## Soliton-emitting AlGaAs waveguide

Optics Express, Vol. 2, Issue 12, pp. 455-461 (1998)

http://dx.doi.org/10.1364/OE.2.000455

Acrobat PDF (88 KB)

### Abstract

Simulations of soliton emission and propagation in a linear AlGaAs waveguide with one nonlinear cladding are presented. The device, which has realistic parameters, operates below half the bandgap and emits light into the cladding for a given input power. The use of selective disordering of the MQW guiding layer to realize the linear/nonlinear sections is discussed.

© Optical Society of America

## 1. Introduction

1. G. I. Stegeman, C. T. Seaton, J. Chilwell, and D. Smith., “Nonlinear waves guided by thin films,” Appl. Phys. Lett. **44**, 830–832 (1984). [CrossRef]

1. G. I. Stegeman, C. T. Seaton, J. Chilwell, and D. Smith., “Nonlinear waves guided by thin films,” Appl. Phys. Lett. **44**, 830–832 (1984). [CrossRef]

4. D. R. Heatley, E. M. Wright, and G. I. Stegeman, “Soliton coupler,” Appl. Phys. Lett. **53**, 172–174 (1988). [CrossRef]

5. C. J. Hamilton, J. H. Marsh, D. C. Hutchings, J. S. Aitchison, G. T. Kennedy, and W. Sibbett, “Localized Kerr-type nonlinearities in GaAs/AlGaAs multiple quantum well structures at 1.55 μm,” Appl. Phys. Lett. **68**, 3078–3080 (1996). [CrossRef]

## 2. Device characteristics

### 2.1 Basic geometry

_{2}strip over the top layer. The waveguide is illustrated in Fig. 1.a). The strip is 8 μm wide, the guiding layer is 1 μm thick, and the refractive-index step between the guiding layer and the cladding layers is of the order of 0.1. The effective index method, which will be explained in section 3.1, is used to study more easily (reduction of a two to one dimension problem) the waveguiding in the plane of the wafer. The effective index step in this plane is in the order of 10

^{-5}. The total length of the device is 5 mm. The waveguide mode is represented in Fig. 1.b. It can be indeed deduced by its shape that the confinement in the wafer plane is much weaker than in the vertical axis. It is in this plane that the spatial nonlinear effects will occur, and the strong evanescent field in the cladding region will be put to use. It should be noted that we need the waveguide in order to couple correctly with the device, at low energy.

### 2.2 Patterning the nonlinearity

_{x}Ga

_{(1-x)}As layer [10

10. C. C. Yang, A. Villeneuve, G. I. Stegeman, Cheng-Hui Lin, and Hao-Hsiung Lin, “Anisotropic Two-Photon Transitions in GaAs/AlGaAs Multiple Quantum Well Waveguides,” IEEE J. Quantum Electron. **29**, 2934–2939 (1993). [CrossRef]

9. M. Sheik-Bahae, D. C. Hutchings, D. J. Hagan, and E. W. Van Stryland, “Dispersion of bound electronic nonlinear refraction in solids,” IEEE J. Quantum Electron. , **27**, 1296–1309 (1991). [CrossRef]

5. C. J. Hamilton, J. H. Marsh, D. C. Hutchings, J. S. Aitchison, G. T. Kennedy, and W. Sibbett, “Localized Kerr-type nonlinearities in GaAs/AlGaAs multiple quantum well structures at 1.55 μm,” Appl. Phys. Lett. **68**, 3078–3080 (1996). [CrossRef]

*n*

_{2}. Our simulations of the propagation within this device were done by means of these real parameters.

5. C. J. Hamilton, J. H. Marsh, D. C. Hutchings, J. S. Aitchison, G. T. Kennedy, and W. Sibbett, “Localized Kerr-type nonlinearities in GaAs/AlGaAs multiple quantum well structures at 1.55 μm,” Appl. Phys. Lett. **68**, 3078–3080 (1996). [CrossRef]

_{2}layer is deposited on the wafer and is etched to form a mask. Second, the exposed surface of the wafer is passivated by a hydrogen plasma. Finally, the wafer is thermally treated with a rapid thermal annealer. Upon thermal processing of the wafer, the vacancies associated with the Ga out-diffusion in the regions covered with the SiO

_{2}caps cause intermixing of the MQWs. Therefore only the portion of the MQW layer that is located under the SiO

_{2}mask is disordered, retaining properties close to that of its average composition. The mask used for this device covers the waveguide region and one of the cladding regions. Thus the MQW layer in the cladding region that is not under the mask will remain close to the as-grown condition. Once the disordering is performed, we can etch away the portion of the SiO

_{2}mask over the linear cladding, keeping only a strip over the waveguide region. This strip provides the confinement effect in the wafer plane.

