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Abstract
We demonstrate a novel method of ring cavity Q-switched pulse erbium-doped fiber laser (EDFL) for liquid ammonia sensors. Q-switched pulse is generated using an indium tin oxide (ITO) deposited onto a side-polished fiber (SPF) as a saturable absorber (SA). The generated Q-switched pulses exhibit a repetition rate from 15.22 kHz to 28.28 kHz when the pump power is tuned from 77.2 mW to 211.60 mW. The shortest pulse width retrieved was 6.42 µs with a pulse energy of 11.23 nJ. A stable Q-switched pulse was obtained from the cavity configuration, with the repetition rate of 28.28 kHz. This pulse was then being used as a reference for the ammonia sensing purposes. When the liquid ammonia was injected into the setup, the wavelength and frequency shifts was observed by increasing the ammonia concentrations. From the results, the sensor can achieve good linear responses. To the best of our knowledge, this is the first report of Q-switched pulse EDFL based on side-polished fiber indium tin oxide (SPF-ITO) as a Q-switcher of the pulsed laser and a sensing transducer at the same time. These results indicates that the proposed SA is suitable for generating ultrashort pulse and optical sensors.
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1. Introduction
Many researchers are giving their attention on the Q-switching pulse in lasers production as this mode of operation has potential in many applications, especially in sensing, material processing, and telecommunications [1–3]. The Q-switched pulse can generate a low repetition rate in the kHz range with a pulse width in the microsecond range [4–6]. Meanwhile, a mode-locked operation producing high repetition rate pulse train, typically in the MHz frequencies with picosecond to femtosecond of pulse duration [7–9]. The passive technique is the most common approach in developing a Q-switched pulse. In this case, a nonlinear optical element device known as saturable absorber (SA) is inserted in the laser resonator. SA helps convert continuous waves lasers into an energetic train of pulses. Semiconductor saturable absorbers mirror (SESAM) is one of the SA types used to generate passive Q-switched pulses, which was first demonstrated in 1996 [10]. SESAMs have high stability and flexibility, but the challenges of using SESAMs are its complex fabrication process, narrow wavelength operation range, expensive, and its limited application [11,12]. Over the past few years, various types of SAs, such as carbon nanotubes [13,14], graphene [15,16], transition metal dichalcogenides (TMDs) [17,18], topological insulators (TIs) [19,20], black phosphorus [21], metal [22] and other SA-based materials [23–26], have been used to demonstrate their performances in generating Q-switched pulse fiber laser. However, carbon nanotubes have strong optical scattering, while graphene, its main issue is its relatively low optical absorption per layer that limits its usability; both materials are limited in applications [27,28].
On the other hand, TMDs have limited application for the mid-infrared (MIR) region due to their optical bandgap and complex fabrication despite of their thickness-dependent band-gap and unique absorption property [29,30]. Furthermore, the material that can cover the near-infrared (NIR) and MIR regions compared to TMDs is black phosphorus, which has more excellent saturable absorption properties but is weak in terms of its thermal stability [31]. Therefore, researchers strive to find SAs suitable for high damage thresholds, extensive saturable absorption, and rapid recovery time.
Indium tin oxide (ITO) is a transparent conductive oxide having unique characteristics which are comprehensive energy bandgap (>3.5eV), high optical transmittance and electrical conductivity. Most of the reports on ITO have been extensively studied in solar cells, optoelectronic devices, and transparent electrodes. Some researchers have proven that this ITO can function as an SA. The advantages of utilizing ITO as SA are large optical nonlinearity (as reported, approximately 360 fs of ultrafast recovery time [32]), high intensity-dependent refractive index [32], and exhibited lower carrier density [33]. In addition, the ITO serves as SA to have the plasmon frequencies situated closer to the infrared region [33] and wide-region of saturable absorption from 1600 nm to 2200 nm by controlling the concentration of tin doping [34]. A few works highlighted ITO as SA, such as Guo et al. [35] successfully generating a dark soliton using ITO colloidal liquid. SA is directly dropped on the fiber ferrules. The final dark solitons were developed at a wavelength of 1561.1 nm with frequency and pulse width of 22.06 MHz and 1.33 ns, respectively. In another work, Guo et al. [36] applied the same method to generate a passive Q-switched pulse. As reported, a Q-switched pulse was generated at a repetition rate of 81.28 kHz with the shortest pulse width of 1.15 µs. Simultaneously, Guo et al. successfully reported an ultrafast pulse as short as 593 fs [37] with an operating wavelength of 1560 nm and a frequency of 16.62 MHz. This SA was also said as the versatile mode-locked operations with single-wavelength pulses, dual-wavelength pulses, and triple-wavelength pulses with pulse widths of 1.67, 6.91, and 1 ns, respectively. The SA is fabricated using radio frequency magnetron sputtering at the end of fiber ferrules [38].
There are two methods to utilize SA in laser resonators: sandwiching thin film between two fiber ferrules and implementing SA material on unique fiber. Among the examples of special fiber are tapered fiber, microfiber, D-shaped fiber, and side-polished fiber. In this study, a side-polished fiber (SPF) based on evanescent field interaction SA is proposed, and it can generate stable Q-switched pulse EDFL. The SPF-based SA is formed by depositing ITO onto the polished surface of fiber using the DC magnetron sputtering technique. The SPF-ITO was then placed inside the ring cavity of EDFL and subjected to performance evaluation in generating Q-switched output pulses.
