What is a NA (numerical aperature) adaptor?

Yokogawa offers each - 735383-A001 50um 735383-A002 62.5um The NA adapter reduces the numerical aperture (NA) of a connected fiber to half and is only applicable to the free space optical input structure on the Yokogawa AQ6370 series OSA. FAQ: Applicable fiber: Multimode fiber (GI50/125µm and GI62.5/125µm) What it does: The NA Conversion Adapter halves the numerical aperture (NA) of a connected fiber by reducing the numerical aperture from 0.2 to 0.1 Benefits of the NA Conversion Adapter: Better dynamic range (SNR) for passive component testing: The use of a multimode fiber causes a high coupling loss with a broadband light source so that high output power cannot be expected, and the direct output of such a fiber is reduced in the Monochromator due to the NA restriction. By attaching the adapter to the end of a multimode fiber, the optical spectral level of a broad band source increases about 5 dB on the OSA. BetterDynamicRange Better level stability for active device testing: With the direct output of multimode fiber, there are cases where the measured power level becomes unstable due to dynamic speckle noise caused by modal interference. The NA conversion adapter can resolve the above issue and improves the level measurement stability by efficiently coupling the output beam with the Monochromator.