A Wavelength Converter Integrated with a Discretely Tunable Laser ...

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28 3. Semiconductor optical amplifier operation and device characterization [mW] P stimulated emmision spontaneous emmision Ith ΔI ΔP I wavelength wavelength spectral power Figure 3.6: A typical LI-curve and its spectra at different injection currents. 3.3.2 Light output power and spectra This section describes the characteristics of a LI-curve, which shows the output power of the laser light as a function of the injection current . An illustration of a typical LI-curve is shown in Fig. 3.6. For injection currents below threshold, £ , the laser output are dominated by spontaneous emission. For © , above threshold, the laser condition is satisfied (see previous section), and stimulated emission dominates the output. The gain clamps due to the feedback from the photons in the cavity. Consequently, since the material gain is a monotonic function of the carrier density , also the carrier density and the level of spontaneous emission clamp. The laser power above threshold can be calculated by taking into account three factors: the number of generated photons per injected electron (internal quantum efficiency ), the number of injected electrons above the threshold current, and the fraction of photons that is coupled out of the cavity. (ASE power can be neglected.) If this is multiplied with the photon energie then the power can be written as, ¡ (3.21) ¡ ¡ (3.22) ¡ where denotes the elementary charge ¡ and all internal loss contributions, thus not the mirror loss, which equals the laser output. The butt-joint loss was assumed to be negligible , is proportional to the differential quantum . The slope of the LI-curve, ¡ efficiency , which is defined as the additional number of photons in the laser output per additionally injected electron into the SOA. The efficiency can be found after differentiating Eq. 3.21 with respect to and by making use of the expression for the laser condition in Eq. 3.15:
3.3 Extended Cavity Lasers and extended waveguide SOAs 29 Inversion of Eq. 3.23 gives ¤ ¤ ¡ ¤ ¡ ¦ ¤ ¦ from which it can be seen that the reciprocal differential quantum efficiency linearly on the laser length , a relation which can be tested experimentally. ¤ (3.23) (3.24) depends Measured LI-curves from the ECL test structures are shown in Fig. 3.7. No coating was applied to the facets. The power on the vertical axis represents fiber coupled power (§ ¨ dB coupling loss). The emitted power from two facets for the 400 long laser is over 1.5 mW at ¤ mA. The curves show an almost linear increase in the output power with increasing current, as expected. From the curves we extracted the threshold current density, , and the differential quantum efficiency, , both as a function of , and compared them to the theory as is described below. Threshold current density The measured values of as a function of ¤ were fitted using Eq. 3.18 and the results for two different sets of lasers (wafers 53a and 53b) are shown in Fig. 3.8a. It can be seen that the measurements are in good agreement with the theory. From the fits we find ¤ ¤¨ ¨ and ¤ and ¨ for wafer 53a, and ¨ for wafer 53b. Here is expressed in kA/cm¦ and in cm, cm, ¤ ¤¨ cm ¡ and . The optimal SOA length at which the threshold current is minimal is calculated using Eq. 3.19, which is simply the slope of the fits in Fig. 3.8. An optimal length is found of § . This is in agreement with the LI-curves. Although lasers with have the lowest they are not are not suitable for high optical output power, because of the high current densities in these short lasers. Differential quantum efficiency The maximum differential quantum efficiencies of the ECLs (Fig. 3.8b) were around ¤ % per facet (corrected for the 4.5 dB fiber-chip coupling loss). According to Eq. 3.24 ¤ depends linearly on , with a slope with is proportional to ¡ (3.22 and ¤ , and an intercept at ¤ . However, the data in Fig. 3.8b shows that ¤¦ is relatively high for £ . This is due to the high current densities in these relatively short lasers, which decreases the internal quantum efficiency due to carrier leakage over the hetero barriers and incomplete clamping of the carrier density above threshold [54]. Fitting the data using Eq. 3.24 and omitting £ devices results in very unreliable values (even negative) for the intercept. Nevertheless, an estimate of ¡ can be made by fixing the intercept at . Values
Page 1 and 2: A Wavelength Converter Integrated w
Page 3 and 4: iii
Page 5 and 6: Contents v 4.3 Waveguide components
Page 7 and 8: Chapter 1 Introduction 1.1 Optical
Page 9 and 10: 1.2 Exploiting optical fiber capaci
Page 11 and 12: 1.3 Wavelength conversion in WDM ne
Page 13 and 14: Chapter 2 Wavelength converter over
Page 15 and 16: 2.2 Optical gating 9 λcontrol λpr
