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169 MHz repetition frequency all-fiber passively mode-locked erbium doped fiber laser
Optics Communications 283 (2010) 109–112
Contents lists available at ScienceDirect
Optics Communications journal homepage: www.elsevier.com/locate/optcom
169 MHz repetition frequency all-fiber passively mode-locked erbium doped fiber laser Michal Nikodem *, Krzysztof Abramski ´ skiego 27, 50-370 Wroclaw, Poland Wroclaw University of Technology, Wybrzeze Wyspian
a r t i c l e
i n f o
Article history: Received 16 July 2009 Received in revised form 28 August 2009 Accepted 24 September 2009
a b s t r a c t Passively mode-locked stretched-pulse erbium fiber laser is presented. With all-fiber configuration 111 fs pulses were achieved with the fundamental repetition rate of 169 MHz and an average output power of more than 30 mW. Proposed setup shows excellent stability, reliability and ‘turn-key’ operation. The impact of the pump power on laser parameters is described. Ó 2009 Elsevier B.V. All rights reserved.
Keywords: Erbium laser Fiber laser Stretched-pulse mode-locking Passive mode-locking
1. Introduction In recent years we have observed growing interest in modelocked fiber lasers. Development of erbium doped fiber (EDF) and wavelength division multiplexing (WDM) technique made 3rd telecommunication window extremely interesting region for ultrafast lasers applications. Passively mode-locked erbium doped fiber lasers have been reported as an effective source of pulses shorter than 100 fs [1,2]. They can also be considered as an optical frequency comb source for optical metrology, since generated comb spectrum could be far more than 4 THz wide. With compact size, high flexibility and robust design fiber-based configurations find application in high-resolution spectroscopy, THz pulses generation, optical clockworks, absolute distance measurements and many others [3–7]. The biggest disadvantage of passively mode-locked fiber lasers is their relatively small repetition frequency which is usually limited by the length of the cavity. The shortest pulse duration can be obtained with the mode-locking due to nonlinear polarization rotation (NPR) but the fundamental repetition rate is typically limited to 30–50 MHz. Configuration up to 200 MHz have also been shown [8–10] but they all have common feature – they are not all-fiber configurations. Usually polarization beam splitter (PBS), isolator and polarization controllers (quarter- and halfwaveplates) are placed between two collimators. In this way cavity length can be significantly reduced but it also complicates the construction.
* Corresponding author. Tel.: +48 713204523. E-mail address: [email protected] (M. Nikodem). 0030-4018/$ - see front matter Ó 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.optcom.2009.09.061
Washburn et al. have shown all-fiber configurations however with the repetition frequency of only 50 MHz [11,12]. Less than 40 MHz repetition rate was reported in Ref. [1] with the 55 fs all-fiber stretched-pulse NPR laser. Recently high repetition rate fiber lasers mode-locked using saturable absorbers has been reported but their parameters are not as good as those that might be obtained using NPR mechanism (270 fs pulses with bandwidth of 10 nm at 447 MHz [13], 180 fs pulses with bandwidth of 15.8 nm at 491 MHz [14]). In this paper all-fiber passively mode-locked stretched-pulse Er-fiber laser is presented. Pulses as short as 111 fs were obtained with the fundamental repetition rate of 169 MHz. To the best of our knowledge this is the highest fundamental repetition frequency obtained with the NPR mode-locked laser constructed with only fiber-based commercially available components. The impact of the pump power on laser parameters is measured. This include the impact of the pump power on both repetition frequency and carrier envelope offset frequency.
2. Laser configuration and experimental results Nowadays all components required for NPR mode-locked laser are commercially available in fiber-based form. Micro-optic devices such as isolator and PBS are not bigger than fused fiber coupler. Fig. 1 shows the configuration of the laser. It is all-fiber setup build with the commercially available components. We have used 30 cm of the Er-doped fiber (attenuation 110 dB/m at 1530 nm) pumped with the 976 nm diode through wavelength division multiplexing coupler (WDM). It is followed by the polarization beam
110
M. Nikodem, K. Abramski / Optics Communications 283 (2010) 109–112
Fig. 1. Configuration of the all-fiber laser (PBS – polarization beam splitter, PC – polarization controller, EDF – erbium doped fiber, LD – laser diode, ISO – isolator, AC – optical autocorrelator, OSA – optical spectrum analyzer).
