Optical levitation has been the subject of science fiction for many years. In 1970, Arthur Ashkin demonstrated acceleration of optically levitated microparticles with a laser beam. In 2010, the trapping and control of mesoscopic particles in vacuum (levitodynamics) was developed. Optically trapped dielectric nanoparticles have been cooled into the quantum ground state. The primary objective of this Field Guide is to provide the reader with the basic principles of optical levitation and levitodynamics using both classical and quantum approaches. Within the Guide, you will find formulae and descriptions of phenomena that are fundamental for understanding the present state-of-the-art of optical trapping and cooling of dielectric micro and nanoparticles.
Our understanding of the interaction of light and matter has a long history that evolved from the ancient corpuscular theory to wave theory and finally to the quantum theory. Matter is composed of charged particles, and among these particles are positively charged nuclei surrounded by electrons that are in motion. Light is an oscillating electromagnetic wave. But light is also particles (photons). The primary objective of this Field Guide is to provide the principles of light–matter interaction using classical, semiclassical, and quantum theories. To this end, the guide provides the formulae for, and descriptions of, phenomena that are fundamental to our current state of knowledge of light–matter interaction.
We propose to mitigate heat generation in Raman lasers and amplifiers by coupling the Raman active waveguide to a wavelengthselective dissipative waveguide. The DW supports (lossy) propagation only at the anti-Stokes wavelength, and hence evacuates the anti- Stokes photons out of the Raman waveguide without affecting the Stokes and pump photons. In this manner, it suppresses the reversed CARS cycles that would otherwise result into heat generation in the Raman waveguide. This mechanism is investigated for different phase mismatches. It is demonstrated represent a promising new avenue to enhance cooling in Raman lasers and amplifiers.
This Field Guide provides an overview of the basic principles of laser cooling of atoms, ions, nanoparticles, and solids, including Doppler cooling, polarization gradient cooling, different sub-recoil schemes of laser cooling, forced evaporation, laser cooling with anti-Stokes fluorescence, hybrid laser cooling, and Raman and Brillouin cooling. It also covers radiation-balanced lasers and Raman lasers with heat mitigation, and considers the basic principles of optical dipole traps, magnetic traps, and magneto-optical traps.
A comprehensive theoretical investigation of a dual wavelength, cascade cavity bismuth-doped fiber (BDF) laser operating in the wavelength range of 1.7μm is presented. The fiber laser model is based on parameters extracted from experimental characterization of the BDF. The BDF serves as an active medium with optical gain in the wavelength region from 1.65μm to 1.8μm. The laser cavity is defined by a 90% mirror on one end of the BDF and two fiber Bragg gratings (FBG1 and FBG2) separated with the BDF on the other end of the laser cavity. One of the gratings FBG1 with the peak reflectivity 95% is centered at 1.725μm. The second one FBG2 with peak reflectivity of 90% is centered at 1.729μm. Both FBGs have a 3-dB bandwidth of ~0.5nm. It is shown that the cascade laser can operate at two 1.725μm and 1.729μm wavelengths with different powers depending on the parameters of the structure.
Laser cooling and trapping of Yb3+:YAG nano-crystals has been theoretically investigated. It has been shown that in the system of Yb3+:YAG nano-crystals pumped at 1030 nm in the long wavelength tail of the Yb3+ absorption spectrum both internal and translational laser cooling processes take place. The internal laser cooling process based on anti-Stokes fluorescence serves as a supplementary process to translational cooling of rare-earth (RE) doped nano-crystals. The internal laser cooling process can help to reach lower equilibrium translational temperatures of RE-doped nano-crystals.
Laser cooling of solids, also known as optical refrigeration, is an area of optical science investigating the interaction of light with condensed matter to remove thermal energy of a solid through the interaction of the pump photons and phonons in a solid. Apart from being of fundamental scientific interest, this topic addresses a number of important practical issues such as the development of all solid state optical cryo-coolers, and biological applications. A short history of laser cooling as well as latest achievement of optical refrigeration in rare-earth (RE) doped macro-samples are presented and discussed in the paper. The main technique of laser cooling of RE doped solids based on anti-Stokes fluorescence is presented in this paper. The new approach to optical refrigeration based on the Raman cooling is also considered. It is shown that the future prospects of the research are connected with laser cooling of μm- and nm-sized samples, are in their applications in biophysics in the fundamental studies of low-temperature physics.
