Ridge Waveguide Distributed Feedback Lasers Research Articles

Coupling characteristics of laterally coupled gratings with slots

Laterally-coupled ridge-waveguide distributed feedback lasers fabricated without epitaxial regrowth steps have the advantages of process simplification and low cost. We present a laterally coupled grating with slots. The slots etched between the ridge and grating area are designed to suppress the lateral diffusion of carriers and to reduce the influence of the aspect-ratio-dependent-etching effect on the grating morphology in the etching process. Moreover, the grating height in this structure can be decreased to lower the aspect ratio significantly, which is advantageous over the conventional laterally coupled ridge waveguide gratings. The effects of five main structural parameters on the coupling characteristics of gratings are studied by MODE Solutions. It is found that varying the lateral width of the grating can be used as an effective way to tune the coupling strength; narrow slots (100 nm and 300 nm) and wide ridge (2 μm–4 μm) promote the stability of grating coupling coefficient and device performance. It is important to note that the grating bottom should be fabricated precisely. The comparative study of carrier distribution and mode field distribution shows that the introduction of narrow slots can strengthen the competitive advantage and stability of the fundamental mode.

The effect of detuned wavelength in the dynamic performance of distributed feedback lasers operating at O band and C band

AbstractA comparison is presented between the experimental dynamic behavior of detuned AlInGaAs ridge waveguide distributed feedback lasers operating at O band and C band at two different temperatures. The nominal center wavelengths at 25°C for the set of devices studied were 1270, 1310, and 1550 nm. Preliminary static characterization of the samples showed consistent trends between wavelength detuning, characteristic temperature, and power output. For all set of samples, the characteristic temperature was substantially higher for the samples detuned to longer wavelengths (red) at room temperature. At the temperature of 85°C, a higher power efficiency was observed for those samples that thermally shifted nearer the peak optical gain. Resonance frequencies were extracted at 25°C and 85°C by means of electro‐optical transmission measurements and relative intensity noise measurements. The extracted values confirmed that at room temperature the samples detuned to shorter wavelengths (blue) showed the highest modulation efficiencies. At the temperature of 85°C, however, the wavelength and optical gain thermal shift makes those same samples to have the lowest resonant frequencies. The dynamic trends over temperature were clearer for the O band set of samples, while the detuning had a less pronounced effect at C band. The range of maximum resonance frequencies studied was from 12 to 14 GHz, which makes the devices suitable for uncooled communication applications at multi‐gigabit data rates.

Dynamic performance of detuned ridge waveguide AlInGaAs distributed feedback laser diodes

The dynamic behavior of AlInGaAs ridge waveguide distributed feedback lasers is reported in this work covering five detuned wavelengths between 1291 nm and 1326 nm for a laser active layer optical peak gain design centered at 1310 nm at room temperature. The detuning is achieved by modifying the laser grating pitch that performs the mode selection within the laser cavity simultaneously across a single processed wafer. The dynamic behavior is evaluated using the resonance frequencies of the detuned lasers measured at a range of injection currents for heatsink temperatures of 25°C and 85°C. The results confirm that a speed improvement can be achieved at 25°C by detuning the laser to shorter wavelengths. However, the results also show that a lower direct modulation bandwidth at 85°C makes the shorter wavelength design less attractive. For communications applications such as 10 Gbps uncooled operation, this trade-off between detuning and modulation bandwidth imply an optimum around −2 nm to +8 nm detuning (measured at 25°C). © 2017 Wiley Periodicals, Inc. Microwave Opt Technol Lett 59:1468–1470, 2017

2004-nm Ridge-Waveguide Distributed Feedback Lasers With InGaAs Multi-Quantum Wells

Fabrication and characteristics of 2004-nm wavelength InP-based ridge-waveguide distributed feedback lasers with InGaAs multi-quantum wells are described. By means of a relatively simple fabrication process, the device can operate stably in a single mode without any mode hopping. A high side-mode suppression ratio of 49 dB is achieved. The emission wavelength can be finely controlled from 2000 to 2008 nm with a current-tuning rate of 0.0047 nm/mA and a temperature-tuning rate of 0.127 nm/K. In addition, the influence of facet coating conditions on the single-mode property of these distributed feedback lasers was investigated.

Distributed feedback lasers in the 760 to 810 nm range and epitaxial grating design

We present the results from distributed feedback (DFB) lasers with emission wavelengths ranging from 760 to 810 nm and focus on the optimization of Bragg gratings realized with a patterned GaAsP layer that is overgrown with an AlGaAs cladding layer. The impact of the thickness and material composition of the GaAsP grating lines on the DFB laser performance is theoretically and experimentally investigated. 767 nm ridge waveguide DFB lasers with optimized gratings show excellent optoelectronic characteristics in terms of slope efficiency (0.9 W A−1) and linewidth (11 kHz).

