Silicon photonic (SiPho) platforms hold vast potential for providing multi-functional processing capabilities, such as filtering, mode-handling, modulation, etc. Structures for polarization manipulation have become essential elements to enhance channel capacity and to facilitate polarization multiplexing functions. Therefore, 1x2 polarization beam splitters (PBS) are introduced as polarization-division key building blocks based on a silicon-on-insulator (SOI) platform for separating/combining the fundamental modes. By cascading three bent directional couplers (DC), high-performance coupling characteristics can be obtained similar to those of asymmetric ones. A first-ever integration of this kind of PBS has been achieved utilizing Tower Semiconductor's PH18MA silicon photonics platform, which offers 180 nm SOI process technology. In this work, both output ports of the proposed PBS are being tested for polarization filtering across a polarization sweep. The advanced features of this integration process pave the way for next-generation coherent transceivers and aim to meet future optical interconnecting requirements. Furthermore, Synopsys OptoCompiler and the Photonic IC Design Flow, featured in Tower’s process design kit (PDK), were used to design the devices.
KEYWORDS: Optical proximity correction, Photomasks, Waveguides, Photonic devices, Lithography, Line edge roughness, Stochastic processes, Photonics, Signal to noise ratio
Photonics represents a growing opportunity to design and manufacture devices and integrated circuits for applications in high-speed data communications, advanced sensing, and imaging. Photonic technologies provide orders-of-magnitude speed improvements with reduced power consumption for data transmission and ultra-sensitive sensing capabilities in multiple application domains. Curvilinear patterns are required to maintain the physical properties of light propagation. We investigate the readiness of state-of-the-art mask synthesis tools to meet the challenges for photonics devices in terms of mask data preparation and verification. We apply OPC and ILT to photonic integrated circuit designs containing components sensitive to fabrication variation, to generate Manhattan and curvilinear mask data. Results are validated using a lithography verification tool considering smoothness of the printed curved structures, a key factor to maintain the correct functionality of the photonic devices. Rather than using ideal targets, we take simulation contours from corrected layouts for initial assessment of light propagation through wave guides. The impact of lithographic patterning related perturbations such as resist line edge roughness on optical performance is investigated based on results from a rigorous lithography process simulation model. Experimental data from fabricated devices underline the usefulness of lithography simulation to predict unwanted impact on device performance and the need of correction tools to counteract these effects.
In the mid-infrared (Mid-IR), arrays of distributed feedback Quantum Cascade Lasers (QCL) have been developed as a
serious alternative to obtain extended wavelength operation range of laser-based gas sensing systems. Narrow-linewidth,
single mode operation and wide tunability are then gathered together on a single chip with high compactness and
intrinsic stability. In order to benefit from this extended wavelength range in a single output beam we have developed a
platform for InP-based photonics. After the validation of all required building blocks such as straight waveguides,
adiabatic couplers between active and passive waveguides, and echelle grating multiplexers, we are tackling the
integration into a single monolithic device.
We present the design, fabrication and performances of a tunable source, fully monolithic based on the echelle grating
approach. Advantages are design flexibility, relatively simple processing and the need for one single epitaxial growth for
the entire structure. The evanescent coupler has been designed to transfer all light adiabatically from the active region to
a low loss passive waveguide, while taking advantage of the high gain available in the quantum wells. The multiplexer is
based on an etched diffraction grating, covering the whole range of the 30 lasers of the array while keeping a very
compact size. These results show the first realization of a monolithic widely tunable source in the Mid-IR and would
therefore benefit to the development of fully integrated spectroscopic sensor systems.
We present the experimental characterization results of a 15-to-1 wavelength multiplexer for a Distributed Feedback Quantum Cascade Laser (DFB QCL) array operating in the 7-8.5 μm (mid-long) infrared (IR) range. This design is customized for its use to combine the output from a DFB QCL array with a 0.1 μm wavelength channel spacing for spectroscopy applications, and it is proposed in order to achieve a continuous tuning range overcoming the limited tunability of a single QCLs, required for multi-gas or complex molecule detection. This multiplexer is based on an Echelle diffraction mirror grating scheme, in which multiple output waveguides are deliberately implemented in the design to de-risk for wavelength deviations in the fabrication process. We optimized the location of the input and output guides in order to allow for monolithic integration of the DFB QCL arrays, which would provide for a number of advantages such as a higher stability, less complexity and lower cost over other technologies such as external cavities. We discuss the effects over the device performance of the design, such as the diffraction effects, input channel width overlapping/crosstalk and input channel profile, which are very important to address in order to avoid unaccounted transmission losses. Other parameters such as the profile of the input and output waveguides and fabrication limitations are also discussed as their effect on the device is observed. A series of characterization tests are presented in order to compare the simulation results to the experimental data, which suggests that these multiplexers are a suitable option compared to other IR multiplexer schemes in terms of size and power transmission.
In this work we introduce the design, optimization, simulation and experimental characterization results of a 30-to-1 wavelength multiplexer for a Distributed Feedback Quantum Cascade Laser (DFB QCL) laser array operating in the 7- 8.5 μm (mid-long) infrared (IR) range based on an Echelle mirror using a dual Rowland circle grating scheme. This design is proposed in order to achieve a continuous tuning range overcoming the limited tunability of individual QCLs. The design is based on a DFB-QCL array with wavelength spacing of 0.05 μm, aiming to reducing coupling between the slab waveguides to a minimum. We discuss the design parameters such as the order of diffraction, the operation wavelength range in the slab waveguides and the position of both the input and output waveguides are optimized for obtaining higher output power in the overall wavelength range of the multiplexer device than in a single Rowland circle grating scheme, providing an improvement in channel transmission. Other design characteristics, such as the structure scalability and reduction in size for these devices are considered and studied, including the input/output waveguide optimization as a function of parameters such as waveguide width, etching depth and wavelength. A systematic process is presented for all steps in the design of these devices, comparing both simulated and experimental results, placing them as suitable options when compared to other IR multiplexer schemes in terms of size and transmission.
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