The influence of a solid-state sample placed in the vicinity of a laser cooled sample is theoretically investigated. The laser cooling process is based on anti-Stokes fluorescence. The laser cooled sample is a rare-earth doped low-phonon energy solid. In this system, all samples can support surface phonon polaritons (SPhPs) in the same or different wavelength regions. Two different cases are considered. In the first case a laser cooled ytterbium-doped yttrium aluminum garnet ( Yb3+:YAG ) sample is placed in a vacuum chamber near a YAG sample, which is at room temperature. In the second case a laser cooled Yb3+:YAG sample is placed near a silicon carbide (SiC) sample, which is at room temperature. It is shown that for short distances between samples, when there is coupling between SPhPs propagating in the sample undergoing laser cooling and SPhPs propagating in the next sample, the laser cooling process can deteriorate substantially. In the opposite case the SPhPs do not influence the laser cooling process significantly even if the distance between the samples is less than the dominant wavelength of thermal radiation.
Oxyfluoride glasses and glass-ceramics (GCs) have some niche advantages over other oxide and fluoride glasses, as they possess combined properties. This paper reports the structural, thermal, and photoluminescence (PL) properties of Yb3+-doped SiO2−Al2O3−CaO−CaF2 oxyfluoride glasses and transparent GCs containing CaF2 nanocrystals. Special efforts were undertaken to minimize the hydroxyl (OH−) content in the prepared samples to improve their optical features. Differential scanning calorimetry analyses were performed to determine the characteristic temperatures of the base glasses. X-ray diffractometry studies have confirmed the fluorite CaF2 nanocrystals to be 10 nm in size. Reduced transparency in the ultraviolet (UV)–visible to the near-infrared (NIR) regions was observed for the GCs compared to the base glass with increasing thermal treatment temperature. A higher PL intensity upon 920-nm excitation was obtained in the GCs compared to that of the base glass. The absolute photoluminescence quantum yield upon 920-nm laser excitation was evaluated using an integrating sphere and an optical spectrum analyzer. It was observed that the lifetime of the F5/22 level of the Yb3+ ions decreases with increasing ceramization temperature. The potential advantages of using such oxyfluoride GCs over commonly studied single crystals for laser cooling applications are discussed.
Laser cooling with anti-Stokes fluorescencewas predicted by Pringsheim in 1929, but for solids was only demonstrated in
1995. There are many difficulties which have hindered laser assisted cooling, principally the chemical purity of a sample
and the availability of suitable hosts. Recent progress has seen the cooled temperature plummet to 93K in Yb:YLF. One
of the challenges for laser cooling to become ubiquitous, is incorporating the rare-earthcooling ion in a more easily
engineered material, rather than a pure crystalline host. Rare-earth-doped nanocrystalline glass-ceramics were first
developed by Wang and Ohwaki for enhanced luminescence and mechanical properties compared to their parent glasses.
Our work has focused on creating a nanocrystalline environment for the cooling ion, in an easy to engineer glass. The
glasses with composition 30SiO2-15Al2O3-27CdF2-22PbF2-4YF3-2YbF3 (mol%), have been prepared by the conventional
melt-quenching technique. By a simple post fabrication thermal treatment, the rare-earth ions are embedded in the
crystalline phase within the glass matrix. Nanocrystals with various sizes and rare-earth concentrations have been
fabricated and their photoluminescence properties assessed in detail. These materials show close to unity
photoluminescence quantum yield (PLQY) when pumped above the band. However, they exhibit strong up-conversion
into the blue, characteristic of Tm trace impurity whose presence was confirmed. The purification of the starting materials
is underway to reduce the background loss to demonstrate laser cooling. Progress in the development of these nano-glass-ceramics
and their experimental characterization will be discussed.
