Semiconductor lasers are the core element in transmitters for fiber-optic communication. The most common types of semiconductor laser transmitters used in fiber optics Fabry–Pérot, DFB (Distributed Feed Back) and VCSEL (Vertical Cavity Surface Emitting Laser).
The majority of lasers used in telecommunication systems - as wavelength-division multiplexing (WDM) and others (SWDM, DWDM, HDWDM) - require the temperature stabilization by thermoelectric cooling.
Wavelength stability is very important in telecom applications. Laser diode (LD) operating temperature is directly connected with wavelength stability. Thermoelectric cooling is the optimal method for temperature regulation, because TEC (thermoelectric coolers, TE coolers) can operate in bi-directional mode (cooling and heating), allowing precise temperature regulation that prevents LD wavelength drift.
Thus the main tasks of the thermal management are to stabilize and keep LD at optimal temperature and dissipate the heat from it. The key advantages of thermoelectric (Peltier) coolers here are in miniature design, reliability and long life time, absence of moving parts, reasonable prices and others.
By combination of size, efficiency and performance in precise temperature stabilization there are no analogs for TE coolers. TECs have a unique reliability of several hundred thousand hours of continuous operating. It means more than 20-25 years of operation without maintenance, which is important for telecommunication systems.
Single-stage TECs typically are used for lasers in fiber-optic communication systems with the following requirements:
RMT manufactures several different series of thermoelectric coolers for telecommunications lasers.
Lasers for telecommunication applications have different packaging solutions, depending on application area, data transmittance rates and types of transmitter-receiver systems. There is a range of industry standard package solutions:
The most common for lasers with data transmittance rates up to 10 Gbit/s is the package standard “Butterfly”, usually 14-pin type.
For the Butterfly style the company RMT produces several special series of . The feature of such thermoelectric modules is in elongated shape, which is comfortable for the most useful location of TEC in boxed Butterfly package and mounting of laser chip with optical and electronic elements on the TEC cold side.
Boxed TOSA MSA
The miniaturization and increasing of data transmittance rates up to 10G, 25, 40 and 100 Gbit/s, these are key trends of telecommunication systems and correspondingly of development of telecom lasers.
The TOSA MSA standard was introduced in Feb 2004 as a universal package for telecom transceivers, proving a unified standard for all manufacturers. The package is somewhat smaller than the standard “Butterfly” solution and has limited space for TE cooler integrating. The new power consumption and efficiency standards put additional requirements for integrated TE cooler in box TOSA MSA form factor.
Volume production and cost reduction trends in telecom industry lead to a new simplified solution for telecom transceivers, based on TO-style headers. This is a cheaper header style and promising to become as a standard for the wide fiber-optic communication market, for instance TO-56 header. For such miniature packages RMT produces unique series of very miniature thermoelectric coolers - and Series. The smallest TECs of the series have about 1 x 1 mm2 cold side and the height of only 0.7 mm.
In telecommunication applications the thermoelectric cooling is widely used not only for laser transceivers (transceiver - transmitting modules), but also for many related components, such as the spectral optical filters (narrow optical filters, tunable optical filters), the compensators (dispersion compensation modules), optical lockers, semiconductor optical amplifiers (SOA), optical receivers, and others.
Design and packages of the elements are similar to the laser transceiver. Thermal management is also required for fine thermal stabilizing of operation parameters. And the requirements are similar to those for telecom lasers.
For these tasks, we also recommend to use series of single-stage TECs of RMT developed for telecom applications – standard series and , special , many solutions from general 1MD04 and 1MD06 series and in certain cases 1MD03 series TEC with low-current concept.
It is important to understand that the choice of the optimal TEC for the application requires a detailed analysis. Simply to take the most powerful TEC is not so correct. The optimal solution can be estimated based on application ambient temperature, total heat load and required DT from ambient. It is important to understand that the value DTmax for a thermoelectric cooler is specified by manufacturers at zero heat load, and maximal cooling capacity Qmax – at zero DT. So, the application conditions and heat load are somewhat in between. So, the most optimal thermoelectric cooler has to be carefully analyzed in specified application conditions.
RMT provides a free service for optimal TEC selection. There is the available for initial search. For detailed modeling and calculations RMT provides free software for Windows and for iPad (PC-free analysis).Or for immediate advice and assistance.