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Dispersion measurement technique based on the self-seeding laser oscillation of a Fabry–Perot laser diode
Optics Communications 273 (2007) 506–509 www.elsevier.com/locate/optcom
Dispersion measurement technique based on the self-seeding laser oscillation of a Fabry–Perot laser diode Ki-Hong Yoon, Jae-Won Song, Hyun Deok Kim
*
School of Electrical Engineering and Computer Science, Kyungpook National University, 1370 Sankyuk-dong, Buk-gu, Daegu 702-701, Republic of Korea Received 14 June 2006; received in revised form 9 January 2007; accepted 17 January 2007
Abstract A simple dispersion measurement technique has been proposed and demonstrated by using the self-seeding laser oscillation of a Fabry–Perot laser diode through an optical closed-loop path. When the multi-mode optical pulses emitted from the laser are re-injected into the laser after traversing a fiber-under-test, a single mode laser oscillation occurs through the closed-loop path due to the group velocity difference between the pulses of different wavelengths. We measured the dispersion parameter of the fiber-under-test from the modulation frequency changes required to induce single-mode laser oscillations through the optical closed-loop path. The maximum measurement error was less than 1.5% for the optical fibers as compared with a commercial instrument. Ó 2007 Elsevier B.V. All rights reserved. PACS: 42.81.i; 42.81.Cn Keywords: Fiber; Dispersion; Measurement; Fabry–Perot laser; Self-seeding laser oscillation
1. Introduction As the bit rate of a fiber-optic transmission system increases, the chromatic dispersion measurements of optical components become more important since the novel high capacity transmission techniques require the accurate value of dispersion parameter. A variety of techniques have been developed to measure the chromatic dispersion of optical fibers such as the time-of-flight measurement technique [1], the phase-shift measurement technique [2] and the interferometric measurement technique [3,4]. The time-of-flight measurement technique is inherently inaccurate due to the laser and the electronics instabilities [4]. Furthermore, it requires expensive equipments such as a high performance short pulse generator and a wide-band optical receiver since its measurement accuracy strongly
*
Corresponding author. Tel.: +82 539507578; fax: +82 539505508. E-mail addresses: [email protected] (K.-H. Yoon), [email protected]. ac.kr (J.-W. Song), [email protected] (H.D. Kim). 0030-4018/$ - see front matter Ó 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.optcom.2007.01.026
depends on the width of the optical pulse used and the characteristics of the optical receiver. The phase-shift measurement technique also incorporates a complicated measurement system including a phase detector, a high-frequency signal generator, a high-speed optical transmitter, a wide-band optical receiver and other complex equipment. While, the interferometric measurement technique is relatively accurate compared with the other techniques, the measurable fiber length is limited to several kilometers, and it requires a complex calibration process [4]. The previous dispersion measurement techniques commonly utilize tunable lasers or broadband light sources combined with tunable optical filters and wavelength meters for wavelength calibration. In this paper, we propose a simple dispersion measurement technique by using the self-seeding laser oscillation of a low-cost Fabry–Perot laser diode (FP-LD). The proposed technique eliminates the need for expensive equipment and components such as tunable lasers, phase detectors, high-speed optical transmitters and wide-band optical receivers.
