126 research outputs found
Cross-polarization effects in sheared 2D grating couplers in a photonic BiCMOS technology
We investigate numerically and experimentally sheared 2D grating couplers in
a photonic BiCMOS technology with a focus on their splitting behavior. Two
realization forms of a waveguide-to-grating shear angle are considered. The
cross-polarization used as a figure-of-merit is shown to be strongly dependent
on the grating perturbation strength and is a crucial limitation not only for
the grating splitting performance, but also for its coupling efficiency.Comment: This is a preprint version of an article accepted for publication in
Japanese Journal of Applied Physics. IOP Publishing Ltd is not responsible
for any errors or omissions in this version of the manuscript or any version
derived from it. The full Version of Record is available online at DOI:
10.35848/1347-4065/ab8e2
A Novel Approach to Interface High-Q Fabry-P\'erot Resonators with Photonic Circuits
The unique benefits of Fabry-P\'erot resonators as frequency-stable reference
cavities and as an efficient interface between atoms and photons make them an
indispensable resource for emerging photonic technologies. To bring these
performance benefits to next-generation communications, computation, and
timekeeping systems, it will be necessary to develop strategies to integrate
compact Fabry-P\'erot resonators with photonic integrated circuits. In this
paper, we demonstrate a novel reflection cancellation circuit that utilizes a
numerically optimized multi-port polarization-splitting grating coupler to
efficiently interface high-finesse Fabry-P\'erot resonators with a silicon
photonic circuit. This circuit interface produces spatial separation of the
incident and reflected waves, as required for on-chip Pound-Drever-Hall
frequency locking, while also suppressing unwanted back reflections from the
Fabry-P\'erot resonator. Using inverse design principles, we design and
fabricate a polarization-splitting grating coupler that achieves 55% coupling
efficiency. This design realizes an insertion loss of 5.8 dB for the circuit
interface and more than 9 dB of back reflection suppression, and we demonstrate
the versatility of this system by using it to interface several reflective
off-chip devices
WDM-compatible polarization-diverse OAM generator and multiplexer in silicon photonics
Spatial multiplexing using orbital angular momentum (OAM) modes is an efficient means of scaling up the capacity
of fiber-optic communications systems; integrated multiplexers
are crucial enablers of this approach. OAM modes are circularly
polarized when propagating in a fiber, however, OAM generators
previously demonstrated in silicon photonics use locally linearly
polarized emitters. Coupling from multiplexers to fibers in
those solutions results in extra loss and complexity. Moreover,
many of those solutions are based on resonator structures with
strong wavelength dependence, and are thus incompatible with
wavelength-division multiplexing (WDM). We experimentally
demonstrate on-chip generation and multiplexing of OAM modes
using an array of circularly polarized 2D antennas with wide
wavelength coverage. The proposed device was implemented on
the standard 220-nm silicon-on-insulator platform. Optical vortex
beams with OAM orders ranging from -3 to +3 in both left and
right circular polarization states were generated from the same
aperture across a wavelength range of 1540 nm to 1557 nm. This
device could serve as a multiplexer or demultiplexer for up to 12
information bearing channels coupling into a
Multi-layer silicon nitride-on-silicon polarization-independent grating couplers
A polarization-independent grating coupler is proposed and demonstrated in a 3-layer silicon nitride-on-silicon photonic platform. Polarization independent coupling was made possible by the supermodes and added degrees of geometric freedom unique to the 3-layer photonic platform. The grating was designed via optimization algorithms, and the simulated peak coupling efficiency was â2.1 dB with a 1 dB polarization dependent loss (PDL) bandwidth of 69 nm. The fabricated grating couplers had a peak coupling efficiency of â4.8 dB with 1 dB PDL bandwidth of over 100 nm
Doctor of Philosophy
dissertationPhotonic integration circuits (PICs) have received overwhelming attention in the past few decades due to various advantages over electronic circuits including absence of Joule effect and huge bandwidth. The most significant problem obstructing their commercial application is the integration density, which is largely determined by a signal wavelength that is in the order of microns. In this dissertation, we are focused on enhancing the integration density of PICs to warrant their practical applications. In general, we believe there are three ways to boost the integration density. The first is to downscale the dimension of individual integrated optical component. As an example, we have experimentally demonstrated an integrated optical diode with footprint 3 Ă- 3 ĂŻÂÂm2, an integrated polarization beamsplitter with footprint 2.4 Ă- 2.4 ĂŻÂÂm2, and a waveguide bend with effective bend radius as small as 0.65 ĂŻÂÂm. All these devices offer the smallest footprint when compared to their alternatives. A second option to increase integration density is to combine the function