- Email: [email protected]
Stabilized and tunable single-longitudinal-mode erbium fiber laser employing ytterbium-doped fiber based interference filter
Optics & Laser Technology 88 (2017) 180–183
Contents lists available at ScienceDirect
Optics & Laser Technology journal homepage: www.elsevier.com/locate/optlastec
Research Note
Stabilized and tunable single-longitudinal-mode erbium fiber laser employing ytterbium-doped fiber based interference filter
crossmark
⁎
Chien-Hung Yeha, , Ning Tsaia, Yuan-Hong Zhuanga, Chi-Wai Chowb, Jing-Heng Chena a b
Department of Photonics, Feng Chia University, Taichung 40724, Taiwan Department of Photonics and Institute of Electro-Optical Engineering, National Chiao Tung University, Hsinchu 30010, Taiwan
A R T I C L E I N F O
A BS T RAC T
Keywords: Erbium-doped fiber laser Single-longitudinal-mode (SLM) Wavelength tunable
In this demonstration, to achieve stabilized and wavelength-selectable single-longitudinal-mode (SLM) erbiumdoped fiber (EDF) laser, a short length of ytterbium-doped fiber (YDF) is utilized to serve as a spatial multimode interference (MMI) inside a fiber cavity for suppressing multi-longitudinal-mode (MLM) significantly. In the measurement, the output powers and optical signal to noise ratios (OSNRs) of proposed EDF ring laser are measured between −9.85 and −5.71 dBm; and 38.03 and 47.95 dB, respectively, in the tuning range of 1530.0– 1560.0 nm. In addition, the output SLM and stability performance are also analyzed and discussed experimentally.
1. Introduction Stable and wavelength-tunable erbium-doped fiber (EDF)-based lasers are fascinated in recent years, due to their useful applications of optical fiber communications [1,2], optical fiber sensors [3], optical instrument testing [4], and light detection and ranging (LIDAR) [5]. Mode-hopping and homogenous broadening of EDF would result in unstable and multi-longitudinal-mode (MLM) output in EDF-based laser [6–8]. Hence, to complete the single-longitudinal-mode (SLM) in EDF ring laser with a longer cavity, several technologies have been proposed and demonstrated, such as utilizing umpumped EDF saturated absorber filter, optical narrow band filter, and compound-ring filter [9–11]. Furthermore, to accomplish wavelength-tuning in EDF laser scheme, the tunable bandpass filter (TBF), Fabry-Perot tunable filter (FP-TF), fiber Bragg grating (FBG) and temperature-controlled mode technique have proposed and employed inside a ring cavity generally [12–15]. In this demonstration, we propose and demonstrate experimentally a stable and wavelength-selectable EDF ring laser scheme with SLM output. To achieve SLM operation, a short length of 10 cm ytterbiumdoped fiber (YDF) is used inside a ring cavity to act as a spatial multimode interference (MMI) for suppressing densely MLM. In this measurement, the observed output power and optical signal to noise ratio (OSNR) of proposed EDF ring laser are between −9.85 and −5.71 dBm; and 38.03 and 47.95 dB, respectively, in a wavelength range of 1530.0–1560.0 nm. Moreover, the output stabilities of power difference and wavelength variation can be maintained within 0.3 dB
⁎
and 0.02 nm, respectively, in a short-term observation measurement of 30 min. 2. Proposed erbium fiber architecture Fig. 1 presents the proposed stable and wavelength-selectable EDF ring laser architecture. The proposed EDF ring laser is consisted of a commercial C-band erbium-doped fiber amplifier (EDFA), a 1×2 and 10:90 optical coupler (OCP), a C-band tunable bandpass filter (TBF), a polarization controller (PC), a 3-port optical circulator (OC), an optical fiber mirror (OFM), and a short length of 10 cm YDF. Here, the YDF (LIEKKI, Yb1200-10/125DC) has the core size of 10 μm diameter and cladding absorption of 1.8 dB/m at the wavelength of 920 nm. In the measurement, the saturated output power and effective amplification bandwidth of EDFA are 13 dBm and 34 nm (1528–1562 nm), respectively. The 3 dB bandwidth and tuning range of TBF are 0.4 nm and 30 nm (1530–1560 nm), respectively. The TBF is used to generate and tune the different lasing wavelengths. The PC is employed to maintain single-polarization status and obtain maximum output power of lasing wavelength. As indicated in Fig. 1, the lasing wavelength would transmit through the YDF and OFM via OC in clockwise direction. Hence, the lasing wavelength would pass through the YDF twice. In this measurement, an optical spectrum analyzer (OSA) is employed to measure the output power and wavelength. Fig. 2 shows the measured absorption spectrum of YDF under a wavelength range of 1520–1560 nm. As seen in Fig. 2, the absorption coefficient of YDF is between 3.52 dB/0.1 m and 4.02 dB/0.1 m in the spectrum range of
Corresponding author. E-mail address: [email protected] (C.-H. Yeh).
