Although coating design software is now quite powerful there are still certain filter designs that benefit from having good starting configurations. This is particularly true when more that two materials are used in the design or when filters function at several angles of incidence. We show in this paper that it is often possible to supply sufficiently good starting designs for the optimization by applying some general principles and having the computer supply the details. This pre-optimization step is accomplished through software specifically designed for particular classes of applications. An example is given for the design of a short wave pass filter that eliminates a harmonic and a dispersion-induced half wave hole in the pass region. Another example uses this design approach for an edge filter operating over a wide angular range.
An inhomogeneous refractive index layer that follows a specific quintic (fifth-order polynomial) profile that smoothly matches the two-media interface is known to drastically reduce the nominal Fresnel reflection at this interface. There is so short wavelength cutoff for a quintic (or quintic-like) layer, as the reflectance continues to decrease with decreasing wavelength. Thus the quintic matching layer is a semi-infinite band antireflection coating. Furthermore, at the long wavelength end of the spectra the reflectance never rises above that of the Fresnel reflection at the bare interface, a feature not shared by multilayers optimized over specific bandwidths. A scaling relationship that relates the long wave cutoff of the total optical thickness of the quintic layer needed for a given reflectance level and for a given difference in media refractive index is described. For example, a quintic layer whose optical thickness is two waves or four halfwaves (at the longest wavelength of the band) will reflect at least four orders of magnitude less than the reflectance of the bare interface for all lower wavelengths. This paper also compares a quintic layer which is inhomogeneous to a needle-optimized multilayer design.
Efficient coupling of high power lasers to optical fibers is desired for many applications. An example of these applications is the medical market, where coherent optical power delivered through fibers is used to perform state-of- the-art surgery. We report an efficient method for coupling optical energy from a laser-diode bar to a fiber. This method uses a single surface collimator combined with a two- surface optical transformer. An array of corrector lenses was used to assure that the output of the collimator was appropriately incident on the transformer. Optical efficiency of the collimator, after AR coating, is about 85 percent. The gratin design of the transformer is based on 4- phase level binary optics blazed grating with minimum feature size of 1.5 micrometers . Test results indicate that all the design aspects of our collimator and optical transformer are as expected, and experimental data are well within theoretical expectations. The average tested diffraction efficiency of the optical transformer is as high as 72 percent for one surface. Considering standard 0.8 micrometers process, the efficiency of the transformer for one surface can increase to > 92 percent. To our knowledge, this is the first practical demonstration of the optical transformer concept. These results demonstrate a low-cost and reliable method for efficient coupling of high power laser arrays to fibers for medical and industrial applications.
A gradient-index coating design that incorporates broadband antireflection, narrowband reflection, and graded absorbing regions is described. The coating is suitable for deposition on reflective substrates such as diamond-turned aluminum or on glass substrates where a spectrally selective reflector with no transmission is required. Theoretical designs and measured performance are presented.
This paper proposes that wavelet construction of the gradient-index refractive index be used to design optical interference coatings. The basic wavelet used is a localized apodized rugate. By incorporating scaled and shifted copies of the basic wavelet, which are other elements of a basis set according to wavelet theory, a variety of interference coatings can be designed.
We report the development of binary optic microlens arrays in GaAs. The application of this microlens array is for (gamma) -hardening of HgCdTe focal plane arrays. We intend to reduce the effective spot size of the picture elements and provide significant nuclear hardening for the focal plane array by considerable volume reduction of the detector elements. The microlens design is an eight-phase level approximation to an ideal kinoform lens. The lenses are designed to focus into the GaAs or air with a focal length of 480 micrometers or 148 micrometers respectively, at (lambda) equals 9 micrometers . Arrays of square lenses and individual circular lenses were fabricated. The square lens dimensions and f-numbers are 120 micrometers X 120 micrometers , f/1.23; 240 micrometers X 240 micrometers , f/0.62; and 480 micrometers X 480 micrometers , f/0.31, respectively. Designs include correction for spherical aberration. A set of four 10X projection masks was designed using graphic language (GPL) interfaced to computer-generated binary optics elements. The binary optic pattern was etched into the 3'' diameter GaAs substrate by reactive ion etching. Highly anisotropic etch profiles were obtained with feature heights in excess of 2 micrometers . Measured microlens efficiency for f/1.23 microlenses was as high as 60. The average measured value for a whole array was 55. Measurement of the point spread function at (lambda) equals 10.6 micrometers demonstrates optical concentration. This demonstration of binary optic microlenses in GaAs is of considerable importance to the future integration of purely optical and optoelectronic functions on a single wafer.
An exact raytrace (Snell''s law refraction) of the discontinuous surfaces of kinoforms (surface relief lenses) can explain their optical performance at different wavelengths without diffraction. A phase-based merit function generated by raytracing can be used to design and optimize systems containing both kinoform and conventional optical surfaces.