Uncooled 1.3-/spl mu/m complex-coupled DFB BH laser diodes with the Fe-doped InGaAsP-InP hybrid current-blocking grating

In this letter, we proposed an alternate method by using the Fe-doped InGaAsP-InP hybrid grating layers to fabricate the 1.3-/spl mu/m current-blocking-grating complex-coupled distributed-feedback (CBG CC-DFB) laser diodes (LDs) grown by metal-organic chemical vapor deposition (MOCVD). By combining the Fe-doped InGaAsP-InP grating layers, the CBG CC-DFB LDs can provide high optical DFB coupling coefficient and high current confining ability. Moreover, the current aperture in the lateral direction can be easily controlled by the self-aligned MOCVD regrowth process. Therefore, the manufacture of CBG CC-DFB buried heterostructure LDs is easy as the ridge-waveguide LDs. The LDs exhibit a low threshold current of 5.3 mA, a high slope efficiency of 0.42 mW/mA, and a stable single mode with a high sidemode suppression ratio of /spl sim/42 dB at two times the threshold (10.5 mA). Even at high temperatures, these LDs still have an extremely low threshold current of 15.8 mA at 90/spl deg/ and a small variation in slope efficient of only -1 dB at the temperatures between 20/spl deg/ and 80/spl deg/. Furthermore, these LDs show a high-speed characteristic of more than 11.8 GHz at 20/spl deg/, which are suitable for 10-Gb/s Ethernet and OC-192 applications.     

Single-transverse mode and stable-polarization operation underhigh-speed modulation of InGaAs-GaAs vertical-cavity surface-emittinglaser grown on GaAs (311) B substrate

We have demonstrated an oxide confinement vertical-cavity surface-emitting laser grown on a GaAs (311)B substrate, and achieved single-transverse mode and single-polarization operation in the entire tested current range. The threshold was 0.6 mA for a 2.7 μm×2.9 μm oxide aperture. Even under high-speed modulation up to 5 GHz, the device showed stable single-transverse mode and polarization. Sidemode suppression ratio and orthogonal polarization suppression ratio were over 30 and 10 dB, respectively     

Stable single-mode operation of an 850-nm VCSEL with a higher ordermode absorber formed by shallow Zn diffusion

We report that an 850-nm vertical-cavity surface-emitting laser with a planar higher order mode absorber, formed by shallow Zn diffusion (<0.3 μm), operated at stable single-mode over the entire drive current range. A device with a 5×5 μm² absorber aperture and a 5×5 μm² oxide confined active region showed a ~0.8 mA threshold and a mode suppression ratio of 40 dB. The modeling indicates that the higher order modes will be suppressed strongly due to the much larger threshold gain, compared to that of the fundamental mode as long as the Zn diffusion depth outside the 5×5 μm² absorber aperture is over ~0.2 μm, which agrees well with the experimental results     

1.3-μm GaInAsN Vertical-Cavity Surface-Emitting Lasers by Oxide-Planarized and Surface-Relief Processes for Single-Mode Operation

In this letter, we investigate and characterize the 1.3-mum single-mode vertical-cavity surface-emitting lasers (VCSELs) with two GaInAsN strained multiple quantum wells as the active region. Surface relief technique and a thick silicon oxide were used for the spatial mode filtering and the planarization processing, respectively. The VCSELs with a 5-mum-diameter surface-relief aperture and a 12-mum-diameter oxide-confined aperture at room temperature exhibit a threshold current of 3 mA, a slope efficiency of 0.14 mW/mA, a maximum operation temperature of 90 degC, and a single-mode behavior. These VCSELs show a maximum light output power of 1 mW for the single fundamental mode with a transverse-mode suppression of more than 30 dB and also show a clear eye-opening feature operated at 2.488 Gb/s and 12.6 mA     

Low-chirp and high-power 1.55-/spl mu/m strained-quantum-well complex-coupled DFB laser

High-power, low-chirp, and low-threshold current characteristics of 1.55 /spl mu/m complex-coupled compressively strained InGaAsP quantum-well DFB laser with a loss grating are presented. Kink-free light-current characteristics with single-mode power over 40 mW are demonstrated for uncoated devices. A relatively low threshold current of 10 mA and a high slope efficiency of 0.23 W/A have been obtained even with the loss grating employed. Stable single-mode emission was demonstrated with a side mode suppression ratio up to 54 dB, a low chirp of less than 0.3 nm under 1 Gb/s pseudorandom digital modulation and a spectral linewidth of 8 MHz.     

