Dual-pump Kerr micro-cavity optical frequency comb with varying FSR spacing

In this paper, we demonstrate a novel dual-pump approach to generate robust optical frequency comb with varying free spectral range (FSR) spacing in a CMOS-compatible high-Q micro-ring resonator (MRR). The frequency spacing of the comb can be tuned by an integer number FSR of the MRR freely in our dual-pump scheme. The dual pumps are self-oscillated in the laser cavity loop and their wavelengths can be tuned flexibly by programming the tunable filter embedded in the cavity. By tuning the pump wavelength, broadband OFC with the bandwidth of >180nm and the frequency-spacing varying from 6 to 46-fold FSRs is realized at a low pump power. This approach could find potential and practical applications in many areas, such as optical metrology, optical communication, and signal processing systems, for its excellent flexibility and robustness

Integrable microwave filter based on a photonic crystal delay line

The availability of a tunable delay line with a chip-size footprint is a crucial step towards the full implementation of integrated microwave photonic signal processors. Achieving a large and tunable group delay on a millimetre-sized chip is not trivial. Slow light concepts are an appropriate solution, if propagation losses are kept acceptable. Here we use a low-loss 1.5 mm-long photonic crystal waveguide to demonstrate both notch and band-pass microwave filters that can be tuned over the 0 50-GHz spectral band. The waveguide is capable of generating a controllable delay with limited signal attenuation (total insertion loss below 10 dB when the delay is below 70 ps) and degradation. Owing to the very small footprint of the delay line, a fully integrated device is feasible, also featuring more complex and elaborate filter functions.This work was funded by the European Union under the project GOSPEL (grant 219299) and by the Valencian Government (Prometeo GVA 2008-92). We thank S. Hughes and P. Lalanne for enlightening discussion about the impact of disorder in photonic crystal waveguides.Sancho Durá, J.; Bourderionnet, J.; Lloret Soler, JA.; Combrie, S.; Gasulla Mestre, I.; Xavier, S.; Sales Maicas, S.... (2012). Integrable microwave filter based on a photonic crystal delay line. Nature Communications. 3:1-9. https://doi.org/10.1038/ncomms2092S193Seeds, A. Microwave photonics. IEEE Trans. Microwave Theory Tech. 50, 877–887 (2002).Capmany, J. & Novak, D. Microwave photonics combines two worlds. Nat. Photon 1, 319–330 (2007).Yao, J. P. Microwave photonics. J. Lightwave Technol. 27, 314–335 (2009).See special technology focus on microwave photonics. Nat. Photon 5, 723–736 (2011).Capmany, J., Ortega, B. & Pastor, D. A tutorial on microwave photonic filters. J. Lightwave. Technol. 24, 201–229 (2006).Long, J. et al. A tunable microstrip bandpass filter with two independently adjustable transmission zeros. IEEE Microw. Wireless Compon. Lett. 21, 74–76 (2011).Velez, A. et al. Tunable coplanar waveguide band-stop and band-pass filters based on open split ring resonators and open complementary split ring resonators. IEEE Microw. Antennas Propag. 5, 277–281 (2011).Sekar, V., Armendariz, M. & Entesari, K. A 1.2-1.6-GHz substrate-integrated-waveguide RF MEMS tunable filter. IEEE Trans. Microwave Theory Tech. 59, 866–876 (2011).Rafique, M. R. et al. Miniaturized superconducting microwave filters. Supercond. Sci. Technol. 21, 075004 (2008).Velu, G. et al. A 360° BST phase shifter with moderate bias voltage at 30 GHz. IEEE Trans. Microwave Theory Tech. 55, 438–444 (2007).Koh, K. J. & Rebeiz, G. M. A 6-18 GHz active phase shifter. In Proceedings IEEE Microwave Symposium Digest 792–795 (2010).Capmany, J., Pastor, D. & Ortega, B. New and flexible fiber-optic delay-line filters using chirped Bragg gratings and laser arrays. IEEE Trans. Microwave Theory Tech. 47, 1321–1326 (1999).Minasian, R. A. Photonic signal processing of microwave signals. IEEE Trans. Microwave Theory Tech. 54, 832–846 (2006).Dai, Y. & Yao, J. P. Nonuniformly-spaced photonic microwave delay-line filter. Opt. Express 16, 4713–4718 (2008).Hamidi, E., Leaird, D. E. & Weiner, A. M. Tunable programmable microwave photonic filters based on an optical frequency comb. IEEE Trans. Microwave Theory Tech. 58, 3269–3278 (2010).Chan, E. H. W. & Minasian, R. A. Coherence-free high-resolution RF/microwave photonic bandpass filter with high skirt selectivity and high stopband attenuation. J. Lightwave Technol. 28, 1646–1651 (2010).Norberg, E. J. et al. Programmable photonic microwave filters monolithically integrated in InPinGaAsP. J. Lightwave. Technol. 