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Pulse width modulation (PWM) is used to generate pulses with variable duty cycle rate. The rapid rising and falling edges of PWM signal minimises the switching transition time and the associated switching losses. This paper presents a DC motor speed controller system using PWM technique. The PWM duty cycle is used to vary the speed of the motor by controlling the motor terminal voltage.The motor voltage and revolutions per minutes (RPM) obtained at different duty cycle rates. As the duty cycle increases, more voltage is applied to the motor. This contributes to the stronger magnetic flux inside the armature windings and the increasethe RPM. The characteristics and performance of the DC motor speed control system was investigated. In this paper, a PIC microcontroller and a DC-DC buck converter are employed in the DC motor speed controller system circuit. The microcontroller provides flexibility to the circuit by incorporating two push button switches in order to increase and to decrease the duty cycle rate. The characteristics and performance of the motor speed controller system using microcontroller was examined at different duty cycle rate ranging from 19% to 99%.

We demonstrate a multi-wavelength fiber laser based on nonlinear polarization rotation (NPR) in dual-cavity configuration with two output ports. The laser employs a piece of erbium doped fiber (EDF) and semiconductor optical amplifier (SOA) as the gain medium in a separate cavity. By incorporating PCF in the dual cavity the non-linear polarization rotation (NPR) effect is enhanced and thus higher output and more oscillating lasing can be achieved. The laser produces three strong lines with a spacing of 2.40 nm and side mode suppression ratio (SMSR) of more than 10 dB at 1535 nm region. Another output produces 8 lines of optical comb with a spacing of 0.54 at 1570 nm region.

A passively self-starting mode-locked fiber ring laser is demonstrated using a highly concentrated Erbium doped fiber (EDF) with a saturable absorber. The effect of EDF length on the performance of the laser is investigated. Stable stretched pulses are obtained at wavelength region of 1560nm with a repetition rate ranging from 10.1 to 12.1 MHz and a pulse width stretching from 0.52 to 0.75 ps as the EDF length is reduced from 4.5 to 1.5 m. The repetition rate goes higher as the cavity length decreases when a shorter EDF is used but the pulse width reduces as the EDF length increases since the total group velocity dispersion (GVD) in the cavity is close to zero. The article is published in the original.

A wideband spectrum-sliced amplified spontaneous emission (ASE) source operating in 1900-nm region is demonstrated using a newly developed double-clad ytterbium-sensitized thulium-doped fiber (YTF) and a Sagnac loop mirror. The YTF used was drawn from a D-shape preform, which was fabricated using the modified chemical vapor deposition (MCVD) and solution doping technique. The YTF was pumped by a 980-nm multimode laser to generate an ASE at 1900 nm through the transition of thulium ion from 3F4 to 3H6 with the assistance of ytterbium to thulium ion energy transfer. The broadband ASE was spectral sliced by the loop mirror, which was constructed using a 3-dB coupler and a piece of polarization maintaining fiber (PMF). A wideband comb with channel spacing of 3.3 nm and an extinction ratio of 9 dB was achieved with a multimode pump power of 1 W within a wavelength range of more than 300 nm. The center of the comb spectrum was at 1888 nm with peak power of around -53 dBm.

A new spacing-switchable multiwavelength erbium-doped fiber laser (EDFL) is demonstrated using switchable nonlinear polarization rotation (NPR) and stimulated Brillouin scattering (SBS) effects. The laser employs a 100-m-long photonic crystal fiber in conjunction with a four-port circulator in a figure-of-eight arrangement to provide the intensity-dependent transmission effect, as well as to discriminate the even-order and odd-order Brillouin Stokes to have a double-frequency Brillouin Stokes output. Without the Brillouin pump (BP), the laser operates in an NPR mode to produce at least 22 lasing wavelengths with a side mode suppression ratio of more than 10 dB and a wavelength spacing of 0.27 nm. In the Brillouin erbium fiber laser mode, at least 30 Brillouin lines with a spacing of 0.16 nm are obtained at BP power of 3 dBm and 980-nm pump power of 120 mW.

