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Optics Express

Optics Express

  • Editor: Andrew M. Weiner
  • Vol. 22, Iss. 9 — May. 5, 2014
  • pp: 10655–10660
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Erbium-doped waveguide DBR and DFB laser arrays integrated within an ultra-low-loss Si3N4 platform

Michael Belt and Daniel J. Blumenthal  »View Author Affiliations


Optics Express, Vol. 22, Issue 9, pp. 10655-10660 (2014)
http://dx.doi.org/10.1364/OE.22.010655


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Abstract

Record low optical threshold power and high slope efficiency are reported for arrays of distributed Bragg reflector lasers integrated within an ultra-low-loss Si3N4 planar waveguide platform. Additionally, arrays of distributed feedback laser designs are presented that show improvements in pump-to-signal conversion efficiency of over two orders of magnitude beyond that found in previously published devices. Lithographically defined sidewall gratings provide the required lasing feedback for both cavity configurations. Lasing emission is shown over a wide wavelength range (1534 to 1570 nm), with output powers up to 2.1 mW and side mode suppression ratios in excess of 50 dB.

© 2014 Optical Society of America

1. Introduction

Low cost, high performance laser integration technologies that establish power efficient, temperature stable, and large scale multiwavelength on-chip arrays are critical for a variety of important applications including coherent optical communications, integrated analog photonics, microwave signal generation, and high spectral resolution light detection and ranging (LIDAR). A silicon nitride (Si3N4) ultra low loss waveguide (ULLW) platform with on-chip propagation losses below 0.1 dB/m [1

1. J. F. Bauters, M. J. R. Heck, D. D. John, J. S. Barton, C. M. Bruinink, A. Leinse, R. G. Heideman, D. J. Blumenthal, and J. E. Bowers, “Planar waveguides with less than 0.1 dB/m propagation loss fabricated with wafer bonding,” Opt. Express 19(24), 24090–24101 (2011). [CrossRef] [PubMed]

] and fiber coupling losses of 0.7 dB [1

1. J. F. Bauters, M. J. R. Heck, D. D. John, J. S. Barton, C. M. Bruinink, A. Leinse, R. G. Heideman, D. J. Blumenthal, and J. E. Bowers, “Planar waveguides with less than 0.1 dB/m propagation loss fabricated with wafer bonding,” Opt. Express 19(24), 24090–24101 (2011). [CrossRef] [PubMed]

] has demonstrated not only low coupling constant sidewall grating filters with narrow passbands [2

2. M. Belt, J. Bovington, R. Moreira, J. F. Bauters, M. J. Heck, J. S. Barton, J. E. Bowers, and D. J. Blumenthal, “Sidewall gratings in ultra-low-loss Si3N4 planar waveguides,” Opt. Express 21(1), 1181–1188 (2013). [CrossRef] [PubMed]

], but recently also integrated erbium-doped waveguide distributed feedback (DFB) laser arrays [3

3. M. Belt, T. Huffman, M. L. Davenport, W. Li, J. S. Barton, and D. J. Blumenthal, “Arrayed narrow linewidth erbium-doped waveguide-distributed feedback lasers on an ultra-low-loss silicon-nitride platform,” Opt. Lett. 38(22), 4825–4828 (2013). [CrossRef] [PubMed]

].

When compared with semiconductor-based gain media [4

4. H. Park, A. Fang, S. Kodama, and J. Bowers, “Hybrid silicon evanescent laser fabricated with a silicon waveguide and III-V offset quantum wells,” Opt. Express 13(23), 9460–9464 (2005). [CrossRef] [PubMed]

6

6. R. E. Camacho-Aguilera, Y. Cai, N. Patel, J. T. Bessette, M. Romagnoli, L. C. Kimerling, and J. Michel, “An electrically pumped germanium laser,” Opt. Express 20(10), 11316–11320 (2012). [CrossRef] [PubMed]

], rare-earth-ion-doped dielectric gain media, such as erbium-doped aluminum oxide (Al2O3:Er3+), exhibit relatively narrower lasing linewidths, higher degrees of temperature stability, and lower amplifier noise figures. When reactively co-sputtered onto oxidized silicon wafers Al2O3:Er3+ has shown relatively low background scattering losses and a broadband, high-gain spectrum for amplification [7

7. J. Bradley, L. Agazzi, D. Geskus, F. Ay, K. Wörhoff, and M. Pollnau, “Gain bandwidth of 80 nm and 2 dB/cm peak gain in Al2O3:Er3+ optical amplifiers on silicon,” J. Opt. Soc. Am. B 27(2), 187–196 (2010). [CrossRef]

]. With the entirety of ULLW platform only requiring a few fabrication steps, the addition of the erbium-doped gain layer by reactive co-sputtering enables streamlined integration of active lasing waveguides with ultra-low loss waveguides and components.

