Ultra-low-power four-wave mixing wavelength conversion in high-Q chalcogenide microring resonators.

A compact Ge11.5As24Se64.5 chalcogenide microring resonator is fabricated with an intrinsic quality factor of 3.0×105 in the telecom band. By taking advantage of the strong nonlinearity and cavity enhancement, highly efficient wavelength conversion via four-wave mixing is demonstrated using a microring resonator. Conversion efficiency of -33.7dB is obtained by using an ultra-low pump power of 63.8 µW. This work shows that Ge11.5As24Se64.5 chalcogenide microring devices are promising for quantum photonics.

Localized quantum walks in quasi-periodic Fibonacci arrays of waveguides.

New quasi-periodic arrays of waveguides (AWs) constructed with Fibonacci sequences are proposed to realize localized quantum walks (LQWs). The proposed Fibonacci arrays of waveguides (FAWs) are simple and straightforward to make, but have a rich set of properties that are of potential use for applications in quantum communication. Our simulations show that, in contrast with randomly disordered AWs, LQWs in FAWs are highly controllable due to the deterministic disorder nature of quasi-periodic systems. Furthermore, unique LQWs with symmetrical probability distribution can be conveniently realized in the FAWs.

Using state tomography for characterizing input principal modes in optically scattering medium.

We propose two new methods to measure principal modes, or Eisenbud-Wigner-Smith eigenstates in optically scattering medium. Both methods use similar techniques as in quantum state tomography, and are based on direct measurement of temporal delays. The first method requires N2 different input launching conditions, and only the mean signal delay of these input states are needed to obtain full information of the principal modes. When the mode delay differences are large and all modes are non-degenerate, a second method can be used, which only requires 3N - 2 input launching conditions.

Using the nonseparability of vector beams to encode information for optical communication.

In this work, it is experimentally demonstrated that the nonseparability of vector beams (e.g., radial and azimuthal polarization) can be used to encode information for optical communication. By exploiting the nonseparability of a vector beam's space and polarization degrees of freedom using conventional wave plates, it is shown that 2 bits of information can be encoded when applying the identity and three Pauli operators to its polarization degree of freedom. It is also shown that vector beams can be efficiently decoded with as low as 2.7% cross talk using a Mach-Zehnder interferometer that exploits a higher-order Pancharatnam-Berry phase and liquid crystal q-plates.

4 × 20 Gbit/s mode division multiplexing over free space using vector modes and a q-plate mode (de)multiplexer.

Vector modes are spatial modes that have spatially inhomogeneous states of polarization, such as, radial and azimuthal polarization. In this work, the spatially inhomogeneous states of polarization of vector modes are used to increase the transmission data rate of free-space optical communication via mode division multiplexing. A mode (de)multiplexer for vector modes based on a liquid crystal q-plate is introduced. As a proof of principle, four vector modes each carrying a 20-Gbit/s quadrature phase shift keying signal (aggregate 80 Gbit/s) on a single wavelength channel (λ∼1550 nm) were transmitted ∼1 m over the lab table with <-16.4 dB mode crosstalk. Bit error rates for all vector modes were measured at the 7% forward error correction threshold with power penalties <3.41 dB.

Quantum Walks in Periodic and Quasiperiodic Fibonacci Fibers.

Quantum walk is a key operation in quantum computing, simulation, communication and information. Here, we report for the first time the demonstration of quantum walks and localized quantum walks in a new type of optical fibers having a ring of cores constructed with both periodic and quasiperiodic Fibonacci sequences, respectively. Good agreement between theoretical and experimental results has been achieved. The new multicore ring fibers provide a new platform for experiments of quantum effects in low-loss optical fibers which is critical for scalability of real applications with large-size problems. Furthermore, our new quasiperiodic Fibonacci multicore ring fibers provide a new class of quasiperiodic photonics lattices possessing both on- and off-diagonal deterministic disorders for realizing localized quantum walks deterministically. The proposed Fibonacci fibers are simple and straightforward to fabricate and have a rich set of properties that are of potential use for quantum applications. Our simulation and experimental results show that, in contrast with randomly disordered structures, localized quantum walks in new proposed quasiperiodic photonics lattices are highly controllable due to the deterministic disordered nature of quasiperiodic systems.

Wide band single polarization and polarization maintaining fibers using stress rods and air holes.

We propose a new fiber design using both stress rods and air holes for making wide band single polarization fibers as well as polarization maintaining fibers. The key factor that makes the fiber design possible is that the stress-induced birefringence from the stress rods and the form birefringence from air holes are added constructively, which increases the total birefringence and allows more flexible choice of fiber parameters. We established a finite element model that is capable to study both the stress-optic effect and the wave-guide effect. Through the detailed modeling, we systematically explore the role of each major parameter. Different aspects of the fiber properties related to the fundamental mode cutoff, fiber birefringence and effective area are revealed. As a result, fibers with very large single polarization bandwidth as well as larger effective area are identified.

Effects of bending on the performance of hole-assisted single polarization fibers.

