Stable single longitudinal mode fiber ring laser based on polarization maintaining erbium doped fiber

A stable single longitudinal mode (SLM) fiber ring laser that incorporates polarization maintaining erbium doped fiber (PM EDF) acting as gain medium and saturable absorber is proposed and demonstrated. Both theoretical deviation and experimental result prove that optical intensity is time invariant when the laser operates in single longitudinal mode, the SLM operation can be approximately verified by optical intensity analysis, which is practical to analyze longitudinal mode in the application of engineering. The linewidth of the fiber ring laser is measured by the delayed self-heterodyne interferometery, and an acousto-optic frequency shifter is employed to shift the lasing frequency and eliminate zero frequency interfere. The SLM operation is verified by the scanning Fabry–Perot interferometer, whereas the lasing frequency drift slowly during a period of 2 h, PM EDF is proved to be effective on suppressing mode hopping and selecting longitudinal mode.     

Single-longitudinal-mode erbium-doped fiber laser with novel scheme utilizing fiber Bragg grating inside ring cavity

In this paper, we experimentally investigate a single-longitudinal-mode (SLM) S-band erbiumdoped fiber (EDF) laser with dualring scheme using a S-band fiber Bragg grating (FBG) inside the gain cavity to restrict the lasing mode. The proposed laser is constructed by two-ring cavities serving as the mode filters. The FBG inside the proposed laser scheme can retrieve the SLM operation. Moreover, the output performance of the proposed fiber laser is also analyzed and discussed.     

Stable single-longitudinal-mode fiber laser using PM FBG F-P etalon and PM fiber saturable absorber

we present a stable and high efficiency single-longitudinal-mode (SLM) fiber ring laser by using polarization-maintaining fiber Bragg grating Fabry-Perot (PM FBG F-P) etalon combining PM fiber saturable absorber. The PM FBG F-P etalon, which is directly fabricated in hydrogen-loaded PM fiber, is used as reflector and mode-selecting component to reduce the longitudinal-mode density greatly. Meanwhile, a segment un-pumped PM Er³⁺-doped fiber (EDF) serves as saturable absorber to suppress mode hopping and ensure the stable SLM operation. Stable SLM laser output at 1550.4 nm with linewidth of 2.0 kHz is observed. Laser output power is 43.7 mW for a pump power of 148 mW, optical-optical efficiency is 29.5% and signal-to-noise ratio (SNR) is larger than 55 dB.     

Stable single longitudinal mode erbium-doped silica fiber laser based on asymmetric linear three-cavity structure

We present a stable linear-cavity single longitudinal mode (SLM) erbium-doped silica fiber laser. It consists of four fiber Bragg gratings (FBGs) directly written in a section of photosensitive erbium-doped fiber (EDF) to form asymmetric three-cavity structure. The stable SLM operation at a wavelength of 1545.112 nm with a 3-dB bandwidth of 0.012 nm and an optical signal-to-noise ratio (OSNR) of about 60 dB is verified experimentally. In laboratory condition, the performance of power fluctuation of less than 0.05 dB observed from the power meter for 6 h and wavelength variation of less than 0.01 nm obtained from the optical spectrum analyzer (OSA) for about 1.5 h are demonstrated. The gain fiber length is no longer limited to only several centimeters for SLM operation because of the excellent mode-selecting ability of the asymmetric three-cavity structure. The proposed scheme provides a simple and cost-effective approach to realizing a stable SLM fiber laser.     

