6. optoelectronic devices. optical waveguides (a) a buried-in rectangular waveguide, (b) a buried-in...
TRANSCRIPT
![Page 1: 6. Optoelectronic Devices. Optical Waveguides (a) A buried-in rectangular waveguide, (b) a buried-in rib waveguide, (c) a strip-loaded waveguide, and](https://reader037.vdocuments.us/reader037/viewer/2022110401/56649de65503460f94ade94a/html5/thumbnails/1.jpg)
6. Optoelectronic Devices
![Page 2: 6. Optoelectronic Devices. Optical Waveguides (a) A buried-in rectangular waveguide, (b) a buried-in rib waveguide, (c) a strip-loaded waveguide, and](https://reader037.vdocuments.us/reader037/viewer/2022110401/56649de65503460f94ade94a/html5/thumbnails/2.jpg)
Optical Waveguides
(a) A buried-in rectangular waveguide, (b) a buried-in rib waveguide, (c) a strip-loaded waveguide, and (d) a diffused waveguide
![Page 3: 6. Optoelectronic Devices. Optical Waveguides (a) A buried-in rectangular waveguide, (b) a buried-in rib waveguide, (c) a strip-loaded waveguide, and](https://reader037.vdocuments.us/reader037/viewer/2022110401/56649de65503460f94ade94a/html5/thumbnails/3.jpg)
Some Fabrication Processes of Optical Waveguides
![Page 4: 6. Optoelectronic Devices. Optical Waveguides (a) A buried-in rectangular waveguide, (b) a buried-in rib waveguide, (c) a strip-loaded waveguide, and](https://reader037.vdocuments.us/reader037/viewer/2022110401/56649de65503460f94ade94a/html5/thumbnails/4.jpg)
Basic Theory of Waveguides
![Page 5: 6. Optoelectronic Devices. Optical Waveguides (a) A buried-in rectangular waveguide, (b) a buried-in rib waveguide, (c) a strip-loaded waveguide, and](https://reader037.vdocuments.us/reader037/viewer/2022110401/56649de65503460f94ade94a/html5/thumbnails/5.jpg)
Theory of Planar Optical Waveguides
![Page 6: 6. Optoelectronic Devices. Optical Waveguides (a) A buried-in rectangular waveguide, (b) a buried-in rib waveguide, (c) a strip-loaded waveguide, and](https://reader037.vdocuments.us/reader037/viewer/2022110401/56649de65503460f94ade94a/html5/thumbnails/6.jpg)
Approximate Theory of Rectangular Optical
Waveguides Surrounding by a Uniform Medium
![Page 7: 6. Optoelectronic Devices. Optical Waveguides (a) A buried-in rectangular waveguide, (b) a buried-in rib waveguide, (c) a strip-loaded waveguide, and](https://reader037.vdocuments.us/reader037/viewer/2022110401/56649de65503460f94ade94a/html5/thumbnails/7.jpg)
Approximate Theory of Rectangular Optical Waveguides Surrounding by a Uniform Medium (Cont’)
![Page 8: 6. Optoelectronic Devices. Optical Waveguides (a) A buried-in rectangular waveguide, (b) a buried-in rib waveguide, (c) a strip-loaded waveguide, and](https://reader037.vdocuments.us/reader037/viewer/2022110401/56649de65503460f94ade94a/html5/thumbnails/8.jpg)
Approximate Theory of Rectangular Optical Waveguides Surrounding by a Uniform Medium (Cont’)
![Page 9: 6. Optoelectronic Devices. Optical Waveguides (a) A buried-in rectangular waveguide, (b) a buried-in rib waveguide, (c) a strip-loaded waveguide, and](https://reader037.vdocuments.us/reader037/viewer/2022110401/56649de65503460f94ade94a/html5/thumbnails/9.jpg)
Applications of Y-Branches and Bends of Conventional Optical Waveguides
![Page 10: 6. Optoelectronic Devices. Optical Waveguides (a) A buried-in rectangular waveguide, (b) a buried-in rib waveguide, (c) a strip-loaded waveguide, and](https://reader037.vdocuments.us/reader037/viewer/2022110401/56649de65503460f94ade94a/html5/thumbnails/10.jpg)
Multimode Interference (MMI) Devices
![Page 11: 6. Optoelectronic Devices. Optical Waveguides (a) A buried-in rectangular waveguide, (b) a buried-in rib waveguide, (c) a strip-loaded waveguide, and](https://reader037.vdocuments.us/reader037/viewer/2022110401/56649de65503460f94ade94a/html5/thumbnails/11.jpg)
