本論文的主題乃以磷化銦為基板，使用N型調變摻雜砷化鋁鎵銦應變平衡多重量子井，設計雷射/半導體光放大器之結構，且利用分子束磊晶成長技術製備材料，進而完成元件之製作。此一量子井之組成，乃由一晶格匹配之砷化鎵銦為其核心，填入一壓縮應變之砷化鎵銦在其核心之兩旁，配合一伸張應變之砷化鋁鎵銦做為與位障之間的緩衝隔離區。兩種具有相似結構，但設計在不同之基本發光波長(1.55微米與1.48微米)的晶片，將分別地被準備用來研究: (1)順偏壓時，光之放大特性。(2)逆偏壓時，電致吸收的特性。在實驗上，以固態源分子束磊晶系統成長高品質之砷化鋁鎵銦的技術已經被建立，且利用雙晶X光繞射儀、穿透式電子顯微鏡、電致螢光與光致螢光光譜量測技術，所成長之塊材與多重量子井晶片的特性也更進一步被檢測確定。
針對波長為1.55微米的晶片，使用一新發展之多次濕蝕刻技術完成脊狀波導雷射的製備，包含有Fabry-Perot (FP)與tilted-end-facet (TEF)兩種形式。電致螢光光譜顯示，當注入電流密度大於20 (A/cm^2)，此量子井之第一電子能階至第二電洞能階的光增益(e1-hh2，波長為1460奈米)大於第一電子能階至第一電洞能階的躍遷(e1-hh1，波長為1550奈米)。FP-laser操作在其臨限電流時，雷射出的波長為1514奈米。隨著注入電流的增加，將依序觀察到兩個額外的雷射發光波長(1528奈米與1545奈米)。然而，在TEF-laser僅發現唯一雷射發光波長在1511奈米。我們也進一步的發現，這些TE極化的雷射發光波長與光電流光譜中發現之δ-like吸收峰之位置呈現一致。此雷射行為與量子線或量子點的光能量躍遷極為相似，極可能工作在激發態。
為了研究調變摻雜半導體光放大器之電致吸收調變的行為，波長為1.48微米的晶片，將被用來量測其在電場下之穿透係數變化量，進而求得其微分吸收頻譜。比較六片不同的樣品，其中，在一結合電洞阻擋位障、具有N型調變摻雜且載子薄片密度為3.5 × 10^11 (cm^-2 per QW)之量子井結構，發現此一結構工作在反向偏壓下，具有最大的揪譜參數。因此，此結構將提供一絕佳的平台讓我們有機會去實現，那些需要較大的折射率變化量，但希望有較小的吸收係數變化量之電致折射元件。
此外，在波導元件的設計上，利用一漸變寬度波導的概念，針對耦和係數為0.15與0.28的兩元件，我們已經成功地使得傳統上固定寬度之多模干涉器之長度縮短超過32%。進一步延伸此一設計概念，我們展示了一個利用串接兩段長度較短之多模干涉器，形成具有新的能量分配比(7%, 64%, 80% 與93%) 之2x2波導耦合器。最後，在兩段長度較短之多模干涉器之中，插入一對不等寬的波導作為相位調整之用，我們更加實現了一任意分光比之波導耦合器。這些耦合器具有簡單的幾何形狀與低損耗的特性，進而在爾後的光積體晶粒之設計上，提供了一新穎元件可供選擇。

