Efficient photonic circuits analysis method based on subnetwork growth approach.

Coronagraph designs that use photonic integrated circuits have the highest theoretical throughput for off-axis signals, and therefore the highest potential exoplanet yield for future high-contrast direct imaging campaigns. Using the rejected starlight, the photonic integrated circuit may also provide simultaneous wavefront sensing, allowing for the correction of non-common-path aberrations. This work considers how a photonic circuit should be configured to maximize its sensitivity to phase aberrations. Two cases are considered: in the first, the photonic circuit is coupled directly to an electric field in a piecewise manner, while in the second, the circuit is coupled to the field via an optical mode sorter. In either case, this work constructs a unitary matrix, which can be applied by a photonic circuit to produce maximum sensitivity.

Integrated lithium niobate (LN) photonic circuits have recently emerged as a promising candidate for advanced photonic functions such as high-speed modulation, nonlinear frequency conversion, and frequency comb generation. For practical applications, optical interfaces that feature low fiber-to-chip coupling losses are essential. So far, the fiber-to-chip loss (commonly >10 dB/facet) has dominated the total insertion losses of typical LN photonic integrated circuits, where on-chip losses can be as low as 0.03-0.1dB/cm. Here we experimentally demonstrate a low-loss mode size converter for coupling between a standard lensed fiber and sub-micrometer LN rib waveguides. The coupler consists of two inverse tapers that convert the small optical mode of a rib waveguide into a symmetrically guided mode of a LN nanowire, featuring a larger mode area matched to that of a tapered optical fiber. The measured fiber-to-chip coupling loss is lower than 1.7dB/facet with high fabrication tolerance and repeatability. Our results open the door for practical integrated LN photonic circuits efficiently interfaced with optical fibers.

Optical links and photonic integrated circuits require integration of photonic and electronic devices at chip, module, or board level. The complexity of such systems is motivating a need for system level CAD tools which can simulate electronic and photonic devices and circuits simultaneously and at multiple levels of abstraction. Furthermore integrating photonic devices into conventional electronic computer and communication systems needs to be justified in terms of cost, performance, and portability of existing computer software and hardware. Thus system level analysis of optoelectronic interconnect system is clearly necessary to ensure that an overall functional and performance requirements are met. The proposed approach for system level modeling is to integrate photonic device simulations into the established electronic design automation environment, particularly VHDL-based one. VHDL description of photonic devices will provide benefits such as portability of individual design, system level performance analysis before building a real system, and synthesis capability for a rapid- prototyping. This paper demonstrates the use of basic VHDL entities of various passive optical waveguide components and a special VHDL package (`Optical_Package') defining physical photonic parameters to verify the feasibility of this approach. It includes modeling and simulation of global signal distribution network on MCMs using optical interconnect and wavelength division (de)multiplexing-based optical link.

A design framework to implement non-unitary input–output operations to a practical unitary photonic integrated circuit is described. This is achieved by utilising the cosine-sine decomposition to recover the unitarity of the original operation. The recovered unitary operation is decomposed into fundamental unitary building blocks, forming a photonic integrated circuit network based on directional couplers and waveguide phase shifters. The individual building blocks are designed and optimised by three-dimensional full-wave simulations and scaled up using a circuit approach. The paper investigates the scalability and robustness of the design approach. Our study demonstrates that the proposed approach of performing unitary matrix completion can be applied to any arbitrary matrices. This design approach allows for implementation of non-unitary operations to perform various linear functions in neuromorphic photonics for computing, sensing, signal processing and communications.

One of the key challenges in Silicon based optical interconnect system remains to be the efficient coupling of optical signals from the submicron size on-chip waveguides to standard single mode (SM) fibers with low insertion loss (IL) and relaxed alignment tolerance. Large optical alignment tolerance allows optical connectors to be attached to on-chip waveguides passively using standard semiconductor pick-and-place assembly tools that have placement accuracies of 10- 15μm. To facilitate the assembly, optical fiber coupling elements need to be modular and compact. They have to also have low profile to avoid blocking air flow or mechanical interference with other elements of the package. In this paper we report the development of a two-dimensional (2D) SM optical fiber coupling architecture that consists of Si based photonic lightwave circuit (PLC) substrate and a high-density micro-lensed fiber optic connector. The system is compact, efficient and has large optical alignment tolerance. At 1300nm an insertion loss of 2.4dB and 1.5dB was measured for the PLC module and the fiber optic connector, respectively. When the PLC module and connector was aligned together, a total insertion loss of 7.8dB was demonstrated with x,y alignment tolerance of 40μm for 1dB optical loss. The SM optical coupling architecture presented here is scalable, alignment tolerant and has the potential to be manufactured in high volume. To our knowledge, such a system has not been reported in the literature so far.

