Silicon optical modulators at 1.3-μm based on free-carrierabsorption

Silicon optical waveguide modulators, appropriate for operation in the 1.3-1.55 μm wavelength region, have been fabricated and their performance characterized at the wavelength of 1.3 μm. The modulator structures consist of p-i-n diodes integrated with silicon waveguides; device operation is based on free-carrier absorption. Modulation depths of -6.2 dB and response times less than 50 ns have been measured. Experimental results are compared with the p-i-n diode theory. It is argued that the device is suitable for integration with silicon electronics and silicon optoelectronic devices. The response times measured for the current devices may be improved by reducing the transverse dimensions of the p-i-n structure     

GaInAsP dual wavelength laser

The fabrication and performance characteristics of a dual wavelength laser emitting near 1.3 μm and 1.55 μm are described. The lasers are of the etched mesa buried heterostructure type, and utilise semi-insulating InP layers both the lateral optical confinement and current confinement. The 1.55 μm emission is at a single wavelength by virtue of the frequency selective feedback provided by a grating etched on the substrate. The lasers have threshold currents in the 20 to 40 mA range, and have quantum efficiencies comparable to single emitter lasers     

Multiple quantum well (MQW) waveguide modulators

Because the electroabsorption effect in semiconductor multiple quantum well material is approximately 50 times larger than in bulk semiconductors, significant interest has been generated in the use of MQW's in optical modulators. Small high-speed devices have been made which show promise for external modulators in optical transmission systems, as well as for encoding and processing components in optical interconnect and signal processing systems. The fact that these modulators are made from III-V semiconductors had led to interest in integration of these components with other active optoelectronic components. Although most devices have operated with light of a wavelength of 0.85 μm, recently much progress has been made in applying this technology to devices operating near 1.55 μm. The author reviews the work of the last few years in this field and indicates some future directions     

Fabrication of polymeric large-core waveguides for opticalinterconnects using a rubber molding process

Polymeric large-core (47 μm×41 μm) optical waveguides for optical interconnects have been fabricated by using a rubber molding process. For low-cost low-loss large-core waveguides, our newly developed thick-photoresist patterning process is used for a master fabrication. Also a low-loss thermocurable polymer, perfluorocyclobutane (PFCB), is used in fabricating optical waveguides by rubber molding for the first time. The propagation loss is measured to be 0.4 dB/cm at the wavelength of 1.3 μm, and 0.7 dB/cm at the wavelength of 1.55 μm     

Electro-optic modulation in a chopped quantum-well electrontransfer structure

The authors demonstrate the first electron-transfer Mach-Zehnder modulators to operate in the 1.55 μm wavelength range. The use of chopped quantum wells provides a wide operating bandwidth compatible with Er-doped fibre amplified systems (>40 nm about 1.54 μm) for electrorefractive waveguide devices. In this wavelength range, obtained voltage-length products are for the 180° optical phase shift V_π×L between 2.7 and 4.0 Vmm     

Guided-wave optical equalizer with α-power chirped grating

A theoretical investigation of a guided-wave optical equalizer with an α-power chirped grating is presented. A group delay dispersion of 3700 ps/nm can be obtained at λ=1.55 μm by a chirped grating with α=0.3. It is shown that the chromatic dispersion of 200 km of a fiber whose zero-dispersion wavelength is located at 1.3 μm can be compensated at 1.55 μm to achieve up to 10 GHz signal bandwidth     

High-power semiconductor edge-emitting light-emitting diodes foroptical low coherence reflectometry

A new semiconductor source was designed for optical low coherence reflectometry, increasing the sidelobe-free dynamic range by three to five orders of magnitude compared to conventional EELED's. Reflectivities internal to an optical fiber circuit separated by as much as eight orders of magnitude can now be detected at wavelengths of 1.3 and 1.55 μm, using compact semiconductor sources. For applications not requiring sidelobe-free operation, the same devices can be operated at high current (200 mA) and low temperatures (near 0°C) to produce nearly 1 mW of 1.5 μm emission coupled into single-mode fiber. The resulting wavelength spectrum is smooth, enabling fiber-based absorption spectral measurements     