In addition, the SPF-based SA is also utilized as an optical transducer to observe ammonia concentration changes in wavelength and frequency domain based on the film structure (compact layers and porous). Innovation of reversible and compassionate ammonia sensing technology is often studied in active areas due to the widespread use of ammonia in industry and its toxic nature to animal and human bodies. Several ammonia monitoring techniques in gas samples have been investigated, including electrochemical sensors [39], optical ammonia sensors based on the up-converting luminescent nanoparticle [40], mobility spectrometry [41], and metal oxide semiconductor detectors [42]. However, these techniques cannot be employed to measure water-soluble ammonia and are only suitable for ammonia gas. Moreover, only a few works of literature are available to detect ammonia in solution [43–46]. Therefore, this study proposes a new concept method to detect ammonia concentration in solution using side-polished fiber coated with ITO as the sensing mechanism.
2. Results
2.1 Q-switched pulse
Initially, the Q-switched pulse is generated without an ammonia solution, and SPF-ITO acts as an SA. The continuous wave (CW) laser changes into a pulse regime when the pump power reaches 35.90 mW. A stable Q-switched pulse is achieved when the pump power is 77.2 mW, and the pump power is increased continuously until it reaches 211.60 mW to enable the optimized performance of the Q-switched pulses. The pulses abate when increasing the pump power above 211.60 mW and only reappear when the pump power is in the range of 77.20 mW to 211.60 mW. This indicates the SPF-ITO has not achieved the damage threshold. A preliminary study has been conducted to investigate the damage threshold of the SPF-ITO. The damage threshold of SPF-ITO is 246.70 mW. The uncoated SPF is integrated into the laser ring cavity to examine whether the Q-switched pulses depend on the ITO material, also known as SA. As a result, no pulse is generated on the oscilloscope, and only CW is observed, signifying that the SPF-ITO generates the Q-switched pulse as the Q-switcher.
Figure 1(a) shows the laser emission spectrum of the continuous wave (CW) and Q-switched pulse with the pump power operating at 211.60 mW. The 3dB bandwidth of CW and Q-switched spectrum is 0.96 nm and 2.80 nm, respectively. The Q-switched spectrum is broadening, caused by the self-phase modulation phenomenon with the central wavelength and output power of 1562.10 nm and -2.16 dBm, respectively. Figure 1(b) illustrates the pulse train where the pulse repetition duration is 34.60 µs corresponds with the pulse duration of 6.42 µs, measured from the full width half maximum of the single pulse obtained. This long pulse duration is due to the longer cavity length [47]. The shortest pulse duration (∼ns level) can be achieved for enhancing Q-switching operation by reducing the cavity losses, shortening the cavity length, and enhancing the cavity birefringence [48]. The repetition rate of a stable Q-switched pulse can be attained at 28.28 kHz, which corresponds to an RF signal with a signal-to-noise ratio (SNR) of 63.00 dB with resolution bandwidth (RBW) of 200 Hz, as shown in Fig. 1(c). The SNR value of the Q-switched pulse is more than 50 dB representing a highly stable pulse in the system. The performance of the Q-switched pulse with SPF-ITO is investigated by varying the pump power and fixing the wavelength. The long-term operation stability is significant for the application of ammonia sensors. Figure 1(d) shows the stability of Q-switched pulse spectra throughout one hour with a 5 minutes interval. Thus, the Q-switched spectrum is relatively stable within one hour, indicating this pulse can be employed for the sensing purposes.
Fig. 1. Q-switched: (a) optical spectrum (b) pulse train (c) RF signal and (d) stability of the spectrum.
The characteristics of the Q-switched pulse, namely the pulse repetition rate, pulse width, pulse energy, and average output power against the pump power, are further being investigated. Based on Fig. 2(a), the pulse repetition rate and pulse width are recorded as the function of the pump power increases from 77.2 mW to 211.60 mW. It can be seen that the pulse repetition rate increases from 15.22 kHz to 28.28 kHz, while the pulse width significantly reduces from 12.33 µs to 6.42 µs. The average output power and corresponding calculated single pulse energy are obtained in Fig. 2(b). As a result, the pulse energy and average output power increase linearly with the pump power. The maximum average output power and pulse energy are 0.318 mW and 11.23 nJ, respectively, when the pump power reaches 211.60 mW. No spectral modulation occurred, signifying the high stability of the laser output of the Q-switched pulse. Nevertheless, high pulse energy could be achieved using high-gain fiber, such as double-clad fiber. The pulse width value can be narrowed by reducing the cavity length and optimizing the ring cavity designs with a suitable output coupling ratio and cavity loss [49].
Fig. 2. The relationship between (a) repetition rate and pulse width, and (b) average output power and pulse energy against pump power.
