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Stabilized 51-wavelength erbium-doped fiber ring laser based on high nonlinear fiber
Optics Communications 318 (2014) 171–174
Contents lists available at ScienceDirect
Optics Communications journal homepage: www.elsevier.com/locate/optcom
Stabilized 51-wavelength erbium-doped fiber ring laser based on high nonlinear fiber Chengliang Yang, Li Xia n, Yuanwu Wang, Deming Liu School of Optical and Electronic Information, National Engineering Laboratory for Next Generation Internet Access System, Huazhong University of Science and Technology, No. 1037 Luoyu Road, Hubei 430074, China
art ic l e i nf o
a b s t r a c t
Article history: Received 18 March 2013 Accepted 26 December 2013 Available online 9 January 2014
A multi-wavelength fiber laser source is demonstrated with a high power erbium-doped fiber amplifier as the gain medium. In order to alleviate the mode competition, a highly nonlinear fiber (HNLF) is inserted in the ring cavity to provide nonlinear effects. A fiber Fabry–Perot filter (FFPF) is incorporated in the ring cavity serving as a comb filter. The comparison between HNLF with different length is discussed. Fifty one simultaneous lasing wavelengths within 3 dB uniformity are observed with channel spacing of 25 GHz and a signal to noise ratio of 48 dB. Moreover, these stable multi-carriers light source is a promising candidate for high capacity optical communication system, such as coherent densewavelength-multiplexing (DWDM) in our project. & 2014 Elsevier B.V. All rights reserved.
Keywords: Multi-wavelength erbium-doped fiber (EDF) ring laser Highly nonlinear fiber (HNLF) Fabry–Perot filter
1. Introduction In recent years, multi-wavelength fiber lasers are of great interest because of their potential applications in wavelengthdivision-multiplexing (WDM) communications, microwave photonic systems, optical instrumentation and optical fiber sensors [1–3]. Various gain mechanisms including erbium-doped fiber amplification (EDFA) [4,5], semiconductor optical amplification (SOA) [6,7], fiber Raman amplification (FRA) [8,9] and hybrid gain media have been implemented to realize multi-wavelength lasing. Compared to SOA or FRA-based multi-wavelength fiber lasers, multi- wavelength lasers based on EDFA have many advantages for their higher saturated power, lower polarization-dependent gain and flatter gain spectrum. However, erbium-doped fiber (EDF) is a homogenous gain medium at room temperature. Fiber lasers based on EDF usually suffer from strong mode competition and unstable multi-wavelength oscillation. How to overcome strong homogeneous line broadening is the main challenge to achieve stable multi-wavelength lasing at room temperature. To obtain stable multi-wavelength lasing, many techniques have been proposed such as cooling EDF in the liquid nitrogen [1], utilizing a frequency-shifted feedback technique [2], using a phase modulator [3] and using nonlinear optical loop mirror (NOLM) or nonlinear amplifying loop mirror (NALM) as an amplitude equalizer [4,5]. For a practical DWDM communication system, stable multiwavelength lasing at room temperature with the standard ITU (International Telecommunication Union) channel spacing of
n
Corresponding author. E-mail address: [email protected] (L. Xia).