K.-H. Yoon et al. / Optics Communications 273 (2007) 506–509
507
2. Operation principle 1/F
Fig. 1 shows the schematic diagram of the proposed dispersion measurement system. It is arranged to form an optical closed-loop path composed of an FP-LD, an optical circulator and a fiber-under-test (FUT). The common port of the optical circulator is connected to the FP-LD, and its output and input ports are connected to the FUT. The FP-LD is biased with dc current and a modulation current generated from the signal generator is applied to the FP-LD to generate optical pulses through a direct laser modulation. We use an optical tap coupler and an optical spectrum analyzer (OSA) to observe the optical spectrum. A polarization controller is used to maximize the re-injection efficiency. When the modulation current is applied to the FP-LD, the FP-LD generates a multi-mode (multi-wavelength) optical pulse trains. The optical pulses are re-injected into the FP-LD through the optical closed-loop path, which will induce a self-seeding laser oscillation. The pulses of each mode have different round-trip times due to the chromatic dispersion of the FUT. We assume the FP-LD has three output modes (k1, k2 and k3). As shown in Fig. 2a, the re-injected optical pulses of each mode arrive at the FPLD at different times even though they leave the FP-LD at the same time. The round-trip time difference (DTD) between the optical pulses of two modes is determined by the chromatic dispersion of the FUT and is given by DT D ¼ DLDk;
ð1Þ
where D and L are the chromatic dispersion parameter and the length of the FUT, respectively and Dk is the difference between the wavelengths of each mode. If the pulse of a specific mode (k2) arrives at the moment when the current applied to the FP-LD is higher than the threshold current of the FP-LD, a single-mode laser oscillation occurs at the mode (k2), which is known as the selfseeding laser oscillation [5–7]. Namely, the single-mode laser oscillation occurs at the mode whose round-trip time is equal to an integer multiple of the modulation period, the inverse of the modulation frequency, and thus the round-trip time of the lasing mode satisfies nL N ¼ ; c F
ð2Þ
N/F •••
Applied current
time 3
a Optical pulse
1
OSA
Signal generator FP-LD
Optical circulator
Tap coupler
Polarization controller
FUT (D)
Fig. 1. The schematic diagram of the proposed dispersion measurement system.
•••
time 1
T
1/(F+ F)
N/(F+ F)
Applied current
•••
2
3
TM time
3
b
2
Optical pulse
1
•••
time 1
Starting pulses
2
3
Feedback pulses
Fig. 2. Time diagrams of the applied current and the optical pulse: (a) when the modulation frequency is F and (b) when the modulation frequency is changed to F + DF.
where n is the refractive index of the FUT, c is the velocity of light in a vacuum, F is the modulation frequency and N is an arbitrary integer. Eq. (2) implies that the optical pulse re-injection time should coincide with the moment when the Nth-delayed modulation current pulse is applied to the FP-LD. The moments when the modulation current pulses are applied to the FP-LD change with the modulation frequency change. Thus, if the modulation frequency is changed, the single-mode laser oscillation may not occur at the k2 mode. Instead, the single-mode laser oscillation can occur at other mode (k1) for a different modulation frequency if the feedback optical pulse of the k1 mode arrives at the moment when the applied current is higher than the threshold current of the FP-LD. As shown in Fig. 2b, the modulation period decreases as the modulation frequency increases from F to F + DF, where DF is a positive value. The modulation period change (DT) is given by DT ¼
1 1 : F þ DF F
ð3Þ
The accumulated modulation period change (DTM) is the sum of the modulation period changes during the N periods and is given by DT M ¼ N DT
Proposed Proposed system system
TD
2
nL DF : c F
ð4Þ
In order to induce laser oscillation at the k1 mode instead of the k2 mode, the accumulated modulation period change should be equal to the round-trip time difference (DTD) between the two modes. It is notable that the round-trip time difference between the two modes can be measured by detecting the modulation frequency changes required for single-mode laser oscillations. From this condition, the dispersion parameter of the FUT is given by D
n DF : cF Dk
ð5Þ
K.-H. Yoon et al. / Optics Communications 273 (2007) 506–509
From Eq. (5), the chromatic dispersion parameter of the FUT can be calculated by measuring the modulation frequency changes required to induce single-mode laser oscillations in the each mode. 3. Experimental results To evaluate the performance of the proposed measurement system, we configured the experimental setup shown in Fig. 1. We used an un-cooled FP-LD without an isolator and the threshold current and the mode spacing of the FPLD were 10 mA and 1.16 nm, respectively. We set the dc bias current applied to the FP-LD at slightly below the threshold current to prevent the optical pulse impairments caused by the nonlinearity of the FUT and to broaden the measurable wavelength range. Fig. 3 shows the measured optical spectra through a 10% optical tap coupler when the FUT was a standard single-mode fiber (SSMF) with a length of 24 km. The selfseeding laser oscillations occurred at different modes when the modulation frequency was swept from 80 MHz to higher. In this case, we applied a sinusoidal modulation current to the FP-LD and the peak-to-peak amplitude of the ac modulation current was about 13 mA. The rising and the falling times of the optical pulses were less than 50 ps. As the modulation frequency increased, the laser oscillations occurred at shorter wavelengths. The peak power varies with the lasing wavelength since the gain spectrum of the FP-LD inherently depends on the wavelength. The maximum peak input power to the FUT was about 13 dBm, when the lasing wavelength was about 1545 nm, which is about one-order below the power level where the fiber nonlinearity causes significant signal impairments through a nonlinear harmonic generation or nonlinear distortion in various optical fibers [8,9].
