Random Distributed Feedback Fiber Laser Research Articles

Implementation of Er-doped random fiber laser self-mixing sensor with ultra-limit sensitivity

This study first demonstrates that the random distributed feedback fiber laser (RDFL) can be implemented for sensing detection by using the self-mixing effect as a sensing mechanism. By constructing a compact self-mixing velocimeter based on Er-doped RDFL with the integration of a laser, sensing element, and transmission platform, we successfully measured the minimum detectable feedback intensity of 38.65 fW for the velocity signal, corresponding to 0.55 photons per Doppler cycle, exhibiting ultra-high sensitivity dynamics characteristics. In addition, the velocity measurement of a non-cooperative target at a single-channel distance of 100 km is accomplished because of the natural feature of long-distance transmission for the random distributed feedback fiber lasers, which greatly improves the ultra-long detection range in the field of self-mixing sensing. The proposed sensing scheme not only unveils a fresh perspective on the exploration of random fiber laser sensing but also showcases its diverse and wide-ranging applications within the realm of remote sensing measurements.

Switchable and tunable multi-wavelength random distributed feedback fiber laser based on parallel Lyot filter

A switchable and tunable multi-wavelength random distributed feedback fiber laser based on a parallel Lyot filter is designed, and the transmission characteristics of the filter are deduced in detail by using the transmission matrix theory. The randomly distributed backward Rayleigh scattering generated in single-mode fiber (SMF) serves as a feedback mechanism. The number of output wavelength increases linearly with the increase of pump power. By adjusting the polarization controller (PC) to control the polarization state of the beam into the polarization maintaining fiber (PMF), laser channels with wavelength interval of 0.88 nm or 0.46 nm can be output. Where the wavelength interval depends on the wavelength phase difference caused by the corresponding branch PMF. The intensity-dependent loss (IDL) caused by the nonlinear optical loop mirror (NOLM) in the experimental structure is not only used to suppress the intense mode competition caused by EDF, but also to control the spectral range of the output wavelength to achieve tunable laser output. When the wavelength interval is 0.88 nm, the wavelength tuning ranges of the three and four laser channels are 4.4 nm and 3.7 nm, respectively. When the wavelength interval is 0.46 nm, the wavelength tuning ranges of the three and four laser channels are 3.7 nm and 4 nm, respectively. Subsequently, the influence of using different lengths of SMF on the output wavelength is analyzed. It is found that longer SMF can increase the linewidth of the laser channel, and the side mode suppression ratio (SMSR) will be improved to 39 dB. In addition, the output power fluctuation of the laser is less than 0.32 dB within 30 min, and the power amplitude and SMSR are stable at −4.47dBm and 34.5 dB, respectively, indicating that the laser can achieve flat and stable multi-wavelength output at room temperature.

Low-spatial coherence vortex beam generation by random distributed feedback fibre laser

Vortex beams with low spatial coherence have great potential in applications such as imaging, medical diagnosis, optical communication, and manipulation. In this study, we experimentally demonstrated a radially polarised vortex beam with extremely low spatial coherence using a random distributed feedback fibre laser (RDFB-FL). The results show that the spatial coherence of vortex beams can be reduced in an RDFB-FL and further reduced by introducing radial polarisation. In addition, the evolution of the spatial coherence of a RDFB-FL-generated vortex beam with varying pump power was clearly revealed for the first time. The spatial coherence first decreases sharply up to a point as the pump power increases and then remains constant, and this behaviour is quite different from that of vortex beams generated by conventional fibre lasers. The present study provides an effective method for achieving a low-spatial coherence vortex beam source for application in telecommunications and imaging systems.

Tunable and switchable multi-wavelength random distributed feedback fiber laser based on SMF and a cascaded Sagnac ring filter.

A tunable and switchable multi-wavelength random distributed feedback fiber laser based on cascaded Sagnac loops is proposed and experimentally demonstrated. The random distribution feedback of the laser is provided by the Rayleigh scattering generated by the single-mode fiber (SMF). The cascaded Sagnac loops act as a filter and a reflector in the half-open cavity laser. The single-, dual-, three-, and four-wavelength channels can be realized by adjusting the angle of the polarization controller at the pump power of 300 mW. In the single-, dual-, and three-wavelength channels, the wavelength spacing can be maintained, and the laser wavelength position can be changed at the same time. The maximum wavelength tuning ranges of single-, dual-, and three-wavelength outputs are about 4.5 nm, 2.6 nm, and 1 nm, respectively. The proposed multi-wavelength random fiber laser has the advantages of simple structure and low threshold, and it has good application prospects in remote sensing and imaging systems.

