Modal analysis of semiconductor cylinder fibers

Semiconductor cylinder fibers (SCFs) are novel amplifying waveguide structures in which a semiconducting film is interlaid between conventional core and cladding fiber layers. We investigate the modal properties of SCFs by way of a comprehensive model which takes into account the wavelength-dependent refractive indexes of both the core and cladding glass layers and the semiconductor. Our semiconductor model also includes both thin-film effects and carrier-induced changes in the complex refractive index. We show that annular modes which are highly confined to the semiconductor are supported, and we calculate the corresponding modal effective indexes. Finally, we demonstrate that, depending on the pump-induced carrier concentration, a large gain is possible across a broad spectral region.     

Wavelength aware receiver for enhanced 2D OCDMA system performance

A novel receiver for two-dimensional (2D) optical code division multiple access (OCDMA) which utilises the wavelength information of the codes to provide enhanced performance than the regular receiver is presented. The performance improvement increases with the number of wavelengths. Maximal spectral efficiency is doubled, for carrier-hopping prime codes.     

Statistical fluctuations of dopant impurities in ion-implanted bipolar transistor structures and the minimum device dimensions for vlsi system reliability

The minimum dimensions of bipolar transistors with ion implanted impurity profiles for predictable device and system behavior is calculated on the basis of limitations arising from the random positions of the implanted impurities. Doubly-stochastic effects arising from uncertainty in exact implantation parameters are included, and are shown to be of first order importance in the specification of minimum size for a given chip yield. For example, a ± 10% uncertainty in the standard deviation of one of the implants has been found to increase the minimum dimension by approximately a factor of 4. For a chip yield of 99% against this limitation, the minimum emitter size is of the order of 1 ? L ? 5 μm when a straight-forward scaling theory is applied to dimensions and impurity concentrations from present device designs and a parity check on a bit word is applied.     

Source-Matched Spreading Codes for Optical CDMA

Puncturing is studied as a physical layer mechanism for efficiently transmitting datastreams containing bits of unequal priority via wavelength-time optical code-division multiple access. Puncturing increases system capacity, while ensuring that important bits are received with low bit-error rate     

Demonstration of all-optical Mach-Zehnder demultiplexer

Recently, Kang et al. reported the demonstration of an all-optical Mach-Zehnder demultiplexer (see ibid., vol.31, no.9, pp.749-50, 1995). In their paper, Kang et al. drew what we believe is an invalid comparison with work previously published by ourselves (see S. Nakamura et al., Appl. Phys. Lett., vol.65, no.3, pp.283-5, 1994). They described the device proposed by us, the symmetric Mach-Zehnder (SMZ) all-optical switch, as a Mach-Zehnder version of the terahertz optical asymmetric demultiplexer (TOAD). The SMZ and TOAD are in fact different independently-developed devices, each of which has its advantages and disadvantages. A reply by Kang et al. to this comment is included     

Coherent subcarrier fiber-optic communication systems withphase-noise cancellation

A phase-noise-cancelled coherent subcarrier fiber-optic communication system that uses integrated-optic Mach-Zehnder waveguide modulators for frequency-pair encoding is introduced. Optical double-sideband suppressed-carrier signals with the same random phase noise and information encoded in the frequency separation of the two sidebands are generated by properly biasing the modulator. Phase noise is eliminated at the receiver by a nonlinear operation on the two sidebands. System performance analysis with numerical examples, taking into account the modulation index and laser normalized linewidth, is presented     

Fabrication of precision fiber-optic time delays with in situ monitoring for subpicosecond accuracy

We have developed a technique to produce precise fiber-optic time delays with subpicosecond accuracy and <0.1-dB loss by heating and stretching optical fiber in a fusion splicer. A fiber Mach-Zehnder interferometer allows in situ measurement of these precise delays using a simple alignment process and requiring only a weak optical signal. To demonstrate this capability, we assembled a six-stage feed-forward delay line that can be used to generate 64 optical pulses with 9.5 +/- 0.8-ps pulse spacings and 4.8-dB total insertion loss.     

Enhanced Trion Emission in Monolayer MoSe2 by Constructing a Type-I Van Der Waals Heterostructure

Trions, quasi-particles consisting of two electrons combined with one hole or of two holes with one electron, have recently been observed in transition metal dichalcogenides (TMDCs) and drawn increasing attention due to potential applications of these materials in light-emitting diodes, valleytronic devices as well as for being a testbed for understanding many-body phenomena. Therefore, it is important to enhance the trion emission and its stability. In this study, a MoSe₂/FePS₃ van der Waals heterostructure (vdWH) with type-I band alignment is constructed, which allows for carriers injection from FePS₃ to MoSe₂. At low temperatures, the neutral exciton (X⁰) emission in this vdWH is almost completely suppressed. The I_Trion/I_x0 intensity ratio increases from 0.44 in a single MoSe₂ monolayer to 20 in this heterostructure with the trion charging state changing from negative in the monolayer to positive in the heterostructure. The optical pumping with circularly polarized light shows a 14% polarization for the trion emission in MoSe₂/FePS₃. Moreover, forming such type-I vdWH also gives rise to a 20-fold enhancement of the room temperature photoluminescence from monolayer MoSe₂. These results demonstrate a novel approach to convert excitons to trions in monolayer 2D TMDCs via interlayer doping effect using type-I band alignment in vdWH.     

Optical spectral bistability in a semiconductor fiber ring laserthrough gain saturation in an SOA

We demonstrate the operation of optical bistability in a widely tunable semiconductor fiber ring laser, using a semiconductor optical amplifier (SOA). The laser can be operated in two bistable states: the spectrum of the first state has one main lasing peak with very narrow linewidth, and the second state has simultaneous oscillation of two main peaks at different wavelengths. The two bistable states can be switched to each other using either electrical or optical methods. We further explain the bistable operation using the theory of two-mode competition through gain saturation in the SOA