Time compression multiplex transmission system using a 1.3 μmsemiconductor laser as a transmitter and a receiver

A bidirectional system using 1.3 μm lasers as a transmitter and a receiver are investigated. The lasers considered are commercially available Fabry-Perot and distributed-feedback lasers. It is found that the poor performance of a laser receiver, compared to a PIN receiver, stems from three factors: low responsivity, high capacitance, and polarization dependence of responsivity, high capacitance, and polarization dependence of responsivity. The effect of each factor is evaluated. It has been clarified that the polarization dependence of sensitivity originates from the TE and TM modes dependence of both mode confinement factor and reflection at a facet. Using the measured parameters, 1.3-μm laser receiver sensitivity for a 10^-9 error rate is estimated. Burst data transmission experiments show that estimated sensitivities agree well with the measured values. Optical ping-pong transmission distance of narrowband services is determined based on estimated sensitivity     

Multichannel FM-TV transmission using an engineered 1.3 μmpraseodymium-doped fluoride fibre amplifier

The authors report the first use of a praseodymium-doped fluoride fibre amplifier (PDFFA) in a 24 TV channel FM-SCM transmission experiment. Twenty-four analogue FM-SCM-TV channels were amplified by a PDFFA without any observable degradation in picture quality. By using a single PDFFA as a post-amplifier, transmission over 104 km of `standard' 1.3 μm optimised fibre was demonstrated with a total loss budget of 45 dB. By using the same PDFFA as an inline amplifier, a loss budget of 53 dB was achieved     

Characteristics measurement of gain and refractive index of traveling-wave semiconductor optical amplifier

A novel method to measure the gain and refractive index characteristics of traveling-wave semiconductor optical amplifier（TMA） is presented. In-out fiber ends of TWA are used to construct an external cavity resonator to produce big ripple on amplified spontaneous emission（ASE） spectrum. By this means,Hakki-Paoli method is adepted to obtain the gain spectra of TWA over a wide spectral range. From measured longitudinal mode spacing and peak wavelength shift due to increased bias current, we further calculate the effective refractive index and the refractive index change. Special feature of refractive index change above lasing threshold is revealed and explained.     

High-gain, monolithic, cascaded fibre Raman amplifier operating at1.3 μm

A 39 dB-gain silica fibre Raman amplifier is demonstrated at 1.3 μm using a 1064 nm pump. Cascaded Raman generation and amplification are achieved in a monolithic ring cavity constructed solely from conventional fibre components, i.e. fusion WDM couplers and standard silica fibre     

Selective regrowth of a wide-bandwidth 1.3 μm integratedlossless tap and optical preamplifier

The authors report the first monolithically integrated wide-bandwidth lossless tap-that is, an optical semiconductor amplifier followed by a colinear reverse-biased waveguiding photodetector with fiber-coupled input and output. The integration was achieved by using off-axis selective epitaxial growth of ridge waveguides on a patterned dielectric layer. The tilted facets produced by the off-axis growth, along with photodetector absorption, serve to reduce the effective facet reflectivity to -36 dB without any antireflection coating. By adjusting the length of the absorbing photodetector section, part or all of the amplified light may be absorbed, allowing the device to function respectively as a lossless tap or an optical preamplifier. A lossless tap with an electrical bandwidth of 7 GHz, a responsivity of 26 A/W, and a fiber-to-fiber gain of 3 dB is shown to have a receiver sensitivity of -22 dB at 3 Gb/s     

Group delay measurement in single-mode fibers with true picosecondresolution using double optical modulation

Highly accurate group delay measurements in long single-mode fibers were achieved over the full 1200-1600 nm spectral range by measuring phase shifts of a modulated lightwave. The high modulation frequency is shifted down to the kilohertz range using a second optical modulation at the fiber output end, so that low-frequency, ultrasensitive detection and phase measurement can be performed with high-frequency resolution conserved. This results in extremely reliable measurements with a <1-ps resolution using a fully remote light source such as an LED or even a halogen lamp     

Long-haul soliton transmission at 1.3 μm using distributed Ramanamplification

10 Gb/s single channel soliton transmission over more than 10000 km in a standard communication fiber with distributed Raman amplification has been demonstrated in a recirculating fiber loop setup. It has been found that the Gordon-Haus timing jitter becomes the main limiting factor, provided that the generation of dispersive waves due to polarization mode dispersion has been minimized by adjusting the polarization state of the signal     

External-cavity semiconductor laser tunable from 1.3 to 1.54 μmfor optical communication

Using semiconductor optical amplifiers with properly designed nonidentical quantum wells made of InGaAsP-InP materials in the external-cavity configuration, the semiconductor laser is broadly tunable. The tuning range covers from 1.3 μm to 1.54 μm. Without additional filtering techniques, the laser beam emitted from the linear external cavity has the sidemode suppression ratio better than 30 dB. Also, the power ratio of the lasing mode to the total output power is 90%-99%, indicating the dominance of the lasing mode in the amplification process due to the broad gain spectrum     

1.55 μm wavelength region high-stability optical fibre lossvariation measurement using fibre coupler

A 1.55 μm-wavelength high-stability optical fibre loss variation measurement system, using a comparison method with an optical fibre coupler, was developed. Long-term stability within ±0.001 dB over a 120 hour period at a room temperature variation of ±2.2°C has been achieved     

