Lect. 14: Waveguide Devices

Issues for practical waveguidesp g

- Precise control of dimension and refractive index - Low loss at desired λ- Mass production possible- Integration desirable (Integrated Optics)- Electrical control of refractive index (Electro-Optic effect)

Materials used for waveguidesMaterials used for waveguides

- Silica Optical fiber- Semiconductors: GaAlAs, InGaAsP, Si/SiO22

- Dielectric materials: LiNbO3 with Ti doping

Optoelectronics (10/2) W.-Y. Choi

Lect. 14: Waveguide Devices

LiNbO3 waveguide

V(t)

d

Thin buffer layerCoplanar strip electrodes

Polarized

Ea LiNbO3

dPolarizedinputlight

L

Cross-sectionEO Substratez

y

x WaveguideLiNbO 3

Integrated tranverse Pockels cell phase modulator in which a waveguide is diffusedinto an electro-optic (EO) substrate. Coplanar strip electrodes apply a transversefield Ea through the waveguide. The substrate is an x-cut LiNbO3 and typically thereis a thin dielectric buffer layer (e.g. ~200 nm thick SiO2) between the surfaceelectrodes and the substrate to separate the electrodes away from the waveguide.?1999 S.O. Kasap, Optoelectronics (Prentice Hall)

Optoelectronics (10/2) W.-Y. Choi

p, p ( )

Lect. 14: Waveguide Devices

Mach-Zehnder Interferometer:

( )2 1 2 1 2 1

2 12 2 2 2,

1 1 e e2 2

l l l l l ljk jk jkjkl j klout sideE e e e

+ − −− −− − ⎛ ⎞

= − = −⎜ ⎟⎝ ⎠

2l2 1 2

, sin2out side

l lI k

⎝ ⎠−⎛ ⎞= ⎜ ⎟

⎝ ⎠⎛ ⎞sideI

Il

( )1 2 1 2 1 2

1 2 2 2 2,

2

2 2

l l l l l ljk jk jkjkl jklout bottom

j jE e e e e e

l l

+ − −− −− − ⎛ ⎞

= + = +⎜ ⎟⎝ ⎠

−⎛ ⎞bottomI1l 2 1 2, cos

2out bottoml lI k⎛ ⎞= ⎜ ⎟

⎝ ⎠

Realize M-Z interferometer with wave devices

Optoelectronics (10/2) W.-Y. Choi

Lect. 14: Waveguide Devices

Mach-Zehnder Modulator

V(t)

BI

OutC B

Electrode

LiNbO EO S b

AIn DA

Waveguide

LiNbO3 EO Substrate

A i d M h Z d i l i i d l Th i li h iAn integrated Mach-Zender optical intensity modulator. The input light issplit into two coherent waves A and B, which are phase shifted by theapplied voltage, and then the two are combined again at the output.?1999 S O O l ( i ll)

Homework: Prob. 3 in 1999 Final (Assume Pout has cos2 dependence on Pin)

Optoelectronics (10/2) W.-Y. Choi

?1999 S.O. Kasap, Optoelectronics (Prentice Hall)

Lect. 14: Waveguide Devices

Homework: Prob. 3 in 1999 Final (See the figure next page Assume P t has cos2 dependence on Pi )(See the figure next page. Assume Pout has cos dependence on Pin)

Optoelectronics (10/2) W.-Y. Choi

Lect. 14: Waveguide Devices

Homework: Prob. 3 in 1999 Final (Assume P t has cos2 dependence on Pi )(Assume Pout has cos dependence on Pin)

Optoelectronics (10/2) W.-Y. Choi