Driven by the exponential growth in interconnect bandwidth required for Large Language Model (LLM) training and AI inference, Co-Packaged Optics (CPO) technology has emerged as a critical architectural evolution. By heterogeneously integrating high-density Optical Engines (OE) with core switching ASICs or compute units (XPUs) on a single 2.5D/3D advanced packaging substrate at extreme proximity, CPO completely bypasses long-distance copper interconnects. This fundamentally reduces parasitic capacitance and significantly preserves high-speed signal integrity. With its disruptive advantages—low power consumption, high bandwidth, and unparalleled density—CPO is positioned as the core optical interconnect framework for next-generation data centers. As industry leaders accelerate CPO commercialization, LightCounting projects a substantial ramp-up in global CPO port volumes between 2026 and 2030. The urgent demand for 3.2T/6.4T iterations in AI data centers will drive the overall CPO market into exponential growth.
However, this high degree of integration introduces geometrically increasing fault tolerances. In the CPO paradigm, where the costs of advanced process nodes and packaging are structurally high, the failure of a single micro-chiplet or optoelectronic component can render an entire multi-thousand-dollar compute package obsolete. Consequently, ensuring that every bare die is a Known Good Die (KGD) prior to final assembly necessitates a strategic "shift-left" in testing methodology. Strict yield control to prevent post-packaging total loss is the defining bottleneck for realizing High-Volume Manufacturing (HVM) in the CPO industry.
As a leading provider of optical communication test solutions globally, Nexustest anticipated this structural industry challenge. Rooted in deep foundational expertise in optical and semiconductor testing, and leveraging autonomous R&D capabilities in core instrumentation and automated test systems, Nexustest has proactively engineered a complete CPO test ecosystem. We have established a full-stack, end-to-end automated testing architecture covering the critical components of the CPO value chain—from CW high-power lasers and PIC Silicon Photonics wafers to Optical Engines (OE)—serving Foundries (Fabs), OSATs, and OEMs. Through this core trajectory, Nexustest is constructing a highly reliable optoelectronic testing foundation for the global HPC/AI ecosystem.
01 Nexustest: A Technological Pioneer in Optical Communication and Semiconductor Testing
To evaluate CPO testing technology objectively, one must first examine the foundational capabilities of Nexustest as a provider of high-end global test instrumentation.
Nexustest’s core operations are precisely focused on optical and semiconductor test solutions. In the High-Performance Computing and Artificial Intelligence (HPC/AI) era, our mandate is to advance global testing efficiency through uncompromising quality and technological innovation. R&D constitutes the structural core of Nexustest’s competitiveness: engineering personnel account for over 40% of the workforce, with annual R&D expenditure consistently exceeding 23% of revenue. Through the deep integration of algorithms, software, and hardware architectures, Nexustest has developed three proprietary technology platforms: High-Speed Signal Testing, Weak Analog Signal Testing, and Complex Probing & Sorting. Supported by a portfolio of over 300 global patents, the company operates five major product lines covering high-speed communication, analog signals, optical chips, power semiconductors, and memory chips.
02 The "Optical Power" Foundation: CW High-Power Laser Testing
Given that silicon is an indirect bandgap semiconductor, Silicon Photonics systems cannot independently achieve efficient stimulated emission. Consequently, the industry standard relies on External Laser Sources (ELS) or blind-mateable source modules, utilizing high-power Continuous Wave (CW) lasers fabricated from III-V compound semiconductors (e.g., InP) to provide the requisite "optical power" for the silicon engines.
Because the core ASICs within CPO switches generate extreme thermal loads—and lasers are highly susceptible to high temperatures (which induce wavelength drift, output degradation, or catastrophic optical damage)—these external sources demand extreme long-term reliability. Every laser bare die and Chip-on-Carrier (CoC) device must undergo comprehensive characterization and high-stress reliability screening. Nexustest has established a globally prominent technological lead in this critical front-end testing phase.
Based on incomplete industry data for 2025, Nexustest commands the leading market share in CW laser bare die testing and CoC burn-in screening equipment. Top-tier global CW laser manufacturers currently deploy Nexustest systems for HVM. Looking toward 2026, as 800G/1.6T transceiver and silicon photonics demands surge alongside CPO scaling, related test equipment revenue is projected to exhibit robust growth.
2.1 Laser Bare Die Testing
To guarantee KGD delivery and maintain high yields before packaging, Nexustest independently developed the CT-820X and CT-830X automated LD Bare Die Test Systems.
