SiO<sub>x</sub>N<sub>y</sub> shows promises for bright emitters of single photons. We successfully fabricated ultra-low-loss SiOxNy waveguide and AWG with low insertion loss <1dB and <3dB total loss (<2dB on-chip loss and <1dB coupling loss) at 1310nm.
Recent advances in optical waveguides have brought long-awaited technologies closer to practical realization. Although the concept of a single-mode (SM) waveguide has been around for a while, SM condition usually posed very stringent conditions in fabrication for small waveguides. Researchers have developed low loss silicon nitride (Si3N4) at 1550nm wavelength, the developments in specific application have down converted to 1310nm (O-band) so they do not have to compete with internet data for bandwidth and could share the existing optical fiber infrastructure. However, wavelengthdemultiplexer technology at this band is not readily commercial available. Custom-made O-band optical devices for wavelength-demultiplexing have typical losses. Such high losses deplete more than 75% of the already-scarce photons. We studied Si3N4 channel waveguide with ultra-thin slab for (SM) condition at 1310nm wavelength using finite element method (FEM) and 3-D imaginary beam propagation method (IDBPM). We have shown that SM condition is possible for ultra-thin slab with wide waveguide width; such condition can ease the constraint of photolithography, allowing deposition of thin Si3N4 layer to be accomplished in minutes. Studies show that for ultra-thin layer, for example, at 60nm, we can achieve a wide range of widths that fulfilled the SM condition, ranging from 2μm to 5μm. SM condition becomes more stringent when the Si3N4 layer increases. Substrate losses are estimated at 0.001 dB/cm, 0.003 dB/cm, and 0.1 dB/cm for slab height at 100nm, 80nm, and 60nm respectively.
Proton beam writing (PBW) is a high-resolution direct write lithographic technique suitable for the fabrication of
micro/nano optical components with smooth vertical sidewalls. In the present work PBW was used to fabricate smooth
micro cavities in negative tone photoresist SU-8 and Rhodamine B doped SU-8. Two different laser cavities based on
whispering gallery mode resonators were fabricated using PBW. The laser cavities in Rhodamine B doped SU-8 resist
were optically pumped with a pulsed frequency doubled Nd: YAG laser, and emits light in the chip plane at 643 nm. The
presented laser cavities showed pump threshold as low as 3 μJ/mm<sup>2</sup>, which is the lowest threshold reported in planar
cavities fabricated in Rhodamine B dye based polymer laser cavities.
Three dimensional metamaterials are fabricated using direct laser writing in SU-8 polymer followed by an electroless
coating process. A method has been developed to allow for selective electroless plating of SU-8 microstructures
with a smooth conformal coating of Ag. The process utilizes radio frequency plasma pretreatment
to modify the SU-8 surface so that Ag ions can nucleate on the surface, leaving the substrate uncoated. An array
of split ring resonators and other 3D microstructures are used to demonstrate how the technique can be applied
to metamaterials applications.
The mid-infrared spectral region is interesting for bio-chemical sensing, environmental monitoring,
free space communications, or military applications. Silicon is relatively low-loss from 1.2 to 8 μm and from
24 to 100 μm, and therefore silicon photonic circuits can be used in mid- and far- infrared wavelength ranges.
In this paper we investigate several silicon based waveguide structures for mid-infrared wavelength region.
In this work, we describe the use of a combination of proton beam irradiation and electrochemical etching to
fabricate high index-contrast waveguides directly in silicon without the need for silicon-on-insulator substrate.
Various types of waveguides with air or porous silicon cladding have been demonstrated. We show that porous
silicon (PS) is a flexible cladding material due to the tunability of its refractive index and thickness. The Si/PS
waveguide system also possesses better transmittance in the ranges of 1.2-9 and 23-200 μm, compared to
Si/SiO<sub>2</sub> waveguides. This is potentially important for mid and far-IR applications. Since it is compatible with
conventional CMOS technology, this process can be used for fabrication of integrated optoelectronics circuits.
The ability to control the porosity and hence the refractive index of porous silicon makes it an interesting material
for photonic applications. Layers with refractive indices as low as 1.5 up to that of bulk crystalline silicon can be
easily fabricated by varying the electrochemical etching parameters during anodization. This ability to control
the refractive index makes it possible to design waveguides that more closely match the properties of silica based
optical fiber, thus reducing insertion loss. In this paper we explore the possibility of using a focused laser in order
to create waveguiding regions in porous silicon substrates comprising of multiple layers. The direct write process
can be used to locally oxidize the porous material forming micron sized channels that can be used for waveguiding.
