Telescope Optical System Research Articles

The KM3NeT Broadcast optical system network

The optical data transport system of the KM3NeT neutrino telescope at the bottom of the Mediterranean Sea will serve more than 6000 optical modules in the detector arrays with a point-to-point optical connection to the control stations onshore. The ARCA and ORCA detectors of KM3NeT are being installed at a depth of about 3500 m and 2500 m, respectively and their distance to the control stations is about 100 km and 40 km. The two detectors are optimised for the detection of cosmic neutrinos with energies above about 1 TeV (ARCA) and of atmospheric neutrinos with energies in the range 1 GeV– 1 TeV (ORCA). The expected maximum data rate is 200 Mbps per optical module. The implemented optical data transport system matches the layouts of the networks of electro-optical cables and junction boxes in the deep sea. For efficient use of the fibres in the system the technology of Dense Wavelength Division Multiplexing is applied. To comply with the scientific goals of KM3NeT, a time calibration of 1 ns between the many optical modules in the detector arrays is essential for the reconstruction of the neutrino events. For the first time in a deep sea neutrino telescope the White Rabbit protocol over Ethernet is used for the clock distribution. Downstream slow control and base module signals are broadcasted to all optical modules in the detector array. Synchronisation is achieved by communication between a White Rabbit master onshore and a White Rabbit slave unit inside the optical modules. In this contribution the KM3NeT broadcast optical data transport system is presented.

Advanced Phase Diversity Method for telescope static aberration compensation

Accurate calibration is essential for high-performance Adaptive Optics (AO) systems in astronomy. This paper presents a novel methodology for AO systems calibration that preserves the optical path integrity while achieving high-quality results. By eliminating the need for optical modifications, this approach simplifies system complexity and accounts for all static aberrations. The main novelty of this proposal is an advanced Phase Diversity (PD) method for estimating static optical aberrations. Unlike conventional PD techniques, this approach uses the AO system’s deformable mirror to introduce different diversities, eliminating the need for additional calibration hardware. Furthermore, the optimizer Adam is introduced for the first time in this field to estimate the optical aberrations. To evaluate the performance of this new methodology, a set of experiments under varying operating conditions and optimization parameters has been conducted. Results demonstrated that the presented methodology is capable of providing diffraction-limited corrected images with a Strehl Ratio (SR) exceeding 0.80 within 2 min. Furthermore, employing a Manhattan distance-based error function effectively balanced estimation speed and accuracy. The method demonstrated effectiveness across a wide range of aberration magnitudes, achieving an error of 3 nm in the best scenarios. This proposal represents an advancement in the identification and correction of static aberrations in telescope optical systems, directly improving the acquisition of high-quality references for AO sensing.

Piston Error Automatic Correction for Segmented Mirrors via Deep Reinforcement Learning.

The segmented mirror co-phase error identification technique based on supervised learning methods has the advantages of simple application conditions, no dependence on custom sensors, a fast calculation speed, and low computing power requirements compared with other methods. However, it is often difficult to obtain a high accuracy in practical application situations with this method because of the difference between the training model and the actual model. The reinforcement learning algorithm does not need to model the real system when operating the system. However, it still retains the advantages of supervised learning. Thus, in this paper, we placed a mask on the pupil plane of the segmented telescope optical system. Moreover, based on the wide spectrum, point spread function, and modulation transfer function of the optical system and deep reinforcement learning-without modeling the optical system-a large-range and high-precision piston error automatic co-phase method with multiple-submirror parallelization was proposed. Finally, we carried out relevant simulation experiments, and the results indicate that the method is effective.