splitter (PBS), isolator and polarization controller (PC). Erbium doped fiber has dispersion of 46 ps/(nm km) thus laser operates in the stretched-pulse regime [1,2,15]. Fig. 2 shows the picture of the laser. Its compact size is emphasized with the ordinary AAA battery that is shown inset. With the all-fiber cavity laser is very robust and reliable. No adjustment is needed since all components are simply spliced together. The total length of the cavity is approximately 1.2 m (we have obtained fundamental repetition frequency 169 MHz). When the polarization controller was properly adjusted modelocking was obtained. It should be mentioned that we have used only one polarization controller and only two knobs were used to adjust the polarization inside the cavity. With only two degrees of freedom it takes just a few seconds to obtain mode-locking. Output spectrum of the laser is shown in Fig. 3. With the maximal pump power Pp = 660 mW average output power of 33 mW was achieved. The important feature of the laser was ‘turn-key’ operation, i.e. there was no need to re-adjust the polarization controller when pump diode was turned ‘off’ and ‘on’, even if the discontinuity was several hours long. Fig. 4 shows the output spectra recorded during 7 h long continuous test. Measurements were taken every 30 min. During the test output spectrum changes were imperceptible and the average output power fluctuations did not exceed 2 mW. Mode-locking was very immune to vibrations and shock (it was uninterrupted even when laser was dropped from a high of 20 cm). The impact of the pump power on the laser operation is shown in Fig. 5. The average output power changes from 15 mW (Pp = 330 mW) to 33 mW (Pp = 660 mW). When PC was in the proper position multiple pulse or pulse-pair generation were not present even when the pump power was at the maximum level. It can be however seen that both centre wavelength and the comb width change with the pump power. The spectrum slopes are rising slightly when the pump power is increased. Nevertheless the
Fig. 3. Output spectrum of the laser (pump power of 660 mW was used).
Fig. 4. Output spectra of the laser recorded during continuous operation over several hours (measurements were taken after every 30 min).
Fig. 5. (a) output spectra of the laser, pump power was (starting from the bottom): 370, 411, 446, 476, 512, 543, 579, 608 and 657 mW; (b–d) impact of the pump power on the output spectrum parameters.
Fig. 2. Picture of the laser (pump diode is not shown). AAA battery is shown to compare the size of the cavity.
optical comb obtained at the output is smooth, cw-breakthrough and pulse breaking were not observed. The resonant sidebands at both slopes of the spectrum are typical for the passively modelocked fiber lasers and even though they are usually linked with soliton lasers, they also might be present in the spectrum of the stretched-pulse laser [16]. Optical autocorrelator was used to measure the pulse duration. Unfortunately, in the stretched-pulse regime, pulse duration strongly depends on the type and the length of the fiber placed between the laser output and the autocorrelator [15]. To obtain the
M. Nikodem, K. Abramski / Optics Communications 283 (2010) 109–112
minimal pulse duration proper combination of the fiber with normal and anomalous dispersion should be used. Firstly, we have reduced the length of the SMF fiber. Three hundred and fifteen centimeters were needed to insert the one arm of the polarization beam splitter, WDM coupler, isolator and collimator. Then we have placed 5 m of erbium doped fiber. It had low Er ion concentration (attenuation 20 dB/m at 1530 nm when unpumped) and the chromatic dispersion of 15 ps/(nm km). Erbium doped fiber was pumped by the laser diode with the maximum pump power of 620 mW. We were reducing the length of the EDF gradually until minimal pulse duration was finally obtained. Optimal length of the erbium doped fiber was found to be 355 cm. Fig. 6 shows the impact of the pump power on the pulse duration. Experimental data are presented together with the results of the simulations. Split step Fourier method (SSFM) was used to simulate the pulse propagation along the 6.7 m long fiber. We can see that the experimental data are in good agreement with the simulation results. The minimal pulse duration of 111 fs was obtained when pump power of 180 mW was used. When the pump power was too strong (more than 360 mW) nonlinear effects caused the pulse broadening and the wings appeared in the autocorrelation trace. The average output power was 7 mW when the EDF was unpumped, 40 mW when the pump power of 180 mW was used and 120 mW with the maximal pump power of 620 mW.
