Continuously tunable thin active layer and multisection DFB laserwith narrow linewidth and high power

The feasibility of a wavelength tuning range of 1 nm with the spectral linewidth around 2.5 MHz at about 10 mW is demonstrated in thin-active-layer and multisection 1.5-μm distributed feedback (DFB) lasers with long cavities. The tuning range is widened to over 3 nm by combining electric and thermal tuning effects. A flat FM response with an efficiency of over 1 GHz/mA from low to high (around 1 GHz) frequency is also achieved     

Frequency noise and modulation of a four-section DBR laser

A theoretical model is presented to describe the tuning, frequency noise, and modulation characteristics of tunable DBR lasers with two active and two passive sections. Analytical expressions are derived for the intensity and frequency modulation responses, frequency noise spectrum, spectral linewidth, effective linewidth enhancement factor, and spontaneous emission rate. It is shown that a nearly flat red-shifted FM response over several gigahertz can be obtained by nonuniform current injection and modulation of the lower carrier density section in the active region. Increasing the tuning current through the passive sections enhances the FM efficiency. However, a higher FM efficiency is generally accompanied by a larger spectral linewidth. The predictions of our theoretical model are in good agreement with the available experimental data     

Frequency modulation and spectral characteristics for a 1.5?m phase-tunable DFB laser

Frequency modulation (FM) and spectral characteristics for a 1.5?m phase-tunable DFB (PT DFB) laser have been studied experimentally. As tuning current was increased, light output, lasting wavelength, FM efficiency and spectral linewidth changed periodically. The continuous-wavelength tuning range was over l.2nm (150 GHz). A high FM efficiency, more than 16GHz/mA, and a flat FM response, up to 100MHz, were obtained.     

A fully integratable 1.55-/spl mu/m wavelength continuously tunable asymmetric twin-waveguide distributed Bragg reflector laser

We demonstrate a single-frequency continuously tunable three-section distributed Bragg reflector laser operating at a center wavelength of /spl lambda//sub 0/=1.548 /spl mu/m using a fully integratable asymmetric twin-waveguide structure. A low-loss tapered mode transformer couples the light between the active waveguide, or gain region, and the passive ridge waveguide where the phase and grating tuning sections are located. The device has a threshold current of 50 mA and output power of nearly 13 mW, with a slope efficiency of 0.12 W/A and a tuning range of 4.8 nm under pulsed operation. An independent phase section is used to continuously tune the wavelength, thus avoiding mode hops. Using a delayed self-heterodyne technique, we determine the linewidth to be (146/spl plusmn/2) kHz.     

High performance 1.5 mu m multiple-quantum-well DFB-DC-PBH-LDs at 30 mW output power for Gb/s range coherent systems

Long cavity (1200 mu m) MQW-DFB-DC-PBH-LDs have been developed. The devices simultaneously showed less than 1 MHz spectral linewidth, lower than 15 kHz FM dip frequency, moderate FM efficiency (250-300 MHz/mA at 100 MHz modulation frequency), as well as 10-GHz FM bandwidth (6 dB down level from the peak), at 30 mW output power condition. Such LDs will be suitable for Gb/s continuous phase frequency shift keying (CPFSK) current optical fiber communication systems.<>     

Wavelength-tunable asymmetric cladding ridge-waveguide distributedBragg reflector lasers with very narrow linewidth

Narrow-linewidth ridge-waveguide distributed Bragg reflector (DBR) lasers with asymmetric cladding are demonstrated. This design requires only a single epitaxial growth of an asymmetric cladding laser structure while the grating and the ridge waveguide are fabricated after the growth. These lasers have a threshold current as low as 9 mA, a slope efficiency of 0.3 W/A, and a T₀ of 100 K. Wavelength tuning of 8 nm is achieved by current injection heating of the DBR section. A spectral-linewidth minimum of 36 kHz is achieved at an output power of 20 mW and is limited by linewidth rebroadening due to current injection in both the gain section and DBR section     

