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Optics Express

Optics Express

  • Editor: Andrew M. Weiner
  • Vol. 21, Iss. 20 — Oct. 7, 2013
  • pp: 24087–24092
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Folded cavity angled-grating broad-area lasers

Yunsong Zhao and Lin Zhu  »View Author Affiliations


Optics Express, Vol. 21, Issue 20, pp. 24087-24092 (2013)
http://dx.doi.org/10.1364/OE.21.024087


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Abstract

The angled-grating broad-area laser is a promising candidate for high power, high brightness diode laser source. The key point in the design is the angled gratings which can simultaneously support the unique snake-like zigzag lasing mode and eliminate the direct Fabry-Perot (FP) feedback. Unlike a conventional laser waveguide mode, the phase front of the zigzag mode periodically changes along the propagation direction. By use of the mirror symmetry of the zigzag mode, we propose and demonstrate the folded cavity angled-grating broad-area lasers. One benefit of this design is to reduce the required wafer space compared to a regular angled-grating broad-area laser, especially in a long cavity laser for high power operation. Experimental results show that the folded cavity laser exhibits good beam quality in far field with a slightly larger threshold and smaller slope efficiency due to the additional interface loss.

© 2013 OSA

1. Introduction

High power and high brightness operation of semiconductor lasers requires a large emitting aperture to avoid catastrophic optical mirror damage (COMD) and effective transverse mode control mechanism to maintain a single lobe (near) diffraction-limited far field. To meet these requirements, the angled-grating broad-area laser has been proposed and demonstrated to deliver over 1W power with diffraction-limited beam quality [1

1. S. D. Demars, K. M. Dzurko, R. J. Lang, D. Welch, D. R. Scifres, and A. Hardy, “Angled-grating distributed feedback laser with 1 W cw single-mode diffraction-limited output at 980nm,” in “Lasers and Electro-Optics, 1996. CLEO ’96., Summaries of papers presented at the Conference on,” (1996), 77–78.

4

4. R. E. Bartolo, W. W. Bewley, I. Vurgaftman, C. L. Felix, J. R. Meyer, and M. J. Yang, “Mid-infrared angled-grating distributed feedback laser,” Appl. Phys. Lett. 76, 3164–3166 (2000). [CrossRef]

]. In the design, the lowest loss Bragg mode confined by the transverse gratings is favored as the lasing mode [5

5. R. J. Lang, K. Dzurko, A. A. Hardy, S. Demars, A. Schoenfelder, and D. F. Welch, “Theory of Grating-Confined Broad-Area Lasers,” IEEE J. Quantum Electron. 34, 2196–2210 (1998). [CrossRef]

7

7. A. Sarangan, M. Wright, J. Marciante, and D. Bossert, “Spectral properties of angled-grating high-power semiconductor lasers,” IEEE J. Quantum Electron. 35, 1220–1230 (1999). [CrossRef]

]. The angled grating is the key point to support the snake-like lasing mode and to eliminate the direct FP feedback between two end facets. In a conventional waveguide laser, the phase front of the guided mode does not change along the propagation direction. But for angled-grating broad-area lasers, the phase front exhibits a zigzag pattern with a large angle (equal to the grating tilt angle) with respect to the propagation direction, which provides an effective method to fold the cavity by use of mirror symmetry. In this paper, we propose and experimentally demonstrate a folded cavity design for angled-grating broad-area lasers. The folded design can be also interpreted as two cascaded angled-grating broad-area lasers with opposite tilting directions. We show that with a careful selection of the cavity length, a low loss lasing mode can be obtained. Compared to the regular angled-grating broad-area laser, we experimentally demonstrate that the folded cavity laser provides similar beam quality, but with a slightly higher threshold and smaller slope efficiency due to the additional loss at the interface.

One instant benefit of the new design is to occupy less wafer space than the regular angled-grating broad-area laser. In a regular angled-grating broad-area laser, the tilt angle is usually from 10° to 20° and the length of cavity can be as long as 4mm. As a result, angled-grating broad-area lasers can use 10 times wafer space more than conventional straight cavity broad-area lasers. The proposed design only takes 50% wafer space of the regular angled-grating broad-area laser with the same cavity length. And in principle, multiple foldings can be used to further reduce the required wafer space for a long cavity laser.

