Enabling photonic integration technology for microwave photonics in 5G systems

A Bloch surface wave (BSW) confined at the surface of a truncated dielectric multilayer is a low-loss platform for chip-scale photonic integration. The guided BSW in a dielectric ridge is confined by the photonic band gap vertically, yet couples into the continuum modes of the multilayered substrate horizontally. We demonstrate that a low-loss BSW waveguide can be realized with the quasibound BSW modes in the continuum by engineering the geometric parameters, due to the destructive interference of multiple leakage channels in the multilayered substrate. In addition, a high-Q BSW resonator is obtained by optimizing the geometric parameter of the multilayered substrate, which provides an alternative way to realize ultrasmall resonators with a high-Q factor. The photonic integrated circuits on a low-loss BSW platform can be utilized for optical communications, enhancing light-matter interactions, and nonlinear optical applications.

Standardization of 3rd Generation (3G) mobile communication systems has produced the first specification releases and the commercial deployment of the 3G systems has started. Whereas 1G and 2G focused on efficiently providing voice services, in 3G a lot of attention has been devoted to solutions that support both Circuit Switched (CS) and Packet Switched (PS) communication. That has called for very flexible air interface and network solutions. 3G will continue to evolve and there are already on-going standardization activities that will, for example, boost the peak data rates up to 5-10 Mbps and improve spectral efficiency by 2-4 times. In the future, 3G evolution will be going towards 10/100 Mbps peak data rates in wide/local are coverage, respectively. This will take place partly because of technical improvements of 3G radio interface solutions, but also due to network evolution which will allow the integration other radio access methods like radio LANs into the 3G system. In longer term the 3G network evolution will be going towards ALL-IP networks. As 3G evolution seems to be going towards 10 Mbps/100 Mbps peak data rates and ALL-IP networks any beyond 3G air interface or network solution should be clearly better in order to justify its technical and commercial feasibility. Given the long evolution time of 3G and integration of other radio access schemes with 3G radio we may not even see a new, complete beyond 3G system being developed. Maybe we will just witness the emergence of a new, more advanced radio access solution which will then be connected to the evolving 3G network. As 3G evolution will continue for several years to come the research targets for any beyond 3G solutions must be set very high. When it comes to air interface, we should aim at 100 Mbps peak data rates for wide area access with high mobility, and at 1 Gbps for local area access with low mobility. Regarding possible commercial launches of any beyond 3G systems or solutions they could then take place around year 2010 or even later.

One of the prominent challenges for widespread adoption of silicon photonics (SiPh) technology is the availability of an integration platform that can simultaneously meet a wide range of power, performance, and cost criteria in different applications. As a result, there is a diversity of SiPh integrated solutions proposed or demonstrated, but none is considered as a common solution. In this paper, we will first survey industry proposed photonic engine structures in monolithic and heterogeneous integration on their strengths and weaknesses. We will then propose a compact and universal PE structure - COUPE (COmpact Universal Photonic Engine) that could consolidate different requirements onto the same integration platform. COUPE has the electrical IC - photonic IC integration with the electrical interface designed to minimize the EIC-PIC coupling loss. Compared with industry proposed PE technology, COUPE can provide low insertion loss for both grating coupler (GC) and edge coupler (EC). For either GC or EC, the COUPE is a solid structure without cavities or mechanically weak parts, thus enabling low insertion loss without contamination or mechanical concerns. COUPE also has the flexibility to be integrated easily with host ASIC to form a co-package structure. The COUPE integration scheme can meet the most demanding system requirements and pave the way for SiPh-based wafer level system integration (WLSI) for high performance computing applications.