We study the effects of bending on single polarization fiber performance through the use of finite element method in conjunction with the perfectly matched layer (PML) in cylindrical geometry. The cylindrical PML used in this paper allows us to calculate the loss associated with each polarization mode at a given wavelength, specified bending diameter, and specific orientation. We identified a series of bending characteristics of the single polarization fiber by choosing different bending diameters and different orientations. We also conducted experiments to study some aspects of the bending. Good qualitative agreement between numerical and experimental results is found, which helps to understand fiber deployment conditions and can potentially facilitate new design efforts.

Transparent Er3+-Doped Y2O3 Ceramics with Long Optical Coherence Lifetime.

Er3+-doped Y2O3 nanoparticles (NPs) are used to synthesize transparent ceramics by hot isostatic pressing. Two sizes of NPs are studied, and 40 nm NPs show better performance than 200 nm NPs in transparent ceramics syntheses. The axial optical transmission through millimeter thickness of the prepared ceramics is about 80% in the wavelength range of 1000-2000 nm. For a sample with 11.5 ppm Er3+, the inhomogeneous broadening of the 4I15/2 to 4I13/2 transition for the C2 site is as low as 0.42 GHz (full width at half-maximum), and the homogeneous line width is 11.2 kHz at a temperature of 2.5 K and in a 0.65 T magnetic field. This indicates that a majority of Er3+ ions are sitting in sites with very low structural disorder.

Wavelength tunable stretched-pulse mode-locked all-fiber erbium ring laser with single polarization fiber.

A wavelength tunable stretched-pulse mode-locked all-fiber ring laser using single polarization fiber (SPF) was demonstrated. In this laser, a segment of SPF was used simultaneously as a polarizer and a tunable filter in the laser cavity. Self-starting mode-locking with femtosecond output pulses was demonstrated. A wavelength tuning of ~20nm was achieved by bending the SPF with different radii.

Mode division multiplexing using an orbital angular momentum mode sorter and MIMO-DSP over a graded-index few-mode optical fibre.

Mode division multiplexing (MDM)- using a multimode optical fiber's N spatial modes as data channels to transmit N independent data streams - has received interest as it can potentially increase optical fiber data transmission capacity N-times with respect to single mode optical fibers. Two challenges of MDM are (1) designing mode (de)multiplexers with high mode selectivity (2) designing mode (de)multiplexers without cascaded beam splitting's 1/N insertion loss. One spatial mode basis that has received interest is that of orbital angular momentum (OAM) modes. In this paper, using a device referred to as an OAM mode sorter, we show that OAM modes can be (de)multiplexed over a multimode optical fiber with higher than -15 dB mode selectivity and without cascaded beam splitting's 1/N insertion loss. As a proof of concept, the OAM modes of the LP11 mode group (OAM-1,0 and OAM+1,0), each carrying 20-Gbit/s polarization division multiplexed and quadrature phase shift keyed data streams, are transmitted 5km over a graded-index, few-mode optical fibre. Channel crosstalk is mitigated using 4 × 4 multiple-input-multiple-output digital-signal-processing with <1.5 dB power penalties at a bit-error-rate of 2 × 10(-3).

Observation of temporal vector soliton propagation and collision in birefringent fiber.

We report the experimental observation of temporal vector soliton propagation and collision in a linearly birefringent optical fiber. To the best of the authors' knowledge, this is both the first demonstration of temporal vector solitons with two mutually incoherent component fields, and of vector soliton collisions in a Kerr nonlinear medium. Collisions are characterized by an intensity redistribution between the two components, and the experimental results agree with numerical predictions of the coupled nonlinear Schrödinger equation.

Experimental observation of orthogonally polarized time-delayed optical soliton trapping in birefringent fibers.

Propagation of two orthogonally polarized time-delayed optical solitons in low-birefringence optical fiber is studied experimentally. We demonstrate soliton trapping and collisions and also the ability to control the separation and shape of soliton pulses by varying the power at the input of the fiber.

Effects of residual stress on polarization mode dispersion of fibers made with different types of spinning.

We analyze the effects of residual stress on the polarization mode dispersion (PMD) of fibers made with different types of spinning. A theoretical scheme is developed from a previous model by the incorporation of a circular birefringence term contributed by residual torsional stress. It is found that the residual stress can significantly affect the PMD of unidirectionally spun fibers when the fiber birefringence is low, but it has little effect on the PMD of bidirectionally spun fibers.

Single-polarization fiber with a high extinction ratio.

An elliptical-core hole assisted single-polarization fiber was designed, fabricated, and characterized. Numerical modeling based on the vectorial Maxwell equation reveals the dependence of the single-polarization bandwidth on core delta and air-hole size. Several single-polarization fibers based on this design with their single-polarization operating windows centered between 0.9 and 1.5 microm were successfully demonstrated. A correlation between fiber birefringence and single-polarization operating bandwidth is qualitatively confirmed. A single-polarization bandwidth as high as 55 nm was observed. These fibers also show very high extinction ratios of 60 dB or higher at lengths much shorter than 1 m. Other properties such as the dependence on length of the single-polarization operating window were also measured.