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A single-mode laser platform has been developed with a simple and high-yield fabrication based on etched slots. We present linewidth measurements on such lasers, which are fabricated without any regrowth steps. The group of slots placed on one side of laser cavity provides sufficient reflectivity for lasing, which allows the laser to be integrated with other devices such as semiconductor optical amplifiers and modulators. The laser with an effective cavity length of 450 μm exhibits a threshold current of 31 mA and a side-mode suppression ratio of 48 dB. The laser shows a minimum Lorentzian linewidth of ~720 kHz at room temperature. The linewidth remains ~1 MHz within the temperature range of 10 °C-60 °C. [ABSTRACT FROM PUBLISHER]

The influence of the limited acceptance angle of a high-finesse microcavity two-photon absorption photodetector on its response has been investigated. It is shown that the limited acceptance angle of the microcavity explains the observed asymmetry seen in the spectral dependence of the microcavity. The theory describing the influence of the acceptance angle allows for an optimum incident beam waist for any cavity structure to be calculated, with an optimum spot diameter of 7 μm having been calculated for the microcavity under test. The theory also enables the calculation of an optimum incident spot size for any micro- cavity. It is shown that a cavity with higher overall reflectivity require larger input spot sizes in order to optimize the level of generated two-photon absorption. [ABSTRACT FROM AUTHOR]

Reflective defects in Fabry-Pérot (FP) laser diodes are characterized through the power transmission spectrum based on the Fourier transform method. From a single measurement, the defect reflection, transmission coefficients and the cosine value of the defect phase shift, are calculated through equations built on the intensities of the peaks associated with defects in the Fourier transformed transmission spectrum. Gain dispersion which is unavoidable in semiconductor laser diodes is taken into account in the calculations. Extensive numerical simulations are made which show that the calculated defect characteristics are not influenced by the defect length and position and better results are obtained as the round-trip gain of the FP laser is relatively low. The simulation also shows that the underestimation of the gain caused by insufficient resolution of the measurement system degrades the calculated parameters. A deconvolution process is accordingly introduced, which is able to greatly reduce the resolution influence. Amplified spontaneous emission from FP laser diodes with a single slot very close to the laser front facet are measured and used to characterize the slot. The slots act as reflective defects in the laser diode and are produced by etching a rectangular well into the laser waveguide. For two lasers on the same bar with nominally the same slot, good agreement in the calculated reflection coefficient and cosine value of the slot phase shift is obtained, but the slot transmission coefficients calculated are different, which is due to the round-trip gain difference observed in the two lasers under the same current injection. [ABSTRACT FROM AUTHOR]

Mode characteristics of equilateral triangle resonators (ETRs) are analyzed based on the symmetry operation of the point group C3v. The results show that doubly degenerate eigenstates can be reduced to the A1 and A2 representations of C3v, if the longitudinal mode number is a multiple of 6; otherwise, they form the E irreducible representation of C3v. And the one-period length for the mode light ray is half of the perimeter of the ETR. Mode Q-factors are calculated by the finite-difference time-domain (FDTD) technique and compared with those calculated from far-field emission based on the analytical near-field pattern for TE and TM modes. The results show that the far-field emission based on the analytical field distribution can be used to estimate the mode Q-factor, especially for TM modes. FDTD numerical results also show that Q-factor of TE modes reaches maximum value as the longitudinal mode number is a multiple of 7. In addition, photoluminescence spectra and measured Q-factors are presented for fabricated ETR with side lengths of 20 and 30 μm, and the mode wavelength intervals are compared with the analytical results. [ABSTRACT FROM PUBLISHER]

Modes in square resonators are analyzed and classified according to the irreducible representations of the point group C[Sub4v],. If the mode numbers p and q that denote the number of wave nodes in the directions of two orthogonal square sides are unequal and have the same even-odd characteristics, the corresponding double modes are accidentally degenerate and can be combined into two new distributions with definite parities relative to the square diagonal mirror planes. The distributions with odd parities belong to the whispering-galler-like modes in square resonators. The mode frequencies and quality factors are also calculated by the finite-difference time-domain technique and Padé approximation method. The numerically calculated mode frequencies agree with the theoretical ones very well and the whispering-gallery-like modes have quality factors much higher than other modes, including their accidentally degenerate counterparts in square resonators. [ABSTRACT FROM AUTHOR]

