半导体激光器调制响应的速率方程小信号近似法研究

速率方程是研究半导体激光器瞬态过程的理论工具。为了能对实际中各种调制响应进行分析,采用小信号近似法求解了在任意调制信号下半导体激光器的速率方程。得到了任意调制信号下半导体激光器的速率方程的实值解析解,并根据得出的实值解析解分析了半导体激光器的一些调制响应特性,给出了一个调制信号为矩形脉冲电流的具体实例。最后研究并得出了小信号近似法准确的严格条件。根据一些半导体激光器的实际参数,给出了该条件在某些情况下的近似表达。     

High-speed modulation of vertical-cavity surface-emitting lasers

The IM (intensity modulation) and FM (frequency modulation) characteristics of vertical-cavity surface-emitting lasers are studied. The laser has high FM efficiency and broad IM bandwidth (near 8 GHz) at a very low bias (4.5 mA). Five Gb/s pseudorandom direct intensity modulation of this laser with open eyes is demonstrated.<>     

High-frequency small-signal modulation characteristics of short-cavity InGaAsP lasers

Measured small-signal frequency-response characteristics of directly modulated long-cavity and short-cavity InGaAsP double-channel buried-heterostructure (DCBH) lasers are reported. Relaxation oscillation resonance frequencies as high as 9.4 GHz at a bias current of twice threshold have been obtained with short-cavity devices.     

Direct modulation of semiconductor lasers

Methods for direct modulation of semiconductor lasers are reviewed with the objective of indicating the advantages and limitations of each method. Techniques for producing amplitude, pulse, and frequency modulation of the optical wave are included. The modulation capabilities of present pulsed lasers are analyzed with special attention given to their operation at room temperature. In addition, several ways of producing analog position or width modulation of microwave-rate optical pulses are described, and the capabilities of optical frequency modulation by acoustic waves are reviewed. A new way of obtaining mode-locked optical pulses with a semiconductor laser is also suggested.     

High-speed modulation of semiconductor lasers

An overview is given of the direct modulation performance of high-speed semiconductor lasers. The high-speed response characteristics are described using a cascaded two-port model of the laser. This model separates the electrical parasitics from the intrinsic laser and enables these subsections to be considered separately. The presentation concentrates on the small-signal intensity modulation and frequency modulation responses, and the large-signal switching transients and chirping. Device-dependent limitations on high-speed performance are explored and circuit modeling techniques are briefly reviewed.     

High-speed modulation of semiconductor lasers

An overview is given of the direct modulation performance of high-speed semiconductor lasers, The high-speed response characteristics are described using a cascaded two-port model of the laser. This model separates the electrical parasitics from the intrinsic laser and enables these subsections to be considered separately. The presentation concentrates on the small-signal intensity modulation and frequency modulation responses, and the large-signal switching transients and chirping. Device-dependent limitations on high-speed performance are explored and circuit modeling techniques are briefly reviewed.     

Pulse-shape effects on frequency chirping in single-frequency semiconductor lasers under current modulation

Directly modulated semiconductor lasers exhibit dynamic frequency shifts (chirping) due to gain-induced variations of the refractive index. Using the small-signal analysis of the single-mode rate equations, the effect of current-pulse shape on frequency chirping is analyzed, and the results are compared for the cases of sinusoidal and square-wave modulations. The chirp is generally larger for the square-wave case. However, its magnitude depends on the pulse rise and fall times, decreasing for a pulse with slower turn-on and turn-off characteristics. Chirp analysis presented here includes the effect of power-dependent gain changes arising from the processes such as spectral hole-burning.     