3. Controlling the frequency of the optical comb The application of the frequency comb in metrology, optical clockworks and high-resolution spectroscopy requires its absolute stabilization. The comb spectrum emitted form the mode-locked lasers is characterized by the repetition frequency (frep) and the carrier envelope offset frequency (fceo). Usually, the cavity length control is used to stabilize the frep and the pump power control is used to stabilize the fceo. With all-fiber cavity that is only 1.2 m long changing the length of the laser might be challenging. It is far more easier to change the comb frequencies using only pump power control. We have used the frequency stabilized distributed feedback (DFB) laser diode to measure the impact of the pump power changes on both repetition frequency and carrier envelope offset frequency. Fig. 7 shows the beating signal between the
111
Fig. 7. Beat signal between optical comb and DFB laser diode (spikes at the multiples of the fundamental repetition rate is the beat signal between comb modes; horizontal axis: 80 MHz/div, vertical axis: 10 dB/div).
28 nm-wide optical comb centered at 1563 nm and DFB laser diode stabilized using hydrogen cyanide molecular absorption line at 1551.3 nm. Beat signal consist of spikes at the multiples of the fundamental repetition frequency. This is the beat signal between optical comb lines. Additional spikes between harmonics are the beat frequencies between the DFB laser diode and particular ‘‘tooth” of the comb. Mode-locked laser was pumped with the power of 600 mW. Small sinusoidal signal was added to the pump diode current to slowly modulate its output power. Analysis of the beating signal between DFB laser diode and the optical comb together with the analysis of the 18th harmonic of the comb beating signal at 3039.735 MHz were used to estimate the impact of the pump power on comb parameters. The impact of the pump power on the repetition frequency was found to be 1.9 Hz/mW. This is in good agreement with the results obtained by Newbury and Wasburn [17] and by Haverkamp et al. [18]. By changing the pump power from 500 to 660 mW we were able to control the repetition frequency in the range of more than 300 Hz. The fceo dependence is measured to be 0.118 MHz/
Fig. 6. Output pulse duration vs. pump power (experimental setup is shown inset). Pump power in the laser setup was set to 650 mW. Pump power of the external amplifier was changed from 0 to 620 mW.
112
M. Nikodem, K. Abramski / Optics Communications 283 (2010) 109–112
mW. This is at least one order of magnitude smaller than previously reported values [17]. We believe that this difference comes from short cavity and high pump power used in our configuration. Higher pump power and all-fiber design significantly increase the role of the self phase modulation which can lead to the reduction of the fceo dependence on the pump power changes (according to the prediction in Ref. [17]). Without controlling the length of the laser absolute stabilization of the generated optical frequency comb is not possible. It is however possible to use pump power control to stabilize only the repetition frequency. We have measured frep stability to be better than 1 ppm when the laser was closed in the thermally isolated box. Repetition frequency fluctuations did not exceed 150 Hz (peak–peak) which is smaller than obtained control range of 300 Hz. An example of such ‘‘frequency ruler” was already proposed but with the repetition frequency of less than 40 MHz [18]. We believe that similar configuration can be made using proposed all-fiber laser with the mode spacing significantly higher than 100 MHz. 4. Conclusions In conclusions, we have presented all-fiber passively modelocked erbium doped fiber ring laser with the fundamental repetition frequency of 169 MHz. Pulses as short as 111 fs were obtained with the average output power of more than 30 mW. The impact of the pump power on the repetition frequency and carrier envelope offset frequency was measured. Laser cavity was constructed with only fiber-based, commercially available components. The biggest advantages of proposed laser is reliable, robust configuration and stable, ‘turn-key’ operation. We believe that with presented all-fiber setup future scaling of the repetition rate above 250 MHz will be possible. With the additional repetition frequency stabilization
