Abstract:
The invention relates to an electro-optical component with a millimeter or submillimeter antenna and an optical receiver. In order, in the case of such an electro-optical component, to achieve the situation in which millimeter waves or submillimeter waves can be generated particularly well, the invention provides for the optical receiver to be an electroabsorption modulator.

Description:
REFERENCE TO RELATED APPLICATIONS 
   This application claims the benefit of the priority date of German application DE 103 03 676.8, filed on Jan. 24, 2003, the contents of which are herein incorporated by reference in their entirety. 
   FIELD OF THE INVENTION 
   The invention relates to an electro-optical component and a method of employing such an element to transmit and receive millimeter or submillimeter waves. 
   BACKGROUND OF THE INVENTION 
   The term “millimeter waves” is understood hereinafter to mean electromagnetic waves whose wavelength (free space wavelength) lies in the millimeters range; correspondingly, the term “submillimeter waves” is understood to mean electromagnetic waves whose wavelength is less than one millimeter. The term “millimeter antenna” and “submillimeter antenna” is used hereinafter to mean antennas which can radiate and/or receive electromagnetic millimeter waves and submillimeter waves, respectively. 
   A component of this type is disclosed in the document “Monolithically integrated Yagi-Uda antenna for photonic emitter operating at 120 GHz” (A. Hirata, T. Furuta and T. Nagatsuma; Electronics Letters, 30 Aug. 2001, Vol. 37, No. 18). This previously known component is an arrangement comprising a photodiode and a Yagi-Uda antenna connected to the photodiode. The photodiode, which is designed as a UTC (UTC: uni-travelling-carrier photodiode), receives optical signals modulated with a signal frequency of 120 GHz and converts them into electrical signals. The electrical signals thus have an electrical frequency of likewise 120 GHz and are radiated by the Yagi-Uda antenna connected to the UTC photodiode. In other words, the previously known component is an electro-optical transducer which converts optical signals with a high modulation frequency into electromagnetic millimeter waves. 
   SUMMARY OF THE INVENTION 
   The invention is based on the object of specifying an electro-optical component which is particularly well suited to the generation of millimeter waves or submillimeter waves. 
   One advantage of the electro-optical component according to the invention can be seen in the fact that it has a particularly high efficiency in the conversion of optical signals into electromagnetic millimeter or submillimeter waves, because an electroabsorption modulator is used for detecting the optical signals. 
   A further advantage of the electro-optical component according to the invention is that it has a double functionality, namely because the electroabsorption modulator can also be operated in the opposite direction and can thus be used for generating modulated optical signals. This is because, in concrete terms, optical light signals with a modulation frequency which have been received by the millimeter or submillimeter antenna connected to the electroabsorption modulator can be applied to the electro-optical component according to the invention. 
   For the already mentioned “opposite” direction in the operation of the electro-optical component—in other words for generating modulated optical light signals—an optical signal source such as a laser, for example, is employed. Therefore, in the context of one development of the electro-optical component, it is regarded as advantageous if the electro-optical component has or contains an optically active element. This is because, in such a case, a connection of a separate light source, in particular of a laser, to the electro-optical component can be dispensed with since the component then already contains such a light source itself. 
   It is possible to produce an electro-optical component with an electroabsorption modulator and an optically active element particularly simply and thus cost-effectively if the optically active element and the electroabsorption modulator are integrated in the same semiconductor substrate. This is because production steps can be saved in the case where the two components are integrated in the same semiconductor substrate. 
   For the generation of modulated optical light signals, it is regarded as advantageous if the optically active element is a laser, in particular a DFB (DFB: distributed feedback laser) or a DBR (DBR: distributed Bragg reflector) laser or an optical amplifier, in particular an SOA (SOA: semiconductor optical amplifier). 
   The electro-optical component can be formed in a particularly compact and thus space-saving manner if the millimeter or submillimeter antenna is arranged on the semiconductor substrate. 
   Instead of the millimeter or submillimeter antenna being integrated on the semiconductor substrate, it may alternatively be provided that the millimeter or submillimeter antenna is arranged on a circuit carrier and the semiconductor substrate is fixed on the circuit carrier. 