The mode frequencies and field distributions of whispering-gallery (WG)-like modes of square resonators are obtained analytically, which agree very well with the numerical results calculated by the FDTD technique and Padé approximation method. In the analysis, a perfect electric wall for the transverse magnetic mode or perfect magnetic wall for the transverse electric mode is assumed at the diagonals of the square resonators, which not only provides the transverse mode confinement, but also requires the longitudinal mode number to be an even integer. The WG-like modes of square resonators are nondegenerate modes with high-quality factors, which make them suitable for fabricating single-mode low-threshold semiconductor microcavity lasers. [ABSTRACT FROM AUTHOR]

To improve the accuracy of measured gain spectra, which is usually limited by the resolution of the optical spectrum analyzer (OSA), a deconvolution process based on the measured spectrum of a narrow linewidth semiconductor laser is applied in the Fourier transform method. The numerical simulation shows that practical gain spectra can be resumed by the Fourier transform method with the deconvolution process. Taking the OSA resolution to be 0.06, 0.1, and 0.2 nm, the gain-reflectivity product spectra with the difference of about 2% are obtained for a 1550-nm semiconductor laser with the cavity length of 720 μm. The spectra obtained by the Fourier transform method without the deconvolution process and the Hakki-Paoli method are presented and compared. The simulation also shows that the Fourier transform method has less sensitivity to noise than the Hakki-Paoli method. [ABSTRACT FROM AUTHOR]

Analyzes semiconductor microlasers with an equilateral triangle resonator (ETR) by rate equations with the mode lifetimes calculated by the finite-difference time-domain technique and the Pade approximation. Proposed gain spectrum based on the relation of the gain spectrum and the spontaneous emission spectrum for considering the mode selection in a wide wavelength span; Corresponding wavelength tuning range and threshold current.

Analyzes the eigenmodes confined in the equilateral triangle resonator by deriving the eigenvalues and the mode field distributions and by the finite difference time domain (FDTD) technique. Quality factor; Resonant frequency; Numerical simulation by the FDTD technique.

An in-band optical signal-to-noise ratio (OSNR) monitoring technique based on a Michelson fiber interferometer and a linear polarizer is presented in this letter. OSNR values of up to 25±0.5 dB were measured for 10-G nonreturn-to-zero-differential phase-OOK (NRZ-OOK) and NRZ-differential phase-shift keyed (NRZ-DPSK) signals without prior knowledge of the signal coherence properties. Measurements were also carried out with signals having 680 ps/nm of chromatic dispersion. [ABSTRACT FROM PUBLISHER]

Suppression of residual single-photon absorption (SPA) relative to two-photon absorption (TPA) in a high finesse GaAs planar microcavity is explored. The TPA photocurrent becomes larger than the SPA photocurrent as long as the incident continuous-wave optical power exceeds 0.09 mW. An optical power of 5 mW would be required if the relative SPA suppression did not exist. [ABSTRACT FROM PUBLISHER]

GaInAsP-InP microsquare resonators with InP pedestals are fabricated by two-step chemical etching, and obvious mode peaks are observed in the photoluminescence spectra of the resonators. The mode Q-factors about 500 are obtained for a microsquare resonator with the side length of 7 μm. The experimental mode interval is in agreement with that predicted by the light ray method based on the cavity length, instead of that of the whispering-gallery (WG)-like modes, which has mode interval twice of that determined by the cavity length. The finite-difference time-domain simulation shows that a little asymmetry may greatly reduce the difference of the Q-factors between the WG-like modes and the other modes. [ABSTRACT FROM PUBLISHER]

The quality factors of modes in square resonators are calculated based on the far-field emission of the analytical field distribution. The obtained quality factors are in reasonable agreement with those calculated by the finite-difference time-domain (FDTD) technique and Pade approximation method. The emission power in the square diagonal directions for whispering-gallery-like modes in square resonators is zero due to the interference cancellation caused by the odd field distributions relative to the diagonal mirror planes, so they have larger quality factors than the modes with even field distribution. [ABSTRACT FROM PUBLISHER]

