Soo Min Kang YONSEI UNIVERSITY Contents Introduction - - PowerPoint PPT Presentation

YONSEI UNIVERSITY

Special Topics in Optical Engineering Ⅱ Paper Review 2015‐05‐22

Converged Advanced Network

Soo‐Min Kang

Nabeel A. Riza and Nicholas Madampoulos

YONSEI

UNIVERSITY

Contents

Introduction Theory

(1) Basic : Beamforming ⊃ Phased Array Antenna (2) General Photonic Delay Line & Limit (3) Proposed System : SSC & DRLC (Synchronous Signal Calibration & Dynamic Range Loss Compensation)

Experiment Result & Discussion Conclusion Introduction Theory

(1) Basic : Beamforming ⊃ Phased Array Antenna (2) General Photonic Delay Line & Limit (3) Proposed System : SSC & DRLC (Synchronous Signal Calibration & Dynamic Range Loss Compensation)

Experiment Result & Discussion Conclusion Cf) Beamforming Research Trend

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 Background

Introduction

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Basic : Beamforming

 Way to beamforming

[ Physical movement of 1‐antenna ] Dish type Parabolic type

Not flexible

[ Phased Array Antenna ] PAA

 What is the beamforming?

Adaptive spatial filter forming beam Beamforming

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Basic : PAA (1)

 PAA Concept : Using delay between adjacent antennas …  PAA Applications

RADAR, Ultrasound, Military, Optical Communications, Optical Memories, Astronomy

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Basic : PAA (2)

 PAA Requirements

• 1. fast estimation & switching
• 2. Dynamic range↑(Variable)
• 3. Time control in synchronism

between adjacent antennas Hard to wideband control Delay loss ↑, EMI Power consuming ↑

Electronic controller

 PAA Control  PAA types

[ Phase‐based Steering ] : Phase‐based control [ True Time Delay Steering ] : Time‐delay based control [ N‐bit Switched Time Delay ] : Make various path using switch “Photonic Delay Line(PDL)” Delete E’s problem

Photonic controller

Focus on

• Ref. Nicholas M., ‘Photonic Delay Lines : Technology Trends and Challenges’,, SPIE, 2003

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Basic : General PDL & Limit

 Without PDL(Photonic Delay Line)

• Fig. 1 Typical FO(Fiber‐optic) Link for PAA

 External modulation : fm↑, BW ↑ , Dynamic Range ↑  To use this link for PAA Application : Variable PDL have to be inserted

 KEY

• 1. fast estimation & switching(<ps)
• 2. Dynamic range↑ (Variable)
• 3. Time control in synchronism

between adjacent antennas

Variable PDL here Connector

 With general PDL in FO Link

PDL

Cf) Typical FO link with PDL

GRIN lens : Gradient‐index lens

Conventional GRIN lens

 Optical Attenuator : 1) Adjusting PD input 2) Equal amplitudes for each channel  Slow switching time : 200ms (demand : <ps)  Optical Insertion loss of PDL → PD input ↓ → Dynamic Range limit ↑ → Antenna input ↓

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• Fig. 3‐(a) Proposed basic structure of SSC & DRLC
• A. Basic structure of SSC & DRLC
• Ref. [21]

SSC & DRLC (1)

 Paper’s purpose : Make SSC & DRLC (Synchronous Signal Calibration and Dynamic Range Loss Compensation) Technique

to improve general PDL problem in PAA

OFF ON

 Sub‐Module N : High speed binary on/off switch  Attenuation : ON(AN) / OFF(A0)  Phase(=time delay) variation : ON(TN) / OFF(T0) ① Digital control ② High speed ③ Binary operation ④ Variable optical attenuator in synchronism SSC & DRLC Properties

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SSC & DRLC (2)

• B. High‐speed, variable optical attenuator based on fast FLC polarization switching

 Three Basic components ① FLC(Ferro‐electric Liquid Crystal) ‐ LC(Liquid Crystal) : material between solid and liquid composed of ‘mesogen’ → molecule has direction, easy to vary SOP(State of Polarization)

