1.95-μm strained InGaAs-InGaAsP-InP distributed-feedbackquantum-well lasers

Distributed-feedback emission from strained InGaAs-InGaAsP-InP quantum well lasers has been examined over a temperature range of 130 K to 300 K. Continuous single-mode output from 190 to 300 K with a side-mode-suppression ratio of about 10 dB was observed. The wavelength was 1.95 μm at 273 K and tuned at a rate of 0.13 nm/K. The current-tuning rate was 0.0043 nm/mA (-340 MHz/mA) at 273 and 283 K     

High-temperature single-mode operation of 1.3-μm strained MQWgain-coupled DFB lasers

Single-mode and high-power operation at temperatures up to 120°C has been achieved in 1.3-μm strained MQW gain-coupled DFB lasers. A stable lasing wavelength is maintained due to a large modal facet loss difference of the two Bragg modes, which is provided by the gain-coupling effect. A very low temperature dependence of the threshold current has been obtained by detuning the lasing wavelength to the long wavelength side of the material gain peak at room temperature, which effectively compensates the waveguide loss at higher temperatures. An infinite characteristic temperature T_o can be realized at certain ranges of temperature depending on the detuning value     

High-speed 1.5-μm compressively strained multi-quantum wellself-aligned constricted mesa DFB lasers

A great improvement in the high-speed characteristics for compressively strained multi-quantum-well (MQW) distributed-feedback (DFB) lasers with self-aligned constricted mesa structures is described. Negative wavelength detuning is an important factor in making possible the extraction of potential advantages for the compressively strained MQW DFB lasers. A 17-GHz bandwidth, which is the highest among the 1.5-μm MQW DFB lasers, is demonstrated. A wavelength chirp width of 0.42 nm at 10 Gb/s is obtained due to a reduced linewidth enhancement factor that has a magnitude of less than 2. Nonlinear damping K factor in a DFB laser with 45-nm negative detuning has drastically decreased to 0.13 ns, about half of that for unstrained MQW lasers. This is mainly due to an enhanced differential gain as large as 6.9×10 ^-12 m³/s. The estimated intrinsic maximum bandwidth is 68 GHz     

1.58-μm band gain-flattened erbium-doped fiber amplifiers forWDM transmission systems

This paper describes the amplification characteristics of gain-flattened Er³⁺-doped fiber amplifiers (EDFAs) by using 0.98-μm and 1.48-μm band pumping for a 1.58-μm band WDM signal. Silica-based Er³⁺-doped fiber (S-EDF) and fluoride-based Er ³⁺-doped fiber (F-EDF) have gain-flattened wavelength ranges from 1570 to 1600 nm and from 1565 to 1600 nm, respectively, and exhibit uniform gain characteristics with gain excursions of 0.7 and 1.0 dB, and the figure of merit of the gain flatness (gain excursion/average signal gain) of 3 and 4.3%, respectively, for an eight-channel signal in the 1.58-μm band. We show that 1.48-μm band pumping has a better quantum conversion efficiency and gain coefficient, and that 0.98-μm band pumping is effective for improving the noise characteristics. We also show that the EDFAs consisting of two cascaded amplification units pumped in the 0.98-μm and 1.48-μm bands are effective in constructing low-noise and high-gain 1.58-μm band amplifiers     

1.3-μm strained MQW-DFB lasers with extremely lowintermodulation distortion for high-speed analog transmission

The intermodulation distortion and the noise characteristics of 1.3-μm strained multiquantum-well distributed feedback (MQW-DFB) lasers have been investigated under the modulation frequency of 1.9 GHz in connection with the device structure. In this study, a strained MQW with strain-compensated layers has been introduced in order to increase in the quantum-well number and well width. This causes increase in the differential gain, resulting in increase of the resonance frequency (FR). The FR as high as 5.1 GHz/mW^1/2 has been obtained which is in good agreement with the theoretical calculation. In addition to the strained MQW structure, a new buried heterostructure entirely grown by MOCVD, named as FSBH (facet selective growth buried heterostructure), has been developed to minimize the leakage current which degrades L-I characteristics at high bias current causing the high distortion. The third-order-intermodulation distortion (IMD3) of -88 dBc and relative intensity noise (RIN) of -152 dB/Hz have been obtained under a two-tone test at 1.9 GHz. This suggests that this newly developed laser is quite suitable for high-speed-subcarrier multiplexing transmission     

Bistable characteristics and all-optical set-reset operations of1.55-μm two-segment strained multiquantum-well DFB lasers

Bistable characteristics and all-optical set-reset operations in 1.55-μm two-segment InGaAsP-InP strained multiquantum-well (MQW) DFB lasers were studied. An extinction ratio as high as 20 dB with a lasing output power of 4 mW was obtained, partially due to the dispersion effect of strained MQW DFB structures. The detailed transient dynamics of the optical set-reset operations were observed for the first time, with optical injection from a single-mode laser, implying a potential for high-speed applications. A switch-on time in subnanosecond region and a switch-off time of 2.5 ns were measured using input pulses with a peak power of 500 μW     