High-power fundamental-mode and polarisation stabilised VCSELs using sub-wavelength surface grating

A monolithic technique is presented for simultaneous mode and polarisation control in oxide-confined VCSELs using a locally etched sub-wavelength surface grating. A single-fundamental-mode emission with an SMSR >30 dB and an OPSR /spl sim/20 dB is achieved over the entire operational current range, with a maximum output power of 4.1 mW.     

All-active tapered 1.55-/spl mu/m InGaAsP BH-DFB laser with continuously chirped grating

We demonstrate the first realization of all-active tapered index coupled 1.55-/spl mu/m InGaAsP buried-heterostructure distributed feedback lasers involving chirped gratings. The variation of the effective refractive index along the tapered active stripe is compensated using an optimized continuously chirped grating. The grating has been formed using a novel direct-write electron-beam lithography technique. Lasers with an antireflection/cleaved cavity show stable single-mode operation and high optical output power up to 60 mW. The yield of lasers with a sidemode suppression ration > 40 dB is more than 70%. The -3-dB farfield angles (full-width at half-maximum) amount to 14/spl deg/ and 20/spl deg/ in lateral and vertical direction, respectively.     

表面光栅垂直腔面发射激光器偏振特性研究

研究了表面光栅结构对垂直腔面发射激光器(VCSEL)的偏振控制作用。引入表面光栅后,对不同刻蚀深度下的偏振相关的镜面损耗进行了仿真,结果表明表面光栅刻蚀深度在44~130 nm范围内均可实现稳定偏振,具有较大的工艺容差。表面光栅VCSEL在基横模工作状态下偏振抑制比(Orthogonal Polarization Suppression Ratio, OPSR)超过20 dB,偏振光谱峰间偏振抑制比达到40 dB,且在多横模状态也实现了有效的偏振控制。为了进一步验证光栅对偏振控制的效果,制作了方向互相垂直的两种表面光栅,具有这两种方向光栅的VCSEL的OPSR均达20 dB以上。测试分析表明表面光栅是VCSEL实现稳定偏振的一种有效手段。     

Highly linear-polarized external cavity lasers hybrid integrated on planar lightwave circuit platform

We propose and demonstrate, for the first time, a highly linear-polarized external cavity laser (ECL) integrated on planar lightwave circuit (PLC) with an in-PLC polarizer designed to improve polarization extinction ratio (PER). The in-PLC polarizer based on a 45/spl deg/-tilted grating was simply formed in the laser cavity composed of a Fabry-Pe/spl acute/rot laser diode and a Bragg grating. The proposed ECL exhibited a PER value as high as 30 dB and single longitudinal mode oscillation with a high sidemode suppression ratio of 50 dB at 1310 nm.     

InAs-InAlGaAs quantum dot DFB lasers based on InP [001]

The InAs-InAlGaAs quantum dot (QD) lasers with the InAlGaAs-InAlAs material system were fabricated on distributed feedback (DFB) grating structures on InP [001]. The single-mode operation of InAs-InAlGaAs QD DFB lasers in continuous-wave mode was successfully achieved at the emission wavelength of 1.564 /spl mu/m at room temperature. This is the first observation on the InP-based QD lasers operating around the emission wavelength window of 1.55 /spl mu/m. The threshold current density of the InAs-InAlGaAs QD DFB laser with a cavity length of 1 mm and a ridge width of 3 /spl mu/m, in which one of the cleaved facets was coated with 95% high-reflection, was 1.23 kA/cm/sup 2/ (176 A/cm/sup 2/ for single QD layer). The sidemode suppression ratio value of the QD DFB laser was as high as 42 dB at the driving current of 100 mA.     

Complex-coupled quantum cascade distributed-feedback laser

Quantum-cascade distributed-feedback lasers (QCDFB) with a grating close to the active region are reported. Feedback is provided by the grating in a refractive index-dominated coupling scheme. Reliable single-mode emission at /spl lambda//sub cm//spl ap/5.4 /spl mu/m with a side-mode suppression ratio (SMSR) /spl ap/30 dB is observed. The laser is continuously tunable over 40 nm with a coefficient of /spl Delta//spl lambda///spl Delta/T/spl ap/0.37 nm/K in the temperature range from 200 K to 300 K. Comparison with Fabry-Perot QC lasers shows an overall improved performance of QC-DFB lasers.     

