Fibre-optic communications systems have traditionally carried data using binary (on-off) encoding of the light amplitude. However, next-generation systems will use both the amplitude and phase of the optical carrier to achieve higher spectral efficiencies and thus higher overall data capacities(1,2). Although this approach requires highly complex transmitters and receivers, the increased capacity and many further practical benefits that accrue from a full knowledge of the amplitude and phase of the optical field(3) more than outweigh this additional hardware complexity and can greatly simplify optical network design. However, use of the complex optical field gives rise to a new dominant limitation to system performance-nonlinear phase noise(4,5). Developing a device to remove this noise is therefore of great technical importance. Here, we report the development of the first practical ('black-box') all-optical regenerator capable of removing both phase and amplitude noise from binary phase-encoded optical communications signals.

/pdf/all-optical-phase-and-amplitude-regenerator-for-next-3wnsxhkves.pdf

All-optical phase and amplitude regenerator for next-generation telecommunications systems

A particular photonic crystal fiber (PCF) designed with all circle air holes is proposed. Its characteristics are studied by full-vector finite element method (FEM) with anisotropic perfectly matched layer (PML). The simulation results indicated that the proposed PCF can realize high birefringence (up to 10(-2)), high nonlinearity (50W(-1)·km(-1) and 68W(-1)·km(-1) in X and Y polarizations respectively) and low confinement loss (less than 10(-3)dB/km at 1.55um wavelength).

High birefringence photonic crystal fiber with high nonlinearity and low confinement loss.

We propose a novel design of photonic crystal fiber (PCF) using an elliptical air hole in the core as a defected core in order to enhance the performance of modal birefringence and to control the properties of chromatic dispersion at the same time. From the simulation results, it is shown that the proposed fiber has high birefringence up to the order of 10−2, negative flattened chromatic dispersion in a broad range of wavelengths, and low confinement loss less than that of the single mode fiber. The outstanding advantage of the proposed PCF is that high birefringence, negative flattened dispersion, and low confinement loss can be achieved just by adding a small sized elliptical air hole in the core to the elliptical air hole PCF, especially at the same time.

Elliptical defected core photonic crystal fiber with high birefringence and negative flattened dispersion.

We propose a novel black-box optical phase sensitive amplifier (PSA) configuration and describe its application to the regeneration of multi-level phase encoded signals. The concept is demonstrated with a 10 Gbaud quadrature phase shift keyed (QPSK) input.

/pdf/first-demonstration-of-all-optical-qpsk-signal-regeneration-3iam6nbws1.pdf

First demonstration of all-optical QPSK signal regeneration in a novel multi-format phase sensitive amplifier

Simultaneous conversion of the two orthogonal phase components of an optical input to different output frequencies has been demonstrated by simulation and experiment. A single stage of four-wave mixing between the input signal and four pumps derived from a frequency comb was employed. The nonlinear device was a semiconductor optical amplifier, which provided overall signal gain and sufficient contrast for phase sensitive signal processing. The decomposition of a quadrature phase-shift keyed signal into a pair of binary phase-shift keyed outputs at different frequencies was also demonstrated by simulation.

Phase discrimination and simultaneous frequency conversion of the orthogonal components of an optical signal by four-wave mixing in an SOA.

A simple photonic crystal fiber (PCF) design with a rectangular array of four airholes in the core region and a traditional circular-airhole cladding is proposed in this work. The modal birefringence is induced by the asymmetry of the rectangular distribution of four airholes and/or the elliptical shape of the holes. The traditional symmetric cladding structure results in good confinement loss performance by limiting the light in the core region. Therefore, the proposed design enables simultaneous realization of high birefringence and low confinement loss. Simulations based on the full-vector finite element method (FEM) with anisotropic (PML) show that ultrahigh single-mode birefringence (~ 10-2) and ultralow confinement losses ( < 0.002 dB/km) can be achieved at 1.55 mum wavelength. Dependence study of the birefringence and losses on several key parameters is also provided. Compared to previously studied PCF with asymmetric core or cladding structures, by having just four relatively large airholes in the core, this design could be much easier to be implemented with even better performance.

Ultrahigh Birefringent Photonic Crystal Fiber With Ultralow Confinement Loss Using Four Airholes in the Core

All-optical regeneration of DQPSK/QPSK signals based on phase-sensitive amplification

We investigate an all-optical (D)QPSK regenerator based on phase-sensitive amplifiers. Simulations show an MZ interferometer with one PSA in each arm can provide significant phase and amplitude noise suppression under optimal pump conditions.

All-Optical Regeneration of DQPSK/QPSK Signals Based on Phase-Sensitive Amplification

https://web.njit.edu/~sirenko/PapersNJIT/TaoOptCom2009.pdf

Ultra-wideband single-polarization single-mode, high nonlinearity photonic crystal fiber

We report a novel design of photonic crystal fiber (PCF) with a rectangular array of four closely-spaced, highly elliptical air holes in the core region and a circular-air-hole cladding. The proposed PCF is able to support ultra-wideband single-polarization single-mode (SPSM) transmission from the visible band to the near infrared band. With the aid of the inner cladding formed by the central air holes, one polarization of the fundamental mode can be cut off at very short wavelengths and ultra-wideband SPSM propagation can be achieved. The inner cladding also suppresses the higher order modes and allows large air filling fraction in the outer cladding while the proposed fiber remains SPSM, which significantly reduces the mode effective area and the confinement loss. Our simulation results indicate that the proposed PCF has a 1540 nm SMSP range with ≪ 0.25 dB/km confinement loss and an effective area of 2.2 µm2. Moreover, the group velocity dispersion (GVD) of the proposed PCF can also be tuned to be flat and near zero at the near infrared band (∼800 nm) by optimizing the outer cladding structure, potentially enabling many nonlinear applications.

Ultra-wideband single-polarization single-mode photonic crystal fiber with high nonlinearity and low dispersion

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