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.

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.

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.

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.

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.

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.

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.

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%.

All-fiber-integrated Yb:YAG-derived silica fiber laser generating 6 W output power.

A Yb:YAG-derived silica fiber was fabricated by a molten-core fabrication method, in which a Yb:YAG crystal was used as the core material and a silica tube was used as the cladding material. The fiber's transmission loss was measured to be 0.49 dB/m at 1.55 µm, using a cut-back method. The fiber microstructure image showed that the cladding region was a uniform glass structure, while the core structure was amorphous. An all-fiber-integrated cladding-pumped laser based on Yb:YAG-derived silica fiber was demonstrated. With an incident pump power of 28 W, an output power of 6 W was obtained at 1.06 µm, with a slope efficiency of 21.7%.

110 mW single-frequency Yb:YAG crystal-derived silica fiber laser at 1064 nm.

A single-frequency laser based on Yb:YAG crystal-derived silica fiber (YDSF) was demonstrated. The YDSF was fabricated by a molten-core method with a doping concentration of 4.8 wt. % for Yb2O3, whose gain coefficient and transmission loss were measured to be 1.7 dB/cm and 0.005 dB/cm, respectively. An over 110 mW stable single-frequency laser at 1064 nm was obtained based on a distributed Bragg reflector setup, showing a slope efficiency of 18.5%. The signal-to-noise ratio was ∼80 dB, and the frequency fluctuation was less than 20 MHz within 10 min.

Design of all-solid W-type index fluorotellurite fibers with near-zero-flattened chromatic dispersion for optical frequency comb generation.

All-solid W-type index fluorotellurite fibers (AWFTFs) with near-zero-flattened dispersion profiles are designed for optical frequency comb (OFC) generation. The fiber core and cladding materials are ${{\rm TeO}_2} {\text - } {{\rm BaF}_2} {\text - } {{\rm Y}_2}{{\rm O}_3}$TeO2-BaF2-Y2O3 (TBY) and fluoroaluminate glasses. Those two glasses have large refractive index contrast as well as similar thermal expansion coefficients and softening temperatures. The zero-dispersion wavelength of the TBY glass is about 2517 nm. By introducing fluoroaluminate glasses with relatively low refractive index as the cladding material and controlling the core diameter, the zero-dispersion wavelength of the fiber is shifted from 2517 nm to the wavelength region of 1500-1600 nm. Furthermore, two layers of thin annular glasses including a fluoroaluminate-glass-based inter-layer and a TBY-glass-based outer layer are added around the fiber core, which makes the fiber have a flat dispersion profile in the wavelength range of 1500-1600 nm. By optimizing the parameters (the core diameter, the thickness of the thin annular glass, etc.) of AWFTFs, the fiber with the chromatic dispersion value between $ - {0.2}$-0.2 and 0.35 ps/nm/km in the wavelength range of 1500-1600 nm is achieved. To investigate the application of the AWFTFs for OFC generation via cascaded four-wave mixing, we perform numerical simulations. The simulated results show that flat-top OFC spectrum expanding from 1450 to 1700 nm with tunable mode spacing from 25 to 100 GHz can be generated in 2 m long fiber by using a 1550 nm laser with a pulse width of 0.825 ps and a peak power of 60 W as the pump source.

Tapered fluorotellurite microstructured fibers for broadband supercontinuum generation.

Fluorotellurite microstructured fibers (MFs) based on TeO2-BaF2-Y2O3 glasses are fabricated by using a rod-in-tube method. Tapered fluorotellurite MFs with varied transition region lengths are prepared by employing an elongation machine. By using a tapered fluorotellurite MF with a transition region length of ∼3.3 cm as the nonlinear medium and a 1560 nm femtosecond fiber laser as the pump source, broadband supercontinuum generation covering from 470 to 2770 nm is obtained. The effects of the transition region length of the tapered fluorotellurite MF on supercontinuum generation are also investigated. Our results show that tapered fluorotellurite MFs are promising nonlinear media for generating broadband supercontinuum light expanding from visible to mid-infrared spectral region.

