IEEE JOURNAL OF QUANTUM ELECTRONICS, VOL. 45, NO. 12, DECEMBER /$ IEEE

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1 IEEE JOURNAL OF QUANTUM ELECTRONICS, VOL. 45, NO. 12, DECEMBER Mode Analysis for Equilateral-Triangle-Resonator Microlasers with Metal Confinement Layers Yue-De Yang, Yong-Zhen Huang, Senior Member, IEEE, and Shi-Jiang Wang Abstract Mode characteristics are analyzed for electrically injected equilateral-triangle-resonator (ETR) semiconductor microlasers, which are laterally confined by insulating barrier SiO 2 and electrode metals Ti-Au. For the ETR without metal layers, the totally confined mode field patterns are derived based on the reflection phase shifts, and the -factors are calculated from the farfield emission of the analytical near field distribution, which are agreement very well with the numerical results of the finite-difference time-domain (FDTD) simulation. The polarization dependence reflections for light rays incident on semiconductor-sio 2 -Ti-Au multi-layer structures are accounted in considering the confinement of TE and TM modes in the ETR with the metal layers. The reflectivity will greatly reduce with a Ti layer between SiO 2 and Au for light rays with incident angle less than 30 especially for the TE mode, even the thickness of the Ti layer is only 10 nm. If the ETR is laterally confined by SiO 2 -Au layers without the Ti layer, the Fabry Pérot type modes with an incident angle of zero on one side of the ETR can also have high -factor. The FDTD simulation for the ETR confined by metal layers verifies the above analysis based on multi-layer reflections. The output spectra with mode intervals of whispering-gallery modes and Fabry Pérot type modes are observed from different ETR lasers with side length of 10 m, respectively. Index Terms Equilateral triangle resonator (ETR), microcavities, microlasers, semiconductor lasers. I. INTRODUCTION OPTICAL microcavities with total internal reflection (TIR) confined modes are suitable to realize ultralow-threshold microlasers. Various microcavities were considered, such as disks [1], [2], rings [3], triangles [4] [6], squares [6] [9], and hexagons [10]. However, the total internal reflection limits the direction emission of the microcavity lasers. Asymmetrical structures in the disk and deformed chaotic resonators were usually applied to realize directional emission microdisk lasers [11], [12]. The equilateral-triangle-resonator (ETR) can realize directional emission by connecting an output waveguide to one of the vertices of the ETR [13]. The ETR semiconductor lasers were fabricated with the cavity cleaved from the wafer grown on (111) direction substrate [14], [15]. Furthermore, triangular-facet laser with an output waveguide Manuscript received July 01, 2008; revised May 08, Current version published November 06, This work was supported by the National Nature Science Foundation of China under Grant , Grant , and Grant , and the Major State Basic Research Program under Grant 2006CB The authors are with the State Key Laboratory on Integrated Optoelectronics, Institute of Semiconductors, Chinese Academy of Sciences, Beijing , China ( yzhuang@red.semi.ac.cn). Digital Object Identifier /JQE was grown by selective area metal organic chemical vapor deposition on (111)B GaAs substrate [16]. Recently, electrically injected InP/GaInAsP ETR microlasers were fabricated from common laser wafer grown on (001) substrate by standard photolithography and inductively-coupled-plasma etching technique [4], [5]. Analytical mode field distributions and mode wavelengths were derived for the perfect ETR surrounded by low index medium, such as air [17], [18]. In addition, mode characteristics were analyzed for the ETR under perfectly confined approximation [15] and more complete boundary conditions of the reflection phase shift of the mode light rays [19]. To obtain the evanescent field distributions in the external regions of the ETRs analytically, we applied some approximate conditions in deriving the analyzed solutions [17], [18]. In this paper, the mode distributions inside the ETR are derived under strict boundary condition for the ETR, and the mode -factors are calculated from far-field emission based on the analytical field distributions. More exact mode wavelengths and mode -factors are obtained than that in Refs. [17], [18], especially for high order transverse modes. Furthermore, the modes confined in the ETR surrounded laterally by insulating barrier and electrode metals are considered with the polarization dependence reflections of multi-layer structures consisted of semiconductor, SiO and electrode metals Ti and Au. The results show that the Ti layer will greatly reduce the mode -factors, especially for the transverse electric (TE) modes. But the ETR laterally confined by SiO and the only metal layer of Au can support high order transverse modes, which are not limited by the critical angle of total international reflection of the semiconductor-air interface. Finite-difference time-domain (FDTD) simulations for the ETR with an output waveguide connected to one of the vertices show that the modes with weak distribution at the vertex can keep high -factors. Two group modes with mode intervals of whispering-gallery type modes and Fabry Pérot type modes are high confined modes, which are verified by the output spectra of the fabricated ETR lasers. II. CONFINED MODE FIELD IN EQUILATERAL TRIANGLE RESONATOR In the two-dimensional (2-D) ETR, the Maxwell s equations lead to separated problems for transverse magnetic (TM) and TE modes. The TM and TE modes have the non-zero electromagnetic components and, respectively. For the ETR with refractive index of surrounded by air, a plane wave parallel to the sides of the ETR will experience total internal reflection on the boundaries of the ETR. Through the image operation, the origin ETR, and the image /$ IEEE

