Analysis of the spectral linewidth of distributed feedback laser diodes

The spectral linewidth of distributed feedback (DFB) laser diodes is theoretically studied. Numerical calculation shows that DFB lasers with long cavity lengths and large coupling coefficients have very narrow spectral linewidth less than 1 MHz, The effects of the phase shift and mirror facets on the spectral characteristics of DFB lasers are also analyzed, It is shown that the phase-shifter further narrows the spectral linewidth of DFB lasers. Its numerical result and physical meaning are also shown.     

Strained multiquantum-well corrugation-pitch-modulated distributed feedback laser with ultranarrow (3.6 kHz) spectral linewidth

Introducing a 1% compressive strained multiquantum-well (MQW) active layer into a corrugation-pitch-modulated distributed feedback (CPM-DFB) laser reduces the linewidth floor (residual linewidth for extrapolated infinite output power) to 2 kHz and results in a linewidth-power product of 140 kHz. mW. Strained MQW CPM-DFB lasers produced a 55 mW output with a spectral linewidth of only 3.6 kHz.<>     

Long-cavity multiple-phase-shift distributed feedback laser diodefor linewidth narrowing

A long-cavity multiple-phase-shift distributed-feedback (MPS-DFB) laser diode with three phase shifts in the corrugation for linewidth narrowing is discussed. The threshold gain difference and the field uniformity along the laser cavity of the MPS-DFB laser are analyzed by varying the amount and the position of phase shifts using the coupled-wave theory. It is shown that a large threshold gain difference and a uniform field distribution are obtained in the MPS-DFB laser with some special amount and position of phase shifts. Based on the analysis, a MPS-DFB laser with a 1200-μm-long cavity and three phase shifts was fabricated. This MPS-DFB laser exhibits stable single-mode operation and shows a very narrow linewidth of 830 kHz at an optical output power of 25 mW     

Lasing mode and spectral linewidth control by phase tunable distributed feedback laser diodes with double channel planar buried heterostructure (DFB-DC-PBH LD's)

Lasing mode selection between ±1 modes across the stop-band and spectral linewidth tunability have been experimentally observed with newly developed phase tunable distributed feedback laser diodes with double channel planar buried hetetostructure (DFB-DC-PBH LD's) for the first time.     

Measurement of spectral linewidth of AlGaAs/GaAs distributed feedback lasers

The spectral linewidth of AlGaAs/GaAs distributed feedback (DFB) lasers was measured for the first time. The linewidth-power product decreased with temperature, which indicates that the relative position of the oscillation wavelength and the gain peak strongly affects the linewidth of DFB lasers.     

Unidirectional laterally gain-coupled distributed feedback ring laser diodes

The authors report the development of laterally gain-coupled ring lasers that exhibit uni-directional and singlemode operation. Counterpropagating modes in the ring are suppressed such that 83% of the light output comes from only one propagation direction. The mode stability of the ring laser is significantly improved through the introduction of a gain-coupled distributed feedback mechanism.     

Effect of phase shift position on spectral linewidth of the π/2distributed feedback laser diode

The dependence of the spectral linewidth on the phase shift position (PSP) of a phase-shifted distributed-feedback (DFB) laser diode is investigated theoretically, using the coupled wave model. In particular, the analysis is performed to find an optimum PSP so as to minimize the spectral linewidth of the laser diode. This optimum PSP is compared to that obtained by maximizing the stability of the laser oscillation. Since both narrow spectral linewidth and good stability are essential for the light source in coherent optical communications, the analysis revealed the suitability of using phase-shifted DFB laser diodes in coherent transmissions     

Long-cavity, multiple-phase-shift, distributed feedback laser for linewidth narrowing

Describes the long-cavity multiple-phase-shift distributed feedback (MPS-DFB) laser diode with three phase shifts in the corrugation for linewidth narrowing. Stable single-mode operation up to 30 mW and narrow linewidth of 830 kHz were obtained for a 1.2 mm cavity MPS-DFB laser.<>     

窄线宽半导体激光器件

分布反馈半导体激光器的线宽一般较大,难以满足光纤传感等领域的要求。根据C.H. Henry于1982年提出的半导体激光器的线宽理论,通过适当设计DFB半导体激光器的腔长、耦合系数、微分增益、光限制因子,能有效地减小激光器的线宽。同时,空间烧孔现象也可限制DFB半导体激光器的线宽,为此需要合理设计光栅结构。在此基础上,DFB激光器的线宽能达到几十千赫兹的量级。此外,采用DBR结构或者外腔结构,也可以获得相当窄的线宽。     

1550 nm GaInNAsSb distributed feedback laser diodes on GaAs

Single mode laser diodes on GaAs substrates were developed using GalnNAsSb double quantum well active regions grown by molecular beam epitaxy. The distributed feedback devices were fabricated using a regrowth-free process in which lateral Cr gratings were deposited adjacent to a dry-etched narrow ridge waveguide. In continuous- wave (CW) operation the devices exhibit a lasing wavelength of 1550 nm at 10degC with a very high sidemode suppression ratio of > 50 dB throughout most of the operational range, and output power up to 15 mW.     

