Telecom Laser Research Articles

Diode laser spectroscopy of two acetylene isotopologues ( 12C 2H 2, 13C 12CH 2) in the 1.533 μm region for the PHOBOS-Grunt space mission

Several line intensities of the ν 1 + ν 3 ( ∑ u + ) − 0 ( ∑ g + ) bands of 12C 2H 2 and 13C 12CH 2 at 1.533 μm have been revised at room temperature. These molecular transitions were selected to measure acetylene within the framework of the Martian space mission PHOBOS-Grunt. In the spectral region ranging from 6518 to 6530 cm −1, 10 lines of both isotopologues have been analyzed using a high resolution tunable diode laser spectrometer. These transitions are well appropriate to the monitoring of C 2H 2 by laser absorption spectroscopy with standard telecommunication laser diodes. Both the Voigt and the Rautian models are used to fit the molecular line shape and to provide accurate line strengths. Our data are thoroughly compared to existing database (including HITRAN08) and former experimental measurements.

Reliable 2.3-$\mu$m Wavelength Highly Strained InAs–InP MQW-DFB Lasers With p-/n-InP Buried Heterostructure

We have realized reliable 2.3-mum wavelength InAs-InP multiquantum-well distributed-feedback (DFB) lasers for trace gas monitoring applications. The estimated median lifetime exceeds 1x105 hours during aging at an ambient temperature of 45degC and with a constant output power of 3 mW. Furthermore, the relative increase in operating current is proportional to the square root of time, and it is clarified that the main degradation mechanism in DFB lasers with highly strained InAs quantum wells is dominated by a diffusion process as found with conventional telecommunication lasers.

Gigahertz modulation of tunable terahertz radiation from photomixers driven at telecom wavelengths

Here, we report the gigahertz-rate modulation of a tunable terahertz carrier. Terahertz radiation, tunable from 300 GHz to 1.2 THz, is generated by mixing two telecom lasers with an offset frequency in an ultrafast In0.53Ga0.47As photoconductive device coupled to a broadband antenna. The microwave modulation applied to the telecom lasers is directly transferred to the terahertz carrier. A maximum modulation rate of 20 GHz has been achieved, and the bandwidth is independent of the carrier frequency.

Power adjustable visible supercontinuum generation using amplified nanosecond gains-witched laser diode

Supercontinuum (SC) light with a continuous spectrum covering 0.45-1.2 microm is scaled from 250-740 mW by varying the repetition rate of an amplified, frequency doubled, telecom laser diode. Efficient SC generation requires minimal non-linearity in the amplifier and anomalous dispersion pumping close to the fiber zero dispersion wavelength. Based on simulations, we present a 2-stage design that separates pulse break-up from spectral broadening to enhance the SC bandwidth for quasi-CW pumping.

Wavelength interrogation of grating-based optical biosensors in the input coupler configuration

Abstract A planar optical waveguide with an input grating coupler was used as a label-free biodetection device. Nanoimprint lithography was used to integrate the grating patterns with low loss silicon oxynitride thin film waveguides. A widely tunable laser source at 1550 nm was used to characterize the device sensitivity to bulk medium changes, to thin film adsorption, and to protein binding. For each test, a comparison was performed between the sensitivity of wavelength interrogation and the more standard angular interrogation approach. The results indicate that these devices used in wavelength interrogation with a telecom laser source are perfectly suited to be integrated in compact and sensitive biodetection systems.

Efficient terahertz emission from ballistic transport enhanced n-i-p-n-i-p superlattice photomixers

The authors report on photomixing terahertz sources that overcome the transit time versus RC-time trade-off and allow for independent optimization of both of them, using a n-i-p-n-i-p superlattice. Furthermore, they take advantage of ballistic transport for reduced transit times. Apart from more favorable material parameters, In(Al)GaAs photomixers benefit from the advanced telecommunication laser technology around 1.55μm as compared to GaAs. In such devices, a terahertz-power output of 1μW has been achieved at 0.4THz at a photocurrent of 3.8mA. A comparison between corresponding GaAs- and InGaAs-based n-i-p-n-i-p photomixers reveals an improvement of performance by at least an order of magnitude for the latter one.

