Low-threshold and narrow-linewidth 1.5 mu m compressive-strained multiquantum-well distributed-feedback lasers

1.5 mu m compressive-strained multiquantum-well distributed-feedback lasers have been fabricated and characterised. 5.5 mA threshold current, 1 MHz mW linewidth-power product, and 600 kHz minimum linewidth were measured on 500 mu m long devices. Measured threshold current as low as 2.2 mA was also obtained on 150 mu m long devices. Both low threshold and narrow linewidth are attributed to the reduced transparency current and linewidth enhancement factor due to the effect of strain.<>     

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     

1.5 μm wavelength distributed reflector lasers with verticalgrating

A 1.5 μm wavelength distributed reflector laser, consisting of a distributed Bragg reflector rear facet and a distributed feedback region, was realised using deep-etching technology. A low threshold current of I_th=12.4 mA and a high differential quantum efficiency of η_d=42% from the front facet was achieved with a submode suppression ratio of 33 dB (I=2.4 I_th) for a fifth-order grating, 220 μm long and 6 μm wide device at room temperature     

High-stability 1.5 μm external-cavity semiconductor lasers forphase-lock applications

Applications using phase-locked semiconductor lasers, such as homodyne detection, require lasers with narrow linewidth and high-frequency stability. The design and operating characteristics of two 1.5 μm external-cavity semiconductor lasers built for such applications are described. The measured beat linewidth is 4 kHz, and the spectral density of relative frequency noise deviates significantly from the intrinsic white spectrum only at frequencies below 4 kHz. It is estimated that this frequency jitter will induce approximately 1.1° RMS phase error in a second-order homodyne optical phase-lock loop that is optimized for the present beat linewidth     

Continuously tunable 1.5 μm multiple-quantum-well GaInAs/GaInAsPdistributed-Bragg-reflector lasers

The authors demonstrate improved performance in tunable distributed-Bragg-reflector lasers using GaInAs/GaInAsP multiple-quantum-well active layers. They observe linewidths as low as 1.9 MHz, differential quantum efficiencies as large as 33%/front facet at 1.5 μm, and rapid electronic access to all frequencies throughout a 1000 GHz range     

Low-threshold-current-density 1.5 μm lasers using compressivelystrained InGaAsP quantum wells

A low-threshold current density (J_th) of 140 A/cm² for broad-area 1.5-μm semiconductor lasers with uncoated facets is demonstrated at a cavity length of 3.5 mm. This was achieved by the use of a single InGaAsP quantum well (QW) of 1.8% compressive strain inside a step-graded InGaAsP waveguide region. Low-cavity losses of 3.5 cm^-1 and a relatively wide quantum well as compared to InGaAs wells of equivalent strain contribute to this high performance. Double QW devices of 2 mm length showed threshold current densities of 241 A/cm². Quaternary single and double QWs of similar width but only 0. 9% strain gave slightly higher threshold current density values, but allowed growth of a 4 QW structure with a J_th of 324 A/cm² at L=1.5 mm     

Tuning ranges for 1.5 μm wavelength tunable DBR lasers

Tuning ranges for 1.5 μm wavelength tunable distributed Bragg reflector (DBR) lasers were studied experimentally. Over 10.0 nm (1.25 THz) quasicontinuous tuning under 5 mW light output conditions and 4.4 nm (550 GHz) continuous tuning at 1 mW were achieved     

High speed performance of 1.5 mu m compressive-strained multiquantum-well gain-coupled distributed-feedback lasers

1.5 mu m compressive-strained multiquantum-well gain-coupled distributed-feedback lasers have been fabricated on semi-insulating InP substrates with very low parasitic capacitance for studying the laser dynamic characteristics. A maximum 3 dB bandwidth of 12.8 GHz under small signal modulation, a 20 dB down chirping width of 0.33 nm under modulation, a 20 dB down chirping width of 0.33 nm under 5 Gbit/s NRZ pseudorandom modulation, and a low chirping short pulse of 20 ps under gain switching are obtained.<>     

High-performance 1.5 μm wavelength InGaAs-InGaAsP strainedquantum well lasers and amplifiers

Improved performance of 1.5-μm wavelength lasers and laser amplifiers using strained In_xGa_1-xAs-InGaAsP quantum well devices is reported. The device structures fabricated to study the effects of strained quantum wells on their performance are described. These devices showed TM mode gain, demonstrating the strain-induced heavy-hole-light hole reversal in the valence band. Lasers using these tensile strained quantum wells show higher and narrower gain spectra and laser amplifiers have a higher differential gain compared to compressively strained quantum well devices. Consequently, the tensile strained quantum well lasers show the smallest linewidth enhancement factor α=1.5 (compression α=2.5) and the lowest K-factor of 0.22 ns (compression K=0.58 ns), resulting in an estimated intrinsic 3 dB modulation bandwidth of 40 GHz (compression 15 GHz)     

High-speed intensity modulation of 1.5 μm DBR lasers withwavelength tuning

Intensity modulation characteristics of a 1.5-μm butt-jointed DBR (distributed-Bragg-reflector) laser with wavelength tuning were studied. A 3-dB modulation bandwidth of 9 GHz and a high relaxation oscillation frequency of more than 10 GHz were obtained for the DBR laser. These characteristics were not affected by changing the lasing wavelength. The chirping width of the DBR laser is lower than that of the distributed feedback (DFB) laser. A clear eye opening and low chirping characteristics were obtained under 5-Gb/s nonreturn to zero (NRZ) pseudorandom modulation with a sufficient extinction ratio     

