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IEEE Photonics Soc. distinguished lecture 1 Tetsuya MIZUMOTO Dept. of Electrical and Electronic Eng. Tokyo Institute of Technology Optical Isolator: Application.

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Presentation on theme: "IEEE Photonics Soc. distinguished lecture 1 Tetsuya MIZUMOTO Dept. of Electrical and Electronic Eng. Tokyo Institute of Technology Optical Isolator: Application."— Presentation transcript:

1 IEEE Photonics Soc. distinguished lecture 1 Tetsuya MIZUMOTO Dept. of Electrical and Electronic Eng. Tokyo Institute of Technology Optical Isolator: Application to Photonic Integrated Circuits

2 IEEE Photonics Soc. distinguished lecture 2  Bulk optical isolator magneto-optic (Faraday) effect operation principle  Waveguide optical isolator TE-TM mode conversion isolator nonreciprocal loss (active) isolator nonreciprocal phase shift isolator integration (direct bonding)  Non-magneto-optic approach Outline

3 IEEE Photonics Soc. distinguished lecture 3 Photon injection  photon-generated carrier  disturbs carrier distribution (amplitude-noise)  carrier-induced index change (phase-noise) What happens? Isolator

4 IEEE Photonics Soc. distinguished lecture 4 Magneto-optic material Requirement - large magneto-optic (MO) effect --> 1-st order MO effect (Faraday rotation) - low optical absorption - temperature insensitive Rare earth iron garnet (R 3 Fe 5 O 12 ) Y 3 Fe 5 O 12 (YIG) --> (Y 3-x Bi x )Fe 5 O 12, (Y 3-x Ce x )Fe 5 O 12 enhancement of Faraday rotation

5 IEEE Photonics Soc. distinguished lecture 5 M. Gomi, et al., J. Appl. Phys., 70(11), (1991). Characteristics of Y 3-x Ce x Fe 5 O 12 (Ce:YIG) Spectra of Faraday coefficient Spectra of optical absorption

6 IEEE Photonics Soc. distinguished lecture 6 Bulk isolator, in either beam interface or fiber interface, uses rotation of polarization. Bulk isolator Basic configuration Input and output : same polarization Namiki

7 IEEE Photonics Soc. distinguished lecture 7 Bulk isolator Fiber in-line isolator --> Walk-off T.Matsumoto (NTT), Trans. IECE, J62-C, (1979). birefringent platespolarization independent operation FDK Isolation>35dB, IL<0.6dB Kyocera Isolation>30dB, IL<2.5dB

8 IEEE Photonics Soc. distinguished lecture 8 Translate Faraday isolator into waveguide one. TE-TM mode conversion type TE-TM mode conversion Isolation:12.5 dB, =1150 nm Length: 6.8 mm K. Ando, T. Okoshi and N. Koshizuka (present AIST), Appl. Phys. Lett., 53(1), 4 (1988). Faraday part Cotton-Mouton part Mode selector Magnetooptic waveguide M mm

9 IEEE Photonics Soc. distinguished lecture 9 TE-TM mode conversion Faraday rotation in a birefringent medium Phase matched:  =  TE  TM = 0 Phase mismatched: Birefringence-free (phase matching) is essential to isolator operation. rotates in a linearly polarized state

10 IEEE Photonics Soc. distinguished lecture 10 Waveguide isolators typemechanism mode conversion filed shift guided TE / guided TM (Faraday & Cotton-Mouton) transversely radiated TE / guided TM (with TM nonreciprocal phase shift) guided TE / radiated TM (semi-leaky) nonreciprocal phase shift (interferometer) nonreciprocal loss (active)

11 IEEE Photonics Soc. distinguished lecture 11 T. Shintaku (NTT), Appl. Phys. Lett., 73(14), 1946 (1998). Nonreciprocal radiation (TM phase shift) Mode conversion: transversely leaky mode Performance: - Isolation: 27 dB ( =1535 nm, L=4.1 mm) - wavelength sensitive (7 dB at =1515 nm)

12 IEEE Photonics Soc. distinguished lecture 12 Semi-leaky isolator: operation principle LiNbO 3 mode conversion  reciprocal Magneto-optic mode conversion  nonreciprocal (changes its sign for F/B) Anisotropy of LiNbO 3  Semi-leaky waveguide  unidirectional mode conversion TE mode TM mode Forward -  (Ce:YIG)+  (LiNbO 3 )=0 Backward  (Ce:YIG)+  (LiNbO 3 )≠0 guided radiated Semi-leaky isolator is attractive; - relaxed fabrication tolerance - simple mono-section structure - easy control of magnetization - but, uniform and tight LiNbO 3 / garnet contact is needed.  direct bonding S.Yamamoto, et al (Osaka U.), IEEE QE, 12, 764 (1976).

