The drive for Ocean pollution prevention requires a significant increase in the extent and type of monitoring of subsea
hydrocarbon production equipment. Sensors, instrumentation, control electronics, data logging and transmission units
comprising such monitoring systems will all require to be powered. Conventionally electrical powering is supplied by
standard subsea electrical cabling.
The ability to visualise the assets being monitored and any changes or faults in the equipment is advantageous to an
overall monitoring system. However the effective use of video cameras, particularly if the transmission of real time high
resolution video is desired, requires a high data rate and low loss communication capability. This can be challenging for
heavy and costly electrical cables over extended distances. For this reason optical fibre is often adopted as the
communication channel. Using optical fibre cables for both communications and power delivery can also reduce the cost
of cabling.
In this paper we report a prototype optically remote powered subsea video monitoring system that provides an alternative
approach to powering subsea video cameras. The source power is transmitted to the subsea module through optical fibre
with an optical-to-electrical converter located in the module. To facilitate intelligent power management in the subsea
module, a supercapacitor based intermediate energy storage is installed. Feasibility of the system will be demonstrated.
This will include energy charging and camera operation times.
Focused ion beam (FIB) etching technology is a highly efficient post-processing technique with the functionality to perform sputter etching and deposition of metals or insulators by means of a computer-generated mask. The high resolution and the ability to remove material directly from the sample in-situ make FIB etching the ideal candidate for device prototyping of novel micro-size photonic component design. Furthermore, the fact that arbitrary profile can be etched directly onto a sample without the need to prepare conventional mask and photolithography process makes novel device research with rapid feedback from characterisation to design activities possible. In this paper, we present a concise summary of the research work in Cambridge based on FIB technology. We demonstrate the applicability of focussed ion beam post processing technology to active photonic devices research. Applications include the integration of advanced waveguide architectures onto active photonic components. We documents details on the integration of lens structure on tapered lasers, photonic crystals on active SOA-integrated waveguides and surface profiling of low-cost gain-guided vertical-cavity surface-emitting lasers. Furthermore, we discuss additional functions of FIB in the measurement of buried waveguide structures or the integration of total-internal-reflection (TIR) mirror in optical interconnect structures.
KEYWORDS: Etching, Thermal effects, Near field optics, Mirrors, High power lasers, Waveguides, Geometrical optics, Semiconductor lasers, Laser processing, Diffraction
This paper approaches the problem of catastrophic optical mirror damage from a geometrical waveguide point of view. Instead of engineering the characteristics of the semiconductor material at the facet of the laser using quantum-well intermixing or other sophisticated wafer growth technique, a simple intra-cavity diverging lens concept is proposed and demonstrated to be capable of effectively expanding the lateral optical mode in order to counter the effect of SHB and thermal lensing effect, thereby reducing the risk of COMD. The Gaussian output beam profile is maintained throughout the whole of the current range tested, showing that expanding the nearfield at facet using integrated lens does not compromise the brightness of the laser. A key finding in this work is that the diverging effect on an optical mode is a thoroughly scalable effect that can be engineered by varying the etch-depth of the integrated lens. Fabrication of the lens is compatible with existing laser manufacturing process flow in that it can be easily implemented either by post-processing technology or by an additional lithographical step. This opens up new possibility in device design, with the beam width along the lateral direction being a parameter that can be optimized in isolation.
A novel transmitter for directed-beam infra-red wireless that utilizes a combination of both gain-guiding and index guiding mechanism to ameliorate the shortcoming of the state-of-the-art technology is proposed and demonstrated. The 3mm long tapered laser consists of an index-guided ridge straight section and a gain-guided tapered section with a full angle of 6°. By implementing multiple contact with a sufficiently high inter-contact resistance, discrete switching between different angles can be obtained by selectively pumping current to different contact (gain-guiding effect), while fine-tuning of a given angle can be achieved by adjusting the injection current of nearby contacts (index-guiding effect). The tapered laser's metal cover is removed using focus ion beam etching technique to form three separate sections: base section as filter, left section and right section for beam steering. The device is biased by current pulses of 1μs width and 0.1% duty cycle. With a 1.6A injection current, an output power of 2W is achieved, which would be suitable to overcome large free space optical loss and facilitate the use of transmitting methods. The beam profile steered by 3.2° and -5.4° from the central lobe when injection current is limited to the left and right section respectively is measured. It is also observed that as injection current increases, the beam profile is steered towards the central position. This is because as the injection current increases, the local refractive index is decreased, thereby shifting the beam profile towards the opposite direction.
KEYWORDS: Semiconductor lasers, Etching, Near field, Laser resonators, Fresnel lenses, High power lasers, Diodes, Lens design, Near field optics, Monochromatic aberrations
We demonstrate, for the first time, a monolithic integrated lens for wide aperture gain-guided tapered laser beam quality enhancement by compensating the quadratic phase curvature. The 3mm long tapered laser with an output aperture of 170μm adopted in this design consists of a gain-guided tapered section and an index-guided ridge section and operated at 980nm. The lens design is implemented by focus ion beam etching (FIBE) technique, whereby the laser diode is mounted p-side up in order to facilitate the etching process. The lens is located 600μm away from the junction of the tapered and ridge sections, and is 40μm wide and 300μm long with a focal length of 800μm. The laser diode is characterised by light-current characteristics together with near- and far- field measurements before and after etching. The device is biased by current pulses of 1μs width and 0.1% duty cycle. Light-current measurement shows a drop of 10.5% in threshold current from 380mA to 340mA after the inclusion of lens. This is an evidence that the lens effectively equalised the curved phase in order to reduce the laser cavity loss by improving the coupling efficiency of backward travelling wave at the output facet. Throughout the whole current range tested, the width of near-field at waist is broadened by an average of 36% after the inclusion of lens. By successfully compensating the quadratic phase curvature of the mode, the beam divergence in the far-field is significantly narrowed by an average of 28.5%. M2 factor is improved by an average of 12%.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.