Barnwell, Nathan

Conklin, John

Ritz, Tyler

Serra, Paul

English

DigitalCommons@USU

Software-DefinedPrototype SetupDelay Chain Calibration and Tracking[2]Drift of the delay chain for a fixed setting through time.Delay calibration and tracking demonstrated.Bias and noise < 2 psThe delay measurement circuit is used both for initial calibration of delay chains and for compensation of delay variation due to process, radiation, voltage, temperature (PVT). The circuit records 60 samples each second. PVT Variations as fast as 1 Hz can be measured.Bit Error Rate20 MHz, 20 ns guard time, based on current calibration error and random string jitter.Calibration errors 𝜺𝒄𝒂𝒍 = 120 ps are achieved. The objective is 𝜺𝒄𝒂𝒍 =  10 ps.Integrated, Software-Defined Pulse Modulator and Laser System for Small Satellite Optical CommunicationPaul Serra, Nathan Barnwell, Samantha Parry, Tyler Ritz, John Conklinpserra@ufl.edu, jwconklin@ufl.eduOverviewMotivationPulsed optical communication systems have different characteristics compared to CW systems:• Lower power consumption• Lower data throughput• Higher range with non-linear detection• Can provide ranging with time of flight, can pass through some cloudsApplications:Ranging, Time-of-Flight experiment, LIDAR, Optical communicationsMiniature Optical Communication Transceiver• Size, Weight and Power within 0.5 U, ~10 W, 2 kg • Data throughput is expected to be between 10 Mb.s-1 to 100 Mb.s-1Pulse Position ModulationTime is cut in slots. Data is encoded in the time between pulses: the symbol sent is the one with a pulse. Achievable slot size depends on timing accuracy. A guard time is inserted to mask dead time in electronics and laser systems.𝑫𝑴−𝑷𝑷𝑴 =𝒅𝒂𝒕𝒂 𝒑𝒆𝒓 𝒑𝒖𝒍𝒔𝒆𝒕𝒊𝒎𝒆 𝒑𝒆𝒓 𝒑𝒖𝒍𝒔𝒆=𝐋𝐨𝐠𝟐𝑴𝑴𝝉 + 𝑻𝒈Software-Defined Pulse ModulatorThe modulator is fully implemented within the FPGA. The only external component is the clock. Since it is based on timestamps, not slots, the modulation is flexible.Calibration circuit[1]A pair of phase lock loops, commanded by a control system, generates a clock signal of period 𝑻𝒗𝒂𝒓. When 𝑻𝒗𝒂𝒓 is equal to the delay under test, the arbiter returns a high bit half of the time. The control system adjusts 𝑻𝒗𝒂𝒓 to maintain a ratio of Ones/Total of 50%, and records the value of 𝑻𝒗𝒂𝒓 over time.Pulse Modulator4 PPM Demonstration, Stacked Random Strings20 MHz, 4PPM, 20 ns guard10 ns by div., more than 1000 samples4 possible symbols at 20 MHz → 40 Mb.s-15 ns pulses are emitted in 5 ns time slots, equivalent slot clock of 200 MHz.32 PPM Demonstration, Stacked Random Strings20 MHz, 32 PPM, 5 ns guard5 ns by div., more than 1000 samples32 possible symbols at 20 MHz → 100 Mb.s-15 ns pulses are emitted in 930 ps time slots, equivalent slot clock of >1 GHzNoise with Random Strings20 MHz, 32 PPM, 20 ns guard1 ns by div, more than 1000 samplesRandom Jitter + Symbol-to-Symbol crosstalk: 200 ps max, ~70 ps standard deviationThe order of modulation is limited by calibration. Slot sizes down to 300 ps could be achieved with a high precision receiving channel, enabling 32 or even 64-PPM.Future MissionCLICK (Cubesat Laser-com Infrared Cross linK) is a mission combining a UF PSSL modulator with an optical system provided by MIT StarLab. Its goal is to establish a laser communication cross-link in orbit and demonstrate ranging capabilities.Seed Laser DriverFLASHE (Fast Laser Advanced Switching High-Frequency Emitter)~100s ps laser diodes pulse driver, designed for low jitter, low symbol-to-symbol crosstalk, max extinction ratio, capable of gain-switching. 20 ns guard time.Principle of operationCurrent from the anode source can be shorted to ground or forced through laser.>300 mA pulses shorter than 1 ns demonstrated. Fine pulse width control.Optical Output20 MHz, 5 ns pulses. 5 ns by div.AcknowledgmentsThis work is funded by NASA ECF Grant NNX14AO53Gand NASA STP Grant NNX16AT13AThanks to Daniel Raible from NASA Glenn Research CenterReferences[1] Serra, P., Barnwell, N., Ritz, T., Conklin, J. 2016. “Deep Space Laser Communication Transmitter and High Precision Timing System for Small Satellites,” Proceedings of the AIAA/USU Conference on Small Satellites, Technical Session VII: Communications, SSC16-VII-1. http://digitalcommons.usu.edu/smallsat/2016/TS7Communication/1/.[2] Serra, P., Conklin J. 2017 “On-Chip System for Fast, High Range, High Precision Measurements of Delays”, IEEE Trans. Instr. Meas., Under review.Current SourceBias adjustmentGaN FETSwitchFET BufferGaN FETSwitchFET BufferCh 3Ch 1Ch 2Ch 1Ch 2Ch 3𝑃1𝐸𝑃1𝐸𝑃𝐺𝑜𝑜𝑑𝑃2𝐸𝑃2𝐸𝜎~jitterτ𝜖cal10 2 3 0 2 3M = 44 65 71M = 8Tg Tgττ = slot widthTg = guard timeClockCSACModulatorFlash FPGAPulsed SeedDFB LaserAmplifierEDFADataPulses1550 nmPhoto Credit: University of Florida team  high altitude balloon flight photo at the S.H.O.T. workshop hosted by UC BoulderClock Counter Delay Chain Delay ChainPVT Compensation / CalibrationPPMDataPulseFPGA𝑻𝒗𝒂𝒓Launcher Delay Chain Delay Chain ArbiterCounter Total Counter OnesPhase Lock Loop Phase Lock Loop ClockControl systemPVT Comp.Calibration

Integrated, Software-Defined Pulse Modulator and Laser System for Small Satellite Optical Communication

https://digitalcommons.usu.edu/cgi/viewcontent.cgi?article=3737&amp;context=smallsat

Integrated, Software-Defined Pulse Modulator and Laser System for Small Satellite Optical Communication

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