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We reported an erbium-doped fiber ring laser (FRL) displacement sensor based on a single-mode fiber (SMF) loop tied into the laser cavity. The proposed fiber loop structure acts as the sensing head as well as the filter of the FRL. A good linear relationship is obtained both in principle and in experiments between the displacement of one end of the loop and the central wavelength of the proposed FRL. The average sensitivity of this sensor reaches 227.5 pm/mm in the displacement range of 0–30 mm. High optical signal-to-noise ratio ( $\sim 52$ dB) and narrow 3-dB bandwidth (<0.7 nm) are also achieved due to the FRL structure. Moreover, the macrofiber loop, as the key sensor head of the proposed sensing system, is tied with simple SMF without removing the coating, which has obvious advantages of firm structure with a wide range of displacement measurement and easy fabrication with low-cost SMF. [ABSTRACT FROM PUBLISHER]

In this letter, we investigate a novel refractive index sensor based on a simple fiber ring laser incorporating a bent fiber filter. The bent fiber structure acted as a fiber filter and a sensing element. The bent fiber filter is made of a section of semicircular bare standard single-mode fiber with a selected bending radius. The gain medium (erbium-doped fiber) is pumped by a 980 nm wavelength laser. Laser emission around 1557.3 nm with a low pumping threshold is obtained when a bent fiber filter with 4.5 mm bending radius is used. The 3 dB bandwidth of the laser is less than 0.3 nm, which is beneficial to high precision sensing. The medium refractive index varied from 1.3259 to 1.3730, and the relationship between the lasing wavelength and the medium refractive index exhibited linear behavior, where good linearity of about 60 nm/RIU was obtained. Finally, we fabricated sensor prototypes with different bending radii. When a 4 mm bending radius was selected, the maximum sensitivity is 124 nm/RIU. The fabrication of the proposed refractive index sensor is simple and cost-effective, which makes it a good candidate for the potential sensing applications. [ABSTRACT FROM PUBLISHER]

In this letter, a narrow line-width ytterbium-doped fiber ring laser with a fiber Bragg grating inside the cavity is proposed and experimentally demonstrated. In order to realize single longitudinal mode (SLM) output, an un-pumped ytterbium-doped fiber is used as an SLM selector. First, the effect of the coupler output ratio on the output power and the threshold power is discussed in this proposed laser, and the coupler output ratio of 30% is adopted at last. Furthermore, the spectrum and frequency spectra are analyzed to obtain the line width and frequency stability. Finally, the output power with fluctuation in half an hour is measured to evaluate the power stability. The results show that the output power of 7 mW, signal-to-noise ratio greater than 65 dB at 1069 nm, line width less than 500 Hz, and power stability below 1.5% can be achieved for the laser. [ABSTRACT FROM PUBLISHER]

A fiber ring laser with a carbon nanotube mode-locker that allows bidirectional oscillation is experimentally demonstrated in the L-band. Through leveraging a double-peak intracavity gain spectrum, two pulse trains in two nonoverlapping wavelength bands are shown to counter-propagate in the simple ring cavity. Ultrashort soliton pulses of \(\sim 800\) fs or less can be stably generated in both directions. It is also demonstrated that bidirectional operation within one of the wavelength bands can also be achieved with much smaller center wavelength separations by tuning the gain spectrum. The repetition rates of the two pulse trains have a slight difference due to the intracavity dispersion. Thus, the directional- and wavelength-multiplexed output from such a cavity-diversity-enabled ultrafast laser could potentially be leveraged in those applications requiring a dual-comb source. [ABSTRACT FROM PUBLISHER]

We have demonstrated a switchable dual wavelength fiber ring laser with a high degree of polarization output by using an intracavity 3-stage all fiber Lyot filter. The filter is formed by concatenating four 45° tilted fiber gratings separated by polarization maintaining fibers with a length ratio of 1:2:4 (20, 40, and 80 cm), giving a compact integrated configuration with reduced bandwidth. Switchable dual wavelength or single wavelength output at 1533.5 and 1563.3 nm has been achieved. The output lasing is considerably stable owing to the in-phase mode-selecting function of the multistage Lyot filter, and has a very high degree of polarization higher than 99.9%. [ABSTRACT FROM PUBLISHER]

We propose and experimentally demonstrate an all-pole-type cavity structure to force single longitudinal mode (SLM) operation in fiber lasers. The proposed structure is based on the modified version of the Smith predictor, which compensates delay in a closed-loop feedback system. This structure is applicable to arbitrary wavelengths and gain media, does not limit the tunability range of the laser, and does not require few centimeters long loops or Fabry–Pérot tunable filters to achieve SLM operation. Thus, the major drawbacks of the conventional SLM forcing mechanisms are alleviated. Therefore, this structure can be considered as a universal approach to SLM operation in fiber lasers. To exemplify this structure, an erbium-doped fiber ring laser in continuous-wave mode is implemented. The SLM operation is confirmed from the RF spectrum over a 10 GHz bandwidth, and the laser is tunable over 62 nm from 1512 to 1574 nm [ABSTRACT FROM PUBLISHER]

