MEMS Technology for Biomedical Imaging Applications

Biomedical imaging is the key technique and process to create informative images of the human body or other organic structures for clinical purposes or medical science. Micro-electro-mechanical systems (MEMS) technology has demonstrated enormous potential in biomedical imaging applications due to its outstanding advantages of, for instance, miniaturization, high speed, higher resolution, and convenience of batch fabrication. There are many advancements and breakthroughs developing in the academic community, and there are a few challenges raised accordingly upon the designs, structures, fabrication, integration, and applications of MEMS for all kinds of biomedical imaging. This Special Issue aims to collate and showcase research papers, short commutations, perspectives, and insightful review articles from esteemed colleagues that demonstrate: (1) original works on the topic of MEMS components or devices based on various kinds of mechanisms for biomedical imaging; and (2) new developments and potentials of applying MEMS technology of any kind in biomedical imaging. The objective of this special session is to provide insightful information regarding the technological advancements for the researchers in the community

Novel sources of near- and mid-infrared femtosecond pulses for applications in gas sensing, pulse shaping and material processing

In this thesis the design, construction process and the performance of two femtosecond optical parametric oscillators and one second–harmonic generation femtosecond pulse shaper is described. One oscillator was applied to gas sensing while potential applications of other devices are outlined. ATi:sapphire oscillator was used to pump a periodically–poled lithium niobate– based optical parametric oscillator. This signal–resonant device was configured to produce broadband idler pulses tunable in the range of 2.7–3.4 μm. This wavelength coverage was matched to the ν3 optical absorption band of methane, and Fourier–transform spectroscopy of a CH4:N2 mixture was implemented by employing a mid–IR silica photonic bandgap fibre simultaneously as a gas cell and an optical waveguide. Methane sensing below a 1% concentration was demonstrated and the main limiting factors were identified and improvements suggested. Another optical parametric oscillator was demonstrated which was pumped by a commercial Yb:fibre master oscillator/power amplifier system and was based on a periodically–poled lithium niobate crystal. The signal was tunable between 1.42–1.57 μm and was intended as a source for a subsequent project for waveguide writing in silicon. The oscillator was a novel long–cavity device operating at 15 MHz. The 130 nJ pump pulse energies allowed for 21 nJ signal pulses at a pump power of 2 W. The performance of the oscillator was characterised via temporal and spectral measurements and the next steps of its development are outlined. Finally a pulse shaper based on second harmonic generation in a grating– engineered periodically–poled lithium niobate crystal was demonstrated. Pulses from a 1.53 μm femtosecond Er:fibre laser were compressed and then used as the input to the shaper. The performance of the shaper was tested by performing cross–correlation frequency–resolved optical gating measurements on the output second harmonic pulses and this confirmed the successful creation of multiple pulses and other tailored shapes including square and chirped pulses, agreeing well with theoretical calculations

The ultrafast laser inscription of photonic devices for integrated optical applications

A study of some key areas in which ultrafast laser inscription may usefully be employed is presented. The thesis includes waveguide inscription in a variety of substrates including passive glass, doped glass and a nonlinear crystal. The work contained can be split into three studies, with some overlap between them. Firstly fused silica glass is used, both in planar substrates and as flat fibre, for the inscription of two sensing elements. The planar substrate is used for a device similar in design to a side-polished fibre and the flat fibre is used for the fabrication of a Bragg grating waveguide array. In the second study, waveguides are inscribed in the nonlinear crystal monoclinic bismuth borate, and used for guided mode second harmonic generation. A novel waveguide design is employed to increase overlap between the pump and second harmonic waveguide modes. The remainder of the thesis investigates the applicability of ultrafast laser inscription to the fabrication of compact modelocked lasers. Lasing is demonstrated, both continuous wave and modelocked, using a laser inscribed erbium doped bismuthate glass waveguide as the gain element. A study is then undertaken into methods of integrating carbon nanotubes, used as saturable absorbers to modelock lasers, into laser inscribed waveguides

Organic lasers: recent developments on materials, device geometries, and fabrication techniques

