Dual-wavelength fiber grating laser in linear overlapping cavity

We report a switchable dual-wavelength fiber grating laser in linear overlapping cavity. The laser features two overlapping cavities sharing a single Yb-doped gain medium fiber and two sets of fiber Bragg gratings. A coiling fiber setup is inserted into the 1035 nm laser cavity. Given that the bending loss is inversely related to the bending radius, the cavity loss of 1035-nm can be modulated. Modulating the bending loss facilitates the switching of the fiber grating laser to a single-or dual-wavelength output at 1030 or 1035 nm and convenient tuning of the power ratio of the two wavelengths. An approximately 152.6-mW output power and up to 38-dB polarization extinction ratio are observed. The simultaneous lasing at I030 and 1035 nm is a qualified seeder source for amplification to high power scale and can be applied to difference frequency generation of a terahertz signal. This dual-wavelength fiber grating laser is a potential pump source for generating terahertz radiation using a novel approach.     

Switchable dual-wavelength fiber ring laser featuring twin-core photonic crystal fiber-based filter

A simple configuration for the generation of a switchable dual-wavelength fiber ring laser is presented.The proposed configuration employs a short twin-core photonic crystal fiber acting as a Mach–Zehnder interferometer at room temperature.A polarization controller is further utilized to enable switchable dualwavelength operation.     

High OSNR and simple configuration dual-wavelength fiber laser with wide tunability in S+C+L band

A simple configuration dual-wavelength fiber laser,by combining the first-order Brillouin laser and the residual pump laser,is proposed and experimentally demonstrated.A 1 km long single-mode fiber is used as the stimulated Brillouin scattering gain medium pumped by a narrow linewidth tunable laser source(TLS).Through simply adjusting the TLS output power,power-equalized dual-wavelength lasing can be achieved with a high optical signal to noise ratio(OSNR) of 80 d B.With the good tunability of the TLS,the dual-wavelength fiber laser has a tunable range of ～130 nm,and simultaneously the beat frequency of the two lasing wavelengths can be tuned from 10.1875 to 11.0815 GHz with the tunable range of 0.8940 GHz.The high stability of the dualwavelength operation is experimentally verified by the measured beat frequency fluctuation of ≤6 MHz in 1 h and power fluctuation of ≤0.03 d B in 2 h.The temporal characteristics of the fiber laser are also investigated experimentally.The fiber laser will find good applications in fiber sensing and microwave photonics areas.     

A Proposal and Demonstration for Photonic Generation of a Microwave Signal by Incorporating a Microring Resonator

A proposal for photonic generation of a microwave signal is presented by employing a dual wavelength erbiumdoped fibre ring laser. In the laser, a microring resonator is cascaded with a tunable bandpass filter to serve as a dual-wavelength selector, an unpumped polarization maintaining erbium-doped fibre is used as a saturable absorber. By replacing the microring resonator with a delay interferometer to verify the proposal, a wavelengthtunable dual wavelength single longitudinal mode laser is demonstrated, and a microwave signal at 10.01 GHz with a linewidth of less than 25 kHz is obtained by beating the two wavelengths at a photodetector.     

Three-channel dual-wavelength fiber laser based on a digital micromirror-device processor and photonic crystal fiber

A stable three-channel dual-wavelength fiber ring laser is proposed and experimentally demonstrated. The digital micromirror-device(DMD) processor can select and recirculate any dual waveband from the gain spectrum of the erbium-doped fiber at each channel. The uniform and stable dual-wavelength oscillation is obtained by a highly nonlinear photonic crystal fiber, which causes two degenerate the four-wave-mixing processes. By loading different reproducibility diffraction gratings on the optoelectronic DMD processor, the laser can be operated stably in a three-channel dual-wavelength scheme at room temperature. The power fluctuation of each laser channel is less than ～0.02 d B.     

Generation of high-energy dual-wavelength domain wall pulse with low repetition rate in an HNLF-based fiber ring laser

The generation of high-energy dual-wavelength domain wall pulse with a low repetition rate is demonstrated in a highly nonlinear fiber （HNLF）-based fiber ring laser. By introducing the intracavity birefringence-induced spectral filtering effect, the dual-wavelength lasing operation can be achieved. In order to enhance the cross coupling effect between the two lasing beams for domain wall pulse formation, a 215-m HNLF is incorporated into the laser cavity. Experimentally, it is found that the dual-wavelength domain wall pulse with a repetition rate of 77.67 kHz could be efficiently obtained through simply rotating the polarization controller （PC）. At a maximum pump power of 322 mW, the 655-nJ single pulse energy in cavity is obtained. The proposed configuration provides a simpler and more efficient way to generate high energy pulse with a low repetition rate.     