Theoretical investigation of gain and linewidth enhancement factorfor 1.55-μm tensile strained quantum-well lasers

The performance of quantum-well laser diodes with tensile strained wells was theoretically calculated. Using 4×4 Luttinger-Kohn Hamiltonian, valence band dispersion was calculated and used for the calculation of material gain. Linewidth enhancement factor was obtained by calculating the change of refractive index due to interband transition and free carrier plasma motion. The tensile well shows smaller material and differential gain compared to the compressive strained one. But smaller linewidth enhancement factor is obtained due to the absence of free carrier plasma effect. Linewidth enhancement factor is further reduced by p-type modulation doping in the barrier     

2-μm GaInSb-AlGaAsSb distributed-feedback lasers

Room temperature continuous-wave operation of 2-μm single-mode InGaSb-AlGaAsSb distributed-feedback (DFB) lasers has been realized. The laser structure has been grown by solid source molecular beam epitaxy (MBE). Single-mode DFB emission is obtained by first-order Cr-Bragg gratings on both sides of the laser ridge. For a cavity with 900 μm length and 4 μm width, the threshold currents are around 20 mA and the continuous-wave output power is 10 mW at a drive current of 200 mA at 20°C. Monomode emission with sidemode suppression ratios of 31 dB has been obtained     

1.3-μm AlGaInAs buried-heterostructure lasers

1.3-μm AlGaInAs-InP strained multiple-quantumwell (MQW) buried-heterostructure (BH) lasers have been successfully fabricated. InP current blocking layers could be smoothly regrown using the simple HF pretreatment, although the etched active region includes Al-containing layers. The threshold current I_th was typically 11 mA for as-cleaved 350-μm-long devices, which is about 30% lower than that of the ridge laser counterparts. A maximum continuous-wave operating temperature as high as 155°C was achieved. For the 200-μm-long device with the high-reflective-coated rear-facet, I_th was as low as 7.5 mA and characteristic temperature T₀ was 80 K. The BH lasers also provided more circular far-field patterns and lower thermal resistances than for ridge lasers     

1.17-μm highly strained GaInAs-GaAs quantum-well laser

Excellent lasing properties and temperature characteristic of a highly strained 1.17-μm GaInAs-GaAs double-quantum-well laser are reported. We show that a strained buffer layer, which is employed in the device, has no tradeoff on the device performance. For a 1500-μm-long laser with cleaved facets a threshold current density of 200 A/cm² is achieved. A transparency current density of 180 A/cm² is estimated for as cleaved devices. A record high characteristic temperature in this wavelength range of 150 K is achieved     

High-power 0.98-μm strained quantum-well lasers fabricated usingin situ monitored reactive ion beam etching

0.98-μm wavelength InGaAs-AlGaAs strained quantum-well buried ridge lasers were fabricated using in situ monitored reactive ion beam etching (RIBE). This technique allowed a very accurate ridge geometry, resulting in high single transverse-mode power more than 250 mW and high-fiber coupled power more than 150 mW     

1.3-μm InAsP modulation-doped MQW lasers

The effect of both n-type and p-type modulation doping on multiple-quantum-well (MQW) laser performances was studied using gas-source molecular beam epitaxy (MBE) with the object of the further improvement of long-wavelength strained MQW lasers. The obtained threshold current density was as low as 250 A/cm² for 1200-μm-long devices in n-type modulation-doped MQW (MD-MQW) lasers. A very low CW threshold current of 0.9 mA was obtained in 1.3-μm InAsP n-type MD-MQW lasers at room temperature, which is the lowest ever reported for long-wavelength lasers using n-type modulation doping, and the lowest value for lasers grown by all kinds of MBE in the long-wavelength region. Both a reduction of the threshold current and the carrier lifetime in n-type MD MQW lasers caused the reduction of the turn-on delay time by about 30%. The 1.3-μm InAsP strained MQW lasers using n-type modulation doping with very low power consumption and small turn-on delay time are very attractive for laser array applications in high-density parallel optical interconnection systems. On the other hand, the differential gain was confirmed to increase by a factor of 1.34 for p-type MD MQW lasers (N_A=5×10¹⁸ cm ^-3) as compared with undoped MQW lasers, and the turn-on delay time was reduced by about 20% as compared with undoped MQW lasers. These results indicate that p-type modulation doping is suitable for high-speed lasers     

1.3-μm GaInNAs-AlGaAs distributed feedback lasers

Room temperature continuous-wave operation of 1.3-μm single-mode GaInNAs-AlGaAs distributed feedback (DFB)-lasers has been realized. The laser structure has been grown by solid source molecular beam epitaxy (MBE) using an electron cyclotron resonance plasma source for nitrogen activation (ECR-MBE). Laterally to the laser ridge a metal grating is patterned in order to obtain DFB. The evanescent field of the laser mode couples to the grating resulting in single-mode DFB emission. The continuous wave threshold currents are around 120 mA for a cavity with 800-μm length and 2 μm width. Monomode emission with side-mode suppression ratios of nearly 40 dB have been obtained     