WAVELENGTH DEPENDENCE OF OCULAR DAMAGE THRESHOLDS IN THE NEAR-IR TO FAR-IR TRANSITION REGION: PROPOSED REVISIONS TO MPES

This report summarizes the results of a series of infrared (IR) laser-induced ocular damage studies conducted over the past decade. The studies examined retinal, lens, and corneal effects of laser exposures in the near-IR to far-IR transition region (wavelengths from 1.3-1.4 mum with exposure durations ranging from Q-switched to continuous wave). The corneal and retinal damage thresholds are tabulated for all pulsewidth regimes, and the wavelength dependence of the IR thresholds is discussed and contrasted to laser safety standard maximum permissible exposure limits. The analysis suggests that the current maximum permissible exposure limits could be beneficially revised to (1) relax the IR limits over wavelength ranges where unusually high safety margins may unintentionally hinder applications of recently developed military and telecommunications laser systems; (2) replace step-function discontinuities in the IR limits by continuously varying analytical functions of wavelength and pulsewidth which more closely follow the trends of the experimental retinal (for point-source laser exposures) and corneal ED50 threshold data; and (3) result in an overall simplification of the permissible exposure limits over the wavelength range from 1.2-2.6 mum. A specific proposal for amending the IR maximum permissible exposure limits over this wavelength range is presented.

Tunable laser in 1575 nm–1225 nm range achieved by pressure tuning combined with grating tuning

AbstractWe demonstrated the pressure and external cavity tuning of commercial telecommunication laser, emitting in the 1500 nm band under normal conditions. The laser had AR coatings on the output mirror and highly reflective coating on its back facet. We measured the tuning ranges of the laser operating CW under four different pressures. The experimental setup was in the Littrow configuration. At each pressure the external cavity arrangement enabled the fine tuning in the range of the positive modal gain. We determined the net gain from the Hakki–Paoli method. The combination of pressure tuning with grating allowed us to obtain the 350 nm tuning range (from 1575 nm to 1225 nm). (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Stacking, polarization control, and lasing of wavelength tunable (1.55 μm region) InAs/InGaAsP/InP (1 0 0) quantum dots

We report the growth, device fabrication, and performance of stacked InAs/InGaAsP/InP (1 0 0) quantum dots (QDs) in telecom lasers. Wavelength tuning of the QDs grown by metalorganic vapor-phase epitaxy (MOVPE) over the 1.55-μm region at room temperature (RT) is achieved using ultrathin GaAs interlayers underneath the QDs, which suppress As/P exchange to reduce the QD height in a controlled way. Unpolarized photoluminescence from the cleaved side, important for realization of polarization-insensitive semiconductor optical amplifiers, is obtained for closely stacked QDs due to vertical electronic coupling. The wavelength shift due to group-V-atom intermixing in the QDs during growth at higher temperatures of device structures is compensated by adjusting the GaAs interlayer thickness and V/III flow ratio during QD growth. Device quality of the QDs is highlighted by continuous-wave ground-state lasing at RT of narrow ridge-waveguide QD lasers.

Bubbler for constant vapor delivery of a solid chemical

Indium containing compounds are used in many electronic and optoelectronic devices. Examples vary from InAlGaP/InGaP materials for red emitters and HBTs, to InGaAs/InAlGaAs/InGaAsP for long-wavelength telecommunication lasers. For metalorganic chemical vapor deposition (MOCVD) of these devices, the chemical precursor used for epitaxial growth is generally trimethylindium (TMIn). TMIn is a solid source precursor and therefore has several issues associated with its reproducible and reliable delivery from the bubbler to the reactor, especially at high molar flow rates. In this work we report results on extremely stable delivery of TMIn under various experimental conditions using a unique bubbler design which overcomes most of the delivery problems associated with solid sources. With this bubbler, named the Hiperloop, we are able to obtain stable TMIn flux with a consumption of greater than 92–95% at various experimental conditions. We concentrate on conditions which are considered challenging but can deliver high throughput such as low pressures, high carrier gas flow rates, and high source temperatures.

