V. Toccafondo

Ion-exchanged Er3+/Yb3+ co-doped waveguide amplifiers longitudinally pumped by broad area lasers

A multimode pumping scheme for Er(3+)/Yb(3+) co-doped waveguide amplifiers based on broad area lasers at around 980 nm is presented. The proposed amplifier is fabricated by ion-exchange (IE) technique on silicate and phosphate glasses. The highly efficient energy transfer from Yb(3+) to Er(3+) ions, combined with the use of low cost and high power broad area laser, allows the realization of high performance and cost-effective integrated amplifiers. The structure has been designed and numerically studied using a 3D finite element modelling tool, and over 3 dB/cm small signal gain has been predicted for an optimized amplifier. Preliminary characterization of an amplifier structure provides a first experimental evidence of the novel multimode longitudinal pumping.

Evanescent Multimode Longitudinal Pumping Scheme for Si-Nanocluster Sensitized Er

We present a multimode longitudinal pumping scheme for integrated rare-earth-doped waveguide amplifiers which allows an efficient use of low cost multimode pump sources. The scheme is based on evanescent pump light coupling from a multimode low loss waveguide to a single mode active core. Multimode pump light is gradually coupled to the active waveguide, which is single mode at the signal wavelengths, providing population inversion along the whole amplifier length and overcoming the main limitation of conventional single mode pump butt-coupling in case of strongly absorbing active materials. We propose this pumping scheme at 477 nm for Si-nanocluster sensitized Erbium doped waveguide amplifiers, in which conventional butt-coupling is inefficient due to the strong pump absorption by the Si- nanoclusters , and top pumping by LED arrays is limited by the low pump intensity values achievable within the active region. The coupling between the multimode waveguide and the active core has been numerically studied for slab waveguide structures using a 2-D split-step finite element method.

^{3+}

We present a longitudinal multimode pumping scheme which allows Yb-sensitized Er-doped silica waveguide amplifiers to be effectively pumped by high-power and low-cost broad-area lasers. The proposed configuration is based on evanescent pump light coupling from a multimode low-loss waveguide to a Er-Yb codoped active core. Theoretical predictions, based on propagation and population-rate equations for the coupled Er-Yb system, show that longitudinal multimode pumping by high-power broad-area lasers at around 980 nm can provide up to 4-dB gain per centimeter, suggesting possible integration of low-cost amplifiers with important applications in wavelength-division-multiplexing metro and access optical networks.

-Doped Waveguide Amplifiers

We present an efficient multimode longitudinal pumping scheme which overcomes the main limitations of single-mode longitudinal pumping as well as top pumping in Si-nanoclusters sensitized Erbium-doped waveguide amplifiers. The proposed configuration is based on evanescent pump light coupling from a multimode waveguide to a Si-nanoclusters sensitized Er(3+)-doped active core. Theoretical predictions, based on propagation and population-rate equations for the coupled Er(3+)/Sinanoclusters system, point out that the proposed pumping scheme can provide high pump intensity within the active core, also ensuring good uniformity of the population inversion along the waveguide amplifier. Although longitudinal multimode pumping by high power LEDs in the visible can potentially lead to low cost integrated amplifiers, further material optimization is required. In particular, we show that when dealing with high pump intensities, confined carrier absorption seriously affects the amplifier performance, and an optimization of both Si-nc and Er(3+) concentrations is necessary.

Er

We present a finite element based model for Si-nc sensitized Er3+ doped waveguide amplifiers (EDWA), longitudinally pumped by a novel pumping scheme using broad-area visible lasers, which accurately describes the effect of the Si-nc to Er3+ coupling ratio on the amplifier performance. We show that by pumping the active material resonantly with the Er3+ absorption spectrum, the Si-nc sensitization is extremely beneficial even at relatively low fractions of Er3+ ions coupled to the nanoclusters. On the other hand, when the pump light is only directly absorbed by the Si-nc, more than 80% of the Er3+ ions should be coupled to the Si-nc in order to achieve significant net gain. In particular, numerical results based on realistic material parameters, point out that resonant multimode pumping at 660 nm provides significant benefits in terms of gain enhancement, with respect to standard EDWAs, even at low fractions of Er3+ ions coupled to the Si-nc (less than 50%). This feature suggests that further material optimization could lead to the realization of compact and cost-effective integrated amplifiers and lasers.