In this letter we report experimental demonstration of both integrated Al2O3:Er3+ waveguide distributed Bragg reflector (DBR) and distributed feedback lasers on a silicon nitride ultra-low-loss waveguide platform. Record low optical threshold power and high slope efficiency are reported through an optimized cavity design utilizing the highly selective sidewall grating filters enabled by the ULLW platform. Such devices require only a single lithography to define the entirety of the lasing cavity. The distributed Bragg reflector laser designs exhibit pump-to-signal conversion efficiencies up to 5.2% when excited with 974 nm pump light. This is two times greater than that shown by similarly reported devices [8

8. J. Purnawirman, J. Sun, T. N. Adam, G. Leake, D. Coolbaugh, J. D. Bradley, E. S. Hosseini, and M. R. Watts, “C- and L-band erbium-doped waveguide lasers with wafer-scale silicon nitride cavities,” Opt. Lett. 38(11), 1760–1762 (2013). [CrossRef] [PubMed]

]. Through structural changes to our previously designed DFB lasers [3

3. M. Belt, T. Huffman, M. L. Davenport, W. Li, J. S. Barton, and D. J. Blumenthal, “Arrayed narrow linewidth erbium-doped waveguide-distributed feedback lasers on an ultra-low-loss silicon-nitride platform,” Opt. Lett. 38(22), 4825–4828 (2013). [CrossRef] [PubMed]

] we show an improvement of over two orders of magnitude in pump-to-signal conversion efficiency. Spectral traces show emission over a wide wavelength range (1534 to 1570 nm), with side mode suppression ratios (SMSR) of over 50 dB for all designs.

2. Fabrication and lasing structure

Through optical backscattering reflectometry measurements [1

1. J. F. Bauters, M. J. R. Heck, D. D. John, J. S. Barton, C. M. Bruinink, A. Leinse, R. G. Heideman, D. J. Blumenthal, and J. E. Bowers, “Planar waveguides with less than 0.1 dB/m propagation loss fabricated with wafer bonding,” Opt. Express 19(24), 24090–24101 (2011). [CrossRef] [PubMed]

], we determined the background scattering losses of un-doped reference samples to be below 0.25 dB/cm over the range of 1530-1600 nm. Secondary ion mass spectroscopy measurements quantify the erbium dopant concentration at 1.3 x 1020 cm−3.

Both the DBR and DFB designs used the sidewall grating structure found in [2

2. M. Belt, J. Bovington, R. Moreira, J. F. Bauters, M. J. Heck, J. S. Barton, J. E. Bowers, and D. J. Blumenthal, “Sidewall gratings in ultra-low-loss Si3N4 planar waveguides,” Opt. Express 21(1), 1181–1188 (2013). [CrossRef] [PubMed]

] to achieve the requisite lasing feedback. Within this configuration periodically varying sections of alternating widths are used to define the grating. It is the width difference between the two waveguide sections that sets the κ parameter, or reflection strength of the grating. For the DBR designs, the high reflectivity mirrors had alternating widths of 1.8 and 3.8 μm, giving a κ value of ~100 cm−1. The set with the best performance had low reflectivity mirrors with alternating widths of 2.4 and 3.2 μm, delivering a κ value of ~30 cm−1. For the DFB designs, the set with the best performance had alternating widths of 2.55 and 3.05 μm, which in turn produces a κ value of ~16 cm−1. The total period length of the sidewall gratings Λ, which sets the lasing wavelength of the devices, was stepped between 478 and 490 nm.

3. Characterization

Figure 3
Fig. 3 Measurement setup of the experiment. The inset photo shows the device under 974 nm excitation. For the DBR devices signal light was collected from the side with the low reflectivity mirror. The green emission seen in the waveguide is due to the cooperative upconversion process the erbium atoms experience when under pump excitation [12].
depicts the experimental setup used to characterize the lasers. Pump light from a 974 nm laser diode is passed through the 980 nm port of a 980/1550 nm wavelength division multiplexer (WDM) and subsequently coupled onto the device die using a 5 μm spot size (at the 1/e2 level) lensed fiber. The lasing signal is collected from the device facet and passed through the 1550 nm port of the WDM, after which the output power is quantified using a power meter while the spectrum is recorded by an optical spectrum analyzer (OSA). The coupling loss for the TE-polarized 1550 nm lasing signal and the 974 nm pump laser diode are approximately 6.3 and 5.4 dB, respectively. The device chip was left uncooled throughout the measurements.