2 1530 IEEE JOURNAL OF QUANTUM ELECTRONICS, VOL. 45, NO. 12, DECEMBER 2009 Fig. 1. The unfolded plane wave and the corresponding cavity are presented for the ETR with one-period light ray inside the resonator, which are shown in the upper right side. regions form a waveguide with width of as shown in Fig. 1, where is the side length of the ETR, and and are unfolded plane waves. The total reflection of the plane wave on the boundary between the different regions is equivalent to transmitting into the next image region with a phase shift of, where is the incident angle and satisfies for the total internal reflection. The boundary conditions of the Maxwell s equations will yield a unity reflection coefficient with the phase shift : with and for TM and TE modes, respectively, where the value of is in the range from 0 to. In Fig. 1, a plane wave is supposed to emerge from side AB of the origin region, and then transmits through the image regions in the sequence,,, etc. Finally, the plane wave emerges from side AB of region with the same angle in, thus region is equivalent to the origin region, and the ETR can be modeled as a cavity with the width of and the one-period length of. Assuming is the electric field for the TM mode or the magnetic field for the TE mode, we have the following wave equation: where the free space wave number is, and is the mode wavelength. The mode field inside the waveguide propagating along the direction is composed of two plane waves with field distributions of and, where the angle is angle between the two plane waves and -axis, and the time-dependence factor is omitted. The angles between the plane wave and sides BC, CA and AB of origin region are, and, respectively. Due to the symmetry of the ETR, we also can choose the sides CA or AB as the -axis, thus angles between plane wave and the axis equal to, and are corresponding to the same mode. The incident angles of the plane waves on the three sides of the ETR, and are expressed by as (1) (2) (3) The angle is set in the range from 0 to 30 to avoid repeated calculation in the following discussions. All of the incident angles should be larger than the critical angle for total internal reflection, thus should satisfies. Considering the phase shifts on the boundaries inside the equivalent cavity, we can express the field distributions for the plane waves and as where and are the phase shifts of the plane waves and in, respectively, and satisfy (4) (5) When and satisfy (6), the reflections of the plane waves on the boundaries inside the cavity satisfy the Maxwell s equations. In addition, according to the boundary conditions at the and planes, the field distributions of the plane waves satisfy Based on (4) (8), we obtain where and are integers. From (9) and (10), we obtain Let, then we have (6) (7) (8) (9) (10) (11) (12)

3 YANG et al.: MODE ANALYSIS FOR EQUILATERAL-TRIANGLE-RESONATOR MICROLASERS WITH METAL CONFINEMENT LAYERS 1531 where, is the transverse mode number. The fields in must be in phase with the fields in to produce a consistent solution, thus From (6), (13) and (14), we obtain then (13) (14) (15) (16) where is the longitudinal mode number. The modes in the ETR are marked as and for the TM and TE modes, respectively. From (1), (3), (12), and (16), we can obtain the mode wavelength and the angle for different modes. The above technique only suits the geometry that can be mapped into a slab waveguide, such as isosceles right triangle and rectangle besides the ETR. In our previous work [17], [18], the perfectly confined approximation was used for the transverse wavefunction, but the approximation is not good for the high order transverse modes. The real field distribution in the ETR at can be obtained as a sum of the fields in the six image points, where (17) for even and odd transverse mode number [18]., respectively, in III. -FACTOR CALCULATED BY FAR-FIELD EMISSION OF ANALYZED FIELD The above analytical field distributions satisfy Maxwell s equations in the ETR except three special corner points, so the analytical solutions provide sufficiently precise mode field distributions in the inner region of the ETR. Based on the analytical field distributions, we can calculate mode -factors for the ETR by far-field emission and compare the results with those obtained by FDTD simulation [20], [21]. The far field based on near field at the sides of the ETR can be expressed as (22) where the time-dependence factor is omitted, represents the electric field and magnetic field for the TM and TE modes, respectively, and (23) where is the unit vector of the position vector, in the external region of the ETR for describing the far field, is the position vector for expressing the near field distribution at the sides of the ETR, the integral is along the perimeter of the ETR, is the unit normal vector of the sides, and. The power emitting from the ETR averaged in one cycle can be calculated by (24) (18) The field distributions of (17) can be combined into even and odd modes relative to the axis as: (19) (20) The new