Multiple-quantum-well Distributed-feedback Lasers Research Articles

43 Gb/s 1.3 $\mu$m DFB Laser for 40 km Transmission

We describe the performance of 1.3 $\mu$ m InGaAlAs ridge waveguide multiple quantum-well distributed feedback lasers. We obtained a 3 dB down bandwidth frequency of around 30 GHz by shortening the cavity length of the laser. We demonstrated experimentally that it is possible to obtain clear eye opening at a 43 Gb/s modulation speed after a 40 km single-mode fiber (SMF) transmission using a directly modulated laser. We fabricated a compact transistor outline (TO)-CAN module whose volume was about $1/19$ that of a conventional butterfly package. We successfully obtained clear eye opening for a 40 km SMF transmission at 43 Gb/s with the TO-CAN module.

Single contact monolithically integrated DFB laser amplifier

A monolithic 1550-nm single-mode AlInGaAs-InP multiple quantum-well distributed feedback laser and amplifier is presented. For the 400-/spl mu/m-long grating section /spl kappa/=112+ 30i cm/sup -1/, while the output is taken from the 200-/spl mu/m-long amplifier section. The slope efficiency of the chip was 0.21 W/A, while the kink free power from the fiber was 34 mW. Narrow linewidths of <50 kHz were measured, and the dispersion penalty remained less than 2.0 dB for a data rate of 2.5 Gb/s over 300 km of SMF-28.

Threshold current, differential gain, and relaxation resonance frequency of 1.55-μm bulk and MQW DFB laser diodes

We investigate threshold currents, differential gains, and relaxation resonance frequencies of 1.55-/spl mu/m bulk and nine-well multiple-quantum-well (MQW) distributed feedback (DFB) laser diodes (LDs) experimentally and theoretically. The experimentally obtained threshold current (I/sub th/), differential gain (dg/dN), and relaxation resonance frequency per square root of output power (fr/(P)/sup 1/2/) of the 1.55-/spl mu/m bulk DFB LD are 19 mA, 2.4/spl times/10/sup -16/ cm/sup 2/, and 3.2 GHz/mW/sup 1/2/, which nearly agree with the calculated I/sub th/ of 21.6 mA, dg/dN of 3.1/spl times/10/sup -16/ cm/sup 2/, and fr/(P)/sup 1/2/ of 3.6 GHz/mW/sup 1/2/, respectively. The experimentally obtained I/sub th/, dg/dN, and fr/(P)/sup 1/2/ of the 1.55-/spl mu/m InGaAs MQW DFB LD with barriers (/spl lambda/g=1.3 /spl mu/m) are 9 mA, 6.0/spl times/10/sup -16/ cm/sup 2/, and 4.6 GHz/mW/sup 1/2/ compared with the calculated I/sub th/ of 7.8 mA, dg/dN of 4.0/spl times/10/sup -16/ cm/sup 2/, and fr/(P)/sup 1/2/ of 3.7 GHz/mW/sup 1/2/, respectively. However, the experimentally obtained I/sub th/, dg/dN, and fr/(P)/sup 1/2/ of the 1.55-/spl mu/m InGaAs MQW DFB LD with barriers (/spl lambda/g=1.15 /spl mu/m) are 20 mA, 2.6/spl times/10/sup -16/ cm/sup 2/, and 2.85 GHz/mW/sup 1/2/, which greatly disagree with the calculated I/sub th/, of 4.9 mA, dg/dN of 6.0/spl times/10/sup -16/ cm/sup 2/, and fr/(P)/sup 1/2/ of 4.3 GHz/mW/sup 1/2/, respectively. Taking into account the nonuniform hole distribution among nine wells, which is attributed to the valence band discontinuity, /spl Delta/E/spl upsi/ (the separation between the first quantized hole level in the well and the top energy of the valence band for the barrier), the corrected I/sub th/ and dg/dN of the 1.55-/spl mu/m MQW DFB LD with /spl lambda/g of 1.15 /spl mu/m are 18.3 mA and 2.2/spl times/10/sup -16/ cm/sup 2/, which fairly agree with the above measured values. By p-type doping to 1.5/spl times/10/sup 18/ cm/sup -3/ into the wells to improve the nonuniform distribution of holes among nine wells, I/sub th/, dg/dN, and fr/(P)/sup 1/2/ of the 1.55-/spl mu/m MQW DFB LD with /spl lambda/g of 1.15 /spl mu/m can be expected to be 3.7 mA, 8.8/spl times/10/sup -16/ cm/sup 2/, and 5.4 GHz/mW/sup 1/2/, respectively.