Example of Optical Performance of MMI Device
![Page 12: 6. Optoelectronic Devices. Optical Waveguides (a) A buried-in rectangular waveguide, (b) a buried-in rib waveguide, (c) a strip-loaded waveguide, and](https://reader037.vdocuments.us/reader037/viewer/2022110401/56649de65503460f94ade94a/html5/thumbnails/12.jpg)
1×n MMI Optical Splitters
![Page 13: 6. Optoelectronic Devices. Optical Waveguides (a) A buried-in rectangular waveguide, (b) a buried-in rib waveguide, (c) a strip-loaded waveguide, and](https://reader037.vdocuments.us/reader037/viewer/2022110401/56649de65503460f94ade94a/html5/thumbnails/13.jpg)
All-optical Logic Gate Based on MMI Waveguide
![Page 14: 6. Optoelectronic Devices. Optical Waveguides (a) A buried-in rectangular waveguide, (b) a buried-in rib waveguide, (c) a strip-loaded waveguide, and](https://reader037.vdocuments.us/reader037/viewer/2022110401/56649de65503460f94ade94a/html5/thumbnails/14.jpg)
All-optical Logic Gate Based on MMI Waveguide (Cont’)
![Page 15: 6. Optoelectronic Devices. Optical Waveguides (a) A buried-in rectangular waveguide, (b) a buried-in rib waveguide, (c) a strip-loaded waveguide, and](https://reader037.vdocuments.us/reader037/viewer/2022110401/56649de65503460f94ade94a/html5/thumbnails/15.jpg)
All-optical Logic Gate Based on MMI Waveguide (Cont’)
![Page 16: 6. Optoelectronic Devices. Optical Waveguides (a) A buried-in rectangular waveguide, (b) a buried-in rib waveguide, (c) a strip-loaded waveguide, and](https://reader037.vdocuments.us/reader037/viewer/2022110401/56649de65503460f94ade94a/html5/thumbnails/16.jpg)
Photonic Crystals
![Page 17: 6. Optoelectronic Devices. Optical Waveguides (a) A buried-in rectangular waveguide, (b) a buried-in rib waveguide, (c) a strip-loaded waveguide, and](https://reader037.vdocuments.us/reader037/viewer/2022110401/56649de65503460f94ade94a/html5/thumbnails/17.jpg)
Square-lattice and Triangular-lattice Photonic Crystals
![Page 18: 6. Optoelectronic Devices. Optical Waveguides (a) A buried-in rectangular waveguide, (b) a buried-in rib waveguide, (c) a strip-loaded waveguide, and](https://reader037.vdocuments.us/reader037/viewer/2022110401/56649de65503460f94ade94a/html5/thumbnails/18.jpg)
Band Structures of Photonic CrystalsEg. The band structures of the 2D square-lattice photonic crystal with the lattice constant is a=0.5μm. The radius of the pillar is Rc=225nm. And the refractive index of the pillar is 3.16227766.
![Page 19: 6. Optoelectronic Devices. Optical Waveguides (a) A buried-in rectangular waveguide, (b) a buried-in rib waveguide, (c) a strip-loaded waveguide, and](https://reader037.vdocuments.us/reader037/viewer/2022110401/56649de65503460f94ade94a/html5/thumbnails/19.jpg)
Photonic Crystals Improving LED Efficiency
• Incorporating a photonic crystal into an indium-gallium-nitride (InGaN) LED increases both the internal quantum efficiency and the amount of light extracted. The light is produced in the quantum-well (QW) active region.
![Page 20: 6. Optoelectronic Devices. Optical Waveguides (a) A buried-in rectangular waveguide, (b) a buried-in rib waveguide, (c) a strip-loaded waveguide, and](https://reader037.vdocuments.us/reader037/viewer/2022110401/56649de65503460f94ade94a/html5/thumbnails/20.jpg)
Photonic Crystals Improving LED Efficiency (Cont’)
Far-field emission patterns from a conventional (left) and a photonic-crystal LED (right) are very different. The latter has a strongly-modified emission pattern due to the scattering of waveguided modes out of the LED chip.
