Space-based optical communication links incorporating high speed photoreceivers, i.e. photodiodes integrated with Transimpedance Amplifiers (TIA), are required for multiple platforms, from low earth orbit satellite communication constellations to inter-planetary links and deep space missions. Our prior studies have demonstrated that InP/InGaAs photodiodes are resilient to radiation induced displacement and ionization damage when irradiated with a wide variety of ions. It is also necessary to qualify TIAs that may exhibit latch ups due to Single Event Effect (SEE) when irradiated with heavy ions having high Linear Energy Transfer (LET). We present a balanced InGaAs photoreceiver, i.e. a matched pair of photodiodes followed by a Silicon CMOS TIA, with automatic gain control mode that supports coherent and direct detection optical communication links with a symbol rate up to 25 Gbaud and aggregate data rate up to 100 Gbps and beyond. These devices were subjected to 76 MeV/n, 96 MeV/n, and 154 MeV/n Bismuth Ions up to a fluence of 1E7 ions/cm2 for each ion energy. The ion energies were chosen with the objective of achieving LET-Si of ⪆70 MeV-cm2 /mg. During the radiation runs, the TIAs were biased and their drive currents and RF output noise spectra were continuously recorded. The in-situ data was complemented by detailed analog and digital characterization of these devices before and after irradiation, including photodiode dark current, TIA drive current, RF response, RF return loss, noise spectrum, 25 Gbps Amplitude Shift Keyed (ASK) eye diagrams and bit error ratio, and 10.709 Gbps Return to Zero Differential Phase Shift Keyed (RZ-DPSK) eye diagrams and bit error ratio. We did not observe any significant impact on these devices due to radiation.
Multiple space applications require infra-red photodiodes, including spectroscopy, optical communication links, and rapid Doppler shift LIDAR. Extended InGaAs photodiodes with 2.4-micron cutoff wavelength have been recently shown to be resilient to irradiation with Protons, Alpha Particles, Carbon Ions, and Iron Ions for fluence levels corresponding to multi-year Low Earth Orbit, Geostationary, inter-planetary, and deep space missions. Our prior studies have shown that the radiation-induced displacement damage may lead to some elevation in photodiode’s leakage current, without significant sign of ionization damage. To further confirm this finding, these devices were subjected to Gamma rays to explicitly measure the effect of ionization damage only. We have successfully tested 290 μm diameter, 2.4-micron wavelength, Extended InGaAs photodiodes coupled with single mode fiber for gamma radiation. Three devices were cooled to dry ice temperatures (~-71° C) and subjected to two rounds of 662 keV gamma rays from Cesium-137 for 15 krad (water) for a cumulative dose of 30 krad (water). The devices were reverse biased at 100 mV and their leakage current was monitored in-situ to simulate their function as exposed to radiation in space environment. The in-situ data showed slight increase in leakage current in the presence of gamma radiation, and returned to original value once the gamma rays were turned off, thus proving the resilience of Extended InGaAs Photodiodes to ionization damage. These results were corroborated with detailed pre- and post-radiation measurements, which also demonstrated unchanged quantum efficiency and bandwidth over a wide range of operating temperatures, from -71 °C to +20 °C.
Free space coupled, InGaAs PIN + TIA Quad Photoreceivers enable multiple space applications that require differential wavefront sensing, such as gravitational wave detectors, and position sensing and tracking, for example inter-satellite optical communication links. Optical crosstalk between the individual quadrants of the 2 × 2 photoreceiver array is a key parameter that limits the position and/or direction sensing error of the system. Therefore, it is imperative to ensure low crosstalk in the quad photoreceivers throughout the mission life. We present 1 mm, 1.5 mm, and 2 mm diameter low noise Quad Photoreceivers that demonstrate crosstalk < -30 dB up to 20 MHz frequency. These devices were subjected to 100 MeV Protons and 100 MeV/n Helium Ions up to a fluence of 1 × 1010 cm-2. These tests not only validate the devices for Geostationary Orbit missions, but also for deep space missions outside of Earth’s protective magnetosphere where Galactic Cosmic Rays are a significant component of the radiation environment. All devices were found to be fully functional after radiation, and their crosstalk was essentially unchanged in all cases. Pre- and Post- radiation results were also measured for Dark Current vs. Reverse Bias Voltage for the Quad Photodiodes, DC Responsivity of the Quad Photodiodes, Conversion Gain and Bandwidth of the PIN + TIA Quad Photoreceiver, TIA Drive Current, and Input Equivalent Noise Density of PIN + TIA. Although we observed an increase in dark current due to radiation induced displacement damage in the Quad Photodiode, we did not observe any change in any other parameter for Quad Photoreceivers.
