Guangning Yang

Comparison of linear-mode avalanche photodiode lidar receivers for use at one-micron wavelength

Silicon avalanche photodiode (APD) detectors have been used in most space lidar receivers to date with a sensitivity that is typically hundreds of photons per pulse at 1064 nm, and is limited by the quantum efficiency, APD gain noise, dark current, and preamplifier noise. We have purchased and tested InGaAs avalanche photodiode based receivers from several US vendors as possible alternatives. We present our measurement results and a comparison of their performance to our baseline silicon APD. Using a multichannel scalar instrument, we observed undesired dark counts in some devices, even though the APDs were biased below the breakdown voltage. These effects are typically associated with over-biased Geiger-mode photoncounting, but we demonstrate that the probability distribution indicates their necessity at the high gains typically associated with operation slightly below the breakdown voltage. We measured the following parameters for our 0.8 mm diameter baseline silicon APD receiver: excess noise factor 2.5, bandwidth 210 MHz, minimum detectable pulse (10 ns) in incident photons 110 photons, noise equivalent power 30 fW/rt-Hz. We present our test procedures and results for the InGaAs based APD receivers.

Laser transceivers for future NASA missions

NASA is currently developing several Earth science laser missions that were recommended by the US National Research Council (NRC) Earth Science Decadal Report. The Ice Cloud and Land Elevation Satellite-2 (ICESat-2) will carry the Advanced Topographic Laser Altimeter System (ATLAS) is scheduled for launch in 2016. The Active Sensing of CO2 Emissions over Nights, Days, and Seasons (ASCENDS) mission and will measure column atmospheric CO2 concentrations from space globally. The Gravity Recovery And Climate Experiment (GRACE) Follow-On (GRACEFO) and GRACE-2 missions measure the spatially resolved seasonal variability in the Earths gravitational field. The objective of the Lidar Surface Topography (LIST) mission is to globally map the topography of the Earths solid surface with 5 m spatial resolution and 10 cm vertical precision, as well as the height of overlying covers of vegetation, water, snow, and ice. This paper gives an overview of the laser transmitter and receiver approaches and technologies for several future missions that are being investigated by the NASA Goddard Space Flight Center.

Photon Detectors with Large Dynamic Range and at Near Infrared Wavelength for Direct Detection Space Lidars

Space-based lidar instruments must be able to detect extremely weak laser return signals from orbital distance. The signals have a wide dynamic range caused by the variability in atmospheric transmission and surface reflectance under a fast moving spacecraft. Ideally, lidar detectors should be able to detect laser signal return pulses at the single photon level and produce linear output for multiple photon events. They should have high quantum efficiency in the nearinfrared wavelength region where high-pulse-energy space-qualified lasers are available. Silicon avalanche photodiode (APD) detectors have been used in most space lidar receivers to date. Their sensitivity is typically hundreds of photons per pulse at 1064 nm, and is limited by the quantum efficiency, APD gain noise, dark current, and preamplifier noise. NASA is investigating photon-sensitive near-infrared detectors with linear response for possible use on the next generation direct-detection space lidars. We have studied several types of linear mode avalanche photodiode detectors that are sensitive from 950 nm to 1600 nm and potentially viable for near term space lidar missions. We present our measurement results and a comparison of their performance.

HgCdTe Avalanche Photodiode Detectors for Airborne and Spaceborne Lidar at Infrared Wavelengths

We report results from characterizing the HgCdTe avalanche photodiode (APD) arrays developed for lidar at infrared wavelengths by using the high density vertically integrated photodiodes (HDVIP®) technique. The results show >90% quantum efficiencies between 0.8 μm and the cut-off wavelength, >600 APD gain, near unity excess noise factor, 6-10 MHz electrical bandwidth and <0.5 fW/Hz1/2 noise equivalent power (NEP). The detectors provide linear analog output with a dynamic range of 2-3 orders of magnitude at a fixed APD gain without averaging, and over 5 orders of magnitude by adjusting the APD gain settings. They have been used successfully in airborne CO2 and CH4 integrated path differential absorption (IPDA) lidar as precursors for use in space lidar.

Photon-counting detectors for space-based laser receivers

Photon-counting detectors are required for numerous NASA future space-based laser receivers including science instruments and free-space optical communication terminals. Silicon avalanche photodiode (APD) single photon counting modules (SPCMs) are used in the Geoscience Laser Altimeter System (GLAS) on Ice, Cloud, and land Elevation Satellite (ICESat) launched in 2003, currently in orbit measuring the Earth surface elevation and atmosphere backscattering. To measure cloud and aerosol backscattering, the SPCMs detect the GLAS laser light at 532-nm wavelength, with quantum efficiencies of 60 to 70% and maximum count rates greater than 13 million per second. The performance of the SPCMs has been monitored since ICESat launch on January 12, 2003. There has been no measurable change in the quantum efficiency, linearity or after-pulsing. The detector dark counts rates monitored while the spacecraft was in the dark side of the Earth have increased linearly at about 60 counts/s per day due to space radiation damage. As the ICESat mission nears completion, we have proposed ground-to-space optical and quantum communication experiments to utilize the on-orbit 1-meter optical receiver telescope with multiple SPCMs in the focal plane. NASA is preparing a follow-on mission to ICESat, called ICESat-2, with a launch date of late 2014. The major candidate photon-counting detectors under evaluation for ICESat-2 include 532 nm and 1064 nm wavelength-sensitive photomultiplier tubes and Geiger-mode avalanche photodiode arrays. Key specifications are high maximum count rate, detection efficiency, photon number resolution, radiation tolerance, power consumption, operating temperature and reliability. Future NASA science instruments and free-space laser communication terminals share a number of these requirements.

