7/17/2025, Optical Fiber Online News, driven by the rapid evolution of AI large models and computing infrastructure, the intelligent computing center is accelerating towards a new era of interconnection with "light as the core". Photonic integrated circuits (PICs) have become a key technology supporting high-performance computing due to their advantages of high bandwidth, low power consumption, and small size. However, the bottleneck restricting the large-scale application of PICs is not in the design, but in the manufacturing and testing process. Traditional module-level testing is no longer able to meet the requirements for consistency and yield of silicon optical chips, and it has become a key path to improve production capacity and accelerate application implementation.

This article will provide an in-depth analysis of the development trends and test challenges of PIC interconnection, and explore the application capabilities of EXFO OPAL automated probe platform in wafer-level edge coupling testing, helping to achieve large-scale and efficient implementation of photonic integrated chips.

AI-driven connectivity bottlenecks and testing challenges

Industry background
In recent years, the scale of AI large model parameters has increased exponentially, GPU computing power has continued to rise, while the network bandwidth has increased by only 1.4 times, forming a significant "scissors difference", and the network system is becoming the core bottleneck that limits the efficiency of intelligent computing centers. Optical interconnection, especially high-speed parallel architectures based on PIC, is seen as a key path to breaking bottlenecks.

However, the large-scale implementation of PICs faces severe challenges, especially in the testing process. As chip capacity evolves to 100 Tb/s or even Pb/s, the integration scale and the number of channels have surged, bringing three major problems:
High manufacturing complexity: a single chip integrates thousands of optical devices, with large area, multiple channels, and complex functional coupling;

Dramatic increase in testing difficulty: the traditional module-level testing stage lags behind, which can easily cause material and process waste, and it is difficult to achieve closed-loop control.

Increased yield risk: Lack of functional verification of wafer-level systems leads to the exposure of defective chips in the later stages of the process, slowing down the pace of mass production.

According to statistics, the cost of TAP (test, assembly and packaging) has accounted for more than 80% of the manufacturing cost of PIC chips, which is much higher than that of traditional electric chips.

From parameter verification to system function guarantee

Test system
To ensure stable performance and manufacturing yield of PIC chips in high-complexity applications, optical testing runs through the entire process from design verification to module delivery. According to different testing stages and purposes, it can be divided into three stages and two types of methods.

Three major testing stages:
Wafer-level testing: Conduct chip cutting and packaging to focus on basic optical parameters such as insertion loss (IL) and polarization-related loss (PDL) to screen out defective chips early, improve yield, and control costs.

Package-level testing: Conducting after chip packaging to verify the impact of coupling efficiency, packaging stress and other factors on performance, is the key link connecting front-end manufacturing and back-end system integration.

Module-level testing: For complete modules (such as OSFP/QSFP), it verifies system-level indicators such as bit error rate (BER), eye diagram, TDECQ, and transmit power, which is a final quality inspection before leaving the factory.

Two types of test methods:
Parameter testing: focusing on device structure and material characteristics, such as bandwidth, loss, response speed, etc., is often used for design verification and process optimization;

Functional testing: Simulate the real application environment to evaluate the overall performance of the chip at specific wavelengths, rates, and modulation formats, such as bit error rate and signal-to-noise ratio.

Scientifically dividing the testing stages and matching appropriate testing methods has become a key strategy to improve the efficiency and consistency of PIC manufacturing. Especially in the mass production stage, wafer-level functional testing is becoming a key starting point for breaking through testing bottlenecks and accelerating industrialization.

Functional testing moves forward, and wafer-level verification becomes the focus

Technology trends
With the continuous improvement of PIC chip integration, complexity, and application scenarios, the industry has formed a consensus that system-level functional testing must move forward from the traditional module stage to the packaging and even wafer stage. This trend is not only the result of technological evolution, but also the way to ensure yield, control costs, and achieve high-quality delivery.

Why do tests have to be moved forward?

