A METHOD AND APPARATUS FOR DETECTING ULTRA-SHORT LIGHT PULSES OF A REPETITIVE LIGHT PULSE SIGNAL, AND FOR DETERMINING THE PULSE WIDTH OF THE LIGHT PULSES

摘要

Apparatus for determining the pulse width of ultra-short light pulses of an input repetitive light pulse signal comprises a two-photon absorption. detector (2) in the form of a microcavity (3) having an active region (4) located between top and bottom distributed Bragg reflectors (5,6). An optical fibre cable 16 directs the input light pulse signal combined with a reference repetitive light pulse signal normal to an incident surface (8) of the detector (2). The input light pulse signal is split in a polarisation light splitter (19) to form the reference light pulse signal which is passed through a delay line (23) to a polarisation light combiner (20) to be combined with the input light pulse signal, and directed at the incident surface (8) by the optical fibre cable (16). The delay line (23) is operated for alternately bringing the respective light pulses of the input and reference light pulse signals into and out of phase with each other to produce a pulsed photocurrent in the microcavity (3). A monitoring circuit (14) monitors the pulsed photocurrent, and the pulse width of the light pulses is determined as the full width half maximum of the pulsed photocurrent trace. By varying the angle of incidence at which the input and reference light pulse signals are incident on the incident surface (8), the apparatus is tuneable to input light pulse signals of different wavelengths within a predetermined range of wavelengths.