Polarization-Stable Single-Mode Tunable VCSELs Using an Internal Mesa Heater

We fabricated polarization single-mode vertical- cavity surface-emitting lasers which are thermally induced wavelength- tunable using an internal mesa heater. A 6.21-nm tuning range was achieved with a 100-mA tuning current and a 6-mA driving current while maintaining continuous polarization- stable single-mode operation. The orthogonal polarization suppression ratio is more than 20 dB. In addition, we found stable linear polarization characteristics from the three mesas aligned along to the $langle 01-1rangle $ crystal axis.      

High-speed direct Modulation of widely tunable MG-Y laser

The dynamic performance of the modulated-grating Y-branch laser is presented. In order to reach over 40-nm tuning range, the devices utilize an additive Vernier effect and relative tuning of two reflecting gratings. The device shows high (>13 dBm ex-facet) and uniform (<1.2-dB variation) steady state output power over the tuning range, and sidemode suppression ratio >40 dB. The laser behavior under small- and large-signal operation conditions is investigated. The laser exhibits a resonance frequency of 7.4-8.8 GHz at 80-mA bias. A 10-Gb/s eye diagram measurement showed high extinction ratio and signal-to-noise ratio.     

Experimental analysis of a broadly tunable InGaAsP laser with compositionally varied quantum wells

Custom-designed InGaAsP lasers have been fabricated, tested, and show a broad spectral output at a bias current of 240 mA. The Fabry-Perot ridge waveguide lasers were grown with one 80-/spl Aring/ and five 100-/spl Aring/ quantum wells in the active region. A different material composition was used for each well and this provided contributions to the gain profile over a broad wavelength range. A 1400-/spl mu/m cavity length laser was found to operate in the spectral region from 1475 to 1650 nm and single-mode operation on the individual Fabry-Perot modes of the uncoated laser was achieved over a 172-nm tuning range using a diffractive optical element short external cavity. The side-mode suppression ratio was measured to be above 30 dB at all wavelengths within the tuning range. Complete spectral coverage, in overlapping short segments, with the device is possible using temperature tuning.     

Compact Thermally Tunable Silicon Wavelength Switch: Modeling and Characterization

A wavelength-selective photonic switch is developed based on a Si microring resonator using thermooptic effect. The 10-mum-diameter microring resonator uses single-mode strip Si waveguides of dimension 0.25 mum times 0.45 mum operating at 1.5 mum. Full-width at half-maximum are in the range 0.1-0.2 nm. The ultrawide tunable range (>6.4 nm) and wide free spectral range (~18 nm) of the switch element enables wavelength reconflgurable multichannel matrix switch by wavelength multiplexing/demultiplexing. Average rise delay time of 14 mus with low switching power of 3.15 mW has been achieved with 0.2-nm wavelength tuning and 78 mus, 104 mW for 6.4-nm tuning. Fall delay times are usually less than 10 mus. Thermal simulations show 10%-20% agreement with the measurements up to 3.2-nm tuning. The compact size of the switch shows its potential as an active element in photonic integrated circuits.     

The Y-laser: a multifunctional device for optical communicationsystems and switching networks

This paper gives a comprehensive review of the recent progress obtained with various operation modes of a Y-shaped all active waveguide device with three optical input/output ports, the so called Y-laser. Used as a monolithic semiconductor light source, single-mode emission with an extremely large cw tuning range of more than 50 nm is accessed. Single current step tuning spans up to 8-nm range. Several-GHz bandwidth AM and FM response is achieved. Operation as a wavelength processing device is demonstrated with data-stream transformation from short wavelength fiber windows (around 780 nm or 1310 nm) to the long wavelength window (1550 nm), as well as with ultra wide range wavelength conversion within the 1550-nm region, across +/-20 nm (blue and red shift). Optical high-speed space switching/gating functions are verified up to 1 Gb/s, and packet switching of 5-Gb/s data streams is demonstrated. Further features as a pulse reshaping device, as an electrically triggerable wavelength bistable device and as a mode locked pulse generator are addressed. Possible applications of this multifunctional device in future optical communication systems and switching networks are discussed     

Tunable WDM filter with 0.8-nm channel spacing using a pair of long-period fiber gratings

A strain-tuned wavelength-division-multiplexing filter with 0.8-nm channel spacing has been demonstrated by using a pair of long-period optical fiber gratings. The response of a transmission spectrum to applied axial strain is studied theoretically and experimentally. A large operation bandwidth of over 20 nm and a linear tuning rate of -0.6 pm//spl mu//spl epsiv/ within a near 3-nm range have been achieved.     