A multiwavelength fiber ring laser is demonstrated using a nonlinear polarization rotation (NPR) effect. An isolator and a photonic crystal fiber are incorporated in an Erbium doped fiber laser (EDFL) to generate intensity-dependent transmission induced by the NPR effect which allows the multiwavelength generation at room temperature. A stable 17 lasing lines in 1560 nm region are generated. The multiwavelength Erbium doped fiber laser (EDFL) exhibits spacing of 0.27 nm. EDF pump power was varied from 30 mW to 120 mW. Higher Erbium doped fiber (EDF) pump power generally leads to more multiwavelength generation at the expense of lower SNR due to higher noise level.

Multi-wavelength Ytterbium-doped fiber laser (YDFL) is demonstrated using a longitudinal mode interference assisted by a four-wave mixing (FWM) effect in a ring laser cavity. The gain medium is a 16 m long of the fabricated (Ytterbium-doped fiber) YDF, which has a core composition of 0.8 wt % of Yb2O3, 1.8 wt % of Al2O3 and 23 wt % of GeO2, Ytterbium ion fluorescence lifetime of 1.1 ms and absorption of 9.0 dB/m at the pump wavelength of 976 nm. 20 m long photonic crystal fiber (PCF) is used to provide FWM effect so that the energy of different oscillating lines can be redistributed to improve multi-wavelength operation. The proposed laser generates 12 lines of optical comb with a line spacing of approximately 0.59 nm at 1035 nm region.

A simple multi-wavelength source is demonstrated based on spectral slicing of supercontinuum (SC) light using a Sagnac loop mirror. A mode locked fiber laser with pulse width of 800 fs is employed to generate the SC in photonic crystal fiber (PCF). The SC light extending from 1200 nm up to the wavelength region above 1750 nm is obtained at the amplified pulse pump power of 30 dBm. By slicing the SC with a loop mirror, a multiwavelength comb spectrum is obtained with different channel spacing for different operating wavelength region. Spacings of 1.5, 2.3, and 2.9 nm are shown at wavelength regions of 1220, 1450, and 1730 nm, respectively. It is also observed that the signal to noise ratio (SNR) increases from 15 to 20 dB as the operating wavelength increases from 1220 to 1730 nm region.

An efficient multi-wavelength Brillouin erbium fiber laser is demonstrated using an improved configuration with a broadband fiber Bragg grating and a piece of photonic crystal fiber. The laser generates more than 55 lines of optical comb with a line spacing of approximately 0.09 nm in a 1,565-5 nm region using pump powers of 3 dBm and 150 mW for the Brillouin and 980-nm pumps, respectively. The Brillouin erbium fiber laser with a fiber Bragg grating's reflectivity of 50% obtained a higher number of comb lines compared to that of 99% reflectivity.

A single wavelength ring Brillouin fiber laser (BFL) is demonstrated using a piece of Photonic crystal fiber (PCF) as a gain medium.The BFL has a peak power of more than 0 dBm, a side mode suppression ratio of more than 26 dB and a BP threshold power of approximately 9.4 dBm with 100-m long PCF. The threshold of the BFL increases with the use of shorter PCFs. The Brillouin gain coefficient was calculated to be 3.2 × 10−11 m/W using the measured BP threshold power. A figure of merit of the proposed BFL is calculated to be nearly 76 times larger than the best silica-based configurations reported to date. The induced time delay is approximately 0.056 (ns/mW/m), which is suitable for slow light-based applications. © 2011 Wiley Periodicals, Inc. Microwave Opt Technol Lett 53:1450–1453, 2011; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.25984

A multi-wavelength laser source is demonstrated with a semiconductor optical amplifier (SOA) as a gain medium. A multi-wavelength comb with equal spacing is achieved due to Fabry-Perot modes of the SOA which oscillates in the ring cavity. A 100 m long photonics crystal fiber (PCF) is inserted in the ring cavity to provide a nonlinear gain by four-wave mixing (FWM) so that the output comb spectrum can be greatly broadened and flattened. The stability of the ring laser is also increased due to the efficient FWM phenomenon occurring in the PCF. The SOA-based laser can generate 35 lasing lines with equal spacing of 0.28 nm and extinction ratios of more than 30 dB at room temperature. The number of channels of the multi-wavelength laser can be controlled flexibly by changing the ratio of the coupler used in the ring cavity configuration as well as controlling the polarization state of the oscillating laser.