The 85-electrode adaptive optics system of the Swedish 1-m Solar Telescope

We discuss the chosen concepts, detailed design, implementation and calibration of the 85-electrode adaptive optics (AO) system of the Swedish 1-meter Solar Telescope (SST), which was installed in 2013. The AO system is unusual in that it uses a combination of a monomorph mirror with a Shack-Hartmann (SH) wavefront sensor (WFS) and a second high-resolution SH microlens array to aid the characterization, calibration, and modal control of the deformable mirror. An Intel PC workstation performs the heavy image processing associated with cross-correlations and real-time control at a 2 kHz update rate with very low latency. The computer and software continue the successful implementation since 1995 of earlier generations of correlation tracker and AO systems at SST and its predecessor, the 50-cm Swedish Vacuum Solar Telescope, by relying entirely on work-station technology and an extremely efficient algorithm for implementing cross-correlations with the large field of view of the WFS. We describe critical aspects of the design, calibrations, software, and functioning of the AO system. The exceptionally high performance is testified through the highest Strehl ratio (inferred from the measured granulation contrast) of existing meter-class solar telescopes, as demonstrated here at wavelengths shorter than 400 nm and discussed in more detail in a previous separate publication We expect that some aspects of this AO system may also be of interest outside the solar community.

Imaging quality evaluation method for large field-of-view telescope optical systems

Imaging quality evaluation method for large field-of-view telescope optical systems

Simulation alignment of optical system for space gravitational wave telescope

The performance of telescopes, important components of space interferometry systems, directly affects the accuracy of gravitational wave signals. Space gravitational wave telescopes typically employ an off-axis four-mirror system. When aligned, this system not only has multiple misalignments, but also exhibits interrelated aberrations from various misalignments. These characteristics may lead to difficult alignment of the telescope system as well as significant deviation between the position of the telescope after alignment and the ideal position. To address these issues, first, a sensitivity matrix equation was established between the misalignment of optical components and the Fringe Zernike coefficients. Based on the sensitivity matrix equation, a damping least-squares evaluation function was constructed to reduce the significant deviation between the aligned and ideal positions. Second, a typical optical system of a space gravitational wave telescope was designed, and the sensitivity matrix was calculated. The relationship between the wavefront distortions caused by misalignments in each optical component was examined. To simplify telescope installation, a strategy using secondary mirrors as compensatory elements was proposed. Finally, to verify the effectiveness of the scheme, 200 sets of tolerance files were randomly generated. Based on the evaluation function of the damping least-squares method, a reasonable damping factor was set to limit the solution range of the misalignment, which enabled calculating the secondary mirror compensation amount. Experimental results indicate that after aligning the 200 random telescope files, the root-mean-square wavefront error was reduced to less than 0.0030λ, and the maximum error between the magnification after alignment and the ideal position magnification was only 0.57%, which confirms the feasibility of this alignment scheme.

Pathfinder value for integration and test of the Webb Telescope optical system

Pathfinder value for integration and test of the Webb Telescope optical system

Jitter error evaluation in large-aperture optical telescopes based on normalized point source sensitivity

To comprehensively analyze the jitter error in large-aperture optical telescopes, this paper introduces normalized point source sensitivity (PSSn) to evaluate the telescope system. First, the concept and basic properties of PSSn were introduced, and then the jitter error under expected random loads and the contribution percentage of each mode to the total jitter were analyzed through a model. The PSSn of the system under the influence of different error sources was studied, and its variation trend was estimated. A comparison of evaluation methods, such as the Strehl ratio, and the proposed method reflects the characteristics of more accurate data and a more concise calculation. The jitter error evaluation method proposed in this article, combined with PSSn, provides practical and beneficial guidance for the design and detection of large-aperture optical telescope systems.

The impact of telescope aberrations on the magnitude of tilt to length coupling noise in space based gravitational wave detectors

Tilt-to-length (TTL) coupling noise is one of the main noise sources that affect space gravitational wave detection, and the Tianqin project requires that the internal TTL coupling noise of the telescope used be less than 0.4 pm/Hz1/2 within the frequency band from 0.1 mHz to 1 Hz. In order to design a telescope that meets the requirements of TTL coupling noise and carry out preliminary error allocation research, it is necessary to analyze and calculate the TTL coupling noise, and then guide the design and optimization of the telescope system. This paper establishes a computational analysis model for the non-geometric TTL coupling noise inside the telescope using the first 36-order edge Zernike polynomials. A method was proposed to reduce the internal TTL coupling noise of the telescope by reducing the proportion of sensitive aberrations caused by non-geometric TTL coupling noise. Simulation results show that, with the RMS value of wavefront aberration at the telescope exit pupil unchanged, reducing the proportion of sensitive aberrations at the telescope exit pupil can effectively reduce the internal TTL coupling noise of the telescope. By optimizing the telescope optical system to reduce the proportion of noise-sensitive aberrations, the non-geometric TTL coupling noise inside the telescope has been reduced from 0.34 pm/Hz1/2 @ 0.1 mHz ∼ 1 Hz to 0.25 pm/Hz1/2. This result can provide some guidance for the design of telescope optics based on the suppression of internal TTL coupling noise in the telescope.