We report on an erbium-doped fiber ring laser using a glass microdisk as a narrow linewidth reflection mirror. The microdisk is made of optical fibers through simple fabrication steps and it has a measured Q-factor of 7.8 × 106. The fiber ring laser has a linewidth of less than 0.16 pm, wavelength stability of ±1.2 pm, and power stability of ±0.3 dB. [ABSTRACT FROM PUBLISHER]

We newly propose a lambda/4-shifted distributed-feedback laser diode (DFB-LD) that employs a fiber ring cavity configuration and which incorporates an ultranarrow band fiber Bragg grating (FBG) in the cavity. By controlling the FBG wavelength to match the oscillation wavelength of the DFB-LD, we achieved stable single-mode oscillation where the sidemodes of the DFB-LD and the Fabry-Perot modes induced by the ring configuration were sufficiently suppressed. Large performance improvements with an optical signal-to-noise ratio of 85 dB and a linewidth of 7 kHz were obtained. [ABSTRACT FROM PUBLISHER]

We experimentally demonstrate a tunable C-band erbium-doped fiber ring laser with ultra-narrow linewidth using a tunable phase-shifted linearly chirped fiber Bragg grating (PS-LCFBG) as an intracavity ultra-narrowband filter. The center wavelength of the PS-LCFBG with an ultra-narrow bandwidth of <10 pm is thermally tuned by scanning a current-controlled resistance wire along its length. The laser has an ultra-narrow linewidth of <1.52 kHz, a tuning range of ~15.5 nm, a good side-mode suppression ratio of >30 dB, an output power of ~10 dBm, a small power variation of <0.2 dB, and a small wavelength variation of <0.01 nm. The laser structure is simple and cost-effective. [ABSTRACT FROM PUBLISHER]

We propose and demonstrate the use of fiber ring lasers and Fabry-Perot laser diodes (FP-LDs) for wavelength-division-multiplexing access networks. The fiber ring laser not only generates downstream data traffic but also serves as the wavelength-selecting injection light source for the FP-LD located at the subscriber site. Moreover, it is wavelength tunable and can be applied to dynamic wavelength assignment networks. The ring laser has a tunable range of 30 nm in the C-band and a power fluctuation smaller than 0.6 dB. For 10-Gb/s downstream and 1.25-Gb/s upstream transmissions over 10-km single-mode fiber, power penalties less than 0.9 and 0.5 dB are demonstrated, respectively. A 40-dB sidemode suppression ratio is obtained for the FP-LD injection-locking at 1544.8 nm. [ABSTRACT FROM PUBLISHER]

We demonstrate a novel approach to increase the Q-switching repetition rate of the fiber ring laser. This Q-switched fiber laser integrates an apodized fiber-Bragg-grating (FBG) reflector and a Fabry-Perot (FP) etalon constructed from cascaded chirped FBGs into the cavity. The apodized FBG reflector acts as wavelength discriminative component for oscillation, while the FP etalon is tuned periodically using the piezoelectric transducer (PZT) and functions as a Q-switching component. By adjusting the tuning range of the FP etalon, we obtain 3.5-, 7-, and 14-kHz Q-switched pulses train with constant PZT modulation frequency of 3.5 kHz. [ABSTRACT FROM PUBLISHER]

In this letter, a new study of self-mixing speckle in an erbium-doped fiber ring (EDFR) laser and its application to velocity sensing is presented. We have experimentally built a fiber laser based on a ring cavity by using a packaged erbium-doped fiber amplifier and applied it to the self-mixing speckle experiments. We have also given theoretical analysis of the model of self-mixing speckle in the EDFR laser and the variation of the output power of the laser is deduced. The speckle signal has been statistically analyzed and found submitting to Gaussian distribution. For its utility to velocity sensing, the speckle signals at different velocities are processed through calculating the number of box by the fractal theory. A linear relationship between the number of box and velocity is obtained. The experimental result shows that the self-mixing speckle signal in EDFR laser can be used in velocity sensing. [ABSTRACT FROM PUBLISHER]

Tunable signal generation in the gigahertz to terahertz range was demonstrated by photomixing of a chirped optical pulse and its time-delayed replica. The chirped pulses were created by chromatically dispersing femtosecond pulses from a mode-locked fiber ring laser, and frequency tuning was achieved by adjusting the time delay and/or the amount of group velocity dispersion. It is shown that the signal phase is locked to the femtosecond-laser pulses and that an extinction ratio close to 100% can be obtained. Analytical calculations on the signal chirp introduced by higher order dispersion are also presented and compared with the experimental data [ABSTRACT FROM PUBLISHER]