29, 1611–1619 (2011).Chen, H. W. et al. Integrated microwave photonic filter on a hybrid silicon platform. IEEE Trans. Microwave Theory Tech. 58, 3213–3219 (2010).Dong, P. et al. GHz-bandwidth optical filters based on high-order silicon ring resonators. Opt. Express 18, 23784–23789 (2010).Lloret, J. et al. Tunable complex-valued multi-tap microwave photonic filter based on single silicon-on-insulator microring resonator. Opt. Express 19, 12402–12407 (2011).Notomi, M. et al. Extremely large group-velocity dispersion of line-defect waveguides in photonic crystal slabs. Phys. Rev. Lett. 87, 253902 (2001).Knight, J. C. Photonic crystal fibres. Nature 424, 847–851 (2003).Supradeepa, V. R. et al. Comb-based radiofrequency photonic filters with rapid tunability and high selectivity. Nat. Photon. 6, 186–194 (2012).Capmany, J., Ortega, B., Pastor, D. & Sales, S. Discrete-time optical processing of microwave signals. J. Lightwave Technol. 23, 702–723 (2005).Hunter, D. B. & Minasian, R. A Tunable microwave fiber-optic bandpass filters. IEEE Photon. Tech. Lett. 11, 874–876 (1999).Baba, T. Slow light in photonic crystals. Nat. Photon. 2, 465–473 (2008).Kuramochi, E. et al. Disorder-induced scattering loss of line-defect waveguides in photonic crystal slabs. Phys. Rev B 72, 161318 (2005).Ishikura, N., Baba, T., Kuramochi, E. & Notomi, M. Large tunable fractional delay of slow light pulse and its application to fast optical correlator. Opt. Express 19, 24102–24108 (2011).O'Faolain, L. et al. Loss engineered slow light waveguides. Opt. Express 18, 27627–27638 (2010).Baron, A., Mazoyer, S., Smigaj, W. & Lalanne, P. Attenuation Coefficient of Single-Mode Periodic Waveguides. Phys. Rev. Lett. 107, 153901 (2011).Patterson, M. et al. Disorder-Induced Coherent Scattering in Slow-Light Photonic Crystal Waveguides. Phys. Rev. Lett. 102, 253903 (2009).Mazoyer, S., Hugonin, J. P. & Lalanne, P. Disorder-Induced Multiple Scattering in Photonic-Crystal Waveguides. Phys. Rev. Lett. 103, 063903 (2009).Combrié, S. et al. Time-delay measurement in singlemode, low-loss photonic crystal waveguides. Electron. Lett. 42, 86–87 (2006).Liang, J. et al. Wideband ultraflat slow light with large group index in a W1 photonic crystal waveguide. J. App. Phys. 110, 063103 (2011).Roy, S. Modeling the dispersion of the nonlinearity in slow mode photonic crystal waveguides. IEEE Photonics. Journal 4, 224–233 (2012).Colman, P., Combrié, S. & De Rossi, A. Control of dispersion in photonic crystal waveguides using group symmetry theory. Opt. Express 20, 13108–13114 (2012).Vy Tran, Q., Combrié, S., Colman, P. & De Rossi, A. Photonic crystal membrane waveguides with low insertion losses. Appl. Phys. Lett. 95, 061105 (2009).Bolea, M., Mora, J., Ortega, B. & Capmany, J. Highly chirped single-bandpass microwave photonic filter with reconfiguration capabilities. Opt. Express 19, 4566–4576 (2011).Binetti, P. et al. Indium phosphide integrated circuits for coherent optical links. IEEE J. Quantum Electron. 48, 279–291 (2012).Thomson, D. J. et al. High contrast 40Gbit/s optical modulation in silicon. Opt. Express 19, 11507–11516 (2011).Asghari, M. & Krishnamoorthy, A. V. Energy efficient communication. Nat. Photon. 5, 268–270 (2011).Vivien, L. et al. Zero-bias 40Gbit/s germanium waveguide photodetector on silicon. Opt. Express 20, 1096–1101 (2012).Feng, N. N. et al. 30GHz Ge electro-absorption modulator integrated with 3 μm silicon-on-insulator waveguide. Opt. Express 19, 7062–7067 (2011).Trinh, P. D., Yegnanarayanan, S., Coppinger, F. & Jalali, B. Compact multimode interference couplers in Silicon-on-insulator technology. Conference on Lasers and Electro-Optics CLEO '97CThV4, 441 (Baltimore, USA, 1997).Loayssa, A., Capmany, J., Sagues, M. & Mora, J. Demonstration of incoherent microwave photonic filters with all-optical complex coefficients. IEEE Photon. Tech. Lett. 18, 1744–1746 (2006).Zhang, W. & Minasian, R. A. Widely tunable single-passband microwave photonic filter based on stimulated Brillouin scattering. IEEE Photon. Tech. Lett. 23, 1775–1777 (2011).Xue, W., Sales, S., Mork, J. & Capmany, J. Widely tunable microwave photonic notch filter based on slow and fast light effects. IEEE Photon. Tech. Lett. 21, 167–169 (2009).Norberg, E. J. et al. A monolithic programmable optical filter for RF signal processing. in Proceedings Microwave Photonics Conf. (Montreal, Canada, 2010).Vlasov, Y. A., O'Boyle, M., Hamann, H. F. & McNab, S. J. Active control of slow light on a chip with photonic crystal waveguides. Nature 438, 65–69 (2005).Eckhouse, V. et al. Highly efficient four wave mixing in GaInP photonic crystal waveguides. Opt. Lett. 35, 1440–1442 (2010).Sagues, M. et al. Multi-tap complex-coefficient incoherent microwave photonic filters based on optical single-sideband modulation and narrow band optical filtering. Opt. Express 16, 295–303 (2008).Huang, T. X. H., Yi, X. & Minasian, R. A. Single passband microwave photonic filter using continuous-time impulse response. Opt. Express 19, 6231–6242 (2011).Burla, M. et al. On-chip CMOS compatible reconfigurable optical delay line with separate carrier tuning for microwave photonic signal processing. Opt. Express 19, 21475–21484 (2011)

