An extensive design study was conducted to find the best optimal power distribution and stop location for a 7.5x afocal zoom lens that controls the pupil walk and pupil location through zoom. This afocal zoom lens is one of the three components in a VIS-SWIR high-resolution microscope for inspection of photonic chips. The microscope consists of an afocal zoom, a nine-element objective and a tube lens and has diffraction limited performance with zero vignetting. In this case, the required change in object (sample) size and resolution is achieved by the magnification change of the afocal component. This creates strict requirements for both the entrance and exit pupil locations of the afocal zoom to couple the two sides successfully. The first phase of the design study looked at conventional four group zoom lenses with positive groups in the front and back and the stop at a fixed location outside the lens but resulted in significant pupil walk. The second phase of the design study focused on several promising unconventional four-group power distribution designs with moving stops that minimized pupil walk and had an acceptable pupil location (as determined by the objective and tube lens).
Discrete zoom systems are commonly used as laser beam expanders and infrared zoom lenses. The reason to design a
discrete zoom lens is that they are often a desirable compromise between fixed-focal length lenses and continuous zoom
lenses, offering many advantages to imaging systems of all types. They have the advantage over continuous zoom systems
for containing fewer elements, thus reducing the weight of the system, and having one mechanical motion instead of two.
In literature there is little information on the first order parameters and starting requirements for discrete systems. This
work derives the first order equations for two different discrete zoom systems. The equations are derived from the
requirements of first order parameters which define the starting group focal lengths. The two design configurations studied
are: one zoom group flipping in and out of the system; one zoom group moving laterally along the optical axis. This work
analyzes the first order equations for both configurations and discusses the starting point for the designs taking into
consideration system limitations. Final designs for both configurations are then compared over several parameters: group
focal lengths, lens diameters, overall length, number of elements, materials, and performance.
A design study is compiled for a VIS-SWIR dual band 3X zoom lens. The initial first order design study investigated zoom motion, power in each lens group, and aperture stop location. All designs were constrained to have both the first and last lens groups fixed, with two middle moving groups. The first order solutions were filtered based on zoom motion, performance, and size constraints, and were then modified to thick lens solutions for the SWIR spectrum. Successful solutions in the SWIR were next extended to the VIS-SWIR. The resulting nine solutions are all nearly diffraction limited using either PNNP or PNPZ (“Z” indicating the fourth group has a near-zero power) design forms with two moving groups. Solutions were found with the aperture stop in each of the four lens groups. Fixed f-number solutions exist when the aperture stop is located at the first and last lens groups, while varying f-number solutions occur when it is placed at either of the middle moving groups. Design exploration included trade-offs between parameters such as diameter, overall length, back focal length, number of elements, materials, and performance.
A design study is conducted in the 1-5μm wavelength band for an F/3, 15 degree full field of view, 38mm focal length imaging system. A survey of preferred materials shows the chromatic properties of homogeneous materials in different regions of this spectrum. A survey of GRIN materials, including zinc selenide zinc sulfide GRIN, aluminum oxynitride GRIN, and chalcogenide GRIN, expands the available chromatic properties in this spectral band. Baseline homogeneous triplet designs are explored and compared to previous studies in the literature. The inclusion of a GRIN material in the three element design improves the chromatic correction and results in a system that is nearly diffraction-limited. The three element design is reduced to two elements, where both elements are GRIN, while maintaining comparable performance to the homogeneous triplet.
This paper presents the first chip-scale demonstration of an intra-chip free-space optical interconnect (FSOI) we recently
proposed. This interconnect system uses point-to-point free-space optical links to construct an all-to-all intra-chip communication
network. Unlike other electrical and waveguide-based optical interconnect systems, FSOI exhibits low latency,
high energy efficiency, and large bandwidth density with little degradation for long distance transmission, and hence can
significantly improve the performance of future many-core chips. A 1x1-cm2 chip prototype is fabricated on a germanium
substrate with integrated photodetectors. A commercial 850-nm GaAs vertical-cavity-surface-emitting-laser (VCSEL) and
fabricated fused silica micro-lenses are 3-D integrated on top of the germanium substrate. At a 1.4-cm distance, the measured
optical transmission loss is 5 dB and crosstalk is less than -20 dB. The electrical-to-electrical bandwidth is 3.3 GHz,
limited by the VCSEL.