A theoretical analysis of linewidth broadening in frequency tunableDBR lasers

Linewidth broadening in frequency tunable distributed-Bragg-reflector (DBR) lasers with tuning sections is analyzed. The analysis is based on a simplified two-section single-mode cavity model and quantum mechanical Langevin treatment. The origin of linewidth broadening is shown to be low frequency excess FM noise caused by carrier fluctuation in the tuning section. A scaling law, which permits optimal device parameter design, is then derived. When a decrease in the carrier lifetime is combined with an increase in the tuning current, linewidth broadening can be suppressed without frequency tuning range reduction     

窄线宽低噪声可调谐非平面环形激光器

针对空间相干光通信和探测等应用,对非平面环形激光器的线宽、噪声和调谐特性进行了系统的实验研究。单频输出功率达到752mW,光光效率42%,斜率效率54%。采用延时自外差拍频法测试了激光线宽,其随泵浦功率的增加而增大,输出功率小于200 mW 时,线宽小于1 kHz,在最高输出功率下线宽为2.3 kHz。激光强度噪声主要由弛豫振荡引起,相对强度噪声（RIN）随着泵浦功率的提高而降低。在1.78W 泵浦功率下,RIN 达到-93 dB/Hz。采用温度和压电两种方式进行了激光调谐。温度调谐范围达到62 GHz。压电调谐范围达到130MHz,响应带宽100 kHz。     

Low-chirp and high-power 1.55-/spl mu/m strained-quantum-well complex-coupled DFB laser

High-power, low-chirp, and low-threshold current characteristics of 1.55 /spl mu/m complex-coupled compressively strained InGaAsP quantum-well DFB laser with a loss grating are presented. Kink-free light-current characteristics with single-mode power over 40 mW are demonstrated for uncoated devices. A relatively low threshold current of 10 mA and a high slope efficiency of 0.23 W/A have been obtained even with the loss grating employed. Stable single-mode emission was demonstrated with a side mode suppression ratio up to 54 dB, a low chirp of less than 0.3 nm under 1 Gb/s pseudorandom digital modulation and a spectral linewidth of 8 MHz.     

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.<>     

High power and narrow spectral linewidth 1.5 μm MQW-DFB-LDs withlow FM dip frequency

FM response as well as spectral linewidth were characterized for 1.5 μm multiple-quantum-well distributed feedback laser diodes (MQW-DFB-LDs). It was experimentally demonstrated that the FM dip frequency where AM-FM phase delay rotates by 180° decreases with reduced thermal resistance and reduced threshold current density, due to reduced thermal effect and enhanced carrier effect. 1.5-μm MQW-DFB-LDs have been developed with <20 kHz FM dip frequency and relatively flat FM response, as well as <1 MHz spectral linewidth, in the 10-35 mW light output power range     

Linewidth and FM characteristics of a distributed feedback laser monolithically integrated with a tunable external cavity

A narrow linewidth has been obtained in a new 1.5 ?m distributed feedback laser integrated monolithically with a tunable external cavity. The linewidth of 18 MHz has been achieved by tuning the current in the external cavity, and the FM response was flat from 100 kHz to 500 MHz.     

High-Performance Bound-to-Continuum Quantum-Cascade Lasers for Broad-Gain Applications

Based on the bound-to-continuum active region design, we shall present a high performance continuous-wave (CW) quantum-cascade laser. In contrast to high performance lasers based on a two-phonon resonance transition and a narrow linewidth (< 165 cm^-1), the device presented here exhibits a spontaneous emission full-width at half-maximum as large as 295 cm^-1. Thus, such devices are very suitable for broadband tuning. At 30degC, it shows a maximum output power and slope efficiency of 188 mW and 500 mW/A, as well as a threshold current density of only 1.79 kA/cm². Furthermore, at this temperature, the device demonstrates an internal differential quantum efficiency of 71% and a wall plug efficiency of 2.0%. The maximum CW operation temperature reached is 110degC. A thermal resistance of 4.3 K/W was attained by epi-down mounting on diamond submounts. The waveguide losses of 14 cm^-1 are explained by intersubband absorption in addition to free-carrier absorption.     

