Omnidirectional mirror design with quarter-wave dielectric stacks.

Quarter-wave stacks may be designed to reflect both polarizations of a specific wavelength band at all angles of incidences (omnidirectional). Expressions are given for both the omnidirectional band center wavelength and the bandwidth for selected values of the low- and the high-refractive-index layer values. It is shown that selecting the low refractive index near 1.45 maximizes the omnidirectional bandwidth for any value of the high refractive index. It is also shown that the omnidirectional bandwidth may be extended by addition of contiguous quarter-wave stacks.

Extended-bandwidth reflector designs by using wavelets.

Optical interference coatings have been designed by using combinations of wavelets (fully apodized sine-wave refractive index groups). Like a single-line rugate filter, a single wavelet produces a stop band without harmonics and, in addition, has no sidelobes. The rules for combining wavelet refractive index structures have been derived for extended-bandwidth reflectors.

Focal-plane pixel-energy redistribution and concentration by use of microlens arrays.

A physical-optics calculation was performed to study the effects of a microlens array placed over a focal-plane detector array. In certain conditions the light is further concentrated to a spot size that is smaller than the point-spread function of the receiver optics. It is also shown that the microlens refocuses a sinc-squared point-spread function to a shape that is more uniform as well as narrower. Numerical examples were made for the far IR.

Ray tracing kinoform lens surfaces.

An exact ray trace (Snell's law of refraction) of discontinuous surfaces of kinoform lenses (surface relief lenses) is used to evaluate optical performance when used alone or when used in conjunction with conventional optical surfaces. A phase-based merit function that is generated by ray tracing is useful for the design and optimization of such systems including color correction. This ray trace approach can also explain and evaluate the dual focal length features of kinoform lens designs.

Antireflection surfaces in silicon using binary optics technology.

Binary optics processing methods were applied to a silicon substrate to generate an array of small pillars in order to enhance transmission. The volume fraction of the silicon in the pillars was chosen to simulate a single homogeneous antireflection layer, and the pillar height was targeted to be a quarter-wave thickness. A mask was generated, using a graphics computer-aided design system; reactive-ion etching was used to generate the pillars. An improvement in long-wavelength infrared transmission is observed, with diffraction and scattering dominating at shorter wavelengths.

Codeposition of continuous composition rugate filters.

Rugate filters are optical thin film interference structures with sinusoidal refractive index profiles. Two-wavelength reflection filters have been fabricated by codeposition of SiO(2) and TiO(2). Composition modulation was monitored and controlled using quartz crystal rate controllers. The resulting filters exhibited two well-defined stopbands. Microscopic examination revealed that the structure is glasslike without pronounced thin film microstructure.

Rugate filter sidelobe suppression using quintic and rugated quintic matching layers.

Sine wave rugate index profiles may be superimposed on a slowly varying average index in such a way as to reduce sidelobes over broad spectral regions and at the same time maintain the strength of the stopband reflectance.

Using apodization functions to reduce sidelobes in rugate filters.

Appending gradient-index matching regions and apodization, which is an amplitude modulation of the rugate sinusoidal index profile, are two effective means to reduce and nearly eliminate the sidelobes. When a combination of these methods is used in the rugate design, the resulting filter will have good sidelobe suppression both near to and far from the stopband and will have high reflectance in the stopband.

Maximum likelihood phase-retrieval algorithm: applications.

The maximum likelihood estimator approach is shown to be effective in determining the wave front aberration in systems involving laser and flow field diagnostics and optical testing. The robustness of the algorithm enables convergence even in cases of severe wave front error and real, nonsymmetrical, obscured amplitude distributions.

Rectangular Luneburg-type lenses for integrated optics.

Compact Luneburg-type lenses of rectangular outline as viewed from above have been made by thermal evaporation of As2S3 glass onto single-mode LiNbO(3):Ti waveguides through suitably shaped masks and subsequent exposure of the glass to ultraviolet light. The best lenses had speeds of f/5.5 at an aperture of 10 mm and focal spots at reduced aperture about 1.2 times the diffraction-limited size. These lenses have a field of view of at least 25 degrees inside the waveguide.

Gradient-index antireflection coatings.

Thin-film gradient-index profiles have been analyzed and new profiles have been synthesized for broadband antireflection coatings on dielectric surfaces. It is shown that the control of the index gradient as a design parameter can significantly enhance the performance of interference coatings.

Planar optical waveguide lens design.

Achieving diffraction-limited planar waveguide lenses is not an easy task in practice. However, conventional lens design principles (ray tracing, intercept and OPD errors, point spread functions, and optimization techniques) may be used to evaluate performance, reduce cost or complexity, and provide alignment and manufacturing tolerances. Presented here (as an example of an optimization technique) is a new diffraction-limited planar waveguide lens. It is f/1.5 and has a compact rectangular shape.

Virtual-source theory of unstable resonator modes.

A new method for understanding and calculating unstable resonator modes has been developed. It consists of propagating an initial uniform plane wave N round trips through the resonator, as in the Fox and Li [Bell Syst. Tech. J. 40, 453 (1961)] approach. The propagation, however, is performed entirely in collimated space that results from unfolding the resonator into its virtual images of the feedback mirror. In this unfolded space, the field after N round trips consists of a single plane-wave propagation plus the sum of diffracted waves from N pairs of virtual sources (for the strip-resonator case). The edge-diffraction function is determined from an asymptotic solution to the Huygens-Fresnel integral for an incident plane wave. The advantages of the method are that it is conceptually simple and numerically accurate and requires only minimal computer time.

Reflective optics for irradiance redistribution of laser beams: design.

The output irradiance of a typical unstable resonator with circular symmetry has a central obscuration and is peaked near the obscuration. A method is presented for designing two-mirror optical systems to convert this beam into a beam of arbitrary obscuration ratio and more uniform irradiance. A method is also given for analyzing the alignment sensitivity of such a system. An example shows that useful irradiance redistributions can be achieved with alignment sensitivities comparable to ordinary Cassegrain systems.

Effect of infrared coating nonuniformity on optical systems.

For precision optical systems, the focus and tilt errors caused by coating thickness nonuniformity can be a serious concern. These errors are wavelength dependent and hence cannot be compensated in an IR optical system by aligning and focusing with an auxiliary visible alignment laser. It is shown here that the coating design can be modified so as to make the aberrations caused by coating thickness nonuniformity approximately equal at the IR design wavelength and the wavelength of the auxiliary laser. In that case, focusing and alignment with an auxiliary laser can substantially correct the effect of coating nonuniformity.

Multilayer coating design achieving a broadband 90 degrees phase shift.

For nonnormal incidence angles, it has been shown that the polarization state may be controlled through the use of specially designed multilayer coatings. An optimization technique has been used to determine layer thicknesses for a coating design that produces a 90 degrees phase shift between the p- and s-polarization components over a wavelength range of Deltalambda/lambda(0) = +/-5% while maintaining high reflectivities for both components. A tolerance analysis indicates that the coating layers must be deposited within +/-1% to achieve a +/-3 degrees phase shift error over the spectral range of the design.

Mode discrimination of unstable resonators with spatial filters and by phase modification.

The effects of an intracavity spatial filter in a half-symmetric unstable bare cavity resonator have been studied using iterative propagation techniques to obtain pure l-mode resonator solutions. The results indicate that the mode-loss difference is highest when the spatial-filter radius is at the first or third dark ring of the Airy pattern at the spatial filter. Furthermore, the results are not directly dependent on the resonator-equivalent Fresnel number. Also presented are results indicating that aspherizing the feedback mirror can be done in such a way as to increase mode discrimination.