High-gain Optical Amplification Research Articles

Plasmonic tuning of nano-antennas for super-gain light amplification

Nanoscale conductive materials are often used for inducing localized free electron oscillations known as plasmons. This is due to their high electronic excitability under optical irradiation owing to their super-small volume. Recently, plasmons have been of interest for enhancing the gain-bandwidth product of optical amplifiers. There are currently two well-established mechanisms for light amplification. The first one is via stimulated emission of radiation (lasers) using a given energy source and often an optical feedback mechanism. The second one is based on the nonlinear coupling of a low-intensity input wave and a high-intensity pump wave for energy exchange (parametric amplifiers). Both techniques have shortcomings. Lasers have a small operation bandwidth and offer a limited gain, but require moderate energy pumping to operate. Whereas optical parametric amplifiers (OPAs) offer a high operation bandwidth along with a much higher optical gain, with the drawback of requiring intense pumping to be functional. The aim of this paper is to introduce a technique that combines the advantages and eliminates the drawbacks of both techniques in the nanoscale to allow for a better amplification performance in integrated optical devices. This is achieved by inducing a plasmonic chirp in conductive nanomaterials a.k.a nano-antennas, which enables the confinement of an enormous electric energy density that can be coupled to an input beam for amplification. Using the Finite Difference Time Domain numerical-method with the material parameters of well-known semiconductors, intramaterial condensation of electric energy density is observed in semiconductor nano-antennas for certain plasmonic chirp-frequencies which enables broadband high-gain optical amplification based on free-electron oscillations that is promising for small-scale optical devices requiring a high gain-bandwidth product. The results are in good agreement with semiempirical data.

Wideband PPLN-Based Phase-Sensitively Amplified Transmission of 20-Channel 96-Gbaud WDM Signal

A periodically poled LiNbO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> (PPLN)-based phase-sensitive amplifier (PSA) has the potential of ultra-low-noise and high-gain optical amplification. For the wideband operation of PSAs in optical fiber transmission, the chromatic dispersion (CD) that causes gain ripples is required to be compensated at the PSA input. We proposed a method to accurately estimate CD from the gain characteristic of a PSA. Estimated CD can be compensated by feed backing it to a spatial light modulator-based CD controller. This paper demonstrates a 2-THz wavelength-division multiplexing (WDM) single-span transmission using a PPLN-based PSA with CD pre-equalization based on our proposed method. The 20-channel WDM signal was modulated with single-polarized 96-Gbaud PS-64QAM, and its net data rate was 400 Gbps/channel. 2-THz signal bandwidth (4-THz bandwidth including an idler band) was the widest bandwidth in the fiber transmission using the PSA. We also discuss the system design of phase-sensitively amplified links for a high-symbol-rate and wideband WDM signal.

Experimental demonstration of optical stochastic cooling

Particle accelerators and storage rings have been transformative instruments of discovery, and, for many applications, innovations in particle-beam cooling have been a principal driver of that success1. Stochastic cooling (SC), one of the most important conceptual and technological advances in this area2–6, cools a beam through granular sampling and correction of its phase-space structure, thus bearing resemblance to a ‘Maxwell’s demon’. The extension of SC from the microwave regime up to optical frequencies and bandwidths has long been pursued, as it could increase the achievable cooling rates by three to four orders of magnitude and provide a powerful tool for future accelerators. First proposed nearly 30 years ago, optical stochastic cooling (OSC) replaces the conventional microwave elements of SC with optical-frequency analogues and is, in principle, compatible with any species of charged-particle beam7,8. Here we describe a demonstration of OSC in a proof-of-principle experiment at the Fermi National Accelerator Laboratory’s Integrable Optics Test Accelerator9,10. The experiment used 100-MeV electrons and a non-amplified configuration of OSC with a radiation wavelength of 950 nm, and achieved strong, simultaneous cooling of the beam in all degrees of freedom. This realization of SC at optical frequencies serves as a foundation for more advanced experiments with high-gain optical amplification, and advances opportunities for future operational OSC systems with potential benefit to a broad user community in the accelerator-based sciences.

