FRANÇOIS COUNY COMPONENT TESTING
techniques using a broadband source. This accessible dynamic range is further enhanced when using tunable lasers with large signal to source spontaneous emission ratio (SSSER), where high insertion loss can readily be measured (Figure 1). The component tester is a specialised instrument that has very short test times and excellent accuracy: it records the test wavelength and output power simultaneously as the laser is being swept, as opposed to a stepped wavelength measurement where the laser is moved one step at a time. The technique allows wavelength resolution of the order of the picometer, sometimes even smaller, with a full spectrum acquired within a few seconds. A larger spectral range, important when characterising components spanning all telecom bands, can also be tested using several tunable lasers, each covering a portion of the total spectrum under test and concatenating the insertion loss or return loss result into a single spectrum. It is also the only method to provide picometer-resolution PDL spectra within a reasonable timescale. Figure 2 shows a typical setup for the swept laser technique and the resulting spectrum when measuring four output ports of a WDM demultiplexer. In this configuration, each laser will successively perform a sweep, the component testing unit taking care of switching between lasers, recording wavelength and the output power on all four ports. The results are then displayed with 1 pm sampling resolution and a 5 pm resolution for PDL measurements.
Fig 3. Photonic integrated circuit parametric testing directly on wafer. Optical and electronic characterisation can be performed by the component tester.>
Photonic integrated circuits (PIC) and the future Integrated photonics is set to be the next disruptive technology, particularly for the development of 5G across the globe. Some key developments of the technology are also underway the electronic processors, photonic integrated circuits are imprinted onto wafers, before being cut into individual chip. To reduce operating costs, PIC manufacturers need to characterise each chip directly on the wafer. Advanced passive optical components now include opto-electronic or electro- optic functions that also need to be in medical, sensing, or military applications. In the same way as
tested. Some component testers can test chips both optically and electrically across a spectral range, drawing a more complete picture of the component characteristics. As the telecom landscape continues its transformation, optical test and measurement vendors and PIC manufacturers are already working together to provide fast and reliable characterisation setups, where the results can then be analysed to sort defective chips, to better understand fabrication tolerances and improve yield or to record those characteristics in a database to improve simulation and PIC design.
ABOUT THE AUTHOR
Fig 2. Typical Setup for a component characterisation over the full telecom range. Bottom right: Spectrum of WDM demultiplexer obtained with an EXFO CT440 component tester.
FRANÇOIS COUNY PRODUCT LINE MANAGER, EXFO
François is EXFO’s Product Line Manager for NEMs Manufacturing Design & Research. He has nearly 20 years of experience in the test and measurement sector and holds a Ph.D. in Photonics from the University of Bath. François is EXFO’s go-to-expert on tunable laser sources and optical component testing for photonic integrated circuits characterisation. EXFO’s leadership in testing fibre optics is recognised worldwide. EXFO helps NEMs, carriers, data centres and webscale companies in overcoming
transformation challenges as networks and services evolve.
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| ISSUE 17 | Q2 2019
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