Beam steering is advantageous for continuous-wave terahertz applications in sensing, imaging, and wireless communication. While wide spread in lower frequency bands, in the terahertz region complex emitter and receiver structures are hardly feasible with discrete devices, due to the shorter wavelengths. Therefore, we propose and demonstrate the use of photonic integration: A 1x4 antenna array based on photodiodes is driven by an optical phased array based on polymer. The packaged emitter features increased directivity and enables beam steering across 30 °.

InP technology is the principal enabler for implementing fully monolithic photonic integrated circuits (PIC), uniquely including transmitter elements. In this article we present an overview of recent achievements on ultra-high speed electro-absorption modulated lasers (EML) which represent a simple transmitter PIC comprising a single-mode laser diode and an electro-absorption modulator. Using a so-called identical-layer approach single-wavelength modulation rates up to 100 Gb/s have been accomplished. By additionally integrating an optical amplifier section modulated optical output power of > 10 dBm has been achieved. Multi-level amplitude modulation was successfully demonstrated. Extended EML chips designed for wavelength-division and space-division multiplexing, respectively, will be presented. For dual-polarization transmission a novel EML related transmitter as well as a corresponding receiver PIC have been introduced. The latter devices were made on a generic PIC platform that is available for open-access foundry service.

We propose and demonstrate a new photonic integrated circuit (PIC) design for Stokes vector reception. Its accuracy is 2.5° across the entire Poincaré sphere and almost than the entire C-band.

We propose and demonstrate a transmit-type photonic integrated circuit (PIC) for polarization multiplexing applications. With a single integrated DFB laser source, the PIC generates two independently modulated states of polarization. The PIC is used for 40 Gbit/s transmission.

We demonstrate PDM-PAM4 generation for the first time from an integrated EAM-based chip with 0.5 mm 2 footprint. The device is used in 112 Gbit/s transmission over 80 km of SSMF.

In this work, we report on experimental results of a fully integrated polarization converter made in InP. The device relies on slanted side wall waveguides. Using a novel design, we are able to demonstrate 15 dB of polarization extinction ratio (PER) for a fabrication tolerance of > 250 nm with respect to the critical waveguide width. The design of the device was derived using a new fully analytical model. No active tuning is required.

Selective area growth (SAG) technology has been added to an established InP monolithic integration platform to fabricate arrays of multi-wavelength distributed feedback (DFB) lasers. The local epitaxy growth rate is controlled by the SiO 2 mask width, and different quantum well (QW) thicknesses can be obtained in one run. The laser wavelengths span from 1447 nm to 1602 nm. The DFB lasers may include amplifying sections at the front and/or rear side. Output power up to 18 mW is achieved. This technology opens up possibilities to integrate various passive and active components such as lasers, modulators, detectors with different operating wavelengths monolithically on one wafer with less regrowth steps and reduced fabrication complexity.

A comprehensive analysis of the crosstalk between integrated photonic waveguides generated by roughness-related scattering is presented. A power-law dependence on the waveguide distance is demonstrated, confirmed also by simulations performed with a specifically developed model based on the volume current method. In the near feature, integrated optics will face a challenging request for larger scale of integration, with the necessity to increase the number of components per unit area of the chips. Crosstalk phenomena will hence become a real limiting factor, eventually compromising the functionality of densely integrated circuits. In particular for high-index-contrast technologies, a source of crosstalk can be represented by the power leakage generated by sidewall roughness. Part of the scattered light can reach a nearby waveguide, causing an unwanted optical power exchange between ideally uncoupled waveguides. In this work we present an experimental characterization of the properties of roughness-induced optical crosstalk in photonic waveguides, demonstrating the emergence of a radiative regime able to support a coupling also beyond the effects of evanescent coupling. The exploited test structure is represented in Fig. 1(a). The device is formed by a S-shaped waveguide comprised between ports A and B (direct waveguide) with a second 3-mm-long straight waveguide (adjacent waveguide) running parallel at a gap distance g and defining the coupling section. Gaps between 2 μm and 30 μm have been considered. The aspect ratio between input port A and output port B is 6 mm × 100 μm and the shape of the device was designed in order to reduce the impact of straylight generated by the input fibre (port A) on the measured power at ports B and C. Two different waveguides has been considered for the fabrication of the device. The first one, represented in Fig. 1(b), is a shallow etched InP-based rib waveguide with a 1-μm-thick InGaAsP core and an etch depth of 600 nm. The second waveguide is a deeply-etched version of the same cross-section (Fig. 1(c)), with an etch depth of 1.7 μm. In both cases the waveguides are 2 μm wide. Fig. 1: (a) Design of the test structure exploited for the experimental characterization of the radiative optical crosstalk. Two different cross-sections have been used for the devices: (b) shallow and (c) deeply etched InPbased waveguides. For all the fabricated structures, the crosstalk was measured coupling light at port A (Pin) and measuring the average power at port B (Pout) and C (Pxt) as function of the gap g. The normalized power Pxt/(Pxt+Pout) represents the crosstalk from the direct to the adjacent waveguide. Results for TE polarized light are reported in Fig. 2(a) and 2(b) for the shallow and deeply etched waveguide crosssections, respectively. In both cases the dynamic range of the measurement is limited by the presence of substrate modes excited by the input fibre and propagating throughout the chip. The power Psub (green squares) carried by these modes was measured laterally shifting the output fibre 50 μm far from port C. For the shallow etched waveguide, the crosstalk is as high as -3dB at g = 2 μm and drops to less than -40 dB at g = 30μm. In order to evaluate the contribution of the pure evanescent coupling to the power transfer between the waveguides, the test structure was simulated with a commercial electromagnetic simulator based on the Film Mode Matching (FMM) method for perfectly smooth sidewalls. Simulation results are shown in Fig. 2(a) with blue and black lines for ports B and C, respectively, and allow to identify different coupling regimes. Evanescent coupling well explains the Tu 3b R2