2. Laser design and fabrication

Fig. 1 Schematic plot of a folded angled-grating broad-area laser.
Fig. 2 (a) and (b) Simulation result and mode profile of an unfolded angled-grating broad-area laser; (c) Mode coupling in a folded cavity angled-grating broad-area laser. The inset is the zoom-in view at the interface; (d) Simulation result of the preferred mode when L = 4NLc; (e) Simulation result of high diffraction loss when L = (4N + 2)Lc.

Fig. 3 (a) Top view of the packaged folded cavity angled-grating broad-area laser. The inset is the zoom-in view at the interface; (b) Cross-section of the folded cavity laser. The inset is the zoom in view of one etched trench.

3. Measurement results and discussion

We measure the folded and unfolded cavity angled-grating broad-area laser with the same cavity length for comparison. The two types of devices are fabricated together with the same fabrication processes and parameters. All the measurements are carried out with a CW current source in a cryostat with the temperature set at 250K. Figure 4(a) shows the near field profiles of the folded cavity and unfolded cavity angled-grating broad-area laser. The widths of aperture are 155.3μm and 156.1μm for folded and unfolded cavity, respectively. The width should be similar because both cavities have the same grating design. The far field profiles and camera images are shown in Fig. 4(b). The divergence angles are 0.96° and 0.78° for the folded cavity and unfolded cavity, respectively. We also include the theoretical far field calculated from a planewave aperture with the same width as what we measured. The simulated result is shown in green dash-dotted line in Fig. 4(b). The divergence angle of the folded cavity is a little bit larger than that of the unfolded cavity due to the existence of the middle interface. The angled gratings can be considered as a waveguide where the desired Bragg mode is filtered. The folded design needs longer cavity or stronger coupling to eliminate the undesired components induced by the interface. This means with the same etching depth and cavity length as in our situation, the folded cavity will have a slightly larger divergence angle along the slow axis. However, the difference is small in our experiments and both devices can be considered as near diffraction-limited. Figure 4(c) shows the light-current (LI) curves of the folded and unfolded cavity. For the unfolded cavity, the threshold and slope efficiency are 365.5mA and 0.21W/A, respectively. Compared to the unfolded cavity, the folded cavity has a larger threshold of 436.4mA and smaller slope efficiency of 0.14W/A. The differences in LI curves are due to the extra optical loss induced by the interface in the folded cavity. The relatively strong spontaneous emission before lasing is due to the scattering loss induced by the deeply etched gratings. We believe that the output power is mainly limited by thermal management and the epitaxy wafer which is not designed or optimized for high power applications. The interface may also be the reason for the different lasing wavelength in the two devices as shown in Fig. 4(d). The lasing wavelengths for the folded and unfolded cavity are 1542.7nm and 1521.8nm, respectively. It is possible that extra heat is generated because of the extra loss induced by the interface in the folded cavity. This reduces the efficiency and the wavelength is red-shifted due to the heat. Since the gratings are only resonant with the transverse wave vector, multiple longitudinal modes are allowed in the angled-grating broad-area lasers [7

7. A. Sarangan, M. Wright, J. Marciante, and D. Bossert, “Spectral properties of angled-grating high-power semiconductor lasers,” IEEE J. Quantum Electron. 35, 1220–1230 (1999). [CrossRef]

]. The existence of the interface also changes the longitudinal mode resonance condition, resulting in the small peak at 1550nm in the spectrum of the folded cavity laser.

Fig. 4 (a) Near field profiles of the folded cavity (blue solid line) and unfolded cavity (red dashed line). (b) Far field profiles and camera images of the folded cavity (blued solid line) and unfolded cavity (red dashed line). The calculated far field is shown in green dash-dotted line. (c) Light-current curves of the folded cavity (blue solid line) and unfolded cavity (red dashed line). (d) Optical spectrum of the folded cavity (blue solid line) and unfolded cavity (red dashed line).

