Transmission line description of optical feedback and injection locking for Fabry-Perot and DFB lasers

A general theory of semiconductor lasers is presented in which the static and dynamic properties are expressed in terms of the effective left and right reflectivities at a given reference plane in the laser. The theory applies to Fabry-Perot and DFB solitary lasers and to laser configurations with strong optical feedback or strong light injection.     

Single-polarization generation in fiber Fabry-Perot laser byself-injection locking in short feedback cavity

Single-frequency and single-polarization lasing can be generated in a compact self-injection locked fiber Fabry-Perot laser with a short fiber Bragg grating feedback cavity. No discrete polarization control components are required. Different wavelengths actress the laser gain bandwidth can be generated by an appropriate combination of cavity designs and feedback fiber Bragg gratings. A 10-Gb/s nonreturn-to-zero transmission test demonstrates the laser's applicability for optical fiber communications     

Novel measurement technique of alpha factor in DFB semiconductor lasers by injection locking

A simple and accurate method to measure the linewidth enhancement factor alpha in DFB semiconductor lasers is proposed. This method, based on the principle of external optical injection locking, does not require the knowledge of the absolute value of optical injection level.<>     

Double-tapered-waveguide distributed feedback lasers for high-powersingle-mode operation

Theoretical analysis of double-tapered-waveguide distributed feedback semiconductor laser for stable single-mode and high-power operation is presented. It is found that the single-mode behavior of a distributed feedback laser with large coupling-length product can be improved significantly by the double-tapered-waveguide structure     

Gain saturation in fiber distributed feedback lasers

Systematic numerical studies of the nonlinear operation of a fiber distributed feedback (DFB) Nd:YAG laser are presented. An approximate formula relating small-signal gain to output power and the parameters of the structure for this kind of laser is derived. Characteristics revealing saturation effects for weak and strong coupling regions are presented. The fiber DFB structure provides the discrimination between the different kinds of transverse modes. An interesting behavior of the laser characteristics is revealed. For large coupling strength the longitudinal mode spectrum is inversed to the one observed at the threshold or to the one above the threshold for weak coupling. This mode inversion strongly depends on the output power level and the normalized loss coefficient. Similar phenomena are observed for the transverse mode     

Passive phase locking of an array of four fiber lasers by mutual injection locking

In this paper, we report the passive phase locking of a four fiber lasers array by mutual injection locking. The four fiber lasers are mutually injected by four 5/5/90 couplers. Through mutual injection locking, good coherence has been obtained in the far field. The four fiber lasers can operate at the same wavelength with a stable output power. This scheme is quite easy to implement and can be extended to combine more beams.     

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.     

Dynamical noise in single-mode distributed feedback fiber lasers

The dynamics of erbium distributed feedback fiber lasers close to steady state is analyzed taking into account spatial hole burning and the nonuniform modefield distribution. A set of linearized equations is derived and used to obtain theoretical amplitude and frequency noise spectra for spontaneous emission noise and generic pump power noise. Analytic formula for important laser characteristics including pump slope efficiency and relaxation oscillation frequency are also obtained. It is found that the spatial distribution of the laser mode plays and important role in determining the output characteristics of the laser.     

Photonic crystal distributed feedback fiber lasers with Bragggratings

Two new types of optical fibers, where air-holes are running down their length, are considered for making fiber lasers with Bragg gratings. The mode areas for pump and signal in these fiber lasers may be either larger or smaller compared to the corresponding mode areas for fiber lasers based on standard step index fibers. This makes possible realization of fiber lasers with a low pump threshold (small mode area), and fiber lasers suitable for high-power applications (large mode area)     

分布反馈光纤激光器自放大特性实验研究

通过相位掩膜板移动法,制作了非对称相移结构分 布反馈光纤激光器(DFB-FL)。为了获得更高的激光功率,利 用同样长度的掺铒光纤(EDF),分别采用同向泵浦和反向泵浦结构方式进行了窄线宽激光信 号的自放大实验,结 果表明,两种自放大结构的DFB-FL均可充分利用泵浦光功率,在保证激 光线宽展宽有限的前 提下,实现了激光信号至少23dB的功率放大。同时,实验结果对比 说明,同向泵浦放大结构更有利于保 持原激光信号的噪声特性。这为较大输出功率的DFB-FL提供了一种简单 可行的方案。     

