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In this work, we present a significant step toward in vivo ophthalmic optical coherence tomography and angiography on a photonic integrated chip. The diffraction gratings used in spectral-domain optical coherence tomography can be replaced by photonic integrated circuits comprising an arrayed waveguide grating. Two arrayed waveguide grating designs with 256 channels were tested, which enabled the first chip-based optical coherence tomography and angiography in vivo three-dimensional human retinal measurements. Design 1 supports a bandwidth of 22 nm, with which a sensitivity of up to 91 dB (830 µW) and an axial resolution of 10.7 µm was measured. Design 2 supports a bandwidth of 48 nm, with which a sensitivity of 90 dB (480 µW) and an axial resolution of 6.5 µm was measured. The silicon nitride-based integrated optical waveguides were fabricated with a fully CMOS-compatible process, which allows their monolithic co-integration on top of an optoelectronic silicon chip. As a benchmark for chip-based optical coherence tomography, tomograms generated by a commercially available clinical spectral-domain optical coherence tomography system were compared to those acquired with on-chip gratings. The similarities in the tomograms demonstrate the significant clinical potential for further integration of optical coherence tomography on a chip system., Optical coherence tomography: chip promise The goal of an optical coherence tomography (OCT) imaging system that is integrated on a photonic chip has taken a step closer to reality. Elisabet Rank and coworkers from Austria have shown that arrayed waveguide gratings (AWGs), integrated-optical devices commonly used to separate different wavelength channels in an optical communications system, can be used to replace diffraction gratings in an OCT system. Several designs of silicon nitride AWGs with 256 channels in the near-infrared were fabricated and then tested in an OCT system which was able to capture in-vivo tomograms and angiography of the human eye’s retina, with comparable quality to a conventional system. The next stage of the OCT-on-a-chip research will focus on exploring the use of multimode interference structures, integrated photodiodes, and compact light sources.

We report the development of CMOS compatible PECVD silicon nitride waveguide based photonic integrated circuits and their application for optical coherence tomography (OCT) and colorimetric gas sensing.

In this paper, we present a novel concept for a multi-channel swept source optical coherence tomography (OCT) system based on photonic integrated circuits (PICs). At the core of this concept is a low-loss polarization dependent path routing approach allowing for lower excess loss compared to previously shown PIC-based OCT systems, facilitating a parallelization of measurement units. As a proof of concept for the low-loss path routing, a silicon nitride PIC-based single-channel swept source OCT system operating at 840 nm was implemented and used to acquire in-vivo tomograms of a human retina. The fabrication of the PIC was done via CMOS-compatible plasma-enhanced chemical vapor deposition to allow future monolithic co-integration with photodiodes and read-out electronics. A performance analysis using the results of the implemented photonic building blocks shows a potential tenfold increase of the acquisition speed for a multi-channel system compared to an ideal lossless single-channel system with the same signal-to-noise ratio., Comment: 15 pages, 6 figures, 3 tables

We present the design, simulation, and technological verification of a compact 256-channel, 42-GHz silicon nitride based AWG-spectrometer dedicated to the realization of an on-chip spectral domain optical coherence tomography (SD-OCT) system. The spectrometer was designed for TM-polarized light with a central wavelength of 850 nm and fabricated with CMOS foundry processes. Spectrometer features small size of (13 x 14) mm2 and high resolution of 0.1 nm.

We present the technological verification of a size-optimized 160-channel, 50-GHz silicon nitride-based AWG-spectrometer. The spectrometer was designed for TM-polarized light with a central wavelength of 850 nm applying our proprietary “AWG-Parameters” tool. For the simulations of AWG layout, the WDM PHASAR photonics tool from Optiwave was used. The simulated results show satisfying optical properties of the designed AWG-spectrometer. However, the high-channel count causes a large AWG size with standard design approaches. To solve this problem we designed a special taper enabling the reduction of AWG structure by about 15% while keeping the same optical properties. The AWG design was fabricated and the measured spectra not only confirm the proposed size-reduction but also the improvement of optical properties of the size-optimized AWG.

