Novel diffractive feedback structures for semiconducting polymer lasers

This paper emphasizes methodology concerning variations of the emission wavelengths of edge-emitting semiconductor lasers. We present a method based on tilted distributed feedback (DFB) gratings to be used in combination with specially bent or tilted straight waveguides for the low-cost and ultraprecise definition of different wavelength channels in lasers for Dense wavelength division multiplexing (DWDM) fiberoptic communication systems. The homogeneous DFB grating field is defined using low-cost processes and is tilted with respect to a preferential direction defined by the device borders or the crystal geometry. Our method allows ultraprecise definitions of the DWDM wavelengths and is applicable index- and complex-coupled DFB gratings in both isolated lasers and arrays. Design, technological implementation, and experimental characterization of the devices is presented in this paper. Thin-film heaters are used for correcting small wavelength deviations occurring due to technologically induced tolerances.

Distributed feedback (DFB) fiber Bragg gratings (FBG) are widely used as narrow-band filters and single-mode cavities for lasers. Recently, a nonlinear generation has been shown in 10-20 cm DFB gratings in a highly nonlinear fiber. First, we show in this Letter a novel fabrication technique of ultra-long DFBs in a standard fiber (SMF-28). Second, we demonstrate nonlinear generation in such gratings. A particular inscription technique was used to fabricate all-in-phase ultra-long FBG and to implement reproducible phase shift to form a DFB mode. We demonstrate stimulated Brillouin scattering (SBS) emission from this DFB mode and characterize the resulting laser. It seems that such a SBS based DFB laser stabilizes a pump's jittering and reduces its linewidth.

DFB lasers with axially distributed phase shifts implemented by distributed feedback (DFB) gratings with axially varied pitch lengths (chirped DFB gratings) have been investigated. It is shown that distributed phase shifts can be used to counteract spatial hole burning and reduce the inhomogeneity of the axial photon-density distribution. Different total amounts of phase shift and axial extensions of the phase shift section have been compared by appropriate chirping functions, and also to the behaviour of abrupt phase shifts. It is shown that different design goals can be reached such as minimum threshold gain, reduced axial photon field inhomogeneities, specific spectral positions of the oscillating mode or increased gain margin. The results are obtained for two different ways of implementing DFB gratings with axially varied pitch length such as bent waveguides on homogeneous grating fields or fractal gratings. For identical chirping functions, both implementation possibilities show identical device properties if homogeneous coupling is assumed and bending losses remain negligible. Finally, the influence of facet phase statistics on the device yield is studied.

InAs-based single-mode distributed feedback (DFB) interband cascade (IC) lasers were investigated. The DFB grating was patterned using interference lithography to etch the cladding-free upper separate confinement layer of the IC laser structure. Single-mode emission with a side mode suppression ratio of $\sim 30$ dB was obtained in continuous wave operation at temperatures up to 180 K near 4.5 $\mu \text{m}$ . A total tuning range of 16 nm could be achieved for a single device, with typical temperature- and current-tuning rates of 0.4 nm/K and 0.016 nm/mA, respectively. The impact of the DFB grating on device performance was evaluated and discussed in comparison with Fabry–Perot lasers.

Distributed feedback (DFB) lasing in permanent volume transmission gratings formed in a laser dye-doped organic–inorganic nanocomposite has been investigated. DFB laser cavities were fabricated using one-step two-beam holographic exposure of Pyrromethene 567 (PM567) doped photopolymerizable acrylate monomers containing inorganic (LaPO4) nanoparticles. Compared to the formulation previously utilized, the material composition presented provides longer lifetime of the laser. Spectral and polarization properties, input–output and stability characteristics of the laser output have been investigated by varying the material composition and the patterning parameters. DFB lasing emission of the second and the third diffraction orders has been demonstrated. The spectral linewidth of ∼0.08 nm has been observed at a pump energy threshold of about 0.2 μJ/pulse for the second-order DFB lasing when pumped with 532 nm 500 ps laser pulses. Spectral tuning of the lasing output over ∼56 and ∼7 nm was obtained by varying the grating period and the content of inorganic nanoparticles in the polymer matrix, respectively.

