Single-mode Laser Emission Research Articles

Long-Wavelength High-Contrast Grating Vertical-Cavity Surface-Emitting Laser

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> A novel long-wavelength vertical-cavity surface-emitting laser (VCSEL) structure based on a subwavelength high-contrast grating (HCG) as the output mirror has been realized. By design, these devices are highly polarization stable, are single mode at large apertures, and solve the VCSEL-mirror problem at long wavelengths in an elegant way. With cost-effective mass fabrication in mind, the top HCG reflector consists of amorphous silicon on isolator (amorphous silica). The single-mode laser emission is tailored to be around 1320-nm wavelength, targeting applications in high-speed optical data transmission, particularly those for passive optical networks. We report single-mode emission for devices with apertures as large as 11 <formula formulatype="inline"><tex Notation="TeX">$\mu\hbox{m}$</tex> </formula> operating in continuous wave with output powers in excess of 0.4 mW. Pulsed operation with output powers up to 4 mW at room temperature is demonstrated as well. This is the first electrically pumped VCSEL structure realized in this wavelength regime utilizing an HCG mirror. </para>

Miniaturized Optical Microwave Source Using a Dual-Wavelength Whispering Gallery Mode Laser

We report on the observation of a compact optical microwave source based on a whispering gallery mode (WGM) laser. The use of a single 160-?m diameter erbium-doped glass microsphere and two half fiber tapers allows a dual single-mode laser emission around 1550 nm to be obtained. The generated beat note at 10.86 GHz has a linewidth of 22 kHz. This preliminary experimental demonstration shows the potentialities of erbium-doped WGM resonators for microwave generation.

Generation of picosecond blue light pulses at 464 nm by frequency doubling an Nd-doped fiber based Master Oscillator Power Amplifier

We demonstrate 308 mW of single-mode laser emission at 464 nm from a frequency doubled picosecond fiber based Master Oscillator Power Amplifier (MOPA). The laser system consisted of a gain-switched and spectrally narrowed Fabry-Perot laser diode emitting at 928 nm, which was amplified in a two-stage amplifier based on W-type double-clad Nd-doped fibers. Output pulses with a duration of 90 ps at a repetition rate of 41 MHz were frequency-doubled in a periodically poled MgO-doped Congruent Lithium Niobate. A conversion efficiency of 14.8% was achieved in single-pass configuration.

Single mode coupled optofluidic ring resonator dye lasers

The authors demonstrate the single mode dye laser from a coupled optofluidic ring resonator that consists of a cylindrical ring resonator fused onto the inner surface of a thin-walled capillary ring resonator. The whispering gallery modes in each ring resonator interact strongly and utilize the Vernier effect to generate single mode laser emission. The lasing threshold is 3.0 μJ/mm2. The light can be coupled out through an optical taper in contact with the capillary.

Compact 1.55 µm room-temperature optically pumped VCSEL using photonic crystal mirror

Reported is the first realisation of a novel vertical cavity surface emitting laser (VCSEL), in which one of the Bragg mirrors is entirely replaced by a single-layer photonic crystal mirror (PCM). The presence of the PCM considerably enhances the vertical compactness of the device. Room-temperature singlemode laser emission has been obtained at 1.55 µm by optical pumping (pulsed regime), with a threshold power around 15 mW.

Discrete mode laser diodes with very narrow linewidth emission

Ex-facet, free-running low linewidth (~100 kHz), singlemode laser emission is demonstrated using low cost, regrowth-free ridge waveguide discrete mode Fabry-Perot laser diode chips. These narrow linewidths are observed even at emission powers as low as 500 muW.

Tailoring holes for improving the efficiency of single-mode photonic crystal waveguide lasers on InP substrate

The authors show that the use of triangular lattice photonic crystals (PhCs) with wide holes can significantly improve the lasing performances of PhC waveguides in the InP substrate approach. The study is carried out on W2-3 waveguides made in PhCs whose air filling factor is varied from ∼25% to 55%. Intrinsically single-mode laser emissions with reduced threshold (/2) are obtained when the laser mode folds deeply into the gap. Concurrently, the slope of the light-light characteristic is increased by a factor of 14. The laser spectral behavior and threshold evolution are explained from three-dimensional finite difference time domain calculations.