Fabrication of wavelength-tunable butt-coupled sampled grating DBR lasers using planar buried heterostructure

Planar buried heterostructure (PBH) was adopted to fabricate a sampled grating distributed Bragg reflector laser diode (SGDBR-LD) having a low threshold current and a stable fundamental transverse mode. The etching process for butt-coupling was optimized to improve the reproducibility and the uniformity of the butt-coupled waveguide. The maximum output power of the fabricated SGDBR-LD was 20 mW at 200-mA continuous-wave operation at 25/spl deg/C. The output power was measured 10 and 9 mW higher than those of ridged waveguide (RWG) structure and buried ridge stripe (BRS), and the threshold current was slightly higher than those of RWG and BRS. The spectra of 25 channels spaced 50 GHz within the tuning range of 44.4 nm was obtained by a precise control of SG and phase control currents. The side-mode suppression ratio of more than 35 dB was obtained in the whole tuning range. The output power variation was less than 5 dB, which is 4 dB smaller than that of RWG structure.     

Compact high-power tunable three-level operation of double cladding Nd-doped fiber laser

We present a compact high-power continuous-wave tunable neodymium-doped double cladding fiber laser operating on three-level /sup 4/F/sub 3/2/-I/sub 9/2/ transition with a maximum output power up to 810 mW. At 926.7 nm, it has a maximum slope efficiency of 49.3% against absorbed 808-nm pump. By compressing the fiber Bragg grating, 15-nm tuning range is achieved.     

N-Type Doping to an Active-Short Cavity DBR Laser to Expand Its Continuous Tuning Range

We propose the use of a short-cavity distributed Bragg reflector (DBR) laser with a modified active DBR structure, which has an n-type-doped active single quantum well, and that achieves fast wavelength switching that is potentially applicable for optical packet switching networks. The laser exhibits 6.4-nm continuous tuning by moderating a steep gain change at a low DBR injection current. Furthermore, 32-nm continuous tuning has also been achieved for an integrated laser with an eight-channel array.     

GaAs MESFET laser-driver IC for 1.7-Gbit/s lightwave transmitter

GaAs monolithic integrated circuits for modulating junction lasers (laser drivers) have been developed for a 1.7-Gb/s lightwave communication system. The modulation currents can be varied continuously from a few mA up to 50 or 100 mA, depending on the types of laser drivers. It has been demonstrated that devices of the low-current type are capable of driving a 50-Ω load with a 50-mA modulation current with pulse rise and fall times (10% to 90%) less than 200 ps, and the high-current devices are capable of driving a 25-Ω load with up to 100-mA modulation current with pulse rise and fall times less than 250 ps. Nearly temperature-independent performance has been achieved from 0°C to 70°C. The laser drivers are also capable of providing output DC currents proportional to the duty cycle of input data for the purpose of duty-cycle-independent feedback control of junction lasers. The circuit designs and performance of these devices are described     

Highly Reliable High-Brightness GaN-Based Flip Chip LEDs

The properties of indium-tin-oxide (ITO)/Ni films as transparent ohmic contacts of nitride-based flip chip (FC) light emitting diodes (LEDs) were studied. It was found that 300degC rapid thermal annealed (RTA) ITO(15 nm)/Ni(1 nm) could provide good electrical and optical properties for FC LED applications. It was also found that 20-mA operation voltage and output power of the 465-nm FC LEDs with ITO/Ni/Ag reflective mirror were 3.16 V and 21 mW, respectively. Furthermore, it was found that output intensity of the proposed LED only decayed by 5% after 1200 h under 30-mA current injection at room temperature.     

Low threshold current 1.3-/spl mu/m GaInNAs VCSELs grown by MOVPE

The structure of the conventional contact 1.3-/spl mu/m GaInNAs-GaAs vertical-cavity surface-emitting lasers (VCSELs) was optimized and low threshold current 1.3-/spl mu/m GaInNAs VCSELs grown by metal-organic vapor-phase epitaxy were reported. The idea is to optimize the active region, the doping profiles, and the pairs of p-distributed Bragg reflectors, and the detuning between the emission wavelength and the photoluminescence gain peak wavelength. The continuous-wave 1.0-mA threshold current was achieved for the single-mode VCSEL. For the multiple-mode VCSELs, the below 2-mA threshold currents at 5/spl deg/C-85/spl deg/C , the 1.13-mA threshold current at 55/spl deg/C, and 1.52-mA threshold current at 85/spl deg/C are the best results for 1.3-/spl mu/m GaInNAs VCSELs.     

