Laser in optoelectronic applications Optical communication systems are rapidly becoming the preferred technology for the majority of long-haul links, metropolitan and local area communication networks. A key component in all optical communication systems is the laser diode, a small device that converts electrical energy into light. In the process of conversion, large amounts of heat can be generated. The dissipation of this built-up heat with an efficient heat sink is necessary to achieve high power laser output levels. Diamond is the ideal heat sink material for this challenge as it conducts heat better than any known material. It has the added benefits of being an insulator and can be machined to tight tolerances. Being a passive device it consumes no power and is a stable platform for very extended time spans. Discrete Laser Diode Assemblies The figure below shows an example of a diamond plate used as a submount for a high power laser diode.   Click image for larger view Example of a diamond plate used as a heat spreader in a laser diode package.   The diamond acts as a heat spreader, reducing the overall thermal resistance of the package as illustrated below.   Click image for larger view Thermal resistance of a laser diode package as a function of the diamond plate thickness. Laser Diode Arrays A laser diode array is an array of laser diodes grouped in one semiconductor chip. A typical laser diode array chip is 10mm wide, 0.1mm thick and has an emitter cavity length of 0.6-1mm. Such a device will require a heat spreader submount of at least 10mm in length that can be produced from CVD diamond.   Click image for larger view Side and front view of a laser diode array package.   The improvement in heat dissipation in laser diode arrays through the use of CVD diamond as the heat spreading material is demonstrated in a finite element calculation of the junction temperature increase.   Click image for larger view Graphic views of the simulation results with and without the use of CVD diamond.    The simulation results show that CVD diamond spreads the heat more effectively away from the active area leading to a better temperature uniformity in the emitter area, as well as a reduction in junction temperature. This enables the device to be run at higher power without raising the junction temperature and with the same device reliability as at lower power levels.  High power laser systems    The high power lasers have increased the demand for high quality optical components capable of withstanding high optical power densities. A common problem for windows used in high power lasers is that of thermal distortion of the beam caused by thermally induced refractive index gradients as the window is heated by the transmitted beam. This problem can be minimized by using CVD diamond with its high thermal conductivity, low absorption coefficient and low value for the temperature coefficient of the refractive index. The table below compares the relevant properties for optical grade CVD diamond and zinc selenide, the current favoured material for CO2 lasers.   Window properties of optical grade CVD diamond and zinc selenide (ZnSe).   The potential advantage for this application is further illustrated through thermal modeling, which demonstrates the benefits of diamond's superior thermal conductivity for an AR/AR coated 25mm diameter wndow and a 5 KW CO2 laser beam and shows that diamond's thermal lensing effect is 240 times less than zinc selenide's in the AR/AR coated case.   Click image for larger view Reduction in thermal gradient resulting from diamond's superior thermal conductivity. (Ref. IDR 4/2000)   These results demonstrate that diamond is able to increase the laser performance (improved beam quality, higher power levels, increased reliability and MTBF) for a new generation of high power CO2 laser systems and lasers operated in the 1µm region. For the latter thermal optical windows are under development.   Return to top >