laser can work as a more than 30 nm wide frequency ruler for the optical metrology and optical communication systems. Acknowledgements The authors would like to thank the Polish Ministry of Science and Higher Education for supporting work presented in this paper under the grant N515 029 32/2079. References [1] [2] [3] [4] [5] [6]
[7] [8] [9] [10] [11] [12] [13] [14] [15] [16] [17] [18]
D. Deng, L. Zhan, Z. Gu, Y. Gu, Y. Xia, Opt. Express 17 (2009) 4284. K. Tamura, E.P. Ippen, H.A. Haus, L.E. Nelson, Opt. Lett. 18 (1993) 1080. T. Udem, R. Holzwarth, T.W. Hansch, Nature 416 (2002) 233. S. Diddams, L. Hollberg, L. Ma, L. Robertsson, Opt. Lett. 27 (2002) 58. S.A. Diddams, D.J. Jones, J. Ye, S.T. Cundiff, J.L. Hall, J.K. Ranka, R.S. Windler, R. Holzwarth, T. Udem, T.W. Hansch, Phys. Rev. Lett. 84 (2000) 5102. T.W. Hansch, J. Alnis, P. Fendel, M. Fisher, C. Gohle, M. Herrmann, R. Holzwarth, N. Kolachevsky, T. Udem, M. Zimmermann, Phil. Trans. R. Soc. A 363 (2005) 2155. T. Shioda, T. Mori, T. Sugimoto, Y. Tanaka, T. Kurosawa, Opt. Commun. 282 (2009) 2909. J. Chen, J.W. Sickler, E.P. Ippen, F.X. Kartner, Opt. Lett. 32 (2007) 1566. F. Adler, K. Moutzouris, A. Leitenstorfer, H. Schnatz, B. Lipphardt, G. Grosche, F. Tauser, Opt. Express 12 (2004) 5872. F.O. Ilday, J. Chen, F.X. Kartner, Opt. Express 13 (2005) 2716. B.R. Washburn, R.W. Fox, N.R. Newbury, J.W. Nicholson, K. Feder, P.S. Westbrook, C.G. Jørgensen, Opt. Express 12 (2004) 4999. B.R. Washburn, S.A. Diddams, N.R. Newbury, J.W. Nicholson, M.F. Yan, C.G. Jørgensen, Opt. Lett. 29 (2004) 250. J.W. Nicholson, D.J. DiGiovanni, IEEE Photon. Technol. Lett. 20 (2008) 2123. H. Byun, D. Pudo, J. Chen, E.P. Ippen, F.X. Kartner, Opt. Lett. 33 (2008) 2221. H.A. Haus, K. Tamura, L.E. Nelson, E.P. Ippen, J. Quantum Electron. 31 (1995) 591. D.J. Jones, Y. Chen, H.A. Haus, E.P. Ippen, Opt. Lett. 23 (1998) 1535. N.R. Newbury, B.R. Washburn, J. Quantum Electron. 41 (2005) 1388. N. Haverkamp, H. Hundertmark, C. Fallnich, H.R. Telle, Appl. Phys. B 78 (2004) 321.
Contents lists available at ScienceDirect
Optics Communications journal homepage: www.elsevier.com/locate/optcom
169 MHz repetition frequency all-fiber passively mode-locked erbium doped fiber laser Michal Nikodem *, Krzysztof Abramski ´ skiego 27, 50-370 Wroclaw, Poland Wroclaw University of Technology, Wybrzeze Wyspian
a r t i c l e
i n f o
Article history: Received 16 July 2009 Received in revised form 28 August 2009 Accepted 24 September 2009
a b s t r a c t Passively mode-locked stretched-pulse erbium fiber laser is presented. With all-fiber configuration 111 fs pulses were achieved with the fundamental repetition rate of 169 MHz and an average output power of more than 30 mW. Proposed setup shows excellent stability, reliability and ‘turn-key’ operation. The impact of the pump power on laser parameters is described. Ó 2009 Elsevier B.V. All rights reserved.
Keywords: Erbium laser Fiber laser Stretched-pulse mode-locking Passive mode-locking
1. Introduction In recent years we have observed growing interest in modelocked fiber lasers. Development of erbium doped fiber (EDF) and wavelength division multiplexing (WDM) technique made 3rd telecommunication window extremely interesting region for ultrafast lasers applications. Passively mode-locked erbium doped fiber lasers have been reported as an effective source of pulses shorter than 100 fs [1,2]. They can also be considered as an optical frequency comb source for optical metrology, since generated comb spectrum could be far more than 4 THz wide. With compact size, high flexibility and robust design fiber-based configurations find application in high-resolution spectroscopy, THz pulses generation, optical clockworks, absolute distance measurements and many others [3–7]. The biggest disadvantage of passively mode-locked fiber lasers is their relatively small repetition frequency which is usually limited by the length of the cavity. The shortest pulse duration can be obtained with the mode-locking due to nonlinear polarization rotation (NPR) but the fundamental repetition rate is typically limited to 30–50 MHz. Configuration up to 200 MHz have also been shown [8–10] but they all have common feature – they are not all-fiber configurations. Usually polarization beam splitter (PBS), isolator and polarization controllers (quarter- and halfwaveplates) are placed between two collimators. In this way cavity length can be significantly reduced but it also complicates the construction.
