High-speed modulation of strain-compensated InGaAs-GaAsP-InGaP multiple-quantum-well lasers

Small signal direct modulation characteristics of InGaAs-GaAsP-InGaP multiple quantum well ridge waveguide lasers (4.5/spl times/220 /spl mu/m/sup 2/) are described. The compressive strain of four InGaAs quantum wells is compensated by the tensile strain of GaAsP barriers. The lasers have a threshold current of 8 mA and an internal differential quantum efficiency of 80%. A 3-dB bandwidth of 25 GHz is obtained at 54 mA. It is found that the strain-compensated lasers have a K factor as low as 0.15 ns, implying a maximum 3-dB bandwidth of 59 GHz.     

Pure strain effects in strained-layer multiple-quantum-well lasers

Pure effects of strain in strained-layer multiple-quantum-well (MQW) lasers are measured separately from quantum effects using Fabry-Perot (FP) lasers with the same well thicknesses but different strains. The differential gain and gain saturation coefficients and the K factors of the lasers are determined by measuring relative-intensity-noise (RIN) spectra with various bias conditions. The differential gain coefficient increases when the compressive strain increases. The gain saturation coefficient also increases with increasing compressive strain. The K factor increases slightly when the compressive strain increases because of the slight increase in the ratio of the gain saturation coefficient to the differential gain coefficient     

Fabrication of dry-etched mirrors in GaAs-based and InP-based lasers using chemically assisted ion-beam etching at low temperatures

We have fabricated dry-etched mirrors in high-speed InGaAs/GaAs/AlGaAs pseudomorphic multiple quantum well ridge-waveguide lasers at 60°C and in InGaAs/InP bulk lasers at 5°C using enhanced chemically assisted ion-beam etching (CAIBE) technique. The technique allows the etching of laser structures with good surface morphology and excellent anisotropy without cold traps in the etching system. Characteristics of the dry-etched facet lasers match those of cleaved devices. The low sample temperatures for etching allowed the use of standard photoresists as etch masks.     

Uniform linear arrays of strained-layer InGaAs-AlGaAs quantum-wellridge-waveguide diode lasers fabricated by ECR-IBAE

Uniform linear arrays of strained-layer multiple-quantum-well InGaAs-AlGaAs ridge-waveguide diode lasers have been fabricated that operate near 980 nm and have low threshold currents I_th and high differential quantum efficiencies η_d. Uniformity was achieved by a combination of uniform ion-beam-assisted etching with an electron cyclotron resonance ion source and uniform organometallic vapor-phase epitaxial (OMVPE) growth. We investigated the effects of device geometry, namely, ridge width, cavity length, and remaining cladding thickness outside the ridge t, on I_th and η_d. For uncoated lasers with 500-μm-long cavities, 2- to 3-μm-wide ridges, and t=165±75 nm fabricated in double-quantum-well OMVPE material, I_th was typically in the range 6-7 mA and η_d was >40% per facet. A 24-element array of 2-μm-wide, 200-μm-long ridge-waveguide lasers with a high reflection coating on the back facet exhibited excellent uniformity, with threshold currents and single-ended differential quantum efficiencies that averaged 3.4 mA and 72%, respectively. Similar arrays with high-reflectivity coatings on both facets exhibited threshold currents as low as 2 mA     

Mode control in vertical-cavity surface-emitting lasers by post-processing using focused ion-beam etching

Single-mode emission is achieved in previously multimode gain-guided vertical-cavity surface-emitting lasers (VCSEL's) by localized modification of the mirror reflectivity using focused ion-beam etching. Reflectivity engineering is also demonstrated to suppress transverse mode emission in an oxide-confined device, reducing the spectral width from 1.2 nm to less than 0.5 nm.     

High-speed modulation of semiconductor lasers

An overview is given of the direct modulation performance of high-speed semiconductor lasers. The high-speed response characteristics are described using a cascaded two-port model of the laser. This model separates the electrical parasitics from the intrinsic laser and enables these subsections to be considered separately. The presentation concentrates on the small-signal intensity modulation and frequency modulation responses, and the large-signal switching transients and chirping. Device-dependent limitations on high-speed performance are explored and circuit modeling techniques are briefly reviewed.     