MCG acknowledges financial support through the ERC Starting Grant ABLASE (640012) and the European Union Marie Curie Career Integration Grant (PCIG12-GA-2012-334407). AJCK acknowledges financial support by the German Federal Ministry for Education and Research through a NanoMatFutur research group (BMBF grant no. 13N13522).Organic dyes have been used as gain medium for lasers since the 1960s, long before the advent of today’s organic electronic devices. Organic gain materials are highly attractive for lasing due to their chemical tunability and large stimulated emission cross section. While the traditional dye laser has been largely replaced by solid-state lasers, a number of new and miniaturized organic lasers have emerged that hold great potential for lab-on-chip applications, biointegration, low-cost sensing and related areas, which benefit from the unique properties of organic gain materials. On the fundamental level, these include high exciton binding energy, low refractive index (compared to inorganic semiconductors), and ease of spectral and chemical tuning. On a technological level, mechanical flexibility and compatibility with simple processing techniques such as printing, roll-to-roll, self-assembly, and soft-lithography are most relevant. Here, the authors provide a comprehensive review of the developments in the field over the past decade, discussing recent advances in organic gain materials, which are today often based on solid-state organic semiconductors, as well as optical feedback structures, and device fabrication. Recent efforts toward continuous wave operation and electrical pumping of solid-state organic lasers are reviewed, and new device concepts and emerging applications are summarized.PostprintPeer reviewe

Compact near-infrared 3-dimensional channel waveguide lasers

This thesis presents the development of ultrafast near-infrared (NIR) waveguide laser sources, through the fabrication of waveguides in Yb-doped bismuthate glass using ultrafast laser inscription (ULI). An integrated linear cavity waveguide laser is demonstrated in the glass with output powers of 163 mW and a slope efficiency of 79%. The laser performance is comparable to bulk systems while providing additional advantages in terms of low threshold ~35 mW and system compactness. The simultaneous achievement of low propagation losses and preservation of the fluorescence properties of Yb ions after the ULI process is key to the outstanding laser performance. Based on the current interest in ultrafast laser development using graphene as a saturable absorber (SA), a systematic study of nonlinear absorption in graphene is presented. The nonlinear optical characterisation of graphene at the wavelengths of 1 μm and 2 μm contributes to the experimental evidence for the wavelength independent absorption saturation in the material. Ultrashort pulse generation from the Yb-doped bismuthate waveguide laser is investigated using SAs based on semiconductor technology and carbon nanostructures. The quasi-monolithic waveguide laser, employing a graphene SA generated ~485 mW output power with a slope efficiency of 49%. The laser generated ~1 ps pulses in a Q-switched mode-locked regime, with the mode-locked pulses measuring a high repetition rate of 1.5 GHz. Ultrafast laser development is also investigated based on a novel evanescent-wave mode-locker device, fabricated by ULI. The device consists of an orthogonal waveguide with the right-angle positioned along its angled facet. The substrate is converted into a mode-locker by depositing carbon nanotube SA at the angled facet. Mode-locked operation is demonstrated by incorporating the substrate in an Er-doped ring laser, generating ~800 fs pulses at 26 MHz. Some preliminary work is done to replicate the device design in an active gain medium, namely, Yb-doped bismuthate glass, for the development of compact laser sources

III-V-on-Si photonic integrated circuits realized using micro-transfer-printing

Silicon photonics (SiPh) enables compact photonic integrated circuits (PICs), showing superior performance for a wide variety of applications. Various optical functions have been demonstrated on this platform that allows for complex and powerful PICs. Nevertheless, laser source integration technologies are not yet as mature, hampering the further cost reduction of the eventual Si photonic systems-on-chip and impeding the expansion of this platform to a broader range of applications. Here, we discuss a promising technology, micro-transfer-printing (μTP), for the realization of III-V-on-Si PICs. By employing a polydimethylsiloxane elastomeric stamp, the integration of III-V devices can be realized in a massively parallel manner on a wafer without substantial modifications to the SiPh process flow, leading to a significant cost reduction of the resulting III-V-on-Si PICs. This paper summarizes some of the recent developments in the use of μTP technology for realizing the integration of III-V photodiodes and lasers on Si PICs