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.     

Switchable triple-wavelength erbium-doped fiber laser using a single fiber Bragg grating in polarization-maintaining fiber

A stable and narrow wavelength spacing multiwavelength erbium-doped fiber laser is proposed and demonstrated. The laser can produce simultaneous dual- and triple-wavelength lasing oscillations with a narrow wavelength spacing of less than 0.1 nm via using a single fiber Bragg gratings written in polarization-maintaining (PM) fiber. By adjusting polarization controller, the wavelength spacing of dual-wavelength lasing oscillations can be tuned to as small as 0.032 nm. The maximum amplitude variation for every lasing wavelength is less than 0.5 dB. The room-temperature operation principle is based on the polarization hole burning and deeply saturated effect in an ordinary erbium-doped fiber ring laser (EDFRL). The laser has the advantages of simple all-fiber configuration, low cost, high stability and operating at room temperature.     

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.     

Switchable dual-wavelength erbium-doped fiber-ring laser based on one polarization maintaining fiber Bragg grating in a Sagnac loop interferometer

A switchable erbium-doped fiber-ring laser providing dual-wavelength outputs with orthogonal polarizations when operating at room temperature is proposed. One polarization-maintaining fiber Bragg grating (PMFBG) in a Sagnac loop interferometer is used as the wavelength-selective filter. 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 optical signal-to-noise ratio (OSNR) is over 42 dB. The amplitude variation over 90 min is less than 0.6 dB for both wavelengths.     

Tunable dual-wavelength fiber laser based on a single fiber Bragg grating in a Sagnac loop interferometer

We propose a simple dual-wavelength Er-doped fiber laser configuration based on a dual-wavelength fiber Bragg grating written on the splice joint between two different fibers for wavelength-selective filter in the Sagnac loop interferometer. The wavelength separation between the adjacent lasing wavelengths is 1.12 nm and the side-mode suppression ratio (SMSR) is over 55 dB. The output power variation is less than 0.8 dB over a two-minute period. Moreover, the lasing wavelength can be effectively tuned using the thermal heating method.     

A stable dual-wavelength fiber laser with tunable wavelength spacing using a polarization-maintaining linear cavity

We propose and experimentally demonstrate a stable dual-wavelength erbium-doped polarization-maintaining (PM) fiber laser with tunable wavelength spacing using an all-PM linear cavity that makes use of two reflection peaks from the PM fiber Bragg grating (PM-FBG). Experimental results show stable dual lasing lines with a wavelength separation of ∼0.22 nm and a large optical signal-to-noise ratio (OSNR) of over 40 dB under room temperature. By applying axial strain to the PM-FBG, the center wavelengths of the two lasing lines can be tuned over several nanometers and the wavelength separation between the lasing lines can also be tuned to as small as 0.05 nm, which, to our knowledge, is the smallest wavelength spacing ever obtained from a stable room-temperature dual-wavelength fiber laser. The proposed laser configuration has the advantages of simple structure, low loss, stable dual-wavelength operation and a very small lasing linewidth of ∼5 kHz . PACS 42.55.Wd; 42.81.-i; 42.81.Gs     

Dual-wavelength high-power Yb-doped double-clad fiber laser based on a few-mode fiber Bragg grating

We report a high-power dual-wavelength Yb-doped double-clad fiber laser based on a few-mode fiber Bragg grating (FMFBG). The FMFBG was fabricated by using a piece of fiber in a length of fiber with a cutoff wavelength of 1225 nm, which supported two modes at 1060 nm. The laser was pumped by a fiber pigtailed laser diode working at 915 nm. Single-wavelength, dual-wavelength and triple-wavelength laser oscillations were observed when the fiber laser operated under different low pump powers. However, stable dual-wavelength operation was achieved at higher pump power of 3.9 W and remained unchanged until the output power reached 5.67 W under the maximum available pump power of 10.7 W. The laser wavelengths were centered at 1059.12 and 1060.80 nm with a full-width at half-maximum of 37 and 43 pm, respectively. The signal-to-noise-ratio was greater than 50 dB and the beam quality factor (M²) was about 1.9.     

Switchable dual-wavelength polarization-maintaining erbium-doped fiber laser using an optical circulator as the all-reflecting mirror

A simple and effective switchable dual-wavelength polarization-maintaining erbium-doped fiber laser is proposed and demonstrated. Only using a uniform fiber Bragg grating written directly in a segment of the photosensitive and polarization-maintaining erbium-doped fiber as the wavelength selector and an optical circulator as the all-reflecting mirror, a stable simultaneous dual-wavelength oscillation is achieved with a wavelength spacing of 0.364 nm experimentally by exploiting the polarization hole burning effect at room temperature. The output can be switched between single- and dual-wavelength by adjusting the polarization controller. The 3-dB bandwidth and the side mode suppression ratio of the laser’s outputs are measured to be less than 0.01 nm and more than 50 dB. The power fluctuation and wavelength drift are measured to be less than 0.50 dB and 0.020 nm over an hour.     

Incorporate, switchable dual-wavelength fiber laser with Bragg gratings written in a polarization-maintaining erbium-doped fiber

A stable, incorporate and switchable dual-wavelength fiber laser with two fiber Bragg gratings written in a photosensitive and polarization-maintaining erbium-doped fiber directly, that is, without splices in the laser cavity, is proposed and demonstrated. Simultaneous dual-wavelength oscillation is achieved at room temperature with a wavelength spacing of 0.343 nm. The power fluctuation and wavelength shift of single-wavelength oscillations are measured to be less than 0.24 dB and 0.013 nm over 2 h. The wavelength switchability between single- and dual-wavelength oscillations is realized by altering the voltage upon the electrostrictive ceramic actuator.     

