Coherent receiver front-end module including a polarizationdiversity waveguide OIC and a high-speed InGaAs twin-dual p-i-nphotodiode OEIC both based on InP

The economic implementation of coherent optical systems requires practical integrated optical front-end receiver devices with reasonable degree of integration. As a precursor to such an OEIC, an InGaAsP/InP polarization diversity waveguide OIC, including two TE/TM-mode splitters, two TE-filters, two 3-dB couplers, and a planar front-illuminated InGaAs twin-dual-p-i-n photodiode-OEIC (including two balanced p-i-n photodiodes) was fabricated. The OIC depicts a TE/TM-mode separation of more than 13 dB, a 3-dB coupler imbalance of less than 10% and an intrinsic loss of less than 2 dB. A single detector device shows a responsivity of 1.05 A/W at a wavelength of 1.55 μm, a total series resistance below 10 Ω, and a 3-dB bandwidth of more than 10 GHz. The O(E)ICs have been (packaged) in a versatile housing for system tests. The operation of the modules has been demonstrated in a heterodyne experiment yielding a bandwidth of more than 2.2 GHz for the whole module     

Beyond 240 Gb/s per Wavelength Optical Transmission Using Coded Hybrid Subcarrier/Amplitude/Phase/Polarization Modulation

In this letter, we propose a low-density parity-check coded hybrid subcarrier/amplitude/phase/polarization (H-SAPP) modulation scheme suitable to achieve a 240-Gb/s single-channel transmission rate over optical channels. The proposed scheme doubles the aggregate transmission rate achievable by eight-quadrature amplitude modulation while providing 2-dB optical signal-to-noise ratio performance improvement at a bit-error-ratio (BER) of $10^{-6}$ . Moreover, H-SAPP can increase the aggregate rate of the hybrid amplitude/phase/polarization scheme while maintaining the BER performance intact.      

Rayleigh scattering influence on performance of 10 Gb/s opticalreceiver with Er-doped optical fiber preamplifier

The achievement of -30.8 dBm (630 photon/bit) receiver sensitivity at 10 Gb/s, with an Er³⁺-doped optical fiber preamplifier, is discussed. This is an 8.3-dB sensitivity improvement over the avalanche-photodiode/FET receiver. Power penalties caused by a noise increase due to Rayleigh backscattering by the transmission optical fiber have been evaluated. Approximately -30-dB Rayleigh scattering from a 20-km optical fiber resulted in a 3.5-dB power penalty for a 25-dB-gain optical amplifier     

InP-based 10-GHz bandwidth polarization diversity heterodynephotoreceiver with electrooptical adjustability

A polarization diversity optical receiver, integrated with two pairs of balanced photodiodes in the InP/InGaAsP material system, is described. This circuit includes two polarization splitters based on modal birefringence and, for the first time, adjustable 3-dB TE and TM directional couplers (relaxing fabrication tolerances). On-chip losses are below 2.5 dB (TE) and 5.5 dB (TM). Waveguide to PIN coupling efficiency is >95%. Polarization crosstalk is in the 9-10-dB range, 3-dB couplers balance can be recovered, and common mode rejection ratio (CMRR) lower than -30 dB is obtained and remains below -20 dB over 6 GHz. Balanced receiver circuit 3-dB bandwidth is in excess of 10 GHz     

Si bipolar chip set for 10-Gb/s optical receiver

Three Si bipolar ICs, a preamplifier, a gain-controllable amplifier, and a decision circuit, have been developed for 10-Gb/s optical receivers. A dual-feedback configuration with a phase adjustment capacitor makes it possible to increase the preamplifier bandwidth up to 11.2 GHz, while still retaining flat frequency response. The gain-controllable amplifier, which utilizes a current-dividing amplifier stage, has an 11.4-GHz bandwidth with 20-dB gain variation. A master-slave D-type flip-flop is also operated as the decision circuit at 10 Gb/s. On-chip coplanar lines were applied to minimize the electrical reflection between the ICs     

Performance and scalability of a single-stage SOA switch for 10/spl times/10 gb/s wavelength striped packet routing

This letter reports successful routing of 10/spl times/10 Gb/s multiwavelength optical packets using single-stage semiconductor optical amplifier switches. Performance under switching is assessed with up to ten wavelengths with particular emphasis being placed on the limit of operation. A 15.2-dB power margin is demonstrated which allows at least eight port connections with a commercially available 0-dBm output 10-Gb/s transmitter and -21-dBm sensitivity receiver.     

