Seminars by Ph.D students

DateNameAbstract

06.10.2017

Amar Ghar

Title: Femtosecond laser based microstructures fabrication for development of miniaturized Photonic devices

In the past few decades, significant effort has been put forth in miniaturization of different optical devices identified as Lab-on-chip systems. Recently, Optofluidics, the merger of optics and microfluidics, appears to be an ideal platform for realizing fully integrated optical sensors. The advent of femtosecond laser micromachining for fabrication on transparent material has opened up new avenues for development of optofluidic lab-on-chip systems. Femtosecond micromachining can also be used for direct fabrication of high speed optical modulator by using electro optic materials. Present seminar going to discuss basic of femtosecond laser micromachining in order to fabricate such lab on chip based devices including some primary results obtained in the lab.

20.10.2017

Arpita Halder

Title: Graded-index anti-reflective surfaces for efficiency enhancement of silicon-based optoelectronic devices

For a good anti-reflection (AR) effect, the difference in refractive index at an interface between two materials has to be gradual as in the case of graded refractive index (GRIN) optics. Bioinspired insect-eye variants that contain micro- or nano-architectures are widely studied AR structures. These types of structures are important mainly because their effective refractive index varies gradually from air to the device material. Inexpensive fabrication of textured PDMS films and the study of their effect on anti-reflection is the highlight of this presentation. Signature of the GRIN profile in patterned PDMS film will be discussed. Nanopatterned PDMS films containing inverted structures of the top layer of self-assembled colloidal photonic crystals are found to possess very good AR properties throughout the visible range of solar spectrum. Additionally, their AR properties have shown a higher degree of improvement at larger incident angles. The extent of anti-reflection and improvement in efficiency when these patterned films are laminated on a bare solar cell are found to increase.

03.11.2017

Arpita Sinha Roy

Title: Low Jitter Measurement of Laser Line-width using Brilluoin Induced Self-Heterodyne Method

Laser phase noise is a detrimental effect in many applications such as coherent communication, coherent optical orthogonal frequency-division-multiplexing (CO-OFDM) receivers, interferometric fiber optic sensors. It occurs due to spontaneous emission and carrier density fluctuation in semiconductor laser. Laser phase noise depends on the linewidth of the laser. Commonly used methods for the measurement of linewidth are self homodyne and heterodyne. The former measures linewidth by beating the laser signal with the delayed version of itself at zero frequency. The self-heterodyne method is similar to self-homodyne method except that the beat signal is shifted to an intermediate frequency greater than zero frequency by modulating the laser. Self heterodyne method is considered better than self homodyne method because it eliminates the problem of noise at zero frequency of electrical spectrum analyzer. However, self heterodyne method is unable to reduce the jitter. Stimulated Brilluoin scattering (SBS) which is one of the non linear effect, can be used to reduce that jitter effect. In SBS induced self heterodyne method, SBS drives the optical frequency beating of the signal under test, modulated at low frequency. We mathematically analyse and experimentally measure the linewidth of a DFB laser using Brilluoin induced self-heterodyne method.

10.11.2017

Govind Kumar

Title: Control of emission by Photonic crystal based optical microcavity

Photonic crystals have interesting characteristics that enable light control and manipulation. In this seminar, I will discuss about the optical properties of photonic crystals and the reasons for control of emission in a photonic crystal environment. Then, I will present the design, fabrication, experimental study and modelling results of a photonic crystal heterostructure cavity for lasing application. In this cavity design, the effect of overlap of defect mode with the band edge of the colloidal photonic crystal aids in achieving enhancement and spectral narrowing in optical emission.

17.11.2017

Gagandeep Kaur

Title: Photonic crystal waveguides and controlled tunneling across such waveguides

Photonic crystals can be used to mold the flow of light. One can create a series of defects and guide light from one location to another through these defect channels. These defect channels act as waveguides. Complete channel drop tunneling can be achieved across two such waveguides when placed parallel, through a resonator system. In this talk, I will discuss few properties of photonic crystal waveguides and how the symmetry properties of resonant states help in achieving complete transfer between two waveguides.

24.11.2017

Monalisa Goswami

Title: Fluorescence lifetime imaging (FLIM): Basic concepts and applications

Fluorescence lifetime imaging is a key fluorescence microscopy technique which is used to probe the details of molecular dynamics and molecular environment and how they interact with their surrounding at a temporal resolution of nanoseconds or less. This technique is advantageous over intensity and wavelength based technique because it is independent of fluorophore concentrations and excitation intensity and can record multiple fluorophores despite them having overlapping spectra. FLIM has many application such as identification of FRET to study protein interactions and conformational changes, imaging viscosity, temperature, pH, refractive index and ion and oxygen concentrations, but I will be mainly discussing imaging tissue autofluorescence.

8.12.2017

Sreeprasad A.

Title: Application of windowed Fourier transform in quantitative phase imaging

Reliable measurement of surface profile of a sample is an important problem in areas such as non-destructive testing, shape sensing and material inspection. The phase in optical profilometry is much more sensitive to the specimen structure than its amplitude. So measuring phase is an important problem in optics. Interferometric methods are mostly used to measure phase by recording fringe patterns. Demodulation of fringe patterns is done using signal processing tools. In this talk, I would be discussing one such demodulation technique to obtain the phase information from the recorded fringe pattern.

More to come