distributions have definite symmetry relative to the -axis. The superscripts and indicate even and odd symmetry modes, respectively. In addition, if and have different parities, we have the following equation based on (4) (6), (12) and (16): (21) where, 2, 3. Thus, (17) leads to a trivial solution for all when and have different parities. The mode numbers used in this paper are the same as [17]. But one period of the cavity was taken as and the longitudinal mode number was replaced by and where for the TM modes and for the TE modes, respectively, and is the power angular spectrum. We can also calculate the energy W stored in the ETR by (25) where for the TM modes and for the TE modes, and represents the refractive index distribution. Finally, based on the emitted power and the stored energy, the analytical quality factor can be calculated by (26) where is the mode angular frequency. In the following numerical calculations, the refractive index of the ETR is set as 3.2, which is close to mode index of semiconductor laser wafer. The mode -factors obtained from (26) based on analytical field distributions are plotted in Fig. 2 as solid and open squares, respectively, for even and odd modes of

4 1532 IEEE JOURNAL OF QUANTUM ELECTRONICS, VOL. 45, NO. 12, DECEMBER 2009 Fig. 3. Schematic diagram of the reflection of plane wave on a multi-layer boundary. Fig. 2. Mode Q-factors versus longitudinal mode number for (a) TM modes and (b) TE modes in an ETR with side length of 10 m. Solid and open squares are Q-factors of the even and odd states, respectively, obtained by far-field emission based on analytical near-field pattern. Solid and open circles are Q-factors of the even and odd states, respectively, obtained by the FDTD simulation. the fundamental and the first order transverse modes. The degenerate modes with longitudinal mode numbers and have the same -factors, and the accidentally degenerate modes with have different -factors, where is an integer. The variations of -factors verify the symmetry analysis for the modes in the ETRs [18]. The mode -factors calculated by the FDTD simulations are also plotted in Fig. 2 as solid and open circle for even and odd states, respectively. The analysis solution of -factors agrees very well with the FDTD results, especially for TM modes, the differences of -factors obtained by two methods are less than 10%. For the TM modes with, both the analytical model and FDTD simulation show that the -factors of odd modes are larger than those of even modes, but the phenomenon is not observed for TE modes. The results show that the far-field emission based on the analytical field distribution is suitable for estimating mode -factors. The -factors of TE modes obtained by the FDTD technique oscillate greatly [18] when the longitudinal mode numbers are small, because the symmetries of the cavities should have great influence on the -factors [22]. However, we find that the oscillation is not distinct for the modes with large longitudinal mode numbers in the ETR with side length of 10 m. The numerical results show that the -factors usually increase with the increase of the longitudinal mode numbers. In [17], the analytical results of mode wavelengths of and modes in the ETR with side length of 5 m are m and m, respectively, and the mode wavelengths obtained from the FDTD technique are m and m, respectively. The mode wavelength differences between the analytical and the FDTD results are 0.45% and 0.77% for the and, respectively. The mode wavelengths of and modes obtained from (1), (3), (12) and (16) are m and m, which are only 0.26% smaller than the FDTD results. The mode wavelength differences are almost the same for the fundamental and second order modes, and the differences are ascribed to that the true size of the ETR is not exactly equal to 5 m in the FDTD simulation due to the step cell. IV. EFFECT OF METAL LAYERS ON MODE CONFINEMENT In the usual ETR surrounded by air, the mode plane waves will not be totally confined if one of the incident angles is less than the critical angle of total internal reflection. So only the modes with plane waves that satisfy total internal reflection condition should be considered, but the electrically injected ETR lasers are not surrounded by air. The ETR lasers are fabricated under the following process [5]. First, a SiO layer was deposited on the laser wafer. The laser patterns were transferred onto the SiO layer using standard photolithography and ICP etching techniques, and then the pattern SiO was used as a hard mask for another ICP etching process to etch InP/InGaAsP. After the residual SiO hard masks were removed using diluted HF solution, a SiO insulating layer was deposited over the laser wafer and a contact window was opened on the SiO at the top of each resonator pattern using wet etching process. Then Ti Au p-contact is deposited over the laser wafer, including the side walls of the ETR laser. Thus, a complicated boundary condition should be considered. We consider an ETR with an insulator layer, a titanium layer and a gold layer between the semiconductor material and air. The insulator used in the calculation is silica with a refractive index of 1.45, and the refractive indexes of titanium and gold are and, respectively [23]. The schematic diagram of the multi-layer structure is shown in Fig. 3, the reflection factor can be calculated from the boundary conditions of the Maxwell s equations, where and are the reflected and incident amplitudes.

