Optical Shutters: Asking the right questions leads to the best shutter design

[Andy L. Goff]

Optical shutters are integral components of many optical assemblies and systems. Sometimes shutter requirements are not apparent during the design process; other times, after the system goes live, they must be addressed. It is also possible that the ultimate end user of a system will add requirements that necessitate the implementation of a shutter.

A shutter is now required.

Only when the product design entered the prototype stage did additional specifications resulting from a late requirement for a shutter in an optical system still being determined. After the procedure and visual design had been completed, the end user revealed the need for a shutter for black-reference calibration. This design requirement delayed the completion of the system.

Developing a shutter whose physical location within the optical system was already tight was necessary. The design specifications prevented an off-the-shelf shutter design from being used. Instead, they required a more custom shutter device, requiring a significant amount of time for design, testing, and implementation. This particular scenario could have been smoother if the black reference specification had been provided earlier in the design process.

Another case involved developing a low-cost, high-speed digital camera application by a camera system designer. Again, the shutter would need to fit within the existing envelope approved and set for the design and use the voltage levels already built into the camera.

This project required multiple design iterations to find solutions to specifications that were unknown at the beginning. Because the high g specification was unknown at the beginning of the project, a secondary design iteration was required. It is rated to remain open under shock loads of up to 40 grams.

Understanding when a shutter is necessary

Optical shutters used for the following applications:

• Calibration based on black reference or nonuniformity correction (NUC)
• Controlling exposure
• Distinct exposures from continuous light sources or continuous-wave lasers that are accurate and repeatable
• Laser control or laser pulse selection
• In laser-safety applications, a shutter turns off a laser quickly when an interlock mechanism is activated.
• Using exposure control to regulate the output of an x-ray source

When the system designer has anticipated the need for a shutter, there are several recommended questions (for a complete list, see https://www.nmlaser.com/faq/ ). Here are a few questions to consider:

1. Considerations include wavelength, surface flatness, coating type, substrate material, and power level. In addition to mass considerations, manufacturability of the substrate material, and cost, this information may influence the type of actuator.

2. An exposure speed of 2 can stipulate a more significant number of blades, design considerations that could limit reliability, an increased actuator complexity, and a smaller actuator size, among other things.

3. What are your shutter envelope considerations, and how much space do you have to design the shutter?

4. Can you tell me about your environmental specifications?

5. What are the shock and vibration specifications?

6. What are the acoustic noise considerations?

7. What are the material considerations?

8. What are the requirements for exposure speed and frequency of operation?

9. How does a shutter failure affect the overall system, for instance, in a laser safety application?

10. Magnetic fields exist?

It is necessary to understand and test each of these criteria, which takes time and effort, illustrating how long it takes to produce a shutter and its impact on the development process.

NM Laser Products, Inc. has been introducing advancements in laser shutter technology since 1987. The company engineers and manufactures the world’s safest and most reliable electromechanical laser shutters and controllers by meeting the production and integration challenges of OEMs and researchers in a continually growing number of broad and niche markets worldwide.

Reliable commercial shutter products for high irradiance lasers were not available in the solid-state boom of the 1980’s. This prompted the staff of NM Laser Products to begin development of new laser shutter technologies beginning in 1987, with a small group of products offered in 1988.