Figure 4(a)
Fig. 4 (a) DBR laser power as a function of launched pump power for the device operating at 1546 nm. (b) DFB laser power as a function of launched pump power for the device operating at 1560 nm.
shows the single-sided lasing output power as a function of pump laser input power for a DBR operating at 1560 nm (grating period of 486 nm). The lasing threshold is observed at 11 mW of launched pump power, and a maximum on-chip pump power of 55 mW generates an on-chip laser power of 2.1 mW. This corresponds to a pump-to-signal conversion efficiency (η) of 5.2%. Such a low operating threshold and high slope efficiency is a consequence of our strongly reflecting cavity design, as well as the low propagation loss of the LPCVD Si3N4. Figure 4(b) shows the single-sided lasing output power as a function of pump laser input power for a DFB operating at 1546 nm (grating period of 482 nm). Here, the lasing threshold is observed at 21 mW of launched pump power, and for a maximum on-chip pump power of 55 mW we obtain an on-chip laser power of 0.27 mW. This corresponds to a pump-to-signal conversion efficiency of 0.77%, which is a factor of more than 130 times improvement over our design reported in [3

3. M. Belt, T. Huffman, M. L. Davenport, W. Li, J. S. Barton, and D. J. Blumenthal, “Arrayed narrow linewidth erbium-doped waveguide-distributed feedback lasers on an ultra-low-loss silicon-nitride platform,” Opt. Lett. 38(22), 4825–4828 (2013). [CrossRef] [PubMed]

]. The main contribution to this improvement in efficiency came from the extension of the total cavity length from 7.5 mm to 21.5 mm, allowing for sufficient pump light absorption to provide useful lasing gain.

Figure 5(a)
Fig. 5 (a) Superimposed DBR output laser spectra. (b) Superimposed DFB output laser spectra.
gives the spectra of five different DBR lasers as recorded by the OSA. A simple modification of the grating period within the Si3N4 core layer from 478 to 486 nm causes the lasers to output light at 1535, 1541, 1547, 1554, and 1560 nm wavelengths. As is shown, the SMSR for all devices exceeds 50 dB. Figure 5(b) gives the spectra of four different DFB lasers as recorded by the OSA. Here, devices with grating periods between 478 and 490 nm operate at 1534, 1546, 1558, and 1570 nm wavelengths. Again the SMSR for all structures is in excess of 50 dB. The differences in output power seen between the devices can be attributed to differences in the gain threshold and the maximum small signal gain spectrum of the erbium-doped active layer.

Table 1

Table 1. Measured Performance Parameters of each DBR and DFB Laser

table-icon
View This Table
summarizes the measured performance of all of the DBR and DFB lasers.

4. Future improvements

When excited under 1480 nm instead of 980 nm light, similar distributed feedback devices [11

11. E. H. Bernhardi, “Bragg-grating-based rare-earth-ion-doped channel waveguide lasers and their applications,” Ph.D. dissertation (Department of Electrical Engineering, Mathematics, and Computer Science, University of Twente, 2012).

,13

13. Purnawirman, E. Hosseini, J. Bradley, J. Sun, G. Leake, T. Adam, D. Coolbaugh, and M. Watts, “CMOS compatible high power erbium doped distributed feedback lasers,” in Advanced Photonics 2013, H. Chang, V. Tolstikhin, T. Krauss, and M. Watts, eds., OSA Technical Digest (online) (Optical Society of America, 2013), paper IM2A.4.

