Download Fiber Optic Cable Beam Delivery Systems

Fiber Optic Cable Beam Delivery Systems
Series LBD/FFO
For most laser processing applications, delivery of the beam from the laser optical head to the
workpiece is as significant as the performance of the laser itself. Few applications of lasers
may be performed successfully by the "raw", unfocused beam, and a variety of optical
schemes are used to deliver and focus the beam onto the workpiece.
Conventional beam delivery techniques involve a combination of reflective and refractive
optics (mirrors and lenses), and must rely on a straight, uninterrupted line of sight between
each optical element. In some cases, especially those involving delivery over significant
distances, this may prove to be costly or impractical.
The Fiber Optics Solution
For some applications, the use of flexible fiber optic (FFO) cables as a beam delivery medium
can be very attractive. As a complement to its Series 800 Nd:YAG Lasers, Lee Laser offers a
comprehensive line of Fiber Optic Beam Delivery Systems. Each Series LBD/FFO system is
engineered to safely accommodate the beam power and divergence of a specific Series 800
laser model.
Three major elements make up a fiber optic beam delivery system:
1. Fiber Optic Coupler: focuses the beam from the laser into the fiber cable
2. Fiber Optic Cable:
an optical cable capable of transmitting the laser beam
3. Beam Focus Head: attached to the output end of the fiber cable to focus the
beam onto the workpiece
Lee Laser's combination of highly efficient Beam Collector Head, low-loss FFO cable, and
compact Output Beam Focus Head provides the user with maximum beam power delivery to a
remotely accessible target.
Fiber Optic Coupler, Model LFC-7X
To efficiently funnel maximum laser beam power into the FFO cable, Lee Laser has designed
the fully integrated Model LFC-7X Fiber Optic Coupler Assembly that consists of:
2
fiber optic coupler head
seven-axis adjustable mount
optical rail carriage
FFO cable clamp to prevent bending stress at the coupler
The Coupler Head focuses the laser beam into the core of the optical fiber. It contains a highquality, fused silica lens that is anti-reflection (AR) coated for the operating laser wavelength
(0.53, 1.06, or 1.32 m). A fiber optic connector receptacle retains the cable securely at the
focal point of the beam.
Position and incident angle of the laser beam with regard to the Coupler Head are critical to
high-efficiency, damage-free beam insertion. Lee Laser uses a precision, 7-axis mount (5
linear and 2 angular adjusts) to ensure core-center and coaxial alignment of the beam with the
fiber optic cable.
The coupler assembly is mounted on an optical rail carriage and positioned immediately after
the laser output coupler (front mirror). Dust protective beam cover hose prevents airborne
matter from contaminating the optical surfaces.
Fiber Optic Cable
Lee Laser uses only the highest quality, low-loss optical transmission fibers. The single-fiber
cable features a high-purity silica glass core available in diameters from 200 m to 1000 m.
Core size is determined by the desired laser beam power throughput, with the largest size
used to handle the multiple-hundred Watt levels of our most powerful Series 800 Lasers.
Lee Laser high-purity FFO cables ensure maximum transmission efficiency. Cable
terminations are highly polished for low insertion loss, and are designed specifically for use
with high-power Nd:YAG lasers. In fact, aside from reflection losses at each end of the FFO
cable, a 5-meter length of cable will transmit 99 % of the laser beam power. With end
reflection losses, typical total beam power loss in a 5-meter FFO cable is 10 %.
FFO cables are available in standard lengths of 1, 2 and 5 meters. Other lengths are
optionally available. The optical fibers are encased inside a multi-layer protective sheath
surrounded by a reinforced monocoil jacket that provides both flexibility and tensile support.
Outside cable diameter typically is 6 mm.
Lee Laser uses industry standard SMA-905 threaded connectors for quick and easy coupling
and decoupling from collector and focus heads.
Beam Focus Head, Model LFL-65FFO
The compact and efficient Model LFL-65FFO Beam Focus Head is used to focus the
emerging laser beam onto the user's workpiece. Similar in basic design to the Beam Coupler
Head, it will produce a focused beam spot at the design work distance of 65 mm. Drawing No.
101071-ASSY illustrates outline dimensions.
3
Although most fiber optic beam delivery systems are limited to an ultimate beam focus spot
diameter equal to the size of the FFO core, the high-quality Lee Laser focus head design will
produce a much smaller beam focus spot equal to 70 % of the FFO core.
Optical Efficiency of Fiber Optic Beam Delivery Systems
Optical losses in a fiber optic beam delivery system have several sources:
1. reflection losses in the coupling optics, typically 1-2 %
2. transmission losses in the fiber optic cable, about 1 % for a 5-meter cable
3. reflection losses at the ends of the fiber cable which cannot be AR coated, typically
4 % at each end or 8 % total.
Reflection losses in a fiber optic cable system can cause heating problems in the coupling
optics, especially when used with Series 8250 High-Power CW Nd:YAG Lasers. The reflected
portion of the beam is absorbed in the coupling optical mounts in the form of heat. For
example, a 500-Watt laser will produce reflection losses about 10 %, or 50 Watts, all of which
is absorbed by the Fiber Optic Coupler and Beam Focus Head. For these high-power lasers,
Lee Laser uses water cooled coupling optics to remove the excess heat.
Helium-Neon Pointing Laser (Optional)
Lee Laser recommends that each Series 800 Laser that is outfitted with a LBD/FFO system
also include the Model LHN-2CM Helium-Neon Pointing Laser as an option. The LHN-2CM
produces a low power (2 mW), visible red beam that can be very useful for aligning the
Coupler Head with the YAG beam which is not visible. With the LHN-2CM HeNe beam
coaxially aligned with the main YAG beam, coupling efficiency into the FFO core may be
visually evaluated with considerable precision by observing the red HeNe emission intensity
from the output end of the FFO cable.
The LHN-2CM also will serve as a useful pointing aid to align the workpiece with the YAG
beam.
Fiber Optic Limitations
Because the FFO core diameter must necessarily be larger than the focused laser beam
entering it, some of the highly parallel quality of the beam is effectively lost by transmission
through a FFO cable. This will cause the minimum beam focus spot diameter at the
workpiece to be limited to a dimension that is nearly the size of the fiber core.
There are some laser applications (such as hybrid microcircuit trimming) that require a very
small beam focus which cannot be performed with a FFO beam delivery system. It is not
possible to achieve the 25-50 m focus spot diameter that is characteristic of these
applications.
4
However, other applications (such as soldering or tape automated bonding) that require only
efficient transmission of beam power without particular regard to power density at the
workpiece can accommodate a larger beam focus spot size and may be performed
extraordinarily well.
Applications that require a Q-switched Nd:YAG laser beam also may be a problem. The very
high peak pulse power density of the laser beam that is focused into the core of the optical
fiber can cause damage to the input end of the FFO cable, and will reduce the lifetime of the
cable. The best protection against this problem is to maintain optimum alignment of the Fiber
Optic Coupler with the FFO cable.
Recommended Series LBD/FFO System
Because of the large number of combinations of FFO core and length, it is difficult to create a
matrix of distinct model numbers. Lee Laser will recommend a configuration that best meets
your performance requirements. The following table lists the sizes of FFO core that are
commonly recommended.
Beam Mode
TEMoo
Multimode
Multimode
Multimode
Max Power
25 Watts
150 Watts
500 Watts
1000 Watts
FFO Core
200
400
600
800
m
m
m
m