Broad Optical Bandwidth Research Articles

Femtosecond Pulse Delivery through Long Multimode Fiber Using Adaptive Pulse Synthesis

We report on a delivery technique for 164-fs optical pulses with a peak power of 1.1 kW through a long multimode optical fiber and a glass block using an adaptive pulse-shaping feedback loop. We used two devices to optimize the input pulse; a pulse stretcher and a pulse shaper. 382-ps chirped pulses are compressed to 370-fs pulses at the output end of a glass block joined to a standard graded-index multimode fiber, 96 m in length and with a core diameter of 50 µm (the output end of the system). The adaptive pulse shaper compensates for the remaining high-order phase dispersion, which results in 164-fs pulses at the output end of the system. Our work shows that an adaptive pulse synthesis technique provides a powerful and convenient technique for programmable fiber dispersion compensation over a broad optical bandwidth.

Integrated optical 2 /spl times/ 2 switch for wavelength multiplexed interconnects

A highly compact integrated optical switch is proposed and demonstrated for broadband optical switching applications. Routing of 8 /spl times/ 10 Gb/s data channels is demonstrated using a low-cost 1250-Mb/s control scheme. The advantages of lossless operation, broad optical bandwidth, and nanosecond switching times are leveraged. Multichannel wavelength is exploited for reduced latency, enhanced capacity, and functionality, while retaining compatibility with existing off-the-shelf electronics and transceiver technology. The requirements for optical header processing, wavelength translation, and optical buffering are avoided. Low-penalty multiwavelength transmission is demonstrated for a highly compact sub-mm/sup 2/ amplifying 2 /spl times/ 2 switch. Pattern dependent gain and amplified spontaneous emission are minimized to facilitate 0.0-0.4 dB penalty. Mitigation techniques compatible with the architecture are deployed to reduce the penalty under adverse operating conditions. Control schemes are proposed and demonstrated to facilitate 8 /spl times/ 10 Gb/s optically switched networking.

Broadband optical modulator of fiber type

A novel lithium niobate optical modulator of fiber type is proposed. The velocity match and the impedance match can be achieved simultaneously. The modulator is analyzed and designed with the finite element method. The designed modulator operates with a low half-wave voltage of 2.28V, a broad 3dB optical bandwidth of 116.3GHz and a characteristic impedance of 50.67? at 1.5microm wavelength.

Effects of Atmospheric Water Vapor on Infrared Interferometry

ABSTRACTWater vapor, while usually a small contributor to the atmospheric refractive index for astronomical observations at IR wavelengths, is highly dispersive and can introduce optical path length errors affecting high‐precision interferometer observing modes. The refractive index of atmospheric water vapor can be computed from a summation over the various IR resonances, and we present values over a range of 1.2–13.5 μm. The dispersion of water vapor introduces phase errors across the instrument passband and produces excess noise in interferometer group delay, residual errors in cophasing using a different source wavelength, and coherence loss over broad optical bandwidths. We quantify these effects for the J through N bands, discuss means of amelioration, and consider their implications for differential phase and nulling observing modes.

Broad optical bandwidth InGaAs-InAlGaAs light-emitting diodes fabricated using a laser annealing process

The use of a laser-induced quantum-well intermixing technique in the InGaAs-InAlGaAs material system is presented. We report blue shifts of up to 240 nm in the 1.55-μm emission wavelength, generated by exposure to a Nd:YAG laser. Variations in the optical intensity across the irradiating beam were used to laterally grade the bandgap along a sample. We used this technique to fabricate broad optical bandwidth, light-emitting diodes. The devices showed an increase in the full width half maximum of the emission spectrum from 125 nm in undisordered devices to over 260 nm in intermixed material. The output spectrum was also observed to be flat-topped (within 5%) across a wavelength range of 140 nm.

