Discretely tunable microwave photonics beamformer based on ring resonators and arrayed waveguide gratings

A device with two identical arrayed waveguide gratings (AWGs) in a DEMUX-MUX configuration within a ring resonator is proposed and modeled. This allows extracting the insertion loss of a single AWG, independent of the coupling efficiency, with less error than previous methods.

We describe a method for measuring the phase error distribution of an arrayed waveguide grating (AWG) in the frequency domain when the free spectral range (FSR) of the AWG is so wide that it cannot be covered by one tunable laser source. Our method is to sweep the light frequency in the neighborhoods of two successive peaks in the AWG transmission spectrum by using two laser sources with different tuning ranges. The method was confirmed experimentally by applying it to a 160 GHz spaced AWG with a FSR of 11 THz. The variations in the derived phase error data were very small at +/-0.02 rad around the central arrayed waveguides.

We present a compact 4x8 wavelength-routing switch that monolithically integrates fast tunable wavelength converters (TWCs) and an arrayed-waveguide grating (AWG) for optical packet switching. The TWC consists of a double-ring-resonator-coupled tunable laser which allows rapid and stable switching, and an optical gate based on a parallel amplifier structure which prevents an input optical signal from being routed through the AWG (filter-free operation). A deep-ridge waveguide technology, employed for the AWG and ring resonators, facilitates the fabrication of the switch and makes the device compact. The filter-free TWCs achieve low crosstalk of the input optical signal of less than -22 dB. The wavelength routing operation of a non-return-to-zero (NRZ) signal at 10 Gbit/s is achieved with a switching time of less than 5 ns.

Fourier methods are widely used in optical information processing for time domain waveform synthesis and detection. In such approaches an input pulse is spectrally decomposed and modulated by an appropriately designed spectral filter. In general, various ultrafast applications may need either generation or characterization of waveforms depending whether their frequency response is or is not known a priori. Ultrafast pulses prove useful in driving or probing such systems because their broad, deterministic complex spectral amplitude “sees” a large continuous portion of the system transfer function. Traditionally, space domain spectral decomposition is used to perform optical Fourier processing, where pairs of gratings and lenses are used to decompose the spectral content of the pulsed, optical waveforms. Liquid crystal and acousto-optic (AO) modulators provide a means for introduction of somewhat arbitrary system transfer functions. More recently, compact waveguide-based approaches have used arrayed waveguide gratings (AWGs) to perform an analogous spectral decomposition to those achieved with traditional, free-space coupled gratings. Information processing arrangements using the space domain for transverse spectral decomposition benefit from the maturity of such techniques, with respect to basic understanding, component quality, and the excellent phase control that free-space manipulations provide. Component insensitivity to optical power permits the shaping and detecting of high peak power pulses used to drive nonlinear optical systems. Furthermore, nonlinear optical elements can be introduced directly into these processors to provide unique ultrafast waveform synthesis capabilities with response times in the range of femtoseconds. Drawbacks to free-space approaches include scaling in volume to achieve large time bandwidth products (TBWPs) and limiting the temporal extent of waveforms coupled back into a single-mode fiber (SMF). The origin of this last restraint is the time∕space interrelation inherent in traditional pulse shaping devices. AWG approaches rely on complex waveguide elements to circumvent large processor volumes and time∕space coupling issues, but they too are practically limited by fabrication requirements. The number of resolvable spots in the output waveform for both Fourier synthesis and direct space-to-time AWG approaches is equal to the number of waveguide channels. An alternative approach to Fourier processing relying on a single transverse spatial mode can better integrate with fiber systems and photonic lightwave circuits and will scale in length only for the achievement of large TBWPs. Fiber-based and fiber-integrated processors can manipulate optical waveforms in the time domain exploiting chromatic dispersion for longitudinal spectral decomposition and applying to it Fourier synthesis techniques. Drawing on the identical mathematical treatments of diffraction in space and dispersion in time, an approximate Fourier transform (FT) of an incident optical signal is achieved via chromatic dispersion after reaching the so-called “far-field approximation.” With such an amount of dispersion, the temporal waveform closely resembles the spectrum. Such a waveform is called a longitudinal spectral decomposition wave (SDW). A time-variant element (e.g., modulator) filters this SDW. And it is possible to recompose the pulse waveform through propagation in a conjugate dispersion source matched (i.e., of opposite sign but equal magnitude) to the first dispersive element. The number of resolvable spots that such a processor offers relies on a suitable modulation scheme and the experimental ability to disperse a sub-picosecond pulse using second-order dispersion.

