Mona Mayeh

Quantum dots as self-referenced optical fibre temperature probes for luminescent chemical sensors

The use of semiconductor nano-particles as temperature probes in luminescence chemical sensing applications is addressed. Temperature changes the intensity, the peak wavelength and the spectral width of the quantum dots luminescent emission in a linear and reversible way. Results are presented that show the feasibility of implementing a self-referenced intensity-based sensor to perform temperature measurements independent of the optical power level in the sensing system. A resolution of 0.3 °C was achieved. In addition, it is demonstrated that self-referenced temperature measurements at multiple points could be performed using reflection or transmission based optical fibre configurations.

Applications of quantum dots in optical fiber luminescent oxygen sensors

The potential applications of luminescent semiconductor nanocrystals to optical oxygen sensing are explored. The suitability of quantum dots to provide a reference signal in luminescence-based chemical sensors is addressed. A CdSe-ZnS nanocrystal, with an emission peak at 520 nm, is used to provide a reference signal. Measurements of oxygen concentration, which are based on the dynamic quenching of the luminescence of a ruthenium complex, are performed. Both the dye and the nanocrystal are immobilized in a solgel matrix and are excited by a blue LED. Experimental results show that the ratio between the reference and the sensor signals is highly insensitive to fluctuations of the excitation optical power. The use of CdTe, near-infrared quantum dots with an emission wavelength of 680 nm, in combination with a ruthenium complex to provide a new mechanism for oxygen sensing, is investigated. The possibility of creating oxygen sensitivity in different spectral regions is demonstrated. The results obtained clearly show that this technique can be applied to develop a wavelength division multiplexed system of oxygen sensors.

A Compact Laparoscopic Probe for Optical Stimulation of the Prostate Nerves

The cavernous nerves (CN) course along the prostate surface and are responsible for sexual function. Optical nerve stimulation (ONS) has recently been tested as a potential alternative to electrical nerve stimulation for identifying and preserving these delicate nerves during prostate cancer surgery. However, the optimal range of laser parameters for safe and consistent laser nerve stimulation is relatively narrow; low-level irradiation may not stimulate the nerve, while high-level irradiation may result in thermal damage to the nerve and loss of erectile function. The objective of this study is to design, build, and provide preliminary data on testing of a laparoscopic probe capable of delivering a collimated, flat-top spatial beam profile to the nerve surface for uniform, safe, and reproducible irradiation of the nerve. Chemical etching of the distal fiber optic tip in combination with an aspheric lens resulted in a 3.4-mm-OD laparoscopic probe capable of delivering a collimated 1-mm-diameter, flat-top laser beam over a working distance of about 20 mm. Successful ONS using this probe was observed in a rat prostate model, in vivo. Upon further testing, this probe may be useful for identifying and preserving the CN during laparoscopic nerve-sparing prostate cancer surgery.

Design and Fabrication of Slotted Multimode Interference Devices for Chemical and Biological Sensing

We present optical sensors based on slotted multimode interference waveguides. The sensor can be tuned to highest sensitivity in the refractive index ranges necessary to detect protein-based molecules or other water-soluble chemical or biological materials. The material of choice is low-loss silicon oxynitride (SiON) which is highly stable to the reactivity with biological agents and processing chemicals. Sensors made with this technology are suited to high volume manufacturing.

Tailoring Gaussian Laser Beam Shape Through Controlled Etching of Single-Mode and Multimode Fibers: Simulation and Experimental Studies

A new class of all-fiber beam shaping devices has been realized by inverse etching the end face of single-mode and multimode fibers to form a concave cone tip. Concave tip fiber can convert a Gaussian beam profile to a flat top beam profile with a uniform intensity distribution. A flat top beam with intensity variation of approximately 5% and flat top diameter to spot diameter ratio of 67% has been achieved. This device can also change the beam shape from a Gaussian to a donut by moving the observation plane. A flat top multimode fiber beam delivery is attractive for applications which require high power and uniform intensity distribution. In single-mode fiber, concave tips could be used to reduce the beam spot size diameter, enabling efficient light coupling from a single-mode fiber to an integrated optical waveguide.

