Minoru Okamoto

1.55 mu m polarization-insensitive high-gain tensile-strained-barrier MQW optical amplifier

A polarization-insensitive semiconductor optical amplifier was realized at a wavelength of 1.55 mu m. The active layer consisted of a tensile-strained-barrier multiple quantum well (MQW) structure. At a driving current of 150 mA, no dependence of the saturation characteristics on modes was obtained. The saturation output power at which the gain decreases 3 dB is 13.3 dBm. A slightly higher saturation output power of 14 dBm was measured at a driving current of 200 mA. No large difference was observed between transverse-electric (TE) and transverse-magnetic (TM) modes. A high gain of 27.5 dB at a polarization sensitivity of 0.5 dB and a high saturation output of 14 dBm were realized simultaneously by using a longer device with reduced residual facet reflectivities.<<ETX>>

Polarization insensitive traveling wave type amplifier using strained multiple quantum well structure

Signal gain agreement between TE and TM modes is realized under a specific operation condition in a traveling wave type amplifier using a strained multiple quantum well structure for the first time. The signal gain of the TM mode completely agrees with that of the TE mode at an amplifier driving current of 70 mA. The identical signal gain is 7.5 dB at present. However, the signal gain could be easily improved by using a device with a longer active region. In order to achieve polarization insensitive TWAs, the design parameter is the only confinement factor for the conventional bulk type.<<ETX>>

160-Gb/s OTDM transmission using integrated all-optical MUX/DEMUX with all-channel modulation and demultiplexing

This letter provides the first report of 160-Gb/s optical time-division-multiplexed transmission with all-channel independent modulation and all-channel simultaneous demultiplexing. By using a multiplexer and a demultiplexer based on periodically poled lithium niobate and semiconductor optical amplifier hybrid integrated planar lightwave circuits, 160-km transmission is successfully demonstrated.

Polarization-insensitive optical amplifier with tensile-strained-barrier MQW structure

A new approach to achieving a polarization-insensitive semiconductor optical amplifier is presented. The active layer consists of a tensile-strained-barrier MQW structure that enhances TM mode gain. Polarization sensitivity below 0.5 dB is realized at a wavelength of 1.56 /spl mu/m. A signal gain of 27.5 dB is obtained along with a saturation output power of 14 dBm. Deriving the refractive indices of well and barrier layers from both experiment and theory, we succeed in separation of the effect of the confinement factor and the gain coefficient. It is determined that TM mode gain enhancement in this structure is primarily due to the increase in the confinement factor. >

Optical spot-size converters for low-loss coupling between fibers and optoelectronic semiconductor devices

Structures of spot size converters that allow low loss and easy coupling between an optical semiconductor device and a fiber are proposed and designed theoretically. These spot-size converters have a tapered small core for expanding the mode field. They also have a double cladding region which consists of an n/sup +/-doped InP substrate as the outer cladding and a p-doped or nondoped InP layer as the inner cladding with a ridge structure. This double cladding utilizes the plasma effect of a carrier which makes the refractive index of highly doped n-InP lower than that of p-doped or nondoped InP. The double-cladding structure can tightly confine an expanded mode field in the inner cladding, and results in low radiation loss at the tapered waveguide, in addition, this structure reforms the mode field shape into a Gaussian-like shape and achieves a low loss coupling of less than 1 dB with a large misalignment tolerance for fiber coupling. These spot-size converters are easily fabricated and applicable to all types of optical semiconductor devices.

A low-drive-voltage, high-speed monolithic multiple-quantum-well modulator/DFB laser light source

A high-speed InGaAs/InAlAs multiple-quantum-well (MQW) intensity modulator and an InGaAsP/InGaAs MQW distributed feedback laser were monolithically integrated by using a hybrid growth technique combining molecular beam epitaxy and metalorganic vapor phase epitaxy. An operating drive voltage of only 2.0 V, a 20-dB on/off ratio, and a 3-dB bandwidth greater than 15 GHz were obtained. This device operated stably in a single mode and with a side-mode suppression ratio of more than 50 dB.<<ETX>>

High-speed and low-drive-voltage monolithic multiple quantum-well modulator/DFB laser light source

Monolithic integration of an InGaAsP/InGaAs multiple quantum well (MQW) distributed-feedback (DFB) laser with a high-speed InGaAs/InAlAs MQW intensity modulator is demonstrated. A 3-dB bandwidth. in excess of 16 GHz and low-drive-voltage operation (4.0 V) for a 20-dB on-off ratio are obtained. Good coupling efficiency between an MQW DFB laser and an MQW modulator is accomplished using hybrid crystal growth of MO-VPE and MBE.<<ETX>>

TM mode gain enhancement in GaInAs-InP lasers with tensile strained-layer superlattice

A novel tensile strained barrier (TSB) structure is proposed as the active layer to enhance the transverse-magnetic (TM) mode gain in long wavelength laser diodes. The band diagram of the TSB structure is described theoretically and experimentally. The gain difference between transverse-electric (TE) and TM modes is discussed for layers with various strain values and well layer thicknesses. The characteristics of TM-mode enhanced devices are reported as applications of the mode gain control using the TSB structure. In Ga/sub 0.27/In/sub 0.53/As-Ga/sub x/ In/sub 1-x/As tensile strained layer superlattice structures, controllability of a mode gain difference is achieved by changing the strain value and/or thickness of wells. >

Highly Stable 160-Gb/s OTDM Technologies Based on Integrated MUX/DEMUX and Drift-Free PLL-Type Clock Recovery

This paper reports 160-Gb/s optical time-division-multiplexed (OTDM) technologies including an all-optical integrated multiplexer (MUX) providing all-channel independent modulation, an all-optical integrated demultiplexer (DEMUX) that offers all-channel simultaneous demultiplexing, and a drift-free phase-locked-loop (PLL)-type clock recovery circuit for ultrahigh-speed OTDM signals. We present the configuration of each technology and the results of experiments on those technologies. Highly stable operation is successfully demonstrated by using a MUX based on periodically-poled lithium niobate (PPLN) hybrid integrated planer lightwave circuit (PLC), a DEMUX based on semiconductor optical amplifier hybrid integrated PLC, and clock recovery circuit based on a PLL with an optical phase modulator and a PPLN waveguide

An InP-based optical multiplexer for 100-GHz pulse-train generation

A 100-GHz optical pulse train is generated using an InP-based optical multiplexer. This device is based on a waveguide array with five paths of different lengths separated by a 10-ps propagation time. We used a multimode interference (MMI) splitter at the input and a taper-type combiner at the output. This device is well-suited for optical time-division multiplexing (OTDM) applications.<<ETX>>