Microwave Photonics combines two world March 6. 2015 Myungjin Shin - - PowerPoint PPT Presentation

Microwave Photonics combines two world

Myungjin Shin

March 6. 2015 High-Speed Circuits & Systems Lab

Department of Electrical and Electronic Engineering Yonsei University

Contents

• Introduction
• Devices and material
• Radio-over-system
• Optical beam forming
• Analog-to-digital converters
• Arbitrary waveform generation

• Microwave photonics(MWP): Study of photonic devices operating at

microwave frequencies and their application to microwave & optical system

• Simple microwave photonic link
• Advantage of microwave photonic link
• Cost, weight, loss, high data-transfer capacity

Introduction

Introduction

• MWP & optical communication runs in parallel
• 3 fundamental historical development in MWP
• Low-loss silica multimode & single-mode optical fibers
• Fast depletion p-i-n
• Avalanche detectors

 Useful microwave bandwidth response

Device & Material

• Modulator
• Modulation bandwidth
• Semiconductor laser
• Lithium niobate interferometric modulator
• Semiconductor material modulator
• Organic polymer
• Electro-absorption modulators(EAMs)
• Photodetector
• Surface illuminated & Vertically illuminated
• Edge illuminated
• UTC-PD

Device

• Modulation bandwidth
• Photon lifetime, differential gain, carrier recombination time,
• ptical output power
• Semiconductor laser
• Incorporation of quantum well and addition of strain

1.55um InGaAsP quantum-well

• Enhance frequency response resonantly
• External cavity laser
• Monolithic multisection laser
• Optical injection locking
• 1.55-um InGaAsP distributed-feedback(DFB) laser injection-

locked to external cavity diode laser

• ptically injection locked 1.55-um vertical cavity surface

emitting laser(VCSEL)

Material

• Lithium niobate interferometric modulator
• 3-dB electrical bandwidth 30 ~ 70GHz with drive voltage 3.5V~5.1V
• Semiconductor material modulator
• Fairly high bandwidth
• Low bulk electro-optic coefficient of semiconductor materials & poor
• verlap of applied electric field & optical mode high driver voltage
• Fiber-to fiber coupling loss higher(10dB) than Lithium niobate(<4dB)
• Organic polymer
• Attractive features for integrated optical application
• Bandwidth, drive voltage similar to semiconductor material

modulator

• Poor power handling capacity & long term bias stability

Material

• Electro-absorption modulators(EAMs)
• 3-5 compound semiconductors
• Bulk semiconductor materials incorporating the Franz-keldysh

effect & quantum-well structure

• Ability to directly integrated with semiconductor lasers
• Large optical loss
• Free-carrier absorption & band to band absorption

 Restrict size

• Poor optical power-handling capabilities & very sensitive

wavelength and temperature change

Device

• Photodetector(in MWP)
• High responsivities, bandwidths and optical power-handling

capability are required

• Surface illuminated & Vertically illuminated
• Trade-off bandwidth & device efficiency
• Edge-illuminated waveguide
• Large bandwidth & efficiency
• Space-charge effect electron velocity & electric field↓  limit

input power(saturation)

• UTC-PD: Only electrons travelling at a velocity much higher

than the saturation velocity contribute to the space charge effect and high output photocurrents can be achieved

• Radio-over-fiber: technology that light is modulated by radio signal and

transmitted over an optical fiber

• Hybrid fiber-radio(HFR): Integration of fiber-optic and wireless networks

form

• Benefit of RoF: flexible approach for remotely interfacing to multiple

antennas, with the ability to reduce system complexity by using a centralized architecture that incorporates a simplified antenna module located closer to the customer

• Challenge of HFR: distribution of the radio signal, while reducing the

complexity of the hardware located at the remote antenna site

Radio-Over-Fiber System

• Uses of HFR technology: cellular networks, indoor distributed antenna

systems and wireless local area networks(WLANs)

Example of ROF

Type of RoF

• Several possible approaches to transporting radio signals over optical

fiber

• RF-over-fiber, Intermediate-frequency-over-fiber, baseband-over-fiber

Type of RoF

• RF-over-fiber: Radio signal transport directly over the fiber at the

wireless transmission frequency, without the need for any subsequent frequency

• Intermediate-frequency-over-fiber & baseband-over-fiber
• make use of mature and reliable RF and digital hardware for signal

processing at the central office and remote antenna site as well as low-cost optoelectronic interference

