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IEC 62496-2-4:2013 — Optical Circuit Boards — Transmission Test Without I/O Fibres
Optical circuit boards — Basic test and measurement procedures — Part 2-4: Optical transmission test for optical circuit boards without input/output fibres
Why OCBs Matter
Optical circuit boards can increase interconnect bandwidth by 100-1000x compared to copper traces while reducing power consumption by 10-100x. They also provide galvanic isolation and EMI immunity.
Optical circuit boards can increase interconnect bandwidth by 100-1000x compared to copper traces while reducing power consumption by 10-100x. They also provide galvanic isolation and EMI immunity.
Alignment Challenge
The most critical aspect of OCB testing is aligning the input light source to the waveguide facet. Typical waveguide dimensions are 30-50 micrometers, requiring sub-micrometer positioning accuracy.
The most critical aspect of OCB testing is aligning the input light source to the waveguide facet. Typical waveguide dimensions are 30-50 micrometers, requiring sub-micrometer positioning accuracy.
Engineering Insight
For production testing of OCBs, the key trade-off is between test coverage and throughput. A practical approach is to use single-wavelength pass/fail testing for production and reserve spectral measurements for design verification.
For production testing of OCBs, the key trade-off is between test coverage and throughput. A practical approach is to use single-wavelength pass/fail testing for production and reserve spectral measurements for design verification.
Introduction to Optical Circuit Board Testing
As data rates in telecommunications and data centers continue to climb, traditional copper interconnects are approaching fundamental physical limits. Optical circuit boards (OCBs) — which integrate optical waveguides directly into the printed circuit board substrate — offer a promising path forward by enabling high-bandwidth optical interconnects between components without the bulk and EMI susceptibility of copper traces. IEC 62496-2-4, published in 2013, specifies the test method for determining whether an optical circuit board without input/output fibres meets the optical transmission requirements.
The standard specifically addresses OCBs without I/O fibres — meaning the optical waveguides are terminated directly at the board edge or at connector interfaces. This configuration is increasingly common in high-volume applications where fibre handling adds cost and complexity.
Test Equipment and Measurement Methodology
The standard specifies a measurement setup consisting of: a light source system with controlled wavelength, power, and launch conditions; an observation system (microscope coupled to a camera or photodetector); and precision positioning stages with sub-micrometer resolution for aligning the input illumination to the waveguide facets. The light source must be selected based on the waveguide material system — polymer waveguides typically use 850 nm or 1310 nm sources.
The inspection method requires: preparation of the OCB by cleaning the waveguide end-facets, alignment of the input light source to each waveguide input port, measurement of the output optical intensity at the corresponding output port, and comparison against the pass/fail threshold.
Pass/Fail Criteria and Quality Assurance
The standard defines the pass/fail decision based on the optical insertion loss of each waveguide channel. Typical acceptance criteria for polymer waveguide OCBs range from -3 dB to -6 dB maximum insertion loss per channel, depending on the application requirements. The measurement must account for coupling losses at the input and output interfaces, propagation losses along the waveguide length, and any losses due to bends, splices, or crossings.
For quality assurance, the standard requires documentation of test results for each OCB, including insertion loss per channel, test source wavelength and power, ambient conditions, and any anomalies observed. The standard also addresses statistical sampling plans for lot testing in production environments.
| Parameter | Test Condition | Typical Acceptance | Measurement Method |
|---|---|---|---|
| Insertion loss (per channel) | 23 °C, 50% RH | -3 dB to -6 dB max | Direct output power measurement |
| Wavelength | 850 / 1310 / 1550 nm | Per design spec | Stabilized laser source |
| Waveguide dimensions | 30-50 μm core | ±3 μm tolerance | Microscope inspection |
| End-face quality | Clean, no defects | No chips >2 μm | Optical microscopy |
| Environmental | 23 ±5 °C | Stable during test | Chamber monitoring |
Frequently Asked Questions
Q: What is an optical circuit board (OCB)?
An optical circuit board integrates optical waveguides into its structure to carry optical signals between components. Unlike traditional PCBs using copper traces, OCBs use polymer or glass waveguides for much higher bandwidth and lower power consumption.
Q: What does without input/output fibres mean?
It means the OCB does not have fibre pigtails attached to its waveguides. The waveguides are terminated directly at the board edge or at optical connector interfaces.
Q: What is the typical insertion loss of an OCB waveguide?
Typical insertion loss for polymer waveguide OCBs ranges from -0.1 dB/cm to -0.5 dB/cm for propagation loss, plus -0.5 dB to -1.5 dB per coupling interface.
Q: How does OCB testing differ from fibre optic testing?
OCB waveguides are terminated at the board edge with no fibre pigtails, requiring precise free-space coupling of the test light source to the waveguide facet with sub-micrometer positioning.