In this paper, we demonstrated several AWG-based silicon photonics devices fabricated with deep UV lithography on SOI platform, including cascaded AWG, AWG-based receiver with fiber-to-waveguide converters, AWG-based OADM and folded AWG with ring-reflectors. In a thin top silicon layer, the silicon nanowire AWG has a performance of relative high crosstalk. In order to reduce the crosstalk, we designed and fabricated a 4-channel cascaded AWG. Compared to the normal single silicon photonics arrayed waveguide grating with a crosstalk of ~ -12.5 dB, the crosstalk of more than 20 dB has been dramatically improved in this cascaded AWG. The AWG-based OADM device is composed of two 1×8 AWGs, MZI thermo-optic switch array and crossing array, by which 8 signals can be loaded or uploaded. The channel spacing is around 3.2 nm at the wavelength of 1550nm and the crosstalk is less than -20 dB. The dynamic extinction is around 15 dB by thermal effect and the power consumption for a single channel is less than 12.3 mW. The 8-channel receiver was designed and fabricated on a SOI wafer with 1µm-thick top silicon layer, which was composed of 5×8 AWG and 8 Ge-based butt-coupled photodetector array. The AWG device was designed on a thick SOI wafer for a good crosstalk performance. However, The silicon waveguide with a height of 1µm has a coupling issue with a cleaved standard optical fiber. In order to reduce the coupling loss with the cleaved fiber, a new cantilevered fiber-to-waveguide converter was designed to integrate at the output/input waveguide of this receiver. The measured coupling loss of this converter is around 2.4dB/facet by using a cleaved single mode fiber. The 3dB-bandwidth of this butt-coupled photodetector is more than 30 GHz at a reverse bias of -1V. The transmission capability of this receiver is more than 400Gbps. Compared to other silicon photonics devices, the AWG size is not small. A 1×4 folded silicon photonics AWG was designed and fabricated on a SOI wafer with 340nm-thick top silicon layer. This folded AWG was integrated with ring-mirrors at the end of arrayed waveguides. The optical signals are launched into the input waveguide and coupled into the arrayed waveguides through the input slab waveguides. At the end of arrayed waveguides, the signals are reflected by the ring-mirrors. The reflected signals go back to the arrayed waveguides and the input slab waveguide in sequence, and then they are separated into the four output waveguides. The measured transmission loss of this folded AWG is about 3.5 dB and the crosstalk is around 20 dB. The measured channel spacing is 6.7 nm. This size of the demonstrated arrayed waveguide grating is only half of the normal arrayed waveguide grating. Acknowledgment： This work was supported by the National Natural Science Foundation of China (No. 61674072, No. 61565011 and No. 51304097).

Astrophotonics is the next-generation approach that provides the means to miniaturize near-infrared (NIR) spectrometers for upcoming large telescopes and make them more robust and inexpensive. The target requirements for our spectrograph are: a resolving power of about 3000, wide spectral range (J and H bands), free spectral range of about 30 nm, high on-chip throughput of about 80% (-1dB) and low crosstalk (high contrast ratio) between adjacent on-chip wavelength channels of less than 1% (-20dB). A promising photonic technology to achieve these requirements is Arrayed Waveguide Gratings (AWGs). We have developed our first generation of AWG devices using a silica-on-silicon substrate with a very thin layer of silicon-nitride in the core of our waveguides. The waveguide bending losses are minimized by optimizing the geometry of the waveguides. Our first generation of AWG devices are designed for H band and have a resolving power of around 1500 and free spectral range of about 10 nm around a central wavelength of 1600 nm. The devices have a footprint of only 12 mm x 6 mm. They are broadband (1450-1650 nm), have a peak on-chip throughput of about 80% (-1 dB) and contrast ratio of about 1.5% (-18 dB). These results confirm the robustness of our design, fabrication and simulation methods. Currently, the devices are designed for Transverse Electric (TE) polarization and all the results are for TE mode. We are developing separate J- and H-band AWGs with higher resolving power, higher throughput and lower crosstalk over a wider free spectral range to make them better suited for astronomical applications.

Ring resonators are one of the fundamental building blocks of advanced integrated optical circuits. They find applications as nonlinear optical elements, filters, sensors, and switches among others. Here, a comprehensive optimization framework and experimental results of thermally tunable microring resonators in silicon photonics is presented, with a focus on standard silicon photonic foundry processes. In order to minimize the total power consumption, the ring resonators are tuned by applying a pulse‐width‐modulated electrical signal to the heaters. The thermal performance of integrated silicon and metal heaters are investigated and compared using an effective model validated by the measurement results. The heater power consumption is minimized by optimizing heater cross section, resistance, and metal contact configurations. Using the multiproject wafer run developed at CEA‐LETI, it is demonstrated that a metal heater provides 30% lower power consumption compared to an integrated silicon one, reaching a power consumption of 27.53 mW per free spectral range. The measurements are in excellent agreement with the theoretically predicted thermal performance, with a deviation as low as 5%. The proposed framework, supported by the experimental results, will serve as a design guideline set that can be easily adapted for other thermo‐optic switches in future silicon photonic applications.

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.

We discuss silicon photonic wires and components based on this technology, such as filters based on ring resonators, interferometers or arrayed waveguide gratings. The devices are fabricated using standard CMOS technology, including 193nm lithography. We also discuss their application in a number of demonstrator devices within different application fields.

