Conventional Laser Diodes Research Articles

Analysis of keratinocytes Proliferation During Repair of Surgical Incisions Performed by Conventional Scapel, Electro Cautery, CO2 and Diode Laser

Analysis of keratinocytes Proliferation During Repair of Surgical Incisions Performed by Conventional Scapel, Electro Cautery, CO2 and Diode Laser

Lateral power-monitoring photodiode monolithically integrated into 1.3 μm GaInAsP laser

This study describes a method to produce a novel Lateral-side Power-Monitoring Photodiode (Lateral PMD) and a ridge stripe waveguide Laser Diode (LD) integrated into a monolithic structure using conventional laser process technology. Compared with the LDs of traditional monolithically integrated Rear-side Power-Monitoring Photodiodes (Rear PMDs), the cleaved facets in the new structural LDs remain undamaged, and therefore have a lower threshold current (28 mA) and red-shift rate (0.31 nm/°C) and higher slope efficiency (11.93%). In addition, the characteristics are close to those of a conventional LD. Furthermore, under −0.2 V, the Lateral PMD still provides high linear monitoring capabilities for an LD with a light output power of 8.33 mW. Even after long periods of operation, the variations in LD output power and Lateral PMD photocurrent both fall within a range of 1%. This indicates that a monolithically integrated Lateral PMD is extremely reliable.

Diode-Pumped Organic Semiconductor Microcone Laser

We report laser action from conical polymeric microcavities. A thin film of the organic semiconductor tris(8-hydroxyquinoline) aluminum (Alq3) doped with the laser dye 4-dicyanmethylene-2-methyl-6-(p-dimethylaminostyryl)-4H-pyran (DCM) on top of the microcones enables low-threshold lasing when pumped with a conventional blu-ray laser diode. This combination might pave the way towards compact, low-cost integrated laser-based sensing systems.

Combless broadband terahertz generation with conventional laser diodes

We present a novel technique to generate a continuous, combless broadband Terahertz spectrum with conventional low-cost laser diodes. A standard time-domain spectroscopy system using photoconductive antennas is pumped by the output of two tunable diode lasers. Using fine tuning for one laser and fine and coarse tuning for the second laser, difference frequency generation results in a continuous broadband THz spectrum. Fast coarse-tuning is achieved by a simple spatial light modulator introduced in an external cavity. The results are compared to multi-mode operation for THz generation.

Simple form of multimode laser diode rate equations incorporating the band filling effect

To derive a simple form of the multimode laser diode rate equations incorporating the band filling effect, the laser diode gain in the direct bandgap model is introduced into the conventional multimode laser diode rate equations. By numerically examining each modal gain under the gain-switching condition, it is found that both the differential gain coefficient and the carrier density at transparency show an approximately linear dependency on the oscillation frequency. As a result, it is possible to derive a simple form of the multimode laser diode rate equations with linearized gain, which can be used to simulate the behaviors of a gain-switched laser diode characterized by the band filling effect, in both the multimode and single-mode oscillation cases.

Large spot transpupillary thermotherapy: A quicker laser for treatment of high risk prethreshold retinopathy of prematurity - A randomized study

To compare structural and functional outcome and time efficiency between standard spot sized conventional pulsed mode diode laser and continuous mode large spot transpupillary thermotherapy (LS TTT) for treatment of high risk prethreshold retinopathy of prematurity (ROP). Ten eyes of five preterm babies having bilateral symmetrical high risk prethreshold ROP were included in this study. One eye of each baby was randomized to get either standard spot sized conventional pulsed mode diode laser or continuous mode LS TTT. There was no significant difference between structural or functional outcome in either group. The mean time taken for conventional diode laser was 20.07 minutes, while that for LS TTT was 12.3 minutes. LS TTT was 40% more time efficient than the conventional laser. It may be better suited for the very small fragile premature infants as it is quicker than the conventional laser.

Oxygen mediated and wavelength tunable cationic photopolymerization reactions under air and low intensity: A new concept

A new concept which allows efficient cationic photopolymerization reactions under air, at any excitation wavelength in the UV–visible range and under low light intensities (conventional Xe lamp and/or laser diodes) is presented. It is based on the use of a versatile free radical promoted cationic process for the photoinitiation step which only requires a radical source, a silane and an usual iodonium salt and takes advantage of the presence of oxygen. The tunable character of the absorption is connected with the choice of the radical source. The oxygen enhancement is due to the particular role played by the silane. In every case, the silylium cation is the most efficient structure for the cationic ring opening reaction. Examples of the performance achieved (e.g. a conversion close to 100%) with such systems over the 390–580nm range using various irradiation devices is shown and discussed.