Narrow linewidth laterally-coupled 1.55 [micro sign]m DFB lasers fabricated using nanoimprint lithography

A report is presented on the use of nanoimprint lithography for the fabrication of InP-based laterally-coupled ridge waveguide distributed feedback laser (DFB) diodes emitting around 1550 nm. At room temperature the uncoated lasers exhibited a sidemode suppression ratio of 50 dB at an output power of 6 mW. The lasers showed extremely pure singlemode spectrum with the Lorentzian part of the measured linewidth being ∼200 kHz. The results prove that nanoimprint lithography is suitable for the low-cost manufacturing of high performance singlemode laser diodes.

1.3-$\mu$m Laterally Tapered Ridge Waveguide DFB Lasers With Second-Order Cr Surface Gratings

We report the laterally tapered ridge waveguide InGaAsP-InGaAsP multiple quantum-well distributed-feedback (DFB) lasers with metal surface gratings, operating at λ ~1.3 μm, by holographic lithography. Single-tapered and double-tapered (bow-tie) ridge waveguide DFB structures with second-order Cr surface gratings are employed to enhance the coupling efficiency. The 600-μm-long laterally coupled DFB laser with a double-tapered ridge waveguide structure exhibits significantly improved single-mode operation without mode hopping, with a maximum sidemode suppression ratio of 42 dB and temperature-dependent wavelength shift up to d λ/dT ~0.071 nm/K.

High speed and wide temperature range uncooled 1.3-\mu m ridge waveguide DFB lasers

A 1.3-\mu m wavelength vertical-mesa ridge waveguide mulitple-quantum-well (MQW) distributed feedback (DFB) laser with high directly modulated bandwidth and wide operation temperature range is reported. With the optimization of the strained-layer MQWs in the active region, the surrounding graded-index separated-confinement-heterostructure waveguide layers, together with the optimization of the detuning and coupling coefficient of the DFB grating, high directly modulation bandwidth of 16 GHz at room temperature and wide working temperature range from ?40 to 85 \circ C are obtained. The mean time to failure (MTTF) is estimated to be over 2×10lsupg6l/supg h. The device is suitable as light source of high-bit-rate optical transmitters with small size and reduced cost.

Laterally-corrugated ridge-waveguide distributed feedback lasers at 980 nm

The paper presents a simulation-based analysis of laterally-corrugated ridge-waveguide distributed feedback semiconductor lasers emitting at 980 nm. The simulations were performed using software developed in-house and the PICS3D software package from Crosslight Software Inc. The effects of the corrugation geometry, phase-shift section, and mirror reflectivities on single longitudinal mode operation are discussed. The lasers, designed along the guidelines derived from the simulation results, were fabricated by using molecular beam epitaxy for wafer growth and low-cost nano-imprint lithography. They exhibited stable single-mode operation with up to 50 dB side-mode suppression ratio.

Optical modeling of laterally-corrugated ridge-waveguide gratings

The paper presents some model improvements for the optical simulation of laterally-corrugated ridge-waveguide distributed feedback lasers. Simulation results are discussed and design principles for achieving single-longitudinal-mode operation are outlined. The effects of the laterally-corrugated ridge geometry both on the coupling coefficient and on the Bragg wavelength of different transverse modes are presented. The improved modeling has been used to design 980 nm distributed feedback lasers with laterally-corrugated ridge-waveguide third-order gratings. The lasers fabricated using nanoimprint lithography exhibited single-mode operation with 50 dB side-mode suppression ratio.

Room temperature continuous-wave operation of InAsSb quantum-dot distributed feedback lasers

InAsSb self-assembled quantum-dot (QD) distributed feedback (DFB) lasers based on (001) InP substrate have been grown by metalorganic vapor-phase epitaxy. A highly tensile-strained InGaAs was used as the barrier layer for InAsSb QDs. Single-mode emissions near 1.87μm have been demonstrated from narrow ridge waveguide DFB lasers in continuous-wave operation at temperatures up to 320K (47°C), with a characteristics temperature of 55K up to temperature of 310K.

980-nm DBR lasers using higher order gratings defined by i-line lithography

We report on the simultaneous definition and fabrication of Bragg gratings and ridge waveguides using wafer stepper lithography and reactive ion etching, respectively. Single-longitudinal mode emission from two-section ridge-waveguide distributed feedback lasers with sixth and seventh order gratings will be reported. This technology enables a cheap fabrication of wavelength-stabilized lasers and a simple variation of the parameters of the gratings on the wafer using optical lithography.

120<tex>$^circhboxC$</tex>10-Gb/s Uncooled Direct Modulated 1.3-<tex>$muhboxm$</tex>AlGaInAs MQW DFB Laser Diodes

A 1.3-/spl mu/m AlGaInAs multiquantum well ridge waveguide distributed feedback laser diode was developed. By forming n-InGaAsP grating in the n-InP cladding layer close to the active region, accumulation of the holes in the grating layer was reduced and over 5 mW of output power was obtained at 120/spl deg/C. Clear eye opening was confirmed with no mask hits for OC-192 under 10-Gb/s direct modulation at the temperature up to 120/spl deg/C.

