Tunable Erbium-doped Fiber Laser Research Articles

Tunable Fiber Laser by Cascading Twin Core Fiber-Based Directional Couplers

A C-band tunable erbium-doped fiber laser is proposed and experimentally demonstrated by cascading two twin-core fiber (TCF)-based directional couplers. Two TCF-based couplers have different TCF lengths and gave rise to a dense fringe pattern modulated by a sparse one. The lasing wavelength was coarsely tuned by bending one TCF-based coupler with TCF length of 0.14 m, and finely tuned by stretching another TCF-based coupler with TCF length of 1.37 m. Experimental results have shown that the lasing wavelength was linearly and monotonously tuned over 23.2 nm (1541.8-1560 nm) with a uniform tuning step of 0.22 nm, side mode suppression ratio of up to 58 dB, power uniformity of ±0.1 dB. In addition, the output power fluctuation and the wavelength drift have been monitored and found to be <;±0.05 dB and 0.004 nm, respectively.

Stable and tunable narrow-linewidth erbium-doped fibre laser based on polarization-maintaining fibre ring filter and PM-FBG

A tunable, narrow-linewidth, ring-cavity, erbium-doped fibre laser (EDFL) incorporating a polarization-maintaining fibre ring filter (PMF-FRF) and a polarization-maintaining fibre Bragg grating (PM-FBG) was designed and used in experiments. In the proposed configuration, the PM-FBG was used as a wavelength selector and the PMF-FRF was fabricated by a 3 dB coupler and a 2 m polarization-maintaining fibre. In order to constrain the mode hopping, a 1 m long segment of erbium-doped fibre was inserted between the circulator and the PM-FBG as a saturable absorber. Based on these enhancements, the side-mode suppression was improved and a stable and tunable single-wavelength laser was achieved within the tuning scope of 1534.36–1535.07 nm by adjusting the polarization controller. In the tunable scope, each wavelength space was ≤0.1 nm, the maximum power drift was ≤0.35 dB, and the 3 dB linewidth was ≤0.15 nm. In the experiment, dual- and triple-wavelength laser emissions were also realized by modifying the polarization condition of the cavity. Over a 20 min monitoring period at room temperature, the wavelength shift and power fluctuation of the single-wavelength emission were ≤0.01 nm and 0.11 dB respectively, while wavelength shift and power fluctuation of the dual-wavelength emission of 1534.39 and 1535.07 nm were ≤0.02 nm and 0.7 dB respectively.

Tunable Erbium-Doped Fiber Laser Based on Random Distributed Feedback

A tunable erbium-doped fiber (EDF) laser based on random distributed feed- back through backward Rayleigh scattering in a 20-km-long single-mode fiber and a tun- able fiber Fabry-Perot interferometer filter is demonstrated. It has a broad wavelength tuning range up to 40 nm (from 1525 to 1565 nm) with a narrow linewidth of 0.04 nm. Due to the half-opened laser cavity design and the efficient gain from the pumped EDF, the measured threshold power is only 13 mW, and the pump efficiency is up to 14%.

Tunable and switchable dual-wavelength single polarization narrow linewidth SLM erbium-doped fiber laser based on a PM-CMFBG filter.

A tunable and switchable dual-wavelength single polarization narrow linewidth single-longitudinal-mode (SLM) erbium-doped fiber (EDF) ring laser based on polarization-maintaining chirped moiré fiber Bragg grating (PM-CMFBG) filter is proposed and demonstrated. For the first time as we know, the CMFBG inscribed on the PM fiber is applied for the wavelength-tunable and-switchable dual-wavelength laser. The PM-CMFBG filter with ultra-narrow transmission band (0.1 pm) and a uniform polarization-maintaining fiber Bragg grating (PM-FBG) are used to select the laser longitudinal mode. The stable single polarization SLM operation is guaranteed by the PM-CMFBG filter and polarization controller. A tuning range of about 0.25 nm with about 0.075 nm step is achieved by stretching the uniform PM-FBG. Meanwhile, the linewidth of the fiber laser for each wavelength is approximate 6.5 and 7.1 kHz with a 20 dB linewidth, which indicates the laser linewidth is approximate 325 Hz and 355 Hz FWHM.