We show theoretically that a bottle resonator with a nanoscale altitude made on the surface of an optical fiber can be
used as a temperature sensor for laser cooling of solids. The operation of such sensors is based on whispering gallery
modes (WGMs). Bottle resonators can be made at different positions along the length of the fiber, which undergoes laser
cooling. A smooth perturbation with a small nanoscale altitude on the surface of the fiber does not couple fiber modes
propagating along the fiber axis and does not influence the laser cooling process. The temperature of the sample at each
of these positions can be monitored as a shift in the dips seen in the transmission spectrum of a biconically tapered fiber
placed perpendicular to the fiber axis on the top of the resonator to excite WGMs. Temperature sensitivities ~12pm/K
and ~16pm/K are obtained for Yb3+:ZBLAN and Yb3+:YAG samples, respectively. The possibility of using bottle
resonators for other applications is also discussed.
We have theoretically investigated the laser cooling process in Yb3+:YAG nanocrystals. We have developed an approach, which permits not only estimate the cooling process in Yb3+:YAG nanocrystals but compare this process with the laser cooling of the Yb3+:YAG bulk samples. The temperature dependences of all parameters of the system are taken into account. The cooperative effects such as re-absorption, the energy migration and cooperative luminescence have been considered.
This paper reports on the characterization of nanocrystalline powders of ytterbium doped YLiF4 for applications in optical refrigeration. Here we used powders with nanocrystals of Yb 3+ concentrations of (10, 15, 20) mol % and lengths (70, 66, 96) nm. Our preliminary spectroscopic measurements did not show an enhancement in the absorption at the long-wavelength tail of the spectra of the nanocrystalline powder when compared with bulk Yb:YLiF4, indicating that the increase of the phonon-assisted excitation is not large enough to play a significant role in cooling in the present conditions. One advantage of nanocrystalline powders over bulk crystals is the possibility of enhancing the absorption by the realization of cavity-less pump recycling through photon localization [1]. While photon localization also increases the reabsorption of the fluorescence depending on the quantum efficiency of the material and can mitigate cooling, it allows the use of crystals of low enough concentrations to avoid deleterious effects such as ion-ion energy transfer followed by quenching. The pump intensity enhancement favors upconversion luminescence to visible wavelengths, which can be used for optical refrigeration and extends the scope of the application for the material. We observed both green and blue emission from the samples and investigate the processes which lead to it. We present the experimental investigation of the nanocrystals’ absorption and emission spectra and the first excited state lifetime measurements, which are used to estimate the nanocrystal’s photoluminescence quantum efficiency.
We present a theoretical scheme for laser cooling of the colloidal cadmium selenide (CbSe) QDs. The laser cooling
process is based on the anti-Stokes fluorescence observed in QDs. We have considered laser cooling in the system of
identical CdSe QDs laser pumped with energy of photons less than mean fluorescence energy. The dependences of all
parameters of the system on the temperature have been taken into account. Following to our simulation the laser cooling
with temperature drop ~100K can be realised with well technologically developed today passivated CdSe QDs.
Although Yb:YAG has been cooled in a vacuum environment1, we report for the first time an experimental demonstration of optical cooling at atmospheric pressure. A Yb:YAG crystal is supported on thin silica fibers, inside a matt-black chamber with air at atmospheric pressure, and pumped at 1029 nm in the pulsed and CW regimes. Direct measurement of the crystal surface temperature during pumping was made possible by using a low thermal-mass, transparent fiber Bragg grating (FBG) sensor. The FBG interrogation system has sufficient sensitivity to measure the background absorption of the sample to below 10-4 cm-1, and bulk cooling at a pump power as low as 17 mW. The dynamical measurement of the temperature allows the determination of the overall heat transfer coefficient of the sample in the air, of 22 W.m-2K-1. A temperature drop of 8.8 K from the chamber temperature is observed in the Yb:YAG crystal in air when pumped with 4.2 W at 1029 nm, close to 8.9 K observed in vacuum1. A background absorption αb = 2.9×10-4 cm-1 is estimated with a pump wavelength at 1550 nm. Simulations predict further cooling when the sample’s cross sectional area and the pump power are optimized, including absorption saturation effects. The choice of an efficient geometry, the use of a readily available temperature sensor in less controlled environments should simplify implementation of laser cooling systems and the development of commercial devices.