0030-4018/$ - see front matter & 2014 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.optcom.2013.12.077
25 GHz or 50 GHz, uniform power distribution, narrow linewidth and high signal to noise ratio (SNR) is more desirable. In 2005, a multi-wavelength EDF fiber laser utilizing a highly nonlinear fiber (HNLF) at room temperature was demonstrated and 488 channels with a wavelength spacing of 10 GHz were obtained [10]. However, the signal to noise ratio of the laser was below 20 dB, which was not suitable for practical application. Thereafter, a lot of experiments were conducted utilizing nonlinear effect in HNLF, photonic crystal fiber (PCF) or silicon waveguide [11–14]. In 2006, simultaneous lasing at more than 70 wavelengths was achieved by using a highly nonlinear fiber combined with a Fabry– Perot filter. As is known to us, laser line-width is decided by the bandwidth of wavelength selection filter. But the finesse of Fabry– Perot filter was only about 10 and SNR of the laser was 44 dB [11]. Zhang et al. [12] proposed multi-wavelength fiber ring lasers by adding highly nonlinear photonic crystal fiber (HN-PCF) into the ring cavity. In order to realize flat spectrum, a Sagnac loop filter as power equalizer had to be used additionally. In this letter, we propose a stable multi-wavelength erbiumdoped fiber laser by incorporating a section of highly nonlinear fiber and a high finesse Fabry–Perot filter (FPF). Based on the nonlinear effect of the HNLF, mode competition of EDF is suppressed. We observe 51 wavelengths simultaneous lasing within 3 dB uniformity and a wavelength space of 25 GHz. The laser has a 3-dB bandwidth of 0.016 nm and a signal to noise ratio of 48 dB. 2. Experimental setup and principle The schematic of our experimental setup is shown in Fig. 1. A high power Er–Yb co-doped optical amplifier (EDFA) is used as
172
C. Yang et al. / Optics Communications 318 (2014) 171–174
the gain media, whose maximum output power is 33 dBm. An isolator is inserted in cavity for unidirectional operation, and polarization controller (PC) ensures appropriate polarization. A fiber Fabry–Perot filter (FFPF, Micron Optics) is incorporated to provide periodic loss in the frequency domain as a narrow band comb filter. The free spectrum range (FSR) and finesse of the fiber Fabry–Perot filter are respectively 25 GHz (0.2 nm) and 120 GHz. A section of commercial high nonlinear fiber (HNLF) is inserted in the ring cavity. The zero dispersion wavelength (ZDW) of HNLF is near 1550 nm, and the dispersion slope, nonlinear coefficient are respectively 0.017 ps/(nm2 km) and 10/(W km). An optical spectrum analyzer (OSA, YOKOGAWA AQ6370, resolution 0.02 nm) is engaged to observe the laser output via a 10/90 fiber coupler.
3. Experimental result and discussion At the first step, the transmission spectrum of the fiber FP filter is obtained by a broadband light source and optical spectrum analyzer. Fig. 2 depicts the transmission spectrum of the FFPF. The extinction ratio is about 25 dB and the wavelength spacing is 0.2 nm, which comply with the standard ITU channel spacing. In the experiment, two sections of HNLF with different length are available. However, the parameters of two sections of HNLF are all the same. At the beginning of experiment, we insert a section of 0.5 km HNLF in the cavity to provide nonlinear effects. By appropriately adjusting the polarization controller, we measured the multi-wavelength fiber laser source spectrum. The output laser spectrum with a span of 20 nm is shown in Fig. 3(a). The resolution bandwidth of optical spectrum analyzer is set at
Fig. 3. Multi-wavelength laser output spectrum (a) with 0.5 km HNLF (b) with 1 km HNLF.
Fig. 1. Schematic of the proposed multi-wavelength EDF fiber ring laser. OC, 10/90 optical coupler; PC, polarization controller; HNLF, high nonlinear fiber.
Fig. 2. Transmission spectrum of the FFPF.
