Thermoelectric Cooling Solutions

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Thermoelectric sub-assemblies

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TOSA (Transmitter Optical Sub-Assembly) header is analog of «Butterfly» header. Like «Butterfly» header it use for optical Telecom transmissions and laser diode pumps. But TOSA has a smaller form factor, which allows it used in the pluggable optical transceiver modules of SFP, XFP and SFP + types. There are two TOSA header design types available - coaxial TOSA with max diameter 5.6 mm and so-called box-like TOSA header, that has been unified with dimensions and electrical parameters requirements by Multi-Source Agreement (MSA) in 2004 to establish compatible sources of 2.5Gb/s and 10Gbit/s TOSA. TOSA XMD MSA header has box-like form factor with more space inside than coaxial TOSA. This provides more flexibility with thermoelectric cooler integration. Although XMD agreement fixes electrical power consumption requirements for thermoelectric cooler inside, there are different TEC types can be applied for TOSA MSA. The material of TOSA header is usually Kovar or cold rolled steel (CRS) for coaxial TOSA and Kovar or Cu(20%)-W(80%) for box-like TOSA coated with nickel and gold. The header surface open both for mounting coaxial and box-like TOSA is about 4.5×5.0 mm2. RMT Ltd specializes in miniature thermoelectric cooling solutions and provides a range of standard and customized TECs for cooled TOSA applications of both types - coaxial and XMD MSA TOSA.

Sub-Assembly Overview

Standard Sub-Assemblies Solutions

This is a list of standard, most common solutions with thermoelectric coolers mounted on TOSA headers. The complete list of possible solutions is wider. TOSA header is suitable for any thermoelectric cooler with hot side dimensions up to 4.5×5.0 mm2. Please, contact RMT Ltd in case if specific solution on TOSA is required.

Single-stage TEC
(CuW base)
Single-stage TEC
(Kovar base)

Exterior Type dTmax
1MD03-024-xx (n=24)
Click to enlarge. 1MD03-024-04 70 1.9 1.1 3.0 0.15 4.2 3.0 1.0 Datasheet
1MD03-024-05 71 1.6 0.9 1.1
1MD03-024-08 72 1.0 0.6 1.4

TEC performance parameters are specified at standard conditions (+27°C, vacuum). The datasheet for each sub-assembly contains also the additional data, specified at +50°C, N2. Please, download the datasheet for detailed info. The affect from TOSA Cu(20%)-W(80%) or Kovar base thermal resistance (Rt) is included into specified performance values. TOSA sub-assembly is required to be attached to an appropriate heatsink to spread the heat, pumped from LD (or another source) and thermoelectric cooler. Heatsink thermal resistance may affect on performance, and is required to be as low as possible. Heatsink thermal resistance influence is not included into specified performance data.

You may use TEC Select Assistant to find other thermoelectric coolers suitable for TOSA header. Press the On-Line Assistant link and specify hot side dimensions as 4.5×5.0 mm2 as a main search criteria. The cooling capacity of TEC is recommended to be as at least 2 times higher than expected heat load in the application. For example - for 2W estimated heat load, please, specify TEC Qmax as at least 4W in the search field. The assistant will specify all thermoelectric coolers compatible for installing on TOSA package. The datasheets for not listed TOSA sub-assemblies are available by request.

Headers Available

It's a typical drawing of TOSA header. The header dimensions may vary to a small extent, depending on the manufacturer.


Note: RMT Ltd provides the sub-assemblies - thermoelectric coolers, mounted on TOSA headers. The company doesn’t manufacture the headers or provide headers separately. The mounting service is also available on Customer’s headers upon request.

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Information furnished by RMT Ltd is reliable. However no responsibility is assumed for possible inaccuracies or omission. Specifications are subject to change without notice.