## Wavelength switchable semiconductor laser using half-wave V-coupled cavities

Optics Express, Vol. 16, Issue 6, pp. 3896-3911 (2008)

http://dx.doi.org/10.1364/OE.16.003896

Acrobat PDF (349 KB)

### Abstract

A new semiconductor laser structure with digitally switchable wavelength is proposed. The device comprises two coupled c.avities with different optical path lengths, which form V-shaped branches with a reflective 2 × 2 half-wave optical coupler at the closed end. The reflective 2 × 2 coupler is designed to have a π-phase difference between cross-coupling and self-coupling so as to produce synchronous power transfer functions. High single-mode selectivity is achieved by optimizing the coupling coefficient. The switchable wavelength range is greatly increased by using Vernier effect. Using deep-etched trenches as partial reflectors, additional waveguide branch structures are used outside the laser cavities to form a complete Mach-Zehnder interferometer, allowing space switching, variable attenuation, or high speed modulation to be realized simultaneously. Detailed design principle and numerical results are presented.

© 2008 Optical Society of America

## 1. Introduction

1. J. W. Raring and L. A. Coldren, “40Gb/s Widely-Tunable Transceivers,” invited paper, IEEE J. Sel. Top. Quantum Electron. **13**, 3–14 (2007). [CrossRef]

2. N. P. Caponio, M. Goano, I. Maio, M. Meliga, G. P. Bava, G. D. Anis, and I. Montrosset, “Analysis and Design criteria of Three-Section DBR Tunable Lasers,” IEEE J. Sel. Areas Commun. **8**, 1203–1213 (1990). [CrossRef]

3. V. Jayaraman, A. Mathur, and L. A Coldren, “Theory, design, and performance of extended tuning range semiconductor lasers with sampled gratings,” IEEE J. Quantum Electron. **29**, 1824–1834 (1993). [CrossRef]

6. Y. Tohmori, Y. Yoshikuni, and H. Ishii, “Broad-range wavelength-tunable superstructure grating (SSG) DBR lasers,” IEEE J. Quantum Electron. **29**, 1817–1823 (1993). [CrossRef]

7. R. C. Alferness, U. Koren, and L. L. Buhl, “Broadly tunable InGaAsP/InP laser based on a vertical coupler filter with 57-nm tuning range,” Appl. Phys. Lett. **60**, 3209–3211 (1992). [CrossRef]

9. D. J. Robbins, G. Busico, L. Ponnampalam, J. P. Duck, P. J. Williams, R. A. Griffin, A. J. Ward, D. C. J. Reid, N. D. Whitbread, and E. Barton, “A high power, broadband tuneable laser module based on a DS-DBR laser with integrated SOA,” Optical Fiber Communication Conference, Washington DC, Paper TuE3 (2004).

10. L. A. Coldren, B. I. Miller, K. Iga, and J. A. Rentschler, “Monolithic two-section GaInAsP/InP active-optical-resonator devices formed by reactive-ion-etching,” Appl. Phys. Lett. **38**, 315~317 (1981). [CrossRef]

11. W. T. Tsang, “The cleaved-coupled-cavity (C3) laser,” Semicond. Semimetals , **22**, 257 (1985). [CrossRef]

12. L. A. Coldren and T. L. Koch, “Analysis and design of coupled-cavity lasers,” IEEE J. Quantum Electron. **20**, 659–682 (1984). [CrossRef]

16. O. Hildebrand, M. Schilling, and D. Baums, et al., “The Y-laser: A Multifunctional Device for Optical Communication Systems and Switching Networks,” J. Lightwave Technol. **11**, 2066–2074 (1993). [CrossRef]

## 2. Device structure and operation principle

_{g}the effective group refractive index of the waveguide, and L the length of the fixed gain cavity.

_{a}and L

_{b}are the lengths of the gain section and wavelength switching section, respectively, n

_{a}and n

_{b}are the corresponding effective group refractive indices. L′=L

_{a}+L

_{b}is the total length, and n′

_{g}=(n

_{a}L

_{a}+n

_{b}L

_{b})/L′ is the average effective group refractive index of the channel selector cavity.

