Design and evaluation of fundamental-mode and polarization-stabilized VCSELs with a subwavelength surface grating

We demonstrate 850-nm oxide-confined vertical-cavity surface-emitting lasers (VCSELs) with a locally etched subwavelength surface grating that are single-mode and polarization stable from threshold up to thermal roll-over, reaching /spl sim/4 mW of output power. The side-mode suppression ratio (SMSR) is >30 dB and the orthogonal polarization suppression ratio (OPSR) is /spl sim/20 dB. Moreover, no distortion of the far-field beam profile is observed as a result of the surface grating. Our numerical calculations show that a carefully designed VCSEL can have a high simultaneous mode and polarization selectivity without a significant increase in loss for the favored fundamental mode with polarization state perpendicular to the grating lines. This indicates characteristics such as threshold current and resonance frequency will not be notably degraded. The calculations also show a low sensitivity to variations in grating etch depth and duty cycle, which relaxes fabrication tolerances. In our experimental parametric study, where the oxide aperture diameter, surface grating diameter, and grating duty cycle were varied, the combined mode and polarization selection was investigated. For an optimum combination of oxide aperture and surface grating diameters of 4.5 and 2.5 /spl mu/m, respectively, the device is found to be single-mode and polarization stable for a broad range of grating duty cycles, from 55% to 75%, with only a small variation in other laser performances, which is in line with theory.     

Dynamic behavior of fundamental-mode stabilized VCSELs using a shallow surface relief

An extensive theoretical study was performed on the dynamic behavior of 850-nm-wavelength oxide-confined fundamental-mode stabilized vertical-cavity surface-emitting lasers (VCSELs), using a shallow surface relief. The surface relief is used to provide lower mirror loss for the fundamental mode, thus acting as a mode discriminator. In this way, single-mode operation at high power levels can be obtained. We utilized a comprehensive model that includes the detailed epitaxial layer structure and device geometry when calculating the optical fields and that accurately accounts for the dynamic effects of carrier density and temperature on the modal distributions. Modulation response, eye diagrams, bit error rate (BER), and relative intensity noise (RIN) were simulated and compared to the performance of VCSELs without a mode discriminator, i.e., conventional multimode VCSELs. The fundamental-mode stabilized VCSELs are associated with a higher out-coupling, which lowers the relaxation oscillation frequency and damping, and strong spatial hole burning, which induces a low-frequency roll-off in the modulation response and contributes to the damping of the relaxation oscillation at low bias. However, their dynamics is fully competitive with conventional multimode VCSELs at both 2.5 and 10 Gb/s although they exhibit a slightly higher eye closure. We only found a 0.5-dB power penalty in the BER. The RIN is enhanced, with a peak that is about 10-15 dB higher, caused by the lower damping of the relaxation oscillation. It should be noted that in the comparison we assume that all modes are equally captured from the multimode VCSEL. A mode-selective loss can severely degrade its performance.     

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.     

Single fundamental-mode output power exceeding 6 mW from VCSELs with a shallow surface relief

A single fundamental-mode output power of 6.5 mW was achieved from an 850-nm vertical-cavity surface-emitting laser (VCSEL) with a shallow surface relief, the highest single-mode power ever reported using this technique. The VCSELs were fabricated from epitaxial material grown to yield an antiphase reflection from the topmost layer. A circular surface relief, acting as a mode discriminator, was etched in the center to reduce the mirror loss for the fundamental mode. This "inverted" surface-relief technique offers relaxed etch depth control and, therefore, improves reproducibility and yield.     

新型亚波长光栅横向腔面发射激光器

本文报道一种新型的横向腔面发射激光器,基于亚波长光栅平面内的横向谐振与垂直发射。器件采用不含DBR结构的商用波导外延材料,不需要晶片键合技术。在1552.44 nm处获得了23.0 dB的边模抑制比,最高输出功率5.32 mW。此单模激射与带边模式计算相吻合。在3维的模拟中,我们观察到光栅表面的光输出。     

Reflected circular polarisation conservation using textured surface

Provided is the first experimental verification that a suitably designed textured surface can reflect a normally incident circularly polarised wave with the same sense. This is achieved by engineering the reflection phase of the orthogonal linearly polarised components of the incident wave by modifying the dimensions of the patches from which the textured surface is constructed such that they are 180deg out of phase with each other. It is shown that the axial ratio of an incident right-hand circularly polarised signal is 0.8 dB at 3.86 GHz and that the reflected signal is also right-hand circular.     

