Alexey V. Gladyshev

High-average-power second-harmonic generation from periodically poled silica fibers

The generation of 236 mW of second-harmonic power in a 32-cm-long periodically poled silica fiber, corresponding to an average conversion efficiency of 15.2+/-0.5%, is reported. This represents the highest normalized second-harmonic conversion and the highest average second-harmonic power ever reported for a periodically poled silica fiber, to our knowledge. The enhancement is attributed to an improved design of the specialty twin-hole fiber and the extension of the nonlinear interaction length.

All-fiber frequency-doubled visible laser

All-fiber ns-pulsed visible laser at λ=521  nm is realized by frequency doubling an Yb-doped fiber laser with a periodically poled silica fiber. A 50-mW second-harmonic (SH) output power is produced that is over 6-orders of magnitude greater than previous results obtained with poled fibers in the visible spectral range. The normalized conversion efficiency of 0.3%/W is to date the largest demonstrated with poled fiber technology. Furthermore, 21% conversion efficiency is achieved for the doubling of 8-ps pulses from a neodymium-doped yttrium vanadate solid-state laser. The advances are made possible by the precision and flexibility offered by using the continuous periodic UV erasure, as opposite to photolithographic methods, for the fabrication of over 20-cm-long χ(2)-gratings for quasi-phase matched SH generation.

Aperiodically poled silica fibers for bandwidth control of quasi-phase-matched second-harmonic generation

Precise control of the bandwidth of quasi-phase-matched second-harmonic generation in silica fibers is realized through chirped-period poling. The bandwidth is expanded by a factor of 33 over a uniform-period poled fiber of the same interaction length.

Yellow All-fiber Bi laser

All-fiber laser operating at 580 nm is realized by frequency-doubling of the Bi-doped fiber laser radiation in a periodically poled optical fiber.

Compensation-free broadband entangled photon pair sources

Quantum sources that provide broadband biphotons entangled in both polarization and time-energy degrees of freedom are a rich quantum resource that finds many applications in quantum communication, sensing, and metrology. Creating such a source while maintaining high entanglement quality over a broad spectral range is a challenge, which conventionally requires various compensation steps to erase temporal, spectral, or spatial distinguishabilities. Here, we point out that in fact compensation is not always necessary. The key to generate broadband polarization-entangled biphotons via type-II spontaneous parametric downcoversion (SPDC) without compensation is to use nonlinear materials with sufficiently low group birefringence that the biphoton bandwidth becomes dispersion-limited. Most nonlinear crystals or waveguides cannot meet this condition, but it is easily met in fiber-based systems. We reveal the interplay of group birefringence and dispersion on SPDC bandwidth and polarization entanglement quality. We show that periodically poled silica fiber (PPSF) is an ideal medium to generate high-concurrence (>0.977) polarization-entangled photons over a broad spectral range (>77nm), directly and without compensation. This is the highest polarization-entanglement concurrence reported that is maintained over a broad spectral range from a compensation-free source.

Negative curvature hollow core fibers for Raman lasing in the mid IR spectral range

In this paper we consider a problem of using negative curvature hollow-core fibers for creation of Raman lasers in the mid IR spectral range. New designs of this type of fibers with cladding formed by one layer of double nested capillaries are discussed and their optical properties are investigated numerically and experimentally. It will be shown that it is possible to reduce the Raman generation threshold by decreasing an effective mode area in such fibers using nested capillaries in the cladding.

Multi-party Agile QKD network with a fiber-based entangled source

A multi-party quantum key distribution scheme is experimentally demonstrated by utilizing a poled fiber-based broadband polarization-entangled source and dense wavelength-division multiplexing. Entangled photon pairs are delivered over 40-km of fiber, with secure key rates of more than 20 bits/s observed.

UV-Induced Absorption in All-Fiber Frequency Doublers: Characterization and Photobleaching

Periodic UV exposure of thermally poled optical fibers is usually used to produce efficient all-fiber frequency doublers based on second-order nonlinearity. To date, no data regarding UV-induced absorption in poled fibers have been reported. In this study, we measured this absorption and showed how it affects the conversion efficiency of second harmonic generation at wavelengths below ~800 nm. Color centers responsible for induced absorption in poled GeO2-doped fibers were identified and photobleached by continuous-wave radiation at 532 nm. We demonstrated that photobleaching does not affect the value of nonlinearity but improves the conversion efficiency of all-fiber frequency doublers. The results obtained can be used to improve the efficiency of all-fiber second harmonic generation in the blue-green part of the spectrum.

236mW average second-harmonic power generated from periodically poled silica fibres

Thermally poled silica fibres are an attractive all-fibre solution to frequency conversion of high power fibre lasers. In comparison to nonlinear crystals, they offer inherently lower insertion losses, higher optical damage threshold, greater stability and ruggedness intrinsic to all-fibre solutions. Moreover, the relatively low second-order-nonlinearity (0.1–0.2pm/V) can be compensated by extending the length of the periodically poled fibre.

Coherent properties of FBG-based external cavity diode lasers

Coherent poperties and fine tuning of two FBG-based external cavity diode lasers were investigated. The external cavity length of each laser was as short as 10 mm. The linewidth was measured to be as narrow as several tens of kHz*m W and side mode suppression ratio of 30 dB was obtained. The tuning rate was measured to be 1MHz/mA that is three orders of magnitude less than typical value of injection lasers. The operating regime, in which tuning rate equals to zero, was observed. This fact makes FBG-based external cavity diode lasers very attractive for fine interferometric applications.