A two-step laterally tapered 1.55-/spl mu/m SSC DFB laser fabricated by using a nonselective grating process

We demonstrate a two-step laterally tapered 1.55-/spl mu/m spot size converter distributed feedback laser diode (SSC DFB LD) having a planar buried heterostructure-type active waveguide and a ridge-type passive waveguide fabricated by using a nonselective grating process. Unlike conventional SSC DFB LDs, where a selective grating is employed, this SSC DFB LD employed a nonselective grating over the entire device region in order to make its fabrication much simpler than that of the conventional SSC DFB LDs. The two-step laterally tapered SSC is effective in removing an unwanted wavelength peak originating from the SSC section having a multiquantum well and a grating under it. The fabricated SSC DFB LD operates at 1.553-/spl mu/m wavelength and shows a far field pattern in horizontal and vertical directions of 13.4/spl deg/ and 19.5/spl deg/, respectively.     

Two-step laterally tapered spot-size converter 1.55-/spl mu/m DFB laser diode having a high slope efficiency

We demonstrate a two-step lateral tapered 1.55-/spl mu/m spot-size converter distributed feedback laser diode (SSC DFB LD) having slope efficiencies as high as 0.457 and 0.319 mW/mA measured at 25 /spl deg/C and 85 /spl deg/C, respectively. The SSC DFB LD fabricated by using a nonselective grating process has a double core waveguide structure including a planar buried heterostructure type active waveguide and a ridge type passive waveguide. The fabricated SSC DFB LD operates at 1.553-/spl mu/m wavelength and shows a far-field pattern in horizontal and vertical directions of 7.3/spl deg/ and 11.6/spl deg/, respectively.     

High-power, wide-temperature range operation of 1.3-/spl mu/m gain-coupled DFB lasers with automatically buried InAsP absorptive grating

DFB lasers operating at 1.3 /spl mu/m with gain-coupling structure show single-mode operation over a wide temperature range of -20/spl sim/85/spl deg/C and up to a high power of 130 mW. These lasers have InAsP absorptive grating, which can be formed by a substantially simplified fabrication process, involving annealing a corrugated InP substrate in an atmosphere of mixed arsine and phosphine.     

Continuous photonic microwave true-time delay using tapered chirped fibre Bragg grating

A photonic microwave true-time delay using a tapered chirped fibre Bragg grating is proposed and fabricated. A resistive heating electrode coated on the tapered fibre and a single-wavelength light was incorporated to control the time delay continuously without any mechanical perturbation and moving. It was achieved by adjusting the reflection positions of the optical signal carrying the microwave signal from within the tapered grating via the thermo-optic effect. The measured time delay was /spl sim/120 ps with electrical power consumption of 250 mW.     

Single-frequency 1310-nm AlGaInAs-InP grating-outcoupled surface-emitting lasers

Single-frequency 1310-nm grating-outcoupled surface-emitting (GSE) semiconductor lasers with output slope efficiencies exceeding 0.1 mW/mA into multimode fibers, threshold currents below 22 mA, and >30-dB sidemode suppression ratios are reported. These GSE lasers consist of 500-/spl mu/m-long active ridges that excite one end of surface-emitting second-order outcoupling gratings with 200-/spl mu/m-long first-order distributed Bragg reflector gratings terminating the laser cavities at both ends. The grating outcouplers range from 10 to 50 /spl mu/m in length. These lasers have an open eye pattern for nonreturn-to-zero signals at 2.5 Gb/s into single-mode fibers. The full-width half-maximum far-field beam divergences range from 1.5/spl deg/ /spl times/ 8/spl deg/ to 5/spl deg/ /spl times/ 8/spl deg/.     

Multiquantum-well lasers with tapered active stripe for direct coupling to single-mode fiber

We demonstrate narrow beam divergence in 1.3-/spl mu/m wavelength multiquantum-well (MQW) lasers with an active stripe horizontally tapered over the whole cavity, for direct coupling to single mode-fibers. The lasers have reduced output beam divergence in a simple structure which does not contain an additional spot-size transformer. The fabricated laser shows narrow beam divergence of /spl sim/12/spl deg/, while a low-threshold current of 6.9 mA and a high efficiency of 0.62 mW/mA are realized. Furthermore, a direct-coupling efficiency to a single-mode fiber is -4.0-dB and -3-dB alignment tolerance is /spl plusmn/2.5 /spl mu/m.     

GaSb-based tapered diode lasers at 1.93 /spl mu/m with 1.5-W nearly diffraction-limited power

High-power high-brightness 1.93-/spl mu/m wavelength (AlGaIn)(AsSb) tapered diode lasers with a narrow vertical waveguide design are reported for the first time. A nearly diffraction-limited continuous-wave output power of 1.5 W together with a remarkable low fast axis divergence of 43/spl deg/ full-width at half-maximum have been demonstrated. The maximum brightness amounts to 32 MW/cm/sup 2/sr.     

