Wei-Yu Chiu

A photonic crystal ring resonator formed by SOI nano-rods

The design, fabrication and measurement of a silicon-on-insulator (SOI) two-dimensional photonic crystal ring resonator are demonstrated in this study. The structure of the photonic crystal is comprised of silicon nano-rods arranged in a hexagonal lattice on an SOI wafer. The photonic crystal ring resonator allows for the simultaneous separation of light at wavelengths of 1.31 and 1.55mum. The device is fabricated by e-beam lithography. The measurement results confirm that a 1.31mum/1.55mum wavelength ring resonator filter with a nano-rod photonic crystal structure can be realized.

Photonic crystal directional couplers formed by InAlGaAs nano-rods.

This study demonstrates the use of photonic crystal directional couplers to separate light of wavelengths 1.31 and 1.55microm. The photonic crystal structure consists of InAlGaAs nano-rods arranged in square lattice. The coupling length of the light in the directional coupler at a wavelength of 1.31microm was designed to be four times greater than that at 1.55microm. This behavior helps in designing devices to split the two wavelengths. The devices are fabricated by e-beam lithography and conventional photolithography. The measurement results confirm that 1.31microm/1.55microm directional couplers can be realized in PC structures formed by nano-rods.

20 GHz CMOS injection-locked frequency divider with variable division ratio

An injection-locked frequency divider (ILFD) with variable division ratio, controlled by the input offset voltage, was realized using a 0.13 /spl mu/m CMOS technology. In this report, the controllable division ratios were made from 2 up to 16 with an input AC signal of 10 GHz, by changing the input DC offset voltages. This divider also performs division ratios of 2, 4, 6 and 8 with a wide-locking range up to 20 GHz at 2.5 GHz self-oscillation. The DC supplied voltage of this circuit is only 2 V and the dividing capability can reach 20 GHz.

The Monolithic Integration of a Wavelength-Demultiplexer With Evanescently Coupled Uni-Traveling-Carrier Photodiodes

In this letter, we discuss a novel integration of a wavelength demultiplexer with a pair of uni-traveling-carrier photodiodes (UTC-PDs). With this integrated module, we could separate incoming wavelengths of 1530 and 1550 nm, which are near the wavelengths utilized for digital and analog signal transmission in coarse wavelength-division multiplexing (CWDM) systems. The integrated UTC-PDs exhibited the following advantages: a wide 3-dB bandwidth (25 GHz), a reasonable responsivity (0.35 A/W), and a high-saturation-current (>17 mA). A low level of radio frequency crosstalk between the two photodiodes (less than -15 dB) could also be achieved for a wide frequency range (near DC to 40 GHz). This is low enough for the multichannel receivers in a WDM broadcast system. In addition, by use of our module, we demonstrated digital/analog signals co-transmission and demultiplexing with speeds of 2.5 Gb/s at optical wavelengths of 1530 and 1550 nm.

Directional Coupler Formed by Photonic Crystal InAlGaAs Nanorods

In this paper, we demonstrate the use of photonic crystal (PC) directional couplers to separate light of wavelengths at 1.31 and 1.55 m. The PC structure consists of InAlGaAs nanorods arranged in hexagonal lattice. The simulation of our device is implemented by the finite-difference time-domain method. The devices are fabricated by e-beam lithography and conventional photolithography. We use the strong inverse method (SIM) of e-beam lithography to make the pattern smoother. The measurement results confirm that 1.31/1.55-m wavelength splitter can be realized in PC structures formed by nanorods.

Leaky-wave photodiodes with a partially p-doped absorption Layer and a distributed Bragg reflector (DBR) for high-power and high-bandwidth-responsivity product performance

In this letter, we describe a novel edge-coupled photodiode (PD) structure, which can greatly relax the dependence of the responsivity on the cleaved length of an evanescently coupled optical waveguide. The integration of a leaky optical waveguide with a distributed Bragg reflector (DBR) and a partially p-doped photoabsorption layer allows the demonstrated device to exhibit a higher saturation current-bandwidth and responsivity than a control sample without the DBR structure. We achieved excellent speed (40-50 GHz), responsivity (0.8 A/W), and saturation current-bandwidth products (720 mAmiddotGHz at 40 GHz), comparable to the high-performance of an evanescently coupled PD, whose variation of responsivity is more sensitive to the cleaved waveguide length (30% versus 7%) than is our demonstrated device

Separate Absorption-Charge Multiplication Heterojunction Phototransistors With the Bandwidth-Enhancement Effect and Ultrahigh Gain-Bandwidth Product Under Near Avalanche Operation

We demonstrate a high-performance heterojunction phototransistor (HPT): separate absorption-charge multiplication HPT. The incorporation of an In0.52Al0.48 As-based multiplication layer in the In0.53 Ga0.47As-based collector layer of our HPT allows for a great shortening of the trapping time ( ~ ns to ~ 30 ps) of electrons at the base-emitter junction under near avalanche operation, without sacrificing the gain performance. The interaction between the photoconductive gain and avalanche gain means that it is not necessary to use high bias voltages (> 30 V ) in our device to attain high-gain (> 1times 104) performance. With this device design, we can achieve an extremely high (90 THz) gain-bandwidth product (1.6 GHz, 5.5 times 104) under a 6-V bias.

Improvement of Mesa-Sidewall Leakage Current Using Benzocyclobuten Sidewall Process in InGaAs/InP MSM Photodetector

In recent decades, metal-semiconductor-metal (MSM) photodetector for optical fiber communication applications have been studied extensively. The dark current in MSM PD is an important parameter that can be reduced by schottky barrier enhancement and fabrication process. By employing a benzocyclobuten (BCB) sidewall passivation process, the leakage issue between Schottky metal fingers and mesa sidewalls can be avoided. Moreover, the parasitic capacitance can also be decreased due to the low dielectric constant of BCB. The BCB passivation process decreases the dark current density from 11 nA/µm2 to 5.7 pA/µm2.

High-speed and high-power InP based photodiode for the applications of microwave photonics

In this paper we reviewed our recent work about InP based high-speed and high-power photodiodes with evanescently-coupled and vertical-illuminated structures and their application to W or V-band microwave photonic.

Photodiode with partially depleted absorber, leaky optical waveguide, and distributed-Bragg-reflector (DBR) for high-power and high-bandwidth-responsivity product performance

We demonstrate a novel structure of photodiode. By incorporating the leaky optical waveguide with distributed-Bragg-reflector (DBR) and partially p-doped photo-absorption layer, this device exhibits much superior performance of speed, saturation power, and responsivity to the control without DBR mirrors