Microcavity Laser Linewidth Close to Threshold

Microcavity laser linewidth behavior close to the threshold transition region is investigated through high-resolution linewidth measurements. A local maximum is found for the linewidth of lasers operating slightly above threshold. The increase in laser linewidth close to threshold is explained by the effective contribution of the linewidth enhancement factor ( $alpha $) to the laser linewidth. The Fokker–Planck model of laser noise is then solved using the eigenfunction expansion method to fit to the measured linewidth data. The behavior of the measured linewidth agrees with the model with an extracted linewidth enhancement factor ($alpha $ ) ranging between 3.5 and 5.0.      

Submicrometer Electron-Beam Direct Writing Technology for 1-Mbit DRAM Fabrication

A 1-Mbit DRAM with 0.5-/spl mu/m minimum linewidth is fabricated using variable shaped e-beam direct writing technology. A simple linewidth control technique using newly developed submicrometer resists is developed to achieve high resolution and better linewidth accuracy. In addition, a highly accurate registration technique is developed to ensure required overlay. These techniques are successfully used to achieve overlay accuracy of 0.04 /spl mu/m(sigma) and linewidth deviation of 0.018 /spl mu/m(sigma) in the fabrication.     

Influence of refractive index nonlinearities on modulation and noise properties of semiconductor lasers

The modulation response and the spectral linewidth of singlemode semiconductor lasers are analysed by taking into account the nonlinear gain and the nonlinear refractive index in the rate equations. It is shown that the effect of nonlinear gain and index can be included through an effective linewidth enhancement factor alpha /sub eff/ that is different for frequency modulation and for spectral linewidth. The effect of the nonlinear index is particularly strong in the case of frequency modulation where alpha /sub eff/ can become zero or even negative for lasers operating on the red side of the gain peak. In the case of laser noise, alpha /sub eff/ causes linewidth saturation but no rebroadening at high output powers. The authors' results indicate that gain and index nonlinearities are not the cause of linewidth rebroadening.<>     

Linewidth of InP-based 1.55 /spl mu/m VCSELs with buried tunnel junction

Spectral linewidth measurements of 1.55 /spl mu/m InGaAlAs/InP vertical-cavity surface-emitting lasers (VCSELs) employing a buried tunnel junction are reported. A narrow linewidth around 28 MHz was obtained at a power level of 0.5 mW using the self-heterodyne method, and an estimation for the linewidth enhancement factor is given.     

Factors limiting the spectral linewidth of CPM-MQW-DFB lasers

A spectral linewidth of 56 kHz is achieved by a CPM-MQW-DFB (corrugation-pitch-modulated multiquantum-well distributed feedback) laser at an output power of 25 mW. To separate effects of the white noise and 1/f noise in limiting the linewidth, the authors measured the delayed-heterodyne lineshape by using a short delay-fiber. The minimum spectral linewidth is shown to be limited by white noise     

Linewidth enhancement in distributed-feedback semiconductor lasers

It is demonstrated that the linewidth enhancement in distributed-feedback (DFB) laser diodes can differ significantly from (1+ alpha /sup 2/), where alpha is Henry's linewidth enhancement factor. The influence of the relevant laser parameters, the detuning of the gain peak wavelength, a pi /2 phase shift and a reflecting end facet on the linewidth enhancement is discussed with respect to an improved DFB laser design.<>     

The effect of side modes with linewidth and intensity fluctuationsin semiconductor lasers

The influence of side modes on the linewidth and intensity fluctuations of the main mode is studied using Monte Carlo techniques. Explicit analytic relations are developed for the side-mode induced linewidth, using impulse responses of the laser obtained from rate equations. It is found that both the absolute level of the main-mode too side-mode power ratio and the passive loss in the side mode influence the main-mode linewidth. A typical 3-mW laser has negligible linewidth enhancement from the side mode if the modal power ratio is about 300/1 (or greater), corresponding to a side-mode loss of 0.2-0.5 dB (or more) for one round trip within the laser resonator. Lower side-mode losses yield an abrupt catastrophic increase in main-mode linewidth     

Spectral linewidth rebroadening in MQW-DFB LDs caused byspontaneous emission noise in SCH/barrier layers

