Flattening effect of four wave mixing on multiwavelength Brillouin-erbium fiber laser

A multiwavelength Brillouin-erbium fiber laser with enhanced output uniformity is demonstrated and its performance with and without the assistance of four wave mixing (FWM) is compared. The presence of FWM effect is proven by the generation of anti-Stokes wave and higher-order Stokes wave. This scheme is successful in flattening the multiwavelength output. At Brillouin pump wavelength of 1,550 nm, between the first and the last output channel, peak power differences of 4.59 and 8.32 dB are recorded for the scheme with and without the assistance of FWM, respectively. This represents 3.73 dB improvement in the multiwavelength output power uniformity.     

Graphene-assisted all-fiber multiwavelength erbium-doped fiber laser functionalized with evanescent field interaction

An all-fiber multiwavelength erbium-doped fiber laser (MEDFL) functionalized with evanescent-field-interacting graphene is proposed and experimentally demonstrated. Graphene-polymer nanocomposites were deposited around the waist region of a fiber taper fabricated by flame-stretching method. Using the graphene-deposited fiber taper (GDFT) to induce four-wave mixing (FWM) as a power-equalizing device for suppressing the unstable mode competition in MEDFL, stable multiwavelength lasing around 1530 nm was obtained with a wavelength spacing of 0.56 nm, an extinction ratio of 33 dB, and a narrow linewidth per channel of <0.01 nm. The output spectrum of the multiwavelength laser has a good flatness, and the power fluctuation of each wavelength is less than 1.5 dB. Comparing with the traditional methods, such evanescent-field-interaction based graphene stabilizing mechanism for multiwavelength generation possesses unique advantages: (1) it can avoid the graphene thermal damage, (2) it’s a real all-fiber integrated structure, and (3) it provides a longer interaction length for exciting FWM more efficiently.     

Wavelength-spacing tunable multiwavelength erbium-doped fiber laser based on four-wave mixing of dispersion-shifted fiber

We experimentally demonstrate a wavelength-spacing tunable multiwavelength erbium-doped fiber laser based on degenerate four-wave mixing in a dispersion-shifted fiber incorporating multiple-fiber Bragg gratings. We have achieved stable operation of the multiwavelength erbium-doped fiber laser, which has 0.8 nm spacing ten-channel lasing wavelengths and a high extinction ratio of more than approximately 45 dB, at room temperature. The output power of the multiwavelength erbium-doped fiber laser is stable, so the peak fluctuation is less than approximately 0.2 dB. By changing the properties such as loss and polarization state of multiple fiber Bragg grating cavities, we can exercise flexible control of the wavelength spacing of the multiwavelength output. We can also obtain switchable multiwavelength lasing operation by elimination of the effects of alternate single-fiber Bragg gratings.     

Multiwavelength erbium-doped fiber laser based on nonlinear polarization rotation assisted by four-wave-mixing

We experimentally demonstrate a simple-structure but efficient multiwavelength erbium-doped fiber laser based on nonlinear polarization rotation assisted by four-wave-mixing (FWM). Based on the combination of these two nonlinear mechanisms contributing to intensity-dependent loss to alleviate mode competition, the stable multiwavelength operation at room temperature can be realized in a length of dispersion-shifted fiber. We achieved up to 38-wavelength generation with a spacing of ∼0.4 nm in the laser. In addition, through tuning the birefringence fiber filter, the lasing wavelength can be accurately tuned in the free spectrum range.     

A pump power controlled 1,060 nm multiwavelength fiber ring laser using nonlinear polarization rotation of SOA

We propose and experimentally demonstrate a both channel spacing and wavelength-tunable 1,060 nm multiwavelength fiber laser using nonlinear polarization rotation of semiconductor optical amplifier (SOA). The SOA in the cavity can not only provide the gain but also generate a pump power controlled phase-shift between two orthogonal linear states of polarization. The experimental result shows that the fast and continuous wavelength tuning is achieved with external light injection, while the channel spacing of the multiwavelength laser can be varied by adjusting the length of polarization maintaining fiber. When an external laser source with 13 dBm power is injected into the SOA as a control pump, optically tunable operation of up to 20 wavelength channels, from 1,042 to 1,058 nm, with a wavelength spacing of 0.8 nm has been demonstrated with the signal-to-spontaneous-noise ratio over 40 dB at room temperature. The lasers are stable with a maximum power fluctuation per channel of less than 0.5 dB during 2-h test.     

