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A new reflective configuration for a monolithically integrated channel selector with power monitor is proposed. One star coupler, one arrayed waveguide grating, and a minimum number of semiconductor optical amplifier (SOA) gates are used to achieve loss-free transmission. A 32-channel device controlled by only 12 SOA gates is realized in InP. Low on-chip losses result in strongly reduced bias currents and an improved signal to noise ratio compared to previously demonstrated devices. The use of SOAs allows for switching on a nanosecond time scale.

A mode-adapted semiconductor optical amplifier (SOA) has been fabricated and packaged. At the gain peak, 1500 nm, the fiber to fiber gain was measured to be 32.5 dB. Statistics for eight packaged devices indicate that a fiber-to-fiber gain of 26.3 dB /spl plusmn/ 1.3 dB and a saturation output power of 12.4 dBm /spl plusmn/ 0.4 dBm are typical at a bias of 500 mA for /spl lambda/ = 1550 nm. Polarization sensitivity at 1550 nm was measured to be 1.1 dB /spl plusmn/ 0.4 dB and the transverse electric (TE) polarization state noise figure (NF) was determined to be 7.0 dB /spl plusmn/ 0.5 dB. The coupling loss was 1.3 dB /spl plusmn/ 0.1 dB per facet. This SOA, with a 1.3-nm filter, was used as an optical preamplifier in a 10-Gb/s return-to-zero (RZ) system testbed with a pseudorandom binary sequence (PRBS) of 2/sup 31/ -1. A 14.5-dB improvement in receiver sensitivity was observed at a bit error rate (BER) of 10/sup -11/.

We present a novel coupling scheme consisting of an integrated beam expander, a specifically tailored TiO/sub 2/ antireflection coating, optical index matching gel, and uncoated flat-end single-mode fiber (SMF). This scheme was used to package four-channel semiconductor optical amplifier arrays. Far-field profiles for each discrete amplifier in the array are typically 80 and 150 FWHM, perpendicular and parallel to the junction plane, respectively. The TiO/sub 2/ AR coating overcomes the indices mismatching of fiber glass and InP based device, and reduce optical reflection to 0.002% at 1.55 /spl mu/m. Misalignment tolerance in the l-dB excess loss range, for a discrete channel, is typically 5 /spl mu/m vertically and 8 /spl mu/m laterally. The average coupling loss is 4.3 dB per facet for the devices measured. Fiber coupled small signal gain for the amplifiers is typically 11.6 dB and a saturation output power of 3.0 dBm. The method of characterization and optimization of the TiO/sub 2/ coating is discussed.

Intraband modulation in semiconductor gain media has recently been shown to provide a wideband nonlinearity which is five orders of magnitude larger than the Kerr non-linearity in silica fiber. We discuss recent work on the application of this nonlinearity to the wavelength conversion function in all optical networks; specifically, carrier wavelength spectral translation by four-wave mixing. In addition to reviewing the current performance of these devices including conversion efficiency, signal-to-noise and a simple system demonstration, we will describe the underlying physics of the ultra-fast four-wave mixing mechanism and its application to TeraHertz spectroscopy of intraband scattering. An overview of wavelength conversion in the context of all-optical networks is provided and competing techniques to four-wave mixing wavelength conversion are also discussed.

Near field holography is a method of using grating photomasks in which the m = -1 and m = 0 diffracted beams of a UV source interfere to form a standing wave pattern. This simple hologram can then be used to expose a grating pattern on a process wafer when held in near- contact. This technique is especially attractive for use in OEICs and PICs when fabrication of the grating masks is accomplished with e-beam lithography and dry etching, since the diffractive properties of the mask can be controlled by the physical parameters of the mask. The grating period on masks made in this way can be precisely controlled to produce arrays of lasers each separated by only a small change in frequency (order 100 GHz) as may be required for WDM applications. We review the phenomenology of fused silica phase grating masks and describe work toward establishing characterization criteria, implementing practical printing methods, improving e-beam precision, and demonstrating laser array performance. We discuss principle issues and progress in each of the technical areas.