We report several PECVD silicon nitride photonic building blocks required for the implementation of a CMOS-compatible photonic integrated circuit technology platform operating in the 850 nm and 600 nm wavelength domain. In particular, for the 850 nm wavelength region we discuss a low-loss broadband 1x2 power splitter and a loop mirror. In the 600 nm wavelength region, we present new results on an optically pumped integrated dye-doped polymer laser that couples its light directly into a silicon nitride waveguide. Moreover, we discuss design considerations for a waveguide based gas sensing concept detecting target gas specific absorption changes in a thin dye-doped polymer cladding layer.

We report the simulation, design and experimental validation of various PECVD silicon nitride photonic building blocks required for the implementation of a CMOS-compatible photonic integrated circuit technology platform operating in the 850 nm and 600 nm wavelength domain. In particular, we discuss an inverted taper structure for efficient coupling of light to and from the chip, propagation and bend losses as well as broadband power and polarization beam splitters in the 850 nm region. In the 600 nm wavelength region, we demonstrate the realization of an optically pumped integrated dye-doped polymer laser that couples its laser light directly into a silicon nitride waveguide.

A swept source optical coherence tomography (SS-OCT) system with the interferometer engine being a photonic integrated circuit (PIC) has been developed. Furthermore, an Arrayed Waveguide Grating (AWG), representing a grating on a PIC, for spectral domain OCT (SD-OCT) has been integrated in a fiber-based OCT system. With measured sensitivities of ~87 dB (SS-OCT) and ~80 dB (SD-OCT), scattering tissue imaging becomes feasible for OCT-on-chip systems. In this study, we present two OCT-on-chip systems and first results of biological tissue imaging in-vivo and ex-vivo.

In this paper we present the size reduction of a 160-channel, 50-GHz Si3N4 based AWG-spectrometer. The spectrometer was designed for TM-polarized light with a central wavelength of 850 nm applying our proprietary “AWG-Parameters” tool. For the simulations of AWG layout, the PHASAR photonics tool from Optiwave was used. The simulated results show satisfying optical properties of the designed AWG-spectrometer. However, such high-channel count AWG features large size. To solve this problem we designed a special taper enabling the reduction of AWG structure by about 15%, while keeping the same optical properties. The technological verification of both AWG designs is also presented.

A colorless ONU is demonstrated on the polymer-based hybrid integration platform. Polymer Bragg gratings provide power-efficient wavelength tuning over the C-band. Thin-film element is inserted in the waveguide circuits for C/L band splitting and bi-directional transmission. On-chip U-groove and 45 degrees mirror allow submount-free and passive attachment of optical fiber and photo detectors, respectively. Arrays of deep-etched air trenches are introduced for cross-talk suppression. With an optical wavelength rejection level larger than 34 dB, 10-Gb/s bidirectional transmission and detection are achieved.

We present the design of 20-channel, 50-GHz Si 3 N 4 based AWG applying our proprietary AWG-Parameters tool. For the simulations of the AWG layout we used PHASAR photonics tool from Optiwave. The simulated transmission characteristics were then evaluated applying our AWG-Analyzer tool. We studied the influence of one of the design parameters – the separation between input/output waveguides, dx on the channel crosstalk. The results show that there is some minimum waveguide separation necessary to keep the crosstalk between transmitting channels low. The AWGs were designed for TM-polarized light with a central wavelength of 850 nm. They will later be used in a photonic integrated circuit dedicated to medical diagnostic imaging applications.

Three aspects of polymer-based external cavity tunable lasers are investigated. First, the tuning efficiency is increased from 0.29 nm/mW to a record 0.52 nm/mW by improving the microheater thermal design. Second, the long-term reliability of such tunable laser modules is investigated through two batches of stress tests at 25 degrees C and 45 degrees C, respectively. No degradation effect is observed in terms of output power drop and wavelength drifting after thousands of hours of continuous operation at tuned wavelength of 20 nm. Finally, a novel TM-emitting tunable laser is demonstrated by inserting a half-wave plate into the polymer output waveguide. Index-matching techniques and the intrinsic curved waveguide design guarantee robust single mode operation. The TM laser exhibits excellent side mode suppression ratio (>40 dB), large tuning range (>20 nm), and high output power (>5 mW at 100-mA drive current).