Direct measurements of localized spectral modes in random distributed feedback fiber laser

We present observation of ultra-narrow spectral modes in the generation of the random fiber laser by using a technique of optical heterodyning in real-time. We found that such modes have a spectral width below 3 MHz. The modes are spatially extended over the whole cavity and remain for tens of roundtrip times.

Switchable and tunable multi-wavelength erbium-doped random distributed feedback fiber laser based on a compound filter

A switchable and tunable multi-wavelength random distributed feedback fiber laser (RDFBFL) is realized based on the compound filter which is comprised of a dual-pass Mach-Zehnder interferometer (MZI) and a Sagnac loop mirror. The lasing threshold of the proposed RDFBFL is suppressed to 50 mW by the pumped erbium-doped fiber (EDF), and the pump efficiency is 1%. By simply adjusting the angle of polarization controller (PC) in the Sagnac loop, 2, 3, 5 and 6 lasing channels can be obtained under the pump power of 200 mW, and the central wavelengths of the 3 lasing channels can be simultaneously tuned with a fixed channel separation. Moreover, the power amplitudes and side mode suppression ratios (SMSRs) of lasing channels are maintained around − 10 dBm and 34 dB, respectively. The proposed RDFBFL has the advantages of ideal tunability and low threshold, which can be widely used in imaging systems and long-distance sensing.

Tunable multi-wavelength random distributed feedback fiber laser based on dual-pass MZI

A tunable half-open cavity multi-wavelength erbium-doped random distributed feedback (RDFB) fiber laser is proposed and experimentally demonstrated. The backward Rayleigh scattering generated by inhomogeneous reflective in the 25-km-long single mode fiber is amplified by the 8-m-long pumped erbium-doped fiber (EDF). The dual-pass Mach–Zehnder interferometer (MZI) acts as the reflection mirror in the half-open cavity. Due to the EDF gain and the half-open structure, the laser threshold is suppressed to 40 mW. The number of laser channel increases linearly with the increasing pump power. Under the pump power of 350 mW, there are seven lasing channels in the spectrum. One arm of the MZI is circled on piezoelectric transducer (PZT) and tunable multi-wavelength lasing operation is realized by adjusting the DC voltage on PZT. When the pump power and the driving voltage attached on PZT are 250 mW and 5 V, the wavelengths of six channels are blue-shifted 0.7 nm. The proposed tunable RDFB fiber laser has the advantages of low cost, simple structure and low threshold, which can be widely used in remote sensing and biomedical imaging.

Tunable and Switchable Multi-Wavelength Random Distributed Feedback Fiber Laser Based on Smf and Cascaded Sagnac Loops Filter

Tunable and Switchable Multi-Wavelength Random Distributed Feedback Fiber Laser Based on Smf and Cascaded Sagnac Loops Filter

Switchable multi-wavelength erbium-doped random distributed feedback fiber laser incorporating two-stage Sagnac filter

A low-threshold and simple structure switchable multi-wavelength fiber laser based on random distributed feedback (RDFB) is presented. The experiment setup incorporates a two-stage Sagnac fiber loop mirror, an 8 m long erbium-doped fiber (EDF), and a 25 km long single-mode fiber (SMF). The SMF provides RDFB via Rayleigh scattering. Due to the implementation of the half-open cavity structure and the gain generated by the EDF, the laser threshold can be significantly suppressed to 60 mW, and the slope efficiency of output lasing power against pump power is ∼0.9%. By adjusting the polarization controllers of the proposed two-stage Sagnac loop mirror, single-, double-, triple-, and quadruple-wavelength lasing channels in the range of 1527–1534 nm are achieved. In the case of quadruple-wavelength channel lasing, the optical signal noise ratio is up to 33 dB under the 180 mW pump power. The proposed random fiber laser can be applied in distributed sensing systems and biomedical imaging.

Poisson distribution of extreme events in radiation of random distributed feedback fiber laser.