Dual-band wavelength tunable nonlinear polarization rotation mode-locked Erbium-doped fiber lasers induced by birefringence variation and gain curvature alteration.

With the combining effects of the fiber birefringence induced round-trip phase variation and the gain profile reshaping induced spectral filtering in the Erbium-doped fiber laser (EDFL) cavity, the mechanism corresponding to the central wavelength tunability of the EDFL passively mode-locked by nonlinear polarization rotation is explored. Bending the intracavity fiber induces the refractive index difference between orthogonal axes, which enables the dual-band central wavelength shift of 2.9 nm at 1570 nm region and up to 10.2 nm at 1600 nm region. The difference between the wavelength shifts at two bands is attributed to the gain dispersion decided by the gain spectral curvature of the EDFA, and the spacing between two switchable bands is provided by the birefringence induced variation on phase delay which causes transmittance variation. In addition, the central wavelength shift can also be controlled by varying the pumping geometry. At 1570 nm regime, an offset of up to 5.9 nm between the central wavelengths obtained under solely forward or backward pumping condition is observed, whereas the bidirectional pumping scheme effectively compensates the gain spectral reshaping effects to minimize the central wavelength shift. In contrast, the wavelength offset shrinks to only 1.1 nm when mode-locking at 1600 nm under single-sided pumping, as the gain profile strongly depends on the spatial distribution of the excited erbium ions under different pumping schemes. Except the birefringence variation and the gain spectral filtering phenomena, the gain-saturation mechanism induced refractive index change and its influence to the dual-band central wavelength tunability are also observed and analyzed.

Tunable dual-wavelength fiber laser based on an MMI filter in a cascaded Sagnac loop interferometer

A widely tunable dual-wavelength erbium-doped fiber laser based on a cascaded Sagnac loop interferometer incorporating a multimode interference filter is proposed and experimentally demonstrated in this paper. The mode selection is implemented by using the cascaded Sagnac loop interferometer with two segments of polarization maintaining fibers, and the wavelength tuning was achieved by using the refractive index characteristic of multimode interference effects. The tunable dual-wavelength fiber laser has a wavelength tuning of about 40 nm with a signal-to-noise ratio of more than 50 dB.

A widely tunable erbium-doped fiber laser using closed loop control

A widely tunable erbium-doped fiber laser using closed loop control

A compact graphene Q-switched erbium-doped fiber laser using optical circulator and tunable fiber Bragg grating

We demonstrate a passively Q-switched tunable erbium-doped fiber laser (EDFL) based on graphene as a saturable absorber (SA). A three-port optical circulator (OC) and a strain-induced tunable fiber Bragg grating (TFBG) are used as the two end mirrors in an all-fiber linear cavity. The Q-switched EDFL has a low pump threshold of 23.8 mW. The pulse repetition rate of the fiber laser can be widely changed from 9.3 kHz to 69.7 kHz by increasing the pump power from 23.8 mW to 219.9 mW. The minimum pulse duration is 1.7 μs and the highest pulse energy is 25.4 nJ. The emission wavelength of the laser can be tuned from 1560.43 nm to 1566.27 nm by changing the central wavelength of the strain-induced TFBG.

Tunable multi-wavelength erbium-doped fiber laser by cascading a standard Mach–Zehnder interferometer and a twin-core fiber-based filter

A tunable multi-wavelength erbium-doped fiber laser (MEDFL) based on a nonlinear optical loop mirror (NOLM) was proposed and experimentally demonstrated by cascading a standard Mach–Zehnder interferometer (MZI) and a twin-core fiber (TCF)-based filter. Due to the ‘blue shift’ of the transmission band of the TCF-based filter when the TCF was bent, a tunable lasing waveband was realized by moving the transmission band of the TCF-based filter to cover different channels provided by the standard MZI. Experimental results showed that the lasing waveband can be linearly tuned over a range of 24 nm from 1542 to 1566 nm with a channel spacing of 0.4 nm, a maximum lasing line amount of 19, and an optical signal to noise ratio (OSNR) of 39 dB. The stability of the laser spectra was verified with a wavelength drift of 0.04 nm and a power fluctuation of ±0.3 dB.

