Theory of direct frequency modulation of semiconductor lasers withintegrated external cavity

Numerical calculations of the frequency modulation responses of monolithically integrated external-cavity semiconductor lasers are performed using G.P. Agrawal's (J. Appl. Phys., vol.56, p.3110-15, 1984) two-section model. Theoretical results show good agreement with the reported experimental results. The comparison of the modulation responses of the solitary semiconductor laser diodes, the conventional external-cavity semiconductor lasers, and the integrated passive external-cavity semiconductor lasers demonstrates that the integrated external-cavity semiconductor laser is the best choice for use in direct frequency modulation     

An open-resonator model for the analysis of a short external-cavitylaser diode and its application to the optical disk head

Based on the open resonator theory, a model of a complex coupling coefficient suitable for the analysis of an ultrashort external-cavity laser diode is presented. It is shown that the effective reflectivity of the short external-cavity laser diode calculated by using this model is a function of the size of the laser-emitting area and is significantly influenced by the phase-modification factor as well as by the amplitude-reduction factor of the complex coupling coefficient. The calculated output power characteristics show good qualitative agreement with experimental observation. The necessary condition that the optical disk head using an external-cavity laser diode does not fail to detect the recorded signal for a broad range of flying height is also derived     

Electrical mode-hopping noise in external-cavity semiconductor lasers and mode-hopping elimination by a nonoptical control loop

The longitudinal mode-hopping and the associated terminal electrical noise in AlGaAs buried heterostructure lasers in an external-cavity configuration are investigated. It is found that the electrical mode-hopping noise has a1/f-dependence when two external-cavity modes are involved in the mode-hopping. Furthermore, it is found that the optical feedback can suppress the electrical noise significantly below the noise level of the free-running laser. This corresponds to a reduction of the emission line width which is in agreement with the reduction of the electrical noise level. A novel, nonoptical, scheme for active elimination of mode-hopping attributable to thermal drift or mechanical disturbances in CW-operated external-cavity lasers is also proposed and demonstrated. Using this method, where the electrical noise is used as an error signal in a control loop, long-term single external-cavity mode operation and low electrical noise and optical intensity noise levels were maintained.     

Spectral stability analysis of weakly coupled external-cavity semiconductor lasers

The spectral stability of weakly coupled external-cavity semiconductor lasers is studied theoretically. The carrier density modulation induced at the frequency of the external-cavity mode spacing fexplays an important role in the spectral instability. Therefore, the laser under optical feedback reveals different spectral behaviors, depending on the relation between the frequency of the external-cavity mode spacing and the relaxation resonance frequency fRof the carrier density. For a better spectral stability, fexmust be larger than fR.     

Characteristics of a semiconductor laser with external feedback

The theoretical analysis of the compound cavity of a semiconductor laser with external optical feedback is conducted. For large optical feedback, the output power from the laser and its oscillation frequency differ from those for small optical feedback. From the rate equations of the compound cavity, the conditions of the laser oscillation are derived in the presence of large optical feedback The dependencies of the output power and the laser oscillation frequency on the external-cavity length are investigated. Some new results involving laser oscillation depending on the external-cavity length are presented. The experimental results are compared with theoretical predictions. The dependence of the laser oscillation on the external-cavity length is qualitatively explained in the present model     

Dynamics and chaos stabilization of semiconductor lasers withoptical feedback from an interferometer

This paper studies dynamical behaviors and noise properties of semiconductor lasers with optical feedback from an interferometer, i.e., two external cavities. Bifurcation diagrams versus external-cavity length and reflectivity reveal the existence of stable regions for fixed states and limit cycles. The steady-state analysis for a laser diode with two external feedbacks is performed, which shows that oscillation modes are locked at minimum excess gain modes. Oscillation frequencies of limit cycles show discrete transitions with the variation of ratios between two external-cavity lengths and reflectivities. It is proposed that such a model might be applied to stabilization of the feedback-induced chaos in external-cavity semiconductor lasers since the stable region is quite robust for wide parameter ranges. Intensity and phase noises are examined and the results indicate that the low-frequency relative intensity noise level and the linewidth can be greatly improved when the laser output is a fixed state or a limit cycle     

基于DMD的外腔量子点激光器性能研究

为了取得更加完善的外腔量子点激光器(QDL)测试 数据,构建了基于数字微镜器件(DMD,digital micro-mirror device)的InAs/InP量子 点外腔QDL。测量了其 光谱特性以及调谐范围,得到了基于DMD的外腔QDL调谐范围和相应的模式变 化。在理论和实验上与基于光栅的外腔QDL性能进行了比较,得到了在角色 散和反射光谱中与光栅的区别,实现了将DMD应用于外腔QDL中而获得的一种 新方法。     

A simple interferometric method for monitoring mode hopping intunable external-cavity semiconductor lasers

The mode-hopping events in a 1.3-μm grating-tuned external-cavity laser are analyzed on the basis of interferometric measurements. The average frequency of mode hopping for a 7.5-cm external-cavity laser is estimated and is expressed as f_c =2.7×10⁶×exp [-1.7/(I/I _th-1)] (hertz) for 0.07⩽(I/I_th -1)⩽0.8 (I=injection current and I_th =threshold current). The mode-hopping monitoring signal was negatively fed back to the laser using an automatic control circuit which maintained single-mode operation while the wavelength of the grating external-cavity laser was tuned     

