Boosting the Downconversion Luminescence of Tm3+-Doped Nanoparticles for S-Band Polymer Waveguide Amplifier.

Polymer waveguide devices have attracted increasing interest in several rapidly developing areas of broadband communications since they are easily adaptable to on-chip integration and promise low propagation losses. As a key member of the waveguide gain medium, lanthanide doped nanoparticles have been intensively studied to improve the downconversion luminescence. However, current research efforts are almost confined to erbium-doped nanoparticles and amplifiers operating at the C-band; boosting the downconversion luminescence of Tm3+ for S-band optical amplification still remains a challenge. Here we report a Tb3+-induced deactivation control to enhance Tm3+ downconversion luminescence in a stoichiometric Yb lattice without suffering from concentration quenching. We also demonstrate their potential application in an S-band waveguide amplifier and record a maximum optical gain of 18 dB at 1464 nm. Our findings provide valuable insights into the fundamental understanding of deactivation-controlled luminescence enhancement and open up a new avenue toward the development of an S-band polymer waveguide amplifier with high gain.

Bidirectional mode-locked erbium-doped fiber laser based on an all-fiber gold nanofilm saturable absorber.

We demonstrate a bidirectional mode-locked erbium-doped fiber laser by incorporating gold nanofilm as a saturable absorber (SA). The gold nanofilm SA has the advantages of high stability and high optical damage threshold. Besides, the SA exhibits a large modulation depth of 26% and a low saturation intensity of 1.22 MW/cm2 at 1.56 µm wavelength band, facilitating the mode-locking of bidirectional propagating solitons within a single laser cavity. Bidirectional mode-locked solitons are achieved, with the clockwise pulse centered at 1568.35 nm and the counter-clockwise one at 1568.6 nm, resulting in a slight repetition rate difference of 19 Hz. Moreover, numerical simulations are performed to reveal the counter-propagating dynamics of the two solitons, showing good agreement with the experimental results. The asymmetric cavity configuration gives rise to distinct buildup and evolution dynamics of the two counter-propagating pulses. These findings highlight the advantage of the gold nanofilm SA in constructing bidirectional mode-locked fiber lasers and provide insights for understanding the bidirectional pulse propagation dynamics.

Strip loaded waveguide amplifiers based on erbium-doped nanocomposites with 17†dB internal net gain.

We propose a strip loaded amplifier employing SU-8 as the loaded waveguide and nanoparticles (NPs)-polymethyl methacrylate (PMMA) as the cladding layer. By leveraging the undoped SU-8 loaded waveguide, the polymer waveguide amplifier accomplished remarkably low transmission losses, reaching as low as 1.8 dB/cm at 1530 nm. We prepared NPs-PMMA nanocomposite by utilizing NaLu0.1Y0.7F4: Er3+, Yb3+ @NaLuF4 core-shell nanoparticles, which exhibited a significantly enhanced lifetime of 6.15 ms. An internal net gain of up to 17.7 dB was achieved on a strip loaded waveguide with a length as short as 0.5 cm when the on-chip pump power was 77 mW. Signal enhancement (SE) was measured at different wavelengths, revealing that the strip loaded waveguide exhibited broadband SE ranging from 1510 nm to 1570 nm, covering the C-band. To the best of our knowledge, this work has achieved the highest gain results reported thus far on a polymer matrix and provides an efficient method for optical amplification in passive devices on silicon and Si3N4 platforms, leveraging the ease of integration of polymer materials with diverse photonic platforms.

Widely tunable S-band ring-cavity Tm3+-doped fluorotellurite fiber laser.

Tm3+-doped fluorotellurite fibers (TDFTFs) are fabricated by using a rod-in-tube method. A 2.1 m long TDFTF is used as the gain medium, in which both ends of the TDFTF are connected to a short piece of a silica fiber by direct fusion splicing. By inserting the above TDFTF and a tunable optical bandpass filter into a ring cavity and employing a 1400/1570 nm dual-wavelength pumping technique, tunable lasing from 1460 to 1526 nm is obtained, which almost covers the whole S-band. To the best of our knowledge, this is the first report of tunable Tm3+-doped fiber laser with a tunable range almost covering the whole S-band. Furthermore, by removing the tunable optical bandpass filter from the ring cavity, free-running multi-wavelength lasers at 1500 and 1901 nm are achieved. Our results show that TDFTFs are promising gain media for constructing S-band fiber lasers.

Intense emission at 605†nm from Pr3+-doped fluorotellurite glass fibers.

