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Testing photonic integrated circuits (PICs)

Flexible, accurate and fast PIC testing to ensure highly reliable next-gen optical components.

Challenges

  • Accuracy/repeatability: Traceable results, no assumption or extrapolation
  • Dynamic range: See the full spectral contrast in single measurement
  • Speed: Keeping total testing time to a minimum
  • Integration: Simple design, easy to connect into an all-in-one system
  • Flexible/scalable: Capability to add functions and features over time
  • Automation: Full test control, quicker configuration

Description

Driving the development of high-speed networks and 5G, photonic integrated circuits (PICs) are a well-known technology in the telecom world—mainly thanks to the frantic development of transceivers and passive components that are smaller, faster, cheaper and greener than their bulk-optics counterparts. PICs are also getting traction—both from a commercial and research perspective⁠—in other sectors too (e.g., lab-on-a-chip, LIDAR technology or quantum computing).

EXFO has worked closely with this fast-paced PIC industry over the years to develop test and measurement (T&M) hardware and software solutions that are automated, scalable, fast, accurate and cost-optimized. These solutions range from simple optical testing to spectral optical characterization or traffic analysis. They have proven interoperability with third-party instrumentation such as wafer disc handling systems. Through memberships in consortiums (such as AIM Photonics, EPIC, LUX Photonics and Optica), EXFO has partnered with major vendors worldwide to offer integrated solutions for testing PICs.

Flexible, accurate and fast PIC testing

With the rise of integrated photonics and the new challenges they bring forth, it can be tricky to keep up with evolving optical test requirements and to equip photonics labs accordingly for testing active (i.e., emitting light) or passive (i.e., guiding light) optical components. You may be asking yourself: what spectral testing capabilities should I be looking for right now or in the near future? How can I obtain traffic analysis for PICs?  Read on to explore the solutions available to you.

Active optical components

Testing active components such as lasers and amplifiers found on PICs is usually done using an optical spectrum analyzer (OSA). This general-purpose test instrument measures the spectral signal of the sources, as shown below.

Testing active components with OSA

Industry-leading OSAs, such as the OSA20, have the advantage of being very fast, performing up to five scans per second at speeds of 2000 nm/s, fast enough for real-time component alignment and with a high enough resolution to allow measurement of key parameters such as OSNR and SMSR.

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Testing passive components

Testing PIC-based passive components is often challenging due to the high port count of some components like arrayed waveguide grating (AWG) or the sheer number of components to test on a single die. A component test platform is a multiport detection system that operates in conjunction with a continuously tunable laser to measure optical insertion loss, return loss and polarization-dependent loss across the laser’s spectral range. The method yields optical spectrum quickly and with a high wavelength resolution, typically on the order of a picometer.

The CTP10 is a modular component test platform that characterizes the spectral properties of high port count devices in one single scan with picometer resolution and a 70-dB dynamic range, even at a sweep speed of 100 nm/s. The CTP10 operates from 1240 to 1680 nm and covers a wide range of applications, including telecom, sensing and LIDAR. Its electronics and internal processor make data transfer a breeze. The CTP10 can be remotely controlled using SCPI commands, facilitating integration as part of an automated PIC testing setup, increasing PIC testing throughput while reducing test time.

Swept IL measurement of ring resonator performed using the CTP10 test platform – see the GUI in action

For the characterization of PIC components with a limited number of outputs, the CT440 is a more compact solution. The CT440 has the same wavelength accuracy and spectral coverage as the CTP10 and can perform IL/PDL measurements.

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Reconfigurable tests

When testing hundreds or even thousands of components on a single wafer, automation quickly becomes essential. This is particularly because the case considering that optical functionalities may vary from device to device or from die to die. As a result, PIC test solutions need to address fast reconfiguration through the use of automated optical switches. Additionally, simpler, single-point tests may also be beneficial to the overall speed of the test and measurement (T&M) process.

