An alternative test to check the validity of convergence results

This paper presents a simple method for identifying distributional dynamic properties of economies using the ideas of concordance and discordance. It can be employed to examine the strength and validity of the results of other methods. The method has the advantage of comparing distributions at two points without relying on intermediary data between the two time points. We present results that suggest there is more ‘strong-divergence’ than ‘strong-convergence’ in GDP between countries over the time period 1960-2000 although the distribution exhibits both convergent and divergent characteristics

1.5µm Er³⁺:Yb³⁺ doped fibre DBF laser

We report the first DFB fiber laser. When pumped with a 980nm diode laser, the 2cm-long laser has an output power of 2mW at 1.534µm and a RIN of < -156dB/Hz

Single-mode tunable erbium:ytterbium fibre Fabry-Perot laser

A compact tunable single-mode fiber laser is developed by using a novel combination of high-gain erbium: ytterbium (Er:Yb) phosphate fiber and fiber Fabry-Perot (FFP) cavity configurations. Experiments demonstrate the shortest Er:Yb phosphate FFP laser ever reported, which has a 100µm cavity length with a continuous wavelength tuning range over 4.52nm, as limited by the sharp fiber gain peak. In addition, an alternative 3-mirror laser design has also demonstrated single-mode lasing operation

Er³⁺:Yb³⁺ co-coped fiber DFB laser

We report what is to our knowledge the first fiber distributed-feedback laser using a single Bragg grating at 1.5µm written directly into a 2-cm-long Er3+-doped fiber codoped with Yb3+. We obtained robust single-frequency operation by either using one end reflector or locally heating the center of the grating to create the necessary phase shift

Bragg gratings in germania-free optical fibres

To date, most research into Bragg fibre gratings has centred on conventional silica-germania optical fibre. Often, fibres co-doped with boron or containing high concentrations of germania are used in order to increase the achievable refractive index modulation

Efficient diode-pumped single-frequency erbium:ytterbium fibre laser

We report a 7.6-mW single-frequency fiber laser operating at 1545 nm, using for the first time an Er3+:Yb3+ doped fiber and a fiber grating output coupler. The laser did not exhibit self-pulsation, which is a typical problem in short three-level fiber lasers, and had a relative intensity noise (RIN) level below -145.5 dB/Hz at frequencies above 10 MHz. The linewidth of the laser was limited by the relaxation oscillation sidebands in the optical spectrum and was typically less than 1 MHz. <br/

Amplified fiber ring resonator gyro

The sensitivity of a fiber-optic ring resonator gyro increases with increasing resonator finesse, which can be achieved by including a fiber amplifier in the ring. The spontaneous emission from a fiber amplifier introduces additional noise. The effect of this noise on the performance of an ARRG is theoretically investigated, assuming an infinity source coherence length. It is found that for a given fiber length, the uncertainty in measuring the rotation rate with an ARRG can be more than one order of magnitude lower than with a shot noise limited PRRG, and about three orders of magnitude lower than with an IFOG

Polarimetric Er³⁺-doped fiber DFB laser sensor for differential pressure and force measurements

We propose and demonstrate a polarimetric Er3+-doped fiber DFB laser sensor where a transversely applied force along the fiber laser induces a birefringence giving rise to a change in the beat-frequency between the two orthogonally-polarized laser modes. We measure a sensitivity of approximately 9.6GHz(N/mm), a wide dynamic range with stable two-mode operation for frequency separations up to 50GHz, and very high sensor resolution owing to the narrow beat frequency bandwidth of &lt;10kHz. The temperature sensitivity is primarily dominated by the temperature dependence of the inherent birefringence, which was measured to be -130kHz/°C. The sensor allows independent pressure/force and temperature measurements

Field statistics modelling of beat noise in an optical amplifier

The authors present a rigorous and self-contained noise analysis of an optical amplifier based on the statistics of the input source field and the amplified spontaneous emission field of the amplifier. The method enables us to obtain the frequency dependence of the output electrical noise power, which has not been derived in previous studies of optical amplifier noise based on the photon statistics master equation. The authors characterise for the first time the noise of an optical amplifier in combination with a super-fluorescent source, taking into account the frequency dependence of the gain and the presence of optional optical filters

Noise in amplified fibre optic recirculating-ring delay lines

We characterize for the first time the noise in fiber optic recirculating-ring delay lines including doped fiber amplifiers, which are interesting components in many fiber optic sensors because of their enhanced total delay times compared to conventional recirculating-ring delay lines