Stable single longitudinal mode erbium-doped silica fiber laser based on an asymmetric linear three-cavity structure

We present a stable linear-cavity single longitudinal mode (SLM) erbium-doped silica fiber laser. It consists of four fiber Bragg gratings (FBGs) directly written in a section of photosensitive erbium-doped fiber (EDF) to form an asymmetric three-cavity structure. The stable SLM operation at a wavelength of 1545.112 nm with a 3-dB bandwidth of 0.012 nm and an optical signal-to-noise ratio (OSNR) of about 60 dB is verified experimentally. Under laboratory conditions, the performance of a power fluctuation of less than 0.05 dB observed from the power meter for 6 h and a wavelength variation of less than 0.01 nm obtained from the optical spectrum analyzer (OSA) for about 1.5 h are demonstrated. The gain fiber length is no longer limited to only several centimeters for SLM operation because of the excellent mode-selecting ability of the asymmetric three-cavity structure. The proposed scheme provides a simple and cost-effective approach to realizing a stable SLM fiber laser.     

Wavelength-selection erbium fiber laser with single-mode operation using simple ring design

In this demonstration, we propose and experimentally investigate a wavelength-selection erbium-doped fiber (EDF) laser in single-longitudinal-mode (SLM) by using simple fiber ring scheme design. We use a tunable bandpass filter (TBF) inside the gain cavity to restrict the lasing frequency. The proposed ring cavities can also serve as the mode filters for side mode suppression. Based on the simple ring cavity design, the mode hopping can be avoided to achieve SLM output. The TBF inside the laser scheme also obtains the wavelength tuning in the range of 1520.02 to 1562.02 nm. In addition, the output performance of the proposed fiber laser has also been discussed.     

Multi-wavelength hybrid gain fiber ring laser based on Raman and erbium-doped fiber

A stable and uniform multi-wavelength fiber laser based on the hybrid gain of a dispersion compensating fiber as the Raman gain medium and an erbium-doped fiber (EDF) is introduced. The gain competition effects in the fiber Raman amplification (FRA) and EDF amplification are analyzed and compared experimentaUy. The FRA gain mechanism can suppress the gain competition effectively and make the present multi-wavelength laser stable at room temperature. The hybrid gain medium can also increase the lasing bandwidth compared with a pure EDF laser, and improve the power conversion efficiency compared with a pure fiber Raman laser.     

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.     

Effect of doped fiber length on the stretch pulses of a mode-locked erbium-doped fiber laser

A passively self-starting mode-locked fiber ring laser is demonstrated using a highly concentrated Erbium doped fiber (EDF) with a saturable absorber. The effect of EDF length on the performance of the laser is investigated. Stable stretched pulses are obtained at wavelength region of 1560nm with a repetition rate ranging from 10.1 to 12.1 MHz and a pulse width stretching from 0.52 to 0.75 ps as the EDF length is reduced from 4.5 to 1.5 m. The repetition rate goes higher as the cavity length decreases when a shorter EDF is used but the pulse width reduces as the EDF length increases since the total group velocity dispersion (GVD) in the cavity is close to zero. The article is published in the original.     

Graphene-based passively Q-switched dual-wavelength erbium-doped fiber laser

We demonstrate a compact Q-switched dual-wavelength erbium-doped fiber (EDF) laser based on graphene as a saturable absorber (SA). By optically driven deposition of graphene on a fiber core, the SA is constructed and inserted into a diode-pumped EDF laser cavity. Also benefiting from the strong third-order optical nonlinearity of graphene to suppress the mode competition of EDF, a stable dual-wavelength Q-switching operation has been achieved using a two-reflection peak fiber Bragg grating as the external cavity mirror. The Q-switched EDF laser has a low pump threshold of 6.5 mW at 974 nm and a wide range of pulse-repetition rate from 3.3 to 65.9 kHz. The pulse duration and the pulse energy have been characterized. This is, to the best of our knowledge, the first demonstration of a graphene-based Q-switched laser.     

Tunable single-longitudinal-mode SOA-based fiber laser based on the spectral narrowing effect in a dispersion-shifted fiber

A tunable single-longitudinal-mode(SLM) semiconductor optical amplifier(SOA)-based fiber laser based on a dispersion-shifted fiber(DSF) is proposed and successfully demonstrated. SLM operation is obtained due to the spectral narrowing effect resulting from inverse four-wave mixing in a DSF. A tunable optical filter performs wavelength selection function. By inserting a length of DSF in the laser cavity, SLM lasing can possibly be obtained when laser oscillation is stably established after traveling through the DSF many roundtrips. Stable tunable SLM oscillation with a signal-to-noise ratio as high as 65 dB over a wavelength range of about 35 nm is achieved experimentally, and each spectral linewidth is less than 6.5 kHz.     

