Double-ring cavity configuration of actively mode-locked multi-wavelength fiber laser with equally tunable wavelength spacing

A novel actively mode-locked multi-wavelength tunable fiber laser with equally increased or decreased wavelength spacing is presented. It is constructed using a double-ring cavity combined with an amplitude modulator and cascaded fiber Bragg gratings (FBGs). The cavity lengths for all FBGs are intrinsically identical due to the double-ring configuration, and simultaneous mode locking of multiple wavelengths is therefore achieved by applying only one mode-locking signal to the modulator. The FBGs are mounted on a organic plate with angles between adjacent gratings such that the forces applied to the FBGs have an equal force increment; thus, stretching or compressing the cascaded FBGs can achieve a wavelength tuning with equally increased or decreased wavelength spacing.This revised version was published online in March 2005. In the previous version, the published online date was missing     

Tunable erbium doped fiber ring laser using fiber Bragg grating-assisted add-drop filter

A stable and low costless tunable erbium doped fiber ring laser using fiber Bragg grating-assisted add-drop filter is proposed and demonstrated. A stable laser output is obtained with a 4 nm tuning range. The power fluctuation, full-width at half maximum and SMSR are measured to be less than 0.50 dB, smaller than 0.015 nm and better than 55 dB in this tuning range.     

Switchable and tunable dual-wavelength ultrashort pulse generation in a passively mode-locked erbium-doped fiber ring laser

A simple switchable and tunable dual-wavelength passively mode-locked erbium-doped fiber ring laser based on nonlinear polarization rotation (NPR) effect is proposed and experimentally demonstrated. The NPR effect effectively induces wavelength- and intensity-dependent loss to readily implement stable dual-wavelength passively mode-locked operation. The wavelength switching and tuning of the dual-wavelength ultrashort pulse laser are achieved only by appropriately rotating the polarization controllers. The side-mode suppression ratio of the output pulse is larger than 41 dB over a wavelength-tuning range of 43.4 nm. Moreover, triple-wavelength ultrashort pulse can also be observed.     

Side-pumped fiber laser

A neodymium-doped side-pumped double-clad fiber laser operating at 1.06 µm is described. We report here, what is, to our knowledge, the first exclusively repetitive side-pumping scheme with two monomode laser diodes. Side-pumping has been realized by prism-fiber couplers. A pump-light-loss analysis at the pump positions has been performed. An output power of 13.5 mW is obtained with both diode lasers. The highest slope efficiency of 66% with respect to absorbed pump power at 809 nm is achieved when pumping with only one diode.     

Performance of a wavelength-tunable erbium-doped fiber laser using a Sagnac interferometer

We experimentally demonstrate a wavelength-tunable erbium-doped fiber laser that is composed of a ring cavity and a single-mode fiber Sagnac interferometer in a new and simple arrangement. We find that the fiber laser output wavelength is tunable by adjusting the filter effect of the Sagnac fiber loop through a fiber polarization controller set there. The quasi-single-wavelength continuously tunable laser outputs could be achieved within some wavelength range. The multi-wavelength laser outputs could also be observed under some appropriate settings of the polarization controller. A theoretical demonstration of the wavelength tunability about the transmission-type Sagnac loop filter has also been achieved using the Jones calculus theory.     

Experimental characterisation, optimisation and design of erbium-doped silica fibre lasers

A new characterisation method is described using the new theoretical model for erbium-doped silica fibre lasers (EDSFLs) based on the energy conservation principle. Using this method, we obtained absorption and emission coefficients for the lasing wavelength at lasing operating conditions. After that, an experimental procedure to deduce the spectral profiles of the absorption and emission coefficients is also presented. This procedure allows us to obtain the values of these parameters for the whole fluorescence spectrum through measurements of gain profiles under the lasing operation. Once the absorption and emission coefficients are known, the new model can be applied and a comparison with experimental results for two different laser configurations is shown. The theoretical model is proved to be accurate and in addition some equations are developed to allow the design and optimisation of EDSFLs. This revised version was published online in March 2005. In the previous version, the published online date was missing     

A tunable narrow-line-width multi-wavelength Er-doped fiber laser based on a high birefringence fiber ring mirror and an auto-tracking filter

A novel multi-wavelength erbium-doped fiber laser operating in C-band is proposed and successfully demonstrated. The wavelength interval between the wavelengths is about 0.22 nm. The 3 dB bandwidth of the laser is about 0.012 nm, and the output power reaches 4.8 mW. By using a high birefringence fiber ring mirror (HiBi-FLM) and a tunable FBG, the laser realizes switchable and tunable characteristic. The mode hopping can be effectively prevented. Moreover, this laser can improve wavelength stability significantly by taking advantage of an un-pumped Er³⁺-doped fiber at the standing-wave section. The laser can operate in stable narrow-line-width with single-, dual-wavelength, and unstable triple-wavelength output at room temperature.     