Integrated nanophotonic circuits allow for realizing complex optical functionality in a compact and reproducible fashion through high-yield nanofabrication. Typically configured for single-mode operation in a single path, the optical propagation direction in such devices is determined by the waveguide layout which inherently requires smooth surfaces without scattering and restricts the device footprint to the limits of total internal reflection. Yet intentionally introducing disorder and scattering can be beneficial for the realization of novel nanophotonic components to overcome fabrication imperfections. Therefore, the understanding of the underlying physics of randomly disordered nanophotonic systems has gained increased attention. In particular on-chip spectrometers may benefit from random disorder. These devices are widely used tools in chemical and biological sensing, materials analysis and light source characterization. Conventional nanophotonic spectrometer designs are based on concepts using ring resonators, arrayed waveguide gratings or echelle gratings. Those devices are based on careful design and rely on high control of the fabrication and are therefore prone to fabrication errors and exhibit a very large footprint. Here, as part of the priority program "Tailored Disorder" (SPP 1839), we utilize multi-path interference and the interaction of light with randomly oriented scatterers to realize broadband and narrow linewidth on-chip integrated spectrometers with small footprint. In combination with integrated superconducting nanowire single-photon detectors such devices allow for resolving optical spectra on the single photon level which is of interest for single-photon spectroscopy or quantum wavelength division multiplexing.

We demonstrate ring and racetrack resonators with Qs of 3.8 to 7.5 million and 100 MHz bandwidth racetrack resonator filters, implemented in a thick silicon-on-insulator foundry platform that features a 3 µm thick device layer. We show that special racetrack resonators (with weakly guiding straight sections that transition to strongly confining bends) implemented in this platform can be preferable to rings for applications such as integrated microwave-photonic signal processing that require filters with sub-GHz bandwidth, tens of GHz of free spectral range (FSR), and a compact footprint for dense system-on-chip integration. We demonstrate ring resonators with 7.5×106 intrinsic Q, but limited FSR of 5.1 GHz and a taxing footprint of 21mm2 due to a large 2.6 mm bend-loss-limited radius. In comparison, we demonstrate two racetrack resonator designs with intrinsic Qs of 3.8×106 and 4.3×106, larger respective FSRs of 11.6 GHz and 7.9 GHz, and less than 1/20th the area of the ring resonator. Using racetrack resonators, we implemented a four-channel, 100 MHz wide passband filter bank with 4.2 to 5.4 dB insertion loss to drop ports.

Characteristics optimization in single and dual coupled silicon-on-insulator ring (disk) photonic biosensors

Optical ring or disk resonators can trap traveling optical waves in a closed path, for example, in a waveguide loop or silicon disk cavity. Energy can be added to or extracted from the cavity with the help of waveguide directional couplers. Ring/disk resonators can be fabricated with high quality factor (Q) in diverse material platforms. The high Q of these devices makes them very sensitive to small variations in (i) optical path length (phase), (ii) optical path loss (attenuation), and (iii) coupling coefficient. Any change in the optical path length can cause a shift in the resonance frequency of the ring. Whereas, the change in path loss and coupling coefficient can lead to a change in the Q of the resonator. The micro or nano opto-electro-mechanical systems (MOEMS/NOEMS) provide unique flexibility with a wide change in the tuning parameters. The tuning is obtained by either (i) displacement of the detached parts or (ii) strain in the waveguide/disk. Displacement of a structure detached from the ring/disk closer to the evanescent field can increase the effective refractive index or attenuation. The displacement of a waveguide in the directional coupler altering the gap can change the coupling coefficient. Strain from various sources can lead to refractive index (phase) and absorption changes, in addition to changing the dimensions. Mechanical, electrothermal, piezoelectric, electrostatic, and magnetic actuators have been demonstrated with MOEMS. Mechanical latching has been used to achieve nonvolatile tuning. Multi-beam supported, freestanding, and diaphragm supported structures have shown applications in sensing, optical switching, and energy conversion. MOEMS/NOEMS has recently been shown to provide the desired properties of modern sensors and photonic integrated circuits (PICs) such as low optical power consumption, high resolution, wide tuning range, low complexity, small footprint, low actuator power consumption, and compatibility with standard fabrication technologies. This chapter will start by briefly covering the basics of MOEM tuned ring/disk resonators. Then, the current technology aspects such as tuning mechanism, actuator types, and the fabrication technology will be discussed along with recent innovations. Furthermore, the evolution into NOEMS with specialized applications and materials will be emphasized along with emerging trends.

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.

The invited talk provides an overview on recent developments of InP-based photodetectors for data center applications. The two key approaches will be discussed: monolithic pre-amplification and WDM demultiplexing. The integration of semiconductor optical amplifiers (SOA) and arrayed waveguide gratings (AWG) within photonic integrated circuits (PIC) will be highlighted in the context of these two approaches. A special emphasis will be on the polarization-independent reception of data signals, which is essential for applications in data centers.