Towards CW modelocked laser on chip - a large mode area and NLI for stretched pulse mode locking.

Integrated modelocked lasers with high power are of utmost importance for next generation optical systems that can be field-deployable and mass produced. Here we study fully integrated modelocked laser designs that have the potential to generate ultrashort, high power, and high quality pulses. We explore a large mode area laser for high power pulse generation and study the various mode-locking regimes of dispersion managed soliton pulses in net anomalous and net normal dispersion cavities.

Optical frequency synthesizer with an integrated erbium tunable laser.

Optical frequency synthesizers have widespread applications in optical spectroscopy, frequency metrology, and many other fields. However, their applicability is currently limited by size, cost, and power consumption. Silicon photonics technology, which is compatible with complementary-metal-oxide-semiconductor fabrication processes, provides a low-cost, compact size, lightweight, and low-power-consumption solution.

Supercontinuum generation in varying dispersion and birefringent silicon waveguide.

Ability to selectively enhance the amplitude and maintain high coherence of the supercontinuum signal with long pulses is gaining significance. In this work, an extra degree of freedom afforded by varying the dispersion profile of a waveguide is utilized to selectively enhance supercontinuum. As much as 16 dB signal enhancement in the telecom window and 100 nm of wavelength extension is achieved with a cascaded waveguide, compared to a fixed dispersion waveguide.

Integrated CMOS-compatible Q-switched mode-locked lasers at 1900nm with an on-chip artificial saturable absorber.

We present a CMOS-compatible, Q-switched mode-locked integrated laser operating at 1.9 µm with a compact footprint of 23.6 × 0.

Transmissive silicon photonic dichroic filters with spectrally selective waveguides.

Many optical systems require broadband filters with sharp roll-offs for efficiently splitting or combining light across wide spectra. While free space dichroic filters can provide broadband selectivity, on-chip integration of these high-performance filters is crucial for the scalability of photonic applications in multi-octave interferometry, spectroscopy, and wideband wavelength-division multiplexing. Here we present the theory, design, and experimental characterization of integrated, transmissive, 1 × 2 port dichroic filters using spectrally selective waveguides.

Octave-spanning coherent supercontinuum generation in silicon on insulator from 1.06 μm to beyond 2.4 μm.

Efficient complementary metal-oxide semiconductor-based nonlinear optical devices in the near-infrared are in strong demand. Due to two-photon absorption in silicon, however, much nonlinear research is shifting towards unconventional photonics platforms. In this work, we demonstrate the generation of an octave-spanning coherent supercontinuum in a silicon waveguide covering the spectral region from the near- to shortwave-infrared.

Monolithically-integrated distributed feedback laser compatible with CMOS processing.

An optically-pumped, integrated distributed feedback laser is demonstrated using a CMOS compatible process, where a record-low-temperature deposited gain medium enables integration with active devices such as modulators and detectors. A pump threshold of 24.9 mW and a slope efficiency of 1.

High-power thulium lasers on a silicon photonics platform.

Mid-infrared laser sources are of great interest for various applications, including light detection and ranging, spectroscopy, communication, trace-gas detection, and medical sensing. Silicon photonics is a promising platform that enables these applications to be integrated on a single chip with low cost and compact size. Silicon-based high-power lasers have been demonstrated at 1.

Multimode phase-matched third-harmonic generation in sub-micrometer-wide anatase TiOâ‚‚ waveguides.

Third-harmonic generation (THG) has applications ranging from wavelength conversion to pulse characterization, and has important implications for quantum sources of entangled photons. However, on-chip THG devices are nearly unexplored because bulk techniques are difficult to adapt to integrated photonic circuits. Using sub-micrometer-wide polycrystalline anatase TiOâ‚‚ waveguides, we demonstrate third-harmonic generation on a CMOS-compatible platform.

Theory of terahertz generation by optical rectification using tilted-pulse-fronts.

A model for terahertz (THz) generation by optical rectification using tilted-pulse-fronts is developed. It simultaneously accounts for in two spatial dimensions (2-D) (i) the spatio-temporal variations of the optical pump pulse imparted by the tilted-pulse-front setup, (ii) the nonlinear coupled interaction of THz and optical radiation, (iii) self-phase modulation and (iv) stimulated Raman scattering. The model is validated by quantitative agreement with experiments and analytic calculations.

Spectral broadening in anatase titanium dioxide waveguides at telecommunication and near-visible wavelengths.

We observe spectral broadening of femtosecond pulses in single-mode anatase-titanium dioxide (TiO(2)) waveguides at telecommunication and near-visible wavelengths (1565 and 794 nm). By fitting our data to nonlinear pulse propagation simulations, we quantify nonlinear optical parameters around 1565 nm. Our fitting yields a nonlinear refractive index of 0.

Photonic ADC: overcoming the bottleneck of electronic jitter.

Accurate conversion of wideband multi-GHz analog signals into the digital domain has long been a target of analog-to-digital converter (ADC) developers, driven by applications in radar systems, software radio, medical imaging, and communication systems. Aperture jitter has been a major bottleneck on the way towards higher speeds and better accuracy. Photonic ADCs, which perform sampling using ultra-stable optical pulse trains generated by mode-locked lasers, have been investigated for many years as a promising approach to overcome the jitter problem and bring ADC performance to new levels.

10 GHz femtosecond pulse interleaver in planar waveguide technology.

Coherent pulse interleaving implemented in planar waveguide technology is presented as a compact and robust solution to generate high repetition rate frequency combs. We demonstrate a 10 GHz pulse train from an Er-doped femtosecond fiber laser that is coupled into waveguide interleavers and multiplied in repetition rate by a factor of 16. With thermal tuning of the chip elements, we achieve optical and RF sidemode suppression levels of at least -30 dB.

