Lecture 9: Electro-optic modulators. Lecture course "Integrated Nanophotonics" by Dmitry Fedyanin

Lecture 9: Electro-optic modulators

Transcript

1. Integrated Nanophotonics Dmitry Yu. Fedyanin Laboratory of Nanooptics and Plasmonics, MIPT Lecture 9: Electro-optic Modulators
2. 2 CONCEPT
3. 3 CONCEPT Digital amplitude modulation Analog amplitude modulation
4. 4 CONCEPT Phase modulation (digital or analog)
5. 5 CONCEPT modulation depth= I max −I min I max +I min modulation efficiency η= I max −I min I max contrast ratio= I max I min ; 10 log I max I min modulation bandwidth Δ ν modulation index η=sin2 Δ ϕ 2 where Δ ϕ is the extreme value of the phase modulation Phase modulation Amplitude modulation 3dB point η is 50% of max η insertion loss L i = max I output I input ; 10log max I output I input power consumption (energy per bit)
6. 6 PHASE MODULATION: POCKELS EFFECT x2 n 1 2 + y2 n 2 2 + z2 n 3 2 +2 yz n 4 2 +2 xz n 5 2 +2 xy n 6 2 =1 Linear electro-optic effect General index ellipsoid For the principle axes X, Y, Z this expression reduces to X2 n x 2 + Y2 n y 2 + Z2 n z 2 =1 The applied electric field modifies the dielectric permittivity tensor [Δ 1/n 1 2 Δ 1/n 2 2 Δ 1/n 3 2 Δ1/n 4 2 Δ 1/n 5 2 Δ1/n 6 2 ]= [r 11 r 12 r 13 r 21 r 22 r 23 r 31 r 32 r 33 r 41 r 42 r 43 r 51 r 52 r 53 r 61 r 62 r 63 ]× [E 1 E 2 E 3 ] Crystals with an inversion symmetry will have all r coefficients identical to zero.
7. 7 PHASE MODULATION: POCKELS EFFECT x2 n 1 2 + y2 n 2 2 + z2 n 3 2 +2 yz n 4 2 +2 xz n 5 2 +2 xy n 6 2 =1 Linear electro-optic effect General index ellipsoid For the principle axes X, Y, Z this expression reduces to X2 n x 2 + Y2 n y 2 + Z2 n z 2 =1 The applied electric field modifies the dielectric permittivity tensor [Δ 1/n 1 2 Δ 1/n 2 2 Δ 1/n 3 2 Δ1/n 4 2 Δ 1/n 5 2 Δ1/n 6 2 ]= [r 11 r 12 r 13 r 21 r 22 r 23 r 31 r 32 r 33 r 41 r 42 r 43 r 51 r 52 r 53 r 61 r 62 r 63 ]× [E 1 E 2 E 3 ] Crystals with an inversion symmetry will have all r coefficients identical to zero. r GaAs = [0 0 0 0 0 0 0 0 0 r 41 0 0 0 r 41 0 0 0 r 41 ] r Quartz = [r 11 0 0 −r 11 0 0 0 0 0 r 41 0 0 0 −r 41 0 0 −r 11 0 ] r 41 =1.4×10−12 m/V r 41 =1.4×10−12 m/V r 11 =0.59×10−12 m/V
8. 8 PHASE MODULATION: FREE-CARRIER PLASMA ε=εr − ωpN 2 ω2 +iΓN ω − ωpP 2 ω2 +iΓP ω ωpN 2 = 4 πe2 m n n ωpP 2 = 4 πe2 m p p Phenomenological model for silicon L. Chrostowski, M. Hochberg, Silicon Photonics Design From Devices to Systems, Cambridge University Press, 2015
9. 9 MACH–ZEHNDER INTERFEROMETER (MZI) Δ φ =−L PS Δ Reβ =−ω c L PS Δ Ren eff ≈−ω c L PS ReΔ n eff
10. 10 MACH–ZEHNDER INTERFEROMETER (MZI) phase modulation intensity modulation
11. 11 MACH–ZEHNDER INTERFEROMETER (MZI) T. Baehr-Jones et al., Ultralow drive voltage silicon traveling-wave modulator, Opt. Express 20, 12014 (2012).
12. 12 MACH–ZEHNDER INTERFEROMETER (MZI) T. Baehr-Jones et al., Ultralow drive voltage silicon traveling-wave modulator, Opt. Express 20, 12014 (2012). 20 Gb/s modulation The drive voltage was as low as 0.63 V The insertion loss was ~14 dB The RF power consumption was 200 fJ/bit
13. 13 MACH–ZEHNDER INTERFEROMETER (MZI) W.M. J. Green et al., Ultra-compact, low RF power, 10 Gb/s silicon Mach-Zehnder modulator, Opt. Express 15, 17106-17113 (2012). Modulation speed 10 Gb/s The drive voltage ~3.5 V The insertion loss was ~12 dB (mainly due to the Ni contacts) Power consumption was 5000 fJ/bit
14. 14 MACH–ZEHNDER INTERFEROMETER (MZI) Δ φ =−L PS Δ Reβ =−ω c L PS Δ Ren eff ≈−ω c L PS ReΔ n eff Cons: 1. Due to the small change in the refractive index, the modulator length L SP should be very long, which is a problem for nanoscale applications. 2. Due to the large length L SP , it consumes too much power. 3. Due to the large length L SP , the insertion loss is not small.
15. 15 MACH–ZEHNDER INTERFEROMETER (MZI) C. Haffner et al., All-plasmonic MZM enabling optical high-speed communication at the microscale, Nat. Photonics 9, 525 (2015). Plasmonic modulator based on the Pockels effect
