ANALYSIS & OPINION:PHOTONIC INTEGRATION


MACRO CELLS WILL NOT BE ABLE TO WITHSTAND THE GROWING SPEED, LATENCY AND BANDWIDTH TO FUTURE-PROOF 5G AND BEYOND


Quality component testers combine multiple lasers to cover the full range of optical components


components contained on each chip can be demanding. Here are the methods currently used for active and passive component testing.


For active component testing An optical spectrum analyser (OSA) provides fast spectral measurement of light sources such as lasers. Leading OSAs are capable of performing up to five scans per second at speeds of 2,000nm/sec, fast enough for real- time component alignment and with sufficiently high resolution to enable measurement of key parameters. Tis provides a simple and effective test method for active component testing.


For passive component testing An OSA can be used with a broadband light source with a very large, flat spectrum, and stable power. When combined with the chip, the light can be collected and coupled to the OSA, which will then perform a sweep to record the spectral response of the device under test (DUT). Tis method is good for real-time alignment because it’s extremely fast; however, there are limitations to its scope. It works well for broadband components (with slowly varying spectrum) but fails in high- contrast spectrum scenarios. Given that PICs are oſten high contrast, the OSA method does not always provide the optimum solution. Te stepped laser technique can be used


with a detection system comprising several hundred power meters. Te dynamic range


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obtained with this technique is very wide due to the laser’s optical power density. Tis method provides good spectral coverage by using one or several lasers between 1,250 and 1,700nm and easy-to-control polarisation for performing polarisation dependent loss (PDL) measurements. Te biggest limitation of the stepped laser


technique is the lengthy time required, given that the laser must ‘stop’ at each wavelength to perform measurement.


Swept laser testing for advanced reliability Te only test approach that is proving to lead the pack when it comes to delivering fast and reliable measurements for today’s complex components is the swept laser technique. Tis elegant solution uses a continuously


tunable laser source along with a component tester that records wavelength and power detection synchronously as the wavelength is scanned by the laser. In seconds it can deliver picometer spectral resolution with a very large optical power dynamic range. Quality component testers combine


multiple lasers to cover the full range of optical components. Te larger spectral range, important when characterising components spanning all telecom bands, can indeed be tested using several tunable lasers – each of which covers a portion of the total spectrum under test – and concatenating the insertion loss or return loss result into a single spectrum. To match the high quality of the laser, the


component tester must be leading-edge, providing very short test times and excellent accuracy to record the test wavelength and output power simultaneously as the laser is being swept. Tis synchronised measurement is performed


automatically by the component tester. Te component tester can also be automated to allow, for example, ‘fixed wavelength’ power measurement which is crucial for the fast fibre- to-PIC alignment algorithm.


Future-ready testing Tiny but powerful PICs are fuelling the future of telecom, unlocking the best of photonic and electronic worlds by merging purely optical components, such as lasers and modulators, with opto-electronic, electro-optical, fully electronic, or even RF features. Te result is a chip with endless potential


in applications ranging from data centres to medicine, and from autonomous cars to quantum computing. Te key to success will be innovative,


reliable and speedy optical component test solutions to keep pace with next-generation networking technology. With ultra-fast optical spectrum analysers and the optimised swept laser technique, component manufacturers are well positioned to deliver during the ongoing bandwidth boom. n


François Couny, product line manager, EXFO


Issue 26 n Winter 2020 n FiBRE SYSTEMS 15


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