91 Fiber for Remote Sensing

Downhole sensing applications enhanced by specialty optical fibers

George Oulundsen, Daniel Hennessey,

and Mike Conroy

96 Components for Fiber Optics

Advanced manufacturing techniques benefit fiberoptic components

Brad Hendrix and Mike Harju

100 Lasers for Biophotonics

Lasers meet changing demands of biomedical applications

Marco Arrigoni, Nigel Gallaher,

Dan Callen, Darryl McCoy, Volker Pfeufer,

and Matthias Schulze

105 Optical Filters

Optical filter performance keeps improving— measurement techniques must keep pace

Amber Czajkowski and Stephan Briggs

110 Resonators

Moving photonics cause singular Fabry–Perot resonance

Zubin Jacob

32 COVER STORY

While laser manufacturers may be happy with their recent mid-single- digit growth sales performance, there is more cause for celebration. Lasers, once an inside secret, literally surround us in our everyday lives and are finally being recognized globally and politically. Turn to page 32 for our full laser market review and forecast! (Cover

illustration by Chris Hipp)

Coming in

February

The February 2015 issue highlights two important areas of Lasers & Sources:

•Contributing editor Jeff Hecht continues his Looking Back and Forward series on the key photonics technologies by describing the history and future of solid-state lasers.

•An article introduces a new photovoltaic cell that enables UAVs to be powered by laser light.

We also look at Optics and Imaging & Detectors with articles on:

•a new hyperspectral imaging system

•optical shutter performance designed for life science applications

Further articles discuss:

•optical coating metrology

•3D optical inspection

•photonics-modeling software

c o o l c o n t e n t

Blog: Photon Focus

Senior editor John Wallace discusses the research being done on photovoltaic solar power generation—and what impediments we need to

overcome to help bring it to fruition. Keep coming back to our blog for more hot topics, cool commentary, and other events-related musings! http://bit.ly/14RIfUO

Technical Digests dig into technology topics

Laser Focus World offers free downloadable technical digests that provide an in-depth resource on photonics and optoelectronics topics such as laser-induced- breakdown spectroscopy

(LIBS) and high-power and

high-energy thin-film antireflection coatings for laser optics. http://bit.ly/ViD38v

Webcasts let you make new discoveries from your desktop

Whether you are looking to get an overview of mid-infrared optical technology and its opportunities or learn the fundamentals of fiber optic sensors, we’ve got webcasts aplenty to meet your educational needs. http://bit.ly/Onhs9J

White papers offer detailed tech specs on many products

Our library of technical white papers delves into performance attributes of several optics and photonics products available on the market, including high-power, fibercoupled diode lasers, miniature spectrometers, and optical bandpass filters, to name a few. http://bit.ly/1BUCpTf

www.laserfocusworld.com

t r e n d i n g n o w

Slide shows engage with cool topics

Whether they are three-point kinematic mounts or another form such as flexure or gimbal mounts, tip/tilt mounts are an essential part of

many optical setups. In this Slide Show, senior editor John Wallace highlights some of the many tip/ tilt optical mounts available today. http://bit.ly/1v1lfNO

Focus on Lasers & Sources

Laser Focus World covers the design and applications of all types of lasers, amplifiers, and other advanced sources like lightemitting diodes (LEDs). Here are two of

our most popular articles on this topic.

Wafer-level LED chip emits 157 W of optical power

A team of Chinese researchers has created a wafer-level LED chip that produces 157 W of blue light from an emitting region approximately

30 mm in diameter. What’s more, the group expects that much larger chips developed over the next decade will lead to light outputs in the tens of kilowatts. http://bit.ly/1q1UpcK

Blue direct-diode laser emits 50 W

Researchers in Japan have created a blueemitting direct-diode laser that focuses light from 30 individual 450-nm-emitting laser diodes

into an optical fiber with a 100-μm- diameter core; the direct-diode laser produces 50 W of optical power at a numerical aperture (NA) of 0.2. http://bit.ly/1z4jbqW

editor’s desk

W. Conard Holton

Associate Publisher/

Editor in Chief

cholton@pennwell.com

Surrounded by light

The UN designation of 2015 as the International Year of Light and Light-based Technologies (light2015. org) provides an excellent framework for highlighting the role and value of light in the world at large. For those of us working within the photonics community of engineers and scientists, the value of lightbased technologies is far more specific—the community is personally and professionally rewarding, and a great place to do research and business.