### 2.3 Operation conditions

## 3. Simulations

### 3.1 Description

*n*(

*x*). It is perhaps important to remark that although the beam profile is strongly affected in the plane of the wafer, the nonlinear contribution to the mode in the vertical axis can still be treated as a negligible perturbation to the linear mode. In fact, this is quite essential in order to express the nonlinear effective refractive index as it appears in Eq. (1).

7. R. J. Deri and M. A. Emanuel, “Consistent formula for the refractive index of Al(1-x)Ga(x)As below the band edge,” J. Appl. Phys., “Optical dispersion relations for GaP, GaAs, GaSb, InP, InAs, InSb, AlxGa1xAs, and In1xGaxAsyP1y”, 77, 4667 (1995). [CrossRef]

8. S. Adachi, “Optical dispersion relations for GaP, GaAs, GaSb, InP, InAs, InSb, Al_{x}Ga_{1-x}As, and In_{1-x}Ga_{x}As_{y}P_{1-y},”J. Appl. Phys. **66**, 6030 (1989). [CrossRef]

*n*

_{2}values for the MQW layer and the disordered layer are based on the experimental results given in ref. 5

**68**, 3078–3080 (1996). [CrossRef]

9. M. Sheik-Bahae, D. C. Hutchings, D. J. Hagan, and E. W. Van Stryland, “Dispersion of bound electronic nonlinear refraction in solids,” IEEE J. Quantum Electron. , **27**, 1296–1309 (1991). [CrossRef]

10. C. C. Yang, A. Villeneuve, G. I. Stegeman, Cheng-Hui Lin, and Hao-Hsiung Lin, “Anisotropic Two-Photon Transitions in GaAs/AlGaAs Multiple Quantum Well Waveguides,” IEEE J. Quantum Electron. **29**, 2934–2939 (1993). [CrossRef]

### 3.2 Results

^{2}for this device length (5 mm).

## 4. Switching mechanism

*effective*index step) at the core-nonlinear cladding interface will decrease as the input power is increased, owing to the difference in nonlinear coefficients between these two regions. At sufficiently high powers, the nonlinear contribution to the refractive features a step that equals and opposes the linear refractive-index step at the interface. The result can be seen in the first frame of Fig. 3. For slightly higher intensities, the index step is reversed and the propagating beam self guides into the cladding region, exiting the waveguide region at an angle. This angle becomes steeper as the input power increases. The minimal switching power is that which makes the index step disappear across the core-nonlinear-cladding interface. We show in Fig. 3 the propagation of the field at this minimal switching power. The total refractive index is also shown. It can be seen already in the second frame of this movie that the right-hand index step is reversed. From the subsequent refractive index profile, it is clear that the emission can be interpreted as self guiding, or as a spatial soliton once it has cleared the waveguide region. At the minimum switching power, the corresponding spatial soliton in the nonlinear cladding region has a width of 33 μm.

## 5. Discussion on device length

## 6. Sensitivity to fabrication variations

^{-1}), etch depth (+- 0.1 μm) and etch width (+- 1 μm) variations, and fuzziness (spread over 2 μm) of the nonlinear coefficient over the disordered/nondisordered interface. Except for over-etching, the device functions properly for any combination of these variations. Indeed, the most critical parameter is the etch depth. The etch determines the effective index step of the waveguide and thus the confinement strength in the wafer plane. The waveguide is also sensitive to asymmetry. If the etch is too deep or too shallow, the waveguide mode can be cut off. The light then drifts towards the highest-index cladding region even at low intensity. In the case of a 0.1 μm overetch, whose high-intensity output is illustrated in curve no. 5 of Fig. 4, the light ends up in the right-hand-side cladding region for both low and high input intensities. The output of the device for a peak input intensity of 1.5 GW/cm

^{2}is shown in Fig. 4 for some variations of waveguide parameters.

## 7. Conclusion

## References

1. | G. I. Stegeman, C. T. Seaton, J. Chilwell, and D. Smith., “Nonlinear waves guided by thin films,” Appl. Phys. Lett. |

2. | C. T. Seaton, J. D. Valera, R. L. Shoemaker, G. I. Stegeman, J. T. Chilwell, and S. D. Smith, “Calculations of nonlinear TE waves guided by Thin Dielectric Films Bounded by Nonlinear Media,” IEEE J. Quantum Electron. |

3. | J. V. Moloney, J. Ariyasu, C. T. Seaton, and G. I. Stegeman, “Stability of nonlinear stationary waves guided by a thin film bounded by nonlinear media,” Appl. Phys. Lett. |

4. | D. R. Heatley, E. M. Wright, and G. I. Stegeman, “Soliton coupler,” Appl. Phys. Lett. |

5. | C. J. Hamilton, J. H. Marsh, D. C. Hutchings, J. S. Aitchison, G. T. Kennedy, and W. Sibbett, “Localized Kerr-type nonlinearities in GaAs/AlGaAs multiple quantum well structures at 1.55 μm,” Appl. Phys. Lett. |