Two-stage high-gain optical amplifier

A two-stage semiconductor optical amplifier is discussed. Net fiber-to-fiber gains as high as 36.5 dB have been achieved. When used in a fiber-optic transmission system, using a commercial 1.7 Gb/s regenerator, the fiber span between transmitter and regenerator is increased to 151 km and 1.3 μm wavelength. With a 1.55 μm two-stage amplifier, a transmission distance of 180 km at 3.4 Gb/s is demonstrated     

Compensation of fibre chromatic dispersion in optical heterodynedetection

Compensation of fibre chromatic dispersion in coherent optical fibre transmission is demonstrated. The chromatic dispersion of a 70 km single-mode fibre with 1.3 μm zero dispersion wavelength is compensated for using a microstrip line equaliser in the intermediate frequency band. Amplitude distortion due to fibre chromatic dispersion at 1.55 μm wave-length is reduced to below 2.5 % with the equaliser     

Optical WDM transceiver module using wavelength-selective couplerand WDM-PD for optical access networks

A new optical wavelet division multiplexing (WDM)-transceiver module has been designed and fabricated for optical access networks. Conventional 1.3/1.55-μm WDM-coupler and Y-branch were replaced by a new wavelength-selective coupler in order to reduce module size. A new WDM-photodiode (PD), which was photosensitive to 1.3 μm light and transparent to 1.55 μm light, and a 1.55-μm PD were arranged in series along the optical axis. An MQW-FP-LD was used as a 1.3-μm transmitter. Fundamental characteristics were measured and discussed. Evaluation results, P_out of 0 dBm, responsivity of 0.36 A/W at 1.31 μm and 0.74 A/W at 1.55 μm, and IMD2 of -76.2 dBc, imply that this WDM-transceiver module design is promising to application for optical access networks     

Threshold currents of 1.2-1.55 μm P-substrate buried crescentlaser diodes

P-substrate buried crescent (PCB) laser diodes whose wavelength ranged from 1.2 to 1.55 μm have been fabricated. The threshold currents as low as 10 mA have been obtained in this wavelength range experimentally. The calculated threshold currents of 13, 13, and 14 mA at 1.2, 1.3, and 1.55 μm almost coincide with the measured values     

Compensation of dispersion in optical fibers for the 1.3-1.6 μmregion with a grating and telescope

The transmission of ultrashort optical pulses over long distances in optical fibers is limited by pulse broadening due to group velocity dispersion. A grating and telescope dispersion compensator with group velocity dispersion of equal magnitude and opposite sign can compensate for the fiber dispersion. The possible benefits of such dispersion compensation in the 1.3-1.6-μm wavelength region are investigated. The results show that compensation of first-order dispersion at 1.55 μm in a fiber with zero dispersion near 1.3 μm is primarily limited by the second-order dispersion of the grating and the telescope compensator. For a wavelength slightly greater than the zero dispersion wavelength, both the first- and second-order group velocity dispersion can be canceled by the grating and telescope dispersion compensator, allowing transmission exceeding 100 Gb/s over 100 km     

A quantum leap in laser emission

Medium- and long-haul, high-speed fiber communication systems are dominated by the need for low optical loss and low dispersion, and these systems require laser diodes and photodiodes that emit and detect at 1.33 and 1.55 μm. InGaAs/GaAs quantum dots enable 1.3 μm wavelengths in GaAs-based lasers for fiber-optic communication     

Wide-range all-optical wavelength conversion usingdual-wavelength-pumped fiber Raman converter