] showed even higher pump-to-signal conversion efficiencies. This difference in performance can mainly be attributed to the long lifetime of the 4I11/2 manifold of the erbium ions, resulting in an energy bottleneck when the devices are excited under 980 nm light rather than 1480 nm light [14

14. D. L. Veasey, J. M. Gary, J. Amin, and J. A. Aust, “Time-dependent modeling of erbium-doped waveguide lasers in lithium niobate pumped at 980 and 1480 nm,” IEEE J. Quantum Electron. 33(10), 1647–1662 (1997). [CrossRef]

]. In the future, pumping the devices with 1480 nm instead of 980 nm light would be the best avenue to show immediate improvements in device performance. This would come with an increase in total cost though, as the price per watt is less for 980 nm laser diodes than for 1480 nm diodes. It is this cost constraint that drove the use of a 974 nm pump laser for this work. Another potential avenue for advancement would be to incorporate ytterbium atoms within the Al2O3 host material as a sensitizing agent. Such a technique may only make a small improvement though, as efficient energy transfer between the Yb and Er atoms in analogous devices has thus far been limited to host glasses with high phosphorus content [15

15. J. Hoyo, V. Berdejo, T. Toney Fernandez, A. Ferrer, A. Ruiz, J. A. Valles, M. A. Rebolledo, I. Ortega-Feliu, and J. Solis, “Femtosecond laser written 16.5 mm long glass-waveguide amplifier and laser with 5.2 dB cm−1 internal gain at 1534 nm,” Laser Phys. Lett. 10(10), 105802 (2013). [CrossRef]

]. Exciting the distributed Bragg reflector devices from both ends as in [8

8. J. Purnawirman, J. Sun, T. N. Adam, G. Leake, D. Coolbaugh, J. D. Bradley, E. S. Hosseini, and M. R. Watts, “C- and L-band erbium-doped waveguide lasers with wafer-scale silicon nitride cavities,” Opt. Lett. 38(11), 1760–1762 (2013). [CrossRef] [PubMed]

] and [15

15. J. Hoyo, V. Berdejo, T. Toney Fernandez, A. Ferrer, A. Ruiz, J. A. Valles, M. A. Rebolledo, I. Ortega-Feliu, and J. Solis, “Femtosecond laser written 16.5 mm long glass-waveguide amplifier and laser with 5.2 dB cm−1 internal gain at 1534 nm,” Laser Phys. Lett. 10(10), 105802 (2013). [CrossRef]

] would allow for more on-chip pump light, and thus create a stronger lasing signal, but further levels of device integration could possibly render such an approach impractical. A better solution would be to integrate a sidewall grating filter for the pump light along the output waveguide, as is schematically shown in Fig. 6
Fig. 6 Top-down schematic of a possible double-pass optical gain DBR structure. Λ1 and Λ2 denote the Bragg period for the signal and pump light, respectively.
.

Such a filter would not only stop the unabsorbed pump light from interfering with subsequent system components down the line, but would also allow for double-pass optical gain. Fabrication of such structures is currently underway.

5. Conclusion

Acknowledgments

The authors thank Michael L. Davenport and Taran Huffman for their insights. This work was supported by DARPA MTO under the iPhoD (grant no. HR0011-09-C-0123) and EPHI(grant no. HR0011-12-C-0006) contracts. The views and conclusions contained in this document are those of the authors and should not be interpreted as representing official policies of the Defense Advanced Research Projects Agency or the U.S. Government.

References and links

1.

J. F. Bauters, M. J. R. Heck, D. D. John, J. S. Barton, C. M. Bruinink, A. Leinse, R. G. Heideman, D. J. Blumenthal, and J. E. Bowers, “Planar waveguides with less than 0.1 dB/m propagation loss fabricated with wafer bonding,” Opt. Express 19(24), 24090–24101 (2011). [CrossRef] [PubMed]

2.

M. Belt, J. Bovington, R. Moreira, J. F. Bauters, M. J. Heck, J. S. Barton, J. E. Bowers, and D. J. Blumenthal, “Sidewall gratings in ultra-low-loss Si3N4 planar waveguides,” Opt. Express 21(1), 1181–1188 (2013). [CrossRef] [PubMed]

3.

M. Belt, T. Huffman, M. L. Davenport, W. Li, J. S. Barton, and D. J. Blumenthal, “Arrayed narrow linewidth erbium-doped waveguide-distributed feedback lasers on an ultra-low-loss silicon-nitride platform,” Opt. Lett. 38(22), 4825–4828 (2013). [CrossRef] [PubMed]

4.

H. Park, A. Fang, S. Kodama, and J. Bowers, “Hybrid silicon evanescent laser fabricated with a silicon waveguide and III-V offset quantum wells,” Opt. Express 13(23), 9460–9464 (2005). [CrossRef] [PubMed]

5.

S. Srinivasan, A. W. Fang, D. Liang, J. Peters, B. Kaye, and J. E. Bowers, “Design of phase-shifted hybrid silicon distributed feedback lasers,” Opt. Express 19(10), 9255–9261 (2011). [CrossRef] [PubMed]

6.