Modulation frequency change [kHz]
508
-0.15
-0.18
-0.21
-0.24 1530
1535
1540
1545
1550
1555
1560
Wavelength [nm] Fig. 4. The measured modulation frequency changes required to induce single-mode laser oscillations.
Fig. 4 shows the measured modulation frequency changes (DF) required to change the laser oscillation mode from one to adjacent one. As the wavelength of the lasing mode became longer, the absolute value of the required frequency change increased due to the dispersion slope of the FUT. Fig. 5 shows the chromatic dispersion parameter of the FUT as a function of the wavelength calculated by using the Eq. (5) and the measured modulation frequency changes. To evaluate the accuracy of the proposed measurement technique, we also measured the dispersion parameter of the FUT by using a commercial instrument (Perkin–Elmer, model: FD440). The measurement results using the proposed technique agreed well with those measured by using the commercial instrument and the maximum relative measurement error was less than 1.5%. We also measured the dispersion parameter of the FUT with a negative dispersion parameter. The length of the FUT was 2 km. The wavelength of the lasing mode became longer as the modulation frequency increased due to the negative dispersion parameter of the FUT. The results measured by using the proposed method agreed well with those measured by using FD440 for the FUT with the negative dispersion parameter as shown in
3.420
1.440
0.419
Mod ulat ion
Optical Power [dBm]
1.639
freq uen cy c
1.842
han ge [ kHz ]
3.031
0.212 0.000
Fig. 3. The optical spectra for different modulation frequencies when the single-mode laser oscillations occur through the optical closed-loop path.
Dispersion parameter [ps/nm/km]
3.227
20 Proposed method PerkinElmer FD440 (±1 %)
19 18 17 16 15 14 1530
1535
1540
1545
1550
1555
Wavelength [nm] Fig. 5. The measured dispersion parameters of the SSMF.
1560
-13 -14 -15
4.5
Proposed method
4.2
PerkinElmer FD440 (±1 %)
3.9 3.6 3.3 1530
1540 1550 Wavelength [nm]
1560
-16 -17 -18 1530
1535
1540
1545
1550
1555
509
4. Conclusions
-12 Frequency change [kHz]
Dispersion parameter [ps/nm/km]
K.-H. Yoon et al. / Optics Communications 273 (2007) 506–509
1560
Wavelength [nm] Fig. 6. The measured dispersion parameters of the optical fiber with a negative dispersion. The inset shows the modulation frequency changes required to induce the single-mode laser oscillations.
Fig. 6. The inset of Fig. 6 shows the modulation frequency changes required to induce single-mode oscillations for different wavelengths. Since the proposed system is based on an optical pulse flight time difference measurement in time domain and the residual dispersion of the FUT may distorts the pulse shape, the measurement accuracy can be affected by the line width of the laser. The line width of the laser varies with the current applied and the lasing wavelength, and the measured line width was several MHz since the cavity effect of the FP-LD narrows the line width during the self-seeding laser oscillation as similar to the filter used in reference [10]. The minimum modulation frequency in the experiment was 80 MHz, and it is much higher than the measured line width. Thus, the effect of the pulse broadening due to the line width enhancement was negligible in the experiment. It is notable that we can easily expand the measurement wavelength range by using multiple FP-LDs even though the dispersion parameters in the experiments were over about 30 nm.