_{c}should generally be larger than the spectral width of the material gain window.

_{b}of the wavelength switching segment. The rate of the tuning is determined by

## 3. Analysis of threshold conditions

_{1}and r

_{2}, respectively (for simplicity, the reflectivities at the open end of the two waveguide braches are assumed to be the same). The coupling between the waveguides occurs at the closed end. We denote the amplitude coupling coefficients from fixed gain cavity to channel selector cavity (cross-coupling), from fixed gain cavity back to fixed gain cavity (self-coupling), from channel selector cavity to fixed gain cavity (cross-coupling), and from channel selector cavity back to channel selector cavity (self-coupling), by C

_{12}, C

_{11}, C

_{21}and C

_{22}, respectively. Note that the reflectivity of the trench is treated separately and is not included in the coupling coefficients.

_{2e}=

**η**r

_{2}, where

**η**is an effective reflection factor (in amplitude) taking into account the coupling effect of the channel selector cavity and is calculated by

_{2e}=η′r

_{2}, where η′ is the effective reflection factor taking into account the coupling effect of the fixed gain cavity and is calculated by

_{12}= C

_{21}= 0, C

_{11}= C

_{22}= 1, we have η=η′ = 1, and Eqs. (7), (9), and (10) reduce to the threshold conditions of conventional Fabry-Perot cavities.

## 4. Design of the reflective optical coupler

_{1}and E

_{2}, respectively. After passing through the coupling section and a round trip propagation including two reflections at the trenches, the electric field E

_{1}′ and E

_{2}′ can be written as

*E*

_{1}′=

*E*

_{1}and

*E*

_{2}′=

*E*

_{2}, we can obtain

_{11}= C

_{22}and C

_{12}= C

_{21}. It will be shown in Section 5 that the highest single-mode selectivity is reached when the two cavities are symmetrically pumped with equal round trip gain, i.e.

*gL*=

*g*′

*L*′ if the cavity mirrors have the same reflectivities. The lowest threshold lasing mode occurs when both of the two cavities are resonant. In this case, from Eqs. (13) and (14), we can derive |

*β*| = 1, i.e., the electric fields from the two waveguide branches have the same amplitudes in the coupling region.

_{11}and C

_{22}can be assumed to be of real positive values (any non-zero phase can be compensated by lengths

*L*and

*L*’, respectively), i.e. C

_{11}= |C

_{11}| and C

_{22}= |C

_{22}|. Assume the cross-coupling coefficients have a relative phase

*φ*with respect to the self-coupling coefficients, i.e. C

_{12}= |C

_{12}|

*e*and C

^{iφ}_{21}= |C

_{21}|

*. Consider the case where the powers in the two input waveguides at the entrance of the coupling region are equal with the total power normalized to 1. The output powers in the two waveguides at the exit of the coupling region can then be written as*

^{eiφ}*ϕ*is the relative phase of the input field at the entrance of the coupling region in the second waveguide with respect to that in the first waveguide.

*φ*=

*π*/

*2*. Therefore, the two output waveguides have complementary output powers when the relative phase of the two input fields changes. Figure 4(a) shows the typical curves of output power versus relative input phase for a 3-dB directional coupler or a 2 × 2 multi-mode interference (MMI) coupler. For an ideal coupler, the energy conservation rule leads to |C

_{11}|

^{2}+ |C

_{21}|

^{2}= 1 and |C

_{12}|

^{2}+ |C

_{22}|

^{2}= 1. Such a coupler (referred as quarter-wave optical coupler below) is commonly used in waveguide based Mach-Zehnder interferometers and optical switches. It is also used in the MMI coupler of Fig. 1 to realize the switch/combiner function outside the laser cavities.

