Overview

Frequency Resolved Electro-Absorption Gating (FREAG) pulse analysers work on the same principle as a Second Harmonic Generation (SHG) autocorrelator, but use electro-absorption gating to sample the pulse in time. It is therefore very sensitive and can resolve sub-picosecond pulses since it is not limiited by the response time of the detector. In addition to this, at each delay position of the gate a complete spectrum is measured, so that both the spectral and temporal characteristics of the pulse are captured simultaneously. So, while a 10Gb/s data stream may look perfectly normal on a conventional oscilloscope, the FREAG will show all the changes in the underlying carrier phase in real-time, allowing complete and rapid optimisation of the system. The setup at CIT is primarily uesd to study mode-locked lasers, and has been customised for operation at 1300nm.

Main Features:

•    Real-time pulse shape and phase recovery
•    300 fs temporal resolution
•    1300 nm operation

The FREAG is part of the PDD's Laser Dynamics Laboratory. Click here for a PDF brochure.

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Location:

PDD, CIT

Case Study

Quantum dot semiconductor mode-locked lasers can spontaneously emit picosecond light pulses at high rates, making them valuable candidates for applications such as optical time division multiplexing. Traditional methods of pulse characterisation such as autocorrelation require high laser intensities and often lose critical pulse information. For example, autocorrelation always returns symmetric traces, regardless of the true pulse shape. Researchers from CIT and DCU employed a linear spectrographic tool (frequency resolved Mach-Zehnder gating) to analyse quantum dot mode-locked lasers at 10 GHz. In this tool, a trigger is derived from the laser pulses and used to open and shut as optical gate. The remaining laser light is passed through this gate and a set of laser spectra gathered as a function of pulse delay with respect to the gate. This spectrogram can then be inverted and the full laser intensity and phase information recovered. With this tool several pulse stabilisation techniques such as dual-tone optical injection have been proven and outstanding pulse jitter performance achieved.