The application of hybrid polymer precursor gel for distributed feedback (DFB) grating laser fabricated by short‐pulse laser interference has been investigated. The precursor gel was prepared by sol–gel process from siloxane‐modified methacrylate monomer. The molecular structure characterization results show the formation of inorganic networks within the precursor gel, which further undergoes the formation of organic–inorganic polymer network by photopolymerization. The laser interference was performed by using the frequency‐tripled output of nanosecond Nd–YAG laser. The fabricated DFB gratings exhibit photopumped lasing actions with high consistency between the grating periodicity (between 380 and 1030 nm) and the lasing wavelength, which appears at the wavelength of the second‐order Bragg reflection. The atomic force microcopy measurements clearly show the formation of surface relief (corrugated) structure in those gratings. The mechanism of surface relief formation is attributed to a fast photo‐induced swelling process, which is unique property belonging to this kind of hybrid polymer precursor gel. Copyright © 2011 John Wiley & Sons, Ltd.

Chirp or wavelength shifts in distributed feedback (DFB) lasers have been the limiting factor in high bit rate transmission systems. Furthermore, dynamic chirp in direct modulation schemes results in pulse broadening because of the chromatic dispersion in the fiber leading to higher power penalties for the link. It is thus crucial to be able to unambiguously quantify the chirp component at the chip level with a quick and inexpensive method. Towards this, we present results of a set of measurements done to understand the extent of correlation between the observed chirp and the system's dispersion penalty. Strained MQW DFB lasers fabricated in the AlInGaAs/InP system were used. The ratio of the conduction to the valence band offsets in the AlInGaAs/InP system is larger than in the InGaAsP/InP system. This is expected to provide better electron confinement minimizing leakage. Coupled with a MQW structure, uniform hole distribution across wells is possible thus enabling higher bandwidth. Different facet coating combinations were also included to provide a rich subset of the device dynamic properties for this study. The tested devices had a lasing wavelength between 1520-1550 nm. We have experimentally shown the existence of a correlation between the transient chirp in the leading edge of the light pulse and the observed dispersion penalty under 2.5 Gbit/s PRBS modulation. This offers a cost-effective solution to screen chips at the chip level without incurring costs associated with module level components. It is important to note, however, that this is a necessary but not sufficient screen due to issues like mode partition noise and timing jitter, which affect the overall power penalty.

We present optofluidic lab-on-a-chip devices (LOCs) for single use as disposables. In our approach we are aiming for systems out of poly(methyl methacrylate) (PMMA) that integrate (a) organic lasers, (b) optical waveguides, (c) microfluidic channels, (d) surface functionalization, and (e) fluorescence excitation on one single chip. We are utilizing mass production techniques to show the applicability of this approach by avoiding electrical interconnects but using optical and fluidic interfaces only. With our experiments we can show the feasibility of this approach by respectively combining two consecutive elements (a - e) of the path of light: Organic semiconductor lasers are integrated by evaporating a thin film of photoactive material on top of a distributed feedback (DFB) grating. For this purpose, grating masters are replicated by hot embossing into PMMA bulk material. The lasing wavelength in the visible light regime is tuned by altering the thickness of the vacuum deposited organic semiconductor active material or the DFB grating period. Emitted light from the DFB laser is coupled into polymer strip optical waveguides realized by Deep UV lithography. The waveguides allow optical guidance to a microfluidic channel. Tailored surface functionalization in the microfluidic channel by Dip-Pen Nanolithography (DPN) enables the local excitation of fluorescent markers and thus a detection of selected components in biomedical or environmentally relevant fluids.

Holographic polymer dispersed liquid crystal (HPDLC) based distributed feedback (DFB) lasers were prepared with poly (-methoxy-5-(2′-ethyl-hexyloxy)-1,4-phenylene-vinylene) (MEH-PPV) film as the active medium layer. The HPDLC grating film was fabricated via holographic induced photopolymerization. The pure film spectra of MEH-PPV and the amplified spontaneous emission (ASE) spectrum were investigated. The laser device was single-longitudinal mode operation. The tunability of the HPDLC DFB laser was achieved by selecting different grating periods. The lasing performances were also characterized and compared from different diffraction orders. The lasing threshold increased with the diffraction order and the third order laser possessed the largest conversion efficiency in this device. The experimental results were in good agreement with the theoretical calculations.