Cf) Liquid Crystal and Order parameter [Ferro‐electric LC]

Smectic C*

‐ FLC : Smectic C*(chiral and tilted type) → spontaneous molecular polarization(ferroelectric) ‐ Clark‐Lagerwall Effect in FLC : Voltage in FLC’s electrode → SOP variation (s↔p pol.) ‐ fast response, stability, memory

* Nematic : 분자가 위치는 불규칙하지만 모두 같은방향으로 향한 상태의 * Smectic : 분자가 일정방향을 향하고 있으며 층으로 쌓여있는 상태의 * Smectic C* : Chiral-smectic C type / chiral : 분자구조가 비대칭성의

‐ Three LC types

[Nematic LC]

Cf)

[Smectic LC]

Smectic A Smectic C Cf)

• Ref. [22‐24]

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③ PBS(Polarization Beam Splitter) ‐ split p‐ & s‐ pol.

[PBS]

• Ref. [18]

SSC & DRLC (2)

• B. High‐speed, variable optical attenuator based on fast FLC polarization switching

 Three Basic components ② HWP(Half Wave Plate) ‐ phase delay plate using birefringence ‐ phase variation =

∆

• (L : thickness of plate, ∆ n : birefringence degree of plate)

‐ vary polarization’s axis

[Half Wave Plate]

s pol. p pol. just p‐pol. s pol. p pol. vector sum

• f p+s pol.

p pol. s pol.

[Birefringence]

Material having a refractive index that depending on polarization direction of light

Cf) Polarizer : optical filter that passes light of a specific polarization and blocks waves of other polarizations

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SSC & DRLC (2)

• B. High‐speed, variable optical attenuator based on fast FLC polarization switching

 By using ①~③

• Fig. 3‐(b) Scheme
• Pol. axis

HWP

p s

PBS Linear Polarizer

• Pol. switch

with FLC

p s

PBS

• Pol. switch

with FLC TIR Prism TIR Prism A0 Absorber An [ Nth‐bit Optical Attenuator Submodule ]

Attenuation Here → ↓

s s s p

SOP On

p p p p p

Off

 Desired attenuation : achieved by adjusting incident polarized light’s rotation degree 

• Pol. switching by applying voltage onto FLC electrode : speedy & fine tunability → more flexible than NLC
• Ref. [21]

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 Desired attenuation can be achieved by adjusting Voltage and suffering different diffraction degree  System size↓  Insertion loss↓ than FLC

• Fig. 3‐(d) PDLC based Optical Attenuator

SSC & DRLC (3,4)

• C. Phase Perturbation based Optical Attenuator
• D. PDLC(Polymer‐Dispersed Liquid Crystal) based Optical Attenuator

PDLC : droplets

dispersed in polymer

• Ref. [26]
• Fig. 3‐(c) FLC‐based Optical Attenuator using phase perturbation distribution
• Ref. [23‐25]

 Individual control of axis of 2D FLC array → areas with alternating 0 and phase variation  Variable fringe spacing 0 ‐ 2D grating → cause phase perturbation on beam phase front Individual control V1 ~ VI Individual control V1 ~ VI Perturbation

• n front

Perturbation

• n front

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SSC & DRLC (5)

• E. N‐bit Electro‐optic Attenuator based on Photoconductive Effect
• Fig. 3‐(e) Photoconductive effect based RF Attenuator

 EHP → Solid state plasma creation in semiconductor → plasma has electrical property → interaction with RF signal → absorption(atten.)  2D VSCEL array : activate each bit, individual controlled  Photoconductive effect : optical beam → EHP generation [Photoconductive effect]  Individual lasers in VSCEL array : computer controlled to be ON or OFF to desired attenuation level  Independently turning ON or OFF lasers → N‐bit RF attenuator realization  High speed, high density PAA control availble → Minimize size of PAA

• Ref. [27]