Ultrafast nonlinear optical studies of silicon nanowaveguides.

Results of a self-consistent ultrafast study of nonlinear optical properties of silicon nanowaveguides using heterodyne pump-probe technique are reported. The two-photon absorption coefficient and free-carrier absorption effective cross-section were determined to be 0.68cm/GW, and 1.

Reconfigurable multi-channel second-order silicon microring-resonator filterbanks for on-chip WDM systems.

We report the fabrication of a reconfigurable wide-band twenty-channel second-order dual filterbank, defined on a silicon-on-insulator (SOI) platform, with tunable channel spacing and 20 GHz single-channel bandwidth. We demonstrate the precise tuning of eleven (out of the twenty) channels, with a channel spacing of 124 GHz (~1 nm) and crosstalk between channels of about -45 dB. The effective thermo-optic tuning efficiency is about 27 μW/GHz/ring.

Compact, stable 1 GHz femtosecond Er-doped fiber lasers.

We demonstrate a high-repetition-rate soliton fiber laser that is based on highly doped anomalously dispersive erbium-doped fiber. By splicing an 11 mm single-mode fiber to the erbium-doped fiber, the thermal damage of the butt-coupled saturable Bragg reflector (SBR) is overcome. The laser generates 187 fs pulses at a repetition rate of 967 MHz with a measured long-term stability of more than 60 h.

Carrier-envelope phase dynamics of octave-spanning dispersion-managed Ti: sapphire lasers.

The carrier-envelope phase dynamics of few-cycle octave-spanning Ti:sapphire lasers are analyzed based on a numerical one-dimensional dispersion-managed laser model. The dominant contribution to the carrier-envelope phase shift with respect to intracavity energy arises from the asymmetric impact of self-steepening on pulse formation and laser output. We show that this term is larger by a factor of four than the energy-dependent round trip phase and is thus more significant than in the corresponding result for conventional soliton lasers.

Scaling of passively mode-locked soliton erbium waveguide lasers based on slow saturable absorbers.

We assess the scaling potential of high repetition rate, passively mode-locked erbium-doped soliton lasers. Our analysis focuses on three recently demonstrated lasers using saturable Bragg reflectors (SBR) as the mode-locking element. We use the soliton Area theorem to establish the limitations to increasing the repetition rate based on insufficient intracavity pulse energy, SBR properties, and dispersion engineering.

High-repetition-rate, 491 MHz, femtosecond fiber laser with low timing jitter.

We demonstrate a soliton fiber laser based on an anomalously dispersive erbium-doped fiber butt-coupled to a saturable absorber mirror for passive mode locking. The laser generates 180 fs pulses at a repetition rate of 491 MHz and exhibits a timing jitter as low as 20 fs over the frequency range 1 kHz-10 MHz.

Purcell effect in nonlinear photonic structures: a coupled mode theory analysis.

We develop a coupled mode theory (CMT) model of the behavior of a polarization source in a general photonic structure, and obtain an analytical expression for the resulting generated electric field; loss, gain and/or nonlinearities can also be modeled. Based on this treatment, we investigate the criteria needed to achieve an enhancement in various nonlinear effects, and to produce efficient sources of terahertz radiation, in particular. Our results agree well with exact finite-difference time-domain (FDTD) results.

Continuous-wave two-photon absorption in a Watt-class semiconductor optical amplifier.

We report the observation of photoluminescence produced by the recombination of free carriers generated via continuous-wave (CW) two-photon absorption (TPA) in a packaged, low-confinement (Gamma approximately 0.5%) InGaAsP/InP quantum-well slab-coupled optical waveguide amplifier (SCOWA) having a saturation output power of 0.8 W and 1/e-mode-field diameters of 5 x 7 microm.

Effect of carrier lifetime on forward-biased silicon Mach-Zehnder modulators.

We present a systematic study of Mach-Zehnder silicon optical modulators based on carrier-injection. Detailed comparisons between modeling and measurement results are made with good agreement obtained for both DC and AC characteristics. A figure of merit, static VpiL, as low as 0.

Efficient performance optimization of SOA-MZI devices.

We present a novel characterization method for semiconductor optical amplifier Mach-Zehnder interferometer (SOA-MZI) switches which combines a pump-probe measurement with an interferometer bias scan. In addition to a wealth of information on the switching dynamics for all operating points of the switch, we can create an extinction map to pinpoint regions of highest extinction for optimizing all-optical ultrafast switching. We experimentally verify the accuracy of this characterization method by performing a wavelength characterization at the optimal bias point and a nearby, non-optimal point.

Generation of low-timing-jitter femtosecond pulse trains with 2 GHz repetition rate via external repetition rate multiplication.

Generation of low-timing-jitter 150 fs pulse trains at 1560 nm with 2 GHz repetition rate is demonstrated by locking a 200 MHz fundamental polarization additive-pulse mode-locked erbium fiber laser to high-finesse external Fabry-Perot cavities. The timing jitter and relative intensity noise of the repetition-rate multiplied pulse train are investigated.

Self-stabilized passive, harmonically mode-locked stretched-pulse erbium fiber ring laser.

We have studied a passive, harmonically mode-locked stretched-pulse erbium fiber ring laser with net positive dispersion that is self-stabilized by gain depletion and electrostriction. Periodic pulses with supermode suppression of >75 dB and picosecond jitter are achieved. The pulses are compressible to 125 fs by external chirp compensation.