PPLN Crystal Research Articles

3.8 µm pulse burst self-optical parametric oscillator utilizing a programmable step-active Q-switch with Nd:MgO:PPLN crystal

This paper reports a 3.8 µm pulse burst self-optical parametric oscillator (SOPO) employing the Nd:MgO:PPLN crystal, achieving programmable mid-infrared pulse burst output based on step-active Q-switching technology. Building on the intracavity optical parametric oscillator (IOPO) theory, a theoretical model for the step-active Q-switched self-optical parametric oscillator is developed by introducing idler photon and step loss terms. The simulation results elucidate the evolution of population inversion and photon numbers and determine step-active Q-switching loss values for different sub-pulse numbers. Additionally, a 3.8 µm pulse burst laser output with a repetition rate of 10 kHz is experimentally achieved using the step-active Q-switching signal designed from the theoretical simulation. The effective programming of the step-active Q-switching signal achieves control over 2-4 sub-pulses, 260-1000 ns intervals, and any amplitude ratios. The experimental and simulation results demonstrate consistency, offering valuable insights for optimizing the Q-switching technology in other SOPO systems.

3- W, 3.8 µm self-optical parametric oscillator by pulsed pumping based on Nd:MgO:PPLN crystal

We present a 3.8 µm self-optical parametric oscillator (SOPO) pumped by a pulsed laser diode (LD) based on only one Nd:MgO:PPLN crystal. The problem of heat accumulation in Nd:MgO:PPLN crystals caused by high-power laser pumping is significantly optimized. The generation of non-matching polarized fundamental light is suppressed, ensuring the output of π-polarized (π-pol) 1084 nm fundamental light across the entire pumping range, and satisfying the polarization matching condition. The mid-infrared SOPO system based on this method is not only compact in structure, and stable in central wavelength, but also improves the self-conversion efficiency. Moreover, a maximum output power of 3.04 W is obtained at 3814 nm in pulse pumping mode, which represents the highest output power in 3.8 µm SOPOs. The corresponding repetition frequency is 25.11 kHz and the single pulse width is 11.45 ns.

1283-1460 nm continuously tunable, watt-level bismuth-doped phosphosilicate fiber laser and its frequency doubling to a visible laser.

We report, to the best of our knowledge, the first demonstration of an O + E-band tunable watt-level bismuth-doped phosphosilicate fiber laser and its frequency doubling to tunable red laser. Benefiting from the two types of bismuth active centers associated with silicon and phosphorus introduced in one fiber, an ultrabroad gain is available in the designed low-water-peak bismuth-doped phosphosilicate fiber (Bi-PSF) pumped by a self-made 1239 nm Raman fiber laser. The high-efficiency tunable lasing is achieved with a maximum output power of 1.705 W around 1320 nm and a slope efficiency of 33.0%. The wavelength can be continuously tuned from 1283 to 1460 nm over a 177 nm spectral range, almost covering the whole O+E-bands. We further employ a polarization beam splitter in the cavity to output an O + E-band linear-polarization laser for second-harmonic generation by a designed multi-period MgO2:PPLN crystal, and a 650-690-nm tunable visible laser is correspondingly obtained. Such an O+E-wideband tunable high-power laser and the SHG red laser may have great potential in the all-band optical communications, biophotonics, and spectroscopy.

Self-injection-locked second-harmonic generation at 532 nm in high-Q Fabry-Perot micro-cavities

Based on the combination of DFB laser self-injection-locking (SIL) and external-cavity frequency-doubling, we have successfully demonstrated, for the first time to our knowledge, the self-injection-locked second-harmonic generation (SHG) at 532 nm by adopting the high-Q Fabry-Perot (FP) micro-cavities. With the DFB incident pump power of 79 mW at 1064 nm, the maximum output SHG power of 20.7 mW at 532 nm was achieved from the 11 mm long plane-concave FP external-cavity of 0.12 mL volume with the 10 mm long PPLN crystal. The corresponding output SHG efficiency of 26.2 % and the Q-factor of 56.5 M both exceeded all known SIL-SHG results reported, and the SIL SHG output power was one order of magnitude higher than the previous maximum of over 2 mW. The reliable SIL has been realized by utilizing the natural birefringence of the intracavity nonlinear crystal to provide laser feedback, and the intrinsic linewidth of the SIL pump laser at 1064 nm was about 30 Hz. Moreover, by replacing the PPLN crystal with the LN and KTP crystals, the output SHG power of 6.1 mW and 2.7 mW at 532 nm were respectively obtained with the Q-factors of 29.3 M and 27.6 M. Our new SIL-SHG design with the high-Q FP micro-cavity paves the way to a new type of the field-deployable ultra-narrow-linewidth visible and near-visible lasers of low size, weight, and power (SWaP).

