A low-loss LNOI edge coupler fabricated on 4-inch wafer with deep ultraviolet lithography was demonstrated. The coupler was fabricated on LNOI with 600 nm thin-film lithium-niobate by 180nm lithography and ICP etch process. The 600nm thin-film lithium-niobate was etched for three times to achieve the coupler with tri-layer structure and narrow taper tips of below 150 nm. The fiber to chip coupling loss is 0.84 dB and 1.3 dB per facet for TE light at 1550 nm, when coupled with lensed fibers, which have 4 μm and 3.5 μm mode field diameter, respectively. Furthermore, the coupling loss is less than 1 dB per facet in the wavelength range between 1520 to 1560 nm.
The responsivity and the bandwidth are both key parameters of a PD but also encounter tradeoff during the device designing due to the thickness of InGaAs layer absorbing light. In this paper, a balanced structure to achieve both high speed and relatively high responsivity is reported. A uni-traveling carrier PD(UTC-PD) structure is taking advantage of the high drift velocity to meet the rather high-speed exhibition. For responsivity enhancing, we apply back reflector beneath the top-illuminated UTC-PD based on micro transfer printing. To further increase the bandwidth of small size PD, we optimize the shape of CPW electrodes of PDs. With our final structure, the UTC-PD exhibits 3dB bandwidth of 100GHz and responsivity of 0.4A/W.
In this paper, we demonstrate a high-Q LNOI microdisk coupling with a silicon nitride (Si3N4) optical waveguide. Its resonance characteristic can be turned by a thermistor on the microdisk resonator. The LNOI microdisk resonator is fabricated by inductively coupled plasma-reactive ion etching (ICP-RIE). Its sidewall is further smoothed by employing chemical mechanical polishing (CMP) to improve the quality factor (Q-factor). The LNOI/Si3N4 heterogeneous integrated resonator shows a Q-factor of 2.58 × 105, and a wavelength tunability of ~14.5 pm/W.
High performance optical transmitter with large bandwidth and high output power is one of the most important device in optical communications, 5th generation wireless systems and microwave photonics. We demonstrated an optical transmitter consisting of an InP-based large bandwidth travelling wave electrode (TWE) Mach-Zehnder electro-optic (EO) modulator hybrid integration with a high power distributed feedback (DFB) laser. The hybrid integration scheme was carefully designed. By using waveguide end-face coupling, the light from the InP-based DFB laser was effectively coupled into the input port of the Mach-Zehnder electro-optic modulator. A bright optical pattern at the output port of the EO modulator was observed. The output power of the integrated transmitter was measured about 0.27 mW with an inject current of 250 mA at room temperature. The transmission performance of high frequency signal was also verified by applying a microwave signal of 33 GHz. The results indicate that the simple and effective solution for hybrid integration of laser and EO modulator has potential applications in high speed optical communications.
The recently emerged photonic integration technology based on thin-film lithium niobate (LN) have been regarded as a very promising candidate for advanced photonic integrated circuits (PICs) due to its attractive nonlinear properties, wide-spread use in electro-optic applications, and etc. Generally, the thin-film LN optical waveguide used in PICs is sub-micrometer scale. Mode mismatch between fiber and sub-micrometer LN waveguide in chip is the main factor of increasing the fiber-to-chip coupling loss and the total insertion loss of LN PICs. Therefore, for practical applications, low-loss mode size converter for coupling between fiber and sub-micrometer LN waveguide is essential. In this paper, an efficient and novel fiber-to-chip mode size converter for thin-film LN PICs was designed and fabricated. The converter consists of a LN nano-taper and a cantilevered SiO2 waveguide. The nano-taper is embedded in the center of SiO2 waveguide. Laterally connected SiO2 cantilever beams are fabricated to provide structural support for the cantilevered SiO2 waveguide. Our work provides an efficient way to realize low-loss fiber-to-chip interface for thin-film LN PICs.
Displacement sensor is one of the most important measuring instruments in many automated systems. We demonstrated an integrated optical displacement sensor based on an asymmetric Mach–Zehnder interferometer chip on a flexible substrate. The sensing chip was made of polymer materials and fabricated by lithography and lift-off techniques. Measured results show that the device has a loss of less than 5 dB and a potential sensitivity of about 0.105 rad/μm with quite a large space for promotion. The sensor has advantages of antielectromagnetic interference, high reliability and stability, simple preparing process, and low cost; it will occupy an important place in displacement sensors.
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