Pr3+-doped fluorotellurite glass fibers (PDFTFs) were fabricated by using a rod-in-tube method. By using a 976/1400 nm dual-wavelength upconversion pump technique, an intense emission at 605 nm was obtained from a 6 cm long PDFTF, which was attributed to the transition 1D2 → 3H4 of Pr3+ ions. With an increase in power of the 1400 nm laser from ∼34 to ∼136 mW, the spectral bandwidth of the 605 nm emission decreased and the intensity of the 605 nm emission increased monotonically, indicating the generation of 605 nm amplified spontaneous emission (ASE). To the best of our knowledge, this is the first report of 605 nm ASE in PDFTFs. Our results showed that PDFTFs had the potential for constructing red fiber lasers and amplifiers.

Over 50 W all-fiber mid-infrared supercontinuum laser.

Broadband supercontinuum laser sources in the mid-infrared region have attracted enormous interest and found significant applications in spectroscopy, imaging, sensing, defense, and security. Despite recent advances in mid-infrared supercontinuum laser sources using infrared fibers, the average power of those laser sources is limited to 10-watt-level, and further power scaling to over 50 W (or hundred-watt-level) remains a significant technological challenge. Here, we report an over 50 W all-fiber mid-infrared supercontinuum laser source with a spectral range from 1220 to 3740 nm, by using low loss (<0.1 dB/m) fluorotellurite fibers we developed as the nonlinear medium and a tilted fusion splicing method for reducing the reflection from the fluorotellurite-silica fiber joint. Furthermore, the scalability of all-fiber mid-infrared supercontinuum laser sources using fluorotellurite fibers is analyzed by considering thermal effects and optical damage, which verifies its potential of power scaling to hundred-watt-level. Our results pave the way for realizing all-fiber hundred-watt-level mid-infrared lasers for real applications.

Gain enhancement technique for S-band polymer-based waveguide amplifiers.

The S-band polymer-based waveguide amplifier has been fabricated, but how to improve the gain performance remains a big challenge. Here, using the technique of establishing the energy transfer between different ions, we successfully improved the efficiency of Tm3+:3F3→3H4 and 3H5→3F4 transitions, resulting in the emission enhancement at 1480 nm and gain improvement in S-band. By doping the NaYF4:Tm,Yb,Ce@NaYF4 nanoparticles into the core layer, the polymer-based waveguide amplifier provided a maximum gain of 12.7 dB at 1480 nm, which was 6 dB higher than previous work. Our results indicated that the gain enhancement technique significantly improved the S-band gain performance and provided guidance for even other communication bands.

Watt-level 815†nm lasing from Tm3+-doped fluorotellurite glass fibers.

Tm3+-doped fluorotellurite fibers based on TeO2-BaF2-Y2O3(TBY) glasses were fabricated by using a rod-in-tube method. By using an 81 cm-long Tm3+-doped fluorotellurite fiber as the gain medium and a 1400 / 1570 nm dual-wavelength pump technique, lasing at 815 nm was obtained for a threshold pump power of 629 mW at 1400 nm and a fixed pump power of 960 mW at 1570 nm. As the 1400 nm pump power is increased to 1803 mW, the obtained maximum output power was about 1616 mW. The corresponding optical-to-optical conversion efficiency was about 58.5%. Our results show that Tm3+-doped fluorotellurite fibers are promising gain media for constructing 815 nm fiber lasers.

(S + C)-band polymer waveguide amplifier based on Tm3+ and Er3+ layer-doped core-shell nanoparticles.

Optical waveguide amplifiers are essential devices in integrated optical systems. Their gain bandwidths directly determine the operating wavelength of optical circuits. Due to the difficulty of developing wideband gain media, it has been a challenge to fabricate devices with broadband amplification capability, resulting in few reports on multi-band polymer waveguide amplifiers. Here, a polymer waveguide amplifier is demonstrated, which achieves loss compensation covering the whole (S + C) band by using NaYF4:Tm,Yb@NaYF4@NaYF4:Er nanoparticles (NPs)-doped SU-8 as the gain medium. The NPs with a layer-doped core-multishell structure not only provided two emitters required for (S + C)-band amplification, but also reduced the energy transfer (ET) between them. Under 980-nm excitation, the full width at half maximum (FWHM) of the emission peak of NPs reached 119 nm, and the relative gain in the (S + C) band was about 6-8 dB, successfully expanding the operating wavelength from single-band to multi-band.

Third-order cascaded Raman shift in all-solid fluorotellurite fiber pumped at 1550†nm.

