How to Select Fiber Optic Transmitters

Fiber optic transmitters convert electrical signals into optical signals and then inject these optical signals into light-conducting cable.  They use light emitting diodes (LED) or laser diodes as their optical source, and are designed for use with either single-mode or multi-mode fiber. Fiber optic transmitters can turn modulated light on or off, or linearly vary the light's intensity between two predetermined levels. They are available as chips or stand-alone units.

Figure 1 - Image Credit: Avago Technologies

How Fiber Optic Transmitters Work?

Fiber optic transmitters consist of an interface circuit, a source drive circuit, and an optical source.  The interface circuit receives electrical signals. The source drive circuit converts them to optical signals and triggers the LED or laser diode that then sends the light signals to the fiber optic cable, where they travel to their destination.

Product Specifications

The GlobalSpec SpecSearch database characterizes fiber optic transmitters by their light source, cable type, and connector type.

Light Sources

Buyers should consider their application requirements when specifying the light source.

• LEDs are used mainly for short-to-moderate transmission distances because they have relatively large emitting areas. They cost less than laser diodes, but have a limited bandwidth.
• Laser diodes can couple many times more power to optical fiber than LEDs. They are more expensive, but are required for applications that must transmit signals over long distances. 

Cable Types

Fiber optic transmitters are designed for use with single mode and/or multi-mode cable.

• Single-mode fibers (SMF) have small cores and are used withlaser sources for high speed, long distance links. They transmit infrared (IR) laser light at wavelength from 1,300 to 1,550 nm.
• Multimode fibers have larger cores and are used mainly with LED sources for lower speed, shorter distance links. The typical transmission speeds and distance limits are 100 Mbit/s for up to 2km, 1Gbit/s to 220-550m, and 10Gbit/s to 300m.

Products that can be used with both types of optical fiber are also available.

Connector Types

Common connector types include Biconic, D4, ESCON, FC, FDDI, LC, Loopback, MTP, MT-RJ, MU, SC, SMA, and ST

Performance and Input Specifications

When selecting fiber optic transmitters, there are five main performance specifications to consider: data rate, transmitter rise time, wavelength, spectral width, and maximum optical output power.  Inputs include TTL, ECL, CMOS, RF, and video.

Resources

What is Fiber Optics? Understanding Optic Transmitters

University of Pennsylvania - Lab 1: Digital Fiber Optical Transmitter and Receiver

Reference Guide to Fiber Optics - Fiber Optic Transmission Systems

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