Silicon photonics is a key enabling technology for scaling AI infrastructure. But producing more photonic chips also means testing more of them, and before an optical measurement can begin, the test system has to get light into and out of each device.

That connection requires precise alignment between optical fibers and the chip’s tiny optical interfaces. Repeating the alignment process across a wafer can consume valuable test time. How that alignment is achieved therefore has a direct effect on manufacturing throughput, measurement stability, and repeatability.

Why getting light into a chip takes precision

A photonic integrated circuit, or PIC, guides light through microscopic structures called waveguides. To test it, an optical fiber must deliver light into a coupling structure on the chip, while another connection may collect the light coming out.

Small errors in position or angle can reduce the amount of light transferred. This matters for both speed and measurement quality: poor coupling can make a working device appear to have excessive optical loss. Reliable testing therefore depends on establishing and maintaining a precise optical connection.

Active alignment: move, measure, adjust

Active alignment uses the optical signal itself to find the right position.

The system brings a fiber or fiber array close to the device, measures the transmitted light, and adjusts its position to improve coupling. Automated algorithms guide these movements until the required alignment is reached. The test then proceeds, and the system moves to the next device.

This is a powerful approach, particularly when engineers need flexibility to accommodate different devices or optimize coupling. Modern active-alignment systems can also align multiple channels simultaneously and perform the search very quickly. Active alignment does not necessarily mean manual adjustment or aligning every fiber separately.

The throughput challenge arises when an optical search must be repeated at each successive test site. Every search adds time before the device measurement can begin.

Small delays become large at wafer scale

Consider an illustrative wafer with 1,000 devices to test. If alignment adds five seconds per device, that amounts to roughly 83 minutes spent establishing optical connections, before accounting for measurements, movement between devices, or wafer handling.

Those figures are hypothetical, but the relationship is straightforward: repeated alignment overhead multiplies with the number of devices.

Faster measurement instruments address only part of this problem. If the system spends substantial time preparing each optical connection, shortening the measurement itself delivers a smaller improvement in total wafer throughput.

The relevant production metric is the complete cycle: position, align, measure, disengage, and move.

Passive alignment: position without repeating the optical search

Passive alignment establishes the optical connection through calibrated geometry and precise positioning, without using an optical-feedback search at every device.

In InZiv’s approach, the fiber array unit, or FAU, is calibrated, and reference marks on the wafer establish where the devices are located. The system uses that known relationship to position the optical probes at each test site.

Precision remains essential. The difference is how the correct position is established: the system applies a calibrated relationship rather than rediscovering the coupling position through repeated optical adjustments.

Contact that improves stability without causing damage

InZiv’s implementation adds another important benefit: the FAU makes controlled physical contact with the wafer during testing.

When a fiber is held above a device, relative vibration between the probe and wafer can disturb the optical connection. By resting on the wafer, InZiv’s FAU dramatically reduces that relative motion, helping maintain stable coupling throughout the measurement.

Crucially, this contact is engineered to occur without damaging either the wafer or the FAU. It combines mechanical stability with the protection required for repeated probing across a wafer.

The result is improved measurement stability and repeatability. Reducing changes in coupling helps engineers distinguish actual differences between devices from variation introduced by the test setup.

What changes across the wafer

Wafer-level passive alignment removes a recurring search step from the test sequence. Devices can remain on the wafer while the system steps between test sites, establishes a stable optical connection, and performs the required measurements.

This does not mean the entire wafer is tested simultaneously. The throughput benefit comes from reducing the work repeated at each site and combining optical probing with an automated wafer-testing workflow.

The engineering requirement shifts toward maintaining accurate calibration, registration, and coupling across the wafer. Device geometry, manufacturing variation, and the required measurement tolerances determine whether a passive approach is suitable for a particular application.

Building alignment into production testing

InZiv’s Glide-SiPh PIC brings passive alignment into automated wafer-scale functional testing. Its proprietary FAU combines non-damaging wafer contact with multichannel optical and electrical characterization. Automated wafer loading, probe engagement, and stepping support testing across 200 mm and 300 mm wafers.

The system establishes optical coupling in seconds per device without iterative active tuning, supporting measurements such as optical insertion loss, functional pass/fail testing, and wafer-level yield mapping.

As silicon photonics moves toward higher production volumes, manufacturers need optical connections that are fast to establish, stable during measurement, and repeatable across successive devices. InZiv’s passive-alignment approach addresses these requirements together, making comprehensive wafer-level testing more practical as production scales.

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