Overview
Luminos U Series Ultra Resolution Positioners utilize the Luminos designed Ultra Precise Linear Stepping Motor Actuator and deliver industry leading 0.1um bi-directional backlash with incremental move capability finer than 10nm resolution on the X and Y axis.
​U Series Positioners provide full 2.5mm x 2.5mm x 12.7mm XYZ travel range and offer significant performance improvements compared to Luminos automated I3000 and I6000 positioners which also provide photonics grade alignment with smaller travel ranges.
​U Series Positioners represent a significant leap in automation capability, delivering a five fold increase in working resolution (actual minimum movement without lost micro-steps) and an overall speed increase of 12x with a 25x greater motor travel envelope.
​U Series Positioners deliver performance that far exceeds SMF-28 Singlemode Fiber Alignment requirements.  Using only stepping motor controls, there is no need for closed loop compensation or fine stages and additional controllers. You can also easily align SM waveguides to within 0.01 dB of optimized without backlash compensation.


Fiber and Photonics Alignment - No Piezos Required
In the Photonics industry it is generally accepted that Alignment Stages need to resolve to about 1% of beam size or waveguide MFD. For aligning SMF-28 with 10um MFD, a resolution of 100nm is usually acceptable – or was.  With the emergence of cutting edge planar photonic devices there is an increasing requirement to align smaller and smaller waveguide structures sometimes as fine as 2um MFD.
It is becoming clear that a new standard of about 20nm resolution is needed for Photonics Positioning Stages. Most major positioning stage manufacturers offer automated alignment systems that employ Coarse + Fine travel stages with multiple levels of controllers, in order to meet Photonics resolution requirements. Many such course travel stages have motor actuators with up to 5-10um of backlash. The use of fine travel piezo stages is therefore not an option, resulting in increased system complexity.

Ultra Low Backlash
Luminos Positioners are unique in industry, delivering consistent micro-stepping performance using a frictionless and inherently time stable in-line configured flexure-based positioning platform, paired with custom open loop stepping motor actuators designed with ample torque margin. Frictionless drive mechanisms are also used to ensure that the actuators operate under uniform preloads. When aligning waveguides, the X & Y axes usually require more than 5X higher resolution than the Z axis. Taking unique advantage of the differing requirements, Luminos stages strategically incorporate patented Ratio Drive™ mechanisms on the X & Y alignment axes. The XYZ actuators all move 12.5mm however, on Luminos Automated U Series Positioners, the X & Y move their full 2.5mm travel under control of the motor. This results in 5X greater precision in the more critical X & Y axes outputting an incredibly low 0.1um bi-directional backlash with 10nm resolution. Most importantly - no Piezo’s required!

Photonic Waveguide Alignment

Lateral Alignment Sensitivity
To help understand the level of precision required for aligning photonic waveguides, consider an Industry Benchmark: the SMF-28 single-mode optical fiber with 10um mode field (MFD). Figure #1 depicts how the ends of two optical fiber waveguides would be moved in the X direction to examine Optical Loss vs Lateral Alignment. Typically, one fiber would be connected to a light source and the other to a power meter. The optical loss is equally sensitive to lateral movement in the X and Y directions for SMF-28 which is a round symmetrical waveguide. As industry moves towards advanced planar optical waveguide devices, it becomes more common to see planar waveguides with a 2-3um MFD. It becomes even more important for positioning systems to have margin.

Optical Loss vs. Lateral X or Y Alignment
Figure #1

Figure #2 shows a plot of the Optical Loss vs Lateral Alignment of SMF-28 optical fibers within the range of +/- 1um of ideal alignment. Most optical power meters have a typical 0.01 dB resolution which can be seen to correspond to a target X displacement range of 0.46um. If a positioning stage were to have less than 0.46um bi-directional backlash, then it becomes possible to write optimization software that does not need to rely heavily on backlash compensation. It also becomes possible to design a positioning system that does not have to switch between coarse and fine movement controls. The majority of actuators on the market that can meet the Figure #2 Target are complex closed loop units with encoders or compound stepping motor actuators often with additional Piezo fine stages built in.  Luminos stages offer many strategic advantages. Luminos U Series Ultra Positioners deliver a positioning stage architecture unique to the market. Luminos offers the only stages that can deliver 0.1um bidirectional backlash on X & Y with simple incremental stepping motor controls. Photonics waveguide alignment without requiring the use of Piezos or encoders. A simplified approach to meeting and exceeding the requirements of photonics waveguide alignment systems. In fact, Figure #2 shows there is margin in accuracy for going far beyond the requirements of aligning SMF-28.

X or Y Axis (um)
Optical Loss vs. Lateral Alignment
Figure #2

Axial Alignment Sensitivity
Figure #3 depicts how the ends of two optical fibers would bemoved to examine Optical Loss vs Axial Alignment. lt isassumed that the optical fibers are in idealX&Yalignmentand only theZ gap spacing is varying. The loss measurementsshown in Figure #2 & Figure #4 were taken with indexmatching fluid between the ends of the optical fibers toeliminate Fresnelinterference effects

Optical Loss vs. Axial Alignment
Figure #3

In Figure #4, Optical Loss vs. Axial Gap Size, optical loss is observed to be far less sensitive to axial movement than to lateral movement, as seen in Figure #2. The difference in target size for a 0.01dB offset is measured as 3.76um vs 0.46um. This differing alignment sensitivity can be significant in low NA optical waveguides and is uniquely taken advantage of with Luminos Ratio Drive™, incorporating highly engineered frictionless flexure drive mechanisms within the X & Y axes of all Luminos stages. Another strategic benefit of Luminos Ratio Drive™ is increased stability. When the motor actuators warm slightly, any resulting thermally induced change in position is also reduced by the same Ratio. As a result, Luminos stages are inherently more stable than comparable direct driven stages and are reputed by customers to maintain very stable alignment while idling for long periods of time even many days

Z Axis (um)

Optical Loss vs. Axial Gap Size SMF28 @ 1550nm (9/125µm fiber) Index Matched

Figure #4