of multiple devices into a single compact device. To illustrate the point, we have experimentally shown an integrated mode-converting polarization beamsplitter, and a free-space to waveguide coupler and polarization beamsplitter. Two distinct functionalities are offered in one single device without significantly sacrificing the footprint. A third option for enhancing integration density is to decrease the spacing between the individual devices. For this case, we have experimentally demonstrated an integrated cloak for nonresonant (waveguide) and resonant (microring-resonator) devices. Neighboring devices are totally invisible to each other even if they are separated as small as ĂŻÂÂŹ/2 apart. Inverse design algorithm is employed in demonstrating all of our devices. The basic premise is that, via nanofabrication, we can locally engineer the refractive index to achieve unique functionalities that are otherwise impossible. A nonlinear optimization algorithm is used to find the best permittivity distribution and a focused ion beam is used to define the fine nanostructures. Our future work lies in demonstrating active nanophotonic devices with compact footprint and high efficiency. Broadband and efficient silicon modulators, and all-optical and high-efficiency switches are envisioned with our design algorithm
Integrated dispersive structures for bandwidth-enhancement of silicon grating couplers
In photonic integrated circuits grating couplers are commonly used to establish an efficient and stable fiber-to-chip link. However, the actual coupling efficiency of a fiber-to-chip interface depends strongly on the used wavelength and exhibits a maximum at a distinct target wavelength, determined by grating design parameters. In this paper, an enhancement of the optical bandwidth of silicon grating couplers by adding integrated dispersive structures is discussed. These are realized by single layers, prism-like geometries and additional silicon nitride gratings. Theoretical considerations for a bandwidth-enhancement by dispersive layers are performed and applied to an existing grating coupler design. A simulated 1dB-bandwidth of up to 90Â nm at a maximum efficiency of - 0.65Â dB in the C-band could be achieved, which is an enhancement to a factor of about 2 compared with the original coupler design.Bundesministerium fĂŒr Wirtschaft und EnergieProjekt DEA
Ultra-short silicon-organic hybrid (SOH) modulator for bidirectional polarization-independent operation
We propose a bidirectional, polarization-independent, recirculating IQ-modulator scheme based on the silicon-organic hybrid (SOH) platform. We demonstrate the viability of the concept by using an SOH Mach-Zehnder modulator, operated at 10 GBd BPSK and 2ASK-2PSK
Hybrid Integrated Photonic Platforms and Devices
Integrated photonics has the potential to revolutionize optical systems by achieving drastic reductions in their size, weight and power. Remote spectroscopy, free-space communications and high-speed telecommunications are critical applications that would benefit directly from these advancements. However, many such applications require extremely wide spectral bandwidths, leading to significant challenges in their integration. The choice of integrated platform influences the optical transparency and functionality which can be ultimately achieved. In this work, several new platforms and technologies have been developed to meet these needs. First, the silicon-on-lithium-niobate (SiLN) platform is discussed, on which the first compact, integrated electro-optic modulator in the mid-infrared has been demonstrated. Next, results are shown in the development of the all-silicon-optical-platform (ASOP), an ultra-stable suspended membrane approach which offers broad optical transparency from 1.2 to 8.5 um and enables efficient nonlinear frequency conversion in the mid-IR. This fabrication approach is then taken further with anchored-membrane waveguides, (T-Guides) enabling single-mode and single-polarization waveguiding over a span exceeding 1.27 octaves. Afterward, a new photonic technology enabling integrated polarization beam-splitters and polarizers over unprecedented bandwidths is introduced, called topographically anisotropic photonics (TAP). Next, results on high-performance microphotonic chalcogenide glass waveguides are presented. Finally, several integrated photonics concepts suitable for further work will be discussed, such as augmentations to T-Guides and a novel technique for quasi-phase-matching
Design of active and passive photonic components for an optical transmitter in silicon-on-insulator technology