15-GHz modulation performance of integrated DFB laser diode EA modulator with identical multiple-quantum-well double-stack active layer

Monolithically integrated InGaAsP 1.55-μm ridge waveguide distributed feedback laser diodes with an electroabsorption modulator using an identical active multiquantum-well (MQW) layer structure with two different QW types exhibit low-threshold currents <18 mA. The 3-dBe cutoff frequency of 200-μm-long modulators exceeds 15 GHz. 10-Gb/s transmission experiments with a voltage swing of 1.0 V/sub pp/ demonstrate the potential of this novel integration scheme.

Laterally coupled InGaAsP/InP distributed feedback lasers at 1.5 [micro sign]m for chemical sensing applications

Data is presented on stable, tunable single-mode operation from laterally coupled InGaAsP/InP ridge waveguide distributed feedback lasers at /spl sim/1.5 /spl mu/m, suitable for chemical sensing, realised by a greatly simplified fabrication process requiring a single MOCVD growth step. Completed lasers show sidemode suppression ratios as high as 47 dB and wavelength shifts with injection current of 0.035 nm/mA (or 4.5 GHz/mA).

Self-aligned current aperture in native oxidized AlInAs buried heterostructure InGaAsP/InP distributed feedback laser

A InGaAsP/InP self-aligned, native oxidized buried heterostructure (BH) distributed feedback (DFB) laser is proposed. It is as easy to process as the ridge waveguide DFB laser and has superior performance. The current aperture can be easily controlled without selective regrowth. The laser exhibits a low threshold of 5.0 mA with 36 dB side mode suppression ratio at the emission wavelength of 1.562 μm. It emits in a single lobe with full width at half maximum angles of 33.6° and 42.6° for the lateral and vertical fields, respectively. Its beam is more circular than that of the as-grown BH laser because the lower refractive index of oxide compared to the as-grown layer and results in a larger lateral optical confinement. Its characteristic temperature (T0) is 50 K at room temperature but increases in value at the higher temperature range.

Laterally coupled strained MQW ridge waveguide distributed-feedback laser diode fabricated by wet-dry hybrid etching process

The fabrication and the characteristics of the laterally coupled GaInAsP-InP quantum-well ridge waveguide distributed-feedback (DFB) lasers are presented. The electron beam (EB) lithography and the wet and dry hybrid etching technique have been used to fabricate the deep grating structures for the DFB lasers on and beside the sidewalls of the narrow ridge waveguide. The threshold current was 18.5 mA at 20/spl deg/C, and the sidemode suppression ratios (SMSRs) were ensured to be more than 40 dB for as-cleaved devices with various cavity lengths. The continuous-wave output powers of over 15 mW/facet have been observed, while transverse and longitudinal modes have remained in single mode at this output level.

Wavelength trimming by photoabsorption-included disordering for multiple-wavelength distributed-feedback laser arrays

We describe a simple method to adjust the oscillation wavelength of distributed-feedback (DFB) lasers after the device fabrication without using any external active tuning. The method utilizes a permanent change of refractive index in the quantum well active layer induced by external laser beam irradiation. We have demonstrated 0.36 nm adjustment in a 1.55-μm ridge waveguide DFB laser.

Realization and characterization of optically pumped GaInN-GaN DFB lasers

Room-temperature (RT) operation of optically pumped GaN-GaInN distributed-feedback (DFB) lasers is demonstrated in the spectral range from 400 to 415 nm. The ridge-waveguide distributed feedback lasers were realized by dry etching on a GaN-GaInN double heterostructure. Laser emission was observed in the entire spectral range of optical gain, which was determined by amplified spontaneous emission (ASE) measurements. The wavelength shift of the distributed feedback laser emission with temperature was investigated. An array of DFB lasers with different grating periods allowed to obtain the spectral dependence of the laser threshold and the effective refractive index of the GaN-GaInN lasers. The lowest laser threshold we achieved was 0.95 MW/cm/sup 2/.

Performance of 1.3 µm ridge waveguide distributed feedback lasers fabricated by one-step metalorganic chemical vapour deposition

Ridge waveguide distributed feedback (DFB) lasers emitting at 1.3 µm wavelength have been fabricated by one-step metal-organic chemical deposition over a first order grating in an InP substrate. Threshold currents as low as 13-18 mA were obtained for devices with as-cleaved facets and 15-20 mA for devices with one AR-coated facet. A slope efficiency as high as 0.32 mW/mA, single mode performance up to 20 mW, and a side mode suppression ratio of 45 dB have been achieved. For lasers with a coupling*length product, kappa L, of 2.5-3.5 and the single longitudinal-mode detuned 10-20 nm to the shorter wavelength side of the material gain peak, a high resonance frequency and a small wavelength chirp have been observed. Small signal frequency responses were measured with a -3 dB bandwidth of 11 GHz at 12 mW output power. The devices showed good open eye patterns under direct modulation up to 10 Gbit/s.