Stray Light Analysis

Increasing demands on sensitivity, dynamic range, and the precision of modern optical systems bring with them an unwelcome guest: stray light. Stray light is unwanted radiation that destroys image contrast and image quality, causes errors in radiometric measurements, and sometimes even damages expensive optical components or detectors. Ghosts, veiling glare, and thermal emissions can keep an instrument from meeting its performance specifications. BRO engineers are respected worldwide as leaders in stray light analysis. A BRO stray light analysis identifies the root causes of stray light, and focuses attention on design changes that do the most good.

BRO performs stray light analyses and designs baffles for space instruments, satellites, laboratory instruments, and commercial optical products. We calculate stray light backgrounds from scatter and ghost reflections off optical components; scatter and glints from baffles, vanes, struts, and spiders; diffraction around edges and apertures; and thermal radiation. With help from BRO, you can expect improved system performance, reduced development cycles, and reduced costs in engineering time and hardware prototyping. Your optical device will perform as expected.

A BRO Stray Light Analysis:

• Identifies the largest stray light paths
• Calculates their absolute and relative contributions
• Determines if a system meets its requirements
• Recommends design enhancements to improve system performance

The Most Advanced Optical Software

ASAP® Optical Software was developed in-house to meet the unique challenges of stray light analysis. Accurate and fast stray light calculations cannot be done with simple brute-force Monte Carlo calculations. That is why ASAP uses directed scatter methods to send scattered light towards the areas of most interest.

Key ASAP Features used in Stray Light Analysis Projects:

• ASAP calculates stray light from scatter
• ASAP models scatter within three-dimensional geometries
• ASAP uses realistic BRDF models
• ASAP calculates stray light from ghosts
• ASAP does diffraction calculations
• ASAP calculates thermal irradiance

We are Experienced

BRO has been doing stray light analyses for over 20 years and has completed over 200 stray light projects, including the Infra-Red Astronomy Satellite (IRAS), SIRTF, ISO, MERIS, Galileo, Cassini, and ESA’s X-Ray Mirror Module Telescope (XMM). In fact, BRO’s first contract was a stray light analysis of the Hubble Space Telescope. BRO increased Hubble’s ability to “see” by a factor of 100,000. We’ve been helping people manage light ever since.

Illumination Systems

Illumination design spans a number of systems, from sources (bulbs and LEDs) to generic applications (luminaires and lightpipes) to specific applications (photocopiers, headlamps, and backlit LCD displays). BRO has extensive experience in the design of all types of illumination systems. System modeling can predetermine desired characteristics such as efficiency, spatial distribution of light (irradiance), and angular distribution of light (intensity), taking into account the specialized optical properties of all structures. Our team can also build prototypes and assist in fabricating the final system. BRO knows illumination systems. Here are some examples.

Backlit Displays

BRO designs, analyzes, and improves the performance of backlit displays. The three primary aspects of optical displays are the light source, the transfer optics, and the display itself. BRO is experienced in all of these areas. We can design light sources, utilizing sources from CCFLs to OLEDs. BRO engineers optimize transfer optics, maximizing battery longevity, minimizing heat, and creating the smallest package possible. And we are able to pair products with their ideal display screens.

Headlamps

BRO has experience in all areas of headlamp design, including smooth and faceted reflectors. In addition to illumination standards maintained by the Society of Automotive Engineers (SAE) and international organizations such as ECE, subjective performance issues and aesthetic design must be taken into account. BRO’s engineers have completed many innovative headlamp designs for off-road vehicles, automobiles, and aircraft.

Lightpipes

Lightpipes can appear deceptively simple. Typically made of plastic, the lightpipe directs light from a source to a distinct output aperture. In reality, it is quite difficult to achieve even illumination. The experts at BRO know how to efficiently design a system that will attain the illumination you desire. BRO has designed lightpipes for numerous applications, including interior automotive and aircraft lighting, medical lighting, and consumer appliance illumination.

Sources

BRO can model virtually every type of light source, from incandescent bulbs, to arc sources, to LEDs. We can assist in the development of novel bulbs, and the analysis and improvement of sources currently in your products. Our modeling process takes into account the complete source geometry.