Ongoing research at SUNY Polytechnic Institute to enable large scale fabrication of quantum devices with tightly controlled performance characteristics will be presented. Josephson junctions and transmon qubits patterned with 193 nm lithography will be used to illustrate how advanced process tools can control critical dimensions of devices, necessary for building larger ensembles of qubits. Advances in the CMOS industry enable superior surface roughness and interface quality to be achieved across the entire 300mm wafer – some examples will be presented. The integration of photonic circuits (waveguides and on-chip cryogenic IR emitters) with superconducting Josephson junctions to enable large-scale neuromorphic computing structures in the near future will be discussed. Ongoing work on developing materials and processes for UV-transparent photonic circuits at 300mm will be presented – such chips could be useful as part of the interface to trapped ion qubits. The talk will wrap up with a discussion of the synergies in technology development, and functionality integration that can be achieved using an advanced fabrication facility.

Planar Photonic Circuits can perform many useful functions in optical communications systems, such as wavelength division multilplexing (WDM), optical channel add/drop, fibre/waveguide coupling, and amplifier gain equalization. They perform these functions by the interaction of the device structure with the light inside them. There are very effective and proven numerical methods available for modelling this interaction, such as the Beam Propagation Method (BPM), the Finite Difference Time Domain (FDTD) method, and coupled mode theory (CMT). However, these methods work on a microscopic level (typically the smallest distance is about 0.1 microns), but photonic circuits, on the other hand, can occupy an entire wafer (scale: 10 cm). The analysis must span 5 or more orders of magnitude in the change in scale. The successful analysis needs to combine the basic microscopic techniques with an approach at a more abstract, or system, level. It is interesting that software designed for the analysis of optical communication systems can be applied to planar photonic circuits. This paper shows an example of a practical photonic circuit, a lattice filter, that cannot be analysed by BPM alone. It will be demonstrated that when used with a system level analysis, the whole device can be simulated.

An on-chip quantum light source based on spontaneous four-wave mixing is an essential element for developing quantum photonic integrated circuit technology, which has the advantage of no connection loss owing to the integration of the source into photonic circuits. The waveguide-based quantum light source inevitably causes propagation loss owing to imperfections in the fabrication process, but the propagation loss effects on photon-pair generation have not been extensively studied. In this study, propagation loss effects were examined using theoretical and experimental methods. In theory, the performance of quantum light sources, such as brightness, heralding efficiency, and coincidence-to-accidental ratio, strongly depend on propagation loss. We fabricate several waveguides with a moderate propagation loss of 2.2 dB/cm to investigate the loss dependence and ascertain that the brightness, heralding efficiency, and coincidence-to-accident ratio strongly correlate with the length of the optical waveguide. The maximum coincidence-count brightness occurred at an optimization length of 1/α, where α is the absorption coefficient. In contrast, the single-count brightness shows slightly different waveguide length dependence owing to loss-induced one-photon states. We expect that the results obtained in this study will greatly assist in determining the proper waveguide length for photon-pair generation according to the source's application fields. The results will be helpful in the development of a quantum light source suitable for practical and quantum optical integrated circuits and will lead to the development of high-fidelity quantum technologies.

Nonreciprocal light transmission is indispensable in many photonic circuits. It forms the basis of optical isolators, which allow the propagation of light in a specific direction while blocking the propagation in the opposite direction [1] . When placed after a laser, an optical isolator inhibits back-reflections in the laser and also alleviates multipath interference [2] . There are three major methods to achieve non-reciprocal optical transmission i.e. modulation, depositing magneto-optic materials, and non-linear effects. The modulation based approach has the potential to deliver high isolation and offers seamless integration with existing silicon photonic integrated circuit components [3] .

We propose and numerically demonstrate operation of a processing-free functional photonic integrated circuit based on a semiconductor quantum template. This template combines monolayer engineering of the well/barrier interfaces in quantum-well structures with their coherent nonlinear effects to spatially form desired patterns of refractive index, gain and absorption without any need for top-down processes such as lithography, etching, postprocessing epitaxial overgrowth, etc. As an example, we investigate an integrated circuit that includes a distributed feedback laser and a multitask functional section that can act as an ultra-fast attenuator, modulator or amplifier on demand. The distributed feedback laser is based on gain-without inversion to overcome various losses and induce single mode operation. The photonic circuit proposed in this paper is optically activated and holds the promise of highly functional multicomponent integrated photonic circuits fabricated in a single epitaxial growth.

To date, several photonic applications have been demonstrated without considerable thermal management efforts. However, in phase-sensitive photonic applications, thermal management becomes of utmost importance. Thermal management of photonic systems requires not only efficient heat dissipation, but also reduction of on-chip temperature gradients. Particularly in highly integrated systems, in which several components are integrated within a single photonic integrated circuit, the reduction of on-chip temperature gradients is necessary to guarantee the correct functionality of the system. Due to their high integration density as well as their extreme temperature sensitivity, optical phased arrays are ideal examples of a system, where thermal management is required. Ideally, thermal management solutions of such systems should not require additional power for operation. Therefore, it is desired to improve the heat dissipation and to reduce temperature gradients by structural modifications of the photonic circuit. Furthermore, to cope with the advantages of silicon photonics, thermal management solutions must be compatible with series fabrication processes. In this work, complementary metal–oxide–semiconductor (CMOS)-compatible measures for thermal management of silicon photonic integrated circuits are proposed and validated by characterization of in-house fabricated thermal demonstrators. The proposed concepts are extremely efficient not only in reducing temperature gradients, but also in improving the heat dissipation from integrated heat sources.

