Channeled-substrate-planar structure distributed-feedback semiconductor lasers

Tapered lasers are extensively employed in high power single-mode lasing, yet still suffering from the potential formation of higher-order transverse modes in the tapered region, which severely degrades the laser beam quality. Herein, we propose a novel supersymmetric segmented tapered laser to achieve stable fundamental transverse mode operation. Our design features a three-segmented tapered waveguide along the light propagation direction, with sub-waveguides of varying widths flanking each main waveguide segment. The main waveguides measure 8 μm, 12 μm, and 16 μm in width. Specifically, the 8 μm main waveguide has a corresponding subsidiary waveguide of 2.67 μm; the 12 μm main waveguide has two subsidiary waveguides measuring 4.82 μm and 6.63 μm; and the 16 μm main waveguide has two subsidiary waveguides measuring 7.13 μm and 3.68 μm. Based on coupled-mode theory, we systematically analyzed the coupling coefficients under different inter-waveguide spacings, leading to an optimized spacing of 1.2 μm through comprehensive theoretical simulations and fabrication compatibility constraints. Furthermore, phase-shifted gratings were integrated between tapered waveguide segments to enable precise longitudinal mode selection. This synergistic design could successfully realize robust single-mode operation, offering a scalable framework for on-chip integrated high-power, high-beam-quality tapered lasers.

Previous works on photorefractive self-organizing laser cavities were about lasers that oscillate, prior the self-organization process occurs, on a set of axial modes sharing the same transverse structure. We have now demonstrated that the insertion of a photorefractive crystal can also create a dynamic spatial filter. In a well-designed extended cavity broad-area laser diode, such a filter can affect the transverse modal structure to force a laser, initially oscillating on several transverse modes, to oscillate on a single transverse and longitudinal mode. A large increase of the single-mode operating range of the laser has been observed.

A longitudinally laser diode (LD)-pumped Nd:YAP microchip master oscillator power amplifier (MOPA) system operating at 1.08 μm was demonstrated. The system consisted of a longitudinally LD-pumped monolithic Nd:YAP microchip master laser and a two-stage disc amplifier. The cavity length of the master oscillator was 500 μm. The short cavity length lead to a large frequency separation between the resonator modes and hence single longitudinal mode operation was achieved. Pumped by a high-brightness LD an output power of 155 mW in both single longitudinal and transverse mode was generated. To scale to a high power, the output power from the master oscillator was amplified by amplifier discs. The amplified output power was 1.43 W. The central wavelength of the laser system was tuned by changing the cavity length and refractive index via temperature. Using a shorter master oscillator (L = 310 μm) a continuous output wavelength tuning over the gain profile of 0.9 nm was realized. To our knowledge this is the first study of a MOPA system based on an LD-pumped microchip Nd:YAP laser.

We demonstrate an electrically pumped, single-mode, large area, edge-emitting InGaAsP/InP two-dimensional photonic crystal (PC) Bragg laser with triangular lattice. The laser operates in the single transverse and longitudinal modes with a single lobe, near-diffraction-limited far field. We compare the performance of the triangular-lattice PC Bragg laser with the rectangular-lattice PC Bragg laser fabricated from the same wafer and find that their performances are comparable. Then, we combine two single triangular-lattice PC Bragg lasers that tilt to opposite directions by taking advantage of the symmetry of the single emitter cavity mode. The measurement results show that the combined PC Bragg lasers provide the near-diffraction-limited output beam, and the single wavelength operation is also maintained in the coherently combined broad-area PC Bragg lasers.

A GaAs-Al <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</inf> Ga <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1-x</inf> As strip buried heterostructure laser with distributed feedback Bragg reflectors is described. In this structure, the active strip is present in the form of an isolated segment completely buried in wide band gap Al <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</inf> Ga <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1-x</inf> As. The diode is shown to operate stably in single transverse (fundamental) and longitudinal modes when the Fabry-Perot modes are suppressed by saw cutting the mirrors.

Single-mode optical fiber communication systems demand lasers to operate in a single longitudinal and fundamental transverse mode. Therefore, various single-mode lasers have recently been studied and fabricated(1), and the stable single-mode operation for a laser under high speed modulation has been realized by means of optical injection locking(2). This paper describes a twin-mesa GaAs-(AlGa)As laser integrated with a passive waveguide, which can be controllablly ocsillated in a single longitudinal and fundamental transverse mode with a Δλ of about 1-1.6 Å.

Single stripe GaAs/AlGaAs, 4 μm wide real refractive index guided lasers are operated at powers up to 500 mW CW with total conversion efficiencies of 60%. Reliability studies of these lasers indicate an average lifetime of greater than 20000 h at 5°C at an operating power of 100 mW CW. The laser operates in a single transverse and longitudinal mode with a spectral linewidth of less than 6 MHz and a side mode suppression ratio of better than −30dB.

In this paper, we demonstrate a scheme to tailor both longitudinal and transverse modes inside a laser cavity and constitute an eye-safe single longitudinal mode Er:Y3Al5O12 (Er:YAG) vector laser. A q-plate is employed as a spin-orbital conversion element to modulate the transverse mode and obtain cylindrical vector beams. An optical isolator is employed as a non-reciprocal element for the ring cavity to enforce unidirectional operation and achieve single longitudinal oscillation. The characteristics of power, transverse intensity, and polarization spectrum of the output beams are observed. The observed typical single longitudinal mode and highly matched special polarizations prove the successful tailoring of both longitudinal and transverse modes.

