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We demonstrate a period poled tapered lithium niobate waveguide and study second harmonic generation (SHG) in this device for the purpose of broadening the quasi-phase matching (QPM) acceptance bandwidth. The finite-difference beam-propagation method is used to simulate the guided modes and calculate the effective indices. The simulation results show that by tapering the width of the cross section linearly, the phase mismatch between a specific input wavelength and its SHG signal can be varied along the propagation length. Ideal SHG phase-matching conditions for a wide range of input wavelengths in communication band from 1 542.5 nm to 1 553.5 nm can be satisfied in different positions of the waveguide.

We report rigorous coupled-wave analysis (RCWA) method to non-destructively characterize the domain structure of periodically poled lithium niobate (PPLN) crystal. The strong light diffraction effect is achieved by applying a proper external voltage. We can observe reversed domain pattern and employ the detected diffraction intensity to optimally fit the result of RCWA based on least square method. Compared with conventional scalar diffraction theory, more accurate domain structure parameters with accuracies of 0.05 μm and 0.005 for the period and duty cycle are obtained respectively. It is proved that accurate, real-time and nondestructive characterization can be realized via this method. 1

We report on simultaneous sum-frequency mixing and doubling of C-band and ∼ 980 n m laser sources using a single segmented periodically poled lithium niobate (PPLN) crystal in a single-pass configuration. Our theoretical analysis on the spectral outputs show that a proper design of a five-segment single PPLN crystal has potential to generate violet, blue, green, and orange wavelengths by simultaneous sum-frequency and second-harmonic generation processes. Such a design has promising potential for a compact, tunable multicolored laser that can find various applications such as in biomedicine, visible light communications, laser-based color displays, and sensing.

In this study, simultaneous second-harmonic generation (SHG), sum frequency generation (SFG), and Raman conversion based on MgO-doped periodically poled lithium niobate (MgO:PPLN) for multi-wavelength generation is demonstrated. The approach used is based on a single MgO:PPLN crystal poled with a uniform period of 10.2 &micro, m that phase matches SHG and SFG, simultaneously. Using a simplified double-pass geometry, up to 0.8 W of blue light at 487 nm is achieved by a frequency-doubling 974 nm laser diode pump, and 0.5 W of orange light at 598 nm is generated by frequency mixing 974 nm pump with C-band (1527&ndash, 1565 nm) tunable laser source. At high pump powers of the 974 nm laser source, other unexpected peaks at 437, 536, 756, 815 and 1038 nm were observed, of which the 1038 nm line is due to Stimulated Raman Scattering within the MgO:PPLN crystal. The resulting multi-wavelength light source may find a wide range of applications in biomedicine and basic research.

We have demonstrated sum-frequency generation of a compact continuous-wave orange laser in a step-chirped magnesium oxide doped periodically poled lithium niobate in single-pass mode. A 974 nm laser diode was mixed with a C-band amplified spontaneous emission laser source to yield a triple-wavelength operation at 594.9, 596.9, and 598.6 nm with a maximum output power of 9.3 mW and broad bandwidth of ~4.4 nm. The triple-wavelength output power stability was ~2.5% in 30 min. This technique provides a path to generate broadband laser sources at shorter wavelengths which are potentially useful for biomedical and spectroscopic applications.

We demonstrate bandwidth broadening in cascaded MgO-doped periodically poled lithium niobate (MgO:PPLN) crystals (Λ=10.3 μm) using the temperature-gradient technique. Up to 2.8 nm bandwidth at 600 nm spectral region is achieved using two 50 mm long cascaded MgO:PPLN crystals via sum frequency generation. This technique combines the merits of high conversion efficiency attributed to cascaded nonlinearity and the reconfigurability of temperature-gradient-induced chirp for broadening of the input wavelength acceptance range.

We demonstrate a compact blue and orange-two color continuous wave laser source emitting at 487 nm and from 597.4 to 600.3 nm, respectively. The temperature tunable coherent orange radiation is achieved by frequency mixing 974 nm laser diode (LD) and a C-band amplified spontaneous emission laser source while the temperature insensitive blue radiation is generated by second-order quasi-phase-matching frequency doubling of 974 nm LD. We implement the simultaneous nonlinear processes in a single magnesium oxide doped periodically poled lithium niobate bulk crystal without the need of an aperiodic design.

We report an all-solid-state continuous wave (CW) tunable orange laser based on cascaded single-pass sum-frequency generation with fundamental wavelengths at 1545.7 and 975.2 nm using two quasi-phase-matched (QPM) MgO-doped periodically poled lithium niobate (MgO:PPLN) crystals. Up to 10 mW of orange laser is generated in the cascaded module corresponding to a 10.4%/W nonlinear conversion efficiency. The orange output showed a temperature tuning rate of ~0.05 nm/°C, and the beam quality (M2) value of the orange laser was about 2.0. We use this technique to combine the high efficiency offered by uniformly poled crystals and the broad input wavelength acceptance characteristic of step-chirped structures.

In this paper, we report on a minized length, compact, low loss Y-branch waveguide based on lithium niobate optical crystal. The Y-branch waveguide device was fabricated using annealed proton exchange technique to achieve single mode guiding at 1550 nm wavelength. The simplified Y-branch structure has a total length of 18.7 mm and calculated bending loss of 0.5 dB has been realized with a splitting ratio found to be 1.25 at 1550 nm wavelength. Such easy to fabricate waveguide could find applications in future photonic communication networks, sensing, and quantum information technology.

A high-efficiency broadband orange laser is demonstrated by use of double-pass sum-frequency mixing in a step-chirped MgO-doped periodically poled lithium niobate (MgO:PPLN) crystal (ᴧ = 10.1-10.4 µm). The temperature-gradient technique is used to enhance the bandwidth of the output spectrum. A maximum orange output power of 129 mW (~65% conversion efficiency) was achieved at room temperature operation, and up to ~7.2 nm bandwidth at a temperature difference of 20 ᵒC was realized. This scheme presents an attractive approach for the generation of high power and broadband short-wavelength lasers from a single crystal, which may extend the potential biomedical and spectroscopic applications.

A Watt-level broadband orange laser is demonstrated by use of double-pass sum frequency mixing in a step-chirped MgO-doped periodically poled lithium niobate (MgO:PPLN) crystal (Λ = 10.1–10.4 µm). The temperature-gradient technique is used to enhance the bandwidth of the output spectrum. The maximum output of the orange laser in the 600 nm spectral region is up to 1.1 W whereas the maximum bandwidth of ~7.2 nm was accomplished employing a 40 mm long MgO:PPLN structure. This scheme presents an attractive approach for the generation of high power and broadband short-wavelength lasers from a single crystal, which may extend the potential biomedical and spectroscopic applications.