Laser Diode Module Thermal Radiation Shielding
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Solution Overview
Problem
Coaxial type laser modules face challenges in accurately controlling the temperature of semiconductor laser diodes due to errors in temperature measurement caused by thermal radiation from the package, leading to excessive cooling or heating and wavelength drift, which is critical in DWDM optical communications where wavelength stability is essential.
Innovation Solution
A light-emitting module design that includes a semiconductor laser diode, thermistor, and thermo-electric cooler enclosed in a package with a cylindrical cap and disk-shaped stem, where the base shields thermal radiation from the cap, and the thermistor is positioned beneath an overhung portion to minimize exposure to package heat, allowing accurate temperature control and reduced wavelength variation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the thermistor is arranged in close to the laser diode to enable accurate temperature control, then the temperature control precision is improved, but the thermistor is influenced by thermal radiation from the case wall surface causing measurement errors
Solution Approach 1:
A heat shielding member is introduced as an intermediary between the thermistor and the case wall surface. This heat shielding member blocks thermal radiation from the case wall surface, preventing it from reaching the thermistor and causing measurement errors, while allowing the thermistor to remain positioned close to the laser diode for accurate temperature control.
Solution Approach 2:
The harmful thermal radiation from the case wall surface is extracted or blocked from reaching the thermistor by positioning the heat shielding member specifically between these two elements. This separates the thermistor from the harmful thermal influence while maintaining its proximity to the laser diode.
2Measurement precision
If the heat shielding member is added to block thermal radiation, then the temperature measurement accuracy is improved, but the device complexity increases
Solution Approach 1:
The heat shielding member is merged with the base structure rather than being a separate, additional component. The base is designed with an integrated heat shielding portion that extends between the thermistor and the case wall surface, combining the supporting function of the base with the heat shielding function in a single structural element.
Solution Approach 2:
The base structure serves multiple functions: it supports the laser diode and thermistor, provides thermal management, and includes an integrated heat shielding portion that blocks thermal radiation from the case wall surface. This multi-functionality reduces the need for additional separate components.
3Volume of moving object
If the spacing between the laser diode and case is reduced in coaxial type package, then the compactness is improved, but it becomes difficult to provide heat-shielding members
Solution Approach 1:
The heat shielding function is merged into the base structure itself, eliminating the need for separate heat-shielding members that would require additional installation steps in the compact coaxial package.
Solution Approach 2:
The base structure is designed with a localized heat shielding portion that specifically targets the region between the thermistor and the case wall surface. This localized approach provides heat shielding exactly where needed without requiring additional space or complex structures throughout the entire package.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The design effectively suppresses radiation to the thermistor, enabling precise temperature control of the laser diode, reducing wavelength variation to less than 20 pm compared to 120 pm in conventional modules, thus improving temperature controllability and focusing efficiency.
Implementation Method 1
a base that mounts a laser diode and a thermistor, and a thermo-electric cooler; The base that mounts a laser diode and a thermistor is mounted on the thermo-electric cooler. Based on the detected information, the thermo-electric cooler keeps the temperature of the laser diode constant.
Implementation Method 2
The thermistor detects the temperature of the laser diode.
Implementation Method 3
The light-emitting module according to the invention has a feature that the base shields the thermal radiation from the cap.
Implementation Method 4
A light-emitting module according to the invention emits an optical signal. The light-emitting module includes a semiconductor laser diode
Data Source
AI summary
There is provided a light-emitting module which suppresses wavelength drift. A light-emitting module according to the invention includes a stem and a cap fixed to the upper surface of the stem. A thermo-electric cooler is mounted on the stem and a base is mounted on the thermo-electric cooler. A laser diode is mounted on one side of the base. A thermistor that measures the temperature of the laser diode is mounted on another side. The other side includes an overhung portion that blocks radiant heat transmitting from the cap toward the thermistor.