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:

• Lasers are thermostabilized usually in the temperature range +20 … +40°C. Deep cooling below room temperature is not required. However, the operating temperature range is wide enough -40 … +85°C. At the high temperature of operation the temperature difference 40-50°C is required.
• The laser itself emits an active heat in a range about 100-300 mW, sometimes more. However, there are additional passive heat loads (convectional heatload in gaseous ambient, conduction through wires, radiation load). So, the total amount of heat to be spread away from LD may vary in a wide range, depending on LD power, application conditions and packaging form factor.
• It is necessary to have enough surface space for laser chip and its arrangement. On the cold side of the TEC a laser chip is usually mounted with a certain set of functional elements as well as elements of alignment with optical fiber. TECs with elongated rectangular shape are most commonly used.

RMT manufactures several different series of thermoelectric coolers for telecommunications lasers.

All the products are manufactured fully in accordance to Telcordia GR468 Core reliability standard.   RMT TE coolers are fully compliant with RoHS and REACH requirements.

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:

Butterfly

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 single-stage TECs. 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.

• Series 1ML06 and 1ML07 contain a set of standard sizes of miniature TECs suitable for Butterfly type package. These TECs are very common for Butterfly form factor and have become de-facto standard during recent years.
• RMT Series 1MDL06 miniature modules with up to 100% higher cooling capacity. Higher cooling capacity gives additional reserve in terms of temperature regulation from ambient, or in certain cases – reduces thermoelectric cooler electrical power consumption.

RMT offers separate thermoelectric coolers or TEC with mounting service into Customer packages. In addition, RMT offers the sub-assembly solutions – thermoelectric coolers mounted in standard Butterfy housing.

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.

RMT developed several special series of miniature TECs for Boxed TOSA designs - series 1MD04, 1MD03 and 1MD02.

TO-Can TOSA

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 - 1MD03 and 1MD02 Series. The smallest TECs of the series have about 1 x 1 mm² cold side and the height of only 0.7 mm.

Telecom Components

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 1ML06 and 1ML07, special 1MDL06, 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 DT_max for a thermoelectric cooler is specified by manufacturers at zero heat load, and maximal cooling capacity Q_max – 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 Online TEC Assistance available for initial search. For detailed modeling and calculations RMT provides free software TECCad for Windows and iTECPad for iPad (PC-free analysis).

Or contact RMT for immediate advice and assistance.