This paper presents a simple fabrication method for a liquid-core optofluidic waveguide and demonstrates efficient light delivery and collection using optical fibers pressure-sealed into a polydimethylsiloxane matrix. Total optical loss as small as 3 dB from an input optical fiber with a core diameter of 9 μm to an output optical fiber with a core diameter of 62.5 μm connected one to another via a 2 cm long liquid-core optofluidic channel is achieved. This strategy allows rapid prototyping of optofluidic waveguides without requiring expensive microfabrication facilities and is suitable for applications that require an efficient optical sensing in a small liquid sample. As a demonstration, we examine the optical Faraday rotation of a fluid sample and identify advantages and limitations by comparison to a macroscopic system of similar length.
High speed optical interconnections offer an attractive alternative to electrical interconnections, particularly when they can be integrated into electrical systems. In particular, waveguide signal distribution and optical to electrical (O/E) conversion are critical to the integration of optical signals into electrical systems. The integration and interfaces between waveguides and O/E devices is a topic under intensive study. One approach to the integration of optical interconnections into electrical systems is to use fully embedded thin film optoelectronic (OE) devices in planar lightwave components on electrical interconnection substrates. In this approach, the propagating optical signal from the optical waveguide can be evanescently or directly coupled into the embedded thin film OE devices based on the embedded structure. Efficient and high speed optical signal distribution and O/E conversion, such as those using planar channel polymer waveguides with embedded thin film photodetectors, are examples of optical interconnection critical functions that are optimally implemented in electrical systems. In this paper, a 1 by 4 thin film metal semiconductor metal (MSM) photodetector (PD) array is embedded in a 1 by 4 photoimageable polymer multimode interference (MMI) coupler. This optical distribution and E/O system was fabricated and experimentally characterized at a wavelength of 1.3 μm. The measured overall loss, including the propagation loss and splitting loss of the MMI coupler was -0.18 dB at λ = 1.3 μm.
Practical, packaged photodetectors (PDs) must be interfaced to bias and transmission lines, which introduce parasitics. These parasitics (resistance, capacitance and inductance) can be used to shape the temporal and frequency response of packaged photodetectors. Thus, the bias circuitry, external passives, and high speed interconnections must be carefully designed to produce the desired response in a packaged photodetector. Applications dictate the desired PD characteristics, which are generally either a flat frequency response, or a fast, ring-free impulse response. In this paper, the effects of the parasitic resistance, capacitance, and inductance are studied to affect the intrinsic response of photodetectors for a flat frequency response or a fast ring-free impulse response. For the optical transmission of microwave and millimeter wave RF signals, such as remote antennas or radar arrays, a flat frequency response is critical. A flat frequency response can be obtained from controlled ringing in the temporal domain. This paper explores the control of ringing in the temporal domain using varied external loads. A fast fall time, ring-free pulse is useful for digital communications applications where ringing can degrade the bit error rate. Fourier transforms show that a ring-free impulse response has a characteristic fall-off at high frequencies. However, this fall-off is detrimental for frequency domain applications, so the optimization condition for the inductance and capacitance is different for these applications. This paper explores the suppression of the impulse response tail by varying the external loads.
The integration of active optoelectronic devices, passive optical devices, and electronics into planar lightwave integrated circuits (PLICs) at the chip level, and planar lightwave integrated systems (PLIS) at the substrate or package level, have applications in optical interconnection, optical signal distribution and processing, and in integrated optical sensing. Heterogeneous integration of thin film devices is an effective method of creating PLICs and PLIS. Thin film InP-based edge emitters and thin film photodetectors have been integrated with polymer waveguides to create planar lightwave systems.
As optoelectronic devices increase in speed, the measurement system used to characterize these devices must have sufficient bandwidth and minimum parasitic loading during test to accurately determine the intrinsic performance of the device under test. Conventional electrical measurement systems have an intrinsic bandwidth due to the available components for test and have parasitic loading due to direct electrical contact to the device under the test. Electro-optic sampling is an excellent measurement technique for characterizing ultra-fast devices because it has high bandwidth, is non-contact, is non-destructive, and relatively non-invasive. In this paper, an optical fiber-based electro-optic sampling system is designed and used for characterizing high speed InGaAs thin film MSM photodetectors. A fiber laser which is operating at 1556 nm wavelength was used for the sampling and excitation beam. Optical fibers were used to connect each component in the system for flexibility. InGaAs thin film MSM photodetectors were fabricated and characterized. InGaAs thin film MSM photodetectors were bonded onto a coplanar strip line deposited on a benzocyclobutene (BCB)-coated glass substrate for characterization. These thin film photodetectors show high speed operation combined with high responsivity and large detection area compared to P-I-N photodetectors operating at similar speeds
As an alternative approach to current electrical interconnection technology, optical interconnections at high speeds offer several potential advantages including small footprint, simple system design (in comparison to transmission lines), and immunity to electromagnetic interference. There are a number of approaches to integrating optical signal paths in electrical interconnection substrates such as backplanes, boards, and modules. One approach utilizes the heterogeneous integration of thin film optoelectronic (OE) devices embedded in waveguides. Optical signals can be coupled in from external fibers or from thin film lasers integrated onto the substrate, propagated, distributed, and processed in a planar waveguide format, and then coupled from the waveguide to an embedded thin film photodetector by evanescent field or direct coupling. This approach achieves alignment through assembly and successive masking layers and thus minimizes alignment issues. In addition, the integrated optical signal distribution system can be integrated onto the electrical interconnection substrate after the substrate has been fabricated using post processing, thus, the board facility is not impacted through the integration of the optical links.
In this paper, a discussion of the fabrication processes as well as coupling efficiency and speed measurement results for thin film InGaAs PDs embedded in polymer waveguides integrated onto Si substrates is included. These results are compared to theoretical estimates of the coupling efficiency, which was estimated using the finite difference beam propagation method.
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