Hank Hogan, Contributing Editor, email@example.com
For Electro Scientific Industries Inc. (ESI) of Portland, Ore., getting fiber into its diet
has been one key to success.
Among other things, the company makes a line of micromachining
systems for the semiconductor, flat panel display, photovoltaic and other industries.
Some of these systems are powered by fiber lasers, a technology in which a fiber
doped by rare earth elements, and typically pumped by a diode, acts as the lasing
medium. The choice of when to go with this approach over an alternative depends
in part on what is being machined and where the system will be used.
“We deploy fiber lasers in places where we require, predominantly,
high average power, and we want industrial robustness that extends well beyond a
year,” said Jeffrey Albelo, ESI’s general manager for interconnect and
As the ESI example shows, fiber lasers are being used for cutting,
marking and other materials processing. They also are showing up in lidar and other
applications. Their efficiency, compactness, relatively high power and ruggedness
often make them the laser technology of choice – provided the wavelengths
offered match the wavelengths needed.
Recent advances promise new fiber laser capabilities, including
the ability to engineer polarization modes not possible before. A look at these
and other developments reveals some of what is in store for the technology, the
industry and applications.
Going down … and up
With increasing peak power and repetition rates, fiber lasers
are moving into applications that were handled in the past by other technologies
at ESI. In part, according to Albelo, that is because fiber lasers are not only
more robust but generally cheaper on a per-watt basis than YAG lasers, the other
solid-state laser technology used by the company. The company does a lot of beam
conditioning in its products, so another plus is that fiber lasers are very amenable
to software manipulation.
One of ESI’s products, for example, puts two fiber lasers
to use, combining them with precise positioning to increase machining speed. The
wavelength of the lasers is about 1 μm, which is appropriate for the metallic
features the system is designed to handle.
But today, fiber lasers aren’t the answer to all of the
company’s needs. When asked what he wants, Albelo replied, “The answer
is very easy: ultraviolet.”
In general, he said, shorter wavelengths allow more efficient
coupling of laser energy into the material being processed. Thus, a fiber laser
with power in the ultraviolet would be helpful, as would one with a polarized beam
and a higher repetition rate. Of course, Albelo wants these advances without sacrificing
any of the current advantages offered by the technology.
The request for lower wavelengths is one that the industry is
aware of and is trying to meet, said William S. Shiner, vice president of industrial
products at high-power fiber laser leader IPG Photonics Corp. in Oxford, Mass.
“We’re already at 532, which is a visible green. We’ve
already frequency-doubled that to the UV. We just haven’t released product
yet,” he noted.
Although efforts aimed at creating an efficient UV fiber laser
are under way, the technology has undergone growth in other areas. Steve Norman
is chief technology officer at SPI Lasers in Southampton, UK, a wholly owned subsidiary
of the Ditzingen, Germany-based Trumpf Group. He noted that his company’s
products have seen a steady increase in power over the past five years.
“We’ve power-scaled from 50 to 100 W to 200 to 400
W. We’re now in volume production with 400-W products,” he said.
The latter power can be ganged together to create multikilowatt
systems, with that power being used to speed materials processing. The trade-off
for achieving higher power in this way involves an increase in the number of modes.
However, in many high-power cutting and welding applications, a multimodal beam
is preferred, in part because it produces a more uniform distribution of energy
on the workpiece.
There’s an app lab for that
Besides power or wavelength, other parameters that can be tailored
to an application involve pulse characteristics. Marking plastic, for example, may
work best by using relatively low pulse energies delivered at a higher repetition
rate and by using a predetermined waveform. All of these settings can differ from
those that are best when working metal.
Figuring out the right laser setup can be a challenge. That’s
one reason SPI runs application labs in both the UK and in Santa Clara, Calif. Equipped
to do cutting, welding, scribing and analysis, these sites do research and development
to prove new application feasibility and to optimize processing parameters.
A fiber laser cuts silicon. Courtesy of SPI Lasers.
Meeting this type of need lies behind a Portland, Ore., micromaterials
processing facility established by ultrafast fiber laser maker Fianium, which also
is based in Southampton. The applications lab is located within and run by Summit
Photonics, which offers third-party photonics engineering services.