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     

Medium power single-mode single-wavelength fiber laser

Medium-power, single-mode, single-wavelength fiber laser working at room temperature using a polarization-maintaining erbium-ytterbium co-doped fiber as the gain medium, and an un-pumped elliptical core erbium-doped fiber as a saturable absorber to reduce linewidth and mode hopping of the lasing wavelength is reported. The effects of length, erbium ion concentration, and polarization-maintaining property of the saturable absorber were explored. The output power of the laser was more than 100 mW and the lasing line was stable for more than 3 h with an intensity fluctuation of less than 0.2 dB. The laser linewidth (FWHM = Full width at half maximum) was 7.5 MHz and the signal to noise ratio was more than 50 dB. The output of the laser was measured using an optical spectrum analyzer (OSA) of resolution 1.25 GHz and a scanning Fabry-Perot spectrum analyzer (SFPSA) of resolution 6.7 MHz.     

Actively mode-locked dual-wavelength fiber laser with close wavelength spacing using a fiber Bragg grating

A simple actively mode-locked fiber ring laser is proposed and successfully demonstrated to generate dual-wavelength picosecond pulses with close wavelength spacing using one Bragg grating in standard single-mode fiber. The proposed laser can be made to operate in stable dual-wavelength at room temperature, due to the birefringence characteristic of the FBG induced by transverse strain. Transverse strain loading on the FBG allows the wavelength spacing to be controlled. Generation of stable dual-wavelength pulses with a pulsewidth of 212–234 ps and a tunable wavelength separation from 0.2 to 0.44 nm at a pulse rate of 1.05 GHz was 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     

基于相位采样光栅的双波长光纤激光器

提出一种基于相位采样的分布反馈式双波长光纤激光器,在不同的空间化置同时引入相位和采样周期的突变.通过理论分析,这种结构能够实现谐振腔的分离,使不同波长的光波利用不同空间位置的增益介质,克服增益介质均匀加宽引起的模式竞争,实现双波长激射.采用准分子激光器和均匀相位模板,在掺铒光纤上制作波长差为0.46 nm的舣波长光纤激光器,能够实现舣波长激射.通过实验,对激光器输出功率和光栅强度的关系进行研究,表明输出功率和光栅强度成反比.     

Stable multiwavelength fiber ring laser with equalized power spectrum based on a semiconductor optical amplifier

We experimentally demonstrated a new structure of a multiwavelength semiconductor optical amplifier (SOA) ring laser based on a fiber Sagnac loop filter that can generate up to 25 stable output lasing wavelengths at room temperature. By varying the length of a polarization-maintaining (PM) fiber within the Sagnac loop filter, the wavelength spacing between the output lasing wavelengths can be changed to a desired value. By tuning a polarization controller (PC) within the Sagnac loop filter, stable multiwavelength 1550-nm operation with up to 17 lasing lines within 3 dB power level variation and with a wavelength spacing of ∼0.8 nm was achieved. The optical signal-to-noise ratios (OSNRs) of all the lasing wavelengths are greater than 40 dB.     

Wavelength spacing tunable dual-wavelength single-longitudinal-mode fiber ring laser based on fiber Bragg gratings

A wavelength spacing tunable dual-wavelength single-longitudinal-mode fiber ring laser is presented by employing separated fiber Bragg gratings. By using a saturable-absorption-induced grating filter and a hybrid gain medium formed by a semiconductor optical amplifier and an erbium-doped fiber amplifier, stable single-longitudinal-mode lasing is achieved at room temperature. Wavelength spacing of the proposed fiber laser can be tuned in a range from 0.1 to 1.3 nm.     

Multiwavelength Linear-Cavity Fiber Laser Source Using a Sagnac Interferemetric Filter and a Strain-Induced Chirped Fiber Grating

A novel multiwavelength linear-cavity fiber laser source using a strain-induced chirped fiber Bragg grating, a Sagnac interferemetric filter, and Erbium-Ytterbium codoped fibers is proposed and demonstrated for the first time. The Sagnac interferemetric filter, which acts as a full-reflecting mirror, consists of a polarization-maintaining directional coupler and two pieces of polarization-maintaining fibers. The strain-induced chirped FBG, which acts as a partial-reflecting mirror, is achieved by bending a uniform FBG bonded at a slant onto the lateral surface of a simply supported beam. By tuning the strain-induced chirped FBG, desirable lasing wavelength and number can be easily achieved.     

All-fiber single polarized Yb-doped fiber laser with a high extinction ratio

We present an all-fiber design for a single polarization Yb-doped fiber laser with all-fiber connections spliced. Single polarization with a high extinction ratio was achieved by the design of a laser cavity consisting of a fiber Bragg grating inscribed on a single-polarization fiber as a high reflective mirror and a piece of end-cleaved single-polarization fiber as an output coupler. The fiber laser operates at 1063.25 nm with an output power of 1.7 W, an optical signal- to-noise ratio of 70 dB and a narrow bandwidth of 54 pm. The laser output has a polarization extinction ratio of 700:1 or 28 dB, and a very stable power output.     

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.     

Switchable multi-wavelength erbium-doped fiber ring laser based on cascaded polarization maintaining fiber Bragg gratings in a Sagnac loop interferometer

A switchable multi-wavelength erbium-doped fiber (EDF) ring laser based on cascaded polarization maintaining fiber Bragg gratings (PMFBGs) in a Sagnac loop interferometer as the wavelength-selective filter at room temperature is proposed. Due to the polarization hole burning (PHB) enhanced by the PMFBGs, stable single-, dual-, three- and four-wavelength lasing operations can be obtained. The laser can be switched among the stable single-, dual-, three- and four-wavelength lasing operations by adjusting the polarization controllers (PCs). The optical signal-to-noise ratio (OSNR) is over 50 dB.