Study on narrow linewidth 2.1 μm self-optical parametric oscillator based on Nd:MgO:PPLN

We report a 2.1 µm miniaturized narrow linewidth self-optical parametric oscillator (SOPO) based on Nd:MgO:PPLN crystal. We attained 2.1 µm narrow linewidth laser output by incorporating an Fabry-Perot (F-P) etalon into the SOPO. By controlling the crystal temperature uniformly, a stable 2.1 µm degenerate light output is obtained at 71 °C. Finally, when inserting the F-P etalon with a thickness of 2.5 mm, a maximum average output power of 0.65 W is obtained, corresponding pulse repetition rate is 60 kHz, the pulse width is 7.77 ns, the degenerate light beam quality M2 < 2. And the linewidth of 2168 nm laser is narrowed from 67.53 nm to 2.23 nm. It is proved by experiments that adding F-P etalon to the SOPO can narrow the linewidth of the 2.1 μm laser and optimize the beam quality. These findings provide technical support for the realization and application of narrow linewidth 2.1 µm laser, which is great significance for the further development of related fields.

Second harmonic of higher-order Poincaré sphere beam with two orthogonal 5%MgO:PPLN crystals

In this work, the second harmonic (SH) of higher-order Poincaré sphere (HOPS) beam was introduced and demonstrated with two orthogonal 5%MgO:PPLN crystals. Based on the quasi-phase-matching technique, the vectorial coupled wave equations were derived to simulate the SH of HOPS beams through the two crystals, including the cylindrical vector beams (CVBs), elliptically polarized CVBs (EPCVBs), and circularly polarized vortex beams. Then, the experimental setup was established to reveal that the SH of CVBs and EPCVBs present the four-lobed structure and still exhibit vector characteristics. Meanwhile, the circularly polarized vortex beams become the linearly polarized vortex beams with double phase topology, confirming the conservation of orbital angular momentum. Moreover, the maximum SH conversion efficiency of CVBs, EPCVBs, and circularly polarized vortex beams can reach 25.3%, 23.4%, and 29.4%, respectively, which may be instructive for promoting the SH generation of vector vortex beams with high efficiency.

Tunable Optical Parametric Oscillator Based on MgO:PPLN and HgGa2S4 Crystals Pumped by an Nd:YAG Laser with Increased Energy Characteristics

Tunable Optical Parametric Oscillator Based on MgO:PPLN and HgGa2S4 Crystals Pumped by an Nd:YAG Laser with Increased Energy Characteristics

Tunable Near and Mid-Infrared (1.3–5 µm) Picosecond Pulsed Optical Vortex Parametric Oscillator

In this paper, we present a picosecond pulsed, synchronously pumped optical parametric oscillator producing vortex beam output with tunable wavelengths in the near- to mid-infrared range. The system utilizes a Nd:YVO4 picosecond pulsed solid-state laser emitting at a wavelength of 1.064 µm to pump a Z-shaped, singly resonant OPO which contains a MgO:PPLN crystal with a fan-shaped grating. The wavelength tuning characteristics of the OPO output are examined both as a function of the MgO:PPLN grating period and crystal temperature. The orbital angular momentum of the pump field can be selectively transferred to either the signal or idler fields by appropriately adjusting the location of the MgO:PPLN crystal within the OPO cavity. The maximum output power of the signal and idler vortex fields are 5.12 W and 3.46 W, respectively, for an incident pump power of 19 W.

