Spectral measurement of diode lasers with a single-mode birefringent fibre

A new, and very simple spectrometer based on birefringent fiber is described. A resolution of 0.02 angstrom has been achieved, and the system has been used to measure diode laser chirp. A length of 10km of fiber would be sufficient to resolve single mode line widths.

Performance of single mode laser components using 2D photonic lattice reflectors

This paper will report studies of the placement of 2D photonic gratings on either side of the ridge in a Fabry Perot laser device in order to cause single mode emission. Using this approach, side mode suppression ratios of up to 30 dB are achieved, the emission remaining single mode even under 10 Gb/s large signal modulation. It is found that the use of the grating not only causes spectrally dependent reflection but in addition can lead to transverse mode fluctuations. The action of the grating has been studied not just in terms of its edge emission where conversion of the transverse modes is achieved, but also through measurement of the vertical emission from the structure where strong filtering action is observed.

Single-gated multiple-mode power semiconductor devices

A new method has been used to design a power semiconductor device which combines IGBT switching and thyristor on-state characteristics. A single gate signal controls the switching and triggers the transitions between the IGBT and thyristor modes of operation. This paper discusses single-gated devices with multiple modes and aspects of their switching behaviour.

2 μm solid-state laser mode-locked by single-layer graphene

We report a 2 μm ultrafast solid-state Tm: Lu2O3 laser, mode-locked by single-layer graphene, generating transform-limited ∼ 410 fs pulses, with a spectral width ∼ 11.1 nm at 2067 nm. The maximum average output power is 270 mW, at a pulse repetition frequency of 110 MHz. This is a convenient high-power transform-limited ultrafast laser at 2 μm for various applications, such as laser surgery and material processing. © 2013 American Institute of Physics.

Nonlinear phenomena in thermoacoustics: A comparison between single-mode and multi-mode methods

Nonlinear analysis of thermoacoustic instability is essential for prediction of frequencies and amplitudes of limit cycles. In frequency domain analyses, a quasi-linear transfer function between acoustic velocity and heat release rate perturbations, called the flame describing function (FDF), is obtained from a flame model or experiments. The FDF is a function of the frequency and amplitude of velocity perturbations but only contains the heat release response at the forcing frequency. While the gain and phase of the FDF provide insight into the nonlinear dynamics of the system, the accuracy of its predictions remains to be verified for different types of nonlinearity. In time domain analyses, the governing equations of the fully coupled problem are solved to find the time evolution of the system. One method is to discretize the governing equations using a suitable basis, such as the natural acoustic modes of the system. The number of modes used in the discretization alters the accuracy of the solution. In our previous work we have shown that predictions using the FDF are almost exactly the same as those obtained from the time-domain using only one mode for the discretization. We call this the single-mode method. In this paper we compare results from the single-mode and multi-mode methods, applied to a thermoacoustic system of a premixed flame in a tube. For some cases, the results differ greatly in both amplitude as well as frequency content. This study shows that the contribution from higher and subharmonics to the nonlinear dynamics can be significant and must be considered for an accurate and comprehensive analysis of thermoacoustic systems. Hence multi-mode simulations are necessary, and the single-mode method or the FDF may be insufficient to capture some of the complex nonlinear behaviour in fhermoacoustics.

Widely tunable picosecond fiber ring laser mode-locked by a single-wall carbon nanotube (SWNT)-polycarbonate composite film saturable absorber

A widely tunable fiber ring laser, utilising a SWNT/polycarbonate film mode-locker and a 3-nm tunable filter, has been realized. 2.3ps pulse generation over 27nm spectral range is achieved for a constant pump power of 25mW. © 2007 Optical Society of America.

Widely tunable picosecond fiber ring laser mode-locked by a single-wall carbon nanotube (SWNT)-polycarbonate composite film saturable absorber

A widely tunable fiber ring laser, utilising a SWNT/polycarbonate film mode-locker and a 3-nm tunable filter, has been realized. 2.3ps pulse generation over 27nm spectral range is achieved for a constant pump power of 25mW. © 2008 Optical Society of America.