dB Optical Loss Research Articles

Efficient optical phase modulator based on an III–V metal-oxide-semiconductor structure with a doped graphene transparent electrode

We propose a III–V metal-oxide-semiconductor (MOS) optical modulator with a graphene gate electrode along with the analysis of the modulation properties. With p-type doped graphene used as a transparent gate electrode, we can fully utilize the electron-induced refractive index change in an n-type InGaAsP waveguide with the reduction of the hole-induced optical absorption observed in a III–V/Si hybrid MOS optical modulator. Numerical analysis displays that up to the phase modulation efficiency of 0.82 V·cm and 0.22 dB optical loss for π phase shift can be achieved when the gate oxide thickness is 100 nm. With the elimination of the unnecessary parasitic capacitance found in the overlapping of graphene on the slab part of the waveguide, in conjunction with the high electron mobility in InGaAsP, the device also enables a modulation bandwidth of greater than 200 GHz.

Low-loss graphene-based optical phase modulator operating at mid-infrared wavelength

We numerically analyzed a graphene optical phase modulator with a Si or Ge waveguide operating at a mid-infrared wavelength. We found that the change in operating wavelength from a near-infrared wavelength to a mid-infrared wavelength enables phase modulation with a significantly small optical loss at a realistic bias voltage. We analyzed the wavelength dependence of the modulation characteristics in the wavelength range from 1.55 to 10 µm, which revealed that the minimum insertion of 4 dB with 1 dB optical loss change during phase modulation can be achieved at a wavelength of 4 µm. The phase modulation efficiency was expected to be 0.045 V·cm. Thus, we can obtain a practical graphene optical phase modulator at a wavelength of 4 µm, which will be useful for optical communication and sensing.

High-speed, low-loss silicon Mach–Zehnder modulators with doping optimization

We demonstrate a high-speed silicon Mach-Zehnder modulator (MZM) with low insertion loss, based on the carrier depletion effect in a lateral PN junction. A 1.9 dB on-chip insertion loss and a VπLπ < 2 V·cm were achieved in an MZM with a 750 μm-long phase shifter by properly choosing the doping concentration and precisely locating the junction. High-speed modulations up to 45-60 Gbit/s have been demonstrated with an additional 1.6 dB optical loss, indicating a total insertion loss of 3.5 dB. A high extinction ratio of 7.5 dB was also realized at the bit rate of 50 Gbit/s with an acceptable insertion loss of 6.5 dB.

Broadband 2 × 2 free-space optical switch using electronically controlled liquid lenses

To the best of our knowledge, proposed is the first liquid lens technology-based 2 × 2 free-space optical switch using a pair of Electronically Controlled Variable Focus Lenses (ECVFLs). By independently controlling the focal lengths of two cascaded liquid ECVFLs, the two input optical beams are spatially adjusted to couple to their respective output beam ports. At 633-nm, the experimental switch demonstrates 26.3 dB crosstalk, 23.0 dB within-channel isolation, 1.1 dB optical loss, and 0.2 dB Polarization Dependent Loss (PDL). A 0.2 dB Wavelength Dependent Loss (WDL) is measured over 633-nm and 514-nm wavelengths. A 1 × 2 optical-fiber coupled switch version is also tested. The proposed switch can be useful in free-space laser systems as well as fiber-based modules.

A Poly(3,4‐alkylenedioxythiophene) Electrochromic Variable Optical Attenuator with Near‐Infrared Reflectivity Tuned Independently of the Visible Region

AbstractDisubstituted poly(3,4‐propylenedioxythiophene)s (PProDOTs) exhibit large electrochromic contrasts in the near infrared (NIR) while showing essentially no color change in the visible region when incorporated into a reflective device platform. The source of this is attributed to a conductive front that propagates through the insulating polymer film, extending from the polymer/electrode interface to the top of the polymer film. A utility of the large contrasts seen in the NIR region is demonstrated with application of the device as an electrochromic variable optical attenuator modulating fiber‐optic signals for optical telecommunications. With bis(ethylhexyloxy)‐substituted PProDOT as the active electrochromic polymer in the device, an optical attenuation of 11 dB at the telecommunications wavelengths of 1.31 and 1.55 μm is achieved with only a 0.1–0.2 dB optical loss in the bleached state. Other favorable properties include optical memory in the absorbing state, switching speeds of under 1 s, a low operating voltage of ±1.2 V, and an improved processability that allows spray‐casting from organic solvents.

First demonstration of multihop all-optical packet switching

Experimenta1 demonstration of all-optical multihop routing through 2/spl times/2 photonic packet switches is described for the first time. As each packet traverses a switch, the functions of routing, contention resolution, header regeneration, and header reinsertion are performed. Three all-optical hops are demonstrated for the payload without optical amplification. The number of hops is currently limited by /spl minus/13 dB optical loss per switch pass. Each packet is coded using six discrete optical wavelengths, making this the widest bit-parallel photonic switch reported to date. >

Compact, wideband coherent receiver module with 78% external quantum efficiency

A compact, low-profile, front-end module consisting of a fused fibre coupler and a twin pin photodiode for balanced heterodyne receivers is described. Special packaging and mounting techniques ensure excellent performance from a module only 7 mm high. Figures of merit include a 16.8 GHz wideband response, an extremely low 0.8 dB optical loss, and an overall external quantum efficiency of 78%