S. Oku

Coupling coefficient modulation of waveguide grating using sampled grating

A new method of modulating the coupling coefficient along the waveguide is proposed. The effect of our method, which uses a nonperiodic sampled grating, is demonstrated both theoretically and experimentally. A Bragg filter is fabricated on an InGaAsP/InP wafer utilizing the method, and the sidelobe level is shown to improve by 7 dB compared with a conventional filter with a uniform coupling coefficient. The experimental results are found to be in good agreement with calculations.<<ETX>>

Controlled beam dry etching of InP by using Br2-N2 gas

Indium phosphide dry etching is carried out using a reactive beam extracted from a Br2-N2 gas discharge plasma. Keeping the N2 gas pressure constant at 0.23 mTorr, the Br2 gas pressure was varied from 0 to 0.1 mTorr and the sample temperature was varied from 40 to 200°C. The etched shapes and etching rates are investigated in terms of the etching beam composition. Two distinct types of etching mechanisms come into play depending on the Br2 gas pressure. Smooth vertical side walls and a temperature independent etching rate can be obtained at a Br2 gas pressure of 0.04 mTorr or less and a temperature above 100°C, where the etching is induced by the ambient Br2 gas species and N2 beam. Undercut etching with a temperature dependent etching rate is seen at a Br2 gas pressure of 0.07 mTorr or higher, where the etching beam contains both N2 and Br2 gas species. Neutralized Br species generated by the discharge of the Br2 gas are shown to form the undercut. A waveguide corner mirror with a loss of less than 1 dB is made by using an etching beam with no neutralized Br species.

A 40-gb/s InGaAlAs-InAlAs MQW n-i-n Mach-Zehnder Modulator with a drive Voltage of 2.3 V

We have developed a traveling-wave Mach-Zehnder modulator using an n-i-n heterostructure fabricated on an InP substrate. We obtained an extremely small /spl pi/ voltage (V/spl pi/) of 2.2 V, even for a short signal-electrode length of 3 mm. We confirmed that the device has an impedance-matched electrode and operates at 40 Gb/s with a single-ended drive voltage of 2.3 V.

200-GHz FSR periodic multi/demultiplexer with flattened transmission and rejection band by using a Mach-Zehnder interferometer with a ring resonator

A periodic multi/demultiplexer that has a square spectrum response with a 200-GHz free spectrum range was fabricated using a modified Mach-Zehnder interferometer with MMI couplers, a delay line, and a ring resonator. A large enhancement of the FSR is obtained by using a deep ridge waveguide. The transmission bandwidths of 1 dB down and -15-dB rejection are about 75 GHz and over 50 GHz, respectively.

Multi-channel modulation in a DWDM monolithic photonic integrated circuit

We present a multi-channel modulation circuit monolithically integrated with one 25-GHz-spacing AWG for both MUX and DEMUX and eight channels of SOAs and EAMs. The circuit can generate individual optical signals for each DWDM channel with a high extinction ratio of >20 dB and loss compensation. The circuit size can be reduced to 15 /spl times/ 7 mm/sup 2/.

Lossless electroabsorption modulator monolithically integrated with a semiconductor optical amplifier and a passive waveguide

We have developed a monolithic integrated device consisting of an electroabsorption modulator and a semiconductor optical amplifier (SOA) connected by a deep-ridge passive waveguide by means of butt-joint selective area growth. Lossless operation with a high extinction ratio of 32 dB and clear eye opening at 10 Gb/s are successfully achieved. We confirm that the optical injection should be from the SOA side of the device to obtain a wide error-free range of incident optical power from -20 to +10 dBm. Our device could lead to richly functional photonic integrated circuits comprising arrayed waveguide gratings (AWGs) for advanced wavelength-division-multiplexing networks, since the passive waveguide has the same structure as AWGs.

Packaged polarization-insensitive WDM monitor with low loss (7.3 dB) and wide tuning range (4.5 nm)

Low-cost high-performance wavelength-division-multiplexing (WDM) monitors and receivers are key components in WDM transmission and local area optical networks. A semiconductor arrayed waveguide grating integrated with a photodiode is attractive because of its small size and simple fabrication process. A low-loss (7.3 dB) polarization-insensitive packaged WDM monitor has been fabricated in an industry-standard butterfly-type module. The eight-channel monitors, which have 200-GHz channel spacing, can be tuned simultaneously in the 4.5-nm range.

Monolithically integrated 100-channel WDM channel selector employing low-crosstalk AWG

A 100-channel wavelength-division-multiplexing channel selector monolithically integrated on an InP substrate is demonstrated. The selector consists of two arrayed waveguide gratings (AWGs), two semiconductor-optical-amplifier (SOA)-gate arrays, and a multimode interference coupler. The selector employs improved AWGs whose crosstalk is reduced with higher order mode filters. Successful channel selection and lossless operation for all channels are achieved. Error-free operation at 10 Gb/s and small sensitivity penalties between 1.8 and 3.3 dB are obtained.

Monolithically integrated WDM channel selectors on InP substrates

8-channel WDM channel selectors were fabricated on InP substrates. A compact device size of 5.2 mm/spl times/3.6 mm is achieved with a combination of deep-ridge waveguides and buried waveguides. The device can select an arbitrary signal from WDM signals with a low crosstalk of less than -40 dB.

Control of higher order leaky modes in deep-ridge waveguides and application to low-crosstalk arrayed waveguide gratings

In a lightwave circuit using a strongly confined waveguide, higher order leaky modes must be suppressed to obtain ideal characteristics, especially in arrayed waveguide gratings (AWGs). Propagation loss for higher order leaky modes in InP-based deep-ridge waveguides was investigated by simulation and experiment. A highly sensitive loss measurement method based on optical low-coherence reflectometry was used to determine the loss, and the relationship between the loss for the higher order mode and AWG crosstalk was investigated. Optimizing the deep-ridge waveguide parameters, especially the core thickness, the refractive index of the core, and the etch depth under the core, significantly reduced the propagation loss for the higher order leaky mode. The effective elimination of the higher order modes will enable fabrication of low-crosstalk AWG routers.