Effective Facet Reflectivity Research Articles

GaAs-based superluminescent diodes with window-like facet structure for low spectral modulation at high output powers

We demonstrate a GaAs-based superluminescent diode (SLD) based on the incorporation of a window-like back facet into a self-aligned stripe structure in order to reduce the effective facet reflectivity. This allows the realisation of SLDs with low spectral modulation depth (SMD) at high power spectral density (PSD), without the application of anti-reflection coatings to either facet. This approach is therefore compatible with ultra-broadband gain active elements. We show that 30 mW output power can be attained in a narrow bandwidth, corresponding to 2.2 mW nm−1 PSD with only 5% SMD, centred about 990 nm. We discuss the design criteria for high power and low SMD and the deviation from a linear dependence of SMD on output power, resulting from Joule heating in the self-aligned stripe.

Experimental and theoretical investigation of mode size effects on tilted facet reflectivity

Facet reflectivity from tilted devices has been investigated as a function of optical mode size. A theoretical approach is developed and completed by numerical simulation in order to calculate the effective facet reflectivity depending on optical mode size. The proposed approach is based on the plane wave expansion. Compared with other methods, the proposed one reveals clearly the physical insights, requires low computational effort and exhibits high reliability. We measured that 7° of mirror tilt introduces a reflectivity of 1.34×10−2% for an optical mode size of 4.5 µm and a reflectivity of 6.25% for a mode size of 1.7 µm. We developed an analytical model that confirms those values.

Effect of facet angle on effective facet reflectivity and operating characteristics of quantum dot edge emitting lasers and superluminescent light-emitting diodes

The authors report the creation of low reflectivity angled facets by focused-ion-beam postfabrication etching. A method to directly measure the effective facet reflectivity of such facets, utilizing gain saturation effects in the quantum dots is described. The reflectivities of the angled facets are shown to decrease by increasing the facet angle from 0° to 15°. With a reflectivity of <1×10−6 obtained for a facet with a 15° angle, allowing quantum dot superluminescent light-emitting diodes to be fabricated. The use of different angled facets to control the emission wavelength of both quantum dot lasers and superluminescent light-emitting diodes is outlined.

Broadband quantum dot superluminescent LED with angled facet formed by focused ion beam etching

Broadband quantum dot superluminescent light emitting diodes (LEDs) are realised by focused ion beam etching an angled facet in an edge emitting dot-in-well laser diode structure. The device exhibits a large and flat emission spectral width up to 142 nm at 0.3 mW, maximum CW output power as high as 3 mW, and effective facet reflectivity -6

Facet reflectivity of a spot-size-converter integrated semiconductor optical amplifier

Traveling-wave type semiconductor optical amplifiers (SOAs) integrated with a spot-size-converter (SSC) are extensively studied for improvement of coupling efficiency with single-mode fibers and for cost reduction in packaging. In this paper, the structural dependence of the SSC on effective facet reflectivity R/sub eff/ is investigated theoretically and experimentally. It is shown that, not only sufficient mode-conversion in the SSC region, but also the introduction of angled facets, are essential for reducing R/sub eff/. A small gain ripple (less than 0.1 dB) in an amplified spontaneous emission (ASE) spectrum, fiber-to-fiber gain of 26 dB, and saturation output power of 7 dBm are observed for the fabricated SOA, which consists of a window length of 20 /spl mu/m, facet angle of 7/spl deg/, and anti-reflection coated facet of less than 1% reflectivity.

Improved gain block for long wavelength (1.55 µm)hybrid integrated devices

A curved waveguide, strained multiple quantum well reflective amplifier with an integrated front facet mode expander has been designed and fabricated. A device without facet coatings has been found to have a chip gain of 36 dB with 6 dB of gain ripple. This equates to an effective facet reflectivity of 8/spl times/10/sup -6/.

A theory of broad-area semiconductor lasers with modal reflectors

This paper provides a theoretical analysis of guided lateral modes in broad-area (BA) semiconductor lasers with modal reflectors formed by patterning the reflectivity of the front facet. The analysis has been performed by using the model based on the effective-index method and the concept of the effective facet reflectivity. The numerical results include mode threshold conditions and far-field patterns of the lasing modes for various reflector configurations.

Selective regrowth of a wide-bandwidth 1.3 mu m integrated lossless tap and optical preamplifier

The authors report the first monolithically integrated wide-bandwidth lossless tap-that is, an optical semiconductor amplifier followed by a colinear reverse-biased waveguiding photodetector with fiber-coupled input and output. The integration was achieved by using off-axis selective epitaxial growth of ridge waveguides on a patterned dielectric layer. The tilted facets produced by the off-axis growth, along with photodetector absorption, serve to reduce the effective facet reflectivity to -36 dB without any antireflection coating. By adjusting the length of the absorbing photodetector section, part or all of the amplified light may be absorbed, allowing the device to function respectively as a lossless tap or an optical preamplifier. A lossless tap with an electrical bandwidth of 7 GHz, a responsivity of 26 A/W, and a fiber-to-fiber gain of 3 dB is shown to have a receiver sensitivity of -22 dB at 3 Gb/s.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Effects of optical feedback on the light-current characteristics of semiconductor lasers

Theoretical and experimental investigations of the continuous wave (CW) output-power current characteristics of semiconductor lasers with optical feedback are reported. An analytical expression is presented which accounts for the external reflection in the form of an effective facet reflectivity. The coherence properties of the compound cavity laser field are incorporated by the correlation function of the optical field. An experimental setup was established to adjust and to control for different feedback levels. The normalized threshold current variation, due to feedback shows a dependence on the laser structure. This results from different confinement factors of the various waveguide structures. Up to reflection levels well within the coherence collapse regime the change of the slope of the light versus current curve is higher than calculated from incoherent feedback.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

1.5 mu m GaInAsP angled-facet flared-waveguide traveling-wave laser amplifiers

A broadband laser amplifier requires extremely low facet reflectivity (<0.1%). Previously, a low effective facet reflectivity of 0.05% was realized by an angle-facet structure in the 1.3- mu m wavelength band. Present work reports an improved structure for the 1.5- mu m wavelength band by flaring the waveguide ends near the angled facets. With a conventional antireflection coating of approximately 1% reflectivity, the measured effective facet reflectivity is less than 0.01% and the resultant devices have a fiber-to-fiber gain of 15 dB centered at 1.49 mu m.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>