An optical fiber amplifier for wide-band wavelength range around1.65 μm

The optical amplification characteristics of a 0.781-μm pumped thulium-doped fiber in the wavelength range of 1.6-1.7 μm are discussed. A maximum net gain of 2.0 dB was obtained for 1.69-μm operation. This optical fiber amplifier is suitable for in-service monitoring and identifying fibers operating at 1.2-1.6 μm     

Group delay dispersion measurements in InGaAsP 1.3-μm opticalamplifiers

Group delay dispersion (GDD) of ~15 ps/nm has been measured in a near-traveling-wave optical amplifier at a wavelength where measured gain ripple was ~2 dB, using the envelope phase-shift technique. This is compared to a measured GDD of ~180 ps/nm in a single-facet antireflection-coated amplifier biased below threshold with a gain ripple of ~17 dB. It is shown that these results agree qualitatively with standard theory. An important result is that GDD increases with the square of amplifier length. GDD can be reduced by an order of magnitude if gain ripple is reduced to 0.5 dB     

1.3-μm polarization-insensitive optical amplifier structurebased on coupled quantum wells

We show that polarization-insensitive optical gain over a wide bandwidth can be realized in a coupled pseudomorphic multiple-quantum-well structure. The barrier width is chosen such that heavy-hole subbands are grouped tightly and light-hole subbands are widely separated in energy. For specific strain conditions, the uppermost valence subbands, which have large occupation probability and strongly contribute to the gain, consist of a single light-hole subband and a group of coupled heavy-hole subbands. This arrangement gives rise to balanced gains for the TE and TM polarizations. We present calculated results for 1.3-μm semiconductor optical amplifier structures based on bands calculated in the framework of an eight-band k·p model. Two different material systems are examined, InAlGaAs and GaInAsP, on InP substrates     

8 Gbit/s transmission over 76 km of optical fibre using a directlymodulated 1.3 μm DFB laser

The authors report an optical transmission experiment at a data rate of 8 Gbit/s over an unrepeatered distance of 76 km. The transmitter was a directly modulated, 1.3 μm-wavelength, distributed-feedback laser. The receiver employed an avalanche photodiode and a high-impedance GaAs MESFET preamplifier     

1.5 μm multiquantum-well semiconductor optical amplifier withtensile and compressively strained wells for polarization-independentgain

A multiquantum-well optical amplifier for 1.5-μm wavelength operation using alternating tensile and compressively strained wells in the active region is described. For each bias level measured, the polarization sensitivity of the amplifier gain is 1 dB or less averaged over the gain bandwidth. This amplifier is suitable for integration with other optical devices in photonic integrated circuits which require polarization-independent gain     

High gain wideband amplifier IC using 0.7 μm GaAs MESFETtechnology

A high gain wideband differential amplifier with a new circuit configuration is proposed and monolithically integrated by using 0.7 μm-gate GaAs MESFET IC technology. The fabricated IC exhibited gain of 16.7 dB and bandwidth of 3.2 GHz. A gain twice that of a conventional differential GaAs-MESFET amplifier was achieved with small bandwidth degradation     

Reduced turn-on delay time in 1.3 μm InGaAsP/lnP n-typemodulation-doped strained multiquantum well lasers

Reductions in carrier lifetime, threshold current, and thus turn-on delay time, due to n-type modulation doping, have been experimentally demonstrated in 1.3 μm InGaAsP strained multiquantum well lasers for the first time     

Frequency-locking of a 1.3 μm DFB laser using a miniature argonglow lamp

The frequency of an InGaAsP distributed-feedback (DFB) laser was locked to the 2p₁₀-3d₅ transition of argon atoms at 1.2960 μm using the optogalvanic signal obtained from a commercial miniature glow lamp. At a discharge current of 500 μA, the signal-to-noise ratio of the optogalvanic signal corresponding to the Ar transition was about 18 dB. The peak-to-peak width of the first derivative signal was 650 MHz. The slope of the signal was 0.32 μV/MHz near the center of the transition. By using the linear portion of the first-derivative signal, the laser frequency was locked to the Ar 2p₁₀-3d₅ transition. The peak-to-peak frequency fluctuations in the free-running condition were estimated to be 650 MHz, which is mainly due to laser temperature fluctuations. When the servo-loop was closed, the frequency stability was improved to better than 13 MHz     

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     

Characteristics of GaAsSb single-quantum-well-lasers emitting near1.3 μm

We report data on GaAsSb single-quantum-well lasers grown on GaAs substrates. Room temperature pulsed emission at 1.275 μm in a 1250-μm-long device has been observed. Minimum threshold current densities of 535 A/cm² were measured in 2000-μm-long lasers. We also measured internal losses of 2-5 cm^-1, internal quantum efficiencies of 30%-38% and characteristic temperatures T₀ of 67°C-77°C. From these parameters, a gain constant G₀ of 1660 cm^-1 and a transparency current density J_tr of 134 A/cm² were calculated. The results indicate the potential for fabricating 1.3-μm vertical-cavity surface-emitting lasers from these materials     

15 Gb/s multichannel optical interconnect laser array transmitteroperating at λ=1.3 μm

We have fabricated and measured detailed bit error rate experiments on a 12 channel optical interconnect transmitter operating at rates up to 1.25 Gb/s per channel, using InGaAsP/InP λ=1.3 μm lasers. The lasers are highly uniform, the channel crosstalk is less than 1 dB, and the mode selective losses are low (<1 dB). This transmitter has been demonstrated in an architecture which would allow the transmission of 120 channels of 100-Mb/s uncompressed video signals