2.2 Ammonia sensor
After obtaining a stable pulse of Q-switched, the sensing study of ammonia solution is performed using optical measurement by Pisco et al. [50], with the pump power fixed at 211.60 mW. The pump power of 211.60 mW was applied for all ammonia concentrations while the liquid ammonia measurement was conducted. The Q-switched spectra, as a function of ammonia concentration, are shown in Fig. 3(a). It is observed from Fig. 3(a) that there is a shift of wavelength from 1558.45 nm to 1554.25 nm when the ammonia concentration of 0.5 × 105 ppm is changed to 3.0 × 105 ppm with a different tuning range of 4.20 nm. The wavelength shifted from 1561.30 nm to 1559.35 nm when the ammonia concentration increased from 1 ppm to 10 ppm with another tuning range of 1.95 nm. The wavelength of 1562.14 nm (red line) indicates the reference wavelength without any ammonia solution. Increasing the ammonia concentration shifts the wavelength to the blue side, which is to the shorter wavelength region. The shifted wavelength spectra have average 3 dB bandwidth of 1.02 nm, which is narrowed with respect to the increase of ammonia concentration. As to compare, the 3 dB bandwidth for the reference wavelength is 2.80 nm. The narrow of wavelength spectra is due to the nonlinear effects when the different concentrations of the ammonia interacts with SPF-ITO, give the average refractive index of the sensing area is increased.
Fig. 3. (a) A plot of shifts in optical spectrum (wavelength shift) as a function of various ammonia concentrations, (b) a graph of shifts in the frequency domain as a function of multiple ammonia concentrations, (c) linear relationship of frequency as a function of low ammonia concentration with R2 of 0.9866, (d) linear relationship of frequency as a function of high ammonia concentration with R2 of 0.9591.
In addition, from the oscilloscope, the shifts of the frequency domain are detected against different ammonia concentration with RBW of 100 Hz as illustrated in Fig. 3(b). The repetition rate in the RF signal increases as the ammonia concentration increases; the 28.08 kHz (red line) indicates the value of the repetition rate without the ammonia solution. The RF signal shifts from 30.10 kHz to 33.70 kHz with the total RF signal different of about 3.6 kHz when the ammonia concentrations change from 1 ppm to 10 ppm. Meanwhile, the RF signal shifts from 35.50 kHz to 43.50 kHz when the ammonia concentration is increased from 0.5 × 105 ppm to 3.0 × 105 ppm, giving the total RF frequency different of about 8.0 kHz. Both wavelength and RF shifting for ammonia concentrations from 1 ppm to 10 ppm has more sensitivity on the ITO device due to the device able to sense in low concentrations of ammonia molecules. Hence, the Q-switched spectra and RF signal can be analyzed, and the ammonia concentration changes can be conducted by employing the proposed setup.
The linear relationship between the repetition rates as a function of different ammonia concentrations is plotted in Fig. 3(c) and Fig. 3(d), respectively. The repetition rate is almost linear, with varying concentrations of ammonia. The correlation factor, R2 is found to be 0.9896 for ammonia concentrations from 1 ppm to 10 ppm with a gradient of 0.3873 kHz/ppm, while the correlation factor for the ammonia concentrations from 0.5 × 105 to 3.0 × 105 ppm is 0.9591 with a slope of 3 × 10−5 kHz/ppm. Ammonia concentrations from 1 ppm to 10 ppm exhibits high sensitivity.
Detecting the repeatability of the sensor is extremely important in the experiment. Hence, it can be seen through a re-test to establish whether the RF signal can return to the initial position or the reference frequency, which is 28.28 kHz. In addition, the structure characteristics of repeatability and response recovery are measured by re-testing whether the RF signal could be returned to the reference frequency by utilizing a 3.0 × 105 ppm concentration of ammonia.
Figure 4(a) illustrates the response characteristics for the frequency over time when the ammonia is detected in four cycles. At room temperature conditions, the SPF coated with ITO is immersed in the ammonia solution (arrow down) with a concentration of 3.0 × 105 ppm. The frequency value increases from the reference until 43.5 kHz, which is the maximum value of the frequency of the ammonia concentrations at 3.0 × 105 ppm. The reading of frequency is recorded every two minutes. After achieving the maximum frequency value, the solution is being removed from the petri dish. The RF signal returns to the reference frequency when the SPF-ITO is placed in the air (arrow up). Based on the plot, it displays a stable growth of response to the ammonia solution by utilizing the SPF-ITO as the transducer. The experiment is repeated several times with the same concentrations of ammonia. It is proven that the sensor RF signal is essentially stable and attains a relatively fast recovery time in the air.
Fig. 4. (a) The repeatability of SPF sensor coated with ITO using 3.0 × 105 ppm of ammonia concentration at room temperature, (b) steady-state response properties of a sensor with different concentrations.
Figure 4(b) shows the steady-state response properties of an optical fiber system coated with ITO with ammonia concentrations of 0.5 × 105 to 3.0 × 105 ppm. It can be observed that when the concentration of ammonia is 0.5 × 105 ppm and the SPF-ITO is immersed in the solution (arrow down), and the RF signal changes from the reference frequency to 35.50 kHz. After 20 minutes, the RF reading remains unchanged, and the SPF-ITO is placed in the air (arrow up) to change the frequency back to the reference frequency within 10 minutes. These steady-state response properties are similar when other ammonia concentrations are used. Thus, this experiment shows that the sensor has good repeatability, reversibility, and steady-state response properties.
