Transcript 01_ECEN

ECEN 4616/5616
“Optoelectronic System Design”
MWF 1:00 → 1:50, ECCS 1B12
Instructor: Bob Cormack
[email protected]
[email protected] (faster response)
OFFICE HOURS: 11:00->12:30 MWF
“Geometrical Optics and Optical Design”
Mouroulis & Macdonald
(ISBN 0-19-508931-6)
Class Notes and other resources available at:
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Issues Specific to CAETE
(Center for Advanced Engineering + Technology Education)
This class is being recorded for use in the CU
Distance Learning program.
The microphones on your desks are always live during
class and will pick up anything you say.
I strongly encourage questions during lectures:
Ask questions when you have them – don't get left
There are no dumb questions – questions aren't
The goal is for you to learn; not to present a fixed
amount of material per class.
Please, however, limit conversation to class issues.
My Teaching Philosophy
The goal is for everyone to understand the material
presented during the course.
Everyone can get an “A”, if they learn the material.
Doing the homework problems is integral to
understanding – learning without practice is ephemeral.
Ask questions: Don't get left behind.
I'm always available after class and by appointment.
Regular office hours TBD (based on class discussion).
a) Every two weeks, with some exceptions.
b) Knowledge/calculation problems have correct answers.
c) Design problems have no unique correct answer.
One Mid Term exam, covering the first half of the course, and a final
exam mostly covering the second half of the course, with some
questions from the first half.
a) Initial “White Paper” (1-2 pages) due by mid-course.
b) Various milestone reports reflecting the design stages presented
in the course.
c) Completed project. (Essentially, the milestone reports tacked
together, if you've done it right) and a short (10 minute) oral
presentation to the class.
Homework, exams, and project all count 25% each.
Goals of the Class
1. Acquire the knowledge of how one goes about specifying and
designing optoelectronic (OE) systems.
While a single course won't make you an expert at the actual skill,
you will learn the methodology – given a design problem, you will
know how to proceed.
If you need to become expert at some point in your career, you will
know how to do it.
2. Become acquainted with a variety of OE systems, including
classical systems and systems involved in current research.
Knowing how diverse problems have been solved in the past is a
key to efficiently solving current problems.
What is an Optoelectronic System?
“A system which transmits, processes, stores (in
any combination) data which is sometimes carried
via light (or other electromagnetic waves) and
sometimes as electronic signals.”
That's pretty general, and perhaps not too useful, so
examples of OE systems are:
Imaging Systems: Cameras, microscopes, telescopes,
etc. Systems are designed differently for electronic output
or the Human eye.
Communication Systems: Using light to transport
Computational Optics Systems: Using computer
processing to supplement (or replace) some of the tasks of
the optics. There is leading-edge research at CU on
various aspects of this:
Extracting 3D information from 2D images.
“Super-resolution” imaging – imaging of fluorescent
molecular structure at a very small fraction of light's
Extended Depth of Field (EDOF) systems.
“Error encoded” optics that allow the signal (image) to
be distinguished from the noise.
Focus of the Course
An optoelectronic system:
It's not feasible to cover the design of all of these components in a single course. The
main focus of the course, therefore, (in decreasing order of emphasis) is:
A) The specification and design of optical systems. The use of a state-of-the-art
optical modeling software (Zemax) is available for the duration of the class.
B) Interfacing optical systems to detectors (both electronic and the human eye),
such that information is not lost.
C) A brief introduction to Computational Optics, where the combination of
computer processing plus specially designed optics is capable of tasks not possible
using optics alone. In effect, the computer algorithm becomes part of the optical
The Basic Problem of Optical Design
A) Given an optical system, we can simulate the propagation of
light through it to derive the transfer function of the optics:
Optical System
Engineering Optical Design Methodology I.
Optical design is not the only engineering disipline which largely
lacks a direct inverse solution – electronic design is similar, and
hence some of the design methods are related.
One is the “cookbook” method:
Most optical design problems involve variations of a set of known
Imaging illuminated objects
Collecting and concentrating light
Creating patterns of light (or shadow)
Coupling light into and out of structures, such as glass fibers .
