Multiquantum-well Distributed-feedback Research Articles

Reliable 2.3-$\mu$m Wavelength Highly Strained InAs–InP MQW-DFB Lasers With p-/n-InP Buried Heterostructure

We have realized reliable 2.3-mum wavelength InAs-InP multiquantum-well distributed-feedback (DFB) lasers for trace gas monitoring applications. The estimated median lifetime exceeds 1x105 hours during aging at an ambient temperature of 45degC and with a constant output power of 3 mW. Furthermore, the relative increase in operating current is proportional to the square root of time, and it is clarified that the main degradation mechanism in DFB lasers with highly strained InAs quantum wells is dominated by a diffusion process as found with conventional telecommunication lasers.

Measurement and characterization of laser chirp of multiquantum-well distributed-feedback lasers

Measurements of relative intensity noise and modulation response, before and after propagation in optical fiber, of the output field of multiquantum-well distributed-feedback (MQW-DFB) lasers are used to determine the influence of the intraband damping mechanisms, the DFB structure and the carrier transport and carrier capture into the QWs on the laser chirp. The power dependence of the linewidth enhancement factor is shown to explain the saturation of the laser linewidth at high optical powers.

1.3-μm uncooled DFB lasers with low distortion for CATV application

Strained-layer multiquantum-well distributed-feedback (MQW-DFB) lasers at a wavelength of 1.3 /spl mu/m operating from -40/spl deg/C to 85/spl deg/C without any coolers are demonstrated. Extremely low threshold current of 17 mA at 85/spl deg/C and operation current of 37 mA at 5 mW and 85/spl deg/C are obtained. To the best of our knowledge, each of them is the lowest value so far reported in InGaAsP-InP based DFB lasers. The lasers also realize low distortion of less than -50 dBc at 65/spl deg/C in 78-channel composite second order distortion (CSO) measurements. An experimental estimation of the leakage current in buried heterostructure presents that the distortion at high temperatures is mostly dominated by the carrier overflow from an active layer, not by the leakage current flowing through current blocking layers. On the basis of the leakage current analysis, a laser structure including the active layer and the current blocking layer is chosen to achieve low distortion over a wide-temperature-range. The uncooled distributed-feedback (DFB) laser we have developed is very useful for several channel transmission in CATV systems.

Low distortion 1.3 μm strained-layer MQW-DFB laser for AM-SCM transmission systems with large channel capacity

1.3-/spl mu/m strained-layer multiquantum-well distributed-feedback (SL-MQW-DFB) lasers with extremely low distortion and low noise characteristics up to high output-power as well as over wide frequency range were successfully fabricated. This was achieved by both the high relaxation oscillation frequency (f/sub r/) characteristics of the laser with the optimized SL-MQW active structure and the suppression of nonradiative current with relatively long laser cavity length. By using the SL-MQW laser with a 400-/spl mu/m long cavity as a light source for CATV transmission system, high quality AM-SCM transmissions with the largest channel capacity (151 channel) was demonstrated due to low distortion characteristics at high output power. Also, for the laser with 300 /spl mu/m long cavity, extremely low bias-current operation (17 mA above threshold) is realized in high quality 100 channel AMSCM transmissions, due to high f/sub r/ at low bias-current.

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

The intermodulation distortion and the noise characteristics of 1.3-/spl mu/m 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/sup 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.

Optical injection effects and all-optical set-reset operations in two-segment strained multiquantum-well distributed feedback bistable lasers

Optical injection effects and all-optical set-reset operations in two-segment strained multiquantum-well (MQW) distributed feedback (DFB) bistable lasers were experimentally investigated. The optical bistable characteristics under detuned optical injection, of strained MQW DFB bistable lasers, show the effect of the residual Fabry–Perot side modes of the DFB structures; optimizing the input wavelength and the input power is suggested for applications. The switching properties of dynamic optical set-reset operations with pulsed optical injection were reported, which appear to be related to the optical bistable characteristics under cw optical injection; however, the switching transients are found to be essential to full understanding of these switching properties.

Longitudinal-mode switching in a two-segment multiquantum-well distributed-feedback laser

Two types of wavelength switching are observed experimentally in two-segment 1.55 μm InGaAsP/InP ridge waveguide multiquantum-well distributed-feedback (DFB) lasers. The first type occurs between the longitudinal modes on the opposite sides of the DFB stop band, while the second type occurs on the same side of the stop band. The physical mechanism is correlated to a slight difference of the effective grating period between the two inhomogeneously injected laser segments.

InGaAs/InGaAsP MQW electroabsorption modulator integrated with a DFB laser fabricated by band-gap energy control selective area MOCVD

The fabrication and basic characteristics of a InGaAs/InGaAsP multi-quantum-well (MQW) electroabsorption modulator with a novel structure integrated with a distributed-feedback (DFB) laser are presented. A fundamental study was performed on the applicability of the InGaAs/InGaAsP MQW structure to an electroabsorption-type modulator. Efficient attenuation small hole pileup and small chirp characteristics of a discrete modulator based on this MQW structure were demonstrated experimentally. A study of the controllability of in-plane band-gap energy by the use of selective-area metal-organic chemical vapor deposition (MOCVD) was also demonstrated. The modulator was monolithically integrated with a MQW DFB laser of the same material. Using a low-capacitance semi-insulating buried heterostructure, over 14 GHz modulation under high-light-output operations up to +10 dBm was achieved. Modulation at 10 Gb/s with a modulation voltage swing of only 1 V/sub pp/ demonstrates the potential value of this system for 1.55- mu m lightwave communications.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Simulation and interpretation of longitudinal-mode behavior in partly gain-coupled InGaAsP/InP multiquantum-well DFB lasers