In the present Letter, we experimentally investigate extreme events in the time dynamics of the random distributed feedback fiber laser. We find that the probability of extreme events depends on the wavelength of the generated light. On spectrum tails, we register extreme events with intensity up to 50 times higher than the average generation power. Analysis of return times between successive rogue waves reveals their exponential distribution. Further investigation proves that the appearance of extreme waves in laser radiation obeys Poisson law. Characteristic radiation time varies from nanoseconds to tens of microseconds for most intense waves.

Dual-wavelength random distributed feedback fiber laser with wavelength, linewidth, and power ratio tunability.

Owing to the special power distribution property, a random distributed feedback Raman fiber laser can achieve a high power spectrally flexible output with a low power spectrally tuning device. Here, an all-fiberized linearly polarized dual-wavelength random distributed feedback Raman laser with wavelength, linewidth, and power ratio tunability is demonstrated. By adopting two watt-level bandwidth adjustable optical filters, a spectrum-manipulable dual-wavelength output with nearly a 10 W output power is achieved. The wavelength separation can be tuned from 2.5 to 13 nm, and the 3 dB linewidth of the output can be doubled by increasing the bandwidth of the optical filter. The power ratio of each laser line can be tuned from 0 to nearly 100% with the help of two variable optical attenuators. A maximum output power of 9.46 W is realized, with a polarization extinction ratio up to 20.5 dB. The proposed dual-wavelength fiber laser can be employed as a pump source in frequency tunable, bandwidth adjustable terahertz microwave generation, and mid-infrared optical parametric oscillators.

Dual-wavelength random fiber laser incorporating micro-air cavity

A dual-wavelength random distributed feedback fiber laser with external micro-air cavity (MAC) is experimentally demonstrated. The structure that comprises of a fixed 200 μm air-gap distance between two flat-angle fiber-end facets behaves similarly to the role of reflectors. The generation of dual-wavelength lasing at 1552.5 and 1557.7 nm was achieved. The accomplishment is associated to the filtering effect of MAC superimposed with Raman gain spectrum. Equal peak power of approximately −12.7 dBm was attained at maximum 2.0 W pump power. In this case, the respective optical signal-to-noise ratios were 18.79 and 18.73 dB. Excellent stability of the spectral width was realized over 60 min observation time at room temperature, which denotes the practicality of this device in addition to the relatively simpler architecture.

Short-cavity random distributed feedback fiber laser with ultra-low threshold

We experimentally demonstrated a random distributed feedback fiber laser (RDFB-FL) with an ultra-low threshold, utilizing a highly nonlinear optical fiber (HNLF). A piece of HNLF was used as the random laser gain medium to resolve the contradiction between the lasing threshold and cavity length. Consisting of a half-open cavity structure, the proposed RDFB-FL had a lasing threshold as low as 0.408 W (record low) with a relatively short cavity length of 850 m. In a ring cavity, the lasing threshold could be further reduced to 0.284 W with a cavity length of 950 m by the combined action of distributed feedback and cavity feedback.

Random distributed feedback fiber lasers: Impact of third-order dispersion

In this paper, one of the most modern random lasers known as random distributed feedback fiber laser is investigated when the third-order dispersion (TOD) is taken into account. The laser characteristics are simulated based on the nonlinear Schrödinger equations (NLSEs) where the power evolution of three interacting waves: the pump, the forward and the backward Stokes waves, are investigated as they propagate down the fiber. The results show that due to TOD, the output characteristics of the laser are changed and particularly, the output power becomes asymmetrical. Moreover, the impacts of fiber nonlinear coefficient and input power on the output power and the output spectrum are studied.

Continuous-Wave Pumping Supercontinuum Generation in Random Distributed Feedback Laser Cavity

In this paper, we demonstrated a continuous-wave pumping supercontinuum generation in a random distributed feedback fiber laser with a completely open laser cavity. A broadband wavelength conversion was obtained by pumping a 36-km long TrueWaveREACH fiber in anomalous dispersion regime with a high power continuous-wave Raman laser. The spectral broadening was assisted via nonlinear mechanism such as modulation instability and stimulated Raman scattering. An extended 10-dB flat supercontinuum with 129-nm bandwidth spanning over C-, L-, and U-band wavelengths was generated in the forward direction of lasing cavity under 3.65-W pump power. The super-continuum exhibited excellent bandwidth stability in 60 minutes of lasing operation. A simultaneous generation of random Raman laser operating in the backward direction of cavity was also demonstrated within the same gain fiber. The simple laser cavity presented significant versatility in its generation of novel light sources for both telecommunication and applied science applications.

