90 degree optical hybrid is the key part of space coherent optical communication and the high efficient mixing technology is an effective means to achieve great detect sensitivity. Most of optical components in optical hybrid are sensitive to polarization state, therefore, the polarization state of incident light will affect the function of hybrid. Through an theoretical analysis and simulation of the performance of hybrid whose incident light is linearly or elliptically polarized light, the result shows that the heterodyne efficiency of hybrid reaches its maximum when incident light is 45°linearly, and the change of polarization orientation can decrease the optical power entering I branch, making the heterodyne efficiency declines. Degree of polarization will increase phase difference of both branch which is orthometric in hybrid, causing the process of phase locking more difficult. Moreover, the effect of deviation of directivity of wave plate on hybrid performance is studied, for 1/4 wave plate, its deviation will change the power allegation and phase error of IandQ branch, but for 1/2 wave plate, phase error cannot be brought in, but it will change the direct current(DC) component of branch. The above polarization state changes will not bring additional phase error in I branch, ensuring the normal functioning of hybrid. This study gives a theoretical foundation to the design of space optical hybrid.
A simple approach to generate passively harmonic mode-locked pulse trains in thulium-doped fiber laser based on nonlinear polarization rotation is proposed and demonstrated. Three different ways of mode-locked techniques have been employed in our structure to generate passively high-order harmonic mode-locked pulse trains; 128th-order passively harmonic mode-locked pulse train is achieved in the experiment and the repetition rate is 406.8 MHz. With the increase of the pump power, multiwavelength output can be tuned. A segment of dispersion compensation fiber is used to compensate the dispersion in the cavity; thus, the single pulse width is compressed from 617 to 48 ps.
A new method that adopt fiber laser phase array source to form all optics
network in the deep space communication was proposed in this paper. The far-field
light intensity figure of 1.55μm fiber laser phase array source was simulated, and the
scanning range with changing among array components the phase was obtained. The
number of array components was 3×3, wavelength was 1.55πm, and core radius
was 10μm. The scanning range was ± 0.9909° when the distance of array
components was 80μm. It was found that applying fiber laser phase array source can
achieve scanning advantages with dynamic range in the all optics network.
A tunable multi-wavelength Brillouin fiber laser with double Brillouin frequency
spacing based on a four-port circulator is experimentally demonstrated. The fiber laser
configuration formed by four-port circulator isolates the odd-order Brillouin stokes signal to
circulate within the cavity only. In addition, it also allows propagation of the incoming Brillouin
pump and even-order Stokes signals from four-port circulator to output coupler .A L-band erbiumdoped
fiber (EDF) with 1480nm pump is used to amplify Stokes signals and to get more output
channels. At the Brillouin pump power of 8dBm and the 1480 nm pump power of 200mw, 5
output channels with double Brillouin frequency spacing and tuning range of 20 nm from 1568nm
to 1588nm are achieved.
A Brillouin-Erbium multi-wavelength tunable fiber laser at C-band is demostrated. A 10 km long singlemode
fiber(SMF), a 6 m long Erbium-doped fiber, two couplers, a wavelength division multiplexer, a isolator, an
optical circulator, a 980nm pump laser and a narrow linewidth tunable laser are included in the structure. A segment
of 10 km-long single-mode fiber (SMF) between the two ports of a 1×2 coupler is used as Brillouin gain. Ebiumdoped
fiber amplifier（EDFA） consists of a segment of 6m er-doped fiber pumped by 980nm laser dioder . A
narrow linewidth tunable laser from 1527 to 1607 nm as Brillouin bump, At the Brillouin pump power of 8mW and
the 980 nm pump power of 400 mw, 16 output channels with 0.08 nm spacing and tuning range of 40 nm from 1527
nm to 1567 nm are achieved. We realize the tunable output of wavelength by adjusting the 980 nm pump power and
the Brillouin pump wavelength. Stability of the multiwavelength fiber laser is also observed.
In this paper, a segment of thulium-doped fiber is pumped by a 976nm laser diode.Broadband gain
at centerwavelength of 1953nm is achieved. The maximum amplified spontaneous emission
bandwidth is 8nm. Simultaneously, self- oscillation of wavelength spacing 0.073nm is
observed. The output power and self- oscillation modes increase with pump power increasing and
wavelength spacing of self-oscillation is unchanged.The relation between fiber length and output
power at pump power 400mW is analyzed. Higher output power can be abtained by selecting a
appropriate fiber length when pump power is unchanged. Through the experiment, a weak
absorption band of thulium-doped fiber near 976nm is verified. The structure can be used as
narrow linewidth broadband source near 1950nm with the characteristic of low cost, simple
structure and good stability.
A dual-wavelength linear cavity erbium-doped fiber (EDF) laser based on a fiber grating
pair is demonstrated experimentally. A circulator, a 980nm/1550nm wavelength division
multiplexing (WDM) coupler, a 1×2 coupler, a polarization controller, a 6m long erbium-doped
fiber and a fiber grating pair for wavelength interval of 0.3nm are included in the structure. A
circulator connected at two ports as reflecting mirror structure. A 980nm pump source pump an
erbium-doped fiber with a length of 6m consist of an erbium doped fiber amplifier. Through
adjusting the state of the polarization controller, the transmission characteristic of cavity is
changed. In both polarization and wavelength, the feedback from the fiber grating pair results in
the laser operating on two longitudinal modes that are separated. The birefringence induced by the
fiber grating pair is beneficial to diversify the polarization states of different wavelength in the
erbium-doped fiber. So it is enhanced the polarization hole burning effect. This polarization hole
burning effect greatly reduced the wavelength competition. Then, it was possible to achieve stable
dual-wavelength. It turns out the structure generated the stable dual-wavelength with the 0.3nm
wavelength interval and the output power is 0.13dBm in the end. The whole system have a simple
and compact structure, it can work stably and laid a foundation for microwave/millimeter wave
generator. It has a good application performance in the future for scientific research and daily life.
