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All-Silicon Active and Passive Guided-Wave Components For λ = 1.3 and 1.6 µm. Hyun-Yong Jung High-Speed Circuits and Systems Laboratory. Outline. Introduction Infrared Transmission Waveguide Structures And Fabrication Optical Switch Design Experimental Work Summary. Introduction.

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All-Silicon Active and Passive Guided-Wave Components For λ = 1.3 and 1.6 µm

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All silicon active and passive guided wave components for 1 3 and 1 6 m

All-Silicon Active and Passive

Guided-Wave Components

For λ = 1.3 and 1.6 µm

Hyun-Yong Jung

High-Speed Circuits and Systems Laboratory


All silicon active and passive guided wave components for 1 3 and 1 6 m

Outline

  • Introduction

  • Infrared Transmission

  • Waveguide Structures And Fabrication

  • Optical Switch Design

  • Experimental Work

  • Summary


All silicon active and passive guided wave components for 1 3 and 1 6 m

Introduction

Silicon is a “new” material in intergrated optics in 1986

Why “Si” ?? (Ta2O5 , ZnO….  Si - as a Substrate)

1) Many of the processes developed for the Si electronic

circuit industrycan be applied to Si optical devices

2) High-speed Si electronic circuits can be combined

monolithically with Si guided-wave devices in an

optoelectronic integration


All silicon active and passive guided wave components for 1 3 and 1 6 m

Infrared Transmission

Si has impurities or is doped deliberately

to provide electrically active impurities

Free Carriers

Changing the real and imaginary

parts of the Si dielectric constant

Changing Refraction & Absorption Indexes!!


All silicon active and passive guided wave components for 1 3 and 1 6 m

Infrared Transmission

The optical properties of Si, the absorption band edge, in the near infrared

were recently(In 1986) remedied by the work of Swimm

  • Crystallinity Effects Propagation Loss

600 Cm-1 at λ = 1.3 um

For un-doped polycrystalline Si

3300 Cm-1 at λ = 1.3 um

For amorphous un-doped Si

Wavelength dependence of optical absorption

For high resistivity single crystal Si

< Absorption Coefficient >

The materials loss in

silicon waveguides will be very low!


All silicon active and passive guided wave components for 1 3 and 1 6 m

Waveguide Structures and Fabrication

  • Forward-biased p-n junction

  • - The refractive index of the intersection was perturbed (Δn = 5 10-3)

  • at 1018 carriers/cm3 , due to plasma dispersion effect

  • - Electrical injection from a forward-biased p-n junction

Δα = q2λ2Ne/4π2c3nε0mce*τ

1/ τ = 1/ τ1 + 1/ τ2 + ……

Relaxation τ≈ 1/Ne (From Celler-ref)

Ne = Free electron concentration

The substrate loss as a function of the

n+, p+ doping density


All silicon active and passive guided wave components for 1 3 and 1 6 m

Waveguide Structures and Fabrication

  • Optical injection

  • - Using creation of electron-hole pairs, with free carriers arising form the

  • absorption of short-wavelength photons ( A band-to-band absorption process)

  • Kerr effect

  • - A changing in the refractive index of a material in response to an applied field

  • Electrorefraction

  • - This effect is related to the electroabsorption effect(Franz-Keldysh effect)

  • - To produce the electric control fields, one would use a reverse-biased

  • p-n junction or a depletion-MOS gate structure on the Si waveguide

  • Acoustooptics

  • - Si is capable of efficient acoustooptic Bragg diffraction

  • - 2X2 switching is feasible with an acoustooptic stimulus


All silicon active and passive guided wave components for 1 3 and 1 6 m

Experimental Work

Sample Preparation

Slab and Channel Waveguides

Optical Power Divider

Discussion of Results


All silicon active and passive guided wave components for 1 3 and 1 6 m

A. Sample Preparation

Lasers

Optical Fibers

Detectors

Flat Ends On The Si Waveguide Samples

First try,

A scribe and break approach  Abandoned (X)

Cleavage Planes Were Not Smooth Enough at The Epitaxial Location

Second try,

A mechanical polishing techniques  Successful (O)

Obtaining Sharp Corners


All silicon active and passive guided wave components for 1 3 and 1 6 m

B. Slab and Channel Waveguides

< Set-up >


All silicon active and passive guided wave components for 1 3 and 1 6 m

C. Optical Power Divider

  • Goal

  • - To Build a 2X2 Electrooptical Switch

  • Channel Widths = 10, 15, 20 um

  • X patterns were 2 cm long

  • The rib height = 3 um


All silicon active and passive guided wave components for 1 3 and 1 6 m

D. Discussion of Results

The present guides represent a “first effort” and were not optimized

  • 5 to 13 dB/cm in the slab guides

  • 15 to 20dB/cm in the rib channels

  • Material loss, Metal loading loss, Substrate loss

  • Channel wall-roughness loss, Epi/substrate interface loss

  • The loss that occurs when the index difference is not large enough to

  • confine the NA of the input beam completely or when the proportions

  • of rib do not produce good mode confinement

  • The loss due to scratches, digs, and chips on the wave guide ends

  • Most of these loss can be reduced

  • by further development of Si waveguide fabrication


All silicon active and passive guided wave components for 1 3 and 1 6 m

Summary

  • Five techniques for making 2X2 optical switches

  • - Forward-biased p-n junction

  • - Optical injection

  • - The Kerr effect

  • - Electrorefraction using a reverse-biased contact

  • - Acoustooptic Bragg diffraction

  • Two advantages of Si guided-wave optical circuits

  • - Monolithic optoelectronic integration with high-speed Si electronic circuit

  • - Utiliztion in optics of well developed processing techniques from

  • the electronics industry

Si will be suitable for every integrated optical component

at λ = 1.3 or 1.6 um except an optical source


All silicon active and passive guided wave components for 1 3 and 1 6 m

Thank you


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