Reduction of the divergence angle of a beam coupled out from an optical waveguide is desired in many applications. Collimation in one dimension has been demonstrated, see e.g. [1-3] However, for some applications such as on-chip optical coherence tomography (OCT) or Raman spectroscopy [4,5], it is necessary to produce a light beam that is collimated in two dimensions in order to increase the efficiency of chip-sample coupling. In our previous work [6], we have designed a fabrication procedure of a direct on-chip reflowed polymer micro-ball lens to enable light collimation in both, horizontal and vertical directions. In this work, we realized the complete design, optical characterization and demonstrate the feasibility of mass production.

Optical coherence tomography (OCT) has enabled clinical applications that revolutionized in vivo medical diagnostics. Nevertheless, its current limitations owing to cost, size, complexity, and the need for accurate alignment must be overcome by radically novel approaches. Exploiting integrated optics, the central components of a spectral-domain OCT (SD-OCT) system can be integrated on a chip. Arrayed-waveguide grating (AWG) spectrometers with their high spectral resolution and compactness are excellent candidates for on-chip SD-OCT systems. However, specific design-related issues of AWG spectrometers limit the performance of on-chip SD-OCT systems. Here we present advanced AWG designs which could overcome the limitations arising from free spectral range, polarization dependency, and curved focal plane of the AWG spectrometers. Using these advanced AWG designs in an SD-OCT system can provide not only better overall performance but also some unique aspects that a commercial system does not have. Additionally, a partially integrated OCT system comprising an AWG spectrometer and an integrated beam splitter, as well as the in vivo imaging using this system are demonstrated.

Optical coherence tomography (OCT) has enabled clinical applications that revolutionized in vivo medical diagnostics. Nevertheless, its current limitations owing to cost, size, complexity, and the need for accurate alignment must be overcome by radically novel approaches. Exploiting integrated optics, we assemble the central components of a spectral-domain OCT system on a silicon chip. The spectrometer comprises an arrayed-waveguide grating with 136-nm free spectral range and 0.21-nm wavelength resolution. The beam splitter is realized by a non-uniform adiabatic coupler with its 3-dB splitting ratio being nearly constant over 150 nm. With this device whose overall volume is 0.36 cm(3) we demonstrate high-quality in vivo imaging in human skin with 1.4-mm penetration depth, 7.5-µm axial resolution, and a signal-to-noise ratio of 74 dB. Considering the reasonable performance of this early OCT on-a-chip system and the anticipated improvements in this technology, a completely different range of devices and new fields of applications may become feasible.

Optical coherence tomography (OCT) is a widely used optical imaging technology [1]. Current OCT systems contain a variety of fiber and free-space optical components, which add to the instrument size and cost. By utilizing a suitable mass-fabrication technology and a monolithic design, integrated optics can provide miniaturized OCT systems that offer dramatic cost and size reduction as well as more stable interferometric detection [2,3]. In this paper we present an important step toward a cheap, compact, and quasi-maintenance-free spectral-domain OCT (SD-OCT) system by integrating its central components, the beam splitter and spectrometer, on a silicon chip as schematically shown in Fig. 1 A. An arrayed waveguide grating (AWG) [4] operating at a center wavelength of 1250 nm with a large free spectral range of 136 nm and a high wavelength resolution of 0.21 nm forms the integrated spectrometer, and a non-uniform adiabatic coupler [5] forms the beam splitter in our device. The coupler and AWG were fabricated in silicon oxynitride (SiON) [6]. Single-mode SiON channel waveguides with a 1.8-μm width, 1-μm height, 1.54 core refractive index, and 1.4485 cladding refractive index, enabling bending radii down to 0.5 mm, were fabricated.

