Optical Fabrication and Fluid Jet Polishing

The world of optical fabrication has been completely transformed by the technique fluid jet polishing. Using this economical, computer controlled method, LightMachinery is able to create near perfect optical components routinely.

LightMachinery's Patented Fluid Jet Polishing System (FJP)

LightMachinery have developed a patented fluid jet polishing system, which removes nanometers of material accurately from an optical surface using a fine stream of slurry. The company has spent several years optimizing this fully computer controlled polishing technique (Figure 1). Although traditional techniques are used in 90% of optical fabrication, the FJP is used in the fabrication of most of LightMachinery’s high accuracy wafers, interferometers, and etalons.

Figure 1. The fluid jet process is 100% computer controlled

LightMachinery can perform some highly intricate and hard-to-achieve optical fabrication tasks reliably using the FJB, paving the way for a new era of optical device manufacturing:

• Optical components like etalon mirrors can be adjusted for the shape and flatness down to a level of a few nanometers
• Fabrication of very thin components such as thin etalons and wafers, which are not possible to be accurately polished with traditional technology
• The final performance of complex assemblies like Michelson Interferometers can be measured and arbitrary surface corrections can be made to correct the overall performance
• Arbitrary optical surfaces, including cyclindrical axicons, axicons, corrector plates, and phase plates

Application Examples of the FJP Process

An interferometer is used to measure the current surface profile, which is then compared against the target surface profile in order to determine the required removal pattern (Figure 2).

Figure 2. The current surface profile is measured and compared against the target surface profile to identify the required removal pattern

A traditionally polished 2” x 2” fused silica substrate before the FJP process is depicted in Figure 3, showing a peak to valley slope of about 115 nm while measured using the tunable laser mapping system in the transmission mode. The peak to valley error of roughly 3 nm is measured for the same substrate after the FJP process using the tunable laser mapping system in transmission (Figure 4)

Figure 3. A conventionally polished 2” x 2” fused silica substrate

Figure 4. The same substrate after the FJP process

A Zygo interferometer was used to measure another 2” x 2” fused silica substrate in the reflection mode, showing a very large error - about 1.8 µm of concave shape. The error is reduced to 10 nm peak to valley after the FJP process (Figure 5).

Figure 5. The error is 10 nm peak to valley after the FJP process

A very flat 4” silicon mirror was measured with a Zygo GPI following the FJP process (Figure 6). The surface variation of this silicon mirror is in line to the zygo test flat to 1/100 wave peak to valley over a clear aperture of 95%.

Figure 6. A very flat 4” silicon mirror was measured with a Zygo GPI following the FJP process.

Figure 7 demonstrates the ability of LightMachinery to produce completely arbitrary shapes with very high precision using the FJP process. The air gap between a flat surface and the designed surface is the reason behind the fringes.

Figure 7. LightMachinery can make completely arbitrary shapes with very high precision using the FJP process.

Optical components, such as axicons have a conical shape, which makes them difficult to fabricate using conventional techniques. However, the FJP process can make such components easily (Figure 9). The axicon consists of constantly spaced fringes as opposed to lens.

Figure 8. The FJP process can easily fabricate axicons

Crossed cylindrical lens are difficult to fabricate using conventional polishing techniques, but the FJP process is ideal to make such strange surfaces.

Figure 9. A top view of the crossed cylinders

The FJP process is suitable for fabricating large aperture fabry perot etalons like the one shown in Figure 10.

Figure 10. The FJP process is crucial for making large aperture fabry perot etalons

This information has been sourced, reviewed and adapted from materials provided by LightMachinery.

For more information on this source, please visit LightMachinery