In this work, we have reported the design, MBE-growth and fabrication of strain-balanced n-type modulation-doped (MD) InGaAlAs/InGaAs multiple quantum wells laser/SOAs on InP. The quantum well contains a lattice-matched InGaAs core, a compressive-strained InGaAs padding, and a tensile-strained InGaAlAs spacer. Two kinds of samples having similar structure but different fundamental transition wavelength of 1.55 μm and 1.48 μm are separately prepared for investigating their characteristics in optical amplification under forward bias and electro-absorption under reversed bias. Also, the technique of growing high-quality InGaAlAs with solid-source molecular beam epitaxy has been established and the resulting InGaAlAs bulk and QWs samples are extensively characterized by double-crystal X-ray diffraction, transmission electron microscopy, electroluminescence, and photoluminescence measurements.
For λ = 1.55 μm samples, ridge-waveguide lasers of Fabry-Perot (FP) type and tilted-end-facet (TEF) type were fabricated by a new developed multi-step wet-etching process. When injection current density > 20A/cm^2, electroluminescence spectra show higher optical gain for the quantum well e1-hh2 transition at λ = 1460 nm than the e1-hh1 transition at λ = 1550 nm. The FP laser shows a lasing peak of λ = 1514 nm at threshold. Additional lasing wavelength at λ =1528 nm and 1545 nm were observed sequentially as the injection current increased. However, for the TEF laser, only the emission at λ = 1511 nm was observed. These TE-polarized lasing wavelengths are consistent with the δ-like absorption peaks in photocurrent spectra. The lasing performance is possible attributed to optical transitions within quantum dots/wires which are formed by the strain-field profile and alloy segregation/migration.
For λ = 1.48 μm samples, the differential absorption spectroscopy, which measures the change of transmission (ΔT/T) in the presence of electric field, is used to study the electro-absorption modulation behavior of MD-SOA’s. A sample with n-type modulation-doping amounting to a sheet density of 3.5 × 10^11 cm^-2 per QW and combining with a hole-stopping barrier represents the largest chirp parameter (Δn/Δk) under reversed bias, which offers an excellent platform to realize electro-refractive devices with larger refractive index changes (Δn) but lower differential absorption (Δα) near λ = 1.55 μm, which is also our interested region of operation.
In addition, we have succeeded in reducing the length of conventional constant-width multimode interference (MMI) coupler of K = 0.15 and 0.28 more than 32% by a novel stepped-width design concept. By extending the stepped-with idea, we show that it is possible to obtain 2x2 waveguide couplers with new power splitting ratios of 7%, 64%, 80% and 93% for cross coupling by cascading two short MMI sections. We further realize freely chosen power splitting ratio by interconnecting a pair of unequal-width waveguides as the phase-tuning section into the middle of two short MMI sections. These compact and low loss MMI-based devices use only rectangular geometry without any bent, curved, and tapered waveguides. They offer valuable new possibilities for designing waveguide-based photonic integrated circuits.

Contents

Chapter 1. Introduction 1
1.1 Benefits of InGaAlAs, strain QWs, and n-type modulation doping 3
1.1.1 Advantage of InGaAlAs 3
1.1.2 Compressively Strained QWs 3
1.1.3 N-type modulation doping 5
1.2 Outline of the thesis 7
Reference 10

Chapter 2. Design of N-type Modulation-Doped InGaAlAs/InP Strained-Balanced MQWs Laser/SOA’s 12
2.1 Important issues for TE-polarized laser/SOA’s QW 12
2.2 Laser/SOA’s QW design for active devices 15
2.3 p-i-n laser/SOA’s structure 19
Reference 26

Chapter 3. MBE Growth of InGa(Al)As Materials and Laser/SOA’s Structures 27
3.1 Calibration of cell flux and growth rate 28
3.1.1 RHEED intensity oscillations 29
3.1.2 Flux measurements 31
3.2 Experiment: MBE-growth of p-i-n laser/SOA’s structures 42
Reference 46

Chapter 4. InGaAlAs/InP Strain-Balanced MQWs Laser/SOA’s 48
4.1 Mesa diode 49
4.2 Ridge waveguide fabrication 49
4.2.1 Multi-step wet-etching process 49
4.2.2 Double-layer photoresist method 51
4.3 Devices: experimental results and discussions .....54
Reference 63

Chapter 5. Electro-Absorption Characteristics in N-type Modulation-Doped Strain-balanced MQWs 64
5.1 Six blue-shifted samples (λ = 1.48 μm) 66
5.2 Photocurrent and electroluminescence (EL) spectra 68
5.3 Transmission and Absorption 69
5.3.1 Kramers-Kronig Transform (KKT) 69
5.3.2 Experimental results and discussions 69
Reference 85

Chapter 6. Compact Multimode Interference Couplers with Arbitrary Power Splitting Ratio 86
6.1 Simulation methods 94
6.1.1 Multi-Mode Interference, MMI 94
6.1.2 An approximate 2-D Waveguide for representing a real 3-D waveguide. 94
6.1.3 Approximations in Guided-Mode Propagation Analysis (MPA). 95
6.2 Conventional 2 x 2 MMIs (K ≥ 0.5) 99
6.2.1 Transfer functions of MMI’s 101
6.3 Cascaded 2 x 2 MMI couplers 105
6.3.1 Transfer Matrix of Cascaded 2 x 2 MMI
Couplers 105
6.3.2 Possible K-values of Cascading MMI’s 106
6.3.3 Wavelength sensitivity of MMI’s 109
6.3.4 Applications 110
6.4 Design of 2 x 2 Couplers with Arbitrary Power Splitting Ratio 117
6.5 Transfer functions of half MMI-D 123
Reference 126

