Adiabatic Light Transfer Research Articles

Shortcut to adiabaticity in a bent mode-evolution coupler

A shortcut to adiabatic light transfer in mode-evolution coupler by axis bending is proposed. Phase mismatch due to waveguide width difference can be cancelled by a proper bending profile, realizing shortcut to adiabatic light transfer in the coupler. The bent coupler is more compact than the conventional straight coupler without compromising the device performance.

Shortcut to adiabaticity in bent waveguide couplers with a sign flip of the phase mismatch.

Bending the axis of a waveguide coupler can result in phase mismatch between the evanescently coupled waveguides. Using a bent waveguide coupler, we realize a shortcut to adiabatic light transfer between waveguides with a sign flip of the phase mismatch. Counterdiabatic driving with unitary transformation cancels non-adiabatic coupling in the waveguide coupler so that light evolution follows the adiabatic modes at short lengths. The counterdiabatic driving protocol is implemented in the waveguide coupler by engineering the waveguide spacing and axis bending profile. The bent waveguide coupler is compact and robust against parameter variations.

Ultra-compact, broadband adiabatic passage optical couplers in thin-film lithium niobate on insulator waveguides.

We report the first demonstration of broadband adiabatic directional couplers in thin-film lithium niobate on insulator (LNOI) waveguides. A three LN-waveguide configuration with each waveguide having a ridge cross section of less than 1 square micron, built atop a layer of SiO2 based on a 500-µm-thick Si substrate, has been designed and constructed to optically emulate a three-state stimulated Raman adiabatic passage system, with which a unique counterintuitive adiabatic light transfer phenomenon in a high coupling efficiency of >97% (corresponding to a >15 dB splitting ratio) spanning telecom S, C, and L bands for both TE and TM polarization modes has been observed for a 2-mm long coupler length. An even broader operating bandwidth of >800 nm of the device can be found from the simulation fitting of the experimental data. The footprint of the realized LNOI adiabatic coupler has been reduced by >99% compared to its bulk counterparts. Such an ultra-compact, broadband LNOI adiabatic coupler can be further used to implement or integrate with various photonic elements, a potential building block for realizing large-scale integrated photonic (quantum) circuits in LN.

Accelerating adiabatic light transfer and split in three-waveguide couplers via dressed state

We theoretically perform a dressed state approach to investigate a fast adiabatic light transfer and split in the three-waveguide coupled system. We compare the performance of the waveguide couplers based on the dressed-state method with the stimulated Raman adiabatic passage (STIRAP) couplers. We find that the dressed-state couplers can achieve a higher fidelity at a shorter device length and can be more robust against various uncertainties than the original STIRAP couplers.

Broadband integrated polarization beam splitting based on anisotropic adiabatic transfer of light

A concept for the realization of waveguide-based polarization beam splitters working over a wide spectral range is presented. The adiabatically evolving three-waveguide system is inspired by the quantum-mechanical stimulated Raman adiabatic passage process and involves waveguides with an anisotropic refractive index contrast. It is shown that an index contrast ratio of 5 is sufficient to obtain excellent efficiency and output polarization purity over a spectral range approximately equal to $350$ nm centered at a wavelength of 1550 nm. The center wavelength can be easily modified by tuning the parameters of the waveguides.

Shortcut to adiabatic light transfer in waveguide couplers with a sign flip in the phase mismatch

Employing counterdiabatic shortcut to adiabaticity (STA), we design short and robust achromatic two- and three- waveguide couplers. We assume that the phase mismatch between the waveguides has a sign flip at maximum coupling, while the coupling between the waveguides has a smooth spatial shape. We show that the presented coupler operates as a complete achromatic optical switch for two coupled waveguides and as an equal superposition beam splitter for three coupled waveguides. An important feature of our devices is that they do not require larger coupling strength as compared to previous designs, which makes them easier to realize in an experimental setting. Additionally, we show that the presented waveguide couplers operate at a shorter device length and are robust against variations in the coupling strength and the phase mismatch.

Quantum-like adiabatic light transfer in photo-induced waveguides with longitudinally varying detuning

Besides longitudinally varying coupling constants, the longitudinal variation of the propagation constants leads to an additional parameter for the control of adiabatic light transfer in coupled waveguide systems. Examples are given using waveguides structures recorded with the help of the photorefractive effect and mimicking the quantum processes of Rapid Adiabatic Passage (RAP) and two-state STImulated Raman Adiabatic Passage (two-state STIRAP).

Control of adiabatic light transfer in coupled waveguides with longitudinally varying detuning

We study adiabatic light transfer in systems of two coupled waveguides with spatially varying detuning of the propagation constants, providing an analogy to the quantum phenomena of rapid adiabatic passage (RAP) and two-state stimulated Raman adiabatic passage (two-state STIRAP). Experimental demonstration using a photoinduction technique confirms the robust and broadband character of the structures that act as broadband directional couplers and broadband beam splitters, respectively.