http://dx.doi.org/10.1016/j.optlastec.2016.09.024 Received 1 August 2016; Received in revised form 9 September 2016; Accepted 14 September 2016 0030-3992/ © 2016 Elsevier Ltd. All rights reserved.
Optics & Laser Technology 88 (2017) 180–183
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Fig. 5. (a) Measured output power and (b) optical signal to noise ratios (OSNR) spectra of proposed EDF laser in the wavelengths of 1530.0–1560.0 nm.
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Fig. 3. Schematic diagram of the points of splicing different-type fibers.
Frequency (Hz) Fig. 6. Observed electrical power spectrum in the frequency range of (a) 1 GHz, (b) 100 MHz and (c) 10 MHz, respectively.
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proposed EDF ring laser can suppress the MLM greatly. Next, to realize the output stabilities of power and wavelength for the proposed EDF laser, a wavelength of 1554.02 nm with −6.91 dBm output power is also used for SLM measurement initially. Fig. 8(a) and (b) present the measured stability performances of output power and wavelength, respectively, under a short-term observation measurement of 30 min. Here, we can observe that the maximum power variation and wavelength fluctuation are 0.3 dB and 0.02 nm (readout resolution of OSA=0.01 nm), as illustrated in Fig. 8(a) and Fig. 8(b) respectively during the observing time of 30 min. In addition, after one hour observation, the observed stabilities of output power and wavelength are still stable within the same measured variances. As a result, the proposed EDF ring laser with a short length YDF of 10 cm not only can achieve SLM output, but also can accomplish stable and tunable operation. In the SLM measurement, we also select three wavelengths of 1533.00, 1548.00 and 1560.00 nm for testing respectively. The entire measured results of these lasing wavelengths are with stable SLM output.
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Observing Time (minute) Fig. 8. Measured stability performances of (a) output power and (b) lasing wavelength, respectively, under a short-term observation measurement of 30 min.
1520–1560 nm. Besides, there are two absorption peaks at the wavelengths of 1527.5 and 1550.0 nm respectively, as shown in Fig. 2. Moreover, the 10 cm YDF is utilized in proposed EDF ring laser to serve as spatial multi-mode interference (MMI) possibly. The short length of YDF would result in great losses for the generating wavelength because of losses in the points of splicing different-type fibers and diffraction in higher-order spatial modes inside this YDF. And the schematic diagram is depicted in Fig. 3. As a result, the proposed EDF ring laser can achieve the SLM output by using an YDF-based filter.
4. Conclusion In this paper, we have first proposed and investigated a stable and wavelength-tunable SLM EDF ring laser by using a short-length YDF of 10 cm long. The YDF was used to serve as spatial multi-mode interference to filter the MLM significantly. In the previous EDF ring laser schemes [16,17], using unpumped EDF-based saturated absorber filter with 1–2 m long was the common method to act as a narrow bandwidth autotracking filter for SLM. However, the proposed EDF ring laser with 10 cm YDF-based filter based on MMI effect to SLM. Hence, the measured output power and OSNR of proposed EDF laser were between −9.85 and −5.71 dBm; and 38.03 and 47.95 dB, respectively, in a wavelength range of 1530.0–1560.0 nm. Moreover, the output stabilities of power difference and wavelength variation could be maintained within 0.3 dB and 0.02 nm, respectively, in an observation measurement of 1 h.