Putting testing ahead can identify functional defects early in manufacturing, prevent defective chips from flowing into high-cost processes, and fundamentally reduce rework and waste. Specific benefits include:
Cost control: early screening of defective products to reduce high losses in the packaging and assembly stage;

Efficiency improvement: streamline the module-level testing process and speed up the pace of product delivery;

Quality assurance: detect system-level deviations earlier to improve chip consistency and reliability;

Process closed-loop: Test data feedback to the manufacturing process to help design and process continuous optimization.

Technical Challenges of Forward Testing:
Despite the clear trends, there are still significant challenges in achieving wafer-level functional verification, including:
Difficult high-precision coupling: It is necessary to achieve multi-channel, large-array, and low-insertion loss edge coupling, which puts forward better requirements for alignment accuracy and repeatability.

Complex index measurement: accurate measurement of key system-level indicators such as BER, TDECQ, Q-factor, IL, RL, PDL, etc.;

High platform compatibility: the test platform needs to be adapted to a variety of materials (Si, InP, LiNbO₃) and packaging forms (CPO, MCM, etc.);

High demand for automation and intelligence: It is necessary to support parallel channel control, real-time data collection and linkage to achieve "testing and adjustment" and "online optimization".

With the continuous improvement of channel density and transmission rate, wafer-level functional testing is not only a powerful tool to control costs, but also a core capability to ensure yield and large-scale delivery. Facing the future, the industry urgently needs to build a flexible automated test platform that supports multi-stage, multi-channel, and multi-coupling forms to promote the comprehensive upgrade of the PIC test system.

EXFO has built a PIC intelligent test platform system

solution
To meet the needs of functional test forward, wafer-level verification and mass production, EXFO launched the OPAL series of automated probe platforms to build an end-to-end test system from scientific verification to batch delivery. The platform has a high degree of automation, modularity and flexible expansion capabilities, supports multi-package form testing and multi-optical coupling from single die to 300mm wafers, and opens up the closed loop of wafer-package-module testing, which is a key tool for achieving high-quality delivery of photonic chips.

1. Multi-package form support: OPAL series probe station
OPAL-EC|Wafer-level edge coupling test flagship platform
Purpose-built for automated testing of wafer-level edge coupling. The platform supports up to 300mm wafers, 105° rotary table and multi-channel parallel coupling, integrates nanoscale alignment modules, upper and lower dual camera systems and autofocus navigation functions, and has 0.5nm alignment resolution and 3nm wafer positioning accuracy, significantly improving coupling efficiency and test consistency.

Typical applications: Batch testing of wafer-level devices such as silicon optical modulators and MRRs; large-scale PIC screening and verification of AI, communication, and sensing scenarios; Rapid verification of multi-port, high-density wafer-level edge coupling.

This is a video, please jump to the link to the corresponding content of the article to view
OPAL-MD|A multi-chip test platform that connects R&D and mass production
It is suitable for multi-die or complex package testing (such as MCM, CPO), and is suitable for pilot testing and low-volume mass production of spinballs. The platform supports multi-chip parallel testing, embedded PILOT automation control software, covering the whole process of chip guidance, calibration, execution and data analysis, and has flexible configuration capabilities to meet the batch verification needs of complex packaging structures.

Typical applications: MPW tape-out project and multi-chip integrated module evaluation; high-speed CPO and complex packaging function testing; telecommunications modules, autonomous driving fields, etc.

OPAL-SD|Flexible platform for scientific research and low-volume validation

An entry-level semi-automated probe platform for universities, research institutions, and start-up teams, suitable for rapid verification of optical/electrical functions on a single chip and in small batches. The platform supports manual and semi-automatic operation, and is equipped with modular optical/electrical probes for precise alignment and flexible switching. Embedded PILOT testing software supports basic automatic control, data acquisition and analysis, making it an ideal choice for scientific research verification and technology incubation.

Typical applications: early design evaluation and functional verification of PIC chips; teaching experiments, technology incubation, and process screening; Academic research, startup low-volume development testing.

