Coercive field (Ec) engineering based upon the monovalent Rb+ ion (Rb/K/Ba-exchange) and the divalent Ba2+ ion (Ba/K-exchange) has enabled the reliable periodic poling of RbKTiOPO4 (RKTP) for quasi-phase-matching (QPM). Previously, there have been no systematic studies to understand and compare the changes in polarization-switching properties induced by these two families of exchanges. In this paper, we compare different compositions of Rb/K/Ba- and Ba/K-exchanges in terms of how they affect the polarization-switching time, ts, and ionic conductivity in RKTP. We discuss the change in switching time, ts, that is ascribed to the interplay between the monovalent and divalent cations in the exchange. Moreover, we propose exchange-induced strain as the cause of bulk phase-matching shift and show that exchanges containing lower amounts of Rb induce less strain. This is corroborated by strain-deformation measurements on the exchanged samples. Finally, we demonstrate highly efficient periodically poled RKTP crystals free of bulk changes, using two different high ts - low strain exchanges.

For ferroelectric ionic-conductors, polarization switching is complicated by the interplay between ion mobility and charge screening effects. When the ionic charge carriers also play a key role in the domain reversal, such as in Rb-doped KTiOPO4 (RKTP), a higher level of complexity is introduced. RKTP provides an ideal platform for investigating the relationship between ionic conductivity and polarization reversal because its highly anisotropic crystal properties allow selective modification of material characteristics through diffusive cation doping. Here, we use indiffused Ba/K doping to create a significant increase in the ionic conductivity. Time-of-flight secondary ion mass spectrometry is employed to map Ba/K doping within the RKTP crystal and correlate it to changes in ionic mobility and polarization switching characteristics under an external field applied to the nonpolar face. Using band-excitation piezoresponse force microscopy, we demonstrate a selective switching-inhibition mechanism driven by the enhanced charge screening.

We investigate a new method of coercive field engineering for periodic poling of RbKTiOPO4 (RKTP). By ion exchanging RKTP in a molten salt containing 7 mol% Ba(NO3)2 and 93 mol% KNO3 we achieve more than an order of magnitude difference in polarization switching time between the exchanged and non-exchanged regions. This method is used to fabricate periodic gratings of 2.92 µm in 1 mm thick bulk RKTP for second harmonic generation at 779 nm with a normalized conversion efficiency of 2%/Wcm. We show that the poled domain structures are stable at 300 °C, and that there is no bulk refractive index modification associated with the periodic ion exchange.

We demonstrate a new method to fabricate waveguides in KTP. It allows for independently fabrication of the periodically poled grating via coercive field engineering and post-poling waveguide inscription via ion exchange.

We demonstrate a new method to fabricate waveguides in KTP. It allows for independently fabrication of the periodically poled grating via coercive field engineering and post-poling waveguide inscription via ion exchange.

Silica fibers are highly desired due to their robustness and easy integration with existing infrastructure. Although fabrication of silica gain fibers can be performed using well-established methods e.g., Modified Chemical Vapor Deposition (MCVD), each production cycle can be time-consuming and expensive. Additive manufacturing (AM) on the other hand is an attractive way of fabrication, where reduced waste and short cycles are widely recognized. Today, AM is commonly used to make functional components and prototypes.

The pursuit of advanced fiber laser technologies has driven research toward unconventional manufacturing techniques. In this work, we present an erbium-doped fiber laser made using powder-based additive manufacturing. An Er3+/Al3+ co-doped silica glass rod was printed using laser powder deposition and then used as the core material in a fiber preform. The fiber drawn from the preform exhibited the complete, desired functionality linked to Er3+ doping. To demonstrate this, a standing wave laser cavity was formed with the feedback attained from the cleaved ends of the manufactured fiber. The high quality of the fiber is showcased through a low background loss, single-mode operation, a 9.4% laser slope efficiency, and an output of 4.5 mW, limited by the available pump power. This proof-of-concept opens up promising areas for rapid fabrication and development of high-performance fibers and fiber lasers.

The development of reliable periodic poling methods that allow for sub-µm quasi-phase matched (QPM) gratings and, at the same time, allow for waveguide implementation, is of paramount importance for a large number of applications. For instance, backward-wave optical parametric oscillators [1] are only viable if the QPM period is on the same order of magnitude as the wavelengths of the interacting waves. Furthermore, the integration of such QPM devices in a waveguide format would unveil countless possibilities in quantum optics employing the crystal as an ultrabright bi-photon source with unique spectral characteristics.

A Nd:YVO4 laser operating at 1064 nm generating a stable mode-locked train of 10 ps-long dark pulses with a 211 MHz repetition rate is presented. The mode-locking relies on a periodic loss modulation produced by intra-cavity sum-frequency mixing with a synchronous bright-pulse train from a mode-locked femtosecond Yb:KYW laser at 1040 nm. A modulation depth of 9050 was achieved for the dark pulses, confirmed by cross-correlation measurements. The ultrafast loss modulation injects power into the Nd:YVO4 laser cavity modes beyond the laser gain bandwidth. At proper laser cavity length, the detuning interaction of these modes with the lasing modes leads to the generation of periodic ultra-fast transients at frequencies above 1.5 THz.