Injection locking suppression of coherence collapse in a diode laser with optical feedback

The effects of injection locking a laser diode which is also subject to varying levels of optical feedback from an external reflector are investigated. It is found that the locking range of a laser diode with optical feedback (LDWOF) is reduced relative to that of a solitary laser diode depending on both the increased photon lifetime and the amount of optical feedback. When the LDWOF is locked in frequency to the external injection source then the coherence collapse, and other low optical feedback regimes of operation, are suppressed. This result can be applied to produce a self-locked or master/slave-locked diode laser system that is insensitive to unwanted feedback typically encountered in practical communication systems. The effect of injection locking a frequency modulated external cavity diode laser (FM ECDL) system by another laser is to inhibit the modulation induced coherence collapse that is characteristic of such FM systems. Due to this, larger bandwidths are attainable than for free running FM ECDLs. This also suggests future device and system designs for obtaining very broad optical bandwidth FM operation.

Complete dispersion compensation for 400-fs pulse transmission over 10-km fiber link using dispersion compensating fiber and spectral phase equalizer

We have demonstrated essentially complete dispersion compensation for 400-fs pulses over a 10-km fiber link using dispersion compensating fiber and a programmable femtosecond pulse shaper functioning as a spectral phase equalizer. The pulse shaper impresses adjustable quadratic and cubic phases onto the spectrum and removes all the residual dispersion and dispersion slope in the dispersion compensated fiber link. Our work shows that the pulse shaper technique provides a powerful and convenient tool for programmable fiber dispersion compensation over broad optical bandwidth. This allows distortion-free femtosecond pulse transmission over a fiber link in excess of 10 km without requiring the exact trimming of the dispersion-compensating fiber.

340 Gbit/s (34 × 10 Gbit/s) WDM transmissionover 8,514 kmusing broadband gain equalisation technique for transoceanic systems

The authors successfully transmit 34 10 Gbit/s RZ signals over 8,514 km. The use of gain equalisation with a broad optical bandwidth of 23 nm and a higher-order dispersion-managed line are found to enable large capacity WDM transmission.

Effects of crosstalk in WDM systems using spectrum-sliced light sources

We report on the effects of intraband crosstalk in the system using spectrum-sliced light sources. The results show that the spectrum-sliced light sources are much less sensitive to intraband crosstalk compared to laser sources. This is mainly because the spectrum-sliced light source should have relatively broad optical bandwidth to obtain the signal-to-noise ratio required for the acceptable bit-error-rate performance. Thus, in the system using spectrum-sliced light sources, the signal-crosstalk beat noise is reduced significantly as the beat components become spread outside of the receiver's bandwidth.

Ultrafast Time-and-Space- Domain Holography by Spectral Hole Burning in Dye-Doped Polymers

Certain photochromic materials exhibit at liquid-helium temperature a special property of very high selectivity in frequency dimension. This phenomenon, commonly known as spectral hole burning (SHB), makes it possible to extend conventional spatial-domain optical data storage into the dimensions of frequency and time. We have applied SHB for ultrafast recording of holograms and coherent optical processing on the timescale of 10-12–10-13 s. To achieve ultrafast performance in the time domain, we use special organic dye-doped polymer materials, which provide SHB recording in a broad optical band width of 5–10 THz. In this paper, we discuss recording and playback of holograms of pico- and femtosecond time-and-space-domain signals using dye-doped SHB polymers at liquid-helium temperature. We discuss unusual properties of SHB holograms such as causality-related asymmetry of diffraction and inversion of the time coordinate, ultrafast frequency-domain processing, and associative recall of events.

Modulation doped SiGe-Si MQW for low-voltage high-speed modulators at 1.3 μm

We propose a new type of light modulator at 1.3 and 1.55 /spl mu/m using a /spl delta/-modulation-doped SiGe-Si multiple-quantum-well quantum-well structure (/spl delta/-MDMQW) integrated in a low-loss silicon-on-insulator (SOI) waveguide, The structure is embedded in the intrinsic region of a vertical p-i-n diode realized on SOI substrate. We present theoretical calculation of the effective index modulation determined by the variation of the confined hole concentration with an applied external field. A practical device is proposed and a calculation of optical modulation efficiency is presented. Estimation of on-off switching time based on evaluation of characteristic time of emission from localized levels in quantum wells and RC characteristics of the device are presented. This device presents the advantage of a broad optical bandwidth in comparison to the modulators based on quantum-defined Stark effect, low insertion loss, high-speed (above 1 GHz), and full compatibility with silicon technology.