A new Faraday rotator using a thick Gd:YIG film grown by liquid-phase epitaxy and its applications to an optical isolator and optical switch

A new Faraday rotator using a thick garnet film grown by liquid-phase epitaxy (LPE) has been proposed and film growth technology for the rotator has been investigated. The new Faraday rotator had good features of very low cost and small size, due to high productivity of the LPE-grown film and low magnetic saturation field, respectively. By using the new Faraday rotator, an optical isolator and magnetooptic switch for single-mode fiber systems have been developed. The optical isolator featured 0.8-dB insertion loss and 25-dB isolation at 1.3-μm wavelength. The magneto-optic 1 × 2 switch was independent of light polarization and featured 1.3-1.7-dB insertion loss, -25-dB crosstalk, and 30-μs switching time at 1.3-μm wavelength. Minimum switching voltage was ±5 V. Magneto-optic devices using the new Faraday rotator is practical for use in1.2-1.7-mum wavelength fiber-optic systems, because of good optical properties, compactness, and low cost.     

Coherence-collapse threshold of 1.3-/spl mu/m semiconductor DFB lasers

The onset of the coherence-collapse threshold is theoretically and experimentally studied for monomode 1.3-/spl mu/m antireflection/high reflection distributed-feedback lasers taking into account facet phase effects. The variation of the coherence collapse from chip to chip due to the facet phase is in the range of 7 dB and remains almost independent of the grating coefficient. Lasers that operate without coherence collapse under -15-dB optical feedback, while exhibiting an efficiency as high as 0.30 W/A, are demonstrated. Such lasers are adequate for 2.5 Gb/s isolator-free transmission without under the International Telecommunication Union recommended return loss.     

Direct Detection of Direct Optically Filtered Millimeter-Wave Signals

Good performance of a direct optical microwave filter combined with direct detection consisting of a single superimposed grating used in reflection has been assessed through bit-error-rate (BER) measurement. In the passband with a 3-dB bandwidth of 2GHz, the BER is below 1.2times10^-11, showing nearly on-off behavior of the filter     

Spot-size converter integrated polarization insensitivesemiconductor optical amplifiers

Spot-size converter integrated polarization-insensitive semiconductor optical amplifier (SSC-SOA) with angled window has been designed and fabricated using both selective area growth and successive lateral tapering. A narrow beam divergence of 80×15°, 0.2-dB amplified-spontaneous-emission ripple, and 1.5-dB polarization sensitivity within the 3-dB optical bandwidth were obtained at 29.7-dB chip gain. The fiber-to-fiber gain of the SOA module was measured to be 22 dB at 200 mA, i.e., the coupling loss was below 4 dB per each facet     

27-dB gain unidirectional 1300-nm polarization-insensitive multiplequantum well laser amplifier module

An unidirectional polarization-insensitive multiple quantum well laser amplifier module for the 1300-nm window with a record high gain of 27 dB and a 3-dB saturation output power of 13 dBm is demonstrated. The module gain has a 3-dB width exceeding 60 nm and shows a typical polarization sensitivity and gain ripple as low as 0.3 dB. To provide immunity for backscattered or reflected light, polarization independent optical isolators were inserted in the input and output coupling optics of the package. A practical optical amplifier module for the 1300-nm window is very desirable, because most of the presently installed fiber has its zero dispersion wavelength around 1310 mm, while much of the older fiber often only can be operated around this wavelength     

Vertical-cavity amplifying modulator at 1.3 μm

The modulation/switching properties of a vertical-cavity semiconductor optical amplifier operating at 1.3 μm wavelength are investigated. The device was optically pumped and operated in reflection mode. A 150-mV (100 mA) modulation of the drive to the pump source produced a 7-dB modulation of the pump power, which produced a 35-dB modulation in the output signal. The maximum extinction ratio was 35 dB, and limited by device heating. Frequency response measurements revealed a modulation bandwidth of 1.8 GHz when the amplifier was saturated. This enabled 2.5-Gb/s modulation of a -10 dBm input signal with 5.5-dB fiber-to-fiber gain     

High-gain, high-power 1550-nm polarization independent MQW optical amplifier

A practical 1550-nm polarization independent semiconductor optical amplifier configuration employing compressively strained quantum wells and a few commercially available optical components is reported. Crosstalk from counter propagating light, which may easily occur in such a configuration, has been sufficiently suppressed for practical use. For the entire configuration a net fiber-to-fiber gain of 17 dB, a 3-dB saturation output power of 13 dBm and a noise figure of 9 dB have been demonstrated. The polarization dependence was only 0.7 dB. The polarization independent 1550-nm semiconductor optical amplifier reported here is attractive when power consumption and compactness are of major concern and especially for applications involving nonlinear signal processing and switching.     