All-optical clock recovery (CR) from 10-Gb/s nonreturn-to-zero differential phase-shift-keying (NRZ-DPSK) signal is demonstrated experimentally by introducing the chromatic-dispersion-induced clock tone into a free-running semiconductor optical amplifier (SOA)-based fiber ring laser for achieving mode-locking. Since no special component is required for NRZ-DPSK demodulation, our proposed method is very promising because of its simple configuration and better stability. The good performance of our proposed configuration is fulfilled with a 20-km standard single-mode fiber to regenerate clock tone of the NRZ-DPSK signal. The recovered clock signal with the extinction ratio of 17 dB and the root-mean-square timing jitter of 718 fs is achieved under 231-1 pseudorandom binary sequence NRZ-DPSK signals measurement [ABSTRACT FROM PUBLISHER]

We analyze the impact of pump phase modulation (PM) on the bandwidth of single-pumped fiber-optic parametric amplifiers. The measured values and the calculations show that the impact on bandwidth by pump PM is small compared to the impact from the dispersion curvature. A bandwidth of 100 nm with a gain of 11.5plusmn2 dB is achieved. This is also used to build a widely tunable fiber ring laser [ABSTRACT FROM PUBLISHER]

A stable 50-pm-spaced triple-wavelength fiber ring laser with nearly equal output power at each lasing line is achieved experimentally by incorporating a triple-transmission-band fiber Bragg grating filter in the fiber ring cavity. Such a laser will be very useful in applications requiring closely spaced multiwavelength components [ABSTRACT FROM PUBLISHER]

Tunable wavelength conversion of picosecond (ps)-pulses based on cascaded sum- and difference frequency generation is proposed and demonstrated by use of a fiber ring laser incorporating a periodically poled lithium niobate waveguide and two parallel-arranged tunable filters (TFs). The pulsed signal with 40-GHz repetition rate and 1.57-ps pulsewidth is employed. No external pump and control sources are required in the wavelength converter. By properly adjusting two TFs to change the lasing pump and control wavelengths, flexible wavelength conversion from a changeable input signal wavelength to a variable output idler wavelength is achieved [ABSTRACT FROM PUBLISHER]

Four pi-phase shifts are introduced in a uniform fiber Bragg grating (FBG) structure to realize a quadruple-transmission-band filter with ultranarrow 40-pm wavelength spacing. Four separate single-wavelength lasings at 1552.60, 1552.63, 1552.67, and 1552.71 nm, and three pairs of dual-wavelength lasings among above four wavelengths, are achieved stably by incorporating the quadruple-transmission-band FBG filter in a fiber ring cavity with a tunable uniform FBG acting as coarse frequency selection. This new kind of laser will be very useful in applications requiring closely spaced and tunable single- or dual-wavelength components [ABSTRACT FROM PUBLISHER]

A low beat-noise highly polarized tunable fiber ring laser is proposed and experimentally demonstrated by using a Fabry-Pe´rot laser diode (FP-LD), which acts as a high-pass filter to suppress both the beat noise and TM-polarized light. The wavelength of the fiber ring lasers can be tuned from 1536.82 to 1570.72 nm in 1.12-nm steps and its maximum output power is about +3 dBm. The degree of polarization and extinction ratio of the laser output are about 99% and 60 dB, respectively. The beat-noise with and without the FP-LD was reduced dramatically by 50 dB. [ABSTRACT FROM PUBLISHER]

All-photonic label-switching of weight four spectral packet labels (concurrent quadruple wavelength conversion) is demonstrated for optical multiprotocol label-switching networks. The experimental setup is based on cross-gain modulation in a fiber ring laser using a semiconductor optical amplifier gain medium and uses commercially available components. Static transfer functions and step response measurements for various input-output label-switching combinations show that a noisy input label with small extinction ratio can be switched to a clean, amplified, output label [ABSTRACT FROM PUBLISHER]

We demonstrate a single-frequency and wavelength-switchable fiber ring laser obtained by a Lyot filter used in combination with a sampled fiber Bragg grating and a saturable absorber. The operating wavelength of the laser can be tuned, with a constant 0.8-nm step, in the range 1552.6-1555.8 nm. The tuning mechanism works on the rotation of the polarization of Lyot filter input signal. The structure of the laser is very simple regarding its characteristics: an output power of 6 dBm, with a signal-to-noise ratio higher than 60 dB and a spectral linewidth of 8 kHz. [ABSTRACT FROM PUBLISHER]