0.02 nm. Owing to the nonlinear effects in HNLF, such as fourwave mixing (FWM) and self-phase modulation (SPM), mode competition of the EDFA is alleviated. Multi-wavelength oscillation at room temperature is achieved. The laser output spectrum and power is very stable. The spectrum covers from 1560.4 nm to 1567.6 nm within 3 dB uniformity. In order to know how the nonlinear effects affect the laser output. In the next, the 0.5 km HNLF is replaced by a section of 1 km HNLF while maintain the EDFA output power at constant. The measured laser output spectrum is shown in Fig. 3(b). As a comparison, we find that the laser output spectrum with 1 km HNLF is more flat than 0.5 km HNLF. The output multi-wavelength spectrum covers from 1559 nm to 1569 nm within 3 dB uniformity. But in Fig. 3(a) with 0.5 km HNLF, optical power varies about 4.5 dB at the same scale. The broadened spectrum is induced by the high nonlinearity in the highly nonlinear fiber. Some wavelengths will be excited in fiber ring laser incipiently. Due to the FWM effect between adjacent wavelengths, these wavelengths with sufficient power will generate new wavelengths through FWM effect. Then the newly generated wavelengths could generate more wavelengths. Thus, multi-wavelength oscillation at room temperature is obtained. Xu et al. [15] have analyzed in theory that the FWM effect can be enhanced by maintaining higher power in the cavity, using fiber with larger nonlinear coefficient and increasing the length of the high nonlinear dispersion shifted fiber (HNDSF). In
C. Yang et al. / Optics Communications 318 (2014) 171–174
Fig. 4. Enlarged laser spectrum with a span of 10 nm.
173
Fig. 6. Measured one channel power fluctuation versus time.
The repeated spectrum scans are shown in Fig. 5. No significant spectral fluctuations are observed. The relative change of amplitudes is smaller than 0.1 dB. In our setup, the fiber FPF is used for the wavelength selection. With well packaged and temperature control, the wavelength drift can be negligible. Finally, the stability of single wavelength optical power is also monitored. An optical bandpass filter (Finisar WaveShaper 4000S) centered at 1558.212 nm with a bandwidth of 20 GHz (0.16 nm) is used to filter out one channel. The one channel power is monitored by an optical powermeter. We measure 32 times and the time interval of each measurement is 10 s. Fig. 6 shows the measured power variation. The one channel power fluctuation is measured to be less than 0.15 dB.
4. Conclusion
Fig. 5. Repeated scans of the output optical spectrum. The time interval of each scan was 10 min.
Ref. [12], Zhang et al. proposed a multi-wavelength fiber ring laser utilizing highly nonlinear photonic crystal fiber (HN-PCF). It points out that spectrum can be even broader if increasing the value of γ U P U L, where γ is the nonlinear coefficient of the PCF, P is the power passing through PCF, and L is the effective fiber length of the PCF. The results show that output spectrum with lower coupling ratio, equal to higher optical power in the ring cavity, is more flat than higher coupling ratio. In our experiment, a high power EDFA is used as gain media, whose output power is enough to exceed threshold of HNLF. Comparing to the experiment with 0.5 km HNLF in the first step, the nonlinear effects are enhanced utilizing 1 km HNLF while keeping EDFA output power at constant, resulting in a more flat spectrum. So increasing the length of the high nonlinear fiber is also an effect way to enhanced nonlinear effects when the optical power is sufficient. Enlarged laser spectrum is shown in Fig. 4. Up to 51 simultaneously lasing lines are obtained within 3 dB uniformity at room temperature with a wavelength spacing of 0.2 nm, which coincides with the transmission profile of the FFP filter. The SNR is measured about 48 dB. Due to the limit of optical spectrum analyzer resolution, the laser 3-dB bandwidth of one channel is measured about 0.016 nm by OSA. For practical applications, it is desirable to have a stable output power. There are two types of variations of the multi-wavelength laser output: wavelength drift and power fluctuation. We investigated the output laser spectrum every 10 min for 40 min.
In summary, we have experimentally demonstrated a stable multi-wavelength erbium-doped fiber ring laser incorporating a section of commercial HNLF and a narrowband FPF in the ring cavity. The proposed scheme can successfully reduce the mode competition in erbium-doped fiber laser and achieve multiwavelength operation at room temperature. Over 51 wavelengths simultaneous lasing within 3 dB uniformity is obtained and the wavelength spacing is 0.2 nm, complying with the standard ITU wavelength spacing. The laser has a signal to noise ratio of 48 dB. The lasing states are monitored to be very stable. We believe this multi-wavelength fiber laser is practical for a lot of applications, such as the optical communications, optical testing and measurement and microwave photonic systems.