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.

Tunable narrowband fiber laser with feedback based on whispering gallery mode resonances of a cylindrical microresonator

Narrowband filtering based on whispering gallery modes of a slightly tapered cylindrical optical microresonator was used to implement a tunable narrowband erbium-doped fiber laser. The laser can be set to emit a single longitudinal cavity mode (single frequency), although the laser cavity is a few meters long. In the single-frequency regime the laser can emit a maximum power of 0.380 mW with a linewidth <35 kHz and a signal-to-noise ratio exceeding 50 dB. Tunability is achieved by sliding the excitation point along the microcylinder. A tuning range of 1.16 nm is demonstrated.

An L-band widely tunable erbium-doped fiber laser with all-fiber structure

We report on a widely tunable L-band erbium-doped fiber ring laser with the exploitation of an all-fiber Lyot fiber. The all-fiber Lyot filter is constructed from a polarizer, a short section of polarization-maintaining fiber and polarization controllers. Theoretical analysis shows that the laser oscillating wavelength can be tuned by changing the polarization rotation angle. By adjusting the polarization controllers, the laser can be tuned continuously over the full L band (1559.84–1603.19 nm) with a tunability of 43 nm, a side-mode suppression ratio over 44 dB, and power uniformity better than 1.2 dB. The simple and efficient tuning mechanism allows the building of inexpensive widely tunable fiber lasers with all-fiber structure.

Multi-wavelength generation by self-seeded four-wave mixing

A cost effective method of generating multi-wavelength based on the cascaded four wave mixing effect is experimentally demonstrated. The proposed scheme is free from external tunable laser sources and pump modulators, resulting from the use of a broadened linewidth tunable dual wavelength erbium-doped fiber laser as intracavity pump. In this configuration, the number of four wave mixing cascades becomes larger in tandem with the increment of erbium-doped fiber amplifier output power. When its output power is set at 20.57 dBm, six waves having optical signal to noise ratio larger than 10 dB are generated. The six waves are stable with peak power fluctuations less than 1 dB within 30 minutes period and tunable with wavelength spacing ranging from 1.03 nm to 11.31 nm.

Tunable graphene-based Q-switched erbium-doped fiber laser using fiber Bragg grating

A graphene-based Q-switched erbium-doped fiber laser (EDFL) with a tunable fiber Bragg grating (TFBG) acting as a wavelength tuning mechanism is proposed and demonstrated. The proposed setup utilizes a newly-developed ‘ferrule-to-ferrule transfer’ technique to obtain a single graphene layer that allows for Q-switch operation in the EDFL using a highly doped-gain medium. A TFBG is used as a wavelength tuning mechanism with a tuning range of 10 nm, covering the wavelength range from 1547.66 nm to 1557.66 nm. The system has a wide repetition rate range of over 206.613 kHz from 1.387 kHz to 208.000 kHz with pulse durations of between 94.80 μs to 0.412 μs. The laser output is dependent on the pump power, with energy per pulse of 4.56 nJ to 16.26 nJ. The system is stable, with power and wavelength variations of less than 0.47 dBm and 0.067 nm. The output pulse train is free from self-mode locking and pulse jitters.

Highly stable graphene-assisted tunable dual-wavelength erbium-doped fiber laser

A highly stable tunable dual-wavelength fiber laser (TDWFL) using graphene as a means to generate a highly stable output is proposed and generated. The TDWFL comprises a 1 m long, highly doped erbium-doped fiber (EDF) acting as the linear gain medium, with a 24-channel arrayed waveguide grating acting as a wavelength slicer as well as a tuning mechanism to generate different wavelength pairs. The tuned wavelength pairs can range from 0.8 to 18.2 nm. A few layers of graphene are incorporated into the laser cavity to induce the four-wave-mixing effect, which stabilizes the dual-wavelength output by suppressing the mode competition that arises as a result of homogenous broadening in the EDF.

