Multiwavelength fiber laser with fine adjustment, based on nonlinear polarization rotation and birefringence fiber filter

We have proposed and demonstrated a multiwavelength fiber laser based on nonlinear polarization rotation (NPR). The mechanism for stable room-temperature multiwavelength operation contributes to the ability of the intensity-dependent loss in NPR to effectively alleviate mode competition. In addition, through tuning the birefringence fiber filter, the lasing wavelength can be accurately tuned in the free spectrum range of the in-line periodic filter.

A multiwavelength low-power wavelength-locked slotted Fabry-Perot laser source for WDM applications

Wavelength-locking of a multiwavelength stabilized slotted Fabry-Perot (SFP) laser to a single-mode laser source is experimentally demonstrated. The SFP resonates at channels spaced by similar to 8 nm between 1510 and 1565 nm over a wide range of temperatures and drive currents. Under low-power (<- 20 dBm) external optical injection, wavelength-locking with a sidemode suppression ratio (SMSR) > 25 dB is achieved. A locking width of > 25 GHz and SMSR > 30 dB can be achieved for each locked wavelength channel at injection power > - 16 dBm.

Multiwavelength generation in a random distributed feedback fiber laser using an all fiber Lyot filter

Multiwavelength lasing in the random distributed feedback fiber laser is demonstrated by employing an all fiber Lyot filter. Stable multiwavelength generation is obtained, with each line exhibiting subnanometer line-widths. A flat power distribution over multiple lines is obtained, which indicates that the power between lines is redistributed in nonlinear mixing processes. The multiwavelength generation is observed both in first and second Stokes waves. © 2014 Optical Society of America.

Fiber Bragg grating Fabry-Perot structures under loading and their applications in switchable multi-wavelength lasers

Characteristics of fiber Bragg grating based Fabry-Perot (FBG-FP) structures under transversal loading are investigated. A novel switchable multi-wavelength fiber laser employing loaded FBG-FP is also demonstrated. © 2012 OSA.

Switchable dual-wavelength Q-switched and mode-locked fiber lasers using a large-angle tilted fiber grating

We proposed and demonstrated pulsed fiber lasers Q-switched and mode-locked by using a large-angle tilted fiber grating, for the first time to our best knowledge. Owing to the unique polarization properties of the large-angle tilted fiber grating (LA-TFG), i.e. polarization-dependent loss and polarization-mode splitting, switchable dual-wavelength Q-switched and mode-locked pulses have been achieved with short and long cavities, respectively. For the mode-locking case, the laser was under the operation of nanosecond rectangular pulses, due to the peak-power clamping effect. With the increasing pump power, the durations of both single-and dual-wavelength rectangular pulses increase. It was also found that each filtered wavelength of the dual-wavelength rectangular pulse corresponds to an individual nanosecond rectangular pulse by employing a tunable bandpass filter.

Lyot-filter based multiwavelength random distributed feedback fiber laser

Multiwavelength lasing in the random distributed feedback fiber laser is demonstrated by employing an all fiber Lyot filter. Stable multiwavelength generation is obtained, with each line exhibiting sub-nanometer line-widths. A flat power distribution over multiple lines is also obtained, which indicates the contribution of nonlinear wave mixing towards power redistribution and equalization in the system. The multiwavelength generation is observed simultaneously in first and second Stokes waves. © 2014 SPIE.

Tunable multiwavelength SOA fiber laser with ultra-narrow wavelength spacing based on nonlinear polarization rotation

A tunable multiwavelength fiber laser with ultra-narrow wavelength spacing and large wavelength number using a semiconductor optical amplifier (SOA) has been demonstrated. Intensity-dependent transmission induced by nonlinear polarization rotation in the SOA accounts for stable multiwavelength operation with wavelength spacing less than the homogenous broadening linewidth of the SOA. Stable multiwavelength lasing with wavelength spacing as small as 0.08 nm and wavelength number up to 126 is achieved at room temperature. Moreover, wavelength tuning of 20.2 nm is implemented via polarization tuning.

Effect of Rayleigh-scattering distributed feedback on multiwavelength Raman fiber laser generation

We experimentally demonstrate a Raman fiber laser based on multiple point-action fiber Bragg grating reflectors and distributed feedback via Rayleigh scattering in an ∼22-km-long optical fiber. Twenty-two lasing lines with spacing of ∼100 GHz (close to International Telecommunication Union grid) in the C band are generated at the watt level. In contrast to the normal cavity with competition between laser lines, the random distributed feedback cavity exhibits highly stable multiwavelength generation with a power-equalized uniform distribution, which is almost independent on power. © 2011 Optical Society of America.