Various designs are simulated using a finite element mode solver in order to optimize the design parameters for
single mode waveguiding. Experimental results showing the effect of laser irradiation on multilayered structures
are also presented.
We report a novel technique for the fabrication of an all-silicon channel waveguide using direct proton beam writing
and subsequent electrochemical etching. A focused beam of high energy protons is used to selectively inhibit porous
silicon formation in the irradiated regions. By over-etching beyond the ion range, the irradiated region becomes
surrounded by porous silicon cladding. Waveguide characterization carried out at 1550 nm on the proton irradiated
waveguide shows that the propagation losses improve significantly from 20±2 dB/cm to 9±2 dB/cm after vacuum
annealing at 800°C for 1 hour.
Mid-infrared wavelength region is interesting for several application areas including sensing, communications, signal
processing, and imaging. Its importance stems from the two atmospheric windows and the fact that nearly all important
molecular gases have strong absorption lines in the mid-infrared. In this paper, we discuss the design, fabrication and
propagation loss measurements of three silicon waveguide structures that can find applications in the mid-infrared region.
The field of Silicon Photonics has gained a significant amount of momentum in recent years. Announcements of high
speed modulators and cost-efficient light sources in the Silicon-on-insulator material system have helped to make Silicon
Photonics a viable contender as a low-cost active photonic platform. As a pioneer in the field, the University of Surrey
continues to investigate the prospects of silicon photonics. Herein we present a summary of our work on several key
areas such as ion implanted grating devices, high-speed modulators, switches and ring resonators. We conclude with a
discussion on an advanced fabrication technique, proton beam writing.
In this paper we report two novel fabrication techniques for silicon photonic circuits and devices. The techniques are
sufficiently flexible to enable waveguides and devices to be developed for telecommunications wavelengths or indeed
other wavelength ranges due to the inherent high resolution of the fabrication tools. Therefore the techniques are
suitable for a wide range of applications. In the paper we discuss the outline fabrication processes, and discuss how they
compare to conventional processing. We compare ease of fabrication, as well as the quality of the devices produced in
preliminary experimental fabrication results. We also discuss preliminary optical results from fabricated waveguide
devices, as measured by conventional means. In these preliminary results we discuss fundamental properties of the
waveguides such as loss and spectral characteristics, as it is these fundamental characteristics that will determine the
viability of the techniques. Issues such as the origins of the loss are discussed in general terms, as resulting fabrication
characteristics such as waveguide surface roughness (and hence loss), or waveguide profile and dimensions may be
traded off against cost of production for some applications. We also propose further work that will help to establish the
potential of the technique for future applications.
Proton beam writing is a lithographic technique that can be used to fabricate microstructures in a variety of materials including PMMA, SU-8 and Foturan<sup>TM</sup>. The technique utilizes a highly focused mega-electron volt beam of protons to direct write latent images into a material which are subsequently developed to form
structures. Furthermore, the energetic protons can also be used to modify the refractive index of the material at a precise depth by using the end of range damage. In this paper we apply the proton beam writing technique to the fabrication of a lab-on-a-chip device that integrates buried waveguides with microfluidic channels. We have chosen to use Foturan<sup>TM</sup> photostructurable glass for the device because both direct patterning and refractive index modification is possible with MeV protons.
High energy helium beam has been utilized to pattern silicon prior to electrochemical etching in hydrofluoric acid. Photoluminescence (PL) studies carried out on medium resistivity silicon showed that the PL wavelength of the irradiated regions is continuously red-shifted by up to 150 nm with increasing dose. On the lower resistivity silicon, the intensity is shown to increase by more than twenty times with dose. Atomic force microscopy (AFM) and scanning electron microscopy (SEM) have been used to determine the surface morphology of the irradiated structure. This technique is potentially important for producing an integrated silicon based optoelectronic device.
We report an alternative technique which utilizes fast proton or helium ion irradiation prior to electrochemical etching for three-dimensional micro-fabrication in bulk p-type silicon. The ion-induced damage increases the resistivity of the irradiated regions and slows down porous silicon formation. A raised structure of the scanned area is left behind after removal of the un-irradiated regions with potassium hydroxide. The thickness of the removed material depends on the irradiated dose at each region so that multiple level structures can be produced with a single irradiation step. By exposing the silicon to different ion energies, the implanted depth and hence structure height can be precisely varied. We demonstrate the versatility of this three-dimensional patterning process to create multilevel cross structure and free-standing bridges in bulk silicon, as well as sub-micron pillars and high aspect-ratio nano-tips.