A broad-band amplifier using GaAs/GaAlAs heterojunction bipolartransistors

A compact wideband amplifier (or gain block) designed around a Darlington pair of GaAs/GaAlAs heterojunction bipolar transistors (HBTs) is discussed. This circuit has been fabricated by an ion-implanted process with a transistor f_t of 40 GHz. Two variants of the circuit gave either a 8.5-dB gain with a DC-to-5-GHz 3-dB bandwidth or a 13-dB gain with a DC-to-3-GHz bandwidth. These amplifiers gave 11.8- and 18.3-dBm output, respectively, at 1-dB gain compression     

High-efficiency 1.3 /spl mu/m InAsP-GaInP MQW electroabsorption waveguide modulators for microwave fiber-optic links

High-efficiency electroabsorption waveguide modulators have been designed and fabricated using strain-compensated InAsP-GaInP multiple quantum wells at 1.32-/spl mu/m wavelength. A typical 200-/spl mu/m-long modulator exhibits a fiber-to-fiber optical insertion loss of 9 dB and an optical saturation intensity larger than 10 mW. The 3-dB electrical bandwidth is in excess of 20 GHz with a 50-/spl Omega/ load termination. When used in an analog microwave fiber-optic link without amplification, a RF link efficiency as high as -38 dB is achieved at 10 mW input optical carrier power. These analog link characteristics are the first reported using MQW electroabsorption waveguide modulators at 1.32 /spl mu/m.     

High-gain 1310-nm reflective semiconductor optical amplifiers with low-gain uncertainty

A 1310-nm reflective semiconductor optical amplifier with a gain uncertainty of only 0.8 dB at an average gain level of over 30 dB has been demonstrated using a microoptic polarization reversing retroreflector. For this amplifier 3-dB saturation output powers of up to 10 dBm and a noise figure of 7.5 dB have been obtained. A low gain uncertainty for undefined input signal polarization states and input signal wavelengths (which may vary over several nanometers) is of primary importance in switching applications.     

Long wavelength vertical-cavity semiconductor optical amplifiers

This paper overviews the properties and possible applications of long wavelength vertical-cavity semiconductor optical amplifiers (VCSOAs). A VCSOA operating in the 1.3-μm wavelength region is presented. The device was fabricated using wafer bonding; it was optically pumped and operated in reflection mode. The reflectivity of the VCSOA top mirror was varied in the characterization of the device. Results are presented for 13 and 12 top mirror periods. By reducing the top mirror reflectivity, the amplifier gain, optical bandwidth, and saturation output power were simultaneously improved. For the case of 12 top mirror periods, rye demonstrate 13-dB fiber-to-fiber gain, 0.6 nm (100 GHz) optical bandwidth, a saturation output power of -3.5 dBm and a noise figure of 8.3 dB. The switching properties of the VCSOA are also briefly investigated. By modulating the pump laser, we have obtained a 46-dB extinction ratio in the output power, with the maximum output power corresponding to 7-dB fiber-to-fiber gain. All results are for continuous wave operation at room temperature     

Theoretical and experimental studies of a spot-size transformerwith integrated waveguide for polarization insensitive opticalamplifiers

The simple fabrication technology of an active waveguide for polarization insensitive optical amplifiers, integrated with tapers and a passive waveguide for fiber coupling, is presented. The spot size transformation along the taper, yielding a mode expansion factor of more than 9 in horizontal direction and about 2 in vertical direction, is experimentally verified and the results are compared to theoretical computations. Using a cleaved single mode fiber, the coupling loss is as low as 2.6 dB with -1-dB positional tolerances of 2.2 μm and 1.5 μm in vertical and horizontal directions. Besides relaxing on fiber coupling, the large spot size transformation in horizontal direction allows for a drastic reduction of the reflection coefficient to less than 10^-3 at a facet tilted by 4° with respect to the waveguide axis     

Polarization independent LiNbO3 8×8 matrix switch

A polarization-independent LiNbO₃ strictly blocking 8×8 matrix switch has been developed. A relatively low insertion loss, below 12 dB, has been obtained by a reduction in bending loss, using a wide bent waveguide width. The switch has less than -18.7-dB crosstalk and about 85-V switching voltage at any incident polarization with 1.3-μ wavelength light     

Widely tunable polarization-independent all-optical wavelengthconverter using a semiconductor optical amplifier

We report a polarization-independent widely tunable four-wave mixing wavelength converter using polarization diversity and broad-band orthogonal pumps in a single semiconductor optical amplifier. The conversion efficiency is nearly constant (less than 3-dB variation) over a 36-nm range with less than 0.34 dB polarization sensitivity. The power penalty at 10^-9 bit error rate for a 10-Gb/s signal is less than 0.9 dB