We consider a theoretical model for laser cooling with anti-Stokes fluorescence of a Yb3+:YAG sample. We have estimated the fluorescence power density removed from the system with spontaneous emission, the power density radiated with stimulated emission as well as the heat power density generated in the system by non-radiative decays from the impurities in the host material. We have investigated the influence of each of these power densities on the cooling process in Yb3+:YAG system. It has been shown how the temperature dependences of the different parameters of the system as well as the concentration of the impurities in the host influence the final temperature of the cooled sample.
The recent achievements devoted to cooling of solids with a laser are presented in this paper. We discuss the latest
results of traditional laser cooling of solids based on rare earth ions and new techniques based on colloidal lead-salt
quantum dots doped in a glass host, laser cooling in Tm3+-doped oxy-fluoride glass ceramic. Relatively short
(microsecond) lifetime of the excited level of the PbSe QDs compared to the millisecond lifetime of the excited level of
RE ions allows an acceleration of the cooling process and provides an opportunity to use new materials with higher
phonon energy as hosts, which are normally considered unsuitable for cooling with RE ions. Another new approach to
the laser cooling problem based on super-radiance has been considered in this paper. The advantages of optical
refrigeration with rare earth doped semiconductors, in which not only optically active electrons of the 4f shell but the
valence and conduction bands of the host material are involved in cooling cycle is discussed. It is shown that involving
the valence and conduction bands of the host in the cooling cycle allows the pump wavelength to be shorter than mean
fluorescence wavelength. Raman laser cooling of solids as well as observation of spontaneous Brillouin cooling have
been presented.
We show for the first time to our knowledge, measurements of anti-Stokes fluorescence and lifetime measurements in
quantum dot (QD) doped glass, which has been proposed as a potential material for optical refrigeration recently. The
glass host studied here is known as SNAB (SiO2, Na2CO3, Al2O3, B2O3) and is doped with PbS QDs. We show that when excited at a proposed pump wavelength (1550 nm) for cooling, anti-Stokes fluorescence is emitted, required for laser cooling. We also show fluorescence lifetime measurements in this glass, which is in the order of 500 ns. This lifetime is 3-4 orders of magnitude shorter than the typical lifetime of rare earth dopants in glass. From additional fluorescence spectrum measurements at a higher pumpenergy (1.064 μm), we estimate the quantum efficiency of such a system. The observation of anti-Stokes fluorescence and the short lifetime is evidence that QDs could be developed as potential candidates for laser cooling in the solid state, however improvements would have to be made in the quantum efficiency as well as in the background absorption of the host glass for successful applications.
We present a theoretical scheme for laser cooling with ytterbium doped indium phosphide (Yb3+:InP). Yb3+:InP is a rareearth doped direct band-gap semiconductor. The cooling process in our system is based on thermal quenching of excited ytterbium ions. The mechanism of cooling in our system consists of laser excitation of ytterbium ions in the long wavelength tail of the Yb3+absorption spectrum followed by thermal quenching of excited ions accompanied by phonon absorption providing cooling. The band-to-band radiative recombination completing the cooling cycle removes energy from the system. This new approach to laser cooling of solids permits an increase in the efficiency of the cooling cycle approximately by the order, to accelerate the cooling process considerably, and allows cooling with pump wavelengths shorter than the mean fluorescence wavelength.