All-selective MOVPE-grown 1.3-μm strained multi-quantum-wellburied-heterostructure laser diodes

Strained InGaAsP multi-quantum-well (MQW) double-channel planar-buried-hetero (DC-PBH) laser diodes (LDs) were fabricated by selective metalorganic-vapor-phase epitaxy (MOVPE). In the laser fabrication process, both the strained MQW active layer and current blocking structure were directly formed by selective MOVPE without any semiconductor etching process. The LDs are called all-selective MOVPE-grown BH LDs. The laser fabrication process can achieve both a precisely controlled gain waveguide structure and an excellent current blocking configuration, realizing the optimized DC-PBH structure. These aspects are essential to the high-performance and low-cost LD, which is strongly demanded for optical access network systems or fiber-to-the-home networks. This paper will show the excellent high-temperature characteristics for 1.3-μm Fabry-Perot LDs which have a record threshold current of 18 mA with a low-operation current of 56 mA for 10 mW, and 74 mA for 15 mW at 100°C with extremely high uniformity. Furthermore, reliable long-term operation at high temperature (85°C) and high-output power of 15 mW has been demonstrated for the first time     

Intracavity 1.549-μm pumped 1.634-μm Er:YAG lasers at 300 K

A novel method of generating 1.634-μm laser action from Er:YAG crystals pumped intracavity by an Er:glass laser emitting at 1.549 μm is described. Operation of the Er:glass laser at 1.549 μm (red shifted from the standard 1.532 μm, but with comparable output) at 500 K was obtained using mirrors with tailored spectral reflectivities. Several Er:YAG crystals ranging in concentration from 0.3% to 2% and in length from 1 cm to 8 cm were lased in the intracavity pumping arrangement. All the Er:YAG crystals lased in the ⁴I_13/2 :Y1(6544 cm^-1)-⁴I_15/2:Z6(424 cm ^-1) 1.634-μm transition at 300 K     

Submilliampere-threshold 1.5-μm strained-layer multiple quantumwell lasers

The effect of high-reflection facet coatings on strained-layer multiple-quantum-well lasers was studied and submilliampere-threshold lasers were made in the 1.5-μm wavelength region with a short cavity and high-reflection-coated facets. As a result of the compressive strain, the threshold current density is loss-limited instead of transparency-limited. By the use of the step-graded-index separate confinement heterostructure to reduce the waveguide loss, a threshold current density of 550 A/cm² was measured on 30-μm wide broad area lasers with 1-mm long cavity     

1.5-μm InGaAs/InAlGaAs quantum-well microdisk lasers

Microdisk lasers with three InGaAs/InAlGaAs quantum wells were demonstrated for the first time. The selective etching method used to fabricate the laser structure is discussed. Lasers 20 μm in diameter lased with single mode at 1.5-μm wavelength when optically pumped by a pulsed argon-ion laser at 80 K     

1.5-μm tapered-gain-region lasers with high-CW output powers

High-power diode lasers consisting of a a tapered region have waveguide section coupled to fabricated in 1.5-μm InGaAsP-InP multiple-quantum-well material. Self-focusing at high current densities and high intensity input into the taper section has been identified as a fundamental problem in these devices that has to be dealt with. To date, continuous-wave output powers of >1 W with ≈80% of the power in the near-diffraction-limited central lobe of the far field have been obtained through a judicious choice of device parameters     

High-temperature characteristics of 1.3-μm InAsP-InAlGaAs ridgewaveguide lasers

High-temperature characteristics of InAsP-InAlGaAs strained multiquantum-well (MQW) lasers with a large conduction band discontinuity (ΔE_c) are demonstrated. The InAsP-InAlGaAs MQW ridge waveguide lasers with narrow stripes exhibited a characteristic temperature as high as 143 K in the range from 25°C to 85°C. This material system is promising for developing a cooling-system-free 1.3-μm laser     

Efficiency of erbium 3-μm crystal and fiber lasers

The population dynamics of erbium 3-μm crystal and fiber lasers are compared experimentally and theoretically. Laser slope efficiencies of 40% in Er:LiYF₄ and 23% in a fluorozirconate fiber are experimentally demonstrated under Ti:sapphire pumping. These are both to our knowledge the highest values reported so far for the different host geometries. On the basis of the excitation and loss mechanisms, the best pump wavelengths are determined to be 970 mm in LiYF4 and 791 nm in a fluorozirconate fiber. The theoretical limit of the slope efficiency with respect to absorbed pump power is redefined as depending on the major population mechanisms of the system. Calculated values are 56% in Er:LiYF4 and 27% in a fluorozirconate fiber