Injection locking of broad-area angled grating DFB lasers

The injection locking properties of an angled-grating distributed feedback laser have been measured experimentally. Fringe visibility measurements were used to ascertain the quality of the phase lock between the master and slave laser as a function of master coupling level and frequency detuning. Experimental results show an asymmetric lockband with the stable lock region increasing in width as the coupling is increased     

Enhanced single-mode operation in multisection DFB lasers with bothlocalized and distributed phase shift

Multisection distributed feedback lasers with both localized (λ/8 phase shift) and distributed phase shift (produced by a phase-adjustment region) are investigated theoretically. It is shown that such a mixed phase shift, combined with a stronger coupling coefficient in the center of the cavity, may enlarge the threshold gain margin as well as the output optical power, enhance the intra cavity field flatness and produce an effective index profile leading to a low sensitivity to spatial-hole burning (SHB) (with respect to conventional λ/4 phase-shifted DFB lasers). As a consequence, the side-mode suppression ratio (SMSR) is improved and single-mode operation up to high bias currents is maintained     

Multiple-waveguide distributed feedback lasers

Coupled wave theory is used to examine the performance of lasers formed from an array of coupled stripe waveguides with a grating overlay. It is found that such lasers exhibit inherent longitudinal mode discrimination, and, if the number of coupled guides is small, inherent transverse mode discrimination as well. The conditions for such selectivity are examined in detail, and it is shown that the correct grating distribution to use is one in which the grating fills the overlap region between the coupled guides.     

Wavelength accuracy in distributed phase-shifted DFB lasers

In the wavelength-division-multiplexed transmission framework, we investigate the ability of the distributed phase-shifted distributed-feedback (DFB) structure by enlarging the ridge to fulfil the wavelength accuracy required for array fabrication. Measurements on three different phase-shift geometries indicate that the poor localization of the optical mode along the cavity is detrimental to the wavelength accuracy. This study points out the best solution for DFB structure implementable in arrays, using already validated low-cost and high-throughput technologies in a production environment     

Performance limitations of high-power DFB fiber lasers

In this letter, we experimentally study several different configurations of high-power single-frequency sources based on distributed-feedback fiber laser (DFB FL). In particular, we have compared two schemes in terms of pumping efficiency, relative intensity noise (RIN) and optical signal-to-noise ratio (OSNR): directly pumped DFB FLs pumped by a high-power fiber-based pump source (stand-alone DFB FL) and a combination of a DFB FL and a power amplifier (amplified DFB FL). At the output powers below 40 mW, a stand-alone DFB FL has the highest OSNR (> 63 dB) and the lowest RIN (< -165 dB/Hz). The net efficiency of a stand-alone DFB FL can be doubled by using an amplified DFB FL at the expense of degraded OSNR and RIN. It is also shown that RIN below -160 dB/Hz and OSNR > 60 dB can be achieved by an amplified DFB with output power greater than 1 W.     

Analysis of multiple wavelength DFB fiber lasers

The behavior of multiwavelength distributed feedback fiber lasers is simulated in a comprehensive numerical model. Multiple fundamental modes can coexist, even though the coupling coefficients of their respective refractive index gratings are not equal, due to induced dynamic gain gratings. We have investigated the effect on the lasing state of variations in coupling strengths, gain parameters, grating Bragg frequency separation, relative phase between the gratings, length of the structure relative to the beat lengths between the gratings, grating center phase-shift errors, and saturation level of the UV-induced refractive index change     

High-frequency pulsations in DFB lasers with amplified feedback

We describe the basic ideas behind the concept of distributed feedback (DFB) lasers with short optical feedback for the generation of high-frequency self-pulsations and show the theoretical background describing realized devices. It is predicted by theory that the self-pulsation frequency increases with increasing feedback strength. To provide evidence for this, we propose a novel device design which employs an amplifier section in the integrated feedback cavity of a DFB laser. We present results from numerical simulations and experiments. It has been shown experimentally that a continuous tuning of the self-pulsation frequency from 12 to 45 GHz can be adjusted via the control of the feedback strength. The numerical simulations, which are in good accordance with experimental investigations, give an explanation for a self-stabilizing effect of the self-pulsations due to the additional carrier dynamic in the integrated feedback cavity.     

Tunable two-segment distributed feedback lasers

The authors describe a two-segment distributed feedback laser at 1.3 mu m with a tuning range of 12.8 AA (209 GHz) and an FM response of 7 GHz/mA. The observed tuning behaviour is in qualitative agreement with an earlier theoretical model. Such two-segment DFB lasers are useful in frequency-multiplexed, frequency-modulated optical networks.<>