The unique longitudinal-mode behavior observed in 1.55- mu m InGaAsP/InP partly gain-coupled multiquantum-well distributed feedback (DFB) lasers has been simulated using a transfer-matrix analysis technique. Experimental results have been successfully reproduced and interpreted according to below-threshold calculation, results. >

Monolithic integration of multiwavelength compressive-strained multiquantum-well distributed-feedback laser array with star coupler and optical amplifiers

The monolithic integration of a multiwavelength multiquantum-well distributed-feedback (DFB) laser array with a star coupler and optical amplifiers on the same chip is reported. As many as 18 individual wavelengths from a given output of the star coupler are launched into a lensed single-mode fibre.

Low distortion up to 2 GHz in 1.55 μm multiquantum well distributed-feedback laser

The distortion characteristics of multiquantum well (MQW) distributed-feedback (DFB) lasers emitting at 1.55 mu m wavelength are investigated over a wide frequency range. The relaxation oscillation frequency f/sub r/ of the MQW DFB laser is 13 GHz at I/sub b/=77 mA, which is about 1.5 times larger than that of a DFB laser with a bulk active layer. Owing to the high relaxation oscillation frequency characteristics and the good linearity of the light-output against injection-current curve of the MQW DFB laser, extremely low distortion characteristics (IM/sub 2/ >

High-speed 1.5- mu m compressively strained multi-quantum well self-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- mu m 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/sup -12/ m/sup 3//s. The estimated intrinsic maximum bandwidth is 68 GHz. >

Direct demodulation of 140 Mb/s FSK signals in an injection-locked multiquantum-well DFB laser

The authors report the transmission of frequency shift keying (FSK) signals using an injection-locked multiquantum-well distributed-feedback (DFB) laser that acts simultaneously as an optical frequency discriminator and a photodetector. 140 Mb/s FSK signals are directly demodulated by detecting changes in the forward voltage of an injection-locked GaInAs/GaInAsP/InP MQW DFB laser. A sensitivity of -25.9 dBm was measured at a bit-error-rate of 10/sup -9/. Bias-current-dependent FM demodulation efficiency is also reported together with the optical-power-dependent linewidth enhancement factor. >

Corrugation-pitch modulated MQW-DFB lasers with narrow spectral linewidth

Narrow spectral linewidth lasers are developed for optical coherent transmission systems. To obtain a narrow spectral linewidth, a CPM (corrugation-pitch modulated) structure is introduced into 1200- mu m-long MQW-DFB (multi-quantum well distributed feedback) lasers. The CPM structure effectively suppresses the axial spatial hole burning effect and stabilized single-mode spectrum at high output powers. A spectral linewidth of 170 kHz was achieved at an output power of 25 mW. Details of corrugation fabrication method that makes the CPM structure possible are described.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Frequency response of an MQW DFB laser injected with intensity-modulated TM-polarized light

The frequency response of a multiquantum-well (MQW) distributed-feedback (DFB) laser was measured by injecting intensity-modulated transverse-magnetic (TM)-polarized light. With low bias currents, the 3-dB bandwidth of the MQW DFB laser's frequency response was anomalously enhanced by injection of intensity-modulated TM-polarized light. The maximum 3-dB bandwidth, 16 GHz, was observed when the normalized bias current (I/I/sub th/-1) was 1. The 3-dB bandwidth behavior of the MQW DFB laser with TM-polarized light injection looks promising for high-speed lasing mode control of semiconductor lasers.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Narrow-linewidth strained-layer 1.5 μm multiquantum well distributed feedback lasers

The performance characteristics of narrow-linewidth strained-layer 1.5 μm multi-quantum-well distributed feedback (MQW-DFB) lasers are presented. Measured linewidth as low as 3.5 MHz has been observed for one of the 250 μm long devices at 14.4 mW output. Under 1.7 Gbit/s 1.0, 1.0, … pattern signal modulation, the lasers have 20 dB down full width chirp in the range of 5–6 Å for the off state at 0.8Ith. The chirp widths are about half of those of bulk-active DFB lasers. A 1.7Gbit/s amplitude-shift-keying transmission experiment using one of the low-chirp lasers has been demonstrated. The transmission over 60 km of standard fibre only result in a 0.8 dB dispersion power penalty and has a receiver sensitivity of −36.2 dBm at BER = 10-9.

Multi-quantum well distributed feedback and distributed Bragg reflector lasers

Unlike bulk semiconductors, quantum well (QW) structures exhibit unique optical features, because their band structure is completely different. In this paper, the authors review the applications of multi-quantum well (MQW) structures to AlGaAs/GaAs distributed feedback (DFB) and distributed Bragg reflector (DBR) lasers. Theoretical and experimental results on the lasing characteristics of MQW DFB lasers are described, mainly focusing on linewidth. Reduction in the chirp and the alpha -parameter were measured, and a linewidth as narrow as 1.5 MHz was obtained. Next they review various characteristics of MQW DBR lasers. In these lasers, MQW structures were used both as an active layer and as a low loss passive waveguide. Highly efficient surface emission from the second-order grating was observed. They also measured the fast bistable switching and beam switching characteristics. In the last part they review the fabrication and characterisation of AlGaAs/GaAs quantum well wires grown on corrugated substrates.