Photonic Packaging Research Articles

Etching-Free Fabrication and Integration of 45° Micro-Mirror for Surface-Compatible Photonic Packaging

Etching-Free Fabrication and Integration of 45° Micro-Mirror for Surface-Compatible Photonic Packaging

Tolerances of the alignment of fibers to photonic integrated circuits

This work presents the solutions to the alignment of two Gaussian beams representing two sides of the optical connection between a fiber and a photonic integrated circuit (PIC). The focus is to use these solutions to derive equations that allow for the straightforward calculation of alignment tolerances for displacement in all three directions, as well as two axes of rotations. These equations can be used to aid in the design of photonic packages by allowing the determination of precision necessary for fabrication of mechanical alignment features, in addition to packaging process development.

Broadband and low-reflection mid-infrared grating coupler for a perfectly vertical fiber-chip interface.

Short-wavelength mid-infrared (SWMIR) silicon photonics has gained significant attention due to its applications in sensing, spectroscopy, and communications. A perfectly vertical grating coupler is a valuable packaging technique that is convenient for chip-to-chip optical interconnects and has low risks of mechanical failure during testing. However, SWMIR grating couplers have fewer periods to tailor the diffracted light, hindering the improvement of bandwidths and backreflections. Herein, we demonstrate a perfectly vertical subwavelength grating coupler by using a modified inverse design approach. The device exhibits a coupling efficiency of -5.9 dB with a 1-dB bandwidth of ∼122 nm and a low backreflection of -19.2 dB at 2200 nm wavelengths. Besides, the device also exhibits exceptional spatial fiber misalignment tolerance. The study underscores the effectiveness of the inverse design strategy in subwavelength grating couplers, charting a path to advance the mid-infrared silicon photonic packaging.

“Be prepared to be humbled, to listen, and learn a lot”

AbstractThe head of the German producer of photonics packaging and integration technology shares his insights with EPIC's photonics technologies program manager.

Simulating polarization characteristics of arbitrary-layer target systems’ infrared radiation by photon tracing strategy

It remains a big challenge to simulate and perceive polarization characteristics of coated targets’ infrared radiations, especially for the targets coated with several layers. In this paper, an arbitrary-layer radiational target system model (ARTSmodel) is constructed based on photon trace strategy (PTS) and Monte Carlo algorithm (MCA) to resolve this problem by continually tracing the evolution of the radiating photons’ state of polarization (SoP). In the proposed ARTSmodel, multiple scattering events among different coat layers are well represented, and the wide-band property of the radiations is accounted as well. Additionally, the infrared radiations are regarded as photon packages, and continually traced until they leave the topmost layer and get captured by the sensors bestrewing the entirely upper hemisphere space, whose values will form an upper-hemisphere-space polarization data (UPD) distribution. The UPD is compared with the analytic method and empirical data, and the consistency of results evidences the effectiveness and reliability of the proposed model. Moreover, the UPD and its representation in the Poincare sphere demonstrate that the proposed model provides a new and practicable way to coated target identification and analysis.

Packaging of micro-lens arrays to photonic integrated circuits using beam shape evaluation

We propose a method for aligning and attaching micro-lens arrays to photonic integrated circuits (PICs). Unlike the conventional approach of assessing power coupled to a fiber directly, our method utilizes a beam profiler. This profiler allows us to optimize the lens position by analyzing the transmitted beam shape from the PIC edge coupler through the lens. In conjunction, we employ grating couplers to introduce external light, acting as a ‘beacon’ for optimization. The use of grating couplers enables efficient coupling of external light into the PIC, providing a reference point for alignment. Importantly, our method accommodates both regular waveguide-side-up and upside-down (through-Silicon) orientations of the PIC. This versatility allows us to reproduce coupling results across a 6-channel array, demonstrating robust performance. This innovative approach not only ensures precise alignment and attachment but also opens up new possibilities for photonic packaging. The flexibility to work in different orientations is likely to lead to advancements in the design and assembly of photonic devices.

