Optical Frequency Up-conversion Research Articles

Optical Generation of Millimeter-Wave Multiband OFDM Ultra-Wideband Wireless Signal and Distribution Over Fiber

Performance of millimeter-wave (MMW) multiband orthogonal frequency-division-multiplexing (OFDM) ultra-wideband (UWB) signal generation using optical frequency up-conversion and transmission over fiber is experimentally investigated. In this work, we propose an optical frequency quadrupling technique using two cascaded Mach-Zehnder modulators (MZMs) biased at quadrature and driven by the same local oscillator frequency but with 180° phase shift between the two MZMs. We demonstrate 30-GHz MMW wireless that carries three bands of OFDM UWB signals.

60-GHz Ultra-Wideband Radio-Over-Fiber System Using a Novel Photonic Monocycle Generation

An impulse-radio ultra-wideband (UWB) photonic generation system targeting high user density in-flight communications with simultaneous ranging capabilities in the 60-GHz radio band is proposed and demonstrated experimentally and the implementation cost is analyzed. Impulse-radio UWB monocycles are employed for signaling. The monocycles are generated employing a pulsed laser and a differential photoreceiver with phase shifting. Optical frequency up-conversion is performed employing a low-frequency RF carrier and a Mach-Zehnder electrooptical modulator operating in the nonlinear regime. In the experiment, Gaussian monocycles at a 1.244-Gbit/s data rate with 3.8-GHz bandwidth are generated and up-converted to 57 GHz. The performance of the 57-GHz UWB signal after the transmission over a standard single-mode fiber at in-cabin distances up to 100 m is studied. The experimental results show that good quality UWB pulses can be obtained with the proposed system. The impact of the system parameters on performance including wireless transmission and associated cost is analyzed, indicating that a high number of UWB access nodes can be cost-effectively supported by the proposed system.

Transmission Quality Measurement of Two Types of 60 GHz Millimeter-Wave Generation and Distribution Systems

In this paper, we demonstrate and compare experimentally two techniques achieving very high-data-rates (> 1 Gb/s) wireless transmission in the 60 GHz window using radio over fiber (RoF) for reach extension. The first RoF link is based on a 10 GHz vertical-cavity surface-emitting laser and uses a multimode fiber. The radio signal is transported on an intermediate frequency of 4.5 GHz and electrically upconverted to 60 GHz after the optical link. The second uses an optical frequency upconversion from 4.5 to 60 GHz by direct modulation of a mode-locked Fabry-PEacuterot laser whose self-pulsating frequency is 54.8 GHz before transmission over a single-mode fiber. For both techniques, two different types of modulation were tested. The first one was an on-off keying at 1.5 Gb/s and the second one was an orthogonal frequency-division multiplexing-QPSK signal compliant to the IEEE 802.15.3.c prestandard (3.03 Gb/s). Radio propagation performance is also reported.

Optical frequency up-conversion by supercontinuum-free widely-tunable fiber-optic Cherenkov radiation

Spectrally-isolated narrowband Cherenkov radiation from commercial nonlinear photonic crystal fibers is demonstrated as an ultrafast optical source with a visible tuning range of 485-690 nm, which complementarily extends the near-infrared tuning range of 690-1020 nm from the corresponding femtosecond Ti:sapphire pump laser. Pump-tosignal conversion efficiency routinely surpasses 10%, enabling multimilliwatt visible output across the entire tuning range. Appropriate selection of fiber parameters and pumping conditions efficiently suppresses the supercontinuum generation typically associated with Cherenkov radiation.

1.244-gb/s data distribution in 60-GHz remote optical frequency up-conversion systems

We experimentally demonstrate 63-GHz 1.244-Gb/s radio-on-fiber downlink data distribution using the remote optical frequency up-conversion technique. Sixty-three-gigahertz optical heterodyne local oscillator signals are cross-gain modulated by optical baseband signals inside a semiconductor optical amplifier. After photodetection, frequency up-converted signals at 63 GHz are generated. The bit-error-rate performance is investigated as a function of optical baseband signal power in a wide wavelength range

Van Hove singularities and nonlinear photoluminescence in multiwalled carbon nanotubes

The absorption spectrum and photoluminescence spectrum of multiwalled carbon nanotubes (MWNTs) and the peaks related with Van Hove singularities (VHS) were obtained experimentally. Both the VHS formation and the change of band gaps in MWNTs depend on the intershell interaction. The VHS makes the probability of optical transitions enhanced, but the intershell interaction suppresses such radiative transitions. The excitation in the experiment involves a two-photon absorption process and the emission light has the effect of the optical frequency up-conversion.

