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J16 Series detectors are high-quality Germanium photodiodes designed for the 800 to 1800nm wavelength range. For applications where temperature stability of response is important near the cutoff, thermoelectrically cooled detectors are available. |
 Figure 1 |
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Responsivity |
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For example, at 1.2 µm the change in response of a room temperature detector is less than 0.1% per °C, while at 1.7 µm the change is approximately 1.5% per °C (Fig. 4). Uniformity of response within the active region of a room-temperature Ge detector is typically better than ± 1% at 1300 nm. |
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Selection of the proper op-amp is
important, as the wrong choice can add excess preamp noise or limit
system bandwidth. Judson has a complete line of preamps designed to
match each detector type and application. Preamp recommendations are
included with the detector specifications. For high frequency
applications, the detector may be reverse biased and terminated into a
low impedance load (Fig. 6). Reverse biasing the detector
significantly reduces junction capacitance for faster pulse response;
however, the dark currents and low-frequency noise are increased.
Applications Shunt Resistance and Dark Current: When
the detector is used in the basic circuit of Figure 5, an undesirable
DC offset current, or "dark current," will be produced. It is
a function of the preamp input bias current Ib, the preamp input offset
voltage Vos, and the detector shunt resistance RD. This total "dark
current" is: Total ID = Ib + (Vos / RD) High shunt resistance detectors will result in lowest overall DC "dark current." Preamp selection is also important; for higher shunt impedance detectors, choose a preamp with low bias current; for lower shunt impedance detectors, choose a preamp with low offset voltage (Fig. 7). When the detector is reverse biased and used in the high-speed circuit of Figure 6, the predominant dark current is a function of the applied bias voltage (Fig. 8).
Two key factors to consider when selecting a Judson Ge detector are
Linearity
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Responsivity
Calibration Packages for Ge Detectors (all dimensions in inches)
Standard packaging and element configurations result in low cost and quick delivery for Judson's high-quality photodiode
arrays. The 4, 16 and 32 element arrays respond to infrared radiation from 500nm to 5.0µm depending on material type. The
J16Si Dual Wavelength "Sandwich" Detectors
Two color detectors consist of a high performance silicon detector mounted in a "sandwich" configuration over another detector. The silicon photodiode responds to radiation from 400 nm to 1000 nm. Longer wavelengths pass through the silicon and are detected by the detector underneath. J16Si Series detectors are ideal for optic power measurements that need to differentiate between 800 nm and either 1300 nm or 1550 nm. They are also useful for two-color temperature measurements. The J14SI Series are used when the temperature measurement range needs to be expanded. Applications
Detector Temperature
Ranges
J16TE Thermoelectrically Cooled Ge Detectors J16TE Series detectors are Judson's high-quality Ge photodiodes mounted on thermoelectric coolers for reduced dark current, improved sensitivity and superior stability. The TE coolers require less than 3W of DC power. The built-in thermistor can be used to monitor or control the detector temperature. J16TE Series detectors are mounted in TO-style packages which are filled with dry nitrogen and hermetically sealed. J16TE1 Series One-Stage
Thermoelectrically Cooled Ge J16TE2 Series Two-Stage
Thermoelectrically Cooled Ge Thermoelectric Cooler
Operation
The following figure shows the effect of heat sink temperature on J16TE2 detector temperature.
Preamplifiers
J16A Ge Avalanche Photodiodes (APDs) The J16A Series Germanium
Avalanche Photodiodes are designed for high-speed applications at 800
and 1300nm. Judson APDs offer low dark currents and bandwidths up
to 1.5GHz with active sizes of 100µm and 300µm diameter. The
J16A Series APDs have undergone extensive reliability testing.
Reliability has been demonstrated to be better than 10 FITs
corresponding to less than 1% failure rate over 20 years service.
Reliability data available upon request. Multiplication
Characteristics Breakdown Voltage and
Dark Current Cutoff Frequency
Click here to view the J16A Series J16D Liquid Nitrogen Cooled Germanium Detectors The J16D Series Ge
detectors offer the ultimate sensitivity for 800 to 1400 nm
detection. Cooling the Ge photodiode to 77°K results in extremely
high shunt impedance for Noise Equivalent Power (NEP) typically below
0.01 pW/Hz1/2. Dewar Packages Preamplifiers and
System Noise
Click here to view the J16D Series Typical Specifications at 77K Contact
Judson's Technical Support staff for more data and specifications. |
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Figure
16
