Analysis of optical directional couplers using shortcuts to adiabaticity

Complete and robust energy conversion by sum frequency generation based on invariant engineering

An analytical method is proposed in this paper to achieve complete energy conversion in sum frequency generation based on the Lewis-Riesenfeld invariants theory. In the proposed scheme, a quasi-adiabatic single control parameter model is established, and the value of single control parameter is selected to make the initial eigenstate perfectly converted to the final eigenstate as needed. Corresponding to the nonlinear frequency conversion process, a nonlinear crystal structure is designed by inverse engineering using the optimal control theory. It is robust against perturbations of the coupling coefficient and phase mismatch, including variations in the pump intensity and crystal polarization period, and achieves almost 100% conversion efficiency at any crystal length. Theoretical simulations show that frequency conversion can be achieved in the wavelength range of 2.6 µm-3.6 µm, and the spectral bandwidth of conversion efficiency exceeds 50% and approaches 400 nm when the crystal length L = 1 mm.

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.

Shortcuts to Adiabaticity for Optical Beam Propagation in Nonlinear Gradient Refractive-Index Media

In recent years, the concept of “shortcuts to adiabaticity" has been originally proposed to speed up sufficiently slow adiabatic process in various quantum systems without final excitation. Based on the analogy between classical optics and quantum mechanics, we present a study on fast non-adiabatic compression of optical beam propagation in nonlinear gradient refractive-index media by using shortcuts to adiabaticity. We first apply the variational approximation method in nonlinear optics to derive the auxiliary equation for connecting the beam width with the refractive index of the medium. Then, the gradient refractive index is inversely designed through the perfect compression of beam width with the appropriate boundary conditions. Finally, the comparison with conventional adiabatic compression is made, showing the advantage of our shortcuts.

High sensitivity active flat optics optical phased array receiver with a two-dimensional aperture

Optical phased arrays (OPAs) on integrated photonic platforms provide a low-cost chip-scale solution for many applications. Despite the numerous demonstrations of OPA transmitters, the realization of a functional OPA receiver presents a challenge due to the low received signal level in the presence of noise and interference that necessitates high sensitivity of the receiver. In this paper, an integrated receiver system is presented that is capable of on-chip adaptive manipulation and processing of the captured waveform. The receiver includes an optoelectronic mixer that down-converts optical signals to radio frequencies while maintaining their phase and amplitude information. The optoelectronic mixer also provides conversion gain that enhances the system sensitivity and its robustness to noise and interference. Using this system, the first OPA receiver with a two-dimensional aperture of 8-by-8 receiving elements is demonstrated which can selectively receive light from 64 different angles. The OPA receiver can form reception beams with a beamwidth of 0.75^° over an 8^° grating-lobe-free field of view.

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.

Inverse incoherent engineering

We propose a protocol to construct shortcuts of adiabaticity for open quantum systems in unitary evolution. Using the dynamical invariants of open quantum systems, we design a convenient form of the driver Hamiltonian to accelerate the adiabatic decoherence free subspaces scheme (TDFs) and engineer a quantum state from the initial state into the target state. Since the trajectory of TDFSs is determined by the incoherent control process, we would like to call it as the inverse incoherent engineering protocol. We apply the method to a two-qubits system which interacts with a time-dependent vacuum squeezed field to prepare some maximally entangled states of it. The results illustrate that our protocol can be used both in the adiabatic and nonadiabatic regime with perfect fidelity.

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.

Shortcuts to adiabaticity in optical waveguides using fast quasiadiabatic dynamics

We propose a fast quasiadiabatic approach to the design of optical waveguide devices. This approach distributes the system adiabaticity homogeneously over the device length, thus providing a shortcut to adiabaticity at a shorter device length. A mode sorting asymmetric Y junction is designed by redistributing the adiabaticity of a conventional linearly separating Y junction. Simple procedures for the design of fast quasiadiabatic devices are outlined, and the designed Y junction features large bandwidth at a shorter length than the conventional linearly separating Y junction. The proposed device is verified with beam propagation simulations. A mode conversion efficiency of larger than 99% is observed for the designed Y junction over a 220 nm range.

Broadband optical waveguide couplers with arbitrary coupling ratios designed using a genetic algorithm

In this work, we present a generalized design of broadband optical waveguide couplers with arbitrary coupling ratios on the silicon-on-insulator platform. The device is segmented into 34 short sections, where the propagation constant and the coupling coefficient of each section are viewed as variables during the optimization process. The optimal variable combination is determined by a genetic algorithm. We can achieve a performance superior to that of other design methods with fewer degrees of freedom. For 75%/25%, 50%/50%, 25%/75%, and 0%/100% couplers, the device lengths are 34 μm and the ±2% bandwidths are all in excess of 100 nm at the central wavelength of 1580 nm.