Monolithically integrated InGaAsP/InP composite-cavity distributedfeedback lasers

Linewidth reduction to 1 MHz for monolithically integrated extended-cavity DFB lasers that are designed to achieve high optical coupling to a low-loss extended cavity is described. Since a high-efficiency extended cavity at the same time degrades the frequency-modulation (FM) response, an active gain section is integrated at the end of the extended cavity, and its use as a modulator section that maintains a flat FM response at 0.7 GHz/mA is shown. The linewidth and FM characteristics of this DFB extended-passive/active-cavity laser are compared to those of the conventional DFB extended-passive-cavity laser and a two-section DFB laser     

Pure frequency modulation or intensity modulation with suppressed frequency chirp using active Bragg reflector integrated laser

The modulation properties of a laser structure which consists of an active Bragg reflector (300 mu m) integrated with an uncorrugated gain region (600 mu m) have been measured. The laser exhibited a flat FM response and very low spurious intensity modulation when modulating the current in the Bragg reflector. Furthermore, broadband intensity modulation with suppressed frequency chirp could also be achieved. An inhomogeneous linewidth enhancement factor alpha caused by the uneven carrier density distribution between the two sections gives a qualitative explanation to our results.<>     

Millimeter-wave orotron oscillation--Part II: Experiment

Experimental observation of orotron oscillation is reported in the frequency band from 53 to 73 GHz. The output power in a quasi-CW mode and beyond an output window is approximately 100 mW at a beam current of 90-100 mA. Oscillation has been observed on several modes of the open resonator of the orotron, with starting currents ranging from 35 to 82 mA. The electronic tuning transconductance within a single mode was measured by mixing the orotron signal with another signal from a klystron, yieldingdf/dV = 0.25MHz/V. The spectrum of the orotron output signal was also measured by this method, and the linewidth was determined to be less than 0.4 MHz at 70 GHz.     

A DBR laser employing passive-section heaters, with 10.8 nm tuningrange and 1.6 MHz linewidth

A wavelength-tunable, three-section, distributed Bragg reflector (DBR) InGaAsP/InP laser diode is described. The refractive indices of the DBR section and the phase-control section are thermally controlled by thin-film heaters embedded on these passive sections. This structure enables wide-range wavelength tuning without the spectral linewidth broadening accompanying conventional tuning by current injection into the passive sections. A tuning range of 10.8 nm and a linewidth of less than 1.6 MHz have been achieved in the 1.5-μm wavelength region. The temperature increase in the active layer is held to within a few degrees, even when the DBR-section temperature reaches 90°C     

FM efficiency and spectral linewidth in two-active-section MQW DBR laser

A large and red-shifted FM response and a spectral linewidth of a few megahertz were obtained in a two-active-section MQW DBR laser. It is found that the FM efficiency can be enhanced by using the inhomogeneity in alpha parameters with a high threshold current density device and that there is a tradeoff in the relationship between spectral linewidth and FM efficiency.<>     

Drive current noise induced linewidth in tunable multielectrode lasers

It is shown that drive current noise could lead to an important increase of linewidth and a Gaussian line shape of tunable multielectrode distributed Bragg reflector (DBR) lasers. As an example, the drive current noise induced linewidth (DCNIL) has been measured to be about 120 MHz using a standard DC source through at 50 Omega resistor to drive the Bragg section of a tested DBR laser. For tunable lasers with an electronic tuning efficiency of more than 1 GHz/mA ultralow noise current sources should be used to ensure a negligible DCNIL.<>     

高斜效率高功率850nm氧化限制型垂直腔面发射激光器

报道了MOCVD生长的高性能850nm氧化限制型垂直腔面发射激光器.研制出的氧化直径为9μm的激光器25℃时的斜效率和阈值电流分别为0.82mW/mA和2.59mA,激光器在23mA时输出16mW最大光功率.氧化直径为5μm的激光器25℃时的最小阈值电流为570μA,其最大饱和光功率为5.5mW.