Semiconductor equilateral triangle microresonators (ETRs) with side length of 5, 10, and 20 μm are fabricated by the two-step inductively coupled plasma (ICP) etching technique. The mode properties of fabricated InGaAsP ETRs are investigated experimentally by photoluminescence (PL) with the pumping source of a 980-nm semiconductor laser and distinct peaks are observed in the measured PL spectra. The wavelength spacings of the distinct peaks agree very well with the theoretical longitudinal mode intervals of the fundamental transverse modes in the ETRs, which verifies that the distinct peaks are corresponding to the enhancement of resonant modes. The mode quality factors are calculated from the width of the resonant peaks of the PL spectra, which are about 100 for the ETR with side length of 20 μm. [ABSTRACT FROM PUBLISHER]

A technique based on the integration of the product of amplified spontaneous emission spectrum and a phase function over one mode interval is proposed for measuring the gain spectrum for Fabry-Perot semiconductor lasers, and a gain correction factor related to the response function of the optical spectrum analyzer (OSA) is obtained for improving the accuracy of the measured spectrum. Gain spectra with a difference less than 1.3 cm-1 from 1500 to 1600 nm are obtained for a 250-μm-long semiconductor laser at an OSA resolution of 0.06, 0.1, 0.2, and 0.5 nm. The corresponding gain correction factor is about 9 cm-1 at a resolution of 0.5 nm. The gain spectrum measured at a resolution of 0.5 nm has the same accuracy as that obtained by the Hakki-Paoli method at a resolution of 0.06 nm for a laser with a mode interval of 1.3 nm. [ABSTRACT FROM PUBLISHER]

The finite-difference time domain (FDTD) technique and the Pade approximation with Baker's algorithm are used to calculate the mode frequencies and quality factors of cavities. Comparing with the fast Fourier transformation/Pade method, we find that the Pade approximation and the Baker's algorithm can obtain exact resonant frequencies and quality factors based on a much shorter time record of the FDTD output [ABSTRACT FROM PUBLISHER]

The mode wavelength and quality factor (Q-factor) for resonant modes in optical equilateral triangle resonators (ETR's) are calculated by the finite-difference time-domain (FDTD) technique and the Pade approximation. For an ETR with the side length of 3 μm and the refractive index of 3.2, we get the mode wavelength interval of about 70 nm and the Q-factor of the fundamental mode over 103. The results show that the ETR is suitable to realize single-mode operation, and that the radiation loss in the corner regions of ETR is rather low. In addition, the numerical results of the mode wavelength agree very well with our analytical formula [ABSTRACT FROM PUBLISHER]

Semiconductor microlasers with an equilateral triangle resonator (ETR) and an output waveguide are proposed and analyzed by the finite-difference time-domain technique and the Padé approximation. The numerical results show that microlasers with an output waveguide still have a high-quality factor (Q factor) and are suitable to realize directional emission. For the ETR with a 0.46-μm-width opening in one of the vertices connected to the output waveguide, we have the Q factor of 1.5x10[sup 3] and 2.5x10[sup 2] for the TM fundamental mode at the wavelength of 1.55 μm, as the side length of the ETR is 5 and 3 μm. The simulated intensity distributions are presented for the fundamental mode in the ETR with a side length of 3 μm and an opening of 0.23 μm. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

In this study, we investigated responses of the mid-successional species Acer truncatum Bunge and the late-successional species Quercus variabilis Blume to three solar illumination conditions: (1) constant low light (CL), (2) constant high light (CH) and (3) low light first and high light afterwards (LH). The last treatment was to simulate a canopy opening. Both species exhibited increases in biomass, totally and in part, and decreases in leaf water content, specific leaf area and chlorophyll concentrations in LH treatment compared to CL treatment. For A. truncatum, exposure to high light condition (LH) increased crown area, and decreased root to shoot ratio, stem mass ratio and leaf perimeter. However, for Q. variabilis, LH treatment increased stem diameter at ground height, effective quantum yield, photochemical quenching and decreased maximum photosystem II quantum yield. The biomass allocation pattern did not change in Q. variabilis among three light conditions. With respect to newly developed leaves, no significant differences were found in leaf size of Q. variabilis between LH treatment and CH treatment while that of A. truncatum decreased in LH treatment. All chlorophyll fluorescence parameters in newly developed oak leaves in LH treatment increased compared to those of CH treatment while no difference was found for A. truncatum between LH and CH treatment. A. truncatum displayed a greater overall plasticity than Q. variabilis although the oak seedlings have a greater plasticity with respect to chlorophyll concentration and chlorophyll fluorescence parameters. A. truncatum should be a better candidate for vegetation recovery, especially in places with heterogeneous light conditions. [ABSTRACT FROM AUTHOR]