5 YANG et al.: MODE ANALYSIS FOR EQUILATERAL-TRIANGLE-RESONATOR MICROLASERS WITH METAL CONFINEMENT LAYERS 1533 Fig. 5. The phase shifts of TM and TE plane waves on the multi-layer boundary with d =0. Fig. 4. The power reflectivity of (a) TM and (b) TE plane waves on the multilayer boundary with different d versus the incident angle. In the following calculation, the thicknesses of the insulator and gold layers are taken to be 0.4 m and 0.2 m, respectively. The power reflectivity of the multi-layer boundary with different thicknesses of titanium layers is shown in Fig. 4 for (a) TM and (b) TE plane waves. With the increase of the thickness of the titanium layer, the power reflectivity R of the plane wave with incident angle less than 30 decreases rapidly, which results in a decrease of the factors for the modes in the ETR. When m, the power reflectivity of TM plane waves at 30 is greater than 95%, but that of TE plane waves is less than 60%. The TE modes with the incident angles near 28, which is close to the Brewster angle of the semiconductor-insulator interface, will be suppressed by the absorption of titanium layer. When the thickness of titanium layer is 0, we find that the reflectivity is close to 1 for all incident angles in the range between 0 and 90. The phase shifts of TM and TE plane waves on the boundary are shown in Fig. 5. The discontinuity of the phase shifts is due to the range of the phase shifts is taken from 0to. Assuming, the analytical field distribution can be obtained similar to the ETR without the metal layer, and the angle is not limited by the critical angle. In the ETR with gold confinement layer, high order transverse modes should be considered. In Fig. 6, the distributions of analytical electric field are plotted for TM modes in the ETR with the side length of 10 m for (a), (b), (c), (d), (e), and (f). The TM modes are marked as, and the superscripts and indicate even and odd symmetry modes relative to the middle plane of the ETR, respectively. The angles for, and are 1.6, 15.5 and 29.1, and the corresponding mode wavelengths are m, m, and m, respectively. The field patterns of and have a weak distribution in the upper vertex. As a general result, we find that the modes with or 30 have weak distributions in the vertices. An output waveguide jointed at the place with weak mode field distribution will not bring a large loss. Thus, the ETR with an output waveguide jointed at the vertex can result in a directional emission for these modes that have weak distributions in the vertex. The modes with are corresponding to the low order transverse modes, these whispering-gallery modes exist in the ETR without metal confinement layer with one period of, and the mode wavelength interval is where is the group index. The modes with are the same modes with due to the symmetry of the ETR, which are corresponding to the Fabry Pérot type modes transmit in the direction of the ETR and can not be confined in the ETR without the metal confinement layer. The Fabry Pérot type modes are equivalent to the modes in a Fabry Pérot cavity with cavity length of, and the mode wavelength interval is. Furthermore, because the longitudinal mode number and transverse mode number should have same parity derived from (21), the mode wavelength intervals for the fundamental transverse mode are the twice of the above value. So the mode intervals for the whispering-gallery modes and the Fabry Pérot type modes are V. INFLUENCE OF OUTPUT WAVEGUIDE (27) (28) For the modes with weak field distribution in one of the vertices, an output waveguide jointed at the vertex can keep high -factors and result in a directional emission [13]. We expect that both the modes with and 30 can have high -factors due to the small loss induced by the output waveguide. However, for the ETR with the output waveguide, the mode field

