4 integrated optics examples

Photonic integrated circuits

Examples

OUTLINE

Arrayed waveguide gratings Microring resonators Biophotonic senzors Optical interconnects

ARRAYED WAVEGUIDE GRATINGS

BASIC PRINCIPLES OF AWGs

(1) input WG or fibre(2) free space or slab waveguide(3) bundle of optical fibers or channel waveguides ; the fibers/waveguides have different length and thus apply a different phase shift. (4) free space or slab waveguide where the input rays interfere at the entries of the output waveguides (5) in such a way that each output chanel receives only light of a certain wavelength. The orange lines only illustrate the light path. The light path from (1) to (5) is a demultiplexer, from (5) to (1) a multiplexer.


Different wavelengths of light will exhibit different amounts of phase change and, due to the increments in length of each waveguide, the phases will change along the AW output plane, causing the focal point to move along the focal plane (e) at the end of the FPR.

An output waveguide is positioned on the output plane to pick up each input frequency (channel).

MATERIALS AND PROCESSES FOR AWGs

SILICA-BASED AWGs

PACKAGING CHALLENGES FOR AWGs

APPLICATIONS OF AWGs

AWG-BASED WDM DEMULTIPLEXER

Compact AWGLow losses large bending radii large sizeSolution to minimize the area: integrating reflecting mirrors into the waveguides to make devices more compactreplace rib waveguides with photonic wire waveguides

Photonic wires are basically index-guiding optical waveguides with a submicron core and a high index contrast (>2)Photonic wires can be bent with extremely small

curvatures of less than a few micrometers of bending radius (due to the high confinement in the core).

AWG with 16 200 GHz channels. Details show broadened photonic wires in straight sections and the two-step star coupler with shallow etchedwaveguides.BOGAERTS et al.:IEEE JOURNAL OF SELECTED TOPICS IN QUANTUM ELECTRONICS, 12, 2006, p1394

Compact AWG (2)

TMI waveguide array.

JIA et al. IEEE JOURNAL OF SELECTED TOPICS IN QUANTUM ELECTRONICS, 2006, p1329.

With turning-mirror-integrated (TMI) waveguide array

Structure of SOI Waveguide

-ring resonators The -ring resonator consists of a waveguide in

closed loop and one or two bus waveguides. The resonances are produced by the requisite

for phase matching at the coupler- -ring is a traveling wave device

The coupling between the bus and the ring is evanescent. Control parameter,

Coupling schemes lateral or vertical The -ring resonator spectral characteristics

defined by and R- FSR (free spectral range), Q

eff

owavelength Rn

FSR

2

2

=eff

frequency RncFSR =

2

22

o

effRnQ

R

The -ring concept

-ring resonatorscharacteristics

No need for optical mirrors or gratings for optical feedback Ideal for integration with other passive or active components Route to photonics

VLSI1

Perspective schematic of a vertically coupled MR resonator adddrop filter. The ring is integrated above a pair of crossing waveguides

Microscope image of a fabricated cross-grid node incorporating a 10-m radius compound glass ring.

1. B. E. Little et al. IEEE Photon. Technol. Lett., vol. 12, pp. 323325, Mar. 2000.

-ring resonatorsApplications

The microring resonator is a multi-functional platform for various all-optical signal processing operations:

Dispersion Compensators Lasers Filters (based on the sensitivity of

the transfer function on the resonant wavelength)

Logic gates that take advantage of the resonant induced nonlinearities enhancement

Wavelength converters (FWM) Sensors (sensitivity of the ring

characteristics on refractive index of the surrounding environment)

Filter

Laser

Dispersion Compensator

Optical Gates

-ring resonatorsVertical and Lateral Coupling 1

The choice of coupling scheme between the MR and the bus waveguide may offset the structural dependent performance

Lateral coupling: the bus and MR are on the same plane

Vertical coupling: the bus and MR waveguides are on vertical planes.

Lateral displacement

Vertical displacement

Rd

Rd

Lateral displacement

Top View

Side view

VERTICAL COUPLING

LATERAL COUPLING

-ring resonatorsVertical and Lateral Coupling 2

Yes (either regrowth or wafer bonding

No Fabrication Complexity

Yes NoCritical alignment

Lateral and vertical positioning of bus

waveguide

Gap between the bus and ring waveguides

Control of coupling Vertical Coupling Lateral CouplingCriterion

The vertical coupling adds up to device design flexibility:The bus and ring waveguides can be tailored independently

/ The vertical coupling scheme is very demanding in terms of fabrication technology: planarized regrowth or wafer bonding

