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Optics Express

Optics Express

  • Editor: Andrew M. Weiner
  • Vol. 21, Iss. 17 — Aug. 26, 2013
  • pp: 19718–19722
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Widely tunable Vernier ring laser on hybrid silicon

J. C. Hulme, J. K. Doylend, and J. E. Bowers  »View Author Affiliations


Optics Express, Vol. 21, Issue 17, pp. 19718-19722 (2013)
http://dx.doi.org/10.1364/OE.21.019718


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Abstract

A hybrid silicon tunable Vernier ring laser is designed and fabricated by integration of two intra-cavity ring resonators, hybrid III-V-on-silicon gain elements, and resistive heaters for thermal tuning. Thermal tuning of more than 40 nm is demonstrated with side mode suppression ratio greater than 35 dB and linewidth of 338 kHz.

© 2013 OSA

1. Introduction

In recent years there has been increasing interest in using silicon-on-insulator (SOI) as a platform for photonic integrated circuits (PICs). Silicon processing is highly developed and the high index contrast provided by the material system allows for high optical confinement and smaller devices. Interest has also focused on hybrid III-V on SOI as a means of leveraging the passive advantages of SOI with the gain and absorption in III-V layers to create large-scale PICs [1

1. A. W. Fang, H. Park, O. Cohen, R. Jones, M. J. Paniccia, and J. E. Bowers, “Electrically pumped hybrid AlGaInAs-silicon evanescent laser,” Opt. Express 14(20), 9203–9210 (2006). [CrossRef] [PubMed]

,2

2. M. J. R. Heck, J. F. Bauters, M. L. Davenport, J. K. Doylend, S. Jain, G. Kurczveil, S. Srinivasan, Y. Tang, and J. E. Bowers, “Hybrid Silicon Photonic Integrated Circuit Technology,” IEEE J. Quantum Electron. 19(4), 6100117 (2013). [CrossRef]

]. A tunable laser is one key component for many applications, including spectroscopic measurements, variable sources for WDM systems, in Light Detection and Ranging (LIDAR), and beam-steering [3

3. J. K. Doylend, M. J. R. Heck, J. T. Bovington, J. D. Peters, M. L. Davenport, L. A. Coldren, and J. E. Bowers, “Hybrid III/V silicon photonic source with integrated 1D free-space beam steering,” Opt. Lett. 37(20), 4257–4259 (2012). [CrossRef] [PubMed]

5

5. J. K. Doylend, M. J. R. Heck, J. T. Bovington, J. D. Peters, M. L. Davenport, L. A. Coldren, and J. E. Bowers, “Hybrid III-V silicon photonic steerable laser,” Photonics Conference (IPC), 2012 IEEE, 1(2), 23–27 (2012). [CrossRef]

]. The double-ring resonator approach for widely tunable lasers was proposed by Liu et al [6

6. B. Liu, A. Shakouri, and J. E. Bowers, “Wide tunable double ring resonator coupled lasers,” IEEE Photon. Technol. Lett. 14(5), 600–602 (2002). [CrossRef]

]. Several groups have demonstrated tunable lasers on hybrid III-V on SOI using distributed Bragg reflectors and distributed feedback (DFB) mirrors, or a combination of ring coupling and DFB mirrors [7

7. S. Keyvaninia, G. Roelkens, D. Van Thourhout, C. Jany, M. Lamponi, A. Le Liepvre, F. Lelarge, D. Make, G.-H. Duan, D. Bordel, and J.-M. Fedeli, “Demonstration of a heterogeneously integrated III-V/SOI single wavelength tunable laser,” Opt. Express 21(3), 3784–3792 (2013). [CrossRef] [PubMed]

9

9. A. Le Liepvre, C. Jany, A. Accard, M. Lamponi, F. Poingt, D. Make, F. Lelarge, J.-M. Fedeli, and S. Messaoudene, D. Bordel, and G.-H. Duan, “Widely wavelength tunable hybrid III-V/silicon laser with 45 nm tuning range fabricated using a wafer bonding technique,” Group IV Photonics (GFP), 2012 IEEE 9th Conference on 54(56), 29–31 (2012).

].

In this work we demonstrate a new widely tunable Vernier ring laser using hybrid III-V on silicon without the need for gratings, combining thermally tuned ring resonator wavelength filters with a ring laser design to offer wavelength selection without costly e-beam lithography. We report a tuning range of more than 40 nm with side mode suppression ratio (SMSR) greater than 35 dB, maximum continuous-wave (CW) on-chip output power of 3.3 mW, and center-wavelength linewidth of 338 kHz.