Discrimination of strain and temperature based on a polarization-maintaining photonic crystal fiber incorporating an erbium-doped fiber

A simple sensing method for simultaneous measurement of temperature and strain is investigated by using a Sagnac fiber loop mirror composed of a polarization-maintaining photonic crystal fiber (PM-PCF) incorporating an erbium-doped fiber (EDF). Amplified spontaneous emission created by a pumped EDF is transmitted to a Sagnac fiber loop mirror. The interference between two counter-propagating signals in a Sagnac fiber loop mirror generates a periodic transmission spectrum with respect to wavelength. When external temperature is increased, the transmission peak power reduces because the amplified spontaneous emission of the EDF is decreased by the applied temperature change (0.04 dB/°C). The peak wavelength is shifted into the shorter wavelength because of the negative temperature dependence of the birefringence of the PM-PCF (0.3 pm/°C). As the applied strain increases, the peak wavelength of the transmission spectrum of the Sagnac loop mirror incorporating the EDF shifts into a longer wavelength (1.3 pm/με) because the phase change of the proposed sensing probe is directly proportional to the applied strain. The transmission peak power, however, is not changed by the applied strain. Since the source and the sensing probe are integrated, the overall system configuration is significantly simplified without requiring any additional broadband light source. Therefore, it is possible to simultaneously measure temperature and strain by monitoring the variation of transmission peak power and peak wavelength, respectively.     

Erbium doped fiber ring laser for optical wavelength conversion

We experimentally investigate the gain saturation effect of a piece of 8 m long Erbium doped fiber (EDF), we introduce a theoretical model for the EDF ring loop, and our simulation results show very good cross-gain modulation (XGM) and wavelength conversion. We also experimentally investigate the XGM in an EDF ring loop system. Based on the study of the XGM in the EDF ring loop system, a wavelength conversion is designed with the EDF ring loop system. The EDF ring loop systems as a wavelength conversion is experimentally demonstrated by converting a sinusoidal modulated optical signal at wavelength of 1551 nm to an optical signal at wavelength of 1553.3 nm.     

Dual-wavelength narrow-linewidth fiber laser based on F-P fiber ring filter

A dual-wavelength fiber laser with a narrow-linewidth, based on a P-F fiber filter has been proposed. Polarization-maintaining fiber Bragg grating (PM-FBG) and a F-P fiber filter are introduced based on the traditional fiber laser. PM-FBG is used as the wavelength selection device. The fiber F-P filter consists of two optical couplers and a section of un-pumped erbium-doped fiber (EDF). Due to the delay of cavity and the loss generated by the EDF, the filter has comb spectral response. The incorporation of the fiber F-P filter leads to the suppression of undesirable modes. At the room temperature, under 980 nm LD pumped, the maximum output of the two wavelengths is respectively ?2.259 dBm and 0.568 dBm, with the 3-dB bandwidth separately 0.1 nm and 0.14 nm, realizing the narrow linewidth and dual-wavelength output.     

Passive erbium-doped fiber seed photon generator for high-power Er(3+)-doped fiber fluorescent sources with an 80-nm bandwidth

A novel structure that converts wasted backward amplified spontaneous emission (ASE) to seed photons for the amplifier stage is suggested for a high-power erbium-doped fiber (EDF) broadband source. A considerable increase in output power and bandwidth extension was achieved by placement of a segment of passive EDF in front of the amplifier stage, thus recycling backward ASE as the secondary pumping source for the passive EDF seed photon generator. Experimental results showed a dramatic increase in output ASE power of more than 10 dB for most radiation bands from 1540 to 1620 nm with the simple addition of an unpumped EDF segment to the ordinary fluorescence-source structure.     

