5 - Passive silicon photonic devices

This important book is a practical guide to the design, fabrication, and testing of passive silicon photonic devices. It outlines the progress of the last decades and is organized into three parts: design principles of silicon waveguides and devices, nano-fabrication processes for passive devices, and testing of waveguide devices including vertical coupling and edge coupling setup for interfacing with fibers.This timely book: • Provides detailed materials on the operation of equipment and methods for fabrication and testing• Teaches researchers and technical staff the skills to implement silicon photonic circuits quickly and successfully• Is authored by an eminent team from Shanghai Jiao Tong University, School of Electronic Information and Electrical Engineering, Shanghai, ChinaResearchers, specialists, and students working in photonics and silicon photonics devices will find Passive Silicon Photonic Devices: Design, Fabrication, and Testing an invaluable resource.

This paper reviews our recent progresses on passive silicon photonic integrated devices and circuits, including microring resonators, polarization-handling devices, and MZI optical switches, hybrid (de)multiplexers, and reconfigurable add-drop multiplexers.

Due to sensitive scaling of the wavelength and the visible-light absorption properties with the device dimension, traditional passive silicon photonic devices with asymmetric waveguide structures cannot achieve polarization control at the visible wavelengths. In this work, a simple and small polarization beam splitter (PBS) for a broad visible-light band, using a tailored silicon nitride (Si3N4) ridge waveguide, is presented, which is based on the distinct optical distribution of two fundamental orthogonal polarized modes in the ridge waveguide. The bending loss for different bending radii and the optical coupling properties of the fundamental modes for different Si3N4 ridge waveguide configurations are analyzed. A PBS composed of a bending ridge waveguide structure and a triple-waveguide directional coupler was fabricated on the Si3N4 thin film. The TM excitation of the device based on a bending ridge waveguide structure shows a polarization extinction ratio (PER) of ≥ 20 dB with 33 nm bandwidth (624-657 nm) and insertion loss (IL) ≤ 1 dB at the through port. The TE excitation of the device, based on a triple-waveguide directional coupler with coupling efficiency distinction between the TE0 and TM0 modes, shows a PER of ≥ 18 dB with 50 nm bandwidth (580-630 nm) and insertion loss (IL) ≤ 1 dB at the cross port. The on-chip Si3N4 PBS device is found to possess the highest known PER at a visible broadband range and small (43 µm) footprint. It should be useful for novel photonic circuit designs and further exploration of Si3N4 PBSs.

Silicon photonics has emerged as a critical enabling technology for a diverse range of applications, from high-speed data communication and computing to advanced sensing and quantum information processing. This paper provides a comprehensive review of recent progress in the foundational passive devices that underpin this technological revolution. We survey the state of the art in fundamental building blocks, including strip, rib, and silicon nitride waveguides, with a focus on achieving ultra-low propagation loss. The review details essential components for light coupling and splitting, such as grating couplers, edge couplers, multimode interference couplers, and directional couplers, citing their typical performance metrics. Key wavelength filtering and routing components, including high-Q ring resonators, Mach–Zehnder interferometers, and arrayed waveguide gratings, are analyzed. Furthermore, we provide a comparative overview of the capabilities of major photonic foundries operating on a multi-project wafer model. The paper concludes by discussing persistent challenges in packaging and polarization management, and explores future trends driven by co-packaged optics, inverse design methodologies, and the expansion of silicon photonics into new application domains.

Recent applications of CRLH unit cells used to design distributed passive and active microwave devices and circuits are presented. In particular, new configurations for small-size passive devices based on quarter-wavelength transmission line sections, as well as microwave amplifiers, oscillators and frequency doublers are analyzed. The performances of these new circuit topologies are put into evidence numerically and the results are validated by experiments.

Recent progress on metamaterials: From effective medium model to real-time information processing system

High-throughput real-time optical integrators are of great importance for applications that require ultrafast optical information processing, such as real-time phase reconstruction of ultrashort optical pulses. In many of these applications, integration of wide optical bandwidth signals is required. Unfortunately, conventional all-optical integrators based on passive devices are usually sensitive to the wavelength and bandwidth of the optical carrier. Here, we propose and demonstrate a passive all-optical intensity integrator whose operation is independent of the optical signal wavelength and bandwidth. The integrator is implemented based on modal dispersion in a multimode waveguide. By controlling the launch conditions of the input beam, the device produces a rectangular temporal impulse response. Consequently, a temporal intensity integration of an arbitrary optical waveform input is performed within the rectangular time window. The key advantage of this device is that the integration operation can be performed independent of the input signal wavelength and optical carrier bandwidth. This is preferred in many applications where optical signals of different wavelengths are involved. Moreover, thanks to the use of a relatively short length of multimode waveguide, lower system latency is achieved compared to the systems using long dispersive fibers. To illustrate the versatility of the optical integrator, we demonstrate temporal intensity integration of optical waveforms with different wavelengths and optical carrier bandwidths. Finally, we use this device to perform high-throughput, single-shot, real-time optical phase reconstruction of phase-modulated signals at telecommunications bit rates.

This paper presents the recent developments of on-chip low-loss passive circuits using customized patterns that are fabricated with standard bump process (C4) for RF, mmWave and sub-THz applications in Intel16 technology. Due to the large cross-sectional area of the C4 layer, passive devices with ultralow-loss and high current capacity can be built. Common high frequency passive components such as inductors, transmission lines, and antenna arrays have been implemented as proof of concepts. To the authors' knowledge, this is the first time that passive circuits are demonstrated using the bump layer directly. These low-loss passive components enable high performance, innovative circuits and systems in a variety of applications.