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.

基于热扩芯光纤的MZ滤波器及其在宽带可调谐光纤激光器中的应用

Thermally expanded core fibers were made by heating a single-mode fiber locally with hydrogen-oxygen flame.An all fiber M-Z filter was fabricated using the thermally expanded core fiber,and it was inserted into a Sagnac filter to make a new structure of tunable fiber Sagnac filter which output spectrum was the uncorrelated superposition between the Sagnac and the M-Z interferences.With the new structure Sagnac fiber filter,a tunable erbium-doped fiber laser was made and investigated experimentally.Tunable output was obtained by adjusting apolarization controller(PC)in the Sagnac interferometer.During the whole tuning process,the laser output wavelength could be tuned from 1 540.3nm to 1 581.2nm with the output power flatness better than 2dB,3dB spectral linewidth narrower than 0.1nm and optical signal-to-noise extinction ratio higher than 45dB.

Widely Tunable Erbium-Doped Fiber Laser Based on Superimposed Core-Cladding-Mode and Sagnac Interferences

A widely tunable erbium-doped fiber laser based on superimposed core-cladding-mode and Sagnac interferences is proposed and demonstrated. The core-cladding-mode interference is elicited by cascading two well-fabricated single mode fiber tapers, which are inserted into the Sagnac loop with one section of polarization maintaining fiber and one polarization controller (PC). By adjusting only the PC in the Sagnac loop, the lasing line may be tuned at a discrete step defined by the core-cladding-mode interference, and its covering range depends on the Sagnac interference. The tunable laser operation is obtained with a discrete step of about 2.5 nm, tuning range more than 50 nm, side mode suppression ratio higher than 45 dB, and 3-dB spectral linewidth narrower than 0.1 nm.

Compact and Tunable Erbium-Doped Fiber Laser With Microfiber Mach–Zehnder Interferometer

A compact and tunable Erbium-doped fiber laser is demonstrated using a highly concentrated Erbium-doped fiber in conjunction with a microfiber Mach-Zehnder interferometer (MMZI) structure for the first time. A stable laser output is achieved at 1531.7 nm region with a peak power of -19 dBm and an optical signal to noise ratio of 30.1 dB using a 980-nm pump at 100 mW power. The operating wavelength of the laser can be tuned from 1530.2 to 1532.7 nm by changing the path length difference (PLD) inside the MMZI from 1.6 to 2.7 mm at room temperature. It is also observed that the operating wavelength linearly shifts to a longer wavelength as the PLD increases with a tuning slope efficiency of 0.17 nm/mm. The tuning ability is due to the alteration of the induced optical phase shift inside the MMZI which affects the optical interference and the dominant peak which is responsible for the lasing action.

A Simple Mechanism to Suppress the Mode Competition for Stable and Tunable Dual-Wavelength Erbium-Doped Fiber Lasers

A suppressant effect for mode competition of dual-wavelength lasing oscillations induced by polarization hole burning effect in an ordinary erbium-doped fiber is proposed and experimentally demonstrated. The polarization hole burning effect is introduced by an all fiber polarization controller directly fused with a segment of erbium-doped fiber. The mechanism of the all fiber polarization controller to suppress the wavelength competition is described in detail. Results show that the mechanism is helpful to obtain stable dual-wavelength lasing oscillations at room temperature in the erbium-doped fiber laser. By adjusting the comb filter, the wavelength tuning between different dual-wavelength oscillations is realized. The side mode suppression ratio of each lasing wavelength is measured to be more than 55dB. The 3dB bandwidth of each lasing oscillation is 0.01nm and the 30dB bandwidth is 0.10nm. The power fluctuation and wavelength shift are measured to be less than 0.8dB and 0.05nm over 32 minutes for all the dual-wavelength lasing oscillations obtained in the experiment.