This paper describes the development of a very-versatile InP-Based Photonic-Integration platform by Butt-Joint integration of the passive waveguides to active waveguides across a relatively high mesa of 34μm. The Butt-Joint losses are currently around 1dB.

We present a receive-type photonic integrated circuit in InP that can demultiplex 100 wavelength channels. The channels are spaced by 1 nm. The device has integrated photodetectors for each channel, with a to-fibre sensitivity > 0.02 A/W for all channels.

We present results on optical crosstalk in the photonic integration platform developed at Fraunhofer HHI. Two fundamental mechanisms are investigated: stray light generation at butt-joints and coupling between two passive waveguides. The latter can happen in two regimes: evanescently or radiatively, depending on the gap between the waveguides. Measurements show the amount of crosstalk that is to be expected on ASPICs. Moreover, means to reduce crosstalk levels that are compatible with the existing technology are demonstrated.

Silicon waveguides can be functionalized with an organic χ(2)-nonlinear cladding. This complements silicon photonics with the electro-optic (EO) effect originating from the cladding and enables functionalities such as pure phase modulation, parametric amplification, or THz-wave generation. Claddings based on a polymer matrix containing chromophores have been introduced, and their strong χ(2) nonlinearity has already been used to demonstrate ultralow power consuming modulators. However, these silicon-organic hybrid (SOH) devices inherit not only the advantageous properties; these polymer claddings require an alignment procedure called poling and must be operated well below their glass transition temperature. This excludes some applications. In contrast, claddings made from organic crystals come with a different set of properties. In particular, there is no need for poling. This new class of claddings also promises stronger resilience to high temperatures, better long-term stability, and photo-chemical stability. We report on the deposition of an organic crystal cladding of N-benzyl-2-methyl-4-nitroaniline (BNA) on silicon-on-insulator (SOI) waveguides, which have a CMOS-like metal stack on top. Adhering to such an architecture, which preserves the principal advantage of using CMOS-based silicon photonic fabrication processes, permits the first demonstration of high-speed modulation at 12.5 Gbit/s in this material class, which proves the availability of the EO effect from BNA on SOI also for other applications.

Silicon-organic hybrid (SOH) devices combine silicon waveguides with a number of specialized materials, ranging from third-order optically-nonlinear molecules to second-order nonlinear polymers and liquid-crystals. Second-order nonlinear materials allow building high-speed and low-voltage electro-optic modulators, which are key components for future silicon-based photonics transceivers. We report on a 90 GHz bandwidth phase modulator, and on a 56 Gbit/s QPSK experiment using an IQ Pockels effect modulator. By using liquid-crystal claddings instead, we show experimentally that phase shifters with record-low power consumption and ultra-low voltage-length product of VπL = 0.06 Vmm. Secondorder nonlinear materials, moreover, allow creating nonlinear waveguides for sum- or difference-frequency generation, and for lowest-noise optical parametric amplification. These processes are exploited for a large variety of applications, like in the emerging field of on-chip generation of mid-IR wavelengths, where pump powers are significantly smaller compared to equivalent devices using third-order nonlinear materials. In this work, we present the first SOH waveguide design suited for second-order nonlinear processes. We predict for our device an amplification of 14 dB/cm assuming a conservative χ(2)-nonlinearity of 230 pm/V and a CW pump power as low as 20 dBm.

Silicon modulators fabricated by scalable, established CMOS technology, promise an answer to today's power consumption challenges. With advanced modulation formats and the resulting higher spectral efficiencies, long-haul applications for silicon modulators come into reach. Energy efficient, high speed modulators were demonstrated as resonant [1] and non-resonant [2] devices. A single-carrier single-polarization data rate of 56 Gbit/s is considered state-of-the-art [3]. Usually, free-carrier dispersion is exploited in silicon modulators.

We report on high-speed multilevel signal generation with silicon-organic hybrid Mach-Zehnder modulators. Pure phase modulation exploiting the linear electro-optic effect allows to generate 28 GBd BPSK, 4-ASK and 8-ASK signals up to 84 Gbit/s.

A new MAC protocol allows communication with both awake and asleep network elements. The protocol and its capabilities are demonstrated in an exemplary sensor network.