13 IEEE Photonics Soc. distinguished lecture 13 H.Shimizu and Y.Nakano (U.Tokyo), JLT, 24, (2006). Nonreciprocal loss (active) isolator Active group: U.Tokyo, AIST, Ghent U. Isolation: 14.7 dB/mm Insertion loss: 14.1 dB/mm (I=150 mA)

14 IEEE Photonics Soc. distinguished lecture 14 4 dB isolation at = nm 4 dB 15 O C Integration with active devices  nonreciprocal loss (active) excellent compatibility to active devices H. Shimizu and Y. Nakano (U.Tokyo), IEEE PTL, 19, (2007). active isolator 0.7 mm DFB LD 0.3 mm 90mA 150mA  compatible waveguide structure material & dimensions

15 IEEE Photonics Soc. distinguished lecture 15 typePassiveActive Integrationtype dependentexcellent NoisenoneASE Power consumption none current injection to SOA Polarization dependence yes, but can be overcome yes Comparison: passive and active isolators

16 IEEE Photonics Soc. distinguished lecture 16 Waveguide isolator: nonreciprocal phase shift Interferometer type - Isolation: 19 dB ( =1540 nm, L=8.0 mm) J. Fujita, M. Levy and M. Osgood, Jr. (U.Columbia), Appl. Phys. Lett., 76(16), 2158 (2000). - Isolation: 25 dB ( =1600 nm, L=4.0 mm) Y. Shoji and T. Mizumoto (Tokyo Tech), Optics Express, 15, (2007). - wavelength insensitive designed to cover both 1.31/1.55  m in a single chip Y. Shoji and T. Mizumoto (Tokyo Tech.), Optics Express, 15, 639 (2007). - polarization independent not by polarization diversity scheme Y. Shoji and T. Mizumoto (Tokyo Tech.) et al, JLT, 25(10), (2007).

17 IEEE Photonics Soc. distinguished lecture 17  Single polarization operation → No need for phase matching → Fabrication tolerant  Simple in-plane magnetization Interferometric isolator: operation principle Interferometric isolator

18 IEEE Photonics Soc. distinguished lecture 18 Nonreciprocal phase shift = (  + -  - ) (m -1 ) Nonreciprocal phase shift 1st–order MO effect linear in  y z x

19 IEEE Photonics Soc. distinguished lecture 19 Nonreciprocal phase shift = (  + -  - ) (m -1 ) Nonreciprocal phase shift Thickness of Ce:YIG guiding layer [  m] NPS/(  /2) [mm -1 ] =1550nm TM 0 mode d (CeY) 3 Fe 5 O 12 SGGG (n=1.94) SiO 2 (n=1.45) cutoff

20 IEEE Photonics Soc. distinguished lecture Wavelength (  m) Forward loss (dB) Interferometric isolator: calculated performance Wavelength (  m) Backward loss (dB)

21 IEEE Photonics Soc. distinguished lecture 21 Cancellation of wavelength dependences in backward propagation Y.Shoji and T.Mizumoto (Tokyo Tech.), Appl. Opt., 45, 7144 (2006). dependences : MO effect waveguide dispersion Interferometric isolator: wideband operation Conventional design Phase shift  R   N (backward)  N (forward)  (backward)     (forward) 

22 IEEE Photonics Soc. distinguished lecture 22 Larger isolation in wider wavelength range Conventional design Wideband design Wideband design: experimental results Y. Shoji and T. Mizumoto (Tokyo Tech.), Optics Express, 15, (2007). measured with a reference of straight waveguide (5 d B loss)

23 IEEE Photonics Soc. distinguished lecture 23 Wideband design covers fully 1310 nm / 1550 nm bands and more. Isolation > 40 dB nm Ultra-wideband design Y. Shoji and T. Mizumoto (Tokyo Tech.), Optics Express, 15, 639 (2007).