6. | B. S. Ooi, K. McIlvaney, M. W. Street, A. Saher Helmy, S. G. Ayling, A. C. Bryce, J. H. Marsh, and J. S. Roberts, “Selective quantum-well intermixing on GaAs-AlGaAs structures using impurity-free vacancy diffusion,” IEEE J. Quantum Electron. |

7. | R. J. Deri and M. A. Emanuel, “Consistent formula for the refractive index of Al(1-x)Ga(x)As below the band edge,” J. Appl. Phys., “Optical dispersion relations for GaP, GaAs, GaSb, InP, InAs, InSb, AlxGa1xAs, and In1xGaxAsyP1y”, 77, 4667 (1995). [CrossRef] |

8. | S. Adachi, “Optical dispersion relations for GaP, GaAs, GaSb, InP, InAs, InSb, Al |

9. | M. Sheik-Bahae, D. C. Hutchings, D. J. Hagan, and E. W. Van Stryland, “Dispersion of bound electronic nonlinear refraction in solids,” IEEE J. Quantum Electron. , |

10. | C. C. Yang, A. Villeneuve, G. I. Stegeman, Cheng-Hui Lin, and Hao-Hsiung Lin, “Anisotropic Two-Photon Transitions in GaAs/AlGaAs Multiple Quantum Well Waveguides,” IEEE J. Quantum Electron. |

**OCIS Codes**

(190.4360) Nonlinear optics : Nonlinear optics, devices

(190.4390) Nonlinear optics : Nonlinear optics, integrated optics

**ToC Category:**

Focus Issue: Nonlinear and photorefractive fibers and waveguides

**History**

Original Manuscript: January 14, 1998

Revised Manuscript: December 15, 1997

Published: June 8, 1998

**Citation**

Patrick Dumais, Alain Villeneuve, Amr Saher-Helmy, and J. Stewart Aitchison, "Soliton-emitting AlGaAs waveguide," Opt. Express **2**, 455-461 (1998)

http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-2-12-455

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### References

- G. I. Stegeman, C. T. Seaton, J. Chilwell and D. Smith., "Nonlinear waves guided by thin films," Appl. Phys. Lett. 44, 830-832 (1984). [CrossRef]
- C. T. Seaton, J. D. Valera, R. L. Shoemaker, G. I. Stegeman, J. T. Chilwell and S. D. Smith, "Calculations of nonlinear TE waves guided by Thin Dielectric Films Bounded by Nonlinear Media," IEEE J. Quantum Electron. QE-21, 774-783 (1985). [CrossRef]
- J. V. Moloney, J. Ariyasu, C. T. Seaton and G. I. Stegeman, "Stability of nonlinear stationary waves guided by a thin film bounded by nonlinear media," Appl. Phys. Lett. 48, 826-828 (1986). [CrossRef]
- D. R. Heatley, E. M. Wright, and G. I. Stegeman, "Soliton coupler," Appl. Phys. Lett. 53, 172-174 (1988). [CrossRef]
- C. J. Hamilton, J. H. Marsh, D. C. Hutchings, J. S. Aitchison, G. T. Kennedy and W. Sibbett, "Localized Kerr-type nonlinearities in GaAs/AlGaAs multiple quantum well structures at 1.55 æm," Appl. Phys. Lett. 68, 3078-3080 (1996). [CrossRef]
- B. S. Ooi, K. McIlvaney, M. W. Street, A. Saher Helmy, S. G. Ayling, A. C. Bryce, J. H. Marsh, and J. S. Roberts, "Selective quantum-well intermixing on GaAs-AlGaAs structures using impurity-free vacancy diffusion," IEEE J. Quantum Electron. QE-33, 1784-1793 (1997).
- R. J. Deri and M. A. Emanuel, "Consistent formula for the refractive index of Al(1-x)Ga(x)As below the band edge," J. Appl. Phys. 77, 4667 (1995). [CrossRef]
- S. Adachi, "Optical dispersion relations for GaP, GaAs, GaSb, InP, InAs, InSb, AlxGa1-xAs, and In1-xGaxAsyP1-y," J. Appl. Phys. 66, 6030 (1989). [CrossRef]
- M. Sheik-Bahae, D. C. Hutchings, D. J. Hagan and E. W. Van Stryland, "Dispersion of bound electronic nonlinear refraction in solids," IEEE J. Quantum Electron., 27, 1296-1309 (1991). [CrossRef]
- C. C. Yang, A. Villeneuve, G. I. Stegeman, Cheng-Hui Lin and Hao-Hsiung Lin, "Anisotropic Two-Photon Transitions in GaAs/AlGaAs Multiple Quantum Well Waveguides," IEEE J. Quantum Electron. 29, 2934-2939 (1993). [CrossRef]

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