Detailed understands the working principle of MEMS VOA smooth attenuator

Detailed understands the working principle of MEMS VOA smooth attenuator

[introduction] MEMS (Micro Electro Mechanical System, system of personal computer cable) the technology is applied extensively in fiber-optic communication system, the union of MEMS technology and optical technology, call MOEMS the skill normally. Most commonly used MOEMS parts of an apparatus includes WSS of select switch of DGE of equalizer of TOF of adjustable and OS of smooth attenuator VOA, smooth switch, optical filter, dynamic gain, wavelengh and matrix smooth switch OXC.
 
MEMS (Micro Electro Mechanical System, system of personal computer cable) the technology is applied extensively in fiber-optic communication system, the union of MEMS technology and optical technology, call MOEMS the skill normally. Most commonly used MOEMS parts of an apparatus includes WSS of select switch of DGE of equalizer of TOF of adjustable and OS of smooth attenuator VOA, smooth switch, optical filter, dynamic gain, wavelengh and matrix smooth switch OXC.
 
VOA is led with Yu Guanggong in middling of fiber-optic communication system balanced, in all sorts of technology program, MEMS VOA has measure small, cost is low with the dominant position that creates easily. The most commonly used MEMS VOA has two kinds: MEMS Shutter with MEMS small lens, former normally with fuel factor drive, latter normally with electrostatic force drive.
 
MEMS Shutter VOA
If the graph is shown 1 times,be based on the VOA structure of MEMS Shutter, MEMS Shutter is inserted two fiber-optic the smooth road between, attenuation depends on the beam of light that is held back is sectional size. In applying actually, this kind of VOA also can design reflection model.

Detailed understands the working principle of MEMS VOA smooth attenuator
Graph 1. Be based on the VOA structure of MEMS Shutter

MEMS small lens VOA
If the graph shows the VOA structure that seizes lens to be based on MEMS 2 times, it with double fiber-optic collimation implement two end fine outputs port as input / , collimation beam of light is reflexed by MEMS small lens deflexion, thereby the smooth road between port of output of UniCom input / . Twist small lens lets deflexion of happening of beam of light, produce the attenuation of smooth power thereby.
 
Detailed understands the working principle of MEMS VOA smooth attenuator
Graph 2. Be based on MEMS to twist the VOA structure of lens
 
MEMS twists lens to have two kinds of structures normally, namely flat electrode and comb tine electrode, if pursue,3 are shown. Consider the attenuation range of 0 ~ 20dB, former the driving voltage that needs > 10V normally, latter can fall driving voltage to 5V the following. However, mere a little dust grain can get stuck to comb tine electrode, rate of its production good people is accordingly inferior. Use comb the MEMS small lens of tine electrode, normally need is in super- enclose below clean environment.
 
Detailed understands the working principle of MEMS VOA smooth attenuator
Graph 3. Two kinds of MEMS seize lens: Flat electrode and comb tine electrode
 
The WDL problem in MEMS small lens VOA
The VOA that is based on small lens of MEMS Shutter and MEMS all has wide application, former function target is better, but assemble craft relatively complex; Latter is assembled easily but WDL (wave appearance involves loss) opposite bigger. In broadband application, this kind of VOA can produce different attenuation to different wavelengh, this phenomenon definition is WDL. In broadband application, yue Xiaoyue of requirement WDL index is good.
 
WDL problem results from the modular field chromatic dispersion in SMF of Chan Moguang fine, we know, fiber-optic medium different wavelengh has different modular field diameter, the modular field diameter of the long wave is a few bigger. The graph is shown 4 times for fiber-optic in the chromatic dispersion circumstance of modular field.
 
Detailed understands the working principle of MEMS VOA smooth attenuator
Graph 4. Fiber-optic in circumstance of modular field chromatic dispersion
 
If the graph is shown 4 times, beam of light is reflexed by MEMS small lens deflexion, of different wavelengh facula all deviate goes out shoot fiber-optic fine core. Be in without optimized VOA in, the facula of all wavelengh has same deflection amount. Be like type (1) , attenuation A depends on deflection quantity X and ω of modular field radius.
 
Detailed understands the working principle of MEMS VOA smooth attenuator
 
 (1) inside a relatively narrow wavelengh range, be like C wave band (1. 53 ~ 1. 57μm) , the circumstance of modular field chromatic dispersion in Chan Moguang fine is OK type (2) make linear and approximate processing [3] .
 
Detailed understands the working principle of MEMS VOA smooth attenuator
 
(2) to SMF of commonly used Kang Ning company – 28 model single standard is fiber-optic, the coefficient in type is A = on 5. = of 2μm, B 3. = of 11 @ λc 1. 55μm. When the attenuation Ac that is in when central wavelengh λc is given, the deflection quantity Xc that gets facula is like type (3) .
 
Detailed understands the working principle of MEMS VOA smooth attenuator
 
(3) integrated type (1 – 3) the WDL inside λl of ~ of λs of attainable wavelengh limits is like type (4) , among them suffix S, c, l represents the shortwave inside wave band limits, medium wave and long wave respectively.
 
