SPP waveguide sensors 1. Optical sensor - Properties - Surface plasmon resonance sensor - Long-range surface plasmon-polariton sensor 2. LR-SPP waveguide - SPP properties in a waveguide - Asymmetric double-electrode waveguides - Basic ADW sensor structure with -fluidic channel 3. Proposed waveguide sensors - Influence of temperature fluctuation - LR-SPP waveguide index sensor - LR-SPP waveguide bio sensor
Contents Optical sensors 1. properties 2. Surface plasmon resonance sensor 3. Long-range surface plasmon-polariton sensor 2
1. properties Properties 1. Immune to electromagnetic interference 2. Capable of performing remote sensing 3. Provide multiplexed detection within a single device Source Measurement Detector 3
1. properties Fluorescence-based detection Label-free detection 4
2. Surface plasmon resonance sensor -Properties 1. Label free sensor (Real-time detection) 2. High sensitivity (Large filed enhancement at the interface between dielectric and metal) Prism is too bulky!!!! Difficult to integrate First SPR bio-sensing was demonstrated by Liedberg (1983) Commercial SPR sensor : 1 10-6 RIU (Biacore TM ) Reference : Biosensors and Bioelectronics 23 (2007) 151-160 5
2. Surface plasmon resonance sensor Other SPR sensor approaches (various SPP excitation method) 1. Only penetrates into the surrounding medium for about 100 nm. Ref. : Biosensors and Bioelectronics 23 (2007) 151-160 2. How can sensitivity be increased? 3. Transmit both light signal and electrical signal? Metallic waveguide with Long-range surface plasmon mode 6
Contents LR-SPP waveguide 1. SPP properties in a metallic waveguide 2. Asymmetric double-electrode waveguides 3. Basic ADW sensor structure with -fluidic channel 7
1. SPP properties in a metallic waveguides Short-range surface plasmon mode Long-range surface plasmon mode 1. Highly enhanced electromagnetic field 2. High propagation loss. 1. Longer penetration depth into dielectric material 2. Low propagation loss. Therefore, LRSPP produce a narrower SPR features. Higher sensitivity!! 8
2. LRSPP waveguide sensors To use LRSPP mode and high Integration for a device. Solution : LRSPP metallic waveguide sensor!! Breakthrough : To excite a LRSPP mode, symmetry requirement is needed!! Dielectric Metal Dielectric The refractive index difference between two embedding materials should be lower than ~ 10-4. 9
3. asymmetric double-electrode waveguides To overcome the symmetry requirement Metal (Au) -fluidic channle Substrate Substrate Substrate Metal (Au) 10
3. asymmetric double-electrode waveguides D metal strip d3 w 2 SPP mode Y-axis d1 D core d3 cladding Substrate metal slab X-axis 1. High degree of freedom of structure. (easy to apply to various applications) 2. Adjusting of core thickness, the symmetry requirement can overcome. 3. LRSPP mode is confined around the core layer. 4. Double metal layers for detecting bio-molecules. 5. Easily tuning the core dielectric layer by sending a current or voltage to double-electrodes 11
3. asymmetric double-electrode waveguides Cutoff Thickness "D c "(nm) 10000 1000 100 10 Core 895 nm 1.45 1.0 1.1 1.2 1.3 1.4 1.5 Core reflactive index ( ε 1 ) r k 0 1.475 1.474 1.473 1.472 1.471 r k 0 1.470 0 200 400 600 800 1000 Core Thickness "D" (nm) (b) Propagation Loss (db/mm) 7.5 5.0 2.5 0.0 (a) (1) (2) (3) 0 200 400 600 800 1000 Core Thickness "D" (nm) (c) 12
3. asymmetric double-electrode waveguides - Fabrication process Si Si Si a. polymer ) 코팅 b. u coating c. polymer ) 코팅 Si d. PR patterning Si e. u coating Si f. PR lift-off Si g. polymer ) 코팅 13
3. asymmetric double-electrode waveguides D metal strip SPP mode metal slab d3 w 2 Y-axis d1 D core d3 cladding X-axis 14
3. asymmetric double-electrode waveguides metal strip S-band metal slab Y-branch :6.67 1.5mm 1.65mm 1mm :1.91 20 μm 20 μm 2mm 3mm 0.5mm <S-band> <Y-branch> Metal (Au) width :5 μm, Thickness:20nm Core thickness :680nm 15
3. asymmetric double-electrode waveguides 16
