Research Papers

Microtube Laser Forming for Precision Component Alignment

[+] Author and Article Information
Ger Folkersma

Chair of Applied Laser Technology
Faculty of Engineering Technology,
University of Twente,
Drienerlolaan 5,
Enschede 7522 NB, The Netherlands
e-mail: k.g.p.folkersma@utwente.nl

Dannis Brouwer, Gert-Willem Römer

Chair of Applied Laser Technology
Faculty of Engineering Technology,
University of Twente,
Drienerlolaan 5,
Enschede 7522 NB, The Netherlands

Manuscript received May 19, 2015; final manuscript received April 5, 2016; published online May 20, 2016. Assoc. Editor: Hongqiang Chen.

J. Manuf. Sci. Eng 138(8), 081012 (May 20, 2016) (6 pages) Paper No: MANU-15-1241; doi: 10.1115/1.4033389 History: Received May 19, 2015; Revised April 05, 2016

A micro-actuator for precision alignment, using laser forming of a tube, is presented. Such an actuator can be used to align components after assembly. The positioning of an optical fiber with respect to a waveguide chip is used as a test case, where a submicron lateral alignment accuracy is required. A stainless steel tube with an outer diameter of 635 μm was used as a simple and compact actuator, where the fiber is mounted concentrically in the tube. An experimental setup has been developed to measure the fiber displacement in real time with a resolution better than 0.1 μm. In addition, this setup allows the axial and radial positioning of the laser spot over the surface of the tube. Several tube samples were (de)formed to move a fiber to a predefined position, using a laser with a wavelength of 1080 nm, a pulse length of 200 ms, and a power between 4 W and 10 W. On average of 18 laser pulses were required to reach the targeted position of the fiber with an accuracy of 0.1 μm. It has been found that increasing the laser power not only results in a larger bending angle but also in a larger uncertainty of this angle. The opposite is true for the radial bending direction, where the uncertainty decreases with increasing laser power.

Copyright © 2016 by ASME
Topics: Lasers , Fibers , Displacement
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Fig. 1

Tube laser bending. (a) Heating due to absorbed laser energy induces a bending of angle β “away” from the laser. (b) After cooling, the tube bends “toward” the laser, finally getting at an angle of α.

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Fig. 2

Optical fiber and tube assembly

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Fig. 3

The experimental setup. (1) Camera for focus measurement, (2) 50:50 beam splitter, (3) PSD, (4) fixed mirrors, (5) aspheric lens (see Fig. 2), (6) tube with fiber (see Fig. 2), (7) tube clamp (see Fig. 2), (8) beam alignment camera for laser, (9) focusing optics, (10) high power laser input, (11) motorized tip/tilt mirror, (12) positioning stages for tube, (13) fiber to align, and (14) position measurement laser.

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Fig. 4

Beam manipulation schematic. The laser can reach the tube from three directions using the tip/tilt mirror. 1: Direct path from above and 2/3: via fixed mirrors. The focus stage is used to keep the spot size on the tube constant.

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Fig. 5

Measurement of the fiber tip position. Laser light emitted from the fiber is collimated and projected on two duo-lateral PSDs and a camera via two beam splitters. A translation of the fiber results in a rotation of the beam, measured by the PSDs.

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Fig. 6

Translation coordinates at the fiber tip

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Fig. 7

Displacement of the fiber tip during heating (0–0.2 s) and cooling (0.2–60 s) at P = 10 W and d = 7 mm. The final displacement is 11.3 μm. Top: (X, Y) path plot. Bottom: time–displacement of the same measurement.

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Fig. 8

Typical path of the fiber tip in one of the nine experiments. Each point is the deformation after cooling. The target (−30, 27) is reached within 12 steps. The dashed lines indicate the direction of thermal expansion at that point. Note that a repetition of this experiment would result in a totally different path due to the uncertainties in bending angle and direction.

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Fig. 9

Power used in experiments versus the maximum expansion angle α. The outliers are indicated by crosses and excluded from the fit.

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Fig. 10

Power used in experiments versus the maximum expansion angle β

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Fig. 11

Difference between direction of expansion and direction final motion. The dashed lines indicate the trend of the extreme values encountered in the measurements. Using higher power ensures a more deterministic bending direction.




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