Degradation of modulation and noise characteristics of semiconductor lasers after propagation in optical fiber due to a phase-shift induced by stimulated Brillouin scattering

Here we demonstrate theoretically that stimulated Brillouin scattering (SBS) can induce a phase shift of the optical carrier relative to its sidebands due to the waveguiding effect of the optical fiber on the acoustic wave. This causes conversion of frequency modulation to intensity modulation, which results in an increase in the relative intensity noise and degradation of the modulation response of directly modulated lasers after propagation in an optical fiber, in agreement with our experimental observations. Suppression of SBS can be achieved at low frequencies and high modulation powers due to the laser adiabatic chirp

Wideband, high efficiency optical modulator requires less than 10 watts drive power

Wideband optical modulation system operates with less than 10-watts drive power. It consists of an optical modulator and transistorized driver that combines small cross-section potassium dideuterium phosphate crystals with laser beam-condensing optics. Optical modulation systems may serve importantly in future space wideband communication systems

Photometric Analysis of the Optical Counterpart of the Black Hole HMXB M33 X-7

Aims: Study the high-mass X-ray binary X-7 in M33 using broad-band optical data. Methods: We used recently published CFHT r' and i' data for variable stars in M33 to extract the light curve of the optical counterpart of X-7. We combined these data with DIRECT B and V measurements in order to search for an independent optical modulation with the X-ray periodicity. The periodic modulation is modelled with the ellipsoidal effect. We used UBVRr'i' magnitudes of the system to constrain the temperature and radius of the optical component. Results: The optical data revealed a periodicity of 3.4530 +- 0.0014 days, which is consistent with the known X-ray period. Double modulation, which we attributed to ellipsoidal modulation, is clearly seen in four different optical bands. The absolute magnitude in six optical bands is most consistent with a stellar counterpart with 33000 < T_{eff} < 47000 K and 15 < R < 20 R_{\sun}. We modelled the optical periodic modulation and derived the masses of the two components as a function of the orbital inclination and the radius of the stellar component. The resulting mass range for the compact object is 1.3 < M < 23 M_{\sun}. Conclusions: The system is probably a black hole HMXB, similar to Cyg X-1, LMC X-1 and LMC X-3.Comment: Accepted for publication in A&

Designing Power-Efficient Modulation Formats for Noncoherent Optical Systems

We optimize modulation formats for the additive white Gaussian noise channel with a nonnegative input constraint, also known as the intensity-modulated direct detection channel, with and without confining them to a lattice structure. Our optimization criteria are the average electrical and optical power. The nonnegativity input signal constraint is translated into a conical constraint in signal space, and modulation formats are designed by sphere packing inside this cone. Some remarkably dense packings are found, which yield more power-efficient modulation formats than previously known. For example, at a spectral efficiency of 1 bit/s/Hz, the obtained modulation format offers a 0.86 dB average electrical power gain and 0.43 dB average optical power gain over the previously best known modulation formats to achieve a symbol error rate of 10^-6. This modulation turns out to have a lattice-based structure. At a spectral efficiency of 3/2 bits/s/Hz and to achieve a symbol error rate of 10^-6, the modulation format obtained for optimizing the average electrical power offers a 0.58 dB average electrical power gain over the best lattice-based modulation and 2.55 dB gain over the best previously known format. However, the modulation format optimized for average optical power offers a 0.46 dB average optical power gain over the best lattice-based modulation and 1.35 dB gain over the best previously known format.Comment: Submitted to Globecom 201

Effective electro-optical modulation with high extinction ratio by a graphene-silicon microring resonator

