Low loss 40 Gbit/s silicon modulator based on interleaved junctions and fabricated on 300 mm SOI wafers

X-Intersected Silicon Modulator of Well-Rounded Performance

In silicon modulator design, implantation is always a key factor, significantly influencing the doping profile and carrier distribution. As waveguide doping is limited by the compact footprint of the modulator rib, three-dimensional complex optimization is a viable option to improve performance. This work proposes an X-intersected modulator based on two inversely slanted junctions using the effective 3D Monte Carlo method for junction generation. The optimized results show that the modulation efficiency of the design is 1.09 V·cm, while the loss is 18 dB/cm, and the 3 dB bandwidth reaches over 35 GHz owing to the decreased resistance and capacitance of the 3D junction. This work demonstrates the benefits of 3D doping design in silicon modulators, contributing to higher efficiency and avoiding additional PN overlap to introduce lower capacitance. The design of 3D doping profiles well balances the DC and AC performance, and provides novel modulator solutions for high-speed datacom.

Silicon modulator based on omni junctions by effective 3D Monte-Carlo method

3D doping structure has significant advantages in modulation efficiency and loss compared with 2D modulator doping profiles. However, to the best of our knowledge, previous work on 3D simulation methods for interdigitated doping designs applied simplified models, which prohibited complex 3D doping. In this work, innovative omni junctions, based on the effective 3D Monte-Carlo method, are believed to be the first proposed for high-performance modulators. Simulation results show that the modulation efficiency reaches 0.88 V·cm, while the loss is only 16 dB/cm, with capacitance below 0.42 pF/mm. This work provides a modulator design with superior modulation efficiency and serviceability for high-speed datacom.

Silicon Photonic Phase Shifters and Their Applications: A Review

With the development of silicon photonics, dense photonic integrated circuits play a significant role in applications such as light detection and ranging systems, photonic computing accelerators, miniaturized spectrometers, and so on. Recently, extensive research work has been carried out on the phase shifter, which acts as the fundamental building block in the photonic integrated circuit. In this review, we overview different types of silicon photonic phase shifters, including micro-electro-mechanical systems (MEMS), thermo-optics, and free-carrier depletion types, highlighting the MEMS-based ones. The major working principles of these phase shifters are introduced and analyzed. Additionally, the related works are summarized and compared. Moreover, some emerging applications utilizing phase shifters are introduced, such as neuromorphic computing systems, photonic accelerators, multi-purpose processing cores, etc. Finally, a discussion on each kind of phase shifter is given based on the figures of merit.

A CMOS-Compatible Carrier-Injection Plasmonic Micro-Ring Modulator (CIPMRM) with Stable Performance as Temperature Varying around 60 K

A CMOS-compatible carrier-injection plasmonic micro-ring modulator (CIPMRM) is proposed and theoretically analyzed. It has a compacted footprint of 43.4 μm2 (R = 2 μm), a data rate of 45 Gbps, an insertion loss of −8 dB, a static extinction ratio of 22 dB, and an energy consumption of 4.5 pJ/bit when 2.5 V peak-to-peak voltage is applied. Moreover, it works well when temperature varies around 60 K. A method of tuning the resonant wavelength based on the carrier concentration is proposed here because the device is reliable when the linewidth varies within ±5%. CIPMRM provides a way to overcome the shortcomings of temperature and process sensitivity, which are characteristics of the photonic micro-ring modulator. It can be used in optoelectronic integration for its small size and stable performance.

Designing an electro-optical encoder based on photonic crystals using the graphene-Al2O3 stacks

In this paper, an electro-optical 4-to-2 encoder based on a photonic crystal is presented. The structure is composed of four silicon waveguides, four photonic crystal structures including the graphene-${{\rm Al}_2}{{\rm O}_3}$Al₂O₃ stacks, and two optical combiners. Two one-dimensional arrays of air holes in the silicon background are designed parallel to the waveguides. Also, a graphene-${{\rm Al}_2}{{\rm O}_3}$Al₂O₃ stack is placed at the center of each array, which provides the desired interferences. This feature is used for controlling the optical wave transmission through the waveguides. Using two optical combiners at the end of two waveguides, the received signals from the waveguides will be guided toward the output ports. The amount of the transmitted signal from input ports to the output of the encoder can be controlled by applying the proper chemical potential to the graphene-based stacks. The simulation results show that the encoding operation can be achieved by using 0.2 eV and 0.8 eV for chemical potentials. In addition, the normalized output power margins for logic 0 and 1 are calculated to be 8.2% and 46.7%, respectively. The footprint for the proposed structure is approximately equal to ${127}\;\unicode{x00B5} {{\rm m}^2}$127µm². Also, the required optical power intensity at input ports is ${100}\;{\rm mW/}\unicode{x00B5} {{\rm m}^2}$100mW/µm².

Monolithically Integrated Perovskite Semiconductor Lasers on Silicon Photonic Chips by Scalable Top-Down Fabrication

Metal-halide perovskites are promising lasing materials for the realization of monolithically integrated laser sources, the key components of silicon photonic integrated circuits (PICs). Perovskites can be deposited from solution and require only low-temperature processing, leading to significant cost reduction and enabling new PIC architectures compared to state-of-the-art lasers realized through the costly and inefficient hybrid integration of III-V semiconductors. Until now, however, due to the chemical sensitivity of perovskites, no microfabrication process based on optical lithography (and, therefore, on existing semiconductor manufacturing infrastructure) has been established. Here, the first methylammonium lead iodide perovskite microdisc lasers monolithically integrated into silicon nitride PICs by such a top-down process are presented. The lasers show a record low lasing threshold of 4.7 μJcm^-2 at room temperature for monolithically integrated lasers, which are complementary metal-oxide-semiconductor compatible and can be integrated in the back-end-of-line processes.