Acknowledgement This work is supported by the National Basic Research Program (973) of China (Grant no. 2010CB328302) References [1] N. Park, P.F. Wysocki, IEEE Photonics Technol. Lett 8 (1996) 1459. [2] A. Bellemare, M. Karasek, M. Rochette, S. LaRochelle, M. Tetu, J. Lightwave Technol 18 (2000) 825. [3] K. Zhou, D. Zhou, F. Dong, N.Q Ngo, Opt. Lett. 28 (2003) 893. [4] X. Feng, H.Y. Tam, H. Liu, P.K.A. Wai, Opt. Commun. 268 (2006) 278. [5] X. Liu, L. Zhan, S. Luo, Z. Gu, J. Liu, Y. Wang, Q. Shen, Opt. Express 20 (2012) 7088. [6] H. Chen, Opt. Lett. 30 (2005) 619. [7] K. Lee, S.D. Lim, C.H. Kim, J.H. Lee, Y.G. Han, S.B. Lee, J. Lightwave Technol. 28 (2010) 739.
174
[8] [9] [10] [11] [12]
C. Yang et al. / Optics Communications 318 (2014) 171–174
X. Dong, P. Shum, N.Q. Ngo, C.C. Chan, Opt. Express 14 (2006) 3288. D. Chen, S. Qin, S. He, Opt. Express 15 (2007) 930. S. Yamashita, Y. Inoue, Jpn. J. Appl. Phys. 44 (Part 2) (2005) L1080. S. Pan, C. Lou, Y. Gao, Opt. Express 14 (2006) 1113. A. Zhang, H. Liu, M.S. Demokan, H.Y. Tam, IEEE Photonics Technol. Lett 17 (2005) 2535.
[13] A. Zhang, M.S. Demokan, H.Y. Tam, Opt. Commun. 260 (2006) 670. [14] C.Y. Wong, F.W. Tong, Z. Cheng, Y.M. Chen, H.K. Tsang, http://dx.doi.org/10. 1109/OECC.2012.6276369, (2012) 57. [15] X. Xu, Y. Yao, D. Chen, Opt. Express 16 (2008) 12397.
Contents lists available at ScienceDirect
Optics Communications journal homepage: www.elsevier.com/locate/optcom
Stabilized 51-wavelength erbium-doped fiber ring laser based on high nonlinear fiber Chengliang Yang, Li Xia n, Yuanwu Wang, Deming Liu School of Optical and Electronic Information, National Engineering Laboratory for Next Generation Internet Access System, Huazhong University of Science and Technology, No. 1037 Luoyu Road, Hubei 430074, China
art ic l e i nf o
a b s t r a c t
Article history: Received 18 March 2013 Accepted 26 December 2013 Available online 9 January 2014
A multi-wavelength fiber laser source is demonstrated with a high power erbium-doped fiber amplifier as the gain medium. In order to alleviate the mode competition, a highly nonlinear fiber (HNLF) is inserted in the ring cavity to provide nonlinear effects. A fiber Fabry–Perot filter (FFPF) is incorporated in the ring cavity serving as a comb filter. The comparison between HNLF with different length is discussed. Fifty one simultaneous lasing wavelengths within 3 dB uniformity are observed with channel spacing of 25 GHz and a signal to noise ratio of 48 dB. Moreover, these stable multi-carriers light source is a promising candidate for high capacity optical communication system, such as coherent densewavelength-multiplexing (DWDM) in our project. & 2014 Elsevier B.V. All rights reserved.