In this Letter, we demonstrate a third-order cascaded Raman shift in an all-solid fluorotellurite fiber pumped by a 1550 nm nanosecond laser. The fluorotellurite glass with a composition of TeO2-BaF2-Y2O3 (TBY) has a usable Raman shift of ∼785 cm-1 and a Raman gain coefficient of ∼1.65 × 10-12 m/W at 1550 nm, which is approximately 25.4 times larger than that of silica glass. By using a 5.38 m fluorotellurite fiber as the Raman gain medium and a 1550 nm nanosecond laser as the pump light, a third-order cascaded Raman shift is obtained via spontaneous cascaded Raman amplification in the fluorotellurite fiber, causing the generation of the first-, second-, and third-order Stokes emissions that peak at 1765, 2049, and 2438 nm, respectively. For an average pump power of ∼491.5 mW, the output power of the generated first-, second-, and third-order Stokes light is approximately 14.1, 67.4, and 31.6 mW, respectively. The corresponding conversion efficiency is approximately 2.87%, 13.70%, and 6.43%, respectively. Our results show that fluorotellurite fibers are promising Raman gain media for constructing cascaded Raman fiber lasers with a wide range of wavelengths.

Thulium-doped fluorotellurite glass fibers for broadband S-band amplifiers.

We demonstrated broadband S-band (1460-1530 nm) amplification in Tm3+-doped fluorotellurite glass fibers (TDFTFs) by using a 1400/1570 nm dual-wavelength pump technique. TDFTFs based on TeO2-BaF2-Y2O3 (TBY) glass were fabricated by using a rod-in-tube method. For an input signal power of 0 dBm (or 1 mW), a broadband positive net gain ranging from <1440 nm to 1546 nm was achieved in a 1.55-m-long TDFTF with a Tm3+ doping concentration of ∼4000 ppm, as the pump powers of the 1400 nm and 1570 nm lasers were 1.7 W and 0.14 W, respectively. The corresponding bandwidth for a net gain of >20 dB was ∼66 nm (1458-1524 nm), and the measured saturated output power was ∼24.84 dBm at 1490 nm. In addition, numerical simulation was performed by using the parameters of the TDFTFs and the pump lasers, and the noise figure was calculated to be <5.6 dB in the S band. Our results showed that the TDFTFs were promising gain media for constructing efficient broadband S-band fiber amplifiers.

Polymer-based S-band waveguide amplifier using NaYF4:Yb,Tm-PMMA nanocomposite as gain medium.

Optical waveguide amplifiers are essential to improve the performance of integrated communication systems. Previous research has mainly focused on C- and L-bands amplification, but there are few reports on S-band waveguide amplifiers. Here, we introduce a polymer-based waveguide amplifier that uses a NaYF4:Yb3+,Tm3+ nanoparticles-PMMA nanocomposite as gain medium, which can provide loss compensation in the S-band. To obtain the strongest emission luminescence at 1480 nm, we optimized the doping concentration of Yb3+ and Tm3+ to 20% and 1%, respectively. By copolymerizing the nanoparticles and methyl methacrylate monomers, the nanocomposite was synthesized and used as the gain medium to fabricate S-band waveguide amplifiers. A relative gain of 5.6 dB/cm was observed at 1480 nm under the excitation of a 980-nm pump laser. To the best of our knowledge, this is the first time that S-band amplification has been observed in a polymer-based waveguide amplifier. This result is expected to extend the waveband of polymer-based waveguide amplifiers to the S-band.

Efficient ∼4 µm emission from Pr3+/Yb3+ co-doped fluoroindate glass.

Pr3+/Yb3+ co-doped fluoroindate (InF3) glasses were prepared by using a traditional melt-quenching method in dry N2 atmosphere. Pumped by a 976 or 1570 nm laser diode, efficient emissions at ∼4µm were obtained from the Pr3+/Yb3+ co-doped glasses, which could be ascribed to the transition 3F4→3H6 of Pr3+ ions. The relative stimulated emission cross section was calculated to be ∼1.44×10-24m2 at 4 µm, which was ∼4.2 times larger than that of transition Ho3+:5I5→5I6 (3.4×10-25m2). In addition, combined with transitions 1G4→3F3 and 1G4→3F4 of Pr3+ ions, ultra-broadband emission ranging from 2.7 to 4.2 µm was also obtained. Our results indicate that Pr3+/Yb3+:InF3 glasses could be used to develop efficient ∼4µm lasers and widely tunable mid-infrared lasers.

Intense emission at ∼3.3 µm from Er3+-doped fluoroindate glass fiber.

Fluoroindate glass fibers with an Er3+ doping concentration of ∼0.5mol% were fabricated by using a rod-in-tube method. Pumped by a 976 nm laser diode, intense emission at ∼3.3µm was obtained from a 40 cm long Er3+-doped fiber, which could be attributed to the transition 4S3/2→4F9/2 of Er3+ ions. The calculated emission cross section at ∼3.3µm was ∼3×10-26m2, which was ∼1.5 times larger than that of transitions Er3+:4F9/2→4I9/2 and Dy3+:6H13/2→6H15/2. In addition, broad emissions ranging from 3.1 µm to 3.85 µm were obtained in the Er3+-doped fiber under a 976 nm/1973 nm dual-wavelength pumping scheme. Our results indicated that Er3+-doped fluoroindate glass fibers had the potential for constructing efficient ∼3.3µm fiber lasers.