Chapter 7. Summary 129

APPENDICES
A. Band Lineup and Effective Mass of Strained Layers 133
B. Achievable Epitaxial Materials 150
C. Riber Compact 21T MBE System 155
D. MBE Growth Process and Conditions 160
E. Ring-Resonator Loop-Mirror Laser 167

Publication List 174

[1.1] T. L. Koch and U. Koren, “Semiconductor Photonic Integrated Circuits,” IEEE J. Quantum Electron., vol. 27, pp. 641- 653, 1991.
[1.2] E. J. Skogen, J. S. Barton, S. P. Denbaars and L. A. Coldren, “A quantum-well-intermixing process for wavelength-agile photonic integrated circuits,” IEEE J. Sel. Topics. Quantum Electron., vol. 8, pp. 863- 869, 2002.
[1.3] M. Kohtoku, S. Oku, Y. Kadota, Y. Shibata, and Y. Yoshikuni, “200-GHz FSR Periodic Multi/Demultiplexer with Flattened Transmission and Rejection Band by using a Mach-Zehnder Interferometer with a Ring Resonator ,” IEEE Photon. Technol. Lett., vol. 12, pp. 1174-1176, 2000.
[1.4] B. Liu, A. Shakouri, and J. E. Bowers, “Wide Tunable Double Ring Resonator Coupled Lasers,” IEEE Photon. Technol. Lett., vol. 14, pp. 600-602, 2002.
[1.5] P. Jayavel, T. Kita, O. Wada, H. Ebe, M. Sugawara, Y. Arakawa, Y. Nakata and T. Akiyama, “Optical Polarization Properties of InAs/GaAs Quantum Dot Semiconductor Optical Amplifier ,” Jpn. J. Appl. Phys. Vol. 44, pp. 2528- 2530, 2005.
[1.6] T. Akiyama, N. Hatori, Y. Nakata, H. Ebe and M. Sugawara, “Pattern-effect-free semiconductor optical amplifier achieved using quantum dots,” Electron. Lett., vol. 38, pp. 1139- 1140, 2002.
[1.7] T. Akiyama, H. Kuwatsuka, T. Simoyama, Y. Nakata, K Mukai, M. Sugawara and O. Wada, “Nonlinear gain dynamics in quantum-dot optical amplifiers and its application to optical communication devices,” IEEE J. Quantum Electron., vol. 37, pp. 1059- 1065, 2001.
[1.8] S. D. McDougall, O. P. Kowalski, C. J. Hamilton, F. Camacho, B. Qiu, M. Ke, R. M. De La Rue, A. C. Bryce and J. H. Marsh, ” Monolithic integration via a universal damage enhanced quantum-well-intermixing technique,” IEEE J. Sel. Topics. Quantum Electron., vol. 40, pp. 636- 646, 1998.
[1.9] M. N. Khan, J. E. Zucker, T. Y. Chang, N. J. Sauer, M. D. Divino, T. L. Coch, C. A. Burrus, and H. M. Presby, “Design and Demonstration of Weighted-Coupling InGaAs/InGaAlAs Electron Transfer Waveguides,” J. Lightwave Technology, vol. 12, pp. 2032-2039, 1994.
[1.10] Y. Siberberg, P. Perlmutter, and J. E. Baran, “Digital Optical Switch,” Appl. Phys. Lett., vol. 51, pp. 1230-1232, 1987.
[1.11] P. J. A. Thijs, L. F. Tiemijer, P. I. Kuindersma, J. J. M. Binsma, and T. Van Dongen, “High performance of 1.5 μm wavelength InGaAs-InGaAsP strained quantum-well lasers and amplifiers,” IEEE J. Quantum Electron., vol. 27, pp. 1426-1438, 1991.
[1.12] P. J. A. Thijs, L. F. Tiemijer, J. J. M. Binsma, and T. Van Dongen, “Progress in long-wavelength strained-layer InGaAs(P) quantum-well semiconductor lasers and amplifiers,” IEEE J. Quantum Electron., vol. 30, pp. 477-499, 1994.
[1.13] J. Minch, S. H. Park, T. Keating, and S. L. Chuang, “Theory and Experiment of In1-xGaxAsyP1-y and In1-x-yGaxAlyAs Long-Wavelength Strained Quantum-Well Lasers,” IEEE J. Quantum Electron., vol. 35, pp. 771-782, 1999.
[1.14] J. C. L. Yong, J. M. Rorison, and I. H. White, “1.3-μm Quantum-Well InGaAsP, AlGaInAs, and InGaAsN Laser Material Gain: A Theoretical Study,” IEEE J. Quantum Electron., vol. 38, pp. 1553-1564, 2002.
[1.15] L. A. Coldren and S. W. Corzine: Diode Laser and Photonic Integrated Circuits, (John Wiley & Sons, New York, 1995), P. 137.
[1.16] H. Haug and S. W. Koch: Quantum theory of the optical and electronic properties of semiconductors, (World Scientific, Singapore, 1994) 3rd ed., p.250.
[1.17] A. Yariv: Optical Electronics in Modern Communications, (Oxford University Press, Oxford, 1997) 5th ed., p. 328.
[1.18] J. E. Zucker, T. Y. Chang, M. Wegener, N. J. Sauer, K. L. Jones, and D. S. Chemla, “Large refractive index changes in tunable-electron-density InGaAs/InAlAs quantum wells,” IEEE Photonics Technol. Lett., vol. 2, pp. 29-31, 1990.
[1.19] T. Mukai, Y. Yamamoto and T. Kimura: Semiconductors and Semimetals, ed. W. T. Tsang (Academic Press, New York, 1985) Vol. 22, Part E.
[1.20] K. J. Vahala and C. E. Zah, “Effect of doping on the optical gain and the spontaneous noise enhancement factor in quantum well amplifiers and lasers studied by simple analytical expressions,” Appl. Phys. Lett., vol. 52, pp.1945-1947, 1988.
[1.21] A. Niwa, T. Ohtoshi, K. Uomi, and K. Nakahara, “Doping-type dependence of turn-on delay time in 1.3 μm InGaAsP-InP modulation-doped strained quantum-well lasers,” IEEE Photon. Technol. Lett., vol. 8, pp. 328-330, 1996.