24 IEEE Photonics Soc. distinguished lecture 24 Photonic integrated circuit: device and material -photonic integrated circuit waveguide alignment  lithography process materials  to be grown (deposited) on a common platform LD, SOA III-V semiconductor modulator, SW LiNbO 3, III-V semiconductor -MUX/DeMUX Silica Isolator Magneto-optic material

25 IEEE Photonics Soc. distinguished lecture 25 Common semiconductor guiding layer (selective growth & mask process) Our approach: integration of isolator and LD Direct bonding H. Yokoi and T.Mizumoto (Tokyo Tech.), Electron. Lett., 33, 1787 (1997). LD integrated with isolator  compatible waveguide structure material & dimensions Single polarization operation

26 IEEE Photonics Soc. distinguished lecture 26 III-V waveguide isolator

27 IEEE Photonics Soc. distinguished lecture 27 Nonreciprocal phase shift = (  + -  - ) (m -1 ) Nonreciprocal phase shift linear in  y z x 1st–order MO effect  F =-4500deg/cm

28 IEEE Photonics Soc. distinguished lecture 28 Bonding garnet on III-V III-VMO garnet crystal structure zinc blendegarnet lattice constant (A) (InP)12.54 thermal expansion (K -1 ) 4.56 X (InP)9.20 X refractive index 3.2 – n (garnet) < n (III-V)  Evanescent field is to be used in MO garnet. direct bonding with no gap in-between garnet InP GaInAsP Challenging: epitaxial growth of III-V on garnet done by Dr. M. Razeghi (Thomson), JAP, 59, 2261 (1986) and Dr. J. Haisma (Philips), J. Cryst. Growth, 83, 466 (1987)

29 IEEE Photonics Soc. distinguished lecture 29 Surface activated bonding Surface activation in vacuum chamber

30 IEEE Photonics Soc. distinguished lecture 30 Direct bonding: garnet on GaInAsP/InP waveguide Bonding strength Fracture in an InP substrate at a tensile > 0.5 MPa Ce:YIG / GaInAsP T.Mizumoto, et al, ECS Meeting, 1258 (2006). Ce:YIG GaInAsP Low temperature heat treatment

31 IEEE Photonics Soc. distinguished lecture 31 Si-waveguide isolator L=364  m MMI R=2.5  m

32 IEEE Photonics Soc. distinguished lecture 32 Nonreciprocal phase shift (NPS):  =  + -  - External magnetic field SiO 2 Ce:YIG Si Ce:YIG Si SiO 2 x y z Ex External magnetic field TM mode L  /2 (Min) ~300   m-thick CeY 2 Fe 5 O 12 (Ce:YIG) :  F = deg/cm H.Yokoi, et al (Tokyo Tech.)., Applied Optics, 42, (2003) Nonreciprocal phase shift in SOI WG

33 IEEE Photonics Soc. distinguished lecture 33 Si-waveguide optical isolator 4.0mm SOI Ce:YIG Rib waveguide for reducing propagation loss (trial fabrication) Bonding condition Anneal: 250 o C Press: 5 MPa, 1 hour H.Yokoi, et al (Tokyo Tech.)., Applied Optics, 42, (2003) 300 Si SiO 2 Si 2m2m 10nm Ce:YIG 300nm Si rib waveguide Ce:YIG SGGG

34 IEEE Photonics Soc. distinguished lecture 34  3-pole magnet --> anti-parallel magnetic field (S-N-S or N-S-N)  2X2 optical SW --> reverses propagation direction (CW  CCW) ASE source N S S Spectrum Analyzer PMF TM mode IR camera TV monitor Polarizer lens Optical switch CW CCW Sample Measurement setup

35 IEEE Photonics Soc. distinguished lecture 35 First demonstration of Si waveguide isolator !  The interference reverses as the propagation direction is reversed. First demonstration of Si-waveguide isolator Y. Shoji, T. Mizumoto (Tokyo Tech), et al. APL, 92, (2008).  The interference reverses as the magnetic field directions are reversed Wavelength (nm) Transmittance (dB) w/o H field CCW CW Mag: N-S-N Wavelength (nm) Transmittance (dB) Isolation: 21dB CW CCW Mag: S-N-S N-S-N S-N-S