*φ*=

*mπ*(

*m*=

*0*,

*±1*,

*±2*, …) with respect to the self-coupling coefficients. Figure 4(b) shows the ideal power transfer functions of such a coupler for the case

*m*=

*1*(which is the easiest to realize). When the input fields have opposite phases, the powers at both output ports reach the maximum simultaneously. When the input fields have the same phase, destructive interference occurs at both output ports and the energy is dissipated into radiative modes out of the waveguides. For such a coupler (referred as half-wave optical coupler hereafter), the energy conservation rule requires that the amplitudes of the coupling coefficients satisfy |C

_{11}| + |C

_{21}| = 1 and |C

_{12}| + |C

_{22}| = 1 for the ideal case when there is no excess loss. In the above example, we have used C

_{11}= C

_{22}= 0.755, and C

_{12}= C

_{21}= -0.245. Although we have |C

_{11}|

^{2}+ |C

_{21}|

^{2}= |C

_{12}|

^{2}+ |C

_{22}|

^{2}< 1, no energy is lost when the two input fields have opposite phases, as shown in Fig. 4(b). The half-wave optical coupler can be realized in the form of a three-waveguide coupler, i.e., by adding a third waveguide in the middle of a conventional 2 × 2 directional coupler. The middle waveguide forms a quarter-wave coupler with each of the adjacent input/output waveguides, resulting in a 180° coupling phase between the input/output waveguides. Theoretically, low coupling loss can be achieved with such a half-wave coupler. However, for fabrication simplicity, we can use a compact 2 × 2 coupler with a multimode coupling region as shown in Fig. 3. It can be seen as if the middle waveguide is merged with the adjacent waveguides in the coupling region. An arbitrary cross-coupling coefficient and phase can be achieved by adjusting the length L

_{c}and the gap W

_{c}of the multimode coupling region. However, such a coupler will incur some excess loss. The excess loss ε (in dB) can be calculated by

*ε*= 10 log

_{10}(|

*C*

_{11}|

^{2}+ |

*C*

_{21}|

^{2}+ 2|

*C*

_{11}‖

*C*

_{21}‖cos(

*φ*)|). From Eq. (13), we can obtain the increased laser threshold gain (in intensity) due to the excess loss Δ

*G*= 2Δ

*g*= -

*ε*/(8.686

*L*) when the cross-coupling phase is near 180°. The detailed analysis will be given in Section 5.

## 5. Numerical results and discussions

_{11}= C

_{22}= 0.755, and C

_{12}= C

_{21}=-0.245. We also assume that the reflecting mirrors of the cavities are formed by air trenches with r

_{1}=r

_{2}= 0.823 and the two cavities are pumped to produce the same round trip gain, i.e.,

*gL*=

*g*′

*L*′.

^{2}(dotted line) and |η′|

^{2}(solid line), which are the effective reflection factors in intensity, as a function of the wavelength when the laser is at the threshold. The periodic peaks of the effective reflection factor |η|

^{2}occur at the resonant wavelengths of the wavelength selector cavity. The effective reflection factor |η|

^{2}effectively modifies the reflectivity of one of the mirrors of the fixed gain cavity, producing a comb of reflectivity peaks. Consequently, a resonant mode of the fixed gain cavity that coincides with one of the peaks of the effective reflection factor |η|

^{2}is selected as the lasing mode. Since the periodic peaks of the effective reflection factor |η′|

^{2}correspond to the resonant wavelengths of the fixed gain cavity, the lasing wavelength occurs at the position where a peak of |η|

^{2}overlaps with a peak of |η′|

^{2}.

20. T. L. Koch and U. Koren, “Semiconductor Lasers for Coherent Optical Fiber Communications”, J. Lightwave Technol. **8**, 274–293 (1990). [CrossRef]

^{2}as a function of wavelength for different

*χ*values. Figure 7 compares the spectra of the effective reflection factor |η|

^{2}for

*χ*= 0.1 (solid line) and

*χ*= 0.5 (dotted line), when the laser is pumped at the lasing threshold. We can see that when the cross-coupling coefficient decreases, the peaks of the effective reflection factor |η|

^{2}, which is proportional to the effective reflectivity of the mirror at the closed end, become narrower while the contrast decreases.