We have demonstrated a novel dispersion measurement technique based on the self-seeding laser oscillation through an optical closed-loop path. Since the FP-LD works as an optical pulse train generator and a dispersion-induced group delay detector, the proposed technique removes the need for using expensive equipment and components such as a tunable laser, a phase detector, a highspeed transmitter and a wide-band receiver, which are commonly used in current dispersion measurement instruments. The proposed technique is easily scalable in the wavelength range by using multiple low-cost FP-LDs with different output wavelengths. Acknowledgements This work was partially supported by Korea Research Foundation Grant (D00184) and by Brain Korea 21 Project. References [1] C. Lin, A.R. Tynes, A. Tomita, P.L. Liu, D.L. Philen, Bell Syst. Tech. J. 62 (1985) 457. [2] Y. Horiuchi, Y. Namihira, H. Wakabayashi, IEEE Photon Technol. Lett. 1 (1982) 458. [3] F.M. Sears, L.G. Cohen, J. Stone, J. Lightwave Technol. 2 (1984) 181. [4] A.V. Belov, A.S. Kurkov, V.A. Semenov, A.V. Chicolini, J. Lightwave Technol. 7 (1989) 863. [5] D. Huhse, M. Schell, J. Kaessner, D. Bimberg, I.S. Tarasov, A.V. Gorbachov, D.Z. Garbuzov, Electron. Lett. 30 (1994) 157. [6] S. Bouchoule, N. Stelmakh, M. Cavelier, J.-M. Lourtioz, IEEE J. Quantum Electron. QE-29 (1993) 1693. [7] K.L. Lee, C. Shu, IEEE Photon Technol. Lett. 12 (2000) 624. [8] M. Fukui, S. Aisawa, O. Ishida, K. Shimano, A. Umeda, T. Sakamoto, K. Oda, N. Takachio, Electron. Lett. 33 (1997) 693. [9] M. Stern, J.P. Heritage, R.N. Thurston, S. Tu, J. Lightwave Technol. 8 (1990) 1009. [10] J.L. Zyskind, J.W. Sulhoff, Y. Sun, J. Stone, L.W. Stulz, G.T. Harvey, D.J. Digiovanni, H.M. Presby, A. Piccirilli, U. Koren, R.M. Jopson, Electron. Lett. 27 (1991) 2148.
Dispersion measurement technique based on the self-seeding laser oscillation of a Fabry–Perot laser diode Ki-Hong Yoon, Jae-Won Song, Hyun Deok Kim
*
School of Electrical Engineering and Computer Science, Kyungpook National University, 1370 Sankyuk-dong, Buk-gu, Daegu 702-701, Republic of Korea Received 14 June 2006; received in revised form 9 January 2007; accepted 17 January 2007
Abstract A simple dispersion measurement technique has been proposed and demonstrated by using the self-seeding laser oscillation of a Fabry–Perot laser diode through an optical closed-loop path. When the multi-mode optical pulses emitted from the laser are re-injected into the laser after traversing a fiber-under-test, a single mode laser oscillation occurs through the closed-loop path due to the group velocity difference between the pulses of different wavelengths. We measured the dispersion parameter of the fiber-under-test from the modulation frequency changes required to induce single-mode laser oscillations through the optical closed-loop path. The maximum measurement error was less than 1.5% for the optical fibers as compared with a commercial instrument. Ó 2007 Elsevier B.V. All rights reserved. PACS: 42.81.i; 42.81.Cn Keywords: Fiber; Dispersion; Measurement; Fabry–Perot laser; Self-seeding laser oscillation
1. Introduction As the bit rate of a fiber-optic transmission system increases, the chromatic dispersion measurements of optical components become more important since the novel high capacity transmission techniques require the accurate value of dispersion parameter. A variety of techniques have been developed to measure the chromatic dispersion of optical fibers such as the time-of-flight measurement technique [1], the phase-shift measurement technique [2] and the interferometric measurement technique [3,4]. The time-of-flight measurement technique is inherently inaccurate due to the laser and the electronics instabilities [4]. Furthermore, it requires expensive equipments such as a high performance short pulse generator and a wide-band optical receiver since its measurement accuracy strongly
*
Corresponding author. Tel.: +82 539507578; fax: +82 539505508. E-mail addresses: [email protected] (K.-H. Yoon), [email protected]. ac.kr (J.-W. Song), [email protected] (H.D. Kim). 0030-4018/$ - see front matter Ó 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.optcom.2007.01.026
depends on the width of the optical pulse used and the characteristics of the optical receiver. The phase-shift measurement technique also incorporates a complicated measurement system including a phase detector, a high-frequency signal generator, a high-speed optical transmitter, a wide-band optical receiver and other complex equipment. While, the interferometric measurement technique is relatively accurate compared with the other techniques, the measurable fiber length is limited to several kilometers, and it requires a complex calibration process [4]. The previous dispersion measurement techniques commonly utilize tunable lasers or broadband light sources combined with tunable optical filters and wavelength meters for wavelength calibration. In this paper, we propose a simple dispersion measurement technique by using the self-seeding laser oscillation of a low-cost Fabry–Perot laser diode (FP-LD). The proposed technique eliminates the need for expensive equipment and components such as tunable lasers, phase detectors, high-speed optical transmitters and wide-band optical receivers.