Single-frequency, single-spatial-mode ROW-DFB diode laser arrays

Single-frequency, stable single-spatial-mode operation from large-aperture (40-60 /spl mu/m) index-guided devices is demonstrated from resonant antiguided phase-locked InGaAs-InGaP-GaAs diode-laser arrays incorporating 2nd-order distributed-feedback gratings (i.e., ROW-DFB arrays). The devices operate in a single-spatial-mode up to 3.6/spl times/threshold, and truly single-mode (i.e., single-spatial-mode and single-frequency) up to 2/spl times/threshold, For 40 (60)-/spl mu/m-aperture 10-element arrays, the beam pattern is in-phase and diffraction-limited with 70% (75%) of the power residing in the main lobe. Single-frequency operation is obtained from 9640-9652 /spl Aring/, over a temperature range of approximately 20/spl deg/C, side-mode suppression ratios /spl ges/20 dB are recorded up to 2/spl times/threshold.     

Optimized integrated surface grating design for polarization-stable VCSELs

Monolithically integrated surface gratings have proven to control the polarization of single-mode and even multimode vertical-cavity surface-emitting lasers (VCSELs) very effectively. Unfortunately, up until now, the grating parameters have had to be known and realized very accurately for proper performance. The simulations and experimental results presented in this paper show in very good agreement that by changing the thickness of the cap layer of the VCSEL structure, the dependence of the polarization control on the grating parameters can be strongly reduced. With this modification, for multimode devices, we have achieved a stable polarization of all modes orthogonal to the grating grooves independent of the investigated grating period, the grating depth, and the orientation of the grating itself. The orthogonal polarization suppression ratio is, on average, 17.1 dB and exceeds 12 dB for 117 out of 120 highly multimode VCSELs. At the same time, the optimized layer design significantly reduces the diffraction in the far field, which occurs for grating periods larger than the emission wavelength of the laser.     

Comprehensive above-threshold analysis of antiresonant reflecting optical waveguide edge-emitting diode laser

A three-dimensional (3-D) above-threshold analysis has been performed for laterally antiguided laser structures of the antiresonant-reflecting-optical-waveguide type, of relatively large core width (/spl sim/ 10 /spl mu/m), for high-power, single-spatial-mode operation. A 3-D numerical code has been developed, which takes into account carrier diffusion in the quantum well as well as edge radiation losses. The laser characteristics are calculated as functions of the above-threshold drive level. Within the simulation, 3-5 higher order optical modes on a "frozen background" are computed by the Arnoldi algorithm. Because of the nonuniform gain saturation of the lasing mode, the modal gains for higher order modes increase with the drive current due to increasing overlap of their fields with the two-dimensional gain distribution. The onset of threshold for higher order modes puts an upper limit on the range for stable single-mode operation. The above-threshold analysis is done for various values of the width of the reflector region, below and above the lateral-antiresonance condition. It is found that the maximum intermodal discrimination, which in turn provides the maximum single-mode power, is obtained when the reflector-region width is /spl sim/25 % larger that its value at antiresonance. Then, for 10-/spl mu/m-core devices, stable, single-mode operation is found to occur to drive levels as high as 41 /spl times/ threshold, with single-mode output powers as high as 1.45 W.     

Modal analysis and engineering on InP-based two-dimensional photonic-crystal microlasers on a Si wafer

We report results on hexagonal-shaped microlasers formed from two-dimensional photonic crystals (PCs) using InP-based materials transferred and bonded onto SiO/sub 2// Si wafers. Two types of hexagonal cavities are investigated : single defect (one hole missing) cavities, so-called H1 cavities (1 /spl mu/m in diameter) and two holes missing per side H2 cavities (2 /spl mu/m in diameter). Their optical properties are analyzed using photoluminescence experiments, and plane wave method simulations have been performed for comparison. High Q modes (/spl sim/600/700) have been measured and they have been shown to enable laser effect at room temperature, under pulsed optical pumping (15% duty cycle and 25-ns pulsewidth). The study of these efficient mode characteristics gives guidance for further improvement of the operation conditions of PC lasers, such as the reduction of the threshold pumping power.     