2. Design

3. Fabrication

Rib waveguides were defined using standard photolithography in 500 nm thick Silicon-on-Insulator (SOI) with 1 μm buried oxide. The waveguides were 0.7 μm wide in the rings and bus waveguides and tapered to 2μm under the gain regions. They were dry-etched to a depth of 260 nm. InP wafers with pre-grown InGaAs quantum wells were bonded directly onto the SOI and thinned using CMP and a wet etch. The gain regions were then defined and etched using an oxide hard mask and reactive-ion etching. N-contacts were deposited in an e-beam chamber, after which 900nm of buffer PECVD oxide was deposited and vias etched over the gain region, P-contacts were deposited in the vias and the heater metal was patterned and deposited on the buffer oxide over the rings. One side of the device was diced and polished for measurement.

4. Characterization

Transmission measurements of the ring resonators were performed on polished and anti-reflection coated passive devices using an external tunable laser, two single-mode lensed fibers, and a power meter. Light was fiber coupled to a bus waveguide which was coupled to a ring resonator and a wavelength sweep was performed. The output of the bus waveguide with two ring spectra superimposed is shown in Fig. 3(a)
Fig. 3 (a) Transmission data for full FSR of coupled rings. (b) Fine tuning data from ring filter 1 with round trip loss of 0.20 dB, coupling loss of 2.6% and FWHM of 0.022 radians. (c) Fine tuning data from ring filter 2 with round trip loss of 0.15 dB, coupling loss of 1.7% and FWHM of 0.020 radians.
where the resonant wavelengths of the rings show a drop in throughput power. The data show individual ring FSRs of 1.60 and 1.53 nm and a coupled FSR greater than 32 nm. The FSRs of both rings are lower than designed, resulting in a lower expected tuning range, but 40 nm tuning may still be achieved by aligning the FSR peaks of the full laser cavity. Fine tuning data of a single peak is shown in Figs. 3(b)-3(c) with a least squares fit modeling transmission. Ring 1 and 2 have unloaded round trip losses of 0.20 dB and 0.15 dB respectively (5.1 and 3.5 dB/cm) and power coupling coefficients to the bus waveguides of 2.6% and 1.7%. The FSR of the full passive cavity is measured to be 0.16 nm.

Loss measurements of the silicon waveguides were performed using the cutback method. Light from an external laser source was passed through waveguides of increasing length to distinguish between fiber coupling and waveguide losses. Waveguide and fiber coupling losses were measured to be 0.58 cm−1 and 11.5 dB respectively. The tapered transitions from silicon waveguides to III-V gain sections as well as the gain section itself were characterized by Davenport et al [10

10. M. L. Davenport, M. J. R. Heck, and J. E. Bowers, “Characterization of a Hybrid Silicon-InP Laser Tapered Mode Converter” presented in CLEO: 2013, OSA Technical Digest (online) (Optical Society of America, 2013), poster JTu4A.25–1.

]. Transition losses were measured to be 10 dB per transition at threshold (there were four such transitions in this device). Gain section losses were measured to be 11.7 cm−1. The total intracavity loss is calculated to be 45 dB which is largely dominated by tapered transition losses. As a result of such high losses, room temperature operation of this laser resulted in insufficient gain for widely tunable operation. Active measurements were taken with the chip mounted on a thermally controlled chuck maintained at 100 C.

A maximum on-chip output power of 3.3 mW from a single output was achieved with a threshold current of 160 mA at 100 C. This value was measured using a lensed fiber and adjusted to subtract out the measured coupling loss. Threshold current density was 2350 A/cm2 for the combined gain element length of 1360 μm. Such high current density is attributed to high losses in the tapered transition sections. Linewidth measurements were made by the delayed self-heterodyne method using a delay length of 5.5 km of fiber and a modulation frequency of 100 MHz. The beat signal captured using an RF spectrum analyzer is shown in Fig. 4(a)
Fig. 4 (a) Beat signal from a delayed self-heterodyne measurement of laser measuring 338 kHz linewidth at 100 C and 260 mA pump current. (b) Single wavelength lasing showing SMSR greater than 45 dB at 100 C and 260 mA pump current.
. A Lorentzian function was fitted to the data with a 3 dB bandwidth of 676 kHz corresponding to a laser linewidth of 338 kHz at 100 C and 260 mA pump current. Figure 4(b) shows single wavelength emission at 1575 nm with SMSR greater than 45 dB under the same conditions. Emission is nearly identical for clockwise and counterclockwise propagating modes for both power and wavelength.

