Microdisk Modulators Research Articles

Low-Loss Ultra-Compact Silicon Photonic Integrated Micro-Disk Modulator for Large-Scale WDM Optical Interconnection

Low-Loss Ultra-Compact Silicon Photonic Integrated Micro-Disk Modulator for Large-Scale WDM Optical Interconnection

Microdisk modulator-assisted optical nonlinear activation functions for photonic neural networks

On-chip implementation of optical nonlinear activation functions (NAFs) is essential for realizing large-scale photonic neural chips. To improve the reconfigurability and enrich the functions of photonic neural network (PNN), an NAF unit with a unique capability of performing multiple types of NAFs is highly preferred. In this work, we propose and experimentally demonstrate a microdisk modulator (MDM)-assisted NAF unit, in which multiple types of electro-optic NAFs with a high response speed and multiple types of all-optical NAFs with a low latency and reduced power consumption are performed in a single device. The fabricated MDM has an add-drop configuration, in which a lateral PN junction is incorporated to achieve high-speed resonance wavelength tuning. With the use of the high-speed nonlinear electro-optic effect, three different kinds of electro-optic NAFs including sigmoid function, radial basis function (RBF), and negative rectified linear unit (ReLU) function are realized by exploiting the free-carrier dispersion effect on silicon. Moreover, thanks to the strong optical confinement in the disk cavity, all-optical NAFs can be performed by exploiting the thermo-optic effect on silicon. In the experiment, four different kinds of all-optical NAFs including softplus function, RBF, clamped ReLU function, and leaky ReLU function are demonstrated. With the use of the realized clamped ReLU function, a convolutional neural network is simulated to perform a handwritten digit classification benchmark task, and an accuracy as high as 98 % is demonstrated. Thanks to its strong electro-optic and thermo-optic effects, the proposed MDM provides a unique capability of performing multiple types of electro-optic and all-optical NAFs, which is potential to be served as a flexible nonlinear unit in large-scale PNN chips.

Electronic-photonic arithmetic logic unit for high-speed computing

The past two decades have witnessed the stagnation of the clock speed of microprocessors followed by the recent faltering of Moore’s law as nanofabrication technology approaches its unavoidable physical limit. Vigorous efforts from various research areas have been made to develop power-efficient and ultrafast computing machines in this post-Moore’s law era. With its unique capacity to integrate complex electro-optic circuits on a single chip, integrated photonics has revolutionized the interconnects and has shown its striking potential in optical computing. Here, we propose an electronic-photonic computing architecture for a wavelength division multiplexing-based electronic-photonic arithmetic logic unit, which disentangles the exponential relationship between power and clock rate, leading to an enhancement in computation speed and power efficiency as compared to the state-of-the-art transistors-based circuits. We experimentally demonstrate its practicality by implementing a 4-bit arithmetic logic unit consisting of 8 high-speed microdisk modulators and operating at 20 GHz. This approach paves the way to future power-saving and high-speed electronic-photonic computing circuits.

A Silicon Photonic Data Link with a Monolithic Erbium-Doped Laser

To meet the increasing demand for data communication bandwidth and overcome the limits of electrical interconnects, silicon photonic technology has been extensively studied, with various photonics devices and optical links being demonstrated. All of the optical data links previously demonstrated have used either heterogeneously integrated lasers or external laser sources. This work presents the first silicon photonic data link using a monolithic rare-earth-ion-doped laser, a silicon microdisk modulator, and a germanium photodetector integrated on a single chip. The fabrication is CMOS compatible, demonstrating data transmission as a proof-of-concept at kHz speed level, and potential data rate of more than 1 Gbps. This work provides a solution for the monolithic integration of laser sources on the silicon photonic platform, which is fully compatible with the CMOS fabrication line, and has potential applications such as free-space communication and integrated LIDAR.

Foundry-Enabled Scalable All-to-All Optical Interconnects Using Silicon Nitride Arrayed Waveguide Router Interposers and Silicon Photonic Transceivers

This paper summarizes our latest results of integrated all-to-all optical interconnect systems using compact, low-loss silicon nitride (SiN) arrayed waveguide grating router (AWGR) through AIM photonics’ multiple-project-wafer services. In particular, we have designed, taped out, and initially characterized a chip-scale silicon photonic low-latency interconnect optical network switch (Si-LIONS) system with an 8 × 8 200 GHz spacing cyclic SiN AWGR, 64 microdisk modulators, and 64 on -chip germanium photodector (PD). The 8 × 8 SiN AWGR in design has a measured insertion loss of 1.8 dB and a crosstalk of –13 dB, with a footprint of 1.3 mm × 0.9 mm. We measured an error-free performance of the microdisk modulator at 10 Gb/s upon 1Vpp voltage swing. We demonstrated wavelength routing with error-free data transmission using the on -chip modulator, SiN AWGR, and an external PD. We have designed and taped out the optical interposer version of the all-to-all system using SiN waveguides and low-loss chip-to-interposer couplers. Finally, we illustrate our preliminary designs and results of 16 × 16 and 32 × 32 SiN AWGRs, and discuss the possibility of scaling beyond 1024 × 1024 all-to-all interconnections with reduced number of wavelengths (e.g., 64) using the Thin-CLOS architecture.

