As an essential component of mode division multiplexing (MDM) system, a multimode 3dB power splitter with low loss, high power balance, and low mode crosstalk is highly desired. In this paper, we propose an ultra-broadband on-chip multimode 3dB optical power splitter using an adiabatic coupler and an S-bend based Y-branch. As an example, a splitter for the four-lowest modes of a rib waveguide on silicon on insulator (SOI) platform is designed. Simulation results show that the device exhibits < 0.12dB insertion losses, within ± 0.38dB power imbalances, and < −18.5dB mode crosstalks for the four-lowest modes within a large operating wavelength range of 165 nm (from 1400 nm to 1565 nm). The fabrication tolerance of gap size at the output end of the adiabatic coupler is also analyzed.

A novel design of a two-mode de/multiplexer (DE/MUX) based on multimode interference (MMI) couplers is presented. Instead of the phase shifter (PS) in the shape of a narrow strip waveguide, which needs tight design and fabrication requirements, a tilted joint is used as a PS in the proposed device, so that the effects of the fabrication errors of the PS on the performance of the device can be reduced greatly. Simulations show that while the size of the device is as small as 39.54 μm, which is more compact than other MMI-based DE/MUX, the fabrication tolerance is larger than $\pm 25\mathrm{nm}$. Within the entire C-band wavelength range, the de-multiplexing crosstalk of the device is lower than $-28\mathrm{dB}$ and the insertion loss is below 1.0 dB.

We present an InP based distributed Bragg reflector (DBR) laser transmitter which has a wide wavelength tuning range and a high chip output power for wavelength division multiplexing passive optical network (WDM-PON) applications. By butt-jointing InGaAsP with 1.45 µm emission wavelength as the material of the grating section, the laser wavelength can be tuned for over 13 nm by the DBR current. Accompanied by varying the chip temperature, the tuning range can be further enlarged to 16 nm. With the help of the integrated semiconductor optical amplifier (SOA), the largest chip output power is over 30 mW. The electroabsorption modulator (EAM) is integrated into the device by the selective-area growth (SAG) technique. The 3 dB small signal modulation bandwidth of the EAM is over 13 GHz. The device has both a simple tuning scheme and a simple fabrication procedure, making it suitable for low cost massive production which is desirable for WDM-PON uses.

We present designs of wavelength-division-multiplexing (WDM) and mode-division-multiplexing (MDM) optical links using mode de/multiplexers (DE/MUXs) based on multimode interference (MMI) couplers with a tilt joint as a phase shifter. The properties of WDM-MDM links with three wavelengths and two optical modes are numerically studied by using 3-D beam propagation method. In the first design, the wavelength combiner is also an MMI coupler type. The insertion loss of the design is around 6 dB because of the inherent loss of the MMI combiner. The size of the main passive optical parts (mode DE/MUXs and wavelength combiner) of the design is only $10.4\ \times 114.2\ \mu\text{m}^{2}$ , making the design promising for future compact and high-capacity optical interconnection applications. In another design, arrayed waveguide gratings are used for wavelength multiplexing, leading to a lower insertion loss of the optical connections. For both designs, the mode crosstalk between the two different modes for the same wavelength are below −22 dB.

In this paper, we design and demonstrate new angled multimode interference (MMI) couplers in silicon-on-insulator that allow arbitrary selection of coupling ratios, while simultaneously achieve low-chromaticity response and improved fabrication variations tolerance. The proposed couplers rely on paired-interference design approach in tandem with a new angled multi-mode junction to mitigate chromatic aberration and geometry-induced waveguide modal shift in conventional angled MMI coupler design. Test devices with footprint of 4.8 μm x 75 μm showed full coupling ratio range addressability with insertion loss below 1.2 dB. Spectral responses across the extended C band (1525 nm — 1575 nm) were also characterized, where coupling ratio varied by less than 2.3% across the spectral region of interest. Furthermore, coupler characteristics variations against line-width and thickness deviations are numerically analyzed, demonstrating robustness within typical fabrication tolerances.

A high extinction ratio (ER) polarization beam splitter with three different multimode interference couplers on InP substrate was designed by a three-dimensional beam propagation method. Simulations show that the polarization ER (PER) is over 34 dB and internal loss is <;0.8 dB for both TE and TM polarizations. The PER imbalance between the two polarization states has been reduced to 22 dB. The total length of the device is <;950 μm. The effects of the width of the input port on the performance of the device are discussed in detail.