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Development of longwave infrared tunable laserline rejection filters

Description:

 
 

TECHNOLOGY AREA(S): Electronics

The technology within this topic is restricted under the International Traffic in Arms Regulation (ITAR), which controls the export and import of defense-related material and services. Offerors must disclose any proposed use of foreign nationals, their country of origin, and what tasks each would accomplish in the statement of work in accordance with section 5.4.c.(8) of the solicitation.

OBJECTIVE: To develop longwave infrared tunable laserline rejection filters for uninterrupted enhanced force protection and situational awareness.

DESCRIPTION: There is a need to develop tunable notch or laserline rejection transmission filters operating in the longwave infrared (LWIR) spectral region to protect and allow uninterrupted operation of the LWIR sensors. Such a filter will efficiently block a single or multiple discrete wavelength band(s), while transmitting light in the rest of the spectral region. Currently, there are a number of optical filters: bandpass, high-pass, low-pass, etc., available for various applications in optics, imaging, spectroscopy, etc. Such tunable filters include acousto-optic tunable filters (AOTFs), liquid crystal tunable filters (LCTFs), Fabry-Perot filters, etc. that operate over many spectral regions. Existing filter technology is inadequate for notch filtering application since these filters transmit only a narrow band of light and reject the rest of the light in the spectral region. Therefore, novel compact notch filters need to be developed which will be useful in applications where a tunable intense light source or laser is used for a specific task and the operator and the environment need to be protected from the intense radiation.

The primary goal of the current SBIR is to develop a tunable LWIR notch filter capable of rejecting greater than 90% of IR light at the notch, while maintaining a greater than 90% transmission in the rest of the LWIR spectral region. A filter linewidth of less than 200 nm is preferred with an optical power handling of 200-500 mW with an acceptance angle close to ± 27 degree over less than an inch clear aperture. Proposed notch filter designs should clearly include an efficient mechanism for dissipating the absorbed or reflected optical energy at the notch wavelength. An electrical or optoelectronic tuning mechanism should be preferred. Materials should not be limited to traditional optical materials; instead exploitation of compatible material platforms suitable for operation in the LWIR spectral range is encouraged. Ability of the chosen material to dissipate the required optical power and operate under standard military specification should be addressed. The proposed designs should be both polarization and vibration insensitive with no-moving-parts. Fabrication techniques needed to realize proposed filter designs should be clearly defined in the Phase I effort. The device size should be less than one cubic inch and per unit cost should be close to $500.00.

PHASE I: Feasibility study for design and analysis of a tunable LWIR notch filter capable of rejecting greater than 90% of IR light at the notch, while maintaining a greater than 90% transmission in the rest of the 8-12 µm LWIR spectral region. A filter linewidth of 200 nm or smaller is preferable with an optical power handling of 200-500 mW with an acceptance angle of ± 27 degree over less than an inch clear aperture. These filters should be both polarization and vibration insensitive. The deliverables shall include a detailed design and simulation results for a tunable optical notch filter along with preliminary experimental characterization results for an early prototype filter.

PHASE II: Fabrication and demonstration of prototype tunable LWIR notch transmission filters which are polarization insensitive with close to an inch clear aperture with an acceptance angle of ± 27 degree and continuous electronic tuning of optical notch across the LWIR spectral region (8 – 12 micron). Tuning of the notch across the optical spectrum must be achieved at greater than 60 Hz with the smallest possible size. The filter should be capable of rejecting greater than 90% of IR light at the notch, while maintaining a greater than 90%transmission in the rest of the 8-12 µm spectral region. The expected deliverables are at least two fully operational prototype tunable LWIR notch transmission filters. Also, potential commercial and military transition partners for a Phase III effort shall be identified.

PHASE III DUAL USE APPLICATIONS: Further research and development during Phase III efforts will be directed towards a final deployable design, incorporating design modifications based on results from tests conducted during Phase II, and improving engineering/form-factors, equipment hardening, and manufacturability designs to meet the U.S. Army CONOPS and end-user requirements. Manufactured LWIR tunable laserline rejection filters shall be integrated into military systems utilizing LWIR sensor technologies. Such LWIR tunable laserline rejection filters are useful for commercial applications that use the LWIR lasers for manufacturing and other industrial applications where protection of the operator and the environment is required to avoid damage from high intensity laser radiation. The LWIR tunable laserline rejection filters will provide uninterrupted enhanced force protection and day/night situational awareness. Military applications for this technology include laser safety devices for Mounted/Dismounted Ground System thermal sensors, and for thermal imaging systems on manned aircraft, unmanned aerial vehicles and unattended ground sensors. Potential commercial applications include laser protection of thermal security cameras for use in Homeland Security applications (perimeter security at airports, coastal ports, nuclear power installations) or other remote viewing scenarios where an intense laser could be used by criminals/terrorists to defeat security at range.

REFERENCES:

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  • N. Gupta, Hyperspectral imager development at Army Research Laboratory, Proc. SPIE 6940, p. 69401P-1-10, 2008.
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  • C. Moser and F. Havermeyer, Ultra-narrow-band tunable laserline notch filter, Appl Phys B 95, p. 597-601, 2009.
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KEYWORDS: longwave infrared, LWIR, tunable, transmission filter, notch filter, laserline rejection filter

 

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