High-performance single-longitudinal-mode operation of InGaAsP/InP DFB-DC-PBH LD's

The lasing performance of InGaAsP/InP distributed feedback laser diodes with double-channel planar buried heterostructure (DFB-DC-PBH LD's) is reported for end-titled and antireflection (AR) coated configuration. High-power CW single-longitudinal-mode (SLM) operation over 55-mW light output at room temperature, high-temperature CW SLM operation over 105°C, as well as stable SLM operation under 2-Gb/s high-speed direct modulation, have been attained for 1.3-μm band DFB-DC-PBH LD's. 1.5-μm band DFB-DC-PBH LD's have also exhibited excellent DFB lasing characteristics, such as high power over 20 mW and high temperature over 75°C CW SLM operation. DFB SLM yield in the laboratory was also examined for 1.3-μm DFB-DC-PBH LD's, giving rise to a good prospect for practical use in optical-fiber communication systems.     

1.5 µm range InGaAsP/InP distributed feedback lasers

Lasing characteristics of InGaAsP/InP distributed feedback (DFB) lasers in the 1.5 μm range were studied theoretically and experimentally. Wave propagation in five-layer DFB waveguides were analyzed to estimate the effect of the structural parameters on threshold conditions. A brief consideration on designing a low threshold laser and its lasing wavelength was made. DFB buried heterostructure lasers with fundamental grating emitting at 1.53 μm were prepared by liquid phase epitaxial techniques. CW operation was confirmed in the temperature rangeof -20° to 58°C, and a CW threshold current was as low as 50 mA at room temperature. A stable single longitudinal mode operation was observed both in dc condition and in modulated condition by a pseudorandom pulse current at 500 Mbits/s. No significant increase in the threshold current was observed after 1400 h continuous CW operation at 20°C.     

Very low-threshold 1.53?m DFB lasers by VPE transport

DFB lasers with CW threshold currents as low as 8 mA at room temperature have been fabricated using the VPE transport process. The low threshold currents are attributed to narrow active stripes and to the high coupling strength of the grating. Single-mode lasing at 1.53?m up to I = 8Ith and during high-speed direct modulation has been confirmed.     

1064-nm DFB laser diode modules applicable to seeder for pulse-on-demand fiber laser systems

Semiconductor DFB (Distributed feedback) laser diodes with an operating wavelength of 1064 nm, which is suitable for pulse-on-demand fiber laser, have been developed. The stable performance of CW and nanosecond/picosecond pulsed operation is reviewed. By applying gain-switching operation with a simple direct modulation technique, 50-ps pulse generation with a stable spectral single-mode property was obtained. For the efficient amplification of the obtained 50-ps pulse, a monolithic semiconductor optical amplifier (SOA) was integrated into the DFB lasers. An improved peak power of 300 mW at 50-ps pulse was observed with limited optical noise injection when the synchronous modulation technique of the DFB and the SOA was employed. Short cavity lasers showed a high-frequency response compared to the original DFB lasers and achieved a short pulse width of 13 ps by standard gain-switched operation.     

Continuous-wave operation of 1.5 ?m distributed-feedback ridge-waveguide lasers

CW operation of 1.5 ?m ridge-waveguide DFB lasers is reported for the first time. The ridge-waveguide DFB laser structure offers the prospect of high modulation speeds due to the absence of parasitic capacitances associated with reverse-biased current-blocking layers. These devices also represent the first report of CW operation of DFB lasers fabricated using the hybrid LPE/MOCVD crystal-growth technique and also of DFB lasers with gratings produced by electron-beam lithography.     

Low-threshold operation of 1.5?m buried-heterostructure DFB lasers grown entirely by low-pressure MOVPE

Buried-heterostructure (BH) distributed feedback (DFB) lasers have been fabricated by a three-step low-pressure MOVPE process. The CW threshold currents were as low as 15mA and a high differential efficiency of 0.21 W/A was obtained. The laser operated in a stable single longitudinal mode over a wide range of driving currents and under highspeed direct modulation.     