We have successfully tested simultaneously 2.4 Micron Wavelength, Extended InGaAs Photodiodes having diameters of 20, 30, 40, 50, 100, 150, 200, 250, and 290 Micron, coupled with a Single Mode Fiber using 100 MeV/n Carbon (C) Ions up to a cumulative dose of ~40 krad. During irradiation, the devices were maintained at dry ice temperature, reverse biased at 100 mV, and their leakage current was continuously monitored in-situ during the run. After the exposure was completed, all nine devices were monitored for any change in their leakage current at 100 mV and room temperature for several weeks to monitor any annealing effects that may occur. Nine Photodiodes with the above varying diameters were radiated with 100 MeV/n Carbon Ions with a fluence of 106, 107, 108, 109, and 1010 ions/cm2 at each fluence level. At 100 MeV/n the Linear Energy Transfer (LET) of Carbon Ion is ~0.156 MeV-cm2/mg in Extended InGaAs, which is an order magnitude more than Proton (H) and Helium (He) Ions of 100 MeV/n energy. Thus, significant displacement damage is anticipated in the Extended InGaAs Photodiode with 100 MeV/n Carbon Ions with a total fluence of 1 × 1010 ions/cm2 . Pre- and Post- radiation results were also measured for: (1) Leakage Current Vs. Voltage for the Extended InGaAs Photodiodes; (2) Responsivity (Quantum Efficiency) in A/W for Photodiodes; and (3) Bandwidth of the Photodiodes. All devices were found to be fully functional at the normal operating conditions and at both dry ice and room temperature. The leakage current increased up to a factor of ~2X at lower bias of 100 mV at the highest fluence of 1010 ions/cm2, but not significantly at higher bias of 2 V. We did not observe any post radiation annealing effect for leakage current at room temperature and 100 mV bias for any of the devices after several weeks of data logging.
We have successfully tested simultaneously 2.4 Micron Wavelength, Extended InGaAs Photodiodes having diameters of 20, 30, 40, 50, 100, 150, 200, 250 and 290 Micron, coupled with a Single Mode Fiber using Hydrogen (H), Helium (He), and Iron (Fe) Ions which collectively make up over 90% of the Galactic Cosmic Rays (GCR). During irradiation, the devices were maintained at dry ice temperature, reverse biased at 100 mV, and their leakage current was continuously monitored in-situ during the run. After the exposure was completed, all nine devices were monitored for any change in their leakage current at 100 mV and room temperature for several weeks to monitor any annealing effects that may occur. Nine Photodiodes with the above varying diameters were radiated with 100, 250, 500 and 1000 MeV/n Hydrogen, Helium, and Iron Ions with a fluence of 106, 107 and 108 ions/cm2 at each energy level. Pre- and Post-radiation results were also measured for: (1) Leakage Current Vs. Voltage for the InGaAs Photodiodes; (2) Responsivity (Quantum Efficiency) in A/W for Photodiodes; and (3) Bandwidth of the Photodiodes. All devices were found to be fully functional at the normal operating conditions and at both dry ice and room temperature. We did not observe any post radiation annealing effect for leakage current at room temperature and 100 mV bias for any of the devices after several weeks of data logging.
We have successfully tested 290 μm diameter, 2.4 micron wavelength, Extended InGaAs photodiodes coupled with single mode fiber using 50 MeV Protons at both dry ice temperature (-75 °C) and room temperature (20 °C). The devices were reverse biased at 100 mV during the radiation run and their leakage current was continuously monitored insitu during the exposure. These devices find multiple applications in space for spectroscopy and sensing, inter-satellite optical communication links, rapid Doppler shift LIDAR, as well as inter-planetary and Earth-to-Moon communication links. Several photodiodes were tested using 50 MeV Protons with an average flux level of 2.11 × 107 protons/cm2 /s, for a total fluence of 1.0 × 1011 protons/cm2 and total dose of 20 krad (water). Pre- and post-radiation results were also measured for leakage current vs. voltage, responsivity (quantum efficiency), and bandwidth of the Extended InGaAs photodiodes. All devices were found to be fully functional at normal operating conditions and at both dry ice and room temperature.
We have comprehensively tested uncooled, free space coupled, InGaAs Quad Photoreceivers having 0.5 mm, 1 mm, and 2 mm diameter integrated with a low noise transimpedance amplifier (TIA) using 30 MeV Protons, 100 MeV Protons, 662 keV Gamma Rays, 1 GeV/n Helium, and 1 GeV/n Iron at room temperature of ~20°C. These devices find multiple applications in space for differential wavefront sensing as part of a Gravitational Wave Observatory, as well as instrumentation and control for next generation space telescopes. The bandwidth of all receivers was 20 MHz which was TIA limited.