![Page 21: 6. Optoelectronic Devices. Optical Waveguides (a) A buried-in rectangular waveguide, (b) a buried-in rib waveguide, (c) a strip-loaded waveguide, and](https://reader037.vdocuments.us/reader037/viewer/2022110401/56649de65503460f94ade94a/html5/thumbnails/21.jpg)
Photonic Crystal Waveguides (PCWGs)
![Page 22: 6. Optoelectronic Devices. Optical Waveguides (a) A buried-in rectangular waveguide, (b) a buried-in rib waveguide, (c) a strip-loaded waveguide, and](https://reader037.vdocuments.us/reader037/viewer/2022110401/56649de65503460f94ade94a/html5/thumbnails/22.jpg)
Comparison between the Conventional
Waveguides and the PCWGs • The conventional optical waveguides are
weakly guided. There exist large power losses in the wide-angle bends/branches. However, the same structures made of line-defect photonic crystals give little losses because the lights were trapped by the defects of the photonic crystals.
• Most of the conventional optical waveguide devices can be easily modulated by EO effect, AO effect, and so on. But only a few photonic crystal waveguide devices can be modulated.
![Page 23: 6. Optoelectronic Devices. Optical Waveguides (a) A buried-in rectangular waveguide, (b) a buried-in rib waveguide, (c) a strip-loaded waveguide, and](https://reader037.vdocuments.us/reader037/viewer/2022110401/56649de65503460f94ade94a/html5/thumbnails/23.jpg)
Periodical Dielectric Waveguides (PDWGs)
![Page 24: 6. Optoelectronic Devices. Optical Waveguides (a) A buried-in rectangular waveguide, (b) a buried-in rib waveguide, (c) a strip-loaded waveguide, and](https://reader037.vdocuments.us/reader037/viewer/2022110401/56649de65503460f94ade94a/html5/thumbnails/24.jpg)
Electro-Optic (EO) Effect
• The electro-optic (EO) effect is a nonlinear optical effect that results in a refractive index that is a function of the applied electric field (voltage)
• Examples of Pockels effect : Ammonium dihydrogen phosphate (ADP), Potassium dihydrogen phosphate (KDP), Lithium Niobate, Lithium Tantalate, etc.
• Examples of Kerr effect: Most glasses, gases, and some crystals Pockels effect:
Kerr effect:
![Page 25: 6. Optoelectronic Devices. Optical Waveguides (a) A buried-in rectangular waveguide, (b) a buried-in rib waveguide, (c) a strip-loaded waveguide, and](https://reader037.vdocuments.us/reader037/viewer/2022110401/56649de65503460f94ade94a/html5/thumbnails/25.jpg)
Phase Modulators
• Phase shift =
, where Vπ (the half-wave voltage) is the voltage applied to achieve a phase shift of π radians.
![Page 26: 6. Optoelectronic Devices. Optical Waveguides (a) A buried-in rectangular waveguide, (b) a buried-in rib waveguide, (c) a strip-loaded waveguide, and](https://reader037.vdocuments.us/reader037/viewer/2022110401/56649de65503460f94ade94a/html5/thumbnails/26.jpg)
Mach-Zehnder Modulator to Modulate Amplitude of Light
2
cos1 0
VV
II inoutOutput Intensity:
Consider the case of φ0=0. If V=Vπ, then Iout=Iin is the maximum, else if V=0, then Iout=0 is the minimum.
![Page 27: 6. Optoelectronic Devices. Optical Waveguides (a) A buried-in rectangular waveguide, (b) a buried-in rib waveguide, (c) a strip-loaded waveguide, and](https://reader037.vdocuments.us/reader037/viewer/2022110401/56649de65503460f94ade94a/html5/thumbnails/27.jpg)
Characteristics of Optical Modulators/Switches
• Extinction Ratio: η=(I0-Im)/I0 if Im≦I0 and η=(Im-I0)/Im if Im≧I0, where Im is the optical intensity when the maximum signal is applied to the modulator and I0 is the optical intensity with no signal applied.
• Insertion Loss: Li=10log(It/Im), where It is the transmitted intensity with no modulator and Im is the transmitted intensity when the maximum signal is applied to the modulator.
• Bandwith: △f=2π/T, where T is the switching time.
