Near-field control in multistripe geometry injection lasers

Control of the intensity and position of the near field is demonstrated in an analysis of twin-stripe and triple-stripe injection lasers. Calculations of file electrooptical properties of the structures are presented, taking into account the interaction between the carrier concentration profile and the optical field. For twin-stripe devices interstripe coupling is investigated as a function of stripe separation. For stripe separation comparable with stripewidth, the properties of triple-stripe lasers become of interest. Nonlinear light-current characteristics for the twin-stripe device are obtained and lead to an interpretation of such characteristics in conventional stripe geometry lasers.     

Numerical solution of lateral current spreading and diffusion in near-threshold DH twin-stripe lasers

A numerical solution is presented to the problem of lateral current spreading in double heterostructure twin-stripe lasers when lateral diffusion of carriers and bimolecular recombination effects are present. The current components flowing into both the p-type confining layer and the active layer are solved simultaneously, subject to the boundary conditions imposed at the heterojunction. This yields the two-dimensional potential and the current density distributions in the p-type confining layer and the lateral carder density distribution in the active region. Diffusion and bimolecular radiative recombination effects are included in the solution of the current distribution in the active layer. The lateral current and carrier density distributions along the active layer are presented for single- and twin-stripe devices for a variety of electrode injection currents. The paper highlights the influence of device geometry and diffusion on the carrier distributions found beneath the stripes of twin-stripe lasers.     

Mode-guiding in bistable twin-stripe lasers

Mode-guiding mechanisms responsible for bistable properties of twin-stripe lasers are discussed with particular reference to optical injection effects. Calculations of the change in lasing field intensity as a function of both optical input power and injection current levels are presented.     

Influence of external mirror on modal behavior of twin-stripeindex-guided injection lasers

The coupled-mode theory of parallel waveguides is used to calculate the influence of an external mirror on the modal behavior of the AR-coated laser array. The case of twin-stripe index-guided injection lasers with separate contacts is treated in detail. It is shown that for asymmetrical current injection, the external cavity couples the laser's guided array modes and creates new laser-cavity modes with a better mode discrimination in favour of the one having a single far-field pattern. These results imply that multiple laser arrays might benefit from an additional external mirror     

Analysis of lateral-mode behavior of twin-stripe lasers related tothe negative slope in their current-light characteristics

The lateral oscillation mode in twin-stripe lasers is analysed with the diffusion constant D in the active layer as a parameter. Characteristics of modal gain and optical intensity distribution vs. current are shown to be strongly dependent on the diffusion constant because the diffusion constant determines the depth of the dip in the carrier distribution. For certain values of D, results which are in good agreement with experimentally observed results were obtained. A negative slope appears in the curves of modal gain vs. current, and the optical field is in the weakly pumped side in the negative slope region. The condition for which the negative slope appears is determined     

A coupled-mode analysis of twin-stripe index-guided lasers

An approximated coupled-mode solution to the problem of lateral mode behavior in twin-stripe index-guided injection lasers near threshold is presented. The optical properties are determined by the coupling coefficients between the two waveguides, taking into account the external current-dependent perturbation to the dielectric constant. In the calculations of the external perturbation, a simple model of current spreading under the contacts and carrier diffusion in the active layer is given for a multistripe structure. Emphasis is on the influence of the current ratio on the lateral field shape and modal gain. It is shown that for symmetrical current injection, the fundamental supermode has a slight advantage (higher gain) over the second 180° phase-shifted mode. As the injected current ratio is driven away from the symmetrical point, the second supermode is favored with increasing modal gain difference. The coupled-mode approach is relatively simple and can describe rather accurately this already-known behavior     

Influence of interstripe gain on crosscoupled-mode operation intwin-stripe lasers

Cross-coupled-mode operation in a twin-stripe laser is analyzed with particular concern for interstripe gain. When the interstripe gain of a twin-stripe laser is high, cross-coupled-mode operation is obtained with a cavity longer than the coupling length of the twin-stripe waveguide. The far-field pattern is single peaked and deflected to the low carrier density side. These characteristics are in contrast to those of the previous model without interstripe gain     

Analysis of the cross-coupled lateral mode in a twin-stripefour-contact laser with diagonal current injection

