Yuichiro Ikuma

Ultra-small, self-holding, optical gate switch using Ge 2 Sb 2 Te 5 with a multi-mode Si waveguide

We report a multi-mode interference-based optical gate switch using a Ge(2)Sb(2)Te(5) thin film with a diameter of only 1 µm. The switching operation was demonstrated by laser pulse irradiation. This switch had a very wide operating wavelength range of 100 nm at around 1575 nm, with an average extinction ratio of 12.6 dB. Repetitive switching over 2,000 irradiation cycles was also successfully demonstrated. In addition, self-holding characteristics were confirmed by observing the dynamic responses, and the rise and fall times were 130 ns and 400 ns, respectively.

Proposal of a small self-holding 2×2 optical switch using phase-change material

A small and fast self-holding 2 × 2 optical switch using phase change material is proposed. This switch is based on a directional coupler in which a short waveguide made of a phase-change material (PCM) is sandwiched between two Si waveguides. The characteristics of the proposed switch were simulated by a beam propagation method (BPM). This switch can be as small as 3µm × 21µm because the change in the refractive index of PCMs between the crystalline and amorphous states is very large; in addition, by utilizing the self-holding characteristics, it has the potential for low power consumption. The loss and the crosstalk were calculated to be 2.5dB and -20.4dB in the bar state and 1.3dB and -14.3dB in the cross state, respectively.

Low loss, small crosstalk offset crossing structure for large-scale planar lightwave circuits

A low loss, small crosstalk offset crossing structure for a Si wire waveguide is proposed. We analyzed the properties of the structure for both the TE and TM modes by 2-D FDTD (two-dimensional finite difference time domain) simulation. By optimizing the offset crossing structure, a transmission loss of 0.021dB, and crosstalk of -55.0dB was achieved with a crossing angle of 20 degrees for the TE mode. A transmission loss of 0.070dB, and crosstalk of -48.6dB was also achieved with the same crossing angle for the TM mode. The low losses achieved with a small crossing angle makes this structure very useful for highly integrated optical matrix switches, etc.

AWG-Based Tunable Optical Dispersion Compensator With Multiple Lens Structure

We propose an arrayed-waveguide grating (AWG)-based tunable optical dispersion compensator (TODC) that uses a multiple lens structure with two lens materials. The lenses are realized by filling lens-shaped trenches in a slab waveguide with optical resins. The thermooptic effect provided by the lens materials realizes the desired dispersion tuning function. The multiple lens structure enables us to design the center dispersion and the dispersion tuning range independently. We fabricate a TODC based on a 10-ch, 10-GHz spacing AWG that uses resins with refractive indexes of 1.393 and 1.510. Its dispersion range is 0 to + 125 ps/nm. We also perform a transmission experiment using a 12.5 Gbps RZ-OOK signal. The power penalty at the bit error rate of 10-9 is less than 3 dB; and error-free transmission is confirmed after dispersion compensation.

Application of Waveguide/Free-Space Optics Hybrid to ROADM Device

As optical networks have evolved from point-to-point systems to ring or mesh networks, the optical devices that are needed to construct optical nodes have become more important and need to be more scalable. Hybridization of waveguide and free-space optics, or spatial and planar optical circuits (SPOCs), may provide the solutions for such needs. An SPOC platform is attractive because it can take advantage of both waveguide technology and free-space optics. Waveguide technology provides a high degree of integration of optical functionality for devices such as splitters and non-wavelength selective switches while free-space optics supplies a high degree of parallelism with two-dimensional spatial light modulators such as a liquid crystal on silicon (LCOS) devices. In this paper, we summarize the basics of SPOC technology and review its application to reconfigurable optical add-drop multiplexing (ROADM) devices. The key elements of a waveguide on an SPOC platform are an arrayed-waveguide grating and a spatial beam transformer. The latter functions as a microlens array and provides attractive features such as dense integration of switches. An LCOS device has numerous phase modulating pixels, enabling flexible manipulation of lightwaves. Using an SPOC platform, we constructed and demonstrated devices for ROADM applications including a wavelength filter, tunable optical dispersion compensators, and wavelength selective switches (WSSs). The WSSs range from an ultrahigh port count WSS to a single module wavelength cross connect.

Low-Loss Transponder Aggregator Using Spatial and Planar Optical Circuit

We propose a compact transponder aggregator (TPA) consisting of a wavelength selective switch (WSS) array and a direction switch array. It has no intrinsic splitting loss and therefore the number of ports can exceed that of a conventional multicast switch. A waveguide-based frontend that incorporates spatial beam transformers enables us to increase the number of ports and integrate multiple WSSs in a simple optical system. The direction switch array is integrated in the frontend. We describe an 8 × 24 prototype, which is the largest port count yet achieved for a TPA with no intrinsic splitting loss.

8 × 8 wavelength cross connect with add/drop ports integrated in spatial and planar optical circuit

We demonstrate a compact 8 × 8 broadcast-and-select wavelength cross connect with add/drop ports for 8-degree node. A combination of waveguide-based frontend and free-space optics allows us to integrate eight arrays of 1 × 8 WSSs and 1 × 8 splitters into a small footprint.

MxN wavelength selective switches using beam splitting by space light modulators

We propose a multiple input and multiple output wavelength selective switch (MxN WSS) with an optical configuration that uses a single diffractive optics deflector. In the proposed WSS, broadcast-and-select functionality is achieved by multi-angle diffraction and control of diffraction angle using the phase modulation patterns on a spatial light modulator such as liquid crystal on silicon (LCOS). The experimental results show that a 5×5 WSS using the spatial modulation patterns designed using the computer-generated hologram (CGH) technique works well.

Compact Wavelength Selective Switch Using a Bragg Reflector Waveguide Array With Ultra-Large Number (>100) of Output Ports

A wavelength selective switch (WSS) is proposed based on a Bragg reflector waveguide array, which has a footprint of only 2 × 6 mm2. We demonstrated arbitrary switching among 182 output ports by using a liquid crystal on silicon as a switching engine. The proposed WSS module length is only 10 cm, taking an advantage of the large angular dispersion in the Bragg reflector waveguide. Wavelength selective switching of 60 channels is carried out, exhibiting the devices excellent capability in providing ultra-large number of port count and wavelength channel operations at the same time. The crosstalk between adjacent ports are below -20 dB by a suitable alignment, which can be further improved by optimizing the module optics and alignments. The flexible lithography defined waveguide array design also reveals versatile potentials in integrating with other functional components.

Integrated 40-

A compact integrated 1×2 wavelength-selective switch (WSS) is demonstrated for which the structure is designed such that the WSS has no waveguide crossings. By employing a loopback configuration, only one arrayed-waveguide grating is needed in the WSS. The channel spacing is 100 GHz and the number of channels is 40. The measured transmission loss of the selected wavelength was <; 8.1dB, and the average crosstalk from two output ports were 23.0 and 40.7 dB.