Adiabatic light transfer in titanium diffused lithium niobate waveguides.

We report on the realization of adiabatic light transfer in lithium niobate (LiNbO3) waveguides. This peculiar adiabatic tunneling scheme was implemented in a three-waveguide coupling configuration with the intermediate waveguide being inclined with respect to the outer waveguides to facilitate the adiabatic passage process. We have investigated and determined the adiabatic conditions of the LiNbO3 device in terms of the structure configuration of the waveguide system and found optimal structure parameters by both simulation and experimental approaches. Broadband adiabatic couplings of bandwidth ~456 and 185 nm and peak coupling efficiencies of >0.96 have been obtained with a 2-cm long device for TE- and TM-polarized fundamental modes, respectively. Longer (5 cm) devices were also studied and found to be useful in increasing the adiabaticity of the device, especially for the TM-polarized mode.

Breakdown of adiabatic transfer of light in waveguides in the presence of absorption

In atomic physics, adiabatic evolution is often used to achieve a robust and efficient population transfer. Many adiabatic schemes have also been implemented in optical waveguide structures. Recently there has been increasing interest in the influence of decay and absorption, and their engineering applications. Here it is shown that even a small decay can significantly influence the dynamical behavior of a system, above and beyond a mere change of the overall norm. In particular, a small decay can lead to a breakdown of adiabatic transfer schemes, even when both the spectrum and the eigenfunctions are only sightly modified. This is demonstrated for the generalization of a stimulated Raman adiabatic passage scheme that has recently been implemented in optical waveguide structures. Here the question how an additional absorption in either the initial or the target waveguide influences the transfer property of the scheme is addressed. It is found that the scheme breaks down for small values of the absorption at a relatively sharp threshold, which can be estimated by simple analytical arguments.

Broadband adiabatic light transfer in optically induced waveguide arrays

We demonstrate experimentally the broadband and adiabatic light transfer in coupled waveguides based on multiple stimulated Raman adiabatic passage. Our experimental platform utilizes planar-type reconfigurable optically induced waveguide arrays and allows for efficient and robust transfer of light from an input waveguide over multiple states (up to nine) to an output waveguide. The same waveguide structures are tested for two propagation wavelengths separated by more than 200 nm, proving the achromaticity of the transfer process.

Planar achromatic multiple beam splitter by adiabatic light transfer

We introduce a novel achromatic and robust scheme for n-fold multiple beam splitting based on adiabatic light transfer in a planar geometry of coupled waveguides (WGs). The concept is experimentally verified for a one-to-three beam splitter by using a reconfigurable light-induced WG structure at two operating wavelengths. The demonstrated planar-type achromatic beam splitter opens new opportunities for the realization of ultra-high bandwidth on-chip photonic devices.

Adiabatic transfer of light in a double cavity and the optical Landau-Zener problem

We analyze the evolution of an electromagnetic field inside a double cavity when the difference in length between the two cavities is changed, e.g., by translating the common mirror. We find that this allows photons to be moved deterministically from one cavity to the other. We are able to obtain the conditions for adiabatic transfer by first mapping the Maxwell wave equation for the electric field onto a Schr\"odinger-like wave equation and then using the Landau-Zener result for the transition probability at an avoided crossing. Our analysis reveals that this mapping only rigorously holds when the two cavities are weakly coupled (i.e., in the regime of a highly reflective common mirror) and that, generally speaking, care is required when attempting a Hamiltonian description of cavity electrodynamics with time-dependent boundary conditions.

Adiabatic transfer of light via a continuum in optical waveguides

The optical analog of the stimulated Raman adiabatic passage via a continuum is experimentally demonstrated for photonic tunneling in femtosecond laser written waveguides. The results clearly show that the mechanism of light transfer relies on destructive interference and on the existence of a photonic dark state.

Adiabatic light transfer via dressed states in optical waveguide arrays

We report on the experimental demonstration of adiabatic light transfer between the outer waveguides in a finite array of evanescently coupled optical waveguides with negligible excitation of all the intermediate waveguides. Such a counterintuitive light transfer scheme is an optical analogue of stimulated Raman adiabatic passage via an auxiliary dressed state proposed in atomic physics for multilevel systems.

Optical realization of multilevel adiabatic population transfer in curved waveguide arrays

Adiabatic transfer of light in tunneling-coupled waveguide arrays made of an odd number of waveguides with curved axis is proposed to mimic multilevel adiabatic population transfer of atoms or molecules driven by a counterintuitive pulse sequence.