Polarizing beam splitter based on the anisotropic spectral reflectivity characteristic of form-birefringent multilayer gratings

We introduce a novel polarizing beam splitter that uses the anisotropic spectral reflectivity (ASR) characteristic of a high-spatial-frequency multilayer binary grating. Such ASR effects allow us to design an optical element that is transparent for TM polarization and reflective for TE polarization. For normally incident light our element acts as a polarization-selective mirror. The properties of this polarizing beam splitter are investigated with rigorous coupled-wave analysis. The design results show that an ASR polarizing beam splitter can provide a high polarization extinction ratio for optical waves from a wide range of incident angles and a broad optical spectral bandwidth.

Compact electro-optic polarization scramblers for optically amplified lightwave systems

Fast polarization scramblers have become important components in optically amplified transoceanic communication systems to eliminate anisotropic gain saturation (polarization hole burning) in the erbium-doped fiber amplifiers by depolarizing the launched optical carrier. This paper reviews the operation and implementation of compact electro-optic polarization scramblers on x-cut and z-cut lithium niobate. These integrated-optic devices employ low-loss single-mode waveguides and allow polarization modulation at variable frequencies ranging from a few 100 Hz to more than 10 GHz. We describe simple linear phase retarders that depolarize light in a fixed, well-maintained polarization state as well as cascaded multi-stage scramblers that are capable of depolarizing arbitrarily polarized light. These scramblers can be operated over a broad optical bandwidth of more than 40 nm with less than 5% residual degree of polarization and are further wavelength-tunable over more than 100 nm.

Dual purpose pyrometer for temperature and solidification velocity measurement

A dual purpose pyrometer is described that allows both accurate radiance temperature measurement and fast temporal response. The system uses two silicon photodiodes with separate optical paths derived from a common spot on the sample. The optical bandwidths and response times of each detection circuit are tailored to the function of each radiometer. The radiance temperature of electromagnetically levitated metallic samples is measured over a narrow optical bandwidth with a high-gain silicon detector. The velocity of solidification of undercooled melts can be deduced from the rise time of the second silicon detector which samples a broad optical bandwidth and has a fast response time. Results from experiments on the undercooling and solidification behavior of electromagnetically levitated pure nickel show that the solidification velocity approaches 17 m/s at high undercooling.

Optical amplifiers. Light boosters in a chip

One potential way of building transmission systems able to accommodate capacity upgrades is to use optical amplifiers. These devices simply amplify the incoming optical signal. They are insensitive to the transmission bit rate and data format, have a broad optical bandwidth, and, in principle, pass signals in either direction. Optical amplifiers are thus highly flexible devices, potentially able to accommodate a wide range of improvements in the transmission system including increases in the bit rate, frequency-division multiplexing and coherent transmission. The author describes the construction of optical amplifiers and their operation including packaging, gain control and fault location. Their use in submarine links between the UK and mainland Europe is also discussed. >

Optical FDM transmission technique

This paper surveys the present state of optical frequency-division multiplexing (optical FDM) technologies. Utilizing a broad optical frequency bandwidth up to several hundred terahertz, optical FDM is expected to find applications in large-capacity trunking and local distribution networks. The present state of the related technologies and the future prospects for these applications are discussed.

CHOLESTERIC LIQUID CRYSTALS FOR OPTICAL APPLICATIONS

The optical and thermal properties of mixtures of MBBA and COC are reported on as an example of cholesteric liquid crystals incorporating molecules which are not cholesterol derivatives. These materials exhibit relatively broad optical bandwidths, efficient polarizing characteristics, extremely weak temperature dependences, and high structural order properties which should be useful in optical devices.