The figure is a simplified cross section of a microscopic optical switch that was partially developed at the time of reporting the information for this article. In a fully developed version, light would be coupled from an input optical fiber to one of two side-by-side output optical fibers. The optical connection between the input and the selected output fiber would be made via a microscopic ball lens. Switching of the optical connection from one output fiber to another would be effected by using a pair of thin-film shape-memory-alloy (SMA) actuators to toggle the lens between two resting switch positions.

There are many optical switches - some made of macroscopic parts by conventional fabrication techniques and some that are microfabricated and, hence, belong to the class of microelectromechanical systems (MEMS). Conventionally fabricated optical switches tend to be expensive. MEMS switches can be mass-produced at relatively low cost, but their attractiveness has been diminished by the fact that, heretofore, MEMS switches have usually been found to exhibit high insertion losses. The present switch is intended to serve as a prototype of low-loss MEMS switches. In addition, this is the first reported SMA-based optical switch.

The SMA Actuators would move the ball lens between its two resting positions. Light would be coupled to one or the other output optical fiber, depending on which position was selected.

The optical fibers would be held in V grooves in a silicon frame. The lens would have a diameter of 1 μm; it would be held by, and positioned between, the SMA actuators, which would be made of thin films of TiNi alloy. Although the SMA actuators are depicted here as having simple shapes for the sake of clarity of illustration, the real actuators would have complex, partly netlike shapes. With the exception of the lens and the optical fibers, the SMA actuators and other components of the switch would be made by microfabrication techniques. The components would be assembled into a sandwich structure to complete the fabrication of the switch.

To effect switching, an electric current would be passed through one of the SMA actuators to heat it above its transition temperature, thereby causing it to deform to a different "remembered" shape. The two SMA actuators would be stiff enough that once switching had taken place and the electrical current was turned off, the lens would remain latched in the most recently selected position.

In a test, the partially developed switch exhibited an insertion loss of only -1.9 dB and a switching contrast of 70 dB. One the basis of prior research on SMA actuators and assuming a lens displacement of 125 µm between extreme positions, it has been estimated that the fully developed switch would be capable of operating at a frequency as high as 10 Hz.

This work was done by Eui-Hyeok Yang of Caltech for NASA's Jet Propulsion Laboratory.

NPO-30434

Topics:
Electrical systems Fabrication Fiber optics Imaging and visualization Manufacturing processes Microelectromechanical devices Optics Photonics Sensors and actuators Switches
This Brief includes a Technical Support Package (TSP).
Document cover
Micro-Ball-Lens Optical Switch Driven by SMA Actuator

(reference NPO30434) is currently available for download from the TSP library.

Don't have an account?

More From SAE Media Group

    Magazine cover
    Photonics Tech Briefs Magazine

    This article first appeared in the January, 2003 issue of Photonics Tech Briefs Magazine (Vol. 27 No. 1).

    Read more articles from the archives here.

    Overview

    The document outlines the development of a Micro-Ball-Lens Optical Switch driven by a Shape Memory Alloy (SMA) actuator, specifically utilizing thin film TiNi. This innovation, reported by NASA's Jet Propulsion Laboratory (JPL), aims to address the challenges faced by conventional optical switches, particularly their high fabrication costs and insertion loss issues.

    The optical switch operates by employing a micro ball lens that is manipulated by an SMA actuator. The actuator's unique properties allow it to change shape in response to temperature variations, enabling precise control over the lens's position. When the SMA is heated above its phase transition temperature, it returns to its original shape, effectively moving the ball lens up and down. This movement facilitates the switching of light paths between input and output optical fibers, thereby enhancing the efficiency of optical connections.

    Key advantages of this SMA-based optical switch include a remarkable contrast of 70 dB and a low insertion loss of -1.9 dB, which significantly outperforms traditional MEMS-based optical switches that often suffer from higher insertion losses. The document emphasizes that this technology could lead to the creation of compact, inexpensive optical switches suitable for mass production, making it a promising solution for the telecommunications industry.

    The report also highlights the novelty of this approach, noting that no prior research has focused on thin film SMA-based optical switches. This positions the invention as a unique contribution to the field of optical switching technology. The document is part of a technical support package prepared under NASA's sponsorship, and it includes a SEM photograph of the fabricated SMA device, as well as a basic measurement scheme for the optical switch.

    In summary, the Micro-Ball-Lens Optical Switch driven by SMA actuators represents a significant advancement in optical switching technology, combining the benefits of super elasticity and low insertion loss to create a more efficient and cost-effective solution for future telecommunications applications. The work is a collaborative effort by JPL and is intended to pave the way for further innovations in the field.