Yasuo Shibata

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>>

Widely Wavelength-Tunable DFB Laser Array Integrated With Funnel Combiner

A wavelength-tunable distributed feedback (DFB) laser array integrated with a funnel combiner is described. Two types of optical combiner, namely a multimode interferometer (MMI) combiner and a funnel combiner, are compared theoretically and experimentally. It is shown that the funnel combiner is superior in terms of wavelength dependence and fabrication tolerance. The laser module covers the full C-band wavelength range ( ~38 nm), and a high fiber output power of 40 mW (16 dBm) is obtained with stable single-mode operation.

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.

50-Gb/s Direct Modulation of a 1.3-μm InGaAlAs-Based DFB Laser With a Ridge Waveguide Structure

We demonstrate 50-Gb/s direct modulation by using 1.3-μm distributed-feedback lasers with a ridge waveguide structure. We employed InGaAlAs material for a multiple-quantum well to obtain a low damping factor K, and fabricated a ridge waveguide structure buried in benzocyclobutene to realize a structure with a low parasitic capacitance. In addition, to obtain high maximum frequency relaxation oscillations fr, we designed the cavity length L), and achieved a 3-dB-down frequency bandwidth of 34 GHz. We realized 50-Gb/s clear eye openings with a back-to-back configuration, and achieved a mean output power of over 5.0 dBm, and a dynamic extinction ratio of 4.5 dB. We measured the 50-Gb/s transmission characteristics, and obtained clear eye openings for transmissions over 20-, 40-, and 60-km single-mode fibers (SMF). We also measured the bit-error-rate performance, and obtained an error-free operation and a power penalty of less than 0.5 dB after a 10-km SMF transmission.

10-Gb/s optical DPSK packet receiver proof against large power fluctuations

Optical differential phase-shift keying direct detection (ODPSK-DD) with balanced receivers has the potential to offer large tolerance to signal-power fluctuations because the threshold voltage for signal regeneration is independent of the input power. This letter demonstrates 10-Gb/s packet reception by employing differential detection with an ODPSK-DD receiving set; packet by packet power fluctuation is 10 dB, and the packet spacing is 3.2 ns.

46.9-nm wavelength-selectable arrayed DFB lasers with integrated MMI coupler and SOA

We have developed wavelength-selectable arrayed DFB lasers with an integrated MMI coupler and SOA for WDM systems. Arrayed DFB lasers having eight and sixteen channels of DFB lasers are fabricated. The good uniformity of the DFB lasers characteristics provides uniform threshold current with the standard deviation of 0.37 mA in the arrayed 16 DFB lasers. The lasing wavelength difference between each laser is set to 3 nm, which corresponds to wavelength tuning range with a 30-degree temperature change. Wavelength range as wide as 46.9 nm is achieved with the 16 DFB lasers with a temperature control of 30-degree.

80-Gb/s Low-Driving-Voltage InP DQPSK Modulator With an n-p-i-n Structure

We present a traveling-wave-electrode InP-based differential quadrature phase-shift keying modulator with a novel n-p-i-n waveguide structure. The structure features low electrical and optical propagation losses, which allow the modulator to operate at a high bit rate together with a low driving voltage and a low insertion loss. We successfully demonstrate 80-Gb/s modulation with a driving voltage of only 3 Vpp in a push-pull configuration. The chip size is just 7.5 mm times 1.3 mm.

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.