Various passive photonic integrated devices have been developed successfully with silicon-on-insulator (SOI) nanowires in the past decade. It is well known that SOI-nanowire waveguides have ultrahigh index contrast ( $\Delta $ ) and ultrahigh birefringence. As a result, the structures and the design rules of a silicon photonic device are probably very different from the conventional case of using low- $\Delta $ optical waveguides. For example, some asymmetric waveguide structures have been used often to realize many silicon photonic devices developed recently. Furthermore, higher order modes have been involved in some of these silicon photonic devices. This paper discusses the special mode properties of silicon nanophotonic waveguides, including birefringence, mode dispersion, and mode hybridness. A review is then given on recent progress of these advanced passive silicon photonic devices with structural asymmetry, including on-chip polarization-handling devices, mode converters/(de)multiplexers, microring-resonator optical filters/switches, and Mach..Zehnder interferometer optical switches. Silicon photonic integrated circuits with these building blocks are also reviewed, including hybrid (de)multiplexers and reconfigurable optical add..drop multiplexers.

The compatibility of silicon photonics with existing CMOS fabrication processes enables the possibility of large scale manufacturing of integrated photonics for communication applications above 100Gbit/s. However, the design of silicon photonics devices that are able to fulfil the high-performance requirements of broad optical bandwidth ( 50nm), low loss (2dB), high-speed (25Gbit/s), low driving voltage (≥ –5V), large fabrication tolerance (±20nm) and high reproducibility across the wafer is a unique practical challenge. In this work, we present a library of passive and active integrated silicon photonic devices that meet the stringent design requirements for communication applications. The design, modelling and experimental results are presented for low loss edge couplers with insertion loss < 2dB, low-loss waveguides and bends, high-performance polarization beam splitter with extinction ratio above 25 dB, broadband directional couplers with optical bandwidth above 50nm, and arrayed waveguide gratings (AWGs) with low insertion loss < 1dB. Last but not least, high-speed silicon modulators (25Gbit/s) with phase efficiency VπL ≤ 2V.cm at DC reverse bias of ≥ –5V and low propagation loss of ≤ ∼1dB/mm are demonstrated.

Planar optical-guided-wave devices have been in existence for over 20 years. Two interesting, informative articles can be found in References 1 and 2. Much of the early work in guided-wave optics was on passive devices, but this was also when much of the theoretical understanding of optical-guided-wave (OGW) devices was developed. This theoretical understanding applies to active devices as well. It's interesting to note that the commercialization of passive, glass-based guided-wave devices has just occurred with product introductions by Corning &amp; Nippon Sheet Glass. Active OGW devices (i.e., ones where the light properties can be altered with an applied voltage) have been reported since about 1975. In 1985, Crystal Technology, Inc. announced the first commercially available product—a high-speed, efficient, intensity modulator. Throughout the ten years in between, a huge amount of technical literature has been generated. Most of the work has centered on the Ti:LiNbO3 waveguide technology although several other material systems have been demonstrated as well.Materials upon which optical-guided-wave modulators have been fabricated include: dielectrics such as lithium niobate (LiNbO3), lithium tantalate (LiTaO3), and potassium titanyl phosphate (KTP); the III-V semiconductor compounds, gallium arsenide (GaAs) and indium phosphide (InP); and a variety of organic polymers. Of these materials, waveguides on LiNbO3 are clearly the most developed and are offered for sale commercially. For this reason I will concentrate on this material system while making comparisons to the other material systems when appropriate.

Design, fabrication and characterization of a photodefinable benzocyclobutene (BCB 4022-35 is a product of DowTM) single mode rib optical waveguide is presented in this work. At first, the refractive index of polymer film is measured by the method of prism coupling. We design the single mode rib waveguide based on the geometrical adjustment of rib width, total waveguide height using conventional R-soft BPM and effective index methods. Based on the design results, BCB waveguides were fabricated by using photolithographic process with wet etching, which is quite complicated and time consuming. In this work, the insertion and propagation losses of waveguide are measured by using the conventional cut back method. The insertion losses of waveguide are 3.95 dB and 4.08 dB for TE and TM modes respectively. The propagation losses of waveguide are 1.09dB/cm and 1.20dB/cm for TE and TM modes respectively. 

This paper presents embedded substrate integrated waveguide (SIW) BPF and microstrip line-to-embedded microstrip line transition based on LTCC for 60-GHz application. The embedded SIW BPF is placed in LTCC substrate for compact system and integrated passive and active device on the other layer. But embedded SIW BPF performance is changed by interconnection via and transition. In order to low-loss interconnection with embedded passive device, microstrip line-to-embedded microstrip line transition with compensation circuit using series and shut line is proposed and implemented. The insertion loss of fabricated transition with compensation circuit is approximately 1 dB and return loss is below 10 dB from 56 GHz to 69 GHz. The proposed embedded SIW BPF including transition with compensation circuit exhibits a total insertion loss 2 dB at 61.8 GHz and the return loss is better than 16.2 dB with a 3-dB fractional bandwidth of 11.7 % (7.23 GHz). The measured insertion loss is lower than those in previous works. The overall size of the fabricated filter is 8 mm × 2.7 mm× 0.3 mm.

Insertion loss characteristics of passive devices fabricated on anodized aluminum oxide layers formed on Si substrates

Optical couplers are used in wavelength division multiplexing (WDM) applications for combining and separating wavelength channels, tapping off power for monitoring purposes, or adding and dropping specific wavelengths at a particular point in an optical fiber communication link. Most optical couplers are passive devices in the sense that they do not need to be powered externally to perform their function on optical signals. Fundamentally, optical couplers connect three or more fibers to combine, split, or redirect light signals. The key optical coupler performance parameters include insertion loss, excess loss, and crosstalk between channels.