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Series G Fast
Compact Photodetector Modules Faster,
more compact, and cheaper than our Award Winning Series 99 Photodetectors.
A new line of inexpensive and compact fiber-coupled photodiode
modules simplify capturing fast transient light signals for analysis. These
devices are intended to approximate as closely as possible, a length of fiber
optic cable that can be connected directly onto the input jacks of your
oscilloscope or other electronic data acquisition device. Conversion of the
optical signal to electronic current and voltage occurs at the last possible
moment, within a mm or so of the input jacks of your scope. Co-ax cable and
the problems of reflections, termination loads, phase distortion and so forth
are totally eliminated. The devices are extremely compact and rugged, taking
up about as much room as a typical BNC terminator. They come in unamplified
versions for use when sufficient light is available, and amplified versions
for low light levels. We will build photodetector modules to your
specifications. Dimensions: 0.65" (16mm) diameter by
1" to 1.75" (25 to 40 mm), excluding connectors and optical fiber We will build your modules with whatever optical fiber, cable
and connectors you specify. We normally stock single-mode 9/125 µm and both
50/125 µm and 62.5/125 µm multimode fiber with 0.9mm polymer buffer and 3mm
Kevlar jacket. Other types such as 100/140 µm are available. The fiber to photodiode
connection is angle polished for low (-45dB) back reflection. The input end of the optical fiber will be fitted with whatever
type of optical fiber connector you desire. The range of normal options
include: none, i.e. a bare fiber pigtail, 2 mm ceramic ferrule only, Optional Light Collecting Optics If the signal you want to analyze is
in the form of a beam in free-space we can provide light collecting optics
instead of or in addition to the optical fiber connectors described above. A
6 mm diameter fixed focus aspheric lens assembly is available. We also offer
a micro-alignable fixture with 18 mm aperture focusable achromatic lens.
Precision fine thread adjustments allow you to maximize the coupling of the
incoming beam into the fiber. The unit is also directly compatible with
"micro-rail" optical component systems made by
For example, Silicon based diodes are most sensitive in the
400nm (nearly UV) to 1000nm (near IR) spectral range and cover the visible
well. InGaAs is relatively insensitive to visible light but responds well to
the IR used in information systems. The intrinsic speed of the photodiode is also determined by the
semiconductor material. The higher electron mobility in InGaAs allows
response times which are simply not attainable with Si. Our latest GaAs model
offers unprecedented speed in the visible range. Other factors which might be
important to your needs, such as Dark Current and Capacitance are also listed
in the table on Photodiode Specifications. The photodiode in all our modules is reverse biased to minimize
intrinsic capacitance for maximally fast response. Specifications are listed for the usual photodiodes. Others are
available, call or write for details.
You can estimate the signal level (voltage) that you can expect
to see, for your light intensity, directly from the Responsivity as shown in
the graph above and in the table below, from: dV [volts] = dI [watts] • Responsivity [amps/watt] • R [ohms] where dV is the change in output signal corresponding to
a change of dI in the light power input and R is the load
resistance. The modules have an
internal load resistance of 1,000 ohms.
The effective load resistance, R,
is thus the parallel combination of this internal 1,000 ohms and any external
termination resistance such as the usual 50 ohms of an oscilloscope
input. Since the Responsivity is near
unity, in general, you will need on the order of 1 mW in the optical input
fiber in order to get output signals in the 50mV range with the Series G
modules with 50 ohm termination. You can get higher sensitivity if your scope
has a high impedance input option. In
this case the 1,000 ohm internal load resistance will dominate and the signal
levels will be twenty times higher.
Note that the bandwidth will also be reduced by this same factor of
twenty. Electronic output connector choices include BNC, TNC, SMA and
SMC in either gender. Wiltron-K, 7/16 and others are available at some extra
cost. Please note that BNC connectors are not recommended above 2 to 4 GHz.
If you need something really unusual, specify on your Request for Quotation
or call to discuss your needs. The output connector is directly coupled to the biased photodiode
so that these Series G modules are DC coupled. The unamplified Series G
modules have very low current drain and the small internal batteries should last
for a year or so of normal use. Series G Photodetector Module Summary and
Prices
We will build your Photodetectors to your specifications. The
price of your detector is simply the sum of the prices of the chosen specified
options. Email us your specifications
from the list under Summary and Prices above. We will return a formal
quotation to confirm your specifications and expected delivery time. Quantity
discounts are available, send a Request for Quotation. Please note that these modules contain technology at the leading
edge of the state of the art. Prices and specifications are subject to
change. Martin, Froeschner
& Associates tel: (+1) 925 989
4930 Last update June 2011 ©1999-2011 |
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