Fiber Alignment Motion Systems

Motion control systems can be customized in many ways, depending on the DUT. Figure 1 shows different configurations of fiber alignment systems, ranging from a simple, single-channel, single-side setup to a more complex double-sided, multiple-channel setup that includes machine vision, adhesive delivery/curing, and pick and place. Other setups may have horizontal and vertical beam inputs and outputs. Every configuration requires a unique set of motion products, depending on the performance required for that device. The basics of motion control systems can be found in Motion Control Systems.
Configurations of fiber alignment systems and example of a single-sided configuration with load/unload
Figure 1. Configurations of fiber alignment systems (left, image used with permission of GBC&S Consulting Services); example of a single-sided configuration with load/unload (right).
Different configurations are available for the motion control systems used in fiber alignment, ranging from simple manual stages suitable for small scale and R&D applications to full-featured automated production systems with high precision motorized stages, pick and place automation, dispensing and curing systems, machine vision, etc. The following systems illustrate, in part, this range of configurations:

  • Manual stages - Mechanically, manual positioning stages are the simplest and the least costly motion control systems that can provide precise linear or rotational motion. They are most often used in academic or industrial R&D centers and are occasionally found in low volume production environments. Figure 2 shows the proven, stable MKS ULTRAlign™ 562 manual stage. The 562 can be motorized by adding NSA12 (Figure 2a) or TRA (Figure 2b) motorized actuators. Long travel precision motorized actuators are also available for longer strokes or faster speeds. These actuators are commonly used in R&D and low volume production applications.
Single fiber, single-end configuration with 562 manual stages and NSA12 actuators
Figure 2. Single fiber, single-end configuration with 562 manual stages and NSA12 actuators (a); single fiber, single-end configuration with 562 manual stages and CONEX-TRA actuators (b).
  • Piezoelectric stagesPiezoelectric stages are compact, four- to six-axis alignment systems that are driven by piezoelectric actuators. This type of actuator is capable of 30 nm linear resolution. The MKS 8071 4-axis aligner, is ideal for remote control of alignment positioning in R&D applications. These multi-axis motorized positioners allow high-resolution (< 30 nm) adjustment for different combinations of X, Y, Z, θx, θy, and θz. These stages can exert a 5 lb. (22 N) force and have exceptional long-term stability and can hold their position with no power applied.

Motorized stages, driven by electromagnetic motors, are commonly used in production environments to enable the automation of alignment processes. They typically feature sub-µm MIM and repeatability, which greatly improves the quality and performance of telecom devices assembled using these stages. The drive technologies that are commonly used in motorized precision fiber alignment systems include:

  • Linear motor stages with direct read encoder - The XMS linear motor stages are the highest precision standard stages with 1 nm MIM capability when used with the XPS-D motion controller. The XMS can quickly and easily search within a 10 µm diameter area of the beam region exhibiting the highest power. Figure 3 shows a double-sided, multi-channel configuration with 5-axis adjustments using XMS stages.
Double-sided configuration with VP-25 and XMS stages
Figure 3. Double-sided configuration with VP-25 and XMS stages.
  • XYZ assembly with ball screw drives - The VP-25XA family of stages was specifically designed for fiber alignment applications. These compact stages are available with either a 100 nm or 10 nm MIM and in left and right versions for single or double-ended configurations. The VP-25 has field-proven reliability in production environments.
  • Hexapods - A hexapod is a parallel kinematic, mechanical device that uses six actuators, all moving in parallel, to provide six-axis range of motion in a Cartesian coordinate system. All axis moves are interdependent, meaning that the motion in one axis reduces the travel in the other axes. A hexapod is capable of complex combinations of linear and angular motions and is particularly useful for critical rotation adjustments.

Hexapods are usually more compact than a stack of stages. The positioning requirements of fiber alignment make hexapods an excellent solution for most, if not all, cases. HXP hexapods feature the following innovations that are advantageous in fiber alignment applications:

  • Work and Tool coordinate systems - A significant innovation in MKS Hexapods is the concept of Work and Tool coordinate systems. These programmable coordinate systems enable the independent manipulation of the Work (sample or device) or Tool (cutter or beam). The Work and Tool coordinate systems are illustrated in Figure 4.
Work and Tool coordinate systems transformation of axes
Figure 4. Work and Tool coordinate systems transformation of axes. Prior to the introduction of MKS HXP hexapods, the user had to calculate the transformation of the actuator motions into hexapod coordinates. The HXP hexapods come with transformation formulas which are embedded in the firmware, so the user simply sends commands in a Cartesian coordinate system, making the motion of the actuators quite transparent. The reader can imagine a path in a familiar coordinate system.
  • RightPath™ Trajectory Control - While hexapods are ideal for point-to-point motion, they encounter some difficulties in scanning applications where a path, whether linear, rotary or arc, is to be followed. RightPath™ trajectory control eliminates the need for a linear or rotation stage for short strokes. In Figure 5, the blue line illustrates the motion of a hexapod when commanded to move from one point to another in the X-axis without RightPath trajectory control. The typical deviation from a straight line could be in the order of more than a millimeter. With RightPath trajectory control, the runout is controlled to a couple of microns, similar to a linear stage. This innovation enables the Hexapod to follow linear, rotational, or arc moves with minimal trajectory run-out.
RightPath™ trajectory showing runout
Figure 5. RightPath™ trajectory showing runout.
  • HexaViz simulationHexaViz is simulation software that allows customers to simulate loads, motions, and potential collision for all MKS HXP hexapods. HexaViz is very useful for simulating the actual devices and fixtures that will be needed in a fiber alignment application that uses an MKS HXP hexapod. Unlike other hexapod simulation software available in the market, HexaViz is free to download.

In addition to the device, device fixture or holder, light source, and motion control system, a complete fiber alignment system includes the following components:

  • Detectors measure the power of a beam. Together with a power meter, they monitor the optical signal and detect the highest transmitted power. A typical detector and power meter combination from MKS is the 818-SL detector and the 1936-R power meter. An alternative detector is MKS' 3A-IS-IRG. If beam profilers are needed to characterize the shape of the beam, an SP928 is recommended. The Newport 1830-R and a 918D-IS-IG detectors are recommended for production environments. Figure 6 shows a fiber alignment system with a power meter and detector.
  • Power meters are matched with detectors for the specific wavelength, the power range measured, and a minimum data transfer rate of 2 kHz to achieve fast alignment and productivity.
  • Vision system are used to detect the proximity of devices and the rough alignment of fiber ends. Since the intensity of a beam is proportional to the inverse of the square of the distance between the source and detector, smaller gaps result in greater transmitted power. However, very small gaps present a higher risk for collision. A vision system allows a very small gap to be used. Depending on the magnification and available lighting, the fiber ends can be adjusted to be almost touching, maximizing the transmitted power.
  • Dispensing/bonding systems dispense an accurate volume of liquid epoxy, evenly apply it over the interface of two materials and cure it using UV light. They typically depend on the devices and materials that are being assembled. The curing process in these systems requires positional stability but at a lower degree of precision than for alignment. Therefore, a less precise motion control system can be used in dispensing and curing the glue.
  • Laser welding is a bonding method that employs highly localized heating to attach two parts together. For example, laser welding is used to attach the output fiber, lenses, and the laser diode in a package. The process is automated, using pick-and-place within an enclosure to ensure both speed and safety.
  • Pick-and-place automation is used for high volume, high speed production. The advantage of employing pick-and-place automation lies in the repeatability and reproducibility achieved in the devices. Components that are to be assembled are inserted into fixtures and, after assembly, the complete device is removed for packaging. During the unload process, a parallel sorting step can be performed that relies on pass/fail criteria to identify parts that can be packaged, reworked, or scrapped.
Single-end fiber alignment system with ULTRAlign 562, VP-25XYZ, power meter, and detector
Figure 6. Single-end fiber alignment system with ULTRAlign 562, VP-25XYZ, power meter, and detector.

The challenge for faster and more accurate fiber alignment continues to evolve. 400 GbE production may start in 2018 and 5G mobile communication standards are near completion, paving the way for adoption of this protocol in cellular networks. Autonomous driving technology will rely on mobile networks that require significantly higher speeds. This means that SiP technology may soon move into the mainstream. SiP will require significantly higher precision and speed in fiber alignment owing to the very small size and very high density of grating couplers on wafer surfaces. Table 1 provides a quick reference guide for component selection in fiber alignment systems.

 Component Research and Development  Assembly/Production  Final Test 
Laser Sources LDC-3726 Controller and LDM Mount LDC-3900 Controller 1784 VCSEL Laser Source
Motion CONEX-TRA/CONEX-LTA562
Manual Stages
Ultra Align XYZ Stages
XMS/VP Linear Stages
HXP50 Hexapod
Not Applicable
Laser Diode Tester Sentry Benchtop LD Tester Not Applicable Sentinel LRS9434 Burn-in
Power Detector 3A-IS-IRG
818-SL/DB
3A-IS-IRG
818-SL/DB
PD300-IRG
918D-IS-IG
Power Meter StarBright
1936-R
Juno
1830-R Power Meter
StarLite
2936-R
Wavemeter OMM 6810 WM-1210  Not Applicable
Beam Profilers SP928 or XC-130 Not Applicable SP928 or XC-130
Photoreceiver Not Applicable Not Applicable 1544
1474A

Table 1. Quick reference guide for the selection of components for fiber alignment.


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