36 IEEE Photonics Soc. distinguished lecture 36 (a) Coupling loss between fiber and waveguide x2 : 37 dB (b) Propagation loss : 4 dB Si waveguide (2.5 dB / 4 mm) + Absorption of Ce:YIG (0.2 dB) + reflection at bonding boundary (0.65 dB x2) (c) Excess loss of MZI : 4 dB Insertion loss of the isolator ((b)+(c)) : 8 dB Si-waveguide isolator: insertion loss MZI Single WG Ce:YIG upper clad 2.0 mm 4.0 mm wavelength (nm) transmittance (dB) (a) (b) (c) 21dB Isolation

37 IEEE Photonics Soc. distinguished lecture 37 Non-magneto-optic approach “Indirect photonic transition” Zongfu Yu and Shanhui Fan (Stanford), Nature Photonics, 3, (2009). Backward: Mode-1 (  1, -k 1 ) is coupled to mode-2 (  2, -k 2 ). (- k 1 - q = -k 2,  2 -  1 =  : phase-matched) --> transition mode-2 (  2, -k 2 ) filtered out Forward: Mode-1 (  1, k 1 ) is uncoupled to mode-2 (  2, k 2 ). ( k 1 - q > k 2, phase-mismatched) --> no transition k z (2  /q)  (2  c/a)  11 22 k1k1 k2k2 -k 1 -k 2

38 IEEE Photonics Soc. distinguished lecture 38 Non-magneto-optic approach Traveling wave (dynamic) modulation Z. Yu and S. Fan (Stanford), Nature Photonics, 3, (2009). Backward: effective coupling  (z,t)=  cos(  t - (-q)z) -k 1 - q = - k 2  2 -  1 =  Example ( =1550 nm):  =5x10 -4, f=20 GHz  w=0.27  m, L=2.19 mm 0-th 1-st

39 IEEE Photonics Soc. distinguished lecture 39 Summary Optical isolators for photonic integrated circuits ★ Mode conversion isolator requirement of phase matching  limited fabrication tolerances ★ Interferometric isolator single polarization operation  no need for phase matching ultra-broad band operation (1.31/1.55  m in a single chip) integration with active devices  Ce:YIG/ III-V, Ce:YIG/ Si low-temperature direct bonding first demonstration of Si waveguide isolator  21 dB isolation ★ Non-magneto-optic approach attractive (less restricted by material), but still challenging

40 IEEE Photonics Soc. distinguished lecture 40

41 IEEE Photonics Soc. distinguished lecture 41

42 IEEE Photonics Soc. distinguished lecture 42 Semi-leaky isolator: performance Measured isolation : 20.2 dB / 1.5 mm=13.5 dB/mm 20.2 dB W=3  m 1.5 mm 4.5 mm External magnetic field (Electromagnetic Coil) Power meter PMF Tunable laser =1550 nm PMF Polarizer constant coupling loss (-15 dB/facet) T.Mizumoto et al, IEICE Trans, J89-C, 423 (2006). T.Mizumoto et al, OFC2007, OThU4 (2007).

43 IEEE Photonics Soc. distinguished lecture 43  Part-1: Bulk nonreciprocal devices magneto-optic effect (Faraday rotation) operation principle of isolators and circulators  Part-2: Waveguide isolators operational principles, design and characterization TE-TM mode conversion isolators Nonreciprocal loss isolator Interferometric isolator Semi-leaky waveguide isolator  Part-3: Waveguide circulators  Part-4: Non-magneto-optic approach Outline

44 IEEE Photonics Soc. distinguished lecture 44 Faraday effect Dielectric tensor Circular polarization CW: CCW:

45 IEEE Photonics Soc. distinguished lecture 45 Faraday effect Linearly polarized wave --> two circular polarized components CW circular polarized CCW circular polarized

46 IEEE Photonics Soc. distinguished lecture 46 Backward Forward Faraday effect Reversal of H-field Reversal of propagation direction

47 IEEE Photonics Soc. distinguished lecture 47 Waveguide Faraday rotator E. Pross, et al. (Philips), APL, 52(9), 682 (1988). N. Sugimoto, et al. (NTT), APL, 63(9), 2744 (1993).