The implementation of state-of-the-art semiconductor lasers with distributed feedback (DFB), and the optimization of the DFB resonator for specific operating characteristics, require, in many cases, a grating with carefully tailored, slowly varying parameters along the cavity axis. A change in the corrugation pitch and incorporation of discrete phase shifts along the cavity may be implemented by E-beam lithographic methods, and by changes in the geometrical parameters of the laser waveguide. A change in the coupling strength, |/spl kappa/|, is more difficult to realize. Recently, a novel method for fabricating a DFB laser with two discrete values of |/spl kappa/| in different sections of the laser cavity, was demonstrated, but the extension of this method to arbitrary variations in |/spl kappa/| along the laser is not straightforward. Selective organometallic vapor phase epitaxy (OMVPE) on masked substrates is an attractive option for epitaxial layer deposition with controllable thickness variations. Both the growth rate and the composition of ternary or quaternary layers are determined by the mask geometry. In this work, a novel method for the formation of DFB gratings is demonstrated, relying on selective OMVPE growth. The method does not require semiconductor etching, and furthermore it allows for a controlled variation of |/spl kappa/| along the laser cavity. >

We demonstrate surface-emitting distributed-feedback (DFB) quantum cascade (QC) lasers - operating in the midinfrared - with double-slit 2nd order DFB gratings which are implemented via the sole patterning of the top metallic layer, directly at the top of the active region. The small-slit design allows one to reduce the high plasmonic losses which would be induced by a standard 2nd order grating. The devices operate at room temperature, in pulsed mode, and exhibit single mode emission at 7.2 μm wavelength. The device far-field consists of an almost single-lobed emission with a low divergence (<1 degree) in the grating direction. This result shows that sub-wavelength patterning of the top metallization layer of mid-infrared surface-plasmon QC lasers allows one to reduce the losses even for higher-order DFB grating devices.

We report high slope efficiency and low noise characteristics in a distributed feedback (DFB) laser lasing at 1.3 /spl mu/m with narrow beam divergence by employment of a laterally tapered active stripe over the whole cavity. This tapered structure is designed to realize narrow beam divergence, low threshold current, and high longitudinal mode selectivity. The fabricated tapered-active-stripe DFB lasers demonstrated of 9.20/spl times/13.40 and a record slope efficiency, for a narrow beam DFB laser, of 0.59 mW/mA. The temperature characteristics from -10/spl deg/C to 85/spl deg/C shows high output power at high temperature, stable single longitudinal mode oscillation and stable far-field patterns. Furthermore, for the first time ever, a low relative intensity noise characteristic of under -155 dB/Hz has been realized when butt-coupling into a single-mode fiber.

Single longitudinal mode (SLM) lasers are important tools for many scientific and commercial applications. SLM operation can be achieved in distributed-feedback (DFB) lasers based on Bragg structures. Semiconductor waveguide DFB lasers are well-established devices, but their output power is limited to a few hundred milliwatts. DFB lasers have also been demonstrated in dielectric waveguides. However, in this case the output power was even lower. Here we present the first monolithic Yb:YAG DFB laser. The waveguide and the DFB structure were fabricated in the volume of an Yb:YAG crystal by ultrafast laser inscription. The DFB laser delivered 2W of output power at a slope efficiency of 61% in SLM operation under pumping with an optically pumped semiconductor laser. This power level outperforms previously demonstrated dielectric DFB waveguide lasers by nearly an order of magnitude. Our approach paves the way for compact, robust, and highly efficient high-power SLM laser sources.

We propose and report a 193 nm narrow-linewidth light generation by a frequency mixing of Yb and Er-fiber lasers as the seed for an ArF excimer laser. The Yb-fiber laser includes a pulsed distributed feedback (DFB) or external cavity diode laser (ECDL), acousto-optic modulator(AOM), fiber amplifiers and an Yb:YAG single crystal fiber (SCF) power amplifier with more than 7 W output. The Er-fiber laser consists of a continuous-wave (CW) DFB laser, a semiconductor optical amplifier (SOA), and fiber amplifiers. The second harmonic generation (SHG) and the fourth harmonic generation (FHG) of Yb laser at 515 nm and 258 nm reach 5 W and 1.5 W, respectively. Two stages of sum-frequency generation (SFG) produce the power of 100 mW for 193 nm laser by use of CLBO crystals.

We report on the fabrication and the characterization of a large-area, low-cost, flexible conjugated polymer planar distributed feedback (DFB) laser and present a detailed investigation of its underlying photophysics. We show a scheme of our device and illustrates the second-order distributed feedback mechanism. A thin film of a ladder-type poly(p-phenylene) was deposited on top of a poly(ethylene terephtalate) substrate.