Selected Papers: A p p l i c a t i o n s o f Te l e c o m L i g h t

Applications of Telecom Light Sources toNon-telecom Fields
Mitsuru Sugo†, Hiroyuki Suzuki, and Yasuhiro Kondo
Abstract
NTT Photonics Laboratories has developed advanced design and fabrication techniques to improve theperformance of light sources for optical communications and boost the communication capacity. This
paper introduces new applications of telecommunications light sources to non-telecommunications
fields. These technologies are being commercialized by NTT Electronics Corp. (NEL) based on NTT’s
Comprehensive Commercialization Functions.

1. Background
Lasers are categorized by their emission sources,
which are generally gas (e.g., the argon laser), solidstate crystal (e.g., the Nd:YAG laser), or semiconductor. Semiconductor lasers have become more common because they are small, light, and inexpensive.
They are employed mainly in the visible-light andnear-infrared regions and have found widespread use
in recording media such as CDs and DVDs as well as
in the telecommunications field. However, semiconductor lasers have not been available for certain
wavelengths such as the 0.5–0.6-µm region (green,lime green, orange) or the 2–5-µm region (midinfrared). For these regions, other emission sources
have been used, but these are more expensive andconsume more power than semiconductor lasers.
NTT Photonics Laboratories has worked to develop
compact lasers that are available for these regions.
One device, a wavelength conversion laser [1], combines a highly efficient optical nonlinear crystal andhigh-output semiconductor lasers designed fortelecommunications by using optical device technology for wavelength conversion. Another, a strainedlayer InGaAs quantum-well laser emitting beyond 2µm [2], is the direct result of optimizing the laser
design and using novel growth techniques.
Wide-wavelength-band light sources are being† NTT Photonics Laboratories
Atsugi-shi, 243-0198 Japan
E-mail: sugo@aecl.ntt.co.jp

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applied not only to telecommunications measurement
systems but also to an ever-expanding range of fields,
including industry and medicine. In particular, they
have recently been finding applications in opticalcoherence tomography (OCT) in the medical field.
OCT is a non-invasive in-vivo tomography techniquethat is already being put to practical use in retinal
examination equipment, but there is still a demand for
improvements to this technique, such as integrating itwith an endoscope. These applications require a highpower wideband light source, but conventional semiconductor light sources have not been able to meetthe requirements. NTT Photonics Laboratories has
also worked to develop a super luminescent diode(SLD) [3] as a compact wideband light source suitable for OCT.
2. New products
The application fields and the bandwidths of thesethree newly developed light sources are shown in Fig.
1. The technical points and features are described indetail in the other selected papers in this issue. Below,
we briefly outline the features and applications ofthese new products.
2.1 Wavelength conversion laserThis laser consists of a highly efficient optical nonlinear lithium niobate (LiNbO3) device and highpower semiconductor lasers. Its output power is 10mW (30 mW is also available), and it is smaller andconsumes less power than a conventional gas laser. ItNTT Technical Review

Sources to Non-telecom Fields

Wavelength conversion laser
Semiconductor laser in excess of 2 µmBroadBandwidth

Wavelength conversion laser
Super luminescent diode

Conventional semiconductor
light sources

Narrow

Medical and measuring
instruments
GlucoseApplication field

OCT (retinal)
hemoglobin

OCT (endoscopes, catheters)

Helicobacter pylori

Na D-line
HF

HCI

H2O

NH3

NH3

CH4 H2O CO2

COH2O

CH2, N2O,CH4, etc.

CH4

SO2 NO2
Gas sensing

HBr N2O
0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

2.0

2.2

2.4

2.62.8

3.0

3.2

3.4

Wavelength (µm)

Fig. 1. Application fields and bandwidths of the new light sources.

is easier to maintain than a gas laser because of its
long operating life. In addition, an external modulator
is unnecessary because direct modulation is possible.
Continuous operation at room temperature is possible
even in the mid-infrared region of 2 µm or longer. The
expected application fields for this product include:(1) Flow cytometers or confocal scanning laser
microscopes, which are used for biotechnological field applications such as cell or DNAanalysis(2) Light sources for environmental gas sensors forcarbon dioxide (CO2), nitrogen oxide (NOx),sulfur oxide (SOx), and various other gases(3) Light sources to replace sodium (D-line) lamps
used to analyze the constituents of medical
products, food, and chemicals.
2.2 Super luminescent diode (SLD)
The central emission wavelength of this product isin the 1.3-µm infrared region. In this wavelength
region, water and hemoglobin both exhibit little
absorption and the light is less susceptible to scattering, so living tissue exhibits the greatest transparency
at this wavelength. Consequently, the light producedby this product can penetrate deep into the body fromVol. 3 No. 8 Aug. 2005