16. 16 MACH–ZEHNDER INTERFEROMETER (MZI) C. Haffner et al., All-plasmonic MZM enabling optical high-speed communication at the microscale, Nat. Photonics 9, 525 (2015).
17. 17 MACH–ZEHNDER INTERFEROMETER (MZI) C. Haffner et al., All-plasmonic MZM enabling optical high-speed communication at the microscale, Nat. Photonics 9, 525 (2015). Electrical bandwidth up to 70 GHz Drive voltage ~8 V (–4 – +4 V) Insertion loss ~9 dB Power consumption down to 25 fJ/bit
18. 18 RING-RESONATOR MODULATOR T=|B|2 = a2 +|t |2 −2a|t |cos(θ−ϕt ) 1+a2 |t |2 −2a|t |cos(θ−ϕt ) a=exp(−2 π R Imβ) n eff = 2 R = 5 μm a2 = 0.64; |t|2 = 0.81 ΔL = 1 μm
19. 19 RING-RESONATOR MODULATOR P. Dong et al., Low Vpp, ultralow-energy, compact, high-speed silicon electro-optic modulator, Opt. Express 17, 22484 (2009).
20. 20 RING-RESONATOR MODULATOR P. Dong et al., Low Vpp, ultralow-energy, compact, high-speed silicon electro-optic modulator, Opt. Express 17, 22484 (2009). Electrical bandwidth up to 11 GHz Drive voltage less than 2 V Insertion loss 2 dB Power consumption about 50 fJ/bit Device active area of ~1000 μm2
21. 21 RING-RESONATOR MODULATOR T=|B|2 = a2 +|t |2 −2a|t |cos(θ−ϕt ) 1+a2 |t |2 −2a|t |cos(θ−ϕt ) a=exp(−2 π R Imβ) Pros: 1. Much smaller than the MZM. 2. Low insertion losses. 3. Outstanding tunability. 4. Relatively simple fabrication process and high reproducability. 5. Spectral selectivity. Cons: 1. Very sensitive to the surrounding environment and temperature. 2. The radius of the ring cannot be reduced below a few light wavelengths.
22. 22 ELECTRO-ABSORPTION MODULATOR T=exp[−2Imβ(V )L]=exp[−2 ω c Imn eff (V )L] Insertion loss L i =exp[−2 ω c Imn eff | V =0 L] Modulation efficiency η=1−exp[−2 ω c (Imn eff | V =V d −Imn eff | V =0 ) L] =1−exp[−2ω c ImΔ n eff L] Pros: 1. Very small size. 2. High robustness: poor sensitivity to the surrounding environment and temperature. 3. Broadband spectral operation. Cons: 1. The insertion loss is higher than that of the ring-resonator modulator. 2. No spectral selectivity and tunability.
23. 23 ELECTRO-ABSORPTION MODULATOR J. Liu et al., Waveguide-integrated, ultralow-energy GeSi electro-absorption modulators, Nat. Photonics 2, 433–437 (2008).
24. 24 ELECTRO-ABSORPTION MODULATOR J. Liu et al., Waveguide-integrated, ultralow-energy GeSi electro-absorption modulators, Nat. Photonics 2, 433–437 (2008). Franz-Keldysh effect (photon-assisted tunneling through the energy barrier of the bandgap)
25. 25 ELECTRO-ABSORPTION MODULATOR Electrical bandwidth ~1.2 GHz; Spectral bandwidth ~14 nm Drive voltage ~3 V Insertion loss 6 dB Power consumption about 50 fJ/bit Device active area of ~200 μm2 J. Liu et al., Waveguide-integrated, ultralow-energy GeSi electro-absorption modulators, Nat. Photonics 2, 433–437 (2008).
26. 26 MORE ON MODULATORS J.A. Dionne et al., PlasMOStor: A Metal-Oxide-Si Field Effect Plasmonic Modulator, Nano Lett. 9, 897 (2009).
27. 27 MORE ON MODULATORS J.A. Dionne et al., PlasMOStor: A Metal-Oxide-Si Field Effect Plasmonic Modulator, Nano Lett. 9, 897 (2009).
28. 28 MORE ON MODULATORS J.A. Dionne et al., PlasMOStor: A Metal-Oxide-Si Field Effect Plasmonic Modulator, Nano Lett. 9, 897 (2009).
29. 29 MORE ON MODULATORS J.A. Dionne et al., PlasMOStor: A Metal-Oxide-Si Field Effect Plasmonic Modulator, Nano Lett. 9, 897 (2009).
30. 30 MORE ON MODULATORS J.A. Dionne et al., PlasMOStor: A Metal-Oxide-Si Field Effect Plasmonic Modulator, Nano Lett. 9, 897 (2009). d 1 = 2.2 μm d 2 = 7 μm
31. 31 MORE ON MODULATORS J.A. Dionne et al., PlasMOStor: A Metal-Oxide-Si Field Effect Plasmonic Modulator, Nano Lett. 9, 897 (2009). Maximum electrical bandwidth up to 3-15 GHz Power consumption down to ~7 fJ/bit Insertion loss ~6 dB (expected) Device active area ~5 μm2
32. 32 NEXT CLASS Light detection at the nanoscale. Literature: L. Chrostowski, M. Hochberg, Silicon Photonics Design From Devices to Systems, Cambridge University Press, 2015. Chapter 6