Substrate integrated micro-thermoelectric coolers in glass substrate for next-generation photonic packages

Substrate integrated micro-thermoelectric coolers in glass substrate for next-generation photonic packages

Improving Monte Carlo radiative transfer simulations: A shift of framework

Monte Carlo radiative transfer (MCRT) simulations are a powerful tool for determining the appearance of astrophysical objects, analyzing the prevalent physical conditions within them, and inferring their properties on the basis of real observations. Consequently, a broad variety of codes has been implemented and optimized with the goal of solving this task efficiently. To that end, two distinct frameworks have emerged, namely, the extinction and the scattering framework, which form the basis of the path determination procedures of those codes. These procedures affect the step length of simulated photon packages and are used for determining flux estimates. Despite the fact that these simulations play an important role at present and thus require significant computational resources, little attention has been paid to the benefits and the drawbacks of both frameworks so far. In this study, we investigate their differences and assess their performance with regard to the quality of thereby obtained flux estimates, with a particular focus on the required computational demand. To that end, we use a testbed composed of an infinite plane-parallel slab, illuminated from one side, and we determine transmitted intensity using MCRT simulations for both frameworks. We find that there are vast differences between the frameworks with regard to their convergence speed. The scattering framework outperforms the extinction framework across all considered optical depths and albedos when solving this task, particularly in the regime of high optical depths. Its implementation can therefore greatly benefit all modern MCRT codes as it has the potential to significantly reduce required computation times. Thus, we highly recommend its consideration for various tasks that require MCRT simulations.

Radial and axial photonic galleries of dielectric rings

A new picture of the photonic eigenmodes of dielectric rings with a rectangular cross section is presented, which is fundamentally different from those of whispering gallery modes of the disc. The low-frequency photonic spectrum is formed by two types of galleries: one type begins with radial Fabry-Pérot-like resonances, and the other with axial Fabry-Pérot-like resonances, in both cases the galleries continue with a set of equidistant longitudinal modes. The new results are: (1) a linear dependence of the wavelength of radial and axial Fabry-Pérot-like resonances on the width or height of the ring, respectively, has been demonstrated; (2) it is established that all longitudinal resonances follow the spectral shifts of the corresponding Fabry-Pérot-like resonances when the width or height of the ring changes, i.e. each gallery is a separate photonic package. As a result, galleries can intersect in parametric space, leading to impressive resonance effects, including bound states in the continuum. The analysis is based on numerical calculations and experiments in near- and far-fields. Our results open the door to new fundamental phenomena and enhanced functionality of dielectric ring resonators.

Ultrafast laser processing of glass waveguide substrates for multi-fiber connectivity in co-packaged optics

High bandwidth demanding applications such as high-performance computing and hyperscale datacenters are drivers for co-packaged optics, which aims to bring optical signals as close as possible to the electrical computing chips by integrating the electro-optic transceivers and ASICs on the same package substrate. These next-generation switches require advanced fiber-to-chip connectivity and novel packaging concepts to enable sufficient power and cost savings. As such, low-loss, high bandwidth, and high fiber-counts are required at the photonic chip interface. In this work, these challenges are addressed by enabling the multi-fiber push-on (MPO) interface at the edge of integrated glass waveguide substrates and thus leverages the existing fiber connector eco-system. An ultrafast laser process is used to singulate glass wafers into individual photonic chips leaving optical-quality end-facets with <1 μm flatness over the 6.5 mm wide connector region thereby directly enabling low-loss fiber-to-chip edge-coupling. To overcome the high-costs and complex photonic packaging associated with active alignment of the fiber connectors to the glass waveguide interfaces, ultrafast laser-ablated features are accurately positioned on the glass substrate to enable self-alignment of the MPO connector guide-pins resulting in a passive alignment approach. Subsequent mating and de-mating of the MPO connector to the glass waveguide interface yields on average a 0.19 dB increase in the coupling loss compared to using active alignment.

Paradigmatic examples for testing models of optical light polarization by spheroidal dust

We present a general framework on how the polarization of radiation due to scattering, dichroic extinction, and birefringence of aligned spheroidal dust grains can be implemented and tested in 3D Monte Carlo radiative transfer (MCRT) codes. We derive a methodology for solving the radiative transfer equation governing the changes of the Stokes parameters in dust-enshrouded objects. We utilize the Müller matrix and the extinction, scattering, linear, and circular polarization cross sections of spheroidal grains as well as electrons. An established MCRT code is used, and its capabilities are extended to include the Stokes formalism. We compute changes in the polarization state of the light by scattering, dichroic extinction, and birefringence on spheroidal grains. The dependency of the optical depth and the albedo on the polarization is treated. The implementation of scattering by spheroidal grains both for random walk steps as well as for directed scattering (peel-off) are described. The observable polarization of radiation of the objects is determined through an angle binning method for photon packages that leaves the model space as well as through an inverse ray-tracing routine for the generation of images. We present paradigmatic examples for which we derive analytical solutions of the optical light polarization by spheroidal dust particles. These tests are suited for benchmark verification of MCPOLand other such codes and allow the numerical precision reached by these codes to be quantified. We demonstrate that MCPOLis in excellent agreement (within ~0.1%) of the Stokes parameters when compared to the analytical solutions.

