* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download Microsoft Word Format - McMaster University > ECE
Thomas Young (scientist) wikipedia , lookup
Optical flat wikipedia , lookup
X-ray fluorescence wikipedia , lookup
Atmospheric optics wikipedia , lookup
Diffraction grating wikipedia , lookup
Ellipsometry wikipedia , lookup
Surface plasmon resonance microscopy wikipedia , lookup
Photoacoustic effect wikipedia , lookup
Optical fiber wikipedia , lookup
Retroreflector wikipedia , lookup
3D optical data storage wikipedia , lookup
Interferometry wikipedia , lookup
Vibrational analysis with scanning probe microscopy wikipedia , lookup
Photon scanning microscopy wikipedia , lookup
Harold Hopkins (physicist) wikipedia , lookup
Fiber Bragg grating wikipedia , lookup
Optical tweezers wikipedia , lookup
Optical coherence tomography wikipedia , lookup
Anti-reflective coating wikipedia , lookup
Ultrafast laser spectroscopy wikipedia , lookup
Astronomical spectroscopy wikipedia , lookup
Dispersion staining wikipedia , lookup
Ultraviolet–visible spectroscopy wikipedia , lookup
Magnetic circular dichroism wikipedia , lookup
Silicon photonics wikipedia , lookup
Nonlinear optics wikipedia , lookup
Optical rogue waves wikipedia , lookup
Fiber-optic communication wikipedia , lookup
Lightwave Transmission and Amplification 1. Optical fibers Principle: total reflection between two dielectric materials with different refractive index: n1 and n2 (< n1). Features: EM field is not fully confined in the core – leading to radiation loss from the structure incompleteness; - possible coupling from waveguide to waveguide through evanescent wave. Behavior model: EM field in fiber (propagating along z ) can be written as: E (r , , z, t ) A( z, t )(r , )e j (ot o z ) It can be viewed as the superposition of many single frequency harmonic waves: E (r , , z, t ) 1 E (r , , z , )e jt d 2 Hence: E (r , , z , ) A( z , o ) (r , )e j o z A( z , t ) 1 2 A( z, o )e j ( o ) t d 1 2 A( z, )e jt d Substituting E (r , , z, ) into Helmholtz equation (wave propagation equation in frequency domain, directly derived from Maxwell equation) yields: A( z, ) 2 o2 A( z, ) 0 z 2 j o plus an eigen value equation that governs (r , ) . Since o , can be expanded as: o j n 2 1 1 1 2 2 3 3 ...... 2 6 | n o n 1 where is the fiber loss, 1, 2,3,...... are the group delay, the chromatic (2nd) dispersion and the higher order (>3rd) dispersions, respectively. Therefore, the governing equation for lightwave propagation along fiber in time domain can be obtained: 2 A( z, t ) 3 3 A( z, t ) A( z, t ) A( z, t ) 1 j 2 A( z, t ) 0 z t 2 6 2 t 2 t 3 Characteristics: Ge-SiO2/SiO2 fiber loss characteristics Loss (dB/km) OH- Absorption Metal Ion Absorption Transmission Windows Rayleigh Scattering Infrared Absorption 1100nm 1200nm 1300nm 1400nm 1500nm Wavelength Ge-SiO2/SiO2 fiber chromatic dispersion characteristics Mode dispersion: different propagation speed from different mode. Polarization dispersion: different propagation speed from different polarized mode. Material dispersion: from material inherent property. Waveguide dispersion: from waveguide structure. 2 Dispersion (ps/nm.km) Material dispersion G. 652/G. 654 SMF Waveguide dispersion G. 653 SMF 1300nm 1550nm Wavelength Numerical aperture NA n1 2 n1 n2 sin n1 From connection and guidance point of view: larger NA is better. However, larger NA may excite high order modes, hence introduce mode dispersion and reduce the transmission bandwidth. In SMF, larger NA yields more negative dispersion. This can be utilized to cancel the positive material dispersion. (DCF is such designed.) Cut-off wavelength Fundamental mode (LP01) has no cut-off wavelength, higher (1st) order mode (LP11) has cut-off wavelength given by: c 2aNA/ Vc , where Vc is calculated from the eigen value equation for LP11 mode, Vc 2.4 for any fiber with step-index profile (the 1st root of zero-order Bessel function). In order to guarantee single mode transmission in fiber, the cut-off wavelength must be designed smaller than the transmission wavelength. Please note that any wavelength can be transmitted in the fiber through at least one spatial pattern (the fundamental mode). The cut-off wavelength only gives the criteria how many spatial patterns are allowed. If the wavelength transmitted