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in a rapidly evolving 5G world The Photonic Integrated Circuit is becoming an increasingly important area of development in the field of optical communications as demand for speed and throughput ramp up. The impending onset of 5G has added even greater impetus to innovation in photonics, however new developments raise new challenges when it comes to test and measurement. Exfo’s François Couny looks at how optical component testing techniques are evolving to meet these challenges. OPTICAL COMPONENT TESTING
Backgrounder Ever since low loss optical fibre was introduced in telecom networks, fibre-based components have been evolving to address new challenges. The examples are many–from couplers allowing easy signal redirection to multiplexers combining several optical signals with low insertion loss. These devices called for innovation in the test & measurement industry to measure power and wavelength with the help of lasers. At the same time, phenomena such as chromatic dispersion, return loss or polarisation dependent loss (PDL), became more important parameters to consider as the optical telecom market started to grow. New challenges Nowadays, testing passive components has become a routine task that typically involves measuring devices over a limited number of parameters to reduce costs. Some characteristics, such as chromatic dispersion, may not be as
used to record the optical power of each output port of the device under test. Lasers have an obvious advantage: the high optical power offered by these sources makes it possible to measure the characteristic loss of devices over a much larger dynamic range than
problematic as they used to when it comes to impacting overall network performance. Others like PDL are now more critical. And there’s more; new optical characterisation challenges are popping up with the bandwidth boom and the advent of 5G. Tests on 5G devices are increasingly stringent and need to be performed reliably, putting more pressure on existing test and measurement systems. The arrival of compact components based on integrated photonics also adds to the need for test and measurement methods to evolve. Measuring loss of passive components To take reliable loss measurements efficiently for today’s complex components, the best option is the swept laser technique. In this setup, a continuously tunable laser is used to scan the wavelength across the spectral range of interest. Operating jointly with the laser, a component tester is then
Fig 1. Spectrum of an optical filter acquired with a laser with high SSSER (green) and low SSSER (red). Transfer function is the additive inverse of insertion loss.
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ISSUE 17 | Q2 2019
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