All-Fibre Ytterbium-Doped Photonic Crystal Fibre Laser with High Efficiency

A double-cladding ytterbium-doped photonic crystal fibre （PCF） with a 350-μm^2 effective area is fabricated. The measurement results show that the PCF has high absorption peak at 915 nm. Its fluorescence lifetime is 840μs. Laser experiments with all-fibre configurations are carried out with this fibre. A continuous-wave output power of 3.96 W is achieved with a 5.2 W launched pump power. The central wavelength of the output spectrum is 1080.22nm. The results show that the PCF laser has a high slope efficiency of 79.6% and light conversion efficiency of 76.2%.     

Multiwavelength fiber laser with ultradense wavelength spacing based on inhomogeneous loss with assistance of nonlinear polarization rotation

We demonstrate a multiwavelength fiber laser with ultradense wavelength spacing and ultrabroad bandwidth based on inhomogeneous loss mechanism with assistance of nonlinear polarization rotation. The inhomogeneous loss, implemented by incorporating a section of highly nonlinear fiber (HNLF) and a Sagnac filter in the laser cavity, can balance mode competition in erbium-doped fiber and result in ultradense multiwavelength generation. The bandwidth of the multiwavelength spectrum is greatly broadened owing to the intensity-dependent loss induced by nonlinear polarization rotation. Stable multiwavelength lasing with wavelength spacing of 0.08 nm and wavelength number up to 254 is achieved at room temperature. Moreover, multiwavelength tuning is realized through modifying polarization-dependent cavity loss.     

Design and demonstration of a novel optical CDMA platform for use in avionics applications

We designed, built, and demonstrated a highly scalable incoherent optical CDMA platform under DARPA contract which was delivered to Lockheed Martin for additional testing in avionic applications. The platform enables users to communicate with each other at ∼1.25 Gbit/s per user with raw BER of less than 10⁻¹². The system architecture uses (3, 11) fast wavelength-hopping, time-spreading prime codes with a chip size of 73 ps utilizing picosecond optical pulses allocated in the time and wavelength domains. A novel design of a “dual code” optical encoder and decoder realized a novel optical layer implementation of an XOR gate and enabled secure network connectivity using a “One-time pad” encryption approach. The testbed is also designed to conduct eavesdropping studies on testbed users. The incoherent OCDMA approach is compatible with existing DWDM optical networks and uses off-the-shelf components.     

A broadband ultra flattened chromatic dispersion microstructured fiber for optical communications

A double-cladding microstructured fiber (MF) is proposed in this paper. The inner cladding of this optical fiber is composed of elliptical air holes and silica. The dependence of dispersion on the diameter of the air holes, the pitch, and the axes of the elliptical holes is investigated numerically. The proposed fiber possesses an ultra flattened dispersion curve over a wide wavelength range, and its dispersion value is small. The effective mode area is approaching to 60 μm², and the confinement loss is as low as <0.025 dB/km at 1550 nm. While choosing suitable structure parameters, an ultra dispersion-flattened MF within a broadband from1000 nm to 1900 nm can be achieved. The dispersion fluctuation is 0.6-1.0 ps/(nm·km) in all S, C and L band.     

Generation of dual wavelength ultrashort pulse outputs from a passive mode locked fiber ring laser

By incorporating two sections of polarization maintaining fibers in the passive mode locked fiber ring laser cavity, dual wavelength ultrashort pulse outputs, around 1558 nm and 1570 nm, having the same direction of polarization and pulse widths of 2.4 ps and 2.1 ps, respectively, were observed simultaneously.     

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.     

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.     