48 IEEE Photonics Soc. distinguished lecture 48 Isolator - two-port device - includes loss mechanism #1 #2 non-unitary matrix --> lossy

49 IEEE Photonics Soc. distinguished lecture 49  Part-1: Bulk nonreciprocal devices magneto-optic effect (Faraday rotation) operation principle of isolators and circulators  Part-2: Waveguide isolators operational principles, design and characterization TE-TM mode conversion isolators Nonreciprocal loss isolator Interferometric isolator Semi-leaky waveguide isolator  Part-3: Waveguide circulators  Part-4: Non-magneto-optic approach Outline

50 IEEE Photonics Soc. distinguished lecture 50 Circulator - many-port device - lossless device #1 #2 #3 unitary matrix --> lossless

51 IEEE Photonics Soc. distinguished lecture 51 Optical circulator H.Iwamura, et al, Electron. Lett., 15, (1979). - uses rotation of polarization - polarization independent operation

52 IEEE Photonics Soc. distinguished lecture 52  Part-1: Bulk nonreciprocal devices magneto-optic effect (Faraday rotation) operation principle of isolators and circulators  Part-2: Waveguide isolators operational principles, design and characterization TE-TM mode conversion isolators Nonreciprocal loss isolator Interferometric isolator Semi-leaky waveguide isolator  Part-3: Waveguide circulators  Part-4: Non-magneto-optic approach Outline

53 IEEE Photonics Soc. distinguished lecture 53 TE-TM mode conversion Faraday rotation  F : Faraday rotation,  : field confinement factor Phase mismatch

54 IEEE Photonics Soc. distinguished lecture 54  Part-1: Bulk nonreciprocal devices magneto-optic effect (Faraday rotation) operation principle of isolators and circulators  Part-2: Waveguide isolators operational principles, design and characterization TE-TM mode conversion isolators Nonreciprocal loss isolator Interferometric isolator Semi-leaky waveguide isolator  Part-3: Waveguide circulators  Part-4: Non-magneto-optic approach Outline

55 IEEE Photonics Soc. distinguished lecture 55 Nonreciprocal phase shift y z x MO perturbation

56 IEEE Photonics Soc. distinguished lecture 56 Interferometric isolator: polarization-independent  N: nonreciprocal phase shifter provides NPS only for TM mode  MC: mode converters provide TE-TM mode conversion Y. Shoji and T. Mizumoto (Tokyo Tech.) et al, JLT, 25(10), (2007).

57 IEEE Photonics Soc. distinguished lecture 57 Issues to be considered ・ surface treatment → hydrophilic ・ mismatch in thermal expansion coefficient → low temperature heat treatment ・ Si / Si ・ Si/SiO 2 / Si, ・ III-V(GaAs,InP) / Si, ・ III-V(GaAs, GaP, InP, InAs) / III-V ・ Ce:YIG / III-V ・ Ce:YIG / SiO 2 ・ Ce:YIG / LiNbO 3 Hydrophilic bonding

58 IEEE Photonics Soc. distinguished lecture 58 Hydrophilic bonding: fabrication

59 IEEE Photonics Soc. distinguished lecture 59 Semiconductor waveguide isolator: demonstration H. Yokoi, et al (Tokyo Tech.), Appl. Opt, 39, 6158 (2000).

60 IEEE Photonics Soc. distinguished lecture 60 Ideal MMI couplers Y.Shoji, T.Mizumoto, et al., APL, 92, (2008) Wavelength (nm) Transmission loss (dB) L asym =0  m L asym =111  m Forward Backward perfectly balanced slightly unbalanced Calculated characteristics

61 IEEE Photonics Soc. distinguished lecture 61  Part-1: Bulk nonreciprocal devices magneto-optic effect (Faraday rotation) operation principle of isolators and circulators  Part-2: Waveguide isolators operational principles, design and characterization TE-TM mode conversion isolators Nonreciprocal loss isolator Interferometric isolator Semi-leaky waveguide isolator  Part-3: Waveguide circulators  Part-4: Non-magneto-optic approach Outline