Random Distributed Feedback Fiber Laser Generating Cylindrical Vector Beams

The invention discloses a random distributed feedback fiber laser generating cylindrical vector beams. Because of the existence of random distributed feedback in the laser, the output cylindrical vector beam has the characteristic of low coherence. The laser mainly includes a highly reflective mirror, a mode output module, an amplifier module and a random distributed feedback module. According tothe invention, random distributed feedback is provided by a fiber resonant ring, and a cylindrical vector beam is output by a mode selection coupler. The random distributed feedback fiber laser of theinvention has the advantages of simple structure, high integration degree and low cost, and is suitable for special fields requiring low-coherence cylindrical vector laser sources.

Spatial location of correlations in a random distributed feedback Raman fiber laser.

Nonlinear interactions between different components of multiwavelength radiation are one of the main processes shaping properties of quasi-CW fiber lasers. In random fiber lasers, nonlinear influence may be more complicated, as there are no distinct longitudinal modes in radiation because of the random nature of the feedback. In this Letter, we experimentally characterize internal correlations in the radiation of a multiwavelength random distributed feedback fiber laser. An analysis of Pearson correlation functions allows us to spatially locate the area over the fiber laser length in which correlations are more likely to occur. This, in turn, leads us to the conclusion about the main mechanism of spectral correlations-the relative intensity noise transfer from the pump wave.

Open Cavity Hybrid Raman-Erbium Random Fiber Laser With Common Pump

A symmetrical 80-km open cavity erbium-integrated hybrid random distributed feedback fiber laser (HRFL) was proposed and experimentally demonstrated. A variation of pumping schemes and cavity lengths was first investigated prior to the integration of the EDF. The impact of Raman and EDF hybrid amplification was then investigated through EDF length variation. The proposed scheme used a single common pump to incite both Raman and erbium gain to produce a single peak at a 1567-nm wavelength with maximum OSNR of 62.37 dB. A maximum total output power generation of 1420 mW was achieved with high-slope efficiency of 38%. The proposed hybrid setup has shown improved performance despite using open-ended cavity sustained by only a single pump in contrast to previous more complex hybrid schemes. Prolonged chaotic regime manifesting spontaneous pulse burst was also observed before the stable regime. The simple operation with the high performance of the proposed configuration offers a great potential for long distance or remote access applications such as heavy metals sensing or even for biological hazard sensing.

Theoretical and experimental study of artificially controlled backscattering fiber using femtosecond laser fabrication

An artificially controlled backscattering (ACBS) fiber is theoretically proposed and experimentally verified using a femtosecond (fs) laser micromachining system. The backscattering power of the ACBS fiber per unit length is similarly defined as the one of the single mode fiber (SMF). We have calculated the relative reflecting power per unit length from a fiber with a reflector fabricated on an SMF core at 5576 m by the fs laser beam. The impact of the pulse energy of the fs laser and the reflector position on the performance of the ACBS fiber are then compared via observing the backscattering trace. The results show that the proposed ACBS fiber can enhance the backscattering of the SMF. High backscattering fibers (HBSFs) can be achieved via appropriate selection of fabrication parameters, offering an efficient way to shorten the fiber length and form a random distributed feedback fiber laser.

Ultra-long (290 km) remote interrogation sensor network based on a random distributed feedback fiber laser.

In this work, an interferometric sensor has been interrogated 290 km away from the monitoring station, reaching the longest distance in fiber optic sensing up to date. This has been attained by employing a double-pumped random distributed feedback fiber laser as the light source for a fiber optic low-coherence interferometry scheme. Additionally, the capability of the system to achieve coherence multiplexing for ultra-long range measurements (up to 270 km) has been proved, without presenting crosstalk between the sensors. The use of coherence multiplexing together with a random distributed feedback fiber laser addresses two of the main limitations of long-range sensing setups: their limited multiplexing capability and the need to reach the maximum monitoring distance.