[2.1] J. C. L. Yong, J. M. Rorison, and I. H. White, “1.3-m Quantum　-Well InGaAsP, AlGaInAs, and InGaAsN Laser Material Gain: A Theorectical Study,” IEEE J. Quantum Electron., vol. 38, pp. 1553-1564, 2002.
[2.2] T. Mukai, Y. Yamamoto and T. Kimura: Semiconductors and Semimetals, ed. W. T. Tsang (Academic Press, New York, 1985) vol. 22, Part E.
[2.3] K. J. Vahala and C. E. Zah, “Effect of doping on the optical gain and the spontaneous noise enhancement factor in quantum well amplifiers and lasers studied by simple analytical expressions,” Appl. Phys. Lett., vol. 52, pp.1945-1947, 1988.
[2.4] M. K. Chin, T. Y. Chang and W. S. Chang, “Generalized blockaded reservoir and quantum-well electron-transfer structures (BRAQWETS): modeling and design considerations for high performance waveguide phase modulators,” IEEE J. Quantum Electron., vol. 28, pp. 2596-2611, 1992.
[2.5] B. W. Wessels, “Morphological stability of strained–layer semiconductors,” J. Vac. Sci. Technol. B, vol. 15, pp. 1056- 1058, 1997.
[2.6] M. J. Mondry, D. I. Babic, J. E. Bowers, and L. A. Coldern, “Refractive index of (Al, Ga, In)As Epilayers on InP for optoelectronic applications”, IEEE Photon. Technol. Lett., vol. 4, pp. 627-630, 1992.
[2.7] S. Nojima and H. Asahi, “Refractive index of InGaAs/InAlAs multi-quantum-well layers grown by molecular beam epitaxy”, J. Appl. Phys., vol. 63, pp. 479-483, 1998.
[2.8] P. Martin, E. M. Skour, L. Chusseau, C. Alibert, and H. Bissessur, “Accurate refractive index measurement of doped and undoped InP by a grating coupling technique”, Appl. Phys. Lett., vol. 67, pp. 881-883, 1995.
[2.9] P. Bhattacharya, Semiconductor Optoelectronic Devices (2nd, Prentice-Hall, New Jersey, 1994), Appendix 18.