R. E. Camacho-Aguilera, Y. Cai, N. Patel, J. T. Bessette, M. Romagnoli, L. C. Kimerling, and J. Michel, “An electrically pumped germanium laser,” Opt. Express 20(10), 11316–11320 (2012). [CrossRef] [PubMed]

7.

J. Bradley, L. Agazzi, D. Geskus, F. Ay, K. Wörhoff, and M. Pollnau, “Gain bandwidth of 80 nm and 2 dB/cm peak gain in Al2O3:Er3+ optical amplifiers on silicon,” J. Opt. Soc. Am. B 27(2), 187–196 (2010). [CrossRef]

8.

J. Purnawirman, J. Sun, T. N. Adam, G. Leake, D. Coolbaugh, J. D. Bradley, E. S. Hosseini, and M. R. Watts, “C- and L-band erbium-doped waveguide lasers with wafer-scale silicon nitride cavities,” Opt. Lett. 38(11), 1760–1762 (2013). [CrossRef] [PubMed]

9.

F. Ay and A. Aydinli, “Comparative investigation of hydrogen bonding in silicon based PECVD grown dielectrics for optical waveguides,” Opt. Mater. 26(1), 33–46 (2004). [CrossRef]

10.

K. Wörhoff, J. D. B. Bradley, F. Ay, D. Geskus, T. P. Blauwendraat, and M. Pollnau, “Reliable low-cost fabrication of low-loss Al2O3:Er3+ waveguides with 5.4-dB optical gain,” IEEE J. Quantum Electron. 45(5), 454–461 (2009). [CrossRef]

11.

E. H. Bernhardi, “Bragg-grating-based rare-earth-ion-doped channel waveguide lasers and their applications,” Ph.D. dissertation (Department of Electrical Engineering, Mathematics, and Computer Science, University of Twente, 2012).

12.

G. N. van den Hoven, E. Snoeks, A. Polman, C. van Dam, J. W. M. van Uffelen, and M. K. Smit, “Upconversion in Er-implanted Al2O3 waveguides,” J. Appl. Phys. 79(3), 1258–1266 (1996). [CrossRef]

13.

Purnawirman, E. Hosseini, J. Bradley, J. Sun, G. Leake, T. Adam, D. Coolbaugh, and M. Watts, “CMOS compatible high power erbium doped distributed feedback lasers,” in Advanced Photonics 2013, H. Chang, V. Tolstikhin, T. Krauss, and M. Watts, eds., OSA Technical Digest (online) (Optical Society of America, 2013), paper IM2A.4.

14.

D. L. Veasey, J. M. Gary, J. Amin, and J. A. Aust, “Time-dependent modeling of erbium-doped waveguide lasers in lithium niobate pumped at 980 and 1480 nm,” IEEE J. Quantum Electron. 33(10), 1647–1662 (1997). [CrossRef]

15.

J. Hoyo, V. Berdejo, T. Toney Fernandez, A. Ferrer, A. Ruiz, J. A. Valles, M. A. Rebolledo, I. Ortega-Feliu, and J. Solis, “Femtosecond laser written 16.5 mm long glass-waveguide amplifier and laser with 5.2 dB cm−1 internal gain at 1534 nm,” Laser Phys. Lett. 10(10), 105802 (2013). [CrossRef]

OCIS Codes
(130.3120) Integrated optics : Integrated optics devices
(140.3500) Lasers and laser optics : Lasers, erbium
(230.1480) Optical devices : Bragg reflectors

ToC Category:
Lasers and Laser Optics

History
Original Manuscript: December 20, 2013
Revised Manuscript: February 4, 2014
Manuscript Accepted: February 4, 2014
Published: April 25, 2014

Citation
Michael Belt and Daniel J. Blumenthal, "Erbium-doped waveguide DBR and DFB laser arrays integrated within an ultra-low-loss Si3N4 platform," Opt. Express 22, 10655-10660 (2014)
http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-22-9-10655