* CPW : Co‐planar Waveguide * PCS : Photoconductive Switch

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Experiment

 Purpose : Synchronous amplitude & time control for optimum dynamic range

• Fig. 2 FO link with PDL & Dynamic rnage loss compensation based on high speed control

 Experiment setup

 Parameters

‐ Nd:YAG laser at 1319nm ‐ LiNbO3 MZM ‐ Lasertron QRX receiver

 Estimation

‐ RF gain, SFDR, Noise Figure, Noise Floor ‐ CDR(Compression Dynamic Range) : difference between maximum detectable power in linear regime to minimum detectible power≅ SNR

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CDR ↑, SFDR ↑ means High dynamic range → good performance Estimation properties

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Results and Discussion (1)

• Fig. 4‐6 FO link two tone intermodulation distrotion output vs. Link fundamental input at 6GHz

W/O PDL, W/ PDL, W/ PDL + Dynamic range compensation techniques

 Experiment Results (1) : Input at 6GHz

 W/PDL : low PD input → lower shot noise (General PDL : Equal attenuation, loss 大)  W/ PDL + : PDL loss compensated → Dynamic range ↑ ( Different attenuation, high speed, loss 小)

W/O PDL W/ PDL W/ PDL + α RF gain[dB] 32.16 43.16 32.16 CDR[dB·kHz] 127.8 120 127.8 SFDR[dB·kHz

• ]

91.8 86.8 91.84 PDL loss [dB] ‐ 5.5~5.7

compensated

* TOI : Third‐order Intermodulation point(=IP3)

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Results and Discussion (2)

• Fig. 7‐9 FO link two tone intermodulation distrotion output vs. Link fundamental input at 3GHz

W/O PDL, W/ PDL, W/ PDL + Dynamic range compensation techniques

 Experiment Results (2) : Input at 3GHz

 MZM’s

at 3GHz is lower than 6GHz

→ 1dB compression output power ↓ → CDR : ‐ 3 / SFDR : ‐5 lower than 6GHz case

W/O PDL W/ PDL W/ PDL + α RF gain[dB] 33.17 43.3 33.18 CDR[dB·kHz] 123.05 116.5 123 SFDR[dB·kHz

• ]

88 83.5 88 PDL loss [dB] ‐ 5.5~5.7

compensated

*

: RF power required for generating

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Results and Discussion (3)

• Fig. 10 Gain for 3~6GHz band : W/O PDL, W/ PDL, W/ PDL + Dynamic range compensation techniques

 Experiment Results (3) : Gain spectrum

 W/ PDL : insertion loss >1.3dB per bit  W/ PDL + : insertion loss < 0.05dB per bit variation  Insertion loss : nonuniformity of optical device

RF Gain [dB] 3GHz 4G 5G 6G W/O PDL 32.10 32.24 32.30 32.61 W/ PDL 31.89 31.97 32.10 32.62 W/ PDL + 42.72 42.82 42.90 43.36

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Cf) Beamforming Research Trend

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 Optical Differential True Time Delay

 ‘Differential’ which means using adjacent antenna’s delay  Attempt to multi‐optical beamforming such as MIMO

• Ref. Jian Wang, ‘Continuous angle steering of an optically

controlled phased array antenna based on differential true time delay constituted by micro‐optical components’, Optics Express, 2015

 Integrated Optical Beamformer

 Chip on beamformer  Multiple wavelength or beam beamformer

• Ref. Chris G.H., ‘Integrated Optical

Beamformers’, OFC 2015

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Conclusion

PDL insertion loss ↑ → Dynamic Range ↓ Also, slow switching time

W/ PDL

Digital control, high speed, switching, fine atten. tuning, loss↓ → Dynamic Range↑

W/

PDL + No spatial & phase diversity→ PDL Needed

W/O PDL

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Special Topics in Optical Engineering Ⅱ Paper Review 2015‐05‐22

Soo‐Min Kang

roemee817@naver.com

Converged Advanced Network