A wavelength conversion scheme based on a fiber Raman converter is proposed, in which an externally injected high power pump laser and the associated Stokes laser are used to assist the Raman conversion process of signal light coded with optical information. Because the Raman gain spectrum in fibers is extremely broad, a wavelength conversion device with wide-range tunability is feasible. We numerically demonstrate that wavelength conversion from 1.31 to 1.42 μm can be realized using a fiber Raman converter at up to 10 Gb/s with an efficiency of 18%. It is also demonstrated that wide range conversion from 1.31 to 1.55 μm for optical fiber communication is feasible at up to 5 Gb/s when the fiber Raman converters are cascaded twice     

Laser primer for fiber-optics users

The basics of semiconductor lasers are reviewed. Specifically, lasers with wavelengths between 1.3 and 1.55 μm, the range most applicable to fiber-optic communications, are discussed. In this range, light experiences lower loss on silica fiber; in addition, 1.3 μm is the wavelength of zero dispersion, where the refraction index and, consequently, the speed of propagation are independent of wavelength. Key properties of semiconductor lasers, including power-current characteristics, beam shape, spectra, modulation, noise characteristics, and reliability, are discussed     

Pulsed electrical operation of 1.5-μm vertical-cavitysurface-emitting lasers

Vertical cavity surface emitting lasers operating in the 1.3- and 1.5-μm wavelength ranges are highly attractive for telecommunications applications. However, they are far less well-developed than devices operating at shorter wavelengths. Pulsed electrically-injected lasing at 1.5 μm, at temperatures up to 240 K, is demonstrated in a vertical-cavity surface-emitting laser with one epitaxial and one dielectric reflector. This is an encouraging result in the development of practical sources for optical fiber communications systems     

Optical PSK synchronous heterodyne detection transmissionexperiment using fiber chromatic dispersion equalization

This letter demonstrates an 8-Gb/s optical PSK (phase shift keying) synchronous detection transmission experiment using external cavity laser diodes. A 188-km 1.3-μm zero-dispersion fiber is used as the transmission medium at the wavelength of 1.55 μm. Fiber chromatic dispersion is successfully compensated with a microstrip-line delay equalizer     

Realization of all-optical wavelength converter based ondirectionally coupled semiconductor optical amplifiers

We propose a novel all-optical wavelength converter based on directionally coupled (DC) semiconductor optical amplifiers (SOA) and simulate its characteristics using a simple model to find out such advantages as extinction enhancement and digital response. We then fabricate devices in the 1.55 μm band, and successfully demonstrate the wavelength conversion operation with the above-mentioned advantages. Very compact size and no need of active/passive integration are other significant merits of DC SOA's     

Ultrafast two-photon nonlinearities in CdSe near 1.5 μm studiedby interferometric autocorrelation

We have used interferometric autocorrelation measurements to study the femtosecond nonlinear optical properties of bulk CdSe crystals in the wavelength region just above the half gap wavelength of 1.42 μm. Between 1.42 and 1.55 μm, we measured an ultrafast third-order nonlinearity with nonlinear refractive index n₂=1.3×10 ^-13 cm²/W^-1. Detailed modeling of the autocorrelations revealed the influence of higher order effects due to free carriers generated by nonlinear absorption. We find that CdSe is an interesting alternative material to AlGaAs for applications in this technologically important wavelength region     

Optical harmonic mixers

Mixing of optical signals in a waveguide via the second-order nonlinear effect in semiconductors was studied theoretically and experimentally. The InP-based material system was the main focus of the investigations. Both the up-conversion leading to second-harmonic generation and the down-conversion leading to optical rectification were analyzed and experimentally verified. Experiments in nonlinear optical waveguide structures at 1.55 μm wavelength have shown the existence of both the quadratic second-harmonic signals as well as the linearly dependent optical rectification signals. Quantitative estimates confirmed a good agreement between the theory and the experiment. Some interesting applications for high-speed optical data processing required in transparent optical telecommunication systems have been identified. Most attractive functions proposed to be implemented with these types of devices are, for example, flexible-to-bit-rate all-optical clock extraction in a transparent high-performance optical telecommunication network or accurate and fast measurement of optical frequency for optical synchronization needs in wavelength-division-multiplexing systems