All-Optical Tuning of Light in WSe2-Coated Microfiber
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The tungsten diselenide (WSe2) has attracted considerable interest owing to their versatile applications, such as p-n junctions, transistors, fiber lasers, spintronics, and conversion of solar energy into electricity. We demonstrate all-optical tuning of light in WSe2-coated microfiber (MF) using WSe2’s broad absorption bandwidth and thermo-optic effect. The transmitted optical power (TOP) can be tuned using external incidence pump lasers (405, 532, and 660 nm). The sensitivity under 405-nm pump light excitation is 0.30 dB/mW. A rise/fall time of ~ 15.3/16.9 ms is achieved under 532-nm pump light excitation. Theoretical simulations are performed to investigate the tuning mechanism of TOP. The advantages of this device are easy fabrication, all-optical control, high sensitivity, and fast response. The proposed all-optical tunable device has potential applications in all-optical circuitry, all-optical modulator, and multi-dimensionally tunable optical devices, etc.
KeywordsTungsten diselenide Microfiber All-optical tuning Thermo-optic effect
Distributed feedback laser; SEM
Scanning electron microscopy
Microfiber knot resonator
Effective refractive index
Transition metal dichalcogenides
Transmitted optical power
Optoelectronics, photonics, and microelectronics are important and indispensable in modern telecommunication systems. Photonic devices composed of micro- or nanometer-scale optical components are developed to achieve miniaturized structure, fast response, and high sensitivity . Tunable all-optical devices can be applied in optical communication and signal processing. The light-control-light in fiber has been reported, but it remains a challenge to enhance the performance especially the transmitted optical power (TOP) sensitivity and response time. One of the good ways to improve the performance is using the two-dimensional (2D) transition metal dichalcogenides (TMDs), which have been extensively used in the applications of sensors , optoelectronic devices , transistors , saturable absorbers , and memory devices . All-optical modulation has been realized with graphene-decorated microfiber (MF) , graphene-covered MF , and stereo graphene-MF structures . Tuning of MF devices has been achieved when the MF is connected to different materials, such as liquid crystal , lithium niobate , and polymer . All-optical tunable microfiber knot resonator (MKR) with its top and bottom covered by graphene has been realized . Coating the smooth and lossless surface of the MF with different 2D materials enables light-control-light functionality of MF and MF resonator. All-optical control of light in WS2-coated MKR has been reported with a transmitted power variation rate of ~ 0.4 dB/mW under violet pump and a response time of ~ 0.1 s . All-optical light-control-light functionality of MKR coated with SnS2 has also been realized; the TOP variation rate with respect to the violet light is ~ 0.22 dB/mW and the response time is as fast as ~ 3.2 ms . The TOP of the MF wrapped with reduced graphene oxide was manipulated by the violet pump light with a variation rate of ~ 0.21 dB/mW . All light-control-light properties of MoSe2-coated-MF have also been investigated; the TOP sensitivity is ~ 0.165 dB/mW under violet pump light and the rise time of the transient response is ~ 0.6 s . The TOP sensitivity and response time are important properties of the MF devices. For applications such as all-optical tuning and optical modulation, improvements of the TOP sensitivity and response time are required.
As a typical example of TMDs materials, tungsten diselenide (WSe2) has received great research interest, and it is potentially important building blocks for electronic and optoelectronic. WSe2 has high Seebeck coefficient, ultralow thermal conductivity, and ambipolarity, making it an attractive candidate for flexible electronics [18, 19]. For example, electrical tuning of p-n junctions has been achieved based on ambipolarity of WSe2 . Electrical control of second-harmonic generation in a WSe2 monolayer transistor has been reported using strong exciton charging effects in WSe2 . WSe2 has large absorption coefficient in the visible and near-infrared regions, which has been exploited in conversion of solar energy into electricity . Compared with the sulfide, the selenide is more stable and resistant to oxidation in ambient conditions . In addition, WSe2 provides a high intrinsic hole mobility of 500 cm2 V−1 s−1, which is much higher than that of MoS2 . Using this property of WSe2, high mobility p- and n-type field-effect transistors have been reported with monolayer WSe2 . The monolayer WSe2 shows a direct bandgap with strong photoluminescence . The nonlinear saturable absorption properties of WSe2 have been applied as saturable absorbers in fiber lasers . The WSe2 shows great potential for all-optical control of light in WSe2-based fiber devices.
