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Index of refraction profiles of optical fibers are obtained by a new interference technique closely related to Mach-Zehnder microscope interferometry. Data are obtained from specially prepared samples using a conventional reflected light microscope. Excellent agreement is obtained with the results using the Mach-Zehnder method but at a considerable reduction in the cost and complexity of instrumentation.

Time-averaged and time-resolved spectra of single-mode, optically pumped, ultrashort-cavity semiconductor film lasers have been studied in detail. The time-averaged spectra are broad (3-17 nm). Time-resolved spectra show that the lasing wavelength increases (chirps) during the picosecond-time-scale duration of the pulse. The chirp is due to free-carrier plasma effects on the refractive index of the highly excited semiconductor (10(20) carriers/ cm(3)). Film-laser pulses are compressed by a factor of 2 in an 8-m length of single-mode optical fiber because of the linear group-velocity dispersion of the fiber, producing a pulse of 3.7-psec duration at 1.264 microm.

Ultrashort-cavity, thin-film lasers from In(1-x)Ga(x)As(y)P(1-y) of five different compositions, including InP and In(0.53)Ga(0.47)As, have been made to lase between 0.83 and 1.59 microm. The multitude of lasing wavelengths observed had line-to-line separations of less than 10 nm. The lasers were pumped with 1-psec pulses from a mode-locked dye laser. An output pulse of 6-psec duration was measured at a wavelength of 1.16 microm.

An optical cross-connect switch using the star-coupler-based frequency-division-multiplex technique are discussed. Two specific tunable receivers have been implanted. The first is a heterodyne receiver with a tunable laser as the local oscillator (LO) and the second is a tunable filter followed by a direct-detection receiver. In the heterodyne receiver, the tunable LO was a monolithic three-section multiple-quantum-well distributed Bragg laser capable of a 1000-GHz tuning range. Receiver sensitivity was measured to be -38 dBm at 1 Gb/s (BER=10/sup -10/). The power margin in the system substantiated feasibility for a 400*400 switch. In the tunable-filter receiver, the tunable filter is a tunable two-stage optical fiber Fabry-Perot filter design consisting of a narrowband filter followed by a wideband filter. The tuning of the filters is computer controlled, and the combined filter has a tuning range of 15000 GHz with a finesse of approximately=5170. Therefore, it is capable of covering over 1000 channels of 2.9 GHz each. >

A key component of Wavelength Division Multiplexed (WDM) networks is a tunable broadband wavelength demultiplexer, with good selectivity and high tuning speed. In this communication we report low waveguide loss InGaAsP Fabry-Perot filters, grown by Metal Organic Vapor Phase Epitaxy, with tuning ranges up to 3.07 nm (380 GHz). These filters have waveguides with bandgap wavelengths between 1.3 and 1.48 /spl mu/m so that they are transparent at zero bias and at low tuning currents ( >

The authors discuss results of research aimed at understanding the use of monolithic tunable lasers and fiber Fabry-Perot filters in implementing an optical cross-connect switch. The switch architecture uses optical frequency division multiplexing where laser signals are transmitted at different frequencies and then summed in a star coupler. At each star coupler output, a tunable receiver is used to retrieve any input signal of choice. The experimental receiver consists of an optical tunable filter followed by a direct-detection receiver. The laboratory demonstration consists of four frequency-locked transmitters with monolithic tunable lasers, each dithered with a slightly different frequency for the dual purpose of frequency locking and positive channel identification upon signal reception. The tunable filter is a tunable two-stage fiber Fabry-Perot filter design consisting of a narrow filter followed by a wide filter. The tuning of the filters is computer controlled, and the combined filter has a tuning range of 15000 GHz with a finesse approximately=5170. Therefore, it is capable of covering over 1000 channels of 2.9-GHz each. Receiver sensitivity was measured to be -30 dBm at 1.7 Gb/s and -29 dBm at 2.5 Gb/s (bit error rate=10/sup -10/). >

A fiber Fabry-Perot resonator containing a Faraday-active medium and measured nonreciprocal resonance-enhanced transmission for circularly polarized light was built. The results show that an 18- mu m length of material producing only 2.1 degrees of Faraday rotation could achieve an optical isolation of 10 dB. The isolation would be larger for interferometers with higher finesse or more single-pass Faraday rotation. The device could also serve as a nonreciprocal wavelength filter transmitting different sets of wavelengths in the two directions. >

Recently, we proposed a spectrum-sliced fiber amplifier light source for multi-channel WDM applications [1]. The high-power ASE from an EDFA could be efficiently divided into many channels using an integrated optic WDM demultiplexer [2]. Thus, this "spectrum-sliced" ASE could be used as light sources for WDM systems rather than several wavelength-selected DFB lasers. However, these incoherent light sources would suffer from excess noise caused by the beating of the various Fourier components within the broad spectrum. In particular, this excess noise becomes dominant over the electrical noise when the optical bandwidth per channel is significantly reduced, as in the proposed WDM light source. Thus, the SNR of the spectrum-sliced ASE source at the receiver is given.

A temperature-insensitive, nontunable fibre Fabry-Perot etalon is demonstrated. This compensation has been obtained for an etalon with a cavity length of 740 μm (free spectral range = 135 GHz), and the principle may be applied for etalons of arbitrary length. This device may prove useful in setting frequencies for WDM applications.

An all fibre, diode-pumped, electrically tunable ring laser is reported. Gain is provided by an erbium-doped fibre and tuning by a fibre Fabry-Perot etalon. The threshold at l.566 μm is 2.9mW, the slope efficiency is 0.15 and the output power is 4.2 mW with 32 mW of pump power. The output wavelength can be tuned from 1.525 to 1.586 μm with a variation in power of less than 3.5 dB.

