All-Optical Generation Of Multiwavelength Brillouinerbium Fiber Laser In Long-Wavelength Band

In this dissertation, the design and development of the multiwavelength Brillouin- Erbium fiber laser (BEFL) sources operating in the L-band transmission window is presented and characterized. Four different laser designs have been successfully demonstrated using a combination of stimulated Brillouin scattering effect in optical fiber and Erbium-doped fiber (EDF) amplification. The experimental results obtained from the characterization and optimization of these laser structures are the threshold power, number of the Stokes signals generated, Stokes signals power, self-lasing oscillation and the tuning range. The results are taken from the studies which have been carried out to analyze the effects of 1480 nm pump power, Brillouin pump (BP) power, BP wavelength and single mode fiber (SMF) length. The first laser structure is an efficient multiwavelength L-band BEFL pumped by a 1480 nm pump laser in a linear cavity configuration with direct BP injection into SMF. The issue of low gain efficiency of the L-band in the EDF lasers is resolved with the efficient linear cavity structure and the 1480 nm pumping scheme. The proposed laser structure exhibits a low threshold power of 18 mW and a maximum number of 26 stable output channels with 0.089 nm (10.5 GHz) channels spacing. The second and third laser structures are focused on the enhanced multiwavelength BEFL, in which the BP power is pre-amplified before entering the SMF within the laser cavity. The BP pre-amplification techniques - single pass and double pass represent a new mode of operation of multiwavelength BEFL’s. This intra-cavity BP pre-amplification provided by the EDF has created higher intensity of Brillouin Stokes signals generated in the single-mode fiber that leads to the homogenous gain saturation. This effect is able to suppress the built-up of the self-lasing cavity modes in a wider wavelength range and the number of output channels is also enhanced as compared to the conventional BP direct injection. Output of more than 33 laser channels is achieved and the tuning range is almost doubled than that of the conventional BP direct injection technique. Finally, for the fourth laser configuration, the multiwavelength BEFL incorporates either the amplified fiber loop mirror (AFLM) or non-linear amplified fiber loop mirror filter (AFLMF). Fifty-four stable output channels, with 0.089 nm channels spacing, have been achieved. A non-linear AFLMF which induces wavelengthdependent cavity loss and serves as an amplitude equalizer is employed to shift and flatten the EDF gain spectrum. Two control mechanisms have been demonstrated to shift and flatten the EDF gain profile through the adjustment of the polarization controller in the AFLMF. Therefore, the multiwavelength BEFL could be tuned over the whole L-band window from 1570 nm to 1610 nm with the average number of 24 output channels. In addition, flattening the EDF laser oscillation overcomes the requirements of the BP wavelength tuning, in conjunction with the adjustment of the polarization controllers in the fiber loop

Design and Development of a Novel Multi wavelength Brillouin-Erbium Fiber Laser

Multi-wavelength laser sources with constant wavelength spacing are of great interest in dense wavelength division multiplexing (DWDM) communication and sensors systems.As the transmission capacity of optical communication systems is approaching a few Tb/s through WDM method in recent years, multiwavelength generation technology becomes more important, considering that the complexity and the cost of the source will increase as the number of WDM channel increases.In this thesis, the design and development of a novel architecture of multi-wavelength Brillouin/Erbium fiber laser (BEFL) utilizing a linear cavity fiber loop technique is presented. Simultaneous and stable multiple wavelength lasing in a linear cavity have been achieved. The results are based completely on the experimental work. The requirement of internal feedback that is commonly used for multiple wavelengths Brillouin/Erbium fiber laser using a ring configuration is achieved by the proposed linear cavity design. This design used only a single 980 nm pump laser for its multiple wavelengths operation. Based on the design parameters namely; 980 nm pump power, Brillouin pump power, Brillouin pump wavelength and single mode fiber (SMF) the performance of a novel BEFL is presented in terms of threshold power, Stokes signal peak power, number of Stokes generated, stability of the Stokes and tuning range. Throughout this work, three lengths of SMF-fiber are used, 1.9 km, 8.8 km and 25 km.The optimization of Brillouin pump wavelength, power and Erbium gain led to a maximum possible number of Stokes. Twenty-two stable output laser lines with 10.88 GHz (0.088 nm) line spacing were obtained at 1558 nm that was the peak of Erbiumdoped fiber (EDF) gain. The injected Brillouin pump power into the 8.8 km SMF-fiber was set at 0.9 dBm and the EDF was pumped by 100 mW of 980 nm pump laser.The most efficient cascaded Brillouin Stokes operation occurred at the peak of Erbium gain centered on 1558 nm. The number of Stokes decreased as the Brillouin pump increased in the highest region of Erbium gain. On the contrary, the number of Stokes was proportional to the intensity of the Brillouin pump power outside this wavelength range. The best performance and conversion efficiency of Brillouin pump to the BEFL signal occurs at the lower levels of injected Brillouin pump power.A low threshold of 4 mW pump power with 2.3 mW launched Brillouin pump into the 8.8 km of SMF-fiber at 1558 nm was obtained. The tuning range of the Stokes signal must be taken into account both the Brillouin and EDF pump powers, at a fixed EDF pump power the Stokes signal can be tuned wider at a higher Brillouin pump power while higher EDF pump power produces smaller tuning range