Precision Extraction: Delivers high-speed, high-precision LIV (Light-Current-Voltage) scanning and spectral analysis, rapidly extracting critical parameters such as threshold current, slope efficiency, and Kink phenomena. Built-in high-resolution optical spectrum modules capture Side-Mode Suppression Ratio (SMSR) and center wavelength drift under high-speed modulation.
Wide Temperature Range: Proprietary high-wear, high-thermal-conductivity chucks support -50°C to 125°C environments. The exceptional thermal management allows chips to withstand higher saturation currents, accurately measuring true optical power limits without false rejections.
Pulse Testing Capabilities: Equipped with a proprietary 1µs narrow-pulse power board for precise pulse LIV and spectral testing of high-power CW lasers.
Mechanical Stability: A patented probe station design ensures force deviation remains ≤ ±0.5g even after 100,000 touchdowns, ensuring absolute data consistency and minimizing downtime.
Industry-Leading UPH: Single DFB (pulse) test cycles operate at 5.2 seconds. Combined with >99.5% AI OCR recognition and <0.1% drop rates, the system supports ultra-fast, fully automated scale production.
Zero Physical Damage: Four-sided AOI integration utilizes micron-level pure visual positioning and flexible probe technology to intercept defects prior to packaging.
2.2 CoC Burn-In System
Laser diodes exhibit a characteristic "bathtub curve" failure rate. To intercept "early failures" caused by latent lattice defects, devices must undergo accelerated Burn-in under high-temperature, high-current stress.
The Nexustest BI620X CoC Burn-in and Test System supports massive concurrent processing of thousands of mounted lasers per unit. Utilizing an advanced Thermal Control Unit (TCU), it injects high-intensity constant current with ultra-low ripple while maintaining strict temperature uniformity across all CoC sites.
Crucially, the BI620X breaks the traditional "blind burn-in" bottleneck by achieving closed-loop In-situ Testing. By continuously monitoring optical power degradation trajectories and utilizing smart algorithms for dynamic lifespan prediction, it ensures every laser entering the CPO supply chain meets extreme long-term reliability criteria.
03 Silicon Photonics Wafer-Level Automated Testing
In the CPO manufacturing chain, yield control at the Foundry (Fab) level dictates the ultimate cost structure. Before entering costly heterogeneous packaging, Silicon Photonic Integrated Circuits (PIC) require exhaustive optical and electrical characterization at the wafer level. Leveraging profound optoelectronic testing expertise, Nexustest developed the sCT9002 Silicon Photonics Wafer Test System. With nearly 100 global installations and data accumulated from tens of thousands of wafers, the system reflects high validation from top-tier users.
3.1 sCT9002: Fully Automated and Comprehensive Wafer-Level Platform
Broad Compatibility: Fully supports mainstream 8-inch to 12-inch silicon wafers with thicknesses ranging from 200µm to 2000µm.Extreme Automation: Automates Wafer Loading and Optical Alignment, minimizing human intervention.
Wide Temperature Probing: Temperature-controlled chucks support rigorous testing from 25°C to 150°C, matching data center reliability standards.
Optical, DC, and RF Integration: Synchronizes Optical, Direct Current (DC), and high-frequency Radio Frequency (RF) testing within a unified process.
3.2 High-Precision Optical Coupling Technology
Versatile Coupling: Seamlessly handles traditional Grating Coupling (GC) and highly complex Edge Coupling (EC). Supports full detection from single fibers to complex Fiber Arrays.
Exceptional Performance: Typical optimization coupling time is merely 1.0 second. Coupling repeatability error is strictly controlled within 0.2dB, representing the industry's highest echelon.
Rapid Calibration: Supports rapid Fiber Array Unit (FAU) replacement with a one-click automatic calibration completing in under 3 minutes, maximizing Overall Equipment Effectiveness (OEE).
Software Flexibility: Supports customized Python scripts, a drag-and-drop GUI for test flow editing, and remote control via Slave mode.
04 CPO Testing: Total Solutions for Bare Die Probing, Sorting, and ATE
Following rigorous laser screening and PIC yield validation, the process enters the most technically demanding and high-value phase: Optical Engine (OE) testing.
OEs utilize 2.5D/3D advanced packaging (e.g., TSMC COUPE) to interconnect PICs and Electronic ICs (EIC—including TIAs and Drivers) via fine-pitch micro-bumps or hybrid bonding, creating a high-density electro-optical interconnect system capable of 6.4Tbps per lane.
