Optics and Applied Physics

David Keith
8618 SE Petticoat Hill
Vancouver, WA 98664, USA


Optics and Applied Physics is an independent consultancy providing expertise in a wide range of applied physics technologies.  


Multiphysics modeling of complex physical systems and processes, including structural analysis, thermal analysis and heat transfer, ac/dc electrical analysis including current spreading and joule heating, and electro and magneto statics.

Optical system design and analysis, including lens design, illumination system design, physical optics, and optical power coupling.


Thermal Analysis, including computational fluid dynamics with conductive and convective heat transport, can predict the temperatures and thermal stress for various design choices.

Structural Analysis models the stress and strain distribution in simple or complex structures, large or small. Often the insight gained can be obtained by no other means.

AC/DC Analysis models current spreading and joule heating, and electro and magneto statics, which can be used to model electrical and magnetic systems and their interaction with the thermal and structural environment.

Optical Design using ZEMAX and OpticStudio optical design software allows us to design and analyze imaging and non-imaging systems, including lens design, illumination system design, polarized optics, colorimetry, diffractive optics, and optical power coupling systems.

Multiphysics Modeling

A heat exchanger

This fluid heat exchanger cools a hot circuit by placing it in thermal contact with a cold circuit by means of conduction through a shared fin structure.

The enclosure is not shown.

Hot water enters at the upper left at 90C and exits at the upper right.

Cold water enters at the lower left at 15C and exits at the lower right.

The central plate and fin structure is aluminum.

We can see from surface temperature that the fins are not working effectively.

And the graph of outlet temperatures vs coolant flow also indicates limited performance.

 Simulation results shown as surface temperatures


Cooling performance depends on coolant flow


A simple mass spectrometer

Particles are released between electrodes which form an ion gun. In the right compartment they encounter a magentic field and are bent according to their cyclotron radii.

Blue particles have the charge and mass of an electron.

Green particles have the charge of an electron but 10X the mass.

All are released with a temperature of 50K.

Beam spreading is due both to the beam temperature and to Coulomb interaction (beam crowding).


A guitar simulation

A guitar is simulated in a model which couples a solid top and back through an air cavity.

The top and back are constructed of wood, modeled as lossy elastic solids.

The back is coupled to the top by mutual coupling to the air cavity modeled with compressible fluid dynamics.

The top is driven by excitation at the bridge, as it would be by the strings.

The geometry


The frequency response to bridge excitation


The eigenmode at 267 Hz


The eigenmode at 544 Hz


The eigenmode at 799 Hz


The eigenmode at 923 Hz

Guitar eigenmode 923.png

Optical Design

A specialized projection lens

This projection lens was designed to project the image formed on a subminiature LCOS imager onto a nearby surface.

Telecentric in object and image space

4X Magnification

Diffraction limited


A miniature wide angle lens for an IR camera

This camera lens was designed to be compatible with a common imaging device.

All elements are molded glass.

120 degrees full field of view

Diffraction limited


A Petzval lens for a flat field astronomical telescope

This telescope lens was designed to be compatible with a common imaging device.

Flat field, apochromatic design with low-dispersion glass

75mm aperture


Spot radius optimized for the imager


An Optical Coupler from an LED Die to 50µm Fiber

This coupler was designed as part of an SMT transmitter component.

Die-mounted ball lens

Package-mounted ball lens

Design optimized for manufacturing tolerance

Provides a quantitative estimate of coupling


An Optical Coupler from an Laser Die to 200µm Fiber

This coupler was designed to accomodate an elliptical emission pattern.

Roithner CHIP-980-P50 emits 50 mW at 980 nm with FWHM of 30 degrees on the fast axis and 13 degrees on the slow axis

The target is the 200µm core of a ThorLabs FG200LCC NA 0.22 fiber

A cruciform cylindrical lens design circularizes the beam

The first cylindrical lens is a molded asphere to accomodate the fast axis

An off-the-shelf best-form doublet focuses the beam on the fiber core


A compensated PBS for an LCOS imaging system

A double pass through a polarizing beam splitter is used as the polarizer and analyzer for a liquid crystal on silicon (LCOS) imaging system. In the diagram below, light enters from the left and is polarized by the first pass through the splitting surface. Illumination light is reflected upward to the imager and waste light proceeds to the right and exits the cube. Illumination light reflects from the imager back down to a second pass through the splitting surface. If its polarization has been rotated by the imager it will pass through the splitting surface down to the projection lens represented by the detector surface, otherwise it will reflect again and not be projected. Each pixel controls its own rays, so an image is formed.

In the case below, the imager if OFF, so no light should reach the detector below the cube. For a non-skew ray this would be true, but for a skew ray, the pass through the cube rotates the polarization and allows light leakage into the dark state, which greatly reduces the system contrast.

A  skew ray leaks into the dark field


A quarter wave plate placed between the cube and imager can improve the contrast by reversing in the second pass the rotation that occurs in the first. This design employs a calcite wave plate. In the first image the compensator is disabled; in the second image the compensator is enabled.

Without the compensator the contrast ratio is only 43:1


With the compensator the contrast increases to 24,800:1



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David Keith
8618 SE Petticoat Hill
Vancouver, WA 98664, USA


Spikey Created with Wolfram Mathematica 9.0