Wavelength tuning is accomplished by pumping current through a resistive heater above one or both of the ring resonators. Wavelength tuning was measured using a single-mode tapered fiber connected to an optical spectrum analyzer with resolution of 0.06nm. Fine wavelength tuning was demonstrated with an arbitrarily chosen resolution of 0.1 nm and is shown in Fig. 5(a)
Fig. 5 (a) Superimposed spectra showing 0.1 nm resolution tuning over 2.5 nm. (b) Wavelength tuning as a function of heater power. (c) Superimposed spectra of coarse wavelength tuning over more than 40 nm with SMSR greater than 35 dB.
for a range of 2.5 nm by tuning both rings simultaneously. The heater tuning powers used are shown in Fig. 5(b); the trend is generally linear with power for Heater 1. No clear trend was shown for Heater 2 which is attributed to thermal crosstalk. Thermal tuning over 40 nm was achieved with a SMSR greater than 35 dB and on-chip output powers greater than 0.45 mW at an operating temperature of 100 C as shown in Fig. 5(c).

5. Conclusions

We have demonstrated a tunable Vernier ring laser with more than 40 nm of tuning, SMSR greater than 35 dB, linewidth of 338 kHz, and a maximum of 3.3 mW on-chip output power using a CMOS compatible hybrid silicon platform.

Acknowledgments

The authors would like to thank Josh Conway, Larry Coldren, Martijn Heck, Michael Davenport, Molly Piels, Mingzhi Lu, Geza Kurczveil, Weihua Guo, Jock Bovington, and Jon Peters for all of their advice and useful discussion. This research was supported by DARPA MTO in the SWEEPER program, grant #HR0011-10-2-0003.

References and links

1.

A. W. Fang, H. Park, O. Cohen, R. Jones, M. J. Paniccia, and J. E. Bowers, “Electrically pumped hybrid AlGaInAs-silicon evanescent laser,” Opt. Express 14(20), 9203–9210 (2006). [CrossRef] [PubMed]

2.

M. J. R. Heck, J. F. Bauters, M. L. Davenport, J. K. Doylend, S. Jain, G. Kurczveil, S. Srinivasan, Y. Tang, and J. E. Bowers, “Hybrid Silicon Photonic Integrated Circuit Technology,” IEEE J. Quantum Electron. 19(4), 6100117 (2013). [CrossRef]

3.

J. K. Doylend, M. J. R. Heck, J. T. Bovington, J. D. Peters, M. L. Davenport, L. A. Coldren, and J. E. Bowers, “Hybrid III/V silicon photonic source with integrated 1D free-space beam steering,” Opt. Lett. 37(20), 4257–4259 (2012). [CrossRef] [PubMed]

4.

J. K. Doylend, M. J. R. Heck, J. T. Bovington, J. D. Peters, M. L. Davenport, L. A. Coldren, and J. E. Bowers, “Hybrid silicon free-space source with integrated beam steering,” SPIE Photonics West 862911, (2013).

5.

J. K. Doylend, M. J. R. Heck, J. T. Bovington, J. D. Peters, M. L. Davenport, L. A. Coldren, and J. E. Bowers, “Hybrid III-V silicon photonic steerable laser,” Photonics Conference (IPC), 2012 IEEE, 1(2), 23–27 (2012). [CrossRef]

6.

B. Liu, A. Shakouri, and J. E. Bowers, “Wide tunable double ring resonator coupled lasers,” IEEE Photon. Technol. Lett. 14(5), 600–602 (2002). [CrossRef]

7.

S. Keyvaninia, G. Roelkens, D. Van Thourhout, C. Jany, M. Lamponi, A. Le Liepvre, F. Lelarge, D. Make, G.-H. Duan, D. Bordel, and J.-M. Fedeli, “Demonstration of a heterogeneously integrated III-V/SOI single wavelength tunable laser,” Opt. Express 21(3), 3784–3792 (2013). [CrossRef] [PubMed]

8.

A. Le Liepvre, C. Jany, A. Accard, M. Lamponi, F. Poingt, D. Make, F. Lelarge, J.-M. Fedeli, and S. Messaoudene, D. Bordel, and G.-H. Duan, “Widely wavelength tunable hybrid III–V/silicon laser with 45 nm tuning range fabricated using a wafer bonding technique,” Group IV Photonics (GFP), 2012 IEEE 9th International Conference on 54(56), 29–31 (2012).

9.

A. Le Liepvre, C. Jany, A. Accard, M. Lamponi, F. Poingt, D. Make, F. Lelarge, J.-M. Fedeli, and S. Messaoudene, D. Bordel, and G.-H. Duan, “Widely wavelength tunable hybrid III-V/silicon laser with 45 nm tuning range fabricated using a wafer bonding technique,” Group IV Photonics (GFP), 2012 IEEE 9th Conference on 54(56), 29–31 (2012).

10.

M. L. Davenport, M. J. R. Heck, and J. E. Bowers, “Characterization of a Hybrid Silicon-InP Laser Tapered Mode Converter” presented in CLEO: 2013, OSA Technical Digest (online) (Optical Society of America, 2013), poster JTu4A.25–1.

