The self-mixing interferometer (SMI) is a sort of optical radar capable of detecting extremely weak optical returns from a remotely located target and measuring the amplitude and phase of it. Different from the traditional radar based on launching a pulse to the target, the SMI uses a continuous coherent beam and operates as a coherent detector. Thanks to this feature, SMI has an unparalleled sensitivity to very small returns (down to 10-8 of the launched power) and can measure the phase – that is the optical pathlength down the target and back-with resolution of milliradian, that translates into optical pathlength attaining fractions of nanometers.

Optical isolators are nonreciprocal devices that allow light to pass in one direction but block light in the opposite direction. They are typically used to prevent unwanted back reflections into optical oscillators such as lasers, and to suppress crosstalk between different optical devices. Nonreciprocal optical elements such as circulators and isolators are essential for the realization of integrated optical circuits. The design of nonreciprocal components requires breaking the time reversal symmetry. This can be achieved through the use of nonlinear materials, materials with time-dependent properties, and magneto-optical materials. However, since the magneto-optical response of natural materials is weak at optical wavelengths, designing nonreciprocal devices that are based on magneto-optical materials results in bulky structures that are much larger than the wavelength. The advent of silicon photonics and photonic crystals has reduced the size of nonreciprocal optical components down to wavelength scale.

The research group led by Prof. Jingliang He, Baitao Zhang from Shandong University co-operated with the group of Prof. Haiping Xia from Ningbo University, have designed and fabricated high-quality Er,Pr:YLF crystal and obtained high-power and high-efficiency 2.7 µm mid-infrared (MIR) radiation. This research result was published in Chinese Optics Letters, Vol. 19, No. 8 (Haiping Xia, Jingliang He, and Baitao Zhang et al, Spectroscopic and laser properties of Er3+, Pr3+ co-doped LiYF4 crystal).

Ultrafast laser has the advantages of flexible design, short pulse width and high peak power, which has a very broad application prospect in the fields of micro-/nano-processing, biomedicine, national defense and military. In order to achieve ultrafast laser output, mode-locking technology is generally needed. To this end, researchers have proposed a variety of schemes. In 2003, Karen Intrachat and J. Nathan Kutz, Department of Applied Mathematics of University of Washington in USA, predicted theoretically that long-period fiber grating has pulse-shaping function, which can be used to construct ultrafast fiber lasers. In 2008, Abdullah S. Karar, Tom Smy and Alan L. Steele, department of electronics of Carlton University in Canada, conducted theoretical research on ultrafast fiber lasers with long-period fiber gratings. They found that this kind of laser can produce a variety of soliton pulses. However, there is a lack of experimental research on (ultra)-long-period fiber gratings as ultrafast optical devices by far.