Dongdong Yin

High-responsivity 40 Gbit/s InGaAs/InP PIN photodetectors integrated on silicon-on-insulator waveguide circuits*

This paper presents a high-responsivity and high-speed InGaAs/InP PIN photodetector integrated onto the silicon waveguide substrate utilizing the divinyltetramethyldisiloxane-benzocyclobutene (DVS-BCB) adhesive bonding method. A grating coupler is adopted to couple light from the fiber to the silicon waveguide. Light in the silicon photonic waveguide is evanescently coupled into the photodetector. The integrated photodetector structure is first simulated using the FDTD (finite difference time domain) solutions software and the simulation results show a detection efficiency of 95%. According to the simulation result, the integrated photodetector is fabricated. The measured responsivity of the fabricated integrated photodetector with a detection length of 30 μm is 0.89 A/W excluding the coupling loss between the fiber and the grating coupler and the silicon propagation loss at the wavelength of 1550 nm with a reverse bias voltage of 3 V. Measured 3-dB bandwidth is 27 GHz using the Lightwave Component Analyzer (LCA). The eye diagram signal test results indicate that the photodetector can operate at a high speed of 40 Gbit/s. The integrated photodetector is of great significance in the silicon-based optoelectronic integrated chip which can be applied to the optical communication and the super node data transmission chip of the high-performance computer.

Design and fabrication of multi-channel photodetector array monolithic with arrayed waveguide grating

We have provided optical simulations of the evanescently coupled waveguide photodiodes integrated with a 13-channels AWGs. The photodiode could exhibit high internal efficiency by appropriate choice of layers geometry and refractive index. Aseamless joint structure has been designed and fabricated for integrating the output waveguides of AWGs with the evanescently coupled waveguide photodiode array. The highest simulation quantum efficiency could achieve 92% when the matching layer thickness of the PD is 120 nm and the insertion length is 2 μm. The fabricated PD with 320-nm-thick matching layer and 2-μm-length insertion matching layer present a responsivity of 0.87 A/W.

A high-efficiency grating coupler between single-mode fiber and silicon-on-insulator waveguide

We present the design of a diffractive grating structure and get the optimal parameters which can achieve more than 75% coupling efficiency (CE) between single-mode fiber and silicon-on-insulator (SOI) waveguide through 2D finite-different time-domain (FDTD) simulation. The proposed architecture has a uniform structure with no bottom reflection element or silicon overlay. The structure, including grating couplers, adiabatic tapers and interconnection waveguides can be fabricated on the SOI waveguide with only a single electron-beam lithography (ICP) step, which is CMOS-compatible. A relatively high coupling efficiency of 47.2% was obtained at a wavelength of 1562 nm.

High-responsivity InGaAs/InP photodetectors integrated on silicon-on-insulator waveguide circuits

This paper presents a high responsivity InGaAs / InP PIN photodetector bonded on silicon-on-insulator (SOI) waveguide circuit with a Si waveguide width of 2000 nm. Divinyltetramethyldisiloxane-benzocyclobutene (DVS-BCB) is used to integrate the InGaAs/InP film epitaxial layers onto the silicon waveguide wafer. A grating coupler is adopted to couple light from the fiber to the Si waveguide. Light in the Si photonic waveguide is evanescently coupled into the InP ridge waveguide and can finally be absorbed in the absorption layer. The simulation results show that the detection efficiency can reach 95%. The measured detector responsivity is 0.87 A/W (excluding the coupling loss between the fiber and the grating coupler and the silicon propagation loss) at a wavelength of 1550nm and a bias voltage of -3V.

A method to transfer an individual graphene flake to a target position with a precision of sub-micrometer*

Graphene field-effect transistors have been intensively studied. However, in order to fabricate devices with more complicated structures, such as the integration with waveguide and other two-dimensional materials, we need to transfer the exfoliated graphene samples to a target position. Due to the small area of exfoliated graphene and its random distribution, the transfer method requires rather high precision. In this paper, we systematically study a method to selectively transfer mechanically exfoliated graphene samples to a target position with a precision of sub-micrometer. To characterize the doping level of this method, we transfer graphene flakes to pre-patterned metal electrodes, forming graphene field-effect transistors. The hole doping of graphene is calculated to be 2.16 . In addition, we fabricate a waveguide-integrated multilayer graphene photodetector to demonstrate the viability and accuracy of this method. A photocurrent as high as 0.4 μA is obtained, corresponding to a photoresponsivity of 0.48 mA/W. The device performs uniformly in nine illumination cycles.

Photoconductive multi-layer graphene photodetectors fabricated on etched silicon-on-insulator substratesr*

Recently, graphene-based photodetectors have been rapidly developed. However, their photoresponsivities are generally low due to the weak optical absorption strength of graphene. In this paper, we fabricate photoconductive multi-layer graphene (MLG) photodetectors on etched silicon-on-insulator substrates. A photoresponsivity exceeding is obtained, which enables most optoelectronic application. In addition, according to the analyses of the high photoresponsivity and long photoresponse time, we conclude that the working mechanism of the device is photoconductive effect. The process of photons conversion into conducting electrons is also described in detail. Finally, according to the distinct difference between the photoresponses at 1550 nm and 808 nm, we estimate that the position of the trapping energy is somewhere between 0.4 eV and 0.76 eV, higher than the Fermi energy of MLG. Our work paves a new way for fabricating the graphene photoconductive photodetectors.

Bolometric effect in a waveguide-integrated graphene photodetector

Graphene is an alternative material for photodetectors owing to its unique properties. These include its uniform absorption of light from ultraviolet to infrared and its ultrahigh mobility for both electrons and holes. Unfortunately, due to the low absorption of light, the photoresponsivity of graphene-based photodetectors is usually low, only a few milliamps per watt. In this letter, we fabricate a waveguide-integrated graphene photodetector. A photoresponsivity exceeding 0.11 AW−1 is obtained which enables most optoelectronic applications. The dominating mechanism of photoresponse is investigated and is attributed to the photo-induced bolometric effect. Theoretical calculation shows that the bolometric photoresponsivity is 4.6 AW−1. The absorption coefficient of the device is estimated to be 0.27 dBμm−1.

Optical design of the high-responsivity evanescently coupled photodiodes integrated with the output waveguides of AWGS

We have provided optical simulations of the evanescently coupled waveguide photodiodes integrated with a 10 channels AWGs. The photodiode could exhibit high internal efficiency by appropriate choice of layers geometry and refractive index. Two structures have been designed for integrating the output waveguides of AWGs with the evanescently coupled waveguide photodiode array : One is a seamless joint between the AWGs output waveguide and the photodiode; the other one has a shallow trench between the AWGs top cladding layer and the photodiode p-doped layer. The simulation results show that the photodiodes have quantum efficiencies as high as 87% and 64%, respectively, at 1.55μm wavelength.