6 1534 IEEE JOURNAL OF QUANTUM ELECTRONICS, VOL. 45, NO. 12, DECEMBER 2009 Fig. 6. The distributions of analytical electric field E for the modes (a) TM, (b) TM, (c) TM, (d) TM, (e) TM, and (f) TM in the ETR with the side length of 10 m. characteristics can not be obtained by the analytical model, thus numerical simulation is needed. The FDTD technique is used to simulate the mode characteristics for the ETR with the output waveguide [21]. A uniform mesh with the cell size of 20 nm, a time step of the Courant lime, and PML absorbing layer are used in the simulation. A 10- m-side ETR laterally confined by SiO -Ti-Au multilayer structures with a 1- m width output waveguide is simulated with the thicknesses of the SiO layer and the gold layers are taken to be 0.4 m and 0.2 m. In Fig. 7, the intensity spectra obtained by the FDTD simulation and Padé approximation [24] are plotted as dashed lines for TM modes as the titanium layer thickness is (a) and (b) m. Low modes do not appear in the spectra, because the fields of low modes vanish quickly in the long time FDTD simulation. The intensity spectrum for the ETR without metal confinement layer is plotted as solid line and compared with the intensity spectra for the ETR with the multi-layer boundary. Only the modes with transverse mode numbers 0 and 1 appear in the spectrum of the ETR without the metal confinement layer, because the -factors of the high order transverse modes are below The -factor of the fundamental transverse mode in the ETR without metal confinement layer is In the ETR with, high order transverse modes also can be confined because of the high power reflectivity of the gold layer. The output waveguide results in a selection of the modes, so only the modes with a weak distribution in the vertex connected to the output waveguide can Fig. 7. Intensity spectra for the TM modes in the ETR without the metal layers are plotted as the solid lines, and those in the ETR with the metal layers at (a) d =0and (b) d =0:02 m are plotted as the dashed lines. keep high factors. Thus, new modes occur in the intensity spectra for the ETR with in Fig. 6(a), such as and. The mode wavelengths of and are m and m, which are 0.3% and 0.1% larger than the analytical wavelengths, respectively. The -factors of and in Fig. 7(a) are 3900 and 3200, respectively. The Fabry Pérot type modes do not occur in Fig. 7(b), because the reflectivity of the TM plane wave at normal incidence is less than 0.8 when m, thus the -factors of those modes are very low. Because of the absorption of the titanium layer, the -factor of is decrease to In Fig. 8, the field patterns of electric field obtained by the FDTD simulation are plotted for the odd states of and in the ETR with the 1- m-width output waveguide and, which are agreement very well with those obtained by analytical model in Fig. 6(b) and (f). The analytical model only give the field distributions inside the ETR, but the field distributions obtained from FDTD simulation have a large distribution in the insulator layer. The intensity spectra obtained from the FDTD simulation for TE modes in the 10- m-side ETR with 1- m width outputwaveguide are plotted in Fig. 9 as the solid and the dashed lines for the ETR without the metal layers and with only the gold layer, respectively. The -factor of for the ETR without metal confinement layer is Similar to TM mode, high order transverse modes also can be confined in the ETR with. New modes occur in the intensity spectra. The -factors of and for the ETR with only gold layer are 4400 and 3200, respectively. As m, the TE

7 YANG et al.: MODE ANALYSIS FOR EQUILATERAL-TRIANGLE-RESONATOR MICROLASERS WITH METAL CONFINEMENT LAYERS 1535 Fig m. Output spectra of two InP-InGaAsP ETR lasers with side length of Fig. 8. Field pattern of the electric field component E for the odd state of (a) TM and (b) TM obtained by FDTD simulation. Fig. 9. Intensity spectra for the TE modes in the ETR without metal layers and with only the gold layer at d =0obtained by FDTD simulation are plotted as solid and dashed lines, respectively. modes have very low -factors because of the low reflectivity for the TE modes as the incident angle. So we do not present the intensity spectrum for the ETR with m. The above discussions are 2-D simulations, the vertical loss is not considered in the simulations. Based on 3-D simulations, we found that the vertical radiation loss of the TM modes in the microcavities is much smaller than that of the TE modes [25], and the TE modes can also have low vertical radiation loss in the semiconductor microcylinder with the radius is larger than 5 m. VI. COMPARISON WITH OUTPUT SPECTRA OF ETR LASER Electrically injected InP-InGaAsP ETR lasers were fabricated using standard photolithography and inductively coupled-plasma etching techniques with the side length from 10 to 30 m [4], [5]. The ETR lasers have a 2-μm-wide output waveguide connected to one of the