[3.1] R. Sacks, R. Sieg, S Ringel, “Investigation of the Accuracy of Pyrometric Interferometry in Determining AlxGa1-xAs Growth Rates and Compositions,” J. Vac. Sci. Tech. B, vol. 12, pp. 2157-2162, 1996.
[3.2] P. Pinsukanjana, A. Jackson, J. Tofte, K. Maranowski, S. Campbell, J. English, S. Chalmers, L. Coldren, and A. Gossard, “Real-time Simultaneous Optical-Based Flux Monitoring of Al, Ga, and In using Atomic Absorption for Molecular Beam Epitaxy,” J. Vac. Sci. Tech. B, vol. 14, pp.2147-2150, 1996.
[3.3] W. Gilmore III, D. Aspnes, “Performance Capabilities of Reflectometers and Ellipsometers for Compositional Analysis during AlxGa1-xAs Epitaxy,” Appl. Phys. Lett., vol. 66, pp.1617-1619, 1995.
[3.4] C. Kuo, M Boonzaayer, D. Schreder, G. Maracas, B. Jons, “Real Time in-situ Thickness Control of Fabry-Perot Cavities in MBE by Wavelength Ellipsometry,” Ninth International Conference on Molecular Beam Epitaxy, Malibu, Ca., 1996.
[3.5] W. Breiland, K. Kileen, “A Virtual Interface Method for Extracting Growth Rates and High Temperature Optical Constants from Thin Semiconductor Films using in situ Normal Incidence Reflectance,” J. Appl. Phys., vol. 78, pp. 6726-6736, 1995.
[3.6] G. Li, W. Yuen, K. Toh, L. Eng, S. Lim, C. Chang-Hasnain, “Accurate Molecular Beam Epitaxial growth of Vertical-Cavity Surface Emitting Laser Using Diode Laser Reflectometry,” IEEE Photonics Tech. Letters, vol. 7, pp. 971-973, 1995.
[3.7] J. Harris, B. Joyce, P. Dobson, “Oscillations in the Surface Structure of Sn-Doped GaAs during Growth by MBE,” Surf. Sci., vol. 103, pp.L90-L96, 1981.
[3.8] J. M. Hove, C. S. Lent, P. R. Pukite, and P. I. Cohen, “Damped oscillations in reflection high energy electron diffraction during GaAs MBE”, J. Vac. Sci. Technol. B, vol. 1, pp. 741-746, 1983.
[3.9] Dieter K. Schroder, Semiconductor Material and Device Characterization (2nd, John Wiley and Sons, New York, 1998), chapter 8.
[3.10] A.Y. Cho, in The Technology and Physics of Molecular Beam Epitaxy, edited by E. H. C. Parker, Plenum Press, New York, pp. 1-13, 1985.
[3.11] Y. G. Chai, “Effect of accelerated growth rate (1–5 μm/h) on molecular beam epitaxial GaAs using Si as a dopant,” Appl. Phys. Lett., vol. 37, pp. 379-382, 1980.
[3.12] M. Ilegems, “Beryllium doping and diffusion in molecular-beam epitaxy of GaAs and AlxGa1–xAs,” Journal of Applied Physics, vol. 48, pp. 1278-1287, 1977.

