Experimental assessment of access guide first-order mode effect on multimode interference couplers

Abstract

Experimental results on multimode interference (MMI) coupler performance, when the access waveguides are not single mode, are shown. The 3-dB MMI couplers based on restricted interference are fabricated in InP/ InGaAsP buried waveguides. Unbalanced measurements for different excitation conditions are shown. A drastically unbalanced decline of 30% is reported for an alignment deviation of 6 m. Less critical effects are measured when misalignment is controlled below 2 m. A beam propagation method and modal analysis are used to validate experimental results.

Effects of annealing on performances of 1.3-μm InAs-InGaAs-GaAs quantum dot electroabsorption modulators

“…The effective index for a 7-μm-wide rib waveguide with an etch depth of 1.2 μm is approximately 3.325 and is still sufficiently narrow to hold single-mode propagation as shown in the simulation in Figure 1 (bottom left). However, careful alignment and cleaving was still necessary in order to avoid exciting higher order modes [13]. Although in actual fabrication the etch depth is 1.4 μm, 0.2 μm has been omitted in this simulation because that is for the GaAs contact layer of higher refractive index and sufficiently far away from the inserted light source that it need not be included when simulating the mode propagation.…”

“…A fiber-device under test (DUT)-free space setup as illustrated in Figure 2 (top) was used during the course of the direct current (DC) measurements for a more accurate positioning [13] and identification of the propagating mode - be it the fundamental mode or a higher order mode that was being modulated. Using an external ground-signal-ground (GSG) pad, a wire bonded to the QD-EAM, and a fiber-DUT-fiber measurement setup as illustrated in Figure 2 (bottom), we were able to perform preliminary radio-frequency (RF) measurements on the devices as shown in Figure 1 (bottom left).…”