Optical coupling between single-mode semiconductor lasers and strip waveguides

This analysis describes the optimum conditions for coupling a single-mode semiconductor laser to a single-mode strip waveguide, when both the laser and the waveguide have asymmetric optical beam profiles. The outputs are approximated by two Gaussian fields. Two waveguide cases are treated: 1) the case where the two orthogonal waveguide waists are independent and 2) where the ratio of these waists is fixed. The effect on the coupling efficiency of a spherical surface on the waveguide input face is discussed. The results demonstrate the importance of coupling in the laser far-field and indicate the advantage of having relatively large waveguide modes. An intrinsic minimum in the optimum coupling efficiency was found to exist in the near-field for asymmetric laser/waveguide systems. Expressions describing the optimum waveguide waists and the focal length of the lensed waveguide are given for the waveguide parameters that yield the best coupling conditions.     

Memory diagram of single-mode semiconductor lasers

A memory diagram, i.e., regions where pattern effects appear at the output of the laser, in the bias-current-versus-modulation-period plane is obtained, both by numerical simulation of the rate equations and by using an analytical approach. A simple method, based on the superposition of the turn-on time probability distribution for the periodic sequence . . .1111. . . of input bits and the turn-on time probability distribution obtained for repetitive gain switching, is used to describe the response of the laser to a pseudorandom word modulation of the injection current     

Dynamic single-mode semiconductor lasers with a distributed reflector

Recent progress in the dynamic single-mode (DSM) semiconductor lasers in the wavelength of1.5-1.6mum are reviewed and the basic principle of DSM operation is given. Study of the DSM laser is originated for application to the wide-band optical-fiber communication in the lowest loss wavelength region of 1.5 to 1.65 μm. A DSM laser consists of a mode-selective resonator and a transverse-mode-controlled waveguide, such as the narrow-striped distributed-Bragg-reflector (DBR) laser, so as to maintain a fixed axial mode under the rapid direct modulation. The technology of monolithic integration for optical circuits is applied to realize some of DSM lasers. Structures, static and dynamic characteristics of lasing wavelength, output power, and reliability of the art DSM lasers are reviewed. The dynamic Spectral width of 0.3 nm, the output power of a few milliwatts, and the reliability over a few thousand hours are reported for experimental DSM lasers.     

Turn-on jitter in zero-biased single-mode semiconductor lasers

An analytical expression for the turn-on delay probability density function (pdf) of single-mode lasers biased below threshold is derived, which is in good agreement with results based on computer simulations and measurements. It is shown, that the pdf obtained only depends on the on-state yielding simple requirements for the transmitter in order to achieve a given BER. The results are of particular interest for designing optical interconnects, where zero-biased lasers are used.     

Improvements in mode-locked semiconductor diode lasers using monolithically integrated passive waveguides made by quantum-well intermixing

By using the technique of quantum-well intermixing (QWI), monolithically integrated passive, and active waveguides can be fabricated. It is shown that mode-locked extended cavity semiconductor lasers with integrated low-loss passive waveguides display superior performance to devices in which the entire waveguide is active: the threshold current is a factor of 3-5 lower, the pulsewidth is reduced from 10.2 ps in the all active laser to 3.5 ps in the extended cavity device and there is a decrease in the free-running jitter level from 15 to 6 ps (10 kHz-10 MHz).     

Multibranch frequency-selective reflectors and application totunable single-mode semiconductor lasers

Multibranch reflectors (MBRs) are proposed as a flexible wavelength-selective element for optical integrated circuits generally and for tunable single-mode lasers specifically. The undesired recurring peaks of reflectivity obtained with two-branch MBRs are spread out in the spectrum by using three or more branches. Design relations are given for the lengths of an arbitrary number of branches, for the selectivity near the peak response, for the wavelength interval to the nearest undesired peak, and for tuning changes in the various branches. It is shown that an MBR is not sensitive to amplitude differences of the order of 20% between the branches, but requires phase control in order to achieve tuning to a specific wavelength. The effects of semiconductor gain variation with wavelength are obtained from a rate-equation solution including MBR. By changing the semiconductor temperature (gain peak) at the same time as the MBR is tuned, a broad range of tuning without jumps is achievable     

