the propagation direction of the optical signal. The structure is plastically deformed to align the optical component relative to the optical link.
The advantage of this positioning system surrounds the fact that conventional robot/pick-and-place machines can be used to locate the deformable structure positioning the optical component with relatively high precision relative to other optical components, especially along the length of the optical path. It is difficult, however, to locate the optical component in a plane that is orthogonal to this optical path, however. This is because there are inaccuracies in how the optical component is positioned on the structure. Moreover, the exact location of the optical signal's path may not be known with great accuracy, either in its height above an optical bench and/or laterally. The ability of the deformable structure to enable optical component positioning in a plane that is orthogonal to the optical signal propagation direction allows the proper alignment of the optical component to be achieved during active alignment. This alignment is performed while minimizing any degradation in alignment in a path that is parallel to the optical signal's path.


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