Research Methods

The research method is based on the possibility to exploit a strong collaboration between the teams involved in the different research areas mentioned in the Work Plan, namely material and devices, nonlinear effects, quantum effects, basic modelling and numerical simulations, systems. In particular,

laser samples, both realised with the best current technologies and with experimental new techniques (by Participants CNET, EPFL, UNI_ULM, KTH) are analysed in laboratories with a strong expertise in nonlinear and quantum optics (in particular, Participants INFM_FI, UCC, IMEDEA, UPMC_LKB).
The understanding of the laser behaviour is obtained by means of joint work of experimental and theoretical groups (in particular, Participants INFM_MI, IMEDEA). The predictions of the models are compared with measurements and indications for the relevant parameters to be experimentally evaluated are deduced from the theory.
As a concluding step, the complete experimental characterisation and the description of the laser behaviour given by the models allow to identify the specific laser features and the best laser geometries useful for an integration in VCSEL based systems. The test of such systems is performed by the Participants with a large experience in the field (in particular, UCC and KTH).

Moreover, the research methods for the different areas are improved.
For the first area they include exploring the possibilities given by novel materials for VCSELs and, as a preliminary step, for RCLEDs, comparing different growth techniques and laser geometries, implementing quantum wire and quantum dot structures in the gain medium.
The characterisation of VCSELs behaviour will be performed by means of spatially and polarisation selective noise and fluctuations measurements, taking care in evidencing correlation in such fluctuations and fast switchings. The analysis will be performed in time and frequency domain and with high resolution pattern analysis. Statistical and dynamic indicators will be used to characterise the behaviour in the critical stability regions. Moreover, new methods will be exploited, such as the use of optical and electro-optical feedback.
Concerning quantum effects the Participants will investigate noise in various kind of VCSELs. In the case where the laser is operating in a single mode, guided by the theory the Participants will determine the conditions to observe squeezing and find the limiting factors for quantum noise reduction. If the VCSEL is not single mode, a strong reduction of the intensity noise of noisy VCSELs can be obtained by injection locking. As a master laser, a laser diode in an external grating configuration can be used. Sub-shot noise operation will be studied in these conditions. The noise properties of VCSELs with optical feedback from an external mirror will also be studied. An important effect to be considered is the anticorrelation between different modes fluctuations, which extend to the quantum level. The correlation will be measured by two methods, one relying on polarisation separation, the other one on the spatial dependence of the noise. The results will be compared with theoretical predictions. This will be done using a quantum version of the Spin Flip Model.
Existing theoretical models will be extended, including proper spatial dependence of the electromagnetic field and of the carrier density. The different sources of noise will be analysed and included in order to describe both small fluctuations (amplitude and phase noise, partition and polarisation noise) and large noise-driven polarisation and transverse modes jumps. The Participants will investigate microscopically the unisotropies (birefringence, dichroism) which are the main responsible for polarisation selection and are usually included phenomenologically in the existing models. The Participants will obtain analytical expressions for the small signal response from the linearisation around multimode steady states, while informations on the large signal response and on the configurations stability will be given by numerical simulations. For a realistic model of VCSELs arrays the Participants will perform the analysis of the different coupling mechanism, through carriers diffusion or by evanescent waves.
The applications of VCSELs to information processing systems will be performed by exploiting polarisation and pattern switching and localised spatial structures, using the informations obtained from the other research areas.