Marta C. de la Fuente

Novel fast catadioptric objective with wide field of view

Using the Simultaneous Multiple Surface method in 2D (SMS2D), we present a fast catadioptric objective with a wide field of view (125°×96°) designed for a microbolometer detector with 640×480 pixels and 25 microns pixel pitch Keywords: Infrared lens design, thermal imaging, Schwarzschild configuration, SMS2D, wide field of view, driving cameras, panoramic systems

SMS-based optimization strategy for ultra-compact SWIR telephoto lens design.

A new optical design strategy for rotational aspheres using very few parameters is presented. It consists of using the SMS method to design the aspheres embedded in a system with additional simpler surfaces (such as spheres, parabolas or other conics) and optimizing the free-parameters. Although the SMS surfaces are designed using only meridian rays, skew rays have proven to be well controlled within the optimization. In the end, the SMS surfaces are expanded using Forbes series and then a second optimization process is carried out with these SMS surfaces as a starting point. The method has been applied to a telephoto lens design in the SWIR band, achieving ultra-compact designs with an excellent performance.

Low-cost wavefront coding using coma and a denoising-based deconvolution

Wavefront coding (WFC) is a powerful hybrid optical-numerical technique for increasing the depth of focus of imaging systems. It is based on two components: (1) an optical phase element that codifies the wavefront, and (2) a numerical deconvolution algorithm that reconstructs the image. Traditionally, some sophisticated optical WFC designs have been used to obtain approximate focus-invariant point spread functions (PSFs). Instead, we present a simple and low cost solution, implemented on infrared (IR) cameras, which uses a decentred lens inducing coma as an adjustable and removable phase element. We have used an advanced deconvolution algorithm for the image reconstruction, which is very robust against high noise levels. These features allow its application to low cost imaging systems. We show encouraging preliminary results based on realistic simulations using optical PSFs and noise power spectral density (PSD) laboratory models of two IR imaging systems. Without induced optical phase, the reconstruction algorithm improves the image quality in all cases, but it performs poorly when there are both in and out-of-focus objects in the scene. When using our coding/decoding scheme with low-noise detectors, the proposed solution provides high quality and robust recovery even for severe defocus. As sensor noise increases, the image suffers a graceful degradation, its quality being still acceptable even when using highly noisy sensors, such as microbolometers. We have experienced that the amount of induced coma is a key design parameter: while it only slightly affects the in-focus image quality, it is determinant for the final depth of focus.

GASIR 1: a promising material for dual waveband systems

There is an increasing interest in multispectral systems that provide spectral coverage in multiple wavebands. In particular two-color detection in the infrared can improve target and signature discrimination with important system benefits in terms of weight and cost. Nowadays dual waveband FPA detectors have achieved a development level enough to consider this kind of systems a reality. As a consequence there is a need of optical systems able to provide superior performance over two wavebands simultaneously while maintaining mono waveband systems volume, weight and element count.

Ultracompact SWIR telephoto lens design with SMS method

In this work, we propose two new optical structures, using the Simultaneous Multiple Surfaces (SMS) method, comprised of 2 reflecting surfaces and 2 refracting surfaces, 800mm focal length, f/8 (aperture diameter 100 mm) and 1.18° diagonal field of view in the SWIR band. The lens surfaces are rotational symmetric and calculated to have good control of non-paraxial rays. We have achieved designs with excellent performance, and with total system length of less than 60 mm.

Solid Catadioptric telephoto lens design with SMS method

Two new optical structures are designed using the Simultaneous Multiple Surfaces (SMS) method, comprised of 2 reflecting surfaces and 2 refracting surfaces, 800mm focal length, f/8 (aperture diameter 100 mm) and 1.180 diagonal field of view in the SWIR band. The lens surfaces are rotational symmetric and calculated to have good control of non-paraxial rays. We have achieved designs with excellent performance, and with total system length of less than 60 mm.

Impact of the 2D structured noise in the post-processing of hybrid optical-digital imaging systems

The effect of the 2D structured noise on the post-processing of images in hybrid optical-digital imaging systems is studied on the basis of the Wiener restoration filter. 2D structured noise is modeled as an additive noise that has the same random value along a row or a column in the image. The restoration is carried out with the Wiener filter in an unsupervised way by the use of well established procedures to determine the filter constant as a function of the noise power. We show that the classical Wiener filter is not satisfactory for the case of systems affected by 2D noise and we conclude that this is caused by an overdetermantion of the 2D noise in the procedure to find the filter constant. From this conclusion we propose a new filter based on the separability of the Optical Transfer Function of the optical system that depends on two constants, one for each principal direction of the 2D noise. Furthermore, we define a procedure for the unsupervised determination of these constants and we evaluate the quality of the restoration obtained by this procedure.

Pupil aberrations control in fish-eye lens with diffractive surfaces

Optical design for fish-eye lenses usually includes a front meniscus lens that reduces the angles of incidence of chief rays towards the rest of the optics. However it also introduces distortion of the pupil, both shape and position. Thus, pupil aberration are one of the most relevant problems when designing this type of lenses. This paper shows the relationships between image and pupil aberrations and describes the design of MWIR fish-eye lenses that include diffractive surfaces in order to properly control entrance pupil size. The design goal is to achieve a constant pupil area over the field of view.

Front Matter: Volume 8550

This PDF file contains the front matter associated with SPIE Proceedings Volume 8550, including the Title Page, Copyright Information, Table of Contents, and the Conference Committee listing.

MWIR zoom with focal extender

This paper describes the design of a 3-5microns 26:1 zoom with a focal length extender capability that increases NFOV focal length by 1.75x. Mechanical restrictions for a payload envelope will be considered as well as cold stop efficiency issues.