3. Experimental results Fig. 4 shows the measured wavelength spectra of proposed EDF ring laser in the wavelength range of 1530.0–1560.0 nm with a tuning step of ~3 nm. Here, we observe that the background amplified spontaneous emission (ASE) noise of 1530 nm can be suppressed significantly. Fig. 5(a) and (b) present the measured output powers and optical signal to noise ratios (OSNRs) of proposed EDF ring laser in the wavelengths of 1530.0–1560.0 nm. In the measurement, the obtained output powers and OSNRs are between −9.85 and −5.71 dBm; and 38.03 and 47.95 dB, respectively. With the increase of lasing lightwave to the longer wavelength progressively, the observed output power is also increase. Besides, the measured trend of output power curve is similar to Fig. 2. The maximum output power and OSNR are measured at the wavelengths of 1560.0 and 1533.0 nm, respectively, as seen in Fig. 5(a) and (b). In addition, the observed side-mode suppress ratio (SMSR) of each lasing wavelength is very closing to measured result of Fig. 5(b). Then, we will verify the SLM output for the proposed EDF laser by using delayed self-homodyne method. The experimental setup is composed by Mach-Zehnder interferometer (MZI) with a 30 km single-mode fiber (SMF) and a 10 GHz PIN-based photodiode (PD). Moreover, a 3 GHz electrical spectrum analyzer (ESA) is utilized to measure the output electrical spectrum. Here, a wavelength of 1554.02 nm is selected for SLM measurement initially. Fig. 6(a)–(c) show the observed electrical power spectra in the frequency range of 1 GHz, 100 MHz and 10 MHz, respectively. There is no electrical spike observed in the three measured bandwidths, as shown in Fig. 6(a)–(c). Furthermore, during 1 h observation time by the same experiment, the measured electrical power spectrum of ESA is very stable and without any MLM spike noise. When the YDF is 15 cm long, we also can observe the same electrical power spectrum with SLM. While we reduce the YDF length to 5 and 7 cm respectively, the observed electrical power spectra are MLM and also increase the background noise, as shown in Fig. 7. Therefore, according to the experimental result, the 10 cm YDF is the optimal length for generating SLM output for the proposed EDF laser scheme. As a result, using YDF-based filter in the
Acknowledgement This paper was supported by Ministry of Science and Technology, Taiwan, under grants MOST 103-2218-E-035-011-MY3, MOST 1032221-E-009-030-MY3, MOST 104-2628-E-009-011-MY3 and MOST 104-2221-E-035-064. References [1] C.-H. Yeh, J.-Y. Chen, H.-Z. Chen, J.-H. Chen, C.-W. Chow, Stable and tunable single-longitudinal-mode erbium-doped fiber triple-ring laser with power-equalized output, IEEE Photonics J. 8 (2016) 1500906. [2] C.-H. Yeh, S. Chi, Fiber-fault monitoring technique for passive optical networks based on fiber Bragg gratings and semiconductor optical amplifier, Opt. Commun. 257 (2006) 306–310. [3] B. Zhou, H. Jiang, R. Wang, C. Lu, Optical fiber Fiber Fabry-Perot filter with tunable cavity for high-precision resonance wavelength adjustment, J. Light. Technol. 33 (2015) 2950–2954. [4] W.C. Swann, N.R. Newbury, Frequency-resolved coherent lidar using a femtosecond fiber laser, Opt. Lett. 31 (2006) 826–828. [5] C.-H. Yeh, H.-Z. Chen, J.-Y. Chen, C.