利用倾斜光纤光栅的可开关双波长光纤激光器

报导了一种在四波混频作用下利用倾斜光纤布拉格光栅进行波长选择的可开关双波长掺铒光纤激光器。通过将倾斜光纤光栅与单模光纤进行横向错位焊接,使光栅的反向LP01和LP11两个模式具有相近的有效反射率,从而可以用来进行激光器的双波长选择。接入腔内的一段高非线性光子晶体光纤引入的四波混频效应克服了模式竞争,使得双波长激光在室温下稳定振荡。腔内起偏器和偏振控制器的联合作用可产生依赖于波长的损耗,以补偿光纤光栅两反射峰峰值的大小差异。基于以上原理,通过调节腔内的偏振态,该激光器实现了室温下稳定的双波长输出,也实现了在两波长之间的转换。两波长激光均有超过45 dB的信噪比,最大的功率波动为0.8 dB     

Power-equalized parallel-type pump-shared fiber lasers based on parameter-adjustment

A parallel-type, pump-shared (PTPS) scheme linear-cavity laser array (LCLA) is proposed and numerically studied. Power-equalization of multiwavelength fiber lasers can be achieved by varying the pumping power ratio, length of the erbium-doped fiber or reflectivity of grating reflector for the individual channels. Before and after power-equalization, the maximum power variation among seven equal-spaced channels, ranging from 1530 to 1560 nm, is 5.8 and 0.2 dB, respectively.     

Multiwavelength erbium-doped fiber laser employing a nonlinear optical loop mirror

A stable and broad bandwidth multiwavelength erbium-doped fiber laser is proposed and demonstrated successfully. A nonlinear optical loop mirror which induces wavelength-dependent cavity loss and behaves as an amplitude equalizer is employed to ensure stable room-temperature multiwavelength operation. Up to 50 wavelengths lasing oscillations with wavelength spacing of 0.8 nm within a 3-dB spectral range of 1562-1605 nm has been achieved. The measured power fluctuation of each wavelength is about 0.1 dB within a 2-h period.     

Multi-wavelength erbium-doped fiber laser using four-wave mixing effect in doped fiber

We demonstrate a multi-wavelength erbium-doped fiber laser (EDFL) using erbium gain and four-wave mixing (FWM) effect in a piece of erbium-doped fiber (EDF) with high erbium ion concentration. The EDF has a pump absorption rate of 24.6 dB/m at 979 nm and is bi-directionally pumped by 980-nm laser diodes. FWM effect redistributes the energy of different oscillating lines and causes multi-wavelength operation. The laser generates more than 22 lines of optical comb with a line spacing of approximately 0.10 nm at the 1569-nm region using only 1.5-m-long EDF.     

Single-frequency polarized eye-safe all-fiber laser with peak power over kilowatt

An all-fiber, single-frequency, linearly polarized, high peak-power, pulsed laser at 1,540 nm for Doppler wind lidar is presented. This laser is composed of a single-frequency, narrow-linewidth external cavity diode laser, and multistage fiber amplifiers. A peak power of 1.08 kW and a pulse width of 500 ns at 10 kHz repetition rate are achieved, which is the highest peak power with a linewidth of 800 kHz in erbium-doped silica fiber to our knowledge. The beam quality of M ² < 1.3 and a polarization extinction ratio over 16 dB are obtained. This laser will be employed in a compact long-range coherent Doppler wind lidar.     

FWM-based multi-wavelength erbium-doped fiber laser using Bi-EDF

We experimentally demonstrate a simple structure but efficient multi-wavelength erbium-doped fiber laser (EDFL) using a 49 cm Bismuth-based erbium-doped fiber (Bi-EDF) as gain medium. The Bi-EDF provides erbium amplification and FWM effect in the cavity to generate a stable multi-wavelength comb operating in C-band region. We have achieved more than 5 lines with peak power of more than −35 dBm and channel spacing of 0.5 nm by incorporating a broadband fiber Bragg grating and polarization controller in the ring cavity.     

Broadly tunable multiwavelength fiber laser with bismuth-oxide EDF using large effective area fiber

A multiwavelength laser comb using 2.49 m Bismuth-oxide erbium-doped fiber (Bi-EDF) with different lengths of large effective area fiber (LEAF) in a ring cavity configuration is realized. The Bi-EDF is used as the linear gain medium and LEAF is used as the non-linear gain medium for stimulated Brillouin scattering. Out of the four different lengths, the longest length of 25 km LEAF exhibits the widest tuning range of 44 nm (1576 to 1620 nm) in the L-band at 264 mW pump power and 5 mW Brillouin pump power. In addition, a total of 15 output channels are achieved with total average output power of −8 dBm from this laser structure. All Brillouin Stokes signals exhibit high peak power of above −20 dBm per signal and their optical signal-to-noise ratio of greater than 15 dB.     

Stable dual-wavelength erbium-doped fiber ring laser with switchable spacing employing controllable channel loss

A stable dual-wavelength erbium-doped fiber ring laser with switchable spacing is proposed and experimentally demonstrated. An arrayed waveguide grating (AWG) incorporating two fiber optic switches (OS) is used to as the wavelength selector. The ring cavity is divided into two cavities by a 30:70 optical coupler. Equalized dual-wavelength outputs are achieved by controlling the variable optical attenuator (VOA) inserted in the lower loss cavity. The wavelength spacing can be tuned from 0.80 to 12.05 nm. The fiber laser has good optical quality with maximum power fluctuation of 1.5 dB and side mode suppression ratios (SMSRs) higher than 71 dB.     