High-speed modulation of semiconductor lasers

An overview is given of the direct modulation performance of high-speed semiconductor lasers, The high-speed response characteristics are described using a cascaded two-port model of the laser. This model separates the electrical parasitics from the intrinsic laser and enables these subsections to be considered separately. The presentation concentrates on the small-signal intensity modulation and frequency modulation responses, and the large-signal switching transients and chirping. Device-dependent limitations on high-speed performance are explored and circuit modeling techniques are briefly reviewed.     

Linewidth enhancement factor of 1.3 mu m InGaAsP/InP strained-layer multiple-quantum-well DFB lasers

The linewidth enhancement factor alpha in a 1.3 mu m InGaAsP/InP strained-layer multiple-quantum-well (SL-MQW) distributed feedback (DFB) laser has been evaluated from the relation between the frequency and intensity modulation indexes, and the spontaneous emission spectra below threshold current. It is demonstrated that the measured alpha -parameter of a 1.3 mu m SL-MQW DFB laser is about two, and is much smaller than that in a conventional bulk DFB laser. From the resonance frequency dependence on the output power, it is concluded that this reduction of the alpha -parameter originates in the increased differential gain. The reduction of wavelength chirping, as a result the low alpha -parameter, was experimentally confirmed for the SL-MQW DFB laser.<>     

GaAs vertical-cavity surface emitting lasers fabricated by reactive ion etching

GaAs quantum well vertical-cavity surface emitting lasers fabricated using low damage reactive ion etching are discussed. Lasers which are partially and completely etched through their structure are compared. The surface recombination velocity of exposed GaAs is not exacerbated in deep etched lasers; other loss mechanisms in shallow etched lasers have comparable impact on laser performance. Etched lasers exhibit low voltage and small differential series resistance at threshold, while devices fabricated by a combination of etching and ion implantation possess lower threshold current. It is found that reactive ion etching has little additional effect on laser operation, whereas the different device structures considered do influence laser performance.<>     

Design criteria for highly-efficient operation of 1.3-μmInP-based strained-layer multiple-quantum-well lasers at elevatedtemperatures

We derive a basic design rule for highly-efficient operation of 1.3-μm InP-based strained-layer (SL) multiple-quantum-well (MQW) lasers at elevated temperatures on the basis of a self-consistent numerical approach including the Poisson equation and effective-mass equations. Following the derived design rule, high-efficiency (0.55 W/A at 363 K) and high-power (over 35 mW at 363 K) InP-based SL-MQW lasers have been fabricated     

High-speed modulation of vertical-cavity surface-emitting lasers

The IM (intensity modulation) and FM (frequency modulation) characteristics of vertical-cavity surface-emitting lasers are studied. The laser has high FM efficiency and broad IM bandwidth (near 8 GHz) at a very low bias (4.5 mA). Five Gb/s pseudorandom direct intensity modulation of this laser with open eyes is demonstrated.<>     

High-speed performance of partly gain-coupled 1.55-μmstrained-layer multiple-quantum-well DFB lasers

A partly-gain-coupled 1.55-μm distributed feedback (DFB) laser with a strained-layer multiple-quantum-well (MQW) active region with high relaxation oscillation frequency and maximum intrinsic bandwidth of 28 GHz is reported. An effective differential gain of 1.80×10^-15 cm² was achieved, which may be attributed to the strain effect in the MQW active region as well as the combination of the longitudinal gain/index coupling mechanism and fast lateral carrier injection from the cladding layers into the wells     

InGaAs-GaAs 980-nm stripe-geometry and circular ring ridge waveguide lasers fabricated with pulsed anodic oxidation

In/sub 0.22/Ga/sub 0.78/As-GaAs quantum-well stripe-geometry and circular ring lasers have been fabricated with pulsed anodic oxidation (PAO). The relationship between ridge heights and laser performance was first studied in the fabrication of stripe lasers. The lowest transparency current density (J/sub tr/) of 61.20 A/cm/sup 2/ was obtained from the stripe laser with a ridge height of 1.23 /spl mu/m, corresponding to an etching depth where all the p-doped layers above active region were removed. With the PAO process, when the ridge height (1.77 /spl mu/m) extended below the active region, J/sub tr/ is 76.03 A/cm/sup 2/, only increased by 24.2%. Based on the experimental results, the circular ring laser, which needs deep etching (below active region) and subsequent PAO, has been fabricated. The fabricated circular ring laser worked under continuous-wave operation at room temperature. Longitudinal mode spacing analysis clearly indicates that the ring resonator is a functional part of the whole circular ring laser.     