![Page 28: 6. Optoelectronic Devices. Optical Waveguides (a) A buried-in rectangular waveguide, (b) a buried-in rib waveguide, (c) a strip-loaded waveguide, and](https://reader037.vdocuments.us/reader037/viewer/2022110401/56649de65503460f94ade94a/html5/thumbnails/28.jpg)
Optical Directional Coupler as a Channel Switch
![Page 29: 6. Optoelectronic Devices. Optical Waveguides (a) A buried-in rectangular waveguide, (b) a buried-in rib waveguide, (c) a strip-loaded waveguide, and](https://reader037.vdocuments.us/reader037/viewer/2022110401/56649de65503460f94ade94a/html5/thumbnails/29.jpg)
A Complicated Optical Directional Coupler
![Page 30: 6. Optoelectronic Devices. Optical Waveguides (a) A buried-in rectangular waveguide, (b) a buried-in rib waveguide, (c) a strip-loaded waveguide, and](https://reader037.vdocuments.us/reader037/viewer/2022110401/56649de65503460f94ade94a/html5/thumbnails/30.jpg)
3dB-Directional Coupler as a Beam Splitter
![Page 31: 6. Optoelectronic Devices. Optical Waveguides (a) A buried-in rectangular waveguide, (b) a buried-in rib waveguide, (c) a strip-loaded waveguide, and](https://reader037.vdocuments.us/reader037/viewer/2022110401/56649de65503460f94ade94a/html5/thumbnails/31.jpg)
Coupled-Mode Equations to Analyze Directional Coupler
![Page 32: 6. Optoelectronic Devices. Optical Waveguides (a) A buried-in rectangular waveguide, (b) a buried-in rib waveguide, (c) a strip-loaded waveguide, and](https://reader037.vdocuments.us/reader037/viewer/2022110401/56649de65503460f94ade94a/html5/thumbnails/32.jpg)
Coupled-Mode Equations (Cont’)
• The coupling length is Lc=π/2κ. Both Lc and κ depend on the refractive index distribution of guide.
• While the waveguiding mode traverses a distance of odd multiple of the coupling length (Lc, 3Lc, …, etc), the optical power is completely transferred into the other waveguide. But it is back to the original waveguide after a distance of even multiple of the coupling lengths (2Lc, 4Lc, …, etc). If the waveguiding mode traverses a distance of odd multiple of the half coupling length (Lc/2, 3Lc/2, …, etc), the optical power is equally distributed in the two guides.
![Page 33: 6. Optoelectronic Devices. Optical Waveguides (a) A buried-in rectangular waveguide, (b) a buried-in rib waveguide, (c) a strip-loaded waveguide, and](https://reader037.vdocuments.us/reader037/viewer/2022110401/56649de65503460f94ade94a/html5/thumbnails/33.jpg)
Acousto-Optic (AO) Modulators
Bragg-type AO modulator: sinθB=/2
Raman-Nath type AO modulator:sinθm=m/2, m: integer
Bragg-type: Width >> 2/Raman-Nath-type: Width << 2/: wavelength of light: wavelength of acoustic wave
![Page 34: 6. Optoelectronic Devices. Optical Waveguides (a) A buried-in rectangular waveguide, (b) a buried-in rib waveguide, (c) a strip-loaded waveguide, and](https://reader037.vdocuments.us/reader037/viewer/2022110401/56649de65503460f94ade94a/html5/thumbnails/34.jpg)
Bragg-type AO Modulator as Spectrum Analyzer
Bragg angle:
2sin 1
d
: wavelength of light: wavelength of acoustic wave
Operations of Bragg-type AO
modulator:
— Bragg diffraction effect
— Driving frequency: 1MHz ~ 1GHz
— Rise time: 150 ns (1-mm diameter laser)
Acousto-optic materials:
Visible and NIR — Flint glass, TeO2, fuse
d quartz
Infrared — Ge
High frequency — LiNbO3, GaP
![Page 35: 6. Optoelectronic Devices. Optical Waveguides (a) A buried-in rectangular waveguide, (b) a buried-in rib waveguide, (c) a strip-loaded waveguide, and](https://reader037.vdocuments.us/reader037/viewer/2022110401/56649de65503460f94ade94a/html5/thumbnails/35.jpg)
Direct Coupling from Laser/Fiber to Waveguide
dxdyyxdxdyyx
dxdyyxyx
22
2
),(),(
),(),(
• Direct Coupling Efficiency:
where is the laser/fiber mode and is the waveguide mode.
