C-band continuously tunable lasers using tunable fiber Bragg gratings

In this paper, we present a continuous-wave tunable fibre ring laser operating in the L-band. A bi-directional pumped L-band erbium-doped fibre amplifier provides gain to the loop. Tunability is achieved by bending a single-mode fibre taper using a micrometer drive, controlling in this way the spectral cavity losses. Laser emission is achieved between 1587 and 1606 nm, and low variation of the output laser power is observed over all the tuning range.

We demonstrate a passively Q-switched tunable erbium-doped fiber laser (EDFL) based on graphene as a saturable absorber (SA). A three-port optical circulator (OC) and a strain-induced tunable fiber Bragg grating (TFBG) are used as the two end mirrors in an all-fiber linear cavity. The Q-switched EDFL has a low pump threshold of 23.8 mW. The pulse repetition rate of the fiber laser can be widely changed from 9.3 kHz to 69.7 kHz by increasing the pump power from 23.8 mW to 219.9 mW. The minimum pulse duration is 1.7 μs and the highest pulse energy is 25.4 nJ. The emission wavelength of the laser can be tuned from 1560.43 nm to 1566.27 nm by changing the central wavelength of the strain-induced TFBG.

Thulium fiber lasers emit light of wavelengths spanning as low as 1650nm to 2200nm. This broad emission band is in the “eye-safety” wavelength regime and intersects with the IR atmospheric transmission window with its opacity subsiding past 1900nm wavelength. Consequently, a high power, single frequency, tunable thulium fiber laser with its tuning range from 1900nm to 2000nm has the unique capability of studying high power beam propagation through the atmosphere in regions of both weak and strong transmission. Moreover, such lasers can be made to tune across individual molecular absorption lines due to chemical species present in the atmosphere. This enables a detailed investigation on how individual molecular absorption lines affect the transmission of high power laser beams. In this paper, a 100kHz linewidth, near diffraction limited, 100W class, widely tunable CW thulium fiber laser system is described for atmospheric propagation studies. The fiber laser is of master oscillator power amplifier(MOPA) architecture with one pre-amp and a final power amplifier. The master oscillator is a 5mW class tunable external cavity diode and is tunable from 1900nm to 2000nm. The pre-amp amplifies the seed to 2-3W level, which is then further amplified to 100W by the final amplifier made from thulium doped 25um core 250um cladding 0.09NA fiber from Nufern. All fiber architecture allows efficient lasing at the lossy molecular absorption wavelengths.

A tunable spacing dual-wavelength Q-switched fiber laser is experimentally demonstrated based on a fiber Bragg grating tunable device incorporated in an erbium-doped fiber laser (EDFL). The system utilizes two identical fiber Bragg gratings (FBGs) at 1547.1 nm origin to enable two laser lines operation. The wavelength separations between two laser lines are controlled by fixing one of the FBGs while applying mechanical stretch and compression to the other one, using a fiber Bragg grating tunable device. The seven steps of wavelength spacing could be tuned from 0.3344 to 0.0469 nm spacing. Pulse characteristics for both close and wide spacing of dual-wavelength Q-switched fiber laser are successfully being recorded. The findings demonstrate the latest idea of dual-wavelength fiber laser based on FBG tunable device, which offers a wide range of future applications.

We have developed a tunable multi-wavelength semiconductor fiber laser (SFL) for chromatic dispersion measurements of optical fiber based on the time-of flight method. The SFL incorporates a programmable high-birefringence fiber loop mirror to select the separation of the lasing wavelengths between 3.2nm and 1.6nm. The SFL emits 5 wavelengths with an average power of 11.96dBm per wavelength and 11 wavelengths with an average power of 18.35dBm per wavelength, for separations of 3.2nm and 1.6nm respectively, all within the C-band. The linewidth of each oscillating wavelength resides in the 0.16nm - 0.28nm range, the signal-to-noise ratio varies between 33.5dB and 39.2dB, and the uniformity of the output power is within 3.2dB. Stability measurements for each lasing peak show a wavelength deviation of +/-0.09nm/hour and a power variation of +/-0.90dB/hour. Results from time-of-flight measurements are compared with standard phase-shift techniques and the differences analyzed. The percent error between the two methods is better than -0.73 to 1.13% for measurements on various standard optical fiber lengths. The time-of-flight method is easier and faster to use for the characterization of sufficiently dispersive media such as deployed fiber spools. Our tunable laser provides a simple low cost solution for such measurement applications. The tunable nature of our SFL source also provides the following advantages for chromatic dispersion measurements: (1) greater precision can be obtained since two independent measurements (one at each wavelength separation) can be performed using a single optical source and (2) there is increased flexibility since the wavelength spacing can be tailored for a specific situation; shorter lengths benefiting from larger wavelength separations.

Two wavelength-spacing continuously tunable multi-wavelength fiber lasers based on four-wave-mixing effect, one with a dispersion-shifted fiber and the Mach-Zehnder interferometer, the other with a highly nonlinear fiber and the two tunable lasers, are proposed.