4. Conclusion

In conclusion, the folded cavity angled-grating broad-area laser is proposed and demonstrated. Compared to the conventional angled-grating broad-area laser, the folded design takes advantage of the mirror symmetry of the zigzag mode and can save 50% wafer space. The length of cavity should be correctly chosen to reduce the interface loss and avoid direct FP feedback between the facets. The measurement results show that the folded design can provide near diffraction-limited beam quality with a slightly higher threshold and smaller slope efficiency.

Acknowledgments

The authors acknowledge funding support from a DARPA Young Faculty Award ( N66001–10–1–4038), ARO Young Investigator Award ( W911NF–11–1–0519), and DURIP Award ( W911NF–11–1–0312). The authors also acknowledge the use of the Gatech Nanotechnology Research Center Facility and associated support services in the completion of this work.

References and links

1.

S. D. Demars, K. M. Dzurko, R. J. Lang, D. Welch, D. R. Scifres, and A. Hardy, “Angled-grating distributed feedback laser with 1 W cw single-mode diffraction-limited output at 980nm,” in “Lasers and Electro-Optics, 1996. CLEO ’96., Summaries of papers presented at the Conference on,” (1996), 77–78.

2.

V. V. DWong, S. D. DeMars, A. Schoenfelder, and R. J. Lang, “Angled-grating distributed-feedback laser with 1.2 W cw single-mode diffraction-limited output at 10.6μm,” in “In Laser and Electro-Optics, 1998. CLEO ’98., Summaries of papers presented at the Conference on,” (1998), 34–35.

3.

K. Paschke, R. Guther, J. Fricke, F. Bugge, G. Erbert, and G. Trankle, “High power and high spectral brightness in 1060 nm alpha-dfb lasers with long resonators,” Electron. Lett. 39, 369–370 (2003). [CrossRef]

4.

R. E. Bartolo, W. W. Bewley, I. Vurgaftman, C. L. Felix, J. R. Meyer, and M. J. Yang, “Mid-infrared angled-grating distributed feedback laser,” Appl. Phys. Lett. 76, 3164–3166 (2000). [CrossRef]

5.

R. J. Lang, K. Dzurko, A. A. Hardy, S. Demars, A. Schoenfelder, and D. F. Welch, “Theory of Grating-Confined Broad-Area Lasers,” IEEE J. Quantum Electron. 34, 2196–2210 (1998). [CrossRef]

6.

R. Guther, “Beam propagation in an active planar waveguide with an angled bragg grating (α laser),” J. Mod. Optic. 45, 1537–1546 (1998). [CrossRef]

7.

A. Sarangan, M. Wright, J. Marciante, and D. Bossert, “Spectral properties of angled-grating high-power semiconductor lasers,” IEEE J. Quantum Electron. 35, 1220–1230 (1999). [CrossRef]

8.

L. Zhu, A. Scherer, and A. Yariv, “Modal Gain Analysis of Transverse Bragg Resonance Waveguide Lasers With and Without Transverse Defects,” IEEE J. Quantum Electron. 43, 934–940 (2007). [CrossRef]

9.

D. Marcuse, “Reflection loss of laser mode from tilted end mirror,” J. Lightwave. Technol. 7, 336–339 (1989). [CrossRef]

10.

Y. Zhao and L. Zhu, “On-chip coherent combining of angled-grating diode lasers toward bar-scale single-mode lasers,” Opt. Express 20, 6375–6384 (2012). [CrossRef] [PubMed]

11.

K. Paschke, A. Bogatov, F. Bugge, A. E. Drakin, J. Fricke, R. Güther, A. A. Stratonnikov, H. Wenzel, G. Erbert, and G. Tränkle, “Properties of ion-implanted high-power angled-grating distributed-feedback lasers,” IEEE J. Sel. Top. Quantum Electron 9, 1172–1178 (2003). [CrossRef]

12.

Y. Zhao and L. Zhu, “Improved beam quality of coherently combined angled-grating broad-area lasers,” Photonics Journal, IEEE 5, 1500307–1500307 (2013). [CrossRef]

13.