We present a new synchronized design for flattening the passband of an arrayed-waveguide grating (AWG) over a broad wavelength range of 90 nm.A wavelength-insensitive 3-dB balanced coupler is designed to be used in duplicate in a Mach-Zehnder interferometer (MZI); the phase deviation created by one of the balanced couplers is cancelled by flipping the other coupler around.This MZI is arranged in tandem with the AWG such that the output signal of the MZI is the input signal of the AWG.We demonstrate a 5-channel, 18-nm-spacing AWG with a 0.5-dB bandwidth of 12 nm over a 90-nm spectral range.A low-loss cascaded AWG system is demonstrated by using the MZI-synchronized flat-top AWG as a primary filter.

Integrated spectrometers are usually of the Rowland mounting type [1]. For applications in which a continuous output spectrum needs to be imaged directly onto a linear detector array, the curved image plane of the Rowland mounting would result in additional losses and aberrations at the outer detector channels. Therefore, a flat-focal-field spectrometer would be highly desirable for such applications. Different methods have been proposed for the design of a flat-focal-field spectrometer [2,3], with limited success. In this work, an alternative way of designing a flat-focal-field arrayed-waveguide grating (AWG) [4] using an integrated field-flattening lens is presented.

In this work, we demonstrate an on-chip reflowed polymer microlens design to enable light collimation in both, horizontal and vertical directions, and the experimental results show reduction of the divergence angle by a factor of 25.

We report on diode-pumped distributed-feedback (DFB) and distributed-Bragg-reflector (DBR) channel waveguide lasers in Er-doped and Yb-doped Al2O3 on standard thermally oxidized silicon substrates. Uniform surface-relief Bragg gratings were patterned by laser-interference lithography and etched into the SiO2 top cladding. The maximum grating reflectivity exceeded 99%. Monolithic DFB and DBR cavities with Q-factors of up to 1.35x10(6) were realized. The Er-doped DFB laser delivered 3 mW of output power with a slope efficiency of 41% versus absorbed pump power. Single-longitudinal-mode operation at a wavelength of 1545.2 nm was achieved with an emission line width of 1.70 +/- 0.58 kHz, corresponding to a laser Q-factor of 1.14x10(11). Yb-doped DFB and DBR lasers were demonstrated at wavelengths near 1020 nm with output powers of 55 mW and a slope efficiency of 67% versus launched pump power. An Yb-doped dual-wavelength laser was achieved based on the optical resonances induced by two local phase shifts in the DFB structure. A stable microwave signal at similar to 15 GHz with a -3-dB width of 9 kHz and a long-term frequency stability of +/- 2.5 MHz was created via the heterodyne photo-detection of the two laser wavelengths. By measuring changes in the microwave beat signal as the intra-cavity evanescent laser field interacts with micro-particles on the waveguide surface, we achieved real-time detection and accurate size measurement of single micro-particles with diameters ranging between 1 mu m and 20 mu m, which represents the typical size of many fungal and bacterial pathogens. A limit of detection of similar to 500 nm was deduced.

Miniaturization of optical instruments for biomedical applications requires the development of efficient means to deliver excitation light to – and collect the resulting signals from – biomedical tissue by an optical microchip, as well as spectral analysis of the acquired information on the chip. We have investigated light collection by integrated waveguides, invented a method for on-chip confocal light delivery and collection, proposed new designs and developed high-resolution arrayedwaveguide gratings (AWGs), and demonstrated Raman spectroscopy and spectral-domain optical coherence tomography (OCT) on a chip.

This paper reviews our recent results on highly efficient rare-earth-ion-doped planar and channel waveguide lasers in crystalline potassium double tungstates and amorphous aluminum oxide on silicon chips.

We demonstrate an integrated optical particle sensor based on a dual-wavelength distributed-feedback waveguide laser. Micro-particles were detected down to a size of 1 μm, which represents the typical size of many fungal and bacterial pathogens.

The effect of discrete output channels and polarization dependency of an arrayed-waveguide-grating (AWG) spectrometer on spectral-domain optical low-coherence reflectometry performance is investigated.

This contribution reviews our recent results on rare-earth-ion-doped integrated amplifiers and lasers. We have concentrated our efforts on complex-doped polymers, amorphous Al2O3, and crystalline potassium double tungstates.