Functional outcome of subthreshold versus threshold diode laser photocoagulation in diabetic macular oedema

To compare the efficacy of subthreshold diode laser photocoagulation with conventional threshold diode laser in clinically significant macular oedema (CSME) in diabetics. Prospective randomised controlled trial. Thirty eyes of 20 patients with CSME having central macular thickness (CMT) >or=250 microm on optical coherence tomography (OCT) and best corrected Snellen visual acuity (BCVA) of 20/80 or better were randomly assigned to receive subthreshold diode laser (group A) or threshold laser (group B). The clinical course of BCVA, CMT on OCT, photo stress recovery time (PSRT), contrast sensitivity (CS) using Pelli Robson chart, and central visual field (10-2 VF, Humphrey Field Analyser II) were monitored regularly for 18 weeks after intervention. Both groups showed significant (P=0.03) and comparable improvement in mean BCVA at 18 weeks visit. There were also significant and comparable reductions (P<0.01) in mean CMT at all visits compared with baseline in both groups. PSRT and CS (75+/-16 (mean+/-SD) and 0.72+/-0.3 in group A and 81+/-12 and 0.68+/-0.2 in group B pre-laser) were significantly better in group A at the final visit (66+/-17 and 1.04+/-0.3) as compared to group B (78+/-11 and 0.73+/-0.3). One patient in group B showed a paracentral scotoma on 10-2 VF after the laser, which persisted till the end of follow-up. Subthreshold diode laser photocoagulation is as effective as conventional threshold laser in reducing or eliminating diabetic macular oedema (on OCT) and in improving BCVA. Recovery of macular function as assessed by CS and PSRT maybe better with subthreshold laser.

Characterizing a Quantum Cascade Tunable Infrared Laser Differential Absorption Spectrometer (QC-TILDAS) for measurements of atmospheric ammonia

Abstract. A compact, fast-response Quantum Cascade Tunable Infrared Laser Differential Absorption Spectrometer (QC-TILDAS) for measurements of ammonia (NH3) has been evaluated under both laboratory and field conditions. Absorption of radiation from a pulsed, thermoelectrically cooled QC laser occurs at reduced pressure in a 0.5 L multiple pass absorption cell with an effective path length of 76 m. Detection is achieved using a thermoelectrically-cooled Mercury Cadmium Telluride (HgCdTe) infrared detector. A novel sampling inlet was used, consisting of a short, heated, quartz tube with a hydrophobic coating to minimize the adsorption of NH3 to surfaces. The inlet contains a critical orifice that reduces the pressure, a virtual impactor for separation of particles, and additional ports for delivering NH3-free background air and calibration gas standards. The level of noise in this instrument has been found to be 0.23 ppb at 1 Hz. The sampling technique has been compared to the results of a conventional lead salt Tunable Diode Laser Absorption Spectrometer (TDLAS) during a laboratory intercomparison. The effect of humidity and heat on the surface interaction of NH3 with sample tubing was investigated at mixing ratios ranging from 30–1000 ppb. Humidity was seen to worsen the NH3 time response and considerable improvement was observed when using a heated sampling line. A field intercomparison of the QC-TILDAS with a modified Thermo 42CTL chemiluminescence-based analyzer was also performed at Environment Canada's Centre for Atmospheric Research Experiments (CARE) in the rural town of Egbert, ON between May–July 2008. Background tests and calibrations using two different permeation tube sources and an NH3 gas cylinder were regularly carried out throughout the study. Results indicate a very good correlation at 1 min time resolution (R2 = 0.93) between the two instruments at the beginning of the study, when regular background subtraction was applied to the QC-TILDAS. An overall good correlation of R2 = 0.85 was obtained over the entire two month data set, where the majority of the spread can be attributed to differences in inlet design and background subtraction methods.

