Improved spectral properties of an optically pumped semiconductor disk laser using a thin diamond heat spreader as an intracavity filter

This letter describes an optically pumped high-power InP-based semiconductor disk laser with a thin (50 /spl mu/m) diamond heat spreader bonded to the surface of the gain chip. The diamond heat spreader performs the multiple functions of heat removal, spectral filtering, and wavelength stabilization by utilizing the high thermal conductivity and the low thermooptic coefficient of diamond, along with the large free-spectral range of a thin intracavity etalon. A pump-power-limited output power of 680 mW at 1.55 /spl mu/m is demonstrated at a heat sink temperature of -30/spl deg/C, and 140 mW at room temperature. The spectral width was measured to be less than 0.08 nm and the spectral drift with temperature and pump power as low as 0.03 nm//spl deg/C and 0.14 nm/W, respectively.     

Tunable polymer optical add/drop filter for multiwavelength networks

We present a polymer optical add/drop filter with a channel cross-talk of -18.5 dB, a free spectral range of 12.8 nm and a channel spacing of 400 GHz (4 channels) as well as a tunable optical filter with a free spectral range of 50 nm. Both filter designs are based on a synthesis which provides the minimum number of filter stages for a given channel crosstalk and number of channels. Wavelength tunability over the entire free-spectral range (FSR) is demonstrated with applied heating powers of 500 mW. For the narrow bandwidth filter we used a fluorinated high temperature stable polymer as the waveguiding material, which has proven to exhibit losses as low as 0.25 dB/cm at a wavelength of 1.55 /spl mu/m.     

Design of polarization-insensitive ring resonators in silicon-on-insulator using MMI couplers and cladding stress engineering

A novel silicon-on-insulator (SOI) ring resonator design is described that uses a 2 /spl times/ 2 multimode interference coupler to achieve polarization-independent coupling, and cladding stress induced birefringence control to eliminate the difference in round-trip phase accumulation between the transverse-electric and transverse-magnetic polarized modes. The design parameters are determined for polarization-independent SOI ring resonators with couplers having a 50 : 50 or 15 : 85 splitting ratio, and 1.5-/spl mu/m ridge height and width. As designed, the resonators offer a polarization-independent free-spectral range of 0.5 nm for a ring radius of 200 /spl mu/m, and a quality factor Q as high as 55 000.     

Laterally coupled InP-based single-mode microracetrack notch filter

We demonstrate an InP-based microracetrack notch filter with >25-dB extinction and 19-nm free-spectral range at 1550 nm. The curved section of the resonator has a radius of 2.25 /spl mu/m. To our knowledge, this represents the best extinction and the smallest radius of curvature for such a device to date.     

Measurement of gain, group index, group velocity dispersion, and linewidth enhancement factor of an InGaN multiple quantum-well laser diode

Gain, group index, group velocity dispersion (GVD), temperature variation of refractive index, and linewidth enhancement factor of an In/sub 0.15/Ga/sub 0.85/N/In/sub 0.02/Ga/sub 0.98/N multiple quantum-well blue laser diode was measured using the Fourier transform method as a function of wavelength from 400 to 410 nm. At the lasing wavelength (403.5 nm), the group index is 3.4, the GVD (dn/sub g//d/spl lambda/) is -37 /spl mu/m/sup -1/, the temperature variation of refractive index dn/dT is 1.3/spl times/10/sup -4/ K/sup -1/, and the linewidth enhancement factor is 5.6.     

A 43-W C-band tunable narrow-linewidth erbium-ytterbium codoped large-core fiber laser

The authors report a widely tunable and highly efficient cladding-pumped erbium-ytterbium codoped large-core fiber laser, generating up to 43 W of output power at /spl sim/1.5 /spl mu/m with a narrow linewidth (0.16-nm full-width at half-maximum) and a good beam quality (M/sup 2/<1.7). By use of a tunable narrow-band fiber Bragg grating, the laser wavelength was tuned from 1532 to 1567 nm, limited upwards by the tuning range of the fiber grating. The overall slope efficiency was 32% with respect to launched pump power.     

A fully integratable 1.55-/spl mu/m wavelength continuously tunable asymmetric twin-waveguide distributed Bragg reflector laser

We demonstrate a single-frequency continuously tunable three-section distributed Bragg reflector laser operating at a center wavelength of /spl lambda//sub 0/=1.548 /spl mu/m using a fully integratable asymmetric twin-waveguide structure. A low-loss tapered mode transformer couples the light between the active waveguide, or gain region, and the passive ridge waveguide where the phase and grating tuning sections are located. The device has a threshold current of 50 mA and output power of nearly 13 mW, with a slope efficiency of 0.12 W/A and a tuning range of 4.8 nm under pulsed operation. An independent phase section is used to continuously tune the wavelength, thus avoiding mode hops. Using a delayed self-heterodyne technique, we determine the linewidth to be (146/spl plusmn/2) kHz.     