The generation of a multiple wavelength source using a bismuth-based erbium-doped fiber (Bi-EDF) in a linear cavity configuration is demonstrated. The configuration uses a pair of optical circulators at the input and output ends of the cavity to form a resonator for multi-wavelength generation in conjunction with optical couplers to inject the Brillouin pump (BP) and to tap the output at the two ends. The Brillouin erbium fiber laser (BEFL) comb with a 2.15 m of Bi-EDF has a wavelength spacing of 0.09 nm and operates in long-wavelength (L-) band region. A stable output laser comb of 50 lines is obtained at a BP of 1568.2 nm and 5 dBm and two 1480 nm pumps at 120 mW. The injected BP wavelength and power as well as the 1480 nm pump powers have a great effect on the number of lines and output power of the BEFL. This configuration is compact due to the use of the significantly shorter Bi-EDF as the linear gain medium, and can be made more compact by replacing the single-mode fiber with highly non-linear fibers such as holey fibers.

A new linear cavity BEFL configuration for increased Stokes-line generation is proposed and demonstrated utilizing a 2 × 2 coupler at the end of the linear cavity. The proposed linear cavity is able to generate up to 33 Stokes lines in the 1590-nm region at a channel spacing of 0.089 nm. The Stokes lines are generated at a BP power of 4 dBm and a 1480-nm pump power of 100 mW. The number of Stokes generated by the proposed BELF is higher compared to conventional BEFL configurations in which the 2 × 2 coupler is placed in the middle of the linear cavity. The number of Stokes lines generated is observed to depend on the 1480-nm pump power as well as the operating wavelength region, which must be as close as possible to the lasing bandwidth of the free-running BEFL. The proposed multiwavelength BEFL is able to operate stably at room temperatures and is also compact due to the use of a 215-cm bismuth-based EDF as the linear gain medium.

A simple fiber laser configuration based on a semiconductor optical amplifier (SOA) is proposed for obtaining multi-wavelength oscillation at room temperature, in which a Sagnac loop mirror is used as the wavelength selective component. The SOA has a flat gain of approximately 23dB within a bandwidth of 12 nm at a small input signal power. The loop mirror was constructed using a 3dB coupler and polarization maintaining fiber (PMF). The output spectrum of the proposed laser can be adjusted by controlling the bias current of the SOA and is quite stable at room temperature. At a bias current of 150 mA, six lines are obtained with at least −40 dBm output power and 25dB signal-to-noise ratio (SNR). The channel spacing and number of lines is determined by the length of polarization maintaining fiber (PMF) used in the loop mirror. The channel spacing of the proposed laser is 1.49 nm with a PMF 3 m. The multi-wavelength comb output can also be tuned by adjusting the operating temperature of the SOA. The multi-wav...

A multi-wavelength Brillouin/erbium-doped fiber laser (BEFL) operating in the 1573 nm region is proposed and demonstrated. The system employs both linear and nonlinear gain from a bismuth-based erbium-doped fiber (Bi-EDF) approximately 215 cm long and a single mode fiber (SMF) of various lengths to generate an optical comb with a spacing of approximately 0.089 nm. Two 3 dB couplers were used to form a looping arm in the system in order to produce cascaded Brillouin Stokes waves as internal feedback for multi-wavelength operation. A stable output laser comb with 10 lines at more than − 13 dBm was obtained with 4.85 dBm Brillouin pump power and two 140 mW pumps at 1480 nm. The 1480 nm pumps' power and SMF length have a significant effect on the number of wavelengths and on the output power of the generated wavelength comb.

