Wavelength aging analysis of DBR lasers using tuning section IMfrequency response measurements

Systematic IM frequency response measurements have been performed on the tuning section of distributed Bragg reflector lasers aged at 60°C and 120°C. The wavelength drift varies exponentially with aging time as well as carrier lifetime of the tuning section. The carrier lifetime increases with time indicating a wavelength drift mainly due to leakage current increase at high carrier density injection     

A DBR laser employing passive-section heaters, with 10.8 nm tuningrange and 1.6 MHz linewidth

A wavelength-tunable, three-section, distributed Bragg reflector (DBR) InGaAsP/InP laser diode is described. The refractive indices of the DBR section and the phase-control section are thermally controlled by thin-film heaters embedded on these passive sections. This structure enables wide-range wavelength tuning without the spectral linewidth broadening accompanying conventional tuning by current injection into the passive sections. A tuning range of 10.8 nm and a linewidth of less than 1.6 MHz have been achieved in the 1.5-μm wavelength region. The temperature increase in the active layer is held to within a few degrees, even when the DBR-section temperature reaches 90°C     

Broadly wavelength-tunable external cavity, mid-infrared quantumcascade lasers

Wavelength tuning over 120 nm for a grating-coupled 5.1-μm quantum-cascade type-I laser was studied for temperature from 80 to 243 K (-30°C). Both the Littman-Metcalf and first-order grating direct feedback cavity configurations were used with similar tuning results. The goal is to achieve broad tunability, and the result is a combined grating and temperature tuning of 245 nm, from 5.040 to 5.285 μm. The laser was designed for predominantly single-mode or at most, two-longitudinal mode operation. The instrument-limited laser linewidth was less than the cavity longitudinal mode spacing. Stepping-motor control of the grating allowed 0.4-GHz wavelength increments (35 pm) to be realized with high reproducibility. A current-induced wavelength shift of ~2-3 GHz was observed, corresponding to an effective refractive index change of ~10^-3. Analysis indicates that single-mode, continuously tunable operation is feasible with a more optimal device and cavity     

Polarization-independent low-crosstalk polymeric AWG-based tunablefilter operating around 1.55 μm

A wavelength tunable optical filter is a beneficial optical component for dense wavelength-division-multiplexed systems. We report a high-performance polymeric arrayed-waveguide grating (AWG)-based tunable filter made of cross-linked silicone and operating around 1.55 μm. This filter exhibited a TE-TM polarization shift of <0.03, a crosstalk of <-35 dB, an insertion loss of <3 dB, and an 8.8-nm tuning range in the 25°C-75°C temperature region     

A novel strain-induced thermally tuned long-period fiber gratingfabricated on a periodic corrugated silicon fixture

We demonstrate a new method for fabricating tunable long-period fiber grating by bonding a cladding etched fiber to a corrugated silicon fixture. The long-period grating is formed by a built-in periodic sheer strain on the fiber/fixture interface. Loss tuning is achieved by varying the temperature of the fixture. Dynamic tuning range as large as 20 dB is obtained at the resonance wavelength over a temperature range from 25°C to 245°C     

Thermally tunable integrated optical ring resonator with poly-Sithermistor

Doped polysilicon is applied as a thermo-optic heating element to temperature tune the ring resonator based on silicon nitride rib waveguides on silicon. The ring diameter is 2 mm allowing a large free spectral range of 26 GHz. For the first time, a poly-Si resistor is used as a thermistor to measure waveguide temperature. The temperature coefficient of the poly-Si thermistor is 9.5×10^-4/°C. The reproducibility of the temperature measurement is 0.3°C. The finesse of the ring resonator is 77. The propagation loss of silicon nitride rib waveguide is 0.5 dB/cm at the wavelength of 1.312 μm. The temperature tuning of the ring resonator and the in situ supervision of the temperature on chip based on the same poly-Si fabrication process may find use especially in optical sensor applications     

Temperature dependence of the properties of DBR mirrors used insurface normal optoelectronic devices

