Microwave Photonics combines two world

Myungjin Shin

March 6. 2015

High-Speed Circuits & Systems LabDepartment 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, optical 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- optically 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

overlap 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

optical 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

overcome 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

outputs and because of frequency limitation of hybrid structure SSB has bandwidth limitation

- Exploitation of the phase diversity that exists between the two outputs of 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-filterspectrally 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