High-precision ranging and range-rate measurements over free-space-laser communication link

We present a high-precision ranging and range-rate measurement system via an optical-ranging or combined ranging-communication link. A complete bench-top optical communication system was built. It included a ground terminal and a space terminal. Ranging and range rate tests were conducted in two configurations. In the communication configuration with 622 data rate, we achieved a two-way range-rate error of 2 μm/s, or a modified Allan deviation of 9×10-15 with 10 second averaging time. Ranging and range-rate as a function of Bit Error Rate of the communication link is reported. They are not sensitive to the link error rate. In the single-frequency amplitude modulation mode, we report a two-way range rate error of 0.8 μm/s, or a modified Allan deviation of 2.6×10-15 with 10 second averaging time. We identified the major noise sources in the current system as the transmitter modulation injected noise and receiver electronics generated noise. A new improved system will be constructed to further improve the system performance for both operating modes.

Photon-counting detectors for space-based applications

Photon-counting detectors are required for numerous NASA future space-based applications including science instruments and free-space optical communication terminals. We discuss the baseline and alternative photon counting detectors that are under evaluation for deployment on the Ice, Cloud and land Elevation Satellite-2 (ICESat2) Advance Topographic Laser Altimeter System (ATLAS). Future NASA science instruments and free space laser communication terminal receiver performance can be improved by using single-photon-sensitive detectors. Photomultipliers and avalanche photodiodes are the primary candidates. Single-photon-sensitive detectors provide efficient receivers that minimize the required space-based resources (size, weight, power and cost).

Development of high-sensitivity SWIR APD receivers

Emerging short wavelength infrared (SWIR) LIght Detection And Ranging (LIDAR) and long range laser rangefinder systems, require large optical aperture avalanche photodiodes (APDs) receivers with high sensitivity and high bandwidth. A large optical aperture is critical to increase the optical coupling efficiency and extend the LIDAR sensing range of the above systems. Both APD excess noise and transimpedance amplifier (TIA) noise need to be reduced in order to achieve high receiver sensitivity. The dark current and capacitance of large area APDs increase with APD aperture and thus limit the sensitivity and bandwidth of receivers. Spectrolab has been developing low excess noise InAlAs/InGaAs APDs with impact ionization engineering (I2E) designs for many years and has demonstrated APDs with optical gain over 100 utilizing multiple period I2E structures in the APD multiplier. These high gain I2E APDs have an excess noise factor less than 0.15. With an optical aperture of 200 μm, low excess noise multiple periods I2E APDs have capacitances about 1.7 pF. In addition, optical gains of InAlAs based APDs show very little temperature dependence and will enable APD photoreceivers without thermal electric cooling.

GHz low noise short wavelength infrared (SWIR) photoreceivers

Next generation LIDAR mapping systems require multiple channels of sensitive photoreceivers that operate in the wavelength region of 1.06 to 1.55 microns, with GHz bandwidth and sensitivity less than 300 fW/√Hz. Spectrolab has been developing high sensitivity photoreceivers using InAlAs impact ionization engineering (I2E) avalanche photodiodes (APDs) structures for this application. APD structures were grown using metal organic vapor epitaxy (MOVPE) and mesa devices were fabricated using these structures. We have achieved low excess noise at high gain in these APD devices; an impact ionization parameter, k, of about 0.15 has been achieved at gains >20 using InAlAs/InGaAlAs as a multiplier layer. Electrical characterization data of these devices show dark current less than 2 nA at a gain of 20 at room temperature; and capacitance of 0.4 pF for a typical 75 micron diameter APD. Photoreceivers were built by integrating I2E APDs with a low noise GHz transimpedance amplifier (TIA). The photoreceivers showed a bandwidth of 1 GHz and a noise equivalent power (NEP) of 150 fW/rt(Hz) at room temperature.

Innovative free space optical communication and navigation system with high data rate communication, precision ranging, range rate measurements, and accurate spacecraft pointing

We report an innovative free Space optical communication and navigation system which provides high data rate communication, precise measurements of spacecraft ranging, range rate, and accurate spacecraft pointing. A complete breadboard system was built. It includes both space and ground terminals. Along with 622MBPS data link, two way ranging were conducted. 23μm ranging and 23μm/s range rate accuracies were achieved in 1 second integrating time. These ranging performance is not sensitive to the communication error rate. The high ranging and range rate accuracies were achieved through the relative phase measurement of transmit and receive clock with Dual Mixer Timer Difference measurement apparatus.