Laser space communication has obvious advantages in interstellar transmission，but the space environment will have a direct impact on laser communication system. The function of the analysis of space environment identity effectively could reduce and avoid the bug and invalidation produced by the overload to prolong the using span of effective load and increase the credibility of effective load, meanwhile it is also the main principle to design and research .This article summarizes the characteristics of vacuum space environment(Effect of vacuum outlet, Molecular contamination effect, Vacuum Mount, Cold welding effect, Heat radiation effect under vacuum), low temperature environment, background radiation (including space background radiation caused by thermal radiation, space background radiation caused by light noise). Space background radiation for the performance of space laser communication load is two aspects: one is the background of space radiation caused by thermal radiation, it mainly affects the satellite platform and payload of the thermal control design; Background spectrum caused by radiation and space, it will affect the space laser communication of the signal-to-noise ratio of the receiving unit, which affect the acquisition probability, tracking accuracy and error rate of communication, and particle radiation environment (Including total dose effects, single event effect), the plasma environment in five areas from the characteristics of space environment, for the problem of Space channel Influence the laser communication system performance. On this basis ,this article analysis the influence of space environment on the laser communication system with some examples, which will lay the foundation for the application of space laser communication system of our country.
We demonstrate a distributed feedback (DFB) random fiber laser based on Rayleigh scattering. Amplified spontaneous
emission is produced by using a segment of erbium doped fiber (EDF) pumped by 980 nm laser diode (LD). An
50km-long single-mode fiber (SMF) and a fiber bragg grate (FBG) are used as random resonate cavity and wavelength
output at 1550 nm is observed which can be amplified through the erbium-doped fiber amplifier. Evaluations on the
spectral evolution and power development are also performed from the results obtained.
An ultra-narrow linewidth multiwavelength Brillouin fiber laser is demonstrated. Erbium-doped fiber amplifier with
linear gain is not used in the structure to avoid the signal broaden. Multiwavelength output with identical interval and
ultra-narrow linewidth will be obtained through the experiment. Because the whole system works with a simple structure,
it can work stably and has a good application performance in the future. A one-way feedback multiwavelength Brillouin
fiber laser structure has been designed. A 2x2 3dB coupler, a 8 km-long single-mode fiber (SMF), a distributed
feedback(DFB) semiconductor laser and two optical circulators are included in the structure. A segment of 8 km-long
single-mode fiber (SMF) between the two ports of a 2x2 3 dB coupler is used as Brillouin gain loop. A distributed
feedback semiconductor laser works as the Brillouin pump (BP). Laser output and feedback are realized by two optical
circulators. We adopt the Brillouin pump power at 80 mW. Seven Stokes signals can be observed excluding BP. The
Brillouin frequency shift is 0.088 nm compares with the wavelength of BP. We have measured multiwavelength
Brillouin fiber laser spectrum ten times in 50 minutes. The experiment result shows that the multiwavelength output of
Brillouin fiber laser is very stable. The 3 dB linewidth of the output laser is 5 kHz measured by the frequency spectrum
We demonstrate a multi-wavelength fiber laser with Brillouin cavity loop. Brillouin-Erbium fiber laser (BEFL) integrates Brillouin and Erbium gains in the resonate cavity to produce high power
multi-wavelength fiber laser. The Brillouin gain loop connects with main ring cavity by port2 of the circulator1. A coil of SMF with a length of 10 km is employed by 3-dB fiber coupler as Brillouin gain medium, and pumped by Brillouin pump (BP), a tunable laser with a maximum output power of 15 dBm to generate Stokes light. The measured results were extracted from the laser system by using 90/10 coupler where 10% power is used for monitoring and measurement purpose while the 90% power is feedback into the laser cavity. A 1550 nm tunable laser diode (LD) provided the BP that can be tuned from 1470 nm to 1580 nm (110 nm tuning range). Two fiber circulators are used as the fiber reflection
loops at both ends of the linear cavity. The effect of the erbium-doped fiber amplifier (EDFA) locating at different locations in the cavity BEFL on Stokes wave is experimentally studied. In the experiment, with
EDFA in position A, the tunable range and the output power of the multi-wavelength laser were limited by gain saturation of the signals and the self-lasing cavity modes. The self-lasing cavity modes were suppressed without EDFA, but the tunable wavelength range was narrower because of the low gain. By using EDFA at the total reflective side of the linear cavity, more Stokes waves and wider tunable range was observed because the more powerful Stokes feedback light was amplified twice by the EDFA. The peak power of -1.8dBm and the tuning range of 60 nm were obtained. It has many
important applications, such as dense wavelength division multiplexing (DWDM) systems, distributed
fiber sensing, slow light, and microwave photonics, etc.