3. Discussions
The mechanism behind the SPF-ITO-based SA helps passive approach to initate the pulse regime according to Pauli Exclusion principle. The band structure of the SA is similar to the two energy-level structures which consists of valence band and conduction band. High- and low- intensity of lights able to pass through the SA when placed it in the laser cavity. Most of the electrons in valence band will absorb photons in low intensity and excite the electron to conduction band. The absorbance of the photons is reduced when a high intensity of light passes through the SA due to the fully occupied electrons in conduction band, thereby blocking further absorption. This occurs due to the excitation by the photons from the low intensity light. High-intensity light passes through the SA with a small loss at each round trip, forming an intensity-dependent attenuation. As a result, low-intensity lasers experience large lossed, while high-intensity lasers experience small losses.
In Q-switching, the SA provides sufficient loss within the cavity laser so that the system will not be lasing at low population inversion. Instead, it allows for an increase in population inversion, which stores energy in the cavity. As the gain level approaches the cavity limits, the systems start to lase and increase the power inside the cavity. Intracavity power is adequate to saturate the absorber, substantially altering the laser oscillator quality (Q). With the decreased cavity loss, the power built up within the gain medium population inversion is rapidly depleted, producing an output pulse. When the gain is adequately depleted, the intracavity power will no longer be sufficient to saturate the SA that begins to recover. If the loss returns faster than the population inversion, then the process will start again, and developing a Q-switched pulse train. Thus, the SPF-ITO-based SA helps to generate a stable Q-switched pulse fiber laser for being used as ammonia sensing.
The stable Q-switched pulse has been used as a laser source to monitor the shifting of wavelength and RF signal due to the interactions between the ammonia molecules and ITO. The interactions cause the average effective refractive index to increase. Figure 5 illustrates the interactions between the ammonia molecules and ITO thin film. The nonlinear effect in the optical fiber affects the spectral broadening caused by the self-phase modulation, narrowing as the ammonia concentration increases.
The mechanisms of this sensor response depend on the structure of the ITO coating, with two basic ITO film structures that can be distinguished: compact layers and porous. Ammonia molecules adsorb the open surface of the ITO film in the case of compact layers. Ammonium adsorption should not interest the bulk refractive index, while surface optical effects should occur depending on the surface structure. Chemisorption of ammonia can lead to two main consequences: the shift of charges with increased free electron concentration and the formation of the small area of charge region at the surface. Thus, high electric tension is formed in this area. The influence mentioned earlier, the high electric field appears on the surface, and the diffusion of the rich atoms of indium, tin, or oxygen vacancies on the grain's surface could be realized.
Direct adsorption of ammonia molecules on the open surface and their diffusion through pores to optical fiber–indium tin oxide interface occurs in the case of porous layers. The sensor's response is controlled by diffusion time and depends on the size of the pore. Ammonia may be another potential interaction factor in the chemisorption of molecules on the grain boundaries, with a consequent diffusion between the ITO grains inside the interstitial sites. The interaction of the target molecules with the sensitive film can increase the average effective refractive index of the sensitive layer. Hence, it increases the transmittance at the fiber-film interface.
4. Material and method
4.1 Preparation and characterization of SPF-ITO
In this study, the Quorum-Q 150R S DC sputtering device is used where the ITO target is placed at the negative cathode to be sputtered under conditions of glow discharge using a DC power supply, as illustrated in Fig. 6(a). The ITO target is bombarded at 80 mA sputtering current, 800 s deposition time, and 9 × 10−2 mBar base vacuum pressure of environmental argon gas. The sputtering technique is the best method as it can provide the counter electrode due to high electrical conductivity. Unlike other ways, it can also yield high-quality and uniform material on the substrate. Figure 2(b) shows the optical microscope images of coated SPF with ITO. The diameter of the polished region after the coating is 136.118 µm. Due to the ITO's transparency, the coated ITO cannot be seen clearly in the images.
Fig. 6. (a) Schematic diagram of the sputtering process onto the side-polished fiber. Microscopic images of coated SPF with ITO (a) before and (b) after sputtering
The nonlinear optical absorption properties of the prepared SPF coated with ITO were investigated using balanced twin detector measurement. A homemade mode-locked EDFL with an operating wavelength of 1564.75 nm, pulse width of 716.5 ps, and repetition rate of 12.64 MHz is used as a seed pulse. The resultant power-dependent absorption data were fitted using the following saturation model [51].
Fig. 7. (a). The modulation depth of side-polished fiber coated with ITO (b) Thickness of ITO over deposited time. (c) Characterization of ITO for selected thickness.