Noise characteristics of single-mode semiconductor lasers underexternal light injection

Presents a theoretical investigation of the noise behavior of a semiconductor laser operating under relatively strong light injection. Equations have been presented to describe the noise effect through the calculation of the relative intensity noise as well as the carrier-to-noise ratio available at the receiving end. Illustrative examples are given, showing the impact of the master and slave laser bias currents. Also, the injection-locked and free-running operation regimes have been comparatively analyzed. The results show how the noise characteristics are affected by optical injection and, consequently, how the operating conditions must be chosen to reduce this effect. In particular, it is shown, in agreement with previous works, that the master laser emission noise will essentially take the lead. As a result, to improve the noise behavior by injection locking a solitary laser, the use of a low-noise master laser is required. To make it easy to apply the present results to any laser diode under the stable-locking condition, the necessary relations are explicitly given before specifying the parameters of simulation     

Observation of WDM crosstalk in passive semiconductor waveguides

We show that passive InP-InGaAsP waveguides exhibit high nonlinear loss due to the highly energetic carriers generated by two-photon absorption. We have further demonstrated, for the first time, that due to this effect, severe crosstalk occurs between wavelength channels when they are transmitted through a semiconductor waveguide operated in the transparency region, at power levels used in typical wavelength-division-multiplexed (WDM) systems. Some solutions are proposed     

The single-mode condition for semiconductor rib waveguides withlarge cross section

A comparison of the single-mode condition for semiconductor rib waveguides with large cross section obtained by the effective index method and the corrected formula proposed by Soref et al. [see IEEE Journal of Quantum Electronics, vol. 27, p. 1971, 1991] with experimental data is carried out. It is found that the effective index method is in a better agreement with Rickman's experimental data than the modified version. Moreover a stronger condition is proposed for single-mode design purposes     

Hybrid integration of semiconductor lasers with Si-basedsingle-mode ridge waveguides

Hybridization is a convenient way for providing silicon-based integrated optical circuits with a laser source. An entirely passive alignment technique exclusively based on the high precision obtainable by lithography and by semiconductor processes was examined. A novel way of cleaving the laser chips by self-aligned cleaving grooves was employed. It resulted in 15.5-dB coupling losses between the laser diode and the single-mode buried ridge waveguide     

有机半导体激光器研究的新进展

近年来,有机半导体激光器已经成为一个新的研究热点。叙述了光泵浦有机半导体激光器的最新研究进展,对实现电泵浦（ 电注入） 有机半导体激光器也进行了评述。     

端面反射率对半导体激光器单模工作性能的影响

本文利用半导体激光器多模速率方程组的隐式解析解，从理论上了端面反射率对半导体激光器单模工作性能的影响，结果表明，在相同的输出功率下，端面反射率越低，单模工作性能越差，与Ｅｔｔｅｎｂｅｒｇ等人通过实验研究所得的结论相同。     

Theoretical stability analysis of single-mode operation inuncontrolled mode-selection semiconductor lasers

An uncontrolled mode-selection laser is a laser containing an intracavity filter under which the cavity mode alignment is uncontrolled. We present a theoretical stability analysis of the single-mode operation of uncontrolled mode-selection semiconductor lasers. We find that to maximize the stability the cavity length and intracavity filter bandwidth must be minimized, and a specific, nonzero, linewidth enhancement parameter must be chosen. For a given cavity mode spacing to filter bandwidth ratio, a shorter cavity is more stable     

Curved waveguides for spatial mode filters in semiconductor lasers

Curved waveguides are used as a lateral spatial mode filter to increase the threshold for the first-order mode in high-power narrow stripe semiconductor lasers. Beam propagation analysis is used to determine optimal waveguide geometries and radii of curvature to establish appropriate amounts of bend loss. Curved waveguide devices are fabricated and compared against conventional devices. Use of a curved waveguide increases the current level at which lateral beam instabilities occur from /spl sim/400 to /spl sim/700 mA with no decline in slope efficiency.     

