Order Gratings Research Articles

Gain coupled distributed feedback lasers realized by masked implantation enhanced intermixing

Long wavelength 1.3 μm gain coupled distributed feedback (GC-DFB) lasers were realized by masked implantation enhanced intermixing. On the basis of this full planar technology GC-DFB lasers with first and second order gratings were fabricated in the InGaAs/InGaAlAs system. The lasers show clear GC-DFB laser emission with a single mode yield of 69% and remain single mode up to several times laser threshold. The results are in good agreement with the theoretical description of our gain coupled lasers by optical matrix theory.

Single-growth-step GaAs/AlGaAs distributed Bragg reflector lasers with holographically-defined recessed gratings

A ridge waveguide GaAs/AlGaAs quantum well DBR laser fabricated with a simplified grating recess-technology and a third order grating is described. The reflector is fabricated on top of a recessed waveguide using holographic exposure followed by reactive ion etching. The laser operates on a single longitudinal and lateral mode with threshold current as low as 20 mA, output power 5 mW per facet and is intended for monolithically integrated interferometer applications.

Demonstration of blazing effect in detuned second order gratings

Surface-emitting InGaAs/AlGaAs lasers with two first order gratings as feedback elements followed by one detuned second order blazed grating as output window were fabricated using electron beam lithography and chemically assisted ion beam etching. A strong dependence of the surface emission efficiency on the blazed grating orientation was observed.

Demonstration of blazing effect in second order gratings under resonant condition

Surface-emitting InGaAs/AlGaAs lasers with a second order blazed surface grating as one feedback element were fabricated using electron beam lithography and chemically assisted ion beam etching. A strong dependence of the surface emission efficiency on the grating orientation was observed.

Second order diffraction efficiency of Bragg gratings written within germanosilicate fibres

Second order diffraction has been observed from Bragg gratings written within germanosilicate glass fibres. Experimental results are reported on the evolution of the first and the second order Bragg grating reflectivities as function of the uv laser shot number used for the inscription. Second order diffraction can be detected once the first order grating reflectivity has begun to saturate. Possible explanations of the second order grating formation are discussed. Our experimental results are consistent with a saturation in the photo-induced change in refractive index.

Wide-band Bragg reflectors made with silica on silicon waveguides

We report the fabrication of strong Bragg reflectors embedded into fiber matched silica on silicon waveguides. First order gratings are dry etched into the waveguide core and are covered with a thin Si3N4 layer prior to cladding deposition. Reflection bands 225 Å wide for TE and 193 Å wide for TM polarizations are obtained with 200 Å Si3N4 cover layers. The TE and TM spectra are overlapping, resulting in nearly polarization independent Bragg reflectors.

Fabrication of DFB laser gratings using synchrotron radiation proximity lithography

First and second order gratings for 1.55 μm distributed feed-back lasers (DFB) have been fabricated in InP using synchrotron radiation proximity lithography. High resolution X-ray masks with 1 st and 2 nd order DFB laser gratings were fabricated by Electron Beam Lithography (EBL) using a single-level resist process and gold electroplating. The resulting 0.23 μm and 0.46 μm period structures were used to transfer a grating image into InP, using synchrotron radiation (SR). A 5μm mask to wafer gap was used. Both positive and negative X-ray resists were used to define the images on InP, and subsequently, were transferred into InP by dry etching process. Issues related to the fidelity of the image transfer process and the control of the line to space ratio on the mask are also discussed.

Shortest wavelength (607 nm) operations of GaInP/AlInP distributed Bragg reflector lasers

Visible light GaInP/AlInP distributed Bragg reflector (DBR) lasers with second order gratings (184.7 nm period) were fabricated by gas source molecular beam epitaxy (GSMBE) and the conventional interference method for the first time. Single mode operations of GaInP/AlInP DBR lasers were maintained up to over 1.8 times the threshold currents with a wavelength of 607 nm at 140 K and a wavelength shift of 0.033 nm/K. No mode hopping was observed in a temperature range from 120 to 165 K.

High power singlemode GaInAs lasers with distributed Bragg reflectors

High power singlemode strained GaInAs lasers have been fabricated which use buried second order gratings as distributed Bragg reflectors. The lasers operate in an edge emitting fashion with CW powers in excess of 110 mW with single longitudinal and transverse mode operation at 971.9 nm up to 42 mW.

