We report compact sub-mW mid-infrared (IR) laser sources based on difference frequency generation (DFG) in a quasiphase
matched (QPM) LiNbO3 (LN) waveguide directly pumped with two laser diodes (LDs). The mid-IR lasers operate in the cw mode at ambient temperatures, and can be used for the tunable diode laser absorption spectroscopy (TDLAS). To construct the mid-IR laser sources, we employed a fiber-pigtailed wavelength conversion module, which
we spliced to a direct-bonded QPM-LN ridge waveguide by using the V-groove connection technique. The modules had
high external conversion efficiencies of 10 and 16 %/W for 3.4 and 2.6 &mgr;m, respectively. The signal was obtained from
a 1.55-&mgr;m-band distributed feedback (DFB)-LD, and the pump from a single-mode LD stabilized with a fiber-Bragg-grating
(FBG). We used 1.064 and 0.976-&mgr;m pump LDs for 3.4 and 2.6-(micron)m generation, respectively. The two LDs and
the wavelength converter were assembled with a polarization maintaining fiber, and then packaged in a box. We
obtained high outputs of up to 0.20 mW for the 3.4-&mgr;m laser source and 0.33 mW for the 2.6-&mgr;m laser source, and
detected CH4 and H2O absorption lines with the 3.4 and 2.6-&mgr;m laser light sources, respectively.
Efficient difference frequency generation (DFG) is obtained in the 2-μm region by using a direct-bonded periodically-poled
LiNbO3 (PPLN) ridge waveguide. The direct-bonding technique can utilize the bulk LN characteristics, which
provide certain advantages including no additional absorption, precise device design and reproducible device
fabrication. We achieved a conversion efficiency of 100%/W in the fabricated waveguide with a 0.94-μm pump laser
diode (LD) and a 1.5-μm band tunable signal LD source. We also achieved a wide tunable range of over 0.1 μm in a
50-mm-long waveguide with a single-pitch PPLN at a constant temperature. This is because the DFG bandwidth is
decided by the phase mismatch Δk. Generally, Δk=0 is only obtained at a certain wavelength, however, the Sellmeier
equation shows that Δk~0 is easy to realize in the 2-μm region when the pump is set at 0.90-0.96 μm. Subtle Δk changes around 0 realized group velocity matching and a broadband output could be obtained. Compact and
broadband tunable light sources are expected to be used for trace gas sensing in the near to medium infrared regions.
This report also describes the bundle observation of carbon monoxide isotopomer absorption lines. The DFG output
bandwidth is sufficient to observe 12CO and 13CO simultaneously. The absorption lines of the P and R branches for
each gas are clearly observed between 2.30 and 2.45 μm. DFG in the 2-μm region using direct-bonded PPLN ridge
waveguides is a promising approach for opening up new broadband applications.
To cope with the explosive growth of IP traffic, we must increase both the link capacity between nodes and the node throughput. These requirements have stimulated research on photonic networks that use optical technologies. Optical packet switching (OPS) is an attractive solution because it maximizes the use of the network bandwidth. The key functions in achieving such networks include synchronization, label processing, compression/decompression, regeneration, and buffering for high-speed asynchronous optical packets. However, it is impractical to implement such functions by using all-optical approaches. We have proposed a new optoelectronic system composed of a packet-by-packet optical clock-pulse generator (OCG), an all-optical serial-to-parallel converter (SPC), a photonic parallel-to-serial converter (PSC), and CMOS circuitry. The OCG provides a single optical pulse synchronized with the incoming packet, and the SPC carries out a parallel conversion of the incoming packet. The parallel converted data are processed in the smart CMOS circuit, and reconstructed into an optical packet by the photonic PSC. Our system makes it possible to carry out various functions for high-speed asynchronous optical packets. This paper reviews our recent work on high-speed optical packet processing technologies such as buffering, packet compression/decompression, and label swapping, which are key technologies for constructing future OPS networks.
The luminescent properties of organic infrared (IR) and near-infrared (NIR) light-emitting materials were investigated for optical communication applications. These materials consisted of two organic ionic dyes, (2-[6-(4-dimethylaminophenyl)-2,4-neopentylene-1,3,5-hexatrienyl]-3-methyl-benzothiazonium perchlorate) (LDS821) and [C41H33Cl2N2]+•BF4- (IR1051), and an organic rare-earth complex, erbium (III) tris(8-hydroxyquinoline) (ErQ). The three materials are both photoluminescent and electroluminescent in the 0.8-, 1.1- and 1.5-μm wavelength regions, respectively, and so can be used as optically active species in devices operated by either optical or current excitation. Three device forms were fabricated with these light-emitting materials as optically active species, namely vacuum-deposited or spin-coated polymer thin-films, monodispersed polymer microparticles and embedded polymeric optical waveguides. Their luminescent processes are discussed and possible optical communication applications are proposed.
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 CMOS RAM as a storage medium. Unlike conventional optical buffers, which merely function as optical delay lines, the photonic RAM provides various advantages, such as compactness, large capacity, long-term storage, and random access at an arbitrary timing for ultrafast asynchronous burst optical packets. We experimentally confirm its basic operation for 40-Gbit/s 16-bit optical packets.
KEYWORDS: Interfaces, Data conversion, Ultrafast phenomena, Data storage, Data communications, Picosecond phenomena, Video, Telecommunications, Data backup, Computing systems
We propose novel ultrafast photonic interfaces for use in storage networking based on all-optical serial-to-parallel and photonic parallel-to-serial conversion. We confirm their operation with 40-Gbit/s 16-bit optical data using compact modules and a potential bandwidth of over 100 Gbit/s. We realize a photonic random access memory (RAM) by sandwiching a CMOS RAM with these two interfaces and achieve the storage and read-out of 40-Gbit/s 16-bit optical data. We also discuss the advantages of the interfaces and their possible applications to storage networking such as the real-time remote back-up of huge quantities of data, disaster recovery and video communication systems.
A new electrical parallel-to-serial converter (PSC) is proposed for optical communication networks. The PSC uses a simple circuit scheme that markedly reduces the fall time of a ordinary MSM-PD without degrading either its sensitivity or ease of fabrication. An InP-based 4:1 PSC is shown to convert 4-ch parallel electrical signals into a serial 10-Gbit/s 4-bit electrical signal when MSM-PDs in the PSC are optically triggered. It has several advantages including support of burst signal input, low driving voltage, compactness, ease of fabrication, and low power consumption. The electrical PSC is used in a new photonic PSC. By effectively combining electrical multiplexing with optical multiplexing, the photonic PSC can generate a 40-Gbit/s 16-bit optical packet from 16-ch parallel electrical signals with frame rates of 40 MHz. The electrical PSC is also applied to a label comparator for bypass/drop self-routing of optical packets. The label comparator, consisting of the 4:1 PSC and an electroabsorption modulator (EAM), properly processed 10-Gbit/s burst optical packets with no preamble even when a local address was changed at 40 MHz.
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