Lecturer: Silvano Donati   Guido Giuliani  

Course name: Optoelectronic Devices
Course code: 503024
Degree course: Ingegneria Elettronica
Disciplinary field of science: ING-INF/01
University credits: CFU 9
Course website: n.d.

Specific course objectives

The course is aimed to building a sound background as well as the engineering-oriented expertise about the building-blocks of optoelectronics and photonics along with the illustration of their numerous applications- from optical communications to laser-based and electro-optical instrumentation, from displays to optical computing. The course targets a scientific mastering of the subject, as required in a career ranging through different professional positions, and aims to a sound design expertise about devices, technologies, application circuits and systems.

Course programme

Optoelectronic (also dubbed photonic) devices are at the root of many important applications, ranging from optical fiber communications to laser instrumentation, from display to optical computing, from T-wave devices to photovoltaic cells. To design either devices or apparatus and system we shall develop a firm grasp of underlying principles, and of system requirements, going from electrical-to-optical converters – photodetectors, optical-to-electrical converters, i.e. lasers, and continuing with modulators and associated devices. A special topic covered in this course will be photovoltaic cells, because of the huge applications developed about this subject recently.

Part I – single-point photodetectors
Detectors from a system standpoint: bandwidth and noise. Quantum and thermal regimes of detection. Merit figures, NEP and detectivity. BLIP limit. Photoelectron mission detectors. Absorption from Einstein coefficients and Lambert-Beers law. Photocathodes: the photoemission process, materials. The PMT (photomultiplier), Single electron response (SER). Integral or charge response, current response, amplitude and time measurements. PMTs in nuclear electronics instrumentation> Scintillation detectors for alfa, beta, gamma, and neutron energy spectrometry. Single-photon counting. Dating with radio-nuclides. Micro-channels and MCP-PMT. Semiconductor photodiodes, structures, materials. Electrical characteristics, electrical equivalent circuits. Extrinsic and intrinsic frequency cutoff of photodiodes. Pn and pin junctions, Schottky junctions, homo- and hetero-structures. Ultrafast photodiodes: Uni-Traveling-Carrier (UTC), waveguide PDs, traveling wave PD (TW-PD)> Avalanche photodiode. Structures (raech-through, SAM) Gain and bandwidth. Opptimal gain. Noise. Beyond the optimal gain. The SPAD. Spad arrays for 3-D picture taking. Other photoemissive devices (phototransistors, photoSCR, photoconductors) Themal detectors: types (bolometer, thermopile, pyroelectric). Non-contact temperature measurements. MIR and FIR. Thermovisions.

Part IA Advanced photodetection techniques
Direct and coherent detection. Coherent gain, coherence factor, S/N ratio, BER, photons/bit ratio. Balanced detector. Microwave and T-wave generators base on photomixing. Advanced techniques based on: optical preamplification, injection, non-demolitive, squeezed states. New model for the noise in photodetectors based on second quantization.

Part IB Image photodetectors
Devices for image pickup, vidicons, CCD arrays, CMOS arrays. Working principle, readout, saturation and dynamic range. Output stage, correlated double sampling differential scheme (CDS). Charge organization and readout options. Spatial resolution in image device: the Modulation Transfer Function approach. OTF, MTF and PTF. Linearity of response, spurious frequency generation (Moire’ or under-sampling). Applications of under-sampling effects (automatic focusing, otpical rules). Image intensifiers and converters. Generations of technologies. Parameters and performance. Applications to LLLTV. Special functions; streak camera for pico-second events, gating, zoom, X-ray converters for biomedicine.

Part IC photovoltaics
Structures, materials. Electrical and optical parameters. Conversion efficiency, fill-factor (FF). The solar constant and the air-mass number (AM#). Optimal energy gap for single-junction. Maximum power out point. Cell technology (materials, contacts, ARC treatment). PV systems, direct exposition and concentration. Applications of PV systems. Annual sun-hours, overview of applicable standards and National subsidizing of PV deployment. Advanced systems, multi-spectral cells, use of PV cell in space, co-generation. PV accessories, inverters, storage, metering and safety/security issues.

Part II semiconductor lasers and related topics
Spontaneous and stimlated emission processes in homogeneous semi conductors, unit-length gain, spectral distribution of gain. Direct and indirect transition amterials. Effect of the lattice mismatch in junctions ans thin layers. Quantum well materials, quantum dot amd quantum wires. Homo- and hetero-junctions. Confinement issues. The Fabry-Perot cavity, electrical and optical confinements, rib and ridge guides, contacts, non-absorbing-mirrors (NAM) by intermixing. Threshold current, emitted power, modal structure, linewidth and alfa factor, thermal runaway effects. Ternary and quaternary materials for teh I II and II window of optical fibers. The Lang-Kobayash and Lamb equations. Retro-reflection regime. Planar waveguide laser with distributed reflectors; DBR, DFB and quarter-wave shifted. Micro-cavity lasers. Photonic Crystal lasers. Quantum cascade lasers. Vertical cavity (VCSEL) lasers and their properties. Gallium nitride lasers and LEDs. Direct modulation of lasers, relaxation frequency, small-signal analysis, gain saturation effects. Optical amplifiers semiconductor structures. Electro-absorption modulators, Franz-Keldysh effect. Semiconductor passive guide components, integrated optics devices. Silicon photonics.

Argomento da modificare

Course entry requirements

working knowledge of basic electronics (devices and analogue) and of laser principles

Course structure and teaching

Lectures (hours/year in lecture theatre): 53
Practical class (hours/year in lecture theatre): 15
Practicals / Workshops (hours/year in lecture theatre): 22

Suggested reading materials

about part I and IA, IC S.Donati: “Photodetectors”, Prentice Hall 2000 about part II S.L.Chuang: "Physics of Photonic Devices", Wiley 2009, Chapters 9-11 and 14 about part I C C.J.Winter at al: “Solar Electric Power Generation”, Springer Verlag 2006.

Testing and exams

a written test, 5 questions 1 hour, plus a oral discussion of the written test, plus complimentary questions, 30 minutes