Spectral properties of strongly coupled 1.5 µm DFB laser diodes

Spectral measurements of strongly coupled DFB lasers operating at 1.5 μm are presented. The magnitude of the coupling coefficientkin these devices was determined to be 80 cm^-1for lasers withlambda = 1.12 mum cladding layers and 160 cm^-1for devices withlambda = 1.3 mum cladding layers. These values forkare believed to be the largest reported for 1.5 μm DFB lasers. CW spectral linewidths as low as 10 MHz at 15 mW output power were obtained, and the linewidth was observed to vary approximately as the inverse of the device length cubed. Spectral measurements performed under 2 Gbit/s direct modulation exhibited a side mode suppression ratio of >38 dB. The effects of transient wavelength chirping were also investigated in detail and the maximum wavelength deviation was found to be ≃1.5 Å.     

Characteristics of diffused-stripe InP/InGaAsP/InP lasers emitting around 1.55 µm

Fabrication and lasing characteristics of InGaAsP/InP lasers emitting around 1.55 μm are described. Zn-diffused stripe-geometry lasers with emission wavelengths in the1.53-1.60mum range were fabricated from InP/InGaAsP/InP DH epitaxial wafers prepared by a low temperature LPE technique. The dependence of the lasing charaeteristics on the stripe width was examined. The lowest threshold current (≃160 mA under CW operation at 27°C) was obtained for a laser with a 13 μm stripe. CW operation of the laser has been achieved at a heat-sink temperature as high as 53°C. For sufficiently narrow stripe widths (simeq6 mum), fundamental-transverse mode and single-longitudinal mode operation was obtained under CW operation. Moreover, the lasers have good high-frequency performance. The lasers showed excellent dynamic properties without waveform distortion under high-frequency (800 Mbits/s) large-signal pulse modulation. The full width at half maximum of the longitudinal mode envelope was approximately 30 Å at 800 Mbits/s.     

Dynamic and CW linewidth measurements of 1.55-μm InGaAs-InGaAsPmultiquantum well distributed feedback lasers

Measurement of the CW linewidth and frequency chirp as functions of modulation data rate and bias level for 1.55-μm InGaAsP multiquantum-well distributed feedback lasers grown by low-pressure MOCVD are presented. The results show that the CW linewidth of asymmetric facet-coated multiquantum-well DFB lasers can be as low as 2.0 MHz at 13.5 mW output power. The frequency chirp increases with modulation data rate and is significantly larger if the laser off-state is below threshold than if it is above threshold. The 20 dB down chirp widths are in the range of 1.9-5 Å for 40 mA peak-to-peak modulation current at 10 Gb/s under above-threshold bias     

Distributed feedback laser emitting at 1.3 µm for gigabit communication systems

A distributed feedback (DFB) laser emitting at 1.3 μm for gigabit lightwave communication systems has been developed. The distributed feedback structure has been introduced in a newly developed buried heterostructure and designs for stable single-mode operation, high speed modulation, and low noise have been done. Threshold current of 10-15 mA, differential efficiency of around 0.28 mW/mA, low noise, small signal modulation bandwidth of 13.9 GHz, and satisfactory modulation waveform at 5-Gbit/s NRZ modulation have been attained with high single-mode operation yield.     

High-power single-longitudinal-mode operation of 1.3 ?m DFB-DC-PBH LD

CW light output power as high as 38 mW at room temperature and with a CW operable temperature as high as 80°C, both under single-longitudinal-mode operation, has been achieved for the first time in newly developed 1.3 ?m distributed-feedback (DFB) laser diodes with a double-channel planar buried heterostructure (DC-PBH).     

Distributed feedback InGaAsP/InP lasers with window region emitting at 1.5 µm range

Distributed feedback (DFB) InGaAsP/InP lasers with a window region formed at an end of the corrugated DFB region were made in order to overcome the problems inherent in the previous structures of DFB lasers with cleaved, sawed, etched, or AR-coated facets, or with an unexcited corrugation region. The window structure DFB lasers showed linear current versus output (I-L) curves, in contrast to those with a hysteresis or a kink appearing in a DFB laser with an unexcited region. Suppression of Fabry-Perot (F-P) resonances due to the two facets were sufficient enough to keep a single longitudinal mode property by DFB up to high excitation level. CW operation up to 65°C was achieved at the 1.5 μm wavelength range. Axial modes concerning the corrugated resonator were measured at about the threshold current. A stop band of a DFB laser was clearly observed with two dominant modes and much smaller submodes, which almost agreed with the axial modes predicted from a basic DFB theory.     

