Organic holographic polymer dispersed liquid crystal distributed feedback laser from different diffraction orders

Performances of organic distributed feedback (DFB) lasers made from holographic polymer dispersed liquid crystal (HPDLC) transmission gratings were greatly improved by replacing common laser dye with organic semiconductor poly(2-methoxy-5-(2′-ethyl-hexyloxy)-p-phenylenevinylene) (MEH-PPV) as the gain medium. The MEH-PPV layer was laminated between the glass substrate and the HPDLC grating layer. Light interaction for feedback is provided by an evanescent wave spread into the grating layer. The device showed single-mode, TE polarized laser emission with a threshold of only 0.17 μJ per pulse (17 μJ cm−2). Slope efficiencies as high as 4.7% and 6.5% were measured for optical pumping of the device with P polarization and S polarization, respectively. Lasing was also coupled by the grating out of the waveguide and into free space. Furthermore, the output laser wavelength was systematically tuned over a range of 43 nm by varying the grating period. The laser thresholds at different wavelengths trace well with the amplified spontaneous emission spectrum of the MEH-PPV film. In terms of the HPDLC technique, our results show there is still plenty of potential to be exploited for fabricating organic DFB lasers.

A tunable surface-emitting dual-wavelength laser emitted from the blended organic gain layer based on a holographic polymer dispersed liquid crystal (HPDLC) transmission grating feedback structure was reported. The organic blended gain layer was formed from Poly (2-methoxy-5-(2’-ethyl-hexyloxy)-p-phenylenevinylene) (MEH-PPV) and Poly (2-methoxy-5-(3′, 7’-dimethyloctyloxy)-1, 4-phenylenevinylene) (MDMO-PPV) with a weight ratio of 2:1. The dual-wavelength laser located at 629.9 nm and 640 nm was obtained in a single beam. The optical characteristics of these two organic semiconducting materials and the dual-wavelength laser performance under an electric field are investigated and illustrated. This simple tunable dual-wavelength laser shows the potential to extend the development of organic lasers.

In this paper, we reported a method to fabricate 2D hexagonal lattice Holographic Polymer-dispersed Liquid Crystal (HPDLC) grating with variable period by using cylindrical waves interfere with plane waves. In order to separate polymer from liquid crystal syrup, a 532nm laser with an exposure intensity of 16mw/cm2 was used to expose. Two steps exposure techniques was adopted in the experiment with the expose time of 2s and 60s in the separate steps to form the 2D gratings. In the second exposure step, the sample was rotated by anti-clockwise 60° to form 2D hexagonal lattice structure within H-PDLC grating. The theoretical equations for describing the variable period grating is analyzed. What’s more, the diffraction efficiency and other characteristics of this grating is also studied experimentally. The experimental result shows that fabricated grating with the continuously changing periods varying from 1.679 micrometer to 2.051 micrometer within the radius of 6 mm circle sample area, which is corresponded to the theoretical simulation quite well. The first-order diffraction efficiency was tested around18.3%. The intensity of transmission beam increased from 15.6% to 73% when applied with the driving voltage from zero to the maximum of 90 V. This 2D grating has the potential application in diffractive optics such as a tunable multi-wavelength organic laser device etc.

Measurement of the spontaneous emission and gain spectra provides a complete characterization of a semiconductor gain medium, however, this requires the observation of emission in two directions to avoid amplification of the spontaneous emission spectrum. We show that both the gain spectrum and the true spontaneous emission spectrum can be obtained from amplified spontaneous emission (ASE) spectra measured from the end of a segmented-contact device. The spontaneous emission spectra agree with spectra measured through a top contact window. If the carrier populations are fully inverted at low photon energy, it is possible to convert the ASE-derived spontaneous emission into real units.

Continuously tunable organic solid-state laser based on the adjustment of effective refractive index

Tunable distributed feedback lasing with low threshold and high slope efficiency from electroluminescent conjugated polymer waveguide

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.

Semiconducting conjugated polymers have recently attracted significant interest as amplifying media for solid-state lasers due to their functional photo-physical properties and simple fabrication. Distributed feedback (DFB) cavities are proving to be the most attractive for polymer lasers, since they can combine the properties of transverse optical pumping, low threshold and practical output beams. To date, in most polymer DFB lasers the feedback is provided by second order diffraction. This has the advantage of surface emission, though it also imposes extensive scattering losses. In this work, we present the use of alternative structures that attempt to reduce the threshold of polymer DFB lasers, and also achieve dual wavelength operation. The former was addressed with cavities formed by alternative symmetries of the Brillouin zone of a square lattice. Using the diagonal ΓM symmetry first order feedback was attained. The threshold energy was thus reduced by almost an order of magnitude as compared with the more commonly used ΓX symmetry of second order square gratings. Finally, we show that two lasing wavelengths may be set independently in a semiconducting polymer laser by using a doubly periodic (i.e. Moiré) DFB grating.

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.

