Patent Application
20080260330
It is desirable for systems having multiple optical components to have those components accurately aligned. For example, systems in which laser light is introduced into an optical fiber for telecommunications purposes often have one lens that collimates the laser light and another lens that focuses the laser light onto the tip of the fiber. To improve the amount of laser light that is coupled to the fiber, the optical components should be accurately aligned with the laser and the fiber tip.
Accurate alignment is desirable not only during the manufacture of optical systems when the components are first assembled and secured, but also during the lifetime of the optical system. Alignment can degrade during the lifetime. Adhesive layers that bond optical components in place can shrink or crack over time causing optical components to drift out of alignment. Also, adhesives, such as epoxy or solder, can have thermal expansion rates that are different from those other components in an optical system. When the system is subject to thermal fluctuations, expansion and contraction causes differential movement between optical components that are secured by adhesive and other components of the system.
The described system and method for accurate alignment of optical components in a system yield an alignment that can be less susceptible to degradation that results from changes occurring within the adhesive from the effects of thermal fluctuations.
A mounting block is attached to a carrier with thin layers of adhesive material, and an optical component is mounted to the block also using thin layers of adhesive. The component mounted to the block and the mount block mounted to the carrier are adjusted along three coordinate axes to provide alignment in an optical system. Additional blocks and components can also be provided. The mounting blocks can be used to align a lens in a system that includes a laser and an optical fiber, or in other systems with optical components. The adhesive that is used can be a solder or a sol-gel, or any other suitable adhesive. It is desired that after attachment, the layers of adhesive have a combined thickness of about 5 microns or less. Such thin layers of adhesive, while not strictly necessary, are advantageous because they can reduce the degradation in the optical alignment that commonly occurs when thicker adhesive layers are used.
The systems and methods described here are thus useful for aligning components in a way that is more accurate at the time of alignment and that stays in accurate alignment over time. Other features and advantages will become apparent from the following detailed description, drawings, and claims.
Laser 102 provides a laser beam that passes through collimating lens 110. Commercially available square lens 110, as manufactured, for example, by ALPS Electric Co., Ltd. or by Lightpath Technologies, Inc., is affixed to lens mounting block 112, which is itself mounted onto main carrier 114 that is typically made of ceramic. The laser beam next passes through surface mounted isolator 116, and then through second lens 118 that focuses the beam onto a tip of an optical fiber (see
The three orthogonal coordinate axes referred to in what follows are shown at bottom left in
A desired position is determined by active alignment. The amount of power coupled to the fiber is monitored, and the alignment is set at the position where the coupled power is at a high level, often at a maximum. A controller (not shown) receives the power coupled to the fiber and provides feedback to the adjustment process. This process may be either manual or robotic depending upon the required degree of accuracy and repeatability and the required volume of throughput.
One useful aspect of the described embodiment is the low thickness, i.e., less than or equal to about 5 microns, of the solder layer that secures the optical components in place. The thin bond layer enables a more precise alignment to be performed than would be possible with a thicker layer because there is less ability for shrinkage and misalignment during the fixing process. A thin bond layer is also expected to have less susceptibility to drift or cracking over time than would thicker layers of adhesive. Thus a thin bond line can maintain optimal alignment longer than systems with thicker adhesive layers. A thin bond layer is also less susceptible to thermal creep, because any differential expansion of the bond compared to the surrounding components is kept to a minimum. Furthermore, with a thin bond layer there is less opportunity for significant variation in bond thickness across a given bond. An advantage of such a uniform thickness bond layer is that temperature variations cause the bond line to shrink or expand uniformly, with the bonded surfaces remaining parallel, thus avoiding undesirable angular translation.
In another embodiment, a thin layer of chemical adhesive, such as a sol-gel, secures the optical components in place.
Referring to
Other embodiments are within the scope of the following claims. For example, the description relates to optical lasers, lenses, and fibers, although the alignment concepts can be employed with other optical components. Although the described embodiment shows the alignment of square lenses, lenses having any shape may be aligned using the disclosed methods and systems. The optical components to be aligned are not limited to lenses, but may include mirrors, prisms and diffraction gratings. In addition to the solder and sol-gel adhesive layers, other adhesives may be used such as epoxy and UV curing epoxy. Adhesives having a low coefficient of thermal expansion are preferred. However, using adhesives in thin films as described above minimizes the effect of thermal expansion, thereby relaxing the requirement for a low coefficient of thermal expansion.
