Adiabatic frequency conversion (AFC) is a promising alternative for shifting the frequency of optical signals. In this paper we present a comprehensive theoretical study of the energy efficiency of AFC in an all-pass resonator. Through the Cauchy-Schwarz inequality, we deduce the upper limit of the energy efficiency of the AFC process and analyze its dependence on the input pulse shape. For a fixed pulse shape, we discuss the dependence of the AFC efficiency on its relevant timescales. We show that maximum efficiency requires overcoupling of the resonator to a degree dependent on the input pulse duration. We compare and contrast the requirements for optimal AFC for pulsed and continuous-wave inputs.
Adiabatic frequency conversion (AFC) is a promising alternative for shifting the frequency of optical signals. In this paper we present a comprehensive theoretical study of the energy efficiency of AFC in an all-pass resonator. Through the Cauchy-Schwarz inequality, we deduce the upper limit of the energy efficiency of the AFC process and analyze its dependence on the input pulse shape. For a fixed pulse shape, we discuss the dependence of the AFC efficiency on its relevant timescales. We show that maximum efficiency requires overcoupling of the resonator to a degree dependent on the input pulse duration. We compare and contrast the requirements for optimal AFC for pulsed and continuous-wave inputs.
Adiabatic frequency conversion (AFC) in microring resonators is a promising alternative for fully integrable and tunable frequency shifting of optical signals. Nonetheless, the magnitude of the frequency shift via simple AFC in a single ring is fundamentally limited by the material platform. To overcome this limitation, we propose and analyze a scheme to induce cascaded AFC (CAFC) along a chain of coupled, yet initially detuned rings, without requiring unloading the optical signal into a bus waveguide between successive modulations. For concreteness, we examine thoroughly the simplest nontrivial case of a chain of two rings and briefly discuss the generalization to a chain of an arbitrary number of rings. We analyze the temporal dynamics of this CAFC process using temporal coupled mode theory. We examine the transformation of the input into the frequency-shifted output as a rank-one linear operator in the vector space of finite-energy pulses. In this way we show that the energy efficiency of CAFC depends on the input pulse shape through a Schwarz inequality, just as in single-ring AFC. We propose a numerical scheme to maximize the CAFC efficiency with respect to the process's timescales and discuss the physics involved. We show that the resulting CAFC efficiency converges in a polynomial manner to a maximum as the process becomes progressively idealized. Furthermore, we show that this maximum efficiency is identical to that for single-ring AFC, e.g., 0.7951 for a symmetric, single-lobe input pulse. Thus, we show that CAFC can become more efficient than multiple instances of single-ring AFC. We explain the polynomial convergence of the CAFC efficiency as a consequence of its real analyticity as a function of the process's timescales under our scheme. We leverage this polynomial convergence to model the CAFC efficiency as a simple polynomial in few normalized timescales. We then utilize this polynomial model to predict optimal values for the remaining free parameters and the scaling of the CAFC with the interring detuning.
Adiabatic frequency conversion (AFC) in add-drop resonators holds promise for enhancing energy efficiency in photonic applications. This theoretical study investigates the conditions for optimizing the energy efficiency of the drop port within an add-drop resonator configuration. The analysis considers both fixed input pulse shapes and continuous wave inputs, taking into account AFC's relative timescales. Specifically, the critical coupling regime is explored, and it is observed that the extrinsic decay rates into the drop port and through port converge to nearly equal values, thereby maximizing drop port efficiency. Moreover, when a global parameter is swept, it is demonstrated that the maximal efficiency of the drop port is achieved when the extrinsic decay rates of both ports are equal. This optimization strategy extends to scenarios involving continuous wave inputs as well. These findings provide valuable insights for designing high-performance add-drop resonators and advancing the practical implementation of AFC in photonic systems.
Adiabatic frequency conversion (AFC) in microring resonators is a promising alternative for integrated, tunable frequency shifting of optical signals. However, the efficiency of AFC in a single-ring resonator is limited to below 80% for symmetric input pulses with a single peak. This is the consequence of a poor match between the pulse shape and the ring's impulse response. To overcome this limitation, we propose inducing AFC over two coupled rings rather than a single ring. We analyze the process's efficiency using temporal coupled mode theory (TCMT). We show that two-ring AFC can attain an efficiency of 97% in the limit of negligible intrinsic ring loss. To explain this higher AFC efficiency, we analyze two-ring AFC as a linear operator of rank two in the vector space of finite-energy pulses. We represent the AFC operator as a $2\ifmmode\times\else\texttimes\fi{}2$ matrix and examine its singular value decomposition. In this way we analyze the dependence of the two-ring AFC efficiency on the input pulse shape and the TCMT parameters.
On the basis of the stimulated Raman adiabatic passage technology, we study the conversion of ultracold atoms into diatomic molecules by using a square-shaped pulse field. By the method of adiabatic fidelity, we analyze the dynamical evolution process of the coherent population trapping state for the atom-molecule conversion system. We introduce two adiabatic fidelities to describe the efficiency of ultracold atom-molecule conversion, i.e.:1) the final adiabatic fidelity, which gives the value of the adiabatic fidelity at the end of the evolution:the closer to 1 it is, the higher the conversion efficiency is; 2) the final maximum adiabatic fidelity, which denotes the maximum value that can be achieved at the end of evolution, indicating the highest conversion efficiency. With these two quantities, we discuss how to achieve higher adiabatic fidelity for the coherent population trapping state through optimizing the pulse-delay time and the pulse-laser intensity of the stimulated Raman adiabatic passage. In addition, we also discuss the effects of the width of pulses on the ultracold atom-molecule conversion efficiency and the feasibility of continuous light. It is shown that the final adiabatic fidelity of the coherent population trapping state demonstrates a large periodic oscillation with the pulse-laser intensity. By calculating and analyzing the final adiabatic fidelity and the final maximum adiabatic fidelity, we obtain the conditions for higher efficiency conversion, which gives the best choice of the pulse-laser intensity, the pulse-delay time, and the width of pulses. The results show that the scheme of square-shaped pulses we discussed has obvious advantages compared with that of Gaussian-shaped pulses, which can achieve high adiabatic fidelity and realize higher ultracold atom-molecule conversion efficiency via employing the pulse-laser field with low intensity. Further detailed comparison between the square-shaped pulses and the Gaussian-shaped pulses is also given. Particularly, we find that the final adiabatic fidelity shows a periodic oscillation with the pulse width, which means that the high efficiency atom-molecule conversion can be achieved by using a pulse field with small width. Moreover, we find that the high efficiency conversion can also be achieved by using special continuous light under certain conditions.
Adiabatic frequency conversion is a method recently developed in nonlinear optics [H. Suchowski, D. Oron, A. Arie, and Y. Silberberg, Phys. Rev. A 78, 063821 (2008)], using ideas from the technique of rapid adiabatic passage (RAP) via a level crossing in quantum physics. In this method, the coupling coefficients are constant and the phase mismatch is chirped adiabatically. In this work, we propose another method for adiabatic frequency conversion, in which the phase mismatch is constant and the coupling is a pulse-shaped function with a sign flip (i.e., a phase step of $\ensuremath{\pi}$) at its maximum. Compared to the RAP method, our technique has comparable efficiency but it is simpler to implement for it only needs two bulk crystals with opposite ${\ensuremath{\chi}}^{(2)}$ nonlinearity. Moreover, because our technique requires constant nonzero frequency mismatch and has zero conversion efficiency on exact frequency matching, it can be used as a frequency filter.