A wavelength filter is a key component for numerous photonic integrated circuit applications in optical communication. Researchers put forward several methods to design wavelength filters for which the Echelle grating de-multiplexers (EGDMUXs) are popular and have been extensively studied. In comparison with the traditional EG-DMUXs based on the Rowland mounting, EG-DMUXs based on the two stigmatic points (TSP) method were reported rather late. This paper will present the basic design theory and a high-performance device fabricated on a 250 nm silicon-on-insulator (SOI) platform for validation. The simulation and measurement results of this 1×7 EG-DMUX with 800 GHz channel spacing will be presented and compared. Although the fabricated device has the merits of compact on-chip footprint, low insertion loss and low crosstalk, its narrow 1-dB bandwidth may limit its application in practice. We present our solution to widen the transmission spectrum based on the TSP EG-DMUXs and multimode interferometers.
One promising solution for the ever increasing transmission capacity demand from fundamental research and data centers is the silicon-photonic integrated WDM transmitter. We designed an easily scalable, high-bandwidth transmitter unit composed of radiation-hardened Mach-Zehnder modulators (MZMs) and Echelle grating (de-)multiplexers (EG-DMUXs).
Our 3 mm MZMs have customized slabs with a reduced etch depth to improve their radiation hardness. Our current MZMs feature a Vπ∙L of 4.6 V∙cm and an insertion loss of 4.84 dB. Additionally, an error-free transmission was achieved successfully at a speed of 11.3 Gb/s while driving the modulators with a PRBS-7 signal and an amplitude of less than 2 Vpp.
The Echelle grating (de-)multiplexers were designed and simulated numerically. The presented 1x7 device is compact and low-loss: the on-chip footprint is 680 μm × 380 μm, the channel spacing is 800 GHz, and the measured average insertion loss and crosstalk are 2.5 dB and -22 dB, respectively. With optimized components, higher bandwidth systems with more channels are achievable.
Driven by the increasing demands of ultra-broad bandwidth transmission in telecommunications as well as in large-scale scientific experiments, interests in developing on-chip DWDM networks based on silicon photonics is increasing rapidly. With compact structures, low loss and robust fabrication, Echelle grating (EG) (de-)multiplexers become one of the key components. Two competitive design methods are the Rowland circle (RC) and the two stigmatic points (TSP) method, with the latter one offering remarkable advantages on optical aberrations and degrees of freedom. We demonstrate a self-developed design kit for both methods involving MATLAB calculation, COMSOL Multiphysics simulation and GDSII layout. In our kit, several parameters are reserved to optimize the geometry in terms of device footprint, reflector configurations etc.. By making rigorous simulation on an HPC cluster, we obtained well-performing, robust and compact EG (de-)multiplexers based on the two stigmatic points method. For the 7-channel, 9th diffraction order and 800 GHz channel spacing device, we get a simulated average optical loss of 2.3 dB and a crosstalk of less than -20 dB with an on-chip footprint of 400×690 μm2. Our silicon-photonic devices were fabricated on a 250 nm silicon-on-insulator (SOI) platform using e-beam lithography and dry etching. The comparison between measurement results of fabricated devices and simulation results was carried out, as well as a comparison between designs based on both design methods. Additionally, the experimental result of a 25- channel (de-)multiplexer with 200 GHz channel spacing in the C-band is presented to study the performance of the TSP method for a narrow channel spacing and large footprint design.
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