4.2 Sensing study of ammonia detection
For the sensing study, about 30% of ammonia solution concentrations from R&M Chemical are diluted with distilled water. The dilution of 30% ammonia solution is prepared to obtain concentrations from 1 to 10 ppm and 0.5 × 105 to 3.0 × 105 ppm for sensing. The procedure to prepare the dilution from the stock solution is shown in Fig. 8. It involves measuring the quantity of the solvent in the final volume of the diluted solution and then measuring the volume of the stock solution containing this amount of solvent. Diluting a given quantity of stock solution with solvent does not change the amount of solute present in the solution; only the volume of the solution changes. The relationship between the volume and concentration of the stock solution and the volume and concentration of the desired diluted solution can be expressed mathematically as Ms Vs = Md Vd where Ms is the concentration of the stock solution, Vs is the volume of the stock solution, Md is the concentration of the diluted solution, and Vd is the volume of the diluted solution.
In Fig. 8(a), Vs contains the desired amount of solute Ms measured from the stock solution of known concentration. First, the measured volume of the stock solution is transferred to a volumetric flask shown in Fig. 8. Then, the measured volume in the flask is diluted with solvent up to the volumetric mark based on Ms Vs = Md Vd. The solution is shaken well to ensure thorough mixing [52].
4.3 Laser configuration of ammonia Q-switched pulse fiber sensor
Figure 9 shows the experimental arrangement of ammonia detection using SPF coated with ITO in a single ring cavity. The cavity consists of a wavelength division multiplexing (WDM), an EDF, an isolator, a polarization controller, an SPF-ITO-based SA, and an optical coupler. Firstly, a 980 nm laser diode is launched in the ring cavity through a 980/1550 nm WDM. The amplification of light occurs using a 5 m length of EDF M-5. The EDF acts as a gain medium with 6.43 dB/m peak absorption at 1530 nm, 5.09 dB/m absorption at 979 nm. The end fiber of EDF is spliced with the input port of the isolator. The isolator forces the light to propagate in a forwarding direction inside the isolator. Three paddles of the polarization controller (PC) are placed between the isolator and SPF-ITO to adjust the polarization state of the laser resonator. The SPF-ITO is integrated after PC by fusion splicing at both ends of the SPF to the cavity. To avoid unfavourable fluctuation, the SPF-ITO is tapped on the glass slide to ensure that the fiber is in a straight-line configuration. The glass slide is also tapped on the petri dish to fix the position of the glass slide. A 90/10 optical coupler is used to extract the output from the cavity where 10% portion of the output is tapped out from the coupler, while 90% is spliced with 1550 nm of WDM port to complete the ring cavity. The total ring cavity is 11.6 m, where 17 mm is the length of the polished region of the SPF. 10% of the optical coupler is connected to a 50/50 optical coupler to observe and analyze the pulses with several optical instruments. An Anritsu MS9740A optical spectrum analyzer (OSA) with a resolution of 1.0 nm is utilized to measure the laser output spectrum. Tektronix MDO3104 oscilloscope is coupled with 5 GHz InGaAs Biased Detector DET08CFC/M photodetector to measure the time-resolved pulsed laser output signal. After achieving a stable Q-switched pulse, the coated SPF is immersed in ammonia solution with different concentrations, as shown in Fig. 10. Changes in output results in terms of wavelength and RF signal can be observed in the optical spectrum analyzer and oscilloscope, respectively.
5. Conclusions
The novel method of Q-switched pulse EDFL for ammonia sensing is successfully designed and analyzed using SPF coated with ITO (SPF-ITO). The Q-switched pulse EDFL exhibited a maximum repetition rate, pulse width, and pulse energy of 28.28 kHz, 6.42 µs, and 10.99 nJ, respectively, at the pump power of 211.60 mW. This stable Q-switched pulse EDFL is used as a laser source to monitor the sensing of ammonia solution by utilizng the SPF-ITO as the sensing device. As a result, ammonia sensing can be observed through the changes in the peak wavelength and frequency obseved from the OSA and oscilloscope, respectively. The wavelength shifts from 1558.45 nm to 1554.25 nm when using ammonia concentrations from 0.5 × 105 to 3.0 × 105 ppm. The wavelengths shift from 1561.30 nm to 1559.35 nm when the ammonia concentrations increase from 1 to 10 ppm. In the oscilloscope, the RF signal shifts from 35.50 kHz to 43.50 kHz when the ammonia concentrations increase from 0.5 × 105 to 3.0 × 105 ppm. Meanwhile, the RF signal shifts from 30.10 kHz to 33.70 kHz when the ammonia concentrations increase from 1 to 10 ppm. The changes in wavelength and frequency domain are observed due to the interactions of ammonia molecules, and the ITO film causes alterations in the refractive index. Thus, the SPF-ITO acts as the SA creating the pulse in the optical cavity as well as working as the sensor in this proposed configuration, which giving it a high potential value for better exploration towards the technique in the future.
Funding
Ministry of Higher Education, Malaysia (FRGS/1/2019/WAB05/UTHM/02/4 (Grant No: K170)).
Acknowledgment
This research was supported by Ministry of Higher Education (MOHE) through Fundamental Research Grant Scheme (FRGS/1/2019/WAB05/UTHM/02/4).
Disclosures
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Author contributions. NUHH Zalkepali: Investigation and Analysis. NA. Awang: Supervision. NNHEN Mahmud: Investigation. A.A. Latif: Supervision. All authors contributed to the paper preparation and discussion
Data availability
Data underlying the results presented in this paper are not publicly available at this time but may be obtained from the authors upon reasonable request.