Keywords: Multi-wavelength erbium-doped fiber (EDF) ring laser Highly nonlinear fiber (HNLF) Fabry–Perot filter
1. Introduction In recent years, multi-wavelength fiber lasers are of great interest because of their potential applications in wavelengthdivision-multiplexing (WDM) communications, microwave photonic systems, optical instrumentation and optical fiber sensors [1–3]. Various gain mechanisms including erbium-doped fiber amplification (EDFA) [4,5], semiconductor optical amplification (SOA) [6,7], fiber Raman amplification (FRA) [8,9] and hybrid gain media have been implemented to realize multi-wavelength lasing. Compared to SOA or FRA-based multi-wavelength fiber lasers, multi- wavelength lasers based on EDFA have many advantages for their higher saturated power, lower polarization-dependent gain and flatter gain spectrum. However, erbium-doped fiber (EDF) is a homogenous gain medium at room temperature. Fiber lasers based on EDF usually suffer from strong mode competition and unstable multi-wavelength oscillation. How to overcome strong homogeneous line broadening is the main challenge to achieve stable multi-wavelength lasing at room temperature. To obtain stable multi-wavelength lasing, many techniques have been proposed such as cooling EDF in the liquid nitrogen [1], utilizing a frequency-shifted feedback technique [2], using a phase modulator [3] and using nonlinear optical loop mirror (NOLM) or nonlinear amplifying loop mirror (NALM) as an amplitude equalizer [4,5]. For a practical DWDM communication system, stable multiwavelength lasing at room temperature with the standard ITU (International Telecommunication Union) channel spacing of
n
Corresponding author. E-mail address: [email protected] (L. Xia).
0030-4018/$ - see front matter & 2014 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.optcom.2013.12.077
25 GHz or 50 GHz, uniform power distribution, narrow linewidth and high signal to noise ratio (SNR) is more desirable. In 2005, a multi-wavelength EDF fiber laser utilizing a highly nonlinear fiber (HNLF) at room temperature was demonstrated and 488 channels with a wavelength spacing of 10 GHz were obtained [10]. However, the signal to noise ratio of the laser was below 20 dB, which was not suitable for practical application. Thereafter, a lot of experiments were conducted utilizing nonlinear effect in HNLF, photonic crystal fiber (PCF) or silicon waveguide [11–14]. In 2006, simultaneous lasing at more than 70 wavelengths was achieved by using a highly nonlinear fiber combined with a Fabry– Perot filter. As is known to us, laser line-width is decided by the bandwidth of wavelength selection filter. But the finesse of Fabry– Perot filter was only about 10 and SNR of the laser was 44 dB [11]. Zhang et al. [12] proposed multi-wavelength fiber ring lasers by adding highly nonlinear photonic crystal fiber (HN-PCF) into the ring cavity. In order to realize flat spectrum, a Sagnac loop filter as power equalizer had to be used additionally. In this letter, we propose a stable multi-wavelength erbiumdoped fiber laser by incorporating a section of highly nonlinear fiber and a high finesse Fabry–Perot filter (FPF). Based on the nonlinear effect of the HNLF, mode competition of EDF is suppressed. We observe 51 wavelengths simultaneous lasing within 3 dB uniformity and a wavelength space of 25 GHz. The laser has a 3-dB bandwidth of 0.016 nm and a signal to noise ratio of 48 dB. 2. Experimental setup and principle The schematic of our experimental setup is shown in Fig. 1. A high power Er–Yb co-doped optical amplifier (EDFA) is used as
172
C. Yang et al. / Optics Communications 318 (2014) 171–174
the gain media, whose maximum output power is 33 dBm. An isolator is inserted in cavity for unidirectional operation, and polarization controller (PC) ensures appropriate polarization. A fiber Fabry–Perot filter (FFPF, Micron Optics) is incorporated to provide periodic loss in the frequency domain as a narrow band comb filter. The free spectrum range (FSR) and finesse of the fiber Fabry–Perot filter are respectively 25 GHz (0.2 nm) and 120 GHz. A section of commercial high nonlinear fiber (HNLF) is inserted in the ring cavity. The zero dispersion wavelength (ZDW) of HNLF is near 1550 nm, and the dispersion slope, nonlinear coefficient are respectively 0.017 ps/(nm2 km) and 10/(W km). An optical spectrum analyzer (OSA, YOKOGAWA AQ6370, resolution 0.02 nm) is engaged to observe the laser output via a 10/90 fiber coupler.