Power penalty in 1.3-/spl mu/m InP-based strained-layer multiple-quantum-well lasers at elevated temperatures

We present a basic design rule for reducing the light output power penalty in 1.3-/spl mu/m InP-based strained layer (SL) multiple-quantum-well (MQW) lasers at elevated temperatures. The power penalty is shown to have a strong correlation with a critical temperature (T/sub c/): above T/sub c/, the power penalty rapidly increases due to a significant reduction in differential quantum efficiency. It is indicated that T/sub c/ can be estimated for an arbitrary laser structure by using a self-consistent numerical method. We show that, to minimize the power penalty, it is essential to design an SL-MQW laser so that its T/sub c/ is larger than the required maximum operation temperature.     

Focal plane arrays mesastructures formation by ion-beam etching

The results of investigation of profiles formed by ion-beam etching of semiconductor structures through a photolithographic mask are presented. The minimum dimensions of unmasked regions on the surfaces of two studied structures are 2 and 5 μm, respectively. It is demonstrated that the etching rate reduces with reduction in the width of the unmasked gap. The effect of reflection of the ion beam from vertical walls formed during etching may be used for fabrication of submicron separating mesaregions.     

GaInAsP/InP lasers with monolithically integrated monitoring photodiodes fabricated by inclined reactive ion etching

Monolithic fabrication of a GaInAsP/InP laser (LD) with a monitoring photodiode (PD) is described. LDs and PDs have etched facets fabricated by inclined reactive ion etching (RIE). The etched LD facing facet PD is perpendicular to the junction plane and the etched PD facet facing LD is inclined by 55 degrees to the plane by the 'windward-leeward effect' of the inclined RIE. Therefore, coupling efficiencies between LDs and PDs are uniform because the multireflection effect of double mirrors does not exist for the LD-PD devices with inclined PD facets. Typical CW threshold current ranges from 20 to 30 mA and light output power from a single facet exceeds 15 mW at 25 degrees C. A PD can detect about 2% of the light beam emitted from an LD facing it.<>     

A novel Ti:LiNbO3ridge waveguide linear mode confinement modulator fabricated by reactive ion-beam etching

In this paper we report the realization of a ridge waveguide linear mode confinement modulator using reactive ion-beam etching (RIBE). With the help of a design analysis, the modulation characteristics are predicted. Along with the measured modulation characteristics, preliminary results of the calibration of ion-beam etching inZ-cut LiNbO3by Ar and a mixture of Ar and CHF3are presented. Differential etching rates between photoresist and LiNbO3of as high as 7 are obtained. Using the proposed design of a ridge waveguide linear modulator, a linear modulation of over 67 percent is measured.     

A relationship for temperature dependence of threshold current for 1.3-/spl mu/m compressively strained-layer multiple-quantum-well lasers

Assuming that the differential gain is a linear function of temperature, a formula is derived to describe the threshold current as a function of temperature. A maximum operating temperature, T/sub max/ which is related to the fundamental physical properties (such as differential gain, free carrier loss and intervalence band absorption) of the lasers appears naturally in the formula, at which lasing ceases. To experimentally investigate the relationship, studies were carried out on 1.3-/spl mu/m strained-layer multiple quantum well (SL-MQW) lasers with variant 0.7% compressively strained wells. The formula shows a good correlation with threshold current versus temperature data over the temperature range 200 K to 450 K.     

Ultralow threshold strained InGaAs-GaAs quantum well lasers by impurity-induced disordering

Stripe-geometry strained InGaAs-GaAs quantum well lasers were fabricated by impurity induced disordering. Threshold currents as low as 2.2 mA at room temperature continuous operation (RT CW) were obtained for uncoated lasers having 1.2 mu m wide, 215 mu m long active stripes. The authors believe that this ultralow threshold is mainly due to the very small active stripe width and the excellent electrical confinement of the laser.<>