R.F. Nabiev

Single-mode, passive antiguide vertical cavity surface emitting laser

We report the characteristics of a single-mode, low threshold, passive antiguide region (PAR) vertical cavity surface emitting laser (VCSEL) using both organometallic chemical vapor deposition (OMCVD) and molecular beam epitaxy (MBE) for the regrowth of the PAR structure. The novel passive antiguide region surrounding the active region is demonstrated to be a highly effective transverse mode and polarization mode selection mechanism. A stable single fundamental mode at high currents has been achieved experimentally for laser aperture as large as 16 /spl mu/m diameter, In addition, very low threshold current of 0.8 mA and current density of 490 A/cm/sup 2/ are achieved with 8 and 32 /spl mu/m diameter VCSELs, respectively. A detailed numerical two- and three-dimensionaI analysis was performed using the beam propagation method. The modal losses were calculated as a function of the cladding refractive index and the laser size. Quantitative results leading to approximate formulae have been achieved. The high mode selectivity obtained from the numerical analysis is in good agreement with the experimental results we have achieved. >

Three-core ARROW-type diode laser: novel high-power, single-mode device, and effective master oscillator for flared antiguided MOPA's

A novel type of strong-index-guided laser structure for achieving coherent, high-power (/spl sim/1 W) reliable operation is proposed, analyzed, and demonstrated for the first time. The three-core antiresonant-reflective-optical waveguide (ARROW) laser combines the relatively large fabrication tolerances of single-core ARROW-type devices with the excellent intermodal-discrimination properties of small-element-number ( 10) ROW arrays, which are known to have tight fabrication tolerances. For single-spatial-mode selectivity the device relies both on ARROW-type (lateral) reflectors and interelement loss. The effect of interelement loss on the resonant in-phase mode and the unwanted nonresonant modes is calculated, and the results are used to design optimal structures. For structures of index step, /spl Delta/n, of 0.1; element/interelement width ratio of 5; 500 cm/sup -1/ interelement-loss coefficient; and 7.5-/spl mu/m-wide individual elements, intermodal discrimination /spl ges/5 cm/sup -1/ is obtained over a relatively large range in /spl Delta/n: /spl sim/0.01. Above-threshold analysis shows that, due to strong index guiding, the structures are virtually immune to gain spatial hole burning. The central-lobe energy content is 65-70%, and the emitting aperture is 25 /spl mu/m, which should provide 1 W CW reliable single-mode power from devices with oxide-free facets. Preliminary experimental results are obtained from Al-free 0.98-/spl mu/m emitting structures: diffraction-limited beam operation up to 30/spl times/ threshold and 0.55 W peak pulsed output power. Finally it is shown that three-core ARROW devices used as integrated master oscillators (MOs) for flared antiguided master-oscillator power amplifiers (MOPAs), provide uniform MOPA near-field intensity profiles, thus opening the way to achieving 3-5 W CW diffraction-limited power from stable, flared MOPAs. >

Electrically-pumped directly-modulated tunable VCSEL for metro DWDM applications

We report the first electrically pumped tunable VCSELs with continuous tuning in 1530-1620 nm wavelength regime. The VCSELs are directly modulated at 2.5 Gbps (OC-48) rates and show error-free transmissions. Wavelength locking to ITU-grids are accomplished in 200 /spl mu/s.

Comprehensive above-threshold analysis of antiguided diode laser arrays

The effect of gain spatial-hole burning (GSHB), carrier diffusion and interelement loss on antiguided laser arrays is thoroughly analyzed. Nonresonant devices, due to the nonuniformity of the in-phase-mode near-field intensity profile, experience self-focusing and multimode operation with increasing drive level above threshold, similar to evanescent-wave-coupled devices. Resonant and near-resonant devices (i.e., resonant-optical-waveguide (ROW) arrays) display substantially uniform in-phase-mode near-field intensity profiles at all drive levels, thus not allowing excitation of high-order modes (i.e., adjacent modes) due to GSHB at the array level. However, GSHB at the individual-array-element level eventually allows adjacent-mode lasing at high drive levels: /spl ges/10/spl times/ fundamental-mode threshold for devices with relatively small ratio of element to interelement widths (so called fill factor): /spl sim/1.1; and /spl ges/7/spl times/ fundamental-mode threshold for devices with moderate fill factor (/spl sim/3) and 60 cm/sup -1/ interelement loss. (The carrier diffusion length is taken to be 3 /spl mu/m, and the index step, /spl Delta/n, is moderate: 0.02-0.03). The calculations agree well with many experimental results, and confirm the inherent single-spatial-mode stability of ROW arrays. The model also predicts that high-index-step (/spl Delta/n/spl ges/0.1) ROW arrays are likely to achieve in-phase-mode stability to drive levels /spl ges/15/spl times/ threshold, powers of /spl ap/3W, in beams with /spl ap/70% of the energy in the main lobe. Practical design guidelines are presented. >