-ring resonatorsLateral Coupling

Polymers: SU 8, BCB

-ring resonatorsVertical coupling

Passive waveguide

Active ringWafer bonding

-ring resonatorsVertical Coupling process 1

1.Deeply etched alignment marksby CH4/H2 RIE

InP-substrate

2.Fabrication of the bus-waveguides by CH4/H2RIE

InP-substrate Courtesy of M. Hamacher HHI


3. after passivation with SiNx/SiO2: spin-on coating of bond material (MPI/EVG) levelling & polishing of the surface

InP-substrateInP-substrate

GaAs-substrate

4.Wafer bond process (MPI/EVG)

5.Removal of the InP-substrateby WCET and RIE

GaAs-substrate

InP-substrate

GaAs-substrate

6.Etching of the laser stripe byRIE & formation of p- and n-contacts by evaporation/sputtering


-ring resonatorsVertical Coupling - on Si substraste

KOKUBUN et al.: FABRICATION TECHNOLOGIES FOR VERTICALLY COUPLED MICRORING RESONATORIEEE JOURNAL OF SELECTED TOPICS IN QUANTUM ELECTRONICS, VOL. 11, NO. 1, JANUARY/FEBRUARY 2005, p.4

OUTLINE

Arrayed waveguide gratings Microring resonators Biophotonic senzors Optical interconnects

Optical Biosenzors

Definition: opto/electronic detection devices that use biological molecules for detection and quantificationof targets of interest.

The heart of the biosensor is the biological recognition element,which is chosen for its specificity and affinity, and can be an enzyme, receptor, antibody, chelator, nucleic acid, or antibiotic.

For use in any optical sensor, the end result must be a change in an optical property induced by interaction of the recognition element with the target; these changes may be due to the formation of a

fluorescent or luminescent product, association of molecules to fluoresce or to quench fluorescence,

modification of refractive index or absorption spectrum.

Optical biosenzors

Link changes in light intensity to changes in mass or concentration ideal biosensors because they give rapid signals with high specificity for

the organism of interest.

Advantages Photons - non-invasive, safe and multi-dimension (intensity,

wavelength, phase, polarization), high spatial resolution and noise-free information

Optical frequency coincide with a wide range of physical properties of bio-related materials in nature

low power usage ease of achieving 2-D array testing lightness and flexibility. cheaper cost

ExamplesOptical fibers, surface plasmonresonance,absorbanceluminescence

Biosensor DeviceTypical sensitivity: ~ng/ml or ppt - ppb

The main parts of a typical biosensor

Biophotonic sensor platforms

Biosensors

Biomolecules

Evanescent Wave sensors

Based on Interference Mach-Zehnder Interferometer

Based on Resonators Fabry-Perot resonator Ring resonator

Mode Coupling Devices Grating Coupling based sensors Surface Plasmon Resonance

Mach Zender Interferometer

Fabry-Perot Resonators

Ring Resonators

Grating Couplers

Surface Plasmon Resonance

Evanescent wave senzors

Segmented WG SensorJOURNAL OF LIGHTWAVE TECHNOLOGY, VOL. 23, NO. 1, JANUARY 2005Joris van Lith et al. , University of Twente, The Netherlands.

This sensor combines a simple technology with a resolutionin the refractive index of the chemo-optical transduction layer better than 5x10-7.

Mach-Zender Interferometer Based sensorsNanotechnology 14 (2003) 907912, Prieto et al. IMM-CNM, CSIC Spain.

Lower detection limit nno,min=7x10-6 (N=4x10-7). Smallest phase sift 0.03x2.The value of the detection limit corresponds to a surface sensitivity of around 2x10-4nm-1close to the maximum surface sensitivity reported up to that time.

MZI measures the changes of the refractive index due to the attached molecules

MZI Based sensors (2)

P. Hua et al. / Sensors and Actuators B 87 (2002) 250257ORC, Southampton, U.K

S. Balslev, B. Bilenberg, O. Geschke, A. M. Jorgensen, A. Kristensen,J. P. Kutter, K. B. Mogensen, and D. Snakenborg

Mikroelektronik Centret (MIC), Technical University of Denmark (DTU)rsteds Plads, Bldg. 345east, DK-2800 Kgs. Lyngby

Integrated biosenzor (laser+WG+PD+ microfluidics)


(v2)

Devide including a light-emitting silicon avalanchediode, a single-mode planar waveguide, a Si photodetector, and a microfluidic channel made from PDMS,Thrush, E., Levi, O., Ha,W.,Wang, K., Smith, S., Harris, J., J. Chromatogr. A 2003, 1013, 103110.

Biosensors based on microring resonators

Homogeneous sensing analytes exist in the surrounding aqueous medium that serves as the top cladding.- no specifity

Surface sensinganalyte molecules adsorb on a sensor surface, which can be modeled as an ultrathin film

These sensors rely on accurate measurement of the effective refractive index change due to the presence of biomolecules on the surface of sensing areas (ring surface) or the presence of a solution surrounding the devices

a porous layer to allow the solution to penetrate

sensing layer is deposited on the ring (with immobilized molecules used to identify the targets

When the target molecules are attached , or the concentration ofthe biomolecules in the surrounding solution is changed the optical properties (refractive index) is modified


Configurations


The presence of biological materials near the surface of the ring modifies the optical properties and thus the couplig coefficients are modified the resonance will occur at another wavelengths.