4. Basic ADW sensor structure with -fluidic channel Cladding Dielectric material Substrate Metal (Au) < Basic LR-SPP sensor structure > -fluidic channle Sensing Material Y Y Y Y Y Y Y Y Y Y Y Y Y Y Y Y Y Y Y Y Cladding Substrate Y Y Y Y Detection process ( protein ) Bio-molecule -Advantages of double LR-SPP bio-sensor structure 1. Reduced the size of the sensor structure comparing to the Kretschmann-reather configuration which use a prism. 2. Double LR-SPP structure can detect low index materials. ex) water, air, etc. 3. Easily excited the LR-SPP using end-fire coupling method with single mode fiber. 4. Double detecting metal layers. ( 1.5 times higher sensitivity then single metallic waveguide biosensor ) 5. Compensate the temperature fluctuation (self referencing). 17
4. Basic LRSPP sensor structure with -fluidic channel - Fabrication process Core layer coating 18
4. Basic LRSPP sensor structure with -fluidic channel y z x cladding y z core fluidic channel cladding gold slab silicon wafer cladding y cladding Si z cladding (b) cladding Si 19
4. Basic LRSPP sensor structure with -fluidic channel Observing the LRSPP mode image 1. Inserting 1.45 index matching oil in the channel. 2. After 10 min inserting the matching oil, inserting an acetone ( n : 1.36 ) in the channel. 3. The LRSPP mode is gradually disappears. 1.47 1.45 1.47 Substrate n = 1.45 Index matching oil n = 1.36 acetone 10 m Cutoff Thickness "D c "(nm) 10000 1000 100 10 895 895 nm nm 130 nm 1.36 1.45 1.45 1.0 1.1 1.2 1.3 1.4 1.5 Core reflactive index ( ε 1 ) (a) Core 20
Contents Proposed waveguide sensors 1. Influence of temperature fluctuation 2. LR-SPP waveguide index sensor 3. LR-SPP waveguide bio sensor 21
1. Influence of temperature fluctuation - To increase measurement accuracy Temperature fluctuations should be reduced!! ex ) Thermal optic coefficient of aqueous solution for the solvent of the bio-molecules : -1 10-4 RIU/ C ~ 10-5 ~ 10-6 RIU (Sensitivity of SPR sensors) -Using reference channel for compensating temperature changes Ref : Proc. Of SPIE Vol. 5728. 22
1. Influence of temperature fluctuation Ref : Applied Optics, Vol. 41, No. 29, PP. 6211 (2002) Ref : IEEE Photonics Tech., Vol. 19, No. 24, 2007. 23
1. Influence of temperature fluctuation - Other method to reduce temperature effects Ref : Measurement science and tech., Vol. 12, 2001. Ref : Sens. And Act. B., Vol. 134, pp. 854, 2008. 24
2. LR-SPP waveguide index sensor L R region : Detecting temperature changes L D region : Detecting refractive index changes of the bulk solutions. Claddings : n=1.47, thickness=15 m Bragg gratings : n=1.6, thickness=120 nm Core : n=1.46, thickness=700 nm period=528.8 nm Buffer layers : 300 nm wavelength : 1550 nm 25
2. LR-SPP waveguide index sensor - Fabrication process 1.47 polymer (15 m) Au coating ( 20nm ) Bragg grating (150nm /525.8nm) Buffer layer coating (250nm ) Core and Channel layer ( 500nm ) Buffer layer coating (250nm ) Au metal stripe (20nm, 5 m) 1.47 polymer (15 m) Removing the PR core layer 26
2. LR-SPP waveguide index sensor 0 OSA Tunable LD LRSPP sensor ASE broad source Polarizer 27
2. LR-SPP waveguide index sensor Transmittance (db) -30-40 -50-60 R TMM experiment D Transmittance (db) -30-40 -50-60 1.470 1.474 1.480 1.484 1554 1556 1558 1560 1562 Wavelength (nm) 1554 1556 1558 1560 1562 Wavelength (nm) Measurement various bulk index solutions in the same sample. To detect other refractive index of the bulk solution, the inserted bulk solution was removed by methanol. Measurement order : 1.47 1.474 1.48 1.484 ( 130 nm/riu ~10-6 RIU with 1 pm OSA resolution) 28
2. LR-SPP waveguide index sensor Transmittance (db) D R (nm) -30-40 -50-60 1554 1556 1558 1560 1562 4 3 2 1 0-1 -2 (c) Wavelength (nm) 1.470 1.475 1.480 1.485 Sample index 1.470 1.474 1.480 1.484 TMM experiment 1.5 1.2 0.9 0.6 0.3 FWHM (nm) - 130 nm/riu ~10-6 RIU - D R = ± 540 pm ± 27 pm/k - R = ± 4.12 nm (with 1 pm OSA resolution and ± 20 K variation) - Thermal optic coefficient Polymer : -1.7 10-4 RIU/K Sample oil : -1.0 10-5 RIU/K D R (nm) 2.4 1560 2.1 1.8 1.5 1.2 1557 1554 0.9 1551 (d) -20-10 0 10 20 Temperature variation( K) 29 R (nm)