This work presents research on active and passive nanooptical structures on silicon-on insulator technology for high speed data communication. The utilized technology is cost efficient and complementary metal-oxide-semiconductor (CMOS) compatible allowing the integration of optical and electrical circuits on the same die. The work consists of two parts presenting the two main structures that are investigated: the two-dimensional grating coupler and the optical modulator. The first chapter introduces the motivation and the goal of the work. The second chapter describes the design and simulation of two-dimensional grating couplers. This is a passive structure used to couple light from the optical fiber into the optical waveguides embedded on a die. Two-dimensional grating couplers with an orthogonal and a focusing grid are investigated. The geometrical parameters of the structure are optimized to achieve high coupling efficiencies and enable the splitting of the two orthogonal polarizations of the input light, i.e. the transversal electric (TE) from the transversal magnetic (TM) polarization, into the two outputs of the coupler. This allows the transmission of one information channel at each polarization increasing the data rate. For periodic orthogonal two-dimensional grating couplers a simulated coupling efficiency of â1.9 dB and â2.1 dB are achieved for TE and TM polarizations, respectively. The coupling efficiency is enhanced by the use of an aperiodic grating achieving a simulated coupling efficiency of â1.7 dB for TE and â1.9 dB for TM polarization at the telecommunication wavelength of 1550 nm. In addition, two-dimensional focusing grating couplers are designed in order to reduce the area of the coupling structure. The spatial dimension of the grating and the taper, used to guide the optical signal from the grating coupler to a single mode waveguide, are optimized maximizing the coupling efficiency. Customized tapers are developed for each focusing grating design. The design and simulation of different focusing grating couplers and tapers are presented achieving a total coupling efficiency of â3.1 dB and a 1 dB-bandwidth of 40 nm with a grating coupler with a side width of less than 13 ”m and a customized taper of 26.2 ”m. Using an adiabatic taper with a length of 100 ”m, the coupling efficiency is â2.4 dB, which is a promising result for a comparably structure which includes the tapered waveguide. At the end of the chapter the measurement results of a fabricated two-dimensional focusing grating coupler with customized taper is presented. A prototypical structure is fabricated at Institut fĂŒr Mikroelektronik Stuttgart (IMS CHIPS) for design validation, which can be optimized in future adding a backside metal mirror to avoid light losses into the substrate increasing the coupling efficiency. The third chapter concentrates on the modulation of light by applying an electrical signal by means of the designed active optical structure. Key parameters for the design of these structures as the geometrical dimensions, the doping profile and the electrical properties are described in detail as well as the impact on the performance of the modulator if these parameters are modified. Different designs of modulators together with various optical and electrical test structures are fabricated with the novel technology of IMS CHIPS. The first fabricated optical modulator using this technology is successfully measured. This is a Mach-Zehnder modulator which exhibits a measured modulation efficiency of 3.1 Vcm at 2 V reverse bias voltage. The total insertion loss on-chip is 4.2 dB for the operating point with the maximum absorption of light. Transmission lines with a 3 dB electrical bandwidth higher than 50 GHz are designed and measured to be used as traveling wave electrode of the modulator. The influence of the phase shifter of the modulator below the transmission lines is analyzed and an equivalent circuit model is developed. The electrical coplanar lines of the modulator are measured showing a 3 dB electrical bandwidth of 27 GHz and a 6 dB electrical bandwidth of 30 GHz at 2 V reverse bias voltage, which theoretically corresponds with the 3 dB electro-optical bandwidth of the modulator. Additionally, modulators and test structures are designed and fabricated in a different technology with a 220 nm silicon-on-insulator substrate at the Leibniz Institute for High Performance Microelectronics (IHP). Optical and electrical measurements of the most relevant designs are presented. A modulation efficiency of 0.25 Vcm at 2 V bias voltage is demonstrated for a push-pull modulator with a 6 dB electrical bandwidth of the traveling wave electrode of 10 GHz. Finally, the most important results are outlined as conclusion and an outlook for further investigations based on the research of this work is given at the end of the thesis
Nearly perfect routing of chiral light by plasmonic grating on slab waveguide
Grating couplers are widely used to couple waveguide modes with the far
field. Their usefulness is determined not only by energy efficiency but also by
additional supported functionality. In this paper, we demonstrate a plasmonic
grating on a silicon nitride slab waveguide that couples both TE and TM
waveguide modes with circularly polarized light in the far field. Specifically,
we experimentally confirmed that circularly polarized light excites TE and TM
modes propagating in opposite directions, and the direction is controlled by
the handedness. The routing efficiency for normally incident light reaches up
to 95%. The same structure operates in the outcoupling regime as well,
demonstrating up to 97% degree of circular polarization, where the handedness
is determined by the polarization and propagation direction of outcoupled
modes. Our results pave the way for the realization of polarization-division
multiplexers and demultiplexers, integrated circular polarization emitters, as
well as detectors of the polarization state of the incident optical field
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