In the past few years the microdisplay-based projection television market has been quickly spreading over what used to be the domain of CRT technology. The demand for larger display sizes and improved image quality, together with more accessible pricing is aggressively driving the transition to microdisplays.
The screen is the component of the projection system that directly conveys the visual information to the user, responsible for distributing the luminous energy from the light engine. However, the projection screen is far from a simple diffuser and today's performance requirements for display systems require sophisticated screens to meet the resolution, transmission efficiency, and contrast required by visual displays.
Unless coupled with some collimating optics, LED sources generally scatter with wide-angle Lambertian intensity profiles. The luminous output of such sources is not amenable to control and redistribution in an efficient manner. In this work we present the design and manufacturing of structures that are able to collect virtually all light from Lambertian LED sources and direct it towards diffusers engineered to illuminate specific regions of space in a controlled fashion. The resulting "engineered luminaire" is thus capable of highly efficient light control and can be applied to a wide variety of illumination situations such as general and architectural lighting.
Lightguide devices are commonly used in a large number of applications such as light-delivery systems, illumination, and displays. The general approach is to outcouple light from the lightguide without concern for its propagation properties within the guiding material. We introduce the concept of a lightguide with controlled numerical-aperture as it propagates within the guiding substrate and demonstrate the advantages with this approach, compared to other methods commonly used. We also demonstrate the application of our lightguide technology for general illumination with controlled light distribution and high efficiency.
We propose and demonstrate the use of Engineered Diffusers for control and distribution of LED light for general lighting applications. These diffusers are based on refractive microstructures and enable the efficient use of energy by controlling light propagation and directing it to specific regions of space. The microstructures are generally microlens-based arrays with each microlens elements individually designed to meet the desired scatter properties. In addition to light control, Engineered Diffusers can be used for RGB mixing to produce white light with variable color temperature, depending on the RGB content of the source. A single Engineered Diffuser component can be used for efficient color mixing and illumination control. We also discuss the fabrication of Engineered Diffusers by means of a single-point laserwriting method with capability to manufacture the deep refractive structures needed for LED beam shaping.
A diffractive optical element is an optical device that utilizes interference and diffraction rather than refraction or reflection, to shape an emerging wavefront. In this talk we will concentrate on the image-forming capabilities of diffractive optics.
Recent advances in single-point diamond turning and single- point laser pattern generation permit diffractive- and micro-optics components to be fabricated with optical performances approaching the theoretical limits. This improved quality is spurring active product development in a number new application areas, including head-mounted displays, laser printing systems, optical telecommunications, optical data storage, and laser projection systems.
Subwavelength structured (SWS) surfaces etched directly into different substrates provide performance equivalent to an ideal anti-reflection thin film. We report on SWS surfaces etched into silicon which present anti-reflection properties for visible light. The fabrication of the SWS component is based on a double holographic exposure of photoresist and reactive ion etching processes. At normal incidence, the reflectivity for the HeNe line is 0.02. This reflectivity measurement includes a 1 percent diffusion by the surface. Measurements of the reflectivity over the whole visible spectrum and over a wide field of view are provided.
Resonant grating filters based on 2D gratings are investigated experimentally. A two-layer structure, which consists of a uniform guiding layer and a grating layer, is used to achieve a symmetric, low-sideband resonance that is suitable for narrow-band filter applications.
Diffractive optics represents a new and fundamental optical manufacturing technology that has tremendous potential in both the government and commercial sectors. Diffractive optics technology provides system designers with new and exciting degrees of freedom for the design and optimization of precision optical systems. Using diffractive optics one can: provide color correction for projection systems using a single, economical refractive material; create aspheric wavefronts without using aspheric surfaces; eliminate the need for exotic (and expensive) flint-type materials; produce high-performance, high-numerical-aperture, lightweight optical elements; produce high performance microlens arrays; construct custom diffusers for beam homogenization and beam shaping; convert Gaussian beams to a square- aperture, flat-top beam profile, create novel polarization components and narrowband filters; athermalize optical systems; and reduce the weight, complexity and cost of optical systems--all of which are important for projection display systems. In this paper, we describe several features of diffractive optical elements that are useful for projection display applications.