All 0.5 mm and 1 mm devices were found to be fully functional at normal operating conditions and at room temperature for Protons, Gamma Rays, 1 GeV/n Helium, and 1 GeV/n Iron. Only one quadrant of a 2 mm InGaAs Quad had hard failure due to 1 GeV/n Helium Ions; otherwise it too survived all other radiation tests. Detailed test results follow in the manuscript including recommendations for future space flights. These radiation test results, combined with the earlier successful mechanical shock and vibration testing mean these devices have passed preliminary testing for space qualification.
We have successfully tested 5 to 8 GHz bandwidth, uncooled, Extended InGaAs 2.2 μm wavelength, linear optical receivers, coupled with single mode fibers for 30 MeV Protons, Gamma rays, 1 GeV/n Iron ions, and 1 GeV/n Helium ions. These devices find multiple applications in outer-space for coherent rapid Doppler shift LIDAR, long wavelength gravitational wave sensing, as well as inter-planetary and Earth-to-Moon coherent communication links. Nine devices comprising of Extended InGaAs 2.2 μm PIN photodiode (PD) and GaAs transimpedance amplifiers (TIA), coupled with single mode fibers, were tested with 30 MeV protons, three each with fluence levels of 4.9 × 1010 cm-2 , 9.8 × 1010 cm-2, and 1.6 × 1011 cm-2 . Three more devices were tested using 1.4 ♦ 108 Helium ions/cm2 at 1 GeV/n over a six minute exposure for a dose of 20 rad (water). Three additional devices were exposed to 1 GeV/n Fe fluence of 2.8 × 105 ions/cm2 for half a minute delivering a dose of 6 rad (water). Another three Extended InGaAs PD and GaAs TIA fibered devices were tested using Cesium-137 gamma rays of 662 keV for 15 krad (water). Pre- and post-radiation results were measured for (1) dark current vs. voltage for the InGaAs photodiodes, (2) responsivity (quantum efficiency) for the photodiodes, (3) optical return loss for the photodiodes, (4) TIA drive current, (5) bandwidth of the PIN + TIA, (6) conversion gain of the PIN-TIA, and (7) Bit Error Ratio (BER) of the PIN-TIA for 10.709 Gbps NRZ-ASK signal. All devices were found to be fully functional at normal operating conditions and at room temperature. All these efforts will advance the Technology Readiness Level (TRL) of these devices by year 2020.
We have successfully tested 10 GHz bandwidth, uncooled, linear InGaAs optical receivers, coupled with a standard single mode fiber for proton and gamma rays. These devices find multiple applications in space for inter-satellite optical communication links, rapid Doppler shift lidar, as well as inter-planetary and Earth-to-Moon communication links. Nine InGaAs PIN photodiode and GaAs transimpedance amplifiers (TIA) were irradiated with 100 MeV protons with a fluence level of 1.6 × 1011 cm-2 corresponding to a total dose of 19.1 krad (water). Devices were also subjected to 30 MeV protons, six each with fluence levels of 4.9 × 1010 cm-2 , 9.8 × 1010 cm-2 , and 1.6 × 1011 cm-2 . Additionally, another nine InGaAs optical receivers were irradiated with 662 keV gamma rays, three devices each for a dose of 15 krad (water), 30 krad (water), and 50 krad (water). Pre- and post-radiation results were measured for (1) dark current vs. voltage for the InGaAs photodiodes, (2) responsivity (quantum efficiency) for the photodiodes, (3) optical return loss at 1550 nm wavelength, (4) drive current of the TIA, and (5) bandwidth of the PIN + TIA. All devices were found to be fully functional at the normal operating conditions and at room temperature.
We have developed ultra-low noise quadrant InGaAs photoreceivers for multiple applications ranging from Laser Interferometric Gravitional Wave Detection, to 3D Wind Profiling. Devices with diameters of 0.5 mm, 1mm, and 2 mm were processed, with the nominal capacitance of a single quadrant of a 1 mm quad photodiode being 2.5 pF. The 1 mm diameter InGaAs quad photoreceivers, using a low-noise, bipolar-input OpAmp circuitry exhibit an equivalent input noise per quadrant of <1.7 pA/√Hz in 2 to 20 MHz frequency range. The InGaAs Quad Photoreceivers have undergone the following reliability tests: 30 MeV Proton Radiation up to a Total Ionizing Dose (TID) of 50 krad, Mechanical Shock, and Sinusoidal Vibration.
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