Effect of Rayleigh-scattering distributed feedback on multiwavelength Raman fiber laser generation

We experimentally demonstrate a Raman fiber laser based on multiple point-action fiber Bragg grating (FBG) reflectors and distributed feedback via Rayleigh scattering in a ∼22 km long optical fiber. Twenty two lasing lines with spacing of ∼100 GHz (close to ITU grid) in C-band are generated at Watts power level. In contrast to the normal cavity with competition between laser lines, the random distributed feedback cavity exhibits highly stable multiwavelength generation with a power-equalized uniform distribution which is almost independent on power. The current set up showing the capability of generating Raman gain of about 100-nm wide giving the possibility of multiwavelength generation at different bands. © 2011 SPIE.

Polarization switchable single/multi-wavelength fiber ring laser with an intra-cavity all fiber Lyot filter

we demonstrate a polarization switchable, single/ multi-wavelength fiber ring laser based on an intra-cavity all fiber Lyot filter. The laser can operate at single-, multi-wavelength by adjusting polarization controller, and givessingle polarization output. © 2015 OSA.

Two-channel fiber Bragg grating fabricated by femtosecond laser and its application in switchable dual-wavelength erbium-doped fiber laser

Two-channel fiber Bragg grating (TC-FBG) consisting of two localized sub-gratings parallel in the fiber core is fabricated by femtosecond laser. Utilizing the fabricated TC-FBG, stable and switchable dual-wavelength erbium-doped fiber laser at room temperature is demonstrated. © 2015 OSA.

Isolator-free switchable uni- and bidirectional hybrid mode-locked erbium-doped fiber laser

An Erbium-doped fibre ring laser hybrid mode-locked with single-wall carbon nanotubes (SWNT) and nonlinear polarisation evolution (NPE) without an optical isolator has been investigated for various cavity conditions. Precise control of the state of polarisation (SOP) in the cavity ensures different losses for counter-propagating optical fields. As the result, the laser operates in quasi-unidirectional regime in both clockwise (CW) and counter-clockwise (CCW) directions with the emission strengths difference of the directions of 22 dB. Furthermore, by adjusting the net birefringence in the cavity, the laser can operate in a bidirectional generation. In this case, a laser pumped with 75 mW power at 980 nm generates almost identical 790 and 570 fs soliton pulses with an average power of 1.17 and 1.11 mW. The operation stability and pulse quality of the soliton pulses in both unidirectional regimes are highly competitive with those generated in conventional ring fibre lasers with isolator in the cavity. Demonstrated bidirectional laser operation can find vital applications in gyroscopes or precision rotation sensing technologies.

Multiscale photoacoustic tomography using reversibly switchable bacterial phytochrome as a near-infrared photochromic probe.

Photoacoustic tomography (PAT) of genetically encoded probes allows for imaging of targeted biological processes deep in tissues with high spatial resolution; however, high background signals from blood can limit the achievable detection sensitivity. Here we describe a reversibly switchable nonfluorescent bacterial phytochrome for use in multiscale photoacoustic imaging, BphP1, with the most red-shifted absorption among genetically encoded probes. BphP1 binds a heme-derived biliverdin chromophore and is reversibly photoconvertible between red and near-infrared light-absorption states. We combined single-wavelength PAT with efficient BphP1 photoswitching, which enabled differential imaging with substantially decreased background signals, enhanced detection sensitivity, increased penetration depth and improved spatial resolution. We monitored tumor growth and metastasis with ∼ 100-μm resolution at depths approaching 10 mm using photoacoustic computed tomography, and we imaged individual cancer cells with a suboptical-diffraction resolution of ∼ 140 nm using photoacoustic microscopy. This technology is promising for biomedical studies at several scales.

Investigating the AGN-starburst connection in a nearby Seyfert galaxy with ALMA and multiwavelength data

The astrophysical context in which this thesis project lies concerns the comprehension of the mutual interaction between the accretion onto a Super Massive Black Hole (SMBH) and the Star Formation (SF), that take place in the host galaxy. This is one of the key topic of the modern extragalactic astrophysical research. Indeed, it is widely accepted that to understand the physics of a galaxy, the contribution of a possible central AGN must be taken into account. The aim of this thesis is the study of the physical processes of the nearby Seyfert galaxy NGC 34. This source was selected because of the wide collection of multiwavelength data available in the literature. In addition, recently, it has been observed with the Atacama Large Submillimeter/Millimeter Array (ALMA) in Band 9. This project is divided in two main parts: first of all, we reduced and analyzed the ALMA data, obtaining the continuum and CO(6-5) maps; then, we looked for a coherent explaination of NGC 34 physical characteristics. In particular, we focused on the ISM physics, in order to understand its properties in terms of density, chemical composition and dominant radiation field (SF or accretion). This work has been done through the analysis of the spectral distribution of several CO transitions as a function of the transition number (CO SLED), obtained joining the CO(6-5) line with other transitions available in the literature. More precisely, the observed CO SLED has been compared with ISM models, including Photo-Dissociation Regions (PDRs) and X-ray-Dominated Regions (XDRs). These models have been obtained through the state-of-the-art photoionization code CLOUDY. Along with the observed CO SLED, we have taken into account other physical properties of NGC 34, such as the Star Formation Rate (SFR), the gas mass and the X-ray luminosity.