Medium frequency (100kHz - 1MHz) measurements of electrical noise power spectrum densitiy in DBR tunable lasers show particular behaviour around threshold, compared to classical edge-emitting structures. In this paper, we consider structures in which tunability is made by current injection. Standard monomode (SMSR > 40 DB) non tunable DBR lasers Noise Level follow a global shot-noise tendancy, except around the laser threshold current level (called Ith). In these structures, a strong excess of noise is classically established at Ith. Next, at Ith+epsilon, the noise level goes down again to the shot noise level. In DBR tunable lasers, this behaviour is exactly the same, except that epsilon grows up when the current level in the Bragg section gets stronger. The aim of this paper is to establish a link between the 'epsilon' factor and the current level in the Bragg section.
Most common monomode tunable laser diodes use carriers injection to change a bulky semi-conductor material's optical index (through absorption), with the aim of switching the emission wavelength, thanks to the phasis comb spectrum or Bragg filtering evolution. This index change existe in the active, phase and Bragg section. Independently, current injection in a laser diode involves the existance of a fundamental shot noise and of excess 1/f noise. This noise power creates optical index fluctuations in all of the 3 sections, and so modulates the laser's light field. As there is a close link between absorption and refraction index in semiconductors, through Kramers-Kronig relationships this modulation has an influence on both phase and amplitude of the laser field. The aim of this paper is to establish the correlations existing between electrical shot noise and 1/f noise of the tuning sections and the laser field's optical noise.
The spectral purity of laser radiation is a key point in the performance of coherent optical network. As 850nm VCSELs are being used in short distance interconnections, the evaluation of the frequency noise level is essential. Using a Fabry-Perot cavity as a frequency discriminator, the frequency noise spectrum is being investigated in the medium frequency and high frequency range (up to 1GHz). Frequency noise spectra show a 1/fn part in the medium frequency domain and a traditional white noise part in the high frequency domain. The aim of this paper is to present our measurements concerning 850nm-selectively-oxidized VCSELs and to investigate the different factors which have a quantitative influence on the frequency noise spectrum.
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