Blue light generation in photonic crystal fibers with 1-μm femtosecond laser pulses

Using 300-fs 1039-nm Yb-doped fiber laser, we experimentally demonstrate blue light generation in a high-△ and high nonlinear photonic crystal fiber (PCF). The zero dispersion wavelength of PCF is 793 nm, detuning 245.8 nm from the pump wavelength. PCF allows a frequency conversion exceeding the octave of pump wavelength. The visible component of the measured output spectrum occurs in the fundamental mode and spans from 391.3 to 492.3 nm. The peak wavelength of 441.8 nm has a frequency detuning of 390 THz from the pump wavelength of 1039 nm.     

Photonic generation of amplitude-and phase-modulated microwave signals with frequency and modulation bit-rate tunability

A photonic approach for the generation of an amplitude- and phase-modulated microwave signal with tun-able frequency and modulation bit-rate is proposed and demonstrated. Two coherent optical wavelengths are generated based on external modulation by biasing a Mach-Zehnder modulator (MZM) at the minimum transmission point to generate ±1-order optical sidebands while suppressing the optical carrier. The two sidebands are sent to a circulator and are then spectrally separated by a fiber Bragg grating notch filter. With one sideband being amplitude-modulated at another MZM and the other being phase-modulated at a phase modulator, a frequency-tunable amplitude-and phase-modulated microwave signal is generated by beating the two sidebands at a photodetector. The proposed technique is investigated theoretically and experimentally. As a result, a 20-GHz amplitude-modulated, 20-GHz phase-modulated, and 25-GHz amplitude-and phase-modulated microwave signals with tunable modulation bit-rate are experimentally generated.     

325 MHz and near transform-limited pulse output directly from an Er：fiber ring laser

A compact Er:fiber ring laser operated at a fundamental repetition rate of 325 MHz is reported.Two gain fibers with opposite dispersion are employed to shorten the fiber laser cavity for high repetition rate and soliton-like pulse generation without losing gain and compactness.The spectral bandwidth of the output pulse is 24 nm and the direct pulse duration is 123 fs without extra-cavity compression,which are values near the transform-limited range.     

Dispersion flattened photonic crystal fiber with high nonlinearity for supercontinuum generation at 1.55 μm

A robust design for a photonic crystal fiber (PCF) based on pure silica with small normal dispersion and high nonlinear coefficient for its dual concentric core structure is presented.This design is suitable for flat broadband supercontinuum (SC) generation in the 1.55-μm region.The numerical results show that the nonlinear coefficient of the proposed eight-ring PCF is 33.8 W -1 ·km -1 at 1550 nm.Ultraflat dispersion with a value between -1.65 and -0.335 ps/(nm·km) is obtained ranging from 1375 to 1625 nm.The 3-dB bandwidth of the SC is 125 nm (1496–1621 nm),with a fiber length of 80 m and a corresponding input peak power of 43.8 W.The amplitude noise is considered to be related to SC generation.For practical fabrication,the influence of the random imperfections of airhole diameters on dispersion and nonlinearity is discussed to verify the robustness of our design.     

A tunable and switchable single-longitudinal-mode dual-wavelength fiber laser incorporating a reconfigurable dual-pass Mach-Zehnder interferometer and its application in microwave generation

A tunable and switchable single-longitudinal-mode (SLM) dual-wavelength fiber laser incorporating a reconfigurable dual-pass Mach-Zehnder interferometer (MZI) filter was proposed and demonstrated, which can be applied in microwave generation. By incorporating a high extinction ratio (ER) dual-pass MZI into an erbium-doped fiber ring cavity, SLM dual-wavelength lasing can be achieved even using a MZI with relatively little free spectrum range (FSR), and by beating the two wavelengths at a photodetector, a 9.76 GHz microwave signal with a 3-dB bandwidth of less than 10 kHz is obtained. Moreover, by direct linking the two outputs of the MZI, the high ER dual-pass MZI is easily reconfigured as a half FSR dual-pass MZI. Using this structure, switchable SLM dual-wavelength lasing can be conveniently realized.     

Tunable dual-wavelength fiber laser based on an opto-VLSI processor and four-wave mixing in a photonic crystal fiber

A stable wavelength and wavelength spacing tunable dual-wavelength fiber laser based on an Opto-very-large-scale-integration (Opto-VLSI) processor and four-wave mixing (FWM) in a high-nonlinear photonic crystal fiber is experimentally demonstrated. The results show that the line width of the tunable dual-wavelength fiber laser is 0.02 nm, and the wavelength spacing can be tuned from 0.8 nm to 4 nm with a 0.15 nm step. Under the influence of the FWM, the uniformity is below 0.6 dB and the measured side mode suppression ratio (SMSR) is above 45 dB.     

Photonic generation of microwave signals using dual-wavelength single-longitudinal-mode fiber lasers

Photonic generation of microwave signals is demonstrated with a dual-wavelength single-longitudinal-mode erbium-doped fiber ring laser. Microwave signal with a frequency of 21.07 GHz is obtained by aligning the reflection band of a uniform fiber Bragg grating to the two transmission peaks within a fiber Bragg grating-based Fabry-Perot filter. Stable dual-wavelength single-longitudinal-mode operation is guaranteed by means of the combined filtering effect of a saturable absorber and the Fabry-Perot filter. This approach provides an effective solution to the photonic generation of high-frequency microwave signals.     

