ECEN 4616/5616 “Optoelectronic System Design” MWF 1:00 → 1:50, ECCS 1B12 Instructor: Bob Cormack [email protected] [email protected] (faster response) (720)-470-1836 OFFICE: ECEE 1B46 OFFICE HOURS: 11:00->12:30 MWF TEXTBOOK: “Geometrical Optics and Optical Design” Mouroulis & Macdonald (ISBN 0-19-508931-6) Class Notes and other resources available at: http://ecee.colorado.edu/~ecen4616/Spring2014/ Legal Fine Print (1) If you qualify for accommodations because of a disability, please submit to your professor a letter from Disability Services in a timely manner (for exam accommodations provide your letter at least one week prior to the exam) so that your needs can be addressed. Disability Services determines accommodations based on documented disabilities. Contact Disability Services at 303-492-8671 or by e-mail at [email protected] If you have a temporary medical condition or injury, see Temporary Injuries under Quick Links at Disability Services website and discuss your needs with your professor. (2) Campus policy regarding religious observances requires that faculty make every effort to deal reasonably and fairly with all students who, because of religious obligations, have conflicts with scheduled exams, assignments or required attendance. In this class, please consult with me in a timely manner. See full details at http://www.colorado.edu/policies/fac_relig.html (3) Students and faculty each have responsibility for maintaining an appropriate learning environment. Those who fail to adhere to such behavioral standards may be subject to discipline. Professional courtesy and sensitivity are especially important with respect to individuals and topics dealing with differences of race, color, culture, religion, creed, politics, veteran’s status, sexual orientation, gender, gender identity and gender expression, age, disability, and nationalities. Class rosters are provided to the instructor with the student's legal name. I will gladly honor your request to address you by an alternate name or gender pronoun. Please advise me of this preference early in the semester so that I may make appropriate changes to my records. See policies at http://www.colorado.edu/policies/classbehavior.html and at http://www.colorado.edu/studentaffairs/judicialaffairs/code.html#student_code 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 behind. There are no dumb questions – questions aren't graded. 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). Grading Homework: 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. DESIGN PROJECT: 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 information. 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 wavelength. 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 design. 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 tasks: 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”: Optics 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 transistors. 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 poorly. 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 include: 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 Descent. 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 lenses? Our knowledge of optical design is essentially the same. 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.