Nicola Brandonisio

Wavelength switching dynamics of two-colour semiconductor lasers with optical injection and feedback

The wavelength switching dynamics of two-colour semiconductor lasers with optical injection and feedback are presented. These devices incorporate slotted regions etched into the laser ridge waveguide for tailoring the output spectrum. Experimental measurements are presented demonstrating that optical injection in one or both modes of these devices can induce wavelength bistability. Measured switching dynamics with modulated optical injection are shown to be in excellent agreement with numerical simulations based on a simple rate equation model. We also demonstrate experimentally that time-delayed optical feedback can induce wavelength bistability for short external cavity lengths. Numerical simulations indicate that this two-colour optical feedback system can provide fast optical memory functionality based on injected optical pulses without the need for an external holding beam.

Optical Synthesis of Terahertz and Millimeter-Wave Frequencies With Discrete Mode Diode Lasers

It is shown that optical synthesis of terahertz and millimeter-wave frequencies can be achieved using two-mode and mode-locked discrete mode diode lasers. These edge-emitting devices incorporate a spatially varying refractive index profile, which is designed according to the spectral output desired of the laser. We first demonstrate a device that supports two primary modes simultaneously with high spectral purity. In this case, sinusoidal modulation of the optical intensity at terahertz frequencies can be obtained. Cross saturation of the material gain in quantum-well lasers prevents simultaneous lasing of two modes with spacings in the millimeter-wave region. We show finally that by mode locking devices that are designed to support a minimal set of four primary modes, we obtain a sinusoidal modulation of the optical intensity in this frequency region.

Fast Wavelength Switching of a Dual-Contact Two-Color Semiconductor Laser With Current Modulation

We present measurements of wavelength switching under current modulation in a dual-contact two-color diode laser. The Fabry-Pérot laser diode considered is designed to support only two primary modes with a spacing of 480 GHz. A heterodyne measurement of the switching dynamics with modulation of the drive current of the long contact shows switching of the intensity in times of 2 ns with 30-dB contrast ratio.

Bistability and All-Optical Memory in Dual-Mode Diode Lasers With Time-Delayed Optical Feedback

A proposal for an all-optical memory based on a bistability of single-mode states in a dual-mode diode laser with time-delayed optical feedback is presented. The system is modeled using a multimode extension of the Lang-Kobayashi equations with injected optical pulses. We uncover the bifurcation structure by deriving analytical expressions for the boundaries of the bistable region and demonstrate how the delay time in the external cavity determines an optimal pulse duration for efficient switching of the memory element. We also show the relevant role played by gain saturation and by the dual-mode solutions of the Lang-Kobayashi equations for the existence of the bistable regions. Our results demonstrate that feedback-induced bistability can lead to significant performance improvements when compared to memory elements based on the injection locking bistability in dual-mode devices.

Wavelength switching performance of single-?and dual-contact two-mode semiconductor lasers with current modulation

The wavelength switching performance of single-?and dual-contact two-mode semiconductor lasers is studied. These devices are characterized experimentally in terms of switching time, frequency chirp, contrast ratio and current modulation amplitude. Models based on multimode rate equations are used for reproducing these experimental results with good agreement between theory and experiment. The benefits of a dual-contact device are shown with respect to a single-contact device.

Point-to-point overlay of a 100Gb/s DP-QPSK channel in LR-PONs for urban and rural areas

The continuing growth in information demand from fixed and mobile end-users, coupled with the need to deliver this content in an economically viable manner, is driving new innovations in access networks. In particular, it is becoming increasingly important to find new ways to enable the coexistence of heterogeneous services types which may require different signal modulation formats over the same fiber infrastructure. For example, the same physical layer can potentially be used to deliver shared 10Gb/s services to residential customers, dedicated point-to-point (P2P) 100Gb/s services to business customers, and wireless fronthaul, in a highly cost-effective manner. In this converged scenario, the performance of phase modulated signals can be heavily affected by nonlinear crosstalk from co-propagating on-off-keying (OOK) channels. In this paper, the overlay of a 100G P2P dual-polarization quadrature phase-shift keying (DP-QPSK) channel in a long-reach passive optical network (LR-PON) in the presence of co-propagating 10Gb/s OOK neighboring channels is studied for two different PON topologies. The first LR-PON topology is particularly suited for densely populated areas while the second is aimed at rural, sparsely populated areas. The experimental results indicate that with an emulated load of 40 channels the urban architecture can support up to 100km span and 512 users, while the rural architecture can support up to 120km span and 1024 users. Finally, a system model is developed to predict the system performance and system margins for configurations different from the experimental setups and to carry out design optimization that could in principle lead to even more efficient and robust schemes.

Multi-service SDN controlled reconfigurable long-reach optical access network

The convergence of multiple service demands and different user types on a single physical layer can be enabled by dynamically reconfigurable time-division multiplexing (TDM) dense wavelength division multiplexing (DWDM) long-reach passive optical networks (PONs). In this paper we demonstrate two TDM-DWDM PON designs, the first one for densely populated urban areas and the second one better suited for rural deployment. Heterogeneous services and modulation formats, i.e. residential 10G PON channels, business 100G dedicated channel and wireless fronthaul are demonstrated experimentally coexisting on long reach TDM-DWDM PON systems, with at least 100km reach, 1024 users and emulated system load of 40 channels. End-to-end software defined networking (SDN) management of the access and core network elements is also implemented and integrated with the PON physical layer in order to demonstrate two service use cases: a fast protection mechanism with end-to-end service restoration in the case of a primary link failure; and dynamic wavelength allocation (DWA) in response to an increased traffic demand.

All-optical memory based on a two-mode diode laser with optical feedback

In this paper we numerically demonstrate that an optical memory can be based on a two-mode laser diode with optical feedback and injection in the short external cavity regime. For modelling this system we use a two-mode extension of the Lang-Kobayashi rate equations with gain saturation and optical injection. The parameters chosen are consistent with the simultaneous oscillation of the two modes in the free running laser, which is possible for frequency spacings greater than approximately 500 GHz at optical frequencies around 200 THz. For certain values of the system parameters, we have found a hysteresis loop between single-mode equilibrium states for increasing and decreasing feedback strength. Our simulations show that injected optical pulses can switch the system between single mode equilibrium states when the feedback parameters are fixed in this bistable region, demonstrating the function of the optical memory. This system has attractive features such as the absence of a holding beam and the symmetry between the two states of the memory element. These properties along with the external cavity length of 1 cm make the system an interesting candidate for optical integration.