A series of tunable filters based on silicon nitride waveguide Bragg gratings buried in polymer are studied, fabricated and analyzed. The gratings are etched completely through the waveguides to improve the peak reflectivity at short grating lengths. Reflectivity from 1% to 70% can be reached when the third-order grating length varies from 16 µm to 160 µm. The experimental results are in good agreement with numerical simulations. Due to its compact size and the thermal advantages of polymer, the filter can be tuned very efficiently by a micro heater buried beneath. A tuning range of 34.5 nm is demonstrated at a heat power of only 22 mW.

Multimode interference couplers (MMIs) are fundamental building blocks in photonic integrated circuits. Here it is experimentally demonstrated, for the first time, a two-fold length reduction in an MMI coupler without any penalty on device performance. The design is based on a slotted 2 × 2 MMI fabricated on a commercial silicon-on-insulator (SOI) substrate. The slot is implemented with a subwavelength grating (SWG) comprising holes fully etched down to the oxide cladding, thereby allowing single etch step fabrication. The device has been designed using an in-house tool based on the Fourier Eigenmode Expansion Method. It has a footprint of only 3.5 μm x 23 μm and it exhibits a measured extinction ratio better than 15 dB within the full C-band (1530 nm‒1570 nm). SWG engineered slots thus offer excellent perspectives for the practical realization of MMIs couplers with substantially reduced footprint yet with outstanding performance.

We present the design of 8-channel, 100 GHz Si 3 N 4 based AWGs applying our proprietary AWG-Parameters tool. This tool was already used in various silica based AWG designs and also technologically verified. The designed AWGs were simulated by two commercial photonics tools and the achieved transmission characteristics were evaluated. The AWGs were designed for TM-polarized light with a central wavelength of 850 nm and will later be used in a photonic integrated circuit dedicated to medical diagnostic imaging applications.

The impressive progress of silicon photonic integrated device technology during the past fifteen years has been primarily driven by the requirements of optical data- and telecommunication. Research and development in silicon photonics has therefore been focused on the telecom wavelengths in the 1.55 µm and 1.31 µm regions and on silicon-on-insulator (SOI) material as waveguide integration platform. The rising cost burden of the traditional healthcare system as well as the increasing health consciousness among people is stimulating the decentralization of healthcare and is creating a strong demand for novel medical diagnostic devices suitable for point-of-care testing. This opens up new possibilities for integrated nanophotonic sensing devices operating in the visible and < 1.1 µm near infrared region. In this talk, we will present our ongoing research activities on the development of a CMOS-compatible photonic integrated circuit technology platform. This platform relies on silicon nitride waveguides fabricated by low-temperature plasma enhanced chemical vapor deposition (PECVD), which allows their monolithic co-integration with silicon photodiodes and CMOS based electronic read-out circuitry. We have achieved propagation losses of less than 1 dB/cm at a wavelength of 850nm in silicon nitride waveguides processed directly on an optoelectronic CMOS chip employing chemical-mechanical planarization (CMP). We will present the design and experimental validation of various nanophotonic building blocks required for the implementation of medical diagnostic sensing devices. We will show results of optical biosensing experiments based on integrated Mach-Zehnder interferometers and demonstrate how inkjet material printing technology can be effectively used to locally functionalize the optical waveguide transducer components. Moreover, we will discuss the potential of this silicon nitride waveguide based nanophotonic integration platform for the miniaturization of optical coherence tomography systems.

Hybrid photonic integration allows individual components to be developed at their best-suited material platforms without sacrificing the overall performance. In the past few years a polymer-enabled hybrid integration platform has been established, comprising 1) EO polymers for constructing low-complexity and low-cost Mach-Zehnder modulators (MZMs) with extremely high modulation bandwidth; 2) InP components for light sources, detectors, and high-speed electronics including MUX drivers and DEMUX circuits; 3) Ceramic (AIN) RF board that links the electronic signals within the package. On this platform, advanced optoelectronic modules have been demonstrated, including serial 100 Gb/s [1] and 2x100 Gb/s [2] optical transmitters, but also 400 Gb/s optoelectronic interfaces for intra-data center networks [3]. To expand the device functionalities to an unprecedented level and at the same time improve the integration compatibility with diversified active / passive photonic components, we have added a passive polymer-based photonic board (polyboard) as the 4th material system. This passive polyboard allows for low-cost fabrication of single-mode waveguide networks, enables fast and convenient integration of various thin-film elements (TFEs) to control the light polarization, and provides efficient thermo-optic elements (TOEs) for wavelength tuning, light amplitude regulation and light-path switching.