*χ*= 0.1 (circles) and

*χ*= 0.5 (crosses). For the lowest threshold mode at the common resonance wavelength of 1550.12nm, the threshold difference between the main mode and the next lowest threshold mode is about 7.2 cm

^{−1}for

*χ*= 0.1, but is only about 1.2 cm

^{−1}for

*χ*= 0.5. Although the threshold gain of the next matched mode is almost the same as the main mode, the limitation of the material gain window (or the spectral gain variation) would in practice prevent the adjacent matched modes from lasing, as schematically shown in Fig. 2.

_{11}= C

_{22}= |C

_{11}|, C

_{12}= C

_{21}=-|C

_{21}|, and |C

_{11}| + |C

_{21}| = 1. When the two cavities are pumped with equal round-trip gains, from Eqs. (13) and (14) we can derive

*β*= -1 for the common resonant mode with the lowest threshold and this threshold is the same as that of the uncoupled Fabry-Perot laser.

*χ*for a cavity length difference of 10% and 5%. The SMSR is calculated for 1mW output power according to the simple model of Ref. [20

20. T. L. Koch and U. Koren, “Semiconductor Lasers for Coherent Optical Fiber Communications”, J. Lightwave Technol. **8**, 274–293 (1990). [CrossRef]

*χ*and is the same as in the case of an uncoupled Fabry-Perot cavity (

*χ*= 0). For the case of 10% cavity length difference, the largest threshold difference occurs around

*χ*= 0.096. The threshold difference increases as

*χ*decreases from 1 to 0.096, because the peak width of the effective reflection factor |η|

^{2}decreases, resulting in an increased selectivity between the main mode and its adjacent modes. As

*χ*further decreases to below 0.096, the threshold difference decreases. This is because the peak width of the effective reflection factor |η|

^{2}becomes narrower than the mode spacing and it no longer affects the threshold difference. Instead, the threshold difference is determined by the contrast in the effective reflection factor |η|

^{2}which decreases with the decreasing cross-coupling coefficient. When the cavity length difference decreases, the largest threshold difference and SMSR decrease and the cross-coupling coefficient at which the largest threshold difference (and SMSR) occurs also decreases.

*r*=

_{1}r_{2}e^{2gL}*r*. Consider the case L = 466.24µm (Δf = 100GHz) and L′ = 582.68µm (Δf′ = 80GHz) with other parameters the same as in the previous example. Figure 10 shows the threshold difference between the lowest threshold mode and the next lowest threshold mode as a function of the cross-coupling coefficient for two different pumping conditions corresponding to gL = g′L′ (solid line) and g = g′ (dotted line). The cavity length difference is about 20%. Compared to the case of 10% cavity length difference, the maximum achievable threshold difference is increased from 7.2cm

_{1}′r_{2}′e^{2g′L′}^{−1}to 16cm

^{−1}(for the case gL = g′L′), and the optimal cross-coupling coefficient at which the maximum threshold difference is achieved is increased from 0.096 to 0.29.

*χ*for different cross-coupling phases. When the cross-coupling phase deviates from 180°, the peak decreases and becomes less pointed, similar to the case when the gain coefficients deviate away from the balanced pumping condition. The optimal cross-coupling coefficient

*χ*

_{opt}at which the maximal threshold gain difference occurs also decreases. For conventional directional couplers with 90° coupling phase, the threshold difference becomes zero, which means there is no mode selectivity.Figure 12 shows the variations of the maximal threshold gain difference and the

*χ*

_{opt}value when the cross-coupling phase changes.

## 6. Comparison of mode selectivity with Y-coupled cavity laser

12. L. A. Coldren and T. L. Koch, “Analysis and design of coupled-cavity lasers,” IEEE J. Quantum Electron. **20**, 659–682 (1984). [CrossRef]

_{A}, L

_{B}and L

_{C}, respectively. The electrodes on the three waveguide sections are separated by shallow isolation trenches. The amplitude coupling coefficients from the common waveguide section C to waveguide A and B are denoted as C

_{1}and C

_{2}, respectively. The amplitude coupling coefficients from waveguide A and B to the common waveguide section C are denoted as C′

_{1}and C′

_{2}, respectively. From the reciprocity of light wave propagation, we have C

_{1}= C′

_{1}, and C

_{2}= C′

_{2}. Assuming there is no coupling loss, we have | C

_{1}|

^{2}+| C

_{2}|

^{2}= 1.