Wavelength controlled InAs/InP quantum dots for telecom laser applications

This article reviews the recent progress in the growth and device applications of InAs/InP quantum dots (QDs) for telecom applications. Wavelength tuning of the metalorganic vapor-phase epitaxy grown single layer and stacked InAs QDs embedded in InGaAsP/InP (100) over the 1.55-μm region at room temperature (RT) is achieved using ultra-thin GaAs interlayers underneath the QDs. The GaAs interlayers, together with reduced growth temperature and V/III ratio, and extended growth interruption suppress As/P exchange to reduce the QD height in a controlled way. Device quality of the QDs is demonstrated by temperature-dependent photoluminescence (PL) measurements, revealing zero-dimensional carrier confinement and defect-free InAs QDs, and is highlighted by continuous-wave ground-state lasing at RT of narrow ridge-waveguide QD lasers, exhibiting a broad gain spectrum. Unpolarized PL from the cleaved side, important for realization of polarization insensitive semiconductor optical amplifiers, is obtained from closely stacked QDs due to vertical electronic coupling.

An adaptive singular value decomposition (SVD) algorithm for analysis of wavelength modulation spectra

Optical interference fringes due to unwanted etalons are often the limiting uncertainty in diode laser spectroscopic trace gas measurements. Temporal variations in the fringe spacings, phases, and amplitudes introduce systematic baseline changes that limit useful signal averaging times to ∼1000 s, and constrain minimum detectable absorbances to between one and three orders of magnitude worse than the fundamental limiting noise sources (shot noise and/or detector thermal noise). We describe an adaptive numerical filtering method based on singular value decomposition (SVD) that shows, for the system studied, a fivefold reduction in baseline drift due to unwanted etalons over a one-week-measurement period. The adaptive algorithm is fast (<1 ms per computation), robust, and uses linear methods. It is computationally equivalent to principal component analysis (PCA). The test system was acetylene detected using a near-infrared telecommunications laser operating at 6541.96 cm-1. The gas detection limit was 20 ppb (1σ) over the one-week measurement.

FEASIBILITY OF AN OPTICAL FREQUENCY MODULATION SYSTEM FOR FREE-SPACE OPTICAL COMMUNICATIONS

We consider a free-space communication system based on optical frequency modulation (FM), where the information is encoded by a time-variable wavelength. As is well known, broadband FM systems use a transmission bandwidth that is larger than the signal's information bandwidth, thus enabling an enhancement of the signal-to-noise ratio (SNR) and hence the effective information rate per unit transmitter power. Because of the atmospheric conditions, any optical free-space communication system, contemplated at a terrestrial level, must operate at mid-infrared wavelengths in the range λ = 2.5 2.8 μ m . Development of rapidly tunable single-frequency lasers in this wavelength range is quite feasible, based on the current experience with tunable telecom lasers at 1.5 μm. Nevertheless, there is no currently available optical FM system. The main difficulty is associated not so much with the tunable optical sources, as with the implementation of a wavelength-discriminating receiver system that would take advantage of the enhanced SNR. In our view, the key enabling solution is optical superheterodyne with a local oscillator implemented as a tunable mid-infrared laser similar to that at the source. The intermediate frequency can be tuned to lie either in a frequency range directly accessible to electronic limiting amplifier and frequency discriminator or, in a multichannel system, to a second heterodyne in the terahertz range.

Solvothermal Synthesis of Monodisperse PbSe Nanocrystals

Size-controllable monodisperse PbSe and PbSe/PbS nanocrystals (NCs) have been successfully synthesized with a solvothermal method. Octadecylamine (ODA) molecules were found effective in organizing the nanocrystals to form an ordered monolayer. It is expected that these narrow-band-gap semiconductor NCs with tunable size would have potential applications in near- and mid-IR telecommunication laser sources, electroluminescence, and solar cell materials.

