Medial Oriented Systems Transport (MOST)
Fiber-Optic Multiplexer & Test Signal Generator
(Environmental Temperature Test, MOST Fiber-Optic Multiplexing)


An automotive OEM requested an environmental and burn-in test system for high-end car audio amplifiers. The amplifiers used MOST fiber-optic link for reception of audio signal and would be tested in an environmental chamber at -40 and +85 deg.C temperatures. To meet test cycle time, 24 DUTs (Device Under Test) would be loaded in the chamber at the same time. The test system must perform a test sequence on each DUT in the series once the test temperature in the chamber has been reached and the dwell time has expired.

A separate burn-in test was required as a large number of DUTs must be tested in parallel for several hours.

The major challenge was deciding which method to use in order to provide test signals to the DUTs over fibre-optic link. One possible solution was to create a large MOST ring by connecting multiple tested DUTs in series. The disadvantage of this method was that if any device failed during the test, the communication to all DUTs would stop and it would not be possible to identify which device in the ring failed.

To resolve this issue, test systems typically use a separate MOST interface for each tested unit. However, the associated hardware costs of these interfaces are significant.

This challenge was common for both the environmental and burn-in tests.


For the environmental test, the optimum solution proved to be the use of a single MOST interface multiplexed between DUTs. However, a compatible multiplexer was not available off-the-shelf.

Therefore, the LCI team developed a custom opto-electronic multiplexer that converted MOST optical signals to high speed electrical signals, multiplexed them in electronic form, and then amplified and converted them back to the optical signals required by the devices.

For the burn-in test, the team developed a microcontroller-based device that generated test signals and converted them back to optical signals. The generator cost was a fraction of a MOST test interface that would have been used otherwise from a leading supplier.

Winning Result:

With custom designed multiplexer and signal generators, LCI delivered a test system with significant hardware cost savings compared to a system based on traditional architecture.

Market Served:

Automotive (tested product is installed in BMW 7-series cars)