K.-H. Yoon et al. / Optics Communications 273 (2007) 506–509
507
2. Operation principle 1/F
Fig. 1 shows the schematic diagram of the proposed dispersion measurement system. It is arranged to form an optical closed-loop path composed of an FP-LD, an optical circulator and a fiber-under-test (FUT). The common port of the optical circulator is connected to the FP-LD, and its output and input ports are connected to the FUT. The FP-LD is biased with dc current and a modulation current generated from the signal generator is applied to the FP-LD to generate optical pulses through a direct laser modulation. We use an optical tap coupler and an optical spectrum analyzer (OSA) to observe the optical spectrum. A polarization controller is used to maximize the re-injection efficiency. When the modulation current is applied to the FP-LD, the FP-LD generates a multi-mode (multi-wavelength) optical pulse trains. The optical pulses are re-injected into the FP-LD through the optical closed-loop path, which will induce a self-seeding laser oscillation. The pulses of each mode have different round-trip times due to the chromatic dispersion of the FUT. We assume the FP-LD has three output modes (k1, k2 and k3). As shown in Fig. 2a, the re-injected optical pulses of each mode arrive at the FPLD at different times even though they leave the FP-LD at the same time. The round-trip time difference (DTD) between the optical pulses of two modes is determined by the chromatic dispersion of the FUT and is given by DT D ¼ DLDk;
ð1Þ
where D and L are the chromatic dispersion parameter and the length of the FUT, respectively and Dk is the difference between the wavelengths of each mode. If the pulse of a specific mode (k2) arrives at the moment when the current applied to the FP-LD is higher than the threshold current of the FP-LD, a single-mode laser oscillation occurs at the mode (k2), which is known as the selfseeding laser oscillation [5–7]. Namely, the single-mode laser oscillation occurs at the mode whose round-trip time is equal to an integer multiple of the modulation period, the inverse of the modulation frequency, and thus the round-trip time of the lasing mode satisfies nL N ¼ ; c F
ð2Þ
N/F •••
Applied current
time 3
a Optical pulse
1
OSA
Signal generator FP-LD
Optical circulator
Tap coupler
Polarization controller
FUT (D)
Fig. 1. The schematic diagram of the proposed dispersion measurement system.
•••
time 1
T
1/(F+ F)
N/(F+ F)
Applied current
•••
2
3
TM time
3
b
2
Optical pulse
1
•••
time 1
Starting pulses
2
3
Feedback pulses
Fig. 2. Time diagrams of the applied current and the optical pulse: (a) when the modulation frequency is F and (b) when the modulation frequency is changed to F + DF.