Stable dual-wavelength single-longitudinal-mode ring erbium-doped fiber laser for optical generation of microwave frequency

We demonstrate a simple dual-wavelength ring erbium-doped fiber laser operating in single-longitudinal-mode (SLM) at room temperature. A pair of reflection type short-period fiber Bragg gratings (FBGs), which have two different center wavelengths of 1545.072 and 1545.284 nm, are used as the wavelength-selective component of the laser. A segment of unpumped polarization maintaining erbium-doped fiber (PM-EDF) is acted as a narrow multiband filter. By turning the polarization controller (PC) to enhance the polarization hole burning (PHB), the single-wavelength and dual-wavelength laser oscillations are observed at 1545.072 and 1545.284 nm. The output power variation is less than 0.6 dB for both wavelengths over a five-minute period and the optical signal to noise ratio (OSNR) is greater than 50 dB. By beating the dual-wavelengths at a photodetector (PD), a microwave signal at 26.44 GHz is demonstrated.     

Photonic generation of microwave signals using a dual-transmission-band FBG filter with controllable wavelength spacing

Two π-phase shifts are introduced in a uniform fiber Bragg grating (FBG) structure and a dual-transmission-band opens in the stopband of FBG. When incorporating this kind of FBG filter in a fiber ring cavity with a semiconductor optical amplifier (SOA) acted as gain medium, a stable dual-wavelength lasing with wavelength spacing of 0.032, 0.052 and 0.068 nm is achieved, respectively. Therefore, the laser output is heterodyned on a photodetector and desired microwave frequencies of 3.15, 6.16 and 8.08 GHz are generated. PACS 41.20.-q; 42.55.Wd; 42.81.-i     

Switchable single-longitudinal-mode dual-wavelength erbium-doped fiber ring laser incorporating a semiconductor optical amplifier

We propose and demonstrate a novel single-longitudinal-mode (SLM) dual-wavelength erbium-doped fiber ring laser incorporating a semiconductor optical amplifier. The SOA biased in its low-gain regime greatly reduces the gain competition of the two wavelengths. The stable SLM operation is guaranteed by a passive triple-ring cavity and a fiber Fabry-Perot filter. The dual-wavelength output with a 40 GHz wavelength spacing is switchable in the range of 1533-1565.4 nm.     

Tunable microwave photonic notch filter using a dual-wavelength fiber laser with phase modulation

A novel tunable microwave photonic notch filter using a phase-modulated dual-wavelength fiber laser is presented. A stable dual-wavelength erbium-doped fiber laser with a linear cavity is formed by a polarization-maintaining uniform fiber Bragg grating (PM-FBG) and a polarization maintaining linearly chirped fiber Bragg grating (PM-LCFBG), both of which were fabricated on a high-birefringence (Hi-Bi) fiber. It is found that a stable room-temperature dual-wavelength operation can be achieved due to the presence of two reflection peaks arising from the orthogonal states of polarization (SOP) of the PM-FBG. Experimental results show stable dual-wavelength lasing operation with a wavelength separation of ∼0.36 nm and a large optical signal-to-noise ratio (OSNR) of over 40 dB under room temperature. The dual-wavelength fiber laser is combined with a phase modulator and a segment of single-mode fiber (SMF) as a dispersive device to form a tunable microwave photonic notch filter. By stretching the PM-FBG to tune the wavelength separation of the dual-wavelength fiber laser, a tunable microwave photonic notch filter with various free spectral ranges (FSRs) and a rejection ratio greater than 35 dB was developed.     

High frequency microwave signal generation using dual-wavelength emission of cascaded DFB fiber lasers with wavelength spacing tunability

A dual-wavelength fiber laser source based on two cascaded phase-shifted fiber Bragg gratings is presented. The gratings are written in an erbium-doped fiber, each configuring the cavity of a distributed feedback fiber laser. The spacing between lasing modes is controlled dynamically by the use of piezoelectric actuators. A continuous tuning range of 5-724 pm of the wavelength difference, which is equivalent to a photodetected 0.72-92 GHz range, is obtained. Efficient generation from the L to the W microwave and millimeter bands has been achieved by heterodyne photodetection of the dual-wavelength optical signal.     

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     

Multi-wavelength bismuth-based erbium-doped fiber laser based on four-wave mixing effect in photonic crystal fiber

A stable multi-wavelength erbium-doped fiber laser based on four-wave mixing (FWM) in a photonic crystal fiber (PCF) is demonstrated in this paper. The phase matching condition for four-wave mixing in the photonic crystal fiber has been enhanced using a seed signal and a polarisation controller to control the states of polarisation in the ring laser cavity. At a maximum pump power of 1480 nm, 5 lines are observed with nearly 2.15 nm spacing between the lines, and with a signal to noise ratio of more than 20 dB. The number of channels and wavelength spacing can be controlled by varying the output coupler ratio.