Linear variable filters have become a common way to impart wavelength selectivity into optical systems with a minimum of optical elements. Measuring the filter in the presence of steep spectral-spatial gradients is the primary difficulty in characterizing these filters, requiring a small aperture beam resulting in a corresponding loss of signal power. We will discuss our approach to mapping the spectral and spatial distribution of these parts as well as a method to specify these filters. We will also suggest methods to calibrate and align the filters onto a detector, camera or chip.
Deep space optical communication is a highly efficient alternative to radio frequency (RF) technology offering higher data bandwidths. The challenge is that deep space optical communication is photon limited. Rejection of extraneous light is critical to maximizing signal quality. High transmitting, ultra-narrow bandpass filters with high out of band optical density (OD) can meet this requirement while improving signal throughput. Design trade-offs and fabrication results are presented for ultra-narrow bandpass filters with bandwidths as narrow as 0.2 nm full width half maximum (FWHM) with on-band transmission greater than 95% and off band rejection of greater that OD 5. Filters are designed to match laser wavelengths in the region of 1550 nm.
High efficiency solar conversion requires collection of a broad spectrum of wavelengths from the ultra-violet into the infrared. Solar collector mirrors must provide high reflection across this spectral band without degrading over time. This work presents the results of a high-performance 200 mm parabolic mirror coated with an ultra-wide broadband dielectric reflector. The mirror was developed to demonstrate high efficiency broadband solar collection and power conversion. Mirror reflection was measured within the limits of NIST capabilities, and averaged over 99.65% from 400 to 1800 nm with an acceptance angle of 30°. Plasma-assisted reactive magnetron sputtering was used to produce these high density and environmentally stable films. These hard oxide films can be repeatedly cleaned in the field. Salt spray, humidity and angle performance results are presented.
Narrow band-pass optical interference filters are used for a variety of applications to improve signal
quality in laser based systems. Applications include LIDAR, sensor processing and free space
communications. A narrow band width optical filter allows for passage of the laser signal while rejecting
ambient light. The more narrow the bandwidth, the better the signal to noise. However, the bandwidth
of a design for a particular application is typically limited by a number of factors including spectral shift
over the operational angles of incidence, thermal shift over the range of operating temperature and, in
the case of laser communication, rejection of adjacent laser channels. The trade-off of these parameters
can significantly impact system design and performance. This paper presents design and material
approaches to maximize the performance of narrow bandpass filters in the infrared.
Ultra-narrow band pass filters are used to maximize LIDAR range and sensitivity. Alternate designs and measured fabrication results are presented for sub-nanometer band pass filters down to quarter nanometer bandwidths with 95% transmission. Thermal and angle sensitivity have been minimized. The filters are fabricated using dual source, plasma assisted magnetron sputtering. Single and multi-cavity designs are presented.