Near to Mid-Infrared (1.3–5 μm) Widely Tunable, High Power Picosecond Pulsed Laser

We present a high-power, widely tunable, synchronously pumped picosecond pulsed optical parametric oscillator (OPO) generating emissions in the near to mid-infrared wavelength ranges. The OPO is pumped using a Nd:YVO4 picosecond pulsed laser and utilizes a fan-shaped, multi-grating MgO doped PPLN crystal (MgO:PPLN). The system generates near to mid-infrared output across the wavelength range 1.3–5 µm, with a high overall conversion efficiency of 75.15%.

Over 3.8 W, 3.4 µm picosecond mid-infrared parametric conversion based on a simplified one-to-many scheme

In this paper, we demonstrate a simplified one-to-many scheme for efficient mid-infrared (MIR) parametric conversion. Such a scheme is based on a continuous wave (CW) single longitudinal mode master oscillator power-amplifier (MOPA) fiber system as the signal source and a picosecond pulsed MOPA fiber system, exhibiting multiple longitudinal modes, as the pump source. The signal and pump beams are combined and co-coupled into a piece of 50-mm long 5% MgO-doped PPLN crystal for the parametric conversion. As high as ∼3.82 W average power at a central idler wavelength of ∼3.4 µm is achieved when the launched pump and signal powers are ∼41.73 and ∼11.45 W, respectively. Above some threshold value, the delivered idler power shows a roll-over effect against the signal power and saturation-like effect against the pump power. Consequently, the highest conversion efficiency is observed at such a threshold pump power. To the best of our knowledge, our result represents the highest average power produced from any single-pass parametric conversion source with &gt;3 µm idler wavelength feeding with a CW signal. Moreover, our proposed scheme can simplify the design of parametric conversion system significantly and meanwhile make the system more robust in applications. This is attributed to two main aspects. Firstly, the scheme’s one-to-many feature can reduce wavelength sensitivity remarkably in the realization of quasi-phase-matching. Secondly, for moderate power requirement it does not always require a high peak power synchronized pulsed signal source; a CW one can be an alternative, thereby making the system free from complex time synchronization and the related time jitter.

Enhancing conversion efficiency of MgO:PPLN and Rb:PPKTP crystal-based subnanosecond optical parametric generators by utilizing a supercontinuum seed

This paper presents an approach to enhance the conversion efficiency of subnanosecond pulse duration microlaser-pumped optical parametric generators (OPGs) tunable from near- to mid-infrared. The method involves generating a supercontinuum (SC) in the photonic crystal fiber (PCF) and using it to seed the subnanosecond OPG based on the fan-out grating design MgO:PPLN crystal. Since the SC spectrum covered the entire signal wave tuning range (1414–2128 nm), seeding and conversion efficiency improvement of 6%–11% was achieved for all OPG signal wavelengths, and the generation threshold was reduced up to 3 times. Such a method allows for improved energy stability, significantly increases the brightness of the OPG output radiation, and is pivotal in mitigating the risk of MgO:PPLN optical damage. The study also extended the method to successfully seed 532 nm pumped Rb-doped PPKTP crystal-based OPG with the same SC, demonstrating broad applicability and performance improvement across different parametric devices.

Study of ppLN crystals for sum frequency generation of CW laser demonstrating 20 nm tunability in the visible range from 616 to 636 nm, through temperature tuning

This work presents the study of custom-made nonlinear ppLN crystals enabling the generation of CW laser around 626 nm demonstrating over 500mW over a 20 nm tunability range using temperature tuning, through SFG of tunable 1 and 1.5µm lasers.

Subnanosecond microlaser pumped fan-out grating design MgO:PPLN optical parametric generator continuously tunable from near- to mid-infrared

An in-depth analysis and description of, to the best of our knowledge, the first subnanosecond pulse duration optical parametric generator (OPG) based on a fan-out grating design MgO-doped periodically-poled lithium niobate (MgO:PPLN) crystal is presented. Pumped by high energy subnanosecond pulse duration Q-switched Nd:YAG microlaser pulses, our OPG provides high output energies ranging from tens to hundreds of μJ with up to 45% conversion efficiency and enables fast and precise wavelength tuning across the near-to-mid infrared spectral regions (1414–4303 nm) just by laterally displacing the fan-out crystal without the need for temperature tuning. Limits of operation of the device were found in terms of the laser-induced damage threshold (LIDT) of the fan-out MgO:PPLN crystal. The OPG was fully characterized in terms of spectral, energy, and spatial properties of the signal wave, and analyzed experimentally and theoretically for the feasibility of producing broadband infrared output through non-collinear quasi-phase-matching and conversion of the fan-out grating structure into a chirped one.