All-fiber actively Q-switched fiber laser tuned by a pair of temperature controlled fiber Bragg gratings

We report an all-fiber actively Q-switched erbium-doped fiber laser, where the linear laser cavity mirrors are composed of two fiber Bragg gratings (FBGs). The laser oscillation wavelength could be tuned by this pair of temperature controlled FBGs. The Q-switching is achieved by an all-fiber phase modulation device. Using this system, we could obtain stable Q-switched laser pulses output, which could be optimized by tuning the reflection wavelengths of the two FBGs to be adjacent to each other. Instead of being modulated by the FBG filter in high-speed oscillation, this fiber laser system is operating in the Q-switched regime using an all-fiber phase modulator, producing a more stable laser output spectrum.     

Photonic crystal fiber with a flattened fundamental mode for the fiber lasers

The 1-hole-missing and 7-hole-missing photonic crystal fibers (PCFs) with flattened fundamental modes (FMs) are proposed by introducing a layer of up-doped silica into the core of the PCFs. The transverse mode competitions are compared between the 7-hole-missing PCF lasers with and without flattened-FMs. The numerical results show that the flattened-FM PCF lasers can support the single transverse mode operation, even for a large value of the ratio of air hole diameter to the spacing between holes (up to 0.53).     

Wavelength-agile fiber laser using group-velocity dispersion of pulsed super-continua and application to broadband absorption spectroscopy

A swept-wavelength source is created by connecting four elements in series: a femtosecond fiber laser at 1.56 μm, a non-linear fiber, a dispersive fiber and a tunable spectral bandpass filter. The 1.56-μm pulses are converted to super-continuum (1.1–2.2 μm) pulses by the non-linear fiber, and these broadband pulses are stretched and arranged into wavelength scans by the dispersive fiber. The tunable bandpass filter is used to select a portion of the super-continuum as a scan-wavelength output. A variety of scan characteristics are possible using this approach. As an example, an output with an effective linewidth of approximately 1 cm^-1 is scanned from 1350–1550 nm every 20 ns. Compared to previous scanning benchmarks of approximately 1 nm/μs, such broad, rapid scans offer new capabilities: a gas sensing application is demonstrated by monitoring absorption bands of H₂O, CO₂, C₂H₂ and C₂H₆O at a pressure of 10 bar. Received: 5 August 2002 / Revised version: 23 September 2002 / Published online: 22 November 2002 RID="*" ID="*"Corresponding author. Fax: +1-608/265-2316, E-mail: ssanders@engr.wisc.edu     

Photonic crystal fiber for fundamental mode operation of multicore fiber lasers and amplifiers

A mode-selection method based on a single-mode photonic crystal fiber (PCF) in the multicore fiber (MCF) lasers is presented. The designed PCF has a central core region formed by a missing air-hole, and three air-hole rings. With an appropriate choice of the design parameters of the PCF, the power coupling between the fundamental mode (FM) of the PCF and the fundamental MCF mode can be much higher than those between the FM and the other supermodes. As a result, the fundamental MCF mode has the maximum power reflection coefficient on the right-hand side of the MCF laser cavity, and dominates the output laser power. Since the maximum power of the fundamental MCF mode will lead to the desired laser beam profile, higher the fraction of the fundamental MCF mode power contained in the total output power contributes to higher beam quality. The numerical simulations show that the effectiveness of the fundamental MCF mode-selection is higher in the MCF lasers with the PCF as a mode-selection component than in the MCF lasers based on the free-space Talbot cavity method. Additionally, for the MCF amplifiers, an approach is presented to decrease the sensitivity of the amplifier performance to the variation of Gaussian beam waist utilizing the coupling between the Gaussian beam and the FM of the PCF. The numerical results show that this method can effectively increase the design flexibility for a broad range of the Gaussian beam waist.     

Ytterbium femtosecond fiber laser without dispersion compensation tunable from 1015 nm to 1050 nm

We report on a widely tunable ytterbium fs-fiber laser without dispersion compensation. The all-normal dispersion laser contains a spectral filter for wavelength tuning and for generating additional amplitude modulation to support the nonlinear polarization evolution as mode-locking mechanism. By tilting the interference filter the center wavelength of the laser can be tuned from 1015 nm to 1050 nm with a pulse energy up to 2.0 nJ. The pulses can be dechirped externally to 108 fs.