Multiquantum-well Distributed-feedback Lasers Research Articles

Recovery of Absorption Line Shapes With Correction for the Wavelength Modulation Characteristics of DFB Lasers

Tunable diode laser spectroscopy combined with wavelength modulation spectroscopy (WMS) is an important technique for noninvasive measurements of gas parameters such as pressure, concentration, and temperature in high-noise harsh environments. A variety of laser types are used for these applications, and the modulation characteristics can have significant effects on line shape recovery. Here, we identify important characteristics of distributed feedback (DFB) lasers that need to be taken into account in the context of WMS and illustrate the effects with a 2- $\mu\textrm{m}$ wavelength multiquantum-well DFB laser used for CO2 detection. The modulation response of the laser is measured, and we demonstrate how the phasor decomposition method (PDM) may be used to obtain accurate line shapes from the first harmonic WMS signals by correcting for phase variation across the laser's low-frequency current sweep. We also demonstrate how the PDM approach can be improved by removing the need to preset the orientation of the lock-in axis to isolate the residual amplitude modulation component, making it more suitable for field applications.

Long-Term Degradation Behavior of 2.3-$\mu\hbox{m}$ Wavelength Highly Strained InAs/InP MQW-DFB Lasers With a p-/n-InP Buried Heterostructure

We investigate the long-term degradation of 2.3-μm wavelength InAs/InP highly strained multiquantum-well distributed-feedback lasers with a p- and n-type InP buried heterostructure during constant power aging. Stable operation beyond 20 000 h is confirmed at an ambient temperature of 45 °C and with a constant output power of 3 mW, and we successfully fabricate a practical optical source for trace gas monitoring applications. A conventional diffusion process dominates the main degradation mechanism as found with conventional telecommunication lasers. Furthermore, we show that some defects are located in the regrown p-type InP layer above the active layer and that downward diffused defects degrade the guide, upper separate confinement heterostructure (SCH), and active layers.

Analysis of optical-injected distributed feedback lasers using complex optical low-coherence reflectometry

A theoretical and experimental investigation of reflectograms obtained for a distributed feedback (DFB) semiconductor laser using a phase-controlled high-resolution optical low-coherence reflectometer was carried out, yielding the effective group refractive index and its variation above threshold, the cavity internal loss, as well as the grating coupling factor of a multiquantum-well DFB laser. In addition, direct measurements of the injection-induced complex-modal index changes are presented for the first time.

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 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.

Partly gain-coupled 1.55 mu m strained-layer multiquantum-well DFB lasers

1.55- mu m gain-coupled InGaAsP-InP distributed feedback (DFB) lasers which use a strained-layer multi-quantum-well (MQW) active grating for a mixed index and gain coupling have been fabricated and studied. The lasers exhibit distinct longitudinal-mode behaviour due to gain-coupling effects, including a high single-mode yield. Cavity length dependence of the mode behavior has been experimentally studied and simulated using a transfer-matrix method. Both experimental and theoretical results indicate that the shorter cavity lasers with the present structure have higher kappa /sub gain/L/ kappa /sub inde/ ratios and wider Fabry-Perot mode spacing than the longer cavity ones; these features enable the shorter cavity lasers to have a high single-mode yield (90%) and a high side-mode-suppression ratio (55 dB).< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

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.

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. >

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/ >

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>

Effect of 1/f noise on the spectral linewidth of corrugation-pitch-modulated multiquantum-well distributed feedback lasers at high output power

The mechanism by which spectral linewidth reduction saturates in CPM-MQW-DFB (corrugated-pitch-modulated multiquantum-well distributed feedback) lasers at high output powers is investigated by measuring the spectral power density of their FM noise. Linewidth saturation is caused by the 1/f component of this noise. >

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>

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

1.5 μm 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 μm long devices. Measured threshold current as low as 2.2 mA was also obtained on 150 μm 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.

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.