Integrated Photonics: Materials, Devices, and Applications IV

After decades of research and more than ten years of successful production in very high volumes Silicon MEMS microphones are mature and unbeatable in form factor and robustness. Audio applications such as video, noise cancellation and speech recognition are key differentiators in smart phones. Microphones with low self-noise enable those functions. Backplate-free microphones enter the signal to noise ratios above 70dB(A). This talk will describe state of the art MEMS technology of Infineon Technologies. An outlook on future technologies such as the comb sensor microphone will be given.

We demonstrate the main goals of the H2020 project PlasmoFab towards a revolutionary yet CMOS-compatible fabrication platform for seamless co-integration of plasmonics with photonic and supporting electronics. We demonstrate recent advances on the hosting SiN photonic hosting platform reporting on low-loss passive SiN waveguides and Grating Couplers for both the TM and TE polarization states. We also present experimental results of plasmonic gold thin-film and hybrid slot waveguide configurations that can allow for high-sensitivity sensing, providing also the ongoing activities towards replacing gold with CMOS metals. Finally, the first experimental results on the co-integrated SiN+plasmonic platform are demonstrated.

In this paper, the fabrication method of waveguide structures and devices as ring resonators for different waveguide applications based on polymer material is presented. The structures were designed in computer-aided design (CAD) software and two-photon polymerization lithography system was used for preparation of desired devices. Morphological properties of prepared devices were investigated using scanning electron microscope (SEM) and confocal microscope. Finally, we performed measurement of optical spectrum characteristics in telecommunication wavelengths range. The results corresponds to calculated parameters. Final polymer devices are promising for lab on a chip and sensing applications due to unique elastic and chemical properties.

Silicon sub-wavelength structures have found widespread applications in devices ranging from fiber-to-chip couplers to spectrometers. So far, these structures have been mainly used to engineer the local refractive index. Here we focus on two further applications. We describe how to engineer the waveguide electromagnetic field distribution for enhanced evanescent field sensing, predicting a 6-fold enhancement of the sensitivity compared to conventional waveguides. We furthermore report experimental results on broadband multimode interference couplers, which, by leveraging the inherent anisotropy of the sub-wavelength structures, achieve virtually perfect operation over a bandwidth of more than 300nm at telecom wavelengths.

We present integrated photonic devices which are interfaced with complex microfluidic systems. They allow precise control of the sample fluids, utilising on chip valves and pumps. The automated measurement system allows a high reproducibility of the acquired results, reduced working volume of reagents and increases assay sensitivity. Our platform makes use of traditional photonic structures like Mach-Zehnder-Interferometers, harnessing integrated photonics to create long, spiralled sensing arms to enhance analyte photon interaction length; as well as novel resonant plasmonic structures with arrays of sub-wavelength nano-antennas to achieve field enhancement and an easily detectable spectral band-gap.

This paper presents a robust integration of PN junction Mach Zehnder modulators in a 200mm silicon photonic platform. Impact of process variations on devices characteristics is evaluated through numerical simulations coupling process and electro-optic simulators. Process is optimized using the same numerical approach and compared with experimental results. Finally, a robust integration scheme leading to modulator insensitive to lithography misalignment is presented. All device architectures are extensively characterized.

High speed optical modulation in silicon photonics is usually achieved using the plasma dispersion effect instead of the faster Pockels effect because silicon is a centrosymmetric crystal, vanishing any second order nonlinear effects. To overcome this limitation, mechanical stresses on silicon to break the crystal symmetry can be used depositing a strained overlayer. In this work, we have studied the effect of the stress layer in the modulation characteristics based on Mach-Zehnder interferometers. The deposition of silicon nitride as the stress layer and its optimization to induce the maximum effect will be presented.

GeSn alloys are attracting a lot of interest for their possible application as integrated laser. However, strain control in GeSn layer is one of the key to further improve the GeSn light emission. Here, we studied the strain impact on optical properties for GeSn layers and micro-devices with Sn content ranging from 6% to 15%. We perform mechanical and optical characterization using different technics: X-ray diffraction, Raman spectroscopy, photocurrent experiment and photoluminescence (PL). Our results give a better understanding of the strain properties in GeSn devices with high Sn content for laser applications.

Fully integrated optoelectronic interfaces in CMOS technology are a very interesting option for optical smart sensors because they are a cost-effective and compact solution. However, CMOS standard n-well/p-bulk differential photodiodes (DPDs) are the bottleneck in this field due to their inherent limited bandwidth which falls below 10 MHz in 65 nm CMOS. This work presents a new equalization approach to enhance the bandwidth of CMOS integrated DPDs used in optical sensors. It is designed based on a split-path topology in which the gain and the boost are completely decoupled and can be externally adjusted by means of independent control voltages. This feature, particularly helpful for calibration, is not present in conventional equalizers based on the degenerated differential pair. The proposed equalization technique has been simulated in a 65 nm process, where it has been able to increase the bandwidth of the DPD up to 3 GHz with a single supply voltage of only 1.2 V.