S. J. Pearton, “Ion implantation for isolation of III–V semiconductors,” Mater. Sci. Rep. 4, 313–363 (1990). [CrossRef]

OCIS Codes
(140.2020) Lasers and laser optics : Diode lasers
(140.3460) Lasers and laser optics : Lasers
(140.5960) Lasers and laser optics : Semiconductor lasers

ToC Category:
Lasers and Laser Optics

History
Original Manuscript: July 29, 2013
Revised Manuscript: September 9, 2013
Manuscript Accepted: September 17, 2013
Published: October 1, 2013

Citation
Yunsong Zhao and Lin Zhu, "Folded cavity angled-grating broad-area lasers," Opt. Express 21, 24087-24092 (2013)
http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-21-20-24087


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References

  1. S. D. Demars, K. M. Dzurko, R. J. Lang, D. Welch, D. R. Scifres, and A. Hardy, “Angled-grating distributed feedback laser with 1 W cw single-mode diffraction-limited output at 980nm,” in “Lasers and Electro-Optics, 1996. CLEO ’96., Summaries of papers presented at the Conference on,” (1996), 77–78.
  2. V. V. DWong, S. D. DeMars, A. Schoenfelder, and R. J. Lang, “Angled-grating distributed-feedback laser with 1.2 W cw single-mode diffraction-limited output at 10.6μm,” in “In Laser and Electro-Optics, 1998. CLEO ’98., Summaries of papers presented at the Conference on,” (1998), 34–35.
  3. K. Paschke, R. Guther, J. Fricke, F. Bugge, G. Erbert, and G. Trankle, “High power and high spectral brightness in 1060 nm alpha-dfb lasers with long resonators,” Electron. Lett.39, 369–370 (2003). [CrossRef]
  4. R. E. Bartolo, W. W. Bewley, I. Vurgaftman, C. L. Felix, J. R. Meyer, and M. J. Yang, “Mid-infrared angled-grating distributed feedback laser,” Appl. Phys. Lett.76, 3164–3166 (2000). [CrossRef]
  5. R. J. Lang, K. Dzurko, A. A. Hardy, S. Demars, A. Schoenfelder, and D. F. Welch, “Theory of Grating-Confined Broad-Area Lasers,” IEEE J. Quantum Electron.34, 2196–2210 (1998). [CrossRef]
  6. R. Guther, “Beam propagation in an active planar waveguide with an angled bragg grating (α laser),” J. Mod. Optic.45, 1537–1546 (1998). [CrossRef]
  7. A. Sarangan, M. Wright, J. Marciante, and D. Bossert, “Spectral properties of angled-grating high-power semiconductor lasers,” IEEE J. Quantum Electron.35, 1220–1230 (1999). [CrossRef]
  8. L. Zhu, A. Scherer, and A. Yariv, “Modal Gain Analysis of Transverse Bragg Resonance Waveguide Lasers With and Without Transverse Defects,” IEEE J. Quantum Electron.43, 934–940 (2007). [CrossRef]
  9. D. Marcuse, “Reflection loss of laser mode from tilted end mirror,” J. Lightwave. Technol.7, 336–339 (1989). [CrossRef]
  10. Y. Zhao and L. Zhu, “On-chip coherent combining of angled-grating diode lasers toward bar-scale single-mode lasers,” Opt. Express20, 6375–6384 (2012). [CrossRef] [PubMed]
  11. K. Paschke, A. Bogatov, F. Bugge, A. E. Drakin, J. Fricke, R. Güther, A. A. Stratonnikov, H. Wenzel, G. Erbert, and G. Tränkle, “Properties of ion-implanted high-power angled-grating distributed-feedback lasers,” IEEE J. Sel. Top. Quantum Electron9, 1172–1178 (2003). [CrossRef]
  12. Y. Zhao and L. Zhu, “Improved beam quality of coherently combined angled-grating broad-area lasers,” Photonics Journal, IEEE5, 1500307–1500307 (2013). [CrossRef]
  13. S. J. Pearton, “Ion implantation for isolation of III–V semiconductors,” Mater. Sci. Rep.4, 313–363 (1990). [CrossRef]

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