Efficient Laser Diodes Research Articles

Design approaches for laser-diode material-processing systems using fibers and micro-optics

Low-cost, efficient, and compact high-power laser diodes (LDs) will make desktop laser manufacturing (rapid prototyping, sintering, drilling, marking, etc.) a reality soon. Laser processing of materials requires not only high average power, from tens of watts to kilowatts, but also high incident beam intensity or power density, from 103 to 108 W/cm2. Current commercial high-power LDs do emit 108 W/cm2; however, they are microscopic in size, and an individual diode emits ~ 1 W (cw) in a highly divergent (~30 x 10 deg) multimode structure. Gathering high power from a large number of such microscopic incoherent diodes into a small spot of high intensity requires micro-optic component and complex system design. Several difterent design approaches for high-intensity laser-diode systems are presented. Some of these are commercial, others will be soon, and still others will need technological developments. Possible applications and some preliminary results of direct diode-laser sintering and transformation hardening of stainless-steel ribbons are also presented.

Erbium-doped silica-based planar waveguide amplifier pumped by 0.98 μm laser diodes

A 0.98 μm laser-diode-pumped waveguide amplifier is successfully realised by using an Er-doped silica-based planar lightwave circuit. The highest signal gain of 9.4 dB is achieved at a signal wavelength of 1.533 μm with a pump power of 99 mW, using a highly efficient erbium-doped waveguide and high power laser diodes.

Low-noise optoelectronic amplifier using sub-shot noise light

A new type of low-noise optoelectronic amplifier is proposed which uses intensity-squeezed light from a tandem array of high quantum efficiency laser diodes or light-emitting diodes. Applications include amplification of intensity-squeezed light, sub-shot noise modulated lightwave generation for free-space and fibre transmission, and low noise small signal RF amplification.

Modular microchannel cooled heatsinks for high average power laser diode arrays

Detailed performance results for an efficient and low thermal impedance laser diode array heatsink are presented. High duty factor or CW operation of fully filled laser diode arrays is made possible at high average power. Low thermal impedance is achieved using a liquid coolant and laminar flow through microchannels. The microchannels are fabricated in silicon using an anisotropic chemical etching process. A modular rack-and-stack architecture is adopted for the heatsink design, allowing arbitrarily large two-dimensional arrays to be fabricated and easily maintained. The excellent thermal control of the microchannel cooled heatsinks is ideally suited to pump array requirements for high average power crystalline lasers.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Taper coupling of laser diode to singlemode fibre: influence of fibre field shape

The coupling efficiency of laser diodes to lensed down-tapered singlemode fibres was measured at λ = 1.318 μm and compared to theoretical results, taking into account the spherical aberration of the taper lens. Good agreement was found irrespective of the details of the fibre near-field function. However, the coupling distance between laser and fibre for maximum efficiency depends strongly on the shape of the fibre mode, and was measured to be (25±5) μm for the configuration presented. Assuming a Bessel field function, an optimum distance of 29 μm is predicted as compared to 39 μm for a Gaussian.

Magneto-optical trapping and its application to helium metastables

A quantitative discussion of several interesting and attractive properties of magneto-optical traps is presented. Calculations are given for the trap depth, sample size, and intrinsic cooling capability of this especially simple example of a radiative force trap. The discussion is directed toward the cooling and confinement of metastable 23S neutral helium, and a new loading procedure suitable for this atom is proposed. It is planned to operate the trap and to cool atoms in it with 1.08-μm light from solid-state, single-mode lasers pumped by efficient diode lasers. Because of the dissipative nature of the radiative force, a trapped sample of atoms may be magnetically compressed without increasing its millikelvin optical temperature, so that a subsequent adiabatic expansion can cool it to the nanokelvin temperature range.

Efficient highly stable laser diode module for single-mode fiber employing a combination of hemispherical ended GRIN rod lens and virtual fiber

An efficient and practical laser diode module is demonstrated for single-mode fiber applications. The module is developed through use of an earlier proposed combination lens method, where a hemispherical ended graded index rod lens and virtual fiber are employed. Since lens and virtual fiber misalignment tolerances are large in this coupling method, the YAG laser welding technique is easily applicable. This laser diode module has not only a simple structure but also high coupling efficiency, excellent reproducibility, and extremely high reliability.

Efficient laser diode to single-mode fiber coupling using a combination of two lenses in confocal condition

A new coupling method of a laser diode to a single-mode fiber is described. It consists of a spherical ruby lens and a graded index (GRIN) rod lens positioned under a confocal condition. A high coupling efficiency of more than 40 percent has been easily obtained for InGaAsP laser diodes. Alignment sensitivities of the proposed coupling circuit have been studied both experimentally and theoretically. The dependence of the coupling efficiency on misalignments has been found to be in agreement with the theoretical consideration, and it has been apparent that the stringent alignment tolerances required for conventional coupling methods have been overcome. A laser diode module using the proposed circuit was also fabricated with high coupling efficiency into the single-mode fiber, and good reproducibility and performance have been obtained.