)(x)(x
![Page 36: 6. Optoelectronic Devices. Optical Waveguides (a) A buried-in rectangular waveguide, (b) a buried-in rib waveguide, (c) a strip-loaded waveguide, and](https://reader037.vdocuments.us/reader037/viewer/2022110401/56649de65503460f94ade94a/html5/thumbnails/36.jpg)
Coupling Efficiency from Laser/Fiber to Waveguide
![Page 37: 6. Optoelectronic Devices. Optical Waveguides (a) A buried-in rectangular waveguide, (b) a buried-in rib waveguide, (c) a strip-loaded waveguide, and](https://reader037.vdocuments.us/reader037/viewer/2022110401/56649de65503460f94ade94a/html5/thumbnails/37.jpg)
Coupling Efficiency from Laser/Fiber to Waveguide (Cont’)
![Page 38: 6. Optoelectronic Devices. Optical Waveguides (a) A buried-in rectangular waveguide, (b) a buried-in rib waveguide, (c) a strip-loaded waveguide, and](https://reader037.vdocuments.us/reader037/viewer/2022110401/56649de65503460f94ade94a/html5/thumbnails/38.jpg)
Coupling Efficiency from Laser/Fiber to Waveguide (Cont’)
![Page 39: 6. Optoelectronic Devices. Optical Waveguides (a) A buried-in rectangular waveguide, (b) a buried-in rib waveguide, (c) a strip-loaded waveguide, and](https://reader037.vdocuments.us/reader037/viewer/2022110401/56649de65503460f94ade94a/html5/thumbnails/39.jpg)
Simulation Results Coupling Efficiency from Laser/Fiber to Waveguide
For given waveguide’s fundamental mode, one can obtained the optimal coupling efficiency by selecting the values of w and c.
![Page 40: 6. Optoelectronic Devices. Optical Waveguides (a) A buried-in rectangular waveguide, (b) a buried-in rib waveguide, (c) a strip-loaded waveguide, and](https://reader037.vdocuments.us/reader037/viewer/2022110401/56649de65503460f94ade94a/html5/thumbnails/40.jpg)
Typical Optical Disks
![Page 41: 6. Optoelectronic Devices. Optical Waveguides (a) A buried-in rectangular waveguide, (b) a buried-in rib waveguide, (c) a strip-loaded waveguide, and](https://reader037.vdocuments.us/reader037/viewer/2022110401/56649de65503460f94ade94a/html5/thumbnails/41.jpg)
DVD Disks
![Page 42: 6. Optoelectronic Devices. Optical Waveguides (a) A buried-in rectangular waveguide, (b) a buried-in rib waveguide, (c) a strip-loaded waveguide, and](https://reader037.vdocuments.us/reader037/viewer/2022110401/56649de65503460f94ade94a/html5/thumbnails/42.jpg)
Lasers in DVD Players
![Page 43: 6. Optoelectronic Devices. Optical Waveguides (a) A buried-in rectangular waveguide, (b) a buried-in rib waveguide, (c) a strip-loaded waveguide, and](https://reader037.vdocuments.us/reader037/viewer/2022110401/56649de65503460f94ade94a/html5/thumbnails/43.jpg)
Optoelectronic Devices in DVD Players
![Page 44: 6. Optoelectronic Devices. Optical Waveguides (a) A buried-in rectangular waveguide, (b) a buried-in rib waveguide, (c) a strip-loaded waveguide, and](https://reader037.vdocuments.us/reader037/viewer/2022110401/56649de65503460f94ade94a/html5/thumbnails/44.jpg)
Band Theory of Semiconductor Devices
• Metal: The conduction band and the valence band may overlap.
• Semiconductor: The bandgap between the conduction band and the valence band is very small. The electron can be easily excited into the conduction band to become a free electron.
• Insulator: The bandgap between the conduction band and the valence band is very large. The electron is hardly excited into the conduction band to become a free electron.
![Page 45: 6. Optoelectronic Devices. Optical Waveguides (a) A buried-in rectangular waveguide, (b) a buried-in rib waveguide, (c) a strip-loaded waveguide, and](https://reader037.vdocuments.us/reader037/viewer/2022110401/56649de65503460f94ade94a/html5/thumbnails/45.jpg)
Semiconductor
Fermi energy level, EF: the highest energy level which an electron can occupy the valance band at 0°k
![Page 46: 6. Optoelectronic Devices. Optical Waveguides (a) A buried-in rectangular waveguide, (b) a buried-in rib waveguide, (c) a strip-loaded waveguide, and](https://reader037.vdocuments.us/reader037/viewer/2022110401/56649de65503460f94ade94a/html5/thumbnails/46.jpg)
Bandgap Theory of Diode
