Inverse design of a dual-mode 3-dB optical power splitter with a 445 nm bandwidth

Low loss and ultra-broadband design of an integrated 3 dB power splitter centered at 2 µm

Because chemical gas is sensitive to absorption in the 2 µm band, and 2 µm matches the absorption band of the remote sensing material, many remote sensors and optical sensors are designed to operate in the 2 µm wavelength region. In this paper, we designed an integrated 3 dB power splitter centered at 2 µm. The study of this device is built on a silicon-on-insulator (SOI) platform. We introduced a subwavelength grating (SWG) to improve the performance of the device. We used the three-dimensional finite-difference time-domain (3D FDTD) method to analyze the effect of the structure on the power splitter. The insertion loss (IL) of the fundamental TE mode is only 0.04 dB at 2 µm and its bandwidth of IL <0.45d B is 940 nm (1570-2510 nm). It is suitable for multidomain and all-band photonic integrated circuits at 2 µm.

Ultra-Compact and Broadband Nano-Integration Optical Phased Array

The on-chip nano-integration of large-scale optical phased arrays (OPAs) is a development trend. However, the current scale of integrated OPAs is not large because of the limitations imposed by the lateral dimensions of beam-splitting structures. Here, we propose an ultra-compact and broadband OPA beam-splitting scheme with a nano-inverse design. We employed a staged design to obtain a T-branch with a wavelength bandwidth of 500 nm (1300-1800 nm) and an insertion loss of -0.2 dB. Owing to the high scalability and width-preserving characteristics, the cascaded T-branch configuration can significantly reduce the lateral dimensions of an OPA, offering a potential solution for the on-chip integration of a large-scale OPA. Based on three-dimensional finite-difference time-domain (3D FDTD) simulations, we demonstrated a 1 × 16 OPA beam-splitter structure composed entirely of inverse-designed elements with a lateral dimension of only 27.3 μm. Additionally, based on the constructed grating couplers, we simulated the range of the diffraction angle θ for the OPA, which varied by 0.6°-41.6° within the wavelength range of 1370-1600 nm.

On-chip Y-junction with adaptive power splitting toward ultrabroad bandwidth

Growing research interests have been directed to the emerging optical communication band at 2-µm wavelengths. The silicon photonic components are highly desired to operate over a broad bandwidth covering both C-band and the emerging 2-µm wave band. However, the dispersions of the silicon waveguides eventually limit the optical bandwidth of the silicon photonic devices. Here, we introduce a topology-optimized Y-junction with a shallow-etched trench and its utility to reverse the detrimental dispersion effect. The shallow trench enables the Y-junction to have an adaptive splitting capability over a broad spectral range. The 0.2-dB bandwidth of the power splitter exceeds 800 nm from 1400 nm to 2200 nm. The device has a compact footprint of 3 µm × 1.64 µm. The device is characterized at the C-band and 2-µm band with a measured excess loss below 0.4 dB for a proof-of-concept demonstration.

Inverse design of an ultra-compact dual-band wavelength demultiplexing power splitter with detailed analysis of hyperparameters

Inverse design has been widely studied as an efficient method to reduce footprint and improve performance for integrated silicon photonic (SiP) devices. In this study, we have used inverse design to develop a series of ultra-compact dual-band wavelength demultiplexing power splitters (WDPSs) that can simultaneously perform both wavelength demultiplexing and 1:1 optical power splitting. These WDPSs could facilitate the potential coexistence of dual-band passive optical networks (PONs). The design is performed on a standard silicon-on-insulator (SOI) platform using, what we believe to be, a novel two-step direct binary search (TS-DBS) method and the impact of different hyperparameters related to the physical structure and the optimization algorithm is analyzed in detail. Our inverse-designed WDPS with a minimum feature size of 130 nm achieves a 12.77-times reduction in footprint and a slight increase in performance compared with the forward-designed WDPS. We utilize the optimal combination of hyperparameters to design another WDPS with a minimum feature size reduced to 65 nm, which achieves ultra-low insertion losses of 0.36 dB and 0.37 dB and crosstalk values of -19.91 dB and -17.02 dB at wavelength channels of 1310 nm and 1550 nm, respectively. To the best of our knowledge, the hyperparameters of optimization-based inverse design are systematically discussed for the first time. Our work demonstrates that appropriate setting of hyperparameters greatly improves device performance, throwing light on the manipulation of hyperparameters for future inverse design.