This is a video, please jump to the link to the corresponding content of the article to view

2. PILOT Software Platform: A data-driven intelligent testing hub

PILOT is EXFO's core control software specially built for the OPAL probe platform, which runs through test configuration, equipment control, process execution, data analysis and report generation, and builds an automated, traceable and scalable PIC chip test closed loop. Its modular architecture and strong interoperability support the full process of testing from single die to wafer, from R&D to production line. Its core competencies include:

Process automation and equipment joint control: automatically read CAD drawings, identify Die layouts, and link lasers, bit error meters, power meters and other equipment to achieve the whole process control of alignment, calibration and acquisition.

Flexible scripting and concurrent scheduling: The built-in sequencer module supports Python/Excel scripting, multi-threaded parallelism, and test sequence scheduling, adapting to multi-channel scenarios.

Structured data management: Built-in cloud/local database to centralize the management of test plans, component definitions, configuration parameters, and test results, and support multi-site collaboration and traceable data analysis.

AI-driven skip test optimization: PILOT is natively compatible with AI tools that can train and deploy models, identify defect patterns, predict results, and intelligently skip redundant tests, significantly improving yield and test efficiency.

Strong Interoperability Ecosystem: It can be seamlessly integrated with Excel, MATLAB, Power BI, and other tools to help users efficiently complete data analysis and report generation.
The PILOT platform has truly realized the leap from "static verification" to "dynamic parameter adjustment", from "single point testing" to "process collaboration", and is the core software hub that supports the industrialization of wafer-level PIC chip automated testing.

Structured data management: Built in cloud/local databases enable centralized management of test plans, component definitions, configuration parameters, and test results, supporting multi site collaboration and traceable data analysis.

AI driven skip test optimization: PILOT is natively compatible with AI tools and can train and deploy models to identify defect patterns, predict results, intelligently skip redundant tests, and significantly improve yield and testing efficiency.

Strong interoperability ecosystem: can seamlessly integrate with tools such as Excel, MATLAB, Power BI, etc., helping users efficiently complete data analysis and report generation.
The PILOT platform has truly achieved a transition from "static verification" to "dynamic parameter tuning" and from "single point testing" to "process collaboration", and is the core software hub supporting the industrialization of wafer level PIC chip automation testing.

3. CTP10 testing platform: high-precision functional testing engine
CTP10 is a high-performance photonic device testing platform launched by EXFO, specifically designed for micro ring resonators MZI、 The parameter verification design of passive and active devices such as filters and VOAs has the advantages of high precision, wide coverage, and strong scalability, and is one of the key testing engines for PIC functional verification. The core advantages include:
Sub picometer resolution: Supports 20fm spectral scanning to meet the precise frequency domain response testing of high-Q micro ring devices;

Ultra wide wavelength coverage: 1240-1680nm full band coverage, suitable for multiple application scenarios such as telecommunications, data communication, and biosensing;

Ultra high dynamic range:>70dB insertion loss dynamic range, capable of measuring multiple parameters such as IL, PDL, and spectral response in a single scan;

Multi channel array support: Supports parallel measurement of 100+channels, suitable for high-density device array testing requirements such as AWG and optical switches;

Laser stability and traceability calibration: Built in DFB laser and power calibration module, achieving output stability and full process data traceability.

CTP10 adopts a modular design, supports dual control of SCPI command line and GUI graphical interface, and seamlessly integrates with PILOT software. It is suitable for research and development, pilot and mass production environments, and is the benchmark solution in current PIC testing that combines accuracy, speed and scalability.

With the continuous increase in integration and complexity of PIC chips, testing is moving from traditional "post validation" to "pre embedding". EXFO uses OPAL probe station, CTP10 measurement platform, and PILOT automation software to build an intelligent testing system covering wafers to systems, achieving high-precision coupling, multi-channel parallelism, AI assisted analysis, and data-driven decision-making, accelerating the transition of PIC chips from the laboratory to large-scale applications. Under the trend of testing strategy moving forward, testing is evolving from an auxiliary tool to a central force driving the optimization of photon manufacturing processes and industry collaboration.