vertices of the ETR. The output spectra of the ETR lasers are measured at room temperature with continuously injected current. In Fig. 10, the output spectra of two different 10- m-side ETR lasers are plotted as the solid and dashed lines at the injection current of 30 and 5 ma, respectively, which have distinct peaks. We can expect that the wavelength intervals of the observed distinct peaks are approximately equal to the longitudinal mode interval. The solid curve shows a lasing mode at wavelength of nm, which is nearly at the valley of the amplified spontaneous emission spectrum. In fact, each peak consists of multiple transverse modes. Furthermore, the fundamental transverse modes may be not in the peak positions of the spectrum, because the higher order transverse modes can have high output coupling efficiency. The wavelength intervals of the peaks in the spectra are quite different for the two ETR lasers. The obtained wavelength intervals of the peaks are 35.9 and 60.7 nm for the solid and dashed lines at the wavelengths of 1500 and 1530 nm, respectively. Fitting the mode wavelength intervals 35.9 and 60.7 nm with (27) and (28), respectively, we obtain the mode group index (2.57) and 7.24 (4.45) for the solid (dashed) curve. Mode group indexes 4.18 and 4.45 are reasonable values. So we conclude that the solid line is the whispering-gallery modes and the dashed line is the Fabry Pérot type modes. VII. CONCLUSION We have analyzed the mode characteristics for the ETR microlaser based on the reflection phase shift of plane waves on the boundaries of the ETR. The analytical results of mode wavelengths and -factors agree well with those calculated by FDTD simulation. For the electrically injected ETR microlaser laterally confined by insulating barrier SiO and electrode metals Ti-Au, the existence of Ti layer will greatly reduce the mode -factors of the confined modes, especially for TE modes. If the side walls of ETR are only covered by SiO -Au layers, the whispering-gallery type and Fabry Pérot type modes can have high -factors and low field distribution at one of the vertices. Due to the low intensity distribution in one of the vertices, we can realize directional emission by connecting an output waveguide to the vertex. The whispering-gallery modes and Fabry Pérot type

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L. Long, R. J. Bell, S. E. Bell, R. R. Bell, R. W. Alexander, Jr., and C. A. Ward, Optical properties of the metals Al, Co, Cu, Au, Fe, Pb, Ni, Pd,Pt, Ag, Ti, and W in the infrared and far infrared, Appl. Opt., vol. 22, p , [24] W. H. Guo, W. J. Li, and Y. Z. Huang, Computation of resonator frequencies and quality factors of cavities by FDTD technique and Padé approximation, IEEE Microw. Wireless Compon. Lett., vol. 11, pp , [25] Y. Z. Huang and Y. D. Yang, Mode coupling and vertical radiation loss for whispering-gallery modes in 3-D microcavities, J. Lightw. Technol., vol. 26, pp , Yue-De Yang was born in Hunan Province, China, in He received the B.Sc. degree in physics from Peking University, Beijing, China, in He is currently working toward the Ph.D. degree at the Institute of Semiconductors, Chinese Academy of Sciences, Beijing, China, and studying the design and fabrication of microcavity lasers and filters. Yong-Zhen Huang (M 95 SM 01) was born in Fujian Province, China, in He received the B.Sc., M.Sc., and Ph.D. degrees in physics from Peking University, Beijing, China, in 1983, 1986, and 1989, respectively. In 1989, he joined the Institute of Semiconductors, Chinese Academy of Sciences, Beijing, China, where he worked on the tunneling time for quantum barriers, asymmetric Fabry Perot cavity light modulators, and VCSELs. In 1994, he was a Visiting Scholar at BT Laboratories, Ipswich, U.K., where he was involved in the fabrication of the 1550-nm InGaAsP VCSEL. Since 1997, he has been a Professor with the Institute of Semiconductors, Chinese Academy of Sciences, where he is also the Director of the Optoelectronic R&D Center. His current research interests include microcavity lasers, semiconductor optical amplifiers, and optical add-drop filters. Shi-Jiang Wang was born in Hainan Province, China, in He received the B.Sc. degree in microelectronics from Peking University, Beijing, China, in He is currently working toward the Ph.D. degree at the Institute of Semiconductors, Chinese Academy of Sciences, Beijing.