62 IEEE Photonics Soc. distinguished lecture 62 Mode conversion: semi-leaky Semi-leaky type Isolation: 20.2 dB ( =1550 nm, L=1.5 mm) - fabrication tolerant - wavelength insensitive proposed by S. Yamamoto, et al (Osaka U.), IEEE QE, 12, 764 (1976). T. Mizumoto et al.(Tokyo Tech), OFC 2007, OThU4 (2007). TE mode TM mode guided radiated Mode conversion - TE-guided and TM-radiation modes - MO and LN mode conversions

63 IEEE Photonics Soc. distinguished lecture 63 Semi-leaky isolator: design To cancel mode conversion in forward direction  offset angle of LiNbO 3 Mode conversion in backward direction  isolation Isolation = 14.1 dB/mm for 50dB isolation : L=3.5 mm Ce:YIG  F =-4500 deg/cm

64 IEEE Photonics Soc. distinguished lecture nm < < 1600nm: Isolation >12.5dB/mm Forward loss < 0.09dB/mm Semi-leaky isolator: calculated performance

65 IEEE Photonics Soc. distinguished lecture 65 Semi-leaky isolator: fabrication x-cut LiNbO 3 Ce:YIG waveguide&terrace Garnet No.CY mm Bonding completed Time : 3 min Anneal : none (RT) Positioning : ~ 10 min High vacuum Sample set Pressure : 4.0 Pa (= 3.0x10-2 Torr) Gas flow : O 2 2 sccm Ar 20 sccm RF power : 250 W Time : 5 min RF plasma : Ar + O2 Press : ~ 1MPa Vacuum : 6.0x10-7 Pa

66 IEEE Photonics Soc. distinguished lecture 66 Semi-leaky guiding characteristics Semi-leaky guiding characteristic partially guided TE mode radiated TM mode

67 IEEE Photonics Soc. distinguished lecture 67  Part-1: Bulk nonreciprocal devices magneto-optic effect (Faraday rotation) operation principle of isolators and circulators  Part-2: Waveguide isolators operational principles, design and characterization TE-TM mode conversion isolators Nonreciprocal loss isolator Interferometric isolator Semi-leaky waveguide isolator  Part-3: Waveguide circulators  Part-4: Non-magneto-optic approach Outline

68 IEEE Photonics Soc. distinguished lecture 68 Waveguide optical circulator: TE-TM Mode conversion - uses TE-TM mode conversion (rotation of polarization plane) N. Sugimoto, et al. (NTT), IEEE PTL, 11, (1999).

69 IEEE Photonics Soc. distinguished lecture 69 #4 #3 #2 #1 Waveguide optical circulator: operation principle #4 #1 #4 #2

70 IEEE Photonics Soc. distinguished lecture 70 Waveguide optical circulator: performance #1 #2 #3 #4 out in #1#2#3#4 # # # # N. Sugimoto, et al. (NTT), IEEE PTL, 11, (1999). Measured transmittance (dB)

71 IEEE Photonics Soc. distinguished lecture 71 Waveguide optical circulator: Interferometric circulator Direction-A (in-phase interference) Direction-B (out-of-phase interference) T. Mizumoto, et al. (Tokyo Tech.), EL, 26, (1990).

72 IEEE Photonics Soc. distinguished lecture 72  Part-1: Bulk nonreciprocal devices magneto-optic effect (Faraday rotation) operation principle of isolators and circulators  Part-2: Waveguide isolators operational principles, design and characterization TE-TM mode conversion isolators Nonreciprocal loss isolator Interferometric isolator Semi-leaky waveguide isolator  Part-3: Waveguide circulators  Part-4: Non-magneto-optic approach Outline

73 IEEE Photonics Soc. distinguished lecture 73 Interferometric isolator - single polarization operation --> no need for phase matching - ultra-wide band operation (1.31 / 1.55  m in a single chip) - integration with active devices --> Ce:YIG/ III-V, Ce:YIG/ Si low-temperature direct bonding - first demonstration of Si waveguide isolator --> 21 dB isolation Semi-leaky waveguide isolator - highly fabrication tolerant - LN/Ce:YIG direct bonding - 20 dB / 1.5 mm Summary 2

74 IEEE Photonics Soc. distinguished lecture 74 Waveguide circulator Hybrid Faraday rotation type MZ interferometer Non-magneto-optic approach dynamic modulation - indirect photonic transition of eigen modes dependent on propagation direction Summary 3


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