Diffusion doped p-i-n/p-n diodes in SOI substrate with a starting device layer thickness of higher than 1µm is proposed for the fabrication of active silicon photonics devices with monolithic and scalable waveguide cross-sections. It has been shown that a phase-shifter with microns to submicron waveguide cross-sectional dimensions can be fabricated using the proposed method and corresponding figures of merit are found to be comparable to conventional ion-implanted p-i-n/p-n waveguide phase-shifters Vπ L ~ 1 V.cm and junction capacitance ~ 1 fF/µm.

A Fast Steering Mirror of 160mm diameter has been designed, built and tested. In order to make continuous tracking ability without loss of target image, a FSM should be equipped with a large scale mirror for a wide field of view and require a high control bandwidth to reduce the tracking error. Finally, this device presented in this paper steers a large aperture mirror about two axes, though an operating range of 1mrad and a small-signal closed-loop bandwidth up to 500Hz which is greater than the structural resonance.

Unique optical properties of photonic crystals (PhCs) cause the effects, which are interesting in applications in optoelectronic devices as light emitting diodes (LEDs) and photodiodes. We propose method for fabrication and application of 2D and 3D PhC prepared in polydimethylsiloxane (PDMS) membranes for application in LEDs and photodiodes. PhC PDMS structures applied in the LED and photodiode surface can modify its directional and spectral optical properties. 2D and 3D PhC structures of different period and symmetry were patterned in photoresist and thin PDMS membranes. The LED and photodiode optical characteristics were investigated in spatial angular measurement using goniophotometer.

We present modification of far field of LED by implementing one dimensional (1D) and two dimensional (2D) Fresnel structure in surface emitting part of LED. The structure consists of drilled lines distributed with square root of distance in order to obtain structures with different foci – f1 = 12,5 µm, f2 = 1 cm and f3 = 3 cm. Structures were prepared using dip in laser lithography combined with PDMS embossing in thin PDMS membrane that can be stack directly on the emitting surface. Implementation of such structures modifies the LED far field what was proved by goniophotometer measurements.

The large transparency window of silicon (1.1 - 8 µm wavelength range) makes it a promising material for the implementation of on-chip sensors operating over an ultra-wide wavelength range. However, the implementation of the silicon-on-insulator platform is restricted by the absorption of buried oxide layer for wavelengths above 4 µm. Here, we report our advances in development of silicon waveguides for broadband operation extending from near- to mid-infrared wavelengths. We present suspended silicon waveguides that exploit a novel periodic corrugation approach to circumvent the buried oxide absorption problem and provide effective single mode operation simultaneously for near- and mid-infrared wavelengths.

A design for high Q factor photonic crystal ring resonator(PCRR) is presented. These types of PCRRs are based on a hexagonal array of holes in silicon slab. The holes will be filled with liquid analyte. A PCRR can be formed by removing elements from the regular PhC grid in an equilatral hexagonal shape. A slot is embedded in this hexagonal ring cavity to create a slot-PCRR. The strong confinement of light in the low index region is the key advantage of the slott- PCRR. The strong overlap between the field of the resonance mode and the analyte, yields a higher sensitivity for the slot-PCRR modes compare to PCRR modes.

In this paper, we demonstrate the capabilities of 3D laser lithography system based on two-photon polymerization. The technology satisfy requirements on complexity, precision and possibility to prepare complex 3D structures. It provides a number of advantages for additive manufacturing of polymer parts with dimensions ranging from a few microns up to the millimeter scale. We designed and prepared 3D optical structures in IP-Dip photoresist. Prepared optical waveguide devices shows well morphological and optical properties. Prepared structures properly combined with polydimethylsiloxane (PDMS) have great potential for applications in integrated optics, optoelectronics, optical sensing and biophotonics.

Establishing a reliable bidirectional communication interface between the nervous system and electronic devices is crucial for exploiting the full potential of neural prostheses. Despite recent advancements, current microelectrode technologies evidence important shortcomings, e.g. challenging high density integration, low signal-to-noise ratio, poor long-term stability, etc. Thus, efforts to explore novel materials are essential for the development of next-generation neural prostheses. Graphene and graphene-based materials possess a rather exclusive set of physicochemical properties holding great potential for biomedical applications, in particular neural prostheses. In this presentation, I will provide an overview on fundamentals and applications of several graphene-based technologies and devices aiming at developing an efficient bidirectional communication with electrogenic cells and nerve tissue. The main goal of this talk is to discuss pros and cons of graphene technologies for bioelectronics and neuroprosthetics, and at the same time to identify the main challenges ahead.