High-power, cascaded random Raman fiber laser with near complete conversion over wide wavelength and power tuning

Cascaded Raman fiber lasers based on random distributed feedback (RDFB) are proven to be wavelength agile, enabling high powers outside rare-earth doped emission windows. In these systems, by simply adjusting the input pump power and wavelength, high-power lasers can be achieved at any wavelength within the transmission window of optical fibers. However, there are two primary limitations associated with these systems, which in turn limits further power scaling and applicability. Firstly, the degree of wavelength conversion or spectral purity (percentage of output power in the desired wavelength band) that can be achieved is limited. This is attributed to intensity noise transfer of input pump source to Raman Stokes orders, which causes incomplete power transfer reducing the spectral purity. Secondly, the output power range over which the high degree of wavelength conversion is maintained is limited. This is due to unwanted Raman conversion to the next Stokes order with increasing power. Here, we demonstrate a high-power, cascaded Raman fiber laser with near complete wavelength conversion over a wide wavelength and power range. We achieve this by culmination of two recent developments in this field. We utilize our recently proposed filtered feedback mechanism to terminate Raman conversion at arbitrary. wavelengths, and we use the recently demonstrated technique (by J Dong and associates) of low-intensity noise pump sources (Fiber ASE sources) to achieve high-purity Raman conversion. Pump-limited output powers >34W and wavelength conversions >97% (highest till date) were achieved over a broad - 1.1 mu m to 1.5 mu m tuning range. In addition, high spectral purity (>90%) was maintained over a broad output power range (>15%), indicating the robustness of this laser against input power variations. (C) 2019 Optical Society of America under the terms of the OSA Open Access Publishing Agreemen

Thermo-optic Degradation of Single-Modedness in Active LMA fibers and Simple Compensation Mechanisms

We demonstrate significant thermo-optic degradation of single-modedness in active large mode area fibers due to heat generation in the fiber. We propose and demonstrate through simulations, simple compensation mechanisms using custom length dependent fiber coiling

Observation of a rainbow of visible colors in a near infrared cascaded Raman fiber laser and its novel application as a diagnostic tool for length resolved spectral analysis