Addressing different OE packaging stages, Nexustest released two flagship systems: the OPB8201 Automated Sorter for OE AST testing, and the OPB8301 High-Precision Prober for OE DLT testing, covering scenarios from "pigtailed finished products" to "receptacle-equipped semi-finished products" and "singulated bare dies." Paired with the high-speed, high-density SP9000e ATE, Nexustest is one of the very few suppliers globally capable of delivering a complete CPO OE testing solution. Nexustest's CPO OE Die testing solutions have already secured orders from top-tier international CPO clients.
4.1 OPB8201: CPO OE Chip-Level Test & Sorting System
Designed for semi-finished OEs equipped with receptacles for Detachable-FAU connections.
Mechanical Mastery: This modular system (2750mm x 1700mm x 2180mm) ensures extreme mechanical flexibility. Compatible with Gel-Paks and customized trays, its Pick & Place robotic arm maintains 10µm positioning accuracy at high velocities.
Air Damper Socket Design: To transmit 100G/200G per lane signals without fracturing the fragile OE substrate, Nexustest engineered an air-damper testing socket. It provides a customized 20kgf bidirectional contact pressure while ensuring a smooth "soft landing," eliminating micro-crack damage.
Throughput and Traceability: Supports absolute parallel testing across 4 sites. Under a 95% OEE metric, the UPH reaches 570 units. Testing occurs within an active 25℃ to 125℃ thermal environment, monitored by a 30µm high-resolution 6S AOI system and comprehensive QR/OCR tracking, granting every KGD a traceable digital passport.
4.2 OPB8301: CPO OE Chip-Level Probing Station
Designed for cutting-edge OE architectures (e.g., TSMC COUPE) where the singulated OE Die lacks receptacles or pigtails, presenting a pure "Bare Die" with electrical micro-bump pitches down to the 50µm scale for Die Level Testing (DLT).
Dual-Sided Probing: Overcoming the limitations of traditional probers on heterogeneous chips, the OPB8301 implements dual-sided probing. High-frequency electrical probe cards compress from the Top, while optical probes capture signals from the Bottom. Precision machining and dynamic compensation algorithms constrain structural planarity errors to within 20µm.
Hexapods & Active Alignment: Features a dedicated coupling chuck comprising 6-DOF Hexapods and Piezo stages. Supporting both GC and EC, the active algorithm completes nano-scale alignment for Edge Coupling (EC) in approximately 6 seconds, strictly limiting optical loss to <0.3dB.
Comprehensive Integration: Combines 5µm electrical probe alignment accuracy with liquid cooling and heating pad active thermal management, creating an optimal testing environment for ultra-fine-pitch OE Bare Dies.
4.3 SP9000e: High-Speed, High-Density CPO ATE
Built upon Nexustest’s high-speed instrumentation pedigree, the SP9000e is a high-density ATE engineered specifically for CPO.
Supporting up to 12 expansion slots within a single chassis, it seamlessly drives 4 parallel test sites:
Digital & Control: Delivers digital vector channels up to 1.6 Gbps (0.9GVec) with built-in PPMU.
Dynamic Power Source (DPS): Supplies multi-core voltage domains with 1.2A up to 25A per channel, supporting ganged configurations for extreme peak power testing.
Precision Measurement Unit (PMU): Features sub-nA level accuracy to detect minute leakage currents and transistor-level defects.
Ultra-High-Frequency External BERT: Provides PRBS pattern generation and BER capture up to 106 GBaud directly at the DUT board level.
Tester-on-DUT-Board Architecture: To mitigate signal attenuation and phase jitter critical in 1.6Tbps+ testing, Nexustest replaced traditional cabling with a direct-docking architecture. During OE DLT testing, high-speed resource boards hard-dock directly with the OPB8301 probe card; during OE AST testing, ultra-short specialized cables connect to the OPB8201 DUT board. This uncompromising design minimizes physical link length, ensuring maximum high-frequency RF signal integrity.
Conclusion: Nexustest — Propelling the Future of the CPO Ecosystem
Co-Packaged Optics is architecting the deep convergence of the semiconductor and optical communication supply chains. As a premier test solution provider, Nexustest recognizes that highly reliable testing is the fundamental anchor for yield assurance and cost control within advanced packaging paradigms. Through our proprietary CPO OE probers, sorters, independent high-performance instruments, and modular ATE platforms, Nexustest covers the most critical junctures of CPO production. We are dedicated to providing the global market with cost-effective, seamlessly scalable high-volume testing architectures. Nexustest stands ready to advance alongside our global partners, engineering the boundless future of the computational optical network era.