11.

G. Roelkens, L. Liu, D. Liang, R. Jones, A. Fang, B. Koch, and J. Bowers, “III-V/silicon photonics for on-chip and intera-chip optical interconnects,” Laser Photon. Rev. 4(6), 751–779 (2010). [CrossRef]

OCIS Codes
(140.3560) Lasers and laser optics : Lasers, ring
(140.3600) Lasers and laser optics : Lasers, tunable
(250.5960) Optoelectronics : Semiconductor lasers

ToC Category:
Lasers and Laser Optics

History
Original Manuscript: June 19, 2013
Revised Manuscript: August 3, 2013
Manuscript Accepted: August 5, 2013
Published: August 14, 2013

Citation
J. C. Hulme, J. K. Doylend, and J. E. Bowers, "Widely tunable Vernier ring laser on hybrid silicon," Opt. Express 21, 19718-19722 (2013)
http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-21-17-19718


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References

  1. A. W. Fang, H. Park, O. Cohen, R. Jones, M. J. Paniccia, and J. E. Bowers, “Electrically pumped hybrid AlGaInAs-silicon evanescent laser,” Opt. Express14(20), 9203–9210 (2006). [CrossRef] [PubMed]
  2. M. J. R. Heck, J. F. Bauters, M. L. Davenport, J. K. Doylend, S. Jain, G. Kurczveil, S. Srinivasan, Y. Tang, and J. E. Bowers, “Hybrid Silicon Photonic Integrated Circuit Technology,” IEEE J. Quantum Electron.19(4), 6100117 (2013). [CrossRef]
  3. J. K. Doylend, M. J. R. Heck, J. T. Bovington, J. D. Peters, M. L. Davenport, L. A. Coldren, and J. E. Bowers, “Hybrid III/V silicon photonic source with integrated 1D free-space beam steering,” Opt. Lett.37(20), 4257–4259 (2012). [CrossRef] [PubMed]
  4. J. K. Doylend, M. J. R. Heck, J. T. Bovington, J. D. Peters, M. L. Davenport, L. A. Coldren, and J. E. Bowers, “Hybrid silicon free-space source with integrated beam steering,” SPIE Photonics West 862911, (2013).
  5. J. K. Doylend, M. J. R. Heck, J. T. Bovington, J. D. Peters, M. L. Davenport, L. A. Coldren, and J. E. Bowers, “Hybrid III-V silicon photonic steerable laser,” Photonics Conference (IPC), 2012 IEEE, 1(2), 23–27 (2012). [CrossRef]
  6. B. Liu, A. Shakouri, and J. E. Bowers, “Wide tunable double ring resonator coupled lasers,” IEEE Photon. Technol. Lett.14(5), 600–602 (2002). [CrossRef]
  7. S. Keyvaninia, G. Roelkens, D. Van Thourhout, C. Jany, M. Lamponi, A. Le Liepvre, F. Lelarge, D. Make, G.-H. Duan, D. Bordel, and J.-M. Fedeli, “Demonstration of a heterogeneously integrated III-V/SOI single wavelength tunable laser,” Opt. Express21(3), 3784–3792 (2013). [CrossRef] [PubMed]
  8. A. Le Liepvre, C. Jany, A. Accard, M. Lamponi, F. Poingt, D. Make, F. Lelarge, J.-M. Fedeli, and S. Messaoudene, D. Bordel, and G.-H. Duan, “Widely wavelength tunable hybrid III–V/silicon laser with 45 nm tuning range fabricated using a wafer bonding technique,” Group IV Photonics (GFP), 2012 IEEE 9th International Conference on 54(56), 29–31 (2012).
  9. A. Le Liepvre, C. Jany, A. Accard, M. Lamponi, F. Poingt, D. Make, F. Lelarge, J.-M. Fedeli, and S. Messaoudene, D. Bordel, and G.-H. Duan, “Widely wavelength tunable hybrid III-V/silicon laser with 45 nm tuning range fabricated using a wafer bonding technique,” Group IV Photonics (GFP), 2012 IEEE 9th Conference on 54(56), 29–31 (2012).
  10. M. L. Davenport, M. J. R. Heck, and J. E. Bowers, “Characterization of a Hybrid Silicon-InP Laser Tapered Mode Converter” presented in CLEO: 2013, OSA Technical Digest (online) (Optical Society of America, 2013), poster JTu4A.25–1.
  11. G. Roelkens, L. Liu, D. Liang, R. Jones, A. Fang, B. Koch, and J. Bowers, “III-V/silicon photonics for on-chip and intera-chip optical interconnects,” Laser Photon. Rev.4(6), 751–779 (2010). [CrossRef]

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