Unlocking the ultrafast potential of gold nanowires for mode-locking in the mid-infrared region.

In this Letter, we present the mode-locking operation of a 2.87 µm Ho3+/Pr3+ codoped fluoride fiber laser, helped by the ultrafast nonlinear optical absorption behavior of gold nanowires (GNWs). The mode locker is fabricated by depositing the GNW solution onto a silver mirror. It has a modulation depth of 14.2%, a saturation intensity of 26.2MW/cm2, and a non-saturation loss of 29.9% at 2.87 µm. With an increased pump power, the laser operates in Q-switched mode-locking, fundamental mode-locking, and harmonic mode-locking (HML) states. This represents the first, to our knowledge, mid-infrared mode-locked laser using gold nanomaterials. Additionally, the HML is also the first observation in a laser in this band using material saturable absorbers, implying the capability of GNWs for high repetition rate generation.

22.7 W mid-infrared supercontinuum generation in fluorotellurite fibers.

In this Letter, we demonstrate 22.7 W mid-infrared (MIR) supercontinuum (SC) generation in all-solid fluorotellurite fibers. All-solid fluorotellurite fibers based on ${{\rm TeO}_2} {\text -} {{\rm BaF}_2}{\text -}{{\rm Y}_2}{{\rm O}_3}$TeO2-BaF2-Y2O3 and ${{\rm TeO}_2}$TeO2 modified fluoroaluminate glasses are fabricated by using a rod-in-tube method. By using a 0.6 m long fluorotellurite fiber with a core diameter of 11 µm as the nonlinear medium and a high-power 1.93-2.5 µm SC fiber laser as the pump source, we obtain 22.7 W SC generation from 0.93 to 3.95 µm in the fiber for a pump power of 39.7 W. The 10 dB bandwidth is about 1633 nm, and the corresponding spectral range is from 1890 to 3523 nm. The optical-to-optical conversion efficiency is about 57.2%. Our results show that all-solid fluorotellurite fibers are promising nonlinear media for constructing high-power MIR SC light sources.

Wideband multiwavelength Brillouin fiber laser based on dual-mode AlGaInAs/InP microcavity lasers.

A multiwavelength Brillouin fiber laser (BFL) is demonstrated using a 1.55-µm AlGaInAs/InP microcavity laser as a seed source. The combination of a nonlinear fiber cavity and a feedback loop leads to multiwavelength generation with a channel spacing of double-Brillouin-frequency assisted by cavity-enhanced four-wave mixing. The amplified output of a dual-mode lasing square microcavity laser with a wavelength interval of 1.5 nm is applied as the pump source for the broadband multiwavelength generation. A wideband multiwavelength BFL covering from 1490 nm to 1590 nm is successfully generated at an optimized pump power of 25 dBm and a feedback power of -17.2dBm. The power stability of 0.82 dB over a 60 min duration of the multiwavelength BFL can satisfy the demands for the optical fiber sensing and microwave photonic systems.

Linearly polarized single-frequency fiber laser based on the Yb:YAG-crystal derived silica fiber.

A linearly polarized low-noise single-frequency fiber laser was demonstrated by using a homemade 1.2-cm-long Yb:YAG crystal derived silica fiber. A maximum output power of greater than 60 mW was obtained with a signal-to-noise ratio of ∼80dB and a polarization extinction ratio of 27.8 dB. Additionally, the relative intensity noise was measured to be -145dB/Hz above 6.5 MHz. A frequency fluctuation of less than 20 MHz was also obtained. The output power was scaled up to 14.5 W with a one-stage all-fiber amplifier scheme with a slope efficiency of 56.4%.

Zn-Alloyed CsPbI3 Nanocrystals for Highly Efficient Perovskite Light-Emitting Devices.

We alloyed Zn2+ into CsPbI3 perovskite nanocrystals by partial substitution of Pb2+ with Zn2+, which does not change their crystalline phase. The resulting alloyed CsPb0.64Zn0.36I3 nanocrystals exhibited an improved, close-to-unity photoluminescence quantum yield of 98.5% due to the increased radiative decay rate and the decreased non-radiative decay rate. They also showed an enhanced stability, which correlated with improved effective Goldschmidt tolerance factors, by the incorporation of Zn2+ ions with a smaller radius than the Pb2+ ions. Simultaneously, the nanocrystals switched from n-type (for CsPbI3) to nearly ambipolar for the alloyed nanoparticles. The hole injection barrier of electroluminescent LEDs was effectively eliminated by using alloyed CsPb0.64Zn0.36I3 nanocrystals, and a high peak external quantum efficiency of 15.1% has been achieved.