Undergraduate Teaching

Engineering Tripos Part IIA, 3B6: Photonic Technology, 2021-22

Engineering Tripos Part IIA, 3B6: Photonic Technology, 2021-22

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Module Leader

Prof R Penty


Prof R Penty


Dr Q Cheng

Lab Leader

Prof R Penty

Timing and Structure

Lent term. 16 lectures.


The aims of the course are to:

  • Introduce key aspects of photonics technology and its applications in fields such as communications, storage, medicine, environmental sensing and solar power.
  • Introduce both optical fibres and photonic components including light emitting diodes, lasers, photodiodes and solar cells.
  • Introduce photonic sub-systems including transmitters and receivers for use in applications such as wide area, metropolitan and local area networks.


As specific objectives, by the end of the course students should be able to:

  • Know of the main applications of optoelectronics.
  • Choose appropriate transmission media with reference to bandwidth and physical environment.
  • Know which semiconductors are used for what optoelectronic tasks and why.
  • Be familiar with the construction of LEDs, and be able to estimate their linewidth, speed and external quantum efficiency.
  • Be familiar with the construction of Fabry-Perot and grating based diode lasers, and how this relates to their spectra and light-current characteristics
  • Estimate the response of semiconductor lasers to changes in their drive current or operating environment.
  • Be familiar with the construction of junction photodiodes, and hence be able to estimate the capacitance and responsivity, and know how to operate them for best sensitivity and speed.
  • Be familiar with the relationship in construction and operation between junction photodiodes, avalanche photodiodes, solar cells and photoconductors.
  • Perform noise calculations for typical optoelectronic circuits.
  • Be aware of the design of typical receiver circuits with reference to the physical characteristics of photodetectors.
  • Be familiar with the construction of fibres as well as the causes of attenuation and dispersion.
  • Perform calculations of link budgets, dispersion and attenuation limits.


Photonic Technology

  • How and why optoelectronics fits within electronics: Outline of major applications areas within engineering, science and medicine. Examples of optoelectronic subsystems, solar cells, lighting, Communication transceivers.
  • Optical processes in semiconductors: Direct and indirect band structures, comparison of Silicon, Germanium, GaAs based and InP based materials. Optical absorption, Optical emission, non-radiative transitions
  • Light emitting diodes: Quantum efficiency, wavelength, optical line width, visible devices, modulation limits, device structures, materials.
  • Laser diodes: Stimulated emission, optical gain. Laser as a feedback amplifier of spontaneous emission, Fabry-Perot laser cavities. Rate equations, modulation characteristics, dynamic linewidth. Examples of common diode laser types.
  • Optical transmitter circuits: LED based circuits, LED types, transmitter power, bandwidth. Laser based circuits, laser types, biassing, feedback circuits. Noise in optical systems, shot noise, thermal noise, noise bandwidths, circuit effects.
  • Photodetectors: PN junction photodiodes, photoconductors, solar cells, avalanche photodiodes, capacitance, transit time, leakage currents, avalanche gain and noise.
  • Optical receiver circuits; Transimpedance amplifiers.
  • Fibres and transmission: Multimode and single mode fibres: Attenuation, dispersion, interfaces to fibre.
  • Transmission systems in a real environment: Power budgets, error rates, monitoring, power penalties, margins for temperature and ageing. Emerging technologies.

Examples papers

Three examples papers are provided during the course.


Laser Experiment

Students are provided with two types of semiconductor lasers and are asked to perform basic electrical and optical measurements to characterise their operation. The measurements are used to derive the basic properties of these laser devices and understand the underlying fundamental physical mechanisms that govern their operation.

Learning objectives

After completing this coursework students should be able to

  • Be familiar with the basic operation of LEDs and lasers,
  • Generate light-current and current-voltage curves for a semiconductor device,
  • Find the laser threshold and stray series resistance of a laser,
  • Characterise the spectrum of light emitted from LEDs and lasers,
  • Estimate the refractive index of the laser.

Practical information:

  • Sessions will take place in EIETL, during weeks 3-8 in Lent term and weeks 1-2 in Easter term.
  • This activity involves preliminary work (~ 2 h): you should read the related lecture notes and experiment information sheet with the appendices, to gain some knowledge background on semiconductor devices and error analysis prior to experiments.

Full Technical Report:

Students will have the option to submit a Full Technical Report.

Students are asked to i). expand on their experimental results based on the feedback provided at the marking session, ii.) perform the Haaki-Paoli analysis to obtain the gain spectrum of a semiconductor laser and iii.) provide an analysis of the effects of temperature on the operation of laser devices.


Please refer to the Booklist for Part IIA Courses for references to this module, this can be found on the associated Moodle course.

Examination Guidelines

Please refer to Form & conduct of the examinations.


The UK Standard for Professional Engineering Competence (UK-SPEC) describes the requirements that have to be met in order to become a Chartered Engineer, and gives examples of ways of doing this.

UK-SPEC is published by the Engineering Council on behalf of the UK engineering profession. The standard has been developed, and is regularly updated, by panels representing professional engineering institutions, employers and engineering educators. Of particular relevance here is the 'Accreditation of Higher Education Programmes' (AHEP) document which sets out the standard for degree accreditation.

The Output Standards Matrices indicate where each of the Output Criteria as specified in the AHEP 3rd edition document is addressed within the Engineering and Manufacturing Engineering Triposes.

Last modified: 20/05/2021 07:36