Design concepts pertaining to resonant width in grating resonant filters are discussed. It is shown that the application of waveguide coupler concepts provides insight into polarization and angular/wavelength width trends.
Computationally efficient and stable implementations of rigorous coupled-wave analysis for 1D and 2D surface-relief gratings are presented. The eigenvalue problem for a 1D grating in a conical mounting is reduced to two eigenvalue problems in the corresponding nonconical mounting. The matrix in the eigenvalue problem of 2D gratings is reduced in size by a factor of two. These simplifications reduce the computation time for the eigenvalue problem by 8 to 32 times compared to the original computation time. The required computer memory is also decreased thus complicated grating diffraction problems can be solved efficiently.
The control of optical distortion is useful for the design of a variety of optical systems including those used for laser scanning. A lens used for focusing a scanned laser beam onto a flat image field with constant intensity profile must also satisfy the f-(theta) condition, i.e., the image height is proportional to the input field angle itself, so that the scan velocity across the image plane remains constant. The lens needs to be free from coma, astigmatism, and field curvature and must have a prescribed amount of distortion. We describe the design and development of a diffractive f-(theta) lens and present experimental verification of the theoretical predictions.
Diffractive optics technology offers optical system designers new degrees of freedom that can be used to optimize the performance of optical systems. For example, the zone spacing of a diffractive lens can be chosen to impart focusing power as well as aspheric correction to the emerging wavefront. The surface (or blaze) profile within a given zone determines the diffraction efficiency of the element, or in other words, determines how the incident energy is distributed among the various diffraction orders. In this review, we present the fundamental properties of diffractive lens systems that can be useful for display applications. We also review briefly the application of multi-order diffractive lenses and subwavelength structured surfaces.
Subwavelength structured surfaces have a multitude of applications. These include antireflection suppression, fabrication of polarization components, narrowband filters, and phase plates. All of these applications offer advantages over conventional components. With advances in manufacturing technologies, the fabrication of these surfaces for visible and infrared portions of the spectrum is increasingly feasible.
Diffractive (or binary) optics offers unique capabilities for the development of high- performance, low-weight optical systems for space-based sensors. The basic operating principles of diffractive optical elements along with fabrication methods suitable for production of diffractive elements for space-based applications are described. Several potential applications where diffractive optics may serve as a key technology for improving the performance and reducing the weight and cost of sensors for the Geostationary Earth Observatory will be discussed. These applications include the use of diffractive/refractive hybrid lenses for the Lightning Mapper Sensor, diffractive telescopes for narrowband imaging and subwavelength structured surfaces for antireflection and polarization control.
It is shown that waveguide lenses, input/output couplers, and beam-splitters can be achromatized using conventional components in combination with diffractive elements. Experimental results are presented which show that it is possible to obtain achromatic performance over wavelength ranges that are larger than the wavelength range associated with conventional laser diodes.
An investigation aimed at reducing chromatic variations in the performance of optical waveguide devices is described. Methods to achromatize the characteristics of integrated optics lenses, input/output couplers, and beam-splitters are presented with the goal of eliminating, or minimizing, any performance variations over a wavelength interval at least on the order of the operating range of presently available laser diode sources. It is shown that an achromatic waveguide lens can be made using a mode-index/diffractive doublet. With this approach, it is possible to cancel the longitudinal chromatic aberrations of the refractive lens with an appropriate diffractive component. Achromatic input/output couplers are described which use an external diffraction grating to correct for the angular dispersion of either prism or grating couplers. It is shown that double grating couplers can be used to obtain an achromatic wavelength range on the order of ten nanometers, and that hybrid prism/grating couplers can yield an achromatic range of several hundred nanometers. It is also shown that the angular chromatic dispersion of waveguide grating beam-splitters can be corrected using a second grating that is appropriately specified. This permits a guided optical beam to be split into two or more separate beams whose directions are independent of wavelength. These achromatic waveguide components can be combined in various configurations to reduce the wavelength sensitivity of devices such as optical disk pickup heads.
Design procedures for simple two- and three-element diffractive telescopes are described. The basic configuration for the two-element design is obtained analytically by solving design equations to set the Seidel aberrations to target values. Computer optimization is used to complete the design of the doublet and triplet telescopes. It is shown that diffraction limited performance can be obtained from these diffractive systems. 1.