Theoretical schemes for laser cooling with nanoparticles have been presented and comprehensively investigated. It is shown that specially designed samples based on nanoparticles can be used to improve the process of laser cooling of solids. One of the proposed schemes is based on lead salt colloidal quantum dots (QDs) doped in a glass host. The second one is based on Tm3+ doped oxy fluoride glass ceramic. It has been shown that lead salt colloidal QDs doped in a glass host can operate as artificial atoms. Very short (microsecond range) radiative lifetimes of the excited 1Sh level of PbSe QDs in comparison with the relatively long (millisecond) radiative lifetime of rare-earth (RE) ions allows the cooling process to be accelerated and to use new hosts with relatively high maximum phonon energy, which have so far been considered not suitable for cooling with RE ions. It has been shown that the second sample, which is based on Tm3+ doped oxy fluoride glass ceramic provides the unique combination of high chemical and mechanical stability of the oxide glass, which is important for a number of applications, and the low phonon energy of the fluoride nano-crystals, which trap a majority of Tm3+ ions participating in the cooling process. This is highly beneficial for laser cooling of solids, since the effective embedding of rare-earth ions in the crystalline phase with low phonon energy provides a high quantum efficiency for the 3F4 → 3H6 transition involved in the cooling cycle in the Tm3+ ions, which is a key parameter for laser cooling of solids.
A theoretical scheme for laser cooling in Tm3+-doped oxy-fluoride glass ceramic (GC) is presented. It is shown that the
unique combination of high chemical and mechanical stability of the oxide glass and low phonon energy of the fluoride
nano-crystals, which trap a majority of Tm3+ ions, is beneficial for laser cooling of solids. The effective embedding of
rare-earth ions in the crystalline phase with low phonon energy provides high quantum efficiency for the 3F4 → 3H6
transition involved in the cooling cycle in the Tm3+ ions, which is a key parameter for laser cooling of solids.
We present a scheme, in which colloidal lead-salt PbSe QDs doped in a glass host are used for laser cooling with anti-
Stokes fluorescence. The relatively short (microsecond range) lifetime of the excited level of the PbSe QD allows the
cooling process to be accelerated, and new materials with higher phonon energy to be used as hosts, which are normally
considered unsuitable for cooling with rare-earth ions. The considerable increase (by ~104) in the absorption cross
section of PbSe QD in comparison with the absorption cross section of the rare-earth ions doped in glasses or crystals
increases the efficiency of the cooling process considerably, lowering the pump power requirements.
A new approach to cool solids with super-radiance (SR) pulses is presented in comparison with laser cooling based on
traditional anti-Stokes fluorescence. Contrary to the anti-Stokes fluorescence, which is in-coherent radiation
propagating in all directions around a sample, SR is the coherent, sharply directed spontaneous emission of photons by a
system of excited ions. We consider an Yb3+ doped ZBLAN sample pumped at the wavelength 1015nm with a
rectangular pulsed source. The intensity of the SR is proportional to the square of the number of excited ions. This
unique feature of SR permits an increase in the rate of the cooling process in comparison with the traditional laser
cooling of the rare earth doped solids with anti-Stokes fluorescence. This scheme overcomes the limitation of using only
low phonon energy glasses for laser cooling.
A new approach to cool rare earth doped solids with optical super-radiance (SR) is presented. SR is the coherent, sharply
directed spontaneous emission of photons by a system excited with a pulsed laser. We consider an Yb3+ doped ZBLAN
sample pumped at the wavelength 1015nm with a rectangular pulsed source with a power of ~700W and duration of
20ns. The intensity of the SR is proportional to the square of the number of excited ions. This unique feature of SR
permits an increase in the rate of the cooling process in comparison with the traditional laser cooling of the rare earth
doped solids with anti-Stokes spontaneous incoherent radiation (fluorescence). This scheme overcomes the limitation of
using only low phonon energy glasses for laser cooling.
The quantum defect caused by the difference between the pump and laser photon energies results in heat generation,
which deteriorates the performance of lasers. This effect is very significant in high power lasers, since it can cause the
stress-induced refractive index change and temperature-induced gain change. The radiation-balanced technique, in
which all photons generated in the laser cycle are annihilated with the cooling cycle, has been proposed to solve the
problem in the case of solid-state lasers. Unfortunately, in the radiation-balanced laser the radiated energy increases
only linearly with the length of the laser medium. We propose a radically new approach to solve the problem of heat
generation in lasers by using a co-doped fiber laser with two pump sources. In this laser Yb3+ ions are responsible for
the lasing process, and Tm3+ ions serve as a cooler incorporated in the body of the laser. This new technique provides an
exponential growth of radiation along the laser medium leading to almost athermal operation.