Facet and grating reflectivity effects in wavelength stabilised uncooled pump lasers

The performance of an uncooled 980 nm fibre Bragg grating stabilised pump laser in miniature dual-in-line package as a function of laser front facet reflectivity (R/sub f/) and grating reflectivity (R/sub g/) is reported. The quantitative analysis on workable bounds for R/sub f/ and R/sub g/ with multiple devices is presented.     

High density self assembled nanoparticle film with temperature-controllable interparticle spacing for deep sub-wavelength nanolithography using localized surface plasmon modes on planar silver nanoparticle tunable grating

A novel photolithographic technique using a periodic hexagonal close packed silver nanoparticle 2D array photo mask has been demonstrated to transfer a nano-pattern into a photoresist using G-I line proximity photolithography. This method can be made to precisely control the spacing between nanoparticles by using temperature. The high-density nanoparticle thin film is accomplished by self assembly through the Langmuir-Schaefer (LS) technique on a water surface and then transferring the particle monolayer to a temperature sensitive polymer membrane. A 30 nm hexagonal close packed silver nanoparticle 2D array pattern with a 50 nm period has been successfully transferred into S1813 photoresist using I-line exposure wavelength. The resultant feature sizes were 34 nm with a period of 46 nm, due to the surface plasmon resonance where the S1813 photoresist feature is approximately 11 times smaller than I-line exposure wavelength.     

Apodised sampled grating using InGaAsP/InP deep-ridge waveguide with vertical-groove surface grating

An apodised sampled grating was fabricated using an InGaAsP/InP deep-ridge waveguide with vertical-groove surface grating for use in a tunable optical filter. The fabricated grating exhibited a comb-like filter response with a relatively wide transmission bandwidth of 52 GHz and a high extinction ratio of 15 dB.     

Optical interconnection using VCSELs and polymeric waveguidecircuits

We investigated the waveguide loss and transmission characteristics for optical interconnection using vertical-cavity surface-emitting lasers (VCSELs) and multimode polymeric waveguide circuits with crossings. The excess loss with 100 crossings is 2.2 dB when the image magnification from a VCSEL to a waveguide is 2.3. We obtained error-free (i.e., bit error rate <10^-11) optical interconnection at 1.0625 Gbps regardless of the number of crossings or the magnification. These results suggest the practicality of large-scale optical interconnection between VCSEL-based smart-pixel chips using multimode waveguides with more than 100 crossings     

Silica-based 2.5%-/spl Delta/ arrayed waveguide grating using simple polarisation compensation method with core width adjustment

Silica-based 2.5%-Delta arrayed waveguide gratings using a polarisation compensation method with simple circuit design are demonstrated based on core width adjustment in the array. Experimental results show that the polarisation-dependent wavelength shift can be adjusted by optimising chirping parameters for core width     

High Q reflection filter using a gradient-index membrane with a grating surface

High Q reflection filter using a gradient-index (GI) membrane with a grating surface is proposed. The thickness of GI membrane is very small comparing with the traditional multilayer reflection filter or the GI reflection filter, and the GI membrane can also break the restriction of the resonant excitation condition of the conventional guided-mode resonance (GMR) filter. High Q filtering features can be maintained even on the high-index substrate. The grating thickness of the GI membrane filter can be used to select the resonance wavelength with different quality factors (QFs), the reflection peak is blue-shifted, and the QF is decreased from 554.4 to 207.8 as the grating thickness is increased from 50 nm to 150 nm. The gradient coefficient of the GI membrane filter can be used to tailor the number of the reflection channels.The resonant excitations of high order waveguide modes confined in the GI membrane are responsible for the high Q filtering properties with multiple channels.     

Fabrication and Characteristics of high-speed oxide-confined VCSELs using InGaAsP-InGaP strain-compensated MQWs

This paper presents the fabrication and characteristics of high-performance 850-nm InGaAsP-InGaP strain-compensated multiple-quantum-well (MQW) vertical-cavity surface-emitting lasers (VCSELs). The InGaAsP-InGaP MQW's composition was optimized through theoretical calculations, and the growth condition was optimized using photoluminescence. These VCSELs exhibit superior performance with characteristics threshold currents /spl sim/0.4 mA and slope efficiencies /spl sim/0.6 mW/mA. The threshold current change with temperature is less than 0.2 mA, and the slope efficiency drops less than /spl sim/30% when the substrate temperature is raised from room temperature to 85/spl deg/C. A high modulation bandwidth of 14.5 GHz and a modulation current efficiency factor of 11.6 GHz/(mA)/sup 1/2/ are demonstrated. The authors have accumulated life test data up to 1000 h at 70/spl deg/C/8 mA.     