1.3 μm Strain-Compensated InGaAsP Planar Buried Heterostructure Laser Diodes with a TO-Can Package for Optical Fiber Communications

In this paper, we report on the realization of the 1.3 μm strain-compensated InGaAsP buried heterostructure (BH) laser diodes (LDs) by using an Fe-doped semi-insulating InP layer. The performances of LDs are characterized by light output power, internal quantum efficiency, modal gain, characteristic temperature , and dynamic response. As a result of the good confinement of the injection carriers within the strained-compensated multiple quantum well (SC-MQW) and the better heat sink for thermal dissipation, the BH LDs exhibit a threshold current of 9 mA, a slope efficiency of 0.296 mW/mA, and a maximum light output power of 11.8 mW/facet at 76 mA. Besides, the transparent current density and modal gain are estimated as and , respectively, for the fabricated LDs. Otherwise, the BH LD with a facet coating is beneficial to get a lower threshold current, a higher light output power, and an improved value as compared to the conventional ridge-waveguide LD. Furthermore, this transistor outlook (TO)-packaged BH LD for small-signal analyses does not show any parasitic effects at low frequencies and has a maximum modulation frequency of 9.6 GHz at 80 mA. Finally, the BH LD also exhibits the promising potential for high speed data transmission as evaluated from the 10 Gb/s eye-opening feature. These results imply that the 1.3 μm TO-packaged SC-MQW InGaAsP LDs are excellent candidates for use in high speed optical fiber communications.

Analysis of hybrid mode-locking of two-section quantum dot lasers operating at 15 μm

For the first time a detailed study of hybrid mode-locking in two-section InAs/InP quantum dot Fabry-Pérot-type lasers is presented. The output pulses have a typical upchirp of approximately 8 ps/nm, leading to very elongated pulses. The mechanism leading to this typical pulse shape and the phase noise is investigated by detailed radio-frequency and optical spectral studies as well as time-domain studies. The pulse shaping mechanism in these lasers is found to be fundamentally different than the mechanism observed in conventional mode-locked laser diodes, based on quantum well gain or bulk material.

Diode laser spectrally fixed at an atomic absorption line

A simple all-optical technique for fixing the spectrum of the output from semiconductor laser at a chosen absorption atomic line is realized and studied. The technique, which is not of a laser locking type, uses a conventional diode laser without any influence on its operation. For implementation of the technique, the diode laser output is fed to a modified Michelson interferometer, and controllable disturbing of phase and amplitude correlation between the interfering beams in the two arms of the interferometer is achieved by frequency scanning through a contour of a reference absorption line of a substance introduced in one of the arms of the interferometer. It is shown both by experiment and theory that, under properly chosen conditions, the spectrum of the obtained light is fixed at the atomic line and has a linewidth comparable to the linewidth of the used absorption line.

InGaN-Based Blue-Violet Laser Diodes Using AlN as the Electrical Insulator

We report on a method for using aluminium nitride (AlN) as the electrical insulator in ridge waveguide blue-violet laser diodes (LDs). The AlN layer is deposited by molecular beam epitaxy, with good sidewall conformality. The slope efficiency (0.66 W/A for uncoated facets) and leakage current (100 pA) of 1.9×700 µm2 devices fabricated using this method are as good as those of conventional LDs with SiO2 insulator. The threshold current is 57 mA compared to 53 mA for SiO2 LDs, accounted for by the higher refractive index of AlN. Self-consistent LD simulations show that a reduction in junction temperature compared to conventional SiO2 LDs is achievable.

Highly External Optical Feedback-Tolerant 1.49-$\mu$ m Single-Mode Lasers With Partially Corrugated Gratings

An InGaAsP single-mode laser diode (LD) highly tolerant to optical feedback was realized utilizing a partially corrugated grating with a window-mirror structure. The length and the coupling coefficient of the grating were properly chosen to enable moderate output power, low feedback sensitivity, and a side mode suppression ratio of 40 dB simultaneously. Under -16 dB external optical feedback, the relative intensity noise (RIN) was improved by 10 dB compared with that of a conventional DFB LD. The RIN was maintained at less than -120 dB/Hz under strong external optical feedback as high as -10 dB. These results show that the fabricated lasers are potentially useful for isolator-free optical modules.

