We proposed a novel wavelength-spread compression technique for spectral beam combining of a diode laser array. A reflector, which is parallel to the grating, is introduced to achieve a double pass with a single grating. This facilitated the reduction of the wavelength spread by half and doubled the number of combined elements in the gain range of the diode laser. We achieved a power of 26.1 W under continuous wave operation using a 19 element single bar with a wavelength spread of 6.3 nm, which is nearly half of the original wavelength spread of 14.2 nm, demonstrating the double-compressed spectrum capability of this structure. The spectral beam combining efficiency was 63.7%. The grating efficiency and reflector reflectance were both over 95%; hence, the efficiency loss of the double-pass grating with a reflector is acceptable. In contrast to double-grating methods, the proposed method introduces a reflector that efficiently uses the single grating and shows significant potential for a more efficient spectral beam combining of diode laser arrays.

We review the recent work of distributed-feedback (DFB) multi-wavelength semiconductor laser arrays (MWLAs) based on the reconstruction equivalent chirp (REC) technique. The experimental results show that the proposed MWLA has very high wavelength precision (<±0.1 nm), while the fabrication cost is low. Only one step of holographic exposure and another step of photolithography are required for grating fabrication. The packaging technique for a high-bandwidth analog DFB laser and laser array was developed. A directly modulated MWLA transmitter module was achieved. In addition, an improved MWLA with an integrated reflector was proposed and successfully applied in a radio-over-fiber system.

We propose a nonparallel double-grating structure in a spectral-beam combining technique, where two gratings are placed nonparallel satisfying the Littrow mount in the focal region of the convergent lens. The most attractive advantage of this approach is that it will compress the spectral span into half of its original spectrum, which means the number of combined elements can be doubled in the gain range of diode lasers. Experimental results demonstrate that the CW output power of the combined beam is 30.9 W with a spectral span of 7.0 nm, compared with its original spectrum span of 13.6 nm, and the spectral beam combining efficiency is 70.5%. In consideration that a single grating could have a high efficiency of >97% in a bandwidth of over ten nanometers, the efficiency loss of the grating pair should be less than 6%, which is acceptable for most applications, so this method of using double gratings should be highly interesting for practical applications when a nearly doubled number of diode lasers could be combined into one single laser compared with the previous single-grating methods.

A laser diode array side-pumped Nd:glass square rod amplifier of the dimensions 12 mm×12 mm is designed. The fluorescence is evenly distributed in the Nd:glass amplifier. When the pump power is 66.32 kW, the small signal gain increases by 3.23 times. Under the condition of a 1 Hz repetition frequency, 50 mJ of injected seed-light energy, and a 10 mm×10 mm aperture, the output energy of the laser beam can reach 1.62 J during the four-pass amplification. The output energy stability of the laser pulse is 2.94% (RMS), and the square pulse distortion is smaller than 2. The energy amplification of the injected laser beam from millijoules to joules is realized.

A hybrid integrated light source was developed with a configuration in which a laser diode (LD) array was mounted on a silicon optical waveguide platform for interchip optical interconnection. This integrated light source is composed of 13-channel stripes with a pitch of 20 or 30 μm. The output power of each LD in the 400 or 600-μm long LD array was over 40 mW at room temperature without cooling. An output power uniformity was 1.3 dB including an LD array power uniformity. The use of a SiON waveguide with a spot size converter resulted in an optical coupling loss of 1 dB between an LD and SiON waveguide. The integrated light source including 52 output ports demonstrated a reduction in the footprint per channel. We also demonstrated a light source with over 100 output ports in which the number of output ports is increased by using a waveguide splitter and multichip bonding. These integrated light sources are practical candidates for use with photonic integrated circuits for high-density optical interconnection.