Hiroshi Yasaka

Monolithic integrated coherent receiver on InP substrate

The fabrication of a monolithic integrated coherent receiver with a wavelength-tunable DFB laser as local oscillator, a 3-dB waveguide directional coupler for mixing, and p-i-n photodiodes for detection is discussed. Optical heterodyne detection with a clear beat signal was experimentally observed using this monolithic integrated coherent receiver. Since an n-type substrate was used in this device, the two p-i-n photodiodes were not implemented in a balanced mixer configuration. Balanced mixing might be possible if the same structure were fabricated on a semi-insulating substrate. The results obtained suggest the possibility of applying this type of monolithic integrated coherent receiver to optical communication systems.<<ETX>>

Transmission performance of chirp-controlled signal by using semiconductor optical amplifier

We examine the fiber transmission performance of the optical signal whose chirp is controlled by utilizing phase modulation in semiconductor optical amplifier (SOA) with both simulations and experiments. This chirp control technique converts a positive chirp created by electroabsorption (EA) modulator into negative chirp, which reduces the waveform degradation due to the chromatic dispersion in transmission over standard single-mode fiber (SMF). It also provides an optical gain that is sufficient to compensate the insertion loss of the EA modulator. We investigate how the chirp control is affected by the input power to the SOA and the carrier lifetime of the SOA. As the SOA input power increases, the negative chirp becomes large, while the waveform is largely distorted due to gain saturation. However, the waveform distortion at high SOA input powers can be shaped by using a frequency discriminator. The acceleration of the carrier lifetime also reduces the waveform distortion due to gain saturation. We demonstrate that the chirp control technique is effective even for a high bit rate optical signal up to 10 Gb/s, when the carrier lifetime is expedited by optical pumping.

Multiwavelength light source with precise frequency spacing using a mode-locked semiconductor laser and an arrayed waveguide grating filter

A multiwavelength light source with precise optical frequency spacing can be created by extracting an individual mode of a semiconductor mode-locked laser using an arrayed waveguide grating filter. The outputs of the light source are locked to wavelength division multiplexing (WDM) optical frequency grids using an optical frequency standard light source. They can be successfully modulated by 5 Gb/s nonreturn-to-zero (NRZ) signals and can be transmitted through 100-km-long optical fiber.

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>>

Tunable optical-wavelength conversion using an optically-triggerable multielectrode distributed feedback laser diode

Tunable optical-wavelength conversion with tunability greater than 5 AA using a multielectrode distributed-feedback laser diode (DFB LD) with a saturable absorber is discussed. This device is not dependent on input polarization and can operate at up to 500 MHz. Preliminary results of an optical switching experiment using the tunable wavelength converter and optical narrowband filter with a DFB LD amplifier are also reported. >

Frequency-stabilized DFB laser module using 1.53159 mu m absorption line of C/sub 2/H/sub 2/

A frequency-stabilized distributed-feedback (DFB) laser module using the vibrational-rotational absorption of acetylene molecules is discussed. The size of this device is about 4.5 cm long, 2 cm wide, and 2 cm high. Frequency stability to within 0.5 MHz peak/peak fluctuation was achieved at the 1.53159 mu m wavelength.<<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.

Broader spectral width InGaAsP stacked active layer superluminescent diodes

Fabrication and characteristics of broader spectral width 1.3 μm and 1.5 μm InGaAsP superluminescent diodes having a novel stacked active layer (STAC‐SLDs) structure are reported. The emission spectral width is successfully broadened as much as twice that of conventional SLDs, yielding spectral widths of 80 and 140 nm for the 1.3 μm and the 1.5 μm SLD, respectively.

Mode stabilization method for superstructure-grating DBR lasers

A wavelength stabilization method for widely tunable superstructure-grating (SSG) distributed Bragg reflector (DBR) laser is described. The output characteristics under tuning are studied theoretically and experimentally. It is found that peak reflectivity states, in which the lasing mode is just aligned with the reflection peaks of both DBRs, are obtained at saddle points in the output characteristics while changing the two SSG-DBR currents. Based on these results, a method for the Bragg frequency control of the two SSG-DBRs is proposed. The feedback control circuit keeps the lasing mode at a peak reflectivity state, and it suppresses mode hopping. Additionally, the oscillation mode is locked to arbitrary reference wavelengths of an optical filter. Stabilization at 200 GHz (1.6 nm)-spaced 16 wavelengths was achieved within the wide tuning range of the SSG-DBR laser. Control was maintained under a laser temperature variation of /spl plusmn/5/spl deg/C as a result of the Bragg frequency control of the two DBRs.

Gain saturation coefficients of strained-layer multiple quantum-well distributed feedback lasers

The gain saturation coefficients were measured for strained and unstrained multiple quantum-well distributed feedback (MQW-DFB) lasers. The gain saturation coefficient depends on the deviation of the lasers transverse-magnetic (TM) mode gain peak wavelength from its transverse-electric (TE) mode gain peak wavelength delta lambda , which is related to the strain on the active-layer wells. The gain saturation coefficient epsilon increased with increasing compressed strain on the active-layer wells. The coefficient epsilon of the unstrained MQW DFB laser with a wavelength deviation delta lambda of -350 AA was 2.45 x 10/sup -17/ cm/sup 3/, and epsilon increased up to 12.6 x 10/sup -17/ cm/sup 3/ in the SL-MQW DFB laser with a wavelength difference delta lambda of -890 AA.