Holmium-doped fluorotellurite microstructured fibers for 2.1 µm lasing.

Holmium (Ho3+)-doped fluorotellurite microstructured fibers based on TeO2-BaF2-Y2O3 glasses are fabricated by using a rod-in-tube method. By using a 1.992 µm fiber laser as the pump source, lasing at 2.077 µm is obtained from a 27 cm long Ho3+-doped fluorotellurite microstructured fiber. The maximum unsaturated power is about 161 mW and the corresponding slope efficiency is up to 67.4%. The influence of fiber length on lasing at 2.1 µm is also investigated. Our results show that Ho3+-doped fluorotellurite microstructured fibers are promising gain media for 2.1 µm laser applications.

Voltage-controlled nonlinear optical properties in gold nanofilms via electrothermal effect.

Dynamic control of the optical properties of gold nanostructures is crucial for advancing photonics technologies spanning optical signal processing, on-chip light sources and optical computing. Despite recent advances in tunable plasmons in gold nanostructures, most studies are limited to the linear or static regime, leaving the dynamic manipulation of nonlinear optical properties unexplored. This study demonstrates the voltage-controlled Kerr nonlinear optical response of gold nanofilms via the electrothermal effect. By applying relatively low voltages (~10 V), the nonlinear absorption coefficient and refractive index are reduced by 40.4% and 33.1%, respectively, due to the increased damping coefficient of gold nanofilm. Furthermore, a voltage-controlled all-fiber gold nanofilm saturable absorber is fabricated and used in mode-locked fiber lasers, enabling reversible wavelength-tuning and operation regimes switching (e.g., mode-locking-Q-switched mode-locking). These findings advance the understanding of electrically controlled nonlinear optical responses in gold nanofilms and offer a flexible approach for controlling fiber laser operations.

Broadband amplification and highly efficient lasing in erbium-doped tellurite microstructured fibers.

We report broadband amplification and highly efficient lasing in erbium-doped tellurite microstructured fibers. A broad positive net gain bandwidth of 113 nm (1524-1637 nm) is obtained in a 17 cm long erbium-doped tellurite microstructured fiber upon a pump power of 94 mW at 1480 nm. An all-fiber lasing at 1561 nm with maximum unsaturated power of 140 mW and slope efficiency of 53.7% is achieved from the fiber by employing a linear cavity. In addition, the influence of the fiber length on amplification and lasing is investigated and laser oscillation at 1535 nm is realized in a 4.3 cm long fiber.

Introduce Ce3+ Ions to Realize Enhancement of C+L Band Luminescence of KMnF3: Yb, Er Nanoparticles.

Polymer-based waveguide amplifiers are essential components in integrated optical systems, as their gain bandwidths directly determine the operating wavelength of optical circuits. However, development of the wideband gain media has been challenging, making it difficult to fabricate devices with broadband amplification capability. Rare earth ion-doped nanoparticles (NPs) are a key component in the gain media, and their full width at half maximum (FWHM) of the emission peak decides the final gain bandwidth of the gain media. Here, KMnF3: Yb, Er, Ce@KMnF3: Yb NPs with the broad full width at half maximum (FWHM) of the emission peak covering the S+C band was prepared. The NPs were synthesized using a hydrothermal method, and the FWHM of the emission peak of NPs reached 76 nm under the excitation of a 980 nm laser. The introduction of Ce3+ ions and a core-shell structure coating greatly enhanced the emission intensity of NPs at C band. Since KMnF3: Yb, Er, Ce@KMnF3: Yb NPs have exceptional broadband luminescence properties at C band, KMnF3: Yb, Er, Ce@KMnF3: Yb NPs can be the potential gain medium in the future polymer-based waveguide amplifiers.