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Optics Express

Optics Express

  • Editor: C. Martijn de Sterke
  • Vol. 17, Iss. 12 — Jun. 8, 2009
  • pp: 10189–10194
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Tunable external cavity laser employing uncooled superluminescent diode

Su Hwan Oh, Ki Soo Kim, Jung Jin Ju, Min-su Kim, Ki-Hong Yoon, Dae Kon Oh, Young-Ouk Noh, and Hyung-Jong Lee  »View Author Affiliations


Optics Express, Vol. 17, Issue 12, pp. 10189-10194 (2009)
http://dx.doi.org/10.1364/OE.17.010189


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Abstract

We have fabricated a tunable external cavity laser (T-ECL) based on a superluminescent diode and a polymeric waveguide Bragg reflector, providing a cost-effective solution for wavelength division multiplexing–passive optical network (WDM-PON) systems. The wavelength of the T-ECL is tuned through 100 GHz-spacing 16 channels by the thermo-optic tuning of the refractive index of the polymer waveguide at a low input power of 70 mW. The maximum output power and the slope efficiency of the uncooled diode at 20 (75) °C are 8.83 (3.80) mW and 0.107 (0.061) W/A, respectively. The T-ECL operated successfully in the direct modulation for 1.25 Gbit/s transmissions over 20 km.

© 2009 OSA

1. Introduction

Tunable lasers are important devices in the wavelength division multiplexing (WDM) transmission systems [1

1. L. A. Coldren, G. A. Fish, Y. Akulova, J. S. Barton, L. Johansson, and C. W. Coldren, “Tunable semiconductor lasers: A Tutorial,” J. Lightwave Technol. 22(1), 193–202 (2004). [CrossRef]

,2

2. Y. Liu, A. R. Davies, J. D. Ingham, R. V. Penty, and I. H. White, “Uncooled DBR laser directly modulated at 3.125Gb/s as athermal transmitter for low-cost WDM systems,” IEEE Photon. Technol. Lett. 17(10), 2026–2028 (2005). [CrossRef]

]. Since the wavelength division multiplexing–passive optical network (WDM-PON) system [3

3. H. S. Chung, B. K. Kim, and K. Kim, “Effects of upstream bit rate on a wavelength-remodulated WDM-PON based on manchester or inverse-return-to-zero coding,” ETRI J. 30, 255–260 (2008). [CrossRef]

,4

4. H.-C. Ji, I. Yamashita, and K.-I. Kitayama, “Cost-effective colorless WDM-PON delivering up/down-stream data and broadcast services on a single wavelength using mutually injected Fabry-Perot laser diodes,” Opt. Express 16(7), 4520–4528 (2008). [CrossRef] [PubMed]

] has required wider bandwidth than other PON systems [5

5. J. G. Kim, C.-J. Chae, and M.-H. Kang, “Mini-Slot-Based Transmission Scheme for Local Customer Internetworking in PONs,” ETRI J. 30, 282–289 (2008). [CrossRef]

,6

6. B. Lung, “PON architecture ‘future proofs’ FTTH,” Lightwave Mag. 16, 104–107 (1999).

], there have been strong demands on widely and rapidly tunable compact laser diodes that can be easily fabricated in mass production. One of the big technical challenges in employing the tunable lasers as a colorless transmitter in the WDM-PON systems is the initialization of the wavelength without any intervention of operation.

In this paper, we discuss the characteristics of a T-ECL with an uncooled SLD and a polymeric tunable Bragg reflector. The temperature characteristics of the T-ECL are better than that of the SLD because the carrier density in the SLD active region is reduced by inserting the reflecting beam into the SLD from the grating region of ECL. The T-ECL can operate at the high temperature of 75°C. This device operated successfully with a total throughput of 1.25-Gbit/s over 20km transmission, demonstrating its possibility of application to WDM-PON systems.