We discuss wavelength tuning and its corresponding quantum efficiency modulated by the standing wave effects in a resonant-cavity enhanced (RCE) photodetector. Specific design conditions are made for a thin In/sub 0.53/Ga/sub 0.47/As (900 /spl Aring/) photodetector wafer-fused to a GaAs-AlAs quarter wavelength stacks (QWS). Analytic expressions for the calculation of resonant wavelength and standing wave effects are derived, using a hard mirror concept of fixed phase upon reflection, and are found to agree reasonably well with the exact numerical approach, using a transmission matrix method. We then experimentally demonstrate that wavelength tuning as large as 140 nm and its corresponding quantum efficiency modulated by the standing wave effects are clearly observed in our wafer-fused photodetectors, consistent with the predictions. The external quantum efficiency at 1.3 /spl mu/m wavelength and absorption bandwidth for the wafer-fused RCE photodiodes integrated with an amorphous Si-SiO/sub 2/ dielectric mirror are measured to be 94% and 14 nm, respectively. This technique allows the formation of multichannel photodetectors with high quantum efficiency and small crosstalk, suitable for application to wavelength demultiplexing and high-speed, high-sensitivity optical communication systems. >

The next generation of undersea lightwave systems is likely to take advantage of the nonlinear properties of the transmission fiber by employing optical solitons [1,2]. A critical component will be the transmitter which generates the solitons and encodes the data. Previously, we have reported a monolithic extended-cavity laser, which actively mode-locked, generates solitons [3], An extended-cavity laser integrated with a modulator exhibited multi-peaked pulses due to internal reflections and a corresponding time bandwidth product of 0.8, which would prohibit soliton applications [4], Here, we report the first monolithic semiconductor transmitter which has applications in soliton systems. An extended-cavity laser section generates 8-ps solitons by active mode-locking and data is encoded by means of the integrated modulator at a bit rate of 4.9 Gbit/s. The optical pulses exhibit a time-bandwidth product of 0.30 and the extinction ratio of the monolithically integrated electro-absorption modulator is 20 dB.

We present a new design for a digitally tunable laser using two waveguide grating routers with different free spectral range. For an N-channel device, both the number of required amplifiers and the number of required grating arms scale as the square root of N, resulting in a more compact device than previously demonstrated and better scaleability. Contrary to previously demonstrated devices with a reduced number of amplifiers, all wavelength channels are multiplexed together in one common channel, allowing for a higher output power. Tuning speeds below 10 ns are envisioned. Experimental results are presented.

A photonic circuit implementing ten frequency reference filters for narrow-channel wavelength division multiplexing (WDM) has been fabricated. A diluted multiquantum-well waveguide structure is shown to yield a very low TE/TM polarization dependence of 1 AA, as well as improved absolute frequency control and reproducibility. A standard deviation in absolute filter wavelength of 3.33 AA is measured on a random set of devices from a 2-in wafer. The ten channels are evenly spaced by 7.2 AA. Such filters can be used to lock tunable lasers to a set of reference frequencies for WDM applications. The demonstrated diluted multiquantum-well waveguide structure with low birefringence and improved absolute wavelength control could potentially be used in other WDM integrated circuits requiring tight wavelength tolerance and polarization insensitivity. >

Details on the design, fabrication and properties of the first interferometric intensity modulators with monolithically integrated optical gain are presented. These guided-wave devices make use of two sets of InP-based quantum well heterostructures that are contained in a single base wafer and individually designed for enhanced electrorefraction and amplification at 1.55 mu m. The unique quantum well electrooptic properties as well as the fabrication techniques and waveguide design issues that determine final device performance are discussed. >

We propose and demonstrate a novel high-speed and wavelength insensitive Y-branch modulator in InGaAsP multiple-quantum-wells that exhibits negligible chirp and is also suitable for achieving controllable chirp. We raise the refractive index on one arm via applied bias and use the unbiased arm as a modulator. As the light switches to the biased arm, the modulated light in the unbiased arm experiences little phase change and therefore exhibits negligible chirp. Tunable chirp may be achieved using a push-pull bias configuration. We demonstrate that our modulator chirp is /spl sim/10 times lower than that of typical electroabsorption modulators.