References
1. L. Wei, D.-P. Zhou, H. Y. Fan, and W.-K. Liu, “Graphene-based Q-switched erbium-doped fiber laser with wide pulse repetition- rate range,” IEEE Photonics Technol. Lett. 24(4), 309–311 (2012). [CrossRef]
2. H. Ahmad, M. Z. Zulkifli, F. D. Muhammad, A. Z. Zulkifli, and S. W. Harun, “Tunable graphene-based Q-switched erbium-doped fiber laser using fiber Bragg grating,” J. Mod. Opt. 60(3), 202–212 (2013). [CrossRef]
3. A. Y. Chamorovskiy, A. V. Marakulin, A. S. Kurkov, T. Leinonen, and O. G. Okhotnikov, “High-repetition-rate Q-switched holmium fiber laser,” IEEE Photonics J. 4(3), 679–683 (2012). [CrossRef]
4. N. U. H. H. Zalkepali, N. A. Awang, Y. R. Yuzaile, Z. Zakaria, A. A. Latif, A. H. Ali, and N. N. H. E. N. Mahmud, “Indium tin oxide thin film based saturable absorber for Q-switching in C-band region,” J. of Phy.: Conference Series.1371(1), IOP Publishing (2019).
5. N. U. H. H. Zalkepali, N. A. Awang, Y. R. Yuzaile, Z. Zakaria, A. A. Latif, A. H. Ali, and N. N. H. E. N. Mahmud, “Tunable indium tin oxide thin film as saturable absorber for generation of passively Q-switched pulse erbium-doped fiber laser,” Indian J. Phys. 95(4), 733–739 (2021). [CrossRef]
6. N. U. H. H. Zalkepali, N. A. Awang, A. A. Latif, Z. Zakaria, Y. R. Yuzaile, and N. N. H. E. N. Mahmud, “Switchable dual-wavelength Q-switched fiber laser based on sputtered indium tin oxide as saturable Absorber,” Results Phys. 17, 103187 (2020). [CrossRef]
7. A. N. Azmi, N. A. Awang, Z. Zakaria, F. S. A. Hadi, and Y. R. Yuzaile, “Saturable Absorption Measurement of Platinum as Saturable Absorber by using Twin Detector Method Based on Mode-Locked Fiber Laser,” J. of Sci. and Techno. 9(3), 3 (2017).
8. J. Wang, X. Liang, G. Hu, Z. Zheng, S. Lin, D. Ouyang, and T. Hasan, “152 fs nanotube-mode-locked thulium-doped all-fiber laser,” Sci. Rep. 6(1), 28885 (2016). [CrossRef]
9. Y. Hu, X. Jin, G. Hu, M. Zhang, Q. Wu, Z. Zheng, and T. Hasan, “Hybrid mode-locked erbium-doped fiber laser with black phosphorus saturable absorber,” In the 2018 Conference on Lasers and Electro-Optics (CLEO.)IEEE. (2018, May).
10. U. Keller, K.J. Weingarten, F.X. Kartner, D. Kopf, B. Braun, I.D. Jung, R. Fluck, C. Honninger, N. Matuschek, and J.A derAu, “Semiconductor saturable absorber mirrors (SESAM's) for femtosecond to nanosecond pulse generation in solid-state lasers,” IEEE J. Sel. Top. Quantum Electron. 2(3), 435–453 (1996). [CrossRef]
11. H. Li, H. Xia, C. Lan, C. Li, X. Zhang, J. Li, and Y. Liu, “Passively Q-switched erbium-doped fiber laser based on few-layer MoS2 saturable absorber,” IEEE Photonics Technol. Lett. 27(1), 69–72 (2015). [CrossRef]
12. Z. Sun, T. Hasan, F. Torrisi, D. Popa, G. Privitera, F. Wang, F. Bonaccorso, D. M. Basko, and A. C. Ferrari, “Graphene mode-locked ultrafast laser,” ACS Nano 4(2), 803–810 (2010). [CrossRef]
13. X. Zhang, S. Zhao, Y. Li, Y. Zhang, D. Li, and K. Yang, “Liquid-phase exfoliated semiconducting single-walled carbon nanotubes as a saturable absorber for passively Q-switched laser,” J. Nanophotonics 12(02), 1 (2018). [CrossRef]
14. H. Ahmad and S. A. Reduan, “Passively Q-switched S-band thulium fluoride fiber laser with multi-walled carbon nanotube,” Chin. Opt. Lett. 16(1), 010609 (2018). [CrossRef]
15. R. Z. R. R. Rosdin, F. Ahmad, N. M. Ali, S. W. Harun, and H. Arof, “Q-switched Er-doped fiber laser with low pumping threshold using graphene saturable absorber,” Chin. Opt. Lett. 12(9), 091404 (2014). [CrossRef]
16. Z. T. Wang, Y. Chen, C. J. Zhao, H. Zhang, and S. C. Wen, “Switchable dual-wavelength synchronously Q-switched erbium-doped fiber laser based on graphene saturable absorber,” IEEE Photonics J. 4(3), 869–876 (2012). [CrossRef]
17. Y. Li, Y. Lou, J. He, G. Zeng, L. Tao, B. Zhou, and Y. Zhao, “Q-switched ytterbium fiber laser based on rhenium diselenide as a saturable absorber,” J. Phys. D: Appl. Phys. 52(46), 465101 (2019). [CrossRef]
18. L. Li, R. Lv, S. Liu, X. Wang, Y. Wang, Z. Chen, and J. Wang, “Transition metal dichalcogenide (WS2 and MoS2) saturable absorbers for Q-switched Er-doped fiber lasers,” Laser Phys. 28(5), 055106 (2018). [CrossRef]