Fabrication Development for SPT-SLIM, a Superconducting Spectrometer for Line Intensity Mapping

Line Intensity Mapping (LIM) is a new observational technique that uses low-resolution observations of line emission to efficiently trace the large-scale structure of the Universe out to high redshift. Common mm/sub-mm emission lines are accessible from ground-based observatories, and the requirements on the detectors for LIM at mm-wavelengths are well matched to the capabilities of large-format arrays of superconducting sensors. We describe the development of an <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$R$</tex-math></inline-formula> = <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\lambda / \Delta \lambda = 300$</tex-math></inline-formula> on-chip superconducting filter-bank spectrometer covering the 120–180 GHz band for future mm-LIM experiments, focusing on SPT-SLIM, a pathfinder LIM instrument for the South Pole Telescope. Radiation is coupled from the telescope optical system to the spectrometer chip via an array of feedhorn-coupled orthomode transducers. Superconducting microstrip transmission lines then carry the signal to an array of channelizing half-wavelength resonators, and the output of each spectral channel is sensed by a lumped element kinetic inductance detector (leKID). Key areas of development include incorporating new low-loss dielectrics to improve both the achievable spectral resolution and optical efficiency and development of a robust fabrication process to create a galvanic connection between ultra-pure superconducting thin-films to realize multi-material (hybrid) leKIDs. We provide an overview of the spectrometer design, fabrication process, and prototype devices.

Phase Alignment of an Array Optical Telescope System Using Balanced Detection

Differential phase shift keying (DPSK) modulation and multi-aperture receiving are effective means for suppressing flickering, deviation, and fragmentation of the light spot by atmospheric turbulence. What is challenging in coherent beam combination of such an array receiver system is to detect and compensate for phase deviation of sub-apertures. In this paper, a method of phase alignment of an array optical telescope system using balanced detection was proposed and demonstrated. The improved Mach Zehnder Interferometer (MZI) can demodulate the digital signal and recover the phase difference at the same time. It also brings a 3 dB gain to the receiver and improves the detection sensitivity of the system. Adequate simulations with OptiSystem and MATLAB were carried out to show that the power value remains near the ideal state of 2.75 mW, and the bit error rate is less than 10-9 after phase compensation, which indicates the effectiveness and accuracy of the proposed method. Furthermore, taking the communication interruption difference of ninety degrees as an example, the system bit error rate was reduced from 1 to 10-35, and communication was established again.

KM3NeT broadcast optical data transport system

The optical data transport system of the KM3NeT neutrino telescope at the bottom of the Mediterranean Sea will provide more than 6000 optical modules in the detector arrays with a point-to-point optical connection to the control stations onshore. The ARCA and ORCA detectors of KM3NeT are being installed at a depth of about 3500 m and 2500 m, respectively and their distance to the control stations is about 100 kilometers and 40 kilometers. In particular, the two detectors are optimised for the detection of cosmic neutrinos with energies above about 1 TeV (ARCA) and for the detection of atmospheric neutrinos with energies in the range 1 GeV–1 TeV (ORCA). The expected maximum data rate is 200 Mbps per optical module. The implemented optical data transport system matches the layouts of the networks of electro-optical cables and junction boxes in the deep sea. For efficient use of the fibres in the system the technology of Dense Wavelength Division Multiplexing is applied. The performance of the optical system in terms of measured bit error rates, optical budget are presented. The next steps in the implementation of the system are also discussed.

Suppression of coupling between optical aberration and tilt-to-length noise in a space-based gravitational wave telescope.