3. Experimental result and discussion At the first step, the transmission spectrum of the fiber FP filter is obtained by a broadband light source and optical spectrum analyzer. Fig. 2 depicts the transmission spectrum of the FFPF. The extinction ratio is about 25 dB and the wavelength spacing is 0.2 nm, which comply with the standard ITU channel spacing. In the experiment, two sections of HNLF with different length are available. However, the parameters of two sections of HNLF are all the same. At the beginning of experiment, we insert a section of 0.5 km HNLF in the cavity to provide nonlinear effects. By appropriately adjusting the polarization controller, we measured the multi-wavelength fiber laser source spectrum. The output laser spectrum with a span of 20 nm is shown in Fig. 3(a). The resolution bandwidth of optical spectrum analyzer is set at
Fig. 3. Multi-wavelength laser output spectrum (a) with 0.5 km HNLF (b) with 1 km HNLF.
Fig. 1. Schematic of the proposed multi-wavelength EDF fiber ring laser. OC, 10/90 optical coupler; PC, polarization controller; HNLF, high nonlinear fiber.
Fig. 2. Transmission spectrum of the FFPF.
0.02 nm. Owing to the nonlinear effects in HNLF, such as fourwave mixing (FWM) and self-phase modulation (SPM), mode competition of the EDFA is alleviated. Multi-wavelength oscillation at room temperature is achieved. The laser output spectrum and power is very stable. The spectrum covers from 1560.4 nm to 1567.6 nm within 3 dB uniformity. In order to know how the nonlinear effects affect the laser output. In the next, the 0.5 km HNLF is replaced by a section of 1 km HNLF while maintain the EDFA output power at constant. The measured laser output spectrum is shown in Fig. 3(b). As a comparison, we find that the laser output spectrum with 1 km HNLF is more flat than 0.5 km HNLF. The output multi-wavelength spectrum covers from 1559 nm to 1569 nm within 3 dB uniformity. But in Fig. 3(a) with 0.5 km HNLF, optical power varies about 4.5 dB at the same scale. The broadened spectrum is induced by the high nonlinearity in the highly nonlinear fiber. Some wavelengths will be excited in fiber ring laser incipiently. Due to the FWM effect between adjacent wavelengths, these wavelengths with sufficient power will generate new wavelengths through FWM effect. Then the newly generated wavelengths could generate more wavelengths. Thus, multi-wavelength oscillation at room temperature is obtained. Xu et al. [15] have analyzed in theory that the FWM effect can be enhanced by maintaining higher power in the cavity, using fiber with larger nonlinear coefficient and increasing the length of the high nonlinear dispersion shifted fiber (HNDSF). In
C. Yang et al. / Optics Communications 318 (2014) 171–174
Fig. 4. Enlarged laser spectrum with a span of 10 nm.
173
Fig. 6. Measured one channel power fluctuation versus time.
The repeated spectrum scans are shown in Fig. 5. No significant spectral fluctuations are observed. The relative change of amplitudes is smaller than 0.1 dB. In our setup, the fiber FPF is used for the wavelength selection. With well packaged and temperature control, the wavelength drift can be negligible. Finally, the stability of single wavelength optical power is also monitored. An optical bandpass filter (Finisar WaveShaper 4000S) centered at 1558.212 nm with a bandwidth of 20 GHz (0.16 nm) is used to filter out one channel. The one channel power is monitored by an optical powermeter. We measure 32 times and the time interval of each measurement is 10 s. Fig. 6 shows the measured power variation. The one channel power fluctuation is measured to be less than 0.15 dB.
4. Conclusion
Fig. 5. Repeated scans of the output optical spectrum. The time interval of each scan was 10 min.