where n is the refractive index of the FUT, c is the velocity of light in a vacuum, F is the modulation frequency and N is an arbitrary integer. Eq. (2) implies that the optical pulse re-injection time should coincide with the moment when the Nth-delayed modulation current pulse is applied to the FP-LD. The moments when the modulation current pulses are applied to the FP-LD change with the modulation frequency change. Thus, if the modulation frequency is changed, the single-mode laser oscillation may not occur at the k2 mode. Instead, the single-mode laser oscillation can occur at other mode (k1) for a different modulation frequency if the feedback optical pulse of the k1 mode arrives at the moment when the applied current is higher than the threshold current of the FP-LD. As shown in Fig. 2b, the modulation period decreases as the modulation frequency increases from F to F + DF, where DF is a positive value. The modulation period change (DT) is given by DT ¼
1 1 : F þ DF F
ð3Þ
The accumulated modulation period change (DTM) is the sum of the modulation period changes during the N periods and is given by DT M ¼ N DT
Proposed Proposed system system
TD
2
nL DF : c F
ð4Þ
In order to induce laser oscillation at the k1 mode instead of the k2 mode, the accumulated modulation period change should be equal to the round-trip time difference (DTD) between the two modes. It is notable that the round-trip time difference between the two modes can be measured by detecting the modulation frequency changes required for single-mode laser oscillations. From this condition, the dispersion parameter of the FUT is given by D
n DF : cF Dk
ð5Þ
K.-H. Yoon et al. / Optics Communications 273 (2007) 506–509
From Eq. (5), the chromatic dispersion parameter of the FUT can be calculated by measuring the modulation frequency changes required to induce single-mode laser oscillations in the each mode. 3. Experimental results To evaluate the performance of the proposed measurement system, we configured the experimental setup shown in Fig. 1. We used an un-cooled FP-LD without an isolator and the threshold current and the mode spacing of the FPLD were 10 mA and 1.16 nm, respectively. We set the dc bias current applied to the FP-LD at slightly below the threshold current to prevent the optical pulse impairments caused by the nonlinearity of the FUT and to broaden the measurable wavelength range. Fig. 3 shows the measured optical spectra through a 10% optical tap coupler when the FUT was a standard single-mode fiber (SSMF) with a length of 24 km. The selfseeding laser oscillations occurred at different modes when the modulation frequency was swept from 80 MHz to higher. In this case, we applied a sinusoidal modulation current to the FP-LD and the peak-to-peak amplitude of the ac modulation current was about 13 mA. The rising and the falling times of the optical pulses were less than 50 ps. As the modulation frequency increased, the laser oscillations occurred at shorter wavelengths. The peak power varies with the lasing wavelength since the gain spectrum of the FP-LD inherently depends on the wavelength. The maximum peak input power to the FUT was about 13 dBm, when the lasing wavelength was about 1545 nm, which is about one-order below the power level where the fiber nonlinearity causes significant signal impairments through a nonlinear harmonic generation or nonlinear distortion in various optical fibers [8,9].
Modulation frequency change [kHz]
508
-0.15
-0.18
-0.21
-0.24 1530
1535
1540
1545
1550
1555
1560
Wavelength [nm] Fig. 4. The measured modulation frequency changes required to induce single-mode laser oscillations.
Fig. 4 shows the measured modulation frequency changes (DF) required to change the laser oscillation mode from one to adjacent one. As the wavelength of the lasing mode became longer, the absolute value of the required frequency change increased due to the dispersion slope of the FUT. Fig. 5 shows the chromatic dispersion parameter of the FUT as a function of the wavelength calculated by using the Eq. (5) and the measured modulation frequency changes. To evaluate the accuracy of the proposed measurement technique, we also measured the dispersion parameter of the FUT by using a commercial instrument (Perkin–Elmer, model: FD440). The measurement results using the proposed technique agreed well with those measured by using the commercial instrument and the maximum relative measurement error was less than 1.5%. We also measured the dispersion parameter of the FUT with a negative dispersion parameter. The length of the FUT was 2 km. The wavelength of the lasing mode became longer as the modulation frequency increased due to the negative dispersion parameter of the FUT. The results measured by using the proposed method agreed well with those measured by using FD440 for the FUT with the negative dispersion parameter as shown in
3.420
1.440
0.419
Mod ulat ion
Optical Power [dBm]
1.639
freq uen cy c
1.842
han ge [ kHz ]
3.031
0.212 0.000
Fig. 3. The optical spectra for different modulation frequencies when the single-mode laser oscillations occur through the optical closed-loop path.
