Reflectometer tracks down optical microcracks

A high resolution reflectometer can analyse the internal structure of optical modules and visualise microcracks in optical connectors to improve reliability in photonic systems.

The AQ7420 developed by Yokogawa Test & Measurement uses optical low-coherence reflectometry) technology (OLCR) to provide a spatial resolution of 40 µm and back reflection measurement sensitivity down to -100 dB or lower, with no spurious noise. Combined with the optional sensor head unit, engineers can measure insertion loss simultaneously alongside back reflection, making the AQ7420 a highly efficient and cost-effective reflectometer for optical market applications.

The resolution f the reflectometer accurately detects the quantity and location of reflections within optical connectors and modules to find microcracks that standard loss measurements might miss, helping to avoid unpredictable and potentially detrimental failures.

In researching silicon photonics and producing fiber optic connectors, the company became aware of several emerging demands that could not be satisfied with existing market solutions. These included: even more reduction of spurious noise; simultaneous measurement of back reflection and insertion loss; enhanced stability of measured waveforms; and faster measurement time.

The objective was to develop a test system that could meet these requirements with two models covering a single-wavelength (1310 nm) and two-wavelength (1310 and 1550 nm).

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As part of general inspection processes involving optical connectors, researchers and engineers are typically tasked with measuring the ratio of multiple reflections, as well as insertion loss and breakage. Since the AQ7420 features an optional optical sensor head, it is possible to perform these measurements simultaneously – while also undertaking crack inspection.

The -100 dB high-sensitivity back reflection range meets the -85 dB or lower required to detect microcracks. It offers back reflection measurement uncertainty of ±3 dB in normal range (-14.7 to -85 dB), while in high-sensitivity range it provides ±3 dB (-50 to -90 dB) and ±5 dB (-90 to -100 dB). With the optional sensor head, the insertion loss measurement range is 0-10 dB, with an uncertainty of ±0.02 dB.

Notably, the AQ7420 has one option which can measure with 1310nm, and the other option is measure with two waves at 1310 and 1550 nm, contributing to faster optical connector inspection. It also has a polarization controller mechanism that eliminates polarization dependence. This feature enables the stable measurement of highly polarization-dependent objects in a unit measuring 430 (W) x 132 (H) x 350 (D) mm (excluding protector and handle) and weighing 8 kg.

Principal among the main new features is the ability of the AQ7420 to reduce spurious noise. With conventional OLCR/OFDR technology-based devices, spurious (ghost) noise is often observable in areas where there is no actual reflection (depending on the characteristics of the equipment), leading to misjudgments. In such situations, correct waveform analysis relies heavily on users with specialist knowledge. In contrast, the new AQ7420 features technology that greatly reduces spurious noise, with ease-of-analysis among its prominent attributes.

Another feature of note is the potential to measure back reflection and insertion loss simultaneously. Conventional OLCR/OFDR instruments are often unable to inspect back reflection amount accurately due to the poor measurement accuracy of the vertical axis (amount of reflection level). The AQ7420 high-resolution reflectometer counters this issue by enabling measurement with an uncertainty of ±3dB. Furthermore, by taking advantage of the optical sensor head, users can measure insertion loss simultaneously with an uncertainty of ±0.02dB.

Compared with the previous-generation product (AQ7410), the measurement time of the AQ7420 reflectometer is around 50% quicker, approximately 6 seconds compared with 12 seconds beforehand.

Also released is control software for Windows 11, an optional dedicated sensor head for loss measurement, various master codes (compatible with a variety of connector types) and a distance adjustment code to adjust the measurement starting position.

The reflectometer is aimed at silicon photonics research teams, manufacturers running productions lines for optical connectors and components and companies involved in the analysis of defective optical components.

tmi.yokogawa.com/p/aq7420/