"All-fiber" tunable laser in the 2 mu m region, designed for CO2 detection

A stable and tunable thulium-doped “all-fiber” laser offering a narrow linewidth has been created specifically to act as a compact and simple laser source for gaseous CO2 detection. This has been done through a careful design to match the laser output wavelengths to the CO2 absorption lines at 1.875 and 1.997 μm, respectively. A sustainable output power of 11 mW over a tuning range of 7 nm has been obtained by using a combination of a high-reflective fiber Bragg grating with a low-reflective broadband mirror, fabricated at the end of the fiber through silver film deposition. The tuning was achieved using the relaxation-compression mechanism of the fiber Bragg grating, which formed an integral part of the laser resonant cavity. A fiber Bragg grating at 1.548 μm was utilized as a wavelength reference to monitor the tuning of the laser output over the 2 μm wavelength range with a simple and inexpensive interrogator, to avoid the use of an expensive optical spectrum analyzer and to facilitate “in-the-field” operation. This “all-fiber” laser resonator has been shown to be superior in terms of laser tuning range, output power, and linewidth compared to that created with a fiber Bragg grating pair, which was limited by the nonuniform strain transfer to both fiber Bragg gratings

Capacity enhancement of virtual-mirror-based multiwavelength Brillouin-Erbium fiber laser.

An enhanced multiwavelength Brillouin-erbium fiber laser with virtual mirror concept is demonstrated. The performance of three linear amplifier schemes is investigated and optimized. Wide tuning range of 39 nm and maximum of nine laser lines are achieved utilizing a 915 nm pump laser at 616 mW pump power

Development of Photonic Crystal Fiber Based Gas/ Chemical Sensors

The development of highly-sensitive and miniaturized sensors that capable of real-time analytes detection is highly desirable. Nowadays, toxic or colorless gas detection, air pollution monitoring, harmful chemical, pressure, strain, humidity, and temperature sensors based on photonic crystal fiber (PCF) are increasing rapidly due to its compact structure, fast response and efficient light controlling capabilities. The propagating light through the PCF can be controlled by varying the structural parameters and core-cladding materials, as a result, evanescent field can be enhanced significantly which is the main component of the PCF based gas/chemical sensors. The aim of this chapter is to (1) describe the principle operation of PCF based gas/ chemical sensors, (2) discuss the important PCF properties for optical sensors, (3) extensively discuss the different types of microstructured optical fiber based gas/ chemical sensors, (4) study the effects of different core-cladding shapes, and fiber background materials on sensing performance, and (5) highlight the main challenges of PCF based gas/ chemical sensors and possible solutions

Seamless tuning range based-on available gain bandwidth in multiwavelength Brillouin fiber laser.

We experimentally demonstrate a simple widely tunable multiwavelength Brillouin/Erbium fiber laser that can be tuned over the entire C-band, thereby greatly improving the tuning range limitation faced by the previous Brillouin-erbium fiber laser architectures. Tuning range of 39 nm from 1527 nm to 1566 nm, which is only limited by the amplification bandwidth of the erbium gain was successfully achieved. At Brillouin pump wavelength of 1550 nm and 1480 nm laser pump and Brillouin pump powers of 130 mW and 2 mW respectively, all the generated output channels have peak power above 0 dBm, with the first output channel having a peak power of 8.52 dBm. The experimental set up that consists of only 4 optical components, is simple, devoid of the complex structure employed previously to enhance the tunability and feedback mechanism normally associated with multiwavelength Brillouin-erbium fiber laser sources. The generated output channels are stable, rigidly separated by 10 GHz (0.08 nm)

Stable single-mode operation of a narrow-linewidth, linear polarization erbium fibre ring laser using a saturable absorber

This paper describes the design and operation of a stable narrow-linewidth linearly polarized fiber ring laser using a polarization-maintaining (PM) erbium-doped fiber as a saturable absorber. The effect of the PM fiber on suppressing mode hopping is experimentally demonstrated and optimum conditions for single-mode operation are identified. Laser output power is ∼ 4.7 mW at 1535 nm for a pump power of 94 mW, the polarization extinction ratio is 24.8 dB, the SNR is larger than 45 dB, the relative intensity noise is below −104 dB/Hz at frequencies above 150 kHz, and the linewidth is less than 1.5 kHz. Potential applications of the fiber laser for interferometric or spectroscopic fiber sensors are briefly discussed

Optical fibre sensors based on the dynamic response of fibre lasers

We propose a optical fibre sensor system based on performing measurements during the transient period of operation of fibre lasers which may have potential for realising several types of sensor. Detailed experimental and theoretical study of the dynamics of a erbium fibre ring laser have been carried out, with simulation of the full transient period in order to characterise its operation. The results reveal how certain features of the dynamic response may be analytically related to the cavity parameters but also indicate the important role of spontaneous emission in determining the exact details of the response due to the involvement of a large number of cavity modes during the relaxation period. The principles may be applied for sensing by use of an intra-cavity sensor element which modifies the cavity properties in response to the measurand and by analysis of the cavity output in both time and spectral domains

Investigation of a tuneable mode-locked fibre laser for application to multi-point gas spectroscopy

This paper reports on an initial investigation into the operation of a mode-locked fiber laser system for application in gas spectroscopy as a multipoint multigas sensor. Wavelength selection is performed by use of multiple chirped gratings and fine tuning by using the dispersion properties of the chirped gratings. A tuning rate of /spl sim/0.014 nm per kHz change in mode-lock frequency (at the third harmonic) has been demonstrated, which is suitable for scanning across gas absorption lines. Key issues that have an important bearing on the tuning are discussed, including gain flattening and polarization drift. This paper investigates a method of multiplexing the sensor cells with the mode-locked system. Preliminary results for a two cavity system are presented to verify the principles of the technique

Tuneable L band multi-wavelength fibre laser using silicon wafers

We discuss a continuous-wave (CW) multi-wavelength fibre laser operating in the L-band, which has applications to gas sensing. Multi-wavelength operation of between two to eight lasing peaks with a spacing of around 0.9nm between each peak was demonstrated by placing silicon wafers in a micro-optic cell in order to produce a Fabry-Perot effect. Tuning over a region of 1565 to 1595nm was done by adjustment of the attenuation within the laser cavity. For our system we are interested in wavelength tuning for the detection of gases such as Hydrogen Sulphide (H2S) and Carbon Dioxide (CO2)