Spectral characteristics of distributed feedback laser diodes withdistributed coupling coefficient

A comprehensive investigation of the spectral characteristics of distributed feedback (DPB) laser diodes (LD's) with a distributed coupling coefficient (DCC) is presented. With a proper selection of both the coupling ratio (r) and a corrugation position (CP), the performance of the DCC laser structure is enhanced with an improved single-mode stability as well as a uniform field distribution. In the analysis, the above threshold characteristics and the influence of non-lasing side modes have been investigated using the transfer matrix method (TMM). Based on a DCC laser structure with r=1/3 and CP=0.46, a normalized gain margin (ΔαL)=0.81 and a side mode suppression ratio (SMSR) of 45 dB have been achieved for a DCC LD at biasing current of 4I_th . The introduction of the DCC laser structure opens a new way of stabilizing the single-mode oscillation in DFB LD's     

Novel measuring method for spectral linewidth of laser diodes using fibre-optic ring resonator

A novel measuring technique for the spectral linewidth of a laser diode was developed by using a fibre-optic ring resonator. Although the method is simple, a measuring accuracy within ±10% was obtained in the wide spectral linewidth range from 1 to 100 MHz.     

Degradation analysis in asymmetric sampled grating distributed feedback laser diodes

This paper presents the experimental observation of the degradation in asymmetric sampled grating DFB lasers by the accelerated life tests. Two degradation phenomena related to the electrical characteristics of LDs are observed during the tests. The first degradation phenomenon by increasing the reverse current is considered as a formation of leakage current path enough to prevent lasing operation in lateral blocking layer near active region of lasers. The second degradation phenomenon by decreasing the forward current is considered as activation of non-radiative Auger recombination process by thermal energy. It is also experimentally observed that the second degradation phenomenon is recovered after remained in room temperature with no electrical stress. Therefore, the criteria for LD reliability can be determined by observing the degradation of the reverse current–voltage characteristics.     

分布反馈激光器温度与电流控制研究

为了精密控制分布反馈激光器的温度与电流, 采用数字信号处理芯片, 设计了分布反馈激光器驱动装置。通过该装置设定激光器温度和电流的参考电压, 经数模转换, 再通过温度和电流驱动模块, 馈入并驱动分布反馈激光器, 进行了实验验证。结果表明, 40min内温度变化极差与标准差分别不超过5mK和0.7mK, 电流变化极差与标准差不超过40μA和6μA; 驱动半导体光放大器, 关断时间小于1μs, 具有良好的瞬间响应特性; 该装置具有较高的温度和电流稳定性, 流控模块具有良好的瞬态特性, 能够精密控制分布反馈激光器的温度和电流。该控制装置可用于光腔衰荡光谱研究, 控制分布反馈激光器并驱动光放大器来关断激光。     

Analysis of multiple-quantum-well distributed feedback laser

The doping and detuning dependences of the threshold, dynamic and spectral properties of multiple-quantum-well distributed feedback lasers were analysed theoretically. It was shown that optimised detuning improves the dynamic and spectral properties. It was also shown that donor doping significantly reduces the threshold current and spectral line-width.     

Highly achromatic, narrow linewidth distributed feedback dye laserpumped by a multimode laser

Highly achromatic operation of a computer-optimized distributed feedback dye laser is reported. Linewidths of between 320 and 500 MHz, a factor of up to 100 less than the pump laser linewidth, have been measured across a scanning range of 70 nm. The dependence of the laser linewidth on pump laser parameters such as linewidth and energy has also been studied. The wavelength dependence of the laser linewidth was well represented by a computer model, and the measured threshold was close to the value predicted by a rate equation model. A conversion efficiency of 20% was obtained     

Excess linewidth broadening in wavelength-tunable laser diodes

Injection-recombination shot noise in the tuning region is identified as significant linewidth broadening mechanism in wavelength tunable laser diodes. Depending on the tuning efficiency this power independent linewidth broadening is typically around 4-20 MHz. Useful formulas for the evaluation of this broadening and design rules for an improvement of the devices are given.<>     

The optimal loop gain design for the spectral linewidth reductionin an electrical feedback semiconductor laser

The design of the optimal feedback loop gain for the spectral linewidth reduction in a semiconductor laser with electrical feedback is presented using a model of self-heterodyne type electrical feedback. The results show that the feedback loop gain must be suitably chosen to satisfy the requirement of narrowing linewidth. Due to the influence of AM noise in the feedback process, there is an optimal value for the feedback loop gain to reduce the linewidth for a given feedback condition. The influence of other feedback parameters on the linewidth reduction is also presented     

Pump-noise-induced linewidth contributions in distributed feedback fiber lasers

We investigate experimentally and theoretically the linewidth of an Er-Yb-doped distributed feedback fiber laser. We find that two noise sources are mainly responsible for the observed behavior, fundamental thermal noise at low pump power levels and temperature fluctuations induced by pump intensity noise at higher powers. Potential techniques to overcome these limitations are discussed.     

Semiconductor laser linewidth in optical feedback configurations

We present a theoretical analysis for semiconductor laser linewidth, employing optical feedback. This analysis is valid not only for weak feedback, but also for strong feedback including multiple reflections. The experimental result reported so far under a strong feedback condition is well explained.