2. Design and fabrication

Figure 1
Fig. 1 a schematic diagram of the hybrid integrated tunable laser consisting of a SLD, an aspheric microlens, and a polymeric tunable Bragg reflector.
shows a schematic diagram of the T-ECL consisting of a SLD, an aspheric microlens, and a polymeric tunable Bragg reflector. The SLD is hermetically packaged in a TO can whose structure and fabrication process are described elsewhere [7

7. S. H. Oh, D.-H. Lee, K. S. Kim, Y.-S. Baek, and K.-R. Oh, “High-performance 1.55-μm superluminescent diode with butt-coupled spot-size converter,” IEEE Photon. Technol. Lett. 20(11), 894–896 (2008). [CrossRef]

]. The polymer waveguide device can be operated in air and does not need a costly hermetic packaging as is employed in Ref [14

14. Y.-O. Noh, C.-H. Lee, J.-M. Kim, W.-Y. Hwang, Y.-H. Won, H.-J. Lee, S.-G. Han, and M.-C. Oh, “Polymer waveguide variable optical attenuator and its reliability,” Opt. Commun. 242(4-6), 533–540 (2004). [CrossRef]

]. The output beam emitting from the spot size converter SLD is coupled to the polymer waveguide through the microlens with a typical coupling efficiency of 40%. Since the polymeric Bragg reflector is actively aligned with the TO can, the coupling efficiency and yield of the fabricated module are higher than those of other hybrid structures. The wavelength of the laser reflected from the Brag reflector can be controlled by applying a current on the integrated heater of the polymer device. In this study, the tuning range of the polymer device is designed and fabricated to cover 15 nm from 1532 nm to 1547 nm. The index contrast and the physical dimension of the polymer waveguide are 0.005 and 6 × 6 μm2, respectively. The fabrication procedure and the performance of the polymeric tunable Bragg reflector are detailed elsewhere [10

10. Y.-O. Noh, H.-J. Lee, J. J. Ju, M.-S. Kim, S. H. Oh, and M. C. Oh, “Continuously tunable compact lasers based on thermo-optic polymer waveguides with Bragg gratings,” Opt. Express 16(22), 18194–18201 (2008). [CrossRef] [PubMed]

].

3. Result and discusssion

The L-I curves of T-ECL at five different temperatures are shown in Fig. 3
Fig. 3 Output power of T-ECL as a function of the injection current at five different temperatures.
. The temperature of the polymer Bragg grating is fixed at 25 °C, while that of T-ECL is changed from 20 to 75 °C. The L-I curves of the present T-ECL show large sharp kinks due to mode hopping at high-current levels over 75 mA depending on various temperature. The large sharp kinks are due to a phase mismatch between the SLD and the polymer grating in the cavity. This result has been observed from the lasers having a long cavity [16

16. J.-U. Shin, S. H. Oh, Y.-J. Park, S.-H. Park, Y.-T. Han, H.-K. Sung, and K.-R. Oh, “External Cavity Lasers Composed of High Order Grating and SLD on PLC Platform,” ETRI J. 29, 452–456 (2007). [CrossRef]

18

18. S. H. Oh, J.-U. Shin, Y.-J. Park, S.-B. Kim, S. Park, H.-K. Sung, and K.-R. Oh, “Multi-Wavelength Lasers for WDM-PON Optical Line Terminal Source by Silica Planar Lightwave Circuit Hybrid Integration,” IEEE Photon. Technol. Lett. 19(20), 1622–1624 (2007). [CrossRef]

]. We measured a mode hopping of 0.09 nm which is good agreement with the calculated result of 0.08 nm. The measured static characteristics are summarized in Table 1

Table 1. Static characteristics of T-ECL at various temperatures.

table-icon
View This Table
. The maximum output power and the slope efficiency are measured at the same condition as those in Fig. 2. At 20 °C, the maximum output power and the slope efficiency are 8.83 mW and 0.107 mW/mA, respectively. In particular, at 75 °C, the device showed a maximum output power and a slope efficiency of 3.80 mW and 0.061 W/A, respectively. The T-ECL is not shown a rapid decrease in output gain over 50 °C differently that of the SLD. For the reason of this result, the temperature characteristics of the T-ECL are better than that of the SLD since the carrier density in the SLD active region is reduced by inserting the reflecting beam into the SLD from the grating region of ECL. This result implies that the proposed T-ECL is definitely useful for the WDM-PON systems at the high temperature of 75 °C. We find that the temperature characteristics of ECL are largely affected by the structure characteristics of ECL rather than uncoold SLD due to reduction of the carrier density in the inside of the ECL.