High-temperature and high-speed operation of a 1.3-/spl mu/m uncooled InGaAsP-InP DFB laser

1.3-/spl mu/m uncooled InGaAsP-InP loss-coupled distributed feedback lasers operating over 10 Gb/s and at 85/spl deg/C were successfully fabricated. In order to achieve high-speed and high-temperature operation simultaneously, the following are thoroughly investigated: modulation-doped and strain-compensated multiple-quantum-well active layers, Fe-doped buried-heterostructure, coupling coefficient of loss-coupled grating, detuning lasing wavelength from the gain peak, and facet coatings. The authors also demonstrate 10 Gb/s transmission with negligible dispersion power penalty over 20 km of nondispersion-shifted fiber at 10 Gb/s for temperatures ranging from 25/spl deg/C to 85/spl deg/C.     

Electron beam direct-write tunable polymeric waveguide grating filter

We report a tunable electron beam direct-write polymeric waveguide Bragg grating filter based on a negative tone epoxy, The waveguide filter, with a 5-mm-long first-order grating, exhibits a transmission peak of -27 dB and a 3-dB bandwidth of /spl sim/0.8 nm, and there is an excellent agreement between experimental data and simulation results. The temperature response of the filter is also characterized. The rate of change of refractive index dn/dT is /spl sim/ -1.8 /spl times/ 10/sup -4///spl deg/1C at 1550-nm wavelength for both transverse electric and transverse magnetic polarizations, and the rate of change of peak wavelength d/spl lambda//dT is /spl sim/ -0.14 nm//spl deg/C. The tuning performance is comparable to other grating devices fabricated using multiple processing steps.     

12.5-gb/s direct Modulation up to 115/spl deg/C in 1.3-/spl mu/m InGaAlAs-MQW RWG DFB lasers with notch-free grating structure

Direct modulation at 12.5 Gb/s of 1.3-/spl mu/m InGaAlAs distributed feedback (DFB) ridge waveguide (RWG) lasers with low-resistance notch-free gratings running up to 115/spl deg/C is experimentally demonstrated. It was achieved by the combination of the high differential gain of an InGaAlAs MQW active layer, high characteristic temperature of RWG structure, and low-resistance notch-free grating. Moreover, successful transmission of 10-Gb/s modulated signals over 30-km standard single-mode fiber was achieved with the laser running at up to 115/spl deg/C. These results confirm the suitability of this type of laser for use as the cost-effective light source in 12.5-Gb/s and 10-Gb/s datacom applications.     

45/spl deg/ slanted fibre Bragg grating design with prism coupled holographic exposure

A holographic technique for forming 45/spl deg/ tilted fibre gratings using two 45/spl deg/-90/spl deg/, -45/spl deg/ fused silica prisms is described. The technique reduces fringe distortion due to the lens effects of the fibre during exposure. Details of the experimental system and grating performance are given.     

Study on high-temperature performances of 1.3-/spl mu/m InGaAsP-InP strained multiquantum-well buried-heterostructure lasers

Stripe-width and cavity length dependencies of high-temperature performances of 1.3-/spl mu/m InGaAsP-InP well-designed buried-heterostructure strained multiquantum-well (MQW) lasers were investigated. The threshold currents as low as 4.5/10.5 mA and slope efficiencies as high as 0.48/0.42 mW/mA at 25/spl deg/C/85/spl deg/C were obtained in the MQW lasers with 1.5-/spl mu/m width, 250-/spl mu/m length, and 0.3/0.85 facet reflectivity. With temperature increasing from 25/spl deg/C to 85/spl deg/C, the MQW lasers exhibited lower output power degradation, the minimum value was 1.78 dB at an operation current of 45 mA. The MQW lasers were suitable for application in optical access networks.     

Room-temperature 2.81-/spl mu/m continuous-wave operation of GaInAsSb-AlGaAsSb laser

GaInAsSb-AlGaAsSb multiple quantum-well (QW) lasers with an emission wavelength of 2.81 /spl mu/m are reported. The ridge waveguide lasers with highly strained QWs show continuous-wave laser emission up to 25/spl deg/C; in pulsed mode, the lasers operate up to 60/spl deg/C. For pulsed operation, a threshold current density of 360 A/cm/sup 2/ is found for devices with 30-/spl mu/m stripe width and 2-mm cavity length at room temperature. A low threshold current density at infinite length of 248 A/cm/sup 2/ is derived.     