The partnership between the two was announced last year, but the
site was only fully equipped and operational in May of this year. Colin Seaton,
global vice president of sales and marketing at Fianium, noted that much of the
initial investigations into materials processing with picosecond lasers has been
done with “scientific-type setups,” systems that offer vendors such
as Fianium an opening.
Processing silicon for solar cells could benefit
from visible picosecond fiber lasers, as shown here with this run of the effects
of 532-nm picosecond pulses on silicon-nitride-coated photovoltaic-grade c-silicon.
Pulse energy increases from upper left to lower right. Courtesy of Brian Baird,
“We’ve got the benefit of cost, complexity and reliability
that the fiber laser brings, compared to those other types of systems,” he
As for the applications that might be done at the lab, Summit’s
managing director, Brian Baird, noted that there is a broad area of interest in
picosecond processing of semiconductors and thin films. He gave a talk at Photonics
West this year in which he pointed out that wafer scribing, silicon micromachining,
laser marking and thin-film trimming are all possible areas where the technology
could be used.
“Those areas requiring high repetition rates and good precision
in the beam quality and pulse energy delivery are prime candidates for being in
picosecond laser products,” he said.
There are, of course, industrial uses of fiber lasers that don’t
involve materials processing. One example can be found in lidar, an application
being pursued by Keopsys SA of Lannion, France. The company’s products are
used for laser ranging systems that measure distance to a point and wind speeds
of the air, or do 3-D scanning of an object. This is done using wavelengths that
range from 532 nm to 2 μm.
With the right settings for power,
repetition rate and pulse waveform, fiber lasers can mark metals or plastics, as
has been done with the parts shown here. Courtesy of SPI Lasers.
Fiber lasers are well suited for lidar for a number of reasons,
said Keopsys’ vice president and founder Jean-Marc Delavaux. “The two
most important are they’re lightweight and [have] low energy consumption.”
Keopsys touts its V-groove side-pumping approach, which leads
to a one-step coupling process of the diode pump laser into the double-cladding
gain fibers used in the company’s lasers. Keopsys believes that this gives
its products a 90 percent coupling efficiency, which it asserts is significantly
higher than would be possible otherwise. That, in turn, helps lower power consumption
and improves performance in lidar and other applications.
Putting polarization to work
Finally, recent research has shown that fiber lasers in the future
may have another knob that can be adjusted. Researchers from the University of Dayton
in Ohio recently reported on a fiber laser with an adjustable polarization output.
In a May 10, 2010, Optics Express paper, Qiwen Zhan, associate professor of electro-optics,
and his team described a specially designed laser cavity. By combining that with
a uniaxial c-cut calcite crystal, they created a cylindrical vector beam with cylindrical
Such polarization is different from the traditional variety, which
is typically either linear or circular. This nontypical polarization, and the ability
to adjust it, could prove useful in optical tweezers and in micromachining, Zhan
In both cases, cylindrical vector polarization has been shown
to yield better results than the traditional variety. Also, in both cases, the best
polarization depends upon the task, so being able to adjust parameters as needed
Zhan said the choice of fiber is critical in the group’s
research because the fiber determines how many polarized modes can be supported
in the laser cavity. The crystal is key to selecting and producing the reconfigurable
vectorial output. Experimental results are shown
of a complex vectorial mode created using a fiber laser (left), with numerical simulation
results (right). (a) The intensity profile of the output mode; (b)-(e) the beam
intensity profiles after a linear polarizer (transmission axis indicated by white
arrow), show the different modes. Courtesy of Qiwen Zhan, University of Dayton.
In their demonstration device, the researchers showed that modes
with radial, azimuthal and generalized cylindrical vector polarizations could be
generated by translating one lens within the laser cavity. They also showed that
more complicated vectorial vortex output modes could be created by introducing some
angular misalignments into the setup.
Transforming these lab results into products will require improving
the output power to something over 1 W in continuous-wave operation, Zhan said.
His research plans also call for exploring Q-switch, mode-locking, frequency conversion
and other operation modes. He also intends to investigate more complicated vectorial
Eventually this could lead to a new type of device, and it is
one that Zhan believes he can build, given the right funding.
“The ultimate goal is to achieve a compact all-fiber high-power
fiber laser producing reconfigurable vectorial mode outputs. I already have a strategy
to achieve this,” he said.