1.5 μ m room-temperature emission of square-lattice photonic-crystal waveguide lasers with a single line defect

Narrow waveguides consisting of a single defect-line (W1) in a square lattice photonic crystal are fabricated on InP using the substrate approach. A single-mode distributed-feedback laser emission is obtained under optical pumping at room temperature. Lasing occurs at the second folding point of the dispersion curve of the fundamental waveguide mode (wave vector k=0). The emitted wavelength ranges from 1420to1580nm for a lattice period varying from 460to520nm and a constant air filling factor of ∼26%. The highly monomode behavior is explained using two-dimensional plane-wave models. Similar experiments conducted on triangular lattice W1 waveguides do not yield a laser emission. Three-dimensional simulations confirm that triangular lattice W1 waveguides suffer higher losses than their square homologues.

High-performance distributed feedback quantum cascade lasers grown by metalorganic vapor phase epitaxy

We report the operation of distributed feedback quantum cascade lasers, grown by metalorganic vapor phase epitaxy. Single-mode laser emission at λ∼10.3μm and λ∼7.8μm is observed from two different samples, with 300 K threshold current densities of Jth∼3 and ∼2.4kAcm−2, respectively. Structural investigation by x-ray diffraction and transmission electron microscopy, and the close correlation between the predicted and observed emission wavelengths indicate exceptional control of the layer thicknesses, including ultrathin (∼8Å) barrier layers in the active region. These results confirm metalorganic vapor phase epitaxy as a viable technology for the growth of high-performance quantum cascade lasers.

Two-dimensional colloid-based photonic crystals for distributed feedback polymer lasers

We report on a process to design highly ordered monolayers of two-dimensional photonic crystals, made of silica nanoparticules, that can be used for the development of organic optical devices. We have used a photopolymerization process to incorporate a dye gain medium into the nanoparticle layers in order to achieve a laser cavity. The high spatial coherence of the deposits allows for single-mode laser emission in the plane of the layer when the light excitation is perpendicular to the plane. Such periodic films should help in reducing the number of layers needed for future electrically pumped distributed feedback lasers.

Continuous wave 2.9 μm dysprosium-doped fluoride fiber laser

Single-mode room-temperature cw laser emission on the H13/26→H15/26 2.9 μm phonon terminated electronic transition of Dy3+ is demonstrated. The maximum output power of 0.275 W was generated at a slope efficiency of 4.5% (with respect to the absorbed pump power) when a Dy3+-doped ZBLAN fiber laser was tandem pumped with the ∼1100 nm output from a diode-cladding-pumped Yb3+-doped silica fiber laser.

Experimental demonstration of oxide-mode influence in a dual-purpose oxide-confined vertical-cavity surface-emitting laser/resonant detector

We report on design, fabrication, and characterization of a vertical-cavity surface-emitting laser (VCSEL) used as a resonant-cavity-enhanced detector for dual-purpose application. The geometry of this oxide-confined VCSEL takes advantage of the properties of the buried oxide layer to allow both single-mode laser emission and detection on a large surface. Here, we demonstrate the presence and the influence of oxide modes in the optical sensitivity spectrum of the device through spatially localized detection measurements. The wavelength of these modes has been correlated to the dip on the reflectivity spectrum measured at the same area of the device surface.

Conjugated polymers: lasing and stimulated emission

The discovery of gain narrowing in electroluminescent conjugated polymers has launched a new field of research aiming towards polymer-based injection lasers. Especially poly( para-phenylene vinylene)- (PPV) and poly( para-phenylene)- (PPP) -type polymers have been applied as active materials. Time-resolved measurements have unravelled the photophysics for low and high excitation levels. If suited resonator configurations of the device are used (e.g. microcavity, microring, microdisc, distributed feedback and distributed Bragg resonators) optically pumped single mode laser emission can be observed for moderate excitation levels. These results represent an important step towards the realisation of future ‘all-plastics’ injection lasers. Conjugated polymer laser devices might lead to novel applications in measurement instrumentation and information technology which rely on large area emitters and geometries not accessible to conventional inorganic laser materials.