Coupling between exiting wavefront error of space gravitational wave telescopes and tilt-to-length (TTL) noise affects the measurement accuracy. Using the LISA Pathfinder signal, we analyzed cancellation and superposition of TTL coupling noise under various optical aberrations. We proposed proportion requirements of any two aberrations amplitude when noise was cancelled and an aberration amplitude control requirement when noise was superposed. Taking them as the aberration control requirements of gravitational wave telescope optical system, the exiting wavefront error requirements was reduced while suppressing the TTL coupling noise. A 40× optical telescope system with detection aperture φ=200 mm was designed. The exiting wavefront error was relaxed from 0.02 λ to 0.0496 λ. The maximum coupling coefficient value did not exceed 6.9448 pm/µrad within a pointing jitter angle of ±300 µrad. The proposed approach should be useful in future telescope design.

A 36 cm robotic optical telescope: Equipment and software

The paper describes an optical telescope system and control software for robotic observation of space debris. The telescope has a main aperture of 355 mm, adopts the optical design scheme of primary focus with a large field of view, and is equipped with a highly sensitive 4 K sCMOS camera to achieve a large field of view of 2.6° × 2.6°. The telescope is equipped with an environmental monitoring system and a highly reliable dome to ensure the safe operation of the telescope. The control software of the telescope consists of two parts. One part is deployed locally to comprehensively schedule the robotic operation of various equipment of the telescope system, and the other part is deployed remotely to realize the functions of equipment status monitoring, networking scheduling, remote control, and data management. At present, four telescopes have been deployed in Korla, Xinjiang, China to form a telescope array, basically realizing the remote “unattended” observation of space debris.

Optical system of aplanatic telescope with a 100 m spherical primary mirror

We propose an optical system of an extremely large telescope for ground-based or planetary use. The system comprises a segmented spherical mirror with a diameter of 100 m and f-number of f / 1. There are three annular zones on the primary mirror, which corresponds to three annular telescopes (ATs) with f-numbers f / 2, f / 3.2, and f / 5.2, all using a concave cardioidal secondary mirror with a maximum diameter of 3.18 m. This two-mirror system satisfies Fermat’s principle and the Abbe’s sine condition. The central zone of the primary mirror with a diameter of 23.8 m is used for the central three-mirror telescope, which is based on an afocal two-mirror system with a convex aspheric secondary mirror with a diameter of 3 m. Four possible configurations are presented for the central telescope, which makes it possible to vary the f-number in a wide range with design examples given for f / 1, f / 4.2, f / 14, and f / 33 systems. The ATs form three coherent images of the same astronomical object, which offers possibilities of simultaneous observations at three different wavelengths or image processing of a combined image with enhanced angular resolution. The main goal of the paper is to investigate the properties of new optical systems for ground-based and space telescopes with a fast spherical primary mirror for which aberration correction is achieved with a minimum number of auxiliary aspheric mirrors near the prime focus.

Circuit designs for construction of pancratic telescopes

The improvement of classical telescopes designed to observe distant objects is currently associated with the provision of operating modes with interchangeable magnification and the possibility of photo and video recording. The purpose of the paper is to propose circuit designs for optical systems of high-magnification pancratic telescopes and substantiate the possibility of their use in engineering. The paper is based on the engineering design of two variants of telescope optical systems with a magnification of 20 to 60 times, in the first of which the pancratic change of magnification is provided by the movements of the components in the ocular part, in the second - in the objective part. The characteristics of pancratic telescopes are considered. It was revealed that in modern models the pancratic change of magnifications is carried out in the ocular and objective parts of the system. Computer simulation methods were used to synthesize optical schemes in the paraxial approximation, followed by the implementation of systems with finite apertures and thicknesses. The developed systems can be used at domestic enterprises of optical instrumentation.