_{1}and E

_{2}, respectively. After a round trip propagation including two reflections at the cavity mirrors, the electric field E

_{1}′ and E

_{2}′ can be written as

_{A}+ L

_{C}and L′ = L

_{B}+ L

_{C}are the total cavity lengths of the branch A and branch B, respectively; g = (g

_{A}L

_{A}+ g

_{C}L

_{C})/L and g′ = (g

_{B}L

_{B}+ g

_{C}L

_{C})/L′ are the average gain coefficients; and k = (k

_{A}L

_{A}+ k

_{C}L

_{C})/L and k′ = (k

_{B}L

_{B}+ k

_{C}L

_{C})/L′ are the average propagation constants of the two cavities. From Eqs. (19) and (20), we can derive the threshold condition for the Y-coupled cavity laser:

_{11}= C

_{1}C′

_{1}, C

_{22}= C

_{2}C′

_{2}, C

_{12}= C′

_{1}C

_{2}, and C

_{21}= C′

_{2}C

_{1}. Substituting these equations into Eq. (10), one can obtain Eq. (21). One can also see that, no matter what is the splitting ratio of the Y-branch coupler, the equation C

_{11}C

_{22}-C

_{12}C

_{21}= 0 always holds. Therefore, in terms of the threshold condition, the Y-coupled cavity laser is equivalent to a special case of the V-coupled cavity laser when C

_{11}C

_{22}-C

_{12}C

_{21}= 0. This means that for the Y-coupled cavity laser, the amplitude of the cross-coupling coefficient is either the same as that of the self-coupling coefficient when the Y-coupler is an equal power splitter, or is between the two different self-coupling coefficients when the Y-coupler is an unequal power splitter. This limitation is removed for the V-coupled cavity proposed in this paper. The V-coupled cavity laser allows the optimized cross-coupling coefficient to be smaller than the self-coupling coefficients of both cavities, resulting in a much larger side-mode threshold difference, i.e. much higher single-mode selectivity.

_{2}|

^{2}(or |C

_{1}|

^{2}). The threshold of the main lasing mode is G = 2g = 8.5 cm

^{−1}which is independent of the coupling coefficient and is the same as the uncoupled cavity of the same length L. It is also the same as the threshold of the V-coupled cavity. However, the largest threshold difference between the lowest threshold mode and the next lowest threshold mode is only 1.2 cm

^{−1}and it occurs at |C

_{1}|

^{2}= |C

_{2}|

^{2}= 0.5, i.e., when the Y-branch is an equal power splitter. This compares to a maximal threshold difference of 7.2 cm

^{−1}for the V-coupled cavity laser of the same cavity lengths with a cross-coupling coefficient of 0.096. Note that the value of the maximal threshold difference of the Y-laser is consistent with the value of the threshold difference corresponding to

*χ*= 0.5 in V-coupled cavity laser for which the condition C

_{11}C

_{22}-C

_{12}C

_{21}= 0 is also satisfied. The six-time improvement in threshold difference for the V-coupled cavity laser translates into 7.8dB improvement in SMSR (see Fig. 9). This improvement in mode selectivity is even more significant when the length difference between the two cavities is smaller (i.e. when a large FSR is needed to accommodate for a large number of wavelength channels), as can be seen from the comparisons between the two cavity length differences in Fig. 9.

## 7. Conclusions

## Acknowledgments

## References and links

1. | J. W. Raring and L. A. Coldren, “40Gb/s Widely-Tunable Transceivers,” invited paper, IEEE J. Sel. Top. Quantum Electron. |

2. | N. P. Caponio, M. Goano, I. Maio, M. Meliga, G. P. Bava, G. D. Anis, and I. Montrosset, “Analysis and Design criteria of Three-Section DBR Tunable Lasers,” IEEE J. Sel. Areas Commun. |

3. | V. Jayaraman, A. Mathur, and L. A Coldren, “Theory, design, and performance of extended tuning range semiconductor lasers with sampled gratings,” IEEE J. Quantum Electron. |