Low-threshold high-T/sub 0/ 1.3-/spl mu/m InAs quantum-dot lasers due to p-type modulation doping of the active region

P-type doping is used to demonstrate high-To, low-threshold 1-3 /spl mu/m InAs quantum-dot lasers. A 5-/spl mu/m-wide oxide confined stripe laser with a 700-/spl mu/m-long cavity exhibits a pulsed T/sub 0/ = 213 K (196 K CW) from 0/spl deg/C to 80/spl deg/C. At room temperature, the devices have a CW threshold current of /spl sim/4.4 mA with an output power over 15 mW. The threshold at 100/spl deg/C is 8.4 mA with an output power over 8 mW.     

Uncooled high-temperature (130/spl deg/C) operation of InGaAs-GaAs multiple quantum-well lasers at 20 Gb/s

Short-haul fiber-optic communication systems require high-speed semiconductor lasers that can operate uncooled over a wide temperature range. In this letter, we describe high-speed short-cavity InGaAs-GaAs multiple-quantum-well lasers operating at 1.1-/spl mu/m wavelength. The Fabry-Perot lasers were fabricated in a triple-mesa geometry suitable for on-wafer probing. With 3/spl times/200 /spl mu/m/sup 2/ ridge-waveguide lasers, which showed the best compromise between high-temperature and high-speed performance, a 3-dB modulation bandwidth of 14.5 GHz at 130/spl deg/C was achieved. Uncooled 20-Gb/s operation of these lasers is presented over a wide-temperature range from 25/spl deg/C to 130/spl deg/C without automatic power control.     

Chirped fiber-optic Bragg grating interrogator in a multiplexed Bragg grating sensor configuration

This paper presents a chirped grating interrogator for fiber Bragg grating sensors. The interrogator uses the wavelength dependence of the phase group-delay response of a chirped fiber Bragg grating to determine the Bragg wavelength of the sensor. The sensitivity of the interrogator is determined by the selection of the grating length and the bandwidth. The experimental results demonstrated strain measurements over a range of more than 10 000 /spl mu/m per meter. Multiplexing can be achieved by using an arrayed-waveguide grating that allows the interrogation of more than one grating sensor with a single chirped grating.     

High-precision high-yield laser source using DFB array

We present high-yield efficient distributed-feedback lasers with excellent wavelength control. An array of 12 lasers with highly reflecting/antireflecting facets is fabricated on a single chip with precisely controlled variations in the grating period or phase relative to the facets. The stripe that best meets requirements is selected for bonding. From 200 unscreened chips, 93% contained lasers that achieved the specified power of 25 mW at 175 mA, 55/spl deg/C, and 41% achieved a /spl plusmn/0.1-nm wavelength tolerance at 25 mW, 55/spl deg/C. This low-cost high-precision device requires little thermal tuning for wavelength-division-multiplexed applications and reduces the power consumption of the transmitter.     

Continuous-wave operation up to 36/spl deg/C of 1.3-/spl mu/m GaInAsP-InP vertical-cavity surface-emitting lasers

We introduced ion-beam assisted deposition in order to improve the quality of Al/sub 2/O/sub 3/ and SiO/sub 2/, which were used as part of the mirrors of 1.3-/spl mu/m GaInAsP-InP vertical-cavity surface-emitting lasers (VCSELs). The refractive index of Al/sub 2/O/sub 3/ was improved to 1.63 from 1.56 and the one of SiO/sub 2/ increased to 1.47 from 1.45. Low-threshold room-temperature continuous-wave (CW) operation of 1.3-/spl mu/m VCSEL with the improved mirrors was demonstrated. The threshold current was 2.4 mA at 20/spl deg/C. The CW operating temperature was raised to 36/spl deg/C, which is a record high temperature for 1.3-/spl mu/m VCSEL.     

Modeling and experimental demonstration of ultracompact multiwavelength distributed Fabry-Pe/spl acute/rot fiber lasers

This work presents a complete model for the design and optimization of multiwavelength distributed Fabry-Pe/spl acute/rot (DFP) fiber lasers that are made by superimposing two chirped fiber Bragg gratings in a photosensitive codoped erbium-ytterbium (Er-Yb) fiber. The model is based on a matrix formulation of coupled-mode equations taking into account the chirped grating superstructure and including a spectrally resolved gain medium. The performed analysis reveals that the signal power of each channel is strongly localized near a minimum of the superstructured-grating envelope. As a consequence, the overlap between the power distributions in neighboring cavities is small, thus reducing the effect of cross-gain saturation and allowing a high number of channels in a short piece of fiber. The simulations also show how the saturation of the cross-relaxation mechanism between ytterbium and erbium leads to flat output spectra without the need for an additional equalization scheme such as a complex grating apodization profile. Furthermore, to validate the theoretical model, we present the experimental realization and characterization of a multiwavelength laser emitting in a single-mode and single-polarization over 16 wavelengths spaced by 50 GHz and with a total output power of 52 mW.