Strip buried heterostructure lasers with passive distributed Bragg reflectors

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.

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.

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.

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.

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.

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.

ALADIN TXA is the first in the world All-Solid-State, Compact, Transmitterlaser Assembly for the first in the world Doppler Wind Lidar inside the ESA Aeolus mission. Its optical architecture is that of a MOPA, medium energy, pulsed, frequency tripled, tunable, almost single transverse and single longitudinal mode Nd:YAG lasers with 50 Hz PRF and a three years in-orbit lifetime. A brief resume of the design, together with the qualification approach and the main experimental results obtained with the two flight models are presented. The main technological challenges faced during the program development and the lesson learnt for future space All-Solid-State lasers will complete the paper.

A single-frequency distributed Bragg reflector (DBR) fiber laser at 1030 nm has been demonstrated using a 0.7 cm long homemade Yb:YAG crystal-derived silica fiber (YCDSF). The absorption and emission cross sections of the YCDSF are 4.93 × 10 − 20 cm 2 at 980 nm and 1.1 × 10 − 20 cm 2 at 1030 nm. Using this gain fiber, an over 255 mW continuous-wave lasing in the constructed laser has been obtained at single transverse and longitudinal mode operation. The slope efficiency and the pump threshold of the fiber laser were up to ∼35% and as low as 25 mW, respectively. The fiber laser also demonstrated an optical signal-to-noise ratio of 79 dB and a beam quality factor of 1.016 in two orthogonal directions. Its power fluctuation at 210.5 mW was less than 0.85% of the average power within 13 h. Moreover, the relative intensity noise and linewidth of the laser are also investigated at the different pump powers. The results indicate that the single-frequency DBR fiber laser has potential applications in high-quality seed sources and high-precision optical sensing.

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.

Distributed-feedback Ga1−xAlxAs lasers with a channeled-substrate-planar structure are fabricated. They operate in single transverse and longitudinal modes. No spectral broadening or excess noise is observed under high-frequency modulation as a result of mode stabilization.

A key element in any optical system is the light source and semi-conductor lasers have become the most attractive candidates for many applications due to their small size, low drive voltages and high output powers. However, their linewidths need to be reduced for operation at ever-increasing modulation rates. Monolithic laser designs such as the distributed feedback (DFE) and distributed Bragg reflector (DER) produce line-narrowed outputs by including an internal grating within the laser cavity [1). If the cavity is extended beyond the active semi-conductor chip then this long external cavity arrangement, with a reflector at the end, can produce far greater line-width reductions provided that a mechanism is included for selection of a single longitudinal lasing mode [2). Applications for tunable LEC lasers have increased dramatically in recent years and now extend from local oscillators in coherent detection schemes to testing of optical components such as filters and amplifiers and they might in future also be employed in sophisticated fibre optic sensor systems. Various designs have been proposed for mechanical arrangements which would enable wide-range tuning whilst maintaining a single longitudinal mode [3-5) but, in practice, suffer from backlash, hysteresis and slow operation which make them non—ideal for field operation. In the present work we seek an improved control system which will enable wavelength tuning to be performed with the ease and consistency of the electronic tuning schemes.

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. In a well-designed broad-area laser diode extended cavity, we theoretically and experimentally demonstrate that the insertion of a photorefractive crystal can also affect the transverse modal structure to force the laser, initially oscillating on several transverse modes, to oscillate on a single transverse and axial mode. This spatial self-organization process leads to an enhancement of the single mode operating range of the laser.

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.

We have recently reported optically-pumped lasing in an InGaP/InAlGaP strained quantum well visible vertical cavity surface emitting laser (VCSEL) with both AlAs/AlGaAs distributed Bragg reflectors (DBRs)~ and with InAlPDnAlGaP DBRs2. We have also studied the critical issues for electrical injection in these promising devices and now report the demonstration of the first visible VCSEL diodes. At room temperature with pulsed excitation, the devices lase in a single longitudinal mode within 639.1 nm to 660.7 nm, depending on wafer position. The structures were grown by metalorganic vapor-phase epitaxy (MOVPE) on GaAs substrates and consist of an InAlGaP optical cavity active region surrounded by AlGaAs DBRs. The bottom Si-doped DBR consists of 55.5 periods of alternating AlAs and Al,Gal-,As (x = 0.5) quarter-wave layers with x = 0.75 barrier reduction layers at each interface to reduce series resistance. An identical 36 period C-doped top coupling DBR is used and includes a (p+) GaAs metal contact layer. The InAlGaP optical cavity contains three In0.56Gao.& strained quantum wells in a step graded-barrier separate confinement configuration. Device injection efficiency was optimized by studying the performance of edge-emitting lasers with InAlGaP active regions and AlGaAs DBR cladding layers. Gain-guided etched post test devices were fabricated. A top annulus contact defines emitting diameters of 10 pm and 20 pm with a 5 pm radial thickness, thus, a large percentage of the injected current does not directly contribute to lasing but to device heating. Despite this, lasing wavelengths from 639.1 nm to 660.7 nm were measured, on unrotated wafers, at room temperature without heat-sinking. The pulsed excitation was - 100 ns pulses at 10 kHz to IMHz. Many devices continued lasing with up to a 40% duty cycle at 1MHz. The larger devices typically have a threshold of 30 mA at 2.7 V. The peak output power is 3.38 mW with a resistance of less than 15 0. Substantially improved performance is expected with more sophisticated device processing techniques. This is the first demonstration of InAlGaP visible VCSEL diodes. This work opens the door for advanced device applications such as plastic fiber communications, arrays for displays, interconnects, and holographic memory, and some scanning applications in place of HeNe lasers.

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.