-W. Chow, Stabilized dual-wavelength erbiumdoped fiber laser with single-longitudinal-mode by utilizing fiber Bragg grating and compound-ring filter, Laser Phys. Lett. 13 (2016) 025106. [6] B. Pan, D. Lu, L. Yu, L. Zhang, and L. Zhao, Generation of broadband chaos signal by self-injection monolithic integrated mode-beating amplified feedback laser, in: Proc. of CLEO, 2015, pp. 1−2. [7] M. Chen, Z. Meng, Y. Zhang, J. Wang, W. Chen, Ultranarrow-linewidth Brillouin/ erbium fiber laser based on 45-cm erbium-doped fiber, IEEE Photonics J. 7 (2015) 1500606. [8] C.-H. Yeh, M.-C. Lin, S. Chi, Stabilized and wavelength-tunable S-band erbiumdoped fiber ring laser with single-longitudinal-mode operation, OptiExpress 13 (2005) 6828–6832. [9] Y. Liu, Y. Hsu, C.-W. Hsu, L.-G. Yang, C.-W. Chow, C.-H. Yeh, Y.-C. Lai, H.K. Tsang, Narrow line-width single-longitudinal-mode fiber laser using silicon-oninsulator based micro-ring-resonator, Laser Phys. Lett. 13 (2016) 025102. [10] H.Y. Ryu, W.-K. Lee, H.S. Moon, S.K. Kim, H.S. Suh, D. Lee, Stable single-
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[14]
frequency fiber ring laser for 25-GHz ITU-T grids utilizing saturable absorber filter, IEEE Photonics Technol. Lett. 17 (2005) 1041–1135. J. Zhang, C.-Y. Yue, G.W. Schinn, W.R.L. Clements, J.W.Y. Lit, Stable single-mode compound-ring erbium-doped fiber laser, J. Light. Technol. 14 (1996) 104–109. H.Zhang, B.Yan, John Noto, R.Kerr, Novel tunable liquid crystal Fabry-Perot filters for fiber optical system, in: Proc. of SPIE 4583, pp. 64–72, 2001 S. Rota-Rodrigo, R.A. Perez-Herrera, M. Fernandez-Vallejo, M. Lopez-Amo, Low noise dual-wavelength erbium fiber laser in single-longitudinal-mode operation, Appl. Phys. B 106 (2012) 563–567. C.-H. Yeh, J.-Y. Chen, H.-Z. Chen, C.-W. Chow, Stable single-longitudinal-mode erbium-doped fiber laser with dual-ring structure, Opt. Fiber Technol. 27 (2016)
46–48. [15] W.L. Zhang, Y.B. Song, X.P. Zeng, R. Ma, Z.J. Yang, Y.J. Rao, Temperaturecontrolled mode selection of Er-doped random fiber laser with disordered Bragg grating, Photonics Res. 4 (2016) 102–1005. [16] H.-C. Chien, C.-H. Yeh, C.-C. Lee, S. Chi, A tunable and single-frequency S-band erbium fiber laser with saturable-absorber-based autotracking filter, Opt. Commun. 250 (2005) 163–167. [17] S.Yang, K. K. Y. Cheung, X. Xu, Y. Zhou, K.K. Y. Wong, Tunable single-longitudinalmode fiber optical parametric oscillator with saturable-absorber-based autotracking filter, in: Proc. of OFC, Paper JWA16, 2010
183
Contents lists available at ScienceDirect
Optics & Laser Technology journal homepage: www.elsevier.com/locate/optlastec
Research Note
Stabilized and tunable single-longitudinal-mode erbium fiber laser employing ytterbium-doped fiber based interference filter
crossmark
⁎
Chien-Hung Yeha, , Ning Tsaia, Yuan-Hong Zhuanga, Chi-Wai Chowb, Jing-Heng Chena a b
Department of Photonics, Feng Chia University, Taichung 40724, Taiwan Department of Photonics and Institute of Electro-Optical Engineering, National Chiao Tung University, Hsinchu 30010, Taiwan
A R T I C L E I N F O
A BS T RAC T
Keywords: Erbium-doped fiber laser Single-longitudinal-mode (SLM) Wavelength tunable
In this demonstration, to achieve stabilized and wavelength-selectable single-longitudinal-mode (SLM) erbiumdoped fiber (EDF) laser, a short length of ytterbium-doped fiber (YDF) is utilized to serve as a spatial multimode interference (MMI) inside a fiber cavity for suppressing multi-longitudinal-mode (MLM) significantly. In the measurement, the output powers and optical signal to noise ratios (OSNRs) of proposed EDF ring laser are measured between −9.85 and −5.71 dBm; and 38.03 and 47.95 dB, respectively, in the tuning range of 1530.0– 1560.0 nm. In addition, the output SLM and stability performance are also analyzed and discussed experimentally.
