News › Fraun­ho­fer IOF · More power for laser com­mu­ni­ca­tion in space

They fly high above our heads and are indis­pensable for our glo­bally net­worked world: satel­li­tes. For a long time, they used radio waves to exch­ange data with each other and with ground sta­ti­ons. But in a highly net­worked world with a rapidly gro­wing volume of data, these have long been insuf­fi­ci­ent to cope with the volume of data. The solu­tion: light. Light enables data to be trans­mit­ted much fas­ter – and, espe­ci­ally with ent­an­gled light par­tic­les known as quanta, much more secu­rely. At SPIE Pho­to­nics West from Janu­ary 31 to Febru­ary 2, the Fraun­ho­fer Insti­tute for Applied Optics and Pre­cis­ion Engi­nee­ring IOF will be pre­sen­ting seve­ral inno­va­tions for laser- and quan­tum-based com­mu­ni­ca­tion tog­e­ther with its pro­ject part­ners from quan­tum com­mu­ni­ca­tion and space research.

The inte­gra­tion of satel­li­tes into ter­restrial fiber optic net­works will signi­fi­cantly improve our way of com­mu­ni­ca­ting in the future and make it more widely available. In the glo­bal pho­to­nic com­mu­ni­ca­ti­ons net­work of the future, satel­li­tes are the fast alter­nate rou­tes, the demand detour, so to speak, that can reli­eve con­ge­sted data highways.

In order to be able to send even hig­her data rates over even grea­ter distances in the future, rese­ar­chers at Fraun­ho­fer IOF have now deve­lo­ped a module for com­bi­ning mul­ti­ple laser beams at dif­fe­rent wave­lengths. The new wave­length mul­ti­ple­xer will be pre­sen­ted at the inter­na­tio­nal trade fair SPIE Pho­to­nics West, tog­e­ther with tech­no­lo­gies for com­mu­ni­ca­tion using quanta.


New wave­length divi­sion mul­ti­ple­xer for trans­mis­sion per­for­mance up to the moon

© Fraun­ho­fer IOF Satel­lite-based laser com­mu­ni­ca­tion enables highly direc­tional trans­mis­sion of data over long distances. A wave­length mul­ti­ple­xer deve­lo­ped at Fraun­ho­fer IOF will make it pos­si­ble to send even hig­her data rates over even grea­ter distances in the future.

The wave­length divi­sion mul­ti­ple­xer (»WDM« for short) was deve­lo­ped by rese­ar­chers from Jena in coope­ra­tion with the Euro­pean Space Agency ESA. The spec­tral com­bi­na­tion module com­bi­nes five laser beams of slightly dif­fe­rent wave­lengths. Each indi­vi­dual laser beam with its spe­ci­fic wave­length repres­ents a sin­gle chan­nel, each of which gene­ra­tes 20 watts of power. Each of these chan­nels can trans­mit data. The mul­ti­ple­xer now com­bi­nes these chan­nels into a sin­gle, more powerful signal. By super­im­po­sing them, the mul­ti­ple­xer achie­ves a total of 100 watts of opti­cal power. Due to the strong bund­ling with simul­ta­neously high power, a con­nec­tion to the moon or even more distant pla­nets would theo­re­ti­cally be con­ceiva­ble in this way.

To com­bine these chan­nels, the Fraun­ho­fer IOF rese­ar­chers used so-cal­led volume Bragg gra­tings with pre­cis­ely spe­ci­fied reflec­ti­vi­ties for the respec­tive chan­nel wave­length. In this way, the chan­nels are super­im­po­sed in the range of 1.5 micro­me­ters wave­length and bund­led into a sin­gle beam. Par­ti­cu­larly chal­len­ging here: With a spec­tral spa­cing of just 1.3 nano­me­ters, the chan­nels are very close to each other. Volume Bragg gra­tings are ideal for this pur­pose. They not only have high reflec­ti­vity, but also very steep spec­tral edges. Accor­din­gly, mul­ti­ple chan­nels can be packed very clo­sely tog­e­ther wit­hout greatly expan­ding the band­width of the com­bi­ned beam. The mul­ti­ple­xer deve­lo­ped has five chan­nels, but depen­ding on the appli­ca­tion, con­sider­a­bly more would be conceivable.

Com­mu­ni­ca­tion with Lasers and Quanta at SPIE Pho­to­nics West

© Fraun­ho­fer IOF A metal mir­ror telescope deve­lo­ped at Fraun­ho­fer IOF enables short-term free-beam trans­mis­sion bet­ween two com­mu­ni­ca­tion part­ners. This makes quan­tum com­mu­ni­ca­tion within cities pos­si­ble, for example.

In addi­tion to the new wave­length mul­ti­ple­xer, the insti­tute pres­ents in par­ti­cu­lar tech­no­lo­gies for highly secure com­mu­ni­ca­tion with ent­an­gled light parts, i.e. quanta. Here, the Fraun­ho­fer IOF is rese­ar­ching in par­ti­cu­lar the exch­ange of quan­tum keys over dif­fe­rent distances. One vari­ant for trans­mit­ting such quan­tum keys is the exch­ange via free beam – i.e. through the air. As part of the QuNET initia­tive, a pilot pro­ject fun­ded by the Ger­man Fede­ral Minis­try of Edu­ca­tion and Rese­arch with 125 mil­lion euros for rese­arch into quan­tum com­mu­ni­ca­tion, a metal mir­ror telescope with active beam sta­bi­liza­tion was deve­lo­ped at Fraun­ho­fer IOF. This makes it pos­si­ble to estab­lish a free-space link bet­ween two com­mu­ni­ca­tion part­ners, for exam­ple within a city, in a short time. In the future, this tech­no­logy will also be sui­ta­ble for exchan­ging quan­tum keys via satellites.

© Fraun­ho­fer IOF An AO box is an adap­tive opti­cal module. It can cor­rect wave­fronts that are dis­tur­bed by tur­bu­lence in the atmo­sphere during free-beam transmission.

Adap­tive optics is an important buil­ding block for this: When­ever opti­cal signals are trans­mit­ted through the lay­ers of our atmo­sphere, they are expo­sed to a wide variety of tur­bu­lence that nega­tively affects the qua­lity of the signal. Such dis­tur­ban­ces can be cor­rec­ted by adap­tive optics. Rese­ar­chers have deve­lo­ped an adap­tive optics module for this pur­pose – also known as »AO boxes«. The AO box, which can be deployed in a ground-based opti­cal sta­tion or telescope, cor­rects for tur­bu­lence-indu­ced wave­front errors or com­pen­sa­tes for them in a pre­ven­tive man­ner. Sub­se­quently, the signal can be mea­su­red or trans­fer­red to a fiber network.

SPIE Pho­to­nics West is one of the lar­gest inter­na­tio­nal trade fairs in the fields of optics and pho­to­nics. It is orga­ni­zed annu­ally by the Society of Photo-Opti­cal Instru­men­ta­tion Engi­neers (SPIE).