^{3+}

A novel silicon photonics integrated reconfigurable nested Mach-Zehnder interferometer including tunable splitters and four independent phase modulators has been designed and fabricated. The architecture enables the generation of offset-free phase-amplitude constellations such as QPSK and 16-QAM by employing simple binary signals with equal peak-to-peak amplitude. The adoption of tunable splitters introduces novel features such as reconfiguration of the output constellation without modification of the RF waveform settings, as well as compensation for imperfections related to fabrication tolerances. The solution presented in this paper is based on travelling wave MZIs and thermally tunable splitters based on doped rib waveguides heated by Joule effect. The scheme minimizes the complexity of the employed architecture together with one of the driving signals. Numerical analysis has been also conducted to better investigate the system behavior and parameter optimization, evaluating the impact of suboptimum settings that might occur in a real implementation. Experimental results show the generation of QPSK signals up to 28 Gbd and 16-QAM signals up to 20 Gbd with measured bit error rate below the conventional FEC level.

–Yb

Integrated waveguide amplifiers based on high concentration Er3+ doped BaY2F8 crystals are numerically studied by combining a full-vectorial finite element based modal analysis and propagation-rate equations. Using realistic input data, such as the absorption/emission cross sections and Er level lifetimes measured on grown crystal samples, we investigate the amplifier performance by optimizing the total Er concentration. We predict optimum gain coefficient up to 5dB∕cm and broad amplification bandwidth exceeding 80nm with 1480nm pumping.

^{3+}

We describe and experimentally demonstrate a measuring technique for Mach–Zehnder interferometer (MZI) based integrated photonic biochemical sensors. Our technique is based on the direct measurement of phase changes between the arms of the MZI, achieved by signal modulation on one of the arms of the interferometer together with pseudoheterodyne detection, and it allows us to avoid the use of costly equipment such as tunable light sources or spectrum analyzers. The obtained output signal is intrinsically independent of wavelength, power variations, and global thermal variations, making it extremely robust and adequate for use in real conditions. Using a silicon-on-insulator MZI, we demonstrate the real-time monitoring of refractive index variations and achieve a detection limit of 4.1×10−6 refractive index units (RIU).

Codoped Silica Waveguide Amplifiers Longitudinally Pumped by Broad-Area Lasers

We investigate the potential of Er3+ doped silicon-on-insulator slot waveguides for realizing small-form factor silicon compatible emitters optically pumped at 980 nm.

Study of an efficient longitudinal multimode pumping scheme for Si-nc sensitized EDWAs

Silicon photonics is becoming a consolidated technology, mainly in the telecom/datacom sector, but with a great potential in the chemical and biomedical sensor market too, mainly due to its CMOS compatibility, which allows massfabrication of huge numbers of miniaturized devices at a very low cost per chip. Integrated photonic sensors, typically based on resonators, interferometers, or periodic structures, are easy to multiplex as the light is confined in optical waveguides. In this work, we present a silicon-photonic sensor capable of measuring refractive index and chemical binding of biomolecules on the surface, using a low-cost phase interrogation scheme. The sensor consists of a pair of balanced Mach-Zehnder interferometers with interaction lengths of 2.5 mm and 22 mm, wound to a sensing area of only 500 μm x500 μm. The phase interrogation is performed with a fixed laser and an active phase demodulation approach based on a phase generated carrier (PGC) technique using a phase demodulator integrated within the chip. No laser tuning is required, and the technique can extract the univocal phase value with no sensitivity fading. The detection only requires a photo-receiver per interferometer, analog-to-digital conversion, and simple processing performed in real-time. We present repeatable and linear refractive index measurements, with a detection limit down to 4.7·10-7 RIU. We also present sensing results on a chemically-functionalized sample, where anti-BSA to BSA (bovine serum albumin) binding curves are clearly visible for concentrations down to 5 ppm. Considering the advantages of silicon photonics, this device has great potential over several applications in the chemical/biochemical sensing industry.