• As wireless network frequency increases the need for frequency

conversion complicate the antenna module architecture design

Future RoF

• Millimetre-wave opto-electronic mixer for frequency conversion to or from

an intermediate frequency

• Using wavelength division multiplexing(WDM) in HFR systems as a

means of increasing network capacity

• Simplifying the antenna-module architecture
• Recently single eletro-absorption transceiver in 60-GHz HFR system
• Transmission of ultrawideband(UWB) signals in HFR system is being

investigated owing to the emergence of new wireless personal area network(WPAN) standards

Optical Beam Forming

• Phase array radar system: controlling the relative phase of an RF signal

between successive radiating elements of an antenna array, beam can be created that will radiate in a specific direction

• Advantage of optical phased array antenna: size, weight, bandwidth,

propagation loss, immunity to electromagnetic interference

• Beam-forming network required phase shifts at the antenna input
• Main issue for phase array radar: distribution of RF signals, phase

shifter control, true time-delay(TTD) beam forming &processing of RF signals

Example of optical beam forming

• True time-delay(TTD) networks incorporated high-dispersion optical

fibers, where the dispersion property of the fiber-optic link used to create variable delays for variable source wavelengths

• Above figure show the single wavelength tunable laser used in

conjunction with dispersive fiber to create fiber-optic prism

Future beam forming

• Switching of the effective optical path length in optically controlled

phased-array systems incorporating TTD

• By replacing microwave phase shifter into spatial light modulator(SLM)
• SLM: object that imposes some form of spatially varying modulation
• WDM techniques to simplify the optical beam-forming architecture is

promising

Analog-to-digital Converter

• In certain analog application, digital signal processing provides superior

performance and ADC is a main bottleneck

• CMOS digitizer are limited in speed with several factor
• Jitter in sampling clock, settling time, sample-and-hold circuit,

speed of comparator  Can be overcome using parallelism to implement time-interleaved ADC architectures but still limited

• Photonic time-stretch(PTS) technique is one of the promising method

by slowing down the electrical signal

• Have to solve calibration & channel matching, impact of noise from
• ptical source, distortion in optical fiber

Photonic time strech

• Process of Photonic time stretch
• Broadband transform limited pulse linearly chirped optical pulse(L1)

input RF signal envelope of the pulse is stretched in a second fiber(L2)

Developed ADC

• Dispersion penalty limits the system performance of ADC can be
• vercome by single-side band(SSB)
• Residual phase distortion that must be corrected using an

electronic equalizer

• SSB relies on the use of microwave hybrid to provide quadrature
• utputs and because of frequency limitation of hybrid structure SSB

has bandwidth limitation

• Exploitation of the phase diversity that exists between the two outputs
• f a dual output Mach-Zehnder modulator can be another method

Arbitrary Waveform Generation

• Arbitrary waveform generation is very useful in variety of application
• Pulsed radar, UWB, optical & electronic test, measurement
• Current electromagnetic AWG is band-limited to below 2GHz

 MWP signal processing technique can overcome

• Generating arbitrary waveform
• Fixed and programmable shaping of the spectrum of a

supercontinuum followed by a wavelength-to-time mapping in a dispersive fiber link

• Combination of chromatic dispersion & nonlinear effects in optical

fiber

Block diagram

• Supercontinuum generate broadband optical pulse bandpass-filter

spectrally dispersed by a diffraction grating different spectral components impinge different pixel of spatial light modulator(SLM) Spectrally generate waveform one-to-one mapping between time & wavelength which convert spectral modulation into time domain amplitude modulation

• Supercontinuum spectral shaping source with wavelength to time mapping

Future Task & Challange

• Challenge: Improving their RF spectral region of operation, conversion

efficiency and dynamic range with low cost

• Possible application: Optical packet switched networks & optical

probing, terahertz-wave generation & processing for non invasive high resolution sensing & MWP-based quantum key distribution

Thanks you