A new theory is proposed to explain spectral linewidth rebroadening in MQW-DFB LDs. This is based on the idea that spontaneous emission recombination in the SCH and barrier layers may cause excess spectral linewidth broadening. Theoretical and experimental studies show that excess spectral linewidth broadening is proportional to the recombination current in the SCH/barrier layers. This current increases monotonically as output power increases     

The effect of linewidth on the efficiency of two-photon-pumped frequency converters

The efficiency of two-photon-pumped frequency converters as a function of the pump laser detuning and linewidth, and of the linewidth of the selected nonallowed atomic transition is studied. We show that pressure broadening of the atomic transition is a key parameter in the design of these converters. A technique is developed to measure this linewidth as a function of either self- or foreign-gas broadening using a broad-band pump laser. Measurements of the linewidth of the3s^{2}S-3d^{2}Dtransition of Na, and its device implications, are presented.     

Electrical feedback and its network analysis for linewidthreduction of a semiconductor laser

The center frequency of the field spectrum of a 1.5-μm InGaAsP distributed-feedback laser was stabilized by negative electrical feedback. The resultant residual frequency fluctuation was σ=3.6×10^-11 for an integration time of 10 s. The linewidth of the field spectrum was simultaneously reduced by using another electrical feedback loop. Its minimum value was 360 kHz, which was 1/27 that of the free-running condition. This linewidth was narrower than the one determined by the magnitude of the spontaneous emission of the free-running laser. The field spectrum was very stable, and the value of the linewidth was constant for more than 40 h. Network analysis was carried out to realize further reductions of the linewidth     

Spectral linewidth of DFB lasers including the effects of spatialholeburning and nonuniform current injection

An analytic expression for the linewidth of distributed-feedback (DFB) lasers is derived. Local fluctuations in carrier density are shown to provide a significant contribution to laser linewidth in the presence of spatial holeburning. In a single-electrode DFB laser the effect can be avoided by careful optimization of the kl-product, but for a multielectrode DFB laser the linewidth can also be reduced by adjusting the injected current profile to compensate for spatial holeburning. Numerical results for a three-electrode λ/4-shifted DFB laser are presented     

Spectral linewidth and resonant frequency characteristics ofInGaAsP/InP multiquantum well lasers

The spectral linewidth and resonant frequency characteristics of 1.3-μm InGaAsP/InP multi-quantum-well lasers grown by liquid-phase epitaxy were investigated and compared to those of the conventional double heterostructure (DH) lasers. A decrease in spectral linewidth and an increase in resonant frequency f_r with decreasing well thickness were observed. Moreover, the linewidth enhancement factor α was reduced to ~2 for well thicknesses of less than ~200 Å, while that of the DH laser was ~6. An f_r of 9 GHz, which is twice as large as that of conventional DH lasers, was achieved at an optical power of 5.3 mW/facet     

Spectral linewidth estimation of a 1.5 µm range InGaAsP/InP distributed feedback laser

Spectral linewidth of a 1.5 μm range distributed feedback buried heterostructure (DFB-BH) laser in CW operation is estimated theoretically and experimentally. Considering the equivalent mirror facet loss coefficient and the confinement factor in the active layer, etc., we modified the conventional formula for the spectral linewidth of single-mode semiconductor lasers and presented a formula for the linewidth of DFB lasers. Furthermore, power-dependent linewidth measurements of a 1.5 μm range InGaAsP/InP DFB-BH laser with a window region were carried out using Fabry-Perot interferometers. The linewidth was observed to increase linearly with inverse output power. The measured result was explained by the calculated result through the modified formula. The full width at half maximum was estimated to be 50 MHz at an output power of 1 mW.     