Accurate parameter estimation plays a pivotal role in basic as well as applied sciences. The ultimate precision limits in the estimation procedure are dictated by the quantum fluctuations of the probing state. E.g. by using coherent states, the precision scaling is 1/Sqrt(N) while for NOON states the scaling is 1/N where N is the number of probing photons. The latter is the ultimate scaling known as the Heisenberg scaling. In this presentation, we show experimentally that the Heisenberg scaling can be attained also by the use of squeezed states of light. This is an important result as the squeezed state is much easier to produce and much more robust against losses than the NOON state. We also discuss our recent work on miniaturizing squeezed states sources, towards quantum sensing on-chip.

A novel approach for tracking of whispering gallery modes (WGM) in real-time for dielectric cavities used in sensing application is presented in this paper. Real-time tracking for the shifts of the WGM can be used to measure the physical quantity of interest precisely, under high repetition rates. The tracking algorithm is based on cross-correlation signal processing technique which has been proved to be accurate in WGM shifts detection. The tracking algorithms accuracy and real-time behavior is verified by preforming simulations based on experiments. Results show that shifts of the WGM are tracked by the algorithm providing real-time force readings.

Infrared (IR) spectroscopy is widely recognized as a gold standard technique for chemical analysis. Traditional IR spectroscopy relies on fragile bench-top instruments located in dedicated laboratory settings, and is thus not suitable for emerging field-deployed applications such as in-line industrial process control, environmental monitoring, and point-of-care diagnosis. Recent strides in photonic integration technologies provide a promising route towards enabling miniaturized, rugged platforms for IR spectroscopic analysis. Chalcogenide glasses, the amorphous compounds containing S, Se or Te, have stand out as a promising material for infrared photonic integration given their broadband infrared transparency and compatibility with silicon photonic integration. In this talk, I will review our work exploring integrated chalcogenide glass based photonic devices for IR spectroscopic chemical analysis. Some recent highlights include the first demonstration of on-chip cavity-enhanced mid-IR sensing and a mid-IR waveguide integrated photodetector monolithically processed on a silicon platform.

We test the recently devised design of vertical-cavity enhanced resonant thermal emitter regarding stability to fabrication tolerances of PVD layer deposition techniques. Such an emitter is composed of an aperiodic multilayer stack of dielectric layers (silicon and silica) on top of a reflective metal (silver) structure. This concept provides optimizable, narrowband and directional thermal emission. Various stack configurations featuring different constraints on maximum layer thickness were designed, exhibiting different behavior under random layer depth deviations. In order to examine this behavior, a Monte-Carlo algorithm was used to apply a Gauss-distributed error in depth for every individual layer. In this way, we evaluate several differing stack configurations and filter the best candidates for practical application.

Performance of photodiodes is limited by reflectance of light, surface recombination, and auger recombination in doped region forming the diode. To overcome these limitations, N-type induced junction photodiodes were developed with ALD alumina surface layer carrying high enough charge to generate an induced junction and providing excellent surface passivation. Very low reflectance was achieved by using surface microstructuring, i.e. black silicon. External quantum efficiency exceeds 96% over wavelength range of 250 to 950 nm and even over 100% between 250 to 300 nm. Particularly the ultraviolet response is extremely high, clearly exceeding that of commercially available photodiodes.

This work demonstrates a robust mmWave photonic emitter consisting of antenna-integrated InP photodiode (PD) monolithically. A novel type of InP-based UTC-PD is fabricated and bonded on silicon (Si) using heterogeneous integration method. All photonics components are formed in InP membrane and Si wafer is used as carrier wafer to carry the integrated photonic/electronic components. The UTC-PD exhibits a 3dB bandwidth of beyond 67GHz with responsivity of 0.7 A/W at 1.55 µm. For sack of performance comparison three self-complementary antennas are grown on PD structure. A hyper-hemispherical Si lens is used for focusing and radiating the electromagnetic radiation. The directivity achieved is around 27dBi. The characterization is done in frequency range of DC-110 GHz.

ABSTRACT Recently, we are exploring Resonator-Quantum Well Infrared Photo detectors (R-QWIPs) for broadband long wavelength applications. In despite of a moderate doping of 0.5 × 1018 cm-3 and a thin active layer thickness of 0.6 or 1.3 µm, we achieved a quantum efficiency 35% and 37% for 8 quantum wells and 19 quantum wells respectively. The NEΔT of the FPAs is estimated to be 22 mK at 2 ms integration time and 60 K operating temperature. This good result thus exemplifies the advantages of R-QWIP.

Plasmonically induced transparency (PIT) in a multi-cavity-coupled graphene-based waveguide system is investigated theoretically and numerically. By using the finite element method (FEM), not only multi-mode can be achieved, but also a blue shift is exhibited by altering the chemical potential of the monolayer graphene dynamically. By investigating carefully such a structure, we find that the increasing number of the graphene rectangle cavity (GRC) placed above the guided graphene waveguide (GGW) gives rises to the PIT peaks. Importantly, we find that the PIT peaks reduce to one when the distance between the center of the third cavity and the center of the second one is 100 nm. Easily to be fabricated, this graphene-based waveguide system has many potential applications for the advancement of 3D ultra-compact, high-performance and dynamical-modulation PIT devices.