There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

A nitride semiconductor device including a light emitting device comprises a n-type region of one or more nitride semiconductor layers having n-type conductivity, a p-type region of one or more nitride semiconductor layers having p-type conductivity and an active layer between the n-type region and the p-type region. In such devices, there is provided with a super lattice layer comprising first layers and second layers which are nitride semiconductors having a different composition respectively. The super lattice structure makes working current and voltage of the device lowered, resulting in realization of more efficient devices.

Nitride semiconductor device

We report a novel method to measure two important parameters for optical fiber intensity modulated transmission systems: dispersion of optical fibers and chirp parameter of modulated light emitters. The method is easy, quick, and accurate for chirp parameter in the -10-to-10 range. >

Simple measurement of fiber dispersion and of chirp parameter of intensity modulated light emitter

Carrier transport can significantly affect the high-speed properties of quantum-well lasers. The authors have developed a model and derived analytical expressions for the modulation response, resonance frequency, damping rate, and K factor to include these effects. They show theoretically and experimentally that carrier transport can lead to significant low-frequency parasitic-like rolloff that reduces the modulation response by as much as a factor of six in quantum-well lasers. They also show that, in addition, it leads to a reduction in the effective differential gain and thus the resonance frequency, while the nonlinear gain compression factor remains largely unaffected by it. The authors present the temperature dependence data for the K factor as further evidence for the effects of carrier transport. >

High speed quantum-well lasers and carrier transport effects

The applications of surface-emitting lasers, in particular vertical-cavity surface-emitting lasers (VCSELs), are currently being extended to various low-power fields including communications and interconnections. However, the fundamental difficulties in increasing their output power by more than several milliwatts while maintaining single-mode operation prevent their application in high-power fields such as material processing, laser medicine and nonlinear optics, despite their advantageous properties of circular beams, the absence of catastrophic optical damage, and their suitability for two-dimensional integration. Here, we demonstrate watt-class high-power, single-mode operation by a two-dimensional photonic-crystal surface-emitting laser under room-temperature, continuous-wave conditions. The two-dimensional band-edge resonant effect of a photonic crystal formed by metal–organic chemical vapour deposition enables a 1,000 times broader coherent-oscillation area, which results in a high beam quality of M2 ≤ 1.1, narrowing the focus spot by two orders of magnitude compared to VCSELs. Our demonstration promises to realize innovative high-power applications for surface-emitting lasers. Researchers demonstrate a watt-class high-power, single-mode photonic-crystal laser operating continuously at room temperature. A beam quality of M2 ≤ 1.1 is achieved.

Watt-class high-power, high-beam-quality photonic-crystal lasers

The authors propose a very simple tunable laser with a striped thin-film heater. The wavelength of this laser changes with a sensitivity of 3.2 nm/W to the input heating power. This laser can be continuously tuned over a range of 4 nm while maintaining an optical power of 20 mW and with a linewidth of less than 2.5 MHz. When this laser is mounted on a module, its 90% response time is 6 ms, which is fast enough for use as a local oscillator in several applications. >

Tunable DFB laser with a striped thin-film heater

Direct modulation at 40 Gb/s of a 1.3-mum InGaAlAs distributed feedback ridge waveguide laser is experimentally demonstrated. By combination of the high differential gain of an InGaAlAs multiquantum well active layer, a short cavity length of 100 mum, and a low-resistance notch-free grating, it achieves high bandwidth of 29 GHz and high-extinction ratio of 5 dB at 40-Gb/s modulation. Moreover, the laser operates at a record maximum ambient temperature of 60degC under 40-Gb/s directly modulation. It also achieves 40-Gb/s modulated transmission over 2 km with a low power penalty of 0.25 dB at 25degC .

40-Gb/s Direct Modulation With High Extinction Ratio Operation of 1.3- $\mu$ m InGaAlAs Multiquantum Well Ridge Waveguide Distributed Feedback Lasers

Narrow spectral linewidth lasers are developed for optical coherent transmission systems. To obtain a narrow spectral linewidth, a CPM (corrugation-pitch modulated) structure is introduced into 1200- mu m-long MQW-DFB (multi-quantum well distributed feedback) lasers. The CPM structure effectively suppresses the axial spatial hole burning effect and stabilized single-mode spectrum at high output powers. A spectral linewidth of 170 kHz was achieved at an output power of 25 mW. Details of corrugation fabrication method that makes the CPM structure possible are described. >

Corrugation-pitch modulated MQW-DFB lasers with narrow spectral linewidth

A spectral linewidth of 170 kHz was achieved at a 1.5- mu m wavelength in a 1200- mu m long corrugation-pitch-modulated (CPM) distributed feedback (DFB) laser having multiple quantum wells (MQW). This is the narrowest linewidth ever reported for InGaAsP DFB lasers. The CPM structure is effective in maintaining the single longitudinal mode at a high output power by suppressing the spatial hole burning effect. The linewidth-power product is 400 kHz-mW, and the extrapolated residual spectral linewidth is 150 kHz. >

Corrugation-pitch-modulated MQW-DFB laser with narrow spectral linewidth (170 kHz)

PURPOSE: To stably oscillated light of a desired wavelength by differentiating the differentiation gain coefficient for an injected carrier density of a gain active layer oscillated through amplification of a light having a specific wavelength from that for a light amplifying active later. CONSTITUTION: A phase regulating region 102 having an optical waveguide 181 in which a refractive index is reduced upon increasing of injected carrier density and a light amplifying region 103 made of an active optical waveguide 105 having a second active layer structure are provided. When a material having shorter wavelength of the wavelength λP 2 of a gain peak than a laser oscillation wavelength λL is used as an active waveguide 141, the wavelength λP 2 does not coincide with the wavelength λL in the material having the short wavelength λP 2 at a gain peak. Accordingly, a gain gradient becomes smooth, and even if carrier density is increased, an increase in a photon density is suppressed, a reduction in carrier density upon inductive emission depending upon the photon density is suppressed to increase the carrier density. Therefore, a region 101 does not reach a gain to self-oscillation, and a wavelength variable width and particularly Bragg's reflection wavelength can be increased. COPYRIGHT: (C)1992,JPO&Japio

Tomonobu Tsuchiya

Papers

Tunable DFB laser with a striped thin-film heater

40-Gb/s Direct Modulation With High Extinction Ratio Operation of 1.3- $\mu$ m InGaAlAs Multiquantum Well Ridge Waveguide Distributed Feedback Lasers

Corrugation-pitch modulated MQW-DFB lasers with narrow spectral linewidth

Corrugation-pitch-modulated MQW-DFB laser with narrow spectral linewidth (170 kHz)

Semiconductor optical element