   For the targeted optimization of the electroabsorption modulator and of the optically active element, it is regarded as advantageous if the semiconductor substrate has at least two different active layers, of which one active layer is optimized for the optically active element and the further active layer is optimized for the electroabsorption modulator. The order of the layers is insignificant in this case, so that the active layer optimized for the optically active element may be arranged above the further layer optimized for the electroabsorption modulator, or conversely below said further layer. 
   QD (QD: quantum dot), MQD (MQD: multiple quantum dot), QW (QW: quantum well) and/or MQW (MQW: multiple quantum well) layers are suitable for the optimization of electroabsorption modulators and of optically active elements, so that it is regarded as advantageous if at least one of the two active layers is a QD layer, an MQD layer, a QW layer or an MQW layer. 
   Slotted antennas, in particular, are highly suitable for receiving and for generating millimeter or submillimeter waves, so that it is regarded as advantageous if a slotted antenna is used as the antenna in the electro-optical component. 
   The slotted antenna is advantageously a CPW-fed antenna fed by a coplanar electrical waveguide. In this case, the abbreviation CPW stands for “coplanar-waveguide-fed”. 
   The millimeter or submillimeter antenna may, for example, also be a Yagi-Uda antenna or a “log-period” antenna. 
   Moreover, it is regarded as advantageous if the electromagnetic millimeter or submillimeter waves are focused in the antenna region; therefore, it is regarded as advantageous if a lens, in particular a silicon lens, for “refocusing” the electromagnetic waves is assigned to or arranged upstream of the millimeter or submillimeter antenna. The lens is advantageously hemispherically curved in order to achieve a particularly efficient focusing of the millimeter or submillimeter waves. 
   Moreover, it is regarded as advantageous if the semiconductor substrate belongs to the III/V material system; in particular, the semiconductor substrate may be, by way of example, an indium phosphite or a gallium arsenide material. 
   The invention is furthermore based on the object of specifying a method for generating millimeter and/or submillimeter waves which can be carried out particularly simply and efficiently. 
   With regard to the advantages of the method according to the invention and with regard to the advantages of the advantageous refinements of the method according to the invention, reference is made to the above explanations in connection with the electro-optical component according to the invention, since the advantages essentially correspond to one another. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In order to elucidate the invention,  FIGS. 1 to 4  show an exemplary embodiment of an electro-optical component according to the invention. 
       FIG. 1  is a cross section diagram illustrating a portion of an electro-optical element including a semiconductor substrate according to one aspect of the present invention; 
       FIG. 2  is a plan view of the semiconductor substrate of  FIG. 1  along with a waveguide coupled thereto according to another aspect of the present invention; 
       FIG. 3  is a plan view of a printed circuit board upon which various aspects of the invention may be implemented; and 
       FIG. 4  is a plan view of the printed circuit board of  FIG. 3  along with a waveguide coupled thereto according to yet another aspect of the present invention. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1  illustrates a semiconductor substrate  1 , which is part of an electro-optical component  2 . The semiconductor substrate  1  may be n-doped, for example. A DFB laser  5 , an electroabsorption modulator  10  and an optical amplifier  15  are integrated in the semiconductor substrate  1 . 
   The layer sequence of the semiconductor substrate  1  is configured as follows: an active layer  20  optimized specifically for the laser  5  is situated on the semiconductor substrate  1 . The active layer  20  may be, by way of example, a QW layer, an MQW layer, a QD layer or an MQD layer. 
   A further active layer  25  specifically optimized for the electroabsorption modulator  10  is situated on the active layer  20 . The order of the two active layers  20  and  25  is arbitrary, moreover; thus, the active layer  20  for the laser  5  may also be arranged above the further active layer  25  instead of below the latter. 
   Situated on the further layer  25  is a p-doped covering layer  30  provided with electrical contacts  35 ,  40  and  45  for making contact with the laser  5 , the electroabsorption modulator  10  and the amplifier  15 . 
   The covering layer  30  is segmented by trenches  50  and  55 , as a result of which the regions for the laser  5 , the electroabsorption modulator  10  and the amplifier  15  are demarcated from one another. 
