Thermal Profiling of Photonic Integrated Circuits

1
Thermal Profiling of Photonic Integrated Circuits

• Sponsors
• National Science Foundation NSF
• Darpa University Optocenter
• Principal Investigators
• Prof. Rajeev Ram at MIT
• Prof. Janice Hudgings at Mount Holyoke College
• Contributors
• Dr. D. Lueerssen Postdoc, MIT and MHC
• K. Pipe Graduate Student, MIT
• E. Fenstermacher Undergraduate Student, MHC

2
Motivation

• Generic ProblemWhen Photonic Devices (Laser,
  Modulator, Amplifier, Waveguide etc.) are
  integrated on one chip, the optical power can no
  longer be measured with a power meter.

• Our SolutionMeasuring surface temperatures on
  the device and keeping a careful energy balance,
  the energy carried away by photons can be found,
  and thus the optical power.

3
The 4 Important Thermal Transport Mechanisms
4
Predictions of Temperature Profile along a Device

• Waveguide InputOutput, ?T0
• AmplifierInputltOutput, ?Tlt0
• AbsorberInputgtOutput, ?Tgt0
• Input and Output refer to the optical power.

optical signal
optical
waveguide
(wave
(wave
guide)
guide)
amplifier
detector
optical power
position
surface temperature
position
5
Sample Results Absorber

• Energy is absorbed from the photons, thus we
  observe heating
• Most heating occurs close to the input facet
• Absorption Coefficient
• From temperature measurements alone
• good agreement with Hakki-Paoli method

22.2
I 0 mA Pinj 15 mW
22
21.8
21.6
surface temperature (C)
a 50 cm-1
21.4
21.2
21
20.8
0
100
200
300
400
500
600
distance from input facet (mm)
6
Sample Results Amplifier

• Energy is carried away by more and more photon,
  thus we observe cooling
• For high enough input powers we can pinpoint the
  spatial onset of saturation in the amplifier

7
Experimental Methods IMicro Thermocouples

• Thermocouples with (25µm)² are placed on the
  device under a microscope
• Temperatures are measured point by point
• Resolution 0.01K, accuracy 0.2K

8
Experimental Methods II Thermoreflectance

• Surface reflectivity changes with surface
  temperature
• Project apply 2D method which exists for
  electronic circuits to photonic circuits
• Spatial resolution diffraction limit of optics