Md. Arafat Hossain

Air-structured optical fiber drawn from a 3D-printed preform.

A structured optical fiber is drawn from a 3D-printed structured preform. Preforms containing a single ring of holes around the core are fabricated using filament made from a modified butadiene polymer. More broadly, 3D printers capable of processing soft glasses, silica, and other materials are likely to come on line in the not-so-distant future. 3D printing of optical preforms signals a new milestone in optical fiber manufacture.

Optical fiber smartphone spectrometer.

An optical fiber-based smartphone spectrometer incorporating an endoscopic fiber bundle is demonstrated. The endoscope allows transmission of the smartphone camera LED light to a sample, removing complications from varying background illumination. The reflected spectra collected from a surface or interface is dispersed onto the camera CMOS using a reflecting diffraction grating. A spectral resolution as low as δλ∼2.0  nm over a bandwidth of Δλ∼250  nm is obtained using a slit width, ωslit=0.7  mm. The instrument has vast potential in a number of industrial applications including agricultural produce analysis. Spectral analysis of apples shows straightforward measurement of the pigments anthocyanins, carotenoid, and chlorophyll, all of which decrease with increasing storage time.

Step-index optical fiber drawn from 3D printed preforms

Optical fiber is drawn from a dual-head 3D printer fabricated preform made of two optically transparent plastics with a high-index core (NA∼0.25, V>60). The asymmetry observed in the fiber arises from asymmetry in the 3D printing process. The highly multimode optical fiber has losses measured by cut-back as low as α∼0.44  dB/cm in the near IR.

Smartphone laser beam spatial profiler.

A simple, low-cost, portable, smartphone-based laser beam profiler for characterizing laser beam profiles is reported. The beam profiler utilizes a phosphor silica glass plate to convert UV light into visible (green) light that can be directly imaged onto an existing smartphone CMOS chip and analyzed using a customized app. 3D printing enables the ready fabrication of the instrument package. The beams diameter, shape, divergence, beam quality factor, and output power are measured for two UV lasers: a CW 244 nm frequency-doubled Ar ion laser and a pulsed 193 nm ArF exciplex laser. The availability of specialized phosphor converters can extend the instrument from the UV to the near infrared and beyond, and the smartphone platform extends the Internet of Things to map laser beam profiles simultaneously in different locations.

Drawing optical fibers from three-dimensional printers

The temperature distribution within extrusion nozzles of three low-cost desktop 3D printers is characterized using fiber Bragg gratings (FBGs) to assess their compatibility as micro-furnaces for optical fiber and taper production. These profiles show remarkably consistent distributions suitable for direct drawing of optical fiber. As proof of principle, coreless optical fibers (φ=30  μm) made from fluorinated acrylonitrile butadiene styrene (ABS) and polyethylene terephthalate glycol (PETG) are drawn. Cutback measurements demonstrate propagation losses as low as α=0.26  dB/cm, which are comparable with standard optical fiber losses with some room for improvement. This work points toward direct optical fiber manufacture of any material from 3D printers.

Bend and twist intramolecular charge transfer and emission for selective metal ion sensing

Zn2+ and Cu2+ complexation of cyclam-triazolyl-naphthalimide fluoro-ionophores lead to increased and decreased fluorescence respectively. The differences between the two metals are accounted for by their Lewis acid and base properties. This difference means the system can be described as an optical diode with characteristics that suggest measurable differences in fluorescence rise and decay times for the mechanical suppression of bend- and/or twist-induced emissions from intramolecular charge transfer. Different fluorescence evolution profiles are observed offering a new way of distinguishing metal ions for applications in biomedical and environmental sensing.

Portable smartphone optical fibre spectrometer

A low cost, optical fibre based spectrometer has been developed on a smartphone platform for field-portable spectral analysis. Light of visible wavelength is collected using a multimode optical fibre and diffracted by a low cost nanoimprinted diffraction grating. A measurement range over 300 nm span (λ = 400 to 700 nm) is obtained using the smartphone CMOS chip. The spectral resolution is Δλ ~ 0.42 nm/screen pixel. A customized Android application processed the spectra on the same platform and shares with other devices. The results compare well with commercially available spectrometer.

Absorption and fluorescence spectroscopy on a smartphone

A self-powered smartphone-based field-portable “dual” spectrometer has been developed for both absorption and fluorescence measurements. The smartphone’s existing flash LED has sufficient optical irradiance to undertake absorption measurements within a 3D-printed case containing a low cost nano-imprinted polymer diffraction grating. A UV (λex ~ 370 nm) and VIS (λex ~ 450 nm) LED are wired into the circuit of the flash LED to provide an excitation source for fluorescence measurements. Using a customized app on the smartphone, measurements of absorption and fluorescence spectra are demonstrated using pH-sensitive and Zn2+-responsive probes. Detection over a 300 nm span with 0.42 nm/pixel spectral resolution is demonstrated. Despite the low cost and small size of the portable spectrometer, the results compare well with bench top instruments.

Hand-held optical fiber smartphone spectrometer for classification of vegetable oils

An optical-fiber-based low-cost, hand-held smartphone spectrometer is demonstrated for differentiating vegetable oils. The visible fluorescence spectrum of extra virgin olive oil is found to be significantly different from other oils, thus making forensic identification straightforward.

Light-induced Au surface modification

We show that the surface properties of Au thin films on a glass prism, typical of the Krestchsmann setup for SPR generation, can be modified or tuned with optical exposure. The wetting properties of the film were investigated by measuring contact angles of water drops at room temperature T=23 °C. These contact angle change with optical irradiation from below the film. This change corresponds to a maximum contact angle reduction of Δθc ∼ 30° when a surface plasmon resonance (SPR) is excited. The variation in contact angle during drop evaporation is evaluated under different irradiation conditions.