TECHNOLOGY AREA(S): Air Platform, Electronics

ACQUISITION PROGRAM: PMA264 Air ASW Systems

OBJECTIVE: Develop a photo-receiver device with high quantum efficiency, low noise, and high dynamic range, and that is optimized for operation in the blue-green region of the electromagnetic spectrum.

DESCRIPTION: Light Detection and Ranging (LIDAR) has proven to be an effective remote sensing technique of the oceans and atmosphere [Ref 1]. The Navy has a strong interest in exploiting this type of sensor to better understand its operating environment. Profiling LIDAR works by emitting a short duration packet of photons and detecting the echo returns from scatter along the path of the emission. Attenuation and geometrical spreading loss results in a large disparity of photons as a function of arrival time. The temporal signature of the LIDAR return follows a decaying exponential over many decades. The ability to resolve range and magnitude information from the scatters over long distances or attenuation lengths requires a large dynamic range and very sensitive detectors that can faithfully reproduce an exponentially decaying photo-signal. Furthermore, large variations in backscatter intensity necessitate use of gating techniques.

Photomultiplier Tubes (PMTs) have been very effective detectors for LIDAR. They are large area detectors with high gain (greater than 60 dB) and bandwidths (greater than 500 MHz); and are nearly ideal current sources with linear responses over many orders of magnitude and noise figures near unity. They can be gated with fast recovery time and minimal ringing. However, they tend to have lower than desired quantum efficiency.

Avalanche photodiodes (APDs) based on Gallium Phosphide (GaP) have been investigated as replacements for PMTs. These detectors can be made with high gain and little excess noise by using the avalanche process. Semiconductor detectors can be less expensive and more robust than PMTs. Recently recessed-window/mesa-structure GaP APDs with low dark currents (< 1 pico-Amp) and high quantum efficiency (70% at 445 nm) have been reported [Ref 2]. However, APDs tend to have signal-induced artifacts, such as after-pulses or long decay constant tails that limit instantaneous dynamic range.

The proposer is encouraged to present novel approaches to maximize the quantum efficiency, dynamic range performance, and noise figure of a photo-detector receiver operating in the blue-green wavelength region.

The performance objectives of the photo-receiver are:
1.� Dynamic range (100 nanoseconds after stimulus): Threshold > 4 orders of magnitude, Goal > 5 orders of magnitude
2.� Quantum Efficiency: Threshold > 50%, Goal > 70%
3.� Intrinsic gain: Threshold >100, Goal >1000
4.� Coupling: single ended DC
5.� Analog bandwidth: >50 MHz
6.� Dark current: Threshold <1 nano-Amp, Goal < 1 pico-Amp
7.� Active area: threshold > 0.5 square centimeter, Goal > 1 square centimeter
8.� Peak wavelength response: 460-490 nm
9.� Optical damage threshold: 100 micro-Joules in 30 ns (>3000 W peak power)
10.� Gate recovery time: Threshold <50 nanoseconds, Goal <5 nanoseconds
11.� Ruggedize: System must withstand the shock, vibration, pressure, temperature, humidity, electrical power conditions, etc. encountered in a system built for airborne use [Ref 3]
12.� Reliability: Mean time between equipment failure�300 operating hours.
13.� Production Unit Cost: Threshold < $10,000 (10's of units); Objective <$1,000 (100's of units)

PHASE I: Determine a design for a photo-receiver device and an approach to achieve the desired performance specified by the requirements identified in the Description. Provide modeling or small-scale test results to validate approach. The Phase I effort will include prototype plans to be developed under Phase II.

PHASE II: Design, fabricate, and demonstrate a prototype photo-receiver and control electronics. Test and fully characterize the system prototype. Optimize gating circuit and analog gain stages.

PHASE III DUAL USE APPLICATIONS: Miniaturize and finalize the design suitable for an externally mounted, aircraft-mounted sensor pod or internally mounted sensor for small aerial vehicles. Fabricate a ruggedized system solution and assist with certification for flight on a NAVAIR R&D aircraft. Provide low-rate production capabilities. Provide testing and analysis of system performance. High Quantum efficiency photodetectors have broad range of applications in areas such as remote sensing LIDAR, Radar, Radiometry, and free-space communications. Oceanographic bathymetry systems for survey and exploration work, in particular, would benefit greatly from this effort.

REFERENCES:

1. Dion McIntosh, Q. Z.� �High quantum efficiency GaP avalanche photodiodes.� Optics Express, 2011, Vol. 19, No. 20.� https://www.osapublishing.org/oe/fulltext.cfm?uri=oe-19-20-19607&id=222690

2. �What is LIDAR?� NOAA, 2013.� https://oceanservice.noaa.gov/facts/lidar.html

3. MIL-STD-810G, DEPARTMENT OF DEFENSE TEST METHOD STANDARD: ENVIRONMENTAL ENGINEERING CONSIDERATIONS AND LABORATORY TESTS (31 OCT 2008), Section 2, p514.6C1 � 514.6C22, p516, http://everyspec.com/MIL-STD/MIL-STD-0800-0899/MIL-STD-810G_12306/

KEYWORDS: High Quantum Efficiency; Photodetector; PMT; APD; LIDAR; Optical Receiver