Gold Enhanced Graphene-Based Photodetector on Optical Fiber with Ultrasensitivity over Near-Infrared Bands.

Graphene has been widely used in photodetectors; however its photoresponsivity is limited due to the intrinsic low absorption of graphene. To enhance the graphene absorption, a waveguide structure with an extended interaction length and plasmonic resonance with light field enhancement are often employed. However, the operation bandwidth is narrowed when this happens. Here, a novel graphene-based all-fiber photodetector (AFPD) was demonstrated with ultrahigh responsivity over a full near-infrared band. The AFPD benefits from the gold-enhanced absorption when an interdigitated Au electrode is fabricated onto a Graphene-PMMA film covered over a side-polished fiber (SFP). Interestingly, the AFPD shows a photoresponsivity of >1 × 104 A/W and an external quantum efficiency of >4.6 × 106% over a broadband region of 980-1620 nm. The proposed device provides a simple, low-cost, efficient, and robust way to detect optical fiber signals with intriguing capabilities in terms of distributed photodetection and on-line power monitoring, which is highly desirable for a fiber-optic communication system.

A broadband all-fiber integrated graphene photodetector with CNT-enhanced responsivity.

Carbon-based nanomaterials such as carbon nanotubes (CNTs) and graphene have great potential for high-performance all-carbon photodetectors due to their unique optical and electronic properties. Here, we assemble a hybrid CNT/graphene film prepared by depositing CNTs on a single layer graphene with a side-polished optical fiber to achieve a novel all-fiber integrated photodetector. Because CNTs strongly enhanced the interaction between graphene and the fiber mode, the photodetector shows an extra-high photoresponsivity over the visible and infrared region. Especially at 1550 nm, the photoresponsivity is found to be ∼1.48 × 105 A W-1, which is 6.5 times larger than those of photodetectors without CNTs. These findings provide a highly versatile, reproducible, and low-cost platform to integrate novel zero-, one-, and two-dimensional materials into optical fibers and deliver more sophisticated functionalities.

A broadband and low-power light-control-light effect in a fiber-optic nano-optomechanical system.

The coupling of the optical and mechanical degrees of freedom using optical force in nano-devices offers a novel mechanism to implement all-optical signal processing. However, the ultra-weak optical force requires a high pump optical power to realize all-optical processing. For such devices, it is still challenging to lower the pump power and simultaneously broaden the bandwidth of the signal light under processing. In this work, a simple and cost-effective optomechanical scheme was demonstrated that was capable of achieving a broadband (208 nm) and micro-Watt (∼624.13 µW) light-control-light effect driven by a relatively weak optical force (∼3 pN). In the scheme, a tapered nanofiber (TNF) was evanescently coupled with a substrate, allowing the pump light guided in the TNF to generate a strong transverse optical force for the light-control-light effect. Additionally, thanks to the low stiffness (5.44 fN nm-1) of the TNF, the light-control-light scheme also provided a simple method to measure the static weak optical force with a minimum detectable optical force down to 380.8 fN. The results establish TNF as a cost-effective scheme to break the limitation of the modulation wavelength bandwidth (MWB) at a low pump power and show that the TNF-optic optomechanical system can be well described as a harmonic oscillator.

Quartz-enhanced photoacoustic spectroscopy employing pilot line manufactured custom tuning forks.

Pilot line manufactured custom quartz tuning forks (QTFs) with a resonance frequency of 28 kHz and a Q value of >30, 000 in a vacuum and ∼ 7500 in the air, were designed and produced for trace gas sensing based on quartz enhanced photoacoustic spectroscopy (QEPAS). The pilot line was able to produce hundreds of low-frequency custom QTFs with small frequency shift < 10 ppm, benefiting the detecting of molecules with slow vibrational-translational (V-T) relaxation rates. An Au film with a thickness of 600 nm were deposited on both sides of QTF to enhance the piezoelectric charge collection efficiency and reduce the environmental electromagnetic noise. The laser focus position and modulation depth were optimized. With an integration time of 84 s, a normalized noise equivalent absorption (NNEA) coefficient of 1.7 × 10-8 cm-1∙W∙Hz-1/2 was achieved which is ∼10 times higher than a commercially available QTF with a resonance frequency of 32 kHz.

Enhanced optical sensitivity of molybdenum diselenide (MoSe2) coated side polished fiber for humidity sensing.

In this paper, a side-polished fiber (SPF) coated with molybdenum diselenide (MoSe2) is proposed, and its characteristic of relative humidity (RH) sensing is investigated. It is found in the experiment that an enhancement in RH sensitivity (0.321 dB/%RH) can be achieved in a very wide RH range of 32%RH to 73%RH for the proposed MoSe2 coated SPF (MoSe2CSPF). It is also shown that the MoSe2CSPF has a rapid response of 1s and recovery time of 4s, which makes the sensor capable of monitoring human breath. The experimental results suggest MoSe2 has a promising potential in photonics applications such as all-fiber optic humidity sensing networks.

Reduced graphene oxide wrapped on microfiber and its light-control-light characteristics.

Reduced graphene oxide (rGO) sheet wrapped on the tapered region of microfiber is demonstrated to enhance the interaction between rGO and strong evanescent field of optical fiber. The 405 nm and 980 nm lasers are employed to illuminate the rGO to investigate the response characteristics of the optical transmitted power (λ = 1550 nm) in the MF. The transmitted optical power of the MF with rGO changes with ~1.7 dB relative variation when the violet light is ranging from 0 mW to 12 mW (~0.21dB/mW) in the outside-pumped experiment. And in the inside-pumped experiment, the change of the 980 nm laser power from 0 mW to 156.5 mW makes ~6 dB relative variation power of the transmitted optical powers of the MF with rGO. These results indicate the optical transmitted power of the MF with wrapped rGO can be manipulated by the 405 and 980 nm light (order of mW), which signifies the device can potentially be applied as all optically and versatilely controllable devices.