Ref. [12], Zhang et al. proposed a multi-wavelength fiber ring laser utilizing highly nonlinear photonic crystal fiber (HN-PCF). It points out that spectrum can be even broader if increasing the value of γ U P U L, where γ is the nonlinear coefficient of the PCF, P is the power passing through PCF, and L is the effective fiber length of the PCF. The results show that output spectrum with lower coupling ratio, equal to higher optical power in the ring cavity, is more flat than higher coupling ratio. In our experiment, a high power EDFA is used as gain media, whose output power is enough to exceed threshold of HNLF. Comparing to the experiment with 0.5 km HNLF in the first step, the nonlinear effects are enhanced utilizing 1 km HNLF while keeping EDFA output power at constant, resulting in a more flat spectrum. So increasing the length of the high nonlinear fiber is also an effect way to enhanced nonlinear effects when the optical power is sufficient. Enlarged laser spectrum is shown in Fig. 4. Up to 51 simultaneously lasing lines are obtained within 3 dB uniformity at room temperature with a wavelength spacing of 0.2 nm, which coincides with the transmission profile of the FFP filter. The SNR is measured about 48 dB. Due to the limit of optical spectrum analyzer resolution, the laser 3-dB bandwidth of one channel is measured about 0.016 nm by OSA. For practical applications, it is desirable to have a stable output power. There are two types of variations of the multi-wavelength laser output: wavelength drift and power fluctuation. We investigated the output laser spectrum every 10 min for 40 min.
In summary, we have experimentally demonstrated a stable multi-wavelength erbium-doped fiber ring laser incorporating a section of commercial HNLF and a narrowband FPF in the ring cavity. The proposed scheme can successfully reduce the mode competition in erbium-doped fiber laser and achieve multiwavelength operation at room temperature. Over 51 wavelengths simultaneous lasing within 3 dB uniformity is obtained and the wavelength spacing is 0.2 nm, complying with the standard ITU wavelength spacing. The laser has a signal to noise ratio of 48 dB. The lasing states are monitored to be very stable. We believe this multi-wavelength fiber laser is practical for a lot of applications, such as the optical communications, optical testing and measurement and microwave photonic systems.
Acknowledgement This work is supported by the National Basic Research Program (973) of China (Grant no. 2010CB328302) References [1] N. Park, P.F. Wysocki, IEEE Photonics Technol. Lett 8 (1996) 1459. [2] A. Bellemare, M. Karasek, M. Rochette, S. LaRochelle, M. Tetu, J. Lightwave Technol 18 (2000) 825. [3] K. Zhou, D. Zhou, F. Dong, N.Q Ngo, Opt. Lett. 28 (2003) 893. [4] X. Feng, H.Y. Tam, H. Liu, P.K.A. Wai, Opt. Commun. 268 (2006) 278. [5] X. Liu, L. Zhan, S. Luo, Z. Gu, J. Liu, Y. Wang, Q. Shen, Opt. Express 20 (2012) 7088. [6] H. Chen, Opt. Lett. 30 (2005) 619. [7] K. Lee, S.D. Lim, C.H. Kim, J.H. Lee, Y.G. Han, S.B. Lee, J. Lightwave Technol. 28 (2010) 739.
174
[8] [9] [10] [11] [12]
C. Yang et al. / Optics Communications 318 (2014) 171–174
X. Dong, P. Shum, N.Q. Ngo, C.C. Chan, Opt. Express 14 (2006) 3288. D. Chen, S. Qin, S. He, Opt. Express 15 (2007) 930. S. Yamashita, Y. Inoue, Jpn. J. Appl. Phys. 44 (Part 2) (2005) L1080. S. Pan, C. Lou, Y. Gao, Opt. Express 14 (2006) 1113. A. Zhang, H. Liu, M.S. Demokan, H.Y. Tam, IEEE Photonics Technol. Lett 17 (2005) 2535.
[13] A. Zhang, M.S. Demokan, H.Y. Tam, Opt. Commun. 260 (2006) 670. [14] C.Y. Wong, F.W. Tong, Z. Cheng, Y.M. Chen, H.K. Tsang, http://dx.doi.org/10. 1109/OECC.2012.6276369, (2012) 57. [15] X. Xu, Y. Yao, D. Chen, Opt. Express 16 (2008) 12397.