Mario A. Usuga

Noise-powered probabilistic concentration of phase information

Amplifying a signal usually also amplifies the noise. A quantum-state amplifier is now demonstrated that can actually decrease uncertainty about the state’s phase. Counterintuitively, the concept involves the addition of thermal noise.

Quadrature phase shift keying coherent state discrimination via a hybrid receiver

We propose and experimentally demonstrate a near-optimal discrimination scheme for the quadrature phase shift keying (QPSK) protocol. We show in theory that the performance of our hybrid scheme is superior to the standard scheme—heterodyne detection—for all signal amplitudes and underpin the predictions with our experimental results. Furthermore, our scheme provides hitherto the best performance in the domain of highly attenuated signals. The discrimination is composed of a quadrature measurement, a conditional displacement and a threshold detector.We propose and experimentally demonstrate a near-optimal discrimination scheme for the quadrature phase shift keying protocol (QPSK). We show in theory that the performance of our hybrid scheme is superior to the standard scheme heterodyne detection for all signal amplitudes and underpin the predictions with our experimental results. Furthermore, our scheme provides the hitherto best performance in the domain of highly attenuated signals. The discrimination is composed of a quadrature measurement, a conditional displacement and a threshold detector. PACS numbers: 03.67.Hk, 03.65.Ta, 42.50.Ex ar X iv :1 20 4. 08 88 v2 [ qu an tph ] 2 6 Ju n 20 12 QPSK coherent state discrimination via a hybrid receiver 2

Quaternary Polarization-Multiplexed Subsystem for High-Capacity IM/DD Optical Data Links

We demonstrate for the first time an intensity-modulated direct-detection link using four states of polarization. The four data-independent tributaries are each assigned distinct states of polarization to enable the receiver to separate the signals. Polarization rotation due to propagation over optical fiber is tracked and compensated with simple digital signal processing in Stokes space. Transmission below the forward error correction limit is shown for maximum net bitrates of 100 Gb/s (4 × 27 GBd) and 120 Gb/s (4 × 32 GBd) over 2-km standard single-mode fiber at a center wavelength of 1550 nm.

Quad-polarization transmission for high-capacity IM/DD links

We report the first experimental demonstration of IM/DD links using four states of polarization. Fiber-Induced polarization rotation is compensated with a simple tracking algorithm operating on the Stokes space. The principle is proven at 128 Gb/s over 2-km SSMF.

OAM-enhanced transmission for multimode short-range links

We propose, experimentally demonstrate, and evaluate the performance of a multimode (MM) transmission fiber data link which is based on orbital angular momentum (OAM) modes. The proposed scheme uses OAM modes to increase capacity or reach without recurring to mode division multiplexing (MDM) or special fibers: we first excite an OAM mode and couple it to a 50 m, 100 m, 200 m and 400m MM fibers. We compare three OAM modes and a conventional optical multimode under the same launch and received optical power conditions. The proposed OAM based solution is a promising candidate for the data centers interconnects and short range links that employ the existing multimode fiber infrastructure.

100 Gbps IM/DD links using quad-polarization: Performance, complexity, and power dissipation.

A computational complexity, power consumption, and receiver sensitivity analysis for three different scenarios for short-range direct detection links is presented: 1) quad-polarization, 2) wavelength division multiplexing (WDM), and 3) parallel optics. Results show that the power consumption penalty associated to the quad-polarization digital signal processing (DSP) is negligibly small. However, the required analog to digital converters account for 47.6% of the total system power consumption. Transmission of 4×32 Gbps over 2 km standard single mode fiber is achieved with a receiver sensitivity of 4.4 dBm.

Interferometric characterization of few-mode fibers (FMF) for mode-division multiplexing (MDM)

The rapid growth of global data traffic demands the continuous search for new technologies and systems that could increase transmission capacity in optical links and recent experiments show that to do so, it is advantageous to explore new degrees of freedom such as polarization, wavelength or optical modes. Mode division multiplexing (MDM) appears in this context as a promising and viable solution for such capacity increase, since it utilizes multiple spatial modes of an optical fiber as individual communication channels for data transmission. In order to evaluate its performance, a MDM system requires advanced characterization methods with regard to the modal content of its photonics components and in particular of the fibers involved for data transmission. In this contribution we present a time-domain interferometric technique for a full modal characterization of few mode fibers (FMF), commonly used in a MDM scenario. This experimental technique requires the use of a Mach-Zehnder interferometer, where the reference’s path length is controlled by an optical delay line. The interference between the output beams of reference and fiber under test (FUT) is recorded on a CCD camera and a careful evaluation of the resulting interferograms allows us to have full access to key parameters such as number of modes, modal weight, differential time delay between propagating modes and intensity profiles. In this work, we apply this simple and complete characterization method to the case of a short link with two optical modes propagating in a FMF, which illustrates its potential as a diagnostic tool for MDM systems.

High capacity optical links for datacentre connectivity

There is a timely and growing demand for high capacity optical data transport solutions to provide connectivity inside data centres and between data centres located at different geographical locations. The requirements for reach are in the order of 2 km for intra-datacentre and up to 100 km for inter-datacentre connectivity. Moreover, the requirements for such connectivity solutions include also low cost, high data rate and desirable features such as energy efficiency and reduced interfacing cost. In this paper we review several approaches for intra and inter datacentre that use advanced modulation formats and multiplexing techniques to cope with the requirement of high capacity as well as techniques for reach extension.

OAM mode converter in twisted fibers

We analyze the case of an OAM mode converter based on a twisted fiber, through finite element simulations where we exploit an equivalence between geometric and material transformations. The obtained converter has potential applications in MDM.

Probabilistic amplification and cloning of phase-covariant coherent states

A fundamental characteristic of quantum mechanics is that amplification of a quantum state is an operation that is inevitably linked to the addition of noise [1]. As a direct consequence, it is in general impossible to generate perfect copies of an unknown quantum state. This is known as the famous no-cloning theorem [2]. However, it was shown recently, that noiseless amplification is possible by releasing the constraint of determinism [3–6], hence allowing the amplifier to generate an output only occasionally. In this probabilistic regime the output states are heralded based on some measurements that indicate successful amplification.