VIAVI Solutions

Application Note

Optical Transceiver

Testing Using the

VIAVI Solutions™

Multiple Application

Platform (MAP-200)

An optical transceiver is a single, packaged device that works as a transmitter and receiver. It is an important part

of optical network equipment that converts electrical signals to optical signals and vice versa. Optical transceivers

are widely deployed today in synchronous optical networking/synchronous digital hierarchy (SONET/SDH),

Gigabit Ethernet (GigE) and Fibre Channel (FC) optical networks. Optical transceiver manufacturers must

perform a set of tests to ensure compliance with the defined specifications. This paper addresses the testing of

two key optical parameters: transmitter optical power and receiver sensitivity, using the VIAVI Multiple Application

Platform (MAP-200).

Optical Transceiver Overview

Several standards bodies govern optical transceiver specifications. The Telecommunication Standardization Sector

of the International Telecommunication Union (ITU-T) and Telcordia are the two major standards organizations

for telecom, while the Institute of Electrical and Electronic Engineers (IEEE) and the American National Standard

Institute (ANSI) are the major standards organizations for datacom. In addition, several transceiver manufacturers

have established a multi-source agreement (MSA) to ensure interoperability. The scope of the MSA includes

mechanical, electrical and optical specifications. In today’s market, transceivers with bit rates below 10 Gb/s come

in two primary form factors: small form-factor (SFF) and small form-factor pluggable (SFP). The 10-Gb/s transceiver

market has also seen a wide variety of other form factors including 300 pins, small form-factor pluggable plus

(SFP+), 10-Gigabit SFP (XFP), X2, XPAK, and XENPAK as a bigger footprint is needed to accommodate the more

complex electronics.

An optical transceiver data sheet usually includes mechanical, electrical, and optical specifications. To guarantee

compliance to specifications and industry standards, testing of the electrical and optical parameters is an essential

step in the manufacturing process. Optical parameters can be further divided into two categories: transmitter and

receiver. Table 1 shows some of the main parameters specified by transceiver manufacturers.

 Optical Transceiver Testing Using the VIAVI Solutions Multiple Application Platform (MAP-)

Transmitter Optical Parameters Receiver Optical Parameters

Average Optical Power Receiver Sensitivity

Extinction Ratio Stressed Receiver Sensitivity

Optical Modulation Amplitude Dispersion Penalty

Center Wavelength Receiver Overload

Spectral Width Loss of Signal/Signal Detect Assert/De-Assert

Optical Eye Loss of Signal/Signal Detect Hysteresis

Table 1. Main parameters specified by transceiver manufacturers

The following section discusses testing of transmitter average optical power and receiver sensitivity. These two

parameters are used in link power budget analysis at the system level to determine the power margin of an

optical link. This margin is allocated for connector, splice, fiber losses, and system margin.

Transmitter Average Optical Power Measurement

The transmitter port of an optical transceiver consists of a light source and associated electronic circuitry.

Semiconductor-based light emitting diodes (LEDs) and laser diodes are used as light sources in optical transceivers.

LEDs and vertical cavity surface emitting lasers (VCSELs) are commonly used in the transmitters for local and

premises networks while Fabry-Perot (FP) lasers and distributed feedback (DFB) lasers are used in the transmitters

for Metro and long-haul networks.

In optical communication, light sources are intensity modulated, which is a process of applying varied current to

the laser to change the output power level. As illustrated in Figure 1, a finite power level represents logic zero rather

than a true complete absence of power.

Figure 1. Optical Modulation on Laser

Output Power

Bias Current

avg

Data transmission up to 10 Gb/s uses the non-return-to-zero (NRZ) modulation scheme. In the NRZ data stream,

there is equal probability of logic 1 and logic 0 over a long period of time. Transmitter average optical power,

Pavg is a measure of the average energy of logic 1, P1, and logic 0, P0, coupled into the fiber over a period of time.

+ P

)

avg