We demonstrate a novel Y-branch digital switch with a double-etch waveguide structure to greatly enhance the loss and crosstalk performance. The double-etch design increases the coupling between the two tapered Y-branch waveguides, which allows for efficient switching while decreasing the radiation loss that arises from the branching angle. This combined advantage also allows us to reduce the switch length, which in turn results in an efficient high-speed design. The measured crosstalk and loss are -19 and 3 dB, respectively, for a 3-mm-long switch. Further crosstalk reduction is expected from the simulation of a more optimized design.

An interferometric wavelength converter with preamplifiers for both the signal input and the continuous-wave probe input is presented. The dynamic range of the device is enhanced: penalty-free conversion is demonstrated at 2.5 Gb/s for input powers ranging from -6 to +4 dBm. Transmission of the converted signal over 480 km of standard fiber shows penalty improvement relative to the unconverted, information-limited signal.

Reconfigurable optoelectronic wavelength conversion to 11 100-GHz spaced wavelengths is achieved using a wavelength selectable laser array with an integrated electroabsorption (EA) modulator at a bit rate of 2.5 Gb/s. Wide dynamic range at the input from -24.2 to -6.5 dBm is achieved and uniform back-to-back transmission performance is measured for all wavelengths.

A polarization-insensitive InP-based p-i-n multiple-quantum-well switch is demonstrated for the first time. Polarization-insensitive switching and loss are achieved. Crosstalk and loss measurements across a wavelength range of 20 nm centered at 1.55 /spl mu/m are reported. A crosstalk of better than -13 dB is achieved for both TE and TM polarizations across the 1.54-1.56-/spl mu/m wavelength range with a switching voltage of -7 V. A low on-chip loss of less than 3 dB is achieved for both TE and TM across the above wavelength range, with a compact switch structure which is 3 mm long.

The first interferometric wavelength converter with an integrated continuous-wave (CW) probe source is presented. The two-port device operates independent of polarization for a broad range of input wavelengths. The input dynamic range is enhanced by an integrated input preamplifier. Input powers as low as -5.4 dBm in the fiber are converted with penalties as low as 0.6 dB at a bit rate of 2.5 Gb/s. The device is shown to operate with the same low penalty for same-wavelength operation as well. The chirp parameter /spl alpha/ is measured to be 2 for wavelength conversion. No chirp is added to the input signal for same-wavelength operation.

Reconfigurable channel drop in a wavelength-division multiplexed system is demonstrated using a packaged semiconductor amplifier/filter. The filter is electrically tunable over 9.0 nm with a 0.9-nm width and is used with an optical circulator to demultiplex three 5.0-Gb/s WDM channels spaced by 2.25 nm. A receiver sensitivity improvement and low optical crosstalk is observed over a dynamic range of nearly 10 dB.

We report on an efficient method for suppressing stimulated Brillouin scattering (SBS) with negligible residual amplitude modulation (AM) using the temperature tunable properties of a semiconductor laser diode. We demonstrate an effective threshold of 23.4 dBm by applying a 16 V/sub pp/, 5 kHz sinusoid to a thin-film resistor on top of the laser diode. The residual AM is measured to be only 1.2/spl middot/10/sup -4/.

Active mode-locking of a broadly tunable monolithic semiconductor laser based on a grating assisted vertical coupler filter resulted in 10 - 12 ps pulses at a repetition rate of 15.8 GHz. Mode-locking was achieved at discrete wavelengths from 1544.5 nm to 1564.7 nm.

A 1.3-/spl mu/m Fabry-Perot laser with a directional coupler power tap inside the laser cavity, used for diverting optical power to an integrated waveguide monitoring photodetector is demonstrated. The monitoring detector provides photocurrent which is linear with the front facet output power, with responsivity as high as 0.37 mA/mW, depending on the length of the directional coupler coupling region.

An 8-channel DWDM multiplexer with per-channel amplification is demonstrated. 10 dB, 3 dB, and 0 dB fiber-to-fiber gain is achieved using lensed fiber, cleaved fiber, and cleaved fiber array respectively. BER performance is also presented.

We demonstrate a long-wavelength detector structure using an undercut mesa and an air-bridged coplanar metal waveguide to significantly reduce both the diode RC constant and the parasitic capacitance. Record electrical bandwidths of 120 GHz are demonstrated for long-wavelength photodetectors.