A tunable fiber ring laser based on an in-line two-taper Mach-Zehnder interferometer (MZI) filter was realized, and the effect of beam waists of the tapers on performance of the laser was investigated with different beam waists of 70 μm, 49 μm, and 33 μm. Experimental results show that the tunable laser with MZI length of 1 m and beam waist of 49 μm can cover 16.1 nm with tuning steps of 0.07-0.5 nm, a bandwidth of 10 pm, and a side mode suppression ratio (SMSR) of 40-50 dB. Tuning range is not only determined by the number of the cladding modes but is also affected by the filter loss. Tuning step is determined by the differences of the effective refractive indexes between the cladding modes and the core mode. SMSR is determined by the balance between the extinction ratio of the filter and the cavity loss of the laser due to MZI filter.

Fault detection technique for wavelength division multiplexing passive optical network using chaotic fiber laser

High-power tunable red laser based on double-cladding Pr3+-doped fiber

Q-switched fiber laser with a tunable wavelength output is experimentally demonstrated utilizing a nonlinear saturable absorption of vanadium pentoxide (V2O5) in conjunction with a tunable bandpass filter (TBF). The V2O5 saturable absorber (SA) was prepared by mixing V2O5 with polyethylene glycol. The SA film exhibits a modulation depth of 7% with a saturation intensity of 90 MW/cm2. By integrating the SA into an erbium-doped fiber laser cavity while controlling the passband wavelength of the TBF, a Q-switched pulsed laser is realized with a tunable wavelength range of 30 nm that extends from 1535 to 1565 nm. At 1565 nm operation, the laser exhibits the highest slope efficiency of 8.31%. The repetition rate varies from 13.32 to 15.25 kHz, while the pulse width shrinks from 21.3 10 12.75 μs when the pump power rises from 14.9 to 37.7 mW. The pulse energy is 102.6 nJ at the maximum pump power of 37.7 mW. This is the first demonstration of a tunable Q-switched fiber laser operating in a 1.5 μm wavelength region utilizing V2O5 SA.

A 2.5W superfluorescent fiber source (SFS) and a tunable PCF laser with 74.4 nm tuning range and 5.5 W output power are experimentally demonstrated by utilizing an ytterbium-doped photonic crystal fiber (PCF) as the gain medium. The tunable operation of the laser is realized by rotating a diffraction grating. Effects of the degrees of the cleaved angle at the anti-reflection fiber end on the output characteristics of the laser and the SFS are investigated. A large cleaved angle is beneficial to realize a broad laser tuning range and beneficial to obtain a high power superfluorescent fiber source without parasitic lasing.

In this paper, we propose a scheme on precisely tunable L-band multi-wavelength fiber laser. This fiber laser has two main characteristics namely broad wavelength band, uniform power spectrum and precise electronic tunability. About 65 wavelengths output within ± 1.5dB power variation with 50GHz channel spacing in broad spectrum range can be obtained at room temperature. The measured optical signal noise ratio (OSNR) and line width of each wavelength are about 20dB and 345.5MHz respectively. Theses 65 wavelengths are able to be tuned simultaneously up or down in frequency domain with a tuning step ranging from 10 MHz to 14 GHz. The tuning resolution can potentially be as low as 1 Hz in our experiment.

In this paper we investigate the impact of intra-band incoherent crosstalk due to bi-directional WDM cross-connect (OXC) based on arrayed waveguide grating (AWG), tunable Fiber Bragg gratings (FBG) and optical circulators (OC) on the bit-error-rate (BER) performance of a WDM transmission system. This paper reveals that there is a power penalty suffered by the system due to OXC. The limiting values of crosstalk factor for a BER of 10-9 are determined. It is found that the limiting value of AWG crosstalk factor is -30dB for which the penalty is approximately 8.0dB corresponding to a FBG crosstalk factor of -60dB and a OC crosstalk factor of -50dB for a WDM system with four wavelength channels operating as 10Gb/s.

This paper proposed and experimentally demonstrated an all-fiber tunable and programmable bandpass filter using a linearly chirped fiber Bragg grating (CFBG). The center wavelength and spacing of the transmission peaks could be independently tuned via computer. The tunable range is about 18 nm. With this filter we demonstrated a tunable fiber ring laser which has an output power of about -7 dBm, full-width at half- maximum linewidth of ~0.017 nm which is limited by the resolution of the optical spectrum analyzer (OSA). Furthermore, a spacing tunable dual-wavelength fiber laser was achieved with the same setup. This all-fiber laser features advantages like simple structure, low cost, flexible and digital tuning capability.

In this paper we review the design and operation of tunable lasers which have outputs in the visible and ultraviolet portions of the spectrum, and which employ organic dyes as amplifying media. The em-phasis will be on continuously operating lasers, and in considering the generation of UV radiation we will restrict our attention to non-linear sum-frequency generation using a tunable visible laser as the fundamental light source.