Wireless-photonic-wireless interfaces based on …w3.ualg.pt/~jlongras/opEuropeanworkshop09.pdfmodulation injected power -30 dBm The phase synchronization of the RTD-LD can be used

1http://w3.ualg.pt/~jlongras/R/Opto.html

Wireless-photonic-wireless interfaces

based on resonant tunnelling diode

optoelectronic oscillators

José Figueiredoa, C. N. Ironsideb, B. Romeiraa,

T. J. Slightb, L. Wangb and E. Wasigeb,

aCentro de Electrónica, Optoelectrónica e Telecomunicações,

Universidade do Algarve, Campus de Gambelas,

8005-139 Faro, Portugal

bDepartment of Electronics and Electrical Engineering,

University of Glasgow, Glasgow G12 8LT, United Kingdom

http://www.ist-iphobac.org/workshop/


Introduction

We report on novel optoelectronic voltage controlled oscillators (OVCOs)

based on the integration of Resonant Tunneling Diodes (RTDs) with Laser

Diodes (RTD-LDs) and Electro-Absorption Modulators (RTD-EAMs)

When combined they can operate as OVCOs with both optical- and electrical

inputs, and optical- and electrical outputs.

The phase synchronization capability can be used to translate digital

information from the wireless-to-optical domain and from the optical-to-

wireless domain.


Outline

Resonant Tunneling Diode (RTD) operation principle

RTD – electro-absorption modulator (RTD-EAM): operation as a nonlinear

photo-detector (RTD-PD)

Integration of a RTD with a laser diode (RTD-LD)

Optoelectronic voltage controlled oscillator (OVCO): operation as

wireless-photonic-wireless interfaces

Chaos-based optical communication using RTD-LD and RTD-PD circuits

Summary and conclusion


Resonant Tunneling Diode

Resonant Tunneling Diodes (RTDs) are nonlinear devices that use quantum

effects to produce negative differential resistance (NDR).

n InGaAs

n InGaAs

Emittern+ InGaAs

Substrate InP

AlAs

AlAsInGaAsDouble-Barrier

n+ InGaAs

Collector

DBQW-RTD Structure

The effect of bias on the conduction band profile

The Electron transmission probability

~10 nm10 nm

Conduction

band

profile

NDRR=1/G<0

Typical I-V characteristic

2 nmnm

2 nmnm

6 nmnm

Zero Bias (i) Off Resonance (iii)Resonance (ii)

E0 V=VvV=VpEF EF

EF

EC EC

EC

EF

EC

EF

EC

EC

EF

I

V


RTD – Electro-absorption modulator (RTD-EAM) Embedding a RTD within an optical waveguide core we obtained an electro-

absorption modulator (RTD-EAM), using Franz-Keldysh or Stark effects.

Wafer structure

Operation as photo-detector (RTD-PD) Optical

waveguide

Current voltage characteristic

+ + +

+

+

hv

n-InGaAlAswaveguide

core

n+ InAlAs

AlAsBarriers

Energy-band diagram

n+ InP

V=VV

V=VVLight outLight out

RF inRF in

Light inLight inLight inLight in

Light inLight inRF outRF out

Built-in amplification regions


Optoelectronic oscillator for photonic systems

Integrating a RTD-EAM with a laser diode it is possible to produce a voltage

controlled oscillator with both optical- and electrical-injection ports, both

optical- and electrical-output ports, and one voltage controlling port.

Light in

Light out

RF in

RF out

Dc bias adjustment

RTD-EAM + LDE

O

E

O

In addition, it is possible to

synchronize or control the

oscillator by both electrical and

optical references or signals.

A close approximation of an ideal oscillator for the photonic systems.


Integration of a RTD with a laser diode

The microwave-photonics interface corresponds to a laser diode (LD)

controlled by a RTD oscillator

RF output

Laser Diode

Au

Printed Circuit Board

Microstrip line

Shunt

Capacitorn

p

RTD Optical Signal

Dc bias + RF signal

Current-voltage (I-V) characteristics

NDRNDR


Optoelectronic voltage controlled oscillator

When dc biased in the NDR region it self-oscillates producing an modulated

optical output: electro-photonic self-sustained oscillations

RF output

d. c. bias

Laser Diode

Au


Microstrip line

Shunt

Capacitorn

pRTD fiber

Laser

Optical

output

RTD-LD

RF

output

L~1 nH

C~3 pF

R~6 Ω

Equivalent circuit


RTD-LD electrical injection locking

RTD-LD oscillations can lock to injected microwave signals.

1 MHz frequency

modulation

injected

power

-30 dBm

The phase synchronization of the RTD-LD can be used to translate phase shift

keyed (PSK) digital information from the electrical to the optical domain.