In this work, we report and analyse the surprising observation of a rainbow of visible colors, spanning 390nm to 620nm, in silica-based, Near Infrared, continuous-wave, cascaded Raman fiber lasers. The cascaded Raman laser is pumped at 1117nm at around 200W and at full power we obtain -100 W at 1480nm. With increasing pump power at 1117nm, the fiber constituting the Raman laser glows in various hues along its length. From spectroscopic analysis of the emitted visible light, it was identified to be harmonic and sum-frequency components of various locally propagating wavelength components. In addition to third harmonic components, surprisingly, even 2nd harmonic components were observed. Despite being a continuous-wave laser, we expect the phase-matching occurring between the core-propagating NIR light with the cladding-propagating visible wavelengths and the intensity fluctuations characteristic of Raman lasers to have played a major role in generation of visible light. In addition, this surprising generation of visible light provides us a powerful non-contact method to deduce the spectrum of light propagating in the fiber. Using static images of the fiber captured by a standard visible camera such as a DSLR, we demonstrate novel, image-processing based techniques to deduce the wavelength component propagating in the fiber at any given spatial location. This provides a powerful diagnostic tool for both length and power resolved spectral analysis in Raman fiber lasers. This helps accurate prediction of the optimal length of fiber required for complete and efficient conversion to a given Stokes wavelength

Generation of tunable, high repetition rate frequency combs with equalized spectra using carrier injection based silicon modulators

High repetition-rate frequency combs with tunable repetition rate and carrier frequency are extensively used in areas like Optical communications, Microwave Photonics and Metrology. A common technique for their generation is strong phase modulation of a CW-laser. This is commonly implemented using Lithium-Niobate based modulators. With phase modulation alone, the combs have poor spectral flatness and significant number of missing lines. To overcome this, a complex cascade of multiple intensity and phase modulators are used. A comb generator on Silicon based on these principles is desirable to enable on-chip integration with other functionalities while reducing power consumption and footprint. In this work, we analyse frequency comb generation in carrier injection based Silicon modulators. We observe an interesting effect in these comb generators. Enhanced absorption accompanying carrier injection, an undesirable effect in data modulators, shapes the amplitude here to enable high quality combs from a single modulator. Thus, along with reduced power consumption to generate a specific number of lines, the complexity has also been significantly reduced. We use a drift-diffusion solver and mode solver (Silvaco TCAD) along with Soref-Bennett relations to calculate the variations in refractive indices and absorption of an optimized Silicon PIN - waveguide modulator driven by an unbiased high frequency (10 Ghz) voltage signal. Our simulations demonstrate that with a device length of 1 cm, a driving voltage of 2V and minor shaping with a passive ring-resonator filter, we obtain 37 lines with a flatness better than 5-dB across the band and power consumption an order of magnitude smaller than Lithium-Niobate modulators

High-Power, Independently Wavelength, Power, and Linewidth Tunable Ytterbium Fiber Laser

We report a high-power, independently tunable wavelength, linewidth, and power, continuous-wave Ytterbium-doped fiber laser. Our system is based on a simple master oscillator power amplifier configuration, which decouples the output power from the output wavelength and linewidth. We demonstrate a continuously tunable laser system that can generate any output power level up to and beyond 100 W, wavelength from 1050 to 1100 nm, and linewidth tuning of 2.5 times from 0.4 to 1 nm completely independent of each other

High-power, widely wavelength tunable, grating-free Raman fiber laser based on filtered feedback

The cascaded Raman fiber laser is a proven technology that provides wavelength agile high-power fiber lasers outside the rare-earth emission windows. However, conventional cascaded Raman fiber lasers lack wavelength agility due to the use of fixed wavelength fiber Bragg gratings. Recently, proposed cascaded Raman fiber lasers based on random distributed feedback have provided a grating-free solution enabling wavelength agility. With these lasers, wide wavelength tunability has been achieved. However, there are still limitations in scaling output power while maintaining high spectral purity of wavelength conversion. Spectral purity is characterized by the in-band power ratio, which is the ratio of the output power in the required wavelength to the total power. The origin of this limitation arises from the inability to efficiently terminate the Raman cascade at a specific wavelength with increasing power. In this Letter, we propose a novel filtered distributed feedback mechanism to terminate the Raman cascade at any desired wavelength, enabling power scaling with high spectral purity. Output power up to 28 W has been achieved with >85% in-band power ratio and >400 nm tuning range from 1118 to 1535 nm. (C) 2019 Optical Society of Americ

Optical frequency comb based on nonlinear spectral broadening of a phase modulated comb source driven by dual offset locked carriers

We demonstrate a versatile technique to generate a broadband optical frequency comb source in the C-band. This is accomplished by nonlinear spectral broadening of a phase modulated comb source driven by dual frequency offset locked carriers. The locking is achieved by setting up a heterodyne optical frequency locked loop to lock two phase modulated electro-optic 25 GHz frequency combs sourced from individual seed carriers offset by 100 GHz, to within 6.7 MHz of each other. We realize spectral broadening in highly nonlinear fiber after suitable amplification to obtain an equalized, nonlinearly broadened frequency comb. We obtain � 86 lines in a 20 dB band spanning over 2 THz