The disadvantages of optical fibres are:
Price - Even though the raw material for making optical fibres, sand, is abundant and cheap,
optical fibres are still more expensive per metre than copper. Although, one fibre can carry many more signals than a single
copper cable and the large transmission distances mean that fewer expensive repeaters are required.
Fragility - Optical fibres
are more fragile than electrical wires.
Affected by chemicals - The
glass can be affected by various chemicals including hydrogen gas (a problem in underwater cables.)
Opaqueness - Despite extensive military use it is known that most fibres become opaque when exposed to radiation.
special skills - Optical fibres
cannot be joined together as a easily as copper cable and requires additional training of personnel and expensive precision
splicing and measurement equipment.