For some applications, instead of standard polished connectors (e.g. FC/PC), angle polished connectors (e.g. FC/APC) may be used, whereby the non-perpendicular polish angle greatly reduces the ratio of reflected signal launched into the guided mode even in the case of a fiber-air interface.
==In microscopy==
{{main|Oil immersion}}
In [[optical microscope|light microscopy]], oil immersion is a technique used to increase the [[Optical resolution|resolution]] of a [[microscope]]. This is achieved by immersing both the [[Objective (optics)|objective lens]] and the specimen in a transparent oil of high [[refractive index]], thereby increasing the [[numerical aperture]] of the objective lens.
Immersion oils are transparent oils that have specific optical and [[viscosity]] characteristics necessary for use in microscopy. Typical oils used have an [[index of refraction]] around 1.515.<ref>[http://www.olympusmicro.com/primer/anatomy/immersion.html "Microscope Objectives: Immersion Media"] by Mortimer Abramowitz and Michael W. Davidson, ''[[Olympus Corporation|Olympus]] Microscopy Resource Center'' (website), 2002.</ref> An oil immersion objective is an objective lens specially designed to be used in this way. The index of the oil is typically chosen to match the index of the microscope lens glass, and of the [[cover slip]].
For more details, see the main article, [[oil immersion]]. Some microscopes also use other index-matching materials besides oil; see [[water immersion objective]] and [[solid immersion lens]].
