Thermal Crosstalk in Photonic Integrated Circuits

Key Takeaways

• The dense integration of optical components and operating temperature are primary factors influencing the performance and service life of photonic integrated circuits.

• Thermal crosstalk refers to the change in temperature in one section of a photonic integrated circuit due to the generation of heat in a nearby section or component. 

• The thermal crosstalk in photonic integrated circuits can be mitigated using thermal isolation trenches, thermoelectric cooling, or by reducing the building block density in chips.

Thermal crosstalk can affect the performance of photonic integrated circuits

Heat generation is a critical problem affecting photonic integrated circuits. Self-generated heat introduces reliability issues in these circuits. Apart from the heat-generating device or section within an integrated circuit, neighboring devices or sections also suffer performance degradation due to temperature variation. The crosstalk caused by the thermal gradient is called thermal crosstalk. The thermal crosstalk in photonic integrated circuits must be eliminated to ensure high performance and reliable control. In this article, we will explore photonic integrated circuits and how thermal crosstalk affects them.   

Photonic Integrated Circuits 

The integrated circuits comprising photonic or optical components are called photonic integrated circuits. Photonic or optical components operate with light energy. Usually, laser sources are used to generate light to inject into other components in photonic integrated circuits. Components such as waveguides, polarizers, lasers, phase shifters, and modulators are examples of photonic or optical components commonly seen in photonic integrated circuits.

Photonic integrated circuits utilize wafer-scale technology on the substrate for fabricating chips. Substrate materials often used for photonic integrated circuits include:

• Silicon
• Silica
• Lithium niobate
• Indium phosphide
• Silicon nitride

Photonic integrated circuits are the main elements in most millimeter or terahertz applications and advanced modulation signal generation systems. In photonic integrated circuits, spectral tunability is achieved either by injection current tuning or temperature tuning. 

Advantages

Photonic integrated circuits overcome challenges faced by electronic integrated circuits; they increase and improve circuit miniaturization, speed, integration capacity, and compatibility more than conventional integrated circuits. 

Challenges

The dense integration of optical components and the operating temperature are primary factors influencing the performance and service life of photonic integrated circuits. The miniaturization of an integrated circuit and the increased amount of heat dissipation in photonic chips provokes thermal crosstalk and challenges the functioning of these circuits. Photonic integrated circuits can face reliability problems and performance degradation due to thermal crosstalk. 

Thermal Crosstalk in Photonic Integrated Circuits  

Both self-heating and passive heating are detrimental to the components in photonic integrated circuits. The additional heating from passive heating within the photonic integrated circuits can cause detrimental thermal effects.

Thermal crosstalk is a significant thermal effect that influences a component due to the temperature gradient of its neighboring heating active component. Thermal crosstalk refers to the change in temperature in one section of a photonic integrated circuit due to the generation of heat in a nearby section or component. The spatial proximity of the sections or components within the same photonic integrated circuit induces thermal crosstalk.

Thermal crosstalk is a critical issue in photonic designs with elements placed adjacent to each other. Thermal crosstalk limits the reliability of control in photonic integrated circuits. The performance degradation is an assured after-effect of thermal crosstalk in photonic integrated circuits.  

Thermal Crosstalk Effects 

Thermal crosstalk is the most significant thermally-induced problem for photonic integrated circuits. The effect of thermal crosstalk varies with the components in photonic integrated circuits. The thermal crosstalk between devices in the same photonic chip reduces the efficiency of the calibration procedure and spectral tuning. The stabilization of photonic integrated circuits is heavily influenced by mutual thermal crosstalk. In general, thermal crosstalk can cause issues such as device performance degradation, reliability issues, and signal distortions. Here are a few examples of ways in which thermal crosstalk can affect photonic integrated circuits. 

Silicon Nanophotonics

In silicon nanophotonics, thermal crosstalk is often due to high-density integration. The interconnects in silicon nanophotonic chips can cause thermal crosstalk, as they act as paths for heat spreading between nearby elements. 

Integrated Distributed Feedback Laser-Electroabsorption Modulation Devices

Integrated distributed feedback laser-electroabsorption modulation devices in photonic integrated circuits are vulnerable to thermal crosstalk. There is a finite wavelength shift observed in these devices due to thermal crosstalk. Phase shifts are another thermal effect in photonic integrated circuits due to thermal crosstalk.

The thermal crosstalk in photonic integrated circuits can be mitigated using thermal isolation trenches, thermoelectric cooling, or by reducing the building block density in chips. Cadence’s suite of design and analysis tools help in the design, simulation, and analysis of photonic integrated circuits and systems.

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