Polarization Resolved Spectral Measurements for Wafers, Bars and Chips

Blog Post created by stmichel Employee on Jul 25, 2017

With the widespread move to wafer-scale production with integrated photonics technology, the throughput for testing needs to be optimized. A significant part of the time for optical testing on wafers and chips is often used for optimizing the probe coupling. An extra aspect of this for optical coupling involves testing with the intended polarization alignment of the light. Planar devices often have differing optical properties for light polarized parallel (TE) or perpendicular (TM) to the device plane. The difference may be intended for the device functionality or just unavoidable. The coupling from the probe often also has strong polarization dependence, especially with surface grating couplers. Often during initial research and development, this is dealt with by manually aligning the polarization as part of the probe adjustment process. But that quickly becomes a bottleneck for getting fast automated and reproducible results. Especially for spectral measurements of wavelength dependence, the attempt to hold this polarization alignment while the wavelength is scanned is a real challenge for both speed and reproducibility.


      Setup for polarization resolved spectral measurements


A powerful way to address this challenge is with fast automated measurements of the complete polarization dependence, from which the results for aligned polarization can be extracted. The Keysight N7700A Photonic Application Suite provides this solution with an IL/PDL Engine that uses tunable lasers and the fast-switching N7786B benchtop polarization synthesizer to measure the polarization matrix of devices with a unique method that uses a single wavelength sweep that samples the necessary polarizations states for each wavelength result in less than 1 ms. This fast sampling with a single-sweep makes the method very robust against vibrations and temperature drift in the fibers during the measurement, which is important when working with probe stations that often require longer fiber cable connections to the instrumentation. The results for the desired state of polarization are then provided by the matrix calculations. Solutions are available for measuring both optical-to-optical devices and optical-to-electrical, when the device includes integrated photodiodes.


Experience this Keysight solution live at ECOC in Gothenburg.