Holographic sight with a one-dimensional telescopic optical system

A scheme of a holographic collimator sight with a one-dimensional telescopic optical system is proposed. The scheme is based on an optical system of a sight comprising a one-dimensional telescopic optical system composed of an achromatizing diffraction grating and hologram forming the image of the aiming mark. We establish that a plane diffraction grating and hologram positioned nonparallelly can function as a one-dimensional telescopic system. This system allows compensation of the different divergences of radiation in the principal cross sections of the laser diode comprising the sight and reducing the aperture of the parallel ray beam formed in the sight and used for hologram reconstruction in one of its principal cross sections. However, such a mutual alignment of the grating and hologram results in limitation of the spectral range in which the compensation of the thermal drift of the aiming line position is ensured. Equations that allow determination of the ratios of the spatial frequency of the grating and carrier spatial frequency of the hologram, which result in minimization of the thermal drift of the aiming line, are presented. Geometric parameters of the sight scheme that ensure the residual thermal drift of the aiming line that does not exceed the angular resolution of the eye while maintaining its minimum dimensions are reported. Technological aspects of the fabrication of the diffractive optical elements of the sight are considered. The scheme of the holographic collimator sight proposed in this study combines the main advantage of the light-guide-type sight scheme, i.e., the small distance from the sight base to the aiming line of 0.8 times the hologram aperture height, with relatively simple assembly and alignment of the elements of the sight optical scheme characteristic of a sight composed of a concave diffraction grating.

OPTICAL SYSTEM DESIGN OF THE DETECTOR FOR SOLAR TERAHERTZ EMISSION MEASUREMENTS

The objectives and scientific tasks of the planned space experiment “Solntse-Terahertz” to be performed onboard the ISS Russian Segment are briefly described in the paper. In particular, the aim of the experiment is to study uninvestigated solar electromagnetic emission in the terahertz domain, in ~ 1012 – 1013 Hz (300-30 µm) frequency range. It is expected to obtain new data on solar active region emission including solar flare emission. These data are necessary to clarify the nature of solar activity and construct physical model of charged particle acceleration in active regions during solar flares and other astrophysical objects. We focus on the telescope optical system design and evaluation of main characteristics of this system. Results of simulations and comparison with the experimental verification of obtained characteristics are presented. A close correlation of the estimations and experimental results was obtained. As a result, main parameters of the telescope optical system of experimental hardware “Solntse-Terahertz” were determined. Key words: Sun, solar flares, terahertz emission, optical system.

Optical design of the laser launch telescope via physical optics theorem for laser guide star facility

The Laser Guide Star Facility (LGSF), as the most important part of the adaptive optics system of the large ground-based telescope, is aimed to generate multiple laser guide stars at the sodium layer. Laser Launch Telescope is employed to implement this requirement by projecting the Gauss beam to the sodium layer with a small beam size in LGSF system. As the diffraction and interference effects of laser’s long-distance transmission, the conventional optical design based on the geometrical optics mechanism cannot achieve the expected laser propagation. In this paper, we propose a method to design optical system for laser launch telescope based on the physical optics theorem to generate an acceptable light spot at the sodium layer in the atmosphere. Besides, a tolerance analysis method based on physical optics propagation is also demonstrated to be necessitated to optimize the system’s instrumentation performance. The numerical results show that the optical design considering physical optics propagation is highly rewarding and even necessitated in many occasions, especially for laser beam propagation systems.

Mathematical simulation of a 3D scanner for controlling the mirror system of the Millimetron Observatory

We develop an original system for controlling the mirror geometry of the Millimetron observatory as a part of the on-board scientific equipment. The system is designed to monitor the quality of the space telescope's mirror system and use the data received as feedback signals for presetting and adjusting the telescope's optical system in outer space. The system aims to determine a multi-dimensional vector of unknown parameters that define the state of the telescope's mirror system by indirect measurements of the telescope with a 3D scanner. An unparalleled mathematical model has been created, numerically describing a process of pre-measurement of the mirror system of the Millimetron Observatory using optical control marks on the surface of the mirror system. Using the mathematical model created and the geometric optics approximation, we numerically simulate the performance of the on-board 3D scanner in the course of preliminary measurements of the mirror system of the Millimetron Observatory using optical control marks applied on the mirror surfaces. A new effective method of pre-estimation of the displacement of elements of the AP telescope by indirect (implicit) measurements performed with the 3D scanner has been created. The method is based on the mathematical transformation of indirect measurements of deviations of the position of the telescope's mirror control marks from their reference position, which provides an easy-to-use list of estimates of the offsets of the unknown parameters of the mirror system elements. A possibility to measure the telescope's mirror system with the aim to pre-configure it using a 3D scanner on board the spacecraft is shown. Estimates of acceptable deviations of the mirror system component needed to ensure the telescope's functionality are given.