   The DFB laser  5  has a grating structure  60  formed in the further active layer  25 . 
     FIG. 2  shows the semiconductor substrate  1  in accordance with  FIG. 1  in plan view. It reveals the grating structure  60  of the laser  5  and also the contacts  35 ,  40  and  45  with which the p-doped covering layer  30  is in each case contact-connected. Furthermore, contact regions  70 ,  75  and  80  can be discerned, in which the p-doped covering layer  30  and also the two active layers  20  and  25  are removed—for example etched away. In said contact regions  70 ,  75  and  80 , the n-doped semiconductor substrate  1 , which is otherwise covered by the layers  20 ,  25  and  30 , can be contact-connected from the front side or top side  85  of the semiconductor substrate. The front side  85  and the rear side  90  of the semiconductor substrate are identified by their reference symbols in  FIG. 1 . 
     FIG. 2  furthermore illustrates an optical waveguide  95 , for example a glass waveguide, which is connected to the semiconductor substrate  1  at the outer side  100  of the semiconductor substrate which faces the amplifier  15 . 
   With this waveguide  95 , it is possible to couple optical signals into the semiconductor substrate  1 , which are converted into electrical signals by the electroabsorption modulator  10 . In the other direction, it is possible to couple optical signals into the waveguide  95  from the semiconductor substrate  1 , said signals being generated by the laser  5  and modulated by the electroabsorption modulator  10  in a manner dependent on electrical signals present at the electroabsorption modulator  10 . 
   The light which is generated in the semiconductor substrate  1  and fed into the optical waveguide  95  is symbolized by an arrow bearing the reference symbol P opt,out  in  FIG. 2 ; the light which is fed into the semiconductor substrate  1  is identified by an arrow bearing the reference symbol P opt,in . 
   The laser  5  preferably has a length L 1  of between 50 μm and 500 μm. The electroabsorption modulator  10  preferably has a length of 50 μm to 300 μm; the length L 3  of the electroabsorption modulator  10  is identified by the reference symbol L 2  in  FIG. 2 . The length L 3  of the amplifier  15  is preferably 50 μm to 350 μm. The width b of the laser  5 , of the electroabsorption modulator  10  and of the amplifier  15  is preferably 1 μm to 3 μm. The total width B of the semiconductor substrate  1  should preferably lie between 200 μm and 500 μm. 
   The wavelength λ1 of the light P opt,in  radiated into the semiconductor substrate  1  may be identical to the wavelength λ2 of the light P opt,out  generated by the laser  5 ; different wavelengths λ1 and λ2 are also possible instead. 
     FIG. 3  reveals a lead frame  200 , for example a printed circuit board on which two coplanar electrical conductors  205  and  210  form an electrical coplanar conductor  215 , that is to say an electrical waveguide suitable for millimeter or submillimeter waves. 
   The two conductors  205  and  210  have a waveguide width w of approximately 10 μm to 50 μm and a distance A of between 20 μm and 80 μm 
   The two conductors  205  and  210  are connected by one of their line ends in each case to an antenna  220 , which is formed from metal pads  225  and  230 . The metal pads  225  and  230  have a width q of approximately 100 μm and a total length r (including distance A) of 500 μm to 2 mm. 
   The two conductors  205  and  210  are connected by their other line end to the contact  40  and the contact region  75  of the electroabsorption modulator  10 , as is explained further below in connection with  FIG. 4 . The electrical coplanar conductor  215  thus connects the antenna  220  and the electroabsorption modulator  10  to one another and is specifically dimensioned and designed for this in such a way that it is specifically suitable for the transmission of electrical millimeter and/or submillimeter waves and adapted in particular with regard to its characteristic impedance. 
     FIG. 3  furthermore reveals connecting lines  235 ,  240 ,  245  and  250 , which serve for making contact with the laser  5  and the amplifier  15 . The way in which the electrical connecting lines  235 ,  240 ,  245  (width s=10 μm–50 μm) and  250  are connected in concrete terms is explained in connection with  FIG. 4 . 