Modal competition via four-wave mixing in single-mode extended-cavity semiconductor lasers

An analysis of the wave-coupling phenomena in extended-cavity semiconductor lasers is carried out to investigate the conditions of mode-hop-free single-mode operation. Taking into account the external cavity selectivity and the mode coupling via four-wave mixing in the active medium, we present a theoretical analysis of the modal competition and perform calculations that are in good agreement with experimental results obtained with a 1.55-/spl mu/m extended-cavity laser.     

Light coupling from a semiconductor laser into a polarisation-maintaining single-mode fibre

For laser to polarisation-maintaining fibre coupling we propose the insertion of a short piece of normal single-mode fibre. As a result a power coupling loss of 2.8 dB is obtained, whereas additional crosspolarisation is very small compared with the unwanted polarisation excitation of the laser itself.     

Low-loss, single-mode, organic polymer waveguides utilizingrefractive index tailoring

Low-loss, single-mode optical waveguides have been fabricated from photopolymerizable acrylic monomers. The material system consists of a low-index cladding resin and a high-index core resin. The two resins are miscible so that precise control over the refractive index can be obtained. This allows the fabrication of single-mode waveguides with specific cross-sectional dimensions. One advantage of this is the ability to fabricate waveguides with high coupling efficiencies to other devices such as optical fiber or semiconductor lasers. The materials adhere to a wide variety of substrates and exhibit average waveguide losses of 0.56 dB/cm at 1300 nm for single-mode waveguides. Details of the fabrication procedure, index of refraction tailoring technique, and waveguide loss data are presented     

Comparison between epi-down and epi-up bonded high-power single-mode 980-nm semiconductor lasers

Epi-down and epi-up bonded high-power single-mode 980-nm lasers have been studied in terms of bonding process, thermal behavior, optical performances, and long-term laser reliability. We demonstrated that epi-down bonding can offer lower thermal resistance and improved optical performance without degrading the long-term laser reliability. An optical power of 630 mW was obtained for the first time from an epi-down bonded 980-nm pump module. Our studies have shown that epi-down bonding of single-mode 980-nm lasers can reduce junction temperature and thermal resistance by up to 30%. Experimental measurements showed over 20% in thermal rollover power improvement and over 25% reduction in wavelength shift versus current in epi-down mounted lasers compared to epi-up mounted lasers. Lifetime test over 14 000 h at 500 mA and 80/spl deg/C of the epi-down bonded lasers is reported for the first time.     

Power spectrum of directly modulated single-mode semiconductor lasers: Chirp-induced fine structure

The time-averaged power spectrum of a single-mode semiconductor laser under direct current modulation is calculated using the small-signal analysis of the stochastic rate equations. The general formalism includes the effect of frequency chirping owing to current modulation as well as the effect of phase diffusion related to spontaneous emission. Chirp-induced dynamic line broadening is shown to result from a superposition of the additional unresolved sidebands generated at multiples of the modulation frequency on both sides of the optical line. The effect of intensity modulation is to introduce an asymmetry such that the low-frequency sideband has a relatively higher amplitude. The theory explains reasonably well the reported experimental observations. At the same time it provides physical insight into the dynamic process of frequency chirping and its relation to the frequency modulation. In particular, the frequency and the decay rate of transient relaxation oscillations govern the interplay between simultaneously occurring intensity and frequency modulations.     

沟道台面衬底三段大光腔激光器

本文报道了一种新型结构的半导体激光器——沟道台面衬底三段大光腔激光器,它具有阈值电流低、高输出功率和易获得基横模单纵模工作的特点.