Detailed understands the working principle of MEMS VOA smooth attenuator
 
(4) according to type (4) , when the attenuation Ac setting of VOA is bigger, the deflection quantity Xc of facula is bigger also, because this meeting produces bigger WDL, if pursue 5, the graph is shown 6 times. The basis pursues 6, in attenuation limits 0 ~ 20dB is mixed wavelengh limits 1. 53 ~ 1. In 57μm, the biggest WDL can be amounted to 0. 96dB. Business can be measured the most greatly with MEMS VOA WDL is 1. 5dB, this is the influence because of optical system chromatic dispersion, the facula that causes different wavelengh differs in the deflection quantity that exports fiber-optic end panel. This kind of circumstance and graph show a circumstance 4 times to differ, in the graph 4 in, all facula have identical deflection to measure.
 
Detailed understands the working principle of MEMS VOA smooth attenuator
Graph 5. The WDL of level of corresponding and different attenuation
 
Detailed understands the working principle of MEMS VOA smooth attenuator
Graph 6. The WDL of level of corresponding and different attenuation
 
The WDL of MEMS small lens VOA is optimized
 
The WDL in MEMS small lens VOA results from two elements: Modular field chromatic dispersion and optical system chromatic dispersion, the effect of two elements is cumulative rise, let the biggest WDL achieve 1. 5dB. So the influence of these two elements whether mutual and quits, in order to aid at reducing WDL? The answer is OK, but the analysis with careful need and design.
 
According to type (1) , the long wave has bigger modular field diameter, its attenuation is accordingly smaller. If pursue 4. 16 are shown, if optical system can produce larger deflection amount to the facula of the long wave, with respect to the attenuation that can increase a long wave, produce balanced effect to attenuation spectral line thereby.
 
Detailed understands the working principle of MEMS VOA smooth attenuator
Graph 7. The chromatic dispersion of optical system and modular field chromatic dispersion offset each other circumstance
 
However, according to type (4) , because of the WDL that two elements produce, can fall to offset completely each other in a certain specific attenuation level Ac only. Be installed to be a different when the attenuation of VOA parts of an apparatus when the numerical value at Ac, will put in odd WDL, if pursue,8 are shown.
 
From the graph 8 be pleasant to the eye, before optimize, when the biggest WDL arises to be 20dB at attenuation. If pass,optimize, the WDL when be attenuation 20dB is completely quits, when the biggest WDL arises to be 4dB at attenuation. If be attenuation the WDL when 13dB to offset completely, it is inside the attenuation limits of 0 ~ 20dB, the biggest WDL < 0. 2dB.
 
Detailed understands the working principle of MEMS VOA smooth attenuator
Graph 8. Two elements that cause WDL offset each other circumstance
 
Already had all sorts of plan at present, can produce contrary chromatic dispersion through optical system. In the graph 9 in, collimation lens inserted a prism between as small as MEMS lens, the chromatic dispersion of optical system and modular field chromatic dispersion are mutual and consequently quits. However, additional the cost that the prism that join can raise VOA parts of an apparatus and complex degree. Graph 10 showed another solution, this plan asks the vitreous material of production collimation lens has very tall chromatic dispersion, and 10° of > of dip of lenticular front face (in existing parts of an apparatus, this angle is 8° normally) [4] .
 
Detailed understands the working principle of MEMS VOA smooth attenuator
Graph 9 will optimize WDL through introducing prism; Graph the collimation lens of 10 exorbitant chromatic dispersion will optimize WDL
 
Be based on the thorough analysis of pair of optical system chromatic dispersion, of university of Hua Zhongke ability 10 thousand aid army waited for a person to offer the 3rd kind of solution, the material of collimation lens is commonly used N – SF11 glass, curvature radius of lens also is commonly used R = 1. 419mm. To optimize WDL index, if the associated curve between the other parameter that gets collimation lens pursues 4. 20 are shown, the random on the curve gave out a group of parameter of collimation lens: φ of end panel angle and lenticular length L. Be based on these parameter to machine collimation lens, the WDL index of VOA parts of an apparatus will get optimizing. The attention pursues φ of 11 medium end panel angle all are negative worth, because of this pair fiber-optic insert needle and collimation lens need according to the graph 12 (D) medium direction undertakes constructional, if and rather than pursues 12 (C) medium existing MEMS VOA assembles means. The VOA of MEMS small lens that they assemble finally is shown 13 times like the graph, according to the report, in attenuation limits 0 ~ 20dB is mixed wavelengh limits 1. 53 ~ 1. In 57μm, measure the most greatly WDL < 0. 4dB.
 
Detailed understands the working principle of MEMS VOA smooth attenuator
Graph 10. After WDL is optimized the relation between collimation lens parameter
 
Detailed understands the working principle of MEMS VOA smooth attenuator
Graph 11. Optimize WDL index through adjusting angle of collimation lens end panel
 
Detailed understands the working principle of MEMS VOA smooth attenuator
Graph 12.  Sample of VOA of MEMS small lens
 
As the rapid development of DWDM technology, the in smooth communication network application of MEMS VOA will be wider and wider. 100 million sources connect base oneself upon the demand at having business and face prospective network to expand demand, rolled out the MEMS technology product of a series of own research and development, include the smooth switch of 1×48 passageway, module of as smooth as the MEMS with WDM, PLC or compositive PD switch, and MCS module.
 
 
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