Cross-coupled resonant lateral modes in a twin-stripe four-contact laser are analyzed by coupled-mode theory for conditions in which the current injection into each diagonal pair of stripes is equal. The dependence of the optical power distribution on the laser length and on the carrier-density or the current-density distribution is investigated. The most interesting result is that the highest optical power interesting result is that the highest optical power appears in the waveguide with the lowest carrier density when the carrier-density difference between the adjacent waveguides is small and the laser is shorter than the coupling length. This makes it possible to show that a cross-coupled mode can be supported even in a two-contact twin-stripe laser and that bistable switching between the mode and its mirror image is possible     

Compensation of line-broadening factor in twin-stripe semiconductor lasers and improved modulation potential

A concept for a twin-stripe semiconductor laser is presented in which the simultaneous gain and refractive index variation induced by carriers injected into one stripe can be converted into either a pure amplitude or a pure frequency variation in the lasing supermode. Applications include high-frequency chirp-free amplitude modulation, reduced line width and pure phase modulation.     

Two cross-coupled-mode operation of a twin-stripe laser:bistability for wide ranges of output power level and current ratio

A theoretical approach is reported which models cases where the twin-stripe laser generates either one resonant mode alone or two resonant modes simultaneously. The model determines the ratio of output powers of the light emitted from the two stripes as a function of the ratio of currents to the two stripes. The model simulates the laser operation in regions for which an earlier single-mode approach does not provide solutions. Bistability is predicted to occur over much wider ranges of output power level and current ratio than the previous single-mode case     

High performance CW 1.26 μm GaInNAsSb-SQW and 1.20 μmGaInAsSb-SQW ridge lasers

Long-wavelength GaInNAsSb SQW lasers and GaInAsSb SQW lasers that include small amounts of Sb have been successfully grown by gas-source molecular beam epitaxy (GSMBE) and processed into ridge lasers. The GaInNAsSb lasers oscillated under CW operation at 1.258 μm at room temperature. A low CW threshold current of 10.2 mA and high characteristic temperature (T₀) of 146 K were obtained for the GaInNAsSb lasers which is the best result for GaInNAs-based narrow-stripe lasers. Furthermore. The GaInAsSb lasers oscillated under CW operation at 1.20 μm at room temperature. A low CW threshold current of 6.3 mA and high characteristic temperature (T₀) of 756 K were obtained for the GaInAsSb lasers, which is also the best result for the 1.2 μm-range of highly strained GaInAs-based narrow-stripe lasers     

1.5 ?m region InP/GaInAsP buried heterostructure lasers on semi-insulating substrates

InP/GaInAsP buried heterostructure (BH) lasers for the 1.5 ?m region have been fabricated on semi-insulating InP substrates. The threshold current of the lasers is as low as 38 mA under CW operation at 25°C, which is nearly the same as for BH lasers fabricated on n-type InP substrates.     

Design of WDM PON With Tunable Lasers: The Upstream Scenario

Tunable lasers are potential upstream optical light generators for wavelength-division-multiplexing (WDM) passive optical network (PON), which is a promising solution for next-generation broad-band optical access. The wavelength provisioning flexibility of tunable lasers can increase the admissible traffic in the network as compared to wavelength-specific lasers. Generally, the broader the lasers' tuning ranges, the more the traffic can be admitted to the network. However, broad tuning range requires sophisticated technology, and probably high cost. To achieve the optimal tradeoff between the admissible traffic and the cost, we investigate the relationship between lasers' tuning ranges and the network's admissible traffic and then design WDM PON by selecting lasers with proper tuning ranges for the upstream data transmission. Specifically, we focus on addressing two issues under three scenarios. The two issues are: how to admit the largest traffic by properly selecting lasers, and how to admit given upstream traffic using lasers with tuning ranges as narrow as possible. The three scenarios are: full-range tunable and wavelength-specific lasers are available, limited-range tunable lasers are available, and the exact number of lasers with specific tuning ranges are given.      