High-power lasers (Raman and traditional solid-state) suffer from heat generated by the quantum defect, which
deteriorates their performance. The radiation-balanced technique was proposed to solve the problem in the case
of solid-state lasers, and the intrinsic heat-mitigation technique, which relies on coherent anti-Stokes Raman
scattering (CARS) was proposed to solve the problem of heat generation in the high power Raman laser.
Unfortunately radiated energy increases only linearly with the length of the laser medium in both schemes. We
propose a radically new approach to solve the problem of heat generation in lasers. We have considered
athermal fiber lasers, where rare-earth (RE) ions based refrigeration sources are incorporated in the body of the
devices. This new technique, which has been developed for Raman and traditional solid-state lasers, ensures
the exponential growth of radiation along the laser medium and provides almost athermal operation.
We present a theoretical scheme for a Tm3+-doped radiation-balanced (athermal) continuous-wave fiber amplifier. This
mode of operation allows amplification without detrimental heating of the fiber with optical pumping. Athermal
amplification is realized by laser cooling in which waste heat is disposed of in the form of spontaneous fluorescence by
balancing the radiated and absorbed power. The athermal fiber amplification can be realized using a specially designed
distributed pumping scheme.
Theoretical models of surface plasmon-polariton (SPP) refractive index sensors with Bragg grating and long period grating (LPG) are presented and comprehensively investigated for fiber and planar structures. The main principle of operation of these devices is based on high efficiency energy transfer between a guided mode propagating in a waveguide layer of the structure and counter- or co-propagating SPP supported by a metal layer separated from the waveguide layer by a buffer. The high efficiency energy transfer is realized by means of a properly designed Bragg grating or LPG imprinted in the waveguide layers of the structures or engraved on the top of the metal layer. These devices are compact, free from any moving parts and can be easily integrated into any fiber or planar schemes. Our simulations are made for telecom wavelengths in the 1500nm window.
The physical mechanism of radiation cooling by anti-Stokes fluorescence was originally proposed in 1929 and
experimentally observed in solid materials in 1995 by Epstein's research team in ytterbium-doped ZBLANP glass. Some
specific combinations of the ions, host materials, and the wavelength of the incident radiation can provide anti-Stokes
interaction resulting in phonon absorption accompanied by the cooling of the host material. Although the optical cooling
of the Yb3+-doped ZBLANP sample was already observed there are broad possibilities for its improvement to increase
the temperature-drop of the sample by optimization of the geometrical parameters of the cooling sample. We propose a
theoretical model for an optimized tapered fiber structure for use as a sample in anti-Stokes laser cooling of solids. This
tapered fiber has a fluorozirconate glass ZBLANP with a core doped with Yb3+ or Tm3+ ions. As evident from the results
of our work, the appropriate choice of the fiber core and the fiber cladding radii can significantly increase the
temperature-drop of the sample for any fixed pump power. The value of the maximum of the temperature-drop of the
sample increases with an increase in the pump power. The depletion of the pump power causes a temperature gradient
along the length of the cooled sample.
A novel theoretical scheme for high-power Er3+ doped fiber amplifier assisted with a long period grating (LPG) is
presented. This device consists of an Er3+ doped cladding pumped with a high power laser at a wavelength 1480 nm and
un-doped core. The LPG imprinted into the fiber core at the beginning of the Er3+ doped region transfers a weak signal
entering the amplifier in the core-mode of a single mode fiber into a cladding mode, dramatically increasing the
effective mode-area of the signal and the threshold powers for unwanted nonlinear effects such as stimulated Raman
and Brillouin scattering. The output fiber with the large core provides a high quality output beam.