Investigation of Chemical Mechanical Polishing of GaAs Wafer by the Effect of a Photocatalyst

The GaAs wafer is widely applied to semiconductor element related to telecommunication and semiconductor laser. In this research, novel fine polishing technology of GaAs wafer was investigated using TiO2-H2O2-H2O slurry system instead of NaOCl which is conventionally used as polishing slurry. And then the ultraviolet ray was applied in order to investigate the effect of TiO2 photocatalyst. The polishing characteristics were estimated by optical microscope and WYKO optical profiler. It was found that the slurry system was available for GaAs wafer polishing although the polishing rate was lower than NaOCl. Moreover, the effect of the photocatalyst of TiO2 including in slurry was investigated. In this polishing system, the effect of the photocatalyst on GaAs wafer CMP mechanism has not been confirmed yet.

Tunable Diode Lasers: Expanding the Horizon for Laser Absorption Spectroscopy

Recent advances in broadly tunable telecommunications lasers will enable new approaches to laser absorption spectroscopy and greatly expand the ability of existing laser-based systems to perform trace gas detection. Researchers have already begun adopting these lasers in tunable diode laser absorption spectroscopy, photo-acoustic absorption spectroscopy and cavity ring-down spectroscopy.

InGaAsN on GaAs (1 1 1)B for telecommunication laser application

In this work we present the GaAs (1 1 1)B as a candidate to develop laser devices working on the second and third fiber optic windows. We show that the ions coming from the radiofrequency plasma cell reduce the optical emission dramatically. This damage can be reduced if a magnetic field is used during the growth of the InGaAsN quantum wells, reducing the ion density impinging on the surface and improving therefore the optical quality. In addition, a lower optimum RTA temperature was found for samples with a lower ion concentration, implying a better structural quality. Finally, a lower blueshift after annealing was also found. The higher optical and structural quality of the samples grown with the magnetic field, the lower optimum RTA temperature and the reduced blueshift after anneling offer interesting perspectives to the development of long-wavelength devices using misoriented GaAs (1 1 1)B substrates.

Accurate tuning of emission of GaInAsP/InP heterostructures in multiwafer gas-source molecular-beam epitaxy

Photoluminescence wavelength emission of Ga x In 1− x As y P 1− y /InP heterostructures grown in multiwafer gas-source molecular-beam epitaxy (GSMBE) is studied in detail for both bulk and multiple quantum well (MQWs) heterostructures. Excellent photoluminescence wavelength uniformity is reported in 4×2-in. configuration, demonstrating the compatibility of GSMBE process with large-scale 1.55 μm telecom laser production. A strong dependence of wavelength uniformity on group-V/group-III flux ratio is reported and analyzed quantitatively. An empirical model based on the interplay between group-V elements incorporation and gas distribution is proposed to predict the influence of AsH 3 and PH 3 fluxes on As content in the solid. This understanding opens the way to an accurate tuning of wavelength dispersion of Ga x In 1− x As y P 1− y /InP MQWs grown in multiwafer GSMBE system.

Thickness Measurement of Thin Transparent Plates With a Broad-Band Wavelength Scanning Interferometer

A novel broad-band telecom laser source is used to make a lateral-shear scanning-wavelength interferometer for measuring the thickness of thin plates. We show that the wide tunability range allows us to detect samples down to tens of microns with a relative uncertainty of less than 0.5%. A comparable accuracy in the thickness characterization of double-layer structures is also demonstrated. In turn, the wide tunability range needs the dispersion law of the materials to be taken into account in the model for correct thickness evaluation, although simultaneous measurement of dispersion and thickness are in principle possible with this technique.

Sensitivity of SHG-FROG for the characterization of ultrahigh-repetition-rate telecommunication laser sources

We analyze experimentally the sensitivity of second-harmonic generation frequency-resolved optical gating (SHG-FROG) for the complete intensity and phase characterization of both a sinusoidal beat signal and a train of 1.3 ps pulses at a repetition rate of 160 GHz at 1550 nm. Using a commercially-available optical spectrum analyzer in the SHG-FROG set-up, incident pulses with energies of only 125 and 190 fJ, which correspond to the beat signal and the 1.3 ps pulse train, respectively, have been accurately characterized.