Variable polarisation compensator using artificial dielectrics formillimetre and submillimetre waves

A variable polarisation compensator has been designed and demonstrated experimentally at 100 GHz. The device uses two silicon plates with interlocking artificial dielectric surfaces to produce a birefringence that varies with the separation distance. The experimental results indicate a maximum differential phase-shift of 74°, and show good agreement with computer simulations     

Polarisation- and pattern-independent optical FSK heterodyne system using data-induced polarisation switching

Data-induced polarisation switching is a simple yet powerful technique to solve the polarisation problem in optical FSK heterodyne systems. The authors achieve a polarisation- and pattern-independent sensitivity of -53.5 dBm for a 140 Mbit/s FSK receiver. The response time to polarisation changes is estimated as 100 ns.<>     

Transmission-type SPR sensor based on coupling of surface plasmons to radiation modes using a dielectric grating

A transmission-type surface plasmon resonance (SPR) sensor is presented. In the transmission-type SPR structure, surface plasmon waves are outcoupled to radia-tion modes by the use of dielectric grating on a thin-film layer of Ag. Compared with the traditional reflection-type SPR sensor, the new method provides larger detectable range, which might be useful to investigate thick targets such as in cell analysis. Theoretical simulations show that the structures provide high transmission efficiency for surface plasmon resonance and the devices present extre-mely linear sensing characteristics. Furthermore, it is found that the transmission efficiency and the refractive index detection sensitivity of the SPR sensor can be improved by the use of a lower refractive index glass prism.     

Non-polarization and high-coupling-efficiency coupler using multilevel grating structure

A multilevel grating coupler based on silicon-on-insulator (SOI) material structure is proposed to realize the coupling between waveguide and waveguide or waveguide and fiber. This coupler is compatible with the current fabrication facilities for complementary metal oxide semiconductor (CMOS) technology with vertical coupling. This structure can realize coupling when the beams with transverse electric (TE) polarization and transverse magnetic (TM) polarization are incident at the same time. The influences of the grating coupler parameters including wavelength, the thickness of waveguide layer, the thickness of SiO₂ layer and the number of steps on the TE mode and TM mode coupling efficiencies are discussed. Theory researches and simulation results indicate that the wavelength range is from 1533 nm to 1580 nm when the TE mode and TM mode coupling efficiencies are both more than 40% as the grating period is 0.99 μm. The coupling efficiencies of the incident TE and TM modes are 49.9% and 49.5% at the wavelength of 1565 nm, respectively, and the difference between them is only 0.4%.     

Generation of 880 MHz surface acoustic wave by transduction from bulk wave using corrugation grating on GaAs

Efficient transduction from bulk to surface waves by a holographic grating on a GaAs crystal has been demonstrated. The beam profiles for 880 MHz surface waves propagating on the GaAs were measured by an optical probing method.     

Optical frequency scanning of a stabilised and linewidth-reduced multielectrode DFB laser using current feedback

Optical frequency scanning of a stabilised and linewidth-reduced multielectrode DFB laser has been demonstrated using a current feedback technique. The scanning range of the linewidth-reduced multielectrode DFB laser was 4? (50 GHz) and 9? (120 GHz) when the linewidth was reduced to 1/50 and 1/20, respectively, of that of a free-running state laser.     

Second- and third-order dispersion compensator using ahigh-resolution arrayed-waveguide grating

We have proposed a dispersion compensation scheme that uses a high-resolution arrayed-waveguide grating (AWG). When the diffraction order of the AWG is 59 and the number of waveguides in an arrayed-waveguide is 340, the calculated maximum second- and third-order dispersion compensation range is 18.0 ps/nm and ±6.0 ps/nm² , and 1100 ps/nm and ±937.5 ps/nm², for a 1 ps-pulse and a 12.5 ps-pulse, respectively. In experiments, second-order dispersion (-0.8 to +5.2 ps/nm) is effectively compensated for 1,1-ps pulses; and. Pulse compression by third-order dispersion compensation is successfully demonstrated