Self-referenced intensity based optical fiber temperature probes for luminescent chemical sensors using quantum dots

The use of semiconductor nano-particles as temperature probes in luminescence chemical sensing applications is addressed. Temperature changes the intensity, the peak wavelength and the spectral width of the quantum dots luminescent emission in a linear and reversible way. Results are presented that show the feasibility of implementing a self-referenced intensity based sensor to perform temperature measurements independent of the optical power level in the sensing system. Additionally, it is demonstrated that self-referenced temperature measurements in multiple points could be performed using reflection or transmission based optical fiber configurations.

Intensity based luminescent optical fiber oxygen sensor using quantum dots

The suitability of semiconductor nanoparticles to provide a reference signal in luminescence based chemical sensors is addressed. A CdSe-ZnS nanocrystal, with emission peak at 520 nm is used to provide a reference signal. Measurements of oxygen concentration, which are based on the dynamic quenching of the luminescence of a Ruthenium complex, are performed. Both dye and the nanocrystal are immobilized in a sol-gel matrix and are excited by a blue LED. Results are presented showing that the ratio between the reference and the sensor signals is highly insensitive to fluctuations of the excitation optical power. Preliminary results show that nanocrystals could be used to measure temperature and provide a reference signal.

Design and optimization of slotted multimode interference devices for chemical and biochemical sensing

The major achievements in the field of optical sensors in the past two decades have remained mostly limited to the laboratory demonstrations. There are very few examples of optical sensors, which have been reduced to practice, and have established themselves in major markets. The main bottleneck in this field is the issue of manufacturability. In this paper we present optical sensors based on slotted multimode interference waveguides. We show that the sensitivity increases proportionally to the number of slots. The sensor can be tuned to highest sensitivity in the refractive index ranges necessary to detect protein-based molecules or other water-soluble chemical or biological materials. The material of choice is a sol-gel (ORMOCER) matrix that after completion of the process becomes mostly glass and it is highly stable. Sensors made with this technology are suited to high volume manufacturing.

An all-fiber beam shaping using multimode fiber

A new beam shaping technique has been developed by inverse etching the end face of a multimode fiber to form a concave cone tip. Concave tip fiber can convert a Gaussian beam profile to a flat top beam with a uniform intensity distribution. A flat top beam with intensity variation of approximately 5% and flat top diameter to spot diameter ratio of 67% has been achieved. With this technique one can also change the beam shape from a Gaussian to a donut by moving the observation plane. A flat top multimode fiber beam delivery has been tested for stimulation of prostate nerves.

Incorporation of fiber optic beam shaping into a laparoscopic probe for laser stimulation of the cavernous nerves

The cavernous nerves (CN) course along the prostate surface and are responsible for erectile function. Improved identification and preservation of the CNs is critical to maintaining sexual potency after prostate cancer surgery. Noncontact optical nerve stimulation (ONS) of the CNs was recently demonstrated in a rat model, in vivo, as a potential alternative to electrical nerve stimulation (ENS) for identification of the CNs during prostate surgery. However, the therapeutic window for ONS is narrow, so optimal design of the fiber optic delivery system is critical for safe, reproducible stimulation. This study describes modeling, assembly, and testing of an ONS probe for delivering a small, collimated, flat-top laser beam for uniform CN stimulation. A direct comparison of the magnitude and response time of the intracavernosal pressure (ICP) for both Gaussian and flat-top spatial beam profiles was performed. Thulium fiber laser radiation (λ=1870 nm) was delivered through a 200-μm fiber, with distal fiber tip chemically etched to convert a Gaussian to flat-top beam profile. The laser beam was collimated to a 1-mm-diameter spot using an aspheric lens. Computer simulations of light propagation were used to optimize the probe design. The 10-Fr (3.4-mm-OD) laparoscopic probe provided a constant radiant exposure at the nerve surface. The probe was tested in four rats, in vivo. ONS of the CNs was performed with a 1-mm-diameter spot, 5- ms pulse duration, and pulse rate of 20 Hz for a duration of 15-30 s. The flat-top laser beam profile consistently produced a faster and higher ICP response at a lower radiant exposure than the Gaussian beam profile due, in part, to easier alignment of the more uniform beam with nerve. With further development, ONS may be used as a diagnostic tool for identification of the CNs during laparoscopic and robotic nerve-sparing prostate cancer surgery.