By measuring Itrans/Iin function on wavelength, the attachment of the target molecules can be identified.

for detecting very small concentration of analytes

Measuring Idrop/Iin at a fixed wavelength-

Biosensors based on microring resonatorsSensing Scheme

Biosensors based on microring resonatorsRequirements

The sensitivity of a microring sensor is determined by the Q factor (Q factor is defined as the ratio of stored energy in the resonator cavity to the energy loss per cycle) of the microresonator Small change in the effective index (neff ) can be detected by measuring the resonance shift c : neff/neff = c/c 1/Q.c is the resonant wavelength, neff the effective index of the guided mode,

For high Q factors, all the cavity losses need to be minimized (bending loss, leakage loss to the substrate, loss induced by surface-roughness scattering).

For sensing purposes, microring resonators are desired to operate at the critical coupling condition, at which the energy coupled into the resonator is balanced by the energy loss in the resonator.It is desirable to have single-mode propagation in the microringwaveguide

to achieve a wider free spectral range (FSR), to eliminate the drawbacks in a multimode waveguide where each mode can create its own periodic resonance and the resonances from different modes may be too close to distinguish.


A. Ksendzov, M.L. Homer and A.M. Manfreda

ELECTRONICS LETTERS 8th January 2004 Vol. 40 No. 1

Polymer Microring ResonatorsChung-Yen Chao, Wayne Fung, and L. Jay Guo,IEEE JOURNAL OF SELECTED TOPICS IN QUANTUM ELECTRONICS, 12, (2006), p.134


YALC IN et al. (14 authors !): OPTICAL SENSING OF BIOMOLECULES USING MICRORING RESONATORS

IEEE JOURNAL OF SELECTED TOPICS IN QUANTUM ELECTRONICS, VOL. 12, NO. 1, JANUARY/FEBRUARY 2006, p. 148-155

Lateral and vertical offsets allow control over the coupling coefficient.

Receptor molecules are attached to the microresonator surface, and binding occurs during flow of ligand molecules over the surface.


chemical vapor deposition (CVD) of a glass-based materialtermed Hydex,1 which has an adjustable refractive indexcontrast of up to 25%.


Advantages

label-free detection, compatibility with microfluidic handling,capability of providing high specificity using surface chemical modifications reducing the device size by orders of magnitude, greatly reduces the amount of analytes needed for detection.reduction in size does not compromise the device sensitivity - the large photon lifetime within the resonator at the resonance provides an equivalently long interaction length to achieve a detectable phase shift.


Drawbacks Complicate detection system how to realize a n x m array ? photodetectors could be

integrated ???


Measurement set-up

SPR based sensors

SPR biosensor- concept

Simulation : Intensity Measurement

Simulation: Wavelength Interrogation

Measurement set-up

Sensitivity

Improving Sensitivity

Sensitivity

Interferometer Sensitivity

Ringresonator Sensitivity

Surface Plasmon Interferometer

Comparison

Sensitivity Comparison

Sensitivity

Optical interconnects

Interconnects = transmission of information


Optical interconnects is a success for telecommunication

long-distance (several km)

shorter distance (tens to hundreds meters): data-communications (LAN) system-level interconnects

(parallel optical datalinks)

And shorter distance is electrical ?


Shorter-distance interconnects benefit from optical technologies !

A good reason for optical interconnects:optics is better than electrical interconnects in terms of

power dissipation is distance independent data density: Gbps per mm2 is larger transmission distance: loss in fibre is negligible and data rate

independent

Interfacing optics to CMOS

Optical interconnect needs ED: digital CMOS circuitry EA: analog driver + receiver circuitry OE: light sources (or modulators) and detectors O: passive optical pathway (fiber, waveguides in board, free space)Options: EA+OE+interface to O in one package in some applications: ED+EA+OE+O in one package

On chip interconnects

On-wafer interconnects

On-wafer interconnectsMnolithic integration

On-wafer interconnectsHeterogeneus integration

On-wafer interconnectsParallel wafer-to-wafer bonding

On-wafer interconnectsAbove IC approach

CMOS circuit

Laser source Photo-detector

Metallicinterconnectlevels

Wave guide

}Laser source

{Optical layer

III-V structure grown on InPsubstrate by SSMBE

InP substrateLaser structure

InGaAs(etch stop)