19. Z. Yu, Y. Song, J. Tian, Z. Dou, H. Guoyu, K. Li, and X. Zhang, “High-repetition-rate Q-switched fiber laser with high quality topological insulator Bi2 Se3 film,” Opt. Express 22(10), 11508–11515 (2014). [CrossRef]
20. N.U.H.H. Zalkepali, N. A. Awang, Y. R. Yuzaile, A. A. Latif, F. Ahmad, A. N. Azmi, F. S. A. Hadi, and Z. Zakaria, “Passively Q-Switched Pulse Erbium Doped Fiber Laser Using Antimony (III) Telluride (Sb2Te3) thin Film as Saturable Absorber,” Int. J. Eng. Technol. 7(4.30), 313–316 (2018). [CrossRef]
21. A. H. H. Al-Masoodi, M. Yasin, M. H. M. Ahmed, A. A. Latiff, H. Arof, and S. W. Harun, “Mode-locked ytterbium-doped fiber laser using mechanically exfoliated black phosphorus as saturable absorber,” Optik 147, 52–58 (2017). [CrossRef]
22. I. A. Alani, M. Q. Lokman, M. H. M. Ahmed, A. H. H. Al-Masoodi, A. A. Latiff, and S. W. Harun, “A few-picosecond and high-peak-power passively mode-locked erbium-doped fibre laser based on zinc oxide polyvinyl alcohol film saturable absorber,” Laser Phys. 28(7), 075105 (2018). [CrossRef]
23. S. Li, Z. Kang, N. Li, H. Jia, M. Liu, J. Liu, N. Zhou, W. Qin, and G. Qin, “Gold nanowires with surface plasmon resonance as saturable absorbers for passively Q-switched fiber lasers at 2 µm,” Opt. Mater. Express 9(5), 2406–2414 (2019). [CrossRef]
24. H. Mu, Z. Liu, Z. Wan, B. Shabbir, L. Li, T. Sun, S. Li, W. Ma, and Q. Bao, “Evanescent Field Functional Cu3-xP Nanoparticles as Effective Saturable Absorbers with high Repeatability for Femtosecond Soliton Pulse generation,” arXiv preprint arXiv:1901.08714 (2019).
25. J. Mohanraj, V. Velmurugan, and S. Sivabalan, “Tunable passively Q-switched ytterbium-doped fiber laser using MoWS2/rGO nanocomposite saturable absorber,” Opto-Electron. Rev. 27(1), 18–24 (2019). [CrossRef]
26. G. Liu, F. Zhang, T. Wu, Z. Li, W. Zhang, K. Han, F. Xing, Z. Man, X. Ge, and S. Fu, “Single-and dual-wavelength passively mode-locked erbium-doped fiber laser based on antimonene saturable absorber,” IEEE Photonics J. 11(3), 1–11 (2019). [CrossRef]
27. H. Zhang, Q. Bao, D. Tang, L. Zhao, and K. Loh, “Large energy soliton erbium-doped fiber laser with a graphene-polymer composite mode locker,” Appl. Phys. Lett. 95(14), 141103 (2009). [CrossRef]
28. A. Martinez and Z. Sun, “Nanotube and graphene saturable absorbers for fibre lasers,” Nat. Photonics 7(11), 842–845 (2013). [CrossRef]
29. S. Wang, H. Yu, H. Zhang, A. Wang, M. Zhao, Y. Chen, L. Mei, and J. Wang, “Broadband few-layer MoS2 saturable absorbers,” Adv. Mater. 26(21), 3538–3544 (2014). [CrossRef]
30. H. Liu, A. P. Luo, F.Z. Wang, R. Tang, M. Liu, Z. C. Luo, W. C. Xu, C. J. Zhao, and H. Zhang, “Femtosecond pulse erbium-doped fiber laser by a few-layer MoS2 saturable absorber,” Opt. Lett. 39(15), 4591–4594 (2014). [CrossRef]
31. J. Sotor, G. Sobon, W. Macherzynski, and K. M. Abramski, “Harmonically mode-locked Er-doped fiber laser based on a Sb2Te3 topological insulator saturable absorber,” Laser Phys. Lett. 11(5), 055102 (2014). [CrossRef]
32. M. Z. Alam, I. De Leon, and R. W. Boyd, “Large optical nonlinearity of indium tin oxide in its epsilon-near region,” Science 352(6287), 795–797 (2016). [CrossRef]
33. G. V. Naik, V. M. Shalaev, and A. Boltasseva, “Alternative plasmonic materials: beyond gold and silver,” Adv. Mater. 25(24), 3264–3294 (2013). [CrossRef]
34. M. Kanehara, H. Koike, T. Yoshinaga, and T. Teranishi, “Indium tin oxide nanoparticles with compositionally tunable surface plasmon resonance frequencies in the near-IR region,” J. Am. Chem. Soc. 131(49), 17736–17737 (2009). [CrossRef]
35. J. Guo, H. Zhang, Z. Li, Y. Sheng, Q. Guo, X. Han, Y. Liu, B. Man, T. Ning, and S. Jiang, “Dark solitons in erbium-doped fiber lasers based on indium tin oxide as saturable absorbers,” Opt. Mater. (Amsterdam, Neth.) 78, 432–437 (2018). [CrossRef]
36. J. Guo, H. Zhang, C. Zhang, Z. Li, Y. Sheng, C. Li, X. Bao, B. Man, Y. Jiao, and S. Jiang, “Indium tin oxide nanocrystals as saturable absorbers for passively Q-switched erbium-doped fiber laser,” Opt. Mater. Express 7(10), 3494–3502 (2017). [CrossRef]
37. Q. Guo, Y. Cui, Y. Yao, Y. Ye, Y. Yang, X. Liu, S. Zhang, X. Liu, J. Qiu, and H. Hosono, “Exploiting ITO colloidal nanocrystals for ultrafast pulse generation,” arXiv preprint arXiv:1701.07586 (2017).