The variation in the center wavelength of distributed Bragg reflectors used in optoelectronic devices, such as surface emitting lasers and Fabry-Perot modulators, is measured as the temperature of the mirrors changes over the range 25°C to 105°C. An analytic expression for the shift in center wavelength with temperature is presented. The mirrors measured are made of InP/InGaAsP (λ_gap=1.15 μm), GaAs/AlAs, and Si/SiN_x. The linear shifts in center wavelength are 0.110±0.003 nm/°C, 0.087±0.003 nm/°C, and 0.067±0.007 nm/°C for the InP/InGaAsP, GaAs/AlAs, and Si/SiN mirrors, respectively. Based on these data, the change in penetration depth with temperature is calculated     

Tunable thulium-doped all-fiber laser

We demonstrate a tunable thulium-doped fiber ring laser wherein a single fused coupler acts simultaneously as the wavelength-division multiplexing for pump radiation, a lasing wavelength selective element, and output mirror. Temperature tuning of up to 2 nm/°C over a range of 40 nm and polarization tuning of over 100 nm within the spectral range from 1810 to 1930 nm have been obtained     

Tunable external-cavity semiconductor laser using monolithicallyintegrated tapered amplifier and grating coupler for collimation

A novel lensless tunable external-cavity laser using monolithically integrated tapered amplifier, grating coupler (GC) and an external half mirror is proposed and demonstrated. It can be fabricated by a simple process and emits a collimated output beam. By making use of wavelength dispersion of the GC, the lasing wavelength can be angle tuned. Wavelength tuning over a wide range of 21.5 nm by 4.5° device rotation and an 84-mW output power were achieved under continuous-wave operation. A well-collimated output beam with a divergence angle as small as 0.3° was maintained over the entire tuning range     

1.5-μm tunable DBR lasers for WDM multiplex spare function

A DBR laser has been developed to realize wavelength-division multiplexing multiplex spare board with a potential at least for 16 wavelengths spaced by 100 GHz or 32 by 50 GHz. Two currents and the temperature are used to fix the emitted wavelength to the International Telecommunications Union grid. The constant output power delivered on all these channels is as high as 10 dBm coupled into the fiber. Burned devices exhibit no wavelength drift on the whole tuning range over more than 4000 h at 60°C     

Polarization-independent LiTaO3 guided-wave electroopticswitches

Polarization-independent LiTaO₃ optical switches that utilize the off-diagonal electrooptic coefficient r₅₁ are discussed. The waveguides are formed by Zn vapor diffusion. Interguide transfer efficiencies of 84 and 88% for TM and TE polarizations, respectively, have been obtained. Modulation efficiency of 99.8% for TM and 95% for TE have been demonstrated at nearly equal voltages by thermally tuning to 20°C. The relatively high voltage-length product (30-35 V-cm) attained in these initial devices at a 0.633-μm wavelength is attributed to a weak overlap between optical and electrical fields in the periodic electrode structure     

Wavelength-independent operation of EA-modulator integratedwavelengthselectable microarray light sources

In this letter, we have simultaneously fabricated five wavelength-selectable microarray light sources (WSLs), each having a different wavelength range integrated with an electroabsorption (EA) modulator on a single wafer. We also introduced a novel device configuration scheme for wavelength-independent modulation. The five EA-WSLs fully covered the entire C-band and had a low uniform threshold current of 6 ± 1 mA at 25°C. Wavelength-independent extinction characteristics were obtained over a tuning wavelength range of 8 nm, and 2.5-Gb/s transmission over 600 km was successfully achieved     

Wavelength dependence of characteristics of 1.2-1.55 μmInGaAsP/InP p-substrate buried crescent laser diodes

Laser diodes with the p-substrate buried-crescent structure have been fabricated for the 1.2-1.55-μm wavelength region. The dependence of laser characteristics on wavelength has been measured. Up to 70°C, the increasing rates of the threshold current with temperature are similar, while, above 70°C, a shorter-wavelength laser shows a larger increasing rate. At the same full width at half maximum of the far-field pattern perpendicular to the junction plane, the external differential quantum efficiency of the 1.55-μm laser diode is only 10% smaller than that of the 1.3-μm laser. The absorption loss coefficients in the active layer of the 1.2-, 1.3-, and 1.55-μm laser are estimated to be 26, 34, and 73 cm^-1, respectively     

