K. Takahata

Ultrafast optoelectronic packet processing for asynchronous,optical-packet-switched networks [Invited]

Feature Issue on Optical Interconnection Networks (OIN). We describe hybridn optical-electrical systems that perform header processing and buffering ofn ultrafast, asynchronous optical packets. Our systems are enabled by three key, noveln devices: an all-optical serial-to-parallel converter, an optical clock-pulsen generator, and a photonic parallel-to-serial-converter. These devices allown utilization of complementary metal-oxide semiconductor technology for compact,n highly functional optical packet processing. A simplified node architecture forn asynchronous, optical- packet-switched networks is made possible by these systemsn with all the necessary node functions integrated compactly. We also demonstrate ann optical label swapper and a photonic random access memory for 40-Gbit/s, 16-bit,n asynchronous optical packets.

Photonic random access memory for 40-Gb/s 16-b burst optical packets

We present a photonic random access memory (RAM) that can write and read high-speed asynchronous burst optical packets freely by specifying addresses. The photonic RAM consists of an optical clock-pulse generator, an all-optical serial-to-parallel converter, a photonic parallel-to-serial converter, all developed by us, and a complementary metal-oxide-semiconductor RAM as a storage medium, and features large capacity, long-term storage, random access at an arbitrary timing, low power consumption, and compactness. We experimentally confirm its basic operation for 40-Gb/s 16-b optical packets.

1.3-

A 1.3- monolithically integrated light source for metro area 100-Gb/s Ethernet is developed. Four 25-Gb/s electroabsorption modulators integrated with distributed-feedback lasers and their multiplexer are monolithically integrated on one chip. A shallow ridge waveguide is used for lasers and modulators for large modulation bandwidth, and a deep ridge waveguide is used for the multiplexer region due to its low bending and radiation losses. The integration of hetero-waveguide devices enables the very small chip size of 22.6 . With the device, 100-Gb/s (4 25-Gb/s simultaneous) operation is demonstrated with the clear eye-openings, and error-free 40-km single-mode fiber transmission is achieved for the first time.

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The gain saturation coefficients were measured for strained and unstrained multiple quantum-well distributed feedback (MQW-DFB) lasers. The gain saturation coefficient depends on the deviation of the lasers transverse-magnetic (TM) mode gain peak wavelength from its transverse-electric (TE) mode gain peak wavelength delta lambda , which is related to the strain on the active-layer wells. The gain saturation coefficient epsilon increased with increasing compressed strain on the active-layer wells. The coefficient epsilon of the unstrained MQW DFB laser with a wavelength deviation delta lambda of -350 AA was 2.45 x 10/sup -17/ cm/sup 3/, and epsilon increased up to 12.6 x 10/sup -17/ cm/sup 3/ in the SL-MQW DFB laser with a wavelength difference delta lambda of -890 AA.

m 4

Gain saturation coefficients of unstrained- and strained-layer multiple-quantum-well lasers were measured experimentally. These coefficients were higher in lasers that had compressive strain in their active-layer wells: 2.45*10/sup -17/ cm/sup 3/ with unstrained wells and 12.6*10/sup -17/ cm/sup 3/ with strained wells. The higher gain saturation coefficient in lasers with strained active-layer wells is related to their higher linear TE mode gain coefficient. The linearity factor (K factor) between a lasers damping constant and the square of the lasers resonant frequency decreased slightly with the introduction of the strain in the lasers active layer wells. This factor, however, took the value of about 0.2*10/sup -9/ s for each of these lasers. >

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A novel optical frequency conversion device that successfully demonstrates optical frequency conversion and unidirectional transmission of optical signals has been designed and fabricated. The device is composed of a gain region and saturable absorber region with monolithically integrated distributed Bragg reflector (DBR) mirrors with different coupling coefficients. The device structure is optimized to achieve three functions: 1) unidirectional light output, 2) converted-light wavelength tuning, and 3) optically triggered optical frequency conversion. The output power of converted light from the light input-end facet of the device is 30 dB smaller than that from the output-end facet, and the converted light wavelength can be scanned over 4 nm without a bias current to the input-end DBR region, and it is widened to 7.8 nm by injecting current to that region. The device emits converted light only when light input is injected and optical signals are unidirectionally transmitted, and its response frequency is estimated to be 0.8 GHz. >

25-Gb/s Monolithically Integrated Light Source for Metro Area 100-Gb/s Ethernet

Tunable wavelength conversion of a 10 Gb/s signal over a broad wavelength range of about 90 nm is achieved by using a super structure grating distributed Bragg reflector laser. The extinction ratio dependence of converted signal light on input signal light power and bias current to the laser active region is discussed. The extinction ratio becomes large when the input signal light power increases and the bias current decreases. Bit error rate measurements show that error-free, penalty-free wavelength conversion is achieved when the extinction ratio is large (12.5 dB) and that the bit rate which error-free wavelength conversion is possible increases as the input signal light power increases. Twenty Gb/s signal wavelength conversion is also demonstrated.

Gain saturation coefficients of strained-layer multiple quantum-well distributed feedback lasers

The frequency response of a unidirectional-output optical frequency conversion device is measured. The device has a saturable absorber region within the active region, which acts as an optical gate for converted light. The 3-dB bandwidth of the device with saturable absorber region is measured up to 800 MHz, and is found to be limited by the frequency response of the saturable absorber region. To operate the device faster, lasing mode intensity modulation by input light is attempted by using the device in a laser diode mode. In this case, the electrodes of the saturable absorber and the gain regions are connected electrically, and the saturable absorber region is also biased far above the threshold condition at the same time with the gain region. The 3-dB bandwidth of the device increases to over 10 GHz, and the 10-Gb/s nonreturn-to-zero (NRZ) eye pattern can be observed when the input TM-polarized light intensity is modulated by a 10-Gb/s NRZ pseudorandom signal.<<ETX>>

Measurement of gain saturation coefficients in strained-layer multiple quantum-well distributed feedback lasers

We have proposed and developed a new type of electroabsorption modulator (EAM) that employs both optical absorption and interferometric extinction. The EAM operates at a record low voltage of 0.2 V at 25.8-Gbit/s modulation, which can reduce optical transmitter power consumption and allows the adoption of cost-effective CMOS drivers.

A unidirectional output optical frequency conversion device with an asymmetric-/spl kappa/ DBR structure

We present two types of optoelectronic time-domain packet switches, a photonic add-drop multiplexer, and a 4/spl times/4 packet switch, for high-speed asynchronous burst optical packets. They employ all-optical serial-to-parallel converters, optical single clock-pulse generators, and photonic parallel-to-serial converters that enable utilization of a compact highly functional complementary metal-oxide-semiconductor circuitry for label processing, packet switching, and buffering for contention resolution. We have experimentally confirmed basic operation of the packet switches for 40-Gb/s 16-bit asynchronous optical packets.