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Testing photonic integrated circuits

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

Challenges

  • Measurement reliability for today’s complex optical components
  • Requires test-on-wafer
  • Speed and efficiency for PIC testing
  • Accuracy of component quality assessment
  • Automation for testing on massive scale
  • No photonic testing expertise

Description

Driving the development of high-speed networks and 5G, photonic integrated circuits (PICs) are a well-known technology in the telecom worldmainly 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).

Flexible, accurate and fast PIC testing

PIC technology poses whole new challenges when it comes to testing active (i.e., emitting light) or passive (i.e., guiding light) optical components: Discover how to take on these challenges with effective testing and best practices.

Testing active components

Testing active components such as lasers and amplifiers found on PICs is quite straightforward.

An optical spectrum analyzer (OSA) can be used to perform tests on active components simply by connecting the light source or laser output to the OSA to get spectral signal of the sources, as seen below.

Figure 5. 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.

Testing passive components

Testing PIC-based passive component is even more 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. The CTP10 component test platform is a multiport detection system that works in conjunction with the T100S-HP swept tunable laser to measure optical insertion loss, return loss and polarization-dependent loss across the telecom spectral range. The instrument yields optical spectrum quickly, reliably and accurately, even under stringent test conditions. 

The CTP10 characterizes the spectral properties of up to 50 optical ports in one single scan with picometer resolution and a dynamic range of >70 dB ―even when scanning at 100 nm/s. 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.

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

Use case for PIC optical components: from design to test & validation 

Design and fabrication 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.

Test, assembly and packaging (commonly referred as TAP) is a crucial step after design and manufacturing to provide feedback and help optimize the design. It is also needed for process control and to ensure that devices operate as expected. The dies 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 wafer probe station, light can be coupled in and out of the wafer using specially designed hardware and software. 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 as a function of wavelength. Testing photonics devices is at the heart of EXFO’s expertise, and the CTP10 has been specifically developed to address the key PIC measurement challenges. The CTP10 can measure optical components with large spectral contrast in a single scan, reliably and accurately.

Example of swept IL measurement performed using the CTP10 test platform.

As in most cases with new technologies, it takes several areas of expertise to build a comprehensive solution. That is why EXFO has combined forces with Hewlett Packard Enterprise (HPE) and MPI Corporation to jointly address the challenges posed by optical component testing through advanced, interoperable measurement techniques.

Automated Wafer Level Testing of Photonics Integrated Circuits

CTP10 – Advanced Component Testing Platform

For passive optical component testing, the CTP10 yields fast, accurate and reliable results, under any test conditions for R&D and manufacturing environments. The CTP10 provides high resolution characterization, even for large contrast spectral features.

Key benefits

Improve production yield with R&D-grade solutions that rapidly provide best-in-class measurements. Active components (e.g., lasers inside transceivers, semi-conductor optical amplifiers) can be characterized within seconds by OSA20.

Passive optical components can be tested by CTP10 to picometer resolutions even under stringent conditions.

Flexibility is key in the race to 5G. Designed with the future in mind by collaborating with research groups, these solutions can be integrated into any wafer-testing handling system, with alignment included. CTP10 is an evolutive modular platform, allowing additional or new functions to be added to the system over time. It is compatible with several tunable lasers.

CTP10 fits into a single mainframe, ready to test components at the push of a button.

OSA20 and CTP10 come already packed with analysis features and special test configurations for easy setup.

User-friendly GUIs without any compromise on performance.

A full suite of SCPI automation commands allows the user to fully control the test gear and integrate it in a research test setup or production test bench.

Applications

  • Active and passive component testing
  • Mach-Zehnder modulator characterization
  • AWG testing
  • Ring resonators spectral measurement
  • Transceiver: transmission laser testing

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