Neodymium-doped cladding-pumped aluminosilicate fiber laser tunable in the 0.9-/spl mu/m wavelength range

A tunable high-power cladding-pumped neodymium-doped aluminosilicate fiber laser is demonstrated. The maximum power reached was 2.4 W with a slope efficiency of 41% and a threshold pump power of 1.68 W, both with respect to launched pump power, when cladding pumped by two 808-nm diode pump sources at both fiber ends. The dependence of the tuning range on the fiber length is investigated. The tuning range changed from 922 to 942 nm for a 25-m-long fiber to 908-938 nm with a 14-m-long fiber, because of reabsorption effects. The output linewidth was 0.26 nm in a diffraction-limited beam. Operation on the challenging 0.9-/spl mu/m three-level transition in neodymium-doped double-clad fiber laser was facilitated by a W-type core refractive index profile. This filtered out the unwanted and competing strong transition at 1.06 /spl mu/m while guidance of 0.9 /spl mu/m remained intact.     

Two-dimensional symmetric multimode interferences in silicon square waveguides

Symmetric interference in two-dimensional multimode silicon waveguides is experimentally investigated. For a 100/spl times/100 /spl mu/m/sup 2/ cross section, 2700-/spl mu/m-long waveguide fabricated on silicon-on-insulator substrate, an 8/spl times/8 matrix of replicated images with high contrast ratio is demonstrated for 1530-1570 nm wavelength range. Symmetric interference results in reduced device length, and the actual device length is consistent with the theoretical expectation. The device also exhibits stable imaging in terms of good loss uniformity, and low wavelength and polarization dependencies among the replicated images.     

1.4-/spl mu/m InGaAsP-InP strained multiple-quantum-well laser for broad-wavelength tunability

InGaAsP-InP strained multiple-quantum-well (MQW) lasers for extended wavelength tunability in external cavity operation were designed, fabricated, and tested. The active layer was a strain compensated structure consisting of three 3.2/spl plusmn/0.3 nm and three 6.4/spl plusmn/0.3 nm 1.0% compressive strained wells and five 10.3/spl plusmn/0.3 nm 0.45% tensile strained barrier layers. A 2-/spl mu/m-wide ridge waveguide laser of length 250 /spl mu/m, when used in a grating external cavity and with no coatings to alter the reflectivity of the facets, was observed to operate over a range >110 nm. The lasers were designed for applications in trace gas and liquid detection with the goal to maximize the tunable range when operated in external cavities and with no facet coatings.     

Triple-frequency operation of an Er-doped twincore fiber loop laser

Simultaneous laser operation of three single-frequency modes from an inhomogeneously broadened Er-doped twincore fiber loop laser is reported. Equal output power of 390 /spl mu/W, separation 0.5 nm, and linewidth <10 kHz were measured for each mode in a travelling wave cavity comprising a single gain medium. In addition up to eight wavelength operation has been observed, demonstrating that twincore EDFA's can provide channel equalization in an eight-channel multiamplifier optical network.     

Arrayed waveguide grating of 70/spl times/60 /spl mu/m/sup 2/ size based on Si photonic wire waveguides

A miniature arrayed waveguide grating of 70/spl times/60 /spl mu/m/sup 2/ size consisting of Si photonic wire waveguides was designed using complete modelling in the finite-difference time-domain simulation. The device was fabricated onto a silicon-on-insulator substrate and evaluated in the wavelength range around 1.55 /spl mu/m. The clear demultiplexing characteristics were observed with a channel spacing of 11 nm and a loss of less than 1 dB.     

InP-based passive ring-resonator-coupled lasers

The design of passive ring-coupled lasers based on InGaAsP waveguides is investigated using a beam propagation method. Mode coupling, propagation loss due to bending, and scattering loss from waveguide sidewall roughness are taken into account. By compromising threshold gain, linewidth and side-mode suppression ratio (SMSR), suitable waveguide width and coupling strength are determined for different ring sizes. Using a ring with radius ranging from 20 to 200 /spl mu/m, it is possible to design passive ring-coupled lasers with threshold gain less than 60/cm and 80/cm for waveguide sidewall roughness 5 and 10 nm, respectively, SMSR larger than 50 dB, and linewidth in the range of /spl sim/3-500 kHz.     