A novel theoretical scheme is presented for a surface plasmon-polariton (SPP) planar refractive index sensor based on
one of the simplest integrated optical devices available, the Mach-Zehnder interferometer (MZI), to monitor relative
phase variations in waveguides. An SPP is excited with the Bragg grating imprinted into core and buffer layers of one of
the arms of the MZI. The main principle of operation of this device is based on the large phase change of the waveguide
mode transmitted through the grating during the SPP excitation caused by the change in the refractive index of the
sensed layer in contact with the SPP supporting metal layer.
Optical coherence tomography (OCT) is an emerging medical diagnostic technology for noninvasive in situ and in vivo
cross-sectional morphological imaging of transparent or nontransparent biological tissues and materials on a micrometer
scale. The technique uses low coherence interferometry to extract the intensity of the reflected signal as a function of
penetration depth in the sample and is analogous to ultrasound except that much shorter wavelength infrared radiation is
used rather than sound waves. Among the key enabling technologies for OCT systems are high-power, broadband
optical sources (BBS). Such sources are required to provide large dynamic range and sensitivity, as well as very high
axial resolution. In this paper, we present our ongoing work on developing BBS based on the amplified spontaneous
emission (ASE) from semiconductor optical amplifiers (SOAs) and erbium-doped fiber amplifiers (EDFAs). We target
sources spanning the S, C, and L bands, with milliwatts of output power and smoothly shaped output spectra. In terms
of shaping the output spectra, we consider different designs of gain flattening filters based on side-tapped fiber Bragg
gratings (FBGs) as well as specially apodized FBGs operating in transmission. In terms of the source development, we
have developed strained multiple-quantum well SOAs and hybrid SOA-EDFA structures. In the hybrid structures, we
have also investigated the possibility of exploiting the unused ASE from the SOA as a secondary input to the L-band
EDFA. We have also explored techniques such as double-passing to enhance efficiency as well as gain-clamping to
provide some inherent spectral flattening.
In this work we investigate the interaction between rectangular-grooved transmission gratings and a resonant plasma layer at IR wavelengths. The gratings are designed to convert quasi-vertically incident light into quasi- horizontally propagating light in a high refractive index GaAs substrate with efficiencies of almost 90 percent in the first diffraction order. This can only be achieved by etching highly asymmetric '(lambda) /4' or '(lambda) ' gratings in a high refractive index material evaporated on the GaAs substrate. The resonant plasma layer (RPL) consists of a very thin highly doped n-GaAs layer whose plasma frequency is almost equal to the frequency of the incident light. Under these conditions Drude's formula shows that the refractive index almost vanishes due to plasma oscillations. The interaction between the diffraction modes and the RPL are investigated and optimized on the base of a rigorous coupled-wave analysis. This analysis reveals to which extent the RPL can influence the distribution of light between the zero and first diffraction orders. In the optimum position of the RPL, the first order diffraction efficiency changes from 90 percent down to 25 percent for a RPL thickness change of 40nm.
The optical grating has been the subject of extensive, sustained research for many years. Field of their application include integrated optics, quantum electronic, holography, and spectroscopy. Grating functions include laser-beam feedback, distributed Bragg reflection, holographic beam combining, wavelength multiplexing, wavelength de-multiplexing, and others. Another interesting object of modern physical research is a layer of a resonant plasma (LRP) in which if the charge equilibrium of this system is distributed, the electron gas performs density oscillations, the so-called plasma oscillations and the complex refractive index of which is described by Dride's formula. It is the purpose of this work to combine this two interesting physical objects and investigate the process of the light diffraction by dielectric grating which enclose LRP. We researched Ge-grating on GaAs-substrate under the service of conversion almost vertically incident light into quasi-horizontally propagating light inside the substrate. It is common knowledge that process of conversion almost vertically incident light into quasi-horizontally propagating light is very interesting from the practical standpoint for many cases for example for introduction of light into different optical structure. In our investigation LRP was placed both in the Ge-grating region and in the region of GaAs-substrate.
In this work we developed a new method of calculation of the spectrum of hybrid eigen modes of structures containing coupled planar and channel waveguides. This method is based on the analysis of the process of total internal reflection of hybrid waveguide mode from division boundary between different integrated optical structures when the condition of transverse resonance for reflected hybrid mode is fulfilled.
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