For given intrinsic losses of a single ring resonator sensor, there exists the maximum sharpness, at the extinction ratio of -6dB. However, the maximum sharpness of a single ring resonator sensor is sensitive for the coupling coefficient. In order to obtain the maximum sharpness, the coupling region of the single rings must have a higher precision of manufacture. To solve this problem, this paper proposed eye-like resonator which is formed by a ring resonator (named inner loop) embedd in the dual-bus-coupled ring resonator (named outer loop). Eye-like resonators can generate the asymmetric Fano-resonance spectra of the drop port, numerical calculation of spectra on the drop port is utilized by the transfer matrix method. As the round trip loss varies, the maximum value of sharpness and the corresponding transmission at the resonant point can be obtained by tuning the phase ratio of the outer loop to the inner loop. The maximum value of sharpness increases with the round trip loss, as the outer loop and inner loop coupling coefficient changing, the maximum value of sharpness of Fano-resonance change slowly in a wide range. As the round trip loss and coupling coefficients of the outer loop and inner loop varies, the corresponding transmission at the resonant point remains almost the same, about -6dB. The sharpness of Fano resonant peak is insensitive for the coupling coefficients, which can reduce the requirements of manufacture of coupling region.
A novel 980nm bottom-emitting VCSELs array with high power density and good beam property of Gaussian far-field
distribution is reported. This array is composed of 5 symmetrically-arranged elements of 200&μm,150μm and
100μm-diameterμwith the center spacings of 300μm and 250μm respectively. The maximum power is 880mW at a
current of 4A, corresponding to 1KW/cm<sup>2</sup> average optical power density. The differential resistance is Ω with a
threshold of 0.56A. The novel array is compared with a 300μm-aperture-size single device and a 4*4 2-D array with
50μm element aperture size and 250μm centre spacing. The three devices have the same lasing area. The conclusion is
that the novel array is better in the property of output power, threshold current, lasing spectra, far-field distribution etc.
Whispering-Gallery-Mode (WGM) photonic crystal microcavity is a kind of photonic crystal application and can
potentially be used for miniaturized photonic devices, such as thresholdless lasers. In this paper we study the WGM of
photonic crystal microcavities focusing on the so called H2 cavities which are formed by removing seven air holes. The
WGM in these large-size cavities has some advantages compared with single defect WGM in the view of real device
applications. We further add a central air hole in the cavity region to analyze the effect on WGM in the microcavity by
finite difference time domain (FDTD) and plane wave expansion (PWE). It is found that the tolerance of WGM is large
enough for the fabrication of electrical injection structure.
Pulsed anodic oxidation technique, a new way of forming current blocking layers, was successfully used in
ridge-waveguide QW laser fabrication. We apply this method in 980nm VCSELs fabrication to form a high-quality
native oxide current blocking layer, which simplify the device process. A significant reduction of threshold current and a
distinguished device performance are achieved. The 500μm-diameter device has a current threshold as low as 0.48W.
The maximum CW operation output power at room temperature is 1.48W. The lateral divergence angle <i>θ</i><i><sub>parallel</sub></i>and vertical divergence angle <i>θ</i><sub>perpendicular</sub> are as low as 15.3° and 13.8° without side-lobes at a current of 6A.
High power vertical cavity surface emitting lasers with large aperture have been fabricated through improving
passivation, lateral oxidation and heat dissipation techniques. Different from conventional three quantum well structure,
a periodic gain active region with nine quantum wells was incorporated into the VCSEL structure, with which high
efficiency and high power operation were expected. The nine quantum wells were divided into three groups with each of
them located at the antinodes of the cavity to enhance the coupling between the optical field and the gain region. Large
aperture and bottom-emitting configuration was used to improve the beam quality and the heat dissipation. A maximum
output power of 1.4W was demonstrated at CW operation for a 400μm-diameter device. The lasing wavelength shifted to
995.5nm with a FWHM of 2nm at a current of 4.8A due to the internal heating and the absence of active water cooling.
A ring-shape farfield pattern was induced by the non-homogeneous lateral current distribution in large diameter device.
The light intensity at the center of the ring increased with increasing current. A symmetric round light spot at the center
and single transverse mode operation with a divergence angle of 16° were observed with current beyond 4.8A.