In this paper, photodetection properties of a Graphene-based device at the third telecommunication window have been reported. The structure of the device is a Graphene-silicon Schottky junction which has been simulated in the form of an Infrared photodetector. Graphene has specific electrical and optical properties which makes this material a good candidate for optoelectronic applications. Photodetection characteristic of Graphene-silicon Schottky junction is investigated by measuring the (current-voltage) curve at the third telecommunication window under 1550nm radiations. The DC electrical characteristic of the device is calculated. The simulated rectifier junction has a potential barrier of 0. 31eV, the ideality factor of 2. 7 and the saturation current of 10-11A. The detector responsivity under 1550nm radiations is measured about 20mA/W which is an order of magnitude larger than other Si-based detectors in this wavelength. The internal quantum efficiency (QEin) is calculated about 60% while the external quantum efficiency (QEex) is measured to be 1. 6%. A comprehensive theoretical justification is presented based on Fowler theory which allows comparison between the simulation results and the theoretical predictions. For simulating Graphene, a user-defined material is introduced to TCAD-SILVACO software which includes all electrical and optical properties of this novel 2D material. Graphene optical properties, specifically at near-IR region (up to 2um wavelength), have been extracted from the real measurement results. Graphene is a Si-compatible material which can provide a sensitive IR detector integrated with other Si-based devices.