in the fiber is longer 3 than the cut-off wavelength, there is only one spatial pattern (the fundamental mode) in the fiber. Otherwise, there are more than one spatial patterns (the fundamental mode plus the higher order mode) in the fiber. For a given index profile, the cut-off wavelength is only determined by the core-size of the fiber. This indicates that the waveguide can be viewed as a “spatial pattern filter” controlled by its size (cut-off wavelength). Fiber products: Transmission Wavelength Loss Dispersion G. 652 SMF 1310nm or 1550nm G. 653 DSF 1550nm G. 654 1550 0.35dB at 1310nm 0.2dB at 1550nm 3.5ps/nm.km at 1310nm 20ps/nm.km at 1550nm 0.22dB 0.15dB 3.5ps/nm.km 20ps/nm.km Application requirement: NA c Loss small to be optimized Dispersion to be optimized small Bending large large Connection large large Mode Profile to be optimized to be optimized small large 2. Other passive photonic devices Passive photonic devices: optical connector, optical isolator, optical coupler, optical attenuator, optical filter. 3. Optical amplifiers 1. Erbium Doped Fiber Amplifier (EDFA) Principle: EDF Energy Level EDF Cross-sectional Structure 4I(11/2) 1S Cladding 4I(13/2) Core Er 3 980nm 1480nm 1550nm/10mS Doped Area 4 Gain spectrum: S-Band L-Band C-Band 20dB 1535nm 1550nm 1570nm Wavelength Configuration: Optical Signal Input EDF ISO Optical Signal Output ISO Pump Laser PhotoDetector PhotoDetector Gain Control Unit Behavior model: dN up dt ( ( p pa Pp Ahv p p pe Pp Ahv p s sa Ps M ni nai Pni )( N o N up ) Ahvs Ahvni i 1 N up s se Ps M ni nei Pni ) N up Ahvs Ahvni up i 1 dPni 1 {v g ni [( nai nei ) N up nai N o ] }Pni Rspi , i 1,2,......M dt n where N up is Er 3 density at exited state 4I 13 / 2 ; N o is Er 3 doping density; A is the fiber core area, p , s , ni are the optical field confinement factor of the pump light, the signal light, and the spontaneous emission light at i_th wavelength, respectively; pa, sa,nai are the stimulated absorption cross-section of the pump light, the signal light, and the spontaneous emission light at i_th wavelength, respectively; pe, se,nei are the stimulated 5 emission cross-section of the pump light, the signal light, and the spontaneous emission light at i_th wavelength, respectively; v p , s ,n are the frequency of the pump light, the signal light, and the spontaneous emission light at i_th wavelength, respectively; h is Planck constant; Pp , s ,ni are the optical power of the pump light, the signal light, and the spontaneous emission light at i_th wavelength, respectively; up, n are the lifetime of Er 3 at its exited state 4I 13 / 2 and the spontaneous emission photon lifetime, respectively; R spi is the spontaneous emission rate at i_th wavelength; i 1,2,......M indicates all the possible wavelengths at which spontaneous emission is generated. Pp is given as the steady state pump power. Ps is the averaged signal power. Both of them can be viewed as constants in solving above rate equations. Characteristics: Optical gains for the signal and the spontaneous noise are given by: Gs s [( sa se ) N up sa N o ] Gni ni [( nai nei ) N up nai N o ] Hence signal light output power can be related to signal light input power: PsO PsI e Gs L where L is the length of EDF. At input end, the signal-to-noise ratio (SNR) can be estimated as: SNRin PsI hv s v The spontaneous noise is also amplified in EDF and its value in the signal band at the output end can be given as: Pns 2nsp (e GnsL 1)hvs v where n sp is the population inversion factor. Hence SNR at output end can be estimated as: SNRout PsO PsI e Gs L ( ) hv s v Pns 1 2nsp (e GnsL 1) hv s v 6 Therefore, the noise figure of EDFA can be given as: G L SNRin 1 2nsp (e ns 1) NF 2nsp 2 SNRout e Gs L Applications: Requirement small signal gain > In-line 20dB Amplification noise figure < 5dB PreAmplification output optical power > Power 10dBm Booster Pump 980nm 1480nm 980nm Remark 980nm pump for better noise figure 1480nm pump for in-line monitoring 980nm pump for better noise figure 980nm 1480nm 980 pump for high efficiency 1480nm pump for stability 2. Semiconductor Optical Amplifier (SOA) Structure: Current Injection Optical Signal Output Optical Signal Input Semiconductor Gain Medium Anti-Reflection Coatings Application: Gain Block Configuration EDFA DEMUX …… SOA DEMUX SOA …… SOA 7