[4.1] D. Marcuse, “Reflection loss of laser mode from tilted end mirror,” J. Lightw. Technol., vol. 7, pp. 336-339, 1989.
[4.2] H. P. Fan, “Photocurrent and Electroabsorption spectroscopy for Semiconductor Quantum Well structures,” Master thesis, Inst. of Electro-optical Engineering, SYSU, 2001.
[4.3] A. Niwa, T. Ohtoshi, K. Uomi, and K. Nakahara, “Doping-type dependence of turn-on delay time in 1.3　m GaAsP-InP modulation-doped strained quantum-well lasers,” IEEE Photon. Technol. Lett., vol. 8, pp. 328- 330, 1996.
[4.4] V. D. Kulakovskii, E. Lach, and A. Forchel, “Band-gap renormalization and band-filling effects in a homogeneous electron-hole plasma in In0.53Ga0.47As/InP single quantum wells,” Phys. Rev. B, vol. 40, pp. 8087-8090, 1989.
[4.5] P. Bhattacharya, Semiconductor Optoelectronic Devices (2nd, Prentice-Hall, New Jersey, 1994), pp.175.
[4.6] (Website of nextnano3: http://www.wsi.tum.de/nextnano3/index.htm)
[4.7] G. Park, O. B. Shchekin, and D. G. Deppe, “Temperature dependence of gain saturation in multilevel quantum dotlasers,” IEEE J. Quantum Electron., vol. 36, pp. 1065-1071, 2000.
[4.8] E. Kapon, D.M. Hwang and R. Bhat, “Stimulated emission in semiconductor quantum wire heterostructures,” Phys. Rev. Lett. vol. 63, pp. 430-433, 1989.
[4.9] U. Bockelmann, and G. Bastard, “Phonon scattering and energy relaxation in two-, one-, and zero-dimensional electron gases,” Phys. Rev. B, vol. 42, pp. 8947-8951, 1990.
[4.10] R. Heitz, M. Veit, N. N. Ledentsov, A. Hoffman, D. Bimberg, V. M. Ustinov, P. S. Kop’ev, and Zh. I. Alferov, “Energy relaxation by multiphonon processes in InAs/GaAs quantum dots,” Phys. Rev. B, vol. 56, pp. 10435-10445, 1997.

[5.1] D. A. B. Miller, D. S. Chemla, T. C. Damen, A. C. Gossard, W. Wiegmann, T. H. Wood and C. A. Burrus, “Electric field dependence of optical absorption near the band gap of quantum-well structures,” Phys. Rev. B, vol. 32 , pp. 1043-1060, 1985.
[5.2] P. Bhattacharya, Semiconductor Optoelectronic Devices (2nd, Prentice-Hall, New Jersey, 1994), pp. 120-140.
[5.3] C. H. Henry, R. A. Logan and K. A. Bertness, “Spectral dependence of the change in refractive index due

