Whenever a connector is installed on the end of fibre, loss is incurred.  Some of this light loss is reflected directly back down the fibre towards the light source that generated it.  These back reflections, or Optical Return Loss (ORL), will damage the Laser Light Sources and also disrupt the transmitted signal.  To reduce back reflections, we can polish connector ferrules to different finishes.  A typical hand polished connector will measure at –30dB.  This polish is referred to as a PC or Physical Contact polish, which for some systems is considered too high of an ORL measurement.  To reduce the back reflection of a connector, we can machine polish it to SPC (Super Physical Contact) polish or UPC (Ultra Physical Contact) polish.  Industry standard is a minimum of –40dB for SPC Back reflection measurement and –50dB for UPC back reflection measurement.  If even less back reflection is required, an APC, or Angled Physical Contact polish, might be necessary.  An APC connector has an 8º angle cut into the ferrule.  These connectors are identifiable by their green color.  An APC polished connector has an Industry Standard Minimum of  –60dB ORL measurement. Most CATV and telephone companies require the use of these low back reflection connectors.