808 nm broad area DFB laser for solid-state laser pumping application

Wavelength stabilised 808 nm broad area distributed feedback (DFB) diode lasers with high continuous-wave (CW) output have been realised. The centre wavelength was locked at the Bragg condition with narrow spectral widths of 0.3 nm FWHM and shifted at a rate of 0.062 nm/°C. The 2 mm-long laser showed a record high 57% wall-plug efficiency and more than 4W CWoutput power at 25°C heatsink temperature. It is an ideal source for pumping solid-state lasers such as Nd-doped YAG and YVO₄.     

1.53 ?m DFB lasers by mass transport

DFB lasers emitting at ?=1.53 ?m made by mass transport have been demonstrated. Output power exceeding 5 mW/ facet was obtained when operated in CW at room temperature. Single-longitudinal-mode operation with a minimum threshold current of 26 mA was achieved. No degradation can be observed after aging at 5 mW continuous power at room temperature for more than 1000 h.     

53% wallplug efficiency 975nm distributed feedback broad area laser

100 mum-stripe, 2 mm-long, DFB diode lasers with narrow spectral widths of 2.3 Aring FWHM were achieved at a CW power of 5 W. The centre wavelength was locked at the Bragg condition and shifts at a rate of 0.065 nm K^-1. 1 mm-long DFB laser showed a record high 53% wallplug efficiency for grating-stabilised semiconductor lasers at 25degC heatsink temperature and 2 W CW output power     

Ultrafast all-optical switching utilizing the optical Kerr effectin polarization-maintaining single-mode fibers

An ultrafast all-optical switching scheme utilizing the optical Kerr effect in two birefringent fibers concatenated with each fast axis crossed is proposed. Stable optical Kerr modulation and all-optical demultiplexing of an ultrashort (30 p.s.) optical pulse train at 1.97 GHz from a gain-switched distributed-feedback laser diode (DFB LD) have been sufficiently demonstrated using CW mode-locking Nd:YAG laser pulses as a pump. Switching speed and required pump powers are studied in terms of fiber bandwidth due to fiber birefringence, and combined effects of chromatic and polarization dispersions on Kerr modulation profiles. By utilizing the optical Kerr modulation properties in the presence of dispersions, the nondiagonal yx component of the nonlinear refractive index is also determined to be 0.34 relative to the diagonal component xx. The intrinsic stability and ultimate switching capabilities are discussed     

Low threshold operation of 1.5-µm DFB laser diodes

Highly reliable distributed feedback (DFB) laser diodes operating at 1.5-μm wavelength range are fabricated through optimizing the device parameters. Thickness control of the active layer is found to be an essential factor in achieving low threshold operation of DFB lasers. The threshold current as low as 11 mA and stable single longitudinal mode CW operation up to 106°C is achieved with these DFB lasers.     

2.0-/spl mu/m single-mode operation of InGaAs-InGaAsP distributed-feedback buried-heterostructure quantum-well lasers

Distributed-feedback (DFB) buried-heterostructure (BH) lasers with quantum-well active region emitting at 2.0 /spl mu/m have been fabricated and characterized. The lasers with four wells showed performance of practical use: threshold current as low as 15 mA for 600-/spl mu/m-long devices and CW single-mode output up to 5 mW at 2.03 /spl mu/m under operation current of 100 mA were observed. The current- and temperature-tuning rates of DFB mode wavelength are 0.004 nm/mA and 0.125 nm/K, respectively.     

Surface emitting InGaAsP/InP distributed feedback laser diode at 1.53 mu m with monolithic integrated microlens

Monolithic integration of a distributed feedback (DFB) surface-emitting laser diode with a microlens is demonstrated. The transverse and longitudinal cross-sectional views of the laser diode are illustrated. The microlens and a DFB laser structure are located on opposite sides of an n-InP substrate. 11 mA minimum continuous wave (CW) threshold current and 5 mW CW emission perpendicular to the InP substrate are achieved at room temperature using a chemically etched 45 degrees mirror. Single mode emission at 1.53 mu m is obtained. The integrated microlens, etched by ion beam and coated with aluminum oxide, provides optical beam collimation and an ultralow laser mode reflectivity of <10/sup -4/.<>