EXFO’s solutions address this challenge from two angles. First, the FTBx series of modules provide the optical testing building blocks for a simple laser + power meter test configuration with ample possibilities of adding attenuators, switches or different types of optical sources. Second, the MXS matrix switch addresses the need for quick but repeatable reconfiguration, switching in a fraction of a second to a new configuration.

Related products:

PIC-based transceivers: Traffic analysis

Photonic integrated circuits are the technology currently deployed to tackle the bandwidth stress taking place in the transceiver industry. This stress is due to ever-increasing performance demands and costs pressures experienced by data centers and 5G applications.

Eye diagram – EA-4000 sampling scope

End-to-end transceiver qualification requires an entire range of high-end optical and electrical testers. To help transceiver vendors ensure compliance throughout the transceiver lifecycle, EXFO offers a range of electrical and optical testing solutions from wafer-level to packaged devices, including the EA-4000 sampling scope and the BA-4000 bit error rate tester.

To learn more about bit-error-rate testers and sampling scopes, download and browse our flyer.

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PIC optical components: from design to test and validation

Design and manufacturing of PIC dies is maturing fast, with photonic wafers now containing thousands of components made available by foundries through process design kits (PDKs). To create and update these PDKs, wafer manufacturers require reliable testing solutions to optimize the different parameters of interest for a given optical component. Ring resonators have attracted a lot of attention in recent years and are commonly found in PIC designs to create extremely narrow peaks/troughs that can be used as modulators, for instance.

Testing is a crucial step after design and manufacturing to provide feedback to the design tools and help optimize them. It is also needed for process control, to ensure that devices operate as expected throughout the assembly and packaging of the PIC chips. The PIC devices are usually tested at the wafer level prior to dicing so as to detect defects as early as possible and to avoid packaging defective dies.

Using a PIC wafer probe station, light can be coupled in and out of each chip using specially designed optical fiber hardware and high-precision alignment software. It is also possible to couple several components simultaneously using a fiber array. Precision alignment and speed allow coupling optimization within a fraction of a second.

View of the wafer under test – courtesy of MPI Corporation

Once the light is coupled into the wafer, the optical characteristics of the DUT can be measured. Testing photonic devices is at the heart of EXFO’s expertise; the CTP10 specifically addresses key PIC measurement challenges. EXFO's PIC testing solutions can measure optical components quickly, reliably and accurately.

A perfect fit for building a complete test solution

As in most cases with new technologies, it takes several areas of expertise to build a comprehensive solution. EXFO is involved in key collaborations with industry leaders of the PIC ecosystem to validate hardware and software interoperability. To ensure optimal performance of the overall test solution, EXFO partners with the major suppliers of high-accuracy wafer positioners such as MPI Corporation, Aerotech and FormFactor.

Typical complete solution for automated wafer-level testing of photonic integrated circuits (PICs) – click here to see it in action

A recent example is the collaboration between Aerotech, EHVA and EXFO in demonstrating an automated integrated photonic test solution that accelerates lab to fab for photonics. Photonics testing software seamlessly integrates with EXFO’s advanced swept continuous laser scanning technology and Aerotech’s ultra-high precision photonics aligners. The combo delivers industry-leading reliability and efficiency.

Accelerating photonics lab to fab with Aerotech, EHVA and EXFO – click here to see it in action

All EXFO’s instruments can be fully automated and operated with third-party software integrators such as EHVA, OptiInstrument and Maple Leaf Photonics to provide turnkey solutions.

Innovative PIC testing solution

EXFO is an industry pioneer in the relatively new field of PIC testing. EXFO’s hardware and software solutions are automated, scalable, fast, accurate, and cost-optimized. These solutions cover active, passive and functional testing.

Key benefits

Improve production yield with R&D-grade solutions that rapidly provide best-in-class measurements.

EXFO offers a wide range of optical and electrical testing instruments for customized turnkey solutions that can evolve with your needs.

EXFO multiplies actively involved in partnerships with key hardware and software companies in the PIC ecosystem to validate interoperability.

Applications

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