[6.1] L. B. Soldano and E. C. M. Pennings, “Optical multi-mode interference devices based on self-imaging: principles and applications,” J. Lightwave Technol., vol. 13, no. 4, pp. 615-627, 1995.
[6.2] D. G. Rabus, M. Hamacher, U. Troppenz, and H. Heidrich, “Optical filters based on ring resonators with integrated semiconductor optical amplifiers in GaInAsP-InP,” IEEE J. Sel. Topics Quantum Electron., vol. 8, pp. 1405-1411, 2002.
[6.3] G. Lenz and C. K. Madsen, “General optical all-pass filter structures for dispersion control in WDM systems,” J. Lightwave Technol., vol. 17, pp. 1248-1254, 1999.
[6.4] S. Suzuki, K. Oda, and Y. Hibino, “Integrated-optic double-ring resonators with a wide free spectral range of 100 GHz,” J. Lightwave Technol., vol. 13, pp. 1766-1770, 1995.
[6.5] S. Matsuo, Y. Yoshikuni, T. Segawa, Y. Ohiso, and H. Okamoto, “A widely tunable optical filter using ladder-type structure,” IEEE Photon. Technol. Lett., vol. 15, pp. 1114-1116, 2003.
[6.6] V. M. Menon, W. Tong, C. Li, F. Xia, I. Glesk, P. R. Prucnal, and S. R. Forrest, “All-optical wavelength conversion using a regrowth-free monolithically integrated Sagnac interferometer,” IEEE Photon. Technol. Lett., vol. 15, pp. 254-256, 2003.
[6.7] M. G. Kane, I. Glesk, J. P. Sokoloff, and P. R. Prucnal, “Asymmetric optical loop mirror: analysis of an all-optical switch,” Appl. Opt., vol. 33, pp. 6833-6842, 1994.
[6.8] D. B. Mortimore, “Fiber loop reflectors,” J. Lightwave Technol., vol. 6, pp. 1217-1224, 1988.
[6.9] M. Bachmann, P. A. Besse, and H. Melchior, “Overlapping-image multimode interference couplers with a reduced number of self-images for uniform and nonuniform power splitting,” Appl. Opt., vol. 34, pp. 6898-6910, 1995.
[6.10] J. Leuthold and C. H. Joyner, “Multimode interference couplers with tunable power splitting ratios,” J. Lightwave Technol., vol. 19, pp. 700-707, 2001.
[6.11] P. A. Besse, E. Gini, M. Bachmann, and H. Melchior. “New 2x2 and 1x3 Multimode Interference Couplers with Free Selection of Power Splitting Ratios,” J. Lightwave Technol., vol. 14, pp. 2286-2293, 1996.
[6.12] N. S. Lagali, M. R. Paiam, and R. I. MacDonald, “Theory of variable-ratio power splitters using multimode interference couplers,” IEEE Photonics Technol. Lett. vol. 11, pp. 665-667, 1999.
[6.13] H. Ohe, H. Shimizu, and Y. Nakano, “InGaAlAs multiple-quantum-well optical phase modulators based on carrier depletion,” IEEE Photon. Technol. Lett., vol. 19, pp. 1816-1818, 2007.
[6.14] Q. Lai, M. Bachmann, W. Hunziker, P. A. Besse, and H. Melchior, “Arbitrary ratio power splitters using angled silica on silicon multimode interference couplers,” Electron. Lett., vol. 32, pp. 1576-1577, 1996.
[6.15] D. S. Levy, Y. M. Li, R. Scarmozzino, and R. M. Osgood Jr. “A multimode interference-based variable power splitter in GaAs-AlGaAs,” IEEE Photon. Technol. Lett., vol. 9, pp. 1373-1375, 1997.
[6.16] T. Saida, A. Himeno, M. Okuno, A. Sugita, and K. Okamoto, “Silica-based 2x2 multimode interference coupler with arbitrary power splitting ratio,” Electron. Lett., vol. 35, pp. 2031-2033, 1999.
[6.17] S. Y. Tseng, C. F. Hernandez, D. Owens, and B. Kippelen, “Variable splitting ratio 2×2 MMI couplers using multimode waveguide holograms,” Opt. Express, vol. 15, pp. 9015-9021, 2007.
[6.18] David J. Y. Feng, P. Y. Chang, T. S. Lay, and T. Y. Chang, “Novel stepped-width design concept for compact multimode-interference couplers with low cross-coupling ratio,” IEEE Photon. Technol. Lett., vol. 19, pp. 224-226, 2007.
[6.19] David J. Y. Feng, T. S. Lay, and T. Y. Chang, “Waveguide couplers with new power splitting ratios made possible by cascading of short multimode interference sections,” Opt. Express, vol. 15, pp. 1588-1593, 2007.
[6.20] C. J. Kaalund and Z. Jin, “Novel multimode interference devices for low index contrast materials systems featuring deeply etched air trenches,” Opt. Commun., vol. 250, pp. 292-296, 2005.
[6.21] A. S. Sudbo, “Film mode matching: a versatile numerical method for vector mode field calculations in dielectric waveguides,” Pure App. Opt., vol. 2, pp. 211-233, 1993.
[6.22] S. Sudbo, “Improved formulation of the film mode matching method for mode field calculations in dielectric waveguides,” Pure App. Opt., vol. 3, pp. 381-388, 1994.
[6.23] FimmProp, version 4.3, Photon Design, Oxford, U.K., 2004.
[6.24] BeamPROP, version 5.1, RSoft Inc., NY, 2005.
[6.25] R. M. Knox and P. P. Toulios, “Integrated circuits for millimiter through optical frequency range,” in Proc. Symp. Submillimiter Waves, J. Fox, Ed., New York,Mar./Apr. 1970, pp. 497-516.
[6.26] M. Bachmann, P. A. Besse, and H. Melchior, “General self-imaging properties in NxN multimode interference couplers including phase relations,” Appl. Opt., vol. 33, pp. 3950-3911, 1994.

[A1] W. A. Harrison, “Elementary theory of heterojunctions,” J. Vac. Sci. Technol., vol. 14, pp. 1016-1021, 1977.
[A2] I. Vurgaftman, J. R. Meyer, and L. R. Ram-Mohan, “Band parameters for III-V compound semiconductors and their alloys,” J. Appl. Phys., vol. 89, pp. 5815-5875, 2001.
[A3] S. L. Chuang, Physics of Optoelectronic Devices (Wiley, New York, 1995).
[A4] D. Olego, T. Y. Chang, E. Silberg, E. A. Caridi, and A. Pinczuk, “Compositional dependence of band-gap energy and conduction-band effective mass of In1-x-yGaxAlyAs lattice matched to InP,” Appl. Phys. Lett., vol. 41, pp. 476-478, 1982.
[A5] X. H. Zhang, S. J. Chua, S. J. Xu, and W. J. Fan, “Band offsets at the InAlGaAs/InAlAs (001) heterostructures lattice matched to an InP substrate,” J. Appl. Phys., vol. 83, pp. 5852- 5854, 1998.
[A6] J. Bohrer, A. Krost, and D. B. Bimnerg, “Composition dependence of band gap and type of lineup in In1-x-yGaxAlyAs/InP heterostructures,” Appl. Phys. Lett., vol. 63, pp.1918-1920, 1993.