Coherent/Diffractive Systems

From interferometers to fiber coupling, lasers to optical switches, BRO’s engineers are experienced in the fields of coherent and diffractive optics. Using BRO’s optical software, ASAP, we investigate such phenomena as diffraction, interference, polarization, and birefringence. BRO’s engineers have mastered the increased complexity of adding coherent propagation to their models. A single model can combine free-space light propagation, Gaussian Beam Decomposition for guided wave propagation, and a unique finite difference Beam Propagation Method (BPM) for photonics calculations.

Experienced in Coherent and Diffractive Engineering

BRO’s engineers have worked on a variety of projects containing coherent optics including laser printers, laser scanners, diffractive systems, optical switches, fiber coupling, interferometers, and other engineering design problems where the wave nature of light matters. Whether you require a basic or complex optical system, you will get the same dedication from BRO’s engineering team.

Most Advanced Optical Software

BRO’s engineers use ASAP optical analysis software for their coherent work. ASAP is extremely accurate, fast, and contains necessary tools to help get the physics right.

Key ASAP Features used in Coherent/Diffractive Systems Design

• Gaussian Beam Propagation method in ASAP allows users to model plane and spherical wave fronts, Hermite-Gauss laser modes, or arbitrary user-defined fields, and propagate them through the optical system.
• ASAP models coherent optical interference effects, so you can visualize and analyze optical systems that utilize coherent illumination.
• BPM makes it relatively easy to transition from the “bulk optics” realm to smaller waveguides, evanescent couplers, fiber branches, and splitters.

Optical Systems Engineering

With increasingly complex optical systems the norm in the marketplace, BRO engineers are the ones to turn to for optical system design. We provide a systems-engineering approach with full electrical, mechanical, and software engineering integration capabilities to deliver design solutions that work in the real world.

BRO designs all kinds of optical systems-LCD projectors and displays, imaging systems, scanners, micro-structures, micro-optical devices, lithography systems-just about any application where light needs to be managed. We lead a team of optical, mechanical, and electrical engineers to develop product prototypes. Through our quality system, we document design, analysis, drawings, test plans, and work instructions, which can be given directly to you, or to your designated manufacturing firm.

An Experienced Team

BRO’s customers appreciate our engineers’ broad experience and diverse professional backgrounds. When you engage BRO Engineering Services as your development team, you get a group of professionals who have helped integrate optics into virtually every kind of product.

Optical Systems for Everyday and Extraordinary Products

Whatever your product, we can help create a high-efficiency optical system that works for you. BRO’s engineers have worked on projects in the bio-photonics industry, the aerospace and defense industries, the electronics industry, and many others. We work with you or your engineering team to develop a system that meets your expectations and budget.

Source Modeling

Generating a source for an optical model is complex and time consuming. It is also critical to the accuracy of the results. BRO excels in the art of creating accurate source models. Our engineering team has done extensive source modeling for the BRO Light Source Library. We have also modeled many custom fluorescent, LED and arc-lamp sources to customer specifications as part of a larger optical system.

BRO Source Models are Special

BRO source models vary from other source models in that we include the source geometry. Emissivity changes and self-obscuration effects are carefully modeled so that the resulting lamp output gives an excellent match to the manufacturer’s published intensity data. Lamp bases, filaments, electrodes, glass envelopes, and any other element of the lamp geometry that could interact with the rays are included with appropriate optical transmissive, reflective, or scattering characteristics. When creating incandescent sources, rays are generated from detailed models of the emitting filaments. These details are essential for accurate ray tracing, since reflections can pass back through the bulb geometry from elsewhere in the optical system.

Source Tolerancing

For those customers interested in tolerancing their illumination systems, we can help. We will create multiple variants on any source throughout a user-defined tolerance box. You define either a tolerance box with the number of tolerance-testing models you want, or specific instructions for making each variant model. The variant models are delivered in library file format (compatible with ASAP), each with an associated help file describing the modifications made to the filament. This tolerancing service makes it possible for illumination system designers to further test virtual prototypes before going to the physical prototype stage.