* Corresponding author. Tel.: +48 713204523. E-mail address: [email protected] (M. Nikodem). 0030-4018/$ - see front matter Ó 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.optcom.2009.09.061
Washburn et al. have shown all-fiber configurations however with the repetition frequency of only 50 MHz [11,12]. Less than 40 MHz repetition rate was reported in Ref. [1] with the 55 fs all-fiber stretched-pulse NPR laser. Recently high repetition rate fiber lasers mode-locked using saturable absorbers has been reported but their parameters are not as good as those that might be obtained using NPR mechanism (270 fs pulses with bandwidth of 10 nm at 447 MHz [13], 180 fs pulses with bandwidth of 15.8 nm at 491 MHz [14]). In this paper all-fiber passively mode-locked stretched-pulse Er-fiber laser is presented. Pulses as short as 111 fs were obtained with the fundamental repetition rate of 169 MHz. To the best of our knowledge this is the highest fundamental repetition frequency obtained with the NPR mode-locked laser constructed with only fiber-based commercially available components. The impact of the pump power on laser parameters is measured. This include the impact of the pump power on both repetition frequency and carrier envelope offset frequency.
2. Laser configuration and experimental results Nowadays all components required for NPR mode-locked laser are commercially available in fiber-based form. Micro-optic devices such as isolator and PBS are not bigger than fused fiber coupler. Fig. 1 shows the configuration of the laser. It is all-fiber setup build with the commercially available components. We have used 30 cm of the Er-doped fiber (attenuation 110 dB/m at 1530 nm) pumped with the 976 nm diode through wavelength division multiplexing coupler (WDM). It is followed by the polarization beam
110
M. Nikodem, K. Abramski / Optics Communications 283 (2010) 109–112
Fig. 1. Configuration of the all-fiber laser (PBS – polarization beam splitter, PC – polarization controller, EDF – erbium doped fiber, LD – laser diode, ISO – isolator, AC – optical autocorrelator, OSA – optical spectrum analyzer).
splitter (PBS), isolator and polarization controller (PC). Erbium doped fiber has dispersion of 46 ps/(nm km) thus laser operates in the stretched-pulse regime [1,2,15]. Fig. 2 shows the picture of the laser. Its compact size is emphasized with the ordinary AAA battery that is shown inset. With the all-fiber cavity laser is very robust and reliable. No adjustment is needed since all components are simply spliced together. The total length of the cavity is approximately 1.2 m (we have obtained fundamental repetition frequency 169 MHz). When the polarization controller was properly adjusted modelocking was obtained. It should be mentioned that we have used only one polarization controller and only two knobs were used to adjust the polarization inside the cavity. With only two degrees of freedom it takes just a few seconds to obtain mode-locking. Output spectrum of the laser is shown in Fig. 3. With the maximal pump power Pp = 660 mW average output power of 33 mW was achieved. The important feature of the laser was ‘turn-key’ operation, i.e. there was no need to re-adjust the polarization controller when pump diode was turned ‘off’ and ‘on’, even if the discontinuity was several hours long. Fig. 4 shows the output spectra recorded during 7 h long continuous test. Measurements were taken every 30 min. During the test output spectrum changes were imperceptible and the average output power fluctuations did not exceed 2 mW. Mode-locking was very immune to vibrations and shock (it was uninterrupted even when laser was dropped from a high of 20 cm). The impact of the pump power on the laser operation is shown in Fig. 5. The average output power changes from 15 mW (Pp = 330 mW) to 33 mW (Pp = 660 mW). When PC was in the proper position multiple pulse or pulse-pair generation were not present even when the pump power was at the maximum level. It can be however seen that both centre wavelength and the comb width change with the pump power. The spectrum slopes are rising slightly when the pump power is increased. Nevertheless the
Fig. 3. Output spectrum of the laser (pump power of 660 mW was used).
Fig. 4. Output spectra of the laser recorded during continuous operation over several hours (measurements were taken after every 30 min).
Fig. 5. (a) output spectra of the laser, pump power was (starting from the bottom): 370, 411, 446, 476, 512, 543, 579, 608 and 657 mW; (b–d) impact of the pump power on the output spectrum parameters.