Broadband tuning (170 nm) of InGaAs quantum well lasers

The wavelength tuning properties of strained InGaAs quantum well lasers using an external grating for feedback is reported. Tunable laser oscillation has been observed over a range of 170 nm, between 840 and 1010 nm, under pulsed current excitation. The optimal conditions for broadband tunability for the InGaAs lasers are different from GaAs lasers, which is attributed to a difference in spectral gain curves. Together with an optimised GaAs quantum well laser the entire region between 740 and 1010 nm is spanned.<>     

Frequency-Doubled Fiber Lasers for RF Spectrum Analysis in Spectral-Hole-Burning Media

We demonstrate an RF spectrum analyzer based on spectral-hole burning (SHB) that operates with unity probability of intercept and resolution under 100 kHz. An SHB crystal, which consists of rare-earth ions doped into a crystal host, records the power spectrum of an RF signal modulated onto an optical carrier as a series of spectral holes that persist for about 10 ms. While the crystal's homogeneous and inhomogeneous linewidths place the fundamental limits on resolution and bandwidth, respectively, the practical limits depend on the lasers used to interrogate the record stored in the crystal's absorption profile. Up to now, SHB spectrum analyzers have used chirped beams from externally modulated, stabilized lasers, which have linewidths of under 10 kHz but cannot chirp over much more than octave bandwidths, or directly modulated diode lasers, which can chirp over more than 20GHz but have linewidths of about 1 MHz. Switching to chirped fiber lasers, which have natural linewidths of under 2 kHz and chirping linewidths on the order of 10 kHz, produces a measurement with fine resolution without any laser stabilization. In addition, by chirping the fiber laser with a sufficiently fast piezo, the resulting chirp could extend over tens of gigahertz in under 10 ms, yielding both fine resolution and broad bandwidth without extraordinary stabilization schemes.     

三点抽运的高功率双包层光纤激光器优化设计

采用侧面抽运技术的三点抽运的高功率双包层光纤激光器是多点抽运的高功率双包层光纤激光器中最简单最基本的形式。为了研究其抽运参数的优化,以便在相同的抽运光功率下获得最大的激光输出功率,首先从掺Yb双包层光纤激光器的速率方程出发,得到了总体抽运损耗功率的表达式,然后根据总体抽运损耗功率最小化的原则,对三点抽运的高功率双包层激光器进行了优化设计,得到了最优抽运点选取的解析表达式。数值仿真分析表明,优化后的光纤激光器输出功率较优化前有所提高,尤其是对于优化前抽运光的总体损耗功率较大时更为明显。三点抽运的高功率双包层光纤激光器的优化结果很有意义,也为多点抽运的双包层光纤的优化设计提供了思路。     

Low-threshold laterally oxidized GaInP-AlGaInP quantum-well laserdiodes

Low-threshold, high-efficiency edge-emitting visible AIGaInP-GaInP laser diodes using a buried AlAs native oxides for carrier and optical confinement are described. The lasers incorporate a thin AlAs layer in the upper cladding region, which when laterally wet oxidized, forms a narrow aperture. The lasers operate with room temperature, continuous-wave (CW) threshold currents of 11 mA with external differential quantum efficiency of 34% per facet for an uncoated 300-μm-long 3.5-μm-wide device. As-fabricated lasers exhibited modest performance under CW operation. Post-fabrication annealing was shown to dramatically improve the device characteristics     

Distributed feedback lasers in chiral media

The combined effects of chirality and gain (or loss) on wave propagation and coupling in periodic structures is investigated here. The focus is on distributed feedback (DFB) lasers in a transversely unbounded periodic slab with spatially modulated electromagnetic parameters. The analysis uses a coupled-mode approach employing a canonical physical model of chiral materials to predict the effects of modulated chirality admittance on DFB lasers. Results for DFB laser behavior in chiral media are compared and contrasted to that in achiral media. It is found that, under certain circumstances, the electric and magnetic field coupling, which is characteristic of chiral materials, results in a lower threshold gain for DFB lasers in media with a given index of refraction and characteristic impedance. It is also found that chiral index-coupled or gain-coupled DFB lasers exhibit the same spectral mode properties as achiral DFB lasers     

Feedback sensitivity and coherence collapse threshold of semiconductor DFB lasers with complex structures

A general method for evaluating the feedback sensitivity of semiconductor lasers is proposed based on Green's functions approach. The rate equations derived in this paper generalize works already published to any type of laser cavities such as those with axially varying parameters. The variation of the lasing frequency occurring under external optical feedback is then used to predict the coherence collapse threshold. The approach is validated for conventional DFB lasers by comparing the calculated feedback sensitivity with those obtained from analytical expressions. Both feedback sensitivity and coherence collapse thresholds are then calculated and analyzed for DFB lasers with a chirped grating. A remarkable agreement on the critical feedback level between simulations and measurements is obtained for all the lasers under study.