Direct modulation of long-cavity semiconductor lasers

The application of a high-speed signal via the drive current to a long-cavity semiconductor laser (cavity length >~1 cm) differs from the short-cavity case in that the variation of the optical field within one round-trip time is not negligible. We theoretically investigate the modulation response for a semiconductor laser of arbitrary length and relate it to experiments on the multifrequency waveguide grating router laser, a long-cavity laser. We find that the largest modulation bandwidth is achieved by having the modulated amplifier and the desired output as far apart as possible, the modulation bandwidth can be further increased by simple electronic precompensation, and because of fast nonlinearities the broadband intensity modulation of long-cavity lasers exhibits substantially less chirp than short-cavity lasers, the chirp essentially equal to that of the amplifiers. Finally, we demonstrate the direct modulation of three channels simultaneously in a multifrequency laser at 1.24 Gb/s each     

Minimizing pattern effects in semiconductor lasers at high rate pulse modulation

This paper deals with analytical and experimental work related to modulation of a semiconductor laser used in high bit rate communication. The approach is based upon minimizing the charge storage effect by a proper choice of the area of the modulating pulses and the bias current. The concept of using additional current pulses to probe for variations in electron density between pulses is investigated. The primary limitation on bit rate is found to be the ability to generate laser drive pulses free of ringing or similar transients. This and the 300 ps pulsewidth, an experimental constraint, limit the bit rate to about 1 Gbit/s. However, by using this approach it appears that bit rates considerably higher than 2 Gbits/s could be reached with sufficiently accurate control of drive pulse shape. It is found that the laser bias and the current pulse area had to be controlled within 1 percent and 10 percent, respectively.     

On the modulation bandwidth of semiconductor microcavity lasers

The small signal injection current modulation bandwidth of vertical cavity microlasers in the conventional macroscopic regime and in the microscopic regime of “controlled spontaneous emission” is investigated. A microlaser, under constraint of nonlinear gain or current density limitations, is found to have the same intrinsic modulation bandwidth as conventional edge-emitting lasers with the same cavity losses and photon density     

Discontinuous modulation response of grating-assistedextended-cavity semiconductor lasers

The resonant enhancement of the small-signal intensity modulation response of a grating-assisted extended-cavity semiconductor laser is shown to occur in dual peaks centred near the harmonics of the cavity resonance fluency. Each response peak is bifurcated into two closely spaced peaks of different amplitudes and bandwidths. The position of the broader of the two peaks depends on the operating power of the laser. A strong discontinuity in the response amplitude is observed near the harmonics of the cavity resonance fluency     

Integrated semiconductor vertical-cavity surface-emitting lasers and PIN photodetectors for biomedical fluorescence sensing

Vertical-cavity surface-emitting lasers (VCSELs), optical emission filters, and PIN photodetectors were fabricated as part of a monolithically integrated near-infrared fluorescence detection system. The integration of these micro-fabricated components with micro-arrays, flow channel arrays, and biochips can drastically reduce cost and enable parallel sensing architectures. An optoelectronic design is presented that integrates VCSELs, optical filters, and photodetectors through a modification to a typical VCSEL structure. System designs were simulated and compared, leading to several innovative approaches for integrated sensors. The laser and detector modules were characterized independently and subsequently integrated to form a complete sensor. VCSELs with oxidation apertures measuring 4, 7, 14, and 20 /spl mu/m showed a lasing wavelength of /spl lambda/=773 nm, threshold current densities from 6400 to 1300 A/spl middot/cm/sup -2/, and maximum output powers of 0.6-4 mW, with transverse single-mode and multimode operation. PIN photodetectors were fabricated with integrated emission filters. Quantum efficiencies above 85% were observed with a dark current of 500 fA/(mm detector diameter). Complete sensor units were tested and near-infrared fluorescent molecules (IR-800) were detected. A theoretical detection limit of 10/sup 5/ fluorophores//spl mu/m/sup 2/ was determined. The compact parallel architecture, high-power laser, and low-noise photodetector make this sensor a good candidate for biomedical fluorescence-based sensing applications.     

Measurement of guiding effects in vertical-cavity surface-emitting lasers

Wave-guiding mechanisms in large area InGaAs-GaAs MQW vertical-cavity surface-emitting lasers (VCSELs) have been investigated using novel spatially and spectrally resolved measurements of spontaneous and stimulated emission. Carrier induced anti-guiding is found to be important despite the presence of other guiding mechanisms.     