   The semiconductor substrate  1  in accordance with  FIG. 2  is additionally shown “rotated” in FIG.  3 —that is to say in a “phantom view” from below of the rear side  90  of the semiconductor substrate. This illustration is intended to indicate that the semiconductor substrate  1  is placed onto the lead frame  200  upside down and then soldered on. For the sake of clarity, only the contacts and the contact regions are shown in this illustration. 
     FIG. 4  shows the lead frame  200  and the semiconductor substrate  1  after the mounting thereof; the lead frame  200  and the semiconductor substrate  1  thus form the electro-optical component  2 . 
   It can be seen in  FIG. 4  that the contact region  70  for making contact with the “n-contact” of the laser  5  is connected to the connecting line  240 . The “p-contact” of the laser  5  is electrically driven via the contact  35  and thus via the connecting line  235 . 
   The optical amplifier  15  is connected to the connecting line  245  via its p-contact  45 ; the connecting line  250  is connected to the contact region  80  for making contact with the n-contact of the optical amplifier  15 . 
   The p-contact  40  of the electroabsorption modulator  10  is connected to the conductor  210  of the electrical coplanar conductor  215 ; the conductor  205  of the electrical coplanar conductor  215  is connected to the contact region  75  for making contact with the n-contact of the electroabsorption modulator  10 . 
   The electrical component  2  in accordance with  FIGS. 1 to 4  can be operated bi-directionally: on the one hand, with the electro-optical component  2 , it is possible to convert optical light signals P opt,in  into electrical waves P electr.,out  in the millimeter and/or submillimeter range. On the other hand, it is possible—thus in the opposite direction—to generate a corresponding optical output signal P opt,out  from electrical waves P electr.,in  in the millimeter and/or submillimeter range. This will now be explained briefly: 
   An optical input light signal P opt,in  is absorbed by the electroabsorption modulator  10 , as a result of which electron-hole pairs are generated, which bring about an electrical voltage at the connections  75  and  40  of the electroabsorption modulator  10 . In the case of a light signal P opt,in  modulated with a frequency of 100 GHz, for example, an electrical AC voltage thus forms at the connections  40  and  75  of the electroabsorption modulator  10 , which voltage is likewise at 100 GHz and is transmitted via the electrical coplanar conductor  215  to the antenna  220  and radiated by the latter as millimeter or, in the case of higher data rates and thus higher frequencies, as submillimeter waves P electr,out . 
   In the opposite direction, the electro-optical component functions as follows: an electrical millimeter wave or submillimeter wave P electr,in  is received by the antenna  220 , whereupon a corresponding electrical signal or a corresponding electrical wave passes via the electrical coplanar conductor  215  to the electroabsorption modulator  10 ; this electrical signal drives the electroabsorption modulator  10  in such a way that the latter modulates its absorption behavior in accordance with the electrical signal. This then has the effect that the light generated by the laser  5  is modulated and modulated optical signals P opt,out  are generated, which are coupled into the optical waveguide  95  from the semiconductor substrate  1 . Although the invention has been illustrated and described with respect to one or more implementations, alterations and/or modifications may be made to the illustrated examples without departing from the spirit and scope of the appended claims. In addition, while a particular feature of the invention may have been disclosed with respect to only one of several implementations, such feature may be combined with one or more other features of the other implementations as may be desired and advantageous for any given or particular application. Furthermore, to the extent that the terms “including”, “includes”, “having”, “has”, “with”, or variants thereof are used in either the detailed description and the claims, such terms are intended to be inclusive in a manner similar to the term “comprising”. 
   List of Reference Symbols 
   
       
         1  Semiconductor substrate 
         2  Electro-optical component 
         5  DFB laser 
         10  Electroabsorption modulator 
         15  Optical amplifier 
         20  Active layer 
         25  Further active layer 
         30  p-doped covering layer 
         35 ,  40 ,  45  Electrical contacts 
         50 ,  55  Trenches 
         60  Grating structure 
         70 ,  75 ,  80  Contact regions 
         85  Front side 
         90  Rear side 
         95  Optical waveguide 
         100  Optical connection side 
         200  Lead frame 
         205 ,  210  Conductors 
         220  Antenna 
         230  Metal pads 
         240 ,  245 ,  250  Connecting line