A hybrid integrated single-wavelength laser with silicon micro-ring reflector is demonstrated theoretically and
experimentally. It consists of a heterogeneously integrated III-V section for optical gain, an adiabatic taper for light
coupling, and a silicon micro-ring reflector for both wavelength selection and light reflection. Heterogeneous integration
processes for multiple III-V chips bonded to an 8-inch Si wafer have been developed, which is promising for massive
production of hybrid lasers on Si. The III-V layer is introduced on top of a 220-nm thick SOI layer through low-temperature
wafer-boning technology. The optical coupling efficiency of >85% between III-V and Si waveguide has
been achieved. The silicon micro-ring reflector, as the key element of the hybrid laser, is studied, with its maximized
reflectivity of 85.6% demonstrated experimentally. The compact single-wavelength laser enables fully monolithic
integration on silicon wafer for optical communication and optical sensing application.
We demonstrate electrically-pumped III-V quantum-well lasers bonded on SiO2 with a metal-coated etched-mirror. The metal-coated etched-mirror allow the lasers to be used as on-chip laser, but our process design make sure that it requires no additional fabrication step to fabricate the metal-coated etched mirror. The bonded III-V on SiO2 also permits tight laser mode confinement in the active region due to high index contrast between III-V and SiO2. Moreover, it promises a flexible choice of host substrate, in which the silicon substrate could also be replaced with other materials. The laser devices demonstrated have the lowest threshold of 50 mA, a maximum output power of 9 mW and a differential quantum efficiency of 27.6%.
We report a low-temperature (220°C) covalent bonding of InP-based epitaxy substrate to silicon substrate through a thin thermal oxide interlayer of around 20 nm. Our SiO2 interlayer is grown only on the silicon substrate, which avoids the challenge in obtaining high quality SiO2 film on III-V substrate. The 20 nm thin oxide is proved to be sufficient as the outgassing medium during the bonding process. It is found that the bonding has minimal effect on the transferred epitaxy layer. This is evident from the X-ray Diffraction and room temperature photoluminescence (PL) characterizations of the III-V sample before (as-grown) and after bonding, where no significant peak shifting or broadening is observed. The high resolution Transmission Electron Micrograph (HR-TEM) also reveals almost zero-defect atomic bonding between III-V and thermal oxide on silicon.
A new heterogeneously integrated III-V/Si laser structure is reported in this letter, which consists of a III-V
ridge waveguide gain section on silicon, III-V/Si optical vertical interconnect accesses (VIAs) and silicon-oninsulator
(SOI) nanophotonic waveguide sections. The III-V semiconductor layers are introduced on top of the 300
nm thick SOI layer through low temperature, plasma assisted direct wafer-bonding and etched to form III-V ridge
waveguide on silicon as the gain section. The optical VIA is formed by tapering the III-V and the beneath SOI in
the same direction with a length of 50 μm for efficient coupling of light down to the 600 nm wide silicon
nanophotonic waveguide or vice versa. Fabrication details and specification characterizations of this heterogeneous
III-V/Si Fabry–Pérot (FP) laser are given. The fabricated FP laser shows a continuous-wave lasing with a threshold
current of 65 mA at room temperature and the slope efficiency from single facet is 144 mW/A. The maximal single
facet emitting power is about 4.5 mW at a current of 100 mA and the side-mode suppression ratio is ~30 dB. This
new heterogeneously integrated III-V/Si laser structure demonstrated enables more complex laser configuration
with a sub-system on-chip for various applications.
Optically-pumped microsquare cavity laser on InP-based multiple-quantum-wells (MQW) material platform is demonstrated. Continuous wave operation is achieved for microsquare cavity with footprint as small as 4×4μm2. Numerical mode analysis and experimental characterization of the microsquare laser are conducted, and the results are compared with the commonly used microdisk cavity laser fabricated on the same platform. The microsquare laser shows a lower lasing threshold and infers a higher differential efficiency than the microdisk counterpart. The microsquare cavity laser has sufficiently high quality factor, and higher pumping injection efficiency due to the more evenly distributed field profile as compared to that of the microdisk. Experimental result also shows that the microsquare laser has better temperature stability than the microdisk. These results promise a potential alternative laser structure for onchip light source applications.
An ultrasmall plasmonic coaxial laser made of metal–semiconductor–metal on a silicon substrate through an interlayer bonding was designed. From the effective refractive indices and the transparent material gain, the nanoscale structural dimensions with both the radius and the width at 80 nm for the coaxial plasmonic waveguide were decided. The influence of the interlayer bonding material on the optimization of resonant wavelength and Q-factor was evaluated. A three-dimensional body-of-revolution finite-difference time-domain method was used to show that a coaxial cavity with a SiO 2 interlayer can laze at around 1480-nm wavelength with a net optical threshold power density of about 800 W/cm 2 and a subwavelength mode volume of 0.014(λ/2n) 3 . This nanolaser on silicon platform will benefit those working on nanophotonic integrated circuits.