Flat amplitude multiwavelength Brillouin–Raman random fiber laser with a half-open cavity

In this paper, we experimentally demonstrate a novel configuration of multiwavelength Brillouin–Raman random fiber laser (MBRRFL) utilizing a half-open cavity. The laser resonator is formed by fiber loop mirror at the Brillouin pump (BP) side and random distributed Rayleigh backscattering in a 10 km dispersion compensating fiber. As a result, we are able to obtain a flat amplitude bandwidth of 16.8 nm from 1,550.0 to 1,566.8 nm built-in 210 uniform Brillouin Stokes lines with 0.08 nm spacing and an average OSNR of 13.5 dB. We also studied the influence of BP power and wavelength on the MBRRFL’s performance. Furthermore, comparing with the open cavity configuration, the discrepancies in power level and linewidth between neighboring channels are overcome by using the half-open cavity.     

Switchable triple-wavelength erbium-doped fiber laser using a single fiber Bragg grating in polarization-maintaining fiber

A stable and narrow wavelength spacing multiwavelength erbium-doped fiber laser is proposed and demonstrated. The laser can produce simultaneous dual- and triple-wavelength lasing oscillations with a narrow wavelength spacing of less than 0.1 nm via using a single fiber Bragg gratings written in polarization-maintaining (PM) fiber. By adjusting polarization controller, the wavelength spacing of dual-wavelength lasing oscillations can be tuned to as small as 0.032 nm. The maximum amplitude variation for every lasing wavelength is less than 0.5 dB. The room-temperature operation principle is based on the polarization hole burning and deeply saturated effect in an ordinary erbium-doped fiber ring laser (EDFRL). The laser has the advantages of simple all-fiber configuration, low cost, high stability and operating at room temperature.     

A linear cavity multiwavelength fiber laser with adjustable lasing line number for fixed spectral regions

We report an experimental demonstration of muliwavelength erbium-doped fiber laser with adjustable wavelength number based on a power-symmetric nonlinear optical loop mirror (NOLM) in a linear cavity. The intensity-dependent loss (IDL) induced by the NOLM is used to suppress the mode competition and realize the stable multiwavelength oscillation. The controlling of the wavelength number is achieved by adjusting the strength of IDL, which is dependent on the pump power. As the pump power increases from 40 to 408 mW, 1–7 lasing line(s) at fixed wavelength around 1601 nm are obtained. The output power stability is also investigated. The most power fluctuation of single wavelength is less than 0.9 dB, when the wavelength number is increased from 1–7.     

Switchable single- and dual-wavelength erbium-doped fiber laser assisted by four-wave mixing with wide and continuous tunability

A widely tunable and stable erbium-doped fiber laser based on four-wave mixing effect in a highly nonlinear fiber is proposed and experimentally demonstrated. By adjusting reflected power from a dual-selective element, the ring laser is switchable between single- and dual-wavelength operations. The tuning range of the single laser is 22.78 nm, from 1,542.07 to 1,564.85 nm, while the wavelength spacing of the dual-wavelength can be continuously tuned from 0.52 to 22.78 nm. The laser is stable with output peak power fluctuation of <1 dB in 30-min interval.     

Multiwavelength fiber laser with ultradense wavelength spacing based on inhomogeneous loss with assistance of nonlinear polarization rotation

We demonstrate a multiwavelength fiber laser with ultradense wavelength spacing and ultrabroad bandwidth based on inhomogeneous loss mechanism with assistance of nonlinear polarization rotation. The inhomogeneous loss, implemented by incorporating a section of highly nonlinear fiber (HNLF) and a Sagnac filter in the laser cavity, can balance mode competition in erbium-doped fiber and result in ultradense multiwavelength generation. The bandwidth of the multiwavelength spectrum is greatly broadened owing to the intensity-dependent loss induced by nonlinear polarization rotation. Stable multiwavelength lasing with wavelength spacing of 0.08 nm and wavelength number up to 254 is achieved at room temperature. Moreover, multiwavelength tuning is realized through modifying polarization-dependent cavity loss.     

Multi-wavelength fiber laser in single-longitudinal mode operation using a photonic crystal fiber Sagnac interferometer

In this paper, we report a new configuration of a tunable multi-wavelength erbium-doped fiber laser based on the commercial optical multiplexers and a Sagnac interferometer which includes a section of a high-birefringent photonic crystal fiber. Four-wavelength laser emission lines were obtained simultaneously in single-longitudinal mode operation showing a power instability lower than 1 dB, and an optical signal-to-noise ratio higher than 65 dB for all the emitted wavelengths. This proposed configuration allows the individual control of the loss of each channel of the laser and because of it is based on the commercial ITU-grid multiplexers, the laser is adapted to the telecommunications channel’s normative.     

Four-wave mixing self-stability based on photonic crystal fiber and its applications on erbium-doped fiber lasers

The analytic solutions of coupled-mode equations of four-wave mixings (FWMs) are achieved by means of the undepleted approximation and the perturbation method. The self-stability mechanism of the FWM processes is theoretically proved and is applicable to design a new kind of triple-wavelength erbium-doped fiber lasers. The proposed fiber lasers with excellent stability and uniformity are demonstrated by using a flat-near-zero-dispersion high-nonlinear photonic-crystal-fiber. The significant excellence is analyzed in theory and is proved in experiment. Our fiber lasers can stably lase three waves with the power ripple of less than 0.4 dB.