Search

We report the broadband spectral performance of a three-stage, high gain, single mode, high output power (25 W) polarization-maintaining (PM) hybrid Ho-doped and Tm-doped fiber amplifier at signal wavelengths of λs = 2004–2108 nm. The three-stage amplifier consists of a two stage high gain Ho-doped PM single clad preamplifier stage followed by a Tm-doped PM double clad power amplifier. We employ narrow linewidth (

Lung transplantation is an established treatment of select patients with end-stage pulmonary disease. Lung transplantation should be considered for patients with end-stage pulmonary disease who have an expected 2-year survival of less than 50% without lung transplant and an expected 5-year survival of greater than 80% after transplant. This article reviews routine postsurgical intensive care unit management, along with management of complications such as acute kidney injury, atrial arrhythmias, deep vein thrombosis, primary graft dysfunction, hyperammonemia syndrome, and thrombocytopenia. Finally, management of long-term issues, including diabetes mellitus, hypertension, and bronchial stenosis, is discussed.

A discrete-mode laser diode, fabricated in the In0.6Ga0.4P/AlGaInP multiple quantum well system, emitting a single mode at $\lambda =689$ nm is reported. The laser has an ex-facet output power >10 mW at 30 °C and operates mode hop free in the temperature range 0 °C to 50 °C.

Compact monolithic single-mode red emitting diode lasers are still not readily available for many wavelengths in the visible spectrum. Strontium lattice and Calcium clocks are some of the most widely investigated optical clocks worldwide and the pertinent transitions wavelengths required are in the red and blue wavelength spectral region. The current state of the art in laser technology employs external cavity laser diodes and frequency doubling crystals in order to hit the desired wavelength with external amplifiers used to meet the power requirements. Compact rugged monolithic narrow linewidth laser sources operating in the red and blue wavelengths have been identified by the European Space Agency as a key technology that could be used to replace all of these costly, energy inefficient and vibration sensitive components and to one day facilitate the optical clock leaving the laboratory and to eventually end up on a satellite in space.

The quality and pulse compression of the 60 GHz millimeter wave signals generated by 750 μm long InAlGaAs Multi Quantum Well (MQW) passively mode locked laser under free running and optical self injection locked conditions are experimentally characterized in terms of longitudinal modes under certain bias currents that range from 24 mA to 90 mA. Initially, the MQW laser is characterized in free running condition with no external injection. The measurements reflect that the free spectral range of laser under test is around 61 GHz and exhibit more than 22 lasing modes. The laser is then integrated into low phase noise self injection locking oscillator by feeding a part of output RF signal back into the laser cavity to enhance passive mode locking. By doing so the microwave line width of our laser is reduced from 900 kHz to 24 kHz with significant increase in output of resultant beat tones which exhibits strong passive mode locking. This is the first time that the free running microwave line width of MQW laser is reduced up to this level. It is evident from our experimental investigation that as we increase the power and phase correlation between different longitudinal modes inside laser cavity through optical self injection, the strength of the passively mode locked mechanism is significantly increased and the phase noise of radio frequency signal is drastically reduced.

We report on a 2.051 μm InxGaAs/InP-based discrete mode laser diode monolithically integrated with a curved tapered semiconductor optical amplifier for CO2 sensing applications. At a heat-sink temperature of 0°C, the laser emits a record InP value of more than 35 mW continuous-wave output power in a single longitudinal mode.

Summary form only given. As the frequency spectrum below 10GHz becomes saturated, it will become increasingly difficult to maintain adequate bandwidth provision for the growing customer demand. For this reason, the possibility of utilizing the unlicensed 57GHz-64GHz band for services such as WPAN is an attractive prospect [1]. Furthermore, the advantages of an optical system to realize this prospect are numerous. Extremely low phase noise can be obtained from laser systems used for millimetre-wave applications, relative to the equivalent electronic components. In addition to this, the costs of such a system are much lower and the footprint smaller, not to mention the additional benefits of low loss and easy switching of carrier frequency. In this paper, a multimode quantum well Fabry-Perot laser with potential application as a carrier signal generator for WPAN is characterized. The laser is passively mode-locked, with no saturable absorber, and exhibits pulsed operation at 60GHz with only d.c. bias applied. The InP-based laser is 700μm long and exhibits multimode emission between 1555nm and 1565nm. A typical output spectrum at 70mA bias current is shown in Fig. 1. Also indicated on the graph are the measured values for optical linewidth for each mode. These values were measured using an optical self-heterodyne setup.The linewidth of the beat tone generated at a photodiode was also measured for various values of bias current. In free-running conditions, a linewidth of 1.7MHz is measured at 61.92GHz. A circulator and an optical delay line are then placed after the laser in the setup, in place of the isolator, thus creating an optical feedback loop. A filter is used to isolate two consecutive modes. The linewidth measured for the beat signal is reduced by a factor of 100, to nearly 10kHz, with lower linewidths being for longitudinal modes near to the centre of the optical spectrum. These results indicate that this laser has potential for application in RoF and WPAN areas, due to its low linewidth, cost and the fact that it exhibits 60GHz operation using only d.c. bias.

An experimental characterisation of a multi-contact semiconductor optical amplifier using ultrashort optical pulses is presented. The SOA in question allows the injection of bias current through multiple independent electrical contacts, allowing the direct control of the carrier density. Picosecond-scale optical pulses are transmitted through the SOA. The non-linear effects on the pulse shape and spectrum after transmission are determined. It is found that the bias current distribution in the SOA is a significant factor in determining the extent of the non-linearities affecting the pulses. Additionally, amplification of negatively chirped pulses in the saturated SOA is found to reduce the spectral width of the pulses.

Experimental characterisation of a novel noise-controlled semiconductor optical amplifier (NCSOA) is presented. The design utilises grooves etched parallel to the active waveguide, at the output sections of the NCSOA, so as to induce lasing laterally to the propagation axis. This clamps the carrier density in a relevant region, allowing for the engineering of a specific longitudinal carrier density profile, corresponding to an improved noise figure performance. Results have demonstrated the effectiveness of carrier density profile engineering as a means of reducing the noise figure in semiconductor optical amplifiers.

In this paper, Cassidy's method is presented and is applied to measure the linewidth enhancement factor (LEF) of a 370 GHz self-pulsating Fabry-Perot laser. The importance of the LEF is addressed, the method is detailed, and the device under test is presented. It exhibits a self-modulation at 370 GHz even though it is DC biased. The measured LEFs vary according to the wavelength, values of 4 have been measured at threshold current, which is typical in the case of multi-quantum well lasers. In this paper we propose to present measurement of the linewidth enhancement factor (LEF) in semiconductor laser based, 370 GHz source generator. First we explain the origin of LEF in semiconductor material, then we present several techniques to measure it. We present a computational simulation using modelled ASE spectra, and in part 4, we detail our device and experimental set-up and provide some results. The linewidth enhancement factor (LEF) or alpha parameter is a distinguishing feature of semiconductor devices. Semiconductor devices generally have a larger linewidth than other solid state lasers. This broadened linewidth leads to effects such as mode instability, filementation in broad area devices and frequency chirping under modulation. This last effect is of particular interest, especially in the field of optical communications. It can be suppressed if the LEF is reduced. Therefore in the design of semiconductor lasers or semiconductor amplifiers (SOA), a number of factors have to be taken into consideration, but one of the most important of these is the linewidth enhancement factor. For instance, when the gain of an SOA is affected by the injection of a pulsed source, refractive index changes caused by changes in carrier density will lead to an instantaneous variation of the frequency. This effect is exacerbated as the gain is saturated.