![Page 47: 6. Optoelectronic Devices. Optical Waveguides (a) A buried-in rectangular waveguide, (b) a buried-in rib waveguide, (c) a strip-loaded waveguide, and](https://reader037.vdocuments.us/reader037/viewer/2022110401/56649de65503460f94ade94a/html5/thumbnails/47.jpg)
Bandgap Theory of Tunnel Diode
![Page 48: 6. Optoelectronic Devices. Optical Waveguides (a) A buried-in rectangular waveguide, (b) a buried-in rib waveguide, (c) a strip-loaded waveguide, and](https://reader037.vdocuments.us/reader037/viewer/2022110401/56649de65503460f94ade94a/html5/thumbnails/48.jpg)
Bandgap Theory of n-p-n Transistor
![Page 49: 6. Optoelectronic Devices. Optical Waveguides (a) A buried-in rectangular waveguide, (b) a buried-in rib waveguide, (c) a strip-loaded waveguide, and](https://reader037.vdocuments.us/reader037/viewer/2022110401/56649de65503460f94ade94a/html5/thumbnails/49.jpg)
Radiation from a Semiconductor Junction
wavelength of radiation:
where : energy gap (ev)
: wavelength of radiation (nm)
e.g. GaAs =1.43 ev, find the radiation wavelength
(nm) )ev(E
1240
(NIR) Infrared Near(nm) 87643.1
1240
![Page 50: 6. Optoelectronic Devices. Optical Waveguides (a) A buried-in rectangular waveguide, (b) a buried-in rib waveguide, (c) a strip-loaded waveguide, and](https://reader037.vdocuments.us/reader037/viewer/2022110401/56649de65503460f94ade94a/html5/thumbnails/50.jpg)
Homojunction Laser Diode
![Page 51: 6. Optoelectronic Devices. Optical Waveguides (a) A buried-in rectangular waveguide, (b) a buried-in rib waveguide, (c) a strip-loaded waveguide, and](https://reader037.vdocuments.us/reader037/viewer/2022110401/56649de65503460f94ade94a/html5/thumbnails/51.jpg)
Formation of Cavity in Laser Diode
![Page 52: 6. Optoelectronic Devices. Optical Waveguides (a) A buried-in rectangular waveguide, (b) a buried-in rib waveguide, (c) a strip-loaded waveguide, and](https://reader037.vdocuments.us/reader037/viewer/2022110401/56649de65503460f94ade94a/html5/thumbnails/52.jpg)
Threshold Current
![Page 53: 6. Optoelectronic Devices. Optical Waveguides (a) A buried-in rectangular waveguide, (b) a buried-in rib waveguide, (c) a strip-loaded waveguide, and](https://reader037.vdocuments.us/reader037/viewer/2022110401/56649de65503460f94ade94a/html5/thumbnails/53.jpg)
Heterostructure Laser Diodes
![Page 54: 6. Optoelectronic Devices. Optical Waveguides (a) A buried-in rectangular waveguide, (b) a buried-in rib waveguide, (c) a strip-loaded waveguide, and](https://reader037.vdocuments.us/reader037/viewer/2022110401/56649de65503460f94ade94a/html5/thumbnails/54.jpg)
Stripe AlGaAs/GaAs/AlGaAs LD
• Advantages of stripe geometry :
1. reduced contact area → Ith↓
2. reduced emission area, easier coupling to optical fibers
• Typical W ~ a few μm, Ith~ tens of mA
• Poor lateral optical confinement of photons
![Page 55: 6. Optoelectronic Devices. Optical Waveguides (a) A buried-in rectangular waveguide, (b) a buried-in rib waveguide, (c) a strip-loaded waveguide, and](https://reader037.vdocuments.us/reader037/viewer/2022110401/56649de65503460f94ade94a/html5/thumbnails/55.jpg)
Buried Double Heterostructure LD
• Good lateral optical confinement by lower refractive index material →stimulated emission rate ↑
• Active region confined to the waveguide defined by the refractive index variation → index guided laser diode
• Buried DH with right dimensions compared with the λ of radiation → only fundamental mode can exist→ single mode laser diode
• DH AlGaAs/GaAs LD • → ~ 900 nm LD• DH InGaAsP/InP LD →
1.3/1.55 μm LD
![Page 56: 6. Optoelectronic Devices. Optical Waveguides (a) A buried-in rectangular waveguide, (b) a buried-in rib waveguide, (c) a strip-loaded waveguide, and](https://reader037.vdocuments.us/reader037/viewer/2022110401/56649de65503460f94ade94a/html5/thumbnails/56.jpg)
Output Modes of LD
• Output spectrum depends on 1. optical gain curve of the ac
tive medium 2. nature of the optical resona
tor• L decides longitudinal mode se
paration. W & H decides lateral mode separation
• With sufficiently small W & H→only TEM00 lateral mode will exist ( longitudinal modes depends on L )
