Integrated tunable quantum dot laser for optical coherence
tomography in the 1.7μm wavelength region
Citation for published version (APA):
Tilma, B. W., Jiao, Y., Kotani, J., Smalbrugge, E., Ambrosius, H. P. M. M., Thijs, P. J. A., Leijtens, X. J. M., Nötzel, R., Smit, M. K., & Bente, E. A. J. M. (2011). Integrated tunable quantum dot laser for optical coherence tomography in the 1.7μm wavelength region. In Proceedings of the European Conference on Lasers and Electro-Optics 2011 and the European Quantum Electronics Conference (CLEO Europe - EQEC 2011), 22-26 May 2011, Munich, Germany Institute of Electrical and Electronics Engineers.
Document status and date: Published: 01/01/2011 Document Version:
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Integrated Tunable Quantum Dot Laser for Optical Coherence
Tomography in the 1.7µm Wavelength Region
Bauke W. Tilma1, Yuqing Jiao1,2, Junji Kotani1, Barry Smalbrugge1, Huub P.M.M. Ambrosius1, Peter J. Thijs3, Xaveer J.M. Leijtens1, Richard Nötzel1, Meint K. Smit1 and Erwin A.J.M. Bente1
1. COBRA, Eindhoven University of Technology, Den Dolech 2, P.O. Box 513, 5600 MB, Eindhoven, The Netherlands 2. Centre for Optical and Electromagnetic Research, Zhejiang University, P.R. China
3. Photonics Labs, Philips Innovation Services, High Tech Campus, 5656 AE, Eindhoven, The Netherlands
We have designed and fabricated a monolithically integrated continuously tunable laser source for frequency domain optical coherence tomography (FD-OCT) in the 1.6 to 1.8µm wavelength region. The InP-based laser consists of two 8mm long quantum dot (QD) semiconductor optical amplifiers and two electro-optically (EO) tunable filters in a 43.5 mm long ring laser cavity. An 8mm long output amplifier is used to boost the output signal. A picture of the mask is given in Fig. 1a.
In this laser the QD-amplifiers are chosen to generate and amplify light in the desired 1.6 to 1.8µm wavelength region. The desired central wavelength of the gain spectrum of these QD-amplifiers can be adjusted by controlling the size of the QDs during the growth process [1]. Furthermore due to the inhomogeneous broadening the bandwidth of the gain spectrum will be more than 100nm which is necessary to tune the laser over at least 100 nm [2]. The two intra-cavity EO tunable filters are used to tune the lasing wavelength of the ring laser. The first, a high resolution (HR) filter, is an arrayed waveguide grating (AWG) filter with a 0.5 nm full-width-half-maximum (FWHM) and a 10nm free spectral range (FSR) (at 1700nm). The second, a low resolution (LR) filter, is an MMI-tree filter with a 25 nm FWHM and a 210 nm FSR. The HR-filter is used as a narrow wavelength filter to allow a maximum of 3 ring laser cavity modes with a 0.02 nm mode spacing and to suppress other neighbor ring cavity modes. The LR-filter is used to select one pass-band of the HR-filter. Both filters are tunable with EO phase modulators (PHM) in the arms of the filters [3]. The laser has been fabricated in the active-passive integration technology used at COBRA [3].
After calibration of the PHMs in both filters [3] we were able to tune the wavelength of the laser reliably and reproducibly. Both ring amplifiers where biased at 1A and the output amplifier at 700mA. In Fig. 1b the lasing spectra are given for 30 different wavelength settings between 1686 nm and 1744 nm. A full characterization within this wavelength region shows a wavelength accuracy within ±0.15nm (+0.1nm thermal detuning) and a FWHM between 0.05nm (instrument limited) and 0.3nm maximum. The spectral suppression of the laser is more than 25dB except for a 5nm region around 1728nm where the spectral suppression is more than 15dB. The total output power fluctuates between -8dBm and -18dBm.
The effective linewidth of the scanning laser has been measured with a free-space Michelson-interferometer setup containing one fixed mirror and one moving mirror [4]. A 0.11nm effective linewidth has been measured for a 500Hz scan over 60nm in 4000 wavelength steps.
This work is supported by the IOP Photonic Devices program managed by the Technology Foundation STW and NL Agency (Ministry of Economic Affairs).
(a)
(b)
Fig. 1 (a)Mask design tunable laser. size: 10 x 6 mm (b) Laser spectra for 30 different laser tuning settings between 1686 nm and 1744 nm.
References
[1] R. Nötzel et al., “Self Assembled InAs/InP Quantum Dots for Telecom Applications in the 1.55 µm Wavelength Range: Wavelength Tuning, Stacking, Polarization Control, and Lasing,” Jpn. J. Appl. Phys., 45, 6544-6549 (2006)
[2] B.W. Tilma M.S. Tahvili, J. Kotani, R. Nötzel M.K. Smit and E.A.J.M. Bente, “Measurement and Analysis of Optical Gain Spectra in 1.6 to 1.8 µm InAs/InP (100) Quantum-Dot Amplifiers,” Opt. Quant. Electron. J., 41, 735-749 (2010)
[3] B.W. Tilma, E.A.J.M. Bente, R. Nötzel, J. Kotani, X.J.M. Leijtens and M.K. Smit, “Integrated Tunable Optical Filters on InP for Continuously Tunable Lasers,” Proc. IEEE/LEOS Annual Meeting, 430-431 (2009)
[4] N.A. Nassif, B. Cense, B.H. Park, M.C. Pierce, S.H. Yun, B.E. Bouma, G.J. Tearney, T.C. Chen and J.F. de Boer “In vivo high-resolution video-rate spectral-domain optical coherence tomography of the human retina and optic nerve,” Optics Express, 12, 367-376 (2004)
