Silicon photonics is a large-scale integration technology that uses photons and electrons as information carriers. Fiber-to-silicon coupling is a crucial aspect of chip design in silicon photonics. The quality of coupling determines the interconnection quality between optical signals on integrated silicon photonic chips and external signals. The most challenging aspect of coupling lies in the mismatch of optical mode sizes between the two mediums. The optical mode size in silicon photonic chips is typically in the order of a few hundred nanometers, while in optical fibers, it’s in the order of a few micrometers. This significant geometric difference leads to severe mode mismatch.
Optical Fiber Micro-Crack Diagnostic Instrument (OLI) has significant advantages in the quality testing of silicon photonic chip coupling. It offers sub-millimeter spatial resolution, precisely detecting each event node in the optical link. It boasts characteristics such as high sensitivity, precise localization, high stability, and user-friendliness. OLI is an excellent choice for silicon photonic chip testing.
1.The Optical Fiber Micro-Crack Detection Instrument (OLI) tests the quality of coupling connections in silicon photonic chips.
Using OLI to measure the quality of coupling connections in silicon photonic chips, both normal and abnormal samples were tested. Figure 1 shows a physical image of the coupling connection in a silicon photonic chip.
Figure 1: Physical Image of Silicon Photonic Chip Coupling Connection
The OLI test results are shown in Figure 2. Figure 2(a) represents a normal coupling sample, and Figure 2(b) represents an abnormal coupling sample. From the figures, it can be observed that the first peak corresponds to the reflection at the fiber-to-silicon waveguide coupling point, and the second peak corresponds to the reflection at the silicon waveguide to air interface. By comparing the two graphs, it’s evident that the return loss for a normally coupled connection is approximately -61dB, while in the case of an abnormal coupling, the return loss is significantly higher, around -42dB. The coupling quality can be determined by evaluating the return loss value at the coupling point.
Figure 2 (a): Sample with normal coupling
Figure 2 (b): Sample with abnormal coupling
2.Conclusion
Using OLI for testing allows for the rapid assessment of coupling quality in silicon photonic chips. It provides precise localization of internal crack positions and return loss information within the silicon photonic chip. OLI achieves sub-millimeter resolution for internal detection of silicon photonic chips, making it versatile for damage detection in optical devices, optical modules, and for determining the qualification of products in bulk shipments.