We propose and demonstrate a simple, potentially low-cost, photonic integrated circuit that can operate as a transceiver in a ping-pong optical data-link configuration. The device is designed for uncooled operation, with a gain section, a detector, and a beam expander inside a Fabry-Perot cavity. The detector has a 1.4 /spl mu/m quaternary layer with a broad spectral responsivity range extending to 33 nm higher than the lasing wavelength of the device. The transmitter can provide 8 dBm inside a single-mode fiber, and the beam expander relaxes the alignment tolerance to a single-mode fiber.

Wavelength conversion using semiconductor optical amplifiers monolithically integrated in a three-part Mach-Zehnder configuration is achieved for data rates of 1 and 2.5 Gb/s. The three-port configuration allows efficient use of pump signal power, as well as counter-propagation of pump and converted signals, eliminating the need for a filter. Operation of the device at 5 Gb/s in a two-port configuration is also achieved. Dynamic extinction ratios larger than 13 dB, as well as both data-inverting and noninverting operation are demonstrated. >

A novel optical translator that can perform 3R-regeneration and wavelength conversion of high-speed return-to-zero signals is demonstrated at 20 Gbit/s. Efficient retiming and bit-error-rate performance is measured using a Mach-Zehnder interferometer with integrated semiconductor optical amplifiers.

We demonstrate a photonic circuit with an optical preamplifier, a WDM filter and a fast photodetector integrated on the same chip. The passive integrated filter is formed by an aspheric waveguide lens and a planar Bragg grating. This arrangements yields narrow filter response (8 /spl Aring/ width at -3 dB is demonstrated) and high rejection ratio of 24 dB. The optical preamplifier consisting of strained multi-quantum well layers provides sufficient amplification to overcome the passive losses. Response curves demonstrate net on-chip gain with low ripple. >

We demonstrate a polarization‐insensitive optical bandpass filter in indium phosphide (InP) with a 3 dB bandwidth of 1.5 nm at a center wavelength of 1.498 μm. The 5‐mm‐long filter is based on a grating‐assisted vertical directional coupler and features a novel double‐periodic coupling grating.

A novel monolithic semiconductor laser is demonstrated. The optical cavity comprises a 1/spl times/N waveguide grating multiplexer connected to N optical amplifiers. By driving a specific output port, laser oscillation is obtained at the wavelength determined by the wavelength path through the multiplexer. Such a laser is very useful for WDM systems because it is capable of producing a comb of precisely spaced frequencies. >

Four-wave mixing in traveling-wave amplifiers (TWA's), when used for wavelength conversion, has several advantages. Owing to their traveling-wave operation, these devices offer the potential for very high speed operation as well as continuous tuning of the input and output wavelengths. In addition, since the converted signal is the phase-conjugate replica of the input signal, the conversion is transparent to the modulation format, and provides the possibility for fiber-dispersion-compensation in lightwave communication systems. In this paper, we present measurements of wavelength conversion efficiencies in TWA's for /spl Delta//spl lambda/-shifts as large as 27 nm. We show that wavelength up-conversion is less efficient than down-conversion and show that the effect results from phase interference between the interband and intraband mechanisms causing four-wave mixing. >

We demonstrate lasing in InGaAsP (1.3 /spl mu/m) vertical cavity lasers employing GaAs/AlAs mirrors on a GaAs substrate. The lasers operate pulsed at 300 K with a threshold current of 9 mA and they operate continuous wave at temperatures as high as 230 K. >

Seven packaged wavelength selectable laser arrays were tested and found to have average chirp parameter of 0.18 /spl Aring/ under 2.5 Gb/Sec modulation. Temperature tuning necessary to reach a standard WDM wavelength for any laser on any of the packages was /spl les/5.2/spl deg/C.

Summary form only given. We demonstrate a novel modulation scheme in which both data-encoding and pulse generation are achieved using a single integrated semiconductor laser/modulator. Data-encoded, near-transform limited 66 ps pulses are obtained at 2.5 Gbit/s and BER performance is reported.