38. Q. Guo, J. Pan, D. Li, Y. Shen, X. Han, J. Gao, B. Man, H. Zhang, and S. Jiang, “Versatile Mode-Locked Operations in an Er-Doped Fiber Laser with a Film-Type Indium Tin Oxide Saturable Absorber,” Nanomaterials 9(5), 701 (2019). [CrossRef]
39. I. Lähdesmäki, A. Lewenstam, and A. Ivaska, “A polypyrrole-based amperometric ammonia sensor,” Talanta 43(1), 125–134 (1996). [CrossRef]
40. H. S. Mader and O. S. Wolfbeis, “Optical ammonia sensor based on upconverting luminescent nanoparticles,” Anal. Chem. 82(12), 5002–5004 (2010). [CrossRef]
41. G. A. Eiceman, M. R. Salazar, M.R. Rodriguez, T. F. Limero, S. W. Beck, J. H Cross, R. Young, and J. T. James, “Ion mobility spectrometry of hydrazine, monomethylhydrazine, and ammonia in air with 5-nonanone reagent gas,” Anal. Chem. 65(13), 1696–1702 (1993). [CrossRef]
42. R. C. Li, P. C. Chan, and P. W. Cheung, “Analysis of a MOS integrated gas sensor using a surface chemistry based model,” Sens. Actuators, B 28(3), 233–242 (1995). [CrossRef]
43. A. I. Vogel and G. H. Jeffery, Vogel's textbook of quantitative chemical analysis. Wiley. (1989).
44. T. V. Duncan, “Applications of nanotechnology in food packaging and food safety: barrier materials, antimicrobials and sensors,” J. Colloid Interface Sci. 363(1), 1–24 (2011). [CrossRef]
45. M. Abaker, A. Umar, S. Baskoutas, G. N. Dar, S. A. Zaidi, S.A. Al-Sayari, A. Al-Hajry, S. H. Kim, and S.W. Hwang, “A highly sensitive ammonia chemical sensor based on α-Fe2O3 nanoellipsoids,” J. Phys. D: Appl. Phys. 44(42), 425401 (2011). [CrossRef]
46. M. M. Rahman, A. Jamal, S. B Khan, and M. Faisal, “Characterization and applications of as-grown β-Fe2O3 nanoparticles prepared by hydrothermal method,” J. Nanopart. Res. 13(9), 3789–3799 (2011). [CrossRef]
47. B. Dong, J. Hao, J. Hu, and C.-Y. Liaw, “Short linear-cavity Q-switched fiber laser with a compact short carbon nanotube based saturable absorber,” Opt. Fiber Technol. 17(2), 105–107 (2011). [CrossRef]
48. J.J. Degnan, “Optimization of passively Q-switched lasers,” IEEE J. Quantum Electron. 31(11), 1890–1901 (1995). [CrossRef]
49. S. T. Dubas and V. Pimpan, “Green synthesis of silver nanoparticles for ammonia sensing,” Talanta 76(1), 29–33 (2008). [CrossRef]
50. M. Pisco, M. Consales, S. Campopiano, R. Viter, V. Smyntyna, M. Giordano, and A. Cusano, “A novel optochemical sensor based on SnO2 sensitive thin film for ppm ammonia detection in liquid environment,” J. Lightwave Technol. 24(12), 5000–5007 (2006). [CrossRef]
51. E. Garmire, “Resonant optical nonlinearities in semiconductors,” IEEE J. Sel. Top. Quantum Electron. 6(6), 1094–1110 (2000). [CrossRef]
52. D. R. Lide, (Ed.). CRC handbook of chemistry and physics (Vol. 85). CRC press. (2004).
