Many are the optical designs that generate curved focal planes for which field flattener must be implemented. This generally implies the use of more optical elements and a consequent loss of throughput and performances. With the recent development of curved sensor this can be avoided. This new technology has been gathering more and more attention from a very broad community, as the potential applications are multiple: from low-cost commercial to high impact scientific systems, to mass-market and on board cameras, defense and security, and astronomical community.
We describe here the first concave curved CMOS detector developed within a collaboration between CNRS-LAM and CEA-LETI. This fully-functional detector 20Mpix (CMOSIS CMV20000) has been curved down to a radius of Rc =150mm over a size of 24x32mm2. We present here the methodology adopted for its characterization and describe in detail all the results obtained. We also discuss the main components of noise, such as the readout noise, the fixed pattern noise and the dark current. Finally we provide a comparison with the at version of the same sensor in order to establish the impact of the curving process on the main characteristics of the sensor.
Exoplanet imaging requires super polished off-axis parabolas (OAP) with the utmost surface quality. In this paper we describe an innovative manufacturing process combining 3D printing and stress polishing, to create a warping harness capable of producing any off axis parabola profile with a single actuator. The warping harness is manufactured by 3D printing. This method will be applied to the production of the WFIRST coronagraph's off axis parabolas. The evolution of the warping harness design is presented, starting from a ring warping harness generating astigmatism, to an innovative thickness distribution harness optimised to generate an off axis parabola shape. Several design options are available for the prototyping phase, with their advantages and disadvantages which will be discussed.
Many astronomical optical systems have the disadvantage of generating curved focal planes requiring flattening optical elements to project the corrected image on at detectors. The use of these designs in combination with a classical at sensor implies an overall degradation of throughput and system performances to obtain the proper corrected image. With the recent development of curved sensor this can be avoided. This new technology has been gathering more and more attention from a very broad community, as the potential applications are multiple: from low-cost commercial to high impact scientific systems, to mass-market and on board cameras, defense and security, and astronomical community. We describe here the first concave curved CMOS detector developed within a collaboration between CNRS- LAM and CEA-LETI. This fully-functional detector 20 Mpix (CMOSIS CMV20000) has been curved down to a radius of Rc =150mm over a size of 24x32mm2. We present here the methodology adopted for its characterization and describe in detail all the results obtained. We also discuss the main components of noise, such as the readout noise, the fixed pattern noise and the dark current. Finally we provide a comparison with the at version of the same sensor in order to establish the impact of the curving process on the main characteristics of the sensor.
The present paper describes the current baseline optical design of POLLUX, a high-resolution spectropolarimeter for the future LUVOIR mission. The instrument will operate in the ultraviolet (UV) domain from 90 to 390 nm in both spectropolarimetric and pure spectroscopic modes. The working range is split between 3 channels – far (90-124.5 nm), medium (118.5-195 nm) and near (195-390 nm) UV. Each of the channels is composed of a polarimeter followed by an echelle spectrograph consisting of a classical off-axis paraboloid collimator, echelle grating with a high grooves frequency and a cross-disperser grating operating also as a camera. The latter component integrates some advanced technologies: it is a blazed grating with a complex grooves pattern formed by holographic recording, which is manufactured on a freeform surface. One of the key features underlying the current design is the large spectral length of each order ~6 nm, which allows to record wide spectral lines without any discontinuities. The modelling results show that the optical design will provide the required spectral resolving power higher than R ~ 120,000 over the entire working range for a point source object with angular size of 30 mas. It is also shown that with the 15-m primary mirror of the LUVOIR telescope the instrument will provide an effective collecting area up to 38 569 cm2 . Such a performance will allow to perform a number of groundbreaking scientific observations. Finally, the future work and the technological risks of the design are discussed in details.
In the present paper we demonstrate the approach to use a holographic grating on a freeform surface for advanced spectrographs design. On the example POLLUX spectropolarimeter medium-UV channel we chow that such a grating can operate as a cross-disperser and a camera mirror at the same time. It provides the image quality high enough to reach the spectral resolving power of 126 359-133 106 between 11.5 and 195 nm, which is higher than the requirement. Also we show a possibility to use a similar element working in transmission to build an unobscured double-Schmidt spectrograph. The spectral resolving power reaches 2750 for a long slit. It is also shown that the parameters of both the gratings are feasible with the current technologies.
In the present paper we consider a family of unobscured telescope designs with curved detectors. They are based on classical two-mirror schemes – Ritchey-Chretien, Gregorian and Couder telescopes. It is shown that all the designs provide nearly diffraction limited image quality in the visible domain for 0.4º×0.4º field of view with the f-number of 7. We also provide a brief ghost analysis and point on special features of the systems with curved detectors. Finally, the detector surface shape obtained in each case is analyzed and its’ technological feasibility is demonstrated.
In the present paper we compare different approaches for estimation of freeform and aspherical surfaces complexity. We consider two unobscured all-reflective telescope designs: a narrow-field Korsch-type system with a slow freeform secaondary and a wide-field Schwarzschild-type system with an extreme freeform secondary. The performance improvement obtained due to the freeforms use is demonstrated. The Korsch telescope provides a diffraction-limited image quality for a small field 0.8x0.1° at F/3. The Schwarzschild design covers a large field of 20x8° and allows to increase the aperture from F/6.7 to F/3. Also, we analyze the freeforms shapes using different techniques. It is shown that the usual measures like root-mean square deviation of the sag are ineffective. One of the recommended way to estimate the surface complexity is computation of the residual slope and its conversion into fringes frequency. A simpler alternative is computation of the sag deviation integral.