First order distributed feedback gratings (92.5–105 nm period) for GaInP/AlGaInP lasers emitting in the visible range

The fabrication of first order gratings for distributed feedback (DFB) GaInP/AlGaInP laser structures with periods in the range of 100 nm will be reported. The laser structures were pumped optically and show single mode emission at 639 and 651 nm with coupling coefficients of 151 cm−1. Due to the principally nonexisting radiation mode loss first order DFB lasers will show lower thresholds than the yet demonstrated third order DFB lasers with three times coarser grating periods. The gratings fabricated by e‐beam lithography and dry etching techniques show strong feedback and moderate damaging of the waveguide properties.

High power, 16 W, grating surface emitting laser with a superlattice substrate reflector

Grating coupled surface emitting lasers with ten gain regions have been fabricated with second order gratings for output coupling, and superlattice reflectors for increased efficiency, emitting over 16 W pulsed with a differential efficiency of 50%.

Resolution limitation in EBL optical grating fabrication on InGaAsP/InP substrate

Abstract Monte Carlo (MC) simulation and experimental point exposure energy distribution on InP substrate are used to described the total energy response of 1 st and 2 nd order gratings for InP based solid state lasers. A good agreement between theoretical calculations and experimental obtained data is achieved. The triple gaussian approximation of the energy density profiles is suggested by an analysis of computed primary electron energy spectra. Examples of both dry and wet etched gratings in InP substrate and InGaAsP epitaxial layers, which fit with calculations are given.

High efficiency, high uniformity, grating coupled surface emitting lasers

Grating coupled surface emitting lasers are fabricated with supeiiattice reflectors on the substrate side to increase the output coupling from the second order grating. Differential efficiencies of 60% are achieved with high uniformity over the wafer surface. Spectral uniformity across a 1 cm wafer is better than 0.4 nm while the far field radiation angle from the individual gratings are within 0.02° of the normal. The high uniformity and good lasing characteristics are critical to the coherent coupling of an array of surface emitting devices.

AlGaAs/GaAs distributed feedback laser diodes grown by MOCVD

AlGaAs/GaAs distributed feedback (DFB) laser diodes emitting at 880 and 760 nm were fabricated by a two-step MOCVD growth technique. Epitaxial growth was carried out in a conventional atmospheric-pressure MOCVD system with a vertical reactor. A mesa-stripe geometry and separate-confinement heterostructure (SCH) was employed for the laser structure. The cladding layer ( x = 0.35, 0.48) was successfully regrown on the guiding layer ( x = 0.15, 0.25) corrugated with a 0.25 μm period (2nd order grating). Continuous wave (CW) operations were achieved up to 53°C for devices emitting at 880 nm and up to 10°C for devices emitting at 760 nm. A threshold current as low as 55 mA was obtained for a device emitting at 880 nm under CW operation at room temperature.

InGaAsP closely spaced dual wavelength laser

The fabrication and performance characteristics of an independently controllable closely spaced dual wavelength laser structure are described. The laser structure utilizes semi-insulating (Fe-doped InP) layers both for confinement of the current to the active regions and for separation of the active regions of the two lasers. Both lasers emit in single frequencies near 1.55 μm by virtue of frequency selective feedback provided by a second order grating. The light coupled into a single mode fiber from both lasers is about 5 dB smaller than that for optimum coupling arrangement of each laser. Dual wavelength laser structures of this type are useful for wavelength multiplexed optical transmission systems.

1.55-μm InGaAsP ridge waveguide distributed feedback laser

Optical and modulation properties of ridge waveguide distributed feedback lasers grown by liquid phase epitaxy and operating in the spectral region of 1.51–1.58 μm have been investigated. These lasers were characterized by room temperature cw threshold currents as low as 40 mA, external quantum efficiency of up to 40%, and lowest order transverse mode operation up to 10 mW. Stable, single longitudinal mode operation under direct modulation of up to 4 GHz was obtained using second order gratings fabricated by electron beam writing as well as optical holography. The absence of partition mode events has allowed routine error free transmission over 60 km of single mode fiber at data rates of 2 Gb/s. The relationship between grating parameters and the Bragg length has been studied experimentally and compared with the theoretical results.