A Monte Carlo simulation for Moving Light Source in Intracavity PDT.

We developed a simulation method for modeling the light fluence delivery in intracavity Photodynamic Therapy (icav-PDT) for pleural lung cancer using a moving light source. Due to the large surface area of the pleural lung cavity, the light source needs to be moved to deliver a uniform dose around the entire cavity. While multiple fixed detectors are used for dosimetry at a few locations, an accurate simulation of light fluence and fluence rate is still needed for the rest of the cavity. We extended an existing Monte Carlo (MC) based light propagation solver to support moving light sources by densely sampling the continuous light source trajectory and assigning the proper number of photon packages launched along the way. The performance of Simphotek GPU CUDA-based implementation of the method - PEDSy-MC - has been demonstrated on a life-size lung-shaped phantom, custom printed for testing icav-PDT navigation system at the Perlman School of Medicine (PSM) - calculations completed under a minute (for some cases) and within minutes have been achieved. We demonstrate results within a 5% error of the analytic solution for multiple detectors in the phantom. PEDSy-MC is accompanied by a dose-cavity visualization tool that allows real-time inspection of dose values of the treated cavity in 2D and 3D, which will be expanded to ongoing clinical trials at PSM. PSM has developed a technology to measure 8-detectors in a pleural cavity phantom using Photofrin-mediated PDT that has been used during validation.

Special Section Guest Editorial: Microendoscopy

The <i>Journal of Optical Microsystems</i> is a Gold Open Access journal that publishes cutting-edge research in all aspects of optical and photonic microsystems, from materials and fabrication of micro-optical and photonic components, through assembly and packaging, to systems and applications. Open access fees will be waived for all submissions through 2023.

Free‐Form Micro‐Optics Enabling Ultra‐Broadband Low‐Loss Off‐Chip Coupling

AbstractEfficient fiber‐to‐chip coupling has been a major hurdle to cost‐effective packaging and scalable interconnections of photonic integrated circuits. Conventional photonic packaging methods relying on edge or grating coupling are constrained by high insertion losses, limited bandwidth density, narrow band operation, and sensitivity to misalignment. This work presents a new fiber‐to‐chip coupling scheme based on free‐form reflective micro‐optics. A design approach which simplifies the high‐dimensional free‐form optimization problem to as few as two full‐wave simulations is implemented to empower computationally efficient design of high‐performance free‐form reflectors while capitalizing on the expanded geometric degrees of freedom. This work demonstrates fiber array coupling to waveguides taped out through a standard foundry shuttle run and backend integrated with 3‐D printed micro‐optics. A low coupling loss down to 0.5 dB is experimentally measured at 1550 nm wavelength with a record 1‐dB bandwidth of 300 nm spanning O to U bands. The coupling scheme further affords large alignment tolerance, high bandwidth density, and solder reflow compatibility, qualifying it as a promising optical packaging solution for applications such as wavelength division multiplexing communications, broadband spectroscopic sensing, and nonlinear optical signal processing.

Beyond CPO: A Motivation and Approach for Bringing Optics Onto the Silicon Interposer

Co-packaged optics (CPO) technology is well positioned to break through the bottlenecks that impede efficient bandwidth scaling in key near-term commercial integrated circuits. We begin by providing some historical context for this important sea change in the optical communications industry. Then, motivated by GPU-based accelerated computing requirements, we investigate the next pain points that are poised to constrain bandwidth and efficiency in future CPO-based systems. We identify 2.5D integrated optics (i.e., bringing optics onto the interposer) as a promising solution that can enable continued scaling for these systems due to the dense wiring available which facilitates more efficient slow-and-wide electrical interfaces. We explore the benefits, challenges, and requirements associated with such tight coupling of the processors and optical engines by considering high-level photonic link design, technology, and packaging. We demonstrate the viability of a control loop which can adequately regulate temperature within the aggressive thermal environment. Then, we introduce a custom simulation framework that allows quantified comparisons of detailed design decisions; the simulations validate the feasibility of the general approach while also providing key guidance to designers on best directions to pursue for efficient optimization.