High-speed modulation of 850-nm intracavity contacted shallowimplant-apertured vertical-cavity surface-emitting lasers

GaAs-AlGaAs quantum-well (850 nn) vertical-cavity surface-emitting lasers, with lateral current injection and shallow implanted apertures, show small signal modulation bandwidths of at least 11 GHz and large signal data rates of at least 10 Gb/s. The devices achieved a maximum output power of 2.1 mW, with a threshold current and voltage of 1 mA and 1.71 V, respectively. The shallow implantation step provides photolithographically precise aperture formation (using O⁺ ions), for efficient lateral current injection into the quantum-well active region of the laser, from intracavity contacts. The device aperture was 7 μm in diameter, and the opening in the annular top contact was 13 μm in diameter. The optical spectrum showed several transverse modes     

Characterization of the dynamics of semiconductor lasers usingoptical modulation

An optical modulation technique for measuring the intrinsic frequency response of semiconductor lasers is described. This technique, which uses an RF-modulated pump laser to create an optical modulation signal to inject into a DC-biased probed laser, offers significant advantages over previous methods such as being affected by electrical parasitics of either the laser to be characterized or the photodetector. The method allows extremely accurate measurements of many important dynamic parameters, including the nonlinear gain coefficients, the amount of spontaneous emission into the guided modes, and the differential carrier lifetime at lasing threshold     

Saturation effects in semiconductor lasers

This paper describes a theory for a semiconductor active medium interacting with a laser field. In a semiconductor laser, the charge carrier transitions are inhomogenously broadened, and electron-electron and electron-phonon collisions tend to dephase the laser transitions and maintain thermal equilibrium among the carriers. These properties cause semiconductor lasers to frequency tune as though they are inhomogeneously broadened and to saturate as though they are homogeneously broadened. A theory that contains these two aspects of semiconductor laser behavior is presented. From it, we are able to calculate the loaded gain, efficiency, intensity, and carrier-induced refractive index of a semiconductor active medium.     

Small-signal modulation of multitransverse modes vertical-cavitysurface-emitting semiconductor lasers

The small-signal modulation response of multi-transverse modes, proton-implanted vertical-cavity semiconductor lasers was studied experimentally and theoretically. Multiresonance frequencies and notches in the modulation response were obtained and the detailed characteristics varied for different overlap levels between the lasing modes. The theoretical modeling matched the experimental results and revealed the coupled oscillators manifestation for highly overlapping transverse modes     

载流子寿命对半导体激光器调制特性的影响

针对通常用来研究半导体激光器调制特性的速率方程中所采用的载流子寿命不变近似所存在的问题，重新对小信号调制下半导体激光器的速率方程组进行了线性化处理。     

Theoretical analysis of modulation response and second-orderharmonic distortion in vertical-cavity surface-emitting lasers

A rate-equation model is developed, with the consideration of size effects, to analyze the steady state and dynamic behavior of index-guided vertical-cavity surface-emitting lasers. The size dependence of spatial hole burning, cavity loss, as well as thermal resistance of device cavity are taken into account. Using this model, the influence of size effects on the amplitude modulation response and second-order harmonic distortion are studied. It is found that a laser with a small core radius exhibits better modulation response and less harmonic distortion than that of a large waveguide device, however, there is a tradeoff between the output power and modulation efficiency of the lasers     

InGaAs vertical-cavity surface-emitting lasers

The authors give theoretical and experimental results for vertical-cavity surface-emitting lasers (VCSELs). The modeling is applied to the design of InGaAs VCSELs. A simple method to calculate the reflectivity of semiconductor stack mirrors with graded interfaces and compound metal/semiconductor stack mirrors is introduced. The theoretical predictions are compared to results from actual device measurements. A novel technique is introduced to determine material parameters: fabrication of in-plane lasers from VCSEL material. The procedure used to determine the optical mode in such an in-plane laser is described. Using the insight gained from modeling, the external efficiency was increased to >30% with a threshold current density of 1 kA/cm²