We describe a scheme for generation of spatial-mode-entangled photon pairs in a few-mode fiber and experimentally demonstrate generation of idler beams from classical seed signals representing various superpositions of fiber LP ₀₁ and LP _11a modes. For every signal mode superposition, we observe the indication of idler mode orthogonality to the signal mode.

We explore the potential of a combination of two fiber parametric wavelength converters and an erbium-doped fiber amplifier to serve as a hybrid amplifier for S-band. We experimentally confirm the validity of a simple quantum model of the wavelength-converter noise figure (NF) and use it to extrapolate the measurement results and find the optimum hybrid amplifier settings. We find that the total NF can be below 6 dB, if the wavelength conversion efficiency of the first stage is above 4 dB. Furthermore, the total NF can be as low as 4 dB, if the conversion efficiency of the first stage is 10 dB or higher. Finally, we estimate the potential impact of pump relative noise on the NF.

We present a scheme for spatial-mode-selective frequency conversion in a few-mode fiber and experimentally demonstrate upconversion of arbitrary superpositions of LP ₀₁ and LP _11a signal modes from C-band to the fundamental mode in S-band with all conversion efficiencies within 1 dB range of one another.

Utilizing the phase-matching conditions of inter-modal four-wave mixing in an elliptical-core few-mode fiber supporting three non-degenerate modes, we experimentally demonstrate schemes for generating orbital-angular-momentum (OAM)-entangled photon pairs with high mode purity and for achieving highly mode-selective frequency conversion of beams in OAM-compatible (LP_11a, LP_11b) mode basis. These techniques expand the toolbox for using OAM modes in both classical and quantum communications and information processing.

The effect of quantum interference from incoherent pump field on the Kerr nonlinearity of V- and Lambda-type three-level systems is investigated. It is found that enhanced Kerr nonlinearity can be obtained via quantum interference of incoherent pump field. It is also demonstrated that the enhanced Kerr nonlinearity is located in the reduced-absorption region. The enhancement of Kerr nonlinearity is attributed mainly to the presence of extra atomic coherence induced by quantum interference from incoherent pump field.

Multi-band optical communication presents a promising avenue for the significant enhancement of fiber-optic transmission capacity without incurring additional costs related to new cable deployment via the utilization of the bandwidth beyond the established C&L bands. However, a big challenge in its field implementation lies in the high cost and suboptimal performance of optical amplifiers, stemming from the underdeveloped state of rare-earth-doped fiber-optic amplifier technologies for these bands. Fiber-optic parametric amplifiers provide an alternative for wideband optical amplification, yet their low power efficiency limits their practical use in the field. In this paper, we study a hybrid optical amplifier that combines the excellent power efficiency of rare-earth-doped amplifiers with broadband wavelength conversion capability of parametric amplifiers. It uses wavelength converters to shift signals between the S- and L-bands, amplifying them with an L-band erbium-doped fiber amplifier, and converting them back to the S-band. We experimentally demonstrate such a hybrid S-band amplifier, characterize its performance with 16-QAM input signals, and evaluate its power efficiency and four-wave-mixing-induced crosstalk. This hybrid approach paves the way for scalable expansion of optical communication bands without waiting for advancements in rare-earth-doped amplifier technology.