Hence, the first step, when faced with a design problem, is to
research how others have solved similar problems.
(Engineering Optical Design Shortcut).
While no individual lenses will do an adequate job of imaging
(which we will show later), there are thousands of off-the-shelf
“camera lenses” (actually systems of lenses) designed for just
that purpose. Going back to our “O-E System”:
Light in
Light out
Sometimes the “optical design” part of the problem is best
solved by finding an appropriate commercial lens:
“Appropriate” here means using a lens that will work
with the rest of the system.
This is analogous to the use of “op-amps” in
electronic design, instead of individual
Optical Engineering Design Methodology II
- Wave Propagation Approximations Approximations of E-M wave propagation:
Finite Element calculations of Maxwell's equations.
Fourier-based wave propagation calculations.
Fast, but difficult to handle complex optics. Good for analyzing
diffraction effects.
Huygens' wave propagation method.
Very accurate and adaptable, but very slow. Only practical for microsized systems.
Slower than Fourier, but more adaptable to complex objects.
Ray tracing. Given a propagating wave, rays are defined as geometric lines
drawn perpendicular to the wavefronts. They don't represent anything
physical, but nevertheless do a good job of approximating wave propagation
in regions where the wavefront radius of curvature is “significantly” greater
than the wavelength.
Optical Engineering Design Methodology III
- Linear Approximations to Lenses Due to the non-linear
nature of refraction, real
single lenses image
In the “Gaussian Optics”
approximation, we describe optical
systems using a fictional “lens”
(known as a “Paraxial Lens”) for
which the ray transfer equations
are linear for all rays.
When rays are confined to be 'near' the optical
axis, imaging improves dramatically.
This is known as the “Paraxial Approximation”.
In the paraxial approximation, ray transfer
equations are approximately linear.
The linear nature of
Gaussian optics allows
us to derive numerous
relations which are
approximately true for
real lenses.
Optical Engineering Design Methodology IV
- Computers Today, computers are universally used to simulate light
propagation through optical systems. The results are used in
two main ways:
1. To analyze the system. The kinds of analyzes possible
a) The “Moduation Transfer Function” (MTF) which gives
the resolution of the system.
b)The aberrations of the system such as Chromatic Focal
Shift (longitudinal color), Chromatic magnification
change (transverse color), distortion, optical path error
(OPD), and etc., etc.
c) Geometric layouts of the system (often in CAD formats).
Optical Engineering Design Methodology IV
- Computers (continued) 2) The other main use of computers in optical design is to refine a
starting system – in effect, to invert the analysis process and find a
system that has better outputs. This is done by heuristic (or guided)
search, also known generically as 'optimization'. Small changes are
made in the system and the analysis results compared. Various
algorithms are then used to decide which “direction” in the multivariable parameter space should be investigated next. Zemax uses
two public algorithms and two proprietary ones:
a) Public algorithms: Damped Least Squares (DLS) and Gradient
b) Proprietary algorithms: “Global Optimization” and “Hammer”.
c) All these algorithms require the user define a “merit function”
which (somehow) collapses the diverse analyzes to a single
number. Current “art” in optical design resides largely in
generating “good” starting solutions, and creating “good” merit
functions. (Neither can be described as a “science”.)
The Art of Optical Design
I) The design of high-end lens systems is largely an art, which
successful practitioners spend multiple years learning. Consider
these two lenses (each of which zooms to 200 mm focal length):
Zoom lens from the 1970s.
Weight: 1 Kg
3 to 1 zoom ratio.
Significant distortion and
chromatic aberration.
Modern zoom lens.
Weight: 0.25 Kg
11 to 1 zoom ratio.
Undetectable aberrations
when used in digital camera.
What has changed in the 40
years between these two
 Our knowledge of optical
design is essentially the
 Our ability to fabricate lenses
has improved somewhat.
Mostly, however:
A)Designers have made
conceptual breakthroughs.
B)Computers have spent
millions of people-years
searching the design space.