Compact and broadband silicon polarization splitter-rotator using adiabaticity engineering.

We propose and demonstrate a short and broadband silicon mode-conversion polarization splitter-rotator (PSR) consisting of a mode-conversion taper and an adiabatic coupler-based mode sorter both optimized by adiabaticity engineering (AE). AE is used to optimize the distribution of adiabaticity parameter over the length of the PSR, providing shortcut to adiabaticity at a shorter device length. The total length of the PSR is 85 µm. The design is compatible with standard silicon photonics platforms and requires only one patterning step. Fabricated PSR has a polarization cross talk of less than -20 dB over the entire O-band for the TE polarization and a polarization cross talk of less than -15 dB from 1267 to 1348 nm for the TM polarization. Overall, the PSR shows low polarization cross talk (-15 dB) over a bandwidth of 81 nm in the O-band. Cross-wafer measurements show that the PSR has good fabrication tolerance.

Compact polarization-independent quasi-adiabatic 2×2 3 dB coupler on silicon.

We demonstrate a quasi-adiabatic polarization-independent 2×2 3 dB coupler based on the silicon-on-insulator platform. Using a quasi-adiabatic taper design for the mode evolution/coupling region, the TE mode evolution is accelerated, and the TM mode coupling is achieved at a short coupling length. The measured working bandwidth is 75 nm with a compact mode evolution/coupling region of 11.7 µm.

Shortcut to adiabaticity in a silicon polarization splitter rotator using multi-wavelength adiabaticity engineering.

We introduce adiabaticity engineering in coupled waveguide devices to achieve shortcuts to adiabaticity in multi-wavelength systems. By engineering the adiabaticity distribution using a single control parameter, we obtain large operating bandwidth in a compact device. Multi-wavelength adiabaticity engineering is applied to the design of silicon polarization splitter-rotators. The total length of the designed polarization splitter-rotator is 141 µm, and simulations show that the device exhibits extinction ratios above 28 dB and 16 dB for the TE0 and TM0 modes, respectively, with a bandwidth of 300 nm (from 1.4 µm to 1.7 µm). The fabrication tolerance of the designed device is also simulated.

Adiabaticity engineering in optical waveguides.

The fast quasi-adiabatic dynamics (FAQUAD) protocol has proven to be an effective approach to provide shortcuts to adiabatic light evolution in optical waveguides, resulting in short and robust devices. However, the FAQUAD approach of homogeneously distributing device adiabaticity only works for a single mode (polarization, wavelength, or spatial mode group) system. We propose an adiabaticity engineering approach to redistribute the adiabaticity of optical waveguides in multi-mode systems. By engineering the adiabaticity distribution using a single control parameter, we obtain shortcuts to adiabaticity in optical waveguides for multi-mode systems. The concept is applied to the design of a compact polarization-independent adiabatic 3-dB coupler on silicon.

Robust silicon arbitrary ratio power splitters using shortcuts to adiabaticity.

We design and fabricate a series of broadband silicon arbitrary power splitters with various split ratios using shortcuts to adiabaticity. In this approach, the system evolution is designed using the decoupled system states, and the desired split ratios are guaranteed by the boundary conditions. Furthermore, the system evolutions are optimized to be as close to the adiabatic states as possible, thus enhancing the robustness to wavelength and fabrication variations. The devices are more compact then the conventional adiabatic designs. Fabricated devices show broadband response for a wide wavelength range from 1.47 to 1.62 µm and also have excellent robustness against fabrication errors across an 8-inch wafer.

Robust arbitrary ratio power splitter by fast quasi-adiabatic elimination in optical waveguides.

We propose a method for the robust splitting of light between the two outer waveguides in a three-waveguide system by mode evolution. Arbitrary power splitting ratio is achieved by engineering the spacings between the middle waveguide and the outer waveguides. Coupling of light into the middle waveguide is suppressed by the adiabatic elimination scheme. To speed up the adiabatic passage in the effective two-mode system involving only the outer waveguides, we introduce the fast quasi-adiabatic dynamics protocol, leading to a shortcut to adiabaticity. Using the proposed fast quasi-adiabatic elimination scheme, power splitters with various power splitting ratios including, 10/90, 20/80, 30/70, 40/60, 50/50, 60/40, 70/30, 80/20, and 90/10, are designed. Simulations show that the splitters have good robustness against wavelength and fabrication variations.

Mode-evolution-based silicon-on-insulator 3 dB coupler using fast quasiadiabatic dynamics.

We report a 2×2 broadband and fabrication tolerant mode-evolution-based 3 dB coupler based on silicon-on-insulator rib waveguides. The operating principle of the coupler is based on the adiabatic evolution of local eigenmodes. The key element of the device is an adiabatically tapered mode evolution region, which converts two dissimilar waveguides into two identical waveguides. Contrary to conventional designs using a linear taper function where the device adiabaticity is uneven during evolution, we use the fast quasiadiabatic approach to homogenize the adiabaticity of the device, leading to a shortcut to adiabaticity. Devices with an optimized taper region of 26.3 µm are designed and fabricated in a complementary metal-oxide-semiconductor compatible process with 193 nm deep ultraviolet lithography. The measured devices exhibit a broadband 3 dB±0.5 dB splitting within a bandwidth of 100 nm, uniformly across a 200-mm wafer, showing good tolerance against fabrication variations.

Ultrashort and broadband silicon polarization splitter-rotator using fast quasiadiabatic dynamics.

We propose an ultrashort and broadband silicon mode-conversion polarization splitter-rotator (PSR) consisting of a taper and a Y-junction both designed by the fast quasiadiabatic dynamics (FAQUAD). The FAQUAD is used to homogeneously distribute adiabaticity over the length of the PSR, providing shortcut to adiabaticity at a shorter device length. The total length of the silicon PSR is 39.2 µm. For a wavelength range from 1.5 µm to 1.6 µm, the PSR exhibits a good performance with > 88% transmission and > 11.4 dB extinction ratio (ER). Simulations also show that the designed devices have good fabrication tolerance.

Short and broadband silicon asymmetric Y-junction two-mode (de)multiplexer using fast quasiadiabatic dynamics.

A short and broadband silicon asymmetric Y-junction two-mode (de)multiplexer is proposed and simulated. An adiabaticity parameter suitable for high index-contrast silicon waveguides is defined. The fast quasiadiabatic dynamics protocol is used to homogeneously distribute adiabaticity over the device length. This protocol limits the power coupled into the unwanted waveguide eigenmode under a fixed value along the propagation. A 16 µm long mode (de)multiplexer with crosstalk < -34 dB is obtained. Simulations show that the optical bandwidth is as large as 300 nm (1400 nm ~ 1700 nm). The design is also fabrication tolerant.