Wavelength conversion is recognized as an important function in future fiber networks employing wavelength division multiplexing. The authors have recently demonstrated broad-band wavelength conversion over spans as large as 27 nm. Their approach uses ultra-fast four-wave mixing dynamics associated with intraband relaxation mechanisms in semiconductor traveling-wave amplifiers (TWA's). In the paper the authors present new results showing conversion over wavelength spans as large as 65 nm. This surpasses the previous record by over a factor of two. Of equal importance, they also verify experimentally their previous theoretical prediction that wavelength conversion efficiency varies as the cube of TWA single pass gain. In the course of our previous work, we have shown that the theoretical efficiency, η, of this process can be expressed by the simple relation: η = 3G + 2P + R(Δ⋋) where η is the ratio in dB of the converted signal output power to the signal input power and G is the single pass TWA optical gain. A crucial point is the presence of 3G in this expression - essentially, the wavelength converter uses the available TWA optimal gain three times. We verified this expression using an experimental setup similar to that described in. Tunable, single-frequency, erbium fiber ring lasers were used as pump and signal sources and TWA devices used contained tensile-strained mutli-quantum well active layers described in. Figure 1 shows conversion efficiency data plotted versus single-pass saturated optical gain. The pump power was -5.2 dBm and the signal power was -11.3 dBm. The measured slope of 3.18 confirms the cubic dependence of efficiency on single pass gain.

We present the transverse mode and temperature characteristics of a novel InGaAsP (1.3 /spl mu/m) vertical cavity laser structure which employs a lattice mismatched GaAs/AlAs mirror and one dielectric mirror. The devices lase in a linearly polarized, single transverse mode up to 2 times threshold. The characteristic temperature of 11 /spl mu/m diameter devices is 67 K at room temperature. >

Summary form only given. In summary, a Mach-Zehnder WDM fibre network wavelength converter with variable input and output wavelengths has been presented. The integrated signal and probe pre-amplifiers potentially reduce input power requirements. Around 25-dB extinction ratio has been demonstrated, as well as operation at 2.5 Gbit/s.

We use a fiber Bragg grating filter to reduce inter-symbol interference in an integrated Mach-Zehnder semiconductor optical amplifier wavelength converter. The grating filter reduced the conversion power penalty by 3.5 dB at 5 Gb/s.

We have examined the performance of an integrated semiconductor optical amplifier/elctroabsorption (SOA-EA) modulator device and find that the device provides good performance at 2.5 Gbit/s modulation, with fiber-to-fiber gain, and low polarization sensitivity. With improvements in packaging, the high-speed performance of this device should be extended to higher modulation rates.

Optical wavelength conversion or wavelength adaptation is a desired functionality for evolving WDM network architectures. The ability to perform routing and switching as a function of wavelength in a network can be achieved through wavelength conversion. The one feature necessary for all wavelength converters is the ability to provide a new wavelength which complies with the specified wavelengths in the system. We describe an optoelectronic wavelength converter in which the new wavelength is provided by an integrated electroabsorption modulated laser (EML) array suitable for low-chirp long haul transmission. The converter consists of a photodiode which converts the input optical signal to an electrical signal. This signal is amplified to drive an EA modulator which is integrated with a DFB laser array, passive optical power combiner and optical amplifier. Each laser in the array has a different grating and thus lases at a different wavelength in the 1550 to 1560 nm region. The transmitter can be configured to provide either selected fixed wavelength output or to switch between output wavelengths as determined by network control. We demonstrate the operation of the wavelength converter at 2.5 Gbits/s. The output wavelength is switched between compliant wavelengths spaced by 200 GHz through software control and bit-error-rate (BER) performance is measured.

Summary form only given. Intraband modulation in semiconductor gain media has recently been shown to provide a wide-band nonlinearity which is over five orders of magnitude larger than the Kerr nonlinearity in silica fiber. We discuss recent work on the application of this nonlinearity to the wavelength conversion function in all optical networks; specifically, carrier wavelength spectral translation by four-wave mixing in semiconductor traveling-wave amplifiers (TWAs).

In conclusion, we have demonstrated a six-wavelength laser array with an integrated amplifier and modulator designed for transmission of a single selectable wavelength. The single step printed gratings provided /spl Lambda//4-shifted DFB lasers with average channel spacing of 200 GHz. Laser thresholds were approximately 20 mA, and output powers of several mW were available from all six lasers through the modulator at an amplifier drive of 75 mA.