Numerical Study of Resonant Optical Parametric Amplification via Gain Factor Optimization in Dispersive Microresonators

The achievement of wideband high-gain optical parametric amplification has not been shown in micrometer-scale cavities. In this paper we have computationally investigated the optical parametric amplification process in a few micrometer-long dispersive microresonator. By performing a gain medium resonance frequency dependent analysis of optical parametric amplification, we have found that it is possible to achieve a wideband high-gain optical amplification in a dispersive microresonator. In order to account for the effects of dispersion (modeled by the polarization damping coefficient) and the resonance frequency of the gain medium on optical parametric amplification, we have solved the wave equation in parallel with the nonlinear equation of electron cloud motion, using the finite difference time domain method. Then we have determined the resonance frequency values that yield an enhanced or a resonant case of optical parametric amplification, via gain factor optimization. It was observed that if the microresonator is more dispersive (has a lower polarization damping coefficient), then there are more resonance frequencies that yield an optical gain resonance. At these gain resonances, a very wideband, high-gain optical amplification seems possible in the micron scale, which, to our knowledge, has not been previously reported in the context of nonlinear wave mixing theory.

Investigation of PPLN-Based PSAs for High-Gain Optical Amplification

In this paper, different configurations of phasesensitive amplifiers (PSAs) built with periodically poled lithium niobate (PPLN) devices are theoretically and numerically investigated, focusing on their application for amplification in optical communications systems. Singleand dual-pump configurations of one-, two-, and four-mode PSAs are discussed. For each configuration, analytical expressions for the maximum and minimum gain of the amplifiers are provided, showing the influence of the power of the pump and signal waves, as well as the length and efficiency of the PPLN waveguide. The analytical expressions are numerically validated by solving the coupled differential equations describing the nonlinear interactions in the PPLN. The obtained results show that the gain of all PSA configurations exponentially increases with the power of the pump waves, and the length and efficiency of the PPLN device, whereas it is almost independent of the power of the signal wave. In addition, it is shown in this paper that PSA configurations where an intermediate interaction is necessary to generate waves at the second-harmonic band have a gain penalty of 6 dB. It is also shown that no significant difference in terms of gain bandwidth is observed for the singleand dual-pump configurations of two-mode PSAs with an intermediate interaction. Finally, it is shown that a four-mode PSA can only be implemented under very strict conditions, with no gain advantage over two-mode PSAs.

High-gain optical amplification in Eu^3+-doped polymer

Europium (Eu(3+))-doped epoxy-based resin Norland optical adhesive (NOA) polymers have been prepared and characterized optically. Quartz capillary tube encapsulated Eu(3+)-doped NOA polymeric waveguides have been fabricated via a simple withdrawal molding technique. Optical amplification at 612 nm wavelength has been demonstrated in these waveguide devices, and the signal enhancements for different lengths of the devices have been measured. A maximum signal enhancement of ~30 dB has been obtained for a 16 mm long device.

AN INVESTIGATION OF MULTI-FUNCTIONAL SEMICONDUCTOR BISTABLE LASER

The co-cavity two-section (CCTS) bistable semiconductor laser with DH and MQW structures has been investigated experimentally and theoretically in this laboratory. Many attractive functions, such as optical bistable switching, optical memory effect, high stability of single longitudinal mode emission spectrum in steady on state, high gain optical amplification, mode conversion effect on injecting signal light, long delay and abnormal relaxation oscillation, ultrafast light pulse generation are investigated in the device. As a high speed, single wavelength, novel laser light source, a monolithic MQW CCTS bistable laser with MQW EA modulator has been fabricated.

Cascaded, stagger-tuned, broadband, low-ripple optical amplifiers

We show theoretically that the gain spectrum obtained by cascading two or more semiconductor optical amplifiers can have a ripple amplitude that is significantly smaller than that currently attainable with a single stage of optical amplification. For example, by cascading two stagger-tuned amplifiers, each having 10 dB of coupling loss and facet reflectivities of 10(-3), one can achieve a net (fiber-to-fiber) gain of 30 dB with less than 2 dB of ripple amplitude. We also show that, under some conditions, simple cascading of optical amplifiers, without the stagger tuning and associated control, can lead to low-ripple, high-gain optical amplification.

High-gain optical amplification of laser diode signal by Raman scattering in single-mode fibres

The letter reports, for the first time, a 45 dB amplification gain of a laser diode signal emitting at 1.24 μm, in a single-mode fibre, with low pump power, using the stimulated Raman scattering effect.