Measurement driven quantum evolution

We study the problem of mapping an unknown mixed quantum state onto a known pure state without the use of unitary transformations. This is achieved with the help of sequential measurements of two non-commuting observables only. We show that the overall success probability is maximized in the case of measuring two observables whose eigenstates define mutually unbiased bases. We find that for this optimal case the success probability quickly converges to unity as the number of measurement processes increases and that it is almost independent of the initial state. In particular, we show that to guarantee a success probability close to one the number of consecutive measurements must be larger than the dimension of the Hilbert space. We connect these results to quantum copying, quantum deleting and entanglement generation.Comment: 7 pages, 1 figur

Widely tunable erbium-doped fiber laser based on multimode interference effect

A widely tunable erbium-doped all-fiber laser has been demonstrated. The tunable mechanism is based on a novel tunable filter using multimode interference effects (MMI). The tunable MMI filter was applied to fabricate a tunable erbium-doped fiber laser via a standard ring cavity. A tuning range of 60 nm was obtained, ranging from 1549 nm to 1609 nm, with a signal to noise ratio of 40 dB. The tunable MMI filter mechanism is very simple and inexpensive, but also quite efficient as a wavelength tunable filter

Tuning characteristics of cladding-pumped neodymium-doped fiber laser

We describe a cladding-pumped neodymium-doped fiber laser, tunable from 1057 to 1118 nm. The power varies significantly over the tuning range. Improved characteristics are obtained with tuning elements in both ends of the cavity

Simple Numerical Modeling Of Yb3+-Doped Fiber Lasers

We present a fast and efficient numerical model for Yb3+-doped fiber lasers based on shooting method. The algorithm is based on the assumption of a starting value for the slope efficiency and the evaluation of the pump power threshold. The starting value of slope efficiency is related to initial conditions through the boundary conditions, and it is subsequently optimized by iteration. The method ensures a fast and efficient convergence of the solution of the coupled first-order differential equations that describes the evolution of pump and signal powers in a Yb3+-doped fiber laser. The results of the numerical solution are compared with experimental and published data giving a good agreement

Mmi-Based 2×2 Photonic Switch

We propose a robust, multi-mode interferometer-based, 2×2 photonic switch, which demonstrates high tolerance to typical fabrication errors and material non-uniformity. This tolerance margin is dependent upon the properties inherent to the MMI design and benefits from the high symmetry of the switch. The key design parameter of the device is to form a pair of well defined self-images from the injected light in the exact center of the switch. In allowing the index modulated regions to precisely overlap these positions, and by creating identical contact features there, any refractive index change induced in the material due to electrical isolation will be duplicated in both self-images. Since the phase relation will remain unchanged between the images, the off-state output will be unaltered. Similarly, offset and dimension errors are reflected symmetrically onto both self-images and, as a result, do not seriously impact the imaging. We investigate the characteristics of the switch under different scenarios using the finite difference beam propagation method. Crosstalk levels better than -20 dB are achievable over a wavelength range of 100 nm when utilizing this configuration. Polarization independence is maintained during device operation

Ultra-Compact Multimode Interference Ingaasp Multiple Quantum Well Modulator

We propose a new structure for an ultra-compact multimode interference (MMI) InGaAsP multiple quantum well modulator. The operating principle is based on restricting the coupling of the self-image produced by the MMI region into a single mode output waveguide. The key is to excite only the even modes within the MMI region, and this is achieved by operating the MMI waveguide under the condition of restricted symmetric interference. By asymmetrically inducing a phase change of π along a selected area within the MMI region, mode conversion of all the even modes to odd modes is achieved. Since only the fundamental mode can be coupled to the output waveguide, neither an individual mode, nor any combination of the modes will be coupled, and therefore the injected light is fully attenuated. The modulation characteristics are analyzed using the finite-difference beam propagation method. Extinction ratios as low as -37 dB are demonstrated without electro-absorption effects. For the case of low electro-absorption, which corresponds to a more realistic situation, this value is only increased to -35 dB. © 2005 Springer

Power combiner for high-power diode lasers

We present a novel approach for the combination of high power multimode diode lasers. The design considered to ensemble several pigtail multimode diode lasers in a radial position on a circular thin disk (the lid) which has a hole-concentrator at the center point. The reflect mirror which is in charge of concentrating the beams at one point and overlapping them without mutual spatial interference is a paraboloidal mirror which is sprayed by a silver thin reflectance film and it is physically covered by the lid. We simulate this device by using commercial software for optical design and we will show the complete analysis of the ray traces as well as the coupling efficiency of the system

Novel optical MUX-DEMUX module for fiber-optic communication applications

We demonstrated a novel design for a multi channel optical MUX/DEMUX module, which uses the principle of a Cassegrein-telescope. We carried out some optical simulations to show the feasibility to build up a multiplexer or de-multiplexer module for Dense Wavelength Division Multiplexing (4 channels). The set-up consists of a concave mirror that receives different beams which are then focused at the centre. For the case of a MUX-module, different radial positions enable injecting the system different wavelength inputs as the concave mirrors concentrates all the beams in one point (collector fibre). Moreover, for the case of a DEMUX-module, a bulk grating is positioned at one point between the concave mirror and the focal point of it, and when a stream of pulses with different wavelengths reaches this point, it automatically distributes the incoming signal in different radial positions (several collector fibers). ©2006 IEEE

Simple Optical Fiber Voltage Sensor Based On An U-Groove Fiber Alignment System

We present an optical fiber voltage sensor where the voltage applied to a piezo-electric actuator is measured by intensity variations due to the relative separation of two optical fibers aligned on a U-groove. © 2006 Optical Society of America