Graphene opens up for novel optoelectronic applications thanks to its high carrier mobility, ultra-large absorption bandwidth, and extremely fast material response. In particular, the opportunity to control optoelectronic properties through tuning of Fermi level enables electro-optical modulation, optical-optical switching, and other optoelectronics applications. However, achieving a high modulation depth remains a challenge because of the modest graphene-light interaction in the graphene-silicon devices, typically, utilizing only a monolayer or few layers of graphene. Here, we comprehensively study the interaction between graphene and a microring resonator, and its influence on the optical modulation depth. We demonstrate graphene-silicon microring devices showing a high modulation depth of 12.5 dB with a relatively low bias voltage of 8.8 V. On-off electro-optical switching with an extinction ratio of 3.8 dB is successfully demonstrated by applying a square-waveform with a 4 V peak-to-peak voltage.Comment: 12 pages, including 7 figure

Adaptive differential amplitude pulse-position modulation technique (DAPPM) using fuzzy logic for optical wireless communication channels

In the past few years, people have become increasingly demanding for high transmission rate, using high-speed data transfer rate, the number of user increased every year, therefore the high-speed optical wireless communication link have become more popular. Optical wireless communication has the potential for extremely high data rates of up to tens of Gigabits per second (Gb/s). An optical wireless channel is usually a non-directed link which can be categorized as either line-of-sight (LOS) or diffuses. Modulation techniques have attracted increasing attention in optical wireless communication, therefore in this project; a hybrid modulation technique named Differential Amplitude Pulse-Position Modulation (DAPPM) is proposed to improve the channel immunity by utilizing optimized modulation to channel. The average symbol length, unit transmission rate, channel capacity, peak-to-average power ratio (PAPR), transmission capacity, bandwidth requirement and power requirement of the DAPPM were determined and compared with other modulation schemes such as On-Off Key (OOK), Pulse-Amplitude Modulation (PAM), Pulse-Position Modulation (PPM), Differential Pulse-Position Modulation (DPPM), and Multilevel Digital Pulse Interval Modulation (MDPIM). Simulation result shows that DAPPM gives better bandwidth and power efficiency depending on the number of amplitude level (A) and the maximum length (L) of a symbol. In addition, the fuzzy logic module is developed to assist the adaptation process of differential amplitude pulse-position modulation. Mamdani fuzzy logic method is used in which the decisions made by the system will be approaching to what would be decided by the user in the real world

Phased array receive antenna steering system using a ring resonator-based optical beam forming network and filter-based optical SSB-SC modulation

A novel phased array receive antenna steering system is introduced. The core of this system is an optical ring resonator-based broadband, continuously tunable optical beam forming network (OBFN). In the proposed system architecture, filter-based optical single-sideband suppressed-carrier modulation and balanced coherent optical detection are used. \ud Such architecture has significant advantages over a straightforward architecture using optical double-sideband modulation and direct optical detection, namely relaxed bandwidth requirements on the optical modulators and detectors, reduced complexity of the OBFN chip, and enhanced dynamic range. Initial measurements on an actual 1×8 OBFN chip and an optical sideband filter chip are presented. Both are realized in CMOS-compatible planar optical waveguide technology.\u

All-Optical Modulation in a Silicon Waveguide Based on a Single-Photon Process

All-optical, low-power modulation is a major goal in photonics. Because of their high mode-field concentration and ease of manufacturing, nanoscale silicon waveguides offer an intriguing platform for photonics. So far, all-optical modulators built with silicon photonic circuits have relied on either two-photon absorption or the Kerr effect. Both effects are weak in silicon, and require extremely high (~5 W) peak optical power levels to achieve modulation. Here, we describe an all-optical Mach-Zehnder modulator based on a single-photon absorption (SPA) process, fabricated entirely in silicon. Our SPA modulator is based on a process by which a single photon at 1.55 mum is absorbed and an apparently free-carrier-mediated process causes an index shift in silicon, even though the photon energy does not exceed that of silicon's bandgap. We demonstrate all-optical modulation with a gate response of 1deg/mW at 0.5 Gb/s. This is over an order of magnitude more responsive than typical previously demonstrated devices. Even without resonant enhancement, further engineering may enable all optical modulation with less than 10 mW of gate power required for complete extinction, and speeds of 5 Gb/s or higher