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International Conference on Space Optics (ICSO)

The SPEQTRE optical delivery system

Ann E. Fitzpatrick, Rebecca Harwin, H. C. Robarts, William Brzozowski, Stephen Todd, Sreekanth Reddy Vallapureddy, Louis Saraff, Oyuki Chang, Weihe Li, David Pearson, Mike Salter, Andy Vick

Published Jul 28, 2025• 0 citations
Publisher

Abstract

The Secure Photon Entangled Quantum communication Technology Readiness Experiment (SPEQTRE) project is a technology demonstration mission aiming to show entanglement-based quantum key distribution (QKD) from a nanosatellite platform. The satellite will be a 12U CubeSat, measuring 20 x 20 x 30 cm. It is being developed in collaboration with SpeQtral, a Singaporean company who are providing the quantum source and receiver, and ISISpace, a company based in the Netherlands who are providing the satellite platform and its control systems. The project involves the design, build, test, launch and operation of a satellite payload as well as the development and operation of associated ground station facilities. RAL Space are developing multiple new systems for this mission, including an off-axis telescope for the satellite, a control system to stabilise the optical pointing and an optical ground station at Chilbolton to receive the entangled photons. This paper discussed the optical delivery system which has been designed to transmit an optical signal from LEO to an optical ground station.

DOI
10.1117/12.3075376

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The Secure Photon Entangled Quantum communication Technology Readiness Experiment (SPEQTRE) project is a technology demonstration mission aiming to show entanglement-based quantum key distribution (QKD) from a nanosatellite platform. The satellite will be a 12U CubeSat, measuring 20 x 20 x 30 cm. It is being developed in collaboration with SpeQtral, a Singaporean company who are providing the quantum source and receiver, and ISISpace, a company based in the Netherlands who are providing the satellite platform and its control systems. The project involves the design, build, test, launch and operation of a satellite payload as well as the development and operation of associated ground station facilities. RAL Space are developing multiple new systems for this mission, including an off-axis telescope for the satellite, a control system to stabilise the optical pointing and an optical ground station at Chilbolton to receive the entangled photons. This paper discussed the optical delivery system which has been designed to transmit an optical signal from LEO to an optical ground station.
Satellite nodes are an enabler of global quantum networks by overcoming the distance limitations of fiber and free-space links on ground. The design of quantum sources and receivers for satellites, however, is challenging in terms of size, weight, and power consumption, as well as mechanical and thermal stability. This is all the more true for cost-efficient nanosatellites such as the popular CubeSat platform standard. Here we report on the follow-up mission of SpooQy-1, a 3U CubeSat that successfully demonstrated the generation of polarization-entangled photons in orbit. The next iteration of the mission will showcase satellite-to-ground quantum key distribution based on a compact source of polarization-entangled photon-pairs, and we have recently completed the integration of a fully functional demonstrator as a milestone towards the flight model. We also briefly describe the design of the optical ground station that we are currently building in Singapore for receiving the quantum signal. We present the most important subsystems and illustrate the concept of operation.
Satellite-based Quantum Key Distribution (QKD) can be used to deliver information-theoretically secure keys for cryptographic applications, no matter where end-users are located. Several space missions using this concept have shown feasibility of systems and component technologies. The QUBE-II mission, with a planned launch in Spring 2026, uses an economic CubeSat platform to show the possibility of a global secure communication by simple means. This paper presents the optical system design of the QUBE-II laser communication terminal (LCT). It is based on the previous developments for the CubeL mission (launched in 2021), for CubeISL, and for the precursor mission QUBE-I (launched in 2024). The 2.5U LCT is integrated into an 8U CubeSat and serves as transmit system for two Alice modules operating at 850 nm and in optical L-band1, 2 respectively. At the same time, bi-directional classical links are used for link acquisition, tracking, and data transmission. With its 85 mm aperture and an 800 mm receiver telescope on the ground station, the antenna gain is sufficiently high enough to perform QKD links. The LCT’s optical system is designed based on a commercially available reflective telescope in combination with custom-designed lenses. It integrates several fiber-optical and electrical components for wavelength combination, wavelength splitting, tracking, and uplink data reception into a compact design. The Alice payloads are connected to the LCT by optical fibres allowing a flexible placement of the modules within the satellite bus. Collimators couple the light into free-space beams which are co-aligned and interfaced to the transmit telescope. In addition to the optical system design, this paper provides further information about the integration of the optical into the mechanical system, and the performed functional and qualification tests.
Within the public funded project CubEnik an ultra-compact payload for an entanglement Quantum Key Distribution (QKD) mission, using a double downlink scenario from a LEO orbit around 700 km, was developed until the Preliminary Design Review (PDR) status of a typical space mission phase B. The optical payload part, consisting of a double telescope with 80 mm apertures, risley-prism based coarse pointing mechanisms to address Alice and Bob recipients on ground at a distance >300 km, and a high-performant, GHz capable entangled photon source, fits into a 8..12U format of a CubeSat, enabling for a 12..16U CubeSat, or mini-sat Entanglement QKD mission. Link simulations reveal a potential key rate >100 bit per contact (satellite flyover), a first engineering model of the coarse pointing mechanism indicated achievable pointing rates that are suitable for the desired link budget. The consortium now is looking to move forward to phase C and the critical design review (CDR), in collaboration with satellite platform, launch, and mission control partners.
SpooQy-1 is a 3-unit nanosatellite that was launched into a Low Earth Orbit from the International Space Station on the 17th of June 2019. The spacecraft hosts a scientific payload capable of producing entangled photon-pairs and measuring their polarization in orthogonal bases to perform a Bell test. Since launch, SpooQy-1 has routinely demonstrated the generation and detection of polarization entangled photon-pairs in Space, something that has previously only been demonstrated by the 630kg Micius mission by the Chinese Academy of Sciences. The measured entanglement correlations can violate Bell's inequality with a CHSH parameter value of 2.60±0.06, over operating temperatures of 16 °C to 21.5 °C. These results demonstrate that quantum entanglement can be generated in space on highly resource-constrained platforms. A follow-on 12U mission, developed in partnership with RAL space,will build on this to demonstrate space-to-ground entanglement distribution, which is required for space-based nodes to support global quantum communication networks.
The NanoQEY (Nano Quantum Encryption) Satellite is a proposed nanosatellite mission concept developed by the Institute for Quantum Computing (IQC) at the University of Waterloo and the Space Flight Laboratory (SFL) at the University of Toronto Institute for Aerospace Studies (UTIAS) that would demonstrate long-distance quantum key distribution (QKD) between two distant ground stations on Earth using an optical uplink. SFL’s existing and proven NEMO (Nanosatellite for Earth Monitoring and Observation) bus forms the baseline spacecraft for NanoQEY, with a QKD receiver payload designed by IQC. The primary objective of the NanoQEY mission would be to successfully distribute at least 10 kbit of secure key between two optical ground stations, where the satellite acts as a trusted node. The secondary mission objective would be to perform Bell tests for entangled photons between ground and space. We designed a compact QKD receiver payload that would be compatible with the mass, volume, power and performance constraints of a low-cost nanosatellite platform. The low-cost rapid schedule “microspace” approach of UTIAS/SFL would allow for the proposed NanoQEY mission to be developed in 2.5 years from project kick-off to launch of the spacecraft, followed by a one-year on-orbit mission.