Optical transitions and frequency upconversion emission of Er 3+ions in novel lead-bismuthate glass

Er 3+-doped strontiam lead bismuth glass for developing upconversion lasers has been fabricated and characterized. The Judd–Ofelt analysis was performed on the absorption spectrum and the transition probabilities, excited state lifetimes, and the fluorescence branching ratios were calculated and discussed. Under 975 nm excitation, intense green and red emissions centered at 525, 546, and 657 nm, corresponding to the transitions 2 H 11 / 2 → 4 I 15 / 2 , 4 S 3 / 2 → 4 I 15 / 2 , and 4 F 9 / 2 → 4 I 15 / 2 , respectively, were observed. The upconversion mechanisms are discussed based on the energy matching and quadratic dependence on excitation power, and the dominant mechanisms are excited state absorption and energy transfer upconversion for the green and red emissions.

Optical Spectroscopy and Frequency Upconversion Properties of Er3+ Doped Lead Germanate Glass

Optical Spectroscopy and Frequency Upconversion Properties of Er3+ Doped Lead Germanate Glass

The Investigation of Erbium Complexes and Erbium Doped Materials

AbstractErbium ion (Er3+) doped materials are of great interest for their optical amplification, lasing and frequency up-conversion properties. When preparing such materials, a major problem that often arises is the formation of Er-rich oxide clusters inducing optical quenching. The materials prepared at low Er3+-ion concentrations to overcome the problem have severely reduced the optical yield. Such clustering might be avoided by preparing suitable precursors. If Er is encapsulated with proper materials, clustering can be avoided and higher doping levels can be achieved. In this study, erbium phenoxide complex was obtained by metathesis reaction of erbium chloride (ErCl3) with potassium phenoxide (KOPh). And heterometallic complexes were also synthesized by encapsulation of the Er with Al or Ti derivatives. The complexes were characterized by elemental analysis, infrared and nuclear magnetic resonance spectroscopic analysis. Their crystal structures were determined by X-ray single crystal diffraction analysis. In addition, the Er-doped organic-inorganic matrices using the erbium complexes were investigated about their optical properties.

Optical properties and frequency upconversion fluorescence in a Tm3+ -doped alkali niobium tellurite glass

Optical spectroscopic properties of Tm3+-doped 60TeO2−10GeO2−10K2O−10Li2O−10Nb2O5 glass are reported. The absorption spectra were obtained and radiative parameters were determined using the Judd–Ofelt theory. Characteristics of excited states were studied in two sets of experiments. Excitation at 360 nm originates a relatively narrow band emission at 450 nm attributed to transition D21→3F4 of the Tm3+ ion with photon energy larger than the band-gap energy of the glass matrix. Excitation at 655 nm originates a frequency upconverted emission at 450 nm (1D2→3F4) and emission at 790 nm (3H4→3H6). The radiative lifetimes of levels D21 and H43 were measured and the differences between their experimental values and the theoretical predictions are understood as due to the contribution of energy transfer among Tm3+ ions.

Optical spectroscopy and frequency upconversion properties of Tm3+ doped tungstate fluorophosphate glasses

Tungstate fluorophosphate glasses of good optical quality were synthesized by fusion of the components and casting under air atmosphere. The absorption spectra from near-infrared to visible were obtained and the Judd–Ofelt parameters determined from the absorption bands. Transition probabilities, excited state lifetimes and transition branching ratios were determined from the measurements. Pumping with a 354.7 nm beam from a pulsed laser resulted in emission at 450 nm due to transition D21→F43 in Tm3+ ions and a broadband emission centered at ≈550 nm attributed to the glass matrix. When pumping at 650 nm, two emission bands at 450 nm (1D2→3F4) and at 790 nm (3H4→3H6) were observed. Excitation spectra were also obtained in order to understand the origin of both emissions. Theoretical and experimental lifetimes were determined and the results were explained in terms of multiphonon relaxation.