600 MHz injected RF signal 580 MHz injected RF signal


RTD-LD as a wireless-to-optical interface

Mobile

terminal

Bias Tee

Patch antenna

Optical Signal

RF

d. c.

bias

RF outputd. c. bias + RF

LD


Microstrip line

ShuntCapacitor

n

p

RTD Optical

fiber

RTD-LD (E/O Converter)

The RTD-LD responds to the wireless

radiation amplifying it

The laser diode delivers the microwave

detected signal as an optical subcarrier

The interface includes a RTD that amplifies the patch antenna detected

microwave signal and a LD that produces a corresponding optical output.


RTD-EAM/RTD-PD response to optical signals

RTD I-V characteristic and RF injection locking capture level for 1 mW @1550

nm optical signal modulated at 1 GHz (a).

Photo-detected RF power as function of wavelength with DC bias voltage as

parameter for 1.9 mW optical signal modulated at 1 GHz (b).

V=VV

V=VP V=VP

V=VV

When the RTD-PD is DC biased in the NRD region it self-oscillates.


RTD-PD optical injection locking

The RTD-PD follows the phase of the RF optical sub-carrier signal. This behavior

can be used in digital communication schemes including PSK digital modulation

as, for example, in RZ-DPSK.

The photo-generated current is amplified by the NDR, optical locking the

RTD oscillations.

Optical phase-locking

15 kHz frequency modulation

Optical injection locking


RTD-PD as an optical-to-wireless interface

The RTD-LD interface characterization setup includes patch antennas for

directional wireless emission-reception.

Patch antenna

Optical Signal

Bias

Tee

Mobile

terminal

RTD-PD VDC

Optical fiber

Optical

sub-carrier

Light in

RF out


Pico and femtocells for radio-over-fiber systems

Light in

Light out

RF out

RF in

Next generation of wireless access networks will have short range cells –

each office in a building with its own cell and base station.

Lots of cells so RTD-LD and RTD-PD offers cheap single chip solutions.


Chaotic signal generation with the RTD-LD

Chaotic operation with a broadband structure up to a few GHz can be

induced by injected electrical signals.

Electrical output Optical output


Chaotic signal generation with the RTD-PD Chaotic operation with a broadband structure up to a few GHz can be

induced by injected optical signals.

0 1 2 3 4 5-80

-70

-60

-50

-40

-30

-20

-10

Ph

oto

de

tecte

d R

F p

ow

er

(dB

m)

Frequency (GHz)0 1 2 3 4 5-80

-70

-60

-50

-40

-30

-20

-10

Pho

todete

cte

d R

F p

ow

er

(dB

m)

Frequency (GHz)

Free-running oscillations around 87 MHz

4 0 60 8 0 10 0 120 14 0-0 ,20

-0 ,15

-0 ,10

-0 ,05

0 ,00

0 ,05

0 ,10

0 ,15

0 ,20

0 ,25

Ph

oto

de

tecte

d a

mp

litu

de

(V

)

T im e (ns)

40 60 8 0 1 00 12 0 14 0-0 ,2 0

-0 ,1 5

-0 ,1 0

-0 ,0 5

0 ,0 0

0 ,0 5

0 ,1 0

0 ,1 5

0 ,2 0

0 ,2 5

Photo

dete

cte

d a

mplit

ude (

V)

T im e (ns)

Chaotic operation

fin=100 MHz, VAC=1.41 V VDC=1.752 V


RTD chaos-based optical communication link

An incoming RF signal can be encrypted at the physical level using a RTD-

LD and decrypted using a PD-RTD

Optical

fiber

Message(sound, video, data)

Original electrical signal

Message(sound, video, data)

Signal transmitted

PD-RTD

PD

tV

RTD-LD (chaos generator)

t

Electrical signal

V

Subtractionunit

coupler

(chaos generator)


Summary and Conclusion

Demonstration of RTD-LD hybrid integration using separated chips, although

monolithic integration of a RTD-LD has been previously demonstrated, that

can operate as optoelectronic voltage controlled oscillators.

Modulation of the phase of the radio frequency sub-carrier was

demonstrated in the laser output.

First demonstration of wireless to optical conversion using synchronization

of a nonlinear oscillator.

Demonstration of RTD-PD that can operate as a microwave oscillator

controlled by light-wave subcarriers.

The RTD-LD and RTD-PD applications include: single chip platform with

reduced size for low cost microwave/photonics devices.

Other potential applications are in chaos-based communications, radio-over-

fibre systems, clock recovery, etc.

This technology can be extend to higher frequencies (tens of GHz)

Documents

Wireless-photonic-wireless interfaces based on …w3.ualg.pt/~jlongras/opEuropeanworkshop09.pdfmodulation injected power -30 dBm The phase synchronization of the RTD-LD can be used