Page 17 and 18: 2.2 Optical gating 11 powers (in th
Page 19 and 20: 2.2 Optical gating 13 Michelson Int
Page 21 and 22: 2.3 Coherent wave mixing (FWM, DFG)
Page 23 and 24: 2.5 Summary 17 2.5 Summary The main
Page 25 and 26: Chapter 3 Semiconductor optical amp
Page 27 and 28: 3.2 Amplification in SOAs 21 Table
Page 29 and 30: 3.3 Extended Cavity Lasers and exte
Page 33: 3.3 Extended Cavity Lasers and exte
Page 45 and 46: Chapter 4 Integration of waveguide
Page 47 and 48: 4.3 Waveguide components 41 Table 4
Page 49 and 50: 4.3 Waveguide components 43 4.3.2 P
Page 51 and 52: 4.4 Integration trade-offs 45 the a
Page 53 and 54: 4.4 Integration trade-offs 47 The c
Page 55 and 56: 4.4 Integration trade-offs 49 speed
Page 57 and 58: 4.4 Integration trade-offs 51 resis
Page 59 and 60: 4.4 Integration trade-offs 53 activ
Page 61 and 62: 4.4 Integration trade-offs 55 a) 60
Page 63 and 64: 4.4 Integration trade-offs 57 due t
Page 65 and 66: 4.4 Integration trade-offs 59 The
Page 67 and 68: 4.5 Conclusions 61 4.5 Conclusions
Page 69 and 70: Chapter 5 Technology 5.1 Introducti
Page 71 and 72: 5.2 Epitaxy 65 of the stack Q(1.25)
Page 73 and 74: 5.3 Waveguide processing 67 InP Q(1
Page 75 and 76: 5.3 Waveguide processing 69 h l h S
Page 77 and 78: 5.4 Contact openings and metalizati
Page 79 and 80: 5.4 Contact openings and metalizati
Page 81 and 82: Chapter 6 MWL with absolute wavelen
Page 83 and 84: 6.3 MWL with absolute wavelength co
Page 85 and 86:
6.3 MWL with absolute wavelength co
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6.5 Measurements 81 facet M 1 O4 O3
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6.5 Measurements 83 127 mA, which e
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Chapter 7 MZI wavelength converter
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7.2 Operating principle of the MZI
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7.3 Converter performance 89 Note t
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7.3 Converter performance 91 Chirp
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7.4 Wavelength converter design 93
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7.5 Fabrication 95 1 2 3 4 5 6 7 8
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7.6 Measurements 97 Power out [dBm]
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7.6 Measurements 99 mental and firs
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7.6 Measurements 101 fiber-to-fiber
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7.6 Measurements 103 P out [dBm] P
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7.6 Measurements 105 Power [dBm] -1
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7.6 Measurements 107 Substituting E
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7.6 Measurements 109 7.6.4 BER meas
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7.7 Conclusion 111 output extinctio
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Chapter 8 Wavelength Converter inte
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8.2 Design 115 MWL1 M1 O1 O2 O3 O4
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8.4 Static measurements 117 Control
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8.4 Static measurements 119 The LI-
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8.5 Dynamic operation 121 BER 2.5 G
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8.6 Discussion 123 Wavelength [μm]
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8.6 Discussion 125 lower then the l
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8.7 Conclusions 127 8.7 Conclusions
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Appendix A Mask plates The mask pla
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References [1] H. Takara, E. Yamada
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References 133 [24] R.G. Broeke, J.
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References 135 [51] C.Q. Xu, K. Shi
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References 137 [88] J.J.M. Binsma,
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Summary A wavelength converter inte
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Samenvatting Een golflengte omzette
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Dankwoord Een dankwoord hoort vol m
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echoduo een glas komen claimen, en
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List of Abbreviations AOWC All Opti
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Curriculum Vitae Ronald Broeke was
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List of publications 1. R.G. Broeke
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18. R.G. Broeke A Chirped phased-ar
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