Silicon photonics ushers in 100G networks

Appendix: Photonic modulators


In a typical Mach-Zehnder interferometer (MZI) modulator, the input waveguide is split into two paths. With no voltage applied, the light is coupled back together for the output waveguide, creating the “on” signal. When the proper Vπ voltage is applied, it changes the refractive index of the waveguide so that the light in the upper path is delayed by a half a wavelength, or 180°. In this case, the two paths of light are out of phase with each other, canceling each other and creating the “off” signal.

 
For data center applications, which require small size and low power, Kotura has developed an electro-absorption (EA) modulator. This tiny modulator is a P-I-N structure constructed from germanium, doped with a small amount of silicon in the silicon waveguide path.  Applying current changes the device from a photon absorber to a transparent waveguide.  

About the author
Arlon Martin is the VP of Marketing, Contracts & Government Affairs for Kotura. Martin has more than 25 years of experience in sales, marketing, product and technical management in the semiconductor and optoelectronics industries. Prior to joining Kotura, Martin held numerous management and marketing positions with such companies as Agility Communications, Lucent Technologies and AT&T. He began his professional career at Bell Laboratories, where he spent five years designing CAD tools. Martin received his MS degree in Computer Engineering from the University of Michigan.

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