Stable SOA-based multi-wavelength fiber ring laser using Sagnac loop mirror incorporating a high-birefringence photonic crystal fiber

Multi-wavelength fiber laser using semiconductor optical amplifier (SOA) and Sagnac loop mirror (SLM) incorporating a newly designed high-birefringence photonic crystal fiber (HB-PCF) is experimentally demonstrated. The modal birefringence of the fabricated HB-PCF is estimated to be 1.1 × 10⁻³. Mainly, by adjusting a polarization controller in the fiber ring laser, the proposed fiber laser can operate at six lasing wavelengths with 2.7 nm intervals, the signal-to-noise ratio (SNR) of around 30 dB. The output power stability is 0.8 dB. In addition, we obtained near-perfect temperature independence in our multi-wavelength fiber laser system. The temperature dependence of the SLM is around 3 pm/°C.     

Single-longitudinal-mode erbium-doped fiber laser based on a fiber Bragg grating Fabry-Perot filter

A novel single-longitudinal-mode (SLM) erbium-doped fiber laser with a simple linear cavity based on a fiber Bragg grating Fabry-Perot filter (FBG-FPF) and a narrowband (～0.06 nm) FBG is proposed and demonstrated experimentally. Two uniform FBGs form the FBG-FPF, which has two ultranarrow transmission bands with a bandwidth of 0.12 pm and a wavelength spacing of 0.095 nm. By slightly tuning the central wavelength of the narrowband FBG, SLM lasing at 1549.658 or 1549.563 nm (corresponding to the two transmission peaks of the FBG-FPF) is achieved with a laser output power of ～4 mW, when the pump power is ～75 mW.     

Simple erbium-doped dual-ring fiber laser configuration for stable and tunable dual-wavelength output

We propose and experimentally investigate a stable and tunable dual-wavelength erbium-doped fiber (EDF) dual-ring laser scheme. Here, two tunable bandpass filters (TBFs) are used inside the dual-ring gain cavity to generate dual-wavelength lasing. And, due to the gain competition of the EDF gain cavity, the mode-spacing (Δλ_s) of lasing dual-wavelength will be limited at different operating wavelengths. Hence, the minimum and maximum mode-spacing in the proposed EDF laser scheme are 0.75 and 15.35 nm in C-band range. Besides, the output performances of proposed fiber laser have also been studied and analyzed.     

Passive Q-switching of a fiber laser using a side-polished birefringent fiber with index matching gel spread on the flat side

We experimentally demonstrate the use of a side-polished birefringent fiber with index matching gel spread on the flat side as a passive Q-switch for the implementation of an all-fiberized, erbium-doped fiber (EDF)-based Q-switched laser. It is shown that Q-switched pulses with a ~2.5-μs temporal width are readily achievable from an EDF ring cavity using the side-polished birefringent fiber-based Q-switch. The tuning capability of the pulse width and the repetition rate by changing the pump power is also investigated.     

Switchable single-longitudinal-mode dual-wavelength erbium-doped fiber ring laser based on one polarization-maintaining fiber Bragg grating incorporating saturable absorber and feedback fiber loop

Switchable single-longitudinal-mode (SLM) dual-wavelength erbium-doped fiber ring laser based on one polarization-maintaining fiber Bragg grating (PMFBG) is demonstrated. Due to the enhancement of the polarization hole burning (PHB) by the PMFBG, the laser can be designed to operate in stable dual-wavelength or wavelength-switching modes with a wavelength spacing of 0.336 nm at room temperature by adjusting a polarization controller (PC). The stable SLM operation is guaranteed by a compound-ring cavity and a saturable absorber (SA). The optical signal-to-noise ratio (OSNR) is over 45 dB. The amplitude variation in nearly one and half an hour is less than 0.2 dB.