Mark Downing

A single-photon CMOS image sensor (CIS) design based on pinned photodiode (PPD) with multiple charge transfers and sampling is described. In the proposed pixel architecture, the photogenerated signal is sampled non-destructively multiple times and the results are averaged. Each signal measurement is statistically independent and by averaging, the electronic readout noise is reduced to a level where single photons can be distinguished reliably. A pixel design using this method was simulated in TCAD and several layouts were generated for a 180-nm CMOS image sensor process. Using simulations, the noise performance of the pixel was determined as a function of the number of samples, sense node capacitance, sampling rate and transistor characteristics. The strengths and limitations of the proposed design are discussed in detail, including the trade-off between noise performance and readout rate and the impact of charge transfer inefficiency (CTI). The projected performance of our first prototype device indicates that single-photon imaging is within reach and could enable ground-breaking performances in many scientific and industrial imaging applications.

The success of the next generation of instruments for 20m plus class optical telescopes will depend upon improving the image quality by exploiting sophisticated Adaptive Optics (AO) systems. For several years now, ESO has been very active in gathering requirements, planning, and developing detectors and controllers/cameras for the AO systems of the telescope and instruments of the ELT. From these requirements, the need for three different types of cameras have been identified: 1) ALICE (smALl vIsible CamEra) for Truth/High Order Natural Guide Star (NGS)/Telescope Guiding which uses the “sub-electron RON” Teledyne-e2v CCD220-DD of 240x240 of 24μm pixels; 2) LISA (Large vISble cAmera) for Shack-Hartmann Laser Guide Star (LGS)/Telescope Wavefront Sensing (WFS) which uses the Teledyne-e2v LVSM of 800x800 of 24μm pixels; 3) SAPHIRA Standalone Camera for Low-/High-Order NGS WFS/Fine Centering which uses the Leonardo SAPHIRA of 320x256 of 24μm pixels. This paper provides an update on the development of these cameras and their detectors. For ALICE and LISA, a single camera design approach is being followed with the only difference being the customizable front-ends to support the different type of detector. ALICE and LISA are being built around a common set of components and will look essentially identical from the exterior. COTS modules are being used wherever possible and practical to reduce the development effort and time, and improve functionality and maintainability. A description of the design approach, the common components and the detector specific front-ends will be presented. The LISA camera detector, the LVSM, is under development by Teledyne-e2v. A brief update on the progress of this development will be provided. For the SAPHIRA standalone camera, a different approach is being followed to that of ALICE and LISA. C-RED ONE cameras are being procured from FLI and will be modified by ESO to comply with ELT standards: 10GbE interfaces to the Real Time Computer (RTC) and NGC control computer, and Precision Time Protocol (PTP). PTP is the time reference system of the ELT and will be used by the cameras to schedule and time stamp frames and for synchronizing with other cameras or hardware devices.

For the first time, sub-electron read noise has been achieved with a camera suitable for astronomical wavefront-sensing (WFS) applications. The OCam system has demonstrated this performance at 1300 Hz frame rate and with 240×240-pixel frame rate. ESO and JRA2 OPTICON² have jointly funded e2v technologies to develop a custom CCD for Adaptive Optics (AO) wavefront sensing applications. The device, called CCD220, is a compact Peltier-cooled 240×240 pixel frame-transfer 8-output back-illuminated sensor using the EMCCD technology. This paper demonstrates sub-electron read noise at frame rates from 25 Hz to 1300 Hz and dark current lower than 0.01 e-/pixel/frame. It reports on the comprehensive, quantitative performance characterization of OCam and the CCD220 such as readout noise, dark current, multiplication gain, quantum efficiency, charge transfer efficiency... OCam includes a low noise preamplifier stage, a digital board to generate the clocks and a microcontroller. The data acquisition system includes a user friendly timer file editor to generate any type of clocking scheme. A second version of OCam, called OCam², was designed offering enhanced performances, a completely sealed camera package and an additional Peltier stage to facilitate operation on a telescope or environmentally rugged applications. OCam² offers two types of built-in data link to the Real Time Computer: the CameraLink industry standard interface and various fiber link options like the sFPDP interface. OCam² includes also a modified mechanical design to ease the integration of microlens arrays for use of this camera in all types of wavefront sensing AO system. The front cover of OCam² can be customized to include a microlens exchange mechanism.

ESO and JRA2 OPTICON have funded e2v technologies to develop a compact packaged Peltier cooled 24 μm square 240x240 pixels split frame transfer 8-output back-illuminated L3Vision CCD3, L3Vision CCD for Adaptive Optic Wave Front Sensor (AO WFS) applications. The device is designed to achieve sub-electron read noise at frame rates from 25 Hz to 1,500 Hz and dark current lower than 0.01 e-/pixel/frame. The development has many unique features. To obtain high frame rates, multi-output EMCCD gain registers and metal buttressing of row clock lines are used. The baseline device is built in standard silicon. In addition, a split wafer run has enabled two speculative variants to be built; deep depletion silicon devices to improve red response and devices with an electronic shutter to extend use to Rayleigh and Pulsed Laser Guide Star applications. These are all firsts for L3Vision CCDs. The designs of the CCD and Peltier package have passed their reviews and fabrication has begun. This paper will describe the progress to date, the requirements and the design of the CCD and compact Peltier package, technology trade-offs, schedule and proposed test plan. High readout speed, low noise and compactness (requirement to fit in confined spaces) provide special challenges to ESO's AO variant of its NGC, New General detector Controller to drive this CCD. This paper will describe progress made on the design of the controller to meet these special needs.