A diode-pumped, broadly tunable, single frequency erbium-doped fibre ring laser is reported. Tuning and single longitudinal mode selection are accomplished by use of two fibre Fabry-Perot etalons. The threshold for 1.48 μm pumping is 8.8 mW and the slope efficiency is 11.5%. The laser can be tuned to wavelengths between 1.530 and 1.575 μm and operates singlemode throughout this range. Its linewidth is measured at 1.56 μm to be less than 5.5 kHz.

The enhancement of Faraday rotation in a rare-earth iron garnet plate inside a fibre Fabry-Perot resonator is demonstrated. An enhancement factor of seven is obtained with a resonator finesse of 10.

The effects of inherent fiber birefringence, packaging stresses, and stress tuning on the behavior of a fiber Fabry-Perot interferometer are examined. A polarization doublet due to birefringence is observed. For birefringence of 1 ps/km, the doublet spacing is 40 MHz, at 1.5- mu m wavelength, independent of the FFP finesse or free spectral range, and is due mainly to the inherent fiber birefringence. It was found that annealing depressed-cladding single-mode fiber reduced the fiber birefringence, for example, from 40-80 MHz to 15-25 MHz. Where the bandpass of the FFP is greater than the birefringence doublet, this device should be polarization insensitive for most applications. >

Fiber Fabry-Perots have been built with a finesse of 500 and throughput of 30-40 percent. The devices are piezoelectrically scanned and operate at 1.52μm, and have free spectral ranges of 1000, 500, 333, and 250 MHz, with linewidth resolution as small as 0.5 MHz. The sources of loss which limit the attainable finesse have been identified and analyzed.

Picosecond pulses from optically pumped, ultrashort cavity semiconductor film lasers have a large positive chirp that is not linear in time. Average chirp values are about 1 nm/psec for InGaAsP film lasers. The chirp is caused by transient change in the refractive index of the semiconductor film during the pulse due to variation of the free carrier concentration. The transient carrier concentrations of 1020 cm-3 caused by the intense picosecond pump pulses is sufficient to account for the observed chirp. For film lasers, the dominant mechanism by which the carriers affect the index of refraction is free carrier plasma refraction. The positively chirped pulses have been compressed by the negative linear group velocity dispersion of 8m of single-mode optical fiber. Pulse compression factors as large as 3.4 have been obtained. Pulses as short as 2.5 psec at 1.23 μm and 3.4 ps at 1.42 μm have been generated by this compression scheme.© (1983) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Optical communication systems operating at rates in the gigabit per second range are currently being explored. To study temporal limits on components and systems, it is necessary to use a source that produces short optical pulses at wavelengths throughout the near-IR spectral range. In this paper we will describe the use of picosecond pulses from optically pumped, ultrashort cavity, semiconductor film lasers to study system components for ultrahigh-speed optical-fiber communication.

In this paper a new type of magnetooptic modulator having a bounce-cavity structure is described. Direct amplitude modulation is achieved by utilizing the Faraday effect in conjunction with the differential reflectivity of dielectric mirrors for polarizations parallel to (TM) or perpendicular to (TE) the plane of incidence. We show that the transmission through the modulator is determined by the number of reflections, the reflectivity of the mirrors, and the difference in the phase shift for TE and TM reflected waves. The operation of this type of modulator has been successfully demonstrated with a preliminary device fabricated from YIG.

We show that fibre-coupled open resonator Fabry-Perot interferometers can be made with reduced insertion loss due to diffraction by using fibre with slightly larger mode size. For a 50% increase in mode size, the insertion loss is reduced by 3–4dB for a 7μm-long resonator at 1.5μm wavelength.

Room-temperature c.w. laser action at 1.3 μm wavelength has been obtained using single-crystal glass-clad Nd:y.a.g. fibres end pumped with a single high-radiance l.e.d. The fibres were 0.5 cm long, 50 μm in diameter and had a cladding 3 μm thick. Threshold in a nonoptimum configuration was less than twice that at 1.06 μm. Application of a transparent, adherent glass cladding to the crystalline fibre is described.

We have made prototypes of three kinds of fibre Fabry-Perot (FFP) tunable filters, each of which can cover a separate free spectral range interval as determined by its resonator length. Free spectral ranges from hundreds of angstroms to tens of megahertz can be realised from the appropriate type. We have built FFPs with free spectral ranges of >1000 A, 25 GHz, 5 GHz and 2.5 GHz. Finesse up to 200 has been demonstrated. The devices are piezoelectrically tuned and are coupled to fibres in-line using standard rotary splices or ST connectors.

A stimulated-Raman-gain medium at 1.56-microm wavelength, consisting of molecular deuterium dissolved in low-loss silica optical fiber and pumped by 1.06-microm Nd:YAG laser light, is described. In a 100-m-long fiber with pump power of 130 W, InGaAsP injection-laser probe light at 1.56 microm was amplified by a factor of 4000 to an output power of 150 mW. The measured stimulated-Raman-gain coefficient at 1.56 microm is 7 x 10(-12) cm/W, about equal to the Raman gain of SiO(2) at the same wavelength.

The impulse responses of very-high-speed photodiodes are determined using 5?15 ps pulses from optically pumped ultrashort-cavity film lasers operating between wavelengths of 1.15 ?m and 1.54 ?m. The measured response time (FWHM) for a back-illuminated InGaAs/InP punch-through PIN photodiode is 30 Ps.