Recent progress on polymer-based photonic devices and hybrid photonic integration technology using InP-based active components is presented. High performance thermo-optic components, including compact polymer variable optical attenuators and switches are powerful tools to regulate and control the light flow in the optical backbone. Polymer arrayed waveguide gratings integrated with InP laser and detector arrays function as low-cost optical line terminals (OLTs) in the WDM-PON network. External cavity tunable lasers combined with C/L band thinfilm filter, on-chip U-groove and 45° mirrors construct a compact, bi-directional and color-less optical network unit (ONU). A tunable laser integrated with VOAs, TFEs and two 90° hybrids builds the optical front-end of a colorless, dual-polarization coherent receiver. Multicore polymer waveguides and multi-step 45°mirrors are demonstrated as bridging devices between the spatialdivision- multiplexing transmission technology using multi-core fibers and the conventional PLCbased photonic platforms, appealing to the fast development of dense 3D photonic integration.

An external cavity laser is demonstrated based on the hybrid integration of an InP-based gain element, a half-wave plate, and thermally drivable polymer waveguide circuits. The laser has one oscillation region but two outputs for TE and TM emissions. The central wavelength can be tuned 20 nm at 20 mW heater electrical power. The TM path undergoes a 1.4 dB power penalty due to the presence of the half-wave plate. However, the on-chip thermo-optic switch (TOS) can compensate for this imbalance and steer the laser into an equal TE and TM output power. The TOS can also be adjusted to prefer one polarization path over the other with similar to 10 dB extinction ratio.

Variable optical attenuators based on a 1 x 1 multimode interference device (MMI) and a Mach-Zehnder interferometer (MZI) have been designed, fabricated, and characterized. Thermo-optic simulations have been performed to find the optimal heater electrode layout in order to improve the heating efficiency, suppress thermal crosstalk, and enhance the dynamic attenuation range. Both types of attenuators feature low optical loss (

The performance of multimode interference (MMI) couplers in silicon waveguides is limited by the high lateral refractive index contrast. Here we propose the use of subwavelength gratings (SWGs) in the lateral cladding regions of the MMI to reduce the index contrast. Our approach significantly reduces the mode phase error while at the same time allowing a single etch step process. Using a $z$-periodic lateral SWG, we design a 2 × 4 MMI that operates as a 90° hybrid for a coherent optical receiver. This complex device exhibits a common mode rejection ratio (CMRR) and a phase error of less than-24 dBe and 2°, respectively, over the full C-band. Compared to MMI with a homogenous lateral cladding, using subwavelength refractive index engineering effectively extends the receiver bandwidth from 36 to 60 nm. © 2011 IEEE.

High contrast structures with a sub-wavelength pitch, small enough to suppress diffraction, exhibit extraordinary optical properties: depending on the design they may behave as perfect mirrors, anti-reflective interfaces, homogenous materials with controllable refractive index, or strongly dispersive materials. Here we discuss on the design possibilities such structures offer in planar waveguide devices in silicon-on-insulator. We briefly review the application of sub-wavelength structures in a variety of waveguide devices. We then focus on some of the latest advances in the design ultra-compact and ultra-wideband multimode interference couplers based on dispersion engineered sub-wavelength structures., High Contrast Metastructures III, February 4-6, 2014, San Francisco, CA, USA, Series: Proceedings of SPIE; no. 8995

Multicore, compact, and low-crosstalk polymer waveguides have been designed, fabricated, and characterized. These single-mode waveguides are arranged in five layers following a hexagonal lattice with 20-\(\mu \) m pitch. The waveguides exhibit similar propagation loss of