The optical MFs are optical fiber tapers with a diameter of several to over 10 μm. The MF is manufactured by simple flame-heated taper drawing the fiber under heat. As a result, the biconical taper is formed proving a platform for interaction between the guided light and the surroundings and connection to other fiberized components . The MF profile can be finely tuned to suit different applications through controlling the pulling speed and time in the fabrication process. The MF has advantages of large evanescent fields, configurability, low optical loss, tight optical confinement, and outstanding mechanical flexibility . The tight optical confinement of MF provides a promising approach to small-footprint optical circuits and low-threshold optical nonlinear effect. Strong and rapid interaction between the guided light and the surroundings can be obtained based on strong evanescent fields of MF. This property of MF has been exploited for optical sensing with different configurations, such as fiber gratings inscribed on MF , surface functionalized MF , and Mach–Zehnder interferometer [32, 33]. Strong light-matter interaction provided by MF has also been applied to realize all-optical modulator, ultrafast fiber lasers [34, 35], and tuning and light-control-light functionality.
In this paper, we employ the broad absorption bandwidth and thermo-optic effect of WSe2 to accomplish all-optical tuning of light in WSe2 coated MF. To realize all-optical tuning, the external pump light with wavelengths of 405, 532, and 660 nm are used to irradiate the MF. By employing the interaction between the external pump light and WSe2, effective index change is realized and subsequently induces output power variation. The measured TOP sensitivity is 0.30 dB/mW under 405-nm pump light excitation. The external pump laser-induced temperature change and response of the device are investigated. Theoretical simulations are performed to verify the tuning mechanism of TOP.
Results and Discussion
Comparison of different light-control-light devices
Type of structure
Wavelength of pump light (nm)
Response time (s)
MF + bi–layer grapheme
1 × 10–6
MF + graphene
MKR + graphene
MKR + WS2
MF + reduced graphene oxide
MF + MoSe2
MF + TiO2
SPF + liquid crystals
0.15 at 25 °C
MF + WS2
MF + WSe2
15.3 × 10–3
We have fabricated and demonstrated all-optical tuning of light in WSe2-coated MF based on the interaction between external pump light and WSe2. Through the external irradiation of pump light (405, 532, and 660 nm), WSe2’s broad absorption bandwidth and thermo-optic effect promise effective index change and subsequently output power variation. The sensitivity and fall time of 0.30 dB/mW and 15.3 ms can be obtained, respectively. The tuning mechanism of TOP is investigated with simulations. The performance of the MF covered with WSe2 such as TOP sensitivity and response time can be further improved by using monolayer thin film, modern nanofabrication methods, and optimized MF dimensions. The work is expected to promote WSe2’s realistic applications in all-optical modulator, multi-dimensionally tunable optical devices, etc.
HZ and ZS contributed equally to this work; Conceptualization, HG, HL; Methodology, WQ, WZ, JY; Software, HZ, ZS and HL; Validation, HZ, GP; Formal analysis, HG, JD,YO; Investigation, HZ, ZS; Resources, YL, ZC; Data curation, ZH, EZ, LL and DL; Writing—original draft preparation, JD, HG; Writing—review and editing, HG, XW, JH, and XG; Supervision, JD, HG; Project administration, HG; Funding acquisition, HG. All authors read and approved the final manuscript.
This work was supported by the National Natural Science Foundation of China (Project No. 61505069, 61705087, 61675092, 61705089, 61775084), National Major Project of China (Project No. J–GFZX0205010501.12, GFZX0205010501.24–J), Guangdong Special Support Program (Project No. 2016TQ03X962), Natural Science Foundation of Guangdong Province (Project No. 2015A030306046, 2016A030310098, 2016A030311019), Science and Technology Project of Guangzhou (Project No. 201605030002, 201607010134, 201704030105), and Fundamental Research Funds for the Central Universities ((Project No. 21619409, 21619410).
The authors declare that they have no competing interests.
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