Recombination dynamics of single quantum dots in a fiber system at telecommunication wavelengths

Abstract

a b s t r a c tCoupling the emitted light from single quantum dots into an optic fiber has been demonstrated as a 'plug and play' single-photon source. In this work, lifetime dynamics measurements were performed with two time-delayed femtosecond optical pulses at different wavelengths. When the energy of the pumping light is less than the energy of the wetting layer (i.e. quasi-resonant excitation), the singlephoton sources can be operated at a speed of 1 GHz.& 2008 Elsevier Ltd. All rights reserved.Semiconductor quantum dot based single photon emission has been investigated intensively to implement quantum information processing [1][2][3][4][5][6][7][8]. Most investigations are concentrating on electrical pumping, high repetition rates, telecommunication wavelengths, high temperature operation and stability. We realized a 'plug and play' single photon sources fully integrated with optical fibers [2]. Great stability of nearly (but not limited to) one month has been demonstrated. Recently, the emission wavelength has been extended to telecommunication wavelengths using same system [9]. The details about the fiber-based system are described in Refs. [2,9]. To improve the repetition rates of the single photons for fast quantum key distribution system, photonic crystal and nano pillar cavities with distributed Bragg reflector (DBR) structure have been used to enhance emission rate, i.e. reducing lifetime of exciton recombination [4,10]. To count the single photons at telecommunication wavelengths, InGaAs single photon detectors are normally used. Because of the large dark counts of InGaAs detectors, the detectors are operated in Geiger mode and gated at 5 MHz with a pulse width of 40 ns. With this detector, it is difficult to verify how fast the single photon sources can be operated. To examine the pulse rate of our single-photon gun at 1:3 mm, time resolved photoluminescence (PL) measurements were performed with two separated optical pulses at different wavelengths.The InAs QD wafer with a 1:3 mm wavelength emission is grown by molecular-beam epitaxy with an InGaAs capping layer. The QD layer is embedded in a 1-lambda cavity between 1-period (top) and 15-period (bottom) GaAs=Al 0:9 Ga 0:1 As DBRs, in order to enhance the extraction efficiency. To achieve very low quantum dot density (around 2 Â