Optical frequency combs have the potential to become key building blocks of wavelength-division multiplexing (WDM) communication systems. The strictly equidistant narrow-band spectral lines of a ...frequency comb can serve either as carriers for parallel WDM transmission or as local-oscillator (LO) tones for parallel coherent reception. When it comes to highly scalable WDM transceivers with compact form factor, chip-sale comb sources are of particular interest, and recent experiments have demonstrated the viability of such devices for high-speed communications with line rates of tens of Tbit/s. However, the output power of chip-scale comb sources is generally lower than that of their conventional discrete-element counterparts, thus requiring additional amplifiers and impairing the optical signal-to-noise ratio (OSNR). In this paper, we investigate the influence of the power and optical carrier-to-noise ratio (OCNR) of the comb lines on the performance of the WDM link. We identify two distinctively different regimes, where the transmission performance is either limited by the comb source or by the link and the associated in-line amplifiers. We further investigate the impact of line-to-line power variations on the achievable OSNR and link capacity using a soliton Kerr frequency comb as a particularly interesting example. We believe that our findings will help to compare different comb generator types and to benchmark them with respect to the achievable transmission performance.
Early and efficient disease diagnosis with low-cost point-of-care devices is gaining importance for personalized medicine and public health protection. Within this context, waveguide-(WG)-based ...optical biosensors on the silicon-nitride (Si3N4) platform represent a particularly promising option, offering highly sensitive detection of indicative biomarkers in multiplexed sensor arrays operated by light in the visible-wavelength range. However, while passive Si3N4-based photonic circuits lend themselves to highly scalable mass production, the integration of low-cost light sources remains a challenge. In this paper, we demonstrate optical biosensors that combine Si3N4 sensor circuits with hybrid on-chip organic lasers. These Si3N4-organic hybrid (SiNOH) lasers rely on a dye-doped cladding material that are deposited on top of a passive WG and that are optically pumped by an external light source. Fabrication of the devices is simple: The underlying Si3N4 WGs are structured in a single lithography step, and the organic gain medium is subsequently applied by dispensing, spin-coating, or ink-jet printing processes. A highly parallel read-out of the optical sensor signals is accomplished with a simple camera. In our proof-of-concept experiment, we demonstrate the viability of the approach by detecting different concentrations of fibrinogen in phosphate-buffered saline solutions with a sensor-length (L-)-related sensitivity of S/L = 0.16 rad nM−1 mm−1. To our knowledge, this is the first demonstration of an integrated optical circuit driven by a co-integrated low-cost organic light source. We expect that the versatility of the device concept, the simple operation principle, and the compatibility with cost-efficient mass production will make the concept a highly attractive option for applications in biophotonics and point-of-care diagnostics.Optical biosensors: light source integrationOptical sensors that comprise integrated lasers and that are compatible with cost-efficient mass manufacturing could be promising for point-of-care diagnostics. Daria Kohler and coworkers at Karlsruhe Institute of Technology (KIT) and Robert Bosch GmbH in Germany have now demonstrated biosensors that combine silicon-nitride (Si3N4) waveguides with co-integrated Si3N4-organic hybrid (SiNOH) lasers. The sensor consists of three main integrated parts: The optically-pumped SiNOH laser, a Mach-Zehnder interferometer acting as a biosensor, and a set of grating couplers for directing the output to a CCD camera. The SiNOH laser relies on a spiral Si3N4 waveguide, which is covered by a dye-doped organic cladding to provide optical gain. The devices are technically simple and can be efficiently realized by wafer-level printing techniques.
Abstract
Combining semiconductor optical amplifiers (SOA) on direct-bandgap III–V substrates with low-loss silicon or silicon-nitride photonic integrated circuits (PIC) has been key to chip-scale ...external-cavity lasers (ECL) that offer wideband tunability along with small optical linewidths. However, fabrication of such devices still relies on technologically demanding monolithic integration of heterogeneous material systems or requires costly high-precision package-level assembly, often based on active alignment, to achieve low-loss coupling between the SOA and the external feedback circuits. In this paper, we demonstrate a novel class of hybrid ECL that overcome these limitations by exploiting 3D-printed photonic wire bonds as intra-cavity coupling elements. Photonic wire bonds can be written in-situ in a fully automated process with shapes adapted to the mode-field sizes and the positions of the chips at both ends, thereby providing low-loss coupling even in presence of limited placement accuracy. In a proof-of-concept experiment, we use an InP-based reflective SOA (RSOA) along with a silicon photonic external feedback circuit and demonstrate a single-mode tuning range from 1515 to 1565 nm along with side mode suppression ratios above 40 dB and intrinsic linewidths down to 105 kHz. Our approach combines the scalability advantages of monolithic integration with the performance and flexibility of hybrid multi-chip assemblies and may thus open a path towards integrated ECL on a wide variety of integration platforms.