We presented the design of metallic-semiconductor nanolasers based on ring configuration lasing at around 1450 nm wavelength. The design and simulation of the nanolaser are done with 3D body-of-revolution (BOR) finite-differencetime- domain (FDTD) simulator based on a multi-level multi-electron system. Both passive cavity optimization and active laser simulation are carried out. New results are reported, but to be more comprehensive we also review some of our previous results. For the smallest design, which corresponds to one resonance order in the cavity, the total footprint of the nanolaser is only about 0.038 μm2, and the physical device volume and the mode volume are only about 1.1(λ/2n)3 and 0.001(λ/2n)3, respectively, where n is the average index of the gain material. This device by us is the smallest reported to date, to the best of our knowledge. We also design for higher resonance orders that have larger dimensions and better fabrication feasibility, as well as taking into consideration the fabrication tolerances. All these are presented in the paper.
As the basic building block for photonic device integration, silicon nanophotonic waveguide requires low-loss
propagation for high-performance ultra-compact photonic device. We experimentally study SiO2 grown by two different
methods (thermal oxidation and PECVD) as hard masks for Si nano-waveguides fabrication and study their effects on
propagation loss. It was found that the denser and smoother quality of thermally grown SiO2 will increase the etch
selectivity of Si and reduce the line-edge roughness transferred to the Si nanowaveguide sidewall, hence giving a lower
loss compared to having PECVD SiO2 hard mask. With thermally grown SiO2 as hard mask, the Si nano-waveguides
loss can have a loss reduction as high as 5.5 times for a 650 nm wide nanowaveguide. Using thermally grown SiO2 as
hard mask will allow the Si nano-waveguide to have as low a propagation loss as direct resist mask and enable III-V
semiconductor on silicon via bonding for multifunctional photonic system on chip.
A new design of vertical coupler (VC) based on only a single mesa is presented. The newly proposed vertical coupler
has the potential of improving the fabrication yield, as it requires much simpler fabrication process. The vertical coupler
comprises a large underlying rib waveguide to which light is coupled. The lower waveguide is formed by the loading
effect provided by the smaller upper ridge waveguide. The upper ridge waveguide contains the actual device (e.g.
modulator or photodetector) and is tapered in a way to maximize the vertical transfer of light from the lower waveguide,
and thus the vertical coupler can be used as a spot-size converter (SSC) between a single-mode fiber and the actual
device. We investigate the transfer efficiency of the single-mesa vertical coupler with different configurations. The
single-mesa design is found to give a lower total loss (i.e., fiber coupling loss plus transfer loss) compared with direct
coupling to the actual device. The transfer efficiencies obtained are more than 90% for both TE and TM polarizations,
and are polarization independent.
In this paper, we present a comparison analysis between directional couplers (DC) and multi-mode interferometers (MMI) based on high-index contrast ridge waveguides. It is found that the two devices are intimately related as the MMI is structurally derived from the DC. For the first time, the continuous evolution from the two-mode coupling characteristic of DC to the two-mode interference and multi-mode interference of MMI is demonstrated. The resulting MMIs are compared with the DC in terms of coupling length, polarization dependence, excess loss, and fabrication tolerances. We show that practical directional couplers with reasonable gap size can also be quite compact and have the same coupling length for both TE and TM polarizations. Consequently, the DC can be just as polarization insensitive as the MMI. These features, however, require careful design control involving a large set of design parameters. By comparison, the MMI design is more robust and involves fewer design variables.
Vertical coupling between waveguides is a critical component for three-dimensional (3-D) integrated optics. Vertical integration adds flexibility in integrating different devices that require different materials, and facilitates coupling of the miniature devices with optical fibers. We propose a systematic design of a relatively simple and versatile vertical coupler that provides not only vertical interconnection, but also mode-size transformation and polarization mode selection all in one. As a vertical polarization splitter, it separates the TE and TM polarizations onto different vertical levels of a 3-D photonics structure, and is thus uniquely different from conventional splitters based on directional couplers or other planar devices. The vertical coupler consists of a larger bottom waveguide that serves to improve the fiber coupling, and a smaller top waveguide that contains the actual photonic device. As a polarization-independent coupler the vertical coupler is shown to transfer light with more than 90% efficiency for all polarizations over a transfer length of only 150 µm. As a polarization mode splitter, the vertical coupler preferentially couples TE or TM polarization with a contrast ratio up to 20dB. This versatility renders the vertical coupler a compact and useful input-stage device that improves the fiber coupling to small active devices and also provides a mechanism of polarization control.
In photonic integration, high index contrast waveguides (e.g. ridge waveguides) have been widely used for interconnection and device construction because of their compactness. However, the strong confinement also means that the ridge waveguide is generally more multi-moded laterally than other waveguides of similar dimensions. A laterally single mode ridge waveguide is typically about 0.5 micrometer or less in width, which could incur high propagation and fiber coupling losses. Hence, a wider waveguide is often used to minimize loss at the expense of the single-mode characteristic, especially for long devices.
However, many devices, such as Mach-Zehnder interferometers and directional couplers, require single-mode waveguides for proper operation. In these cases, the multimode waveguides can still be used if appropriate mode-filters are strategically located at the input and within the device to remove potential higher-order modes.
We propose a higher-order mode filter using two back-to-back lateral waveguide tapers, which could be as short as 150 micrometers. Mode discrimination occurs in the down-taper where the higher-order modes become leaky when the taper width reaches their cut-off points (i.e., points where the modes are no longer guided by total internal reflection). The taper imposes only about 0.2dB loss to the fundamental mode itself. The up-taper at the other end restores the fundamental mode back to the original size. Simulations using Beam Propagation Method (BPM) shows that this mode filter is insensitive to the taper lengths and has reasonable fabrication tolerances.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.