High-temperature operation of InGaAs/InGaAsP compressive-strainedQW lasers with low threshold currents

We investigated the influence of the band gap wavelength of barrier layers and separate confinement heterostructure (SCH) layers λ_SCH on the high-temperature operation of InGaAs/InGaAsP compressive-strained quantum-well (QW) lasers. The optimum λ_SCH was 1.2 μm, at which carriers were sufficiently confined into quantum wells. The QW laser with λ_SCH = 1.2 μm exhibited low threshold currents of 2.3 mA at 20°C and 9.7 mA at 100°C and CW lasing up to 150°C     

Low-threshold, high-temperature operation of 1.2 μm InGaAsvertical cavity lasers

The growth and characterisation of high performance InGaAs/GaAs quantum-well vertical cavity lasers with an emission wavelength of 1215 nm is reported. Continuous wave operation is demonstrated up to 105°C with a threshold current below 1 mA for T<80°C. For a 2.5 μm device the room temperature threshold current, output power and slope efficiency is 0.6 mA, 0.6 mW and 0.2 W/A, respectively     

High-performance 1.6 μm single-epitaxy top-emitting VCSEL

The first single-epitaxy top-emitting vertical-cavity surface-emitting laser emitting in the 1.55-1.61 μm wavelength region is reported. CW operation is achieved up to 55°C with an optical power of 0.45 mW obtained at 25°C. Error free transmission by these lasers at 2.5 Gbit/s is obtained over 50 km of singlemode fibre without the need for optical amplification     

Method for setting the absolute frequency of a tunable, 1.5 μmtwo-section DBR laser

A technique for setting the absolute frequency of a 1.5-μm two-section distributed Bragg reflector (DBR) laser using an Er:YAG optical filter as a frequency discriminator is described. The absolute frequency of the laser was controlled with an accuracy better than 300 MHz over a tuning range of several hundred gigahertz. The frequency drift with laser temperature was -130 MHz/°C, and the tuning rate with current in the active region was 40 MHz/mA     

1.55-μm wavelength-selectable microarray DFB-LD's withmonolithically integrated MMI combiner, SOA, and EA-modulator

We developed compact (1.136 mm²) eight-channel wavelength-selectable microarray distributed feedback laser diodes (DFB-LD's) with a monolithically integrated 8×1 multimode-interference (MMI) optical combiner, a semiconductor optical amplifier (SOA), and an electro-absorption (EA) modulator. By using ±10°C thermal tuning, an addressable wavelength range of 15.3 nm with uniform device characteristics and 2.5-Gb/s modulation performance were successfully demonstrated     

High T0 long-wavelength InGaAsN quantum-well lasersgrown by GSMBE using a solid arsenic source

We demonstrate high performance, λ=1.3- and 1.4-μm wavelength InGaAsN-GaAs-InGaP quantum-well (QW) lasers grown lattice-matched to GaAs substrates by gas source molecular beam epitaxy (GSMBE) using a solid As source. Threshold current densities of 1.15 and 1.85 kA/cm² at λ=1.3 and 1.4 μm, respectively, were obtained for the lasers with a 7-μm ridge width and a 3-mm-long cavity. Internal quantum efficiencies of 82% and 52% were obtained for λ=1.3 and 1.4 μm emission, respectively, indicating that nonradiative processes are significantly reduced in the quantum well at λ=1.3 μm due to reduced N-H complex formation. These Fabry-Perot lasers also show high characteristic temperatures of T₀ =122 K and 100 K at λ=1.3 and 1.4 μm, respectively, as well as a low emission wavelength temperature dependence of (0.39±0.01) nm/°C over a temperature range of from 10°C to 60°C     

Sea-spike backscatter from a steepening wave

H-pol and V-pol backscatter cross sections at incidence angles of 85°, 60°, and 40° are computed at X-band for two temporal sequences of simulated sea waves, one with a wavelength of 1 m and the other with a 2.3 m wavelength, that are steepening as they undergo breaking. At an incidence angle of 85° (5° grazing) H-pol and V-pol backscatter from these waves are shown to have the characteristics of a sea spike. At a 60° incidence angle only the l m sequence produces a sea spike. No sea spike is seen from either sequence at 40