Hamamatsu News 2-2016 - page 7

News 2016 Vol. 2 7
In new product development by an equipment manufacturer,
it’s very important to increase the accuracy in the initial development
stage. Attaining an optimal state of light sensor and light emitter per­
formance is the quickest road to increasing the accuracy. Our company
understands how to do this for both devices, so we can help equipment
manufacturers obtain the desired accuracy.
Why does only Hamamatsu Photonics offer sets consisting of both
light sensor and light emitter?
There are numerous challenges in developing both light
emitters and light sensors, so there are very, very few manufacturers
capable of taking up these challenges of dual development. For example,
light emitter development requires developing laser light sources that
are equal in number to the target gases for measurement at “1 wave­
length for 1 component.” This means large development costs and
involves high risks in creating a new business.
Viewed from a customer standpoint, purchasing the light
emitters and light sensors from the same company offers huge advan­
tages. For example, when equipment manufacturers are developing
an optical measuring instrument, currently in most cases, they use
the light sensors and light emitters procured from different manu­
facturers. However, in this case, if the measuring instrument they
are manufacturing won’t perform as expected, then it’s difficult to
determine whether the problem is caused by light emission or light
detection. This becomes an obstacle in product development.
If the light emitters and the light sensors are produced by the
same manufacturer, then it’s easy to mutually evaluate both devices
and in this way to boost performance of the measuring instrument.
This advantage also contributes to shortening the customer’s product
development period. Laser absorption spectrometry using a QCL in
the mid-infrared range is still a relatively new method and I think it
will become a widespread method for selective gas measurement
with high sensitivity and high resolution. Quantum cascade lasers
(QCL) emitting a single wavelength of light and InAsSb photovoltaic
detectors provide stable characteristics.
What kind of products do you have available for light emitters
and for light sensors?
Our flagship product for light emitters is the QCL. It origi­
nally started under Chairman Teruo Hiruma as an effort at our own
expense to develop a light source for establishing breath analysis for
cancer screening. Unfortunately, breath analysis testing for detecting
cancer has still not been established as a technology. However, it has
shown possibilities for detection of acetone, etc.
A typical light sensor for receiving light from the QCL is the
InAsSb (indium arsenide antimonide) photovoltaic detector. We
currently offer two types of sensors that cover the wavelength range
from 2.5 μm to 8 μm.
What are the respective features or characteristics of the QCL
and InAsSb photovoltaic detector?
First let’s talk about the QCL. A typical laser diode emits
light at multiple wavelengths spanning several hundred nanometers
and so the spectral range becomes wide. This causes measurement
accuracy to drop because of interference by multiple gas absorption.
The QCL employs a DFB (distributed feedback structure) that has a
diffraction grating fabricated within the chip and allows laser emission
at a single wavelength in an extremely narrow spectral range.
However, DFB is extremely difficult to produce in large amounts and
we initially had a very tough time trying to get a satisfactory yield
rates for making good products.
Simultaneous with in-house development work to improve
manufacturing technology for DFB structures to raise the yield rate
of good products, we also proceeded with developing new products
having an internal collimation lens. The light emitted from the laser
chip broadens, so the products available until that time required the
customers to design an optical system to change the shape of the
light so that the laser light passes through the target object. To
eliminate all that work, we incorporated a collimation lens into the
package, so the customers no longer need to make this delicate
optical alignment.
Was incorporating the collimation lens into the package
a tough task?
In the case of a conventional QCL without a collimation lens,
the customers had to align the optical axis on their own. Mid-infrared
light is invisible and special optical materials are utilized, so design of
the optical system requires a lot of time and effort. Placing the colli­
mation lens outside the package does give the advantage that there
is no limit on lens size making it easy to adapt for use along with the
package. However, placing the lens inside the package requires high-
precision alignment and clamping of the optical axis in an extremely
limited space of the package. The effects from noise also have to be
taken into account due to light reflection from the optical material.
R&D Interview
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