Design of a 40 Watt 1.55μm uplink transmitter for Lunar Laser Communications

Abstract

A ground-based 40W 1.55μm uplink transmitter for lunar laser communications is described. The transmitter, which generates wavelength multiplexed communication and beacon signals, is implemented using four 10W spatial-diversity channels to reduce far-field atmospheric-turbulence-induced fading and facilitate high-power signal generation via parallel-spatial-combining of commercially-available EDFAs. Each transmitter channel can generate a 1 kHz modulated beacon for spatial acquisition, and a multi-rate 4-PPM communication signal at a 311 MHz slot rate with 16:1 and 32:1 duty cycles to support 38.9 Mbit/s and 19.4 Mbit/s channel rates, respectively. Details on the transmitter design, including the mitigation of optical nonlinear effects are discussed.

Multi-rate DPSK optical transceivers for free-space applications

“…The basic framework for laser wavelength control and stabilization leverages the fact that the wavelength of commercially available DFB lasers is typically a stable and well-behaved function of set current and temperature 9,20,37,38 , and ambient temperature, e.g.,  = (i set ,T set ,T amb, ). Set temperature provides an accurate power-independent tuning range, and small ambient-temperature-based wavelength-dependencies can be compensated using feed-forward digital control following the approach described in more detail below.…”

Implementation and validation of a CubeSat laser transmitter

“…The loopback receiver has utility beyond laboratory or ground-based testing, [12][13][14]16 since a variant of this receiver can be integrated into the flight design to provide a built-in self-test (BIST) functionality. With this configuration, BIST provides important diagnostic information about the health of the optical transmitter.…”

“…Therefore, power-sensitive applications with duty cycles as low as M = 1/128 (i.e., 128-PPM) that require ER > 36 dB, it is important to be able measure and optimize the peak signal output power to confirm adequate transmitter ER and EDFA gain, and ensure efficient transmitter operation. 11,12 Previously, we reported ER measurements of the source seed laser >40 dB that were collected using a swept duty cycle measurement approach.…”

“…[12][13][14] This receiver consists of a comparator-based analog front-end that converts the input analog electrical signal into digital for processing by the FPGA. A digital to analog converter (DAC) is used to generate a threshold voltage that can be adjusted to optimize the error rate.…”

The Lunar Laser Communication Demonstration: NASA’s First Step Toward Very High Data Rate Support of Science and Exploration Missions

“…Its main features were its array of four 15 cm uplink telescopes, each transmitting a 10 W replica of the uplink which was delivered via single-mode fiber (Caplan et al 2012) and tracking the downlink; its array of four 40 cm downlink telescope , each coupled via multi-mode, polarization-maintaining fiber (Grein 2011) to an array of superconducting nanowire single photon detectors (Dauler et al 2007;Willis et al 2012); a single gimbal carrying all 8 telescopes in an environmentally-controlled enclosure; and a nearby control room containing the cryogenic nanowire systems, the rest of the modem electronics and opto-electronics, the various control computers, and the local operations center.…”