Chi-Jui Chung

High Performance Optical Modulator Based on Electro-Optic Polymer Filled Silicon Slot Photonic Crystal Waveguide

Silicon-organic hybrid integrated devices have emerging applications ranging from high-speed optical interconnects to photonic electromagnetic-field sensors. Silicon slot photonic crystal waveguides (PCWs) filled with electro-optic (EO) polymers combine the slow-light effect in PCWs with the high polarizability of EO polymers, which promises the realization of high-performance optical modulators. In this paper, a high-speed, power-efficient, low-dispersion, and compact optical modulator based on an EO polymer filled silicon slot PCW is presented. Lattice-shifted PCWs are utilized to engineer the photonic band diagram and thus enable an 8 nm-wide low-dispersion spectrum range, which is over an order of magnitude wider than that in modulators based on non-band-engineered PCWs and ring-resonators. A small voltage-length product of Vπ × L = 0.282 V × mm measured at 100 KHz is achieved by slow-light enhancement, corresponding to an unprecedented record-high effective in-device EO coefficient (r33) of 1230 pm/V among silicon-organic hybrid modulators. Excluding the slow-light effect, the actual in-device r33 is estimated to be 98 pm/V. By engineering the RC time constant via silicon doping and also utilizing a backside gate technique, the 3-dB modulation bandwidth of the device is measured to be 15 GHz. In addition, the RF power consumption of the modulator is estimated to be 24 mW at 10 GHz, and the estimated energy consumption for potential digital modulations is approximately 94.4 fJ/bit at 10 Gb/s.

Integrated Broadband Bowtie Antenna on Transparent Silica Substrate

The bowtie antenna is a topic of growing interest in recent years. In this letter, we design, fabricate, and characterize a modified gold bowtie antenna integrated on a transparent silica substrate. The bowtie antenna is designed with broad RF bandwidth to cover the X-band in the electromagnetic spectrum. We numerically investigate the antenna characteristics, specifically its resonant frequency and enhancement factor. Our designed bowtie antenna provides a strong broadband electric field enhancement in its feed gap. Taking advantage of the low-k silica substrate, high enhancement factor can be achieved without the unwanted reflection and scattering from the backside silicon handle, which is the issue of using a silicon-on-insulator (SOI) substrate. We simulate the dependence of resonance frequency on bowtie geometry, and verify the simulation results through experimental investigation, by fabricating different sets of bowtie antennas on silica substrates and then measuring their resonance frequencies. In addition, the far-field radiation pattern of the bowtie antenna is measured, and it shows dipole-like characteristics with large beamwidth. Such a broadband antenna will be useful for a myriad of applications, ranging from photonic electromagnetic wave sensing to wireless communications.

One-Dimensional Photonic Crystal Slot Waveguide for Silicon-Organic Hybrid Electro-Optic Modulators

In an on-chip silicon-organic hybrid electro-optic (EO) modulator, the mode overlap with EO materials, in-device effective r33, and propagation loss are among the most critical factors that determine the performance of the modulator. Various waveguide structures have been proposed to optimize these factors, yet there is a lack of comprehensive consideration on all of them. In this Letter, a one-dimensional (1D) photonic crystal (PC) slot waveguide structure is proposed that takes all these factors into consideration. The proposed structure takes advantage of the strong mode confinement within a low-index region in a conventional slot waveguide and the slow-light enhancement from the 1D PC structure. Its simple geometry makes it robust to resist fabrication imperfections and helps reduce the propagation loss. Using it as a phase shifter in a Mach-Zehnder interferometer structure, an integrated silicon-organic hybrid EO modulator was experimentally demonstrated. The observed effective EO coefficient is as high as 490 pm/V. The measured half-wave voltage and length product is less than 1  V·cm and can be further improved. A potential bandwidth of 61 GHz can be achieved and further improved by tailoring the doping profile. The proposed structure offers a competitive novel phase-shifter design, which is simple, highly efficient, and with low optical loss, for on-chip silicon-organic hybrid EO modulators.

Design of a plasmonic-organic hybrid slot waveguide integrated with a bowtie-antenna for terahertz wave detection

Electromagnetic (EM) wave detection over a large spectrum has recently attracted significant amount of attention. Traditional electronic EM wave sensors use large metallic probes which distort the field to be measured and also have strict limitations on the detectable RF bandwidth. To address these problems, integrated photonic EM wave sensors have been developed to provide high sensitivity and broad bandwidth. Previously we demonstrated a compact, broadband, and sensitive integrated photonic EM wave sensor, consisting of an organic electro-optic (EO) polymer refilled silicon slot photonic crystal waveguide (PCW) modulator integrated with a gold bowtie antenna, to detect the X band of the electromagnetic spectrum. However, due to the relative large RC constant of the silicon PCW, such EM wave sensors can only work up to tens of GHz. In this work, we present a detailed design and discussion of a new generation of EM wave sensors based on EO polymer refilled plasmonic slot waveguides in conjunction with bowtie antennas to cover a wider electromagnetic spectrum from 1 GHz up to 10THz, including the range of microwave, millimeter wave and even terahertz waves. This antennacoupled plasmonic-organic hybrid (POH) structure is designed to provide an ultra-small RC constant, a large overlap between plasmonic mode and RF field, and strong electric field enhancement, as well as negligible field perturbation. A taper is designed to bridge silicon strip waveguide to plasmonic slot waveguide. Simulation results show that our device can have an EM wave sensing ability up to 10 THz. To the best of our knowledge, this is the first POH device for photonic terahertz wave detection.

