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We investigate electrical signals generated in passive sections of a sampled-grating distributed Bragg reflector laser. A DC voltage is applied to one of the passive sections, and a negative current in the circuit is observed with a low voltage biased. Experimental results demonstrate that the negative current is generated due to photovoltaic effect. This effect could be enhanced or suppressed by adjusting the parameters of p–n junctions in the passive sections. On account of this effect, the passive sections can be utilized as inner photodetectors to control the laser power, which greatly simplifies the laser packaging and reduces the cost.

This paper presents the lineshape analysis of the beat signal between the optical carrier and the shifted and delayed sidebands produced by sinusoidal amplitude modulation. It is shown that the beat signal has a typical lineshape with a very narrow ? -peak superposed on a quasi-Lorentzian profile. Theoretical explanation for the appearance of this peak has been given based on optical spectral structure constructed by a large number of optical wave trains. It is predicted that the ?-peak is originated from the beat between the wave trains in the carrier and those in the delayed sidebands when their average coherence length is longer than the delay line. Experiments carried out using different delay lines clearly show that the ? -peak is always located at the modulation frequency and decreases with the increasing delay line. Our analysis explicitly indicates that the linewidth is related to the observation time. It is also suggested that the disappearance of the ? -peak can be used as the criterion of coherence elimination.

This article presents the investigation of frequency and temporal coherence properties of distributed Bragg reflector laser. In this scheme, a square-wavefrom voltage is applied to the phase section of the laser to little optical wavelength, and delayed optical heterodyne technique is used for the analysis of spectral characteristics. Experiments show that lightwaves emitted from the same active region asynchronously are partially frequency and temporal coherent. When the two wavelengths are closer, the two waves are strong v coherent, and the coherence properties get weak as the delay v time increases. (C) 2010 Wiley Periodicals, Inc. Microwave Opt Technol Left 52: 822-825, 2010 Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.25031

A discretely tunable Er-doped fiber-ring laser using a fiber Mach-Zehnder interferometer (MZI) and a tunable fiber Bragg grating (FBG) is proposed. In this scheme, the combination of MZI and FBG acts as a discrete wavelength selector. Analysis of its transmission function shows that discrete wavelength tuning can be realized, and experiments demonstrate 64 single-mode outputs with a mode spacing of 181.7 pm, and the output power is quite stable in the whole tuning range. (C) 2009 Wiley Periodicals, Inc. Microwave Opt Technol Lett 51 2595-2598, 2009; Published online in Wiley InterScience (www. interscience.wiley.com). DOI 10.1002/mop.24690

Neutron source has broad application prospects in crystallography, neutron irradiation, neutron therapy for cancer, and so on. As a new scheme to produce bright pulsed neutron source, the laser-driven neutron has attracted wide interest. In recent years, laser driven neutron sources have been extensively studied and the great progress has been made. Short pulsed laser driven neutron sources could be a compact and relatively cheap way to produce quasi-monoenergetic neutrons. The yields and the angular distributions of the laser-driven neutron sources are important in the research of laser-driven neutron sources and relevant applications. We conduct experimental investigation of this respect by using the XingGuang-Ⅲ high intense laser facility, which delivers synchronized picosecond and nanosecond laser pulses. The picosecond laser energy is 100 J, the pulse width is 1 ps, and the focusing spot diameter is 20 μm. At this time, the corresponding laser power density reaches 3×1019 W/cm2. A high-energy deuterium ion beam is produced by focusing the picosecond laser on a deuterated polyethylene foil, and the deuterium ion beam is incident on a secondary deuterated polyethylene planar target to activate the D-D reaction to obtain the neutron beam. In the experiment, the neutron yield and its angular distribution are measured by the different-sensitivity BD-PND bubble detectors, which are placed in the target chamber around the target. The emission of the neutron beam is found to be non-uniform. A maximum intensity of 5.13×107 n/sr is observed in the forward direction. The angular distribution of the neutron beam is theoretically calculated by taking into account the energy-angle cross section, the angular and energy distribution of the incident deuterium ion beam. The probability of the neutron energy-angle distribution in the laboratory system is obtained by the coordinate transformation from the probability in the center of mass frame. The results show good agreement with the experimental measurements. This experiment has a certain reference value in the practical application of D-D reaction neutron source.

We develop a novel method to measure the frequency response of the optoelectronic devices. In this method, an electro-absorption modulator is utilized not only as a modulator but also as a photodetector with the identical frequency response. Based on this property, the frequency responses of the optoelectronic devices can be obtained and the results show good consistency with the measurement results by traditional methods. Instead of using broadband modulators or photodetectors, the frequency response of high bandwidth optoelectronic devices can be measured by using the low bandwidth optoelectronic devices.

A directly-modulated distributed-feedback laser module has been achieved with a ridge-waveguide laser chip in our laboratory. It is packaged in butterfly housing with a K connector, and the bandwidth of the laser module is up to 24 GHz with in-band flatness of ±3 dB. It shows a high linearity with input 1-dB compression point of higher than 23 dBm and third-order intercept of 32.2 dBm at 24 GHz. Meanwhile, the packaged DFB laser module gives rather low relative intensity noise of less than -150 dB/Hz when the bias current is 75 mA and it can show a great performance in analog optical communication systems.