the surface of the skin.
Our SLD can achieve a spatial output of at least 50mW and a single-mode fiber-coupled output of atleast 30 mW, so it dispels the conventional idea that
SLD light sources have low optical output. Due to thetrade-off between bandwidth and optical output, there
have never before been any SLDs that combine alarge optical output with a wide bandwidth. However, by optimizing the active layer structure of our SLDdevice, which is the core region where light emission
takes place, we have managed to achieve a large
bandwidth of at least 50 nm even when operatingwith a large spatial output power of 50 mW or more.
The expected application fields for this product are:(1) Optical coherence tomography in the medicalfield(2) Molecule or gas sensing systems(3) Evaluation and measurement of optical components such as optical time domain reflectometers (OTDRs).
2.3 Strained-layer InGaAs quantum-well laser
emitting beyond 2 µm
This laser emits light with wavelengths of 2.0–2.1µm. In this wavelength region, light is strongly
13

Selected Papers

absorbed by CO x, NO x, and glucose, which areimportant substances in the medical and environmental fields. Although light absorption by these substances can also be detected at communication wavelengths, the intensity is weak and detection is difficult. This newly developed laser emission source ismuch more sensitive to these substances. For example, a 100-fold improvement in sensitivity has beenachieved for COx compared with the use of the communication wavelength band. This allows realtime
monitoring of COx or other substances.
Until now, solid-state lasers have been the main
source light for a wavelength of 2.0 µm. These lasers
have several drawbacks such as large equipment configurations and a high price. NTT’s new producteliminates these shortcomings by radically reducing
the laser body size to 1/100 and lowering the unit
price by 80%. In addition, direct modulation of theoptical output intensity is possible, and the simplified
equipment configuration will allow us to develop
portable devices in the near future. This product ismore compact and simpler than the wavelength conversion laser. The expected application fields for thisproduct are:(1) Sensors for helicobacter pylori and blood glucose in the medical field(2) Monitoring and exhaust control systems for
COx/NOx in the environmental field.
3. Conclusion

Mitsuru Sugo
Senior Research Engineer, Supervisor, Project
Leader, High Temperature Operation Laser
Development Project, NTT Photonics Laboratories.
He received the B.S. and M.S. degrees inphysics from Hokkaido University, Sapporo,
Hokkaido in 1982 and 1984, respectively. He
received the Ph.D. degree in electronics engineering from the University of Tokyo, Tokyo in
1993. In 1984, he joined NTT Laboratories,
where he has been studying III-V compound
semiconductor optical devices. He is a memberof the Japan Society of Applied Physics (JSAP)and the Institute of Electronics, Information andCommunication Engineers of Japan.

Hiroyuki Suzuki
Senior Research Engineer, Supervisor, Project
Leader, Novel Color Laser Development Project,
NTT Photonics Laboratories.
He received the B.S., M.S., and Ph.D. degrees
in chemistry from the University of Tokyo,
Tokyo in 1981, 1983, and 1986, respectively. Hejoined NTT in 1986. He is currently in charge ofthe development of various types of optical functional materials and devices ranging from organics and semiconductors to LiNbO3 for future
photonic communication and information processing.

Yasuhiro Kondo
Senior Research Engineer, Supervisor, Project
Leader, Extra Long Wavelength Laser Development Project, NTT Photonics Laboratories.
He received the B.S. degree in physics from
Kumamoto University, Kumamoto in 1984 andthe M.S. and Ph.D. degrees in physics and electronic device engineering from Kyushu University, Fukuoka in 1986 and 1999, respectively. In1986, he joined NTT Laboratories, where he has
been engaged in research on MOVPE growth ofIII-V semiconductors and the development ofsemiconductor lasers. He is a member of theIEEE Lasers and Electro-Optics Society (LEOS)and JSAP.

NTT Photonics Laboratories has developed
advanced design and fabrication techniques for semiconductor laser light sources for optical communications. These technologies have led to new lightsources for non-telecommunications fields. The commercialization of these technologies by NTT Electronics Corp. (NEL) is based on NTT’s Comprehensive Commercialization Functions. It is hoped that
this policy, which has been in effect since July 2003,
will continue to promote the widespread commercialization of various R&D achievements in the future.
References
[1]

[2]
[3]

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“Compact Lasers Generate Light of any Desired Wavelength Filling
the Wavelength Gaps of Semiconductor Lasers—Suitable for Applications in Biotechnology, Medicine, and Environmental Measurement,” NTT Technical Review, Vol. 2, No. 4, pp. 82-85, 2004.
http://www.ntt.co.jp/news/news05e/0503/050302.html
http://www.ntt.co.jp/news/news04e/0409/040902.html

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