Efficient femtosecond optical parametric generation in group-velocity-matched MgO:PPLN at 10 MHz.

We report on efficient single-pass optical parametric generation (OPG) of broadband femtosecond pulses in the mid-infrared at 10 MHz by exploiting group-velocity-matched interaction in a 42-mm-long MgO:PPLN crystal. Using a microchip-started femtosecond amplified Mamyshev oscillator at 1064 nm as the pump, the OPG source can provide tunable femtosecond pulses across 1516-1566 nm in the signal and 3318-3568 nm in the idler, with slope efficiencies of ∼93% and ∼41%, respectively. For 650 mW of average input pump power, signal powers of up to 283 mW at 1524 nm are generated, with more than 200 mW over the entire tuning range. Idler average powers of up to 104 mW at 3450 nm, with more than 80 mW across the full range, are also obtained. For input pump pulses of ∼182 fs, the generated signal pulses have a duration of ∼460 fs at 1516 nm. The idler pulses have a typical bandwidth of ≥100 nm over the entire tuning range, and as wide as 181 nm at 3457 nm. The OPG source exhibits excellent passive power stability, better than 0.5% rms in the signal and 0.6% rms in the idler, over 1 h, both in Gaussian TEM00 spatial profile with M2 < 1.5.

10 Hz Stable Mode-locked Er-Fiber Laser

Abstract: In this paper, a stable output at the reduction repetition rate from 80 MHz mode-locked Er-doped fiber laser (EDFL) was demonstrated by adjusting the operating point for external LiNbO3 Mach-Zehnder‎ electro-optic intensity modulator to suppress harmonic mode-locked pulses. More than 70% of the laser beam was launched into the external pigtail Mach-Zehnder intensity modulator using single mode fiber with collimating lens and fiber (ferrule connector) FC adapter. The optimum values of Mach-Zehnder modulator bias voltages V0 and Vπ (half wave voltage) which resulted in maximum and minimum laser output power to leave the modulator were found at 6.5 and 0.29 V, respectively. The best modulation was achieved for the RF modulating signal with an opening time of about 8 ns. For driving voltage equal to Vπ, a clean mode-locked pulse train was generated with a pulse shape and energy similar to the input pulse, albeit with a low repetition rate. The minimum repetition rate reached as low as 10 Hz, resulting in pulse energy and peak power of 0.32 nJ and 1.5 kW, respectively. Second-harmonic generation of the low repetition rate pulse train was also produced by using a PPLN crystal. This opens up the potential for using this laser in single photon detection experiments and as a seed laser for many applications. Keywords: Er-fiber laser, Passively mode-locked fiber laser, Nonlinear polarization rotation, Mach-Zehnder modulator, Fast electro-optic modulator. PACS: Fiber lasers, 42.55.Wd, Mode locking, 42.60.Fc.

