Session
Poster Session 1
Location
Salt Palace Convention Center, Salt Lake City, UT
Abstract
The Polarization-modUlated Laser Satellite Experiment (PULSE-A) at the University of Chicago aims to demonstrate the feasibility of circular polarization shift keyed (CPolSK) satellite-to-ground laser communication links. The project aims to advance high-speed optical satellite-to-ground communications as an alternative to the traditionally used radio frequencies. PULSE-A thus requires the development of a compact, low-loss optical communications terminal capable of emitting collimated and high-power circularly polarized light modulated at high frequencies. Here we present a design for an optical communications terminal capable of achieving output powers of up to 230 mW at modulation frequencies from 1 to 10 MHz with a maximum coupled pointing error of less than 1 mrad. The optical communications terminal consists of two primary interrelated paths: (1) a collection path to gather, filter, and detect a 1064 nm beacon laser from the optical ground station and (2) a transmission path to emit, modulate, and amplify an outgoing 1550 nm transmission beam. During a pass, body-pointing aims the satellite’s optical aperture towards the ground station. The collection path gathers and focuses beacon light via a Keplerian beam condenser, blocks irrelevant wavelengths with a filter stack, and focuses the remaining light onto a quadrant photodiode detector. This detector supplies feedback to a fine steering mirror, which performs slight adjustments to center the beacon on the detector. The transmission path begins with two linear, orthogonally polarized seed lasers which encode data by alternately turning ON and OFF at a frequency of 1–10 MHz. This signal is then amplified to 250 mW using a random polarization erbium-doped fiber amplifier (EDFA) and passed through a quarter wave plate to convert the signal to circular polarization states. The collection and transmission paths are combined via an 1180 nm-cutoff shortpass dichroic mirror into a single optical path as they approach the fine steering mirror (FSM). This FSM- and detector-based feedback loop, pioneered by MIT’s CLICK-A and DLR’s OSIRIS4CubeSat missions for the CubeSat form factor, allows for a simple fine-pointing scheme where when the received beacon is aimed at the center of the quadrant photodiode in the collection path, the transmission beam and the ground station beacon are co-boresight. A 638 nm beacon subassembly with a significantly wider divergence assists the optical ground station with tracking the satellite’s location throughout transmission. Structurally, the use of fiber-optic connections and a baffling system will mitigate stray light and reduce the overall volume of the communications terminal. Current development includes optical component selection, simulation in Zemax OpticStudio, and testing of fiber-optic systems and the quadrant photodiode on the bench. The optical terminal design, along with its driving requirements, simulations and testing, and our approaches to various hurdles in creating a small form factor CPolSK optical communications terminal are presented here.
Document Type
Event
Development of a Compact Optical Communications Terminal for the PULSE-A CubeSat
Salt Palace Convention Center, Salt Lake City, UT
The Polarization-modUlated Laser Satellite Experiment (PULSE-A) at the University of Chicago aims to demonstrate the feasibility of circular polarization shift keyed (CPolSK) satellite-to-ground laser communication links. The project aims to advance high-speed optical satellite-to-ground communications as an alternative to the traditionally used radio frequencies. PULSE-A thus requires the development of a compact, low-loss optical communications terminal capable of emitting collimated and high-power circularly polarized light modulated at high frequencies. Here we present a design for an optical communications terminal capable of achieving output powers of up to 230 mW at modulation frequencies from 1 to 10 MHz with a maximum coupled pointing error of less than 1 mrad. The optical communications terminal consists of two primary interrelated paths: (1) a collection path to gather, filter, and detect a 1064 nm beacon laser from the optical ground station and (2) a transmission path to emit, modulate, and amplify an outgoing 1550 nm transmission beam. During a pass, body-pointing aims the satellite’s optical aperture towards the ground station. The collection path gathers and focuses beacon light via a Keplerian beam condenser, blocks irrelevant wavelengths with a filter stack, and focuses the remaining light onto a quadrant photodiode detector. This detector supplies feedback to a fine steering mirror, which performs slight adjustments to center the beacon on the detector. The transmission path begins with two linear, orthogonally polarized seed lasers which encode data by alternately turning ON and OFF at a frequency of 1–10 MHz. This signal is then amplified to 250 mW using a random polarization erbium-doped fiber amplifier (EDFA) and passed through a quarter wave plate to convert the signal to circular polarization states. The collection and transmission paths are combined via an 1180 nm-cutoff shortpass dichroic mirror into a single optical path as they approach the fine steering mirror (FSM). This FSM- and detector-based feedback loop, pioneered by MIT’s CLICK-A and DLR’s OSIRIS4CubeSat missions for the CubeSat form factor, allows for a simple fine-pointing scheme where when the received beacon is aimed at the center of the quadrant photodiode in the collection path, the transmission beam and the ground station beacon are co-boresight. A 638 nm beacon subassembly with a significantly wider divergence assists the optical ground station with tracking the satellite’s location throughout transmission. Structurally, the use of fiber-optic connections and a baffling system will mitigate stray light and reduce the overall volume of the communications terminal. Current development includes optical component selection, simulation in Zemax OpticStudio, and testing of fiber-optic systems and the quadrant photodiode on the bench. The optical terminal design, along with its driving requirements, simulations and testing, and our approaches to various hurdles in creating a small form factor CPolSK optical communications terminal are presented here.