Electro-Optic Ripple-Carry Adder in Integrated Silicon Photonics for Optical Computing

Photonic integrated circuits with compact size and low power consumption have opened the possibility of realization of ultrahigh-speed and energy-efficient optical computing in an integrated system that may be comparable to CMOS-based electrical integrated circuits in many aspects. Directed logic is an innovative paradigm that can make full use of the advantages of electronics and photonics for optical computing. In this paper, we propose various designs of directed-logic-based electro-optic ripple-carry adders in integrated silicon photonics, which replace the electrical components in the critical path using optical counterparts. All control signals are applied simultaneously through ultralow-power microdisk modulators so that the propagation delay could be reduced significantly. A two-bit thermal-optic full adder based on microdisk modulators is demonstrated as a proof of concept along with a projection of high-speed performance. The proposed electro-optic full adder paves the way to future low-power-consumption and large-bandwidth optical computing in integrated silicon photonics.

Comparison of microrings and microdisks for high-speed optical modulation in silicon photonics

The past several decades have witnessed the gradual transition from electrical to optical interconnects, ranging from long-haul telecommunication to chip-to-chip interconnects. As one type of key component in integrated optical interconnect and high-performance computing, optical modulators have been well developed these past few years, including ultrahigh-speed microring and microdisk modulators. In this paper, a comparison between microring and microdisk modulators is well analyzed in terms of dimensions, static and dynamic power consumption, and fabrication tolerance. The results show that microdisks have advantages over microrings in these aspects, which gives instructions to the chip design of high-density integrated systems for optical interconnects and optical computing.

Operation of high-speed silicon photonic micro-disk modulators at cryogenic temperatures

Significant progress has been made in the field of silicon photonics over the past two decades. Silicon photonics provides substantial performance advantages in many data processing and transfer applications. Until now, the benefits of active silicon photonics in cryogenic systems have remained unexplored. Here we demonstrate the operation of a high-speed, CMOS compatible silicon micro-disk modulator transmitting data at rates up to 10 Gb/s and at temperatures down to 4.8 K. This opens the door for the use of silicon photonics as an interface to low temperature, bandwidth intensive systems such as high-performance superconducting-based computing and integrated quantum optics circuits interfacing to superconducting single-photon detectors.

Analytical Modeling of Silicon Microring and Microdisk Modulators With Electrical and Optical Dynamics

We propose an analytical time-domain model for microring and microdisk modulators, which considers both their electrical and optical properties. Theory of the dynamics of microring/microdisk is discussed, and general solutions to the transfer matrix representation are presented. Both static and dynamic predictions from the model are compared to measurement results to demonstrate the accuracy of our model. Static predictions and measurements are presented for power and phase responses, whereas dynamic predictions and measurements are presented for small-signal and large-signal operations. The model verifies that the chirping and modulation bandwidth of the modulators depend on the detuning state. Finally, the accuracy and scalability of several techniques employed in the model are discussed.

Compact Thermally Tunable Silicon Racetrack Modulators Based on an Asymmetric Waveguide

A compact wavelength-tunable 10-Gb/s silicon racetrack modulator with integrated thermo-optic heater is demonstrated by using a waveguide with an asymmetric cross section, combining the compact footprint of microdisk modulators with the design simplicity of regular racetrack or ring modulators. The outer perimeter of the asymmetric racetrack modulator is fully etched to maximize optical confinement, and the inner waveguide edge is shallowly etched to maintain an electrically conductive path to the embedded p-n diode and to control the propagation of the asymmetric optical mode and its coupling to the bus waveguide. The resistive heating elements based on highly doped Si strips are implemented at the outer edge of the modulator for thermo-optic control. The asymmetric modulators can be fabricated along with Si wire waveguides and shallowly etched fiber-grating couplers using a simple process flow involving just two Si-patterning steps. Devices with a bending radius of 10 μm and a novel “T”-shaped p-n diode layout have been fabricated, and exhibit electro-optic modulation and heater efficiencies of 28 pm/V and 42 pm/mW, respectively. At 10 Gb/s, a stable extinction ratio of 10 dB is demonstrated from a 2V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">pp</sub> drive swing, which can be maintained over a wavelength range of 4.6 nm by thermally tuning the modulator. This is equivalent with a temperature variation of about 62°C.