978 Nm All-Polarization-Maintaining Mode-Locked Fiber Laser Based on Phase-Biased Nonlinear Amplifying Loop Mirror

Terahertz (THz) wave generation based on ultrafast laser are one of the most predominant and popular technologies. In particular, for THz generation by photoconductor antenna and optical rectification, higher optical to THz conversion efficiency usually requires ultrafast laser excitation into semiconductor or nonlinear crystal, therefore it is of great desire to develop ultrafast laser with high performance. CW Yb-doped lasers at 980 nm have been applied to generate THz wave range from 0.5 to 6 THz by DFG technique. To meet the demand of some THz wave generation (e.g. BNA crystal, gold nanoplasma), 980 nm ultrafast fiber laser are ideal pump sources and in desire to be developed. Here we demonstrate a 978 nm robust all-polarization-maintaining (PM) picosecond fiber laser mode- locked by phase-biased nonlinear amplifying loop mirror (PB- NALM). By introducing a nonreciprocal - <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\pi$</tex-math></inline-formula> /2 phase shifter into the fiber loop, a self-starting stable mode-locking is obtained with the center wavelength of 978.14 nm and a 3-dB bandwidth of 0.43 nm. The pulse duration is 8.1 ps corresponding to the time bandwidth product (TBP) of 1.09. The maximum average output power is 14.5 mW with a repetition rate of 45.438 MHz. After a master oscillator power amplification system, the 978 nm average output power reaches 2.12 W, which is then injected into a PPLN crystal for second harmonic generation and 52 mW 489 nm ultrashort lasers is obtained. This is, to the best of our knowledge, the first report of PB-NALM-based mode-locked fiber laser at 978 nm. The 978 nm ultrafast fiber laser and SHG to 489 nm have great potential in terahertz emission by shorter NIR and blue light.

Free-space transmission of picosecond-level, high-speed optical pulse streams in the 3 µm band.

The utilization of mid-infrared (mid-IR) light spanning the 3-5 µm range presents notable merits over the 1.5 µm band when operating in adverse atmospheric conditions. Consequently, it emerges as a promising prospect for serving as optical carriers in free-space communication (FSO) through atmospheric channels. However, due to the insufficient performance level of devices in the mid-IR band, the capability of mid-IR communication is hindered in terms of transmission capacity and signal format. In this study, we conduct experimental investigations on the transmission of time-domain multiplexed ultra-short optical pulse streams, with a pulse width of 1.8 ps and a data rate of up to 40 Gbps at 3.6 µm, based on the difference frequency generation (DFG) effect. The mid-IR transmitter realizes an effective wavelength conversion of optical time division multiplexing (OTDM) signals from 1.5 µm to 3.6 µm, and the obtained power of the 40 Gbps mid-IR OTDM signal at the optimum temperature of 54.8 °C is 7.4 dBm. The mid-IR receiver successfully achieves the regeneration of the 40 Gbps 1.5 µm OTDM signal, and the corresponding regenerated power at the optimum temperature of 51.5 °C is -30.56 dBm. Detailed results pertaining to the demodulation of regeneration 1.5 µm OTDM signal have been acquired, encompassing parameters such as pulse waveform diagram, bit error rate (BER), and Q factor. The estimated power penalty of the 40 Gbps mid-IR OTDM transmission is 2.4 dB at a BER of 1E-6, compared with the back-to-back (BTB) transmission. Moreover, it is feasible by using chirped PPLN crystals with wider bandwidth to increase the data rate to the order of one hundred gigabits.

High efficient optical parametric amplification of femtosecond pulses in MgO doped PPLN crystals at 3.4 µm

High efficient optical parametric amplification of femtosecond pulses in MgO doped PPLN crystals at 3.4 µm

Accurate derivation of THG conversion efficiency in periodically poled nonlinear medium and optimizing conversion parameters

We have derived a novel equation to accurately predict the third harmonic generation (THG) conversion efficiency in hybrid periodically poled nonlinear medium. Our equation considers the general case that takes both depleted pump regime and phase mismatching cases, resulting in more precise predictions of efficiency. This level of accuracy is crucial for certain applications like high-power THG lasers. Moreover, accurate calculation of THG power density is essential to prevent exceeding the crystal damage threshold. We applied our equation on hybrid MgO:PPLN crystal to determine the optimal SHG region length corresponding to two different power densities, namely, 0.25 and 0.5MW/cm2. The effect of crystal temperature on efficiency was also studies. Furthermore, a comparison between the derived equation and the commonly used nondepleted pump regime equation was performed. We found that the latter equation is significantly less accurate, particularly at high power densities, with the efficiency of the depleted pump regime being 50.6% less than nondepleted one. To demonstrate the effectiveness of the equation, our results were compared with experimental data, and we observed a good agreement between them.

Continuous-wave 2.9–3.8 µm random lasing via temperature-tunning free difference-frequency generation of random fiber lasers in PPLN crystal

Continuous-wave 2.9–3.8 µm random lasing via temperature-tunning free difference-frequency generation of random fiber lasers in PPLN crystal