What do we mean by a direct detection system?

What do we mean by a direct detection system in an optical network?

In a direct detection system, the information is coded into the intensity or amplitude of the light to be transmitted along the fibre. At the receive end, we need a detector, a photo-diode, which will convert the intensity of light into an electrical signal. The information is directly recovered from this electrical signal.

A photodiode can convert light signals directly to electrical signals. The more light that hits the photodiode then the greater the electrical current that flows. So that is where the term, direct detection, comes from.
Direct detection can be used for a simple on-off keying modulation format such as Non-return to Zero, and also for a multilevel modulation format such as PAM4.

Direct detection is cheap and mature technology. So direct detection systems are often used to provide the simplest and the lowest cost optical networking solutions for a wide range of applications and data rates.

Applications for CONA: Metro networks, DCI, FTTA, Utility networks, Fibre for 5G, Campus networks

Where are direct detection systems used?

Generally speaking, direct detection systems are used to provide the simplest and lowest cost optical networking solutions. These may be used:

for Local area networks (LANs), within and between buildings around campus and industrial sites

within data centres, where data rates can reach up to 800Gb/s, often using SDM to multiply the capacity

between data centres in a metro network (metro DCI) where data rates of 100Gb/s and 400Gb/s are commonly used, often with WWDM to multiply the capacity

for 5G front haul networks and FTTA, with data rates of 10Gb/s and 25Gb/s, often using CWDM to multiply the capacity

in point-to-point access networks for business connections (FTTB), and very high capacity broadband (PTP FTTH) commonly at data rates of 1Gb/s, 10Gb/s and 100Gb/s

in long distance telecom, transport and utility networks that may use ITU OTN networks with DWDM and amplifiers to operate over hundreds or thousands of kilometres with capacity approaching 1Tb/s per fibre pair

Which course should I go on to learn about direct detection systems?

The foundation level Certified Optical Networking Associate (CONA) course covers direct detection transmission systems and their associated optical networking technologies:

fibre infrastructure including fibre types, cables, connectors, splicing, termination and testing (from a project manager’s perspective)*

managing light using passive optical components

multiplexing to increase capacity: TDM, SDM, SWDM, WWDM, OWDM, CWDM, DWDM

loss budgets and power budgets

optical amplifiers including EDFAs and Raman amplifiers

Chromatic dispersion (CD), Polarisation Mode Dispersion (PMD) and optical dispersion management (DCMs etc.)

network performance, configuration and control

*Note that CONA is a Project Manager or Planners course, it is not a practical installation or testing course. If you want to acquire the skills to install cabling professionally, then attend the practical hands-on Certified Optical Fibre Installer (COFI) course and if you want to gain in-depth testing skills, then attend the practical hands-on Certified Fibre Characterization Engineer (CFCE) course.

Ask us for the full course programme for the Certified Optical Networking Associate (CONA) course using the form below. Find out about the difference between direct detection systems and coherent detection systems here.

Find a course

The CONA course is currently delivered by OTT’s training delivery partners in the UK, Ireland, USA, South Africa, Nigeria and New Zealand. It may be possible to arrange courses onsite for company groups located in other regions. Some of their dates will be listed here. If you’d like to keep up-to-date with future dates for this course then why not follow us on your preferred social media.

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