The development of fiber optic interferometric sensor systems has created new demands for single mode semiconductor diode lasers with low output noise power. Recently, several single longitudinal and transverse mode GaAlAs laser diodes have become available. Several experimenters have reported the deleterious effects of optical feedback resulting from fiber optic coupling on the laser's mode structure and high frequency noise spectrum.1-3 Our interest for interferometric sensors is in the low frequency noise, up to a few kilohertz. We report here the first such low frequency noise measurements in fiber coupled and uncoupled single mode diode lasers. Additionally, we also show that the use of index matching fluid can be used to greatly reduce optical feedback and its associated low frequency noise, upon coupling into an optical fiber.

We describe an undergraduate laboratory that combines an accurate measurement of the speed of light, a fundamental investigation of a basic laser system, and a nontrivial use of statistical analysis. Students grapple with the existence of longitudinal modes in a laser cavity as they change the cavity length of an adjustable-cavity HeNe laser and tune the cavity to produce lasing in the TEM00 mode. For appropriate laser cavity lengths, the laser gain curve of a HeNe laser allows the simultaneous operation of multiple longitudinal modes. The difference frequency between the modes is measured using a self-heterodyne detection with a diode photodetector and a radio frequency spectrum analyzer. Asymmetric effects due to frequency pushing and frequency pulling, as well as transverse modes, are minimized by simultaneously monitoring and adjusting the mode structure as viewed with a Fabry–Pérot interferometer. The frequency spacing of longitudinal modes is proportional to the inverse of the cavity length with a proportionality constant equal to half the speed of light. By changing the length of the cavity, without changing the path length within the HeNe gas, the speed of light in air can be measured to be (2.9972±0.0002)×108 m/s, which is to high enough precision to distinguish between the speed of light in air and in vacuum.

Semiconductor lasers with ring cavities are attractive as possible sources for future fibreto-the-home systems that require affordable components. Ring resonator lasers can readily be integrated and do not require gratings or facets for feedback. They can be operated cw [1] in a single transverse and longitudinal mode [2] without the need for accurate gratings or overgrowth and hence offer themselves strongly for low-cost mass-production.

The dynamics of a surface-emitting laser (SEL) with cw optical injection are studied. The molecular-beam-epitaxy grown SEL has an active region consisting of 0.72-μm bulk GaAs and two high-reflectivity mirrors with 22 and 27 periods of 62.5-nm AlGaAs (x = 0.143)/73.3-nm AlAs, respectively. Lasing occurs in a single longitudinal and transverse mode at 886 nm when pumped by an 830-nm edge-emitting diode laser. A tunable dye laser generates the injection signal. At a detuning of 3 GHz, the lasing frequency is pulled toward the injection until complete locking is achieved at an injection level of 5 μW. Asymmetric relaxation-oscillation side-bands spaced about 6 GHz from the injection frequency are observed at higher injection powers, the low-frequency band being stronger. When the injected power is increased further to 0.2 mW, a new lower-frequency sideband appears and is pushed away by as much as 30 GHz as the injection power is increased to 5 mW. Preliminary calculations show that the observed complex phenomena can only be understood by including both the gain saturation and nonlinear index change in the theoretical modelling.

Measurements were made of the resolution of holograms formed with a Q-switched ruby laser operating in a single longitudinal and transverse mode. Diffraction limited, 4 μ detail was observed in the reconstructed real image as viewed in CW He–Ne illumination.

GaInAsP/InP terraced substrate (TS) lasers (λ=1.3 µm) have been fabricated and stabilized single transverse mode operation has been demonstrated. The wafers were prepared by a single-step LPE growth on (100) n-InP terraced substrates which was terraced along <011> orientation. Pulsed threshold current was less than 50 mA at room temperature. Single transverse and longitudinal mode operation was obtained up to 2.8 times the threshold. Cw operation was also achieved at room temperatures.

Laser shock induced lateral compression has been demonstrated to controllably flatten cylindrical silver nanowires. Nanowires with circular cross-sections of diameter 70 nm are significantly shaped laterally, which transformed them to metallic ribbons of huge width of 290 nm and of thickness down to 13 nm, amounting the aspect ratio to as high as 22, at a laser intensity of 0.30 GW cm(-2). Above the laser intensity of 0.30 GW cm(-2) though, nanowires are observed to be ruptured. Lateral deformations of nanowires are achieved without altering longitudinal dimensions. Selected area electron diffraction patterns on the laterally deformed nanowires reveal that the flattening gives rise to twinning under high strain rate deformation without actually degrading crystallinity. As the 1D nanowire turns into a 2D metallic nanoribbon, new plasmonic modes and their combinations emerge. The transverse plasmon mode does not shift substantially, whereas longitudinal modes and their combinations are greatly influenced by lateral deformation. Apart from the transverse mode, which is dominant in a 1D nanowire and diminishes heavily when lateral deformation occurs, there is a presence of several longitudinal plasmonic modes and their combinations for metallic nanoribbons, which are revealed by experimental extinction spectra and also supported by finite-difference time-domain (FDTD) simulation. Such plasmonic tuning of silver nanowires across the visible range demonstrates the capability of a laser shock induced lateral compression technique for various emerging plasmonic applications. The laser shock compression technique has the advantages of flexibility, selectivity and tunability while retaining crystallinity of metallic nanowires, all of which enable it to be a potential candidate for plasmonic tuning of nanogeometries.