4. | L. A. Coldren, “Monolithic Tunable Diode Lasers,” IEEE J. Sel. Top. Quantum Electron. |

5. | P. M. Anandarajah, R. Maher, and L. P. Barry, et al., “Characterization of frequency drift of sampled-grating DBR Laser module under direct modulation”, IEEE Photon. Technol. Lett. |

6. | Y. Tohmori, Y. Yoshikuni, and H. Ishii, “Broad-range wavelength-tunable superstructure grating (SSG) DBR lasers,” IEEE J. Quantum Electron. |

7. | R. C. Alferness, U. Koren, and L. L. Buhl, “Broadly tunable InGaAsP/InP laser based on a vertical coupler filter with 57-nm tuning range,” Appl. Phys. Lett. |

8. | J.-O. Wesström, G. Sarlet, and S. Hammerfeldt, “State of the art performance of widely tunable modulated grating Y-branch lasers,” Optical Fiber Communication Conference, Washington DC, paper TuE2 (2004). |

9. | D. J. Robbins, G. Busico, L. Ponnampalam, J. P. Duck, P. J. Williams, R. A. Griffin, A. J. Ward, D. C. J. Reid, N. D. Whitbread, and E. Barton, “A high power, broadband tuneable laser module based on a DS-DBR laser with integrated SOA,” Optical Fiber Communication Conference, Washington DC, Paper TuE3 (2004). |

10. | L. A. Coldren, B. I. Miller, K. Iga, and J. A. Rentschler, “Monolithic two-section GaInAsP/InP active-optical-resonator devices formed by reactive-ion-etching,” Appl. Phys. Lett. |

11. | W. T. Tsang, “The cleaved-coupled-cavity (C3) laser,” Semicond. Semimetals , |

12. | L. A. Coldren and T. L. Koch, “Analysis and design of coupled-cavity lasers,” IEEE J. Quantum Electron. |

13. | T. L. Koch and L. A. Coldren, “Optimum coupling junction and cavity lengths for coupled-cavity semiconductor lasers,” J. Appl. Phys. |

14. | D. Marcuse, “Coupling coefficients of coupled laser cavities,” IEEE J. Quantum Electron. |

15. | R. J. Lang and A. Yariv, “An exact formulation of coupled-mode theory for coupled-cavity lasers,” IEEE J. Quantum Electron. |

16. | O. Hildebrand, M. Schilling, and D. Baums, et al., “The Y-laser: A Multifunctional Device for Optical Communication Systems and Switching Networks,” J. Lightwave Technol. |

17. | M. Kuznetsov, P. Verlangieri, and A. G. Dentai, “Asymmetric Y-Branch Tunable Semiconductor Laser with 1.0 THz Tuning Range,” IEEE Photon. Technol. Lett. |

18. | M. Schilling, K. Diitting, and W. Idler, “Asymmetrical Y laser with simple single current tuning response,” Electron. Lett. |

19. | M. Kuznetsov, “Design of widely tunable semiconductor three-branch lasers,” J. Lightwave Technol. |

20. | T. L. Koch and U. Koren, “Semiconductor Lasers for Coherent Optical Fiber Communications”, J. Lightwave Technol. |

**OCIS Codes**

(140.5960) Lasers and laser optics : Semiconductor lasers

(250.5300) Optoelectronics : Photonic integrated circuits

**ToC Category:**

Lasers and Laser Optics

**History**

Original Manuscript: February 27, 2008

Revised Manuscript: March 4, 2008

Manuscript Accepted: March 5, 2008

Published: March 10, 2008

**Citation**

Jian-Jun He and Dekun Liu, "Wavelength switchable semiconductor laser using half-wave V-coupled cavities," Opt. Express **16**, 3896-3911 (2008)

