Special Topics in Optical Engineering II (15/1) Soonyoung Cha

Special Topics in Optical Engineering II (15/1) Soonyoung Cha

Contents

• Introduction

• Review of integrated microwave photonics

• Review: Arbitrary waveform generation

• Conclusion

Special Topics in Optical Engineering II (15/1) Soonyoung Cha

Introduction

- Widely used nowadays

- Speed of DSPs > several GHz

(Limit from sampling rate)

Digital electronics

- Front-end analog signal process

- Microwave photonics (MWP)

:Bulky, expensive, not flexible

Solution of limitation

Integrated Microwave Photonics

Processing in

optical domain

Special Topics in Optical Engineering II (15/1) Soonyoung Cha

Category of MWP applications

High dynamic range MWP link Microwave photonic filters

Optical delay line & beamforming Microwave signal generation

Special Topics in Optical Engineering II (15/1) Soonyoung Cha

Ultrabroad-bandwidth arbitrary waveform generation

Electronic arbitrary waveform generation (AWG)

- Limited in frequency and bandwidth

- Maximum bandwidth of 5.6 GHz

- Maximum frequency up to 9.6 GHz

Direct space-to-time pulse shaper

Generated by spatial pattern & distance

Wavelength-to-time mapping

Suitable for time time-stretch operation

Optic device: expensive, complicated, bulky → On-chip integrated pulse shaper

Progress on MWP-based AWG techniques

J. D. McKinney, D. E. Leaird, and A. M. Weiner, Opt. Lett. 27(15),

1345–1347 (2002). J. Chou, Y. Han, and B. Jalali, IEEE Photonics Technol. Lett. 15(4),

581–583 (2003).

Special Topics in Optical Engineering II (15/1) Soonyoung Cha

Ultrabroad-bandwidth arbitrary waveform generation

Special Topics in Optical Engineering II (15/1) Soonyoung Cha

Ultrabroad-bandwidth arbitrary waveform generation

Femtosecond laser pulse

- 100 fs pulse duration

- 1,525 ~ 1,610 nm band

- Coupled into Si waveguide

8 cascaded microring resonators

- Power transfer at resonant wavelength of each microring

: Creates dip in the output spectrum

- Microrings: slightly different resonance

Broadband optical source

On-chip spectral shaper

Micro-heater

- Local & independent control of temperature of each rings

: Resonance λ can be tuned (thermo-optical effect of Si)

Special Topics in Optical Engineering II (15/1) Soonyoung Cha

Ultrabroad-bandwidth arbitrary waveform generation

Chromatic dispersion: propagate different speeds for λ

- Pulse envelope is broadened (wavelength-time mapping)

→ Time-domain profile follows spectral shape

5.5 km single-mode fiber

Same shape of the

optical spectrum(10GHz)

→ Tunable profile

RF conversion

Output after resonators

Controllable RF waveform generation using microring silicon photonics

Special Topics in Optical Engineering II (15/1) Soonyoung Cha

Ultrabroad-bandwidth arbitrary waveform generation

First-generation design: Heating the ring itself cannot lead wide λ control

Solution: Mach-Zehnder (MZ) input coupler & heat this coupler

Problem

Second-generation design

Thermally tuning the phase shift of two arms

→ Coupling coefficient into a ring changes

→ Loaded quality factor changes

Phase shift : 0

π

Special Topics in Optical Engineering II (15/1) Soonyoung Cha

Ultrabroad-bandwidth arbitrary waveform generation

Optical signals from the common port: consists of peaks (dip for output signal)

Application for apodization

: control the suppression of side lobes

in Fourier transform domain

(Used in signal & filter design)

Tunable waveform shape

Without apodization

Flat-topped envelope

: Weak side-lobe suppression

~ -12 dB

With apodization

Waveform with uppressed edge

: Enhanced side-lobe suppression

~ -20 dB

Special Topics in Optical Engineering II (15/1) Soonyoung Cha

Ultrabroad-bandwidth arbitrary waveform generation

4 cycle – phase shift – 4 cycle (10 GHz)

: Doublet in the RF spectrum (dip @ 10 GHz)

→ Phase shift within the pulse burst

Phase shift inside waveform

60 GHz waveform with π-phase shift

: Strong dip near 60 GHz

→ Beyond the edge of time-domain

electronic measurement instrumentation

Could contribute to the realization of multi-GHz BW

Wireless LAN, portable multimedia streaming, vehicular networks, etc.

Special Topics in Optical Engineering II (15/1) Soonyoung Cha

Ultrabroad-bandwidth arbitrary waveform generation

Frequency-modulated waveforms

Two-tone waveform

- Abrupt frequency change

: 60 GHz to 40 GHz in single waveform

- Difficult to achieve using electronic circuits

Chirped waveform

: Sweep from low to high freq. (up)

: Sweep from high to low freq. (down)

Special Topics in Optical Engineering II (15/1) Soonyoung Cha

Conclusion

• Integrated microwave photonics

: to avoid bulky & expensive & complicated system

• Limitation of current DSP-based electronics

• Arbitrary waveform generation using MPF system

: High-frequency up to tens of GHz

• On-chip implementation of MPF-based AWG system

Special Topics in Optical Engineering II (15/1) Soonyoung Cha

Reference

D. Marpaung et al., Laser Photonics Rev. 7, 506–538 (2013)

J. D. McKinney, D. E. Leaird, and A. M. Weiner, Opt. Lett. 27(15), 1345–1347 (2002).

J. Chou, Y. Han, and B. Jalali, IEEE Photonics Technol. Lett. 15(4), 581–583 (2003).

M. H. Khan et al., Nat. Photonics 4, 117-122 (2010).

Lin, I. S., McKinney, J. D. & Weiner, A. M. IEEE Microw. Wirel. Compon. Lett. 15, 226–228 (2005).