Ningren Han

Miniature, sub-nanometer resolution Talbot spectrometer

Miniaturization of optical spectrometers has a significant practical value as it can enable compact, affordable spectroscopic systems for chemical and biological sensing applications. For many applications, the spectrometer must gather light from sources that span a wide range of emission angles and wavelengths. Here, we report a lens-free spectrometer that is simultaneously compact (<0.6  cm3), of high resolution (<1  nm), and has a clear aperture (of 10×10  mm). The wavelength-scale pattern in the dispersive element strongly diffracts the input light to produce non-paraxial mid-field diffraction patterns that are then recorded using an optimally matched image sensor and processed to reconstruct the spectrum.

Effective mode selector for tunable terahertz wire lasers

We demonstrate an effective mode selector design that enables a terahertz quantum cascade wire laser to have a robust single-mode operation at frequencies much lower than the gain peak. This is achieved by selectively guiding the undesired modes into a lossy session while keeping the desired lasing mode largely unperturbed. The large mode discrimination obtained by this mode selector is necessary to further extend the tuning range to the lower half of the gain curve. Additionally, the connectors of this mode selector conveniently provide electrical bias to the wire lasers without degrading the lasing performance.

Non-paraxial Talbot Effect for Building Compact Spectrometers

We explore the possibility of utilizing mid-field Talbot effect under non-paraxial diffraction for building compact spectrometers. Our experiment demonstrates nanometer resolution with a bandwidth over at least 100 nm for a Talbot spectrometer built using a standard 1-D transmission grating and a commercial CMOS imager. The effect of angular spread at the grating surface on spectral resolution is also investigated theoretically.