Calibration of single-mode content of semiconductor diode laser emission

Spectral radiance of single-mode semiconductor diode laser emission was investigated. The contribution of broadband and sideband emission was determined by absorption measurements at an optically thick absorption line. Essential single-mode operation was controlled by a Fabry–Perot interferometer. Since no additional dispersive elements are used, spatial displacement is avoided, which is essential for spatially resolved spectroscopy.

Zeolite-Dye Microlasers

We present a new class of micro lasers based on nanoporous molecular sieve host-guest systems. Organic dye guest molecules of 1-Ethyl-4-(4-(p-Dimethylaminophenyl)-1,3-butadienyl)-pyridinium Perchlorat were inserted into the 0.73-nm-wide channel pores of a zeolite AlPO$_4$-5 host. The zeolitic micro crystal compounds where hydrothermally synthesized according to a particular host-guest chemical process. The dye molecules are found not only to be aligned along the host channel axis, but to be oriented as well. Single mode laser emission at 687 nm was obtained from a whispering gallery mode oscillating in a 8-$\mu$m-diameter monolithic micro resonator, in which the field is confined by total internal reflection at the natural hexagonal boundaries inside the zeolitic microcrystals.

Single-mode picosecond blue laser emission from a solid conjugated polymer

We demonstrate single-mode laser emission at 490 nm from a stable cavity based on a methyl-substituted poly-(para-phenylene)-type ladder polymer. The laser emission is characterized by a well-defined excitation fluence threshold, a high directionality, and a drastic spectral narrowing. The laser generates picosecond pulses of excellent amplitude stability.

A Flexible Conjugated Polymer Laser

Collective stimulated emission processes in conjugated polymers makes these materials potential candidates for laser applications. The fabrication of a low-cost flexible distributed feedback laser (see Figure and also the cover) by spin-coating a conjugated polymer onto a specially structured, flexible plastic substrate is reported. Single-mode laser emission in the blue-green spectral region has been achieved.

Subband emissions of InGaN multi-quantum-well laser diodes under room-temperature continuous wave operation

The emission spectra of InGaN multi-quantum-well (MQW) laser diodes (LDs) under continuous-wave (CW) operation at room temperature (RT) showed periodic subband emissions with an energy separation of 2 meV. The peak wavelength of the laser emission was measured as a function of the operating current. The peak wavelength showed mode hopping toward higher energy with increasing operating current. Each single-mode laser emission was located at a peak of each periodic subband emission. These periodic subband emissions probably result from the transitions between the subband energy levels of the InGaN quantum dots formed from In-rich regions in the InGaN well layers. High-power InGaN MQW LDs with an output power of 40 mW were performed under RT CW operation.

Polarization state of the emission of external grating diode lasers

The laser emission of transverse electric (TE) and transverse magnetic (TM) polarization, in alternating successive spectral ranges, that can occur when external grating diode lasers are wavelength tuned, is theoretically and experimentally investigated. The modulated threshold gain curves of the external cavity for the two polarizations can be made to intersect with each other if a grating is used in such a way as to practically eliminate the difference between the laser diode losses and confinement factors for TE and TM polarization. The result is a sequence of wavelength ranges where the threshold gain is alternately lower for the TE resp. TM polarization. Within each range, a wavelength tunable single mode laser emission is obtained. The phenomenon is described, taking into account the characteristics of the key components of the external cavity, i.e., laser diode structure, antireflective (AR) coating, and grating efficiency. Design tools are proposed for the characteristics of the components necessary for the development of such an external cavity. The theoretical and design concepts are experimentally confirmed in a number of external cavities, using diode lasers emitting around 1.5 /spl mu/m, with different types of antireflective coatings, as well as different grating configurations. >

Standing waves and single-mode room-temperature laser emission from electron-beam-pumped cadmium sulfide

A thin crystal of CdS produced well-defined standing waves in spontaneous light emission when end-pumped by an electron beam at excitation levels six orders of magnitude below that necessary for stimulated emission. Single-frequency mode output was observed in stimulated emission at 5205 A at room temperature. At 77°K and at excitation levels well above threshold, laser emission was observed to occur continuously over a spectral range of nearly 200 A, from 4960 to 5150 A.