N15A-T011 TITLE: Low Level Visible-Light Photo Detectors for Laser Range Finding

TECHNOLOGY AREAS: Sensors, Electronics, Battlespace

ACQUISITION PROGRAM: PEO IWS 2, Above Water Sensors, AN/SPQ-9B Program Office

OBJECTIVE: Develop a highly sensitive photo detector to improve laser range finding with eye-safe levels of visible laser light at operational distances.

DESCRIPTION: The Navy is seeking to develop a highly sensitive photo detector to improve laser range finding with eye-safe levels of visible laser light at operational distances. Laser range finding is a proven technique, but for distances relevant to a Fleet battle group, the transmitted laser power must be high. This is normally not a problem if the laser wavelength is in the infrared and the power is kept below the thermal damage level. However, operational considerations require that this effort utilize visible wavelengths and the transmitted laser power must be kept below the absolute eye-safe level.

In the future, naval sensors, for example those used by radar and Electronic Warfare (EW) systems, will be networked together to increase performance capabilities well above that of individual sensors acting alone. This is true for sensors located on the same ship and for sensors located throughout a battle group. Effective sensor netting will depend on obtaining precise distances between ships and the ships� relative velocities (both speed and bearing). Laser ranging is a possible means to obtain and monitor such position and velocity data in real time (Ref. 1). However, shipboard laser systems must be eye safe, especially when the intention is to "target" friendly vessels (Ref. 2). Therefore, laser transmitter power is restricted when used for such purposes and the sensitivity of the receiver becomes the key variable in the system design.

Avalanche photodiodes (APDs) are the most sensitive photo detectors commercially available and lend themselves to this task (Ref. 3, 4). Future operational concepts will require more sensitive laser detection than the current state-of-the-art APDs. Expanding operational coverage and operation in poor conditions will always demand more sensitivity of any such sensor. This effort seeks to develop an innovative photo detector sensor that detects low light level visible laser light with an order-of-magnitude improvement in sensitivity over existing APDs, making the use of laser ranging systems possible at increased operational distances. Without a sufficiently sensitive photo detector, safety concerns will preclude development of a viable system.

The innovative photo detectors must be capable of absolute sensitivity (the lowest incident power level detectable), and fast response times. There are photo detector technologies, such as photo multipliers, which are far more sensitive than APDs; however, they typically have relatively slow response characteristics. The laser range finding systems envisioned as recipients of this technology will employ extremely short pulse modulations with high repetition rates for the basic range finding function, and accommodate embedded communications. These systems will incorporate pulse and amplitude modulation; therefore, rise time, fall time, and linearity are key attributes of photo detectors developed under this effort. Performance must be an inherent function of the device for range detection in real time. Methods that require integration (within a single pulse, or for multiple pulses), specific modulation schemes, or rely on significant post-detection signal processing are not of interest.

Finally, the sensor�s detection wavelength is required to be in the visible band for operational reasons and to preclude interference with existing systems utilizing the infrared bands. The minimum threshold for detectable power should therefore be as low as possible to allow the transmitting laser to be eye-safe at the transmission aperture. Although exact measures of utility are hard to quantify, detector operation at 10 km with the eye-safe transmission requirement may be taken as the minimum performance threshold of interest with much farther detection ranges as a goal. In any case, an order-of-magnitude increase in detection performance is the desired result.

PHASE I: The company will define and develop a concept for an improved photo detector sensor for laser range finding that meets the requirements as stated in the topic description. The company will demonstrate the feasibility of the concept in meeting Navy needs and will establish that the concept can be developed into a useful product for the Navy. Device testing, analysis and/or modeling will establish feasibility.

PHASE II: Based on the results of Phase I and the Phase II contract statement of work, the company will develop a prototype photo detector for evaluation. The prototype will be evaluated to determine its capability to meet Navy requirements for a photo detector sensor for laser range finding. System performance will be extrapolated based on prototype device evaluation using modeling or analytical methods over the required range of parameters relevant to range finding over long distances with eye-safe visible lasers in a maritime environment. Evaluation results will be used to refine the prototype into a design that will meet Navy requirements. The company will prepare a Phase III development plan to transition the technology to Navy use.

PHASE III: The company will support the Navy in transitioning the photo detector sensor technology for Navy use. The company will develop a photo detector sensor for laser range finding according to the Phase III development plan for evaluation in order to determine its effectiveness in an operationally relevant environment. The company will support the Navy for test and validation to certify and qualify the device for Navy use.

PRIVATE SECTOR COMMERCIAL POTENTIAL/DUAL-USE APPLICATIONS: The device developed under this effort will have multiple uses (for example, commercial, scientific as well as military). Laser range finding is used in a variety of commercial applications such as surveying. Laser measurement of position is used in the construction and scientific instrumentation industries. There will be potential to translate technology developed under this effort to other wavelength bands (infrared) where additional applications are abundant. Additionally, the pulse modulation requirements of this technology make it suitable for various line-of-sight communication applications.

REFERENCES:
1. Ruiz, Antonio Ramón Jiménez and Granja, Fernando Seco "A Short-Range Ship Navigation System Based on Ladar Imaging and Target Tracking for Improved Safety and Efficiency", IEEE Trans. Intelligent Transport Systems 10 March 2009: pp. 186-197.

2. Wilkins, Gary D. "Eye-Safe Free-Space Laser Communications", Proc. IEEE 1996 National Aerospace and Electronics Conf. 2, May 1996: pp. 710-715.

3. Achouche, M, et al. "InGaAs Communication Photodiodes: From Low- to High-Power-Level Designs", IEEE Photonics Journal 2 June 2010: pp. 460-468.

4. Tsng, Chih-Kou, et al. "A High-Speed and Low-Breakdown-Voltage Silicon Avalanche Photodetector", IEEE Photonics Technology Letters 26 March 2014: pp. 591-594.

KEYWORDS: Photo detectors; laser range finding; eye-safe lasers; laser detection; laser pulse modulation; avalanche photodiode

** TOPIC AUTHOR (TPOC) **

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