Before the 1960s, all anti-Stokes emissions, which were known to exist, involved emission energies in excess of excitation energies by only a few kT. They were linked to thermal population of energy states above excitation states by such an energy amount. It was the well-known case of anti-Stokes emission for the so-called thermal bands or in the Raman effect for the well-known anti-Stokes sidebands. Thermoluminescence, where traps are emptied by excitation energies of the order of kT, also constituted a field of anti-Stokes emission of its own. Superexcitation, i.e., raising an already excited electron to an even higher level by excited-state absorption (ESA), was also known but with very weak emissions. These types of well-known anti-Stokes processes have been reviewed in classical textbooks on luminescence.1 All fluorescence light emitters usually follow the well-known principle of the Stokes law which simply states that excitation photons are at a higher energy than emitted ones or, in other words, that output photon energy is weaker than input photon energy. This, in a sense, is an indirect statement that efficiency cannot be larger than 1. This principle is

Upconversion and Anti-Stokes Processes with f and d Ions in Solids

Since the discovery of photosensitivity in optical fibers there has been great interest in the fabrication of Bragg gratings within the core of a fiber. The ability to inscribe intracore Bragg gratings in these photosensitive fibers has revolutionized the field of telecommunications and optical fiber based sensor technology. Over the last few years, the number of researchers investigating fundamental, as well as application aspects of these gratings has increased dramatically. This article reviews the technology of Bragg gratings in optical fibers. It introduces the phenomenon of photosensitivity in optical fibers, examines the properties of Bragg gratings, and presents some of the important developments in devices and applications. The most common fabrication techniques (interferometric, phase mask, and point by point) are examined in detail with reference to the advantages and the disadvantages in utilizing them for inscribing Bragg gratings. Reflectivity, bandwidth, temperature, and strain sensitivity of the Bragg reflectors are examined and novel and special Bragg grating structures such as chirped gratings, blazed gratings, phase-shifted gratings, and superimposed multiple gratings are discussed. A formalism for calculating the spectral response of Bragg grating structures is described. Finally, devices and applications for telecommunication and fiber-optic sensors are described, and the impact of this technology on the future of the above areas is discussed.

Fiber Bragg gratings

Material-dependent properties influencing the performance of fiber amplifiers are reviewed together with the available data for Er/sup 3+/. The major glass types potentially useful in this application are considered and compared to silica. The topics addressed include quenching processes and the solubility of rare-earth ions, transition strengths and bandwidths at the 1500-nm gain transition, and the characteristics at the 800-, 980-, and 1480-nm pump bands. Aluminum is shown to be an extremely useful codopant for silica, improving its ability to dissolve rare-earth ions and providing desirable spectroscopic properties for Er/sup 3+/. For some of the attributes considered, other glasses have advantages over Al silica, but only with respect to gain bandwidth and pumping performance at 800 nm is significantly better than expected from other glass compositions. >

Erbium-doped glasses for fiber amplifiers at 1500 nm

https://engineering.purdue.edu/~fsoptics/articles/Ultrafast_optical_pulse_shaping_tutorial-Weiner.pdf

Ultrafast optical pulse shaping: A tutorial review

Researcher demonstrate the line-by-line pulse shaping of frequency combs generated in silicon nitride ring resonators, and observe two distinct paths to comb formation that exhibit strikingly different time domain behaviours.

/pdf/spectral-line-by-line-pulse-shaping-of-on-chip-1asyfgr94t.pdf

Spectral line-by-line pulse shaping of on-chip microresonator frequency combs

A 1.064-/spl mu/m band upconversion pumped Tm/sup 3+/-doped fluoride fiber amplifier and a laser both operating at 1.47 /spl mu/m are investigated in detail. The two devices are based on the /sup 3/F/sub 4//spl rarr//sup 3/H/sub 4/ transition in a trivalent thulium ion, which is a self-terminating system. When pumped at 1.064 /spl mu/m, the amplifier has a gain of over 10 dB from 1.44 to 1.51 /spl mu/m and a low-noise characteristic. Also, the fiber laser generates a high-output power of over 100 mW with a slope efficiency of 59% at around 1.47 /spl mu/m. These levels of performance will be important for optical communication systems. >

Upconversion pumped thulium-doped fluoride fiber amplifier and laser operating at 1.47 /spl mu/m

We propose a new method for controlling the chirp of a linearly chirped fiber Bragg grating (FBG) without a center wavelength shift by using beam bending. The beam consists of a plastic sleeve enclosing a 10-cm-long chirped FBG and a metal rod. The grating pitch could be varied to give positive or negative chirp as well as zero chirp (i.e. uniform pitch) as applying displacement to one end of the beam without rotation. The dispersion at the two extremes of mechanical displacement were -791 ps/nm and +932 ps/nm. The center wavelength shift of the FBG was as small as 0.09 nm over the dispersion tuning range.

Dispersion tuning of a linearly chirped fiber Bragg grating without a center wavelength shift by applying a strain gradient

We present a novel optical pulse generator, in which continuous-wave light is modulated by an electrooptic phase modulator and compressed into pulses by linearly chirped fiber Bragg gratings. Two types of pulses are successfully obtained by changing the parameters. One is a very short pulse with a low duty ratio and the other is a flat top pulse with a duty ratio of 50%.

Optical pulse generator using phase modulator and linearly chirped fiber Bragg gratings

This paper describes a phase-locked multicarrier light source that employs a continuous wave (CW) light source, two phase modulators, and a dispersion medium. A sinusoidal phase modulation (PM) with a modulation index of ?/4 and a group velocity dispersion of ±1/(4?fm 2), where fm is the modulation frequency, are applied to a CW light followed by a large sinusoidal PM. This configuration provides a multicarrier light with a flattened optical power spectrum for any modulation index of the second PM. By adopting a chirped fiber Bragg grating (FBG) as a dispersion medium instead of a long normal dispersion fiber, we can increase the stability of the optical output spectrum and reduce the size of the multicarrier light generator. We have built a prototype with this configuration that generates a 61-carrier light with a 25 GHz interval and a power deviation of less than 8 dB.

Multicarrier Light Source With Flattened Spectrum Using Phase Modulators and Dispersion Medium

Communication demand is paramount for disaster-affected people to confirm safety, seek help, and gather evacuation information. However, the communication infrastructure is likely to be crippled due to a natural disaster, which makes disaster response excruciatingly difficult. Although traditional approaches can partially fulfill the most important requirements from the user perspective, including prompt deployment, high capacity, large coverage, useful disaster-time application, and carrier-free usability, a complete solution that provides all those features is still required. Our collaborative research and development group has developed the Movable and Deployable Resource Unit, which is referred to as the MDRU and has been proven to have all those required features. Via extensive field tests using a compact version of an MDRU (i.e., the van-type MDRU), we verify the effectiveness of the MDRU-based disaster recovery network. Moreover, we demonstrate the further improvement of the MDRU’s performance when it is complemented by other technologies such as relay-by-smartphone or satellites.

/pdf/bringing-movable-and-deployable-networks-to-disaster-areas-3nui7e3qd6.pdf

Tetsuro Komukai

Papers

Upconversion pumped thulium-doped fluoride fiber amplifier and laser operating at 1.47 /spl mu/m

Dispersion tuning of a linearly chirped fiber Bragg grating without a center wavelength shift by applying a strain gradient

Optical pulse generator using phase modulator and linearly chirped fiber Bragg gratings

Multicarrier Light Source With Flattened Spectrum Using Phase Modulators and Dispersion Medium

Bringing movable and deployable networks to disaster areas: development and field test of MDRU