A multi-wavelength Brillouin/erbium-doped fiber laser (BEFL) which operates in 1594 nm region is demonstrated using a 215 cm long Bismuth-based EDF and SMF. Two optical circulators were used at the output ends of the system to form a linear cavity to produce a cascaded Brillouin Stokes and anti-Stokes. A stable output laser comb of more than 20 lines was obtained with a spacing of approximately 0.089 nm at a Brillouin pump power of 4 dBm and two 1,480-nm pumps at powers of 100 mW. The number of lines is relatively higher compared with the ring cavity BEFL.

A Supercontinuum (SC) generation in photonic crystal fiber (PCF) is demonstrated using an amplified picosecond stretched-pulses from a passive mode-locked Bismuth-based Erbium-doped fiber laser (Bi-EDFL). The Bi-EDFL employs of a piece of a highly nonlinear 49 cm long Bismuth-based Erbium-doped fiber (Bi-EDF), an optical isolator and a polarization controller in a cavity to generate a mode-locked stretched-pulse via a nonlinear polarization rotation technique. It operates at 1560 nm with a repetition rate of 42 MHz and a pulse width of 131 fs. The SC lights, which extends from 1250 nm to 1910 nm as well as in the visible green wavelength region are obtained with a 100 m long PCF and the amplified pump power of 30 dBm.

All-fiber passively mode-locked (ML) soliton fiber laser is demonstrated based on the combination of two ML mechanisms, single wall carbon nanotube saturable absorber, and nonlinear polarization rotation.The gain medium is a 10-m long erbium-doped fiber, which is pumped by a 980-nm laser diode in a ring configuration. A stable soliton laser is succesfully achieved using the filter, which functions to reshape and maintain the soliton pulse in the cavity. It operates at 1588 nm with a repetition rate of 8.3 MHz and a pulse width of 0.79 ps. The output spectrum shows strong Kelly sidebands indicating that the pulse duration is near the minimum possible value. © 2012 Wiley Periodicals, Inc. Microwave Opt Technol Lett 54:1430–1432, 2012; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.26850

A stable multi-wavelength erbium-doped fiber laser based on four-wave mixing (FWM) in a photonic crystal fiber (PCF) is demonstrated in this paper. The phase matching condition for four-wave mixing in the photonic crystal fiber has been enhanced using a seed signal and a polarisation controller to control the states of polarisation in the ring laser cavity. At a maximum pump power of 1480 nm, 5 lines are observed with nearly 2.15 nm spacing between the lines, and with a signal to noise ratio of more than 20 dB. The number of channels and wavelength spacing can be controlled by varying the output coupler ratio.

The performance of single-wavelength Brillouin fiber lasers (BFLs) is investigated for different gain medium. An efficient BFL is demonstrated using a piece of 100-m-long PCF as the gain medium. The BFL provides a peak power of 0 am and a side mode suppression ratio of more than 30 dB with the threshold power of 8.5 dBm for the BFL generation. However, the threshold is much lower for the BFL configured with 20 km long non-zero dispersion shifted fiber, which has a smaller core size. With this fiber, the threshold power of the BFL is obtained at 5 am, and this power increases with the shorter length of the gain medium. (C) 2010 Wiley Periodicals, Inc. Microwave Opt Technol Lett 52: 2158-2160, 2010; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.25386

A linear cavity Brillouin fiber laser (BFL) is proposed and demonstrated for multi-wavelength operation. The BFL uses a single mode fiber (SMF) as a non-linear gain medium and an optical circulator to generate a linear cavity resonator. Two couplers are used to inject the Brillouin Pump (BP) and tap the BFL output respectively. The effect of the coupler ratio on the BFL performance is studied by keeping constant the ratio of the first coupler and varying the ratio of the second coupler. 11 simultaneous lines with a line spacing of 0.8 nm are obtained at a BP of 11.7 dBm and a coupler ratio of 95:5. The laser output is stable at room temperature with 5 lines obtained at above – 30 dBm, and has the largest signal to noise ratio observed at the remaining lines. The proposed BFL has the advantage of being able to operate at any wavelength and is only dependent on the available BP wavelength.