• Diffraction at the cavity ends →laser beam divergence ( aperture ↓→diffraction ↑)
![Page 57: 6. Optoelectronic Devices. Optical Waveguides (a) A buried-in rectangular waveguide, (b) a buried-in rib waveguide, (c) a strip-loaded waveguide, and](https://reader037.vdocuments.us/reader037/viewer/2022110401/56649de65503460f94ade94a/html5/thumbnails/57.jpg)
Current Dependence of Power Spectrum in LD
• Output spectrum depends on
1. optical gain curve of the active medium, and
2. nature of the optical resonator
• Output spectrum from an index guided LD
low current →multimode
high current →single mode
![Page 58: 6. Optoelectronic Devices. Optical Waveguides (a) A buried-in rectangular waveguide, (b) a buried-in rib waveguide, (c) a strip-loaded waveguide, and](https://reader037.vdocuments.us/reader037/viewer/2022110401/56649de65503460f94ade94a/html5/thumbnails/58.jpg)
Light Detectors
Principles of photodetection
External photoelectric effect Eg. vacuum photodiode photomultiplier
Internal photoelectric effect Eg. p-n junction photodiode PIN photodiode avalanche photodiode
Classification by spectral response
wide spectral response
narrow spectral response
![Page 59: 6. Optoelectronic Devices. Optical Waveguides (a) A buried-in rectangular waveguide, (b) a buried-in rib waveguide, (c) a strip-loaded waveguide, and](https://reader037.vdocuments.us/reader037/viewer/2022110401/56649de65503460f94ade94a/html5/thumbnails/59.jpg)
Characteristics of Light Detectors
(A)detector thefromcurrent output :
(V)detector thefrom tageoutput vol :
lm)or (W flux liminousor radiant applied :
or
inputradiant output to of ratio :tyResponsivi
o
o
I
I
o
I
o
I
V
IV
m)(radiation theofh wavelengt:
24.1
photonsincident ofnumber
electrons emitted ofnumber
efficiency Quantum
![Page 60: 6. Optoelectronic Devices. Optical Waveguides (a) A buried-in rectangular waveguide, (b) a buried-in rib waveguide, (c) a strip-loaded waveguide, and](https://reader037.vdocuments.us/reader037/viewer/2022110401/56649de65503460f94ade94a/html5/thumbnails/60.jpg)
External Photoelectric Detector Vacuum Photodiode
ntPhotocurre
hc
Pei
![Page 61: 6. Optoelectronic Devices. Optical Waveguides (a) A buried-in rectangular waveguide, (b) a buried-in rib waveguide, (c) a strip-loaded waveguide, and](https://reader037.vdocuments.us/reader037/viewer/2022110401/56649de65503460f94ade94a/html5/thumbnails/61.jpg)
External Photoelectric Detector Photomultiplier
dynodes ofnumber :N
dynodeeach at gain :
ntPhotocurre
hc
Pei N
![Page 62: 6. Optoelectronic Devices. Optical Waveguides (a) A buried-in rectangular waveguide, (b) a buried-in rib waveguide, (c) a strip-loaded waveguide, and](https://reader037.vdocuments.us/reader037/viewer/2022110401/56649de65503460f94ade94a/html5/thumbnails/62.jpg)
Internal Photoelectric Detector (Semiconductor Photodiode)
P-N photodiode
![Page 63: 6. Optoelectronic Devices. Optical Waveguides (a) A buried-in rectangular waveguide, (b) a buried-in rib waveguide, (c) a strip-loaded waveguide, and](https://reader037.vdocuments.us/reader037/viewer/2022110401/56649de65503460f94ade94a/html5/thumbnails/63.jpg)
PIN and Avalanche Photodiodes
Operating modes:
(1) photoconductive mode (reverse biased)
(2) Photovoltaic mode (forward biased)
![Page 64: 6. Optoelectronic Devices. Optical Waveguides (a) A buried-in rectangular waveguide, (b) a buried-in rib waveguide, (c) a strip-loaded waveguide, and](https://reader037.vdocuments.us/reader037/viewer/2022110401/56649de65503460f94ade94a/html5/thumbnails/64.jpg)
Typical Characteristics of Photodetectors
![Page 65: 6. Optoelectronic Devices. Optical Waveguides (a) A buried-in rectangular waveguide, (b) a buried-in rib waveguide, (c) a strip-loaded waveguide, and](https://reader037.vdocuments.us/reader037/viewer/2022110401/56649de65503460f94ade94a/html5/thumbnails/65.jpg)
Principle of OP Circuit for Photodiodes
![Page 66: 6. Optoelectronic Devices. Optical Waveguides (a) A buried-in rectangular waveguide, (b) a buried-in rib waveguide, (c) a strip-loaded waveguide, and](https://reader037.vdocuments.us/reader037/viewer/2022110401/56649de65503460f94ade94a/html5/thumbnails/66.jpg)