In the present paper we consider quantitative estimation of the tolerances widening in optical systems with curved detectors. The gain in image quality allows to loosen the margins for manufacturing and assembling errors. On another hand, the requirements for the detector shape and positioning become more tight. We demonstrate both of the effects on example of two optical designs. The first one is a rotationally-symmetrical lens with focal length of 25 mm, f-ratio of 3.5 and field of view equal to 72°, working in the visible domain. The second design is a three-mirror anastigmat telescope with focal length of 250 mm, f-ratio of 2.0 and field of view equal to 4°x4°. In both of the cases use of curved detectors allow to increase the image quality and substantially decrease the requirements for manufacturing precision.
3D printing, also called additive manufacturing, offers a new vision for optical fabrication in term of achievable optical quality and reduction of weight and cost. In this paper we describe two different ways to use this technique in the fabrication process. The first method makes use of 3D printing in the fabrication of warping harnesses for stress polishing, and we apply that to the fabrication of the WFIRST coronagraph off axis parabolas. The second method considers a proof of concept for 3D printing of lightweight X-Ray mirrors, targeting the next generation of X-rays telescopes. Stress polishing is well suited for the fabrication of the high quality off axis parabolas required by the coronagraph to image exoplanets.. Here we describe a new design of warping harness which can generate astigmatism and coma with only one actuator. The idea is to incorporate 3D printing in the manufacturing of the warping harness. The method depicted in this paper demonstrates that we reach the tight precision required at the mirrors surface. Moreover the error introduced by the warping harness fabricated by 3D printing does not impact the final error budget. Concerning the proof of concept project, we investigate 3D printing towards lightweight X-ray mirrors. We present the surface metrology of test samples fabricated by stereo lithography (SLA) and Selective Laser Sintering (SLS) with different materials. The lightweighting of the samples is composed of a series of arches. By complementing 3D printing with finite element analysis topology optimization we can simulate a specific optimum shape for the given input parameters and external boundary conditions. The next set of prototypes is designed taking to account the calculation of topology optimisation.
Over the recent years, a huge interest has grown for curved electronics, particularly for opto-electronics systems. Curved sensors help the correction of off-axis aberrations, such as Petzval Field Curvature, astigmatism, and bring significant optical and size benefits for imaging systems. In this paper, we first describe advantages of curved sensor and associated packaging process applied on a 1/1.8’’ format 1.3Mpx global shutter CMOS sensor (Teledyne EV76C560) into its standard ceramic package with a spherical radius of curvature Rc=65mm and 55mm. The mechanical limits of the die are discussed (Finite Element Modelling and experimental), and electro-optical performances are investigated. Then, based on the monocentric optical architecture, we proposed a new design, compact and with a high resolution, developed specifically for a curved image sensor including optical optimization, tolerances, assembly and optical tests. Finally, a functional prototype is presented through a benchmark approach and compared to an existing standard optical system with same performances and a x2.5 reduction of length. The finality of this work was a functional prototype demonstration on the CEA-LETI during Photonics West 2018 conference. All these experiments and optical results demonstrate the feasibility and high performances of systems with curved sensors.
Over the recent years, a huge interest has grown for curved electronics, particularly for opto-electronics systems. Indeed, curved sensors help the correction of off-axis aberrations, such as Petzval Field Curvature and astigmatism. In this paper, we describe benefits of curvature and tunable curvature on an existing fish-eye lens. We proposed a new design architecture, compact and with a high resolution, developed specifically for a curved image sensor. We discuss about aberrations and effect of higher sensor curvature on third order aberrations. Besides, we show results of sensors’ mechanical limits and its electro-optical characterization. Finally, all these experiments and optical results demonstrate the feasibility and high performances of systems with curved sensors.
The SNIFS CALibration Apparatus (SCALA), a device to calibrate the Supernova Integral Field Spectrograph on the University Hawaii 2.2m telescope, was developed and installed in Spring 2014. SCALA produces an artificial planet with a diameter of 1° and a constant surface brightness. The wavelength of the beam can be tuned between 3200 Å and 10000 Å and has a bandwidth of 35 Å. The amount of light injected into the telescope is monitored with NIST calibrated photodiodes. SCALA was upgraded in 2015 with a mask installed at the entrance pupil of the UH88 telescope, ensuring that the illumination of the telescope by stars is similar to that of SCALA. With this setup, a first calibration run was performed in conjunction with the spectrophotometric observations of standard stars. We present first estimates for the expected systematic uncertainties of the in-situ calibration and discuss the results of tests that examine the influence of stray light produced in the optics.
Frequency Division Multiplexing technique for reading TES detectors with SQuID devices, requires high loop-gain up to MHz frequency range in the SQuID feedback loop. Such a requirement is difficult to achieve when the feedback loop has a physical length that makes the propagation times of signals not negligible, as in the case in which the readout electronics is placed at room temperature. A novel SQuID readout scheme, called Double Loop-Flux Locked loop (DLFLL), has been proposed earlier. According to this scheme it is possible to make use of a simplified cryogenic electronics, AC coupled, featuring low power dissipation, in order to obtain a cryogenic feedback loop that results in reduced propagation times of signals. The DC and low frequency signals are managed by a standard FLL electronics working at room temperature. Here we present the progress of the integrated Double Loop system.
Observational cosmology employing optical surveys often require precise flux calibration. In this context we present SNIFS Calibration Apparatus (SCALA), a flux calibration system developed for the SuperNova Integral Field Spectrograph (SNIFS), operating at the University of Hawaii 2.2 m telescope. SCALA consists of a hexagonal array of 18 small parabolic mirrors distributed over the face of, and feeding parallel light to, the telescope entrance pupil. The mirrors are illuminated by integrating spheres and a wavelength-tunable (from UV to IR) light source, generating light beams with opening angles of 1°. These nearly parallel beams are flat and flux-calibrated at a subpercent level, enabling us to calibrate our “telescope + SNIFS system” at the required precision.