In this paper, a Reflective Semiconductor Optical Amplifier based, Radio-over-Fibre access network configuration has been proposed to feed future millimeter-wave radio systems. The system architecture combines several approaches to overcome the challenges of millimeter-wave signal transmission. Reflective semiconductor optical amplifier modulator realizes a colorless and relatively cost-effective Remote Antenna Unit. The same optical carrier is used for both downlink and uplink. Optical single-sideband modulation is used at the downlink, which is robust against chromatic dispersion, but the complex realization of this modulation format is not possible at the Remote Antenna Unit. Optical intermediate frequency transmission is applied at the uplink direction, and the required local oscillator signal originates from the central station. The critical element is the reflective optical amplifier, as it compensates for the optical loss and works as an external intensity modulator. The operation of the reflective optical amplifier is modeled by multisection rate and wave equation-based description. The amplification and modulation behaviors of an available reflective optical amplifier are also measured. The experimental work validated the colorless operation and the quality of the modulation versus bias current and input optical power. Finally, system simulation was realized. The uplink and downlink power budgets were balanced, and optimal values for the optical coupling rate and RSOA bias current have been selected.

Photonic integration is an enabling technology for photonic quantum science, offering greater scalability, stability, and functionality than traditional bulk optics. Here, we describe a scalable, heterogeneous III-V/silicon integration platform to produce Si3N4 photonic circuits incorporating GaAs-based nanophotonic devices containing self-assembled InAs/GaAs quantum dots. We demonstrate pure single-photon emission from individual quantum dots in GaAs waveguides and cavities - where strong control of spontaneous emission rate is observed - directly launched into Si3N4 waveguides with > 90 % efficiency through evanescent coupling. To date, InAs/GaAs quantum dots constitute the most promising solid state triggered single-photon sources, offering bright, pure and indistinguishable emission that can be electrically and optically controlled. Si3N4 waveguides offer low-loss propagation, tailorable dispersion and high Kerr nonlinearities, desirable for linear and nonlinear optical signal processing down to the quantum level. We combine these two in an integration platform that will enable a new class of scalable, efficient and versatile integrated quantum photonic devices.

Brillouin optical time‐domain analysis (BOTDA) is a powerful distributed fiber‐optic sensing technique, widely used in various fields. However, its widespread adoption is hindered by bulky and costly discrete‐component systems. Photonic integration technology offers a compelling solution to this challenge. In this paper, we demonstrate a highly integrated BOTDA transmitter, realized through the hybrid integration of an indium phosphide (InP) distributed feedback (DFB) laser chip with a silicon‐on‐insulator (SOI) photonic integrated circuit (PIC). This in‐house‐designed SOI PIC comprises three main functional sections: light selection and distribution, pump light generation, and probe light generation. The integrated BOTDA transmitter supports various modulation schemes, while a conventional single‐pulse configuration is adopted in this work for system performance evaluation. A Brillouin frequency shift (BFS) uncertainty of is achieved over a standard single‐mode fiber, with a spatial resolution (SR) of and 1000 times of averaging. At a higher SR of , a BFS uncertainty of is realized over a sensing fiber with 1000‐time averaging. To the best of our knowledge, this work presents the first dedicated on‐chip BOTDA transmitter, offering a promising path toward compact, scalable, and cost‐effective BOTDA solutions.

In this paper, we explore the potential of silicon oxycarbide (SiOC) as a novel dielectric platform for integrated photonics and present photonic waveguides. The interesting features of SiOC are its wide tunable window of refractive index and low absorption, that are considered key for large scale photonic integration. It is possible to tune SiOC refractive index from silica glass (1.45) to silicon carbide (3.2) that allows to realize a myriad of photonic passive devices. We have prepared SiOC thin films by employing reactive RF sputtering technique and examined their structural and optical properties using several techniques such as SEM, AFM, ellipsometry, profilometry, and prism coupling. For the first time, SiOC thin films with index of refraction of 1.554 at the standard telecom wavelength 1.55 μm are exploited for the fabrication of photonic waveguides and the propagation losses around 0.37 dB/mm are measured. SiOC photonic waveguides exhibit relatively higher index contrast with silica cladding when compared to traditional Ge-doped silica platform.