Adiabatic microring modulators

In this work, we demonstrate and experimentally characterize a new class of high-performance silicon photonic modulators-the adiabatic microring modulator. The adiabatic microring modulator utilizes a vertical PN junction and interior electrical contacts, leveraging all the advantages of previously-demonstrated microdisk modulators. However, this device also incorporates an adiabatic transition from the wide, multimode contact region, to a narrow, single-mode coupling region, eliminating unwanted spatial modes common to microdisks. As a result, the adiabatic microring modulator demonstrated in this work is the smallest microring modulator demonstrated to date, with a diameter of only 4 μm, yielding a 6.92-THz uncorrupted free spectral range. Here, we perform an experimental comparative analysis between silicon adiabatic microring modulators, silicon microdisk modulators, and a commercial lithium-niobate Mach-Zehnder modulator. We show that the silicon adiabatic microring modulator using partial doping is capable of operating at 12.5-Gb/s data rates and beyond. This device combines the best of all modulator designs, leveraging the depletion-based method to maximize the speed, utilizing the vertical-junction configuration to minimize the power consumption, employing a unique adiabatic design to eliminate higher-order modes, and using partial doping to reduce resistance, further enhancing the speed of the device.

A low–power high–speed InP microdisk modulator heterogeneously integrated on a SOI waveguide

We report on the modulation characteristics of indium phosphide (InP) based microdisks heterogeneously integrated on a silicon-on-insulator (SOI) waveguide. We present static extinction ratios and dynamic operation up to 10 Gb/s. Operation with a bit-error rate below 1 × 10(-9) is demonstrated at 2.5, 5.0 and 10.0 Gb/s and the performance is compared with that of a commercial modulator. Power penalties are analyzed with respect to the pattern length. The power consumption is calculated and compared with state-of-the-art integrated modulator concepts. We demonstrate that InP microdisk modulators combine low-power and low-voltage operation with low footprint and high-speed. Moreover, the devices can be fabricated using the same technology as for lasers, detectors and wavelength converters, making them very attractive for co-integration.

Vertical junction silicon microdisk modulators and switches

Vertical junction resonant microdisk modulators and switches have been demonstrated with exceptionally low power consumption, low-voltage operation, high-speed, and compact size. This paper reviews the progress of vertical junction microdisk modulators, provides detailed design data, and compares vertical junction performance to lateral junction performance. The use of a vertical junction maximizes the overlap of the depletion region with the optical mode thereby minimizing both the drive voltage and power consumption of a depletion-mode modulator. Further, the vertical junction enables contact to be made from the interior of the resonator and therein a hard outer wall to be formed that minimizes radiation in small diameter resonators, further reducing the capacitance and drive power of the modulator. Initial simple vertical junction modulators using depletion-mode operation demonstrated the first sub-100 fJ/bit silicon modulators. With more intricate doping schemes and through the use of AC-coupled drive signals, 3.5 μm diameter vertical junction microdisk modulators have recently achieved a communications efficiency of 3 fJ/bit, making these modulators the smallest and lowest power modulators demonstrated to date, in any material system. Additionally, the demonstration was performed at 12.5 Gb/s, required a peak-to-peak signal level of only 1 V, and achieved bit-error-rates below 10(-12) without requiring signal pre-emphasis. As an additional benefit to the use of interior contacts, higher-order active filters can be constructed from multiple vertical-junction modulators without interference of the electrodes. Doing so, we demonstrated second-order active high-speed bandpass switches with ~2.5 ns switching speeds, and power penalties of only 0.4 dB. Through the use of vertical junctions in resonant modulators, we have achieved the lowest power consumption, lowest voltage, and smallest silicon modulators demonstrated to date.

14.6-GHz LiNbO/sub 3/ microdisk photonic self-homodyne RF receiver

Nonlinear optical modulation combined with simultaneous photonic and RF resonance in an LiNbO/sub 3/ microdisk modulator is used to create a self-homodyne photonic RF receiver. Carrier and sidebands are mixed in the optical domain, and the modulated optical signal is detected using a photodetector. The photodetector has a bandwidth matched to the baseband signal. It filters out the high-frequency components and generates the baseband photocurrent. Receiver operation is demonstrated by demodulating up to 100-Mb/s digital data from a 14.6-GHz carrier frequency without any high-speed electronic components. A bit error rate of 10/sup -9/ is measured for 10-Mb/s downconverted digital data at -15-dBm received RF power. Preliminary results of employing this photonic RF receiver in a short-distance Ku-band wireless link demonstrate the potential of using high-quality optical microresonators in RF receiver applications.

Self-homodyne RF-optical LiNbO 3 microdisk receiver

A novel RF-optical receiver architecture based on nonlinear optical modulation in a LiNbO 3 microdisk modulator is presented. This is the first RF-optical receiver without high-speed electronic components for transmitted carrier links. We demonstrate receiver operation by demodulating 50 Mb/s digital data from a 8.7 GHz carrier frequency.

Active semiconductor microdisk devices

The design of active semiconductor microdisk switches, modulators, or wavelength routers enabled by modulating the transfer characteristics of a resonant cavity is investigated. A simple theoretical model based on coupled-mode theory is used to elucidate design trends and constraints in the cases where electroabsorption, gain, and free carrier injection are employed to modulate the resonator characteristic.