Holger Mönch

Optimised Light Sources for Projection Displays

The fast developments in projection display technology require a corresponding development of short arc lamps. Arc length and high luminance determine light collection rather than lamp power. The new UHP lamps combine highest brightness, extremely long life and system compactness.

P-81: Source Imaging Goniometer Method of Light Source Characterization for Accurate Projection System Design

By collecting data containing both the spatial and angular characteristics of the light emitted from a short arc light source, a set of rays may be created in optical design software that accurately predicts the performance of the light source in a projection system.

Analysis of single-mode efficiency of electrically pumped VECSELs

We present a model and results of simulations and experiments investigating the L-I characteristics of electrically pumped (EP-) VECSELs in the single- and multi-mode regime. In our model we use a mode expansion ansatz to treat the electromagnetic field inside the VECSEL cavity. The eigenmodes of the passive cavity are computed using the bidirectional beam propagation method (BDBPM) to solve the Helmholtz equation. The BDBPM allows us to account for the complex refractive index distribution within the semiconductor heterostucture, composed of approximately thousand interfaces along the optical axis in addition to lateral refractive index variations in oxide-confined devices as well as the macroscopic external cavity. We simulate the time evolution of the modal powers of several transverse modes and the spatial distribution of the inversion carriers in the quantum well plane. Therefore we solve an differential equation system composed of multimode rate equations and the carrier diffusion equation. With this ansatz we are able to identify cavity geometries suitable for single-mode operation assuming typical current profiles that are taken from photoluminescence measurements of the devices under investigation. Furthermore, we identify effects limiting the single-mode efficiency, such as poor gain and mode matching, reabsorption in unpumped regions of the quantum wells or enhanced carrier losses due to strong spatial hole burning. Critical parameters of the equations, such as optical losses, injection effciency, carrier recombination constants and gain parameters are obtained from experiments, microscopic models and literature. The simulation results are compared to experimental results from EP-VECSELs from Philips Technologie GmbH U-L-M Photonics.

Optical Modes in a Rectangular VCSEL Resonator With Properties of Both Gaussian and Fourier Modes

We present the optical modes of a vertical-cavity surface-emitting laser resonator with a large Fresnel number in one direction, and a small Fresnel number in the other direction. The modes show properties of both the well-known Gaussian modes in lasers with a small Fresnel number and the modes of the Fourier type, which have been observed in lasers with a large Fresnel number. Also simultaneous oscillation of two modes near threshold and a higher-order mode in the direction of the small Fresnel number is observed experimentally.

Optical components and optical systems for VCSEL diode laser systems

Abstract High power vertical-cavity surface-emitting laser (VCSEL) arrays can be used as a versatile illumination and heating source. They are widely scalable in power and offer a robust and economic solution for many new applications with moderate brightness requirements. The use of VCSEL arrays for high power laser diode applications enables multiple benefits: full wafer level production of VCSELs including combination with micro-optics; assembly technologies allowing large synergy with LED assembly thus profiting from the fast development in solid state lighting; outstanding reliability and a modular approach on all levels. With the use of μ-lenses, the described optical principle of near field imaging and superpositioning of many thousands of VCSELs gives perfect control over intensity distribution and is inherently robust. With a slightly modified approach, lines of any desired length can be built from modules of 1-cm length and are therefore scalable for a wide range of applications.

Invited Paper: UHP‐lamp systems for projection applications

— Projection systems have found widespread use in conference rooms and other professional applications during the last decade and are now entering the home-TV market with considerable pace. Projectors as small as about one liter are nowadays able to deliver a screen flux of several thousand lumens and are, with a system efficacy of more than 10 lm/W, the most-efficient display system realized today. Because such highly efficient projectors employ microdisplays as light valves, short-arc lamps are a key component in realizing these properties. The introduction of the UHP-lamp system by Philips in 1995 can be identified as one of the key enablers for the commercial success of projection systems. The ultra-high-performance (UHP) lamp concept features outstanding arc luminance, a well-suited spectrum, long life, and excellent flux maintenance. For the first time, it combines a very-high-pressure mercury-discharge lamp having an extremely short and stable arc length with a regenerative chemical cycle that keeps the discharge walls free from blackening, leading to lifetimes of over 10,000 hours. In this review, the most important aspects of the UHP concept that enabled its success in the projection market are described, followed by a discussion of some recent additions to the UHP-product portfolio.