A high-power simultaneous multiwavelength lasing in an Er3+-Yb3+ codoped double-cladding fiber (EYCDF) ring laser is demonstrated based on a wavelength-dependent filter through spatial mode beating within the multimode fiber section. We have investigated the relationship between the lasing wavelengths and the length of the EYCDFs. The experimental results indicate that both the number of lasing wavelength lines and the spacing between two adjacent lasing lines can be controlled by the changes of the lasing light polarization states. [ABSTRACT FROM PUBLISHER]

A novel single-longitudinal-mode (SLM) fiber ring laser that incorporates an equivalent phase-shifted fiber Bragg grating acting as an ultra-narrow bandpass filter in the laser cavity is proposed. The equivalent phase-shifted fiber Bragg grating has an ultra-narrow transmission bandwidth which ensures an SLM lasing. Stable SLM operation without mode hopping is demonstrated. [ABSTRACT FROM PUBLISHER]

A wavelength-switchable La-codoped bismuth-based erbium-doped fiber ring laser with the capability to switch to one of 35 lasing wavelengths, spaced at 0.8 nm from 1545 to 1575 nm, is reported. Excellent wavelength stability of better than 1 pm and power fluctuation of less than 0.15 dB were observed during a 2-h stability test. [ABSTRACT FROM PUBLISHER]

Ultrawide-band tunable fiber ring lasers using 84.6-cm-long lanthanum-codoped bismuth-based erbium doped fiber and a narrow-band tunable microelectromechanical system filter are reported. The fiber ring lasers can be continuously tuned from 1520 to 1626 nm, covering both the C- and L-bands. The laser has two outputs; the high output power port exhibits better than 35-dB wavelength extinction ratio, and the second output has much lower power but exhibits a large extinction ratio of better than 60 dB. [ABSTRACT FROM PUBLISHER]

Rational harmonic mode-locking of an Erbium-doped fiber ring laser (EDFL) at repetition frequency of 40 GHz is demonstrated by using a purely loss-modulated Fabry-Pe´rot laser diode (FPLD) at 1 GHz. The FPLD is neither lasing nor gain-switching, which requires a threshold modulation power of 18 dBm to initiate harmonic mode-locking of the EDFL. After chirp compensation, the nearly transform-limited pulsewidth and spectral linewidth of 3 ps and 1.3 nm are obtained at repetition frequency of 40 GHz, which corresponds to a time-bandwidth product of 0.31. The EDFL gradually evolves from harmonic mode-locking to injection-locking mode as the FPLD changes from loss-modulation to gain-switching mode by increasing its dc driving current. [ABSTRACT FROM PUBLISHER]

We describe and demonstrate a tunable triple-wavelength erbium-doped fiber ring laser along with a method of measuring polarization-mode dispersion (PMD) in optical fibers based on a broad-band orthogonal-pump four-wave mixing in a semiconductor optical amplifier. The measured PMD results for optical fibers are in good agreement with values measured by means of commercial PMD testing equipment. [ABSTRACT FROM PUBLISHER]

We report on subharmonic optical clock recovery (OCR) at 10 GHz from 160-Gb/s optical time-division multiplexed signals. The OCR circuit is based on a passively mode-locked principle in a fiber ring laser that utilizes fast gain dynamics of a linear semiconductor optical amplifier. To decrease the jitter amount in the clock pulse considerably, postelectrical signal processing is performed. The recovered clock is a 1.8-ps 10-GHz pulse train with 0.37 pulsewidth-bandwidth product. [ABSTRACT FROM PUBLISHER]

A simple configuration to perform wavelength switching in an actively mode-locked fiber ring laser is demonstrated. A Fabry-Perot laser diode was used as a modulator and a HiBi fiber loop mirror was used as a periodic multichannel wavelength filter in the cavity. By setting the channel spacing of nm can be achieved by tuning the fiber loop mirror filter. In the wavelength-switched process, the modulation frequency was not required to be changed [ABSTRACT FROM PUBLISHER]

A simple mode-locked fiber ring laser for generating wavelength-switched picosecond pulses was developed in which a laser diode played the role of both an intensity modulator and a tunable filter. A serially cascaded sampled fiber Bragg grating predefined the set of four allowable output wavelengths spaced 1.6 nm apart. Wavelength switching between the longest and shortest wavelengths required only a temperature change of the laser diode by 7.63°C [ABSTRACT FROM PUBLISHER]

All-optical clock recovery based on injection mode locking of a fiber ring laser is demonstrated by utilizing a fast semiconductor saturable absorber. The recovered clock is jitter free and completely insensitive to the state of polarization of the injection signal. Moreover, the clock wavelength can be tuned over the whole gain bandwidth of the EDFA [ABSTRACT FROM PUBLISHER]