3. LR-SPP waveguide bio sensor y a. Before inserting bio-material with solution x z Cladding D c D g L w Substrate L L w Cladding y Bragg grating unit cell g Substrate z D c : core thickness ( 500 nm ) D g : grating depth t : bio-molecule thickness Solution Bio-molecule L g : grating length L g b. After inserting bio-material with solution Cladding D c ( n n ) bragg eff 1 eff 2 Cladding Substrate L g y z D g D g area D c area 575 nm 30
3. LR-SPP waveguide bio sensor - Two important properties of a bio-sensor 1. Sensitivity : The ratio of the change in sensor output to the change in the measurand. 2. Resolution : The smallest change in measurand which produces a detectable change in the sensor output. B Sensitivity, S, t : bio-molcule layer thickness t 10% FWHM 10% FWHM Resolution, tmin ( nm) t B S t Sensitivity, FWHM D g 31
3. LR-SPP waveguide bio sensor Sensitivity, S 0.0530 0.0525 0.0520 0.0515 0 20 40 60 80 100 Grating depth, Dg (nm) Resolution, t min (nm) 1.6 1.2 0.8 0.4 20nm 40nm 60nm 80nm 0.0 0 2 4 6 8 10 Grating length, Lg (mm) 1 nm Cladding 450 nm n cladding : 1.35, n core : 1.33 Bio-molecule : n protein (1.5), n solution : 1.33 Cladding Substrate L g y z D g Over 2 mm grating length (L g ), possible to detect under 1 nm thickness variation of bio-molecule layer (t) 32
3. LR-SPP waveguide bio sensor < Experiment scheme of LR-SPP waveguide bio-sensor> Input signal Circulator Propagation efficiency ( w ) Maximum reflection ( R max ) L w Substrate L g L w Output signal L w Coupling efficiency ( c ) L g L w Propagation efficiency ( g ) 2 2 2 Total Loss, T loss(db) = 10 log( c w g Rmax ) Propagation efficiency, η = P /P = 10 out in Propagation loss path length ( ) 10 where Propagation loss (db/mm) = 10 log (P /P ) out in Path length (mm) Coupling efficiency ( c ) : 80 % ( Overlap integral method ) Propagation efficiency ( w ) : 42 % ( at 450 nm core thickness with 1mm length ) 33
3. LR-SPP waveguide bio sensor Cladding Cladding L g y D g 450 nm constant Substrate z 2 2 2 Total Loss, T loss(db) = 10 log( c w g Rmax ) g 0.5 0.4 0.3 0.2 0.1 20 nm 40 nm 60 nm 80 nm 0.0 0 2 4 6 8 10 Grating length, Lg (mm) Maximum reflection, R max 1.0 0.8 0.6 0.4 0.2 0.0 0 2 4 6 8 10 Grating length, Lg (mm) 34
3. LR-SPP waveguide bio sensor Detectable range Total Loss "T loss " (db) 50 45 40 35 30 25 20 20nm 40nm 60nm 80nm 15 0 2 4 6 8 10 Grating length, Lg (mm) Detectable limit line Resolution, t min (nm) 1.6 1.2 0.8 0.4 20nm 40nm 60nm 80nm 1 nm 0.0 0 2 4 6 8 10 Grating length, Lg (mm) - Possible detecting grating length (L g ) is under 5.5 mm. - 1 nm thickness variation of the bio-molecule layer can be detected over 2 mm grating length (L g ). - Calculated minimum thickness variation of the bio-molecule layer is 0.36 nm at 40 nm grating depth.. 35
3. LR-SPP waveguide bio sensor y z x Cladding 450 nm -fluidic channel Bragg grating Cladding Substrate L g y z D g gold strip Cladding index : 1.35 Core index : 1.33 Grating period : 528 nm Wavelength : 1550 nm Index resolution ( x10 RIU) 3 2 1 0 20 nm 40 nm 60 nm 80 nm 2 3 4 5 6 7 grating length, L g (mm) Sample index : 1.325 ~ 1.340 The sensitivity increases as increasing the Bragg grating length or thickness ( ~ 10-6 RIU ) 36
3. LR-SPP waveguide bio sensor 37
6. Conclusion Proposing a novel model of LRSPP sensor on asymmetric double metallic structure. - Easy to excite the LRSPP mode using end-fire coupling method. - Still having the advantages of double metallic waveguide. - Easy to control the sensor properties adjusting the core thickness or grating depth. - Compensating temperature fluctuation (self-referencing) due to thermal-optic polymers. -~ 10-6 RIU (sensitivity), ± 27 pm/k (temperature inaccuracy) Possible to detect the under 1 nm thickness variation of a target bio-molecule layer. - Possible Bragg grating length under 30dB: 2 mm ~ 5.5 mm - Maximum detectable resolution is 0.36 nm 38