Mode selection and stability of a semiconductor laser with weakoptical feedback

The authors present measurements that show that a semiconductor laser with weak optical feedback oscillates in the external-cavity mode with the narrowest linewidth rather than the mode with minimum threshold gain. A frequency fluctuation model that explains this narrowest linewidth operation is proposed. This model also correctly predicts mode-hopping frequencies. It is shown that the frequency span of the external-cavity modes determines the critical feedback level that causes coherence collapse     

GHz bandwidth message transmission using chaotic diode lasers

Synchronised external-cavity diode lasers are used for chaotic optical communication. The encoding, transmission and decoding of a 1 GHz sinusoidal message is demonstrated for the first time     

Microwave spectra in external-cavity semiconductor lasers:theoretical modeling of multipass resonances

We show theoretically that the behavior of an external-cavity semiconductor laser depends on the microscopic intensity distribution of the feedback light. Adapted rate equations are developed based on the traveling-wave model. This model successfully predicts the double-peaked structure of the external-cavity resonance (centered around c/2L) and multiple-pass resonances when the system is misaligned     

1.5mm腔长InAs/InP量子点激光器镜面外腔光谱特性研究

基于研制的1.5mm腔长InAs/InP共面条状量子点激光器,搭建了其镜面外腔结构,并对其光谱特性进行了测试,获得了镜面外腔周期性调制光谱,并在周期性的产生、多模激射和模式随电流的变化等方面对其光谱特性进行了分析研究。相比以前为获得单模使用的超短腔长超短外腔量子阱激光器,长腔长InAs/InP量子点激光器表现出较小的模式压缩比,更容易发生多模激射。     

Lateral-mode selectivity in external-cavity diode lasers withresidual facet reflectivity

The relatively flat lateral gain profile across a wide-strip laser diode does not allow sufficient overlap with the Gaussian fundamental mode of an external resonator to achieve saturation of the gain in the wings of the mode profile. Thus, parasitic free-running oscillation of the diode in an external-cavity laser is permitted by residual facet reflectivity of the antireflection-coated diode, and degrades the lateral-mode-selectivity of the external resonator at injection currents exceeding the threshold of the solitary diode. A relation between the maximum injection current at which the external-cavity laser will operate in a single mode and the diode's facet reflectivity is given     

Regimes of chaotic synchronization in external-cavity laser diodes

Chaotic synchronization is investigated experimentally using two diode lasers as transmitter and receiver. The transmitter laser is rendered chaotic by application of an optical feedback in an external-cavity configuration. Experimental conditions are found under which the synchronization diagram makes a transition from a positive to a negative gradient. A regime of operating conditions is identified in which the receiver laser is found to anticipate the dynamics of the transmitter laser. The anticipation time does not depend on the external-cavity length, but rather on the time of flight between the two lasers. Changes in the spectrum of the synchronized system are shown to be associated with the transition between anticipating and lag synchronization.     

Time-wavelength multiplexing of mode-locked external-cavity semiconductor lasers

A technique for obtaining multicolor operation of mode-locked lasers has been applied to an external-cavity semiconductor laser. The generation of two perfectly synchronized optical pulse trains of different wavelengths from such a laser is demonstrated.     

Intensity noise of laser diodes with optical feedback

We examine the intensity noise of laser diodes with optical feedback for several feedback conditions. Three stable feedback conditions have been observed, which are defined as follows: an external mirror length shorter than 15 mm, small and large ratios of mirror to laser-front facet reflectivities. Reduction of the external-cavity length, notably to less than 15 mm, stabilized the laser diode and resulted in low intensity noise. A new theoretical treatment of optical feedback is proposed, wherein the feedback field is taken into account in the boundary condition at the feedback coupling laser facet. Theoretical derivations of the intensity noise of external-cavity feedback laser diodes are in good agreement with measured results     

The dependence of the output of an external-cavity laser on therelative phases of inputs from five gain elements

Five diode lasers that each have one facet antireflection (AR) coated are fiber coupled into an external-cavity and operated as a coherent ensemble. The external-cavity laser output power and spectrum are functions of the relative phases of the inputs from the optical fibers. The phases can be adjusted for an optimum single-mode spectrum simultaneous with maximum output power. In this case, the residual reflections from the AR-coated facets are also properly phased. Dephasing reduces the output power and tunes the wavelength through a series of discrete, lower-power maxima. These maxima occur at wavelengths for which the fiber inputs to the cavity are again in phase but the reflections from the AR-coated facets are not in phase     

Dual-mode semiconductor-optical-amplifier external-cavity laser

A dual-mode semiconductor-optical-amplifier external-cavity laser is presented. The dual-mode optical output can produce a radio frequency beat signal at 31.6 GHz with a 3 dB linewidth of 700 kHz.     

Message encoding and decoding using chaotic external-cavity diodelasers

Synchronization of chaotic external-cavity diode lasers has been studied in a master-slave configuration. A message is encoded into the chaotic master laser by amplitude modulation and transmitted to the slave laser. A scheme for decoding the message at the slave is demonstrated     

Fast frequency-tunable external-cavity laser

We describe a tunable, single-frequency, narrow-line external-cavity laser that can be FSK up to 100Mbit/s by modulating the laser current. The result is obtained by using a two-section laser: one section for lasing and the other for FSK modulation.