Static and dynamic simulation for ridge-waveguide MQW DFB lasers

An efficient and versatile computer-aided simulator for the design and analysis of ridge-waveguide (RWG) multiple-quantum-well (MQW) distributed-feedback (DFB) lasers has been developed and is presented. This simulator combines spectral index method and Green's function-based transfer-matrix method (TMM) to deal with the transverse RWG MQW structure and longitudinal DFB structure, respectively. It is capable of simulating both static and dynamic behaviors for a variety of RWG MQW DFB lasers. The major difference from most of the existing models and analyses is that this simulator is capable of linking important device characteristics with practical material and geometrical parameters directly and self-consistently. For instance, the effects of lateral ridge width, vertical MQW layers and longitudinal nonuniformity are all explicitly included in the simulator. important laser characteristics, such as L-I curve, effective linewidth enchancement factor, static lasing wavelength shift, spectral linewidth, facet-power spectrum, AM and FM modulation responses, dynamic-wavelength chirping, as well as longitudinal photon and carrier distribution, can be predicted based on material and waveguide parameters. Therefore, this simulator may be used as an efficient and versatile tool for the systematic exploitation and optimization of a wide range of practical RWG MQW DFB lasers. Analysis of a /spl lambda//4 shifted SCH RWG MQW DFB laser is performed to illustrate the capability of this simulator.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Thermal frequency drift suppression in tunable DFB lasers by plasma induced frequency shift enhancement

The authors propose enhanced-plasma-effect (EPE) lasers for coherent optical frequency division multiplexed networks. In the EPE lasers, the blue frequency shift due to the plasma effect is enhanced by incorporating a very thick p-side optical guide layer as a carrier reservoir for multiple quantum-well distributed feedback laser and it surpasses the red frequency shift due to the thermal effect. The results of demonstrating a frequency step response maintained in the blue shift region and an enhanced blue shift frequency modulation response over the whole modulation frequency range from DC are presented for the first time. >

Effect of linear gain saturation on small-signal dynamics of MQW DFB lasers

The linear gain saturation effect is shown to be important in determining the dynamics of multiple-quantum-well (MQW) distributed-feedback (DFB) lasers. A more realistic logarithmic dependence of material gain on carrier density is assumed in a comprehensive MQW DFB laser model. It is found through simulation that because of the linear gain saturation, the interplay between modal gain and differential gain leads to an optimal kappa L for maximum small-signal modulation bandwidth in lambda /4-shifted MQW DFB lasers.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Spectral linewidth reduction in partly gain-coupled 1.55 μm strained multiple quantum-well distributed feedback laser

The effective linewidth enhancement factor αeff and the spectral linewidth Δυ are reported for the first time for a partly gain-coupled distributed feedback laser with a gain corrugation in a strained multiple quantum-well active region emitting at 1.55 μm wavelength. The αeff value is estimated to be as low as 1 and is independent of the laser cavity length L, while a decrease in the linewidth-power product ΔυPo with L has been observed, with a measured linewidth of 2 MHz at 10 mW optical output power for 300-μm-long devices. The experimental results demonstrate that a small αeff is obtained due to the strain and the gain coupling effects, while further reduction of the spectral linewidth with L is the result of longitudinal index coupling effects.

Proposal of novel gain-levered MQW DFB laser with high and red-shifted FM response

A gain-levered multiple quantum well (MQW) distributed feedback (DFB) laser with high FM efficiency is discussed. The device consists of three sections with different bandgap energy. It can be fabricated by a selective area metalorganic vapor phase epitaxy (MOVPE) growth technique. Numerical analysis shows that a flat, red-shifted, and high FM efficiency of above 1 GHz/mA at 20-mW output power can be realized using the gain levering scheme. >

Modeling of ridge-waveguide MQW DFB lasers based on spectral index transfer matrix method

An efficient and accurate method is developed for the analysis of ridge-waveguide multiple-quantum-well (MQW) distributed-feedback (DFB) lasers. Based on the combination of the mode-matching transfer-matrix method for the longitudinal grating-assisted coupling and the discrete spectral-index method for the transverse mode characteristics, this method provides a semianalytical approach to the modeling of three-dimensional ridge-waveguide semiconductor lasers. Compared with the conventional combination of effective-index method and the coupled-mode theory, as well as other numerical methods, this approach offers versatility, simplicity, and a compromise between the accuracy and the computation effort. >

A low-drive-voltage, high-speed monolithic multiple-quantum-well modulator/DFB laser light source