Multiwavelength sources are expected to play a major role in future photonic networks, where optical time-division multiplexing (OTDM) and wavelength division multiplexing (WDM) are employed (Teh et al., 2002; Ye et al., 2010; Liu et al., 2006; Parvizi et al., 2011; Harun et al., 2010; Zhong et al., 2010). Various approaches have been taken to develop this source such as by exploiting the nonlinear effects in an optical fiber as well as spectral slicing of a supercontinuum source.

This study investigates the capability of an ultrashort pulse laser in a ring cavity of erbium-doped fiber laser (EDFL). Generation of pulses was performed by inserting a carbon-nanotube saturable absorber in this EDFL. Mode-locked laser was achieved with an average power of 20mW and a peak power of 3.37kW. Pulse duration laser of 950fs with repetition rate of 6.24MHz was obtained at 3dB bandwidth of 3.65nm. Higher power with better pulse duration can be achieved by optimizing the cavity length.

We demonstrate a multiwavelength Brillouin Erbium fiber laser with double channel spacing operating at room temperature using a hybrid linear-ring cavity. 7 simultaneous lines with 0.175nm line spacing using both a 100mW pump at 980nm and a 4dBm Brillouin pump are achieved by circulating the odd-order Stokes signals in a 7km long single mode fiber based sub-ring cavity, allowing for the formation of even-order Stokes signals at the output

A multiwavelength generation was demonstrated using a Brillouin/Erbium fiber laser (BEFL) with stimulated Brillouin scattering (SBS) effect. BEFL utilizes single‐mode fiber (SMF) and erbium‐doped fiber as nonlinear and linear gain medium [1–4]. The linear gain of the EDF provides high gain to amplify the Stokes signal produced through SBS in the SMF. We demonstrate a linear cavity BEFL utilizing a fiber Bragg grating (FBG) to act as a cavity loop mirror. The effect of FBG reflectivity ranging from 5 nm to 40 nm in brillouin erbium fiber laser cavity is studied. The bandwidth of the oscillating modes is determined by the FBG bandwidth. 19 stable output channels with 0.088 nm line spacing were obtained for the 40 nm setup. 23 Stokes were achieved when the FBG bandwidth was reduced to 10 nm. Though more Stokes were generated at smaller FBG bandwidth, there is a trade‐off for the tuning range.

An Erbium‐doped fiber laser and amplifier (EDFLA) system has been demonstrated. The setup consists of an erbium‐doped fiber (EDF), a wavelength selective coupler, a tunable bandpass filter (TBF), single mode fiber (SMF), a 980‐nm pump, two circulators, and a 90:10 output coupler. EDFLA functions as a widely stable tunable fiber laser covering C and L bands simultaneously as an amplifier. The amplifier has shown flattened gain for both C‐ and L‐bands.

A multiwavelength Brillouin-erbium fiber laser based on highly non linear fiber in a ring cavity is presented. With utilization of a partially reflective Fiber Bragg grating of 50% reflection as loop mirror up to 21 stable Brillouin stokes lines of 0.08nm spacing could be generated. This was achieved utilizing short length of 1km highly non-linear fiber and pre-amplified by erbium doped fiber of only 7m.

This paper presents properties and characterizations of different Erbium-Ytterbium doped fiber (EYDF) lengths in Brillouin Erbium-Ytterbium Doped Fiber Laser (BEYDFL) system. BEYDFL systems have the potential to become multi-channel source in Dense Wavelength Division Multiplexing (DWDM) system. BEYDFL is a unique laser source that can produces multiple channels simultaneously with dense and constant channel line spacing of about 0.08 nm. This system utilizes both linear and nonlinear gain from EYDF (8 m and 12 m lengths) and an 7 km single mode fiber. The 12 m EYDF is pumped with 100 mW 1058 nm laser diode to generate 30 lines with a total peak power of 4.5 mW at a Brillouin pump power of −2 dBm at wavelength of 1565 nm. The BEYDFL with 12 m EYDF generates more lines but the BEYDFL with 8 m EYDF shows a wider operating tuning range.