Above‐threshold behavior of high‐power, single‐mode antiresonant reflecting optical waveguide diode lasers

Above‐threshold analysis of antiresonant reflecting optical waveguide (ARROW) diode lasers has been performed. One key finding is that preferential pumping of the (central) low‐index core region dramatically enhances the device single‐mode power capability, as a result of defocusing and subsequent radiation‐loss increase for the first‐order spatial mode. Stable, single‐mode operation to drive levels ≳10× threshold is predicted for 6‐μm wide core devices, in excellent agreement with experiment. Similar performance is found to hold true for ARROW devices with cores as wide as 10 μm, although due to gain spatial hole burning, the far‐field beam pattern experiences mild broadening. Study of triple‐core ARROW structures of 20‐μm‐wide aperture shows stable fundamental‐mode operation to ≳10× threshold, thus raising the prospect for stable, single‐mode reliable operation to power levels as high as 1 W cw.

Temperature dependence of light-current characteristics of 0.98-/spl mu/m Al-free strained-quantum-well lasers

The decrease of the differential efficiency of 0.98-/spl mu/m semiconductor lasers with temperature can make high power, high temperature applications difficult. We present an experimental and theoretical study of the temperature dependence of the internal quantum efficiency, internal loss and differential gain of 0.98-/spl mu/m InGaAs/InGaAsP/InGaP strained quantum well lasers. In contrast to some earlier results, our measurements show the dominance of internal loss, attributed to free carrier absorption, in determining the temperature dependence of the differential efficiency, and show that leakage current is negligible below 120/spl deg/C.<<ETX>>

Temperature dependent efficiency and modulation characteristics of Al-free 980-nm laser diodes

Temperature dependent efficiency and modulation characteristics of strained quantum-well (QW) InGaAs-InGaAsP-InGaP 980-nm laser diodes of various designs are analyzed using self consistent carrier transport analysis including stimulated emission. The decrease of the differential efficiency of 980-nm laser diodes with temperature is found to be caused by an increased modal loss attributed to the free carrier (electron and hole) absorption. The obtained results agree well with experimentally observed increase of internal loss at higher temperatures. Modulation characteristics are determined mainly by drift-diffusion in separate confinement region along with processes of carrier capture and escape in QWs. At high temperatures modulation bandwidth is reduced because of the decrease in differential gain. Graded index separate confinement heterostructure and multi-QW lasers show superior efficiency and modulation behavior at high temperatures. >

Flat‐phasefront fanout‐type power amplifier employing resonant‐optical‐waveguide structures

A novel type of fanout master‐oscillator power amplifier (MOPA) device using resonant antiguided structures is proposed, modeled, and demonstrated. Light injected in the central antiguide of an antiguided structure fans out, with increasing device length, due to resonant transmission between adjacent antiguide cores. After 1‐mm device length the emitting aperture becomes ≊100 μm wide, and the beam has a flat phasefront. The device has a strong built‐in index step (Δn=0.02–0.05), which makes it insensitive to the problems encountered with conventional fanout‐type amplifiers: filamentation and drive‐dependent beam pattern. Experimental results include flat‐phasefront and a diffraction‐limited emission from a 130‐μm‐wide exit aperture when the entry aperture is a 3‐μm‐wide antiguide core.

Transverse mode selection with a passive antiguide region in vertical cavity surface emitting lasers

We report a numerical analysis on the transverse mode behavior of a novel passive antiguide region buried heterostructure vertical cavity surface emitting laser, which emits a single stable transverse mode from a large aperture. Two- and three-dimensional beam propagation methods were used to calculate the threshold gains and the actual modal profiles for the fundamental and first order modes. We show that the passive antiguide structure is the main modal selection mechanism and the high order modes suffer much higher losses such that they are highly suppressed from reaching thresholds.<<ETX>>

VCSELs Go the Distance

Vertical-cavity surface-emitting la- sers (VCSELs) have come a long way in the past decade, evolving from a laboratory curiosity to a key component in fiber-optic communications in local area networks (LANs). Rapid advances are reported in 1.5-1.6-µm wavelength VCSELs with tunability and long-reach single-mode fiber transmission. With proven cost benefits in LAN applications, VCSELs are poised to meet the rising market demands of metropolitan area applications.