http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-16-6-3896

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### References

- J. W. Raring and L. A. Coldren, "40Gb/s Widely-Tunable Transceivers," invited paper, IEEE J. Sel. Top. Quantum Electron. 13, 3-14 (2007). [CrossRef]
- N. P. Caponio, M. Goano, I. Maio, M. Meliga, G. P. Bava, G. D. Anis, and I. Montrosset, "Analysis and Design criteria of Three-Section DBR Tunable Lasers," IEEE J. Sel. Areas Commun. 8, 1203-1213 (1990). [CrossRef]
- V. Jayaraman, A. Mathur, and L. A Coldren, "Theory, design, and performance of extended tuning range semiconductor lasers with sampled gratings," IEEE J. Quantum Electron. 29, 1824-1834 (1993). [CrossRef]
- L. A. Coldren, "Monolithic Tunable Diode Lasers," IEEE J. Sel. Top. Quantum Electron. 6, 988 (2000). [CrossRef]
- P. M. Anandarajah, R. Maher, and L. P. Barry, et al., "Characterization of frequency drift of sampled-grating DBR Laser module under direct modulation," IEEE Photon. Technol. Lett. 20, 239-241 (2008). [CrossRef]
- Y. Tohmori, Y. Yoshikuni, and H. Ishii, "Broad-range wavelength-tunable superstructure grating (SSG) DBR lasers," IEEE J. Quantum Electron. 29, 1817-1823 (1993). [CrossRef]
- R. C. Alferness, U. Koren, and L. L. Buhl, "Broadly tunable InGaAsP/InP laser based on a vertical coupler filter with 57-nm tuning range," Appl. Phys. Lett. 60, 3209-3211 (1992). [CrossRef]
- J.-O. Wesström, G. Sarlet, and S. Hammerfeldt, "State of the art performance of widely tunable modulated grating Y-branch lasers," Optical Fiber Communication Conference, Washington DC, paper TuE2 (2004).
- D. J. Robbins, G. Busico, L. Ponnampalam, J. P. Duck, P. J. Williams, R. A. Griffin, A. J. Ward, D. C. J. Reid, N. D. Whitbread, and E. Barton, "A high power, broadband tuneable laser module based on a DS-DBR laser with integrated SOA," Optical Fiber Communication Conference, Washington DC, Paper TuE3 (2004).
- L. A. Coldren, B. I. Miller, K. Iga, and J. A. Rentschler, "Monolithic two-section GaInAsP/InP active-optical-resonator devices formed by reactive-ion-etching," Appl. Phys. Lett. 38, 315-317 (1981). [CrossRef]
- W. T. Tsang, "The cleaved-coupled-cavity (C3) laser," Semicond. Semimetals 22, 257 (1985). [CrossRef]
- L. A. Coldren and T. L. Koch, "Analysis and design of coupled-cavity lasers," IEEE J. Quantum Electron. 20, 659-682 (1984). [CrossRef]
- T. L. Koch and L. A. Coldren, "Optimum coupling junction and cavity lengths for coupled-cavity semiconductor lasers," J. Appl. Phys. 57, 742-754 (1985). [CrossRef]
- D. Marcuse, "Coupling coefficients of coupled laser cavities," IEEE J. Quantum Electron. 22, 223-226 (1986). [CrossRef]
- R. J. Lang and A. Yariv, "An exact formulation of coupled-mode theory for coupled-cavity lasers," IEEE J. Quantum Electron. 24, 66-72 (1988). [CrossRef]
- O. Hildebrand, M. Schilling, D. Baums, et al., "The Y-laser: A Multifunctional Device for Optical Communication Systems and Switching Networks," J. Lightwave Technol. 11, 2066-2074 (1993). [CrossRef]
- M. Kuznetsov, P. Verlangieri, and A. G. Dentai, "Asymmetric Y-Branch Tunable Semiconductor Laser with 1.0 THz Tuning Range," IEEE Photon. Technol. Lett. 4, 1093-1095 (1992). [CrossRef]
- M. Schilling, K. Diitting, and W. Idler, "Asymmetrical Y laser with simple single current tuning response," Electron. Lett. 28, 1698-1699 (1992). [CrossRef]
- M. Kuznetsov, "Design of widely tunable semiconductor three-branch lasers," J. Lightwave Technol. 12, 2100-2106 (1994). [CrossRef]
- T. L. Koch and U. Koren, "Semiconductor Lasers for Coherent Optical Fiber Communications," J. Lightwave Technol. 8, 274-293 (1990). [CrossRef]

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