Fig. 2. Picture of the laser (pump diode is not shown). AAA battery is shown to compare the size of the cavity.
optical comb obtained at the output is smooth, cw-breakthrough and pulse breaking were not observed. The resonant sidebands at both slopes of the spectrum are typical for the passively modelocked fiber lasers and even though they are usually linked with soliton lasers, they also might be present in the spectrum of the stretched-pulse laser [16]. Optical autocorrelator was used to measure the pulse duration. Unfortunately, in the stretched-pulse regime, pulse duration strongly depends on the type and the length of the fiber placed between the laser output and the autocorrelator [15]. To obtain the
M. Nikodem, K. Abramski / Optics Communications 283 (2010) 109–112
minimal pulse duration proper combination of the fiber with normal and anomalous dispersion should be used. Firstly, we have reduced the length of the SMF fiber. Three hundred and fifteen centimeters were needed to insert the one arm of the polarization beam splitter, WDM coupler, isolator and collimator. Then we have placed 5 m of erbium doped fiber. It had low Er ion concentration (attenuation 20 dB/m at 1530 nm when unpumped) and the chromatic dispersion of 15 ps/(nm km). Erbium doped fiber was pumped by the laser diode with the maximum pump power of 620 mW. We were reducing the length of the EDF gradually until minimal pulse duration was finally obtained. Optimal length of the erbium doped fiber was found to be 355 cm. Fig. 6 shows the impact of the pump power on the pulse duration. Experimental data are presented together with the results of the simulations. Split step Fourier method (SSFM) was used to simulate the pulse propagation along the 6.7 m long fiber. We can see that the experimental data are in good agreement with the simulation results. The minimal pulse duration of 111 fs was obtained when pump power of 180 mW was used. When the pump power was too strong (more than 360 mW) nonlinear effects caused the pulse broadening and the wings appeared in the autocorrelation trace. The average output power was 7 mW when the EDF was unpumped, 40 mW when the pump power of 180 mW was used and 120 mW with the maximal pump power of 620 mW.
3. Controlling the frequency of the optical comb The application of the frequency comb in metrology, optical clockworks and high-resolution spectroscopy requires its absolute stabilization. The comb spectrum emitted form the mode-locked lasers is characterized by the repetition frequency (frep) and the carrier envelope offset frequency (fceo). Usually, the cavity length control is used to stabilize the frep and the pump power control is used to stabilize the fceo. With all-fiber cavity that is only 1.2 m long changing the length of the laser might be challenging. It is far more easier to change the comb frequencies using only pump power control. We have used the frequency stabilized distributed feedback (DFB) laser diode to measure the impact of the pump power changes on both repetition frequency and carrier envelope offset frequency. Fig. 7 shows the beating signal between the
111
Fig. 7. Beat signal between optical comb and DFB laser diode (spikes at the multiples of the fundamental repetition rate is the beat signal between comb modes; horizontal axis: 80 MHz/div, vertical axis: 10 dB/div).
28 nm-wide optical comb centered at 1563 nm and DFB laser diode stabilized using hydrogen cyanide molecular absorption line at 1551.3 nm. Beat signal consist of spikes at the multiples of the fundamental repetition frequency. This is the beat signal between optical comb lines. Additional spikes between harmonics are the beat frequencies between the DFB laser diode and particular ‘‘tooth” of the comb. Mode-locked laser was pumped with the power of 600 mW. Small sinusoidal signal was added to the pump diode current to slowly modulate its output power. Analysis of the beating signal between DFB laser diode and the optical comb together with the analysis of the 18th harmonic of the comb beating signal at 3039.735 MHz were used to estimate the impact of the pump power on comb parameters. The impact of the pump power on the repetition frequency was found to be 1.9 Hz/mW. This is in good agreement with the results obtained by Newbury and Wasburn [17] and by Haverkamp et al. [18]. By changing the pump power from 500 to 660 mW we were able to control the repetition frequency in the range of more than 300 Hz. The fceo dependence is measured to be 0.118 MHz/
Fig. 6. Output pulse duration vs. pump power (experimental setup is shown inset). Pump power in the laser setup was set to 650 mW. Pump power of the external amplifier was changed from 0 to 620 mW.