1. Introduction Stable and wavelength-tunable erbium-doped fiber (EDF)-based lasers are fascinated in recent years, due to their useful applications of optical fiber communications [1,2], optical fiber sensors [3], optical instrument testing [4], and light detection and ranging (LIDAR) [5]. Mode-hopping and homogenous broadening of EDF would result in unstable and multi-longitudinal-mode (MLM) output in EDF-based laser [6–8]. Hence, to complete the single-longitudinal-mode (SLM) in EDF ring laser with a longer cavity, several technologies have been proposed and demonstrated, such as utilizing umpumped EDF saturated absorber filter, optical narrow band filter, and compound-ring filter [9–11]. Furthermore, to accomplish wavelength-tuning in EDF laser scheme, the tunable bandpass filter (TBF), Fabry-Perot tunable filter (FP-TF), fiber Bragg grating (FBG) and temperature-controlled mode technique have proposed and employed inside a ring cavity generally [12–15]. In this demonstration, we propose and demonstrate experimentally a stable and wavelength-selectable EDF ring laser scheme with SLM output. To achieve SLM operation, a short length of 10 cm ytterbiumdoped fiber (YDF) is used inside a ring cavity to act as a spatial multimode interference (MMI) for suppressing densely MLM. In this measurement, the observed output power and optical signal to noise ratio (OSNR) of proposed EDF ring laser are between −9.85 and −5.71 dBm; and 38.03 and 47.95 dB, respectively, in a wavelength range of 1530.0–1560.0 nm. Moreover, the output stabilities of power difference and wavelength variation can be maintained within 0.3 dB
⁎
and 0.02 nm, respectively, in a short-term observation measurement of 30 min. 2. Proposed erbium fiber architecture Fig. 1 presents the proposed stable and wavelength-selectable EDF ring laser architecture. The proposed EDF ring laser is consisted of a commercial C-band erbium-doped fiber amplifier (EDFA), a 1×2 and 10:90 optical coupler (OCP), a C-band tunable bandpass filter (TBF), a polarization controller (PC), a 3-port optical circulator (OC), an optical fiber mirror (OFM), and a short length of 10 cm YDF. Here, the YDF (LIEKKI, Yb1200-10/125DC) has the core size of 10 μm diameter and cladding absorption of 1.8 dB/m at the wavelength of 920 nm. In the measurement, the saturated output power and effective amplification bandwidth of EDFA are 13 dBm and 34 nm (1528–1562 nm), respectively. The 3 dB bandwidth and tuning range of TBF are 0.4 nm and 30 nm (1530–1560 nm), respectively. The TBF is used to generate and tune the different lasing wavelengths. The PC is employed to maintain single-polarization status and obtain maximum output power of lasing wavelength. As indicated in Fig. 1, the lasing wavelength would transmit through the YDF and OFM via OC in clockwise direction. Hence, the lasing wavelength would pass through the YDF twice. In this measurement, an optical spectrum analyzer (OSA) is employed to measure the output power and wavelength. Fig. 2 shows the measured absorption spectrum of YDF under a wavelength range of 1520–1560 nm. As seen in Fig. 2, the absorption coefficient of YDF is between 3.52 dB/0.1 m and 4.02 dB/0.1 m in the spectrum range of
Corresponding author. E-mail address: [email protected] (C.-H. Yeh).
http://dx.doi.org/10.1016/j.optlastec.2016.09.024 Received 1 August 2016; Received in revised form 9 September 2016; Accepted 14 September 2016 0030-3992/ © 2016 Elsevier Ltd. All rights reserved.
Optics & Laser Technology 88 (2017) 180–183
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Fig. 1. Proposed stable and wavelength-selectable EDF ring laser architecture.
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Fig. 5. (a) Measured output power and (b) optical signal to noise ratios (OSNR) spectra of proposed EDF laser in the wavelengths of 1530.0–1560.0 nm.
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Wavelength (nm) Fig. 2. Measured absorption spectrum of YDF under a wavelength range of 1520– 1560 nm.
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Fig. 3. Schematic diagram of the points of splicing different-type fibers.
Frequency (Hz) Fig. 6. Observed electrical power spectrum in the frequency range of (a) 1 GHz, (b) 100 MHz and (c) 10 MHz, respectively.
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Wavelength (nm) Fig. 4. Observed output wavelengths of proposed EDF ring laser in the wavelength range of 1530.0–1560.0 nm.
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Frequency (Hz) Fig. 7. Observed electrical power spectra in the frequency range of 1 GHz, when the YDF-based filter are 5, 7 and 15 cm, respectively.