Numerical aperture of single-mode photonic crystal fibers

We consider the problem of radiation into free space from the end-facet of a single-mode photonic crystal fiber (PCF). We calculate the numerical aperture NA = sin /spl theta/ from the half-divergence angle /spl theta/ /spl sim/ tan/sup -1/ (/spl lambda///spl pi//spl omega/) with /spl pi//spl omega//sup 2/ being the effective area of the mode in the PCF. For the fiber first presented by Knight et al. (1996), we find a NA /spl sim/ 0.07 which compares to standard fiber technology. We also study the effect of different hole sizes and demonstrate that the PCF technology provides a large freedom for NA engineering. Comparing to experiments we find good agreement.     

High-power single-mode antiresonant reflecting optical waveguide-type vertical-cavity surface-emitting lasers

Antiresonant reflecting optical waveguide (ARROW) techniques are employed in vertical cavity surface emitting lasers (VCSELs) to achieve high-power single-mode emission. Using the effective-index method and fiber mode approximation, the cold-cavity lateral modal behavior for the circular shaped ARROW VCSEL demonstrates significant reduction of radiation loss from that of a single antiguide, while maintaining strong discrimination against high-order modes. The circular-waveguide is created by selective chemical etching and two-step metal-organic chemical vapor deposition growth, with proton implantation used to confine the current injection to the low-index core region. A single-mode CW power of 7.1 mW has been achieved from an 8 /spl mu/m diameter ARROW device (index step /spl Delta/n = 0.05, emission at /spl lambda//sub 0/ = 980 nm) with a far-field FWHM of 10/spl deg/. Larger aperture (12 /spl mu/m) devices exhibit multimode operation at lower drive currents with a maximum single-mode continuous-wave output power of 4.3 mW.     

Low-threshold loss-coupled laser diode by new grating fabrication technique

In this letter, we introduce a novel fabrication method to make InGaAs absorptive first-order grating for loss-coupled distributed feedback laser diode (DFB-LD) using reactive ion etching. By this technique, it is possible to control duty rate of the first-order grating. A very-low-threshold current of 6 mA was obtained from our loss-coupled LD at the wavelength of 1.547 /spl mu/m, which was unusually high for a loss-coupled LD because of the excessive light absorption. In addition to the low-threshold current, it shows high SMSR and longitudinal single-mode yield as high as 50 dB and 90%, respectively.     

Single-mode and polarization-independent silicon-on-insulator waveguides with small cross section

The fabrication restrictions that must be imposed on the geometry of optical waveguides to make them behave as single-mode devices are well known for relatively large waveguides, with shallow etch depth. However, the restrictions for small waveguides (/spl sim/1 /spl mu/m or less in cross section) are not well understood. Furthermore, it is usually a requirement that these waveguides are polarization independent, which further complicates the issues. This paper reports on the simulations of the conditions for both single-mode behavior and polarization independence, for small and deeply etched silicon-on-insulator (SOI) waveguides. The aim is to satisfy both conditions simultaneously. The results show that at larger waveguide widths, waveguide etch depth has little effect on the mode birefringence because the transverse-electric (TE) mode (horizontal-polarized mode) is well confined under the rib region. However, at smaller rib widths, the etch depth has a large influence on birefringence. An approximate equation relating the rib-waveguide width and etch depth to obtain polarization-independent operation is derived. It is possible to achieve single-mode operation at both polarizations while maintaining polarization independence for each of the waveguide heights used in this paper but may be difficult for other dimensions. For example, a 1-/spl mu/m SOI rib waveguide with an etch depth of 0.64 /spl mu/m and rib width of 0.52 /spl mu/m is predicted to exhibit such characteristics.     

Wavelength-switchable erbium-doped fiber ring laser using spectral polarization-dependent loss element

We propose a wavelength-switchable erbium-doped fiber ring laser that uses a spectral polarization-dependent loss element. The element was fabricated by inscribing a long-period grating on a polarization-maintaining fiber. Dual-wavelength switching operation was accomplished by rotating the polarization plane of the fiber laser cavity. The amplitude variation of both laser lines was measured to be less than 1 dB and the signal-to-amplified spontaneous emission ratio was more than /spl sim/40 dB.