Our cover story, the Annual Laser Market Review & Forecast, provides one explanation of why photonics is so rewarding: for the second consecutive year, global sales of lasers in 2015 are expected to grow more than 6%, reaching $9.754 billion (see page 32). It’s not only the strengths of the laser market in traditional application areas like materials processing and communications that feed this growth, but the continued development of new applications, from 3D printing and optogenetics to silicon photonics and the Internet of Things, as described in our SPIE Photonics West preview article (see page 52).

LFW at 50

As the applications for photonics technologies have grown, Laser Focus World has grown and changed, yet remained true to the words of founding editor Bill Bushor, to be “a publication unlike any now in existence.” For a sense of that heritage, here are a few titles from the first issue, dated January 1, 1965, of the newsletter then known as Laser Focus: “What are biomedicine’s laser needs?” “Laser aids in oil and gas exploration,” “Laser beam’s interaction with metal explored,” and “Miniature laser integrating gyro bows in”—not much of a stretch from these topics to the ones we cover now in every issue (and every day online).

Celebrating the 50th anniversary, Jeff Hecht, our long-time contributing editor and managing editor of LFW from 1974–1981, is writing a year-long series looking back and looking forward for each major category of technologies and products that we cover. His topic in this issue is optics—a core photonics technology (see page 65).

Finally, to our loyal readers, thank you—you have been the foundation of our 50 years of success.

EDITORIAL ADVISORY BOARD

Stephen G. Anderson, SPIE;

Dan Botez, University of Wisconsin-

Madison; Walter Burgess, Power

Technology; Connie Chang-Hasnain,

UC Berkeley Center for Opto-electronic

Nanostructured Semiconductor

Technologies; Pat Edsell, Avanex;

Jason Eichenholz, Open Photonics;

Thomas Giallorenzi, Naval Research

Laboratory; Ron Gibbs, Ron Gibbs

Associates; Anthony M. Johnson,

Center for Advanced Studies in

Photonics Research, University of

Maryland Baltimore County;

Kenneth Kaufmann, Hamamatsu

Corp.; Larry Marshall, Southern Cross

Venture Partners; Jan Melles,

Photonics Investments;

Masahiro Joe Nagasawa, TEM Co. Ltd.;

David Richardson, University of

Southampton; Ralph A. Rotolante,

Vicon Infrared; Samuel Sadoulet,

Edmund Optics; Toby Strite,

IPG Photonics.

of molybdenum disulfide

A group of researchers from the Australian National University (Canberra) and the University of Wisconsin (Madison) has discovered that a single molecular layer L of molybdenum disulfide (MoS2) has a giant optical path length (OPL); in comparison to another monolayer material, graphene, the OPL of MoS2 is about 10 times greater. Although this may seem like an esoteric result, it has a very practical consequence

for photonics: as the researchers have demonstrated, just a few monolayers of MoS2 can be used to create what the

researchers call the “world’s thinnest optical lens,” only 6.3 nm thick. With a diameter of about 20 µm, the concave MoS2 lens the researchers fabricated has a calculated focal length of −248 µm at a 535 nm wavelength.

For experimentation, the researchers transferred singleor few-layer MoS2 flakes onto a silicon wafer (under a microscope, regions of differing colors corresponded to layers of different thickness). To create the lens, they used a focused ion beam to mill a concave bowl shape, producing a continuous, curved OPL profile. The giant OPL arises from a corresponding giant elastic photon scattering efficiency. The researchers discovered that the strength of the elastic interaction in the thin 2D MoS2 increases greatly with a growing refractive index as a result of the ultrathin-film geometry. For every layer thickness increase of 1 nm, the OPL increases by more than 50 nm. The researchers say that other high-index ultrathin-film transition-metal dichalcogenide 2D semiconductors (of which MoS2 is an example) are particularly well-suited for this approach. Reference: Jiong Yang et al., arXiv:1411.6200 [cond-mat.mtrl-sci] (2014).