112
M. Nikodem, K. Abramski / Optics Communications 283 (2010) 109–112
mW. This is at least one order of magnitude smaller than previously reported values [17]. We believe that this difference comes from short cavity and high pump power used in our configuration. Higher pump power and all-fiber design significantly increase the role of the self phase modulation which can lead to the reduction of the fceo dependence on the pump power changes (according to the prediction in Ref. [17]). Without controlling the length of the laser absolute stabilization of the generated optical frequency comb is not possible. It is however possible to use pump power control to stabilize only the repetition frequency. We have measured frep stability to be better than 1 ppm when the laser was closed in the thermally isolated box. Repetition frequency fluctuations did not exceed 150 Hz (peak–peak) which is smaller than obtained control range of 300 Hz. An example of such ‘‘frequency ruler” was already proposed but with the repetition frequency of less than 40 MHz [18]. We believe that similar configuration can be made using proposed all-fiber laser with the mode spacing significantly higher than 100 MHz. 4. Conclusions In conclusions, we have presented all-fiber passively modelocked erbium doped fiber ring laser with the fundamental repetition frequency of 169 MHz. Pulses as short as 111 fs were obtained with the average output power of more than 30 mW. The impact of the pump power on the repetition frequency and carrier envelope offset frequency was measured. Laser cavity was constructed with only fiber-based, commercially available components. The biggest advantages of proposed laser is reliable, robust configuration and stable, ‘turn-key’ operation. We believe that with presented all-fiber setup future scaling of the repetition rate above 250 MHz will be possible. With the additional repetition frequency stabilization
laser can work as a more than 30 nm wide frequency ruler for the optical metrology and optical communication systems. Acknowledgements The authors would like to thank the Polish Ministry of Science and Higher Education for supporting work presented in this paper under the grant N515 029 32/2079. References [1] [2] [3] [4] [5] [6]
[7] [8] [9] [10] [11] [12] [13] [14] [15] [16] [17] [18]
D. Deng, L. Zhan, Z. Gu, Y. Gu, Y. Xia, Opt. Express 17 (2009) 4284. K. Tamura, E.P. Ippen, H.A. Haus, L.E. Nelson, Opt. Lett. 18 (1993) 1080. T. Udem, R. Holzwarth, T.W. Hansch, Nature 416 (2002) 233. S. Diddams, L. Hollberg, L. Ma, L. Robertsson, Opt. Lett. 27 (2002) 58. S.A. Diddams, D.J. Jones, J. Ye, S.T. Cundiff, J.L. Hall, J.K. Ranka, R.S. Windler, R. Holzwarth, T. Udem, T.W. Hansch, Phys. Rev. Lett. 84 (2000) 5102. T.W. Hansch, J. Alnis, P. Fendel, M. Fisher, C. Gohle, M. Herrmann, R. Holzwarth, N. Kolachevsky, T. Udem, M. Zimmermann, Phil. Trans. R. Soc. A 363 (2005) 2155. T. Shioda, T. Mori, T. Sugimoto, Y. Tanaka, T. Kurosawa, Opt. Commun. 282 (2009) 2909. J. Chen, J.W. Sickler, E.P. Ippen, F.X. Kartner, Opt. Lett. 32 (2007) 1566. F. Adler, K. Moutzouris, A. Leitenstorfer, H. Schnatz, B. Lipphardt, G. Grosche, F. Tauser, Opt. Express 12 (2004) 5872. F.O. Ilday, J. Chen, F.X. Kartner, Opt. Express 13 (2005) 2716. B.R. Washburn, R.W. Fox, N.R. Newbury, J.W. Nicholson, K. Feder, P.S. Westbrook, C.G. Jørgensen, Opt. Express 12 (2004) 4999. B.R. Washburn, S.A. Diddams, N.R. Newbury, J.W. Nicholson, M.F. Yan, C.G. Jørgensen, Opt. Lett. 29 (2004) 250. J.W. Nicholson, D.J. DiGiovanni, IEEE Photon. Technol. Lett. 20 (2008) 2123. H. Byun, D. Pudo, J. Chen, E.P. Ippen, F.X. Kartner, Opt. Lett. 33 (2008) 2221. H.A. Haus, K. Tamura, L.E. Nelson, E.P. Ippen, J. Quantum Electron. 31 (1995) 591. D.J. Jones, Y. Chen, H.A. Haus, E.P. Ippen, Opt. Lett. 23 (1998) 1535. N.R. Newbury, B.R. Washburn, J. Quantum Electron. 41 (2005) 1388. N. Haverkamp, H. Hundertmark, C. Fallnich, H.R. Telle, Appl. Phys. B 78 (2004) 321.