Positive gain is obtained in 1460 to 1520 nm region of single pass configuration erbium doped fiber amplifier (EDFA) using macro-bending approach. The standard step index EDF is bent on a 0.65 cm radius rod to suppress the ASE at the longer wavelength in order to achieve the amplification in shorter wavelength region. The bent EDF shows gain and noise figure improvement than that of unbent EDF. The effect of multiple EDF lengths on gain and noise figure across S-band region is also studied.

A nanosecond pulsed laser is demonstrated using the stimulated Brillouin scattering (SBS) effect in a nonlinear photonic crystal fiber (PCF). The Brillouin fiber laser (BFL) uses a 50-m-long PCF in a simple ring cavity to generate a self-starting pulse as the Brillouin power reaches 16.5 dBm based on the relaxation oscillation technique. The BFL generates a pulse train with repetition rates of 2.7 MHz and 5.4 MHz depending on the BP power. The pulse width of the laser is obtained to be 190 ns at the BP power of 16.5 dBm and is maintained at around 72 ns as the pump power is set within 17.7 dBm and 18.5 dBm. The maximum pulse energy of 20 nJ is obtained at BP power of 17.4 dBm. This SBS based pulse laser is fairly stable at room temperature.

A tunable multiwavelength Brillouin-erbium fiber laser is experimentally demonstrated with a double-Brillouin-frequency spacing. This double-frequency shifter is constructed by incorporating a four-port circulator to isolate and circulate the odd-Stokes signals through the 10 km long non-zero dispersion shifted fiber, which acts as a Brillouin gain medium. The output even-order Stokes signals are amplified in the erbium gain block formed in a ring cavity. Up to 15 lasing lines with a wavelength spacing of 0.173 nm have been achieved at a 980 nm pump power of 50 mW and a Brillouin pump of 3 dB m. The multiwavelength laser source exhibits a 10 nm tuning range from 1552 to 1562 nm with the optical signal-to-noise ratio of the desired output channels at around 34.5 dB.

A mode-locked erbium-doped fiber laser (EDFL) is demonstrated using a highly concentrated erbium-doped fiber (EDF) as the gain medium in a ring configuration with and without a saturable absorber (SA). Without the SA, the proposed laser generates soliton pulses with a repetition rate of 12 MHz, pulse width of 1.11 ps and energy pulse of 1.6 pJ. By incorporating SA in the ring cavity, the optical output of the laser changes from soliton to stretched pulses due to the slight change in the group velocity dispersion. With the SA, a cleaner pulse is obtained with a repetition rate of 11.3 MHz, a pulse width of 0.58 ps and a pulse energy of 2.3 pJ.

We demonstrate a multi-wavelength erbium-doped fiber laser (EDFL) using erbium gain and four-wave mixing (FWM) effect in a piece of erbium-doped fiber (EDF) with high erbium ion concentration. The EDF has a pump absorption rate of 24.6 dB/m at 979 nm and is bi-directionally pumped by 980-nm laser diodes. FWM effect redistributes the energy of different oscillating lines and causes multi-wavelength operation. The laser generates more than 22 lines of optical comb with a line spacing of approximately 0.10 nm at the 1569-nm region using only 1.5-m-long EDF.

Utilization of a partially reflective fiber Bragg grating in the development of a multiwavelength Brillouin-erbium fiber laser is proposed. A ring cavity with a preamplified Brillouin pump configuration is implemented to demonstrate much better performance in comparison with the previously reported results obtained with different configurations. The combination of a 7 km long single-mode fiber and a 10 m long erbium-doped fiber ultimately yields the generation of up to twenty-one Brillouin Stokes lines. The laser configuration provides a greater tuning range of 21 nm at a Brillouin pump power of 2 mW and 980 nm pump power of 20 mW, and requires a much lower pump power to initiate lasing.

Brillouin fibre laser is demonstrated using a very short length of photonic crystal fibre (PCF). A simple ring resonator is used in the experiment which consists of a 20 m long highly nonlinear PCF and 49 cm long Bismuth-based erbium-doped fibre (Bi-EDF). The proposed Brillouin laser is able to generate up to 3 Stokes and 3 anti-Stokes lines in the 1560 nm region at a channel spacing of 0.09 nm.