  The Cherenkov Telescope Array (CTA) project, led by an international
collaboration of institutes, aims to create the world's largest next generation
observatory for Very High Energy (VHE) gamma-ray astronomy. It will be devoted
to observations in a wide band of energy, from a few tens of GeV to a few
hundreds of TeV with Large, Medium and Small-sized telescopes. The Small-Size
Telescopes (SSTs) are dedicated to the highest energy range above a few TeV and
up to 300 TeV. GCT is an imaging atmospheric Cherenkov telescope (IACT)
proposed for the subarray of about 70 SSTs to be installed on the Southern site
of CTA in Chile. The Observatory of Paris and the National Institute for Earth
Sciences and Astronomy (INSU/CNRS) have developed the mechanical structure,
mirrors (aspherical lightweight aluminium segments) and control system of the
GCT. The GCT is based on a Schwarzschild- Couder (S-C) dual-mirror optical
design which has the advantages, compared to the current IACTs, to offer a wide
field of view (~ 9{\deg}) while decreasing the cost and volume (~ 9 m x 4 m x 6
m for ~ 11 tons) of the telescope structure, as well as the camera. The
prototype (pGCT) has been installed at the Meudon's site of the Observatory of
Paris and was the first S-C telescope and the first CTA prototype to record VHE
events on-sky in November 2015. After three years of intensive testing, pGCT
has now been commissioned. This paper is a status report on the complete GCT
telescope optical system and the performance it can provide for CTA.