Dynamic UV microstereolithography

A new process of microstereolithography to manufacture freeform solid three-dimensional micro-components with outer dimensions in the millimetre size range is presented. The process, based on the use of a liquid crystal display as a dynamic mask generator, works with conventional industrial UV-sensitive stereolithographic materials. The main innovation of the process consists in using the optical frequency up-conversion of images from the visible to the UV range in order to overcome the opacity of LCD's in the UV domain. 400 × 400 points up-converted images have been obtained to generate solid three-dimensional objects.

Image upconversion from the visible to the UV domain: application to dynamic UV microstereolithography

We present what to our knowledge is a new application of optical frequency upconversion of images in quadratic materials to dynamic UV microstereolithography. A 150 x 150 point visible image transmitted by a liquid-crystal display was upconverted in a lithium triborate crystal, and the UV image was successfully used to polymerize a commercial stereolithographic resin.

Optical transitions and frequency upconversion of Er^3+ ions in Na_2O୼Ca_3Al_2Ge_3O_12 glasses

Er3+-doped and Er3+/Yb3+-codoped Na2O·Ca3Al2Ge3O12 glasses that are suitable for use in optical waveguide devices have been fabricated and characterized. The density, the refractive indices, the optical absorption, the Judd–Ofelt parameters, and the spontaneous transition probabilities of the glasses have been measured and calculated. Intense 1.533-µm fluorescence was observed in these glass systems under 798- and 973-nm excitation, and the quantum efficiency was ∼100%. Efficient upconversion luminescence at 525, 547, and 659 nm at room temperature was also observed. At a pump intensity of 1220 W/cm2 at 798 nm, frequency upconversion efficiencies of 0.98×10-2 and 1.03×10-2 were obtained for green and red emissions, respectively. The standardized value for green emission is higher than those reported for lead germanate, lead tellurium germanate, silicate, and phosphate glasses. Under 973-nm excitation, the enhancement of 1533-nm emission and visible upconversion fluorescence in Er3+/Yb3+-codoped glasses are confirmed, and the sensitizing is due to efficient energy transfer from Yb3+ to Er3+.

Optical transitions and frequency upconversion emission of Er3+ ions in Ga2S3–GeS2–La2S3 glasses

Spectroscopic properties of Er3+ in Ga2S3–GeS2–La2S3 glasses are investigated on the basis of the spontaneous emission probabilities calculated by the use of the Judd–Ofelt theory and lifetime data. Frequency upconversion spectra are also measured with excitation at 800 and 980 nm. The spontaneous emission probabilities are much larger than those of the other glass systems such as oxides and fluorides. This is mainly attributed to the large refractive indices of the sulfide glasses. The quantum efficiencies of I11/24 and F9/24 levels are comparable or larger than the typical values of Er3+ in a fluoride glass. This is a consequence of the large spontaneous emission probabilities and low phonon energies of the sulfide glasses. However, the quantum efficiency of the S3/24 level is less than one-half of the value in the fluoride glass. The nonradiative transition probability of the S3/24 level is much larger than the value which is evaluated from the multiphonon relaxation theory. This suggests the presence of the other nonradiative relaxation process in addition to the multiphonon relaxation. This process is considered to be the energy transfer from the excited Er3+ to the band-gap excitation of the matrix glass. In upconversion spectra, the 497 nm emission from the F7/24 level is observed in addition to the red (665 nm) and the green (533 and 552 nm) emission bands.

Incoherent effects in the optical up-conversion process

The theoretical treatment of the optical frequency up-conversion process with stochastic pumping is presented. This process consists of exchange of photons between two modes of different frequencies. It is assumed that the two modes are coupled by a short memory stochastic function. Statistically averaged occupation numbers of both modes were calculated exactly by means of the theory of multiplicative stochastic processes. The obtained nonperturbative solution sums secular terms and is valid for arbitrary times. The oscillatory-damped nature of the exchange of energy between two modes and the role of partial incoherence of the pump is discussed. It is shown that stochastic coupling causes the equipartition of energy between two modes for sufficiently long times. Analogies between an up-converter and a two-level atom driven by a single mode electromagnetic field are indicated. Optical Bloch equations for an up-conversion process are derived.

Photon statistics of optical frequency up-conversion with stochastic pumping

The frequency up-conversion process with stochastic coupling function is considered. It is shown that the total photon number increases with time. The antibunching effect (g(2)<1) is predicted regardless of the mean photon numbers available in the process.