Integrated Optical Modulator Based on Transition between Photonic Bands

An area efficient novel optical modulator with low operation voltage is designed based on integrated Mach-Zehnder Interferometer with a photonic crystal slab structure as the phase shifter. Plasma dispersion effect is utilized so that photonic band-to-band transition occurs at the operating frequency leading to a high index change (Δn = ~4) for π-phase shift on the modulator. This approach reduces the phase shifter length to a few micrometers (~5 µm) in a silicon on insulator platform and operating voltage required is around 1 V. Low voltage together with short optical interaction length decrease optical losses and power consumption during modulation process providing a great opportunity for size and system cost optimization.

Low voltage 25Gbps silicon Mach-Zehnder modulator in the O-band

In this work, a 25 Gb ps silicon push-pull Mach-Zehnder modulator operating in the O-Band (1260 nm - 1360 nm) of optical communications and fabricated on a 300 mm platform is presented. The measured modulation efficiency (VπLπ) was comprised between 0.95 V cm and 1.15 V cm, which is comparable to the state-of-the-art modulators in the C-Band, that enabled its use with a driving voltage of 3.3 V_pp, compatible with BiCMOS technology. An extinction ratio of 5 dB and an on-chip insertion losses of 3.6 dB were then demonstrated at 25 Gb ps.

Ring modulators with enhanced efficiency based on standing-wave operation on a field-matched, interdigitated p-n junction

We propose ring modulators based on interdigitated p-n junctions that exploit standing rather than traveling-wave resonant modes to improve modulation efficiency, insertion loss and speed. Matching the longitudinal nodes and antinodes of a standing-wave mode with high (contacts) and low (depletion regions) carrier density regions, respectively, simultaneously lowers loss and increases sensitivity significantly. This approach permits further to relax optical constraints on contacts placement and can lead to lower device capacitance. Such structures are well-matched to fabrication in advanced microelectronics CMOS processes. Device architectures that exploit this concept are presented along with their benefits and drawbacks. A temporal coupled mode theory model is used to investigate the static and dynamic response. We show that modulation efficiencies or loss Q factors up to 2 times higher than in previous traveling-wave geometries can be achieved leading to much larger extinction ratios. Finally, we discuss more complex doping geometries that can improve carrier dynamics for higher modulation speeds in this context.

Simplified modeling and optimization of silicon modulators based on free-carrier plasma dispersion effect

In this paper, a simplified model of silicon phase modulators is presented that enables favorable accuracy together with a substantial reduction in computational effort and without the requirement of semiconductor TCAD device simulation software. This permits fast optimization of the different parameters of a modulator. The model was successfully implemented in Phoenix Optodesigner optical software allowing the optimization of silicon phase shifters for different applications. Moreover, this model presents a great potential for the simulation of modulators based on PN interdigitated junctions, which normally require complex and time consuming 3D simulations. Simulation time was reduced by a factor of 6 for the lateral PN junction based modulator, and two orders of magnitude reduction was obtained for interdigitated PN junctions based modulators.

TiO₂ ring-resonator-based EO polymer modulator

In this work, an electro-optic (EO) ring resonator modulator was designed and fabricated in a waveguide consisting of a titanium dioxide (TiO)₂ core, silicon dioxide (SiO₂) buffer layer, EO polymer claddings, and electrodes. By optimizing the thickness of the TiO₂ and SiO₂layers, the modulator could satisfy the single-mode requirement; furthermore 52.5% TM mode was confined in the active EO polymer layers. The designed modulator could also pole the EO polymer effectively regardless of its resistivity. Therefore, the EO modulator was observed to show a high resonance wavelength shift of 2.25 × 10(-2) nm/V. The intensity modulation at 1550 nm showed a Vp-p = 1.9 V for a 3dB distinction ratio.

A 40 Gbit/s optical link on a 300-mm silicon platform

We demonstrated 40 Gbit/s optical link by coupling a silicon (Si) optical modulator to a germanium (Ge) photo-detector from two separate photonic chips. The optical modulator was based on carrier depletion in a pn diode integrated in a 950-µm long Mach-Zehnder interferometer. The Ge photo-detector was a lateral pin diode butt coupled to a silicon waveguide. The overall loss, which is mainly due to coupling (3 grating couplers times ~4 dB) was estimated to be lower than 18 dB. That also included modulator loss (4.9-dB) and propagation loss (<1 dB/cm). Both optoelectronic devices have been fabricated on a 300-mm CMOS platform to address high volume production markets.

Ultrasensitive silicon photonic-crystal nanobeam electro-optical modulator: design and simulation

Design and simulation results are presented for an ultralow switching energy, resonator based, silicon-on-insulator (SOI) electro-optical modulator. The nanowire waveguide and Q ~8500 resonator are seamlessly integrated via a high-transmission tapered 1D photonic crystal cavity waveguide structure. A lateral p-n junction of modulation length L(m) ~λ is used to alter the index of refraction and, therefore, shift the resonance wavelength via fast carrier depletion. Differential signaling of the device with ΔV ~0.6 Volts allows for a 6 dB extinction ratio at telecom wavelengths with an energy cost as low as 14 attojoules/bit.