The bandwidth-efficiency product of ultra high-speed pin photodetectors has been severely limited by the thickness of the absorbing layer, the diode RC time constant, and the parasitic capacitance from the periphery of device. In this paper, we propose and demonstrate a novel long-wavelength detector structure with a mushroom-like mesa and an air-bridged coplanar metal to significantly cut down both the diode RC constant as well as the parasitic capacitance. The quantum efficiency of this structure can be further enhanced to close to 100 % if wafer fusion is used to bond the In/sub 0.53/Ga/sub 0.47/-InP detector to a GaAs/AlAs quarter-wave stack (QWS), followed by deposition of a Si/SiO/sub 2/ QWS to form a Fabry-Perot cavity.

A monolithically integrated photonic circuit with an InGaAs/InGaAsP multiple-quantum-well (MQW) traveling-wave optical amplifier, a Bragg reflection grating-folded noise filter, and an MQW photodetector has been demonstrated. This photonic circuit offers potential as a preamplified lightwave receiver in high-data-rate applications because of its compactness and potentially low cost. >

A photonic integrated circuit with an InGaAs/InGaAsP multiple-quantum-well (MQW) traveling-wave optical amplifier and a grating-assisted vertical-coupler filter as a noise filter have been demonstrated. A fiber-to-amplifier/filter gain of approximately 0.5 dB and a 3-dB filter bandwidth (FWHM) of approximately 70 AA at 1.56 mu m filter center wavelength have been achieved. This photonic circuit is potentially suitable as a building-block for preamplifier lightwave receivers or high-gain, high-power optical amplifiers which are essential for optical communication systems and lightwave networks. >

A mode-locked monolithic extended-cavity laser is employed as a soliton source in an 8.2 Gbit/s recirculating fiber loop experiment. The 20-ps solitons exhibit a time-bandwidth product of 0.34. Pulse profiles are measured with a streak camera at propagation distances up to 15000 km. Numerical simulations showed that the measured data transmission distance, 4200 km for a bit error rate of 10/sup -9/, may increase to approximately 8000 km with improved receiver immunity to Gordon Haus pulse jitter. >

We present a distributed Bragg reflector (DBR) laser/modulator photonic integrated circuit capable of transmission over 674 km of conventional fiber at 2.5 Gb/s. Transmission was performed at four wavelengths over a range of >4 nm. The bit error rate (BER) sensitivity achieved at each wavelength varied by less than 1.1 dB. These results produce a record bit rate-distance product at each wavelength of 1.7 Tb.km/s for monolithic transmitters through nondispersion shifted fiber. Such devices are ideal sources for multichannel wavelength-division-multiplexed (WDM) transmission systems. >

The integrated operation of a 16*1 wavelength-division-multiplexed (WDM) source with distributed Bragg reflector (DBR) lasers and electroabsorption modulators has been demonstrated. By using repeated holographic exposures and wet chemical etching, 16 different wavelengths from 1.544 to 1.553 mu m with an average channel spacing of 6 AA are obtained. A high-performance combiner is used to obtain a very uniform coupling into the single-output waveguide, and with the integration of an optical amplifier an average optical power of -8 dBm per channel is coupled into a single-mode fiber. >

An 8-wavelength distributed Bragg reflector (DBR) array for narrow channel wavelength division multiplexing (WDM) has been fabricated with a new technique for printing first-order Bragg gratings using a phase mask and a conventional incoherent source. All the distributed gratings were printed in a single photolithographic step with a slightly modified mask aligner. The DBR's excellent wavelength control for channels separated by as little as 0.8 nm is described. Many advanced photonic devices relying on gratings like quarter-wave shifted distributed feedback (DFB) lasers and wavelength division multiplexing (WDM) components can potentially be manufactured with this technique in a simple and cost-effective way. >

Highly nondegenerate four-wave mixing was investigated in a 1.5 µm compressively strained multi-quantum-well semiconductor traveling-wave optical amplifier at detuning frequencies up to 600 GHz. A gain nonlinearity with a characteristic relaxation time of 650 fs was determined from the data, and the nonlinear gain coefficient was estimated to be 4.3×10^–23 m^3. Dynamic carrier heating is believed to be the major source of nonlinear gain in this device at the wavelengths investigated.

A multiquantum-well optical amplifier for 1.5- mu m 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. >