A high bandwidth optical transceiver module for an analog optical link in Ku band is developed using a directly modulated distributed-feedback laser module. A bandwidth of 18 GHz can be achieved with in-band flatness less than ±3 dB. The gain can reach about -1 dB. The transceiver module performs with high linearity, with an input 1-dB compression point of 2.9 dBm and an input third-order intermodulation point of 9.8 dBm at 18 GHz. A spurious free dynamic range of about 101 dB·Hz2/3 can be achieved.

In this letter, a continuous-wave (CW) continuously wavelength-tunable laser source employing a self-injected Fabry-Perot laser diode (FP-LD) is achieved and investigated experimentally. Through carefully tuning the fiber Fabry-Perot tunable filter (FFP-TF) and chip temperature of the FP-LD, 80 C-band International Telecommunication Union (ITU) wavelengths with 50-GHz mode spacing were obtained with a good performance of the output peak power >;-4.74 dBm (ΔPmax = 2.40 dB) and optical sidemode suppression ratio (SMSR) >;41 dB.

A novel technique for generating narrow-linewidth microwave or millimeter-wave signals is proposed. In this scheme, a delayed self-injected distributed Bragg reflector laser diode, which is tuned by a low-frequency square-wave voltage, is used to generate two correlated lightwaves simultaneously. Experiments show that the 10-dB linewidth of generated microwave signals is reduced from 147 MHz to 68 kHz utilizing the proposed self-injection technique.

To account for the various phenomena of light, two theories have been proposed: the corpuscular and the undulatory. The former assumes that the light is a stream of corpuscles, namely photons, discrete photons carrying packets of energy and momentum. The undulatory theory, on the other hand, requires that light consists of a series of wave trains (Michelson, 1927). Each wave train is followed by another which has a random change in phase (Mathieu, 1975). A single wave train is made up of monochromatic components, i.e. the wave train is polychromatic. Although wave trains are supposed not to be strictly monochromatic, experimental demonstration is extremely difficult and has not been reported to date (Diitchburn, 1963). In addition, many efforts have been made to measure the laser coherence length which is regarded as the length of the wave train. Among the methods for measuring the coherence length of lasers (Geng et al., 2005; Ryabukho et. al., 2005 ; Wheeler et al., 2003), Michelson interferometer-based method (Ryabukho et al., 2005) is the one widely used in the past. However, these methods suffer from mechanic vibration, thermal and acoustic fluctuations, and beam divergence, and errors in the observation of the spatial coherence are difficult to eliminate. For lightwave from a real laser source, the wave trains are neither identical nor of simple form (Born & Wolf, 1999). Unfortunately, a complete description of other properties, such as linewidth, intensity profile, and frequency spacings among wave trains, has not been explicitly given due to resolution limitations in both measuring techniques and instruments. Understanding the spectral structure of semiconductor laser is a fundamental issue. The spectral analysis, especially for the fine spectral structure, reveals the important properties of semiconductor laser, such as mode characteristics, atom emission behavior, highfrequency performances, and coherence features. Spectral lines of light are broadened by various processes. For semiconductor lasers, Henry’s model (Henry, 1982) can be used to explain linewidth broadening of the laser by two mechanisms: 1) the instantaneous phase change caused by the spontaneous emission results in the linewidth broadening of the light; 2) the instantaneous fluctuations of the field intensity through linewidth enhancement parameter ┙ results in a delayed phase change, which further broadens the linewidth. However, this model also can not describe the properties of wave trains mentioned above distinctly. Indeed, it implies that the spectral linewidth we observed, in fact, results from the

A high-speed DFB laser module in butterfly housing has been fabricated in our laboratory, which is operated in direct modulation for Ku-band. The bandwidth of the laser module is measured up to 18 GHz with highly linear characteristics and low relative intensity noise. The input points for 1 dB compression and third order interception of the laser have also been obtained as 23 dBm and 30 dBm respectively, and it can be utilized in analog optical link systems with good performance.

This paper presents a new technique to generate microwave signal using an electro-absorption modulator (EAM) integrated with a distributed feedback (DFB) laser subject to optical injection. Experiments show that the frequency of the generated microwave can be tuned by changing the wavelength of the external laser or adjusting the bias voltage of the EAM. The frequency response of the EAM is studied and found to be unsmooth due to packaging parasitic effects and four-wave mixing effect occurring in the active layer of the DFB laser. It is also demonstrated that an EA modulator integrated in between two DFB lasers can be used instead of the EML under optical injection. This integrated chip can be used to realize a monolithically integrated tunable microwave source.

A new modulator for the optical signal in a fiber based on multi-beam interference is designed. In the experiment, the distance of a couple of abutted fibers was modulated through a piezoelectric ceramic pipe driven by 50 Hz AC voltage, so that the amplitude of the transmitted optical signal was modulated. The modulation ratio is about 10%, S/N ratio is about 60 dB and the bandwidth is about 200 KHz.