Light Emitting Diode (LED)Construction
Optical design
![Page 67: 6. Optoelectronic Devices. Optical Waveguides (a) A buried-in rectangular waveguide, (b) a buried-in rib waveguide, (c) a strip-loaded waveguide, and](https://reader037.vdocuments.us/reader037/viewer/2022110401/56649de65503460f94ade94a/html5/thumbnails/67.jpg)
Choice of LED Materials
![Page 68: 6. Optoelectronic Devices. Optical Waveguides (a) A buried-in rectangular waveguide, (b) a buried-in rib waveguide, (c) a strip-loaded waveguide, and](https://reader037.vdocuments.us/reader037/viewer/2022110401/56649de65503460f94ade94a/html5/thumbnails/68.jpg)
Typical Choice of Materials for LEDs
![Page 69: 6. Optoelectronic Devices. Optical Waveguides (a) A buried-in rectangular waveguide, (b) a buried-in rib waveguide, (c) a strip-loaded waveguide, and](https://reader037.vdocuments.us/reader037/viewer/2022110401/56649de65503460f94ade94a/html5/thumbnails/69.jpg)
Radiative Transition Through Isoelectronic Centers
• For indirect band-gap semiconductors→use recombination of bound excitons at isoelectronic centers to generate radiative recombination
• Isoelectronic center : produced by replacing one host atom in the crystal with another kind of atom having the same number of valence electrons
• Isoelectronic center attract electron and hole pair → exciton radiative recombination can occur without phonon assistance → hυslightly smaller than bandgap energy Eg
• Common isoelectronic centers : • N in GaP → 565 nm • N in GaAs0.35P0.65 → 632 nm • N in GaAs0.15P0.85 → 589 nm • ZnO pair in GaP ( neutral molecular center ) → 700 nm
![Page 70: 6. Optoelectronic Devices. Optical Waveguides (a) A buried-in rectangular waveguide, (b) a buried-in rib waveguide, (c) a strip-loaded waveguide, and](https://reader037.vdocuments.us/reader037/viewer/2022110401/56649de65503460f94ade94a/html5/thumbnails/70.jpg)
Choice of Substrates for Red and Yellow LEDs
![Page 71: 6. Optoelectronic Devices. Optical Waveguides (a) A buried-in rectangular waveguide, (b) a buried-in rib waveguide, (c) a strip-loaded waveguide, and](https://reader037.vdocuments.us/reader037/viewer/2022110401/56649de65503460f94ade94a/html5/thumbnails/71.jpg)
Material System for High Brightness Red/Yellow LEDs
![Page 72: 6. Optoelectronic Devices. Optical Waveguides (a) A buried-in rectangular waveguide, (b) a buried-in rib waveguide, (c) a strip-loaded waveguide, and](https://reader037.vdocuments.us/reader037/viewer/2022110401/56649de65503460f94ade94a/html5/thumbnails/72.jpg)
Choice of Substrates for Blue LEDs
• Choices of light emitting material for blue LEDs ( before 1994 ) : GaN system, ZnSe system, SiC, etc. And the winner is : GaN
![Page 73: 6. Optoelectronic Devices. Optical Waveguides (a) A buried-in rectangular waveguide, (b) a buried-in rib waveguide, (c) a strip-loaded waveguide, and](https://reader037.vdocuments.us/reader037/viewer/2022110401/56649de65503460f94ade94a/html5/thumbnails/73.jpg)
Earlier LED Structures
![Page 74: 6. Optoelectronic Devices. Optical Waveguides (a) A buried-in rectangular waveguide, (b) a buried-in rib waveguide, (c) a strip-loaded waveguide, and](https://reader037.vdocuments.us/reader037/viewer/2022110401/56649de65503460f94ade94a/html5/thumbnails/74.jpg)
Basic Structures of High Brightness Visible LEDs
![Page 75: 6. Optoelectronic Devices. Optical Waveguides (a) A buried-in rectangular waveguide, (b) a buried-in rib waveguide, (c) a strip-loaded waveguide, and](https://reader037.vdocuments.us/reader037/viewer/2022110401/56649de65503460f94ade94a/html5/thumbnails/75.jpg)
High Brightness Blue LEDs
![Page 76: 6. Optoelectronic Devices. Optical Waveguides (a) A buried-in rectangular waveguide, (b) a buried-in rib waveguide, (c) a strip-loaded waveguide, and](https://reader037.vdocuments.us/reader037/viewer/2022110401/56649de65503460f94ade94a/html5/thumbnails/76.jpg)
Output spectra
Note : response time
~ 90ns (yellow and red LED)
~ 500ns (green LED)
Radiation pattern