Optical transmission of video signals using pulse time modulated sub-carriers over optical delays carriers

Use of pulse time modulated (PTM) subcarriers in optical links represents an attractive alternative for transmitting analog and digital signals over optical fiber channels. A novel approach for the optical transmission of multiplexed audio and video signals using a pulse width modulated (PWM) electrical subcarrier over optical delays is reported in this paper. The generation optical delays, is achieved by Lithium Niobate (LiNbO₃) electro-optic retarders, which act, at the same time, as optical modulators. Under this technique, an optical delay is generated when 45° polarized light is injected and travels through a LiNbO₃ birefringent optical waveguide. The optical delay can be modulated by the electrical subcarrier and transmitted through an optical fiber channel. At the receiver, the electrical subcarrier can be recuperated only when a second optical delay, which is matched to the transmitter's one, is introduced. An experimental set-up for transmitting multiplexed audio and video signals using a PWM electrical subcarrier over optical delays is reported in this paper.

I. Introduction

Nowadays, commonly the fiber optic communications employ Digital Modulation Formats implemented under Intensity-Modulation and Direct-Detection (IM/DD), using Laser Diodes (LD) with an external electro-optic intensity modulator Mach-Zehnder [1]. However, an efficient alternative in analog communication systems that allow interact between analog and digital signals is to use analog pulses under some modulation technique PTM [2]. The subcarriers PTM can to drive electro-optic phase modulator and coupled to optical broadband sources (LED and DSL) for coding and propagating on optical delays.