Manabu Shiozaki

Fiber-Bragg-grating external cavity semiconductor laser (FGL) module for DWDM transmission

We report on the use of butterfly-type fiber-Bragg-grating external cavity semiconductor laser (FGL) modules in dense wavelength-division multiplexing (DWDM) applications. In a dense wavelength-multiplexing experiment, we demonstrated that successive four-channel multiplexing with 25-GHz spacing and with almost the same peak power was realized by using the FGLs. The lasing wavelength of each channel was tuned to the corresponding wavelength grids with an accuracy of /spl plusmn/1 pm. In the DWDM transmission with 25-GHz channel spacing and 2.5-Gb/s direct modulation using a standard single mode fiber (SMF), a good bit-error ratio (BER) performance without floor phenomenon was achieved up to 300 km. There was no degradation of transmission characteristics caused by the optical crosstalk from adjacent channel. Even in the DWDM transmission where channel spacing was 12.5 GHz, good transmission characteristics were maintained up to 300 km and little degradation of BER performance occurred at 300 km compared with the single-channel transmission. In addition, we investigated the influence of external temperature change on the FGL reliability using temperature-cycling test. As a result, we clarified that the characteristic degradation of FGL after this test was sufficiently small and that this device had a high tolerance to the severe external temperature variation.

The dispersion-free filters for DWDM systems using 30 mm long symmetric fiber Bragg gratings

The dispersion-free FBG is designed by applying the optimized cosine-progression to the apodization profile. As experimental results show that it offers the suitable filter, with 25 dB crosstalk, 15 ps group delay, for high bit-rate DWDM systems.

Pluggable fan-out realizing physical-contact and low coupling loss for multi-core fiber

We investigated Physical-contact condition between a multi-core fiber and a fiber bundle fan-out. Based on this, we fabricated a pluggable fan-out and achieved the back-reflection and the coupling-loss lower than -50 dB and 0.3 dB, respectively.

EMI suppression of 10Gbit/s optical transceiver by using EBG structure

The fiber optic data transmission system plays an important role in broadband communication. According to the market trend, data traffic is significantly increasing and larger throughput of communication systems is required. Many opto-electronic conversion devices (so called optical transceivers) are used in the system. Because of that, the electro-magnetic noise radiation becomes a serious consideration. Although noise level is proportional to the number of transceivers, a qualitative relationship between the number of transceivers and emission level is not clear. Furthermore, since theres no general design guideline to suppress EMI, it is difficult to solve this problem once it emerges. In these circumstances, recent dispersion control technology such as Electro-magnetic Band Gap (EBG) is a potential solution for this problem. In this paper, the method of how to predict total emission level with the superimposed effect of thousands of transceivers and how to determine the EMI suppression design target are described. Then, the method of how to reach the goal with a newly introduced shielding scheme is described. And, it is demonstrated that the EBG structure is suitable for optical transceivers. Its verification is shown by utilization of FEM/FDTD simulation and an experiment of an in-house prototype.

Optical properties of ZnSe diffractive optical elements for spot array generation

The diffractive optical element (DOE) is a revolutionary technology for sophisticated optical systems. It has recently been launched within the optical industry, which is constantly seeking improvements over conventional optics. We have designed and fabricated three types of binary-phase DOE for array generation. The surface relief of a ZnSe substrate was patterned and etched with each intended phase distribution by using photolithography and reactive ion etching (RIE) technologies. The optical properties of anti-reflection coated samples were then examined by measuring the intensity distribution of their converging diffractive beams and the results compared with the calculated beam propagation.