High-speed 1.5 μm self-aligned constricted mesa lasers grownentirely by MOCVD

A self-aligning (SA) process technique to fabricate constricted mesa (CM) lasers is proposed. The controllability of GaInAsP active region volume and InP lateral confining layer widths were greatly improved. Lasers grown entirely by metalorganic chemical vapour deposition (MOCVD) showed very small variation in threshold currents ( I_th=15.2±1.1 mA) and in stray junction capacitances (C=1.62±0.08 pF). A record bandwidth of 10 GHz in the 1.5 μm-wavelength region was demonstrated     

Low-threshold, high-power, single-longitudinal-mode operation i 1.5μm multiple-quantum-well, distributed-feedback laser diodes

Extremely low-threshold, single-longitudinal-mode operation is reported for 1.5 μm band GaInAs multiple quantum well, distributed feedback laser diodes. A 5.5 mA minimum threshold current as well as 40 mW maximum light output power and 0.33 W/A maximum quantum efficiency have been attained under CW condition at room temperature     

High-speed 1.5 μm self-aligned constricted mesa DFB lasers grownentirely by MOCVD

Ultrahigh-speed 1.5 μm wavelength self-aligned constricted mesa GaInAsP-InP distributed-feedback lasers grown entirely by low-pressure metalorganic chemical-vapor deposition are discussed. A self-aligned process was applied to lower the stray InP junction capacitance to as low as 1.6 pF. A record bandwidth of 13 GHz in the 1.5 μm wavelength region was demonstrated     

Wavelength-dependent optimum output coupling enhances performanceof external-cavity-tuned semiconductor lasers at 1.5 μm

The output power of an external-cavity-tuned laser has been significantly increased by using an output coupler with a wavelength-dependent reflectivity. Our algorithm for determining the optimum wavelength dependence uses a simple gain model, and all necessary parameters can be determined from measurements of the same actual gain medium that will be used in the tunable laser source. This approach also increases tuning range     

Low-threshold strain-compensated InGaAs(N) (λ = 1.19-1.31μm) quantum-well lasers

Highly strained (Δa/a ~ 2.5%) In_0.4Ga_0.6 As and In_0.4Ga_0.6As_0.995N_0.005 -quantum-well (QW) active lasers utilizing strain-compensating InGaP-GaAsP buffer layers and GaAs_0.85P_0.15 barrier layers, grown by metal-organic chemical vapor deposition (MOCVD), are demonstrated with lasing emission wavelength of 1.185 and 1.307 μm, respectively. Threshold and transparency current density for the strain compensated InGaAsN QW lasers, with emission wavelength of 1.295 μm, are measured to be as low as 290 A/cm² (L = 1500 μm) and 110 A/cm², respectively, with characteristic temperature of T₀ and T₁ of 130 K and 400 K     

1.5 μm GaInAsP/InP distributed reflector (DR) lasers with SCHstructure

The large differential quantum efficiency η_df with one-directional output operation obtained in 1.5-μm distributed reflector (DR) lasers using a thin active layer of 50 nm and the separate-confinement heterostructure (SCH) structure is discussed. η _df of the DR laser was experimentally determined to be twice that of distributed-feedback (DFB) lasers cleaved from the same wafer, which indicates high efficiency and high power characteristics of DR lasers     

Femtosecond time domain measurements of group velocity dispersionin diode lasers at 1.5 μm

The authors have measured the group velocity dispersion of bulk V-groove semiconductor lasers and multiple quantum well lasers operating at a wavelength near 1.5 μm. The data yield group velocity dispersions in the range from -0.63 to -0.95 μm^-1 and indicate that material dispersion is the dominant factor in the diodes. Cross-correlation traces of transmitted femtosecond pulses confirm the measured values of dispersion     

Numerical simulations of 1.5 μm actively mode-lockedsemiconductor lasers including dispersive elements and chirp

A transmission-line laser model (TLLM) for mode-locked lasers is modified to include carrier-induced index variations which is the cause of laser chirp. Time-domain dynamic simulations show this to cause pulse narrowing, spectral shifting, and spectral broadening. The effects of AC drive, DC bias, unwanted reflections, and higher-harmonic RF drive are also investigated. The authors present results showing how chirp, drive conditions, facet reflectivity, and harmonic operation affect pulse shape, stability, and pulse spectra     

Tunable absolute-frequency laser at 1.5 μm

Frequency stabilisation of a two-frequency diode-pumped Er,Yb:glass laser is demonstrated using Doppler-broadened or saturated-absorption lines of ¹³C₂H₂. Continuous tunability in the 1530-1550 nm range is obtained. Beat note measurements lead to a frequency accuracy better than 10 kHz for a 10s response time     

A low-noise-figure 1.5 μm multiple-quantum-well opticalamplifier

The authors report on the noise characteristics of InGaAs/InGaAsP multiple-quantum-well optical amplifiers operating near 1.5 μm. A noise figure of 4.4 dB is reported, verifying the predicted low-noise properties of quantum-well amplifiers