A high-speed InGaAs/InAlAs multiple-quantum-well (MQW) intensity modulator and an InGaAsP/InGaAs MQW distributed feedback laser were monolithically integrated by using a hybrid growth technique combining molecular beam epitaxy and metalorganic vapor phase epitaxy. An operating drive voltage of only 2.0 V, a 20-dB on/off ratio, and a 3-dB bandwidth greater than 15 GHz were obtained. This device operated stably in a single mode and with a side-mode suppression ratio of more than 50 dB. >

Spectral linewidth of MQW DFB lasers with intensity-modulated TM-polarized light injection

The spectral linewidth of a multiple-quantum-well (MQW) distributed feedback (DFB) laser is measured when intensity-modulated orthogonally polarized (transverse magnetic (TM) mode) is injected into the laser. The spectral linewidth does not change when the modulation frequency is higher than several hundred megahertz and is almost the same as without light injection. However, it broadens when the injected orthogonally polarized light modulation frequency is close to zero. The line shape of the MQW DFB laser's lasing light becomes non-Lorentzian in shape below a modulation frequency of 500 MHz. >

Measurement of gain saturation coefficients in strained-layer multiple quantum-well distributed feedback lasers

Gain saturation coefficients of unstrained- and strained-layer multiple-quantum-well lasers were measured experimentally. These coefficients were higher in lasers that had compressive strain in their active-layer wells: 2.45*10/sup -17/ cm/sup 3/ with unstrained wells and 12.6*10/sup -17/ cm/sup 3/ with strained wells. The higher gain saturation coefficient in lasers with strained active-layer wells is related to their higher linear TE mode gain coefficient. The linearity factor (K factor) between a laser's damping constant and the square of the laser's resonant frequency decreased slightly with the introduction of the strain in the laser's active layer wells. This factor, however, took the value of about 0.2*10/sup -9/ s for each of these lasers.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Spectral aspect of degradation in 1.55 mu m long-cavity MQW DFB lasers

Degradation behaviors, particularly for the increase in spectral linewidth and FM efficiency, in 1.55 mu m long-cavity MQW (multiple quantum well) DFB (distributed feedback) lasers, with a spectral linewidth of around 1 MHz, are presented from the viewpoint of coherent system application. Through the clarification of the behaviors, it is shown that highly coherent lasers are sufficiently durable in coherent transmission systems.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

High-speed and low-drive-voltage monolithic multiple quantum-well modulator/DFB laser light source

Monolithic integration of an InGaAsP/InGaAs multiple quantum well (MQW) distributed-feedback (DFB) laser with a high-speed InGaAs/InAlAs MQW intensity modulator is demonstrated. A 3-dB bandwidth. in excess of 16 GHz and low-drive-voltage operation (4.0 V) for a 20-dB on-off ratio are obtained. Good coupling efficiency between an MQW DFB laser and an MQW modulator is accomplished using hybrid crystal growth of MO-VPE and MBE. >

Gain saturation coefficients of strained-layer multiple quantum-well distributed feedback lasers

The gain saturation coefficients were measured for strained and unstrained multiple quantum-well distributed feedback (MQW-DFB) lasers. The gain saturation coefficient depends on the deviation of the laser's transverse-magnetic (TM) mode gain peak wavelength from its transverse-electric (TE) mode gain peak wavelength delta lambda , which is related to the strain on the active-layer wells. The gain saturation coefficient epsilon increased with increasing compressed strain on the active-layer wells. The coefficient epsilon of the unstrained MQW DFB laser with a wavelength deviation delta lambda of -350 AA was 2.45 x 10/sup -17/ cm/sup 3/, and epsilon increased up to 12.6 x 10/sup -17/ cm/sup 3/ in the SL-MQW DFB laser with a wavelength difference delta lambda of -890 AA.

A 1.7 Gb/s ASK and a 622 Mb/s incoherent FSK transmission experiment using a 1.55- mu m multiquantum well distributed feedback laser

A multiple-quantum-well distributed-feedback (MQW-DFB) laser with narrow linewidth and low frequency chirp at low output power may experience linewidth rebroadening at high output power. the rebroadening is mostly due to a large carrier-induced change of refractive index, which also causes a large frequency modulation response for the MQW-DFB lasers. Using a 1.55- mu m MQW-DFB laser, a 622-Mb/s amplitude-shift-keying (ASK) transmission experiment employing 200-km of fiber and an erbium-doped fiber amplifier has been demonstrated having a dispersion power penalty less than 9.8 dB. The receiver sensitivities at BER=10/sup -9/ of the ASK system are -34.5 dBm and -42.5 dBm for 1.7-Gb/s and 622-Mb/s modulation, respectively. A 622-Mb/s incoherent frequency-shift-keying (FSK) transmission experiment using the same laser has also achieved a receiver sensitivity of -42.5 dBm. >