A novel super-fluorescence fiber source (SFS) in the wavelength range that covers the C+L-band with stable spectrum, high output power and high slope efficiency is demonstrated. The topology consists of two stages: the first stage provides primarily the L-band gain spectrum whilst the second is solely for the C-band. These two stages are combined in series. We merely used the low erbium-doped fiber (EDF) 10.8m long as a gain medium in the second stage, which was pumped backward by a 980nm semiconductor laser diode (LD). As a result, the Amplified Spontaneous Emission (ASE) spectrum had a threshold of 5.1mW and a slope efficiency of 13.48% in the C-band. With a 980 nm LD pumping forward at 11-m-long moderate EDF and 58-m-long low EDF in series, L-band ASE was yielded with 52.3 mW threshold and a slope efficiency of 35.82% in the first stage. The ASE in the L-band was put into the second stage through an isolator and combined with C-band ASE as an output then a broad ASE spectrum of C+L-band was observed. The maximum output power of the C+L-band source was 33mW (15.3dBm) and its power stability was better than ±0.02 dB. Through the optimization of fiber parameters and the adjustment of pumping power in both stages, the flatness of ASE spectrum was improved. The optical bandwidth for the SFS output power, which ripples in 3 dB, was 63.7 nm (1536.92-1600.62 nm) of optical bandwidth without gain flattening filter.

Tunable semiconductor laser has various applications including Wavelength Division Multiplexing (WDM), Frequency Division Multiplexing (FDM), optical switching in Local Area Networks (LAN) and Chemical Sensing, or Spectroscopy. There are different approa ches for tunable semiconductor lasers. Large wavelength tuning range is required for communication applications, such as WDM. Whereas a frequency modulation (FM) requires small but fast frequency shifts. Two-Segmen t laser is one of the methods to realize continuous optical tuning. The device consists of two coupled cav ities having a series of well-defined modes. The modes are equally spaced within a cavity but the mode spacing between the two cavities is slightly different. Characterization results of such lasers are very important. In this paper we will present the characterization results of two segment InGaAs/InP distributed feed back (DFB) tunable lasers. Keywords: DFB Lasers, tunable laser, two segment laser, semiconductor lasers. 1.0 Introduction

In this research, Amplified Spontaneous Emission (ASE) spectrum characteristics for a highly Yb3+ doped glass fiber with different pump powers and pump wavelengths are scrutinized. ASE spectral profile and wavelength shift corresponding to different optical fiber lengths are measured. Highly-doped Yb3+ fiber lasers in a linear-cavity are both experimentally and analytically investigated. Rate equations are solved using quasi-numerical models. Numerical results are reported for wide range of operating conditions to enable design optimization. The model takes into account the scattering loss and the distributed laser loss power density in strongly pump condition. The effects of various parameters such as pump power, pump wavelength, signal wavelength and fiber length on the output power and laser threshold are studied. Theoretical results are shown to be in good agreement with the experimental data.

With built-in periodic corrugations along the direction of propagation, phase-shifted (PS) DFB laser diodes represent an attractive option as light sources since, with a suitable choice of structural combination, single longitudinal mode (SLM) operation may be achieved. With a single π/2 phase-shifted DFB laser, commonly designated as a quarter-wavelength-shifted (QWS) DFB, located at the center of the cavity, the diode is allowed to oscillate at the Bragg wavelength with maximum gain selectivity in the near-threshold regime. However, for higher current values, the spatial hole-burning (SHB) correction foresee a quick degradation of the laser performance. The present work shows that, in those cases, better solutions exist if more complex DFB structures are considered, such as those presenting multiphase discontinuities along the corrugation ©1999 John Wiley & Sons, Inc. Microwave Opt Technol Lett 22: 171–177, 1999.

We report on hard x-ray phase contrast imaging experiments using a grating interferometer of approximately 1/10th the grating period achieved in previous studies. We designed the gratings as a staircase array of multilayer stacks which are fabricated in a single thin film deposition process. We performed the experiments at 19 keV x-ray energy and 0.8 μm pixel resolution. The small grating period resulted in clear separation of different diffraction orders and multiple images on the detector. A slitted beam was used to remove overlap of the images from the different diffraction orders. The phase contrast images showed detailed features as small as 10 μm, and demonstrated the feasibility of high resolution x-ray phase contrast imaging with nanometer scale gratings.

A tunable fiber ring laser based on an in-line two-taper Mach-Zehnder interferometer (MZI) filter was realized, and the effect of beam waists of the tapers on performance of the laser was investigated with different beam waists of 70 μm, 49 μm, and 33 μm. Experimental results show that the tunable laser with MZI length of 1 m and beam waist of 49 μm can cover 16.1 nm with tuning steps of 0.07-0.5 nm, a bandwidth of 10 pm, and a side mode suppression ratio (SMSR) of 40-50 dB. Tuning range is not only determined by the number of the cladding modes but is also affected by the filter loss. Tuning step is determined by the differences of the effective refractive indexes between the cladding modes and the core mode. SMSR is determined by the balance between the extinction ratio of the filter and the cavity loss of the laser due to MZI filter.