[D1] W. Y. Choi, "MBE-Grown Long Wavelength InGaAlAs/InP Laser Diodes," Ph.D thesis, Dept. of Electrical Engineering and Computer Science., MIT, 1994.

[E1] T. L. Koch and U. Koren, “Semiconductor Photonic Integrated Circuits,” IEEE J. Quantum Electron., vol. 27, pp. 641- 653, 1991.
[E2] E. J. Skogen, J. S. Barton, S. P. Denbaars and L. A. Coldren, “A quantum-well-intermixing process for wavelength-agile photonic integrated circuits,” IEEE J. Sel. Topics. Quantum Electron., vol. 8, pp. 863- 869, 2002.
[E3] V. Jayaraman, Z. Chuang, and L. Coldren, “Theory, design, and performance of extended tuning range semiconductor lasers with sampled gratings,” IEEE J. Quantum Electron., vol. 29, pp. 1824–1834, June 1993.
[E4] H. Ishii, H. Tanobe, F. Kano, Y. Tohmori, Y. Kondo, and Y. Yoshikuni, “Quasicontinuous wavelength tuning in super-structure-grating (SSG) DBR lasers,” IEEE J. Quantum Electron., vol. 32, pp. 433–441, Mar. 1996.
[E5] I. Avrutsky, D. Ellis, A. Tager, H. Anis, and J. Xu, “Design of widely tunable semiconductor lasers and the concept of binary superimposed gratings (BSG’s),” IEEE J. Quantum Electron., vol. 34, pp. 729–741, Apr. 1998.
[E6] N. Holonyak, Jr., “Impurity-induced layer disordering of quantum-well heterostructures: Discovery and prospects,” IEEE J. Select. Topics Quantum Electron., vol. 4, pp. 584–594, July-Aug. 1998.
[E7] S. K. Si, D. H. Yeo, K. H. Yoon, and S. J. Kim, “Area selectivity of InGaAsP–InP multiquantum–well intermixing by impurity-free vacancy diffusion,” IEEE J. Select. Topics Quantum Electron., vol. 4, pp. 619–623, July-Aug. 1998.
[E8] A. McKee, C. McLean, G. Lullo, A. Bryce, R. De La Rue, J. Marsh, and C. Button, “Monolithic integration in InGaAs–InGaAsP multiple-quantum-well structures using laser intermixing,” IEEE J. Quantum Electron., vol. 33, pp. 45–55, Jan. 1997.
[E9] S. Charbonneau, E. Kotels, P. Poole, J. He, G. Aers, J. Haysom, M. Buchanan, Y. Feng, A. Delage, F. Yang, M. Davies, R. Goldberg, P. Piva, and I. Mitchell, “Photonic integrated circuits fabricated using ion implantation,” IEEE J. Select. Topics Quantum Electron., vol. 4, pp. 772–793, July-Aug. 1998.
[E10] D. Deppe and N. Holonyak, Jr., “Atom diffusion and impurity-induced layer disordering in quantum well III–V semiconductor heterostructures,” J. Appl. Phys., vol. 64, pp. 93–113, 1988.
[E11] B. Qui, A. Bryce, R. De La Rue, and J. Marsh, “Monolithic integration in InGaAs–InGaAsP multiquantum-well structure using laser processing,” IEEE Photon. Technol. Lett., vol. 10, pp. 769–771, June 1998.
[E12] S. McDougall, O. Kowalski, C. Hamilton, F. Camacho, B. Qiu, M. Ke, R. De La Rue, A. Bryce, and J. Marsh, “Monolithic integration via a universal damage enhanced quantum-well intermixing technique,” IEEE J. Select. Topics Quantum Electron., vol. 4, pp. 636–646, July-Aug. 1998.
[E13] M. Paquette, J. Beauvais, J. Beerens, P. Poole, S. Charbonneau, C. Miner, and C. Blaauw, “Blueshifting of InGaAsP/InP laser diodes by low-energy ion implantation,” Appl. Phys. Lett., vol. 71, pp. 3749–3751, 1997.