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References

  1. J. F. Bauters, M. J. R. Heck, D. D. John, J. S. Barton, C. M. Bruinink, A. Leinse, R. G. Heideman, D. J. Blumenthal, J. E. Bowers, “Planar waveguides with less than 0.1 dB/m propagation loss fabricated with wafer bonding,” Opt. Express 19(24), 24090–24101 (2011). [CrossRef] [PubMed]
  2. M. Belt, J. Bovington, R. Moreira, J. F. Bauters, M. J. Heck, J. S. Barton, J. E. Bowers, D. J. Blumenthal, “Sidewall gratings in ultra-low-loss Si3N4 planar waveguides,” Opt. Express 21(1), 1181–1188 (2013). [CrossRef] [PubMed]
  3. M. Belt, T. Huffman, M. L. Davenport, W. Li, J. S. Barton, D. J. Blumenthal, “Arrayed narrow linewidth erbium-doped waveguide-distributed feedback lasers on an ultra-low-loss silicon-nitride platform,” Opt. Lett. 38(22), 4825–4828 (2013). [CrossRef] [PubMed]
  4. H. Park, A. Fang, S. Kodama, J. Bowers, “Hybrid silicon evanescent laser fabricated with a silicon waveguide and III-V offset quantum wells,” Opt. Express 13(23), 9460–9464 (2005). [CrossRef] [PubMed]
  5. S. Srinivasan, A. W. Fang, D. Liang, J. Peters, B. Kaye, J. E. Bowers, “Design of phase-shifted hybrid silicon distributed feedback lasers,” Opt. Express 19(10), 9255–9261 (2011). [CrossRef] [PubMed]
  6. R. E. Camacho-Aguilera, Y. Cai, N. Patel, J. T. Bessette, M. Romagnoli, L. C. Kimerling, J. Michel, “An electrically pumped germanium laser,” Opt. Express 20(10), 11316–11320 (2012). [CrossRef] [PubMed]
  7. J. Bradley, L. Agazzi, D. Geskus, F. Ay, K. Wörhoff, M. Pollnau, “Gain bandwidth of 80 nm and 2 dB/cm peak gain in Al2O3:Er3+ optical amplifiers on silicon,” J. Opt. Soc. Am. B 27(2), 187–196 (2010). [CrossRef]
  8. J. Purnawirman, J. Sun, T. N. Adam, G. Leake, D. Coolbaugh, J. D. Bradley, E. S. Hosseini, M. R. Watts, “C- and L-band erbium-doped waveguide lasers with wafer-scale silicon nitride cavities,” Opt. Lett. 38(11), 1760–1762 (2013). [CrossRef] [PubMed]
  9. F. Ay, A. Aydinli, “Comparative investigation of hydrogen bonding in silicon based PECVD grown dielectrics for optical waveguides,” Opt. Mater. 26(1), 33–46 (2004). [CrossRef]
  10. K. Wörhoff, J. D. B. Bradley, F. Ay, D. Geskus, T. P. Blauwendraat, M. Pollnau, “Reliable low-cost fabrication of low-loss Al2O3:Er3+ waveguides with 5.4-dB optical gain,” IEEE J. Quantum Electron. 45(5), 454–461 (2009). [CrossRef]
  11. E. H. Bernhardi, “Bragg-grating-based rare-earth-ion-doped channel waveguide lasers and their applications,” Ph.D. dissertation (Department of Electrical Engineering, Mathematics, and Computer Science, University of Twente, 2012).
  12. G. N. van den Hoven, E. Snoeks, A. Polman, C. van Dam, J. W. M. van Uffelen, M. K. Smit, “Upconversion in Er-implanted Al2O3 waveguides,” J. Appl. Phys. 79(3), 1258–1266 (1996). [CrossRef]
  13. Purnawirman, E. Hosseini, J. Bradley, J. Sun, G. Leake, T. Adam, D. Coolbaugh, and M. Watts, “CMOS compatible high power erbium doped distributed feedback lasers,” in Advanced Photonics 2013, H. Chang, V. Tolstikhin, T. Krauss, and M. Watts, eds., OSA Technical Digest (online) (Optical Society of America, 2013), paper IM2A.4.
  14. D. L. Veasey, J. M. Gary, J. Amin, J. A. Aust, “Time-dependent modeling of erbium-doped waveguide lasers in lithium niobate pumped at 980 and 1480 nm,” IEEE J. Quantum Electron. 33(10), 1647–1662 (1997). [CrossRef]
  15. J. Hoyo, V. Berdejo, T. Toney Fernandez, A. Ferrer, A. Ruiz, J. A. Valles, M. A. Rebolledo, I. Ortega-Feliu, J. Solis, “Femtosecond laser written 16.5 mm long glass-waveguide amplifier and laser with 5.2 dB cm−1 internal gain at 1534 nm,” Laser Phys. Lett. 10(10), 105802 (2013). [CrossRef]

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