Thermal noise of quantum IR detectors is defined by the number of thermal carriers with energy higher or equal to the
detector's energy threshold. The energy distribution function of these carriers is of Boltzmann-type with a high energy
tail dictated solely by the device temperature. Therefore, thermal noise in such detectors can be suppressed only by
cooling the device down.
Sirica presents new technology for tunable quantum IR detector that requires no cooling. The detection is based on the
response of non-equilibrium free carriers to IR photons. Sirica's IR detector uses pumping light (NIR/Visible) to form a
steady-state non-equilibrium distribution (SNED) of free carriers with a narrow high-energy tail (i.e. low effective
temperature), which is then used to absorb and detect IR photons. Simulations of the SNED formed in the case where
the free carrier's lifetime is shorter than their energy relaxation time is presented, showing that the free carriers' effective
temperature, is significantly lower than the device temperature.
Although the total number of carriers in the SNED formed is small, IR photon absorption coefficient in Sirica's detector
is very high (equivalent to MCT). This is due to the very high effective cross-section achieved in Sirica's proprietary
detector substance. Parameters of this composite structure will be discussed.
Last year SCD presented an un-cooled detector product line based on the high-end VOx microbolometer technology. The first PFA (BIRD384) launched was a 384x288 software configurable (to 320x240 or other) format with 25μm pitch1. NETD values for these FPAs are better then 50mK with an F/1 aperture and 60 Hz frame rate.
Since then SCD has concentrated in improving both spatial and temporal performance. In order to reduce the Residual
Non-Uniformity (RNU) and increase the time span between shutter operations, SCD has incorporated various features within the FPA and supporting algorithms2.
Improved temporal performance was achieved by optimizing concurrently the membrane structure and ROIC electronics. SCD has demonstrated temporal NETD of ~ 20mK @ F/1 at 30Hz on a 160x120 BIRD compatible array.
This figure of merit, accompanied by the superior stability and reduced power consumption, makes SCD's VOx based detectors suitable candidates for a broad range of "high-end" military and commercial applications.
SCD has recently presented an uncooled detector product line based on the high-end VOx bolometer technology. The first FPA launched, named BIRD - short for Bolometer Infra Red Detector, is a 384x288 (or 320x240) configurable format with 25μm pitch. Typical NETD values for these FPAs range at 50mK with an F/1 aperture and 60 Hz frame rate. These detectors also exhibit a relatively fast thermal time constant of approximately 10 msec, as reported previously.
In this paper, the special features of BIRD optimized for unattended sensor applications are presented and discussed.
Unattended surveillance using sensors on unattended aerial vehicles (UAV's) or micro air vehicles (MAV's) , unattended ground vehicles (UGV's) or unattended ground sensor (UGS) are growing applications for uncooled detectors. This is due to their low power consumption, low weight, negligible acoustic noise and reduced price. On the other hand, uncooled detectors are vulnerable to ambient drift. Even minor temperature fluctuations are manifested as fixed pattern noise (FPN). As a result, frequent, shutter operation must be applied, with the risk of blocking the scenery in critical time frames and loosing information for various scenarios.
In order to increase the time span between shutter operations, SCD has incorporated various features within the FPA and supporting algorithms. This paper will discuss these features and present some illustrative examples.
Minimum power consumption is another critical issue for unattended applications. SCD has addressed this topic by introducing the "Power Save" concept. For very low power applications or for TEC-less (Thermo-Electric-Cooler) applications, the flexible dilution architecture enables the system to operate the detector at a number of formats. This, together with a smooth frame rate and format transition capability turns SCD's uncooled detector to be well suited for unattended applications. These issues will be described in detail as well.
SCD has recently presented an un-cooled detector product line based on the high-end VOx bolometer technology1. The
first PFA launched, BIRD, is a 384x288 (or 320x240) configurable format with 25μm pitch. Typical NETD values for
these FPAs range at 50mK with an F/1 aperture and 60 Hz frame rate. These detectors also exhibit a relatively fast
thermal time constant of approximately 10 msec.
In this paper we elaborate on the special advanced features that were incorporated within the ROIC and supporting
algorithms. In this framework we have addressed two important issues: the power consumption and the time span
between shutter activations. Minimum power consumption is a critical issue for many un-cooled applications. SCD has
addressed this by introducing the "Power-Save" concept accompanied with flexible dilution architecture. The paper will
present recent results exhibiting the various advantages.
One of the limiting factors on the performance of un-cooled detectors is their vulnerability to ambient drift. Usually,
even minor temperature fluctuations are manifested as high residual non-uniformity (RNU) or fixed pattern noise (FPN).
As a result frequent shutter operations must be applied, with the risk of blocking the scenery in critical time frames. The
challenge is thus twofold: increase the time span between shutter corrections and achieve better control of its activation.
For this purpose BIRD provides two complementing mechanisms: A real-time (frame-by-frame) ambient drift compensation accompanied by an RNU prediction mechanism. The paper will discuss these features in detail and present illustrative system implementations.
SCD is unveiling the first member of its new uncooled product line based on the high-end VOx technology. The detector is software configurable to various format standards including 384x288, 320x240 and others with 25μm pitch. The NETD values for these FPAs are better then 50mK with F#/1 aperture and 60 Hz frame rate. These detectors also exhibit a relatively fast thermal time constant of approximately 10msec. In order to improve the system level "cost-performance" in terms of power consumption and weight, SCD has introduced special features within the FPA & package. Among them is a proprietary "Power Save" architecture, in which the die temperature can be stabilized to the ambient temperature or a close enough discrete value, covering the range between -40c and 70c. Thus, the TEC power consumption is considerably reduced with minimal performance degradation. An additional benefit is improved "mission readiness" which is of vital importance for various system applications. A major limitation of systems based on uncooled detectors is the poor resilience to the ambient temperature drift. This drift degrades the spatial non-uniformity. As a result, frequent corrections using an optical shutter are required, specifically during the camera stabilization period. In order to increase the time span between shutter operations, SCD has incorporated various real-time monitoring features within the FPA and supporting algorithms. These features reduce the spatial noise by an order of magnitude.
A spectroradiometer was modified to test the stability, uniformity, and accuracy of radiance differentials of state-of-the-art FLIR test systems. It is shown that the radiometric tests make it possible to obtain important information which cannot be obtained with conventional contact temperature probes. The output radiance of the FLIR test equipment was measured as a function of time and angle with respect to the collimator optical axis.