Revisiting the future All-Optical Network within its Transport, Switching and Access functionalities or considering the increasing demand for Datacommunications, it appears that a wide range of optoelectronic components with balanced performances and costs will be required. Concerning this balance, it has been recognised that package structures based on silicon boards might contribute to a generic and flexible technological approach. The more popular has been the flip-chip assembly of optoelectronic components on silicon boards with V-grooves in order to perform passive, and therefore cost-effective alignment with single mode fibers [1]. More recently [2,3,4,5,6], it has been proposed to extend this approach to silicon boards with integrated silica waveguides. This opens the way for the planar integration of several Photonic Integrated Circuits (PICs) [7, 81 that is, several monolitnically integrated optoelectronic circuits (figure 1). This approach can be considered as the photonic counterpart of the Multi-chip Module Integrated Circuits (MMICs) approach previously developed for electrical chips. These new photonic circuits might be therefore described as Multi-chips Photonic Integrated Devices (MPICs).

Maskless selective area cw Nd:YAG laser annealing of GaInAsP/InP quantum well (QW) structures has been investigated as a possible route towards the fabrication of monolithically integrated photonic circuits. Laser irradiation of a 5 QW laser structure, originally designed for lasers emitting at 1.52 μm, yielded material having a continuously changing band gap ranging from 1.52 to 1.4 μm over the distance of about 3 mm. Bars with arrays of ridge waveguide lasers, having cavity lengths from 300 to 600 μm, were fabricated from the processed material. An individual bar, 2–3 mm long, comprised lasers operating typically between 1.4 and 1.52 μm. The lasers showed stable threshold current density and high quantum efficiency at all operating wavelengths. The results indicate that the applied approach has the potential to realize the cost-effective fabrication of advanced photonic devices and photonic integrated circuits.

In this paper, we present the development of a miniaturized Laser Doppler Vibrometer (LDV) system, based on the 3D hybrid integration of the Si3N4 platform of LioniX (TriPleX) and the polymer platform of FhG-HHI (PolyBoard). The photonic integrated circuit (PIC) supports all the functionalities of an LDV system including the splitting of the input light to the measurement and the reference beam, the introduction of an optical frequency shift up to 100 kHz, polarization handling and detection of the reflected measurement beam, using a heterodyne detection technique. The optical frequency shift is accommodated in the TriPleX section of the PIC based on a simple serrodyne scheme, where a phase modulator is driven with a sawtooth signal with the desired frequency. The modulation of the optical field is based on the stress-optic effect utilizing thin-films of PZT deposited on top of the waveguide structures of the TriPleX platform, capable of supporting modulation frequencies up to several MHz. The PolyBoard part enables polarization handling and heterodyne detection of the reflected beam using micro-optic elements on chip, including a polarization beam splitter (PBS), a half wave plate (HWP), and a pair of balanced detectors with four photodiodes that are flip chip bonded on the top. The TriPleX and the PolyBoard platform were brought together based on the 3D hybrid integration, using mode size converters and vertical directional couplers with coupling losses lower than 15 dB. On-chip beating, using the integrated photodiodes is experimentally demonstrated.

Photonic integrated circuits (PICs) increasingly require more advanced integrated functionalities and devices to meet the key application challenges. This evolution with the serial integration of optical functions in the same photonic circuit often results in internal reflections and optical feedback, which can specifically destabilize lasers. One solution to overcome this issue is to integrate an optical isolator at the output of the lasers. Among various proposed designs, magneto-optical-based isolators have significantly improved over the past decades in terms of compactness, insertion loss, isolation ratio, and spectral isolation bandwidth. Despite these improvements, the TE optical isolator still lacks performance. This paper introduces a new operational principle for a TE optical isolator based on modal beating in a transverse magneto-optical Kerr effect (TMOKE) coupled-waveguide system. This approach combines evanescent-coupled silicon waveguides and the magneto-optical effect, resulting in a nonreciprocal propagation that can be optimized for optical isolation. This new concept shows promise in achieving a high-performing TE optical isolator, as it does not depend on resonance and is free from constraints associated with interferometers. Based on data from magneto-optical garnet materials, the simulated device has a length of 500 and its 20 dB-isolation bandwidth is as high as 35 nm. With broadband and high isolation, this simulated device opens possibilities for miniaturizing complex photonic circuits used in optical communication, data communication, and optical sensing.