The CubeSat Laser Infrared CrosslinK mission is a joint Massachusetts Institute of Technology (MIT), University of Florida (UF), and NASA Ames Research Center effort to develop laser communications (lasercom) transceivers. The terminals demonstrate full-duplex intersatellite communications and ranging capability using commercial components to enable future large constellations or swarms of nanosatellites as coordinated distributed sensor systems.CLICK will demonstrate a crosslink between two CubeSats that each host a < 2U lasercom payload. Range control is achieved using differential drag in Low Earth Orbit (LEO), with attitude controlled using a three-axis reaction wheel assembly and attitude sensors, including star trackers.The lasercom terminals are direct-detect and rate scalable, designed to achieve a 20 Mbps crosslink at ranges from 25 km to 580 km and operate full-duplex at 1537 nm and 1563 nm with 200 mW of transmit power and a 14.6 arcscecond (0.07 milliradian) full width half max (FWHM) beamwidth. The terminals also use a 976 nm, 500 mW, 0.75 degree FWHM beacon and a quadcell for initial acquisition, and a low-rate radio crosslink for exchanging orbit information.The payload transmitter is a master oscillator power amplifier (MOPA) with fiber Bragg grating for pulse shaping and MEMS fast steering mirror (FSM) for fine pointing, modeled after the MIT Nanosatellite Optical Downlink Experiment. The transceiver leverages UF's Miniature Optical Communications Transmitter (MOCT) including a chip-scale atomic clock (CSAC). The receiver implements both a time to digital converter (TDC) as well as pulse recovery and matched filtering for precision ranging.

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Optical communication is becoming more prevalent in orbit due to the need for increased data throughput. Nanosatellites, which are satellites that typically weigh less than 10 kg, are also becoming more common due to lower launch costs that enable the rapid testing of technology in a space environment. Nanosatellites are cheaper to launch than their larger counterparts and may be a viable option for communicating beyond Earth’s orbit, but have strict Size,Weight, and Power (SWaP) requirements. The Miniature Optical Communication Transceiver (MOCT) is a compact optical transceiver designed to provide modest data rates to SWaP constrained platforms, like nanosatellites. This paper will cover the optical amplifier characterization and simulated performance of the MOCT amplifier design that produces 1 kW peak power pulses and closes three optical links which include Low Earth Orbit (LEO) to Earth, LEO to LEO, and Moon to Earth. Additionally, a benchtop version of the amplifier design was constructed and was able to produce amplified pulses with 1.37 W peak power, including a 35.7% transmit optics loss, at a pump power of 500 mW. Finally, the modulator, seed laser, amplifier, receiver, and time-to-digital converter were all used together to measure the Bit Error Ratio (BER), which was 0.00257 for a received optical peak power of 176 nW.

Free-space optical communication (FSOC) systems require precise pointing, acquisition, and tracking to send and receive optical beams for effective operation. In a lens-assisted beam steering (LABS) system, light is steered by controlling the emission location in a focal plane. The emitted light is directed into the scene by a lens, like a camera but operating in reverse. In this paper, we demonstrate a novel free-space optical communications link using a micro-opto-electro-mechanical-system (MOEMS) based photonic integrated circuit (PIC) for LABS between multiple receive locations. The MOEMS PIC operates via selective electrical actuation of an array of small grating switches (30 µm x 30 µm footprint, 100 µm pitch). Data rates up to 10 Gbps and a 3 dB optical bandwidth covering the infrared C and L bands (1530 nm to 1625 nm) are measured over a 1 m free-space link distance. Eye diagrams indicate a quality communications link for data rates up to 10 Gbps and bit-error-rates < 10 -10 are measured for on-off keying (OOK) modulation. A measured beam profile is propagated into the far-field via simulation, and used to calculate link budgets for example CubeSat crosslink and downlink scenarios. Link budget calculations indicate potential > 1 Gbps CubeSat FSOC crosslinks for link lengths > 1000 km and 1 W of input optical power, using identical 90 mm transmit and receive apertures and a commercially-available fiber-coupled InGaAs avalanche photodiode (APD) receive detector.

Laser crosslinks can provide high data rate communications and precision time transfer and ranging, using low size, weight, and power (SWaP) terminals to enable constellations of small satellites. The CubeSat Laser Infrared CrosslinK (CLICK) mission will demonstrate terminals capable of conducting fullduplex, high data rate crosslinks and enabling high precision ranging on 3U CubeSats in low Earth orbit (LEO). An initial risk reduction mission, CLICK-A, will demonstrate a downlink of at least 10 Mbps to a 28 cm aperture optical ground station. CLICK-B and CLICK-C will follow to demonstrate laser crosslinks with data rates of at least 20 Mbps over separation distances ranging from 25 km to 580 km. The CLICK-B/C mission will also demonstrate precision ranging better than 50 cm. Key to achieving these capabilities are the performances of the transmitter and fine pointing, acquisition, and tracking (PAT) system. We present results from recent testing and characterization of the transmitter and PAT subsystems. The testing of the transmitter includes confirming the output power and modulation of the seed laser and semiconductor optical amplifier (SOA) and characterizing the output pulse shape. For the PAT system, testing focuses on characterizing the noise of the quadrant photodiode used for the closed-loop, fine PAT sequence. This testing was conducted using a dedicated hardware-in-the-loop testbed with an optical test setup. CLICK-A is expected to launch no earlier than May 2022 for deployment from the International Space Station (ISS) in June 2022, while CLICK-B/C is anticipated to launch in late 2022.

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Constellations of CubeSats will benefit from high data rate communications links and precision time transfer and ranging. The CubeSat Laser Infrared CrosslinK (CLICK) mission intends to demonstrate low size, weight, and power (SWaP) laser communication terminals, capable of conducting full-duplex high data rate downlinks and crosslinks, as well as high precision ranging and time transfer. A joint project between the Massachusetts Institute of Technology (MIT), the University of Florida (UF), and NASA Ames Research Center, CLICK consists of two separate demonstration flights: the initial CLICK-A, which will demonstrate a space-to-ground downlink and serve as a risk-reduction mission, and CLICK-B/C, a crosslink demonstration mission.The CLICK payloads each consist of laser transceivers and pointing, acquisition, and tracking (PAT) systems, and will fly on 3U CubeSat buses from Blue Canyon Technologies to perform their optical downlink and crosslink experiments in low Earth orbit (LEO). We present an update on the status of both the CLICK-A and CLICK-B/C payloads. At the time of writing, the final assembly and testing of the CLICK-A payload has been completed and the payload has been delivered for integration with the spacecraft bus. The final testing included the validation of the transmitter and the PAT system, the performance of both of which was characterized under various environmental test conditions and shown to meet their requirements for operation on orbit. On CLICK-B/C, the payload electronics have been designed and are under test. The optical bench of the payload has been assembled, the characterization of which is ongoing.