Figure 5
Fig. 5 Eye diagram of optical signals generated from 1.25 Gbit/s direct modulations of the ch1, ch6, ch11, and ch16 among the 16 channels of T-ECL.
shows the eye diagrams of ch1, ch6, ch11, and ch16 among the 16 channels of T-ECL with 20-km transmission when the SLD is operated at 1.25 Gbit/s with a pseudo random bit sequence (PRBS) of 223-1 (non-return-to-zero) at a bias current of 30 mA and an amplitude of 20 mA ( ± 10 mA). A clear eye patterns are obtained with a mask margin of 10% and the extinction ratio is larger than of 9dB.

4. Conclusion

Employing uncooled SLD, we have developed a T-ECL that can operate at the high temperature over 70°C by decreasing the carrier density in the active region. We show that the temperature characteristics of ECL are largely affected by the structure characteristics of ECL rather than uncoold SLD. The maximum output power and the slope efficiency are 8.83 mW and 0.16 mW/mA at 20°C, respectively. In particular, at an operation temperature of 75°C, the device shows a maximum output power of 3.80 mW and a slope efficiency of 0.06 W/A. The output wavelength is tuned to the 16 channels by using a low power consumption of 70 mW for maximum tuning. We also demonstrate that the module operates successfully with a total throughput of 1.25-Gbit/s over 20Km transmission. This result implies that the proposed T-ECL is useful for WDM-PON systems.

Acknowledgments

This work is supported by the IT R&D Program of MK/IIT (2008-S-008-1) Rep. of Korea.

References and links

1.

L. A. Coldren, G. A. Fish, Y. Akulova, J. S. Barton, L. Johansson, and C. W. Coldren, “Tunable semiconductor lasers: A Tutorial,” J. Lightwave Technol. 22(1), 193–202 (2004). [CrossRef]

2.

Y. Liu, A. R. Davies, J. D. Ingham, R. V. Penty, and I. H. White, “Uncooled DBR laser directly modulated at 3.125Gb/s as athermal transmitter for low-cost WDM systems,” IEEE Photon. Technol. Lett. 17(10), 2026–2028 (2005). [CrossRef]

3.

H. S. Chung, B. K. Kim, and K. Kim, “Effects of upstream bit rate on a wavelength-remodulated WDM-PON based on manchester or inverse-return-to-zero coding,” ETRI J. 30, 255–260 (2008). [CrossRef]

4.

H.-C. Ji, I. Yamashita, and K.-I. Kitayama, “Cost-effective colorless WDM-PON delivering up/down-stream data and broadcast services on a single wavelength using mutually injected Fabry-Perot laser diodes,” Opt. Express 16(7), 4520–4528 (2008). [CrossRef] [PubMed]

5.

J. G. Kim, C.-J. Chae, and M.-H. Kang, “Mini-Slot-Based Transmission Scheme for Local Customer Internetworking in PONs,” ETRI J. 30, 282–289 (2008). [CrossRef]

6.

B. Lung, “PON architecture ‘future proofs’ FTTH,” Lightwave Mag. 16, 104–107 (1999).

7.

S. H. Oh, D.-H. Lee, K. S. Kim, Y.-S. Baek, and K.-R. Oh, “High-performance 1.55-μm superluminescent diode with butt-coupled spot-size converter,” IEEE Photon. Technol. Lett. 20(11), 894–896 (2008). [CrossRef]

8.

D.-H. Kim, W.-J. Chin, S.-S. Lee, S.-W. Ahn, and K.-D. Lee, “Tunable polymeric Bragg grating filter using nanoimprint technique,” Appl. Phys. Lett. 88(7), 71120 (2006). [CrossRef]

9.

K.-J. Kim, J.-K. Seo, and M.-C. Oh, “Strain induced tunable wavelength filters based on flexible polymer waveguide Bragg reflector,” Opt. Express 16(3), 1423–1430 (2008). [CrossRef] [PubMed]

10.

Y.-O. Noh, H.-J. Lee, J. J. Ju, M.-S. Kim, S. H. Oh, and M. C. Oh, “Continuously tunable compact lasers based on thermo-optic polymer waveguides with Bragg gratings,” Opt. Express 16(22), 18194–18201 (2008). [CrossRef] [PubMed]

11.