We examine the relation between optical signal-to-noise ratio (OSNR), error vector magnitude (EVM), and bit-error ratio (BER). Theoretical results and numerical simulations are compared to measured ...values of OSNR, EVM, and BER. We conclude that the EVM is an appropriate metric for optical channels limited by additive white Gaussian noise. Results are supported by experiments with six modulation formats at symbol rates of 20 and 25 GBd generated by a software-defined transmitter.
We report on the hybrid integration of silicon-on-insulator slot waveguides with organic electro-optic materials. We investigate and compare a polymer composite, a dendron-based material, and a ...binary-chromophore organic glass (BCOG). A record-high in-device electro-optic coefficient of 230 pm/V is found for the BCOG approach resulting in silicon-organic hybrid Mach-Zehnder modulators that feature low U π L-products of down to 0.52 Vmm and support data rates of up to 40 Gbit/s.
Laser-based light detection and ranging (LiDAR) is key to many applications in science and industry. For many use cases, compactness and power efficiency are key, especially in high-volume ...applications such as industrial sensing, navigation of autonomous objects, or digitization of 3D scenes using hand-held devices. In this context, comb-based ranging systems are of particular interest, combining high accuracy with high measurement speed. However, the technical complexity of miniaturized comb sources is still prohibitive for many applications, in particular when high optical output powers and high efficiency are required. Here we show that quantum-dash mode-locked laser diodes (QD-MLLD) offer a particularly attractive route towards high-performance chip-scale ranging systems. QD-MLLDs are compact, can be easily operated by a simple DC drive current, and provide spectrally flat frequency combs with bandwidths in excess of 2 THz, thus lending themselves to coherent dual-comb ranging. In our experiments, we show measurement rates of up to 500 MHz-the highest rate demonstrated with any ranging system so far. We attain reliable measurement results with optical return powers of only - 40 dBm, corresponding to a total loss of 49 dB in the ranging path, which corresponds to the highest loss tolerance demonstrated so far for dual-comb ranging with chip-scale comb sources. Combing QD-MLLDs with advanced silicon photonic receivers offers an attractive route towards robust and technically simple chip-scale LiDAR systems.
Photonic wire bonding is demonstrated to enable highly efficient coupling between multicore fibers and planar silicon photonic circuits. The technique relies on in-situ fabrication of ...three-dimensional interconnect waveguides between the fiber facet and tapered silicon-on-insulator waveguides. Photonic wire bonding can easily compensate inaccuracies of core placement in the fiber cross-section, does not require active alignment, and is well suited for automated fabrication. We report on the design, on fabrication, and on characterization of photonic wire bonds. In a proof-of-principle experiment, a four-core fiber is coupled to a silicon photonic chip, leading to measured coupling losses as small as 1.7 dB.
Abstract
Electro-optic modulation at frequencies of 100 GHz and beyond is important for photonic-electronic signal processing at the highest speeds. To date, however, only a small number of devices ...exist that can operate up to this frequency. In this study, we demonstrate that this frequency range can be addressed by nanophotonic, silicon-based modulators. We exploit the ultrafast Pockels effect by using the silicon–organic hybrid (SOH) platform, which combines highly nonlinear organic molecules with silicon waveguides. Until now, the bandwidth of these devices was limited by the losses of the radiofrequency (RF) signal and the RC (resistor-capacitor) time constant of the silicon structure. The RF losses are overcome by using a device as short as 500 µm, and the RC time constant is decreased by using a highly conductive electron accumulation layer and an improved gate insulator. Using this method, we demonstrate for the first time an integrated silicon modulator with a 3dB bandwidth at an operating frequency beyond 100 GHz. Our results clearly indicate that the RC time constant is not a fundamental speed limitation of SOH devices at these frequencies. Our device has a voltage–length product of only
V
π
L
=11 V mm, which compares favorably with the best silicon-photonic modulators available today. Using cladding materials with stronger nonlinearities, the voltage–length product is expected to improve by more than an order of magnitude.
PDF