MEMS tunable resonant leaky mode filters

A tunable double-grating resonant leaky mode microelectromechanical-type element is introduced. A significant level of tunability is demonstrated by adjusting mechanically the structural symmetry of the grating profile. Tuning is also possible by variation of the thickness of the resonant layer. For a particular example silicon-on-insulator structure treated, it is shown that the resonance wavelength can be shifted by /spl sim/300 nm with a horizontal movement of /spl sim/120 nm within the 1.4-1.7-/spl mu/m wavelength band. Additionally, the reflectance can be varied from /spl sim/10/sup -3/ to 1 at central wavelength of 1.55 /spl mu/m with a vertical movement of /spl sim/200 nm. These results demonstrate new possibilities in design of tunable optical devices.     

Compact fully fibre integrated source of 100 fs pulses at 1.1 /spl mu/m based on compression in holey fibre

A simple, compact, fully fibre integrated source of /spl sim/100 fs pulses at a wavelength of 1.1 /spl mu/m is reported. 4 ps pulses at 1063 nm from a modelocked fibre laser were amplified to 23 mW in a ytterbium-doped fibre amplifier and subsequently propagated through 62 m of holey fibre with a zero dispersion wavelength at 1040 nm. Soliton formation, breakup and self frequency shift resulted in the formation of /spl sim/100 fs pulses at 1.1 /spl mu/m. Wavelength tunability from 1113 to 1220 nm is demonstrated.     

Submicrometer Electron-Beam Direct Writing Technology for 1-Mbit DRAM Fabrication

A 1-Mbit DRAM with 0.5-/spl mu/m minimum linewidth is fabricated using variable shaped e-beam direct writing technology. A simple linewidth control technique using newly developed submicrometer resists is developed to achieve high resolution and better linewidth accuracy. In addition, a highly accurate registration technique is developed to ensure required overlay. These techniques are successfully used to achieve overlay accuracy of 0.04 /spl mu/m(sigma) and linewidth deviation of 0.018 /spl mu/m(sigma) in the fabrication.     

Low-voltage high-contrast n-i-p-i-based waveguide modulators with alloyed selective contacts

We investigated an electroabsorptive n-i-p-i waveguide modulator based on the Franz-Keldysh effect (FKE), which is especially designed to operate with very low voltage swings over a broad wavelength range. In order to contact the n-i-p-i structure, the layer sequence and annealing conditions of Au-Zn-Au and Ni-Ge-Au contacts were optimized with respect to good selectivity and low contact resistance. The transmission measurements yield a contrast ratio of 30 dB, achieved with a voltage swing less than 1.5 V at a wavelength of 910 /spl mu/m with a 900-/spl mu/m-long waveguide modulator. Contrast ratios of /spl ges/20 dB have been obtained within the whole spectral range from 910 nm to 940 mm with a voltage swing less than 2 V. The absorption loss due to the FKE is below 3 dB.     

Eight-channel microdisk CW laser arrays vertically coupled to common output bus waveguides

1.6-nm spectrally spaced eight-channel semiconductor microdisk laser arrays are presented, where high-Q disk lasing modes are vertically coupled out through a common bus waveguide. The spectral channel spacing is achieved by varying the disk resonator radii from 10.6 to 10.95 /spl mu/m. Typical linewidth of 0.25 nm and side-mode suppression ratio of -20dB are observed under continuous-wave lasing operation near /spl lambda/=1.51 /spl mu/m. This is the first demonstration of integrated microresonator laser arrays.     

Chirp and linewidth enhancement factor of tunable, optically-pumped long wavelength VCSEL

Small-signal frequency modulation response and chirp characteristics of a tunable, optically-pumped 1.6 /spl mu/m vertical cavity surface emitting laser (VCSEL) based on microelectromechanical at wavelength tuning are presented for the first time. From the measurements the linewidth enhancement factor /spl alpha//sub H/ has been derived and is discussed.     

Damping-limited modulation bandwidths up to 40 GHz in undoped short-cavity In/sub 0.35/Ga/sub 0.65/As-GaAs multiple-quantum-well lasers

We demonstrate record direct modulation bandwidths from MBE-grown In/sub 0.35/Ga/sub 0.65/As-GaAs multiple-quantum-well lasers with undoped active regions and with the upper and lower cladding layers grown at different growth temperatures. Short-cavity ridge waveguide lasers achieve CW direct modulation bandwidths up to 40 GHz for 6/spl times/130 /spl mu/m/sup 2/ devices at a bias current of 155 mA, which is the damping limit for this structure. We further demonstrate large-signal digital modulation up to 20 Gb/s (limited by the measurement setup) and linewidth enhancement factors of 1.4 at the lasing wavelength at threshold of /spl sim/1.1 /spl mu/m for these devices.