Mode-controlled vertical cavity surface emitting lasers for bandwidth enhancement of multimode fibre links

A GaAs Vertical Cavity Surface Emitting Laser (VCSEL) that generates controlled modes offset from the center is described. The device is modulated with a 27-1 pseudo-random bit sequence and its output is transmitted along a 1 km length of multimode fiber (MMF). Open eyes are obtained for data rates as high as 1.4Gb/s. The transmission bandwidth increases by a factor of 4 over over-filled launch (OFL). This enhancement is stable against environment influences on the fiber.

High bandwidth multimode fiber links using subcarrier multiplexing in vertical-cavity surface-emitting lasers

The usage of subcarrier multiplexing (SCM) techniques to allow link transmission in excess of the specified fiber bandwidth is described. A series of 200-Mbit/s channels with carrier frequencies of up to more than twenty times the 3-dB fiber bandwidth have been successfully used, the maximum being limited by the available electronics. To assess the transmission of the fiber, digitally modulated channels are placed on high frequency carrier signals and then used to modulate a vertical-cavity surface-emitting lasers (VCSEL).

Spatial emission control of vertical cavity surface emitting lasers to provide bandwidth gain in multimode fibre links using a simple alignment technique

Etched VCSEL sources are reported which avoid bandwidth collapse in multimode fibre using a simple coupling technique to control the launch. These devices have allowed better than over-filled launch bandwidth for alignment tolerances of ±7 microns.

High bandwidth optical links over multimode fibre

A Fabry-Perot laser source operating at 1300 nm was modulated at 2.5 Gb/s with a 27-1 pseudo-random bit sequence. Three techniques were examined for increasing the bandwidth of optical links using multimode fiber (MMF). With an offset launch of 14 μm, the eye remained open after the 2 km link of 50 μm core MMF containing seven connectors and three splices. An approximate four-fold bandwidth improvement was obtained using the offset launch with a bandwidth-length product of 7.5 Gb/s.km and a bit error rate below 10-10. The bandwidth enhancement was stable against environmental influences on the fiber link, such as mechanical agitation. Detailed simulations demonstrated that the technique allows enhanced operating bandwidths in over 99% of existing link.

On the use of a decimative spectral estimation method based on eigenanalysis and SVD for formant and bandwidth tracking of speech signals

In this paper, a Decimative Spectral estimation method based on Eigenanalysis and SVD (Singular Value Decomposition) is presented and applied to speech signals in order to estimate Formant/Bandwidth values. The underlying model decomposes a signal into complex damped sinusoids. The algorithm is applied not only on speech samples but on a small amount of the autocorrelation coefficients of a speech frame as well, for finer estimation. Correct estimation of Formant/Bandwidth values depend on the model order thus, the requested number of poles. Overall, experimentation results indicate that the proposed methodology successfully estimates formant trajectories and their respective bandwidths.

First real-time experimental demonstrations of 11.25Gb/s optical OFDMA PONs with adaptive dynamic bandwidth allocation.

End-to-end real-time experimental demonstrations are reported, for the first time, of aggregated 11.25Gb/s over 26.4km standard SMF, optical orthogonal frequency division multiple access (OOFDMA) PONs with adaptive dynamic bandwidth allocation (DBA). The demonstrated intensity-modulation and direct-detection (IMDD) OOFDMA PON system consists of two optical network units (ONUs), each of which employs a DFB-based directly modulated laser (DML) or a VCSEL-based DML for modulating upstream signals. Extensive experimental explorations of dynamic OOFDMA PON system properties are undertaken utilizing identified optimum DML operating conditions. It is shown that, for simultaneously achieving acceptable BERs for all upstream signals, the OOFDMA PON system has a >3dB dynamic ONU launch power variation range, and the BER performance of the system is insusceptible to any upstream symbol offsets slightly smaller than the adopted cyclic prefix. In addition, experimental results also indicate that, in addition to maximizing the aggregated system transmission capacity, adaptive DBA can also effectively reduce imperfections in transmission channel properties without affecting signal bit rates offered to individual ONUs.

Holographic offset launch for dynamic optimization and characterization of multimode fiber bandwidth

Optimization of the bandwidth of a 2 km 50 μm multimode fiber at 850 nm is investigated theoretically and experimentally by steering a single spot, or two in antiphase spots across the core of the fiber in two dimensions using a ferroelectric liquid-crystal-based spatial light modulator. This method not only allows an optimal offset launch position to be chosen in situ but can also characterize the geometry and position of the core, identify defects, and measure the maximum differential mode delay. Its ability to selectively excite specific mode groups is also of relevance to mode-group division multiplexing. © 2012 IEEE.

Adaptive enhancement of multimode fibre bandwidth by twin-spot offset launch

A binary grating on a Spatial Light Modulator generates twin antiphase spots with adjustable positions across the core of a multimode fibre allowing adaptive excitation of antisymmetric mode-groups for improving modal dispersion or modal multiplexing. © 2011 IEEE.

Generation of bandwidth-limited 2 ps pulses with 100 GHz repetition rate from multisegmented injection laser

A new dynamic regime in a multisegmented AlGaAs/GaAs DH injection laser has been realised. Generation of bandwidth-limited 100 GHz repetition rate pulses has been demonstrated. This value is claimed to be the largest ever reported for an ultrashort pulse repetition frequency obtained directly from a laser.

Instantaneous frequency and bandwidth estimation using filterbank arrays

Accurate estimation of the instantaneous frequency of speech resonances is a hard problem mainly due to phase discontinuities in the speech signal associated with excitation instants. We review a variety of approaches for enhanced frequency and bandwidth estimation in the time-domain and propose a new cognitively motivated approach using filterbank arrays. We show that by filtering speech resonances using filters of different center frequency, bandwidth and shape, the ambiguity in instantaneous frequency estimation associated with amplitude envelope minima and phase discontinuities can be significantly reduced. The novel estimators are shown to perform well on synthetic speech signals with frequency and bandwidth micro-modulations (i.e., modulations within a pitch period), as well as on real speech signals. Filterbank arrays, when applied to frequency and bandwidth modulation index estimation, are shown to reduce the estimation error variance by 85% and 70% respectively. © 2013 IEEE.