1/f frequency noise effects on self-heterodyne linewidthmeasurements

The effects of a 1/f frequency noise on self-heterodyne detection are described, and the results are applied to the problem of laser diode linewidth measurement. The self-heterodyne autocorrelation function and power spectrum are evaluated for both the white and the 1/ f components of the frequency noise. From numerical analysis, the power spectrum resulting from the 1/f frequency noise is shown to be approximately Gaussian, and an empirical expression is given for its linewidth. These results are applied to the problem of self-heterodyne linewidth measurements for coherent optical communications, and the amount of broadening due to 1/f frequency noise is predicted     

延时自外差法线宽测量误差分析仿真及修正

讨论了移频延时自外差探测的基本原理,并对外差得到的功率谱进行了公式推导。在此基础上,对外差测量中出现的测量误差进行分析,同时设计了自外差测量实验装置进行实验对比,确定了由于延时线长度不够导致的线宽测量误差来源是因为延时时间短导致幂指数函数项波动加剧造成的;同时针对外差信号频谱为洛仑兹型和类高斯型的混合谱型,在高斯功率谱密度函数的基础上,对延时时间和1/f谱宽的影响进行了仿真计算,采用Voigt分析,提取出1/f导致的测量误差,提高了线宽测量的精度。以高斯谱宽4.5 kHz的谱型为例,对应的洛仑兹线宽约为0.68 kHz,提高了一个数量级的测量精度。     

Calculation of differential gain and linewidth enhancement factorin 980-nm InGaAs vertical cavity surface-emitting lasers

The optimization of differential gain and linewidth enhancement factor within VCSEL's is required to achieve improved performance under dynamic conditions. In this paper, the differential gain and linewidth enhancement factor in an InGaAs-GaAs VCSEL have been calculated over a range of carrier densities and at various wavelengths across the gain spectrum. The results show the importance of low threshold gain values in achieving high differential gain/low linewidth enhancement factor. By temperature tuning the lasing wavelength to shorter wavelengths than the gain peak, values of α_H as low as 0.6 can be achieved     

Fabrication approach for antiphase narrow linewidth complex coupled 1.55 /spl mu/m DFB lasers

A new method for fabricating narrow linewidth antiphase complex coupled MQW DFB lasers by periodically etching the active layer and quarternary InGaAsP overgrowth is reported. The minimum linewidth for a 375 /spl mu/m long ridge waveguide laser is only 250 kHz at an optical output power of 4 mW.     

PLL propagation delay-time influence on linewidth requirements ofoptical PSK homodyne detection

Phase-locked loop (PLL) propagation delay-time influence on optical homodyne detection was investigated both theoretically and experimentally. Applying the Pade approximation, which is often used in the control system, to the calculation of the phase-error variance with the nonzero loop delay time, a high-accuracy analytic expression phase-error variance is obtained. The linewidth requirement with the nonnegligible loop delay time for phase-shift-keying (PSK) homodyne detection is obtained as δν=2.04×10^-3/τ where δν (hertz) is beat linewidth and τ (seconds) is the loop delay time. The linewidth requirement with small delay time approaches δν=6.2×10^-4 R_b where R_b (bits-per-second) is the system bit rate. Results were confirmed by a 10-GB/s optical PSK homodyne detection experiment using external cavity laser diodes. Receiver sensitivity degradations due to loop delay time and beat linewidth are in good agreement with theoretical results     

Measurement of linewidth and FM-noise spectrum of 1.52 ?m InGaAsP lasers

The linewidth of 1.52 ?m InGaAsP lasers was measured as a function of the output power. The result shows that the linewidth is about 15 MHz when the output power is 1 mW. The FM-noise spectrum was also measured in the frequency range from 10 Hz to 100 MHz. The measured spectrum consists of the 1/f-noise and white-noise components. The linewidth calculated from the FM-noise spectrum is in good agreement with the measured value.     

Lasing characteristics for four-section MQW-DBR laser

A MQW-DBR laser with two active sections and low tuning efficiency has been developed. The device showed excellent lasing characteristics: a low threshold current of 10 mA, a high slope efficiency of 0.26 mW/mA, and a narrow linewidth of 280 kHz at P_out=15 mW. A red-shift carrier-induced FM response was obtained by nonuniform current injection to two active sections. A flat FM response with wide bandwidth (>2 GHz) was confirmed. The linewidth broadening due to wavelength tuning was suppressed through the reduction of tuning efficiency. A continuous tuning range of 0.8 nm was observed while maintaining the linewidth below 4 MHz