S.-W. Ryu, S.-B. Kim, J.-S. Sim, and J. Kim, “1.55-μm spot-size converter integrated laser diode with conventional buried-heterostructure laser process,” IEEE Photon. Technol. Lett. 15(1), 12–14 (2003). [CrossRef]

12.

S. W. Park, J. H. Han, Y. T. Han, S. S. Park, B. Y. Yoon, B. K. Kim, H. K. Sung, and J. I. Song, “Two-step laterally tapered spot-size converter 1.55-mm DFB laser diode having a high slope efficiengy,” IEEE Photon. Technol. Lett. 18(20), 2138–2140 (2006). [CrossRef]

13.

S. H. Oh, K. S. Kim, O. K. Kwon, and K.-R. Oh, “InGaAaP/InP buried ridge waveguide laser: a new waveguide structure with an improved lateral single mode property,” ETRI J. 30, 480–482 (2008). [CrossRef]

14.

Y.-O. Noh, C.-H. Lee, J.-M. Kim, W.-Y. Hwang, Y.-H. Won, H.-J. Lee, S.-G. Han, and M.-C. Oh, “Polymer waveguide variable optical attenuator and its reliability,” Opt. Commun. 242(4-6), 533–540 (2004). [CrossRef]

15.

B. W. Hakki and T. L. Paoli, “Gain spectra in GaAs double heterostructure injection laser,” J. Appl. Phys. 46(3), 1299–1306 (1975). [CrossRef]

16.

J.-U. Shin, S. H. Oh, Y.-J. Park, S.-H. Park, Y.-T. Han, H.-K. Sung, and K.-R. Oh, “External Cavity Lasers Composed of High Order Grating and SLD on PLC Platform,” ETRI J. 29, 452–456 (2007). [CrossRef]

17.

D. Van Thourhout, A. Van Hove, T. Van Caenegem, I. Moerman, P. Van Daele, R. Baets, X. J. M. Leijtens, and M. K. Smit, “Packaged hybrid integrated phased-array multi-wavelength laser,” Electron. Lett. 36(5), 434–436 (2000). [CrossRef]

18.

S. H. Oh, J.-U. Shin, Y.-J. Park, S.-B. Kim, S. Park, H.-K. Sung, and K.-R. Oh, “Multi-Wavelength Lasers for WDM-PON Optical Line Terminal Source by Silica Planar Lightwave Circuit Hybrid Integration,” IEEE Photon. Technol. Lett. 19(20), 1622–1624 (2007). [CrossRef]

OCIS Codes
(250.5960) Optoelectronics : Semiconductor lasers
(130.5460) Integrated optics : Polymer waveguides

ToC Category:
Integrated Optics

History
Original Manuscript: April 9, 2009
Revised Manuscript: May 22, 2009
Manuscript Accepted: May 29, 2009
Published: June 3, 2009

Citation
Su Hwan Oh, Ki Soo Kim, Jung Jin Ju, Min-su Kim, Ki-Hong Yoon, Dae Kon Oh, Young-Ouk Noh, and Hyung-Jong Lee, "Tunable external cavity laser employing uncooled superluminescent diode," Opt. Express 17, 10189-10194 (2009)
http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-17-12-10189