10 nm SiO2

III-V dies

PatternedSOI200 mmwafer

Si waveguides

InP substrate removal InGaAs etch stop layer removal III-V device process

Die bondingOn SOI waferPrecise alignment

Integration of optical interconnects on board level

Approaches Fiber based Waveguide based

glass sheet polymers

http://www.circuitree.comPrinted Optical Waveguides: The Next Interconnect (H.Holden)

Integration of optical interconnects on board level ORMOCERs

ORganic Modified CERamics Inorganic-Organic Hybrid Polymers Applications

microoptical elements (lenses, lens arrays, gratings, prisms) vertical integration: stacked optical waveguides (wafer scale) board level optical interconnects

General properties Compatibility with PCB manufacturing

lamination 180C 200 Pascals assembly (solder reflow) up to 250C

Good planarisation properties RMS roughness 2 - 4 nm Long-term stability under variable environmental conditions

(humidity, temperature) Low shrinkage

optical interconnects on board levelORMOCERs

Optical properties (www.microresist.de) Refractive index @ 830 nm (adjustable)

CORE 1.5475 CLADDING 1.5306

Attenuation

Waveguides Photolithography Laser ablation

ORMOCERs Application scheme

applicationspin-coating

softbake80-120 C,

Laser ablation Set-up

KrF Excimer Laser(can be tilted)248 nm

Frequency tripledNd-YAG Laser355 nm

CO2 Laser

9.6 m

optical interconnects on board levelWaveguides

1. UV-Defined Cross section: 20 x 20 m2 waveguides (250 m pitch)

2. Laser-ablated Compatible with standard electrical PCB manufacturing (microvias) Adapt the pattern as a function of distortion in the substrate (FR4) Rapid prototyping Define microstructures and microoptics on a top surface of a heterogeneous

optoelectronic module in a very late phase of the assembly process Entire optical interconnection using one technology

OPTICAL LAYERS

COPPER

FR4

optical interconnects on board levelWaveguidesLaser-ablated

Laser beam moves over surface Technology sequence

bottom cladding layer core layer laser ablation microstructuring upper cladding layer

Experimental results KrF Excimer laser (248 nm)

50 x 50 m2

trapezoidal shape low ablation speed roughness to high

1st ablation2nd ablation

optical interconnects on board levelWaveguides

Frequency tripled Nd-YAG laser (355 nm) 50 x 50 m2

clean surfaces ablation speed: 1 mm/s

photo-dissociation

photo-thermal ablation

optical interconnects on board levelDeflecting optics 45 micromirrors

micro machining techniques (90 V-shaped diamond blade) excellent cut surface difficult to cut individual waveguides on the same substrate (physical size of the

machining tool)

remove waveguide film from substrate

cutting from back-side

diamond blade

claddingcorecladding

substrate

optical interconnects on board levelDeflecting optics

45 micromirrors reactive ion etching RIE (45 oblique etching)

limited by directional freedom different process steps

temperature controlled RIE (90 RIE + heat treatment) not limited by directional freedom material dependent

laser ablation set-up: excimer laser beam can be tilted

Total Internal Reflection (TIR)negative facet

coated mirror (Al, Au)positive facet

RIE

Al maskcladdingcorecladding

substrate

TIR condition crucialglue (mounting lens plate)humidity

optical interconnects on board levelDeflecting optics

Total Internal Reflection Smooth surface Tapering compensated Flatness of the mirror at core layer

optical interconnects on board levelCoupling structure

Example: MT-compatible coupling Microlenses and 700 m holes

ablated in a polycarbonate (PC) plate(Kris Naessens, Ph.D. thesis Ghent University)

Alignment: ribbon - lenses: 700 m pins match holes in PC plate

Alignment: micromirror - lenses: flip chip set-up (alignment marks)

Lenses ablated in upper-cladding layer Visual alignment under ablation set-up

with respect to 45 micromirror

Conclusions Integration of optical interconnects on board level

polymer waveguides Compatibility with the manufacturing and assembly

processes of the conventional electrical board technology ORMOCERs Laser ablation

Entire optical interconnection using one technology Waveguides Micromirrors Microlenses Alignment features

SEM pictures show very smooth surfaces

Optical layers

PPC Electronic OPTOBOARD Technology

V erticalC avityS urfaceE mittingL aser

VCSEL

VCSEL/Diode

VCSEL/Diode

LayersOpto-electronicalcomponents

electricaldielectricaloptical

Connector

Optoboard Technology Keyelements

1. Transparent Medium Thinglass

2. Multimode Waveguide Technology

3. Optical Connector

4. Parallel Optical Module with VCSEL and Pin Diode Arrays

5. In- Out-Coupler

Daughter boardswith fan-outpatchcords

Backplane

12 MM single-channeloptical connectors

Waveguide

In-Coupler Out-Coupler

Etched Glass Multimode Waveguide (250m Pitch)