The performance of integrated planar waveguide mode locked lasers can be enhanced using the available photonic integration platform technology in indium-phosphide. Extended cavity mode locked oscillators including DBR mirrors and phase modulators can be realized at telecom wavelengths to improve performance and control over the device. Integrated pulse shapers and special amplifiers can be used to improve the output properties further.

The fast-maturing photonic integration technology is calling for a versatile platform that supports both active and passive functions as well as high scalability through component miniaturization. Indium phosphide (InP) has long been recognized for its ability to deliver a comprehensive suite of photonic components. InP membrane technology has emerged as a next-generation solution that could unite the functional completeness with high scalability. This paper describes recent advancements in the InP-membrane-on-Si (IMOS) platform, which supports high-performance passives, polarization and mode handling, native light sources, amplifiers, modulators and detectors, and novel material integration.

We introduce a three-dimensional modulation format using a Stokes-vector direct-detection system, where a pulse amplitude modulation (PAM) signal is polarization multiplexed with a quadrature amplitude modulation (QAM) signal. The phase reference of the PAM signal enables the retrieval of the phase information of the QAM signal using a Stokes vector receiver (SVR). A dual-polarization in-phase–quadrature modulator is employed to generate QAM-PAM optical signals with chromatic dispersion precompensation. We show direct detection of dual-polarization 16QAM-PAM2 and 16QAM-PAM4 signals delivering 280 and 336 Gb/s (net bit rate 233 and 280 Gb/s) below the soft-decision forward error correction threshold of 2 $\times$ 10 $^{-2}$ at 320 and 80 km, respectively. In addition, we study system performance at different modulation formats and symbol rates. Our findings indicate that increasing the order of modulation formats of the QAM signal is better than increasing that of the PAM signal to achieve the same bit rate. Finally, the performance of a 56 Gbaud 16QAM signal with PAM2 modulation on one polarization and a 56 Gbaud 16QAM signal with a pilot carrier on the orthogonal polarization detected with an SVR is experimentally investigated.

Integrated photonic platforms such as the SOI platform, the InP platform and the Si3N4 platforms have their own advantages and limitations. To achieve more diverse functionalities on a photonic chip, the combination of different material platforms is extremely important. This is generally carried out by either hybrid integration, heterogeneous integration or monolithic integration. The goal of this thesis is to develop generic integrated platforms and building blocks that enable various active-passive photonic integrations based on the Si3N4 platform. Chapter 1 reviewed the challenges, integration schemes in photonic integrated circuits (PIC), and recent advances in the Si3N4 PICs. Benefiting from excellent optical features of the Si3N4, i.e., the low-loss and large transparency window (0.4–2.35 µm), in Chapter 2, we investigated passive building blocks with optical designs, providing favorable performance of individual components in the Si3N4 platform. Then in Chapter 3, we demonstrated the hybrid integration and monolithic integration between the Si3N4 and polymer material with high-performance optical couplings. In order to realize the active-passive integration in the Si3N4 platform, in Chapter 4, we developed a double-layer photonic platform with standardized processes and good overlay by monolithic integration between the Si3N4 and rare-earth-ion doped Al2O3 material, showing great potentials of scalable and tolerant integrations of active functionalities in the Si3N4 platform. Chapter 5 demonstrated the first application of the double-layer platform, i.e., the integrated Al2O3:Er3+-Si3N4 amplifiers. A novel gain characterization methodology is introduced and high optical gain (~18 dB) has been achieved. Overall, the work in this thesis provides advances in understanding the characteristics of different integration platforms, especially in the development of the double-layer platforms for the active-passive integration of the Si3N4 and rare-earth-ion doped Al2O3, and the integrated Al2O3:Er3+-Si3N4 amplifiers. The investigations pave the way of various applications based on active-passive integration of the Si3N4 and rare-earth-ion based materials.