Characteristics of multiple wavelengths L-band Brillouin-erbium comb fiber laser at low pumping powers

This paper presents the characteristics of multiple wavelength L-band Brillouin-erbium comb fiber laser with intra-cavity pre-amplified Brillouin pump power technique at low pumping powers. The issue of EDF gain depletion and Brillouin gain saturation are resolved by the proposed structure. The laser structure achieves a low threshold power and is able to produce high number of output channels at low pumping powers. It produces up to 33 channels at 50 mW and 0.042 mW of 1480 nm pump and Brillouin pump powers, respectively

Reduction of gain depletion and saturation on a Brillouin–erbium fiber laser utilizing a Brillouin pump preamplification technique

This paper presents the characteristics of a multiwavelength L-band Brillouin–erbium comb fiber laser with a preamplified Brillouin pump (BP) power technique at low pumping powers. The issue of erbium-doped fiber gain depletion and Brillouin gain saturation are resolved by the proposed structure. For long single-mode fiber length, the Stokes line emission occurs at low pumping powers because of the high strength of spontaneous Brillouin scattering, which provides a strong seed for coherent regenerative amplification of the Stokes line in the laser cavity. The laser structure achieves a low threshold power of 17 mW and is able to produce high number of output channels at low pumping powers. We experimentally show that the fiber laser structure can produce up to 37 channels at 55 and 0.045 mW of 1480 nm pump and BP powers, respectively

Enhanced Brillouin-erbium fiber laser with Brillouin pump pre-amplification technique

We demonstrate an enhanced multiwavelength Brillouin-Erbium comb fiber-laser in which the Brillouin-pump is pre-amplified before entering the single-mode fiber. By using this simple scheme, a lower external Brillouin pump power is required to create the Brillouin gain and suppress the laser cavity modes as compared to direct injection of Brillouin pump into the single-mode fiber. The proposed technique also demonstrates that the BEFL exhibits a wide tunability and can produce up to 27-stable output channels with 10.5 GHz channels spacing

Multiwavelength Brillouin-erbium fiber laser with double-Brillouin-frequency spacing

We demonstrate a multiwavelength Brillouin-erbium fiber laser with double-Brillouin-frequency spacing. The wider channel spacing is realized by circulating the odd-order Stokes signals in the Brillouin gain medium through a four-port circulator. The circulated odd-order Stokes signals are amplified by the Brillouin gain and thus produce even-order Stokes signals at the output. These signals are then amplified by erbium gain block to form a ring-cavity laser. Ten channels with 0.174 nm spacing that are generated at 0.5 mW Brillouin pump power and 150 mW pump power at 1480 nm can be tuned from 1556 nm to 1564 nm. The minimum optical signal-to-noise ratio of the generated output channels is 30 dB with maximum power fluctuations of ±0.5 dB

Broadly tunable multiple wavelength Brillouin fiber laser exploiting erbium amplification

We experimentally demonstrate a highly stable and flawless-tuning-range multiple wavelength Brillouin fiber laser incorporating an erbium gain block. Free-running cavity modes that inherently circulate in the cavity of a Brillouin/erbium fiber laser, which limits wavelength tunability, are completely suppressed. At a Brillouin pump power of 2 mW and 130 mW of 1480 nm pump power, we obtained seven output channels. The tunability of the generated channels is only limited to 35 nm by the amplification bandwidth of the erbium gain used in the experiment. The first four channels have an output power each above 1.6 dBm with the first and the seventh channels having a peak power of 8.19 dBm and −8.30 dBm

Enhanced flatness of 20 Ghz channel spacing multiwavelength Brillouin-Raman fiber laser with sub-millimeter air gap

We discover the technique of controlling the flatness in signal amplitude of a multiwavelength Brillouin-Raman fiber laser by employing an air-gap outside of the cavity. The structure that is adjustable within sub-millimeter length behaves as flexible optical feedback that provides modifiable portions of multiple Fresnel reflectivities. This is the main benchmark that allows the efficient management of gain competition between self-lasing modes and Brillouin Stokes waves that is vital for self-flattening initiation. When setting the Brillouin pump wavelength at 1529 nm and the air-gap distance to 0.4 mm, 296 Stokes lines are produced with a channel spacing of 0.158 nm. The lasing bandwidth is 46.60 nm that covers from 1529.16 to 1575.76 nm wavelength. In this case at Raman power of 950 mW, the intense Brillouin pump power of 2 dBm saturates the cascaded higher-orders lasing lines. As a result, the overall peak power discrepancy is maintained at just 1.8 dB where an average optical-signal-to-noise ratio of 20 dB is realized. To date, this is the widest bandwidth with the flattest spectrum attained in multiwavelength fiber lasers that incorporate a single Raman pump unit