High-power AlInGaN-based violet laser diodes with InGaN optical confinement layers

InGaN optical confinement layers (OCLs) were introduced into blue-violet AlInGaN-based laser diodes (LDs), resulting in the drastic improvements of lasing performance. Comparing with conventional LD structure, the lowest threshold current density of 2.3kA∕cm2 has been achieved by adding 100-nm-thick InGaN OCLs which represented maximum optical confinement factor. Additionally, we observed the high quantum efficiency and the uniform emission intensity distribution of InGaN quantum wells grown on lower InGaN OCL than on typical GaN layer. Upper InGaN OCL can reduce Mg diffusion from p-type layers to InGaN active region by separating the distance between InGaN quantum wells and p-type layers.

Time-Domain Analysis of Tunability and Modulation Characteristics in Coupled-Ring Reflector Laser Diode

The characteristics of a widely tunable coupled-ring reflector laser diode are studied using a time-domain modeling approach. The coupled-ring reflector is a planar waveguide reflector which does not require distributed Bragg gratings. Instead, the coupled-ring reflector consists of a bus waveguide and two coupled ring resonators coupled to the bus. It is shown that the tuning range can be a few tens of nanometers with a side mode suppression ratio exceeding 35 dB through the adjustment of currents into the phase control sections in the rings. The coupled-ring reflector laser diode has a long effective cavity compared with conventional laser diodes. Accordingly, a broad additional resonance peak in the amplitude modulation characteristics is observed between 20 to 30 GHz, implying the extension of amplitude modulation bandwidth.

First Direct Observation of Small Linewidth Enhancement Factor of Fabry–Perot Quantum Cascade Laser

We investigated the linewidth enhancement factor α of a Fabry–Perot quantum cascade laser by self-mixing interferometry. For the first time, the theoretically predicted characteristic waveform resulting from a small α of about -0.3 could be obtained when the optical feedback parameter was greater than one. The shape of this waveform was totally different from that of a conventional distributed-feedback laser diode with a large α. We demonstrated that subband nonparabolicity is one of the reasons why quantum cascade lasers have a small, but non-zero, α value.

Quantum Dashes on InP Substrate for Broadband Emitter Applications

We report on the development of InAs/InGaAlAs quantum-dash-in-well structure on InP substrate for wideband emitter applications. A spectral width as broad as 58 meV observed from both photoluminescence and surface photovoltage spectroscopy on the sample indicating the formation of highly inhomogeneous InAs-dash structure that results from the quasi-continuous interband transition. The two-section superluminescent diodes (SLDs), with integrated photon absorber slab as lasing suppression section, fabricated on the InAs dash-in-well structure exhibits the close-to-Gaussian emission with a bandwidth (full-width at half-maximum) of up to 140 nm at ~ 1.6 mum peak wavelength. The SLD produces a low spectrum ripple of 0.3 dB and an integrated power of ~ 2 mW measured at 20degC under 8 kA/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> . The oxide stripe laser exhibits wide lasing wavelength coverage of up to 76 nm at ~ 1.64 mum center wavelength and an output optical power of ~ 400 mW from simultaneous multiple confined states lasing at room temperature. This rule changing broadband lasing signature, different from the conventional interband diode laser, is achieved from the quasi-continuous interband transition formed by the inhomogeneous quantum-dash nanostructure.

The art of illumination

Optical frequency 'combs' are light sources that emit at discrete, equally spaced frequencies, so the spectrum has a characteristic comb-like appearance. Frequency combs have revolutionized the fields of spectroscopy and metrology: clocks using the technology now beat atomic clocks, such as the current caesium standard, for accuracy. But the instrumentation required to generate a frequency comb is cumbersome and complex, usually involving a bulky femtosecond laser. Del'Haye et al. have now developed a radically different approach to comb generation: a tiny disc-like resonator structure on a silicon chip is simply illuminated by a conventional laser diode. The resulting interaction between the laser light and the resonator gives rise to an optical frequency comb emitting in the infrared. The simplicity of the scheme — and the prospects of a reduction in size, cost and power — should enhance the utility of optical frequency combs in a broad number of fields.

Ultrabroad stimulated emission from quantum-dash laser

The authors demonstrate the generation of ultrabroadband stimulated emission in the quasi-zero-dimensional InAs∕InAlGaAs quantum-dash laser grown on InP substrate. The laser exhibits lasing wavelength coverage of up to 76nm at ∼1.64μm from simultaneous multiple confined states lasing at room temperature. Unlike the conventional interband diode laser, the rule changing broadband lasing signature is achieved from the quasicontinuous interband transition formed by the inhomogeneous quantum-dash nanostructure.