Future flexible transceivers will be able to adjust modulation format, symbol rate and FEC scheme according to the channel and network conditions. This paper uses a combination of theoretical derivations and experimental results to recommend the best set of parameters to satisfy a specific demand to be routed along the network. In particular, for a given required OSNR (which is related to reach) and desired net bit rate, and assuming a capacity-achieving FEC scheme, the paper provides the set of modulation format, symbol rate and code rate which requires the minimum bandwidth, while offering an arbitrarily low bit error rate. We observed that optimum operating points required FEC schemes with overheads ranging from almost 0 to 100%, which is an important guideline for future flexible optical communications systems.

The deployment of the new 5G system and ultra-broadband access networks, on one side, and the advent of network disaggregation and cloudification paradigms, on the other, are producing disruptive changes in metropolitan area networks (MANs). The new central offices will be more like small data centers than traditional Telco-type central offices. The presence of general-purpose servers, in partial or total replacement of specialized equipment or cards, and also hosting new functions and services, significantly changes the way the central office is organized and how the equipment internetworks. After having defined a reference architecture named cloudified-MAN, the paper briefly introduces the enabling technologies that include information technology (IT) systems, packet switches, and optical equipment. A disaggregated model is applied to all layers and systems. In the optics field, special insight on high data rate (up to 1.6 Tb/s) transceiver technology developed by the TERIPHIC project is provided as an example of low-cost and low-power technology. Through a quantitative techno-economic case study on a realistic network scenario aimed at short-term and medium-term time horizons, the paper provides indications on what could be the impact of the new architecture on costs and energy consumption. The main outcome of the study is that the IT and optical parts are those with the highest fractions of overall cost, and specifically for the optics, the cost of wavelength division multiplexing transceivers increases significantly in the medium term due to the demand for high-capacity connections ( > 400 G b / s ), while the line system cost (reconfigurable optical add-drop multiplexer) decreases in percentage. Another significant result is that in terms of energy consumption, the IT component has been found to be the dominant one (70%–75% of the total), followed by packet devices (about 20%–25%) and optical systems, the latter with significantly lower percentage values (less than 5%) in all cases analyzed.

Quantum-photonic chips, which integrate quantum light sources alongside active and passive optical elements, as well as single-photon detectors, show great potential for photonic quantum information processing and quantum technology. Mature semiconductor nanofabrication processes allow for scaling such photonic integrated circuits to on-chip networks of increasing complexity. Second-order nonlinear materials are the method of choice for generating photonic quantum states in the overwhelming majority of linear optic experiments using bulk components, but integration with waveguide circuitry on a nanophotonic chip proved to be challenging. Here, we demonstrate such an on-chip parametric down-conversion source of photon pairs based on second-order nonlinearity in an aluminum-nitride microring resonator. We show the potential of our source for quantum information processing by measuring the high visibility anti-bunching of heralded single photons with nearly ideal state purity. Our down-conversion source yields measured coincidence rates of 80 Hz, which implies MHz generation rates of correlated photon pairs. Low noise performance is demonstrated by measuring high coincidence-to-accidental ratios. The generated photon pairs are spectrally far separated from the pump field, providing great potential for realizing sufficient on-chip filtering and monolithic integration of quantum light sources, waveguide circuits and single-photon detectors.

Photonic integration opens the potential to reduce size, power, and cost of applications normally relegated to table- and rack-sized systems. Today, a wide range of precision, high-end, ultra-sensitive, communication and computation, and measurement and scientific applications, including atomic clocks, quantum communications, processing, and high resolution spectroscopy, are ready to make the leap from the lab to the chip. However, many of these applications operate at wavelengths not accessible to the silicon on insulator-based silicon photonics integration platform due to absorption, power handling, unwanted nonlinearities, and other factors. Next generation photonic integration will require ultra-wideband photonic circuit platforms that scale from the ultraviolet to the infrared and that offer a rich set of linear and nonlinear circuit functions as well as low loss and high power handling capabilities. This article provides an assessment of the field in ultra-wideband photonic waveguides to bring power efficient, ultra-high performance systems to the chip-scale and enable compact transformative precision measurement, signal processing, computation, and communication techniques.