Stacked image sensor enables ‘Internet of Things’ fire sensing

As the number of devices connected to the Internet is expected to grow to more than 50 billion devices by 2020, this interconnected network of sensors—de- scribed as the Internet of Things (IoT)— has become the focus of a number of leading technology companies. Recognizing the growing

65 nm–0.18 µm CIS process

Imaging array

Sample and hold

Top chip

Imaging array

Multiple diamond defects provide subpicotesla magnetometer sensitivity

is reconfigurable for different system interfaces, image-processing tasks, frame rates, power levels, and noise levels, for example. The sensor enables the ability to field-reconfigure the device for additional functions or firmware changes without the need for replacement of the physical product. It integrates image processing at the point of image capture (“edge”) to ensure quick and accurate decision-making by these smart devices. In the fire-sensing application, the chip is attached to a standard smoke detec-

tor and programmed to monitor ambient light level, awaken when the level changes due to a fire event, and send a livestream video notification of the event to the homeowner’s cell phone. Contact Annie Suede at annie@forzasilicon.com.

DIAMOND DEFECTS. from p. 9

magnetic-field sensitivity of

0.9 pT/Hz0.5, an improvement of three orders of magnitude over previous results. The detector volume of 8.5 x 10-4 mm3 contained about 1.4 x 1011 nitrogen-vacan- cy defect centers.

In the setup, a parabolically shaped glass lens contacting the diamond collected the fluorescence photons, directing them to a single photodetector. Software simulations of the arrangement showed a collection efficiency >60%. A laser power of 400 mW focused to a 47-µm-diameter spot provides the excitation and readout light. To make a measurement, the nitrogen-vacancy spins are first polarized with a laser pulse; microwaves then prepare the centers for readout. A second laser pulse then triggers and reads out the fluorescence signal. Improvements should result in a sensitivity of 40 fT/Hz0.5, which would allow detection of proton spins with-

in a second in a microscopic volume. Ref: Thomas Wolf et al., arXiv:1411.6553 [quant-ph] (2014).

Photonic-device designs often cannot be transferred between different platforms due to substrate-specific constraints, meaning that photonic-integration technologies on common substrates (CMOS on silicon or III-V optoelectronics on indium phosphide) are well-developed, while designs on unconventional materials like polymers, metals, or optical crystals are still in their infancy. But by using transition metal oxides and high-in- dex amorphous chalcogenide glasses, researchers from the University of Delaware (Newark) collaborating with international researchers from the University of Central Florida (UCF; Orlando), Massachusetts Institute of Technology (MIT; Cambridge), the University of Texas at Austin, and the University of Southampton (England) have developed a substrate-blind platform

-12 5220 5230 5240 5250 5260

Wavelength (nm)

that can tolerate deposition on a host of relevant substrates without requiring epitaxial growth and can be performed at temperatures <250°C.

The substrate-blind integration process was demonstrated on three emerging substrate platforms: infrared (IR) optical crystals, flexible polymer materials, and 2D materials like graphene. The glasses were deposited on these substrates using thermal evaporation or solution-based processing and then patterned as waveguides, resonators, or gratings via photolithography or direct nanoimprinting. For microdisk resonators fabricated on mid-IR transparent calcium fluoride (CaF2) crystals and flexible polymer substrates, quality (Q) factors of 4 x 105 and 5 x 105 at wavelengths of 5.2 μm and 1550

nm were achieved—world records for planar mid-IR resona-

tors and flexible resonator de-

vices. Complex 3D structures

can also be fabricated through sequential multilayer glass deposition and patterning. Ref-

erence: Juejun Hu, SPIE News- 5253.3 room, October 2014; doi:

10.1117/2.1201410.005643.

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gratings have a diffraction efficiency of more than 98% and a compressor efficiency of more than 80%. The large-pitch-fiber amplifier is directly water-cooled and counter-pumped with light from a 790 nm laser diode. Future use of a vacuum or nitrogen atmosphere in various parts of the optical path could reduce thermal-

ly induced beam degradation as well as nonlinear effects; larger modefield areas will lead to even higher powers. Reference: Fabian Stutzki et al., Opt. Lett. (2015); http://dx.doi. org/10.1364/OL.40.000009.

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