Special Section on InterPACK2021

The International Technical Conference and Exhibition on Packaging and Integration of Electronic and Photonic Microsystems (InterPACK) is a flagship conference of ASME Electronic and Photonic Packaging Division (EPPD). It has served as an international forum within the ASME society to share and exchange latest progresses in the research, development, and applications of electronic and photonic packaging since 1992. The aim of ASME Journal of Electronic Packaging (JEP) Special Section for InterPACK is to publish outstanding papers from technical tracks of InterPACK2021, which was held virtually amid COVID-19 pandemic worldwide. This Special Section of the ASME JEP publishes nine papers presented at the InterPACK2021 in the areas of electronics and photonics packaging, micro-electronics reliability, and advanced thermal management from the silicon, package, to data center level. All nine papers published in this JEP Special Section for InterPACK2021 went through a standard peer-review process for journal papers published by ASME.The micro-electronics industry is facing challenges to meet demanding performance and functional needs of high-performance computing (HPC), artificial intelligence (AI), 5 G/mm Wave, and power electronic devices. In order to close this gap, in parallel with new breakthroughs in advancing silicon node, the semiconductor industry is also embracing advanced integrated circuits (IC) packaging technologies, including heterogeneous integration, 2.5D/3D IC packaging, chiplet, additive manufacturing, novel modeling and characterization techniques, and others. This Special Section reflects latest progresses in the IC packaging by publishing nine papers presented at ASME InterPACK2021. We gratefully acknowledge all the authors who have revised their original conference papers for this Special Section and the reviewers who have spent tremendous time and efforts to help improve overall quality of the papers for this Special Section. We also would like to thank the ASME JEP Editor-in-Chief (EIC), Professor Shi-Wei Ricky Lee for his guidance and support, and the assistant to EIC, Dr. Jeffery Lo for his help in this journey.

Two-photon lithography for integrated photonic packaging

Two-photon lithography for integrated photonic packaging

Simulation of hybrid silicon nitride/polymer Mach-Zehnder optical modulator beyond 170 GHz

In this paper, a hybrid Mach-Zehnder optical modulator is proposed based on silicon nitride/organic polymer waveguides, which is expected to break through the performance bottleneck of the silicon-based optical modulator by exploiting the low-loss optical transmission property of silicon nitride waveguides and the excellent modulation performance of organic polymers. For reduction of the optical loss and ease of photonic packaging, perfectly vertical silicon nitride bidirectional grating couplers are utilized for both input/output optical coupling and power splitting/combining. Thus, a Mach-Zehnder interferometer can be constructed with a back-to-back configuration of such grating couplers. With grating apodization, the coupler can achieve a simulated coupling efficiency of 70%. To bridge the silicon nitride waveguides and the polymer waveguides, a longitudinal adiabatic mode-spot converter with a transmission efficiency of 99.2% was designed. In this paper, high-β donor-π bridge-accepter molecule YLD-124 combined with HD-BB-OH as the host polymer is utilized for a design example. The polymer waveguides with inverted ridge structure can be realized through the processes of silica cladding etching, spin coating or microfluidic trench filling of polymer. Following this design, we numerically demonstrate a hybrid silicon nitride-polymer Mach-Zehnder modulator with modulation efficiency of 1.57 Vcm and Electric-Optical bandwidth of 174 GHz. The total insertion loss is less than 5.74 dB, including two grating coupler losses of about 3.08 dB.

Time-dependent Monte Carlo continuum radiative transfer

Context. Variability is a characteristic feature of young stellar objects that is caused by various underlying physical processes. Multi-epoch observations in the optical and infrared combined with radiative transfer simulations are key to study these processes in detail. Aims. We present an implementation of an algorithm for 3D time-dependent Monte Carlo radiative transfer. It allows one to simulate temperature distributions as well as images and spectral energy distributions of the scattered light and thermal reemission radiation for variable illuminating and heating sources embedded in dust distributions, such as circumstellar disks and dust shells on time scales up to weeks. Methods. We extended the publicly available 3D Monte Carlo radiative transfer code POLARIS with efficient methods for the simulation of temperature distributions, scattering, and thermal reemission of dust distributions illuminated by temporally variable radiation sources. The influence of the chosen temporal step width and the number of photon packages per time step as key parameters for a given configuration is shown by simulating the temperature distribution in a spherical envelope around an embedded central star. The effect of the optical depth on the temperature simulation is discussed for the spherical envelope as well as for a model of a circumstellar disk with an embedded star. Finally, we present simulations of an outburst of a star surrounded by a circumstellar disk. Results. The presented algorithm for time-dependent 3D continuum Monte Carlo radiative transfer is a valuable basis for preparatory studies as well as for the analysis of continuum observations of the dusty environment around variable sources, such as accreting young stellar objects. In particular, the combined study of light echos in the optical and near-infrared wavelength range and the corresponding time-dependent thermal reemission observables of variable, for example outbursting sources, becomes possible on all involved spatial scales.

Integrated Photonics Packaging: Challenges and Opportunities

Integrated Photonics Packaging: Challenges and Opportunities