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proposed EDF ring laser can suppress the MLM greatly. Next, to realize the output stabilities of power and wavelength for the proposed EDF laser, a wavelength of 1554.02 nm with −6.91 dBm output power is also used for SLM measurement initially. Fig. 8(a) and (b) present the measured stability performances of output power and wavelength, respectively, under a short-term observation measurement of 30 min. Here, we can observe that the maximum power variation and wavelength fluctuation are 0.3 dB and 0.02 nm (readout resolution of OSA=0.01 nm), as illustrated in Fig. 8(a) and Fig. 8(b) respectively during the observing time of 30 min. In addition, after one hour observation, the observed stabilities of output power and wavelength are still stable within the same measured variances. As a result, the proposed EDF ring laser with a short length YDF of 10 cm not only can achieve SLM output, but also can accomplish stable and tunable operation. In the SLM measurement, we also select three wavelengths of 1533.00, 1548.00 and 1560.00 nm for testing respectively. The entire measured results of these lasing wavelengths are with stable SLM output.
Power (dBm)
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1520–1560 nm. Besides, there are two absorption peaks at the wavelengths of 1527.5 and 1550.0 nm respectively, as shown in Fig. 2. Moreover, the 10 cm YDF is utilized in proposed EDF ring laser to serve as spatial multi-mode interference (MMI) possibly. The short length of YDF would result in great losses for the generating wavelength because of losses in the points of splicing different-type fibers and diffraction in higher-order spatial modes inside this YDF. And the schematic diagram is depicted in Fig. 3. As a result, the proposed EDF ring laser can achieve the SLM output by using an YDF-based filter.
4. Conclusion In this paper, we have first proposed and investigated a stable and wavelength-tunable SLM EDF ring laser by using a short-length YDF of 10 cm long. The YDF was used to serve as spatial multi-mode interference to filter the MLM significantly. In the previous EDF ring laser schemes [16,17], using unpumped EDF-based saturated absorber filter with 1–2 m long was the common method to act as a narrow bandwidth autotracking filter for SLM. However, the proposed EDF ring laser with 10 cm YDF-based filter based on MMI effect to SLM. Hence, the measured output power and OSNR of proposed EDF laser were between −9.85 and −5.71 dBm; and 38.03 and 47.95 dB, respectively, in a wavelength range of 1530.0–1560.0 nm. Moreover, the output stabilities of power difference and wavelength variation could be maintained within 0.3 dB and 0.02 nm, respectively, in an observation measurement of 1 h.
3. Experimental results Fig. 4 shows the measured wavelength spectra of proposed EDF ring laser in the wavelength range of 1530.0–1560.0 nm with a tuning step of ~3 nm. Here, we observe that the background amplified spontaneous emission (ASE) noise of 1530 nm can be suppressed significantly. Fig. 5(a) and (b) present the measured output powers and optical signal to noise ratios (OSNRs) of proposed EDF ring laser in the wavelengths of 1530.0–1560.0 nm. In the measurement, the obtained output powers and OSNRs are between −9.85 and −5.71 dBm; and 38.03 and 47.95 dB, respectively. With the increase of lasing lightwave to the longer wavelength progressively, the observed output power is also increase. Besides, the measured trend of output power curve is similar to Fig. 2. The maximum output power and OSNR are measured at the wavelengths of 1560.0 and 1533.0 nm, respectively, as seen in Fig. 5(a) and (b). In addition, the observed side-mode suppress ratio (SMSR) of each lasing wavelength is very closing to measured result of Fig. 5(b). Then, we will verify the SLM output for the proposed EDF laser by using delayed self-homodyne method. The experimental setup is composed by Mach-Zehnder interferometer (MZI) with a 30 km single-mode fiber (SMF) and a 10 GHz PIN-based photodiode (PD). Moreover, a 3 GHz electrical spectrum analyzer (ESA) is utilized to measure the output electrical spectrum. Here, a wavelength of 1554.02 nm is selected for SLM measurement initially. Fig. 6(a)–(c) show the observed electrical power spectra in the frequency range of 1 GHz, 100 MHz and 10 MHz, respectively. There is no electrical spike observed in the three measured bandwidths, as shown in Fig. 6(a)–(c). Furthermore, during 1 h observation time by the same experiment, the measured electrical power spectrum of ESA is very stable and without any MLM spike noise. When the YDF is 15 cm long, we also can observe the same electrical power spectrum with SLM. While we reduce the YDF length to 5 and 7 cm respectively, the observed electrical power spectra are MLM and also increase the background noise, as shown in Fig. 7. Therefore, according to the experimental result, the 10 cm YDF is the optimal length for generating SLM output for the proposed EDF laser scheme. As a result, using YDF-based filter in the
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