silicon optical modulator [호환 모드] - yonsei...

High-Speed Circuits & Systems Lab.Dept. of Electrical and Electronic Engineering

Yonsei University

Silicon Optical Modulator

Silicon Optical Photonics Nature Photonics Published online: 30 July 2010

Byung-Min Yu

24 April 2014

2/20 pageYonsei University

Content

1. Introduction

2. Modulation method

3. Performance metrics

4. State-of-art device

5. Conclusion


Introduction

From (www.bretswanson.com)

- Large loss in high frequency

- Cross talks

- Bulky size

Electrical interconnect

- Small loss in high frequency

- EMI insensitive

- Small size

Optical interconnect


Introduction

From (http://citrix.cleanrooms.com/index/packaging/packaging-blogs/ap-blog-display._archives.201104.blogs.ap-blog.html)

Increasing demands for interconnect speed in short-range

communication Optical interconnect !


Introduction

(From http://www.cs.utk.edu/~dongarra/ccgsc2006/Slides)

Silicon photonics: integrate optical devices and electronic circuits on a single chip with SOI (Silicon-On-Insulator) process


Kinds of optical modulator

- Low sensitivity

- Large hard to integrate

(From http://www.cs.utk.edu/~dongarra/ccgsc2006/Slides)

~60 m

MZI Modulator

- High sensitivity

- Small easy to integrate

Ring Modulator


Modulation method

Modulation method

Electro-refractive or electro-absorptive modulation

Electric field: real part (∆n) and imaginary part (∆ ) change in material

1. Pockels effect, Kerr effect (∆n): Refractive index change depending on electric field in semi-conductor

2. Franz-Keldysh effect (∆ ) : Optical absorption change depending on electric field in semi-conductor

3. Thermo-optic effect (∆ ) : Refractive index change depending on temperature

4. Free carrier plasma dispersion effect (∆n): Refractive index change depending on free carriers in material


Modulation method

Free carrier plasma dispersion effect

∆ = −8.8 × 10 × ∆ − 8.5 × 10 × ∆ . = 1550∆ = 8.5 × 10 × ∆ + 6.0 × 10 × ∆ = 1550


Modulation method

Electrical manipulation of the charge density

Carrier accumulation Carrier injection Carrier depletion

1. Carrier accumulation: capacitor structure

2. Carrier injection: p-i-n structure, forward bias

3. Carrier depletion: p-n structure, reverse bias (width of depletion region change)


Performance metrics

Kinds of performance metrics

1. Modulation speed or bandwidth

2. Modulation depth (extinction ratio, on/off ratio)

3. Insertion loss

4. Power consumption

5. Footprint (device size)

6. Optical bandwidth

7. Temperature


Performance metrics

Modulation speed & electro-optic bandwidth

- Electro-optic bandwidth: defined by 3dB bandwidth

- Modulation speed: eye opening

- High modulation speed is imperative for optical interconnect

3GHz optical modulator 10Gb/s eye diagram


Performance metrics

Modulation depth & Insertion loss

- Modulation depth: >7dB for interconnect application, 4~5dB for overall system

- Insertion loss: passive loss because of reflection, absorption and mode coupling

Nor

mal

ized

Tra

nsm

itted

Pow

er

Wavelength [ m]

= 0 V

= -2 V

on/off ratio

Insertion loss


Power consumption & Footprint

- Power consumption: commonly small compare to electrical circuits! optical interconnect target: electrical interconnect(~1 pJ/bit) modulator target: ~10 fJ/bit

- MZI modulator: ~5 pJ/bit @10 Gb/s, 200-μm-long device

- Footprint

- MZI modulator: about hundreds or thousands of μm

- Ring modulator: about dozens of μm

Performance metrics


Optical bandwidth & Temperature

- Optical bandwidth: operational wavelength range of a device

- MZI modulator: relatively large bandwidth (~20 nm)

- Ring modulator: relatively small bandwidth (~100 pm)

- Temperature: device characteristics change due to temperature

- Ring modulator is relatively large temperature sensitive

1. Thermo-electric controller (±1℃) must be needed (power consumption)

2. Temperature robust device (multiple rings, ring coupled to and MZI)

3. Electro absorption device (low speed)

Performance metrics


Trade off in performance metrics

Reducing footprint

- Reducing power consumption, drive signal loss

- Phase shift reduce in MZM, reducing modulation depth

Multiple ring modulator

- Reduce optical bandwidth and thermal sensitivity

- Complexity increased, large footprint and power consumption

Speed increased (MRM)

- Modulation depth decreased


State-of-art devices• Research start of silicon optical modulator: mid-1980s

• Carrier injection

• p-i-n structure with carrier injection device is usually used (very slow)

• mid-2000s: GHz optical modulator (optimizing and reducing structure)

• Carrier accumulation

• 2004: >1GHz carrier accumulation device is developed (Intel)

• Optimized to ~10GHz and 3.8dB E.R. (2005) & ~10GHz and 9dB E.R. (2009)

• ! Resistance and capacitance is major speed limit rather than minority carrier life time

• Carrier depletion

• Theoretically ~50GHz 3dB bandwidth

• 2007: 30Gb/s optical modulator is developed (Intel)

Improved to 40Gb/s data transmission


State-of-art devices

• 2005: High-speed ring modulator was first introducedCarrier injection based ring modulator (~1.5 Gb/s) ~10 GHz using pre-emphasis driving signal

• Carrier depletion based ring modulator (>35 GHz)


State-of-art devices


Conclusion

1. Modulator type

1) MZI based modulator

2) Ring resonator based modulator

2. Modulation method

1) Pockels effect, Kurr effect

2) Franz-Keldysh effect

3) Thermo-optic effect

4) Free carrier plasma dispersion effect

3. Electrical carrier change

1) Carrier accumulation

2) Carrier injection

3) Carrier depletion

4. Performance metrics

- Modulation speed, Modulation depth, Insertion lossPower consumption, Foot print, Optical bandwidth, Temperature


Paper review

Silicon Optical Modulator, Nature photonics (2010)

Byung-Min Yu

[email protected]

silicon optical modulator [호환 모드] - yonsei...

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