We are studying Photonic Integrated Circuits.　　　▷Japanese

• WDM: Wavelength Division Multiplexing

One of the high speed and high capacity transmission system. Multiple wavelength lights are tranmitted through one fiber.

• Refractive index change in semiconductor material

Refractive index change in the semiconductor material is occurred by the temperature change, current injection or applied electric field.

	Physical effect
Temperature change	Thermo-Optic effect
Current injection	Burstain-Moss effect
	Plasma effect
	Bandgap shrinkage
Applied electric field	Franz-Keldysh
	Quantum confined stark effect

These effects have merits and demerits for the speed, consumption power, and wavelegth dependence.

	Speed	Consumption power	Wavelength dependence
TO effect	△	△	◎
Plasma effect	○	△	◎
Burstain-Moss effect	○	△	△
QCSE	◎	◎	△

• Kramers-Kronigh relationship

Refractive index coefficient in the semiconductor material is complex number. Real part shows the refractive index and imaginary part shows the absorption. These real part and imaginary part are related by the complex integration that is called Kramers-Kronigh relationship.

When the electric field is applied to the semiconductor material, the absorption edge wavelength is shifted to the longer wavelength by the Franz-Keldysh or QCSE effect, and the refractive index is changed at the same time. The following figure shows the refractive index change and absorption change as a function of wavelength.