Monolithic Microphotonic Optical Isolator Lei Bi, Juejun Hu, Dong Hun Kim, Peng Jiang, Gerald F Dionne, Caroline A Ross, L.C. Kimerling Dept. of Materials Science and Engineering Massachusetts Institute of Technology Air CeYIG YIG Si SiO 2
Nonreciprocal Photonic Devices l Optical Isolators l A one way valve for light Laser Modulator Detector Isolator l Optical Circulators l A traffic circle for light Port 4 Isolators Circulators Port 1 Port 3 Port 2 Circulator Port 1 Port 2 Port 3 Port 4 Port 1
l Isolator Device Structures Optical Isolators Using Faraday effect Non-Reciprocal Mode Conversion (NRMC) Faraday Effect 2 Polarizers, 1 MO crystal l Integrated Optical Isolators Using Voigt/Cotton-Mouton effect Non-Reciprocal Phase Shift (NRPS) SOI Mach-Zehnder structure (TM isolation ratio 21 db, insertion loss ~8dB, Shoji et al. Appl. Phys. Lett., 92, 071117 (2008) Non Reciprocal Loss (NRL) Fe one side of InP optical amplifier. (TE isol. ratio 9.9 db/mm, insertion loss 7dB/mm, active. Shimizu et al, J. Lightw Technol., 24, 38 (2006)
Iron Garnets l Iron garnets: A 3 Fe 5 O 12 A = Y, substitute Ce or Bi to enhance magnetoptical properties FOM = Θ α Q: Faraday rotation per length a: Optical absorption per length Room temperature ferrimagnet with excellent FoM in single crystals. (340 deg/db, CeYIG, Shintaku, APL 71, 1640 (1997)) Cubic lattice with low saturation magnetization field How to accomplish integration on silicon? h"p://www.angelfire.com/extreme/geochem/
Polycrystalline Y 3 Fe 5 O 12 on Si " Phase pure polycrystalline YIG " Low surface roughness, 0.36 nm " M s ~130 emu/ cm 3, ~ 95% of YIG " In-plane easy axis, H s ~ 100 Oe " FR ~ 100 deg/ cm, lower than single crystal YIG Bi et al., Proc. SPIE vol 7604 760406 (2010)
Polycrystalline Bi:YIG and Ce:YIG on Si/YIG " Phase pure polycrystalline Bi:YIG and Ce:YIG on 20 nm YIG buffered SiO 2 (3 mm)/si Bi 1.8 Y 1.2 Fe 5 O 12 Ce 1 Y 2 Fe 5 O 12 Bi 1.8 Y 1.2 Fe 5 O 12 Ce 1 Y 2 Fe 5 O 12 " In-plane EA Bi1.8YIG: H s ~ 500 Oe CeYIG: H s ~ 200 Oe " Faraday Rotation fn P O2 Bi1.8YIG: -838 deg/db CeYIG: -830 deg/db
Device integration on Si l As 2 S 3 /Garnet Waveguides 1 µm " Waveguide loss by cutback and paperclip methods " Garnet material loss from confinement factor a(yig)~50 db/cm a(bi0.8yig)~150 db/cm a(ceyig)~40 db/cm Bi et al., Proc. SPIE vol 7604 760406 (2010), SPIE 7941, 794105 (2011) l First GeS 2 /Garnet and YIG/SOI resonators also demonstrated
Integrated Isolator based on a Racetrack Resonator Device consists of SOI waveguide and resonator. Part of the racetrack is covered with a magnetooptical garnet film to give different resonant conditions for forward and backward propagating light. Prior:. Ring resonator with bonded CeYIG isolation ratio 9 db, insertion loss ~18 db, 1.8 mm diameter, Tien et al., Optics Express, 19, 11740 (2011)
Integrated Isolator Fabrication
Racetrack with Silica cladding only (no magnetooptical effect but shows resonance peaks, Q = 130,000)
Racetrack with CeYIG/YIG cladding Magnet H~ ±1500 Oe Optical Resonance Observed for TE and TM modes at NIR Q(TM)~5,500 at critical coupling, corresponding to a res. ~58 db/cm
Racetrack with CeYIG cladding shows nonreciprocity on reversing the external magnetic field TM TE Dl: 18.2±1.6 pm Dl: 3.5±2.4 pm Isolation Ratio: -19.5±2.9dB, Insertion Loss: 18.8±1.1dB 10 db isolation bandwidth: 1.6 GHz Bi et al., Nature Photonics 5, 758 762 (2011)
Nonreciprocal Resonators: Modeling Device structure L 1 =285µm L 1 =273µm Air CeYIG YIG Resonance spectrum Si SiO 2 Dl(simul.)~15.9 pm vs. Dl(exp.)~18.2 pm a(junc=on)~4 db/cm a(mo WG)~54 db/cm Bi et al., Nature Photonics 5, 758 762 (2011)
Conclusions Polycrystalline iron garnets Phase pure Bi:YIG and Ce:YIG magnetooptical films on Si using two step deposition strategies. Figure of merit about 10x lower than single crystal CeYIG. Monolithically integrated optical isolator on silicon with isolation ratio up to 19.5±2.9 db for TM polarized modes at 1542 nm: Ultra compact footprint, simple architecture, high isolation ratio in homogeneous magnetic field. Acknowledgements: NSF, Samsung, MIT Lincoln Laboratories
Nonreciprocal phase shift (NRPS) simulations As 2 S 3 /YIG SU-8 As 2 S 3 Δβ TM TM 2β = ωε N 0 K M n 4 0 y H y x H y dxdy Garnet Optimum WG geometry design achieved by modal simulations SiO 2
Polycrystalline Bi:YIG and Ce:YIG on Si/YIG Bi 0.8,1.8 Y 2.2,1.2 Fe 5 O 12 " Phase-pure polycrystalline Bi:YIG and Ce:YIG on 20 nm YIG buffered SiO 2 (3 µm)/si Ce 1 Y 2 Fe 5 O 12 " RMS roughness: Bi0.8YIG: 1.81 nm Bi1.8YIG: 4.50 nm CeYIG: 0.92 nm " Lattice constants following Vegard s Law
Model of free spectral response and nonreciprocal resonance shift vs. waveguide thickness Measurement
On-Chip Integration Challenge Isolator is the only missing component of Si-photonics Material Figure of Merit FOM = Θ α Q: Faraday rotation per length a: Optical absorption per length Monolithic Integration Challenge Spinel Materials Q a Integrability Garnet Spinel Mag. Sc. Device Foot Print Garnets: YIG, Bi:YIG, Ce:YIG thermal and lattice mismatch with Si Spinels: CoFe 2 O 4, Fe 3 O 4, g-fe 2 O 3 high FR but too opaque Magnetic Semiconductors: Mn:CdTe, Fe: InP Paramagnetic, need permanent field
Magnetooptical Thin Film Growth & Characterization - Pulsed Laser Deposition R. Ramesh, N. Spaldin, Nat. Materials, 6, Jan. 2007, 21 Deposition Chamber Preablation with Laser Use PLD to - develop new MO materials based on perovskites - grow MO garnets on Si