Bio-imaging

Through egg imaging with NIR backlighting

Laser diagnostic

Diffraction rings of a laser beam through a pinhole (SIRIS, lin/log mode)

Deep-cooled vibration and cryogenic-free cooling system

To detect faint signals, it is necessary to collect incident photons over extended exposure periods. This can only be achieved with a FPA that is sufficiently cooled to eliminate dark signals and associated noise, allowing only useful signals to accumulate. For SIRIS, we employ a cryocooler in conjunction with an active vibration canceling system, ensuring vibrations are kept below 1µm on the cold finger. This cooling system allows the sensor temperature to be adjusted from ambient temperature to 77K (typ. 150K). Consequently, SIRIS is capable of adjusting its sensor temperature to optimize the ratio of (useful signal)/(dark signal).

Sensitivity of the InGaAs cameras to SWIR range makes them prone to thermal noise and dark current, which can interfere with image quality. Dark current is the electrical current generated by the sensor even in the absence of light, and it increases as the temperature of the detector rises. Without effective cooling, this noise can overshadow faint signals, especially during long exposure times or low-light scenarios.

A well-designed cooling system is essential for controlling dark current in InGaAs SWIR cameras, allowing them to achieve high-performance imaging. By reducing the sensor’s temperature, the cooling system minimizes the dark current, resulting in a cleaner signal and better overall image quality. This is particularly critical for applications where sensitivity to faint signals is necessary.

SIRIS Camera’s Advanced Cooling System

The SIRIS camera incorporates an advanced cooling system that not only addresses the issue of dark current but also brings a range of performance benefits. The system allows users to select temperatures ranging from ambient levels down to 77K, offering flexibility depending on the application. This wide temperature range ensures that the camera can be optimized for various imaging scenarios, from short exposure, high-speed captures to long-exposure, low-light conditions. The cooling system reaches and stabilizes at the desired temperature within just a few minutes, making it efficient for time-sensitive operations.

Another key feature of the SIRIS cooling system is its low vibration, with vibrations at the cold finger being less than 1 µm. This is crucial because vibrations can negatively impact image quality, particularly during long exposure times. By maintaining minimal vibration, the cooling system ensures the camera’s high-precision performance is preserved, allowing it to capture highly accurate data without the distortions caused by mechanical interference.

Moreover, the cooling system in SIRIS is designed to function in any orientation, giving users the flexibility to operate the camera in a variety of positions without affecting its cooling efficiency. This versatility is essential in field operations, where the camera’s placement may vary depending on the setup. Whether used in a laboratory setting or in dynamic environments, the SIRIS cooling system maintains its high performance, ensuring the camera is always ready for demanding tasks.

Dual Readout Mode: Linear and Logarithmic Performance

The SIRIS SWIR camera stands out due to its dual readout mode, allowing it to operate in both logarithmic and linear readout modes. This feature offers unprecedented flexibility, ensuring optimal performance across a wide range of illumination conditions, from very bright to very low light scenarios.

The logarithmic mode, enabled by NIT’s (New Imaging Technologies) ROIC, allows the camera to achieve a high dynamic range of over 140 dB. This mode ensures that the camera can simultaneously capture bright and faint details without saturating the brighter regions of the image. As shown in the attached response curve, the logarithmic curve (LOG) demonstrates a non-linear response to increasing illuminance. The curve rises sharply at low illumination, allowing the detection of faint signals, and then gradually flattens as the illumination increases. This behavior prevents saturation, even at very high photon flux levels, maintaining image details across a wide dynamic range. This makes it ideal for applications like astronomy, where capturing both faint stars and bright objects like moons or planets in a single frame is essential.

On the other hand, the linear mode (CTIA), as shown by the dashed line in the curve, provides a direct proportionality between pixel output and illuminance. This mode is particularly useful for detecting low signals under controlled lighting conditions, such as in laboratory settings or low-light environments. The linear response provides high accuracy in detecting small variations in illumination, especially in low light.

As illustrated in the curve, the logarithmic mode prevents the image from reaching saturation even at high illumination (the flat part of the LOG curve), while the linear mode continues to increase, eventually saturating when the pixel output reaches its maximum capacity. The curve visually demonstrates how the logarithmic mode effectively compresses high illumination levels, allowing for a broader range of signals to be captured without saturation, while the linear mode provides a more straightforward, direct response until it reaches saturation.

In applications where both high and low signals need to be captured within the same image, the camera can toggle between these modes. Additionally, the SIRIS camera utilizes a CTIA based linear readout mode for high sensitivity and a noise-reducing Non-Destructive ReadOut (NDRO) capability. This results in a camera that can deliver exceptional image quality, capturing the full range of light intensities in real-time.

This dual-readout flexibility—paired with SIRIS’s ability to cool the sensor to as low as 70K—makes the camera highly versatile. It can adapt its sensor temperature to minimize noise and optimize the detection of faint signals, ensuring exceptional performance in demanding applications like astronomy, where detecting both bright celestial objects and faint details in the same frame is critical.

Noise reduction with Non-destructive read-out

This camera comes with an interesting feature called NDRO (Non-Destructive Read Out). This feature allows one to read the accumulated charges during an exposure without destroying them, This helps in achieving efficient readout noise reduction, resulting in very low levels of readout noise (under 5e-), even if the FPA has an inherently high readout noise of 50e- at its higher usable gain in low working temperatures.

What is NDRO?

Non-Destructive Readout (NDRO) is a revolutionary feature of the SIRIS SWIR camera, designed to significantly enhance imaging capabilities. Unlike traditional sensors that capture only a single image at the end of an exposure—resetting and losing accumulated charge—NDRO allows the SIRIS camera to read the sensor multiple times during an exposure without resetting. This results in a sequence of images that contain a wealth of data, integrating light intensity information from the entire duration of the exposure. This advanced capability provides greater flexibility and depth in data analysis, making NDRO a standout feature in SWIR imaging

How NDRO Works

NDRO fundamentally alters the imaging process by enabling multiple readouts during a single exposure period. Traditionally, cameras perform a single readout at the end of an exposure, which can result in loss of data and limited flexibility. However, with NDRO, the SIRIS SWIR camera can perform multiple readouts at intervals as short as 5 milliseconds, without resetting the sensor.

Each readout contributes additional information to the final image, effectively layering data from the entire exposure time. This capability is crucial in environments where light conditions change rapidly, or where capturing subtle temporal variations is important. NDRO ensures that all collected data is preserved and available for subsequent processing, providing more detailed and accurate imaging results.

Advantages of NDRO

1.Enhanced Noise Reduction:

The ability to capture multiple readouts during an exposure allows for advanced noise reduction techniques, such as Fowler Sampling. This technique involves averaging multiple readouts to drastically reduce read noise, which is typically consistent across a sequence. The result is a cleaner, high-quality image with a superior signal-to-noise ratio, critical for precision imaging in low-light conditions.

2.Real-Time Processing Capabilities:

NDRO sequences are ideal for real-time processing, enabling immediate analysis and decision-making. This capability is crucial in applications like surveillance, where timely information is essential. The real-time processing of NDRO sequences ensures that no detail is overlooked, making it easier to respond quickly to changing conditions.