The rapid growth of AI computing is placing enormous pressure on the connections between processors, memory, and other computing resources. As more data moves through these systems, conventional electrical interconnects face increasing constraints in bandwidth density and power consumption.

Optical interconnects offer a path forward. By moving data using light, they can support high bandwidth while reducing the energy required to transmit each bit. The industry is therefore exploring ways to bring optical communication closer to compute and memory, including highly parallel architectures with many optical channels operating simultaneously.

MicroLED arrays are emerging as one possible transmitter technology for these systems. Their small size, high modulation potential, and compatibility with dense arrays make them well suited to parallel optical links. Researchers have already demonstrated microLED-based CMOS transceivers with hundreds of channels, aggregate data rates in the terabit-per-second range, and the potential for sub-picojoule-per-bit operation.

But moving from a promising device demonstration to a scalable interconnect architecture introduces a fundamental testing challenge. A microLED used for communication must be evaluated differently from a microLED intended for a display.

A functioning emitter is only the beginning

For a display application, microLED testing generally focuses on whether each pixel produces the required brightness and color with sufficient uniformity. Those parameters remain important in an optical interconnect, but they become part of a more demanding system-level question:

Can every emitter deliver enough usable optical power, at the required operating current, to support a reliable communication channel?

In a highly parallel architecture, the answer must be established across hundreds or thousands of devices. A small number of weak or inconsistent emitters can create imbalanced channels, reduce system margin, and affect the performance of the complete link.

This means that average wafer performance is not enough. Manufacturers need to understand the distribution of device behavior, identify outliers, and locate spatial patterns that may indicate variation in epitaxy, fabrication, or processing.

Several measurements become particularly important.

Low-current behavior determines energy efficiency

One of the main attractions of microLED optical interconnects is their potential to operate at very low energy per bit. Realizing that potential requires the emitters to perform efficiently at low drive currents.

Measurements made only at conventional display operating currents may not reveal what happens in this regime. Leakage, turn-on behavior, optical output, and external quantum efficiency can all change as current decreases. Two devices that appear similar at a higher current may perform very differently at the current relevant to the communication architecture.

Low-current IV, LIV, and EQE characterization can expose these differences. It allows development teams to determine whether an emitter is genuinely suited to low-power operation and to define acceptance limits based on the intended use rather than on a generic LED specification.

Parallel channels make uniformity critical

The bandwidth density of a microLED interconnect comes from operating many optical channels in parallel. This makes array-level uniformity a functional requirement.

Variation in optical intensity can produce different power margins from one channel to another. Wavelength variation may affect the response of optical components in the path. Electrical differences can also complicate the design of the driver circuitry or require additional compensation.

Wafer-level mapping provides a much clearer picture than measurements from a small number of selected devices. It can reveal the full distribution of intensity, wavelength, current, voltage, and efficiency, as well as systematic patterns across the wafer. This information supports process optimization, device classification, and the development of meaningful pass/fail criteria.

The tails of these distributions often matter as much as their averages. In a large parallel array, even a low percentage of outliers can translate into a significant number of marginal channels.

Optical power must reach the receiver

The amount of light emitted by a microLED does not, by itself, determine how much light reaches the receiving element. The direction in which that light is emitted also matters.

Depending on the architecture, the microLED may need to couple into a fiber, waveguide, lens, or detector. Each optical interface accepts light within a defined spatial and angular range. An emitter can therefore produce sufficient total optical power while delivering too little usable power into the intended optical path.

Angular emission measurements help connect device performance to coupling performance. By measuring how intensity changes with emission angle, engineers can evaluate how the microLED interacts with the surrounding optical design and compare different device structures, materials, and processing conditions.

This is particularly important during development, when emitter design and optical coupling architecture must be optimized together. The link budget begins with the light that can actually be collected, not simply the total light generated by the device.

Temperature adds another source of variation

Optical interconnects located close to processors and memory may operate in demanding thermal environments. Changes in temperature can affect wavelength, optical output, efficiency, and electrical behavior.

A device that meets its target under laboratory conditions may behave differently at the temperatures expected in the final system. Temperature-controlled electro-optical characterization allows engineers to observe these changes early and determine whether sufficient operating margin exists across the relevant range.

Thermal measurements can also help separate different failure mechanisms and provide useful data for reliability studies. For densely integrated systems, this information becomes part of understanding how device-level behavior will translate into link-level stability.

Testing before integration reduces downstream risk

MicroLED optical interconnects may require the emitter array to be bonded or otherwise integrated with CMOS and optical components. At that point, a defective or marginal emitter is no longer an isolated wafer-level problem. It is part of a more valuable and complex assembly.

Finding weak devices before integration can therefore have a significant effect on development cost and manufacturing yield. Detailed wafer-level characterization supports process learning and device selection, while high-throughput inspection provides the data needed to apply those criteria across production volumes.

The goal is to move from simply identifying visibly non-functioning devices to determining which devices are suitable for the intended communication system. That requires measurements that reflect actual operating conditions and produce actionable data at both device and wafer level.

From device measurements to link requirements

InZiv provides electro-optical testing and inspection capabilities for both microLED development and production. The OmniPix 3.0 platform supports low-current IV, LIV, and EQE characterization, high-resolution spectral and intensity mapping, angular emission measurement, localized EL and PL analysis, and temperature-controlled testing. These capabilities allow development teams to investigate how device design and process variation affect communication-relevant performance.

For production environments, the R-EL Glide performs high-throughput true-EL wafer inspection, collecting wavelength, intensity, and IV data with configurable pass/fail logic. This provides a path for translating the criteria established during R&D into scalable wafer-level screening.

MicroLED optical interconnects will depend on more than achieving high data rates in individual demonstrations. Their commercial viability will also depend on uniformity, coupling efficiency, low-current performance, thermal stability, and manufacturing yield across large arrays.

Measuring those properties before integration gives manufacturers the information they need to improve the process, select suitable devices, and reduce the risk carried into later manufacturing stages. As optical I/O moves closer to compute, wafer-level electro-optical testing will become an increasingly important part of building reliable, energy-efficient links at scale.

To learn more or arrange a confidential demonstration on your device, visit inziv.com or contact info@inziv.com