93-THz ultra-broadband and ultra-low loss Y-junction photonic power splitter with phased inverse design

Optical power splitters with ultra-broadband and ultra-low insertion loss are desired in the field of photonic integration. Combining two inverse design algorithms for staged optimization, we present the design of a Y-junction photonic power splitter with 700 nm wavelength bandwidth (from 1200 nm to 1900 nm) within a 0.2 dB insertion loss, corresponding to a 93 THz frequency bandwidth. The average insertion loss is approximately -0.057 dB in the valuable C-band. Moreover, we comprehensively compared the insertion loss performance of different types and sizes of curved waveguides, and also give the cases of 1:4 and 1:6 cascaded power splitters. These scalable Y-junction splitters provide new alternatives for high-performance photonic integration.

Silicon MMI-based power splitter for multi-band operation at the 1.55 and 2 µm wave bands

Multimode interference (MMI)-based power splitters are fundamental building blocks for integrated photonic devices consisting of an interferometer structure. In order to forestall the 'capacity crunch' in optical communications, integrated devices capable of operating in multiple spectral bands (e.g., the conventional telecom window and the emerging 2 µm wave band) have been proposed and are attracting increasing interest. Here, we demonstrate for the first time, to the best of our knowledge, the realization of a dual-band MMI-based 3 dB power splitter operating at the 1.55 and 2 µm wave bands. The fabricated power splitter exhibits low excess losses of 0.21 dB and 0.32 dB with 1 dB bandwidths for 1500-1600 nm and 1979-2050 nm, respectively.

Wideband and Channel Switchable Mode Division Multiplexing (MDM) Optical Power Divider Supporting 7.682 Tbit/s for On-Chip Optical Interconnects

Silicon photonics (SiPh) are considered a promising technology for increasing interconnect speed and capacity while decreasing power consumption. Mode division multiplexing (MDM) enables signals to be transmitted in different orthogonal modes in a single waveguide core. Wideband MDM components simultaneously supporting wavelength division multiplexing (WDM) and orthogonal frequency-division multiplexing (OFDM) can significantly increase the transmission capacity for optical interconnects. In this work, we propose, fabricate and demonstrate a wideband and channel switchable MDM optical power divider on an SOI platform, supporting single, dual and triple modes. The switchable MDM power divider consists of two parts. The first part is a cascaded Mach-Zehnder interferometer (MZI) for switching the data from their original TE₀, TE₁ and TE₂ modes to different modes among themselves. After the target modes are identified, mode up-conversion and Y-branch are utilized in the second part for the MDM power division. Here, 48 WDM wavelength channels carrying OFDM data are successfully switched and power divided. An aggregated capacity of 7.682 Tbit/s is achieved, satisfying the pre-forward error correction (pre-FEC) threshold (bit-error-rate, BER = 3.8 × 10^-3). Although up to three MDM modes are presented in the proof-of-concept demonstration here, the proposed scheme can be scaled to higher order modes operation.

Broadband multimode 3 dB optical power splitter using tapered couplers

A design of a 1 × 2 multimode 3 dB optical power splitter using tapered couplers is proposed and investigated in this paper. As an example, a 1 × 2 splitter processing five-lowest order transverse-electric-polarized modes is designed and optimized by utilizing finite difference time domain method and particle swarm optimization algorithm. To verify the feasibility of this novel design, the optimized device is fabricated on a silicon-on-insulator platform. The coupling lengths of tapered couplers are respectively 6.5 µm, 6.0 µm, 3.5 µm, 5.0 µm, 5.0 µm, 7.5 µm, 6.0 µm, 5.0 µm, and 8.0 µm. Measurement results reveal that, for the fabricated splitter, the power uniformity varies from 0.041 to 0.88 dB, the crosstalk ranges from -23.96 to -14.12 dB, and the insertion loss changes from 0.089 to 1.50 dB within a bandwidth from 1520 to 1600 nm.

Highly scalable and flexible on-chip all-silicon mode filter using backward mode conversion gratings

Mode filters are fundamental elements in a mode-division multiplexing (MDM) system for reducing modal cross-talk or realizing modal routing. However, the previously reported silicon mode filters can only filter one specific mode at a time and multiple modes filtering usually needs a cascade of several filters, which is adverse to highly integrated MDM systems. Here, we propose a unique concept to realize compact, scalable and flexible mode filters based on backward mode conversion gratings elaborately embedded in a multimode waveguide. Our proposed method is highly scalable for realizing a higher-order-mode-pass or band-mode-pass filter of any order and capable of flexibly filtering one or multiple modes simultaneously. We have demonstrated the concept through the design of four filters for different order of mode(s) and one mode demultiplexer based on such a filter, and the measurement of two fabricated 11μm length filters (TE1-pass/TE2-pass) show that an excellent performance of insertion loss <1.0dB/1.5dB and extinction ratio >29dB/28.5dB is achieved over a bandwidth of 51.2nm/48.3nm, which are competitive with the state-of-the-art.