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References

  1. L. A. Coldren, G. A. Fish, Y. Akulova, J. S. Barton, L. Johansson, and C. W. Coldren, “Tunable semiconductor lasers: A Tutorial,” J. Lightwave Technol. 22(1), 193–202 (2004). [CrossRef]
  2. Y. Liu, A. R. Davies, J. D. Ingham, R. V. Penty, and I. H. White, “Uncooled DBR laser directly modulated at 3.125Gb/s as athermal transmitter for low-cost WDM systems,” IEEE Photon. Technol. Lett. 17(10), 2026–2028 (2005). [CrossRef]
  3. H. S. Chung, B. K. Kim, and K. Kim, “Effects of upstream bit rate on a wavelength-remodulated WDM-PON based on manchester or inverse-return-to-zero coding,” ETRI J. 30, 255–260 (2008). [CrossRef]
  4. H.-C. Ji, I. Yamashita, and K.-I. Kitayama, “Cost-effective colorless WDM-PON delivering up/down-stream data and broadcast services on a single wavelength using mutually injected Fabry-Perot laser diodes,” Opt. Express 16(7), 4520–4528 (2008). [CrossRef] [PubMed]
  5. J. G. Kim, C.-J. Chae, and M.-H. Kang, “Mini-Slot-Based Transmission Scheme for Local Customer Internetworking in PONs,” ETRI J. 30, 282–289 (2008). [CrossRef]
  6. B. Lung, “PON architecture ‘future proofs’ FTTH,” Lightwave Mag. 16, 104–107 (1999).
  7. S. H. Oh, D.-H. Lee, K. S. Kim, Y.-S. Baek, and K.-R. Oh, “High-performance 1.55-μm superluminescent diode with butt-coupled spot-size converter,” IEEE Photon. Technol. Lett. 20(11), 894–896 (2008). [CrossRef]
  8. D.-H. Kim, W.-J. Chin, S.-S. Lee, S.-W. Ahn, and K.-D. Lee, “Tunable polymeric Bragg grating filter using nanoimprint technique,” Appl. Phys. Lett. 88(7), 71120 (2006). [CrossRef]
  9. K.-J. Kim, J.-K. Seo, and M.-C. Oh, “Strain induced tunable wavelength filters based on flexible polymer waveguide Bragg reflector,” Opt. Express 16(3), 1423–1430 (2008). [CrossRef] [PubMed]
  10. Y.-O. Noh, H.-J. Lee, J. J. Ju, M.-S. Kim, S. H. Oh, and M. C. Oh, “Continuously tunable compact lasers based on thermo-optic polymer waveguides with Bragg gratings,” Opt. Express 16(22), 18194–18201 (2008). [CrossRef] [PubMed]
  11. S.-W. Ryu, S.-B. Kim, J.-S. Sim, and J. Kim, “1.55-μm spot-size converter integrated laser diode with conventional buried-heterostructure laser process,” IEEE Photon. Technol. Lett. 15(1), 12–14 (2003). [CrossRef]
  12. S. W. Park, J. H. Han, Y. T. Han, S. S. Park, B. Y. Yoon, B. K. Kim, H. K. Sung, and J. I. Song, “Two-step laterally tapered spot-size converter 1.55-mm DFB laser diode having a high slope efficiengy,” IEEE Photon. Technol. Lett. 18(20), 2138–2140 (2006). [CrossRef]
  13. S. H. Oh, K. S. Kim, O. K. Kwon, and K.-R. Oh, “InGaAaP/InP buried ridge waveguide laser: a new waveguide structure with an improved lateral single mode property,” ETRI J. 30, 480–482 (2008). [CrossRef]
  14. Y.-O. Noh, C.-H. Lee, J.-M. Kim, W.-Y. Hwang, Y.-H. Won, H.-J. Lee, S.-G. Han, and M.-C. Oh, “Polymer waveguide variable optical attenuator and its reliability,” Opt. Commun. 242(4-6), 533–540 (2004). [CrossRef]
  15. B. W. Hakki and T. L. Paoli, “Gain spectra in GaAs double heterostructure injection laser,” J. Appl. Phys. 46(3), 1299–1306 (1975). [CrossRef]
  16. J.-U. Shin, S. H. Oh, Y.-J. Park, S.-H. Park, Y.-T. Han, H.-K. Sung, and K.-R. Oh, “External Cavity Lasers Composed of High Order Grating and SLD on PLC Platform,” ETRI J. 29, 452–456 (2007). [CrossRef]
  17. D. Van Thourhout, A. Van Hove, T. Van Caenegem, I. Moerman, P. Van Daele, R. Baets, X. J. M. Leijtens, and M. K. Smit, “Packaged hybrid integrated phased-array multi-wavelength laser,” Electron. Lett. 36(5), 434–436 (2000). [CrossRef]
  18. S. H. Oh, J.-U. Shin, Y.-J. Park, S.-B. Kim, S. Park, H.-K. Sung, and K.-R. Oh, “Multi-Wavelength Lasers for WDM-PON Optical Line Terminal Source by Silica Planar Lightwave Circuit Hybrid Integration,” IEEE Photon. Technol. Lett. 19(20), 1622–1624 (2007). [CrossRef]

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