Modular fiber optic cassette, system and method

A modular fiber optic cassette system, the system comprising:

• a case comprising a top and a bottom wall and two opposed side walls, each of said sidewalls attached between respective side edges of said top and bottom wall, said walls together defining a tray receiving space there between and a forward edge of each said wall together defining an opening to said tray receiving space;
• at least one tray slideably received within said tray receiving space for movement between a stored position wherein said tray is completely inside said tray receiving space and an accessible position wherein a front end of said tray is in front of said opening and outside of said tray receiving space;
• a set of fiber optic cassettes, a selected plurality of the cassettes arrangeable side by side along said tray front end wherein each of said cassettes comprises a plurality of optic plug receiving receptacles arranged side by side in a row along a front thereof, a first of said set of cassettes comprising a first cassette width of one of one, two, three, four and six standard width units and a second of said cassettes comprising a second cassette width different from said first cassette width and one of one, two, three, four and six standard width units;
• and
• a fastener for removeably securing each of said cassettes to said tray.