Creation of Colloidal Periodic Structure

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1 광통신 (Optical Communication)

2 광통신의발전 - 봉화, 횃불, 등대 , J. Tyndall : 자유낙하하는물줄기에빛이가두어짐을발견 , A.G. Bell : 태양광으로 213m 소리전송 , T. Maiman : 반도체레이저개발 , 영국스탠더드통신연, K.C. Kao, Hockham : 광섬유원거리전송제안 초, 미국코닝사, R.D. Maurer (20dB/km) , 미국벨연구소, 1.55 μm LD 개발, 저손실광섬유 (0.2dB/km) , 태평양횡단해저광케이블설치

3 광통신의장점 - Compact : 전선에비해가볍고작음 - Low Cost : 같은전송능력에서전선보다매우저렴. - No electrical connection (ground loop) - No EMI (electromagnetic interference) - Transmission capacity : 10Gbps 상용, 100Gbps 연구중 - Long repeater spacing : 40km 상용, 120 km 가능 ( 전선 : 12km) - Better security : tapping 불가

4 광통신의원리 TIR(total internal reflection, 내부전반사 ) θ cladding (n 2 ) 2 θ 1 θ>θ c1 core (n 1 ) core (n 1 ) (n 1 > n 2 ) cladding (n 2 ) < 광섬유 (optical fiber) 기본구조 > * critical angle (θ 2 =π/2) : θ c1 = sin -1 (n 2 /n 1 ) < 실제광섬유구조 >

5 광통신의제한점 - Optoelectric conversion efficiency energy loss - Difficulty in joining fiber cable : fusion splice, connector transmission loss - Cable bending loss - Relatively expensive components - Difficulty in controlling optical signal exceed the critical angle condition : bending loss core

6 광통신시스템의개요 signal in splice coupler receiver (photodiode) transmitter (laser/led) optical fiber repeater (photodiode/ laser/led) signal out Main issues - High quality fiber (low loss/dispersion) - Efficient laser/led (low power consumption /narrow single mode) - High speed switching (>100Gb rate)

7 광섬유손실

8 NA(numerical aperture) of optical fiber : light accepting capability n 0 θ 0 θ 1 θ 2 cladding (n 2 ) core (n 1 ) NA = n 0 sinθ 0 = n 1 sinθ 1 θ 2 = π/2 θ 1 = sin -1 (n 2 /n 1 ) NA = 2 n 1 n 2 2

9 광섬유의분산특성 1. Modal dispersion : multimode fiber( 다중모드광섬유 ) 에서고차모드일수록군속도가느림. optical pulse의 broadening 1 Δτ =L( v g v 1, min g,max ) low order mode high order mode

10 Modal dispersion 의제거 - Single mode fiber 사용 - Graded-index fiber 사용 Higher order mode 의군속도가 빨라져, 펄스확대가줄게됨.

11 Nonlinear Optics Lab Nonlinear Optics Lab. Hanyang Hanyang Univ. Univ. 2. Intramodal dispersion : Material dispersion & waveguide dispersion - Material dispersion : 단일모드라도일정주파수폭을가지므로, v g =v g (ω) : fiber material property - Waveguide dispersion : Core 와 cladding 에서광에너지전파속도가다르기때문 : fiber geometrical (& doping) property c n n n c d d v w m g + + = = ω ω λ ω β 1 + = w m n n c D ω ω λ : group velocity dispersion

12 Intramodal dispersion의제거 - Phase conjugation에의한보상 - Material, waveguide dispersion의상쇄 <Phase conjugation에의한보상 > phase conjugator fiber1 fiber1 DSF EDFA1 EDFA2 Pump LD

13 <Material, waveguide dispersion 의상쇄 > 20 material dispersion 20 Dispersion (ps/km.nm) Wavelength (μm) waveguide dispersion Dispersion (ps/km.nm) dispersion flattened Wavelength (μm) dispersion shifted

14 광자밴드갭 (photonic bandgap) 을이용한신개념광섬유 광결정 (photonic crystals)

15 광결정섬유 (photonic crystal fibers) 와도파로 (waveguide)

16 광통신용레이저광원 p n + - LED(light emitting diode) - forward-biased heavily doped p-n junction - pumping by injection current => Spontaneous emission LD(laser diode) - optical feedback by cleaved surface => Stimulated emission LD(laser diode) - small size, high efficiency, integrability with electronic components - ease of pumping and modulation by current injection - spectral linewidth is larger than that of other lasers

17 LED(light emitting diode) -GaNseries Blue color - OLED(organic LED) high efficiency -Display - Traffic signal lamp -Memory - Laser disk -Lighting

18 LD(laser diode) <Characteristic optical properties of LDs> + Output power(p) & oscillation frequency(ν) sensitively depend on temperature, injection current and also feedback light. short cavity length polarization (TE) - elliptical beam

19 Output power Differential responsibility of laser dp di o R d = = η d Overall efficiency η = ηd 1 i t i 1.24 λ 0 hν ev (above threshold)

20 Oscillation frequency - Laser oscillation condition : r - Phase condition : ν n ν, ( q = 1, 2,...) ν - FWHM linewidth : F γ 0 ( ν ) > α 2nd q F ν F = 1/ 2 c r δν where, = : finesse of resonator 1 r πfwhere, : mode spacing Fig

6 nm Gain width ~ 7 nm => ~ 11 modes oscillation 10Gbps DFB-LD/module * Since the mode

21 example) InGaAsP laser, 1.3 μm / 1.5 μm InGaAsP laser(n = 3.5), d = 400 μm => ν F ~ 107 GHz λ 0 ~ 1.3 μm => λ F = λ 02 ν F / ν = λ 0 2 /2nd ~ 0.6 nm Gain width ~ 7 nm => ~ 11 modes oscillation 10Gbps DFB-LD/module * Since the mode closest to the gain maximum Increases in power while the side peaks saturate, the number of modes decreases as the injection current increases.

22 Internal feedback laser - DBR(distributed Bragg reflector) - DFB(distributed feedback) <DBR structure> <DFB structure>

23 Surface emitting laser <Surface emitting LD> <Edge emitting LD> SEM image of a VCSEL

Surface emitting laser ( 광주과기원 ) Fabrication of oxide-confined VCSEL Light output P-metal(Ti/Pt/Au) Polyimide(PI2555) Pad metal Oxide aperture p- DBR QW Output window n- DBR Substrate n-

24 Surface emitting laser ( 광주과기원 ) Fabrication of oxide-confined VCSEL Light output P-metal(Ti/Pt/Au) Polyimide(PI2555) Pad metal Oxide aperture p- DBR QW Output window n- DBR Substrate n- metal(ni/au/ge/ni/au) Mesa diameter : 40μm Current aperture diameter : 5 μm Output window diameter : 20 μm Bonding pad : 200 X 120 μm 2 Kwangju Institute of Science & Technology(K-JIST) Optoelectronics Lab.

25 광결정을이용한고효율레이저광원 Surface emitting laser ( 과기원 science 게재 )

歯4.PDF

歯4.PDF 21 WDM * OADM MUX/DEMUX EDFA Er + Doped Fiber Isolator Isolator GFF WDM Coupler 1.48 um LD 1.48 um LD Transmitter Receiver MUX EDFA OADM DEMUX Switch Fiber Optics Micro Optics Waveguide Optics Isolator,