Dispersion parameter [ps/nm/km]
3.227
20 Proposed method PerkinElmer FD440 (±1 %)
19 18 17 16 15 14 1530
1535
1540
1545
1550
1555
Wavelength [nm] Fig. 5. The measured dispersion parameters of the SSMF.
1560
-13 -14 -15
4.5
Proposed method
4.2
PerkinElmer FD440 (±1 %)
3.9 3.6 3.3 1530
1540 1550 Wavelength [nm]
1560
-16 -17 -18 1530
1535
1540
1545
1550
1555
509
4. Conclusions
-12 Frequency change [kHz]
Dispersion parameter [ps/nm/km]
K.-H. Yoon et al. / Optics Communications 273 (2007) 506–509
1560
Wavelength [nm] Fig. 6. The measured dispersion parameters of the optical fiber with a negative dispersion. The inset shows the modulation frequency changes required to induce the single-mode laser oscillations.
Fig. 6. The inset of Fig. 6 shows the modulation frequency changes required to induce single-mode oscillations for different wavelengths. Since the proposed system is based on an optical pulse flight time difference measurement in time domain and the residual dispersion of the FUT may distorts the pulse shape, the measurement accuracy can be affected by the line width of the laser. The line width of the laser varies with the current applied and the lasing wavelength, and the measured line width was several MHz since the cavity effect of the FP-LD narrows the line width during the self-seeding laser oscillation as similar to the filter used in reference [10]. The minimum modulation frequency in the experiment was 80 MHz, and it is much higher than the measured line width. Thus, the effect of the pulse broadening due to the line width enhancement was negligible in the experiment. It is notable that we can easily expand the measurement wavelength range by using multiple FP-LDs even though the dispersion parameters in the experiments were over about 30 nm.
We have demonstrated a novel dispersion measurement technique based on the self-seeding laser oscillation through an optical closed-loop path. Since the FP-LD works as an optical pulse train generator and a dispersion-induced group delay detector, the proposed technique removes the need for using expensive equipment and components such as a tunable laser, a phase detector, a highspeed transmitter and a wide-band receiver, which are commonly used in current dispersion measurement instruments. The proposed technique is easily scalable in the wavelength range by using multiple low-cost FP-LDs with different output wavelengths. Acknowledgements This work was partially supported by Korea Research Foundation Grant (D00184) and by Brain Korea 21 Project. References [1] C. Lin, A.R. Tynes, A. Tomita, P.L. Liu, D.L. Philen, Bell Syst. Tech. J. 62 (1985) 457. [2] Y. Horiuchi, Y. Namihira, H. Wakabayashi, IEEE Photon Technol. Lett. 1 (1982) 458. [3] F.M. Sears, L.G. Cohen, J. Stone, J. Lightwave Technol. 2 (1984) 181. [4] A.V. Belov, A.S. Kurkov, V.A. Semenov, A.V. Chicolini, J. Lightwave Technol. 7 (1989) 863. [5] D. Huhse, M. Schell, J. Kaessner, D. Bimberg, I.S. Tarasov, A.V. Gorbachov, D.Z. Garbuzov, Electron. Lett. 30 (1994) 157. [6] S. Bouchoule, N. Stelmakh, M. Cavelier, J.-M. Lourtioz, IEEE J. Quantum Electron. QE-29 (1993) 1693. [7] K.L. Lee, C. Shu, IEEE Photon Technol. Lett. 12 (2000) 624. [8] M. Fukui, S. Aisawa, O. Ishida, K. Shimano, A. Umeda, T. Sakamoto, K. Oda, N. Takachio, Electron. Lett. 33 (1997) 693. [9] M. Stern, J.P. Heritage, R.N. Thurston, S. Tu, J. Lightwave Technol. 8 (1990) 1009. [10] J.L. Zyskind, J.W. Sulhoff, Y. Sun, J. Stone, L.W. Stulz, G.T. Harvey, D.J. Digiovanni, H.M. Presby, A. Piccirilli, U. Koren, R.M. Jopson, Electron. Lett. 27 (1991) 2148.