Antenna-coupled silicon-organic hybrid integrated photonic crystal modulator for broadband electromagnetic wave detection

The detection and measurement of electromagnetic fields have attracted significant amounts of attention in recent years. Traditional electronic electromagnetic field sensors use large active conductive probes which perturb the field to be measured and also make the devices bulky. In order to address these problems, integrated photonic electromagnetic field sensors have been developed, in which an optical signal is modulated by an RF signal collected by a miniaturized antenna. In this work, we design, fabricate and characterize a compact, broadband and highly sensitive integrated photonic electromagnetic field sensor based on a silicon-organic hybrid modulator driven by a bowtie antenna. The large electro-optic (EO) coefficient of organic polymer, the slow-light effects in the silicon slot photonic crystal waveguide (PCW), and the broadband field enhancement provided by the bowtie antenna, are all combined to enhance the interaction of microwaves and optical waves, enabling a high EO modulation efficiency and thus a high sensitivity. The modulator is experimentally demonstrated with a record-high effective in-device EO modulation efficiency of r33=1230pm/V. Modulation response up to 40GHz is measured, with a 3-dB bandwidth of 11GHz. The slot PCW has an interaction length of 300μm, and the bowtie antenna has an area smaller than 1cm2. The bowtie antenna in the device is experimentally demonstrated to have a broadband characteristics with a central resonance frequency of 10GHz, as well as a large beam width which enables the detection of electromagnetic waves from a large range of incident angles. The sensor is experimentally demonstrated with a minimum detectable electromagnetic power density of 8.4mW/m2 at 8.4GHz, corresponding to a minimum detectable electric field of 2.5V/m and an ultra-high sensitivity of 0.000027V/m Hz-1/2 ever demonstrated. To the best of our knowledge, this is the first silicon-organic hybrid device and also the first PCW device used for the photonic detection of electromagnetic waves. Finally, we propose some future work, including a Teraherz wave sensor based on antenna-coupled electrooptic polymer filled plasmonic slot waveguide, as well as a fully packaged and tailgated device.

On-chip optical true time delay lines featuring one-dimensional fishbone photonic crystal waveguide

In this paper, we present on-chip optical true time delay lines based on slow light one-dimensional (1D) fishbone photonic crystal waveguides (FPCWs). The structural slow light is generated by modulating the index guided optical mode with periodically arranged sidewalls along the propagation direction. Due to the reduced mode overlap with the rough etched surface, the propagation loss of the 1D FPCW is significantly reduced compared to the two-dimensional photonic crystal waveguide. A delay time of 65 ps/mm is observed experimentally.

Microheater-integrated silicon coupled photonic crystal microcavities for low-power thermo-optic switching over a wide spectrum

We design, fabricate and experimentally demonstrate a compact thermo-optic gate switch comprising a 3.78μm-long coupled L0-type photonic crystal microcavities on a silicon-on-insulator substrate. A nanohole is inserted in the center of each individual L0 photonic crystal microcavity. Coupling between identical microcavities gives rise to bonding and antibonding states of the coupled photonic molecules. The coupled photonic crystal microcavities are numerically simulated and experimentally verified with a 6nm-wide flat-bottom resonance in its transmission spectrum, which enables wider operational spectrum range than microring resonators. An integrated micro-heater is in direct contact with the silicon core to efficiently drive the device. The thermo-optic switch is measured with an optical extinction ratio of 20dB, an on-off switching power of 18.2mW, a therm-optic tuning efficiency of 0.63nm/mW, a rise time of 14.8μsec and a fall time of 18.5μsec. The measured on-chip loss on the transmission band is as low as 1dB.

Miniature mid-infrared thermooptic switch with photonic crystal waveguide based silicon-on-sapphire Mach–Zehnder interferometers

Ultracompact thermooptically tuned photonic crystal waveguide (PCW) based Mach–Zehnder interferometers (MZIs) working in silicon-on-sapphire in mid-infrared regime have been proposed and demonstrated. We designed and fabricated a PCW based silicon thermo-optic (TO) switch operating at 3.43 μm. Both steady-state and transient thermal analyses were performed to evaluate the thermal performance of the TO MZIs. The required π phase shift between the two arms of the MZI has been successfully achieved within an 80 μm interaction distance. The maximum modulation depth of 74% was demonstrated for switching power of 170 mW.

High Speed Modulator Based on Electro-optic Polymer Infiltrated Subwavelength Grating Waveguide Ring Resonator

We present a high-speed modulator based on electro-optic polymer infiltrated subwavelength grating waveguide ring resonator. A 3-dB small signal modulation bandwidth of 41.36 GHz has been demonstrated.

On-chip microwave photonic sensor featuring silicon-polymer hybrid subwavelength grating waveguide and bowtie antenna (Conference Presentation)

A photonic microwave sensor based on electro-optic (EO) polymer infiltrated silicon subwavelength grating (SWG) waveguide and bowtie antenna is designed and experimentally demonstrated. The microwave sensor receives wireless microwave signals via the bowtie antenna. The electrical field between the extension bars of the bowtie antenna modulates the light guided in the SWG based Mach–Zehnder interferometer (MZI). Thus, microwave signals can be detected by measuring the intensity variation of light from the MZI output. The EO polymer infiltrated SWG does not require ion implantation and has low optical propagation loss. Furthermore, compared to slotted silicon waveguides, the EO polymer poling efficiency on SWG structure can be greatly increased due to wider poling separations and thus the increased breakdown voltage. In order to achieve strong microwave field enhancement, the impedance of the bowtie antennas is tailored. The optimized bowtie antennas operate at 15 GHz and provide >1000X field enhancement while only occupy an area of 7.6 mm X 0.3 mm. Leveraging the folded SWG waveguide, high EO coefficient polymer, and large field enhancement from bowtie antenna, an ultra-sensitive and compact microwave photonic sensor has been demonstrated.