Broad-range wavelength tuning in DBR lasers with super structuregrating (SSG)

Broad-range wavelength tuning is demonstrated in tunable distributed Bragg reflector (DBR) lasers with the super structure grating (SSG) proposed. The SSG is fabricated by electron beam exposure lithography. The grating performance is measured by transmittance characteristics of the SSG reflector. A maximum tuning range of 63 nm is obtained under the CW condition while keeping a single longitudinal mode. In a 50-nm tuning range, the threshold current variation is as low as 5.0-9.5 mA     

150-nm tuning range in a grating-coupled external cavityquantum-dot laser

An antireflection (AR) coated single-stack quantum-dot (QD) laser in a grating-coupled external cavity is shown to operate across a tuning range from 1.095 μm to 1.245 μm. This 150-nm range extends from the energy levels of the ground state to excited states. At any wavelength, the threshold current density is no greater than 1.1 kA/cm ². This large tunable range is the product of the rapid carrier filling of the higher energy states under a low pumping current and homogeneous broadening in the QD ensemble. The possibility of a larger tuning range is discussed with the further improvement of the AR-coating     

Tunable grating coupled surface-emitting tapered laser

We report on the design and fabrication of a wavelength-tunable grating coupled surface-emitting laser. A curved second-order grating is used at the end of a tapered gain section to provide feedback as well as collimated surface out-coupling. Wavelength tuning is achieved by current injection into the grating section through a film of indium-tin oxide deposited on the grating surface. Low divergence single-frequency surface emission with ~1-nm wavelength tuning is demonstrated     

Highly reliable high-power 980-nm pump laser

We report on highly reliable, high-power, and high-performance 980-nm quantum-well laser chips and modules. Ridge waveguide laser diode chips with 750-mW output power and 500-mW fiber Bragg grating stabilized modules have been achieved and Telcordia-qualified. Long-term reliability tests show a very low failure rate of 400 FIT (failures in time) at 900-mA operating current or 500-mW module power. The kink-free fiber coupled module output power can be as high as 640 mW with grating stabilization, which produces very good wavelength stability and power stability. A further improved structure shows a record continuous-wave rollover chip power of 1.6 W for the 5-/spl mu/m-wide ridge waveguide laser diodes.     

40-nm-wide tunable fiber ring laser with single-mode operationusing a highly stretchable FBG

We demonstrate a 750-Hz linewidth single-mode erbium-doped fiber (EDF) ring laser with wide tunability using a widely tunable fiber Bragg grating (FBG). The stable single-mode operation is realized by using the FBG as a narrow wavelength-selective element and 4 m of unpumped EDF as a saturable absorber in the cavity. The 40-nm continuous tuning range of 1522-1562 nm is achieved using a highly stretchable FBG that exhibits a filter tuning range of over 52 nm. The grating is prepared with chemically stripped deuterium-loaded fiber to eliminate degrading factors for the grating strength, thereby achieving the wide tunability. The tuning range represents a 3.5-fold increase in wavelength tuning over previous use of FBGs     

Wide-range tunability of GaInP-AlGaInP DFB lasers with superstructure gratings

Wide range wavelength tuning is demonstrated for short wavelength GaInP-AlGaInP distributed feedback lasers by controlling the injection currents in a two-section laser. Simple superstructure gratings were used to tune the emission wavelength over 4.9 nm in the 690-nm emission range. In a combination of current and temperature variation, the tuning range could be increased to more than 12 nm.     

Single frequency electrooptical tuning of an extended cavity diodelaser at 1500 nm wavelength

A wavelength-tunable, single-frequency GaInAsP-InP laser diode using an intracavity electrooptic LiNbO₃ crystal as the wavelength selective component is discussed. Wavelength tuning is achieved by applying a driving voltage on the crystal electrodes. First results indicate a tuning rate of 1 GHz/V over a tuning range of about 4 nm. This performance was obtained using a nonoptimized X-cut, Z-propagating LiNbO₃ crystal. A potential tuning rate of 6.5 GHz/V is possible with reasonable improvements     

AlGaInP-sapphire glue bonded light-emitting diodes

A novel method was proposed to glue an AlGaInP-GaAs light-emitting diode (LED) onto a transparent sapphire substrate. The absorbing GaAs was subsequently removed by selective wet etching. It was found that the emission efficiency could reach 401 m/W under 20-mA current injection for the 622-nm glue bonded (GB) AlGaInP-sapphire LED. It was also found that these GB LEDs are highly reliable, with small variations in operation voltage and luminescence intensity during the life test.