Development of a practical electro-magnetic interference (EMI) simulation in high speed optical transceivers

The growing bandwidth of optical communication systems has made great improvements to information technology infrastructures. However, electro-magnetic compatibility becomes an issue due to the high frequency of the components. EMI problems occur due to the miniaturization and high density of the Printed Circuit Board (PCB) mounted on the system. Generally, electro-magnetic radiation is generated by the circuit elements. For example, switching in the LSI raises the voltage swing between the power source and ground which is known as “ground bounce”. EMI problems related to the ground and power source are linked to the power integrity, and is influenced by the structure of the patch antenna parasitically existing between the power source and ground. That is to say, most of the time this problem can be solved by utilizing the appropriate power source and ground pattern layout at the PCB design stage. However, high speed digital signals measuring at more than 10 Gigabit per second (Gbit/s) typically have high frequency components in excess of 40GHz. There is little feasible knowledge available that illustrates guidelines for the perfect layout method to prevent the emission on the PCB for such a high frequency application. Therefore, we focused on the Finite Element Method used in the 3D electromagnetic field analysis simulator so that we could solve the emission within the frequency domain. We first correlated both qualitatively and quantitatively the actual measurements and the simulation results. Then we investigated the countermeasure for the emission intensity (EMI level) from the 10 Gbit/s optical transceiver by simulation and then verified it.

A highly dense MEMS optical switch array integrated with planar lightwave circuit

We propose a novel MEMS 2/spl times/2 optical switch array integrated with a Planar Lightwave Circuit (PLC) for application to Optical Add Drop Multiplexing (OADM) in Wavelength Division Multiplexed (WDM) transmission systems. This switch array consists of two chips connected together by flip chip bonding. One is the MEMS device which has 16 channel latched silicon actuators with micro-mirrors, and the other is a PLC which has a 16 channel 2 /spl times/ 2 cross type waveguide array. In order to achieve highly dense integration, the MEMS actuator has a long beam cantilever arranged with a 500 /spl mu/m period.

Development of adaptive mirror for CO2 laser

Material processing using CO2 laser is one of the most highly industrialized laser technologies. Recently, there have been growing demands to improve the processing quality by flexibly controlling the beam properties. Development of the adaptive mirror with variable curvature function, which is one of the vital optics to realization of these demands, has been extensively pursued. We developed the AM. It maintains the same accuracy of surface figure (PV value: 1 micrometer or below) as the conventional mirrors even when the curvature is changed, and is capable of high speed curvature control (maximum frequency: 1 kHz) aiming at application to beam sawing. Further, we applied the AM to laser cutting of mild steel as an example of its practical use, and studied smoothing of the cut surface by beam sawing.

Focussing properties of 45 degree-off-axis parabolic mirrors

The focussing properties of 45 degree-off-axis parabolic mirrors were examined using a Prometec Laser Scope, with comparison to those of 90, 60 and 30 degree-off-axis parabolic mirrors. These mirrors are all SPDT (Single Point Diamond Turning)-treated, Mo-coated surface and their focal lengths are 254mm. We examined (1) The focussing properties (focal spot size, spot elliptical shape and ellipticity) differ depending on misalignment and mode (Power). (2) With attention to the fact that ZnSe window is frequently used with parabolic mirrors, and the affect on focussing properties of parabolic mirror by the thermally induced optical distortion of this window. And (3) The condition of the parabolic mirrors under irradiation of 5kw laser was simulated.The focussing properties of 45 degree-off-axis parabolic mirrors were examined using a Prometec Laser Scope, with comparison to those of 90, 60 and 30 degree-off-axis parabolic mirrors. These mirrors are all SPDT (Single Point Diamond Turning)-treated, Mo-coated surface and their focal lengths are 254mm. We examined (1) The focussing properties (focal spot size, spot elliptical shape and ellipticity) differ depending on misalignment and mode (Power). (2) With attention to the fact that ZnSe window is frequently used with parabolic mirrors, and the affect on focussing properties of parabolic mirror by the thermally induced optical distortion of this window. And (3) The condition of the parabolic mirrors under irradiation of 5kw laser was simulated.

Ultra-compact multichannel optical components based on PLC technologies

We propose multichannel based on PLC and MEMS technologies. 12 channel optical switch arrays and VOA arrays have been successfully developed by integrating 2/spl times/2 cross type and MEMS micro-mirrors connected together by flip chip bonding.